Salt Wells Geothermal Area

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GEOTHERMAL ENERGYGeothermal Home
Salt Wells Geothermal Area

Area Overview

 Geothermal Area Profile

 Location: Nevada Exploration Region: Northwest Basin and Range Geothermal Region GEA Development Phase: Operational"Operational" is not in the list of possible values (Phase I - Resource Procurement and Identification, Phase II - Resource Exploration and Confirmation, Phase III - Permitting and Initial Development, Phase IV - Resource Production and Power Plant Construction) for this property. Coordinates: 39.315372312574°, -118.56072387695°

 Resource Estimate
 Mean Reservoir Temp: 193°C466.15 K 379.4 °F 839.07 °R [1] Estimated Reservoir Volume: 16.5916.59 m³ 1.659e-8 km³ 3.980153e-9 mi³ 585.87 ft³ 21.699 yd³ [1] Mean Capacity: 23.6 MW23,600 kW 23,600,000 W 23,600,000,000 mW 0.0236 GW 2.36e-5 TW [2] USGS Mean Reservoir Temp: USGS Estimated Reservoir Volume: USGS Mean Capacity:

The Salt Wells geothermal field, also known as Eight Mile Flat, occupies the west-southwest margin of the Salt Wells basin about 24 km southeast of Fallon in Churchill County, Nevada, along the east flank of the Bunejug Mountains and north edge of the Cocoon Mountains. The geology of the area has been described by Morrison (1964)[3] and Willden & Speed (1974).[3] [4] The area lies near the intersection of the Walker Lane structural belt and the Humbolt Structural Zone (HSZ), which incorporates the central Nevada seismic belt.[5] Initial temperature gradient drilling at the site in the early 1980s by Anadarko Petroleum Corporation (APC) defined a large, 12-km-long heat flow anomaly associated with the blind Salt Wells geothermal system.[6] An 18 MW binary power plant completed in 2009 has tapped a shallow geothermal reservoir with an estimated temperature of ~140°C. Geothermometers applied to waters sampled from springs and wells over the lifetime of the prospect suggest that a deeper, unexploited reservoir may exist at temperatures of 180-220°C, although the upper limit of this temperature range is expected to be artificially high.[6][5][7]

History and Infrastructure

 Operating Power Plants: 1

 Developing Power Projects: 1
 Salt Wells Geothermal Project (60 MW60,000 kW 60,000,000 W 60,000,000,000 mW 0.06 GW 6.0e-5 TW MW, Phase II - Resource Exploration and Confirmation) Add a new Developing Power Project

 Power Production Profile
 Gross Production Capacity: Net Production Capacity: 20.2 MW20,200 kW 20,200,000 W 20,200,000,000 mW 0.0202 GW 2.02e-5 TW Owners  : Enel North America Power Purchasers : Other Uses:

One of the earliest documented hot spring occurrences in the Salt Wells basin, the Borax Spring, dates back to 1885.[8] Seasonal fluctuation of the elevation of the water table in the basin has resulted in intermittent activity of the spring, and has made re-locating it for the purposes of geochemical water sampling considerably difficult for recent researchers.[9][10]

APC drilled the first geothermal exploration wells at Salt Wells in the late 1970s and early 1980s.[11] Temperature gradient drilling during this period defined a large, 12-km-long heat flow anomaly associated with the blind geothermal system.[6] Geothermometers have been applied to waters sampled from springs and wells from the outset of the early drilling program, and suggest that a deep reservoir exists at temperatures > 200°C.[6] These initial temperature estimates were expected to be artificially high; additional geothermometric estimates acquired at various times over the lifetime of the prospect suggest more conservative temperatures of 180-190°C in the deep reservoir, which show better agreement with temperatures measured in deep exploration wells.[5][7]

Revisions to the U.S. Bureau of Land Management’s (BLM) standards for leasing geothermal resources sparked renewed interest in geothermal exploration in the Salt Wells basin area in 2002.[12] Vulcan Power Company was granted a geothermal resource exploration lease later that year, encompassing 15,354 acres of BLM and U.S. Bureau of Reclamation land. In 2004, Nevada Geothermal Specialists, LLC obtained permits from the Nevada Division of Minerals to develop 20 new wells within the Salt Wells leasing area.[11] Six production wells were planned with an estimated depth of approximately 305 m, along with four injection wells with an estimated depth of 914 m, and 10 observation wells at 305 m. As a part of this development plan, the BLM approved permits for Nevada Geothermal Specialists, LLC to construct two 10 MW power plants at Salt Wells.[13] The company made plans to build a 10 MW binary power plant by the end of 2005, with a second 10 MW facility scheduled to begin operations by the end of 2006. Construction also began on a new 9-kilometer-long, 230-kV power line to link the two proposed plants to the Sierra Pacific Power Company grid.[11][13]

The Salt Wells project and all associated resource assets were purchased from Nevada Geothermal Specialists, LLC at the end of 2004 by AMP Resources, LLC.[11] One of the first operating wells, Industrial Production Well PW-2, was drilled in the spring of 2005 under this geothermal project area permit (permit #568). The well was completed to a depth of 143.6 m and a peak temperature of 145°C, as indicated by static temperature surveys. Wellhead temperatures at PW-2 were 140°C at a flow rate of 157.7 L/s, and no drawdown was detected after 46 hours of continuous discharge. In 2006, AMP began construction of a 10 MWe binary power plant, however the site was sold again in March 2007 to Enel North America, Inc. before the plant was completed.[5][14] Construction on the Stillwater and Salt Wells projects continued under Enel, generating more than 300 jobs in the Churchill County area.[15] In 2008, the company renamed its North American division to Enel Green Power.

Vulcan Power Company was also exploring for geothermal resources in the area during this time period. The company was granted a permit by the BLM in February 2007 that approved drilling of ten exploratory wells in the project area at locations identified in the Environmental Assessment Report as Pads 1, 2, 3, 4, 5, 6, 7, 8, 9, and 13.[12] Vulcan increased exploration efforts in the summer and fall of 2008, during which time the company drilled two temperature gradient holes (86-15 O on Pad 1 and 17-16 O on Pad 3); conducted seismic, gravity and magnetotelluric surveys; and drilled deep exploration wells at Pads 6 and 8 and binary wells at Pads 1, 2, 4, and 7. Data from these wells is proprietary, and so were unavailable for inclusion in this review.

In 2009, Enel Green Power received federal stimulus funding of \$61.52 million through the American Recovery and Reinvestment Act’s 1603 Program for the construction of new power plants at the Stillwater and Salt Wells geothermal fields. The Economic Development Authority of Western Nevada anticipated that the investment would have a positive impact on the area, amounting to over \$4 million of economic stimulus in Churchill County and creating 25 permanent jobs for the next thirty years.[15] Later in 2009, two turboexpanders from Atlas Copco were installed in Enel Green Power’s Salt Wells geothermal facility, completing construction of the plant. Between the new Stillwater 2 (47 MW) and Salt Wells (18 MW) plants, the geothermal development project added a combined gross installed capacity of 65 MW.[16] The 65 MWe can generate more than 400 million kWh of electricity per year, and Enel states that it prevents the emission of more than 300,000 tons of $CO_2$ that would have been produced by a conventional coal-fired power plant of the same capacity. The plants use isobutane as a working fluid that receives its energy from a medium-enthalpy geothermal fluid at 130 - 150°C.[15]

Vulcan also remained active at Salt Wells in 2009. The company sought BLM approval to drill and test exploratory wells at ten new locations, identified by the exploration activities conducted in 2008 (Pads 10, 11, 12, 14a, 15 16, 17, 18, 19 and 20).[12] Pending successful identification of a viable geothermal resource, Vulcan planned to drill production wells at these locations.

