Analysis of ground-water level time-series for hydrogeologic conceptualization, Hanford Site, Washington

Transcription

1 Analysis of ground-water level time-series for hydrogeologic conceptualization, Hanford Site, Washington Item Type Thesis-Reproduction (electronic); text Authors Nevulis, Richard Henry,1959- Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 09/05/ :14:17 Link to Item

2 1 ANALYSIS OF GROUND-WATER LEVEL TIME-SERIES FOR HYDROGEOLOGIC CONCEPTUALIZATICN, HANFCED SITE, WASHINGTON by Richard Henry Nevulis A Thesis Submitted to the Faculty of the DEPARIMENT OF HYDROLOGY AND WATER RESOURCES in Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIIIsICE WEIR A MAJOR IN HYDROLOGY In the Graduate College THE UNIVERSITY Cf ARIZONA 1988

3 2 STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgement the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED??..,Ye.,f 4/44.,X, APPROVAL BY THE THESIS DIRECTOR This thesis has been approved on the date shown below: Donald Davis Professor of Hydrology and Water Resources re a <ee /7E(

4 3 TABLE OF CONTENTS LIST OF ILLUSTRATIONS 7 LIST OF TABLES 10 ABSTRACT INTRODUCTION 13 Page Study Area 14 Previous Investigations 14 Purposes of the Study 17 Study Outline STUDY SEWING 19 Geography 19 Geology 20 Stcatigraphy 20 Basement rocks 20 Columbia River basalt group 20 Intercalated sediments 24 Suprabasalt sediments 24 Lithology 24 Basalt flows 24 Sedimentary interbeds 26 Post-basalt deposits 26 Structural Geology and Tectonics 26 Folding 27 Faulting 27 Fractures 29 Hydrology 29 Surface Water 29 Rivers and streams 29 Lakes and ponds 30 Groundwater 30

5 4 TABLE OF CONTENTS- -Continued Page Unconfined aquifer 30 Confined Aquifers 31 Ground-water Flow Barriers 34 Ground-water Uses 34 Man-made Ground-water Disturbances 35 Ground-water Levels EFFECTS OF NATURAL AND INCIDENTAL FLUCTUATIONS ON GROUND-WATER LEVELS 37 Seasonal Fluctuations 38 Columbia River Stage 38 Cross-correlations 40 River-aquifer model 44 Ground-water Withdrawals 56 Drawdown calculations 56 Cross-correlations 62 Reservoir Fluctuations 64 Rainfall-Recharge 66 Sumary of Seasonal Fluctuations 68 Daily Fluctuations 69 Columbia River Stage 70 Frequency analysis 70 Cross-correlations 73 River-aquifer interaction 73 4 Barometric Pressure 77 Earth Tides 78 Summary of Daily Fluctuations GROUND-WATER BARRIERS 80 Unrtanum Ridge Anticline 81 Columbia River Stage Effects 81 Drilling Disturbances 82 Geologic Explanations 84

6 5 TABLE OF CONTENTS- -Continued Cold Creek Barrier 86 Page Ground-water Withdrawals 87 Drilling Disturbances 87 Geologic Explanations 89 Summary and Conclusions VERTICAL CONNECTIVITY OF HYDROSTRATIGRAPHIC UNITS 95 Cross-Correlation 95 Surface Waste Water Disposal 98 Effects an Ground-Water Levels in the Unconfined Aquifer 99 Effects an Ground-Water Levels in the Confined Aquifer 102 Loading 106 Changes in water table mound with time 108 Loading response 108 Piezometric mound dissipation 110 Procedure 111 Results 111 Hydraulic Carmunication--Steady State Approach Procedure 115 Results 120 Hydraulic Cammication--Transient Approach 123 Procedure 123 Results 125 Summary and Conclusions HYDROGEOLOGIC CONCEPTUALIZATION 129 Past 129 Present 131 Future DISCUSSION, SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS FOR FUTURE STUDY 138

7 6 TABLE OF CONTENTS- -Continued Discussion 138 Page Lagged Cross-Correlations 138 Detection of Pumping Disturbances 140 Analytical Methods 140 Summary 142 Conclusions 143 Recommendations for Future Study 145 APPENDIX A. WELL HYDROGRAPHS 148 APPENDIX B. RESIDUAL GROUND-WATER LEVELS AT DC-19, DC-20, AND DC APPENDIX C. CALCULATION OF PUMPING RATES FOR IRRIGATION IN THE UPPER COLD CREEK VALLEY 183 APPENDIX D. RIVER-AQUIFER ANALYTICAL MODEL 186 APPENDIX E. SEASONAL CORRELOGRAMS 190 LIST OF REFERENCES 195

8 7 LIST OF ILLUSTRATIONS Figure Page 1.1 Map of the study area within the Hanford Site, Washington Stratigraphic section at the reference repository location (DOE-SCR, 1982) Basalt intraflow structures (DOE-SCR, 1982) Geologic structures in the study area Areas of upward and downwimxlvertical groundwater flow (DOE-SCR, 1982) Hydrcgraph of smoothed Columbia River stage from 1981 to 1986 measured two miles downstream from the Priest Rapids Dam Hydrcgraphs of smoothed Columbia River stage and ground-water levels at borehole DB-12 lagged 13 days behind the River Hydrcgraphs of smoothed Columbia River stage and residual ground-water levels in the Mabton interbed at piezometer DC-22 lagged 67 days behind the River Interaction between the Columbia River and groundwater levels through (a) subaqueous outcrop, and (b) confining layer Estimated areas of contact between the Rosalia flow top and the Columbia River based on the (a) fluctuation magnitudes, and (b) response time lag in the river-aquifer model Location of upper Cold Creek Valley pumping wells used in the drawdown analysis Predicted and observed drawdowns at the O'Brian well due to ground-water withdrawals in the upper Cold Creek Valley Hydrcgraphs of average monthly reservoir levels behind the Priest Rapids Dam and ground-water levels at borehole DB-12 65

9 8 LIST OF ILLUSTRATIONS Continued Figure Page 3.9 Graph of ground-water levels at the O'Brian well and monthly deviations from the yearly average precipitation at the Hanford Site Segment of Columbia River stage hydrograph with a daily cycle Output from frequency analysis on Columbia River stage data showing a 24-hour cycle Correlogram of DB-12 ground-water levels and Columbia River stage with a two-hour time lag increment Hydrographs of ground-water levels at wells DB-12 and DC-20:Rosalia flow top during drilling and development of piezometer DC-23W Conceptual cross-section of a reverse fault along the Unitanun Ridge anticlinal axis Effects of pumping in the upper Cold Creek Valley on ground-water levels at wells O'Brian and DB-11 on the west side of the barrier and DC-22:Rosalia flow top on the east side Stratigraphic correlations of DB-11 on the west side of the barrier and DC-22 on the east side Conceptual cross-section of the Cold Creek barrier Maximum cross-correlation coefficients and the corresponding time lags (in days) between units at piezometers DC-19, DC-20, and DC-22 with recovery trends and barometric effects removed Location of surface waste water disposal ponds in the study area Ground-water levels in the unconfined aquifer (a) before the beginning of the waste water disposal activity in 1944, and (b) in 1984 (DOE-SCR, 1982; Schatz, 1984) Maps of estimated 1985 piezometric levels in the a-b (a) Rattlesnake Ridge interbed, and (b) Mabton interbed 103

10 9 LIST OF ILLUSTRATIONS - -Continued Figure 5.4 Maps of estimated 1985 piezometric levels in c-d the (c) Rosalia flow top, and (d) Sentinel Gap flow top Distribution of stress caused by a change in the overlying load from surface waste water disposal activity Estimated change in load through 1985 from surface waste water disposal activity (a) with U-pond decommission, (b) assuming no U-pond decommission Finite difference grid used to model the dissipation of a piezometric mound Conceptual ground-water flow through the basalt flow tops, interiors, and a sedimentary interbed under a disposal pond Vertical hydraulic gradients measured at piezometers DC-19, DC-20, and DC Conceptual steady-state flaw through the Elephant Mountain Member used to calculate the vertical flow, Q., Hydrcgraphs of DC-19:basal Ringold unit and DC-l9 :Rattlesnake Ridge interbed showing a change in trend Finite difference grid used to model the transport vertical ground-water response through the Elephant Mountain member Conceptual areal map of pre-hanford (1944) groundwater flow in the (a) unconfined, and (b) confined units Conceptual cross-section of pre-hanford (1944) ground-water flow in the study area Conceptual areal map of present ground-water flow in the (a) unconfined, and (b) confined units Conceptual eross-section of present ground-water flow in the study area 136 Page

11 10 LIST OF TABLES TablePage 2.1 Boreholes and the Monitored Hydrostratigraphic Units Maximum Correlation Coefficients and the Corresponding Time Lag from Lagged Cross-Correlations of Average Daily Columbia River Stage and Ground-water Levels Predicted Seasonal Ground-Water Level Fluctuations and Time Lags from Seasonal Columbia River Stage Changes Versus Observed Seasonal Ground-Water Level Variations Predicted Drawdowns as a Result of Ground-Water Withdrawals in the Upper Cold Creek Valley Assuming the Presence or Absence of the Cold Creek Barrier Versus Observed Seasonal Fluctuations in the Rosalia Flow Top Maximum Correlatian Coefficients and the Corresponding Time Lag (Days) Between the Cold Creek Wells and Other Walls Which Mbnitor the Priest Rapids Member (Time Lag Behind the Cold Creek Wells) Time Lags of Daily Ground-Water Level Cycles Behind the River Stage Changes at Various Boreholes Indicated by the Cross-Correlation with the Columbia River Stage Predicted Amplitudes and Time Lags of Daily Ground- Water Level Fluctuations Due to Daily Columbia River Stage Changes Values for the Hydrostratigraphic Units Used in the Calculation of Steady-State Flow Through the Elephant Mountain Member 121

12 11 ACKNCWLEDGMENTS I would like to thank those people who helped with the development and completion of this thesis. Mast importantly, the guidance and friendship of Dr. Donald Davis made the task easier and more enjoyable. Dr. Soroosh Sorocshian offered timely advice and suggestions that kept the project advancing smoothly. At Rockwell Hanford Operations, Leo Leonhart's helpful and willing support is also appreciated. Thanks to Dr. Shlomo Neuman for agreeing to participate as a member of my thesis committee. Finally, thanks to Corla Thies, who helped put this material into a presentable form. This research was supported by the Northwest College and University Association for Science (University of Washington) under Contract DE-AM06-76-RL02225 with the U. S. Department of Energy.

13 12 ABSTRACT Evaluations of natural ground-water level variations may be used to infer hydrogeologic characteristics of an area. This study analyzes ground-water level time-series by statistical and analytical methods in a section of the Hanford Site near Richland, Washington. Advantages of such passive methods of analysis may include relative simplicity, low cost, and avoidance of disturbances typically associated with stress testing of aquifers. Seasonal variations of the Columbia River stage are shown to affect ground-water levels in two hydrostratigraphic units. Seasonal ground-water withdrawals for irrigation in the upper Cold Creek Valley influence water levels In several wells west of the Cold Creek barrier. Vertical connectivity of the hydrostratigraphic units is also considered by studying the effects of surface waste water disposal activity on the underlying units. Estimates of the vertical hydraulic conductivity through a basalt flow interior are obtained.

14 13 CHAPTER ONE INTRCIDUCTICN Conceptualization of the hydrogeology in the Pasco Basin is critical for the characterization of the Hanford Site as a possible location for a high-level nuclear waste repository. The site selection process involves a thorough hydrogeologic characterization of the Reference Repository Location (RRL) and surrounding areas. This study involves the analysis of ground-water level variations at several boreholes at the Hanford Site centered near the RRL. The goal is to determine whether the examination of natural ground-water level fluctuations can yield hydrogeologic information about an area. This study attempts to use this method to characterize the hydrogeology in a section of the Hanford Site. Mach of the information about the hydrogeology of the site will be attained by conventional aquifer pumping tests. Small-scale aquifer tests have been performed at existing boreholes, and more boreholes are currently being drilled or planned for large-scale hydraulic tests in the future. Because it is desirable to have undisturbed or predictable ground-water levels during the large scale aquifer tests, ground-water level disturbances caused by smaller tests have been reduced. Additional information about the hydrogeology, however, may be attained from the analysis of natural and incidental, man-made disturbances in the area. This type of analysis has advantages and disadvantages. Several desirable features include (1) relative simplicity, (2) low

15 14 cost, and (3) no disturbance to the ground-water system. Passive methods such as the ones used in this study may yield useful information that can be incorporated into the hydrogeologic conceptualization of the area. Possible disadvantages of the method include (1) the need for ground-water level data that enable the detection of all fluctuations, and (2) a relatively large number of ground-water level monitoring locations. It is also desirable to have extraneous influences on ground-water levels such as river or tidal fluctuations. In this analysis, though there is a relatively significant amount of ground-water level data at the site, the monitoring periods do not always overlap in time or a well may not be monitored for a time long enough to detect seasonal variations. This was the situation with some of the wells at the RRL which had been monitored less than two years at the time of this study. Study Area The study area is in southcentral Washington In the Pasco Basin (Figure 1.1). The Pasco Basin is a 1900 square mile topographic depression in the Columbia River Plateau. Mbre specifically, the study area is within the Hanford Site which is one of the candidate sites for the underground disposal of high-level nuclear wastes. The primary focus of this study is the area south of the Columbia River centered at the reference repository location (RRL). Previous Investiga -tions Early investigations of the Columbia River Basalt were primarily the work of the U.S. Geological Survey. The earliest studies were

16 15 Gaging Station O'Brian Ford upper,/,7,,, :.:Cold Creek :yalleyv DB- 11 <<:-;;:-;0»r DB-12 DC-22 DC-23W DC-20 Reference Repository Location Borehole Location It! 0 1,. miles DO-14 DC-19 Washington Pasco Basin N4-11 Figure 1.1. Nap of the study area within the Hanford Site, Washington.

17 16 done in the late 19th century on the geology and water resources of the area (Russell, 1897). Later investigations provided more information about the ground-water hydrology of the area as more boreholes were dug or drilled for a water supply source (Calkins, 1905; Landes, 1905; Waring, 1913). Among the qualitative descriptions of the ground-water hydrology was the observation that certain areas had artesian wells. One of these areas was the upper Cold Creek Valley in the study area. A few of the wells drilled during the early period (1920's) still provide ground-water level data today. The Hanford Site was set up by the federal government in Detailed characterization of the ground-water hydrology at the site began at this time, especially of the unconfined aquifer. Investigations included the study of ground-water flow in the unconfined aquifer and contaminant movement. Many investigations of the hydrogeology for the area during this period were by R. C. NSweemb (Newcomb, 1961; 1973). Subjects covered in his publications include the effects of the Columbia River on the ground-water levels in the unconfined aquifer and the examination of "subsurface dams" (hydraulic barriers) in the Columbia River Basalt. Not much information about the hydrogeology of the deeper confined units was available before the late 1970's because few boreholes monitored those stratigraphic units. The beginning of the site selection process for the high-level nuclear waste repository necessitated the characterization of the hydrogeology of the deeper units. Subsequently, numerous boreholes were drilled and ground-water levels in the confined horizons were monitored at the site. Prelim-

18 17 inary results from recent developments have been compiled to give an initial characterization of the site (DOE-SCR, 1982; DOE-DEA, 1984). Currently, there are plans to continue the characterization of the hydrogeology by drilling additional boreholes and conducting more aquifer tests. Purposes of the Study The purpose of this study is to determine whether natural and incidental, man-made disturbances in ground-water levels can provide additional useful hydrogeologic information. Specific goals include: (1)determining whether analysis of natural ground-water variations is a practical method for hydrogeologic investigations, (2)identifying the source(s) of influence on ground-water levels in the study area, (3)estimating the effect of the Columbia River on groundwater level fluctuations, (4)identification of possible hydrogeological barriers, and (5) examining the vertical connectivity of the hydrostratigraphic units. Study Outline Several steps are taken in the study to address the goals previously outlined. (1) Provide a general description cf the geography, geology, and hydrology of the study area (Chapter TWo),

19 18 (2) Examination of the ground-water variations present in the time-series is made in Chapter Three. These include the analysis of effects vala - Columbia River - Ground-water withdrawals in the upper Cold Creek Valley - drilling disturbances (3) The possible presence of hydraulic barriers in the study area is examined in Chapter Four. The effectiveness and extent of the barriers are examined. (4) Vertical relationships between ground-water levels in hydrostratigraphic units are studied in Chapter Five. Possible vertical connection or communication is studied. (5) Results from the previous three chapters are combined with current knowledge to form a conceptual franewcmrk for the hydrogeolcgy in the study area (Chapter Six).

20 19 CHAPTER TWO STUDY SETTING Geogray The study area is in sputhcertral Washing-Um (Figure 1.1). Mbre specifically, it is in a regional topographic low in the Pasco Basin bordered to the north by the Columbia River, to the east by the eastern extent of the reference repository location (RRL), to the south by the Yakima Ridge anticline, and to the west by the upper Cold Creek Valley. Land surface elevations in the study area range from 400 to 1600 feet above mean sea level (MSL) at the Columbia River and UMtanum Ridges, respectively. The elevation in the center of the RRL is approximately 700 feet above L. Major population centers near the study area are the cities of Richland, Kennewick, and Pasco. Richland, which is the closest city to the study area, had a population of 33,478 in 1980 (U. S. Census Bureau, 1981). Land use is currently controlled at the Hanford Site to characterize the site for a potential high-level nuclear waste repository. The upper Cold Creek Valley an the western edge of the study area is privately owned. A variety of crops are grown an land irrigated by ground water pumped from wells in the area. The climate is semi-arid. Annual precipitation at the Hanford Meteorological Station is 6.3 inches. Mbst precipitation occurs in the

21 20 late fall and early winter. Average monthly temperatures range from 29.3 F (-1.5 C) in January to 76.4 F (24.7 C) in July (DOE-DEA, 1984). Geology Stratigraphy The Pasco Basin, which is near the center of the Columbia Plateau, is underlain by Miocene tholiitic flood basalte interbedded with sedimentary deposits. The basalt flows are part of the Columbia River Basalt Group which consists of the (1) Grande Ronde, (2) Wanapum, and (3) Saddle Mbuntain Basalt Formations (Swanson et al., 1979). A complete stratigraphic section of the RRL is shown in Figure 2.1. Table 2.1 gives a list of the wells analyzed in this report and the hydrostratigraphic units which they monitor. The stratigraphy may be divided into four groups: (1) pre-baqalt or basement rocks, (2) Columbia River Basalt Group, (3) intercalated sediments, and (4) suprabasalt sediments. Basement rocks. Rocks older than the Columbia River Basalt Group are exposed at the outer regions of the basin. Within the study area, basement rocks are generally a few thousand feet below the land surface. For this reason, pre-basalt rocks will not be a pert of this report. Columbia River Basalt group. The Columbia River Basalt Group was formed from 16.5 to 6 million years ago. Flows were more voluminous and frequent in the early times and became less extensive with subsequent events. Therefore, the intercalated sedimentary deposits are more numerous in the yourver Saddle Mountain Formation. Individual

22 21 Hanford formation SOO Ringoid Formation ELEPPIANT MOUNTAIN MEMBER RATTLESNAKE RIDGE INTERRED 0 POMONA MEURER SELAPI INTERRED , ESGUATZEL WEISER COLD CREEK \ROOMED UMATILLA MEMOIR MARTON INTFRIIED 2 2 V ,500 PRIEST RAPIOS MEANER o w ROZA IMEAMER , , FRENCHMAN SPRINGS MINIMA , , /VANTAGE INTENSE MIDDLE SENTINEL BLUFFS FLOW ( Z 0 WW MW , %%COY CANYON FLOW LNATANUM FLOW , VERY HIGH \Mg FLOW Al' LEAST 30 FLOWS TO IASI OP GRANDE RONDE BASALT Figure 2.1. Stratigraphic section at the reference repository location (DOE-SCR, 1982).

