NOTICE CONCERNING COPYRIGHT RESTRICTIONS

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1 NOTCE CONCERNNG COPYRGHT RESTRCTONS This document may contain copyrighted materials. These materials have been made available for use in research, teaching, and private study, but may not be used for any commercial purpose. Users may not otherwise copy, reproduce, retransmit, distribute, publish, commercially exploit or otherwise transfer any material. The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specific conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." f a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law.

2 Geothermal Resources Council TRANSACTONS, Vol. 14, Part, August 1990 SHALLOW GROUND WATER MAPPNG N THE LOWER EAST RFT SONE KLAUEA VOLCANO, HAWA J. L. OVENTT CONSULTANT 310 CORTSEN ROAD PLEASANT HLL, CALFORNA ABSTRACT Three types of shallow ground waters have been identified in the lower East Rift Zone of Kilauea Volcano: fresh, geothermal and mixed. Geothermal waters occur proximal to a major structural intersection of the east-northeast trending lower East Rift Zone with a north-northwest trending transverse fault, and in the region south of this structure where a geothermal plume discharges along the coast as a series of hot springs and seeps. This structural intersection is interpreted as a principal conduit for the upward migration of geothermal fluids from a deep geothermal reservoir into the overlying shallow and intermediate depth ground water system. Fresh ground water exists north of the lower East Rift Zone and south of the rift in the region southwest of this transverse fault. Mixed ground water is located downgradient of the region of upwelling geothermal fluids. This paper presents an integrated analysis of the geological, hydrological and chemical setting of shallow ground waters in the LERZ. These observations previously reported in ovenitti (1986;1987), have been re-presented herein at the request of the Chairperson of the "Groundwater Problems Session" of this meeting. NTRODUCTON Characterization of the geohydrochemical nature of the ground water regime in and around a geothermal system is of critical importance to the development of a geothermal resource. Such definition provides an additional data base from which exploration, development, production and environmental decisions can be formulated. For example, during the exploration well drilling phase, drilling objectives can be optimized by targeting zones of upwelling geothermal fluids instead of their outflow zones. Similarly, areas of cold water recharge, if identified, must be avoided. n the lower East Rift Zone (LERZ) of Kilauea Volcano, the Puna Geothermal Venture (PGV) plans to develop a 25 MW geothermal project (Figure 1). An integral component of this development will be the injection of all produced geothermal fluids (brine, steam condensate and non-condensible gases) back into the geothermal reservoir (Environmental Management ASSOCiateS, 1989). Concomitant with this field development approach is the responsibility of the geothermal developer to protect underground sources of drinking water from any pollution caused by the subsurface disposal of these fluids. Delineation of the shallow ground water system in the LERZ has been one of the contributing factors that has enabled this innovative field development approach. Figure 1. Location map for wells in the LERZ. GBElERAL GgoHyD61oLoGCAL SETTW The East Rift Zone is one of the main conduits for the lateral migration of basaltic magma from the holding chamber beneath the volcano' s summit caldera. t is manifested at the surface as a 1-2 mile, linear belt consisting of parallel open fissures, faults, small gardens, pit craters, cones and vents related to numerous volcano-tectonic events. Surface eruptions have occurred in the LERZ as recently as 1740, 1840, 1955, 1960 and

Lovenitti n the subsurface, the rift is characterized by swarms of closely spaced, parallel to subparallel, vertical to steeply dipping dikes referred to a dike complex.