Salt Wells Area Timeline

1885: Rare hot spring occurrences, including the Borax Spring, are documented in the Salt Wells Basin.[8]

1964-1974: USGS and Nevada Bureau of Mines and Geology investigations of the Bunejug Mountains geology.[3] [4]

Late 1970s: Anadarko Petroleum Corporation drills several temperature gradient wells in the Salt Wells Basin.[6]

Early 1980s: Anadarko encounters a hot water reservoir with favorable flow rates after drilling a slim hole discovery well and exploratory confirmation well in Simpson Pass.[17] [6]

2002: Vulcan Power Company resumes geothermal exploration in the Salt Wells Basin area after the BLM revises geothermal leasing standards.[12]

2004: Nevada Geothermal Specialists, LLC obtains permits to develop new geothermal wells in the Salt Wells lease area.[11]

Late 2004: The Salt Wells Project is purchased by AMP Resources, LLC.[11]

2005: Borax Spring is rediscovered as a seasonal hot spring discharge in the Salt Wells Basin.[10]

2005: Industrial Production Well PW-2, one of the first operating wells at Salt Wells, is completed under permit #568.[11]

2006: AMP begins construction on a 10 MWe binary power plant at the Salt Wells site.[5]

2007: The Salt Wells Project is sold again to Enel North America, Inc. before the AMP plant is completed.[5]

2007: The BLM approves permits for Enel to drill ten new exploratory wells in the Salt Wells area.[12]

2008: Vulcan drills additional exploratory wells and conducts geophysical surveys in the Salt Wells Basin.[12]

2009: 18 MW binary power plant is completed at Salt Wells.[15]

2009: Enel receives \$61.52 million in federal stimulus funding through the ARRA for the construction of new power plants at the Salt Wells and Stillwater Geothermal Fields. The company installs two Atlas Copco turboexpanders to the Slat Wells Geothermal Facility.[15]

2009: Vulcan remains active in the area, obtaining approval from the BLM to drill exploratory wells in ten new locations in the Salt Wells Basin.[12]

2011: After completing an environmental impact assessment for the Salt Wells area, the BLM approves three new development projects under Ormat Technologies, Inc., NV Energy (formerly Sierra Pacific Power Company), and Gradient Resources, Inc. (formerly Vulcan Power Company). Known as the Salt Wells Energy Projects, the proposal includes plans for several new power plants and a 35-km-long transmission line.[18][19]

Regulatory and Environmental Issues

Environmental issues at Salt Wells are relatively few. Concerns pertain mostly to water usage for injection needed to maintain the reservoir, siting of transmission lines, and potential impacts on migratory bird species, all of which have been accounted for in the BLM’s 2011 Environmental Impact Statement.[18]

Exploration History

 First Discovery Well
 Completion Date: 1980/01/01 Well Name: “Slim hole discovery well” Location: Depth: 162 m0.162 km 0.101 mi 531.496 ft 177.165 yd [17] Initial Flow Rate: 3.1 kg/s186 kg/min 11,160 kg/hour 267,840 kg/day 3.1 L/s 49.136 gal/min [17] Flow Test Comment: Initial Temperature: 133°C406.15 K 271.4 °F 731.07 °R [17]

The blind Salt Wells geothermal system was first identified when APC drilled a slim hole and a geothermal exploration well at the site in the early 1980s. Geothermal surface indications at Salt Wells are subtle, consisting only of a cold NaCl spring and of sinter deposited from hot springs that were allegedly active during the late 1880s. APC defined a 46 km2 thermal anomaly at the site that extends over 12 km to the south to the Cocoon Mountains. About half of this anomaly is underlain by shallow aquifers that exhibited temperatures of >100°C at less than 100 m depth. In 1980, APC drilled a slim hole discovery well near Simpson Pass.[17] Completion practices applied to the slim hole discovery well have been described in detail in the Well Field Description. Maximum temperature log readings taken after the flow measured 132.8°C.

An exploratory confirmation well was drilled to a total depth of 2,591 m in Simpson Pass (approximately 30.5 m from the slim hole), in an attempt to intersect a deep fracture system predicted by geological and geophysical studies to occur within a large horst block between two active fault systems.[6] The well penetrated 670 m of volcanic rock before encountering 1921 m of quartz monzonite, both of which were fractured and hydrothermally altered. A temperature gradient reversal was encountered in the well at 106 m depth and 142°C. A temperature gradient of 40°C /km in quartz monzonite indicates a heat flow of approximately 104 mW/m2. During drilling, the well produced up to about 21 L/s of NaCl water from fractures across a depth interval between 1,859 and 2,057 m, with maximum reservoir temperatures of 160°C. Deeper fractures were also encountered, with fluid entry temperatures up to 177°C, but showed less productive flow rates. Maximum temperatures encountered at the bottom of the hole were measured at 181°C.

APC also purportedly conducted many additional exploration surveys at Salt Wells during the late 1970s and early 1980s in order to define the geothermal resource.[22] These activities included numerous temperature-gradient holes, a soil-mercury survey, gravity and ground magnetic surveys, and a self-potential resistivity survey. Unfortunately, the details and results of these activities could not be verified over the course of this literature review, and are therefore excluded from this summary of exploration activities.

Coolbaugh et al. conducted a study at Salt Wells in 2004 to evaluate the application of inexpensive hand-held digital GPS devices for the rapid mapping of structures and geothermal surface features in the field.[23] A Hewlett-Packard iPAQ model 5550 pocket PC (purchased with extra battery packs, chargers, memory cards, and GPS unit for a total cost of US \$1300) equipped with ArcPad, a GIS-functional software package capable of capturing and exporting spatial data to ArcView and ArcGIS, was used to map controlling structures and geothermal surface features at Salt Wells. A custom geologic mapping software applet developed by Gary Edmondo (MiniGIS, Inc., Reno, NV)[24] modified by the Great Basin Center for Geothermal Energy to include symbols for geothermal surface features was used to actively build the GIS database in the field in real time. Numerous modern and relict geothermal surface features were mapped, including a few small areas of warm ground; silicified rocks; sinter deposits consisting of either massive opaline sinter, siliceous oolites, or silicified roots/mud/algal matter; silcrete; CaCO3-cemented sands; tufa deposits; and opal/chalcedony veins. In some locations, textural indicators of the growth direction of silicified filiform algal mats are thought to indicate the flow direction of inactive hot springs, similar to what is seen in modern hot springs in the Great Basin region. Opal veins typically show north to northeast strikes. Most of the mapped silicification occurs along the southwest margin of the Salt Wells basin in a broad northwest-trending zone, the northern and southern ends of which are associated with north to northeast-trending structures. These results suggest that relict geothermal activity at Salt Wells may have been controlled by stepover faults or cross faults between two sub-parallel north-northeast-striking fault zones. Overall, the geothermal surface features and associated structures at Salt Wells were mapped over several square kilometers in only a few days, and were captured in greater detail and with a higher level of accuracy compared to what was accomplished in previous mapping efforts.[23]

AMP Resource contracted Willowstick Technologies, LLC in 2004 to conduct a Controlled Source-Frequency Domain Magnetics (CS-FDM) geophysical investigation at Salt Wells in order to characterize and delineate areas showing the greatest concentrations and highest temperatures of geothermal groundwater.[22] The investigation also sought to map blind faults beneath the site that were inferred to contain and conduct high temperature geothermal fluids. The objectives were intended to aid in site selection of production and injection wells for a planned AMP Resources power plant, in order to optimize hot water production from the geothermal resource. The CS-FDM survey targeted geothermal groundwater within a 700x1000 m area, across a depth interval from approximately 100 to 170 m below the land surface. Subsurface faults within this area were suspected to have the greatest amount of geothermal fluid flow at the site. Details of the antenna/electrode configuration and magnetic field sensor station spacing are reported in the text.[22] Data were integrated into a contoured map of conductive highs and lows that equate to areas of high or low groundwater saturation. Results indicate that migration of geothermal waters is strongly affected by subsurface features that inhibit fluid flow and concentrate thermal waters along east-west channels that likely represent faults that cut the subsurface basalt sequence. Geothermal waters are inferred to ascend along permeable fracture zones produced by the intersecting faults that form Simpson Pass and then flow laterally towards the northeast along channels and/or blind fault intersections in the fractured basalt. Production well sites recommended by Willowstick based on the survey results were drilled by AMP following completion of the exploration work, and showed favorable flow rates exceeding 170 L/s with no drawdown and temperatures >140°C.