23 22 Table 2.1. Boreholes and the Mbnitcred Hydrostrattyraphic Units Borehole/Piezometer Mbnitored Unit(s) DB-12 Rosalia flow top O'Brian Rosalia flow top Ford Rosalia flow top DB-11 Rosalia flow top DC-19, 20, and 22 basal Ringold unit Rattlesnake Ridge interbed Mabton interbed Rosalia flow top Sentinel Gap flow top Ginkgo flow top Rocky CCulee flow top Cohassett flow top Umtanan flow top DC-23W Rosalia flow top Sentinel Gap flow top Ginkgo flow top DB-14 Rosalia flow top

24 23 flows in the Columbia River Basalt Group range up to 300 feet thick; the average is 100 to 150 feet (Swanson and Wright, 1976). The Grande Ronde Basalt is the thickest formation in the Columbia River Basalt Group. It is approximately 85 volume percent of the Columbia River Basalt Group and consists of at least 56 basalt flows. Separation of the Grande Ronde Basalt and the overlying Wanapum Basalt is marked by the Vantage interbed which was deposited between flow regimes. This study concentrates an the units above the Grande Ronde Basalt. The Wanapum Basalt was extruded 14 to 13.5 million years ago. It ccmprcrnises approximately 3 volume percent of the Columbia River Basalt Group (Myers/Price et al., 1979). The Wanapum Basalt is separated from the underlyingcande Ronde Basalt by the Vantage interbed and the overlying SaddleMountainBasalt by the Mabton interbed. The Wanapun Basalt consists of ten to 13 flows divided into the Frenchman Springs, Roza, and Priest Rapids Members. This study will concentrate on the Priest Rapids member. Some of the analysis involves the Sentinel Gap flow which is in the Frenchman Springs Member. The Priest Rapids Member is the ycungest member of the Wanapum Basalt Formation and consists of the (1) Rosalie flow, and (2) overlying Lolo flow. Thickness of the Priest Rapids Member is 150 feet at the RRL. The flows, however, thin across structural highs such as anticlines. The Priest Rapids Member is overlain by the Mabtan interbed which separates it from the Saddle Mbuntain Basalt Formation. The Saddle Mountain Basalt is the youngest formation in the Columbia River Basalt Group. Deposition occurred during a period of

25 24 declining volcanic activity from 13.5 to 8.5 million years before present (Watkins and Baksi, 1974: McKee et al., 1977; ARHCO, 1976). The Saddle Mountain Basalt, which cartoranises less than one volume percent of the Columbia River Basalt Group, is divided into the ESguatzel, Pomona, and Elephant Mountain Waters. Intercalated sediments. Sedimentary interbeds are scarce in the Grande Ronde and Wanapum Basalts but are more common in the Saddle Mbuntain Basalt Formation. In this study, the ground-water levels In the Mbton and Rattlesnake Ridge interbeds will be exaninecimost extensively. Suprabasalt sediments. A majority of the study area is covered by sedimentary deposits which post-date the Columbia River Basalt Group. The sediments are from two sources: (1) Pleistocene sediments from catastrophic flooding, and (2) Halocene sediments, primarily alluvium, and eolian deposits. The basal Ringold unit will receive the most examin'ation in this report. Lithology Basalt flows. Internal structures found within basalt flows, as a result of their emplacement and cooling, are termed intraflaa structures. The structures are defined by the (1) abundance and geometry of fractures, and (2) number and size of vesicles or flow top breccia. Intraflcw structures typically present in basalt flaws are shown in Figure 2.2. The intraflow structures may vary in thickness or may be repeated in a single flow. Three primary inttaflow structures are the (1) vesicular or brecciated flow top, (2) entablature, and (3)

26 25 APPROXIMATE VERTICAL SCALE METERS 10 FEET 30 5] [15 1) 0 Figure 2.2. Basalt intraflow structures (DOE-SCR, 1982).

27 26 colonnade (Long and WC, 1984). Flow tops are generally located in the top ten feet of a flow and are less than 25% of the flow thickness. The flow interiors consist of the entablature and colonnade. The entablature is highly fractured. The colonade has less fractures but has relatively well-formed cooling joints which are generally vertically oriented. Sedimentary interbeds. Sedimentary interbeds are characterized by two major lithologies: (1) volcaniclastic sediments deposited by ashfall and tributary rivers, and (2) clastic, plutonic, and metamorphic rock derived from Rockylviountain terrain. Post-Basalt deposits. Sedimentary deposits in the Pasco Basin are in the Ringold and Hanford formations. The older Ringold formation is from 8.5 to 3.7 million years old and is divided into basal, lower, middle, and upper textural units. The basal Ringold, which is examined in this study, represents a fining-upward fluvial cycle from a coarse facies to a paleosol. The Hanford Formation was deposited when ice dams in western Mbntana and northern Idaho were breached. Most of the sediments are from the late Pleistocene. Deposits include the Pasco gravels which are restricted to the high-energy pathways of the flood channel and the Touchet Beds, which are a fine grained, slackwater flood facies. Structural Geology and Tectonics The structural geology in the study area is characterized by east-trending, linear, anticlinal highs separated by broad synclinal valleys. Structures are characterized by east-trending, narrow,

28 27 asynmetrical anticlines with steep north limbs and gently-sloping south limbs. The Uhrtanum Ridge anticline is an example of this type of structure (Figure 2.3). The Cold Creek syncline, which lies between the anticlinal ridges, is a broad, gently-sloping structure trending to the southeast. Most known faults in the Pasco Basin are associated with the compressional stress which formed the anticlinal ridges. Identified faults in or near the study area are thrust (reverse) faults, although normal faults have been identified (i lwciomb, 1973). Folding. As mentioned previously, two major fold axes in the study area are the UMtanum anticline and the Cold Creek syncline. The Umtanum Ridge anticline is asymmetric and has second-order folds associated with its hinge zone. The Cold Creek syncline is a broad, sediment-filled structure. Distribution of flows in the subsurface suggests that initial folding and uplift in the Pasco Basin occurred during Grande Ronde time. The Ringold Formation, which was deposited 3.7 to 8.5 million years ago, is deformed suggesting a low rate of deformation from the Miocene through to possibly the present. Faulting. Folds and faults appear to have been contemporaneously formed from a north-south compression during the Miocene and later time. Most of the known faults are associated with the anticlinal axes. The dominant type of anticlinal faults are reverse faults with an east-west strike. Reverse faults are generally thought to be caused by interlayer slip which occurs when two stratigraphic layers slide relative to one another due to the ccmpression and resultant

29 mtari um F.-,lage Anti ci i n e n DB-12 O'Brian DC-23W 41 Ford Cold Creek,_ Ifalleg7 11 Cold Creek Barrier DC-22 Borehole Lof.,-ation Ii 1 CI 1 -.> miles DB-14 t rie DC-19 Figure 2.3. Geologic structures in the study area.

30 29 folding. The synclinal axes are thought to be less strained due to their broad configuration. Normal faults with north-south strikes have also been mapped in the region (Newcanb, 1973). Tear faults, which generally have strikes perpendicular to reverse faults, are also expected to be present in this type of tectonic environment. The orientation of the tear fault plane is generally vertical and the displacement is primarily strikeslip, although dip-slip is also possible. Fractures. Fractures may be associated with the cooling of the basalt flow or subsequent forces exerted on the flows. Major tectonic structures in the study area are a result of horizontal, north-south ccmpressional stresses. Well-defined fracture patterns can often be related to the resultant folds such as the Untanum Ridge. Two sets of fractures which develop as a result of a north-south compression are (1) subparallel to the regional stress, and (2) oriented parallel to the fold axis. The sets of fractures are generally well-developed along the crest of the fold axis and may extend through the entire thickness of the fold. Hydrology Surface Water Rivers and streams. The Columbia River is the only perennial river in the area. The River flows to the east in this area and is controlled by a series of dams upstream. The closest upstream dam is the Priest Rapids Dam five miles west of the study area boundary. Grant County Public Utility District operates the dam for electrical

31 3 0 power generation. Two miles below the dam, the U.S. Geological Survey ncnitors a river stage gauging station. Cold Creek, which is in the southern section of the study area, is an ephemeral stream that drains the upper Cold Creek Valley. The southwestern two-thirds of the study area is within the Cold Creek watershed. Lakes and ponds. Several man-made ponds are located within the study area. These ponds are used for the disposal of low-level radioactive wastes, industrial wastes, laboratory and sanitary wastes, and discharge of water used for plant cooling. Most of the ponds In the study area are in the central portion of the RRL. Groundwater Unoonfined aquifer. The unconfined aquifer in the study area consists of fluvial and lacustrine sediments 0 to 250 feet thick, lying above the basalt flows. Water table elevations have risen approximately 80 feet in some areas due to local water disposal in surface ponds. The water table is approximately 470 feet above mean sea level at the RRL which corresponds to a depth of approximately 165 feet below the land surface in the center of the RRL. Recharge to the unconfined aquifer is from (1) the Columbia River during high river stage, (2) infiltration from precipitation in the higher elevations to the west, and (3) infiltration from waste water disposal ponds at the RRL. Discharge is primarily into the Columbia River at the eastern edge of the Hanford Site, but also into the river on the northern

32 31 boundary of the study area during low river stage. Bank storage fit the Columbia River has been shown to affect the water table elevations north of the Uhtanum Ridge axis (Newcomb, 1973). Hydraulic conductivities of the unconfined aquifer range from 102 to 100 ft/day for the sand and gravels to ft/day for finer sediments (Gephart et al., 1979). Stcrativities are typically 10-2 to Confined Aquifers Hundreds of feet of basalt flows with intermittent sedimentary interbeds lie below the thin layer of saturated, unconfined units. Vesicular zones in the flow tops have the highest transmissivities but are only 5% to 25% of the basalt flow thickness (DOE-SCR, 1982). Horizontal hydraulic conductivities in the Wanapum and Saddle Mbuntain flow tops range from 1075 to 103 feet per day. The mean horizontal conductivity is approximately 2 ft/day. Flaw interiors are thought to be effective aquitards because of their relatively low conductivities. Conductivities of the flow interiors range from 1077 to 10-6 ft/day; however, not much data are available for the flow properties of the interiors of the Wanapum and Saddle Mountain basalts. Storativities range from 1075 to 10-4 for the flaw tops. Sedimentary interbeds ccopramise approximately 25% of the total thickness of the Saddle Mountain Basalt and a lesser percentage of the Wanapum Basalts. Inbadoeds, depending on the clay content, may be aquitards or moderately transnissive aquifers. Horizontal conductivities range from 10" to 10 feet per day in the Saddle Mountain Basalt. Interbed

33 32 storativities reflect the percentage of fine material such as clay (10-4 to 10-3 ). Natural sources of recharge to the confined aquifers are primarily from rainfall infiltration and possibly river recharge. Basalt outcrops and greater precipitation in the higher elevations west of the study area provide recharge to the confined aquifers in the study area. Outcrops along the Untanum Ridge may also provide a source of recharge from the Columbia River. In certain areas, the unconfined aquifer may contribute to the recharge of the underlying confined units. Recharge to the confined units may also be the result of man's activity in the area. Waste water disposal ponds at the RRL have caused the increased elevation of the water table in the area. As a result, a downward hydraulic gradient has developed atilt the unconfined to the confined aquifers. Discharge from the confined aquifers is (1) to the unconfined aquifer, (2) to the Columbia River, and (3) the result of ground-water pumping in the upper Cold Creek Valley. Discharge to the unconfined aquifer and Columbia River appears to be prevalent in the eastern section of the Hanford Site from available head data (Figure 2.4). Discharge from the Wanapum Basalt in the upper Cold Creek Valley from several wells which supply irrigation for the crops in the area. Pumping occurs primarily from April through October.

34 33 HANFORD StTE BOUNDARY 118 n n n DC.14 COLUMBIA 110 :UMTANUM GABLE MOUNTAIN GABLE MOUNTAIN POND REFERENCE REPOSITORY LOCATION OB-15 DC **" AREA OF DOWNWARD / HYDRAULIC GRADIENT / ( AREA OF UPWARD HYDRAULIC GRADIENT D8-14 OB 13 IMO- 14-E119 BOREHOLE LOCATION BOREHOLE INDENTWICATION WATER TABLE RATTLESNAKE RIDGE INTERBED NUMBERS INDICATE HYDRAULIC HEAD ELEVATION ABOVE MEAN SEA LEVEL (m) - n 1/0 WATER LEVEL IN COLUMBIA OR YAKIMA RIVER ABOVE MEAN SEA LEVEL Intl O 5 10 KILOMETERS llllllll RICHLAND 0 5 MILES RCPB Figure 2.4. Areas of upward and downward vertical ground-water flow (DOE-SCR, 1982).

35 3 4 Ground-water Flow Barriers Geologic structures which alter ground-water flow in the Columbia River Basalt have been recognized for many years. The effects of "subsurface dans" in this area have been examined (Newcomb, 1961). The types of structures which affect the regional ground-water flow and the forces that may produce than were examined. Fault zones can dramatically alter ground-water flow. Most of the ground-water flow in the basalt occurs through the thin flow tops. Faults may displace and destroy the transmissive conduit and produce a zone of low permeability. As a result, the lateral movement of ground water can be impeded. Structural deformation along the Uhrtanum Ridge anticline and its associated secondary folds may contain faults which may act as ground-water barriers. The Cold Creek impediment, which is thought to be a fault, is a known ground-water barrier within the study area. The effectiveness and extent of the barrier, however, are unknown. Ground-water Uses Ground-water pumping in the majority of the study area is restricted because of the research at the Hanford Site which currently includes a period to establish a ground-water level baseline. The only consistent use of ground water in the study area has been for the irrigation of crops and pasture in the upper Cold Creek Valley. Mbst of the pumping is from four wells within a one-mile radius from each other. Estimated annual ground-water pumpage from a oonamptive use analysis (James, 1982) is 140 million cubic feet in 1985 (Appendix C).

36 35 Current rates of withdrawal in the Valley began in 1981, but there was little or no pumping in the area from 1952 to the late 1970's (Livesay, 1986). Man-made Ground-water Disturbances Nbmerous men-made disturbances to ground-water levels have occurred in the study area since the late 1970's. As previously mentioned, privately-owned irrigation wells in the upper Cold Creek Valley have been withdrawing ground water from the Wanapum Basalts during this period. Aquifer tests have also been done at the O'Brian and Ford wells on the western edge of the Hanford Site. Ground-water disturbances are also caused by the drilling of new wells and deepening of existing wells. Numerous new wells were drilled since 1979 within the Hanford Site. Drilling disturbances which affect this research include those at (1) DC-19, DC-20, and DC-22 in the last half of 1983 and into 1984, and (2) DC-23 during the fall of Ground-water disturbances at these wells may be greater because they are large diameter piezometer nests which penetrate the entire basalt sequence into the Grande Ronde Basalt. Ground-water Levels Piezcmetric levels in the confined units are significantly different in the study area due to a ground-water barrier. The Cold Creek barrier, which has been identified as possibly a low-permeability fault zone, appears to be the cause for the head differential. Groundwater levels in the Wanapum Basalt on the western side of the Cold Creek impediment range from 920 feet above MSL at the O'Brian and Ford

37 3 6 wells to 850 feet above MSL at well DB-11. Horizontal gradients in the area appear to cause eastward flow; however, the ground-water pumping in the upper Cold Creek Valley appears to produce a cone of depression large enough to reverse the gradient direction based on ground-water levels at the O'Brian and Ford wells. West of the Cold Creek barrier, the vertical and horizontal hydraulic gradient appear to be significantly greater than the eastern side. On the west side, ground-water levels in the overlying Saddle Mbuntain and underlying Grande Ronde Basalt Formations are lower than the Wanapum Basalt. The ground-water levels in the Priest Rapids Member drop approximately 70 feet in less than three miles from O'Brian to DB-11. East of the Cold Creek impediment, ground-water levels are relatively uniform with depth and areal extent. Horizontal differences in piezometric levels in the Wanapum and Grande Ronde basalte are less than a few feet in the study area. Gradient directions within the study area have been estimated with several methods (Sorooshian et al., 1986; Djerrari, 1986). Due to the relatively flat piezometric surfaces in those formations, hcwever, the gradient direction has not been positively identified. Vertical differences in the piezometric surface on the eastern side of the barrier are small relative to those to the west of the barrier. Values range from approximately 450 feet above MISL in the basal Ringold unit to 400 feet above MSL for the Grande Ronde and Wanapum Basalte. Current data indicate a downward gradient at the RRL down to the Rosalia flow top.

