APPENDIX C. Supplemental Information on Aquifer Properties

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1 APPENDIX C Supplemental Information on Aquifer Properties

3 TECHNICAL MEMORANDUM TO: Tom Culhane; Ecology DATE: June 10, 2013 FROM: Eric Tuppan PROJECT: CC RE: Revised Aquifer Properties-Headquarters Landfill Project (Rev. 1) As stated in the revised Hydrogeologic Report for the Proposed Cowlitz County Headquarters Landfill Project (dated November 26, 2012) and Conceptual Workplan for Site Characterization (Appendix I to that report), this technical memorandum and associated report supplement information on aquifer properties at the landfill. The newly acquired data are used to update estimates of average horizontal hydraulic conductivity (K) and horizontal groundwater velocity presented in Sections and of the Hydrogeologic Report. This technical memorandum briefly summarizes findings from the slug testing report (attached) and with that information, revises the discussion in the Hydrogeologic Report. Details of slug testing field methodology, evaluation methods, and assumptions are provided in the attached report by JBR Consultants, Inc. (JBR). Logs of wells used in the testing can be found in Appendix C of the Hydrogeologic Report. SUMMARY OF HYDRAULIC TESTING Hydraulic testing in the form of slug tests was performed over an area within the landfill footprint as well as at the compliance boundary for Basin 1. The purpose of the testing was to gain additional information about the horizontal K, which is used in estimating groundwater flow rates of subsurface units. The list of wells tested and the testing rationale include: C-1 and C-2: both compliance wells downgradient of Basin 1 cells along flow paths; testing in these wells provides K values for relatively fresh basalt (C-2) and moderately weathered basalt and a gravelly silt (C-1), which is likely deeply weathered basalt. U-1, P-9, and P-10: upgradient of landfill cells south and east of the current footprint in sequence for development over the next 40 years. This provides K values for lithic tuff weathered to silty clay (U-1); and weakly to moderately weathered basalt/andesite flows (P-9 and P-10). P-19: within the landfill footprint likely to be developed in the next 10 year permit cycle. Provides K value for lithic tuff that has been moderately to deeply weathered to sandy silt and silty sand with cobbles. TUPPAN CONSULTANTS LLC TEL Second Street, Suite 103, Lake Oswego, OR Aqfr Prop-HQ LF mem061013

4 Tom Culhane June 10, 2013 Page 2 Project: CC P-20: within the landfill footprint likely to be developed in the next 10 year permit cycle. Provides K value for moderate to weakly weathered basalt. P-13R: within landfill footprint in area north of existing footprint. Provides K value for deeply weathered to fresh basalt. Field testing was conducted by JBR from October 29 to 31, Slug tests at each monitoring well were done by adding (falling head test) and removing (rising head test) a slug of known volume from the wells and measuring the response of the piezometric surface as it returned to pre-test static conditions. An exception was made at monitoring well P-10 in which only a falling head slug test was conducted because the 95 percent recovery objective was not satisfied after 60 minutes of monitoring recovery. An In-Situ, Inc. Level Troll 700TM was used to monitor changes in water level over time during each test. The Level Troll 700TM, which is a combination pressure transducer and datalogger, was attached to a laptop computer to allow JBR personnel to monitor the change in water levels as they returned to static conditions. Water level data were analyzed using both the Bouwer and Rice (1976) and the Hvorslev (1951) methods for unconfined and confined aquifers using AQTESOLV Pro software, Version The volume of the slug added to the wells, displaced volume of water, and assumptions inherent in the analytical solutions for these test methods, predict that the area of influence of the slug (i.e., effective radius of influence in the equations) is minimal, estimated at 1 to 5 feet from the well bore. This is based on a review of the construction data for site wells and equations in Bouwer and Rice (1976) and page 244 of Kruseman and de Ridder (2000). Consequently, it is unlikely that the outcome of the testing was influenced by possible effects that the landfill liner system might have on underlying hydrogeologic conditions, given the wells' proximity to the landfill (e.g., P-19 and P-20 are approximately 40 feet from the southern toe of the landfill). The estimated horizontal K for the 2012 testing ranged from ft/day to 340 ft/day. The average estimated horizontal K calculated using the geometric mean 1 from these rising and falling head slug tests combining both analytical methods is 0.63 ft/day. Horizontal K estimates for each of the eight monitoring wells are presented in Table 1 (recreated from Table 3 of the JBR report). 1 Because the magnitudes of horizontal hydraulic conductivity estimates ranged over multiple orders of magnitude (i.e., lognormal distribution), it is more technically appropriate to calculate the average horizontal hydraulic conductivity using the geometric mean than the arithmetic mean (Domenico and Schwartz, 1990). Aqfr Prop-HQ LF mem061013