Adsorbed mercury soil geochemical surveys and radiometric geophysical surveys were carried out in conjunction with geologic mapping to test the application of these ground-based techniques to geothermal exploration at three prospects in Nevada.[25] Mercury soil vapor surveys were not widely used in geothermal exploration in the western United States prior to 2005, although the association of mercury vapors with geothermal fluids, hot springs, and/or soils has been recognized at the Steamboat Springs, NV,[26] Roosevelt Hot Springs, UT,[27][28] Dixie Valley, NV,[28] Noya, Japan,[28] and Moana, NV[29] geothermal areas. Soil sampling and geophysical surveys were conducted at 26 stations along an approximately 1981-m-long line oriented perpendicular to known major structures at Salt Wells. The same Gas’m technique used to measure desorbed mercury vapors in soils from known fault traces at the Moana Geothermal Area[29] was utilized for the soil geochemical work in this study. The technique measures adsorbed mercury deposited on the silt- and clay-sized fractions of soils as mercury vapors sourced from buried active geothermal systems migrate upward from depth. The association of uranium mineralization with active and fossil hot springs systems in Nevada has also been documented by several authors.[30] [31] A Mt. Sopris SC-132 scintillometer was used during the radiometric survey to measure gamma rays (total counts per second) at each station in order to identify trace uranium mineralization and assist in the identification of rock types. Both the low- and high-temperature mercury desorb data show elevated values above or near the outcrop of both the mapped and the inferred fault. For the low-temperature data, peaks in the mercury content of the soils occur with a slight offset to the north of the “Pony Express” and the inferred Rock Springs faults, and measured 0.11 and 0.20 ppb, respectively. Peaks in the mercury content of similar magnitude were also encountered at stations 4.5N and 5.0S along the traverse, and may indicate the presence of additional buried faults. The high-temperature desorb data show a broader anomaly in the mercury content of the soils that spans six stations above both faults, with a maximum concentration of > 2.0 ppb occurring at the inferred Rock Springs fault. This finding suggests that substantial leakage of mercury vapors occurs along the Rock Springs fault.

Geochemical water sampling, mineral distribution mapping, and shallow (30 cm) temperature probe measurements were conducted in 2005 to expand on a previous field mapping study of surface geothermal features at Salt Wells, in order to evaluate the relationship between these features and structures that control geothermal fluid flow.[10] The distribution of sinter deposits and siliceous surface alteration are described in detail by Coolbaugh et al. (2004), and were mapped using the same iPAQ pocket computer and GPS device described in that study.[23] Advanced argillic alteration was also mapped along the southern end of the thermal anomaly defined during this study, and is believed to evidence the effects of acid steam condensation associated with now-extinct fumarolic activity. The 2005 study used a modified version of the 2 m temperature probe survey, adapted for the Salt Wells site (where the water table is at or near the land surface) to measure temperatures at relatively shallow depths of 30 cm. Temperature surveys were conducted during the winter in February 2005, when background temperatures at 30 cm depth were near a seasonal minimum of 3 to 10°C. A temperature threshold of 12°C was used to distinguish thermal anomalies from background temperatures; of the several thousand temperature measures taken for this study, a total of 286 readings were above the 12°C cutoff, with 133 measures of > 20°C, and 32 measures of > 38°C. The maximum temperature encountered was 67.2°C. Figure 2 shows the locations and approximate temperatures of the measurement stations throughout the Salt Wells basin area. The measured areas of warm ground showed considerably better correlation with major northwest- and north- to northeast-striking structural controls than the more sporadically distributed springs and seeps, and in some cases were used to locate seasonal springs and seeps for water sampling. The authors concluded that the semi-continuous distribution of silicification and warm ground along the northwestern margin and central portion of the Salt Wells basin define a 6-km-long, thermally active north- to northeast-striking structure that broadly aligns with the thermal anomaly identified by the early Anadarko geothermal gradient drilling. This thermal anomaly is thought to relate either to northward flow of thermal groundwater in the subsurface from the inferred zone of upwelling in the southwest corner of the basin, or to intermittent upflow along the north- to northeast-striking structure on the basin’s western margin.

Borate minerals tincalconite and borax, sodium sulfate minerals mirabilite and thenardite, and common salt (NaCl) were also encountered during the 2005 field study, identified using a hand-held Analytical Spectral Devices, Inc. Fieldspec® spectroradiometer.[10] Borate minerals identified at Eight Mile Flat on the higher elevation, thermally active structures on the northwestern side of the basin and high NaCl concentrations on the lower elevation, southeastern side of the basin suggest that mapping of evaporite mineral occurrences could be used as a vectoring tool in geothermal exploration in playa environments. Distribution of these minerals reflects a rough, basin-scale evaporite mineral zonation that relates to the high temperature dependence of borax precipitation and the susceptibility of NaCl to remobilization in meteoric water at low temperature. Remote sensing methods for identifying regional-scale zoning of these minerals using ASTER satellite imagery is explored in subsequent studies of other geothermal areas in the Great Basin.[32] Sulfate evaporates were more widely distributed, and may therefore be less useful from an exploration standpoint.

Vulcan Power Company was also actively exploring for geothermal resources in the Salt Wells basin from 2007-2009 under several permits issued by the BLM. Approval was granted in February 2007 to drill ten exploratory wells in the project area at locations identified in the Environmental Assessment Report as Pads 1, 2, 3, 4, 5, 6, 7, 8, 9, and 13.[12] Vulcan increased exploration efforts in the summer and fall of 2008, during which time the company drilled two temperature gradient holes (86-15 O on Pad 1 and 17-16 O on Pad 3); conducted seismic, gravity and magnetotelluric surveys; and drilled deep exploration wells at Pads 6 and 8 and binary wells at Pads 1, 2, 4, and 7. The company sought BLM approval again in 2009 to drill and test exploratory wells at ten new locations identified by the exploration activities conducted in 2008 (Pads 10, 11, 12, 14a, 15, 16, 17, 18, 19 and 20).[12] Pending successful identification of a viable geothermal resource, Vulcan planned to drill production wells at these locations. Data from these wells is proprietary, and so were unavailable for inclusion in this review.

Two-meter temperature surveys were conducted at Salt Wells Basin from February to May 2011, with the goal of distinguishing and mapping zones of upwelling and outflow of hydrothermal fluids.[7] The study also tests the ability of shallow temperature survey methods recently refined by the Great Basin Center for Geothermal Energy to evaluate the structural controls of geothermal areas.[33][34][35] Two-meter temperature data were measured at approximately 50 stations using a Resistance Temperature Device lowered through a hollow steel temperature probe tipped with tungsten for easier ground penetration. Corrections were applied to these data to account for seasonal temperature drift of +4°C, measured in several base stations between the months of February and May. Two-meter temperatures ranged from 10°C to 45°C, with high temperature measurement stations defining a roughly north-south trending anomaly spanning several kilometers that is believed to represent an outflow zone along the eastern flank of the Bunejug Mountains. Subtle to moderate temperature anomalies (between 13 and 25°C) were measured in Simpson Pass, and are interpreted as the main zone of upwelling within the Salt Wells geothermal system. The highest temperature measurements occurred to the north of the producing geothermal plant, and may represent an additional upwelling zone within the outflow plume associated with known fault scarps on the Basin’s western margin.

