Nevada Low-Temperature Geothermal Resource Assessment

Nevada Bureau of Mines and Geology

Open-File Report 94-2

1994

Larry Garside
Nevada Bureau of Mines and Geology (NBMG)
University of Nevada, M.S. 178
Reno, Nevada 89557-0088
Email: lgarside@unr.edu
Phone: (775)784-6691 Ext. 137


Final report prepared for the Oregon Institute of Technology GeoHeat Center as part of a study of low- to moderate-temperature geothermal resources of Nevada under the U.S. Department of Energy Low-Temperature Geothermal Resources and Technology Transfer Program.

The text of the report, references, and Appendix 1 can be downloaded in a pkzip file format by clicking here. Text and references are in ascii text and Appendix 1 is in Lotus wk1 format and dBase III+ format.


INTRODUCTION
    Previous Geothermal Assessments
    Need for a New Assessment
    Nevada Assessment Program
DATA SOURCES
    Preliminary Data Compilation
DATA FORMAT
FLUID CHEMISTRY
DISCUSSION
SUMMARY
RECOMMENDATIONS
BIBLIOGRAPHY

APPENDIX 1 (Excel file)

TABLE
1.    Nevada county abbreviations

FIGURES
1. Map of mean annual temperatures
2. Temperature vs. number of geothermal occurrences
3. Original Report Map of Nevada geothermal resource occurrences
3a. Map of Nevada geothermal resource occurrences
3b. Map of Nevada geothermal resource occurrences with major roads

PLATE
1. Million-scale map of geothermal resource occurrences available in black and white from the Nevada Bureau of Mines and Geology


INTRODUCTION

Previous Geothermal Assessments

A statewide inventory of the geology and geochemistry of Nevada's geothermal resources was begun at the Nevada Bureau of Mines and Geology (NBMG) in the late 1970s. NBMG had previously published a 1:1,000,000-scale map of hot springs, sinters, and volcanic cinder cones (Horton, 1964b) and several brief summaries of Nevada's geothermal resources (Horton, 1964a; Garside and Schilling, 1972; Garside, 1974). This inventory, published as NBMG Bulletin 91 (Garside and Schilling, 1979), followed a format used in a number of NBMG publications on mineral commodities of Nevada. The bulletin contained descriptions, by county and hot spring area, of the better known geothermal areas. These descriptions included, where available, maps and other data on the geology, and descriptions of historical and present use. Temperature and water chemistry data were presented in an appendix having about 1,400 individual entries (records). These records commonly included multiple entries for the same or adjacent springs as well as numerous well records from geothermal areas which have a larger areal extent than individual spring sites. A 1:1,000,000-scale map was included in the pocket of NBMG Bulletin 91; nearly 400 geothermal sites (springs, spring groups, well groups, etc.) were included on that map. The lower temperature cut-off for inclusion of data in Bulletin 91 was 70F (21.1C).

The location, chemical data, and references for the geothermal springs and wells listed in Bulletin 91 were collected by an extensive and relatively complete search of the available literature. These data were entered by hand on data-collection forms, and these forms were used to typeset the listing of data in the bulletin (Appendix 1). A source of unpublished data was a computer database of water-quality data maintained by the Desert Research Institute at Reno.

GEOTHERM is an acronym for a U.S. Geological Survey (USGS) computerized information system designed to maintain data on the geology, geochemistry, and hydrology of geothermal sites primarily within the United States (Teshin and others, 1979; Bliss, 1983). The system was first proposed in 1974, and was active until 1983. The system utilized a mainframe computer, and most of the data were entered by use of key-punch cards. Key punching was done from a rather extensive data-entry form. When the GEOTHERM database was taken off line, a number of products were published or made available to preserve the data. These include basic data for thermal springs and wells on a state-by- state basis (for Nevada, see Bliss, 1983a) and a listing of each record on a state-by state basis, as microfiche (for Nevada, see Bliss, 1983b). The GEOTHERM database was also filed with the National Technical Information Service (NTIS) as digital data. A 9-track one-half inch reel-to-reel tape in ASCII format of this GEOTHERM database was provided to NBMG after the start of this project by Howard Ross at the University of Utah Research Institute (UURI). This tape, containing 8,082 records, was originally from NTIS.

GEOTHERM contained 1,367 records for Nevada when it was taken off line in 1983; the is the number of Nevada records on the NTIS tape as well. The great majority of these records are from the published sources used to compile Appendix 1 of Bulletin 91. Unpublished site data and analyses from the files of D.E. White (USGS) make up a significant section of the database also. About 75% of this GEOTHERM data was added to the original database during 1978 and 1979 by personnel at NBMG as part of the U.S. Department of Energy State Coupled Program (see Trexler and others, 1979a). In addition to the entry of new data and the editing and verifying of existing data in GEOTHERM, the longitude and latitude locations of springs and wells were determined by plotting them on 1:250,000-scale maps and hand digitization (Trexler and others, 1979a). New analyses were done during this period, and these data were added to GEOTHERM.