38 37 CHAPTER THREE EFFECTS OF NATURAL AND INCIDENTAL FLUCIUATICNS ON GRCUND-WATER LEVELS Natural and incidental ground-water fluctuations are examined to gain information about the hydrogeologic characteristics of the study area. Potential sources of seasonal and daily fluctuations are: (1) Columbia River stage, (2) ground-water withdrawal in the upper Cold Creek Valley, (3) Priest Rapids Reservoir elevation, (4) rainfall-recharge, (5) barometric pressure, and (6) earth tides. Ground-water level time-series from eight boreholes in the study area are examined (Figure 1.1). Hydrographs for the eight wells are presented in Appendix A. The well(s) and the general area which they monitor are: (1) DB-12: north of the UMtanum Ridge anticline, (2) Cold Creek Walls (O'Brian, Ford, and DB-11): west of the Cold Creek impediment, and (3) RRL piezometers (DC-19, DC-20, DC-22, and DB-14): reference repository location. Several methods including statistical correlations, frequency analysis, and analytical solutions for drawdowns from pumped wells and

39 38 river-aquifer interaction are used to determine the possible causes of ground-water level variations. Initially, seasonal cycles are examined followed by an analysis of daily ground-water level fluctuations. Seasonal Fluctuations Seasonal fluctuations in ground-water levels are observed in the hydrographs of several boreholes in the study area (Appendix A). Possible causes of the seasonal fluctuations are: (1)Columbia River stage, (2)ground-water pumping in the upper Cold Creek Valley, (3)rainfall-recharge, and (4)Priest Rapids Reservoir elevation. Each of these potential seasonal influences are examined to determine whether they are affecting ground-water levels in various sections of the study area. Columbia River Stage Columbia River stage has a seasonal cycle due to the increased runoff in late winter and low flows in late summer. Figure 3.1 is a hydrograph of average daily Columbia River stage from 1981 through the summer of 1986 at a gauging station two miles downstream from the Priest Rapids Dam. Seasonal changes in the river stage may be causing ground-water level fluctuations, especially in the area closest to the river. The interaction between the river stage and ground-water levels is studied using two methods. First, lagged cross-correlations are

40 39 otd 0.0 cd Cf1 sc4 1-4 cd Pn4 Pla /40 o e o o 4;1' 444 4;14 (u) ahls IaATH CI NIP 1.4 CO

41 40 performed to give a statistical indication of the relationship. They provide a measure of the relationship and the time lag between the changes in river stage and the resulting changes in ground-water levels, if they exist. Second, the river-aquifer analytical solution is used to understand the interaction between the river and aquifer. The hydrogeologic relationship between the Rosalia flow top and the Columbia River is mostly unknown. The flow top outcrops at the Priest Rapids Reservoir and likely abuts the Columbia River along the relatively pronounced section of the UMtanum Ridge anticline at the western edge of the study area. The relationship is more speculative to the east. Solutions of the river-aquifer model are used to estimate the distance to a subaqueous outcrop and predict the responses from seasonal changes in the river stage at other wells in the area. Cross-correlations. Lagged cross-correlations between the river stage data and ground-water level data are done to estimate the statistical relationship. Columbia River stage data are smoothed using a centered 24-hour moving average intended to eliminate daily stage fluctuations and conserve the seasonal changes. Weekly time lag increments are used to obtain cross-correlation coefficients for each river/well canbination. The resulting acre:lamaze are presented in Appendix E. A summary of the results for the maximum correlations and the corresponding time lags are presented in Table 3.1. The highest correlation (r = 0.86) between the river stage and ground-water levels is at borehole DB-12. The corresponding time lag shows that ground-water level fluctuations are 13 days behind the river stage changes. Hydrographs of the smoothed Columbia River stage data

42 41 Table 3.1. Maximum Correlation Coefficients and the Correspcnding Time Lag from Lagged Cross-Correlations of Average Daily Columbia River Stage and Gcrcund-Water Levels Well Correlation Time Lag Behind Coefficient River Stage (days) D18, O'Brian.65 61* Ford.67 47* DB * DC-19: basal Ringold.17 1* Rattlesnake Ridge Mabbon.36 15* Rosalia Sentinel Gap DC-20: basal Ringold Rattlesnake Ridge Mabton.60 9 Rosalia Sentinel Gap DC-22: basal Ringold Rattlesnake Ridge Mabton Rosalia Sentinel Gap * - indicates a time lag ahead of the Columbia River stage.

43 42 and DB-12 ground-water levels adjusted for the 13-day lag are shown in Figure 3.2. The Columbia River stage data are smoothed using a 31-day centered moving average to show the seasonal fluctuations. A strong relationship between the river and DB-12 water levels is indicated by the hydrographs. Results of the cross-correlations of the river stage with the Cold Creek wells show a moderate correlation. Maximum correlation coefficients range from 0.54 at well DB-11 to 0.67 at the Ford well. The most important result, however, is that the seasonal grcund-water fluctuations at the Cold Creek wells are ahead of the river stage fluctuations as indicated in Table 3.1 and shown in Appendix E. This indicates that the seasonal changes in the Columbia River stage are not the primary cause of the seasonal ground-water level fluctuations in the Cold Creek wells. The correlations may be spuriously high due to two similar, physically independent seasonal trends. Lagged cross-correlations are performed on five hydrostratigraphic units at each of the RRL wells. Ground-water level data for the (1) basal Ringold unit, (2) Rattlesnake Ridge, (3) Wotan interbed, (4) Rosalia flow top, and (5) Sentinel Gap flow top are correlated with the river stage data at various time lags to produce the correlograms in Appendix E. The maximum correlations and the corresponding time lags are shown in Table 3.1. Maximum correlation coefficients between the RRL wells and river stage range from to 0.64 with time lags of the river stage changes and ground-water level responses from 15 days ahead of the River to 286 days behind. The unit with the greatest correlation at

44 43 I I tr) II 1 I I IIJIJI I I I 1 1 II IIIII (Jill 0 LO It n41 Tta Nzti (ii) IgAal aalvit

45 44 each piezometer is the Mabton intarbed. The highest correlations are at piezcmeters DC-20 (0.60), and DC-22 (0.64). Time lags of the reponses in the Mabton interbed behind the seasonal river stage fluctuations, however, are unexplainably different at DC-20 (9 days) and DC-22 (67 days). Hydrographs of the Columbia River stage and Mabton interbed residnai ground-water levels at DC-22 indicate that there is also a visual similarity (Figure 3.3). Residual ground-water levels such as those shown for the Mabton interbed in Figure 3.3 are =Natal by ranoving barometric effects and recovery trend (Appendix B). It is difficult to draw any conclusions about the interaction between the residual ground-water levels of the other units and the Columbia River stage because of the poor to moderate correlations (Table 3.1) and the lack of any visual similarity. River-aquifer model. Results from the cross-correlations show that ground-water levels in the Rcsalia flow top at DB-12 are affected by the seasonal Columbia River stage variation and also indicate that the Mabton interbed at DC-20 and DC-22 may be affected. An analytical solution for the propagation of cyclic pressure waves through a confined aquifer (Ferris, 1951) is used to explain the unknown relationship between the Columbia River and the hydrostratigraphic units. The river-aquifer model explains the interaction by direct hydraulic contact between the river and aquifer (contact model) and stress carmunication through a confining layer (loading model). A complete explanation of the underlying assumptions and mathematical derivation of the model is presented in Appendix D.

46 Mabton Residuals (ft) v.4 Cri Lf) Cf3 v I 6 6 co 11 a 0 _ 0..., -_ E g 6; uirse. 0 te 0. _ 0c../ : 14-0 CM V g ni,. ;A's 0 c u.,-i.--i In cm...) - 1 gl.e1 a) o -,-1 o. m :co 1 1 i f4 o a) _co 0.p.014 d 4 - M :}5 d (to r2 5-i-) : d 9 d o - cu P c\i 731cv 14,1 -_ 0 o 1-4 o a2v 1 s aanizi co

47 46 Ground-water levels at DB-12 were shown to be highly correlated with the river stage changes. The river-aquifer model is used to evaluate the physical relationship between the well and the river. The critical assumptions of the model for this analysis are aquifer homogeneity, the great inland extent of the Rosalie flow top, and the simplification of one-digensional ground-water flow. Docamentxxlvaaues for the flow top transmissivity range from 740 ft2 /day to 120,000 ft2 /day (Bruce, 1983). Lack of information 'about the flow top between DB-12 and the Columbia River, however, cannot improve the simple assumption of the model. The continuous inland extent of the flow top is also questionable based an results in the next chapter. Geologic information indicates that the Rosalie flow top may outcrop along a section of the Columbia River and farther to the east the flow top may be seperated from the river by a confining layer. In this case, ground-water level respcnses from the river stage variations would be more complex than the assumptions of the analytical solution. The first process which may explain responses in ground-water levels from the Columbia River is the loading of the aquifer by changes in river stage. This process is illustrated in Figure 3.4b. A change in weight caused by river stage fluctuations causes a change in stress in the underlying aquifer. The pressure change is propagated through the aquifer and detected as a water level fluctuation in a well. The magnitude and time lag of the fluctuations are predicted using the river-aquifer model.

48 47 Well Ground Surface I : :,,,,-:-: : : ::: :: : : :.. :.: , _:: -,..: : : : : :-: : : ::: :-: -: : : : ::: i _.....,.... IFiezon-tetric Surf:eel. - : : : : -. Rnqe a of Fluctuation.z.h "-- :-H--;4-:.: ' : ' :- :: : : : - - : :: : !.. : Idi3tdnt.e.4 t lean Stage 1% --'0" -."? ::> Confined Aquifer Columbia River (a) Well Ground Surface 1n1 Range of Fluctuation 2hC : : 1- : : r distawe x : :::::: I Stage Rand«2h... Piezornetric : : Range 2 hoc : : : Columbia River.. (b) Figure 3.4. Interaction between the Columbia River and ground-water levels through a (a) subaqueous outcrop, and (b) confining layer.

49 48 The predicted ratio of the amplitudes for the river stage, hb, and ground-water level, hb,, for the loading model can be calculated using the equaticxl: ho _ cesit T (3.1) where ho = amplitude of the river stage fluctuation 1 = amplitude of the ground-water level fluctuation T = aquifer transmissivity, S = aquifer storativity, to = period of the fluctuation, - x = distance from the river to the well, and C = aquifer tidal efficiency. Tidal efficiency, C, is used to approximate the percentage of the change in stress caused by the river stage change that is borne by the aquifer pore fluid. Estimates for the tidal efficiency were obtained by using the relationship: C = 1 - B (3.2) where B is the barometric efficiency which has been estimated from regressions of water level time-series and barometric pressure data (Scrooshian et al., 1985). The observed ratio of the ground-water

50 49 level at DB-12, hi, and the seascnad fluctuation arplitwies of the river, ho, is: N/ho = 0.70 The calculated tidal efficiency for the Rosalie flow top is: C = 0.30 Substituting these values into Equation (3.1) and solving for the exponential term: 2.3 = e -inirtr-s7te:t. Limits on the exponential term are: 0 < e Sit <1 for all positive values of T, S, and to ; therefore, the fluctuation amplitude at DB-12 cannot be explained by this loading model or any loading which involves exclusively the distribution of vertical stress through a confining layer. A second process which may explain the observed seasonal relationship between the Columbia River and DB-12 ground-water levels is a hydraulic contact between the Rosalie flow top and the Columbia

51 50 River. This process is illuslrated in Figure 3.4a. A change in the river stage directly affects the head in the aquifer, and the cyclic fluctuations are propagated through the aquifer. The predicted ratio of the amplitudes of the river stage and ground-water levels for the contact model is given by the equation: J11 e -04S/t0 T ho (3.3) where x is the distance from the subaqueous outcrop to the well. The only difference with the loading mcdel [Equation (3.1)] is the absence of the tidal efficiency. The predicted time lag, tl, for a change In river stage in a well a distance, x, away is: tl = Oft0 S/47rT (3.4) The distance from DB-12 to the potential outcrop with the river, x, is the unknown value in Equations (3.3) and (3.4). Observed or estimated values for the other parameters in the equations are: T = 1.3 x 103 ft2 /day to 2.9 x 100 ft2 /day (Bruce, 1983) S = 1 x 10r 5 (DOE-SCR, 1982) to = 365 days h,/b0 = 0.70

52 51 tl =13days Values for to, N/hb, and t are obtained from the examination of the water level time-series. The distance to the subaqueous outcrop, x, can be found by using Equation 3.3. Because there is a range of values for the transmissivity of the Rosalie flaw top, the calculated distance to the outcrop is a range. 8.3 miles < x < 18.0 miles Equation 3.4 provides a calculated range based on the observed time lag of the seasonal fluctuation. 5.9 miles < x < 12.9 miles Geologic information indicates that the Rosalie flow top does not contact the Columbia River east of DB-12. This is the reason that the above calculated distances to the outcrop are to the northwest of DB- 12. The possible areas of the subaqueous outcrop of the Rosalie flow top and the Columbia River based on these calculations are illustrated in Figures 3.5a and 3.5b. There is also a possibility that the Rosalie flow top may have a outcrop directly north of DB-12. Results from this analysis do not corroborate this possibility. Instead, the model indicates that the contact area is where the Ubtanum Ridge abuts the river.

53 52 basalt outcrop ixrssi ble sub - aqueous o uto ro p / 030 nq station - - (6) Priest Rapids Rese rvoi r basalt outc ro poni bl e sub:- ag ueo gaging station Col urn bia RI ve r Figure 3.5. Estimated areas of and the Columbia magnitudes, and (b) model. (b) contact between the Rosalia flow top River based on the (a) fluctuation response time lag in the river-aquifer

54 53 Analysis of the relationship between the river stage and DB-12 ground-water levels gave an estimate of the nature of the interaction and distance to the Columbia Ftiver/Rosalia flow top contact. With this information, the river-aquifer model is used to predict seasonal ground-water level fluctuations in the Rosalia flow top and other units at the remaining wells in the study area. The magnitude and time lag of the seasonal ground-water level fluctuations can be predicted by the model from Equations (3.3) and (3.4). Predicted and observed seasonal fluctuations from the Columbia River stage are given in Table 3.2. Results for the Cold Creek wells show that the predictednognitude of the seasonal fluctuations is approximately four feet, with a two-day time lag. The observed ground-water level fluctuations at the Cold Creek wells, as illustrated in Appendix A, show a seasonal trend, but the cycle is ahead of the river cycle. The predicted effects, therefore, do not appear in the water level time-series at the Cold Creek wells either because the ground-water levels are not affected possibly due to the presence of a hydraulic barrier or the river's effects are present but are ovendhelmed by another seasonal source. Predicted and observed effects from the seasonal river stage changes on ground-water levels at the RRL piezareters are presented in Table 3.2. Predictions for the Rosalie flow top are based on a contact with the river near the gauging station as indicated by the previous analysis. Predictions for the other monitored units at the RRL piezameters assume the shortest distance between the river and the piezometer. This assumption will result in higher predicted groundwater level fluctuaticns and a lower bound on the predicted time lag,

55 54 Table 3.2. Predicted Seasonal Ground-Water Level Fluctuations and Time Lags from Seasonal Columbia River Stage Changes Versus Observed Seasonal Ground-Water Level Variations Amplitude (ft) Time Lag (days) Well Predicted Contact Loading Observed Predicted Observed O'Brian * Ford DB DB * DC-19: Rattlesnake Ridge interbed * Mabton interbed Rosalia flow top Sentinel Gap flow top DC-20: Rattlesnake Ridge interbed Mabton interbed Rcsalia flow top Sentinel Gap flow top DC-22: Rattlesnake Ridge interbed * Mabton interbed Rosalia flow top Sentinel Gap flag top * - no evidence of seasonal ground-water level fluctuations + - time lag ahead of the Columbia River stage

56 55 but without any better information it is a reasonable assarptial. The loading model is considered in addition to the contact model for the other units because the physical relationship with the river is unknown in this area. The predicted magnitudes of the seasonal ground-water level fluctuations in the Rosalia and Sentinel Gap flow tops at each piezometer are at least one order of magnitude greater than the observed fluctuations. The predicted fluctuations in the Mebton and Rattlesnake Ridge interbeds are within four times the observation. In review, Columbia River stage fluctuations affect groundwater levels in the Rosalia flow top at DB-12 and apparently the Mebton interhed at DC-20 and DC-22, but are not clearly observed in other units at the remaining wells. The correlations also indicate that the seasonal Columbia River stage changes are not the primary cause of the ground-water level fluctuations at the Cold Creek wells. Crosscorrelations with the remainder of the units in the RRL piezcmeters do not indicate any clear relationship with the seasonal river stage changes. A river-aquifer model was used to understand the interaction between the river and the aquifer. First, ground-water levels at DB-12 were studied. The model suggests as a possibility that a hydraulic contact exists between the Rosalie flow top and the Columbia River at least six or seven miles northwest of DB-12. This information was then used to predict the river stage effects in the Rosalia flow top at the other wells in the area. Predictions for other units at the RRL wells were also made. With the exception of the Mebton and Rattlesnake interbeds at piezometers DC-20 and DC-22, the predicted effects are

57 56 significantly higher than the observed responses. Possible reasons for these results are given in Chapter Four. Ground-water Withdrawals Ground-water withdrawals in the upper Cold Creek Valley for irrigation are expected to have a seasonal effect an ground-water levels in the study area, especially at the Cold Creek wells. Two methods are used to examine the potential and observed effects of the grourn7withdrawals: (1) Calculate the expected drawdowns at the observation wells by using the Theis equation. (2)Use lagged cross-correlations between the ground-water levels at the Cold Creek wells (assuming they primarily reflect the responses to the pumping) and other wells in the study area to find "hidden" effects in the timeseries. Drawdown calculations. Seasonal ground-water level fluctuations from the pumping in the upper Cold Creek Valley are estimated by using the Theis solution. Drawdowns at other points in the study area, which monitor the ground-water levels in the Priest Rapids member, are calculated for the irrigation season (April-October) by using the equation: Q r e-u s = du (3.5) 4-ra j u

58 57 where s = drawdown, Q = pumping rate, T = transmissivity, u = r2 S/4tT, S = storativity, t = time since pumping began, and r = distance between the pumping and observation wells. A monthly pumping rate, Q, is estimated from a consumptive use analysis for the crops in the upper Cold Creek Valley (Appendix C). CUmulative effects of the variable monthly pumping rates are calculated using the equation: 1 s = 4TrT EA w(u) (3.6) = change in monthly pumping rate (Q ) w(u) = well function' u = r2 S/4T(t-ti ), t = time since pumping began, ti = time since pumping rate (Q10 began, T = transmissivity, S = storativity, and r = distance between the pumping and observation wells.