Well Field Description

 Well Field Information
 Development Area: Number of Production Wells: 6? [11] Number of Injection Wells: 4? [11] Number of Replacement Wells: Average Temperature of Geofluid: 140°C413.15 K 284 °F 743.67 °R [7] Sanyal Classification (Wellhead): Very Low Temperature Reservoir Temp (Geothermometry): Reservoir Temp (Measured): 220°C493.15 K 428 °F 887.67 °R [5] Sanyal Classification (Reservoir): Low Temperature Depth to Top of Reservoir: 76 m0.076 km 0.0472 mi 249.344 ft 83.114 yd [36] Depth to Bottom of Reservoir: 213 m0.213 km 0.132 mi 698.819 ft 232.939 yd [36] Average Depth to Reservoir: 145 m0.145 km 0.0901 mi 475.722 ft 158.573 yd

Combs et al. (1999) provide a detailed summary of completion practices applied to the slim hole discovery well drilled near Simpson Pass in 1980 by APC.[17] The hole was initially rotary-drilled to 161.5 m for shallow temperature-gradient measurements and was completed with 6-5/8”casing and 2” line pipe. Later, the line pipe was withdrawn and an inflatable packer on 4-1/2” tubing was set at approximately 122 m. One-inch line pipe was run down hole to 32 m and was used as an air-lift, establishing a stable flow rate of 3.1 L/s through the packer (2” ID) and tubing. Maximum temperature log readings taken after the flow measured 132.8°C.

An exploratory confirmation well was drilled to a total depth of 2,591 m in Simpson Pass (approximately 30.5 m from the slim hole), in an attempt to intersect a deep fracture system predicted by geological and geophysical studies to occur within a large horst block between two active fault systems.[6] This well was initially drilled to a depth of 213.4 m, and 13-3/8” casing was set to approximately 117 m. The exploratory well penetrated 670 m of volcanic rock before encountering 1921 m of quartz monzonite, both of which were fractured and hydrothermally altered. A temperature gradient reversal was encountered in the well at 106 m depth and 142°C. A temperature gradient of 40°C /km in quartz monzonite indicates a heat flow of approximately 104 mW/m2. During drilling, the well produced up to about 21 L/s of NaCl water from fractures across a depth interval between 1,859 and 2,057 m, with maximum reservoir temperatures of 160°C. Later, the well was pumped for 100 hours at rates of 110.4 L/s. Flow rates of deeper fractures with fluid entry temperatures up to 177°C were less productive. Maximum temperatures encountered at the bottom of the hole were measured at 181°C. Transmissivity of the reservoir was determined to be 800-900 darcy-feet, as indicated by pressure data from the well.

APC also purportedly conducted many additional exploration surveys at Salt Wells during the late 1970s and early 1980s in order to define the geothermal resource.[22] These activities included numerous temperature-gradient holes, a soil-mercury survey, gravity and ground magnetic surveys, and a self-potential resistivity survey. Unfortunately, the details and results of these activities could not be verified over the course of this literature review, and are therefore excluded from this summary of exploration activities.

In 2004, Nevada Geothermal Specialists, LLC obtained permits from the Nevada Division of Minerals to develop 20 new wells within the Salt Wells leasing area.[11] Six production wells were planned with an estimated depth of approximately 305 m, along with four injection wells with an estimated depth of 914 m, and 10 observation wells at 305 m. As a part of this development plan, the BLM approved permits for Nevada Geothermal Specialists, LLC to construct two 10 MW power plants at Salt Wells.[13] The company made plans to build a 10 MW binary power plant by the end of 2005, with a second 10 MW facility scheduled to begin operations by the end of 2006.

One of the first operating wells, Industrial Production Well PW-2, was drilled in the spring of 2005 under geothermal project area permit #568 after the Salt Wells project was purchased by AMP Resources, LLC. [11] The well was completed to a depth of 143.6 m and a peak temperature of 145°C, as indicated by static temperature surveys. Wellhead temperatures at PW-2 were 140°C at a flow rate of 157.7 L/s, and no drawdown was detected after 46 hours of continuous discharge. In 2006, AMP began construction of a 10 MWe binary power plant, however the site was sold again in 2007 to Enel North America, Inc before the plant was completed.[5]

Additional exploratory drilling was conducted in the Salt Wells basin through Vulcan Power Company from 2007-2009 under several permits issued by the BLM. Approval was granted in February 2007 to drill ten exploratory wells in the project area at locations identified in the Environmental Assessment Report as Pads 1, 2, 3, 4, 5, 6, 7, 8, 9, and 13.[12] Vulcan increased exploration efforts in the summer and fall of 2008, during which time the company drilled two temperature gradient holes (86-15 O on Pad 1 and 17-16 O on Pad 3); conducted seismic, gravity and magnetotelluric surveys; and drilled deep exploration wells at Pads 6 and 8 and binary wells at Pads 1, 2, 4, and 7. The company sought BLM approval again in 2009 to drill and test exploratory wells at ten new locations identified by the exploration activities conducted in 2008 (Pads 10, 11, 12, 14a, 15 16, 17, 18, 19 and 20).[12] Pending successful identification of a viable geothermal resource, Vulcan planned to drill production wells at these locations. Data from these wells is proprietary, and so were unavailable for inclusion in this review.

Research and Development Activities

In 2011, Faulds et al. reported on the first phase of a three-stage DOE American Recovery and Reinvestment Act-funded study that integrates knowledge of favorable structural settings in the Great Basin region, with the goal of developing a structural catalogue that can be used to refine exploration strategies for geothermal resources (particularly for blind/hidden systems) and reduce drilling risks.[37] The work expands upon previous research efforts to characterize controlling structures at select geothermal areas in the Great Basin.[5] This compilation integrates geologic and geophysical data from numerous studies in order to characterize structural controls associated with geothermal areas of the Great Basin, including the Salt Wells geothermal field. Salt Wells is unique in that it is a relatively high enthalpy system that relates to more than one type of favorable structural settings discussed in the report. The system occurs within an accommodation zone between west- and east-dipping normal faults, at the south end of the major east-dipping HSZ, and possibly within a small displacement transfer zone that appears to relate to the Walker Lane structural belt. The intersection of these features likely results in increased permeability that enhances hydrothermal fluid flow.

Technical Problems and Solutions

Both the Stillwater and Salt Wells plants have suffered from utility tie-line issues due to their remote locations and have resulted in loss-of-full-load events at the plants. These events have the potential to cause generator overspeed trips, which in turn can result in total plant shutdowns. Addressing these issues is technically challenging and responding to a loss-of-full-load event is similarly difficult, with full recovery taking hours or even days in extreme cases. Concerns over the plant’s ability to maintain capacity prompted Enel to install a new turbine generator control system that was able to quickly respond to loss-of-full-load situations. The control system is able to automatically switch from load control to frequency control (island mode) upon sensing a utility tie breaker open condition, providing the plant with power to maintain parasitic loads.

The new control system was installed by CSE Engineering, Inc. and utilizes the Woodward 505 enhanced controller system, selected due to its rapid scan rates and anticipation logic that would detect a loss-of-load condition. The 505 controller is able to sense the rate of change of the turbine generator to quickly detect when a power loss situation is occurring, and automatically responds to this event by stepping the turbine steam valve to the correct position. Alongside the 505 system, Woodward ProTech 203 overspeed protection devices were used on the generators to safeguard each unit from overspeed trips.