The database available in GEOTHERM during the early 1980s was used, along with other data developed from specific geothermal site studies funded by the U.S. Department of Energy (see numerous reports by Trexler and co-workers, 1980-83) to produce two 1:500,000-scale maps illustrating Nevada's geothermal resources (Trexler and others, 1979, 1983). No statewide resource studies were done after the publication of the 1938 NOAA map (Trexler and others, 1983). A nationwide assessment of low- temperature geothermal resources (USGS Circular 892) included data for Nevada, and an open-file report (Reed and others, 1983) included about 350 records for Nevada that were used in that assessment. These records were selected from the GEOTHERM database by use of charge balance determinations and other screening methods (Marshall Reed, written commun., 1993). During this period of time, an increase in exploration for geothermal resources by private industry (mainly for electric-power generation) resulted in the drilling of thousands of gradient and slim holes, and several hundred larger diameter wells for industrial and commercial use (space heating, electric power generation, etc.). Developments in Nevada's geothermal industry are documented in yearly summaries of the Nevada mineral industry, published yearly by NBMG since 1979 (e.g., Hess, 1993). Information that is available on geothermal drilling in Nevada has been summarized by Barton and Purkey (1993).

Need for a New Assessment

Low- and moderate-temperature geothermal resources are widely distributed in the western United States. Although there has been a substantial increase over the last decade in utilization of these resources in direct-heat applications, the large resource base is greatly underutilized (Ross and others, 1994). Previous studies have demonstrated that Nevada is well endowed with geothermal resources, and much of the state must be considered as having potential for direct use. As Ross and others (1994) describe, the expanded use of low- and moderate-temperature geothermal resources requires, as a start, a current inventory of the resources. Such an inventory, combined with collocation studies (the study of resource location near population centers or areas of potential industrial users), will provide some of the basic information that the potential developers of the geothermal resources need to make sound economic decisions. Collocation factors are of particular significance in Nevada, as well as a number of other western states, because people and most industries are concentrated in a few areas; geothermal resources, on the other hand, are rather widely distributed.

There are many factors that can affect the viability of direct- use geothermal applications. These include not only the suitability of the fluid and the resource for the application (water temperature, chemistry, amount of available heat, etc.) but also the information available to the developer on the technology of the proposed application, and contractual and other economic factors less closely related to the geothermal resource. The collection of data on these geothermal resources and their present uses is only one factor in encouraging their increased use. Other components of the 1992-1993 low-temperature program include development of better techniques to discover and evaluate the resources, and technical assistance to potential developers (Ross and others, 1994).

Nevada Assessment Program

Data compilation for the low-temperature program is being done by State Teams in ten western states. The Nevada program, under the direction of Larry J. Garside at the Nevada Bureau of Mines and Geology at the University of Nevada began data collection in early 1993 (the contract for the research between the University of Nevada and the Oregon Institute of Technology was signed on March 23, 1993). The original contract was to end on December 31, 1993, but was later extended to June 30, 1994. The Technical Project Managers for the agreement were Howard P. Ross (University of Utah Research Institute) and Paul J. Lienau (Oregon Institute of Technology - GeoHeat Center).

The final products of the study include the following: 1) a geothermal database, in hardcopy and as digital data (diskette) listing information on all known low- and moderate-temperature springs and wells in Nevada; 2) a 1:1,000,000-scale map displaying these geothermal localities, and; 3) a bibliography of references on Nevada geothermal resources. The format for presentation of these data was worked out through discussions among State Teams and the Project Managers during the first half of the contract period; the model for this database has been described by Blackett (1993).

DATA SOURCES

Information on Nevada's geothermal resources is widely distributed in published reports, in unpublished and limited-distribution sources (commonly referred to as "gray literature"), and as digital information in databases such as GEOTHERM and WATSTORE. The sources of data and methods of data manipulation are discussed below, followed by a description of the bibliography.

Preliminary Data Compilation

The Nevada geothermal database (Appendices 1 and 2) includes "records" (that is, single reports of chemistry, temperature, location, etc. that are represented by a single spreadsheet row) for all known (reported or suspected) geothermal sites in the state. A number of preliminary databases and spreadsheets were compiled before selection of records for the final listing (Appendices to this report). To get the data from various sources into a common format for comparison required months of work using a variety of computer hardware and software available at NBMG. In the following paragraphs I have summarized the major sources of information, the techniques used to modify and utilize them effectively, and some of the sources of error and other problems that were encountered.

