ATTACHMENT A. Area of Review

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1 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. The project occupies approximately 35 to 40 acres on an 815-acre parcel of land leased by PGV, as shown on Figure 1. The property is located within the Kapoho section of the Kilauea Lower East Rift Zone (LERZ), which was designated in 1984 as a geothermal resource subzone for geothermal exploration and development pursuant to Hawaii Revised Statues (HRS) The Area of Review (AOR) listed in the current EPA-approved UIC permit has been defined as the leased boundary, plus an additional 1/4-mile strip around the lease perimeter. This area covers the entire width of the LERZ in which the geothermal resource is located, and the site monitoring wells (see Figures 1 and 2). However, there has been no other groundwater development within this or a much wider area, so the effective AOR covered by previous Ormat studies and monitoring reports was expanded to include all area groundwater and wells. To better understand the proposed AOR, and the potential for the facility to impact Underground Sources of Drinking Water (USDW), a summary of the geothermal field s geology and operating conditions is provided in the following sections. For more information see Evans (2015) and Lyon Associates (2017). The PGV geothermal system is deep and limited in areal extent. A numerical model of the geothermal system based on 25 years of production and injection history, and nearly 500 downhole pressure and temperature runs in over 30 wells indicates that the system recirculates the injected fluids as designed. Finally, recent studies by both the U.S. Geological Survey and PGV s groundwater monitoring consultant (Lyon, 2016) have shown that PGV operations have had no effect on groundwater either within the original AOR or a much wider study area. In summary, due to the geologic constraints on the system, there is no potential to impact groundwater or USDWs north (upgradient) of the LERZ where a highly productive aquifer and several municipal water supply wells exist. Within the LERZ there is no groundwater development due to lower water quality, a deep water table, and residential use of rainwater catchment systems. South of the LERZ there is an outflow zone of poor quality groundwater and only a few nonpotable wells. 2 BACKGROUND INFORMATION 2.1 Geology The Puna geothermal field is located within a small portion of the Kilauea Lower East Rift Zone (LERZ) (Figure 2). The LERZ is a narrow, linear feature that extends 25 miles from Kilauea's central caldera to the NE coast, and another 43 miles out to sea. The rift is a zone of extensional tectonics that has allowed development of dilational, open-space fracture sets that parallel the rift boundaries. At the surface, the LERZ is marked by open parallel fissures locally filled with basaltic vents, cinder and spatter cones. Older rifts in the Hawaiian Islands, now exposed by erosion, Page A-1

2 indicate that the rift zone fracture sets are filled by swarms of closely spaced, nearly vertical, and nearly parallel dikes. At PGV, the fractures are locally occupied at depth by geothermal fluids. At PGV, one set of fissures at the surface host a linear trend of small craters and scarps through which lava erupted in The 1955 eruption overlies an active dacitic intrusive that was encountered in well KS-13 at a depth of 8,000 feet. Well logs at PGV record a sequence of basalts from the ground surface to their total depth. A change from sub-aerial (more vesicular) to shoreline-deposited flows (less vesicular) occurs at about 3,000 feet depth, followed by 1,000 feet of "transition zone" flows (glassy, shallow water volcanics called hyaloclastites) that are locally clay-altered (see Figure 6).. The clay forms a lowpermeability cap over the deeper, hotter, geothermal resource. Submarine flows are present to about 6,500 feet in depth, and intrusive dikes are common below 6,500 feet. Injection well KS-13, was directionally-drilled under the Puu Hanuaula crater area (see Figure 2), and encountered molten rock of dacitic (a higher silica magma) composition. Although dacite intrusives are relatively common near geothermal systems worldwide, lavas of this composition are unknown on Hawaii, except for a small flow of similar composition on Oahu. 2.2 PGV Resource The PGV geothermal power plant currently utilizes six (6) production wells and four (4) injection wells (see Figures 4 and 5). The PGV resource and production zones are restricted to a very small area within the property boundary, and are present at great depth (see Figures 3 and 6). Permeable zones of lost circulation are common in the unaltered subaerial basalt flows above a depth of 2,000 feet. The water table is present within these basalts at a depth of about 600 feet. Water at that depth is warm (30 to 40 C). The temperature slowly increases with depth due to conductive heating, and increases rapidly below a depth of about 2,000 feet. PGV Production comes from two closely-spaced, steeply-dipping interconnected fracture zones known as the KS-8 and KS-11 fissures that strike parallel to the rift zone boundaries. A third parallel fissure may exist between these zones. The productive fracture zones aren t encountered until depths of 3,500 to 7,000 feet. The injection wells target another parallel fracture set less than 1,500 feet to the north of the production area. The resource is only about 2,000 feet in length (see Figure 3). Even within this short distance, permeability is variable and may not be encountered, as indicated by the numerous redrills that have been required in some wells to locate the permeable segments. Permeability abruptly terminates along strike to the east, as indicated by well KS-15, which did not encounter the resource. In general, permeability in the dense host basalts is low perpendicular to the fractures. Because the injection fissure is parallel to the production fissures, injectate return to the production wells appears to migrate largely along interflow boundaries. The behavior of the production wells indicates that the Puna geothermal field has been steady in its overall enthalpy, with only modest declines in reservoir pressure over time. Individual well production may decline over time from mineral precipitates and scaling, but is generally restored with regular workovers. Periods of reduced power output do not appear to have resulted from cooling, lack of reservoir pressure support, or influx of cooler water from injection wells. Page A-2