3 Lovenitti n the subsurface, the rift is characterized by swarms of closely spaced, parallel to subparallel, vertical to steeply dipping dikes referred to a dike complex. Furumoto (1978) has reported that the dike complex is locally above the Curie Point (1000OF) and in places, may even approach the melting point of basalt (1900OF). The rift zone is a constructional feature throughout its length except in its lower portion where the ridge disappears into a series of grabens and splatter deposits (Moore, 1983). This change in topography corresponds to a transverse structural break (Figure 1) identified by Holcomb (1987); Zablocki (1977); Flanigan and Long (1987). The Ghyben-Herzberg principal and a generalized geohydrological model from the east-trending rift zone of Mauna Kea through the East Rift Zone to the sea (cross-section A-A' in Figure 1) are given in Figure 2. The former describes the ground water relationship found in the Hawaiian slands where fresh water (or basal water) floats as a lensshaped body on the heavier salt water. Basal water is expected north and south of the rift. However within the rift, this relationship does not apply and fresh water is considered to be both dikeconfined and dike-controlled. Dike-confined (or dike-impounded) water occurs where the relatively impermeable, near-vertical dikes within the rift form permeable compartments which allow fresh water to both rise significantly above mean sea level and extend to much deeper depths than expected in geologic environments outside of the rift. The term dike-controlled refers to the strong constraint imposed on water flow within the rift by the structural grain of the rift, itself. Annual meteoric recharge in the LERZ is about 120 inches and virtually no standing water bodies exist, except for Green Lake in Kapoho Crater (Figure 1). The subaerial lava flows are very SEA LEVEL permeable which allows most of this precipitation to infiltrate to ground water. Additional sources of recharge to the ground water system are: (1) cold sea water, (2) hydrothermally altered meteoric water, (3) hydrothermally altered sea water and (4) some combination of the above four sources. Kroopnick et al. (1978) have reported that ground water residence time in the LERZ is less than tens of years based on tritium data. The high annual rainfall, infiltration rate and permeability of the subaerial lavas create a vigorous, ground water flow system with a very short residence time. THE PU GEOTHERMAL SYSTEM Deep exploratory geothermal drilling has focused on the area of the structural offset in the LERZ (Figure 1) which has been interpreted to localize the geothermal system (ovenitti and D'Olier, 1985). The Hawaii geothermal resource discovery well: HGP- A, and the PGV 25 MW project are proximal to this structure. n spite of the tremendous heat flux generated by the rift zone, no surface geothermal manifestations (e. g., hot springs, fumaroles, etc. ) are evident in the LERZ except for several hot springs discharging along the southeastern coast of the island and for isolated steam vents within the rift associated with the 1955 fissure eruption. The lack of geothermal surface manifestations is attributed to a relatively impermeable seal around the reservoir and to the vigorous, cool ground water system which "hydraulically masks" its presence. However, leakage of geothermal fluids into the overlying ground water system does occur where the seal is locally broken by geologic structure. HYDROGEOCHEMSTRY OF THE LERZ A review of some 400 ground water samples in the State of Hawaii by Cox and Thomas (1979) determined that three parameters are diagnostic of geothermal water: temperature (T) > 84OF, ch1oride:magnesium ratio (Cl/Mg) 2 15, and silica (SiOz) concentration > mg/l depending on location. A i A' Table 1 presents water chemical data for the 13 wells in the LERZ; their locations are shown in Figure 1. The chemical data pertain to the top of the basal water or top of the dike-confined water. The only exceptions are the analyses for HGP-A which is completed in the intermediate level ground water system, and well 9. This well is essentially completed in a perched aquifer (Davis and Yamanaga, 1968) and as such, will not be considered any further herein. Figure 2. Generalized model of the geohydrologic setting of ground water in the Hawaiian slands and in a rift zone; Bee text for an explanation. Limited water elevation data north of the LERZ suggest southerly ground water flow toward the ocean. The rift zone forms an excellent barrier to ground water flow (Druecker and Fan, 1976), however, and it is inferred that a significant portion of the water north of the rift is actually moving to the northeast following topography. Within the LERZ, minor dike-impoundment has been reported by Kauahikaua et al. (1980). Water flow within the rift is thought to be to the east-northeast toward 700