GEOTHERM

The history of the GEOTHERM database is summarized above under the description of previous assessments. Because the database was taken off line in 1983, it does not contain data collected after that date. A tape GEOTHERM records that was obtained from UURI was read on to a large magnetic disk at NBMG. Information supplied by NTIS with this tape gave the field lengths of each field in the database. With this information, computer database specialists at NBMG were able to design a database having fixed- length fields and read the GEOTHERM ASCII file into that database. The database on tape contained over 8000 records, with approximately 120 fields for each record. The database software used for this database was INFO, a subset of the ARC/INFO software utilized in many GIS (Geographic Information Systems) applications; hardware was a UNIX-based SUN SPARC II workstation. The database in INFO was nearly 19 MB (megabytes). From this database, the 1367 Nevada records could be exported, by use of PC ARC/INFO, in a format compatible with modern database-management software (such as dBASE). We used PC-File (a product of ButtonWare, Inc.) as the PC-based database software. The Nevada GEOTHERM database in PC-File is about 3.2 MB, and has a number of problems that make it difficult to use. One of the most notable problem is that in the PC-File format (essentially a dBASE format), most of the numerical data (temperature, water chemistry, etc.) are preceded by a five sided graphic figure which resembles the outline of a small house (or a baseball field "home plate"). This non-ASCII character was apparently a pad character or "punch" symbol in the original database that acted as a space. It can not be searched for, and was only eliminated after a short version of the database was retrieved into spreadsheet software (Quattro Pro, a product of Borland International, Inc.). In addition, some records had data reported in different units from other records (for example ppm or epm); the units used were reported in a separate database field. Fortunately, these problems were overcome in the shortened (spreadsheet) version.

Additionally, a number of other operations were done on a short database of GEOTHERM data that contained only the fields required for this study (Appendix 1). These include: 1) replacing the county name with a two-letter code (abbreviation) for each county, 2) conversion of numerical data from labels to values and insertion by hand of certain qualifiers on some analyses (N for not detected, t for trace, < for less than), 3) addition of calculated columns for ion balance, total calculated dissolved solids, and a major constituents test (is Na>K and Ca>Mg and Cl>F?), 4) rearrangement of columns into final format. Before final column rearrangement, formulas were converted to values, and a fixed number of decimal places was selected for display. About 455 records were finally selected from this spreadsheet to be included in the final tables listed in the Appendix.

WATSTORE

The acronym WATSTORE stands for the National WATer Data STOrage and REtrieval System, a large-scale computerized system developed for the storage and retrieval of water data collected as part of the activities of the USGS, particularly the Water Resources Division (from a 1981 pamphlet, U.S. Government Printing Office: 1981 - 341-618:52). The system was begun in 1971, and contains a very large set of data on surface and groundwater in the U.S. The water-quality file alone is reported to have (in 1991) 34 million observations from over 200,000 stations; 5,000 parameters (major and trace elements, pesticides, organics, etc.) are included. The database contains information on the analyzing and collecting agency, but does not report whether the data has been published or list references. The WATSTORE database can be searched through arrangements with USGS Water Resources district offices or through a national system of water data exchange (NAWDEX); assistance centers for NAWDEX are also commonly located at USGS Water Resources District Offices. The NAWDEX database also has access to other Federal agency water data, for example the Environmental Protection Agency (EPA), in addition to WATSTORE.

Water quality and other WATSTORE database file information is also available through a commercial outlet, EarthInfo, Inc. of Boulder, Colorado. EarthInfo makes certain data from WATSTORE available on CD-ROMs along with a software retrieval system that can be used by IBM-compatible personal computers. NBMG obtained a CD-ROM that included all Nevada data (current to early 1993) from EarthInfo. Personnel at NBMG (particularly Ron Hess) were able to search the CD-ROM and extract the parameters required for this study (water quality, location, site name, etc.) for all springs and wells having a measured temperature of 18C or greater. To avoid the combination of parameters (e.g., water chemistry analyses) from different collection dates for the same site, a combination number was created (consisting of the site and collection date numbers) so that a later relational combination of the data would produce records that represent one site visit. These geothermal data were converted to a dBASE format and PC- File was used to eliminate records having temperatures less than 20C for the area of Nevada south of 38 latitude. At this point, the database consisted of 1,708 records. These records were imported into a spreadsheet format using Quattro Pro software, and a multitude of operations were performed on the data to make it similar to the planned format for the final tables (Appendices 1 and 2). These operations include: 1) conversion of longitude and latitude to decimal degrees, 2) addition of calculated fields for ion balance, total calculated dissolved solids, major constituents test (is Na>K and Ca>Mg and Cl>F?), 3) conversion of depth in feet to meters and flow from cubic feet per second to liters per minute, 4) addition of a reference column for listing of WATSTORE as the reference, 5) convert GW (groundwater) to W (well) and SP to S (spring), 6) conversion of the state-county FIPS code to a two-letter abbreviation (see listing below), 7) conversion of the collection date format to the year/month/ day format, 8) re-arrangement of columns, and 9) a sort of rows (records) by longitude and latitude.