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4 Figure 1: Topographic Map of Well Field and Property Boundary (from Lyon Associates, 2017). Page A-4

5 Figure 2: LERZ, PGV Lease boundary (red), original AOR (green line), area water supply wells (blue) and non-potable wells (green). Page A-5

6 KS-16 Figure 3: Topographic map of PGV area showing wells, well paths, major fracture zones at depth, and location of deep production zones.. Page A-6

7 Figure 4: List of PGV Geothermal Wells and coordinates. Page A-7

8 Well ID Depth (ft) Date Curre nt Usag e KS ' 1981 Condctr Diam (in) Condctr Depth (ft) Surf Diam (in) Casing Depth and Size Surf Depth (ft) Intermed Diam (in) Intermed Depth (ft) Prodctn Diam (in) Prodctn Depth (ft) Diam (in) Liner Depth and Size Bottom Diam (in) KS 1A 6506' 1985 Injector 30" 70' 20" 1376' 13 3/8" 2701' 7" 3510' 4 1/2" 7" 3874' KS ' 1982 not used KS ' 1991 Injector 30' 70' 20" 1030' 13 3/8" 2209' 9 5/8" 3897' 5" 7" 3767' KS ' 1992 KS 4 RD2 6697' 2006 P&A 7" 4.5" 3803' KS ' /4" 5077' 8 5/8" 5077' KS 5 RD2 6463' 2009 Producer 30" 88' 22" 900' 16" 2205' 9 5/8" & 7" 5510' 4.5" 5437' KS ' /4" 5082' 8 5/8" 6584 KS 6 RD 6887' 2006 Producer 30" 56' 22" 917' 16" 2053' 11 3/4" KS ' 1991 not used KS ' 1992 not used 7 5/8" open hole KS ' Producer 42" 101' 20" 936' 13 3/8" 2005' 9 5/8" 3224' 7" 3024' KS ' /8" 3798' 7" KS 10 RD 5201' 2005 Producer 30" 75' 20" 954' 9 5/8" 1846' 7" 3550' 3798' 4692' Top (ft) 9 5/8" 7" 3798' no liner, 6" open hole KS 11 RD2 6872', fill to 5861' 2009 Injector 30" 75' 22" 1102' 16" 2102' 11 3/4" & 9 5/8" 3029' 7" & 5 1/2" 4 1/2" 4755' KS ', fill to 6970' 2005 Injector 30" 100' 22" 954' 16" 2076' 11 3/4" 4866' 8 5/8" 8 5/8" ~4615' KS ' 2010 Producer 11 3/4" 8.625" 4742' KS 15 OH 8020' /4" 4705' na KS 15 RD3 5182' 2012 Injector- 30" 132' 22" 1042' 16" 2292' 11 3/4" 2789' 8 5/8" 6 5/8" 3756' KS Producer /8 2, /8 5, ,921 Redrilled well legs that are no longer in use Old unused wells with little data available Figure 5: PGV Well Construction Summary Page A-8

9 Figure 6: Cross section looking east, showing generalized geology, groundwater depth and flow direction, productive and abandoned well paths, and well feed zones Page A-9

$production and injection fractures P = Production zone; I = Injection zone.$

10 . Figure 7: Thermal Cross Section across AOR looking east, showing proximity of production and injection fractures P = Production zone; I = Injection zone. Page A-10

11 Page A-11

12 Figure 12: Map showing wells and coastal springs (Evans, 2015). 2.3 Groundwater within the LERZ As previously described, vertical system permeability is largely confined by the overlying clayaltered cap (Figure 6). However, some geothermal fluid and steam ascends through this cap into shallower zones above the resource, so groundwater near PGV is mostly a mixture of cold meteoric water, seawater, and steam condensate with higher than normal temperatures. This outflow zone of mixed fluids then migrates laterally towards the coast. Some wells have been drilled southeast of PGV, but because of increased salinity, they are not used as a source of underground drinking water (Figure 13). Currently, no groundwater development occurs within in the LERZ, because groundwater is deep (about 600 ft), warm and lower quality. Because of copious precipitation, rainfall is sufficient for landscaping and most agricultural products, such as papayas and bananas, and residences in Leilani Estates and other nearby residential areas use individual rainwater catchment systems for their water supply. Wells in the LERZ consist of one well (Kapoho Shaft) to the east of PGV. Perched water at the Kapoho Shaft was originally used as a public supply, but has not been used since The USGS sampled the well in 2014, and determined that the Mg, Ca and SO4 concentrations provide no evidence for influence of PGV injectate (Evans, 2015). Page A-12