4 Table 1. Shallow ground water chemistry data for wells in the LERZ. All data are in mg/l unless otherwise indicated. See Figure1 for locations. The term well for the purposes of this report also includes shafts, holes, etc. Data sources are listed below. We1 1 D Total K Ca Mg Cl SO4 HC03 SiOz P Fe TDS CL/Mg 9-Sa b 74 PVFW 75 KS KS-1A,100 KS HGP-A GTW-la 199 GTW-lb GTW-c a b ~ 9g GTW-V 9a b c 9d A a b 9-9~ 9-9d e 9-7a ,000 2,008 2,050 2,000 1, ,105 2, 890 2,935 2, 695 3, , , , , , , , , , , , , go ,158 2, ,140 7,865 6,084 6,080 5, , ,018 9,295 10, , , b , Sa = Pahoa Station, 1/6/75 analysis from Water Resources Research center (WRRC), university of Hawaii, Manoa (UH-M) 9-6b = Kapoho hole, 7/22/75 analysis from WRRC, UH-M 9-5b = Pahoa Station, 7/21/75 analysis from WRRC, UH-M 9-6c = Kapoho hole, analysis from Cox and Thomas (1979) PVFW = Pahoa Village Fresh Water, 10/85, analysis from Thermal Power GTW-V Geothermal hole, 6/21/61 analysis from Hawaii Dept. of Health Company 9a = Kapoho Shaft, 1/6/75 analysis from WRRC, UH-M KS-1 = Geothermal Well, Kapoho State 1, top of dike-inpounded water, Ob Kapoho Shaft, 7/21/75 analysis from WRRC, UH-M analysis 1983 from Hawaii Dept. of Land and Natural Resources 9c Kapoho Shaft, 3/15/68 analysis from Hawaii Board of Water Supply (DLNR) 9d = Kapoho Shaft, analysis from DLNR KS-1A = Geothermal Well, Kapoho State 1-A, top of dike-impounded water, A = Well Allison, 1/7/75 analysis from WRRC, UH-M analysis 1985 from DLNR 9-9a = Malama-Ki Well, 1/7/75 analysis from WRRC, UH-M KS-2 = Geothermal Well, Kapoho State 2, top of dike-impounded water, 9-9b = Malama-Ki Well, 7/22/75 analysis from WRRC, UH-M analysis 1984 from DLNR 9-9c = Malama-Ki Well, 9/6/62 analysis from USGS HGP-A = Geothermal Well HGP-A, analysis from 2270', Kroopnick et al. 9-9d = Malama-Ki Well, analysis analysis from Cox and Thomas (1979) (1978) 9-9e = Malama-Ki Yell, 9/28/62 analysis from DLNR GTW-lla Geothermal hole, 1/7/75 analysis from WRRC, UH-M 9-7a = Kalapana Station, 1/6/75 analysis from WRRC, UH-M GTW-llb = Geothermal hole, 7/21/75 analysis from WRRC, UH-M 9-7b = Kalapana Station, unspecified date analysis from WRRC, UH-M GTW-lc = Geothermal hole, (Thief) 7/21/75 analysis from WRRC, UH-M 9-6a = Kapoho hole, 1/6/75 analysis from WRRC, UH-M = Not Available the ocean. South of the LERZ, ground water is interpreted to follow topography and flow in a south-southeasterly direction towards the ocean. Maximum water temperatures in the LERZ wells indicate ambient conditions north of the rift and elevated temperatures throughout it. Wells south of the LERZ show variable temperatures but significantly greater than ambient, south and southeast of the structural offset in the rift. Variability in the hydrochemical data occurs on the individual well basis (e.g., Well 9-9 samples 9-9a through 9-9e, Table l), and on an areal basis (e.g., Wells KS-1, KS-lA, KS-2 and GTW-111). These data represent analyses conducted by different State and Federal agencies at different times. The variations can be attributed to: (1) different sampling procedures; (2) different analytical methods; (3) environmental factors affecting water chemical data; (4) natural variations in water chemistry; and (5) some combination of the above factors. To evaluate the consistency of individual well chemical data, Schoeller diagrams or vertical scale chemical concentration plots, were used. The data were found to be coherent, in general. The observed variability (e.g., Well 9-9) most likely reflects only dilution/concentration effects related to the dynamics of the geohydrochemical setting. To discern different ground water chemical types, a semi-logarithmic frequency distribution diagram of total dissolved solids content (TDS) was constructed for all the available shallow ground water data in the LERZ, and coded for the three principal geothermal water indicators: T, Cl/Mg and SiOZ (Figure 3). TDS was chosen because it reflects the gross chemical character of the water. Also included in these data were four fresh water supply wells from the island of Oahu to provide independent internal data control (ovenitti, 1986). Conservatively, all wells with a TDS greater than 2000 mg/l, exhibit a Cl/Mg ratio > 15 and a T h 701