A number of additional operations were later performed on about 140 WATSTORE records selected for the final tables. These include: 1) conversion of Fe, and B from micrograms per liter to milligrams per liter (essentially equivalent to parts per million - ppm), and 2) separation of the site name column into two columns (one for name and one for the legal land location, if reported). Following this, Li, oxygen and hydrogen isotope data, and HCO3-CO3 concentrations were added to the short spreadsheet of WATSTORE records. Li, and the 2H and 18O were inadvertently left out of the first search of the EarthInfo CD-ROM. The search for HCO3-CO3 data in WATSTORE presented a more complicated problem, as these constituents are reported as several different parameters (fields) in the database. A number of the records generated by the first search were lacking data for these constituents; a second search was done for data in all possible related parameters (about eight of them, including bicarbonate and carbonate field results, laboratory results, dissolved, incremental titration, titration to pH 4.5 and pH 8.3, and alkalinity (field and laboratory). The data were entered by hand into the intermediate spreadsheet of WATSTORE records destined for the final tables.

Table 1. County names for Nevada, FIPS (Federal Information Processing Standard) code (32 is Nevada), and abbreviations used in this report.

County FIPS Code Abbreviation

Churchill 32001 CH
Clark 32003 CL
Douglas 32005 DG
Elko 32007 EL
Esmeralda 32009 ES
Eureka 32011 EU
Humboldt 32013 Hu
Lander 32015 LA
Lincoln 32017 LI
Lyon 32019 LY
Mineral 32021 MN
Nye 32023 NY
Pershing 32027 PE
Story 32029 ST
Washoe 32031 WA
White Pine 32033 WP
Carson City 32510 CC

Topographic Map Digital Data

A complete examination was made by David Davis at NBMG of the approximately 1,900 7.5-minute topographic maps for Nevada. The entire state has this coverage, and a visual examination was made of each map for any mention of hot or warm springs, geothermal wells, etc. In addition, a 1981 version of GEOTHERM was available in paper copy (Jim Bliss, written commun., 1981) and this was used to identify other geothermal spring and well locations on these topographic maps. About 2700 individual points were marked on the maps, and the locations were digitized in the NBMG GIS laboratory using ARC/INFO software, a CalComp 9500 digitizer, and digital map coordinate data (TIC file) from the USGS. A database of the location and other data collected for this part of the project was created, and about a dozen records in the final table were from the spreadsheet equivalent of that database. In general, the records from this database were for locations where no data were available in other sources. The references are usually the 7.5-minute quadrangle map that the spring or well appears on. Additionally, when more precise longitude and/or latitude locations were required for records taken from any of the other sources used, the appropriate information from this database was entered in intermediate spreadsheets of selected records.

Other Data Sources

During the selection of records for the final database, if water quality or other data in WATSTORE or GEOTHERM was lacking, incomplete, or appeared to be of poor quality, other sources of information were checked for possible inclusion in the database. Some of these sources were originally cited in NBMG Bulletin 91, but no record of a particular site was ever entered in GEOTHERM. A number of such records refer to dubious thermal spring locations, but must be included in any database that is purported to be complete. Other sources used for one or two sites include Hulen and others (1994), Trexler and others (1990), and Lawrence Livermore Laboratory (1976). Unpublished information in NBMG files and field notes of L. Garside for this and previous geothermal studies was also used. In particular, a number of good analyses and locations reported by Flynn and Buchannan (1990) were used. Their Table 3.1 was scanned, imported into Quattro Pro, and parsed into a spreadsheet of similar format to others used during this study. Also available in spreadsheet format to be checked during the data selection process were the analyses reported by Reed and others (1983) from the GEOTHERM database, and digital data on water analyses done in some areas of Nevada for the NURE (National Uranium Resource Evaluation) program (Hoffman and others, 1991).

Selection Criteria

In the early stages of this study, it became apparent that the bulk of the data on Nevada's low- an moderate-temperature geothermal resources was contained in two databases, GEOTHERM and WATSTORE. Usually, for individual thermal springs and wells, the best one or two records available from either WATSTORE or GEOTHERM was selected. If the data in these databases were incomplete or nonexistent, other known sources were checked.