5 Tom Culhane June 10, 2013 Page 3 Project: CC UPDATE TO HYDROGEOLOGIC REPORT Aquifer Properties The results from this recent testing were combined with slug testing data done at the four wells in 1991 and the results shown on the second page of Table 1. On average, the earlier testing had lower horizontal K values, a geometric mean for the four tests was ft/day. However, the geometric mean calculation for the site using data from both testing events results in an average K of 0.15 ft/day. As discussed in the Hydrogeologic Report, porosity estimates were taken from technical literature for the types of fine- to medium-grained derivative soil lithologies encountered at the site. Morris and Johnson (1967) report average porosities for clay, silt, and medium sand of 42, 46 and 39 percent, respectively. The effective porosity is lower, and can be estimated from the results of physical tests for specific yield, which are between 6 and 20 percent for clay and silt, up to 32 percent for medium sand (see Table 12 in Morris and Johnson, 1967). Groundwater Rate of Movement Horizontal linear groundwater velocity depends on horizontal K, horizontal hydraulic gradient, and effective porosity of the water-bearing medium. The horizontal velocity (V h ) of groundwater is calculated by the following equation: where V h Ki n e V h = horizontal groundwater velocity. K = hydraulic conductivity. i = horizontal hydraulic gradient. = effective porosity. n e Estimates of V h in shallow groundwater in the deeply weathered fine-grained soils are calculated for two areas at the site: between U-1 and P-3 which is an area of relatively low hydraulic gradient; and an area of higher gradient, between P-6 and MW-4. For the low gradient estimate, at ft/ft, V h ranges from 8 to 42 feet per year (ft/yr), given a K of 0.15 ft/day and a range of effective porosity of 6 to 32 percent (literature values in Morris and Johnson, 1967). For the area with the steeper gradient, at 0.12 ft/ft, V h ranges from 21 to 110 ft/yr, given a K of 0.15 ft/day, and the same range of effective porosity. Groundwater velocity calculations are shown in Tables 2a and 2b. Aqfr Prop-HQ LF mem061013

6 Tom Culhane June 10, 2013 Page 4 Project: CC Attachments: Table 1 - Slug Testing-Hydraulic Conductivity Estimates Table 2 - Calculated Range for Groundwater Velocity Slug Testing Report (JBR Environmental Consultants, Inc.) Aqfr Prop-HQ LF mem061013

7 Table 1 Slug Testing - Horizontal Hydraulic Conductivity Estimates Cowlitz County Headquarters Landfill Cowlitz County, Washington UNCONFINED Monitoring Well Identification Bouwer-Rice (R.H.) ft/day Hvorslev (R.H.) ft/day Bouwer-Rice (F.H.) ft/day Hvorslev (F.H.) ft/day Geomean by Well (ft/day) Screened Interval Lithology 1 U Silty Clay C Silt and Gravely Silt C Weathered Basalt and Basalt P Weathered Andesite Flows P-10 N/A N/A Basalt and Andesite Lava P-13R Andesitic Basalt P Sandy Silt and Silty Sand P Basalt Geometric Mean (ft/day) Bouwer-Rice Geometric Mean (ft/day) 0.55 Hvorslev Geometric Mean (ft/day) 0.74 Geometric Mean for All Values (ft/day) 0.63 CONFINED Monitoring Well Identification Bouwer-Rice (R.H.) ft/day Hvorslev (R.H.) ft/day Bouwer-Rice (F.H.) ft/day Hvorslev (F.H.) ft/day Geomean by Well (ft/day) Screened Interval Lithology 1 U Silty Clay C Silt and Gravely Silt C Weathered Basalt and Basalt P Weathered Andesite Flows P-10 N/A N/A Basalt and Andesite Lava P-13R Andesitic Basalt P Sandy Silt and Silty Sand P Basalt Geometric Mean (ft/day) Bouwer Rice Geometric Mean (ft/day) 0.54 Hvorslev Geometric Mean (ft/day) 0.74 Geometric Mean for All Values (ft/day) 0.63 Table 1- Aquifer_Test_Data-r2_061013\Tab1