59 58 Two wells discharge nearly all the grotind-water for irrigation in the upper Cold Creek Valley (Figure 3.6). The principle of superposition is used to get the cumulative drawdown from the pumping at these two wells during the growing season. Predicted 1985 drawdowns from this analysis are shown with the observed ground-water level fluctuations during the same period in Table 3.3. Drawdowns are calculated assuming the presence or absence of an impermeable boundary at the location of the Cold Creek Barrier. The predicted magnitude of the seasonal drawdowns assuming the presence of the barrier match the observed fluctuations best at boreholes O'Brian and Ford and also predict the absence (or near absence) of drawdowns at the RRL piezometers east- of the barrier. It has been shown that the observed fluctuations at DB-12 are due to the Columbia River stage changes. The assumed presence of the Cold Creek Barrier, therefore, predicts the observed fluctuations better for every well except DB-11. Table 3.3 shows that the predicted drawdowns from the groundwater withdrawals at the Cold Creek wells are better represented when the presence of the Cold Creek Barrier is assumed. The time lag of the predicted fluctuations is also insignificant compared with the observed drawdowns as shown in Figure 3.7. Discrepancies in this analysis between the calculated and observed drawdowns are from several causes. First, there may be multiple seasonal influences on the ground-water levels at a well which would disguise the true effect of the pumping. Second, the aquifer was assumed to be homogeneous. Documented values for the transmissivity

60 59 DB-12 -CUB ri a n DC-23W DB-11 DC-22 pumping Cold Creek 0 2 y Col d Creek #1 Figure 3.6. Location of upper Cold Creek Valley pumping wells used in the drawdown analysis.

61 60 Table 3.3. Predicted Drawdowns as a Result of Ground-4*Am- Withdrawals in the Upper Cold Creek Valley Assuming the Presence or Absence of the Cold Creek Barrier Versus Observed Seasonal Flucbmitims in the Rosalia Flaw Top Well Predicted Drawdown (ft) No Barrier Barrier Observed Drawdoval/Fluctuaticn (ft) O'Brian Ford DB DB DC DC DC

62 61 li.11 -Co v....),., $.., 0,., E Q) n p-4... Ti 4 W ". A 1.1"4 0 n I "C, ra 14 W.4.) I"' g f: PvCCi _ 1:51 i 8 _ ;t i CO.. _ ril M g Cra 5 ' g Cli PI _.8 p) rf _ vig q4, _ ig #,> 0,-4 tt, IIIIIIITTIIIIIIIII co If) o in o tf3 m -i Cf3 CA CA CA CA CO ( 1 j ) TaAal aalpm

63 62 range from 740 ft2 /day to 120,000 ft2 /day. Third, the pumping rates are discretized into monthly segnents, therefore, the predictions for the amplitude and time of the drawdowns are not very precise. Cross-correlations. Comparison of actual and predicted groundwater level fluctuations using the Theis solution indicates that the Cold Creek wells are the only wells noticeably affected by the groundwater withdrawals in the study area. Cross-correlations are used to verify the conclusion that all of the Cold Creek wells are responding to the same external source and to possibly reveal a "hidden" relationship between the ground-water levels in the Cold Creek wells and other wells in the study area. Drawdown calculations have shown that the ground-water levels in the Cold Creek wells are primarily responding to pumping in the upper valley. If this conclusion is correct, the cross-correlations between the ground-water level data for these wells should produce a high correlation coefficient with a all time lag. Results of the lagged cross-correlations listed in Table 3.4 show this to be true. Correlation coefficients are greater than 0.96 with no time lag greater than seven days. Lagged cross-correlations between the Cold Creek well data and other well data are not conclusive. Table 3.4 shows that the correlation coefficients are moderately high (0.46 to 0.67), and that the ground-water levels at the other wells are from seven to 19 weeks behind the levels in the Cold Creek wells. The moderately high correlation coefficients are probably spurious because the other wells have similar but physically unrelated seasonal trends.

64 63 Table 3.4. Maximum Correlation Coefficients and the Corresponding Time Lag (Days) Between the Cold Creek Wells and Other Wells Which Monitor the Priest Rapids Member (Time Lag Behind the Cold Creek Wells) Cold Creek Wells O'Brian Ford DB-11 O'Brian -.96 (0-7).99 (0-7) Ford.96 (0-7) -.98 (0-7) DB (0-7).98 (0-7) - DB (49).67 (70).57 (49) DC (98).61 (98).67 (98) DC (91).41 (11).41 (91) DC (110).59 (105).55 (154)

65 64 In review, irrigation activity in the upper Cold Creek Valley appears to be affecting the ground-water levels only at wells O'Brian, Ford, and DB-11. Predicted drawdowns from the Theis solution and cross-correlations between the water level data confirm this conclusion. Predicted drawdowns fll1il the pumping are up to 30 times greater than the observed seasonal fluctuations in the RRL piezometers. Crosscorrelations between ground-water levels at the Cold Creek wells and the RRL piezometers also do not show any significant relationship. Finally, there is no indication from the drawdown calculation or crosscorrelations that the ground-water levels at DB-12 are affected by the irrigation activity. Reservoir Fluctuations Seasonal changes in the level of the reservoir behind the Priest Rapids may be causing ground-water level fluctuations in the same way that the Columbia River stage may be affecting water levels. A previous analysis in this report suggests that the fluctuations at borehole DB-12 are due to Columbia River stage changes below the reservoir, but the possible effect of the reservoir fluctuations must also be considered. Average monthly levels in the reservoir are shown in Figure 3.8. The amplitude of the seasonal fluctuations in the reservoir forebay is approximately 0.75 feet. The reservoir level is kept fairly constant to optimize power generation. Ground-water levels at DB-12 are also shown in Figure 3.8 to contrast the magnitudicks of the fluctuations. Reservoir level changes appear to be too small to be a sig-

66 65 Reservoir Level (ft) If) 0 Cb CA It N r- al o a) a).14cf) C., (1J) IaAai dalvx Zi EIG co

67 66 nificant effect on the ground-water levels in the study area based on this qualitative examination. Rainfall-Recharge Aquifer recharge from precipitation may be a possible source of seasonal ground-water level fluctuations. Recharge is the most important factor in the process. It depends on (1) rainfall intensity, (2) distribution, and (3) surface runoff. Unfortunately, not much information is available for these factors. lalt and dry periods have been shown to affect water levels over many years. Years of higher than average precipitation cause the ground-water levels to rise, and the opposite is also true. Perhaps deviations from the annual mean precipitation may cause seasonal ground-water fluctuations. Figure 3.9 is a graph of the deviations from the mean of precipitation at the RRL plotted with the hydrograph of the O'Brian well which is the closest well to the recharge areas. The figure shows that the deviations in precipitation are about.08 feet compared to the 18 feet fluctuations at O'Brian. The magnitude of the ground-water fluctuations from rainfall-recharge, f, is dependent on the amount of precipitation, p, the percentage recharged, r, and the effective porosity of the rock matrix, n- Estimates of these parameters are: p = 0.8 feet (DOE-SCR, 1982) r = 4% (Livesay, 1986) n = 1% (Sublette, 1986)

68 67 Precip. Deviation (it) o Ill 0 li, 0 qr40 c;c6 I i CO o N-4 CO tr ri.0 p-4.4 ilti Mal bfil.. al >1 4-),.. r-i i' - co V (1-.5 g - 1,_, 0 16, 5 49 a; It.11 cn - 4, tho i (1) 11) v..4 0 CA CA (u) utlas I o

69 68 The magnitude of the fluctuation from rainfall-recharge is calculated using the relation: f = p r / n = 0.32 ft. This fluctuation would be hidden by the overwhelming effects of the pumping in the upper Cold Creek Valley. Any potential effects of rainfall-recharge on the ground-water levels, therefore, cannot be evaluated. Summary of Seasonal Fluctuations Annual ground-water level fluctuations in the study area are expected to be the result of four possible sources: (1)Columbia River stage, (2)ground-water withdrawals in the upper Cold Creek Valley, (3)Priest Rapids Reservoir, and (4)rainfall-recharge. Ground-water level time-series at eight wells are examined using crosscorrelations and analytical solutions for river-aquifer interaction and water level drawdowns to determine the cause of seasonal fluctuations, if present. Time-series in each section are studied, and the results show that seasonal ground-water level fluctuations in the: (1) Rosalie flow top at DB-12 in the northern section are primarily affected by the seasonal fluctuations in Columbia River stage,

70 69 (2) Cold Creek Valley in the Priest Rapids Mbmber is primarily affected by seasonal ground-water withdrawals for irrigation, and (3)RRL are not well defined in the basal Ringold unit, Rattlesnake Ridge interbed, and the Rosalia and Sentinel Gap flow tops with the available data. The ground-water levels in the Mlabton interbed, hcwever, appear to be affected by the seasonal Columbia River stage fluctuations. Daily Fluctuations Daily fluctuations are also expected to be evident in the ground-water levels. Daily fluctuations could be the result of one or many sources, including: (1)Columbia River stage, (2)barcinetric pressure, and (3) earth tides Detection of the daily fluctuations in the available time-series, however, may not be possible. Weekly water level readings are taken at boreholes DB-12, DB-14, and the Cold Creek wells (O'Brian, Ford, and DB-11). Daily measurements are taken at RRL piezometers DC-19, DC-20, and DC-22. There are no available data taken frequently enough to detect daily cycles with the exception of the Columbia River stage data, which are recorded two hours apart.

71 70 Columbia River Stage Columbia River stage is expected to have a daily cycle due to releases upstream at the Priest Rapids Dam for power generation. Figure 3.10 shows a segment of the river stage time-series with a daily cycle.!last of the river stage time-series, however, do not show an obvious daily cycle, as is seen in Figure To provide a quantitative estimate of the presence of the daily cycle, frequency analysis is used. Frequency analysis. Ground-water level data can be presented and studied in either the time or frequency domain. Mbst of the results and conclusions in this report are obtained by studying timeseries, however, the water levels can be given an amplitude as a function of frequency. A fast Fourier transform technique is used to calculate the amplitudes and frequencies of the fluctuations. A frequency analysis is performed on the Columbia River stage data to establish the existence and strength of a daily cycle. Figure 3.11 is a plot of cycle period and the power of the period in the data. A one-day cycle is shown by the spike at a period equal to 24 hours on the graph. Daily cycles, therefore, are present in the river stage time-series. Seasonal river stage fluctuations have been shown to affect water levels at DB-12 and at the RRL. It is possible that daily fluctuations in the river stage could also be affecting the groundwater levels. Similar methods (cross-correlations, aquifer-river model) are used to examine the relationship between the daily stage changes and ground-water level fluctuations.

72 n n i i co (1.j) 2P 1S 19 ATH o

73 ap -nviduly 72

74 73 Cross-correlations. Lagged cross-correlations are used to determine if daily river stage fluctuations are related to ground-water levels in the study area. The procedure is similar to the seasonal cycle analysis, except that the time scale has been narrowed. Available ground-water levels are matched with river stage data within the nearest river stage recording ( 1 hour). Time lag increments of two hours produce a correlogram. The correlogran for DB-12 ground-water levels and the river stage are presented in Figure An important result from the lagged correlations for each well is that the correlation peaks are 24 hours apart, indicating that a daily cycle exists in both river stage and ground-water level timeseries. Closer inspection of the correlograms for the RRL piezometers, however, shows that the time lags at each of the piezometers are generally identical (Table 3.5). Identical propagation of daily river cycles through the various hydrostratigraphic units would not be expected because of the different transmissivities and storativities for each unit [Equation 3.4)]. River-aquifer interaction. According to Equations (3.3) and (3.4), the magnitude and time lag of the cyclic pressure waves through an aquifer are dependent on the period of the cycle. Daily cycles will dampen more quickly through an aquifer than an annual cycle. Using the river-aquifer model, the predicted magnitudes and time lags of the wave are calculated at each well (Table 3.6). Predicted fluctuations in the Rosalia flow top at DB-12, O'Brian, Ford, and DB-11 are greater than the lower limit of detection which is assumed to be 0.01 ft. when measured by steel tape. Predicted daily fluctuations in all the units

75 c i IS r ILIOTOTH@OD

76 75 Table 3.5. Time Lags of Daily Ground-Water Level Cycles Behind the River Stage Changes at Various Boreholes Indicated by the Cross-Correlation with the Columbia River Stage Well Time Lag (hours) DB-12 4 O'Brian 20 Ford 24 DB DB DC-19: basal Ringold 4 Rattlesnake Ridge 14 Mebton interbed 4 Rosalia flow top 22 Sentinel Gap flaw top 22 Ginkgo flow top 2 Rocky Coulee flow top 4 Cbhassett flow top 2 UMtanum flow top 2 DC-20: basal Ringold 12 Rattlesnake Ridge 18 Nabton interbed 4 Rosalia flow top 22 Sentinel Gap flow top 22 Ginkgo flow top 18 Rocky Coulee flow top 18 Cbhassett flow top 18 UMtanum flow top 10 DC-22: basal Ringold 18 Rattlesnake Ridge 20 Mbbton interbed 18 Rosalia flow top 18 Sentinel Gap flow top 18 Ginkgo flow top 20 Rocky Coulee flow top 18 Cohassett flow top 10 Uttanum flow top 18

77 76 Table 3.6. Predicted Amplitudes and Time Lags of Daily Gtound-Water Level Fluctuations Due to Daily Columbia River Stage Changes Fluctuation Time Lag, Well Amplitude, hx tl (ft) (hours) DB O'Brian Ford DB DC-19: Rattlesnake Ridge interbed Mlabton interbed Rosalia flow top Sentinel Gap flow top DC-20: Rattlesnake Ridge interbed mabton interbed Rosalia flow top Sentinel Gap flow top DC-22: Rattlesnake Ridge interbed Miabton interbed Rosalia flow top Sentinel Gap flow top - indicates a predicted fluctuation less than 0.01 ft.

78 77 at DC-19, DC-20, and DC-22 are not expected to be observed; however, the correlograms show that all the ground-water level time-series in the study area have a daily cycle with nearly identical time lags at each well. The conclusion from these results is that either the correlations are spurious or the river-aquifer model is not able to accurately predict the observed results. Perhaps the daily groundwater level cycle is due to another source (earth tides), and the cross-oorrelaticns with the river stage are spurious. It is not possible to identify the source of the fluctuations with the available data. Barometric Pressure Diurnal atmospheric pressure changes are a potential source of daily ground-water level fluctuations. Ground-water levels may be affected in the same way as weather-related pressure changes except with a daily cycle. The considerations are (1) whether the daily barometric changes are present, and (2) if they are large enough to affect ground-water levels. Daily atnospheric pressure changes are present, especially in the tropics. The cycle is more defined at the equator than at higher latitudes. Maximum pressures occur around 10:00 A.M. and 10:00 P.M. and low pressures around 4:00 A.M. and 4:00 P.M.. Largest pressure differences are approximately 2.5 mb (1 inch of water). Assuming this pressure difference at the study area, the daily pressure effects are within detectable limits of ground-water level changes.

79 78 Studies of hourly barometric pressures at the Hanford Site using frequency analysis have shown that daily fluctuations do exist, and their effects on ground-water levels are within detectable limits (Sorooshian et al., 1986). Assuming the effects are evident at all the other wells examined in the cross-correlations, the different time lags of the daily cycles are not explained. The barometric effects should be affectingueter levels with a small or no time lag. Earth Tides Gravitational interaction of the earth, moon, and sun has been shown to cause detectable fluctuations in ground-water levels at the RRL (Sorooshian et al., 1986). The frequency analysis of atmospheric pressure in that report showed that it is difficult to separate the atmospheric and earth Uri/as. Earth-moon attraction, which dominates the earth tide effects, has an approximate twice daily cycle similar to the atmospheric tides. Earth tide effects are not daily, but they may explain the apparent daily cycle indicated by the cross-correlation analysis with the river stage. Correlation between ground-water levels and river stage shows a daily cycle. This may be explained by the presence of earth or atmospheric tide effects and the monitoring schedule. Examination of the ground-water level data at each of the RRL piezometers for all hydrostratigraphic units shows that water level measurements were generally taken:

80 79 DC-20: early to mid-morning DC-22: 1-2 hours following the recording at DC-20 DC-19: 6 hours following the recording at DC-20 It may be that this monitoring schedule and the presence of atmospheric and earth tide effects could cause the cross-correlation results between the river stage and ground-water levels, but without better data, it is difficult to be certain. Summary of Daily Fluctuations Due to limitations in the available data, cross-correlations between the river stage and ground-water levels were the only methods to uncover daily cycles. A daily cycle was present in the ccrrelc, grams; howlaver, the uniformity of the time lags indicated that the correlations may be spurious. Atmospheric and earth tides were shown in a previous investigation to be influencing the levels at the RRL. Because of the lack of frequent ground-water level data, the effects of atmospheric and earth tides and river stage could not be separated to successfully examine the daily fluctuations in ground-water levels.

81 80 CHAPTER FOUR GRIMM-MUIR BARRIERS In the previous chapter, analyses of cyclic ground-water fluctuations in hydrostratigraphic units indicated that geologic barriers created by structural deformatian of the units may be the cause for the lack of water level responses observed in certain areas. Seasonal Columbia River stage fluctuations apparently cause significant seasonal variations in the ground-water levels in the Rosalia flow top at borehole DB-12, but predicted effects were not observed at other wells. Also, ground-water withdrawals in the upper Cold Creek Valley do not seem to affect the ground-water levels in wells east of the Cold Creek barrier. Structurally-disturbed areas could act as hydraulic barriers in the study area. Previous investigations of structural barriers in the Columbia River Basalt provide conclusions that barriers do influence the regional hydrology (Newomb, 1961). Results from Chapter Three indicate that the Uttanum Ridge anticline and Cold Creek impediment are two possible structural barriers. Uttanum Ridge Anticline The Ubtanum Ridge anticline is an east-west trending asymmetric, plunging anticline in the northern part of the study area (Figure 2.3). The anticline is better defined in the western section compared to its eastern flank near Gable Butte. A more detailed description of the anticline is provided in Chapter Two.

82 81 There are two indications that the UMtanum Ridge anticline is acting as an impediment to ground-water flow in at least one aquifer. First, the seasonal effects of the Columbia River stage, which are evident and predictable at borehole DB-12, are not clearly observed or predictable in the Rcsalia flow top at any of the wells to the south of the anticline even though an aquifer-river model predicts that the fluctuations should exist at the wells. Second, man-made disturbances south of the axis do not appear in the ground-water level time-series at DB-12 north of the anticlinal axis even though the disturbance was clearly detected at a well an the south side of the axis the same distance away. Both cases are examined and possible explanations are given. Columbia River Stage Effects In Chapter Three, results indicate that effects of the annual Columbia River stage fluctuations are either undetectable or unexplainably insignificant in most of the monitored units at boreholes south of the Utmtanum Ridge anticline. Table 3.2 shows the predicted and observed amplitudes for the seasonal ground-water level fluctuations at various boreholes due to river stage changes. Seasonal river stage effects are: (1)undectectable or unpredictable in the ground-water levels at wells south of the anticline which mcnitor the Rosalia flaw top, and (2)apparently affecting ground-water levels in the Mabton interbed at DC-20 and DC-22.