The process of record selection for the final database began with hardcopy printouts of the spreadsheets described above (e.g., GEOTHERM, WATSTORE, and the topographic maps). Digital files of the longitude and latitude information for these three databases were used to plot the geothermal localities on 1:1,000,000-scale maps of Nevada in NBMG's GIS lab, using ARC/INFO software. Each of the points or point groups on these maps was checked in a regular fashion for possible errors of location. The 1:1,000,000- scale maps were examined, on 1 by 1 blocks of latitude- longitude (about 34 partial or complete blocks for Nevada). Every 7.5-minute topographic map that was shown to have a geothermal locality was re-examined, and the locations displayed on the million-scale maps were compared to those on the 7.5-minute quadrangles. From the available records for a particular spring, the best one, or in a few cases, two records was selected. For groups of springs that are found over several square kilometers, several records were commonly selected to best represent the geographic range and provide a more varied data set of water chemistry. The records selected were numbered, notes were taken on any problems recognized, and the number was written on a million-scale map and on the hardcopy of the appropriate database. This record selection process proceeded from west to east across the state, beginning in northwest Nevada and ending at its southern tip. The selection of the "best" records was somewhat subjective, but generally proceeded as follows. If a point on the maps was determined to be a valid geothermal site, GEOTHERM and WATSTORE records of that site or site area were examined. Selection from one of these databases was generally based on having an ion balance between 0.90 and 1.10, and a check to see if Na>K and Ca>Mg and Cl>F. The ion balance formula used was Na*0.04350+K*0.02558+Ca*0.04990+Mg*0.08229/Cl*0.02821+F*0.05264+H CO3*0.01639+CO3*0.03333+SO4*0.02082; resulting in a value in milliequivalents per liter, cations/anions. For those records that met these criteria, selection was based on completeness of the other analytical data (temperature, pH, minor constituents, etc.).

During the record selection process, spring and well records that did not meet certain minimum temperature criteria were eliminated from further consideration. According to the statement of work for this project, the minimum temperature for a low temperature resource is defined to be 10C above the mean annual air temperature at the surface, and should increase by 25C/km with depth (for wells). The mean annual air temperature in Nevada varies from somewhat less than 7C to over 18C (Houghton and others, 1975, figure 17; see figure 1). This variation is an effect of both latitude and elevation; southern Nevada's higher mean annual temperature results from its lower latitude and its lower average elevation (Houghton and others, 1975). Based on this map of mean annual temperature, a lower spring and well temperature limit was set for certain latitude ranges in the state. For springs, the decision whether to include or not was relatively simple - if the spring temperature was at or above the set limit, it was included. For wells, only those were considered for inclusion that fell above a gradient of 25C per kilometer with a beginning (surface) temperature at or above the minimum selected for that latitude range. The total well depth provided in the database was used to calculate this gradient. The following temperature limits were applied during record selection: 1) north of 39 latitude, 18C or above; 2) 38 to 39 latitude, 19C and above (20C was used for some sites, mostly wells, in the 38-38.5 range, 3) 37 to 38 latitude, 20C or above, and 35 to 37 latitude, 25C and above. No upper temperature limit was used to restrict inclusion in the final data compilation. The statement of work for this project listed an upper limit of 150C for occurrences to be included in the compilation. Seven occurrences with temperatures above 150C were included in the database; mainly for completeness. The only data available for some geothermal occurrences was the analysis and associated location information for the high-temperature fluid. It is obvious that lower temperature geothermal fluids are available at these sites (in peripheral areas or, in the case of electric-power generation areas, as condensed steam or reinjection fluids). Because analyses of these lower temperature fluids were not often available, the high temperature fluid analysis was listed as a substitute.

Figure 1. Map of mean annual temperatures in Nevada (from Houghton and others, 1975).

A number of problems were noted for both the GEOTHERM and WATSTORE databases as each plotted point on the million-scale maps was checked to see if it matched a known geothermal site. In quite a number of cases, certain geothermal locations were found to have an incorrect longitude or latitude or both. These were commonly discovered when the 7.5-minute topographic map was compared to the million-scale plot. In some cases, the legal description (section-township-range) was correct, but the longitude or latitude had an error of, for example, one whole degree or one whole minute. These inaccurate site locations were noted, but not corrected in the individual databases unless the record was needed for the final table.

DATA FORMAT

Data on Nevada's low- to moderate-temperature geothermal resources are presented in Appendices 1 and 2. The data in these tables are in spreadsheet format, and the digital data used to produce them (and provided separately on diskette) can be searched and otherwise manipulated in a great variety of ways utilizing a number of commercially available spreadsheet and database management software packages. Although there are two Appendices, they were printed from a single spreadsheet. The software and data manipulation methods used at NBMG during this study are further described above, under data sources. The format of the tables and, thus, the spreadsheets, in most respects follows rather closely that of Blackett (1993).

The column headings and data in the columns are generally self- explanatory, but a few comments should be made. Each column heading is listed below, with a description of the data and a discussion of format and problems.

# The site number is used to identify the site on the 1:1,000,000-scale map. It was added to the record when that record was selected for inclusion in the final database. The process of record selection was done in 1-degree blocks, proceeding from west to east, beginning in northwestern Nevada. Sites added later may not entirely follow this numbering progression, and to prevent renumbering of many of the sites, some added sites use decimal tenths (e.g., 143.1 and 142.2).