Geology of the Area

 Geologic Setting
 Tectonic Setting: Extensional Tectonics Controlling Structure: [5][37] Topographic Features: Horst and Graben Brophy Model: Type E: Extensional Tectonic, Fault-Controlled Resource Moeck-Beardsmore Play Type: CV-3: Extensional Domain

 Geologic Features
 Modern Geothermal Features: Hot Springs, Warm or Steaming Ground [6][23][10] Relict Geothermal Features: Argillic-Advanced Argillic Alteration, Carbonate Deposition, Other Hydrothermal Alteration Products, Silica Deposition, Silicification [3][6][23][10] Volcanic Age: No recent volcanism Host Rock Age: Host Rock Lithology: Cap Rock Age: Cap Rock Lithology:

Regional Setting
Figure 1. Map showing the location of the geothermal areas and major structural trends in the Great Basin region. Systems with maximum temperatures of 100-160°C are marked with yellow circles. System with maximum temperatures >160°C are marked with red circles. Major labeled trends include: BRD=Black Rock Desert geothermal belt; ECSZ=Eastern California shear zone; HSZ=Humboldt structural zone; SD=Sevier Desert belt; SV=Surprise Valley belt; WLG=Walker Lane belt. Abbreviations for individual geothermal areas include: Br-DP=Brady’s-Desert Peak; DV=Dixie Valley; RP=Rye Patch; SW=Salt Wells. Modified from Faulds et al. (2011) Figure 1.[37]

The Salt Wells geothermal field occupies the west-southwest margin of the Salt Wells basin ~24 km southeast of Fallon, Nevada, along the east flank of the Bunejug Mountains and northwestern edge of the Cocoon Mountains. This area lies near the intersection of the Walker Lane structural belt, a major northwest-striking system of dextral strike-slip faults along Nevada’s western border, and the southern boundary of the HSZ, a system of north- to northeast-striking faults that transects the Great Basin (see Figure 1).[37] The Walker Lane structural belt accommodates 15 to 25% of the right-lateral movement between the Pacific and North American plates.[38][39][40] This motion is absorbed and progressively declines to the northwest along the Walker Lane, diffusing into the northwestern Great Basin to produce west-northwest extension throughout the region.[41][42][43] Approximately 75% of the geothermal fields in the Great Basin appear to occur predominantly within northeast-trending basin and range belts, and are typically localized along north-northeast-striking normal faults (N0°E-N60°E) produced by the regional extension.[44][45][46][47][48] Other geothermal areas within the Great Basin region exhibit this structural style, although secondary structures exist in individual systems that contribute to permeability development and concentration of upwelling geothermal fluids. Of the roughly 245 geothermal areas reviewed in the Great Basin region, ~32% were associated with step-overs or relay ramps in normal fault zones (e.g. Desert Peak, Tungsten Mountain); ~22% were associated with intersections between normal faults and either transversely oriented oblique-slip or strike-slip faults (e.g. Roosevelt Hot Springs, Blue Mountain, Crump Geyser); ~22% were associated with normal fault terminations or tip-lines where horse-tailing creates multiple closely-spaced fault splays (e.g. Gerlach, Desert Queen, Grover's Hot Springs); and ~13% were associated with a subset of fault intersection types that include accommodation zones and displacement transfer zones (e.g. Moana, McGinness Hills, Amedee, etc.).[37] A more complete list of structural settings (including less common host structures not listed here) associated with geothermal areas can be found in Faulds et al. (2011).

The structural framework of the Salt Wells geothermal area is characterized by gently tilted fault blocks and north-striking normal faults with steep dips that bound the Bunejug and Cocoon Mountains.[5][7] Most major faults in the Bunejug and Cocoon Mountains are inferred to dip steeply to the west, inferred from the gentle eastward tilts (<30°) of associated fault blocks. In contrast, one small fault block on the southeast flank of the Bunejug Mountains (at the Salt Wells site on the west side of the basin) shows a gentle westward tilt and is associated with major north-striking faults that dip steeply to the east, as indicated by several scarps that cut silicified Lake Lahontan sand deposits and unpublished gravity data.[5] This fault system appears to terminate at the southern end of the Salt Wells basin, where it splits into a horse-tailing pattern consisting of multiple splays of subparallel faults.[7] Normal range front faults on the northwestern flank of the Cocoon Mountains are inferred to dip steeply to the west, and are thought to intersect the east-dipping Bunejug fault system in the subsurface beneath Simpson Pass. A small northwest-striking displacement transfer zone also occurs along the southern margin of the basin and appears to be roughly on strike with the Walker Lane structural belt. The lateral extent of this northwest-striking splay is unknown and may continue to the southeast of the geothermal field along the northeastern edge of the Cocoon Mountains.[5]

Stratigraphy

The stratigraphy of the Salt Wells project area consists of a surface cover of Quaternary alluvial sand and lacustrine clayey silt deposits associated with the Pleistocene Lake Lahontan.[22][5] It is interesting to note that the geothermal systems at Brady’s Hot Spring, Desert Peak, Allen Springs, and Salt Wells all exist within the extent of the Lake Lahontan paleolake.[23] Alluvial fans are present basin-ward within the Lahontan sequence, however the low topographic relief of the mountains and thick lacustrine sediment basin fill have prevented the formation of alluvial fans on the flanks of the mountains.[22][5] The greater Salt Wells Basin encompasses two evaporite playas, Eight Mile Flat in the northwest and Four Mile Flat in the southeast, that show rough mineral zonation that may relate to fossil geothermal surface discharges (see summary surface exploration work in the Exploration History section or the equivalent summary in the Exploration Activities list).[10] Quaternary sediments are underlain by a thick sequence of middle to late Miocene basaltic lava flows of the Bunejug Formation, erupted between ~13 to 8 Ma during formation of the Bunejug Mountains.[5] The basalt is interbedded with minor amounts of volcaniclastic sandstone, conglomerate, and siltstone. Lithologic data from the initial exploratory well drilled in 1980 suggests that the basalt is approximately 700 m thick in the vicinity of Simpson Pass.[6] On a regional scale, the basalt is underlain by Oligocene (~30 to 25 Ma) ash-flow tuffs and/or Mesozoic granitic and metamorphic basement.[5] In the vicinity of Salt Wells, the basalt is known to overlie at least 1921 m of quartz monzonite basement of unknown age.[6][22]

Structure

The Salt Wells geothermal field occurs at the southern end of the major north-northwest-striking HSZ, within a small accommodation zone between west- and east-dipping, north-striking normal range front faults.[37] The system appears to be localized along the southern end of the steeply east-dipping normal fault system that bounds the eastern flank of the Bunejug Mountains, where it loses displacement and intersects the west-dipping normal fault system emanating from the Cocoon Mountains.[5][7] The Bunejug range front fault system appears to die out to the south approaching Simpson Pass, and splits into several splays consisting of numerous subparallel fault scarps (i.e., horse-tailing) in the southern part of the Salt Wells basin.[5] Multiple intersections between these steeply east-dipping horse-tailing fault splays and west-dipping normal range front faults of the Cocoon Mountains serve as highly permeable subvertical conduits within the bedrock that provide convenient channel ways for the ascending geothermal fluids. Merging of the Bunejug range front fault system with a northwest-striking, right-lateral fault that runs along the northeast flank of the Cocoon Mountains may further enhance the dilation beneath the Salt Wells geothermal field.[5] This strike-slip fault represents a small displacement transfer zone that appears to relate to the Walker Lane structural belt. The structural geometry at the inferred intersection of these features would likely generate a small pull-apart in the southwest corner of the basin in the vicinity of the Salt Wells development site. The distribution of these structures in the Salt Wells basin is shown in Figure 2.