83 82 It appears that river stage effects are nonexistent or insignificant south of the anticlinal axis for the highly-transmissive Rosalia flow top, but are evident in the less conductive Mabton interbed. Drilling Disturbances Another potentially useful way to analyze the effectiveness of the anticlinal barrier is to examine the influences of drilling disturbances on the ground-water levels. TWo disturbances that may be helpful are (1) drilling and development of piezometer DC-23W in the fall of 1985, and (2) drilling and development of piezometer nests DC- 19, DC-20, and DC-22 in late 1983 and early Effects of these disturbances significantly affected ground-water levels in the Rosalie flow top and can be studied at monitoring locations on either side of the anticlinal axis. Drilling and development of piezometer DC-23W in the Wanapum Basalt provides a good opportunity to analyze its influence on groundwater levels at various locations. Figure 2.3 shows that DC-23W is approximately equidistant from boreholes DC-20 and DB-12. Each borehole mcnitors the ground-water levels in the Rosalia flow top; however, they are on opposite sides of the anticlinal axis. Figure 4.1 is a hydrograph of the water levels at DC-20 and DB-12 during the drilling and development at DC-23W. Ground-water levels at DC-20 are significantly disturbed, but levels at DB-12, which is approximately the same distance from the disturbance, appear unaffected during the drilling period, therefore indicating that there is a reduced hydraulic communication in the Rosalia flow top between DC-23W and DB-12.

84 83 0 Cn1 8 w LL LL. w.â c liii ij II U'.) i 1 id a in co n tn r KS) () 13A VM,-; 4

85 84 Geologic Explanations The relatively complex structural geology associated with the Ubtanum Ridge anticline may provide answers about the barrier. Faults are commonly related to folds. Faults along or near the anticlinal axis are the most likely explanations for a hydraulic barrier. Northsouth canpressicnal forces, which produced the Ubtanum Ridge anticline, could also cause reverse or thrust faults along the axis, especially in the western section. The extent of any existing reverse faults along the anticlinal axis is uncertain. Basalt outcrops along the UMtanum Ridge in the western section and Gable Mbuntain provide clues that such structures exist (PSPL, 1982; NRC, 1982b, Appendices G and H); however, a significant portion of the anticline is burled under suprabasalts. Studies of the Uttanum Ridge anticline and other similar structures in the area indicate that the faults are not areally extensive and therefore the anticlinal axis may not act as a perfect barrier, but as an area which significantly deters the propagation of ground-water disturbances across it. A ocnceptual cross-section of the reverse fault is shown in Figure 4.2. Relative thicknesses of the Rosalie flow top and Mabton interbed are maintained. The figure shows that a relatively small displacement of the stratigraphic units by the fault may: (1)completely offset the thin, transmissive Rosalie flow tor), (2)not offset the thicker Mabton interbed, and (3) cause a lcw-permeability fault zone.

86 85 south north Figure 4.2. Calceptual cross-section of a reverse fault along the Umtanum Ridge anticlinal axis.

87 86 If these speculations are valid, a ground-water disturbance propagating through the Rosalie flow top might be stopped from traveling across the fault zone. This confirms the observation from the river stage and drilling disturbance analyses for the Rosalie flow top. Ground-water level disturbances in the thicker Mabton inbadoed, however, might be reduced by the low-permeability fault zone, but the dampened effects may be able to propagate across the zone, especially if the fault does not disect the entire unit. The area of influence of the Columbia River stage in the Mabton interbed May be different than the Rosalie flaw top. Hydraulic contact between the river and Mabton interbed is expected to be east of the underlying Rosalie flow top contact because the dip of the units is generally to the east. The contact between the Mabton interbed and the Columbia River, therefore, may be to the east of the most structurallydeformed area of the anticline. These observations agree with the fact that river stage fluctuations are observed in the Mabton interbed across the anticline at the RRL wells much clearer than the more transmissive Rosalie flow top. Cold Creek Harrier Ground-water withdrawals in the upper Cold Creek Valley are shown in Chapter Three to have a significant effect on ground-water levels in the Cad Creek wells. Influence of the pumping, however, was not detected in the ground-water level time-series at the RRL wells on the opposite side of the Cold Creek barrier. Disturbances from the

88 8 7 drilling and develcpment of wells on the west side of the barrier are also used to study the effectiveness of the structure. Ground-water Withdrawals Table 3.3 summarizes the results of the drawdowns from the pumping in the Cold Creek Valley. Observed drawdowns are presented with the estimated drawdowns from the Theis solution, assuming no hydraulic boundaries exist. Drawdowns at the Cold Creek wells are close to the observed responses; however, the drawdowns (or fluctuations) at the RRL piezometers on the opposite side of the barrier are 30 times less than the prediction. Figure 4.3 shows that the Rosalia flow top at DC-22, which is on the opposite side of the Cold Creek barrier one mile to the east of DB-11, is not affected by the pumping. Because the north-south extent of the barrier is not known, it is uncertain whether ground-water withdrawals in the upper Cold Creek Valley could influence levels at borehole DB-12. Relatively lower ground-water levels at DB-12 indicate that the "damming effect" is evident in this area and that the borehole is "behind" or east of the barrier. Ground-water levels at DB-12 are shown to be unaffected by the pumping described in Chapter Three. Drilling Disturbances Two ground-water disturbances in the Priest Rapids member have occurred in or near the RRL during the period of interest. First, the drilling of the RRL piezometers DC-19, DC-20, and DC-22 in late 1983 caused a ground-water disturbance in many hydrostratigraphic units, including the Rosalia flow top. Second, the construction of piezometer

89 88 Antplfbnle of Fluctuation (ft) O'Brian 7 DB DC EFFECT OF IRRIGATION PUMPAGE WITH DISTANCE do.; O'Brian Well 2 miles away DB-11 4 miles away Barometric Effects Not Removed DC-22 5 miles away t 7 YEAR Figure 4.3. Effects of pumping in the per Cold Creek Valley cm ground-water levels at wells O'Brien and DB-11 on the west side of the barrier and DC-22:Rosalia flow top on the east side.

90 89 DC-23W caused a ground-water level disturbance in the Rosalia flow top that was observed in each of the RRL wells. Estimates of the water loss or gain Iliad the drilling and development of the RRL wells are not available. The only available information is that ground-water levels at the RRL piezometers were lowered several tens of feet following the development of the boreholes, and the drawdown observed in the Rosalia flow top at DB-14. Unfortunately, ground-water level data for the closest well on the opposite side of the Cold Creek barrier (DB-11) are not available during this period. Ground-water levels at O'Brien and Ford are available, but they are about four miles away from the disturbance and do not show any effects. Drilling effects in the Wanapum Basalt from DC-23W are less evident in the area of the Cold Creek impediment. Its influence, however, was observed at DC-22 in the Rosalia flaw top in September 1985 (Appendix A). Borehole DB-11, which also mcnitors the Rosalia flow top and is the same distance from the disturbance as DC-22 but on the opposite side of the barrier, does not show any effects. Geologic Explanations Past investigations have shown that "subsurface dams" are fairly common in the Columbia River Basalt. Ground-water barriers may be the result of faults which are perpendicular to regional groundwater flow. The larger faults may offset beds thousands of feet and create a low-permeable zone of shattered rock tens of feet thick (Newcomb, 1961).

91 90 The Cold Creek barrier appears to be the type of "subsurface dam" described by Newcomb. Although there is no basalt outcrop at the known location of the barrier, stratigraphie correlaticns show that the Pomona marker in the Saddle Mbuntain Basalt is 400 feet higher on the west side. Deeper stratigraphie information is not available at the boreholes straddling the barrier, but the lags at DB-11 and DC-22 approximately aie mile an opposite sides indicate that there may be a significant offset of the beds to the Priest Rapids Member (Figure 4.4). A conceptual cross-section of the Cold Creek barrier is illustrated in Figure 4.5. Past geophysical studies (Holmes and Mitchell, 1981; Berkman, 1983) have shown that the structure extends at least one mile north and south of DB-11, but only qualitative estimates of its north-south extent can be made from the analysis of ground-water levels. First, the head differential (400 feet) an the apposite sides of the barrier indicates that the extent may be greater than the geophysical results show. Second, the ground-water disturbances an the east (drilling) and west (irrigation activity) sides of the barrier were not observed at any wells on the opposite side. Summary and Conclusions Analysis of cyclic fluctuations and disturbances of groundwater levels in the study area concluded that two geologic structures may be significantly affecting the ground-water system. First, the Umtanum Ridge anticline appears to be an impediment to water level disturbances north and south of its axis. Second, the Cold Creek

92 91 northwest 1.5 miles > f southeast D5-1 1 DC-22 feet above MSL.1n11 n nn n 1. n n -500.n11.1n 1 01.n n n Figure 4.4. Stratigraphic correlations of DB-11 on the west side of the barrier and DC-22 on the east side.

93 A A A A 92 upper Cold Creek Valley / / I / I / I / / / N. N. % \ N / I / f I,,r r r / % \ N. N. N. N. \ N. N A A A A A A A A A A A A A., A A A A A. A A A A A A A A A A A A A A A A. A A A A A A A A, A A AAA A AAAAA AAA A AAAA AAAAAAAA AAA h AA A AAAAA AAAA AAA o. A AAA A A A A A A. A A A Ah A A. A A A^ A A A A A. A A A, A A A A AA h A.S. A A A A A A A A A. A A A A A A A A A A A A A h A A. AAAA A A A A... -.Basait -.AAAA A An A A.. A A A A A A A A A A A A A A A A A A A A A A A A A A A AAAAA A A A A A A A A A A A -fault Figure 4.5. Conceptual cross-section of the Cold Creek barrier.

94 93 barrier is shown to isolate ground-water level disturbances on opposite sides. The effectiveness of the Ubtanum Ridge anticline is judged on the propagation of (1) Columbia River stage fluctuations, and (2) a drilling disturbance at DC-23W. Seasonal river stage influences are observed in the Mabton interbed at DC-20 and DC-22 but are significantly impeded or negated in the Rosalie flow top. The drilling disturbance at DC-23W did not appear to affect ground-water levels at DB-12 on the opposite side of the anticlinal axis. Reverse fault(s) parallel to the axis are a possible cause for the anticline to act as an impediment. Because the thinner Rosalia flow top appears to be affected more than the thicker Mabton interbed, the offset from the fault(s) may be less than several tens of feet. Also, DB-12 showed no response to a drilling disturbance from the south, indicating that a fault may be south of the borehole. Information about the Cold Creek barrier was available from previous investigations. The information included: (1) "subsurface dams" exist in other regions within the Columbia River Basalt Group, (2)ground-water levels were several hundred feet higher on the west side of the barrier, (3)the known north-south extent is two miles according to magnetic geophysical studies, and (4)basalt units down to the Pomona member are offset 400 feet.

95 94 Examinations of the ground-water level tine-series were not able to provide any quantitative estimates of the effectiveness of the barrier. Ground-water withdrawals to the west and drilling disturbances to the east were sham not to influence water levels on the opposite side of the barrier. These results indicated that the proposed fault is acting as a low-permeable zone at least to the depth of the Rcsalia flow top. The north-south extent of the barrier appears to be beyond the two miles estimated from the geophysical survey; however, a more accurate determinaticn cannot be made from the results of this study.

96 95 CHAPTER FIVE VERTICAL CONNECTIVITY OF HYDROSTRATIGRAPHIC UNITS Analyses of the hydrogeology in the previous two chapters have concentrated on ground-water level influences within individual stratigraphic units. Vertical hydraulic connectivity between units can also be examined by studying the ground-water level time-series at piezometer nests DC-19, DC-20, and DC-22. Each piezometer monitors levels in nine hydrostratigraphic units. The upper five units which are examined in this study are the: (1)basal Rinwadunit, (2)Rattlesnake Ridge interbed, (3)Mabton interbed, (4)Rosalia flow top, and (5) Sentinel flow top. TWo methods of analysis used to determine the vertical relationship between these units are (1) cross-correlation of ground-water levels in a vertical sequence at the RRL piezometers, and (2) studying the effects of surface waste water disposal activity at the RRL on the underlying confined units. Cross-Correlation Lagged cross-correlations of ground-water levels at piezometer nests DC-19, DC-20, and DC-22 are performed to obtain a vertical relationship between water levels in the area. Data from a particular

97 96 mcnitored horizon are matched with data from the unit above and below at various time lags. Ground-water level recovery trends and barometric effects are removed to eliminate the possibility of getting spuriously high correlation coefficients (Appendix B). The relationship between these units was measured by the maximum correlation coefficient. Figure 5.1 illustrates the results from the lagged crosscorrelations in the vertical direction at these - piezemeters. The maximum correlation coefficients and the corresponding time lags are shown. The highest correlation is between the Resalia and Sentinel Gap flow tops at each piezometer. The correlation coefficient (0.98) and time lag (0-1 day) indicate that the ground-water level variations are similar in these flow tops. Evaluation of the drilling effects of DC- 23W at the RRL piezometers by Spane (1985) corroborated the results from this and previous studies (Sorooshian et al., 1985). Four possible scenarios for the similarity between responses at the Rosalie and Sentinel Gap flow tops presented by Spane include: (1)lack of piezometer isolation within the immediate vicinity of the boreholes due to formational fracturing incurred during drilling and/or lack of sufficient sealing cement, (2)enhanced vertical hydraulic canmunication within these formations due to the presence of cross-cutting, highly-conductive geologic features such as faults or multiple flow fronts,

98 97 DC-22 I , DC-20 basal Ringo ld unit i it DC H H 0.57 ( 05) (84).55 (91) R. R. inter bed ahead b. Ringold ahead b. Ringold ahead I l I I i I 0.28 Rattlesnake Ridge interbed I 0) I I II 0.54 (49).58-0 (98) Mabton ahead R. R. i nter bed ahead H M bton interbe d i 0.47 (26) )70) (1 49) Mabton ahead Mabtonahead Mabton ahead Rosaliaflow to p (0) ) ) Sen tinel Gapflowtop I I Ii I Figure 5.1 Maximum cross-correlation coefficients and the corresponding time lags (in days) between units at piezameters DC- 19, DC-20, and DC-22 with recovery trends and barometric effects removed.

99 98 (3)the presence of natural, pervasive vertical fracturing within the basalt flows, and (4)the existence of a single hydrogeologic unit. In his report, Spane concludes that there is insufficient information to determine the cause of the similarities. The properties of the Roza member, which separates the Rosalia and Sentinel Gap flow tops, are uncertain at the RRL. Multiple flow lobes or pervasive vertical fracturing in the Roza member, as enumerated above, could explain the hydraulic canunication. Additional information about the properties of the Roza member and the cement seals in the piezameters is needed to explain the similarity between the ground-water levels in the Rosalia and Sentinel Gap flow tops. The results from this cross-correlation analysis and Spane's report do not lead to any specific explanation for the similarity between ground-water levels in the Rosalia and Sentinel Gap flow tops. The fact that the levels are similar at all three RRL piezometer nests indicates that there may be a pervasive geologic cause instead of being induced by drilling. Surface Waste Water Disposal In the previous section, cross-correlations of ground-water levels were used to determine the relationships between five hydrostratigraphic units at DC-19, DC-20, and DC-22. Evaluation of drilling effects in certain units have also been used to examine the vertical connectivity at the RRL (Spane, 1985). Analyses in this section

100 99 involve the "disturbance" of ground-water levels at the RRL due to surface wastewater disposal. Surface waste water disposal began at the Hanford Site in Locations of some disposal ponds at the RRL are shown in Figure 5.2. As a result of the disposal activity, a mound has developed in the unconfined aquifer. The purpose of this analysis is to examine the ground-water levels at the monitored hydrostratigraphic units to determine: (1)if the effects of the water table mound beneath the disposal activity have affected ground-water levels in the underlying confined units, and (2)how the effects of the disposal activity, if present, are transmitted to the underlying units. Effects on Ground-Water Levels in the UnocnfinedAqpifer Effects of the surface waste water disposal activity on the unconfined aquifer have been studied for many years (Bierschenk, 1959; Newcomb, 1973). An estimated water level contour map for the unconfined aquifer prior to the commencement of the disposal activity in 1944 is presented in Figure 5.3a. Information about the unconfined aquifer at that time indicated that a regional hydraulic gradient existed which caused flow towards the east and northeast with recharge to the Columbia River. A contour map of the water table elevation in 1984 shows that a mound has developed as a result of the disposal activity (Figure 5.3b). The growth of the water table mound from 1944 to the present can be estimated from studies done on the unconfined

101 100 Reference Re posi to r y Location x DC-19 surface pct rids arid ditches x borehole Figure 5.2. Location of surface waste water disposal ponds in the study area.

102 101 Gable Butte Gable Mountain Reference / Repository Z, Location miles 1 2 co nto r s ft - MS L (a) Gable Butte, 460 Reference / / Pe po.;i tn r y Location /- 480 (b) contour:. fi - MS L Figure 5.3. Ground-water levels in the unconfined aquifer (a) before the beginning of the waste water disposal activity in 1944, and (b) in 1984 (DOE-SCR, 1982; Schatz, 1984).

103 102 aquifer during this period (Bierschenk,1959; Newcomb, 1973; Schatz, 1986). Effects on Ground-Water Levels in the ConfinerlAquifer Effects of the disposal activity on the underlying confined units are more difficult to study than the unconfined aquifer for two reasons. First, no ground-water level data are available for the confined units in the RRL prior to the beginning of the disposal activity in Second, fewer boreholes monitor the ground-water levels in the confined units in this area. These facts are important because (1) there are no reference (pre-hanford) ground-water levels for the confined units by which to measure the possible effects of the disposal activity that began in 1944, and (2) the estimation of the ground-water levels contours in the confined units must be based an fewer observations, therefore, making them less reliable. Estimated contours of the piezcmetric levels in 1985 for the Rattlesnake Ridge inbarbed, Mabton inbmrbed, Rosalia flow top, and Sentinel Gap flow top are shown in Figures 5.4(a-d). The contours are fairly subjective, especially for the Rattlesnake Ridge and Mabton interbeds and the Sentinel Gap flow top, due to the lack of monitoring locations in the area. The piezcmetric surface could be interpreted differently because of this fact; however, these contour maps are reasonable approximations based on the available data. The piezcmetric surfaces show that: (1) the apparent height of the piezometric mounds is

104 103 DC-22 Gable Butte --- \\ I ---- x..-dc Reference /Repository Location LI-pond miles contours ft -MSL x well data used (a) Urntanurn Ridu_ erk4 mmom=mussamamoto- Reference Gable Butte Repository Location miles 1 2 contours ft -M51. x well data used Figure 5.4. Maps of estimated 1985 piezometric levels in the (a) Rattlesnake Ridge interbed, and (b) Mabton interbed.