NAME The site name is commonly that listed in the source reference. In some cases, corrections, additions, or modifications were made to provide more information.

CO The two-letter abbreviation for one of Nevada's 17 counties is listed here. These abbreviations are listed above, under the Data Sources heading, with their FIPS code.

T, R, SC The legal land description, Township, Range, and Section are listed under these columns. These were commonly taken from the cited source, but some additions and corrections were made during the data evaluation. Because some of these location data were derived (in the original studies) from maps of varying ages or scales, or by projecting section lines into unsurveyed areas, there is a chance for error. Although some of these errors were noted and corrected, there are certainly many that were not. The best location data for the sites is generally the longitude and latitude; however, if correct, the section-township-range location can be used to confirm a site on topographic maps. Some section locations were determined by use of 1:100,000-scale topographic maps, on which the protracted sections are commonly displayed.

QSEC The data in this column, if present, describe the portion of the section in which the geothermal site is located. The quarter-quarter-quarter system (for example: NE SE NW) indicates an approximately 10 acre parcel in the 1 square mile section (640 acres) that is located in the northeast quarter of the southeast quarter of the northwest quarter. For data from the WATSTORE database, letters are used to indicate (from left to right) the quarter section, quarter-quarter section, and so on; the letters A, B, C, and D designate the northeast, northwest, southwest, and southeast quarters, respectively. Thus, for example, ABC would represent the southeast(C) quarter of the northwest quarter(B) of the northeast(A) quarter. The A-B-C-D system thus lists the largest quarter first, followed by progressively smaller quarters; the NE-NW-SW-SE system lists the smallest quarter section first.

T This column lists the type of occurrence, either spring (S) or well (W). In a few cases, the original listing did not fall into these two categories, and it was modified. For example, a hot pool was listed as a spring, and mine shafts or mineral exploration drill holes were listed as wells.

TEMP The reported temperature of the well or spring is listed, in degrees Celsius, in this column. Many of these reported temperatures were measured and originally reported in degrees Fahrenheit; those converted to degrees Celsius were rounded to one decimal place after conversion. If the only information reported on temperature is "warm" or "hot" (for example, from a topographic map), this is listed. The reported temperature is that of the cited reference. It is not necessarily the highest temperature reported in all of the available data for a particular spring or well; a particular record may have been selected because of its complete analysis, rather than because it had the highest reported temperature.

FLOW The flow, in liters per minute (L/min) is shown in this column. For wells, this value is commonly the discharge during pumping. Values are reported to one decimal place.

DEPTH For wells, the depth in meters is listed, if available from the original source.

CDATE The date of collection is listed here, in the format: year/month/day. For many records that list only the year of collection, this was added during this study, based on other information.

pH The reported pH is listed here.

Chemical constituents (Na, Cl, etc.) For most of the chemical constituents, they are listed as reported in the original references or databases. The reporting units are milligrams per liter (mg/L); these are essentially equivalent to parts per million at the concentration levels of the fluids listed in the Appendix. For some analyses, constituent values originally reported in gm/L (micrograms per liter or parts per billion - ppb) were converted to mg/L. If the original source listed a particular constituent as less than a certain value, this was reported using the symbol "<". Similarly, "t" indicates that a trace amount was detected, and "N" indicates the constituent was analyzed for but not detected. The number of decimal places displayed for each element is generally based on that reported in the sources of data. For most of the reported analyses, bicarbonate (HCO3) and carbonate (CO3) are listed as reported in the sources. Carbonate values are usually only found in waters with a pH of 8.2 or greater. A few sources (e.g., Lawrence Livermore Laboratory, 1976) report total alkalinity; these values were recalculated and reported as bicarbonate, as were the values reported in a HCO3 + CO3 column of Table 3.1 of Flynn and Buchannan (1990). Some analyses are noted to be relatively complete, but lack Na and K values. Commonly, the reason for this absence is that the original analysis reported Na + K as a single value, and thus, no data was entered in the Na and K fields in databases such as GEOTHERM.

TDSm, TDSc These columns present the total dissolved solids, measured and calculated. The measured value, if present, is from the original data source (presumed to be a residue on evaporation at 105C). The calculated value was determined by summing the constituents reported. Thus, the TDSc value reported for incomplete analyses only represents a partial sum. A few analyses were summed before Li was added, and may be one to several ppm low. The HCO3 value was multiplied by 0.492 to make the calculated TSDS values comparable with residue values.

ChgBal The electroneutrality of the analysis was evaluated using a charge (ion) balance formula (described further in the section on selection criteria). No value is reported for records which have no or extremely limited analytical data, as such a calculation would be meaningless. The most common reason for a charge balance that varies considerably from 1.00 is a lack of data for HCO3. Other missing major ions can also result in a "poor" charge balance.

delD, delO18 These columns contain isotopic compositions for the stable isotopes 18O and deuterium (3H). Data are reported to zero or one decimal place for 18O and one or two decimal places for deuterium.