ovenit t i v 1 10, lo= Geothermal waters 7 A w f lo2 - c E f E 10 p 1 7 1 0 V waters V Na K Ca Fa Hg Sl%HCO, C SO, P ph TDSCUMg CUM9 mtlo plotted on cononlration scale -50

5 ovenit t i v 1 10, lo= Geothermal waters 7 A w f lo2 - c E f E 10 p V waters V Na K Ca Fa Hg Sl%HCO, C SO, P ph TDSCUMg CUM9 mtlo plotted on cononlration scale Total Disolved Solids Content (x 103mg/1) Figure 4. Schoeller diagram for geothermal and fresh waters. Figure 3. Frequency distribution of total dissolved solids content coded for the three geothermal indicators described in the text. 10O0F. These characteristics clearly identify these waters as geothermal. The silica content, however, displays a more ambiguous pattern which is attributed to not only the data variation factors described above but also to precipitation reactions lowering the silica content of the geothermal waters. This four-parameter ana-lysis provides a basis for discriminating between two types of ground water: fresh and geothermal. An independent validation of water type was made by utilizing all 13 chemical parameters given in Table 1. t was postulated that unique geothermal and fresh water Schoeller Diagram patterns exist and that a consistent relationship observed in any single analysis is reflective of a meaningful geologic phenomenon. Figure 4 presents the Schoeller Diagram pattern for both geothermal and fresh waters. The geothermal pattern was constructed by plotting all well data containing at least, two of the three geothermal characteristics described above. The fresh water pattern was derived from wells which did not con- tain any of the aforementioned geothermal characteristics. Chemical data from Wells 9a, 9b, 9-6a and 9-6b were not plotted because of data inconsistencies (ovenitti, 1986). The resulting Schoeller Diagram pattern for fresh and geothermal waters are distinct. As expected, not only does the geothermal water contain markedly higher concentrations than the fresh water, but it is also anomalous in Mg, SiOz, HC%, C1, Cl/Mg and ph. These data enable delineation of three shallow ground water types in the LERZ: fresh, mixed and geothermal (Figure 5). The mixed water type is intermediate between the fresh and geothermal categories. The temperature and chemical signatures observed in Wells KS-l, KS-lA, KS-2 and GTW- 11 within the rift, and Wells 9-9 and A south of the rift are interpreted to result from relatively direct leakage of geothermal fluid into the dikeconfined and basal waters, respectively. The transverse structural break in the LERZ is believed to be the principal cause for the upwelling of geothermal fluids from the geothermal reservoir. This is consistent with a 0.2 volt self-potential anomaly identified by Zablocki (1977) in this area. Well 9-9, proximal to this transverse fault shows a much stronger geothermal signature than Well A, located some two miles away from the rift break. 702

ovenit t i Figure 5. Shallow ground water types in the LERZ. Progressive dilution of the geothermal water as it flows away from the source readily explains this difference.