105 104 Gable Mountain upper Cold Creek Valle y "744'77:21"54V7'7'''. 'al-ima Ridge Fo: T DC-16 p.rseetztx.- DC 22 Refe re nce Re posi to r u Location DB-14 rni I es a :ortou rs ft -MSL well date u5ed (c) (d) Figure 5.4. Maps of estimated 1985 piezometric levels in the (c) Rosalia flow top, and (d) Sentinel Gap flow top.

106 105 greatest in the upper units and generally declines with depth to the Sentinel Gap flow top, and (2) the piezometric surfaces for the monitored units at the RRL wells below the Sentinel Gap flow top (Ginkgo, Cohassett, Rocky Coulee, and UMtanum flow tops) do not indicate the presence cl mounds. Paucity of ground-water level data for the confined units creates uncertainty in the study. Subsequent analyses of the effects of the disposal activity on the confined units, therefore, must be based on two assumptions: (1)piezometric mounds exist in the confined units at the RRL as far down as the Sentinel Gap flow top based on the available data, and (2)piezometric mounds are the result of the disposal activity at the RRL. Surface waste water disposal activity and the resulting water table mound appear to be affecting the piezomtric levels in the underlying confined units. TWo possible, but not independent, explanations for the formation of piezanetric mcunds in the area are: (1) loading of the confined units caused by the change in overlying weight from the additional water above, and (2)vertical hydraulic ccmmunicaticn between the mound in the unconfined aquifer and the underlying confined units.

107 106 The two causes can be separated depending on the assumed properties of the basalt flow interiors. If the interiors are assumed to be impermeable, loading could be the only cause of the piezometric mounds. If the interiors are assumed to be permeable, vertical communication between the unconfined aquifer and the underlying confined units could explain the piezcmetric mounds in addition to any loading effect. Because the properties of the basalt flow interiors in the Saddle Mbuntain Basalt are unknown, both potential causes will be examined separately. Loading A change in the load overlying the confined hydrostratigraphic units would cause a change in the piezcaetric level. A change in the overlying weight caused by the disposal of waste water, dat, at the surface causes a change in the total stress in the aquifer which is borne by the rock matrix, aye, and the pore fluid, dp, as illustrated in Figure 5.5. The fraction borne by the pore fluid is reflected in the change of the piezometric level at that point. To determine if loading could be the cause of the apparent piezanatric mounds, the next steps are to estimate the: (1)growth or decay of the load (water table mound) with time, (2)pore fluid pressure response in the confined unit for a given change in weight of the water table mound, and (3) dissipation rate of the piezometric mound due to flow away from the load source.

108 Figure 5.5. Distribution of stress caused by a change in the overlying load from surface waste water disposal activity. 107

109 108 Changes in water table mound with time. Characteristics of the water table mound at the RRL have been studied in several early reports (Bierschenk, 1959; Newccmb, 1973) and recently by the Rockwell-Hanford Operations (Schatz, 1986). Based an water table elevations presented in these reports, an estimate of the change in magnitude of the water table mound with time is made (Figure 5.6). Figure 5.6b is identical to Figure 5.6a, except that the height of the mound doas not decrease in the last year of study (1985). Loading response. A change in the total vertical stress in the underlying confined units is estimated using an analytical solution (Sowers, 1979). The solution attempts to represent the elastic conditions of a stratified mass. The assumptions are a homogeneous, elastic mass reinforced by thin, nonyielding, horizontal sheets of negligible thickness. The resulting vertical stress at a point can be computed for a given mass applied over a given area. The effective area of the water table mound was approximated by a rectangular 15 mi2 surface with a uniformly-applied pressure. The depth to the apparent deepest affected unit, (Sentinel Gap flow top), is approximately 0.2 miles. Because the distance to the confined units is small compared with the affected area, the analytical solution gives a pressure change at the deepest formation approximately equal to the change in total vertical stress. For this reason, the change in stress at the surface will be considered equal to the change in vertical stress at depth. Piezometric levels reflect the fraction of the change in total stress that is borne by the pore fluid, p. The fraction is given by the equation:

110 YEAR ft/yr yearl y increments of load change (a) 1944 YEAR yea ri y increments 7 of load change 5 ft/kir k 0.2 ftlyr iiluuhtlii Figure 5.6. Estimated change in load through 1985 from surface waste water disposal activity (a) with U-pand decatmissim, assuming no U-pmd decommision.

111 110 P=P/(P+nB) (5.1) where p = vertical compressibility of the rock, B = compressibility of the pore fluid, and n = porosity of the rock. Because documented values for the compressibility of the rock are variable, the tidal efficiency, C, of the rock was used to estimate dp. The tidal efficiency was obtained by using the relation: C = 1 - B (5.2) where B is the barometric efficiency of the aquifer. Barometric efficiencies for the nine monitored hydrostratigraphic horizons at DC- 19, DC-20, and DC-22 were obtained from a regression analysis of ground-water levels and barcmetric pressure the data (Sorccshian et al., 1985). The piezometric response, dp, at any unit at or above the Sentinel Gap flow top from a unit increase in pressure at the water table, dt, can be approximated by the equation: dp = C dat (5.3) Piezanetric mound dissipation. Changes in the piezometric levels induced by loading create hydraulic gradients in the confined

112 111 units which cause outward, radial flow of water from the area underneath the center of the water table mound. Assuming that the confined aquifers are homogeneous, isotropic, and have no structures to impede the outward flow of water, the dissipation rate of the piezometric mound created by loading can be easily estimated. A one-dimensional finite difference model was used to obtain an estimate of the dissipation rate of a piezometric mound. A diagram of the model is shown in Figure 5.7. A two-dimensional radial flow model would more accurately represent the flow conditions; however, the fact that the one-dimensional model gives a slower dissipation rate than the radial model will be used to justify the conclusion at the end of this section. Procedure. The effect of the water disposal on the 1985 piezometric levels due to loading is estimated at the point below the center of the water table mound by the following steps: (1) discretize the changes in the weight of the water table mound into yearly increments (Figure 5.6a), (2)estimate a piezometric response from each weight change, and (3) determine the residual effects on the piezometric levels in 1985 from each weight change increment by using the finite difference model. Results. Several factors involved in the estimation of the loading effect in the Rosalie flow top are chosen to obtain an artifi-

113 112 piezometric surface center of - mound mit of nfl uence approximated mound cross-section 'n 6x. (.,( initial condition? (ft - MSL ) finite difference grid Transmissivity = 10 ftvday Storativity = 10-4 X = 3168 ft M = 1 day Figure 5.7. Finite difference grid used to model the dissipation of a piezametric mound.

114 113 cially-high value for the piezometric mound height in The biased factors include: (1)assuming the continuous growth of the water table mound (Figure 5.6b), (2)estimating that 100% of the change in stress at the surface is propagated to the underlying Rosalia flow top, (3)using low values within the range of hydraulic diffusivities documented for the Rosalia flow top (DOE- SCR, 1982), and (4)using a one-dimensional flow model instead of the twodimensional radial flaw model. The artificially-high calculated value and observed apparent maximum height of the piezametric mounds from loading in the Rosalia flow top are: calculated: 0.06 ft., observed: 2 ft., This result shows that loading is not able to explain the presence of the observed piezometric mound. Hydraulic Communication Steady State Approach It has been shown that loading is not the only cause for the apparent piezometric mounds in the confined units; therefore, hydraulic communication may exist between the water table mound and the under-

115 114 lying units. The purpose of this analysis is to determine if it is reasonable, with the given and estimated properties of the rock mass underlying the unconfined aquifer, to expect the observed piezometric mounds as shown in Figure 5.4. A two-dimensional, multi-layer numerical flow model would be a means of determining whether hydraulic cannunication is the cause; however, it would be a complicated task with many unknowns. One of the unknown values crucial to the analysis of vertical flow is the vertical hydraulic conductivity of the basalt flow interiors in the Saddle Mountain Basalt. There have been no successful tests to determine the conductivities of the interiors; however, a few tests have been performed on the Wanapum Basalt flow interiors. The range for the horizontal hydraulic conductivities for the Wanapum Basalt flow interiors is 3 x 10r 7 to 3 x 10-6 ft/day (DOE-SCR, 1982). Vertical conductivities are expected to be higher. Because of the uncertainties and complexities using a twodimensional multi-layered numerical model, the problem will be simply analyzed by estimating the vertical conductivity of a flow interior in the Saddle Mbuntain Basalt from the observed effects of the disposal activity and comparing than with documented values for the Wanapum Basalt. In this section, steady-state flow through the Elephant Mbuntain Member of the Saddle Mbuntain Basalt is used to estimate the vertical conductivity in that particular basalt flow. It is situated between the basal Ringold unit and the Rattlesnake Ridge interbed at the RRL (Figure 2.1).

116 115 Figure 5.8 illustrates the conceptual flow from the water table mound through a series of basalt flows and an interbed. Because the hydraulic conductivities for the flow tops and interbeds are estimated to be several orders of magnitude higher than the flow interiors, it is assumed that there is horizontal flow in the flow tops and interbeds and vertical flow in the flaw interiors. The steady-state assumption is based on an observation of the ground-water levels in the affected area. Figure 5.9 shows that a nearly linear vertical hydraulic gradient exists at piezameters DC-19, DC-20, and DC-22 across the Saddle Mbuntain and Wanapum basalte based on the monitored hcrizons. Gradients will differ within the various lithologies (flow tops, interteds, and interiors), but an a larger scale, the gradient appears linear if the Saddle Mbuntain Basalt is considered as an equivalent isotropic unit. The vertical gradient has also not significantly changed with time since the monitoring at the RRL piezometers began in Procedure. The equation used to describe the steady-state vertical flow is the Darcy equation: Q, = IS, k dh where A = cross-sectional area through which vertical flow occurs, = vertical flow rate through the area, A, dh = vertical hydraulic gradient, and = vertical hydraulic conductivity.

117 116 ground surface dispos& pond " \ flow top.- I Pi. '. '. " N. ' flow interior ;..irterbed: now top ' -. \ s e's I %,. \ \ 1 \ \ \ S. 1. ". \ Figure 5.8. Conceptual ground-water flow through the basalt flow tops, interiors, and a sedimentary interbed under a disposal pond.

118 117 basal Ringold unit Rattlesnake Ridge interbed D DC-19 0:0 DC-20 DC-22 rlabton interbed E. r4 Water Level (ft) Figure 5.9. Vertical hydraulic gradients measured at piezameters DC- 19, DC-20, and DC-22.

119 118 The goal of this analysis is to estimate the vertical hydraulic conductivity, Kv, for the Elephant Mbuntain flow interior in the Saddle Muntain Basalt. To solve for the hydraulic conductivity, the flow rate, Q, and area, A, must be determined. The vertical gradient, dh, is considered to be a known value (0.05) based on results shown in Figure 5.9. Disregarding the possibility cf isolated, highly-permeable zones (i.e., fractures) or gradual changes in the properties of the rock, the effective vertical conductivity should be relatively independent of the area that is chosen. The area Should be less than or equal to the area of influence of the water table mound (about 15 m12 ) and also maximize the amount of the data within that area, if possible. Because piezometers DC-19, DC-20, and DC-22 provide the best vertical data and are each approximately two miles from the center of the water table mound, this radius was chosen to represent the area. The next step is to estimate the flow rate through the chosen area. Figure 5.10 illustrates the process of estimating the vertical flow rate, Q1, through the Elephant Mbuntain member. The flow rate is equal to the flow out of and through the underlying Rattlesnake Ridge interbed. A qualitative estimate of the flow through the chosen area can be made by assuming the vertical flow through the Elephant Mbuntain flow interior is equal to the summed horizontal flow, out of the hypothetical cylinder in the underlying flow tops and interbeds down to the Sentinel Gap flow top. Qv = Qh (5.4)

120 119 hypothetical cylinder Scs basal Ringo ld unit Elephant Mountain member \ Q h Rattlesnake Ridge interbed h Q L o Q + Q y h L Figure Conceptual steady-state flow through the Elephant Mountain Member used to calculate the vertical flaa, Q.

121 120 The horizontal flow rate through the underlying flow tops and interbeds was calculated using the equation: E Qh = E ki A dhi (5.5) where 1(1 = estimated or documented value for the horizontal conductivities, A = product of the cross-sectional circumference of the hypothetical cylinder and the flow tops/interbeds thickness, and dhi = horizontal gradient in the flow top/interbed at a radius equal to two miles from the center of the RRL determined from Figures 5.4(a-d) or estimated (Table 5.1). The result from Equation (5.5) is substituted into Equation 5.4 to determine Q. Results. The calculated vertical conductivity of the Elephant Mountain flow interior is: K = 3 x 10r 3 ft/day Hydraulic conductivities of the deeper flow interiors might be expected to be lower possibly because of decreased fracturing. In fact, a qualitative examination of the vertical gradients at DC-19, DC- 20, and DC-22 indicates that this may be the case in the Saddle

122 121 Table 5.1. Values for the Hydrostratigraphic Units Used In the Calculation of Steady-State Flow Through The Elephant MountainNlember Hydrostratigraphic Horizontal Unit Conductivity (ft/day) Circumferential Area (ft2) Horizontal Gradient Rattlesnake Ridge interbled 3* 2 x x 10r 4 Pomona flow top 3 2 x x 10-4 Esguatzel flow top 3 2 x x 10r 4 Cold Creek intetbed 3 1 x x 10r 4 UMatilla flow top 3 2 x x 10r 4 Mabbm interbed 0.5* 2 x x 10r 4 Rosalia flow top 30* 2 x x 10r 4 Sentinel Gap flow top 20* 2 x x 10r 4 * - Geometric mean of documntelxivalues (Bruce, 1983)

123 122 Mbuntain Basalt. If the conceptualization in Figure 5.10 is correct, the vertical flow in the hypothetical cylinder should decrease with depth due to a "loss" from horizontal flow out of the flow tops and into/beds. Noting the constant vertical gradient with depth (Figure 5.9), and using Darcy's equation: A dh = constant therefore, If the vertical flow, Qv, decreases with depth as expected, the decrease in conductivity is directly proportional. In review, the estimated vertical conductivities for the Saddle Mbuntain Basalt flow interiors (3 x 10r 3 ft/day) from the steady-state approach is three to four orders of magnitude greater than the horizontal conductivities of the deeper Wanapum Basalt flow interiors (3 x 7 to 3 x 10r 6 ft/day). As mentioned previously, the vertical conductivities of the Wanapum Basalt flow interiors are expected to be greater than the horizontal conductivities. Also, the shallower Saddle Mbuntain Basalt flow interiors might be expected to have a greater vertical conductivity than the Wanapum Basalt flow interiors. The calculated vertical conductivity for the Saddle Mbuntain Basalt flow interiors, therefore, appears to be a reasonable value. An attempt to

124 123 estimate the vertical conductivities by a transient analysis is the next approach. Hydraulic Ctmmunication--Transient Approach Forty years of waste water disposal at the surface has created a ground-water flow situation that was considered to be at steadystate in the previous analysis. At the end of 1985, the disposal activity decreased abruptly at the RRL because of the decommissioning of the Ur-pond (Figure 5.2). An apparent ground-water level response occurred at DC-19 due to the decrease in disposal. Figure 5.11 shows the hydrogrephs of the baqa1 Ringold unit and the Rattlesnake Ridge interbed at piezometer DC-19. The trends in the ground-water levels show a distinct change following the decrease in disposal activity. The response time lag from the basal Ringold to the Rattlesnake Ridge interbed is a function of the vertical hydraulic diffusivity (VS,) of the Elephant Mountain member which is between the two units. The goal is to calculate the diffusivity of the Elephant Mountain flow interior and ultimately the vertical hydraulic conductivity. Procedure. Hydraulic diffusivity can be estimated from the observed ground-water level responses in the basal Ringold and Rattlesnake Ridge by the following steps: (1)estimate the time lag between ground-level responses in the basal Ringold unit and Rattlesnake Ridge interbed, and (2)use a one-dimensional finite difference model which can alter the hydraulic diffusivity until the observed time

125 124 Rattlesnake ; Rdg. (ft) m14 j lit Itl iii , al tf) to n:14gct (u) piovuth

126 125 lag is matched. A downward deflection in the groundwater level trend in the basal Ringold unit and the Rattlesnake Ridge interbed is shown to be approximately 50 days apart (Figure 5.11). The one-dimensicnal finite difference grid is shown in Figure Initial and boundary conditions are indicated in the figure. The model uses an initial diffusivity and calculates the time lag for a measurable (> 0.1 ft.) response to reach the Rattlesnake Ridge interbed as a result of the change in level in the basal Ringold unit. The value for the diffusivity is autanatic,ally changed by the model until the observed 50-day time lag is matched. Results. Output from the numerical model indicated that the hydraulic diffusivity for the EleptentMountain flow interior is: = 69.1 f t2 /day Estimates for the specific storage of the Elephant Mbuntain Member based on documented values for the storativity in the Saddle Mbuntain Basalts (DOE-SCR, 1982) range from: 3 x 10r 7 1/ft < Ss < 3 x 10r 6 1/ft Solving for the vertical conductivity, Kv, across the Elephant Mountain flow interior:

127 126 re prescribed changing basal Ringold unit head ftiday) Lt. = 1 day Elephant 'Mountain Member (flow interior) oz =8.2 ft initial conditions (ft-m,sl) Rattlesnake Ridge interbed,..a 440 L no flov boundary Figure Finite difference grid used to model the -transient vertical ground-water response through the Elephant Mountainmemter.

128 127 2 x 1or5 ft/day < K,, < 2 x 10-4 ft/day This result is one to three orders of magnitude greater than the documented horizontal conductivities in the Wanapum Basalt. As previously outlined, the vertical conductivities of the Wanapum Basalt flow interiors are expected to be greater; therefore, the above estimate appears to be a reasonable estimate of the conductive property in a Saddle Mountain Basalt flow interior. Summary and Conclusions Examination of the vertical connectivity of the hydrostratigraphic units began with a cross-correlation study at piezometer nests DC-19, DC-20, and DC-22. The cross-correlations Showed that the variations in the ground-water levels within the Rosalia and Sentinel Gap flow tops are similar. The reason for the similarity cannot be fully explained, but several man-made and hydrogeologic causes were outlined. Waste water disposal activity at the RRL was examined to determine the effect on ground-water levels. Piezometric levels appeared to be affected by the activity, and two possible causes were analyzed. A loading effect by the water disposal was eliminated as the sole cause. Vertical cœmunication of the water table mound beneath the disposal activity was then studied and found to be the primary cause of the piezometric mounds in the confined units. Two methods were used to determine the feasibilty of vertical communication as the cause of the piezometric responses. First, a

129 128 steady-state approach was used. Second, a transit response to the end of the disposal activity at the ii-pond was examined. Both methods indicated that vertical carmunication is a reasonable cause for the piezametric responses in the underlying confined units. Calculated values for the vertical conductivities of the confining flow interior frail both methods are within the expected range.