REFERENCE The reference citation in this column is that for the source of the data. The records that were taken from the GEOTHERM database include the reference listed therein. The WATSTORE citation is from the database search described above under data sources. An asterisk (*) precedes some citations; this was used in the GEOTHERM database to indicate unpublished data from individuals or agencies (for example, *WHITE, D., USGS, MENLO PARK or *DESERT RESEARCH INSTITUTE, 1973). The *NEVADA BUREAU OF MINES AND GEOLOGY citation includes unpublished data from that agency's files entered into the original GEOTHERM database as well as some entries made during this study. The *WATSTORE reference refers to data from GEOTHERM that originated from a WATSTORE search, probably in the late 1970s.

USE This data category lists the geothermal application for which the thermal water is presently used, or has been used for in the recent past but is not presently (in parentheses). The source of most of this data is Garside and Hess (1994), with some later additions during the later part of this study. Garside and Hess (1994) is reproduced as Appendix 3. No attempt was made to list uses of only the water but not the contained heat (livestock watering, for example). At least a dozen hot spring areas in Nevada have had hotel spas at them; most were built in the late 19th and early 20th Centuries. These were not listed as a past use, but present spas, swimming pools, etc., were reported.

FLUID CHEMISTRY

The geochemistry of thermal water in Nevada (and adjacent areas) has been discussed by a number of authors (e.g., Mariner and others, 1983; Flynn and Buchanan,1990; Welch and Preissler, 1990; Young and Lewis, 1982). A simplification of the pattern of chemistry exhibited by Nevada thermal water is that eastern Nevada geothermal fluids are calcium bicarbonate dominated, central and northern Nevada has mainly sodium bicarbonate type fluids, and the western part of the state has mostly sodium chloride and sodium sulfate types. The reasons for this pattern are, no doubt, relatively complex; however, water-rock interactions are certainly a significant factor. Thus, eastern Nevada calcium bicarbonate geothermal fluids are strongly influenced by the presence of a regional carbonate aquifer. At least some of the sodium bicarbonate geothermal fluids of the central and north-central parts of the state may result from the exchange of sodium (possibly from volcanic rocks) for calcium in fluids that were originally calcium bicarbonate in character. Western Nevada sodium chloride and sodium sulfate waters may reflect increased water-rock interaction (and thus generally higher temperatures) as well as possible evaporative concentration of fluids prior to deep circulation and/or extraction of salts from Quaternary playa lake deposits.

DISCUSSION

Nevada is well endowed with both high- and low-temperature geothermal resources. Based on a generalized map of known and potential geothermal resource areas of the United States (e.g., Lienau, 1988) over 40% of the state is believed to have potential for the discovery of high-temperature geothermal resources, and another 50% has potential for low- to moderate-temperature resources. This potential is well illustrated by the 1:1,000,000- scale map of geothermal occurrences produced during this study (Plate 1). The database for this study consists of 455 individual records, representing more than 300 resource areas. The geothermal springs and wells are distributed over the entire state, with an increased concentration in the northwestern part of the state (fig. 3). Maximum spring and well temperatures are higher in the north and northwest parts of the state. Geothermal occurrence temperatures greater than 75C are confined to the northwestern half of the state, a pattern that closely follows that of heat flow (see Sass and others, 1981). The distribution of reported temperature vs. number of occurrences is shown below (fig.e 2). About 400 springs and wells plot in 11 temperature ranges; additionally 30 sites are listed as "warm" and 23 as "hot."

Figure 2. Bar graph of temperature vs. number of geothermal occurrences.

Geothermal reservoirs in the northwestern part of the state have generally higher temperatures; these reservoirs are usually interpreted as being related to circulation of ground water to deep levels along faults in a region of higher-than-average heat flow (the Battle Mountain heat flow high). In east-central and southern Nevada, the low- to moderate-temperature geothermal resources are generally believed to be related to regional groundwater circulation in fractured carbonate-rock aquifers. Discharge areas (like warm springs) may be up to several hundred kilometers from the area of recharge, and the waters may have circulated for hundreds to thousands of years to depths of several kilometers. Maximum temperatures attained during this journey could be 100C or higher, but spring temperatures at discharge points are generally less than 65C.

The Eureka heat flow low, a region of less than 1.5 HFU (heat flow units; 41.8 milliWatts per square meter, mWm-2) located in eastern Nye and northwestern Lincoln Counties, is centered on the Nevada portion of a large area of Middle Cambrian to Lower Triassic carbonate rocks (the carbonate rock province). This carbonate rock province underlies southern and eastern Nevada and northeastern Utah (Plume and Carlton, 1988). The Eureka Low is most likely a regional-scale hydrologic feature, representing colder groundwater recharge to regional aquifers.