Figure 2. Map of the Salt Wells basin geothermal area showing key mapped faults,[3] and interpreted hydrologic gradient (inferred from the area topography and geomorphology). Marked data points show the results of shallow 30 cm temperature surveys performed in 2005.[10] Modified from Skord et al. (2011) Figure 4.[22]

Much of the eastern Bunejug range front fault system is concealed beneath aeolian deposits or is otherwise obscured by the effects of shoreline processes; however, wave modified fault scarps, tilted Quaternary deposits, fault breccias, and silica deposits all point to the existence of a north-striking, left-stepping series of faults beneath the surface cover.[5] Some Holocene displacement along the Bunejug range front fault system is indicated by offset of both playa muds and silicified Lahontan sands. Displacement along the fault system is predominantly down to the east, although some minor dextral movement is also suggested by the linearity of individual traces and the left-stepping pattern of the faults, which resemble the structural style of ruptures produced along the east flank of Rainbow Mountain 15 km to the north during the 1954 earthquake.[49]

Hydrothermal System

Figure 3. Map showing the CS-FDM survey results performed at Salt Wells by Willowstick Technologies, LLC. Dark shading highlights conductive highs and lightly shaded to white areas highlight conductive lows, which equate to zones of high or low groundwater saturation. From Montgomery et al. (2005) Figure 1.[22]

Geothermal surface indications at Salt Wells are described as scant, consisting only of a cold NaCl spring and of sinter deposited from hot springs that were allegedly active during the late 1880s. [6] However, close inspection reveals an abundance of hydrothermal alteration features associated with past and ongoing seasonal hot spring activity. These features can be mapped, and include argillic to advanced argillic alteration; silicified rocks, roots, mud, algal matter, silcrete (silicified sand), and siliceous oolites; massive opaline sinter deposits; CaCO3-cemented sands; opal and chalcedony veins; and tufa deposits.[23][10] Most of the mapped silicification occurs along the southwest margin of the Salt Wells basin in a broad northwest-trending zone, the northern and southern ends of which are associated with north to northeast-trending structures. These results suggest that relict geothermal activity at Salt Wells may have been controlled by stepover faults or cross faults between two sub-parallel north-northeast-striking fault zones.

A 46 km2 thermal anomaly broadly underlies the area of silicic alteration, and extends over 12 km to the south to the Cocoon Mountains, as defined by early geothermal gradient drilling by APC in the 1980s.[6] About half of this anomaly is situated above shallow aquifers that exhibited temperatures of >100°C at less than 100 m depth. The prevailing theory suggests that the hydrothermal system is fed by multiple fault intersections beneath Simpson Pass between the west-dipping normal range front faults of the Cocoon Mountains and the steeply east-dipping horse-tailing fault splays at the southern end of the Bunejug range front fault system.[5] These fault intersections serve as highly permeable subvertical conduits within the bedrock that provide convenient channel ways for the ascending geothermal fluids, and are inferred to feed the upflow zone thought to exist beneath Simpson Pass. One of the first geothermal exploration wells was drilled in 1980 by APC at Simpson Pass to test a similar theory.[6] This well discharged freely during drilling, producing up to about 21 L/s of NaCl water from fractures across a depth interval between 1,859 and 2,057 m, with maximum reservoir temperatures of 160°C. The maximum temperature measured at the bottom of the hole was 181°C at a depth of 2,591 m.

Partial visualization of the hydrothermal system at Salt Wells was achieved in 2004, when AMP Resource contracted Willowstick Technologies, LLC to conduct a Controlled Source-Frequency Domain Magnetics (CS-FDM) geophysical investigation to characterize and delineate areas showing the greatest concentrations and highest temperatures of geothermal groundwater.[22] The CS-FDM survey targeted geothermal groundwater within a 700x1000 m area, across a shallow depth interval from approximately 100 to 170 m below the land surface. Subsurface faults within this area were suspected to have the greatest amount of geothermal fluid flow at the site. After raw data reductions and background interference corrections were applied to some 450 magnetic field measurements, data were integrated into a contoured map of conductive highs and lows that equate to areas of high or low groundwater saturation (see Figure 3). Results indicate that migration of geothermal waters is strongly affected by subsurface features that inhibit fluid flow and concentrate thermal waters along east-west channels that likely represent faults cutting the subsurface basalt sequence. Geothermal waters are inferred to ascend along permeable fracture zones produced by the intersecting faults that form Simpson Pass, and then flow laterally towards the northeast along channels and/or blind fault intersections in the fractured basalt. Production well sites recommended by Willowstick based on the survey results were drilled by AMP following completion of the exploration work, and showed favorable flow rates exceeding 170 L/s with no drawdown and temperatures >140°C.

Heat Source

The heat source of the Salt Wells geothermal system is believed to be deep circulation of fluid in a highly fractured, high heat flow upper crust zone. There is no evidence of any recent significant magmatic thermal input. The high enthalpy of the Salt Wells system compared to other geothermal areas in the region may relate to the presence of as many as three characteristic structural styles associated with increased fracture permeability and geothermal activity in the Great Basin.[37]

Geofluid Geochemistry

 Geochemistry
 Salinity (low): 1300 [10] Salinity (high): Salinity (average): Brine Constituents: Cl, Na, SO4, SiO2, HCO3, and minor Ca, K [10] Water Resistivity:

Geothermometers were applied to geothermal fluids sampled from the early APC exploration wells drilled in the 1980s.[6] Major cation and anion geochemical data used for geothermometry were taken from a variety of sources, some of which were of questionable quality. Na-K-Ca geothermometry of a nearby cold spring yielded a temperature of 207°C. Geothermometers applied to waters from shallow depths in the exploratory well indicated silica temperatures of 220°C and Na-K-Ca temperatures of 235°C. Na-K-Ca temperatures of deeply sourced waters were slightly lower at 205°C. Silica and Na-K-Ca temperatures from shallow samples were significantly higher than measured temperatures in the geothermal well, presumably due to rapid reequilibration of the fluid as it cooled along its path to the surface. The Na-K-Ca temperature from the deeply sourced sample was also artificially high, but showed better agreement with maximum temperatures of 181°C measured in the well. The Quartz (no steam loss), Chalcedony, and Na-K-Ca-Mg geothermometers were re-applied to data from a selection of the early APC geothermal wells in 2006 (provided courtesy of AMP Resources, LLC), and averaged together yielded temperatures between 178.2 and 203.7°C, with a maximum temperature estimate of 214.2°C using the Quartz geothermometer.[10]

A geochemical sampling program was undertaken by Shevenell and Garside in 2002 to expand knowledge of Nevada's geothermal resource potential by providing new geochemical data from springs in less studied geothermal areas and to refine geochemical data from springs for which only incomplete data were available. This work fills in gaps in publically available geochemical data, thereby enabling comprehensive evaluation of Nevada's geothermal resource potential.[9] Waters from over 70 springs at numerous sites were sampled in the summer and fall of 2002 and subsequently analyzed for their chemical and isotopic constituents. Salt Wells was included among the sites visited; however, the spring intended for sampling (Borax Spring) had reportedly been inactive since the early 1980s, and could not be located.