130 129 CHAPTER SIX HYDROGEOLOGIC CONCEPTUALIZATION A hydrogeologic conceptualization is presented based on past information and the conclusions of this study. One of the most important considerations for the location of an underground waste repository is the travel time for pollutants which may escape into the groundwater. Critical factors involving contaminant travel times include aquifer properties (transmissivities and storativities), hydraulic gradients, and barriers to flow. Some information about the properties of the aquifers at the RRL has been determined by aquifer tests in the past, and large-scale hydraulic tests in the future will yield additional information. Hydraulic gradient direction and location of barriers in and around the RRL are currently unknown or speculative. Hydraulic head surfaces have been calculated using various techniques such as kriging (Ejerrari, 1986) and linear regression (Sorooshian et al., 1985). In both cases, the amount and quality of the ground-water level data for the various hydrostratigraphic units are limited. This section presents a general conceptualization of the ground-water flow in the study area for the past, present, and future. Past Figures 6.1a-b are areal maps of the estimated ground-water flow in the unconfined and confined units before the beginning of the Hanford Site in Pre-Hanford information on the unconfined

131 130 (8) rt7,777777,',.: di n htt-ge to Col un-ibia Per roil e:e, 0 1 ()) Figure 6.1. Conceptual areal map of pre-hanford (1944) ground-water flow in the (a) uncx:snfined, and (b) confined units.

132 131 aquifer is substantial =pared to the scarce data on the confined units, especially in the area of the RRL. Flow in the unconfined aquifer is to the east, recharging to the Columbia River on the eastern boundary of the site. The water table elevation near the river is affected by the seasonal stage fluctuations by bank storage. Information about the confined units in the past may be estimated by looking at the ground-water characteristics in the relatively unaffected areas at the present Hanford Site. The information indicates that the horizontal hydraulic gradients are relatively flat east of the Cold Creek barrier and may follow a similar pattern as the unconfined aquifer with easterly flow and recharge upwards to the Columbia River on the eastern end of the site. A conceptual east-west cross-section from the RRL to the upper Cold Creek Valley of the past ground-water flow is shown in Figure 6.2. At the RRL, a relatively small vertical upward gradient is assumed. A greater vertical gradient in the upper Cold Creek Valley is towards the more transmissive Priest Rapids Member. Flow in the confined units is impeded by the Cold Creek barrier. Present Surface waste water disposal activity at the RRL and groundwater withdrawals in the upper Cold Creek Valley have altered the ground-water flow in the study area. Figures 6.3a-b are areal maps of conceptualized present ground-water flow in the unconfined and confined units. The water table surface of the unconfined aquifer has been significantly altered from the disposal activity at the RRL. A mound

133 132 CSIL East upper Cold Creek Nalleg PPL co nfi ned flow f :. s..17: ".:: -r:ie_..77rrm.- An,A,04:2 regional ft, j. I.1 component of vertical fl ow 4_4., Figure 6.2. Conceptual cross-section of pre-hanford (1944) groundwater flow in the study area.

134 133 Columbia River r seasonal sist river effec t Jmtanum Ridge. ;;; ;;ayammeasuilie. -,.- ïakirria Rid9e mi le co n t urs ft -ML (a) I '7) I Cṛ. -- water di 5po3a1 effect; (b) Figure 6.3. Conceptual areal map of present ground-water flow in the (a) unconfined, and (b) confined units.

135 134 centered under the disposal ponds has created outward flow in the unconfined aquifer. Although there is much less available information about the unconfined aquifer in the upper Cold Creek Valley, a similar water table mound may be developing under the irrigated areas. Effects on the piezometric levels are more difficult to evaluate because relatively few confined units are mcnitored. In this study, it was shown that at least two of the units (Rosalie flow top and Mabton interbed) are affected by the seasonal changes in the Columbia River stage. The Rosalie flow top was shown to be in hydraulic contact with the river. The Mabton intexbed, which overlies the Rosalie flow top, probably has a contact farther to the east. Based on data from DB-12, the Rosalie flow top appears to be recharged by the river in this area. Ground-water withdrawals in the upper Cold Creek Valley are causing the decline in water levels in the Priest Rapids Member (Livesay, 1986). During the summer months, the direction of the gradient in the Priest Rapids Member is reversed at least as far as the O'Brian and Ford wells. Effects of the pumping, however, are not detected at any wells east of the Cold Creek barrier. Horizontal gradients in the confined units at the RRL are relatively flat (DOE-SCR, 1982), making it difficult to determine the gradient directicn. Results from this study indicate that due to surface waste water disposal activity, piezometric mounds have developed down to the Sentinel Gap flow top. Gradient direction and magnitude, therefore, have changed from the pre-hanford conditions.

136 135 The horizontal gradient magnitude appears to be greater in the shallower confined units. A conceptual vertical cross-section of the present ground-water levels in the study area from the upper Cold Creek Valley to the RRL is shown in Figure 6.4. Horizontal gradient magnitude and direction are affected by the withdrawals on the upper Cold Creek Valley, and a water table mound beneath the irrigation is shown. Horizontal gradients across the Cold Creek barrier are reduced because of the pumping. Vertical gradients under the RRL are downward through the Sentinel Gap flow top due to surface water disposal activity. Future Future ground-water flow characteristics are primarily dependent on the effects controlled by man. Seasonal effects from the Columbia River are assumed to remain the same; however, ground-water withdrawals in the upper Cold Creek Valley and surface water disposal are activities contiolled by man. Future consequences of sustained or increased pumping in the Cold Creek Valley have been studied (Livesay, 1986). The piezometric surface in the valley has already declined approximately 200 feet, and continued withdrawals may reverse the direction of the hydraulic gradient across the Cold Creek barrier. Disposal activity at the RRL has declined since the decommission of the U-pond at the end of If waste water disposal activity slows or stops in the future, there may be two consequences. First, ground-water level mounds in the unconfined and confined aquifer will dissipate beneath the disposal area. This may cause the regional

137 :rif:71:. % * *:.17:17 FT.t7:: * 136 West East upper Cold Creek Valley A, rate r table / mound from irrigation.:/ate r table mound from -- di3po3a1 pond5 PP L confined Qtagt.toz :!;e8 rai c ha nge$ in flow direction from pumping confined Figure 6.4. Conceptual cross-section of present ground-water flow in the study area.

138 137 gradient directions to return to the pre-hanford conditions (Figure 6.1a). The rate at which the mcunds dissipate would depend an the decline of the disposal activity and the characteristics (conductivity, storativity) of the aquifers. Second, the end cf water disposal would decrease the magnitude cf the vertical gradient. As the water table and piezometric mcunds decrease, the magnitude of the vertical gradient should decrease. Depending on the properties of the aquifers and aquitards, the gradient magnitude and possibly the direction will change. Vertical gradients from undisturbed parts of the site indicate that given enough time after the disposal activity ceases, the vertical flow direction may reverse at the RRL.

139 138 CHAPTER SEVEN DISCUSSION, SUMMARY, OONCLUSICNS, AND RECOMMENDATIONS FOR FUrIURE STUDY Discussion Lagged Cross-Correlations The analysis of natural and incidental ground-water level variations, unlike planned aquifer tests, deals with uncontrollable, relatively small water level fluctuations. For this reason, the ground-water level time-series may need to be examined by several methods. Results from statistical analyses should be combined with physically based solutions or models to obtain a better understanding of the hydrogeology. Lagged cross-correlations are used in this study to discover relationships between the small-scale variations such as the similarity of Rosalia and Sentinel Gap flow top ground-water level time-series. The analysis can also statistically validate obvious relationships such as the one between the Columbia River stage and ground-water levels at borehole DB-12. Correlation coefficients, however, may be spuriously high or low due to common external effects or unrelated effects. To mitigate the ambiguities, the identified external effects on groundwater levels must be removed if possible. Recovery trends and barometric effects are removed from the ground-water level time-series at the RRL wells. Ground-water pumping effects in the upper Cold Creek Valley, however, could not be removed because the lack of needed data. As a result of the inadequacies of the data and methods, an attempt is

140 139 made in this study to combine cross-correlation results with qualitative or analytical analyses to substantiate (or refute) the initial conclusions drawn from the correlaticn analysis. The cross-correlaticn results between the Columbia River stage and the ground-water levels in the Cold Creek wells exemplify the situation. The range of correlation coefficients ( ) are spuriously high because both time-series exhibit a similar, unrelated seasonal trend. The river stage is influenced by precipitation/runoff and dams upstream; the ground-water levels in the upper Cold Creek Valley are primarily affected by seasonal pumping. Because the groundwater fluctuations pmeceed the seasonal river stage variations by seven weeks, the correlation coefficients are concluded to be spuriously high due to a common, unrelated seasonal trend. The river stage variations, therefore, are not the primary cause of the ground-water level fluctuations in the Cold Creek wells. A similar situation exists for the cross-correlation results between the ground-water levels in the Cold Creek and RRL wells. The correlation coefficients between the time-series range from 0.41 to Without additional information no definite conclusions can be made, however, the facts that the seasonal fluctuations in the Cold Creek wells are 91 to 154 days ahead of the RRL wells and pumping disturbances have no detectable effect across the Cold Creek barrier indicate that the correlation coefficients are spuriously high and the seasonal fluctuations are unrelated. Conclusions from the cross-correlation analyses are broad because of data scarcity and the inability to seperate potential

141 140 influences on the ground-water levels. For the Cold Creek wells, the conclusions can only be made with respect to the primary causes and effects because secondary effects cannot be identified. Effects of the Columbia River stage variations or drilling disturbances at the Cold Creek wells may be hidden by the overwhelning pumping effects in the valley. Detection of Pumping Disturbances Qualitative examinations of the ground-water level time-series are used to verify, refute or clarify the cross-correlation results. The time-series for the Rosalia flow top at DB-12 and DC-20 are examined to show the lack of significant disturbance across the Uintanum Ridge anticline due to the drilling at DC-23W (Figure 4.1). Inspection of the ground-water levels at the Cold Creek wells and DC-22:Rosalia flow top shows that the effects from the pumping in the upper Cold Creek Valley do not propogate across the Cold Creek barrier. Analytical Methods Two physically based analytical solutions are used in conjunction with the cross-correlation results to better understand the processes and give predictions for the ground-water influences in different areas. First, the Theis solution for flow to a well is used to predict the magnitude of influence from the pumping in the upper Cold Creek Valley. The most significant problem with its application is the estimation of the discharge from the wells in the valley. Estimations and assumptions are also made concerning the transmissivity and storativity of the flow top. The purpose of this analysis, which

142 141 is to estimate and predict the pumping effects, is adequately served within these estimations and assumptions. Results from this analysis are combined with the cross-correlations and qualitative time-series analysis to allow a more definitive oonclusion on the influence of the pumping in the valley and the effectiveness of the Cold Creek barrier. The second analytical solution used in this study is a riveraquifer model which relates the fluctuating Columbia River stage and ground-water levels (Ferris, 1951). This particular approach to understanding the physical relationship is simple, however, it reflects the scarcity of data which is needed to fully understand the interaction. Simplifying assumptions of the solution which may not be valid and may significantly affect the results are (1) aquifer hamogemity, and (2) great inland extent of the aquifer. Homogeneity of the Rosalia flow top is not indicated by the documented values (740 ft 2 /day to 120,000 ft2 /day), however, it is a reasonable assumption based on the abscence of any transmissivity values between borehole DB-12 and the Columbia River. The continuous inland extent of the Rosalia flow top is questionable based an results of this study which indicate that structural discontinuities may have offset the unit. A three-dimensional analysis of the interaction between the Columbia River and the ground-water levels would be more accurate, hcwever, such an analysis would need a quality and quantity of data to reflect its complexities. Because of the paucity of data for this area, a simpler model such as the one used in this study is justified.

143 142 Summary Natural and incidental ground-water level variations in the time-series were analyzed to determine whether hydrogeologic information can be attained. Weekly and daily water level observations at eight wells in a section of the Hanford Site were examined to attempt to accmplish this task. Drilling disturbances were studied in addition to natural seasonal and daily water level fluctuations by using statistical and analytical methods. Vertical connectivity between hydrostratigraphic units was also examined using similar techniques and simple numerical methods. Initial evaluations of the ground-water level time-series in Chapter Three included the study of cyclic fluctuations (seasonal and daily) at wells in the area. First, the effects of the changes in Columbia River stage were examined using cross-correlations and an analytical river-aquifer model. Second, seascnal ground-water withdrawals for irrigation in the upper Cold Creek Valley were studied to determine their effects on ground-water levels. Finally, reservoir fluctuations and rainfall-recharge were considered as potential sources of seasonal fluctuations. Results from the analyses of ground-water fluctuations indicated that hydraulic barriers may be affecting the propagation of ground-water disturbances in the study area. Chapter Four examined the effectiveness and extent of two potential barriers. The Cold Creek barrier, which had been previously identified by geophysical surveys and its effect on ground-water levels, was studied by looking at the propagation of disturbances on opposite sides. Similar tactics were

144 143 used to undbrstand the effectiveness of the Ubtanum Ridge anticline as a ground-water barrier between the Columbia River and the RRL. Chapter Five addressed the vertical connectivity of the hydro stratigraphic units at the RRL. Cross-correlaticns of the groundwater levels at DC-19, DC-20, and DC-22 were performed to determine the vertical relationship between the units. Vertical effects from surface waste water disposal activity at the RRL were studied to determine if ground-water levels in the underlying confined units are being affected. Relatively simple analyses including numerical models were used. Finally, the conclusions from this study were combined with current hydrogeologic knowledge to form a hydrogeologic conceptualization for the study area. Past, present, and future characteristics of the ground-water flow were presented. Conclusions The purposes of the study, as outlined in Chapter One, were to determine if natural variations in ground-water levels can be used to gain information about the hydrogeology of an area, specifically a section of the Hanford Site. Conclusions from the analyses are: (1) This method of analysis can provide useful information about the hydrogeology of an area. It is necessary, however, to have sufficient sources of ground-water level fluctuations such as river or tidal changes in addition to any incidental man-made disturbances. Assuming natural ground-water level fluctuations are

145 144 present, it is necessary to have an ample number of monitoring locations that are able to detect the fluctuations and statistical methods such as crosscorrelations are needed to detect similarities in small-sale ground-water level variations. (2)Three areas in the study area appear to be predominantly affected by different influences on the groundwater levels. North of the UWrtanum Ridge anticline, the seasonal Columbia River stage fluctuations daninate the ground-water level variations. West of the Cold Creek impediment, ground-water withdrawals for irrigation affect water levels. On the east side of the barrier at the RRL, ground-water levels are primarily responding to the recent development of piezameter nests DC-19, DC-20, DC-22, and DC-23. (3)Seasonal Columbia River stage fluctuations are shown to affect ground-water levels in the Rosalia flow top at DB-12 and in the Mebton interbed at piezaneters DC-20 and DC-22 at the RRL. Propagation of the River's effects in the Rosalia flow top is through a subaqueous outcrop in the area of the gauging station and possibly an outcrop of the Nebton interbed farther to the east. Levels in the Cold Creek Valley are not significantly influenced by the river. (4) Two hydraulic barriers were identified. First, the Cold Creek barrier, which had been previously

146 145 acknowledged as an influence on ground-water levels, was shown to effectively isolate the ground-water systems on either side. Second, possible faults along the UMtanum Ridge anticline appear to be acting as impediments to ground-water communication in the Rosalia flow top, but may transmit disturbances in the Mabton interbed. (5)Apparent responses in the piezometric surfaces at the RRL are due to surface waste water disposal activity. Hydraulic communication between the existing water table mound and the confined units down to the Sentinel Gap flow top may be the cause of the observed responses in the plezometric surfaces. (6)Ground-water level variations in the Rosalia and Sentinel Gap flow top are nearly identical at each of the RRL piezometers (DC-19, DC-20, and DC-22). The cause for the similarity is not known based an available information. Recarrnendations for Future Study Additional data, which have been recorded at the Hanford Site but were unavailable for this study, could be helpful in future analyses. Seasonal ground-water level fluctuations were an important aspect of the examination. Unfortunately, less than two years of data were available at piezometers DC-19, DC-20, and DC-22. Seasonal effects are difficult to analyze with that data record length. In the

147 146 future, additional recorded data should be analyzed to allow a better examination of any seasonal cycles in the ground-water level fluctuations at these piezometers. Lack of frequent ground-water level recordings at all of the wells in this study disallowed the examination of daily level fluctuations. Presently, hourly recordings are taken at piezometers DC-19, DC-20, and DC-22 from downhole pressure transducers. Many of the other wells have continuous strip chart recordings of the water levels. To properly analyze the effects of daily influences such as earth and atmospheric tides and Columbia River stage effects, the data from the transducers and strip charts are needed. With the proper data, multiple daily influences may be able to be separated in the ground-water level time-series. Earth tide and atmospheric pressure effects, which have been identified by frequency analysis of the data (Sorooshian et al., 1986), could also be removed by (1) filtering the data In the frequency domain, or (2) statistical regression of atrrospheric pressure data and earth tide potentials. If these techniques are successful, then the possibility of daily river stage effects could be analyzed by the methods used in this report. The advantage of understanding the effects of daily fluctuations in the ground-water levels is that two frequencies (including the seasonal cycle) are available. The river-aquifer model could then be used to obtain an additional estimate of the distance to a subaqueous outcrop. This would provide more certainty about the conclusions obtained from the model and hopefully yield additional information

148 147 about the relationship between the Columbia River and hydrostratigraphic units in the area. Finally, the analysis of the vertical connectivity, which was relatively simple, could be done with a more sophisticated numerical model if more reliable results are desired. A multi-layered inverse model could be employed to obtain estimates of the flow properties of the basalt flows.

149 148 APPENDIX A WELL HYDROGRAPHS

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155 154 e -1 qms ts - O to o oa 111F J J I liii Ilijil J I J J J II CA (1j) TaAari aate.m.