SUMMARY

Nevada is a large state with sparse but locally concentrated population. It has a wide range in average annual temperature, and thus a wide range in the lower limit of temperatures considered anomalous for geothermal fluids. The state's complex pattern of geology and heat flow results in geothermal resource areas of diverse character located throughout the state.

There have been many studies, both general and specific, on Nevada's geothermal resources (see Bibliography). Considerable data are available on specific geothermal spring and well sites but some remote areas are still poorly understood and information on their geothermal resources are incomplete or possibly inaccurate. There are many accurate and complete water analyses and associated location information for well-studied geothermal areas. However, many remote individual springs and wells throughout the state lack complete analyses, and some lack good location information; in some cases, there is uncertainty about the existence of certain springs. For example, Appendix 1 lists over 50 sites for which the only temperature information is "warm" or "hot."

In Nevada, as in many arid areas of the west, most water (whether thermal or nonthermal) has been put to use. Some nonthermal applications actually require cooling before use. Present and recent past uses of the contained heat of Nevada thermal waters are quite varied (see Appendix 3). However, more such use is feasible if potential developers are well informed and encouraged to be conservative in their use of fossil fuels.

FIGURE 3. Map of Nevada geothermal resource occurrences

FIGURE 3a. Map of Nevada geothermal resource occurrences

FIGURE 3b. Map of Nevada geothermal resource occurrences with major roads

RECOMMENDATIONS

There are many remote geothermal sites for which no complete data set could be found in the sources examined. For completeness, some of these should be visited and sampled but most of them are unlikely to be put to any low-temperature use because of their remoteness. Having a more complete data set would, however, be useful in regional studies, and might result in the discovery of previously unknown higher temperature resources.

No attempt was made during this study to combine trace-element water chemistry data from more than one analysis into a single record. For example, analyses of B, Li, and F may have been reported in a analysis with poor ion balance while the best analysis in terms of major constituents may have been lacking some of the trace-element data. Some of this type of trace- element data could be added to the final database, but it seemed like a poor practice for this original compilation.

Some sources of information on geothermal springs and wells that were not used during this study might be useful to pinpoint previously unknown (especially low-temperature) geothermal sites. However, the mass of data available and its concentration in populated areas (where good information already exists), make searching such data relatively unproductive. Some examples of such available data include the water well records (submitted by well drillers) for the state available from the Nevada Division of Water Resources. These water well records have many errors (especially in location); searching and confirming previously unknown geothermal sites would take considerable effort. Other sources of water data that are likely to have similar potential errors include the analyses of agencies like the Nevada Division of Health, the Nevada Division of Environmental Protection, and the U.S. Environmental Protection Agency. One source of information that might have a higher potential for adding to the geothermal database is the largely confidential files of geothermal exploration companies. Thousands of shallow to moderately deep (100 to 1000 m) geothermal gradient and "slim holes" were drilled in the search for high temperature geothermal resources (for electric power generation) over the last 30 years. This source of geothermal data was suggested by a number of industry representatives at a March 1994 symposium sponsored by the Geothermal Resources Council on the geothermal resources and exploration of the Basin and Range Province. The extent of the data is not presently known.

Finally, increased future use of geothermal energy in low- to moderate-temperature applications will require not only studies that demonstrate the availability of the resource but also dissemination of information (such as case histories) that illustrate the details of these uses. Such case histories should be understandable by the general public, but also make available details of the technical data. Because some uses, such as district heating systems, require considerable front-end investment compared to individual fossil fuel heating units, projects that can bring together several funding sources have a better chance of success.

One task of the study was the identification of geological, geophysical, geochemical, and hydrologic studies that have been done since the last resource assessment. The bibliography is the result of that literature search. There are 907 citations listed in the bibliography; of these, nearly one-half are from the bibliography in Garside and Schilling (1979). This bibliography was nearly exhaustive, at least for published sources, through about 1978. That bibliography was scanned and converted with text-recognition software to a format useable by word-processing software. The references from this 1979 bulletin included general references to the geology of geothermal areas as well as references specific to geothermal resources. The additional references were obtained from a variety of sources; most were entered in the document by hand, rather than taken directly from other digital data sources. Several methods were used to find these additional references. The bibliography for GEOTHERM (Bliss, 1983a) was checked for references not in Garside and Schilling (1979). Additionally, the geothermal files in the Public Information Office of the Nevada Bureau of Mines and Geology were a good source, especially for unpublished reports. My own library of geothermal references was searched, and the CD-ROM for GeoRef (the bibliographic database of the American Geological Institute) was searched for any Nevada geothermal references. A similar search was done of the WolfPAC NALIS library information system (the Northern Nevada Academic Libraries Information System). The Geothermal Resources Council Bulletin and Transactions, and the GeoHeat Center Quarterly Bulletin were also scanned for any Nevada references.


Go to top of document.