Mapping of modern thermal surface features at Salt Wells in 2005 revealed that occurrences of warm ground and some 20 seasonal hot spring/cold seeps were present near areas of pervasive silicification/sinter deposition.[10] The hottest and best documented of these seasonal springs is the Borax Spring, which was rediscovered that year. Hot springs and cold seeps sampled in the area yielded temperature measurements ranging from 39.1-81.6°C and 5-7°C, respectively. Playa groundwaters were also sampled during the same field study for chemical analysis.[10] Various geothermometers applied to these samples (including the Quartz -no steam loss, Chalcedony, and Na-K-Ca-Mg geothermometers) yielded temperature estimates that together produced an average range of 164.5-198.9°C, similar to temperatures measured in the early APC geothermal wells. An NaCl cold spring also discharges at Salt Wells, and yielded a temperature of 207°C using the Na-K-Ca geothermometer.[6]

Warm spring waters were also sampled from the Rock Springs and from an artesian water well located approximately 520 m to the west-southwest (about 33 m basinward of the “Pony Express” fault scarp) during the absorbed mercury vapor soil geochemical survey conducted by Henkle Jr. et al. (2005). [25] Chemical analysis of the samples showed dissolved silica concentrations of 79.6 ppm for Rock Springs and 104 ppm for artesian well water, suggesting a potential reservoir temperature between 125°C and 139°C for faults of the “Pony Express” fault system, as determined using the quartz conductive geothermometer.

Collectively, these results suggest that a deeper, untapped reservoir exists beneath Salt Wells that feeds the shallow hydrothermal system. This supposed deep reservoir is estimated to host temperatures between 180 and 190°C, much greater than the ~140°C water currently being produced from the shallow reservoir by the existing 18 MW geothermal power plant.

NEPA-Related Analyses (10)

Below is a list of NEPA-related analyses that have been conducted in the area - and logged on OpenEI. To add an additional NEPA-related analysis, see the NEPA Database.

Document # Analysis
Type
Applicant Application
Date
Decision
Date
Agency
Development
Phase(s)
Techniques
DOI-BLM-NV-C010-2009-0006-EA EA Gradient Resources 26 May 2009 26 May 2009 BLM Stillwater Field Office Geothermal/Exploration Thermal Gradient Holes
DOI-BLM-NV-C010-2012-0016-DNA DNA Ormat Technologies Inc 6 December 2011 26 January 2012 Bureau of Land Management Geothermal/Well Field Production Wells
DOI-BLM-NV-C010-2012-0019-DNA DNA Ormat Technologies Inc 6 December 2011 26 January 2012 Bureau of Land Management Geothermal/Well Field Observation Wells
DOI-BLM-NV-C010-2012-0020-DNA DNA Ormat Technologies Inc 31 December 2011 27 January 2012 Bureau of Land Management Geothermal/Well Field Observation Wells
DOI-BLM-NV-C010-2012-0048-DNA DNA Enel Salt Wells LLC 4 April 2012 25 April 2012 BLM Nevada State Office Geothermal/Well Field Observation Wells
DOI-BLM-NV-CC-ES-11-10-1793 EIS Ormat Technologies Inc, Gradient Resources (formerly Vulcan Power), Sierra Pacific Power Co, 30 September 2011 BLM Geothermal/Power Plant Development Drilling
EA-NV-030-05-08 EA Nevada Geothermal Specialists, LLC 25 February 2005 Bureau of Land Management Geothermal/Exploration
NV-EA-030-07-05 EA Vulcan Power Company 1 September 2006 6 February 2007 BLM Geothermal/Exploration Thermal Gradient Holes
NVN-084575 CU Vulcan Power Company 7 December 2007 17 January 2008 BLM Geothermal/Exploration Reflection Survey
Seismic Techniques
NVN-087388 CU Enel North America 29 April 2009 30 April 2009 BLM Stillwater Field Office Geothermal/Exploration Audio-Magnetotellurics

Exploration Activities (21)

Below is a list of Exploration that have been conducted in the area - and cataloged on OpenEI. Add a new Exploration Activity