156 INA 155 PIP PO _co co IMO co WW1 NIP ill III I -do (1j) Tanal Jaiem

157 156 cd G) o CNi 44 "44 o. ai co cr) el nt /44 (1J3 TaAal daleak.

158 IMP co 1=11. WO ImP Co d (1) -i IM1 I I I li I II I I I III ' II t i CV 441N4P (i.j) TaAari

159 158 IM IMI, MO MI, 04 o 4..) o 1nnn1 404 d r r4 TEl rn 0 f:4 I. IM MI PM 6 I--i I 0 A OD MO MI MO OM WO Ti Iiiiiiiiii i i i iiiiiiiiii iiiiiiiiii co to 0.-1 cz; ci oi oi o o o o) cu to t4 t4 CO Cr3 (-1.j) TaAari aalpiii

160 M. 159 t- oo W. IM., IN= MD NM!MI WIII n ' FM, IND NM MD Ima WO NINO PO cs Q) -1 MO n.. WI MD OM MII MI PO I m NEB. MO I 1 1 ri co ?ii 74 (4j) TaA.01 jalp. m.

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162 IMP 161 I.. PM NM, NM MID MO PM co -co OM WO INN MO MO MP Iwo IMO I." N O _in TRID co WO II MD NO MO N., MD MP WI I Go mr (I j ) p Aar'..I@ 4PM

163 lab 162 OW 1. 1 P O IRV Im Pe ci a) 0 /MD Im ONO ow Co /MOO 0.0 WM, 11111j co O Co NED j) laaal dalp.m Ni

164 WOO 163 IMO Nob Mit NO& II (14) TaAai cc; ct,

165 164 MI MINI Om NM M. WW1 IM1 MD PM IMI, MD MO ali Q) -I MID PM MP Milk IMP WO MO M. MO m. MO 1 1 I II 1 III I 1 I ( su ) 0. C:I4 441 III PAarl la 1.P.M. OM o oi cm cr)

166 P P 165 MD MO MI. NM MO MO lim MD MI =No - N D PO PM MO WO NM _ Pol. MD - Im. MI Im - Im lalg PM o o wci c i II 1 I I I (4j) TaAai dai.p.m.

167 1=1. /NIP Co MP Iwo TWO In MO INIM _co Ma co 1=1 li= - MP - WO Ma Mall d 4) -I NM =Iv _ID CO M. OW - M MD MD - IMMI t ; 1 I I i I 1 1 I co cv c i c i (1J) I@Aarl W

168 167 WI. WO MD lom 1=1 Iln MI' W10 ci a)..0 s.-4 a).4..) z.,-1 o o 4-) rra co MO IMO MO - MI IMO ono M. NO MI, Im. IMP MI csi cv 1 0 a) Im. WI WM WO WI, MI PO NM MO CO Nit ci ci 74-1 r-i lit (ii) I9Aarl 191-PAi

169 168 "g; /011 OP PO -(39 PO.44 co I I I 1 1 I I I 0 c i Ni (1j) paal 131P.m. oi

170 1 n -co IMO IND IMP ; ; ; ; jill, Ii I 1 0 Ln 6 41 gt TaAari.194PM 44 co

171 170 APPENDIX B RESIDUAL GRCUND-WATER LEVELS AT DC-19, DC-20, AND DC-22

172 171 APPENDIX B RESIDUAL GROUND-WATER LEVELS AT DC-19, DC-20, AND DC-22 Two sources of ground-water level disturbances are removed at piezometers DC-19, DC-20, and DC-22 to allow a better examination of underlying natural water level variations. Recent drilling and development disturbances, in addition to atmospheric pressure changes, are the sources of disturbances that are able to be removed. Statistical regression is used to remove the recovery trends and barometric effects to obtain the residual ground-water levels. Mbdels for the prediction of ground-water recovery trends at DC-19, DC-20, and DC-22 were developed to establish the baseline levels (Sorooshian et al., 1985). Three types of recovery models were calibrated: (1) Jacob-Cooper, (2) linear, and (3) mixed (combination of Jacob-Cooper and linear). Ground-water levels in the deeper units were best fit by the Cooper-Jacob and mixed models; however, the recoveries of the shallower units studied in this report were best fit by the linear model. The linear model is of the form: h(t)=b0-1-b1 [r p(t)-]+b2 t where h(t) = measured ground-water level (feet), bo = ground-water level at time t=0 (feet), = barometric efficiency (dimensionless),

173 172 = trend (feet/day), r = density of the water column (2.3 ft/psi), p(t) = departure of the atmospheric pressure reading from the mean for the hour nearest to when the ground-water level was measured (lbs/in?), = mean atmospheric pressure (33.1 feet), and t = time, in days beginning March 1, The equations for the recovery models for each of the nine monitored hydrostratigraphic horizons at DC-19, DC-20, and DC-22 are given in Table 3.5 of Sorocshian et al. (1985). The barometric efficiencies for each model/horizon combination are also shown. Resicinal ground-water levels are obtained by subtracting the observed ground-water levels from the levels predicted by the models. Residual ground-water levels for the upper five units at DC-19, DC-20, and DC-22 are presented in this appendix Levels for the units which were not fit by any of the models are not shown.

174 SO 173 WI IM. 1m IM PO MID OM g... m, IMO WWI IIIMII I. Me los.e o Lr) 6 o 6 o 6 i (1j) paari aalviti Tvnptsazi IMII _ MI NO.4 I

175 FM. 174 WO WIA. MR OW OM OM _ MO co _ co INM N M IIM WO POO... IMO' _ WO =III MP IMO 1m. MO PM WM ISM -44 Co o o ocr) 1-# Lo 6 ci c:i 1 i (u) Iazi 0 1 aalvhi ivrtptsazi IIIIIihiliiIIIIII me _

176 175 OM We ION ONO Ow _ VW PIII co _NM NM NM WI MO MIA IN. _ OW NM _to co _n 6 OM MP MD Li.) f::) litiiiiiiiiiiiiiiiiiiiiiiiiiiiiiimo wiliglii III CO,4 0 NCP CD CV ci cj c6 ci ci I I I I (u) lanai aalviii ignmsaa W. WM WM. MP _ Me OE)

177 IMI 176 WO Imp.. lim IWO s..1 (ci a) >4 OM 11= _In Co YEW 1m. we I. lim Iwo n mi. Iwo I I 1 I l I 1 1 I I I I I 1 1 I I CO al 1-4 0,-1 al ci ci ci ci ci I 1 1 (1.1) IaAari aalviyi ivnpisaa mti

178 177, MO - Im MI OW - ca Q) -I W I MI _In co 1=1, - - MN -, - 'Mk MO IIIIIIIIIIIIIIIIIItilliii N 0 N 4:5 c6 ci I I ( 1) Pixel laipm. IPrEPTsaH

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180 179 VI 4-, o o.44 co o c4i (1J) 'anal Jaip ivrtptsazi

181 180 - _co o3 _ 1=, - - 1=11 ON MI MO >14 Im -ONO ID 03 - I I o o o o o 1-4 c i crvi I I I (ii) -WO - Me CO jaaal Japm ivnpisaa

182 181 NNO Om» IMn :Co co NIP S.4 ai -i _Ln co IMO liii Ilijil I I co o Ln o e1 (1j) TaAai Jalvm, renpisaa

183 IND MP 84 ) NO 0 m ni 44nI MM. NED 04 CO 0 - I. 71 ) a) rn cki c I 1 0 A WO NM WO IMP - Igo MO I. n n - M. - Hill 1 liji l l I t CO o o to o in o ci ci ci n.4 I I (1i) IaAari ialpia ignmsaa

184 183 APPENDIX C CALCULATION OF PUMPING RATES FOR IRRIGATION IN THE UPPER COLD CREEK VALLEY

185 184 APPENDIX C CALCULATION OF PUMPING RATES FOR IRRIGATION IN THE UPPER COLD CREEK VALLEY To obtain the seasonal drawdowns from pumping in the upper Cold Creek Valley, the discharge rate needs to be estimated. No discharge data were available for the area, so an empirical formula is used to calculate the consumptive use for the crops in the valley (James, 1982). The formula is based on climatalogical data and past research on consumptive-use data in the area. The equation used to calculate the consumptive, use is: u = k- f where u =monthly consumptive use (inches), k = monthly consumptive use coefficient, f = t - p1100 = niontliw consumptive use factor, t = meanmathly temperature ( F), and p = monthly percentage of daytime hours of the year. The monthly consumptive use coefficient depends on the crop. In the upper Cold Creek Valley in 1985, it was estimated (Livesay, 1986) that the irrigated acreage is: grapes = 750 acres pasture = 100 acres

186 185 Mbnthly oonsurgotive use coefficients, k, for grapes and pasture in Washington are (James, 1982): April May June July August Sept Oct Grapes Pasture The Berk well, in the upper Cold Creek Valley, withdrew approximately 700 ac/ft in 1985 in addition to the amount pumped from Cold Creek wells #1 and #2 for crop requirements (Livesay, 1986). Adding the consumptive use and discharge from the Berk well, the monthly discharge rate in the valley in 1985 was: Monthly Discharge ( ft3 /month) April 1.3 x 107 May 1.5 x 107 June 2.1 x 107 July 2.7 x 107 August 2.5 x 107 September 1.9 x 107 October 1.4 x 167

187 186 APPENDIX D RIVER-AQUIFER ANALYTICAL MODEL

188 187 APPENDIX D RIVER-AQUIFER ANALYTICAL MODEL An analytical solution is used to describe the effects of the Columbia River stage in the study area (Ferris, 1951). To obtain the solution, several assumptions were made. (1)homogeneous aquifer (2)uniform aquifer thickness (3)great inland extent of the aquifer (4)water is released immediately with a decline in pressure (5)ground-water flow is unidimensional (6) entire thickness of the aquifer abuts the river (contact model) If the aquifer's entire thickness does not contact the river, the final assumption is acceptable when the distance to the observation well is great relative to the aquifer thickness. The differential equation used to describe the linear groundwater flow is: d2h S dh dx2 = Tdt where h = net rise or decline of ground-water level; S = storativity: T = transmissivity;

189 188 x = distance from the subaqueous outcrop to an observation well; and t = time. Let 110 be the amplitude of the river stage fluctuation. The boundary condition at x=0 is: h = ho sin w t The solution for the amplitude of the wave motion expressed in radians per unit time is: h =e...311/17777 where to is the period of the cyclic fluctuation. When the groundwater levels are affected through a confining layer (loading model), the amplitude must be reduced by the ratio: p/ ( p+ne ) where p is the vertical compressibility of the skeletal aquifer, S is the compressibility of water, and n is the porosity of the skeletal aquifer. In this study, the ratio is approximated by the tidal efficiency, C, which is obtained from a previous calculation (Sorooshian et al., 1985) of the barometric efficiency, B, by the equation:

190 189 The derived time lag, tl, for the change in river stage to be observed at a well is: tl = il/ 0 S/74rr17

191 190 APPENDIX E SEASONAL CORRELOGRAMS

192 RM. 191 NO OM NO : CV MD : 0 - o In 0 In 0 W i.4 c; ci c;,e.1 1 I 1UOT3TJJ@OD

193 192 o o o ci al CD T-4 rti nn 0 CC/ ci o o w-1 II ( J O to o to 0,-; ci ci watoupop o 1 1 MOD

194 193 : o -o - o :co n NM n 1 IRO :o -o - o : cv I, o Ln o Ln,i d ci cis I 1 1 I 1 7 O TIP OD '1103 : 0 - o 7o v-i _ i : o -oo 0.7

195 NMI 0 -ci in o in o. 8 1 ci c:i ci,-. I I ' JJ

196 195 LIST OF REFERENCES Atlantic Richfield Hanford Canpany, "Preliminary feasibility study on storage of radioactive wastes in Columbia River basalts", Two vols., Atlantic Richfield Hanford Company, ARH-ST-137, Richland, Washington, Berkman, E., "Reprocessing and interpolation of seismic reflection data Hanford Site, Pasco Basin, south-central Washington'', SD-BWI-TI- 177, Rockwell Hanford Operations, Richland, Washington, Bierschenk, W. H., "Aquifer characteristics and groundwalmrmovment at Hanford", Hanford Atomic Products Operation, HW-60601, Richland, Washington, 81 p., Bruce, S. R., "Preliminary estimates of selected hydrologic properties", Internal Letter NO , Rockwell Hanford Operations, Richland, Washington, Calkins, F. C., "Geology and water resources of a portion of eastcentral Washington", U. S. Geological Survey Water-Supply Paper 118, 96 p., Djerrari, A. M., and V. V. Nguyen, "Stochastic parameter estimation for nuclear repository site characterization at Hanford, Washington", EWA, Incorporated, Minneapolis, Minnesota, DOE (1J% S. Department of Energy), "Site characterization report for the basalt waste isolation project", DOE/RL 82-3, Three vols., Rockwell Hanford Operations for the U. S. Department of Energy, Washington, D. C., DOE (U. S. Department of Energy), "Draft envirornental asse.immnt for characterization of the Hanford Site", Nuclear Waste Policy Act (Section 112), DOE/RW-0017, Washingtcm, D. C., Ferris, J. G., "Cyclic fluctuations of water level as a basis for determining aquifer transmissibility", Intl. Assoc. Sci. Hydrology Publ. 33, pp , Gephart, R. E., R. C. Arnett, R. G. Baca, L. S. Leonhart, and F. A. Spane, Jr., "Hydrologic studies within the Columbia Plateau, Washington, an integration of current knowledge", RHO-BWI-ST-5, Rockwell HanamiCperations, Richland, Washington, Goff, F. E., "Preliminary geology of eastern Untanum Ridge, southcentral Washington":, RHO-BWI-C-21, F. E. Goff, Consulting Engineer, for Rockwell Hanford Operations, Richland, Washington, 1981.

197 196 LIST OF REFERENCES - -Continued Holmes, G. E., and T. H. Mitchell, "Seismic reflection and multilevel aercmagnetic surveys in Cold Creek syncline area", RHO-BWI-ST-14, Rockwell Hanford Operations, Richland, Washington, James, L. G., J. M. Erpenbeck, D. L. Bassett, J. E. Middleton, "Irrigation requirements for Washington--estimates and methodology", Research Bulletin XB 0925, Agricultural Research Center, Washington State University, Pullman, Washington, Landes, H., "Preliminary report on the underground waters of Washington", U. S. Geological Survey Water-Supply PapPr. 111, 85 p., Livesay, D. M., "The hydrogeology of the upper Wanapum Basalt, upper Cold Creek Valley, Washington", M. S. Thesis, Geological Eng., Washington State University, Pullman, Washington, Long, P. E. and Davidson, N. J., "lithology of the Grande Ronde Basalt with emphasis on the UMtanum and McCoy Canyon flows", in Myers, C. W. and S. M. Price, eds., "subsurface geology of the Cold Creek Syncline, RHO-BWI-ST-14, Rockwell Hanford Operations, Richland, Washington, Long, and WCC (Long, P. E., and Woodward-Clyde Consultants), "Repository horizon identification report": Vols. 1 and 2, DRAFT SD-BWI- TY-001, Woodward-Clyde Consultants for Rockwell Hanford Operations, Richland, Washington, MbKee, E. H., D. A. Swanson, and T. L. Wright, "Duration and volume of Columbia River Basalt volcanism; Washington, Oregon and Idaho", Geological Society of America Abstracts with Programs, Vol. 9, No. 4, pp , Myers, C.W., S. M. Price, and J. A. Caggiano, M. P. Cochran, W. H. Czimer, N. J. Davidson, R. C. Edwards, K. R. Fecht, G. E. Holmes,M. G. Jones, J. R. KUnk, R. D. Landon, R. K. Ledgerwood, J. T. Lillie, P. E. Long, T. H. Mitchell, E. H. Price, S. P. Reidel, and A. M. Tallman, "Geologic studies of the Columbia Plateau: a status report", RHO-BWI-ST-4, Rockwell Hanford Operations, Richland, Washington, Newcomb, R. C., "Storage of ground water behind subsurface dams in the Columbia River Basalt, Washington, Oregon, and Idaho", U. S. Geol. Survey Prof. Paper 383-A, A 1-A15, Newcomb, R. C., J. R. Strand, and F. J. Frank, "Geology and groundwater characteristics of the Hanford Reservation of the IL S. Atomic Energy Cc:emission, Washington", U. S. Geological Survey Prof. Paper 717, 78 p., 1973.

198 197 LIST OF REFERENCES--Continued NRC (U. S. Nuclear Regulatory Camdssion), "Safety Evaluation Report, Washington Plant No. 2", NURM-0892 Supplement No. 1, U. S. Nuclear Regulatory Cairnission, Washingixxl, D. C., 1982b. PSPL (Puget Project, Sound Power and Light Company), "Skagit-Hanford Nuclear Preliminary Safety Analysis Report", Bellevue, Washington, Russell, I. ton", U. C., "A geological reconnaissance of southeastern Washing- S. Geological Survey Water-Supply Paper 4, 96 p., Schatz, A. L., and E. J. Jensen, "Unconfined water-table map", SD-WM- TI-273, Rockwell Hanford Operations, Richland, Washington, Sorooshian, S., and D. R. Davis, "Baseline prediction models, baseline prediction model validations, ground-water level correlations, direction and magnitude of ground-water gradients, and optimal sampling frequencies for ground-water levels measured in nine hydrostratigraphic units at well clusters DC-19, DC-20, and DC-22", Department of Hydrology and Water Resources, University of Arizona, Tucson, Arizona, Scrocshian, S., and D. R. Davis, "Statistical criteria for baselining of time-variant hydrogeolcgic parameters", Department of Hydrology and Water Resources, adversity of Arizona, Tucson, Arizona, Sowers, G. F., Soil Mechanics and Foundations: Geotechnichal Engineering, 4th ed., MacMillan, New York, Spane, F. A., "Preliminary evaluation of the effects of borehole DC-23W drilling and development activities on baseline water-level and pressure measurements at DC-19, -20, and -22 piezometer installations", Rockwell Hanford Operations, Richland, Washilvton, Sublette, W. R., "Rock Mechanics Data Package", SD-BWI-DP-041, Rockwell Hanford Operations, Richland, Washington, Swanson, D. A., "Yakima Basalt of the Tieton River area, south-central Washington", Geological Society of America Bulletin, Vol. 78, pp , Swanson, D. A., R. D. Bentley, G. R. Byerley, J. N. Gardner, and T. L. Wright, "Preliminary reconnaissance geologic maps of the Columbia River basalt group in parts of eastern Washington and northern Idaho", U. S. Geological Survey Open-File Report , 25 p., 1979.