13 2.4 Groundwater North of the LERZ The closest source of underground drinking water are six municipal and privately-owned wells in the Pahoa area. The wells are more than one mile up-gradient of the LERZ boundary, and more than three miles from the PGV injection wells. Groundwater is good quality and ranges from 68 to 75 F and 106 to 143 mg/l TDS. The well tap thin flows of unweathered, hard Pahoehoe basalt (M&E Pacific, 1995). This groundwater is meteoric and is mixed with neither seawater nor hydrothermal fluid. These wells produce water from a highly productive aquifer that has an estimated sustainable yield of 435 mgd (about 300,000 gpm). However, the Pahoa Water System total capacity is only 2.9 mgd (actual production is even less). Existing water demands are approximately 1 percent of the sustainable yield (SY), and 2025 projected demands range between 1 and 2 percent of the SY. If worst case agricultural demands are included, the full build-out water demand scenarios would require only 15 to 21 percent of the SY. 2.5 Groundwater South of the LERZ Groundwater is hot and saline immediately south of Kapoho near the eastern end of the LERZ. The Keauohana wells, more than 5 miles to the southwest of PGV (Nos. 3 and 4 on Figure 12, and shown to the west of Sea View Estates on Figure 13), have slightly elevated TDS over wells north of the LERZ, but have no discernable component of geothermal fluid (Evans, 2015). Southeast of PGV, groundwater is warm, more saline and non-potable, as evidenced by two groundwater exploration wells south of the LERZ shown on Figure 13. Water from these wells has a relatively high temperature and high chloride concentration compared to wells supplying the Pahoa system. 3 Groundwater Monitoring The PGV lease block has three monitoring wells, labeled MW-1 to MW-3 on Figure 1. Wells MW-1 and MW-3 are upgradient of the system, while MW-2 is down-gradient. Wells 1 and 3 are 720 feet deep, while well 2 is 640 feet deep. The static water level in the wells is between 8 and 16 feet above mean sea level, or about 600 feet below surface. Wells GTW-III and Malama Ki (see Figures 1 and 2) are set aside to be sampled in the event that these wells cannot be sampled. Because the structures that control the geothermal system at depth are near-vertical, and the geothermal system has limited lateral extent, direct leakage of deep geothermal water or gas into shallow groundwater would likely first be detected at these well sites. However, because the system is capped by low permeability altered rock, and the shallower groundwater zone has high permeability, no pressure responses to pumping or injection would be expected in the monitoring wells, or in other wells outside of the LERZ. Instead, minor fluid, along with steam and some entrained H2S pass through the altered zone and interact with shallow groundwater, which heats it slightly, and increases its dissolved solids content. Ormat has collected samples from monitoring wells MW-1 and MW-2 semi-annually since sample results were described in the Puna Geothermal Semi-annual Hydrologic Monitoring Program Report, prepared by LYON Associates, Inc. The 2016 data for MW-1 and MW-2 fall within the range previous historical samples (LYON Associates, 2017). As expected, water in down-gradient well MW-2 is lower quality than MW-1 and contains greater dissolve solids, sodium, chloride, and bromide. It does, however, contain lower concentrations of silica and sulfate. Page A-13

14 A copy of a scientific investigation performed by the USGS (Evans, 2015) on behalf of the County of Hawai I is attached to this section. This investigative report is provided as a supplemental document that examined the influence of the PGV geothermal wells on the groundwater (USDW) for the past 20 years. The USGS analyzed MW samples for chemistry and for the plant s motive fluid, pentane. The report concludes that the data are consistent with a long-held view that heat moves by conduction from the geothermal reservoir into shallow groundwaters through a zone of low permeability rock that blocks passage of geothermal water (p. 1). The postulated hot saline groundwater is diluted by shallow groundwater before emerging at the coastal springs or, after great dilution, being pumped from the Keauohana wells (p. 24). The USGS water chemistry data fit this general model. Evans concludes that apart from these changes, the similarity between our results, the results from mandated monitoring over the previous 20 years, and results from samples from the 1970s 1990s imply that geothermal production has not had a significant impact on groundwater chemistry. Similarly, Lyon Associates (2017) has concluded that to date, there is no evidence that reinjection of geothermal fluids form operations at PGV have had any effect on the ground water hydraulically down gradient from the geothermal power plant. Page A-14

15 Figure 13: AOR. Known water supply wells (blue) and non-potable wells (green) in the PGV area. Page A-15

16 4 References Documents reviewed for this section include: Evans, W.C. et al: 2015: Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai i, After Two Decades of Production, USGS Scientific Investigations Report Fukunaga & Associates, Inc., Consulting Engineers: Hawaii County Water Use and Development Plan Update, August 2010: Hawaii Water Plan. M&E Pacific, Inc., December 1995: Final Environmental Assessment Report on Pahoa s Keonopolo Iki Deep Well. Staub and Reed, 1995: Environmental Resources of Selected Areas of Hawaii: Groundwater in the Puna District the Island of Hawaii. Oak Ridge National Laboratory, Report ORNL/TM LYON Associates, Inc. 2017: Puna Geothermal Venture Semi-Annual Hydrologic Monitoring Program Report, February Page A-16

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