References

1. Geothermex Inc.. 2004. New Geothermal Site Identification and Qualification. Richmond, CA: California Energy Commission. Report No.: P500-04-051. Contract No.: 500-04-051.
2. Nevada Bureau of Mines and Geology. 2012. Nevada Bureau of Mines and Geology Open-File Report 12-3: Data Tables and graphs of geothermal power production in Nevada 1985-2011, 2012. .: Nevada Bureau of Mines and Geology.
3. Lake Lahontan: Geology of Southern Carson Desert, Nevada
4. Ronald Willden,Robert C. Speed (Nevada Bureau of Mines and Geology). 1974. Geology and Mineral Deposits of Churchill County, Nevada. Reno, NV: Nevada Bureau of Mines and Geology. Report No.: NBMG Bulletin-83.
5. James E. Faulds,Mark F. Coolbaugh,Garrett S. Vice,Melissa L. Edwards. 2006. Characterizing Structural Controls of Geothermal Fields in the Northwestern Great Basin- A Progress Report. In: Transactions. GRC Annual Meeting; 2006/09/10; San Diego, CA. Davis, CA: Geothermal Resources Council; p. 69-76
6. R.C. Edmiston,W.R. Benoit. 1984. Characteristics of Basin and Range Geothermal Systems with Fluid Temperatures of 150°C to 200°C. In: Transactions. GRC Annual Meeting; 1984/08/26; Reno, NV. Davis, CA: Geothermal Resources Council; p. 417-424
7. Justin Skord,Patricia H. Cashman,Mark Coolbaugh,Nicholas Hinz. 2011. Mapping Hydrothermal Upwelling and Outflow Zones: Preliminary Results from Two-Meter Temperature Data and Geologic Analysis at Lee Allen Springs and Salt Wells Basin. In: Transactions. GRC Annual Meeting; 2011/10/23; San Diego, CA. Davis, CA: Geothermal Resources Council; p.
8. Israel C. Russell (U.S. Geological Survey). 1885. Geological History of Lake Lahontan, a Quaternary Lake of Northwestern Nevada. Washington, District of Columbia: U.S. Government Printing Office. Report No.: Monograph M11.
9. Lisa Shevenell,Larry Garside. 2003. Geochemical Sampling of Thermal Waters in Nevada. In: Transactions. GRC Annual Meeting; 2003/10/12; Morelia, Mexico. Davis, CA: Geothermal Resources Council; p. 27–32
10. Mark F. Coolbaugh,Chris Sladek,Chris Kratt,Lisa Shevenell. 2006. Surface Indicators of Geothermal Activity at Salt Wells, Nevada, USA, Including Warm Ground, Borate Deposits, and Siliceous Alteration. In: Transactions. GRC Annual Meeting; 2006/09/10; San Diego, California. Davis, CA: Geothermal Resources Council; p. 399-405
11. Nevada Bureau of Mines and Geology. Salt Wells, Eight Mile Flat [Internet]. 2009. Online Nevada Encyclopedia. [updated 2009/03/24;cited 2013/08/07]. Available from: http://www.onlinenevada.org/articles/salt-wells-eight-mile-flat
12. Bureau of Land Management. Salt Wells Geothermal Exploratory Drilling Program EA (DOI-BLM-NV-C010-2009-0006-EA) [Internet]. 09/14/2009. Carson City, NV. U.S. Department of the Interior- Bureau of Land Management, Carson City Field Office, Nevada. [updated 2009/09/14;cited 2013/08/21]. Available from: http://www.blm.gov/nv/st/en/fo/carson_city_field/blm_information/nepa/salt_wells_geothermal0.html
13. Mark Struble. BLM Approves Salt Wells Geothermal Plant in Churchill County [Internet]. 02/13/2005. Carson City, NV. U.S. Department of the Interior- Bureau of Land Management, Carson City Field Office, Nevada. [updated 2005/02/13;cited 2013/08/21]. Available from: http://www.blm.gov/nv/st/en/info/newsroom/Carson_City_News_Archives/2005/02/blm_approves_salt.html
14. Enel (Enel S.p.A.). 2008. 2007 Annual Report. Enel Website: Enel S.p.A..
15. Hank Sennott. 04/15/2009. Enel Green Power- Innovative Geothermal Power for Nevada. Press Release. 1-2.
16. John Snow,Fausto Batini. 04/22/2008. Enel North America Utah Geothermal Working Group Meeting. Cedar City, UT. Enel Nort America. 24p.
17. Jim Combs,John T. Finger,Colin Goranson,Charles E. Hockox Jr.,Ronald D. Jacobsen,Gene Polik (Sandia National Laboratories). 1999. Slimhole Handbook- Procedures and Recommendations for Slimhole Drilling and Testing in Geothermal Exploration. Albuquerque, NM: Geothermal Technologies Legacy Collection. Report No.: SAND99-1976.
18. Bureau of Land Management. Salt Wells Geothermal Energy Projects Environmental Impact Statement [Internet]. 07/22/2011. Carson City, NV. U.S. Department of the Interior- Bureau of Land Management, Carson City Field Office, Nevada. [updated 2011/07/22;cited 2013/08/07]. Available from: http://www.blm.gov/nv/st/en/fo/carson_city_field/blm_information/nepa/salt_wells_energy.html
19. Colleen Sievers. BLM Approves Salt Wells Geothermal Energy Projects [Internet]. 09/28/2011. Carson City, NV. U.S. Department of the Interior- Bureau of Land Management, Carson City Field Office, Nevada. [updated 2011/09/28;cited 2013/08/21]. Available from: http://www.blm.gov/nv/st/en/fo/carson_city_field/blm_information/newsroom/2011/september/blm_approves_salt.html
20. Bureau of Land Management (Bureau of Land Management, Carson City Field Office, Nevada). 2011. BLM Fact Sheet- Vulcan Power Company Salt Wells Geothermal Energy Project. Carson City, Nevada: U.S. Department of the Interior.
21. Bureau of Land Management (Bureau of Land Management, Carson City Field Office, Nevada). 2011. BLM Fact Sheet- Ormat Technologies Salt Wells Geothermal Energy Project. Carson City, Nevada: U.S. Department of the Interior.
22. Jerry Montgomery,Roger L. Bowers,Val Kofoed. 2005. Characterization Of Geothermal Resources Using New Geophysical Technology. In: (!) ; (!) ; (!) . (!) : GRC; p. (!)
23. Mark F. Coolbaugh,Chris Sladek,Chris Kratt,Gary Edomondo. 2004. Digital Mapping Of Structurally Controlled Geothermal Features With GPS Units And Pocket Computers. In: Transactions. GRC Annual Meeting; 2004/08/29; Indian Wells, CA. Davis, CA: Geothermal Resources Council; p. 321-325
24. G.P. Edmondo,D.R. Soller (U.S. Geological Survey). 2002. Digital Geologic Field Mapping Using Arcpad, In: Digital Mapping Techniques ’02- Workshop Proceedings. Online Article: U.S. Geological Survey. Report No.: Open-File Report 02-370.
25. William R. Henkle Jr.,Wayne C. Gundersen,Thomas D. Gundersen. 2005. Mercury Geochemical, Groundwater Geochemical, And Radiometric Geophysical Signatures At Three Geothermal Prospects In Northern Nevada. In: (!) ; (!) ; (!) . (!) : GRC; p. (!)
26. D.E. White,M.E. Hinkle,I. Barnes. 1970. Mercury Contents of Natural Thermal and Mineral Fluids, In- U.S. Geological Survey Professional Paper 713. Washington, D.C.: U.S. Government Printing Office. 25-28p.
27. O.D. Christensen,J.N. Moore,R.M. Capuano. 1980. Trace Element Geochemical Zoning in the Roosevelt Hot Springs Thermal Area, Utah. In: Transactions. GRC Annual Meeting; 09/09/1980; Salt Lake City, UT. Salt Lake City, UT: Geothermal Resources Council; p. 149-152
28. J.S. Matlick,M. Shiraki. 1981. Evaluation of the Mercury Soil Mapping Geothermal Exploration Techniques. In: Transactions. GRC Annual Meeting; 1981/10/25; Houston, TX. Davis, CA: Geothermal Resources Council; p. 95-98
29. S.C. Smith. 2003. Thermally Speciated Mercury in Mineral Exploration. In: Programs & Abstracts: Soil and Regolith Geochemistry in the Search for Mineral Deposits. IGES; 2003/09/01; Dublin, CA. Dublin, CA: IGES; p. 78
30. Larry J. Garside (Nevada Bureau of Mines and Geology). 1973. Radioactive Mineral Occurences in Nevada. Reno, NV: Nevada Bureau of Mines and Geology. Report No.: Open File Report 94-2.
31. Larry J. Garside,John H. Schilling (Nevada Bureau of Mines and Geology). 1979. Thermal Waters of Nevada. Reno, NV: Nevada Bureau of Mines and Geology. Report No.: Bulletin 91.
32. Chris Kratt,Mark F. Coolbaugh,Wendy M. Calvin. 2006. Remote Detection of Quaternary Borate Deposits with ASTER Satellite Imagery as a Geothermal Exploration Tool. In: Transactions. GRC Annual Meeting; 2013/09/10; San Diego, CA. Davis, CA: Geothermal Resources Council; p. 435–439
33. Mark F. Coolbaugh,Chris Sladek,James E. Faulds,Richard E. Zehner,Gary L. Oppliger. 2007. Use of Rapid Temperature Measurements at a 2-Meter Depth to Augment Deeper Temperature Gradient Drilling. In: Proceedings of Thirty-Second Workshop on Geothermal Reservoir Engineering. Thirty-Second Workshop on Geothermal Reservoir Engineering; 2007/01/22; Stanford, CA. Stanford, CA: Stanford University, Stanford Geothermal Program; p. 109-116
34. Chris Sladek,Mark F. Coolbaugh,Christopher Kratt. 2009. Improvements in Shallow (Two-Meter) Temperature Measurements and Data Interpretation. In: Transactions. GRC Annual Meeting; 2009/10/04; Reno, NV. Davis, CA: Geothermal Resources Council; p. 535–541
35. Christopher Kratt,Mark F. Coolbaugh,Bill Peppin,Chris Sladek. 2009. Identification of a New Blind Geothermal System with Hyperspectral Remote Sensing and Shallow Temperature Measurements at Columbus Salt Marsh, Esmeralda County, Nevada. In: Transactions. GRC Annual Meeting; 2009/10/04; Reno, NV. Davis, CA: Geothermal Resources Council; p. 481–485
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37. Assessment of Favorable Structural Settings of Geothermal Systems in the Great Basin, Western USA
38. Contemporary Strain Rates in the Northern Basin and Range Province from GPS Data
39. Contemporary Tectonic Deformation of the Basin and Range Province, Western United States: 10 Years of Observation with the Global Positioning System
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41. Sierra Nevada–Basin and Range Transition Near Reno, Nevada: Two-Stage Development at 12 and 3 Ma
42. Two-Phase Westward Encroachment of Basin and Range Extension into the Northern Sierra Nevada
43. Diachroneity of Basin and Range Extension and Yellowstone Hotspot Volcanism in Northwestern Nevada
44. Exploration and Development Techniques for Basin and Range Geothermal Systems: Examples from Dixie Valley, Nevada
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46. The Humboldt House-Rye Patch Geothermal District: An Interim View
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48. Historic Surface Faulting and Paleoseismicity in the Area of the 1954 Rainbow Mountain-Stillwater Earthquake Sequence, Central Nevada

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