8 Table 1 Slug Testing - Horizontal Hydraulic Conductivity Estimates Cowlitz County Headquarters Landfill Cowlitz County, Washington UNCONFINED Monitoring Well Identification Bouwer-Rice (R.H.) ft/day Hvorslev (R.H.) ft/day Bouwer-Rice (F.H.) ft/day Hvorslev (F.H.) ft/day Geomean by Well (ft/day) Screened Interval Lithology 1 U Silty Clay C Silt and Gravely Silt C Weathered Basalt and Basalt P Weathered Andesite Flows P-10 N/A N/A Basalt and Andesite Lava P-13R Andesitic Basalt P Sandy Silt and Silty Sand P Basalt BW Lithic Tuff MW Lithic Tuff/Basalt MW Lithic Tuff P Lithic Tuff Geometric Mean (ft/day) Bouwer-Rice Geometric Mean (ft/day) 0.55 Hvorslev Geometric Mean (ft/day) 0.74 Geometric Mean for All Wells (ft/day) 0.15 Notes: R.H. = Rising Head F.H. = Falling head 1 = as described in well logs 1990s testing Table 1- Aquifer_Test_Data-r2_061013\Tab1

9 Table 2a Calculated Range for Groundwater Velocity Headquarters Landfill 2012 (Upgradient) By: EJT Calculated Ranges of Horizontal Groundwater Velocity V h = Ki/n e Monitoring event date Annual Average Hydraulic K = 0.15 ft/day (geometric mean of 14 wells) Conductivity dh (ft) dl (ft) Hydraulic i =dh/dl Gradient i = (measured betweeen U-1 and P-3) Effective n e = 0.06 Low n e Porosity 0.32 High n e High Estimate (low n e ) V h = (0.15)(0.046)/0.06 = 0.12 ft/day V h (ft/day) x 365 (day/year) = 42.0 ft/year Low Estimate (high n e ) V h = (0.15)(0.046)/0.32 = ft/day V h (ft/day) x 365 (day/year) = 7.9 ft/year Table 1- Aquifer_Test_Data-r2_061013\Tab2a

10 Table 2b Calculated Range for Groundwater Velocity Headquarters Landfill 2012 (Downgradient) By: EJT Calculated Ranges of Horizontal Groundwater Velocity V h = Ki/n e Monitoring event date Annual Average Hydraulic K = 0.15 ft/day (geometric mean of 14 wells) Conductivity dh (ft) dl (ft) Hydraulic i =dh/dl Gradient i = 0.12 (measured betweeen P-6 and MW-4) Effective n e = 0.06 Low n e Porosity 0.32 High n e High Estimate (low n e ) V h = (0.15)(0.12)/0.06 = 0.30 ft/day V h (ft/day) x 365 (day/year) = 110 ft/year Low Estimate (high n e ) V h = (0.15)(0.12)/0.32 = 0.06 ft/day V h (ft/day) x 365 (day/year) = 20.5 ft/year Table 1- Aquifer_Test_Data-r2_061013\Tab2b

17 APPENDIX D Three Rivers Regional Wastewater Plant Letter Regarding Leachate Treatment

Evolution of the conceptual hydrogeologic and ground-water flow model for Las Vegas Valley, Clark County, Nevada

Evolution of the conceptual hydrogeologic and ground-water flow model for Las Vegas Valley, Clark County, Nevada Geological Society of America Annual Meeting November 14, 2 David J. Donovan Southern Nevada