6 ovenit t i Figure 5. Shallow ground water types in the LERZ. Progressive dilution of the geothermal water as it flows away from the source readily explains this difference. Previous studies (Davis and Yamanaga, 1968; Druecker and Fan, 1976; McMurty et al., 1977) attributed the saline nature of the waters south of the LERZ to result at least in part, from a decrease in the fresh water recharge rate to the basal water. The anomalously high water temperature of these wells clearly indicates their geothermal character. Mixed water Wells 9-6 and GTW- V display only a partial geothermal character. These wells occur downgradient from the primary area of geothermal fluid upwelling. Only Wells 9-5 and 9-7, located north and southwest of the primary area of geothermal fluid upwelling, contain fresh water. A relatively high Cl/Mg ratio in waters from Well 9-7 (Table 1) suggest a minor geothermal component. This is partially supported by a near-surface resistivity anomaly defined by Flanigan and Long (1987) in the region of this well. As the upwelling geothermal fluid reaches shallow depths, it moves laterally following topography toward the ocean. Two plumes of geothermal water are interpreted. One forms a relatively broad plume flowing south-southeast of the rift discharging along a portion of the island's southeastern coast as hot springs and seeps. This plume is consistent with a near surface resistivity anomaly defined by Flanigan and Long (1987). The other plume flows within and parallel to the rift, progressively interacting with increasing amounts of meteoric water recharge to form the mixed water zone near Kapoho Crater. REFERENCE8 CTED Cox, M.E. and D.M. Thomas, 1979, Chloride/magnesiun ratio as a regional geothermal indicator in Hawaii: Hauaii nstitute of Geophysics Report 3. Davis, D.A. and G. Yamanega, 1968, Preliminary report on the water resources of the Hi lo-puna Area, Hawai i: U.S. Geological Survey Circ. 45. Druecker, M. and P. Fan, 1976, Hydrology and chemistry of groundwater in Puna, Hauaii: Groundwater, 14, 5, p Environmental Management Associates, 1989, Application for underground injection control permit for the Puna Geothermal Venture project, submitted by Puna Geothermal Venture to the Hawaii Department of Health in June Furmto, S.D., 1978, Nature of the magma conduit under the East Rift Zone of Ki lauea Volcano, Hawaii : Bul letin Volcanologique, 41, 4, p Flanigan, V.J. and Long, C.L., 1987, Aeromagnetic and near-surface electrical expression of the Kilauea and Mauna Loa volcanic rift systems: in Volcanism in Hawaii: USGS Professional Paper 1350, p Holcomb, R.T., 1987, Eruptive history and long-term behavior of Kilauea Volcano: in Volcanism in Hawaii: USGS Professional paper 1350, p ovenitti, J. L., 1987, Geothermal fluid Leakage, lower East Rift Zone, Kilauea Volcano, Hawaii, Hawaii: in Abstract Vol~e of the Hawaii Syrrposium on How Volcanos Work, held in Hilo, Hawaii, January, 1977; also in Geothermal Resources Council Trans., 11, p lovenitti, J.L., 1986, Geohydrochemical setting of the lower East Rift Zone with special emphasis on the relationship between geothermal f luid injection and Hawai i Department of Health, Underground njection Control regulations: in the Petition to Modify the UC Line in the Lower East Rift Zone, Puna, Hawaii, Hawaii, submitted to the Hawaii State Department of Health in July ovenitti, J.L. and W.L. D'OLier, 1985, Preliminary results of drilling and testing in the Puna geothermal system, Hawaii: Proceedings of the Tenth Workshop on Geothermal Reservoir Engineering, Stanford University, p Kauahikaua, J., M. Mattice and D. Jackson, 1980, Mise-a-la-Masse mapping of the HGP-A geothermal reservoir, Hawai i : Geothermal Resources Council Trans., 4, p Kroopnick, P.M., R.W. Buddemeir and D. M. Thomas, 1978, Hydrology and geochemistry of a Hawaiian geothermal system, HGP-A: Hawaii nstitute of Geophysics Report HG McMurty, G., P. Fan, and T.B. Coplen, 1977, Chemical and isotopic investigations of groundwater in potential geothermal areas in Hawai i: American Jour. Science, 277, p Moore, R.B., 1983, Distribution of differentiated tholeiitic basalts on the lower East Rift Zone of Kilauea Volcano: A possible guide to geothermal exploration: Geology, 11, 3, p Zablocki, C.J., 1977, Self-potential studies in east puna, hawaii: in Geoelectric studies on the East Rift, Kilauea Volcano, Hawaii sland: Hawaii nstitute of Geophysics Report

ATTACHMENT A. Area of Review

ATTACHMENT A. Area of Review 1 SUMMARY ATTACHMENT A Area of Review Puna Geothermal Venture (PGV) operates a geothermal power plant on the Island of Hawai i. The facility is located approximately 21 miles southwest of the city of Hilo.