U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5139

Groundwater Chemistry in the Vicinity of the Puna 

Geothermal Venture Power Plant, Hawai‘i, After Two 

Decades of Production
COVER

Groundwater pumps at the Kapoho Shaft, Puna District, Hawaiʻi. Photograph by Deborah Bergfeld, U.S. Geological Survey.
Groundwater Chemistry in the Vicinity of 

the Puna Geothermal Venture Power Plant, 

Hawai‘i, After Two Decades of Production

By W.C. Evans, D. Bergfeld, A.J. Sutton, R.C. Lee, and T.D. Lorenson

Scientific Investigations Report 2015–5139

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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must be secured from the copyright owner.

Suggested citation:

Evans, W.C., Bergfeld, D., Sutton, A.J., Lee, R.C., and Lorenson, T.D., 2015, Groundwater chemistry in 

the vicinity of the Puna Geothermal Venture power plant, Hawai‘i, after two decades of production: U.S. 

Geological Survey Scientific Investigations Report 2015-5139, 26 p., http://dx.doi.org/10.3133/sir20155139.

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155139
iii

Contents

Acknowledgments .......................................................................................................................................................... iii

Abstract ..........................................................................................................................................................................1

Introduction......................................................................................................................................................................1

Geothermal Development and Operations......................................................................................................................3

Methods ..........................................................................................................................................................................3

Results ..........................................................................................................................................................................4

Water Chemistry ....................................................................................................................................................4

Gas Chemistry .......................................................................................................................................................7

Pentane in Water Samples .................................................................................................................................11

Isopropanol .........................................................................................................................................................12

Injectate Composition Over Time ..................................................................................................................................13

Pentane and Isopropanol.....................................................................................................................................13

Water and Gas Composition of Injectate .............................................................................................................15

Groundwater Chemistry.................................................................................................................................................16

Springs ..............................................................................................................................................................19

Groundwater Wells ..............................................................................................................................................19

Thermal Wells......................................................................................................................................................20

Stable Isotopes ....................................................................................................................................................21

Conclusions...................................................................................................................................................................24

References Cited...........................................................................................................................................................25

Figures

 1. Map of study area showing sample locations and features of interest ..................................................................2

 2. Concentration of alkane hydrocarbons in gas samples from the steam and injectate pipelines 

at Puna Geothermal Venture ......................................................................................................................10

 3. Concentration of alkane hydrocarbons in both wells where pentane was detected, MW-2 and Keonepoko 

Nui #2..........................................................................................................................................................12

 4. Concentration of pentane in the noncondensable gas line at Puna Geothermal Venture, as reported 

in Hawai‘i State Department of Health records for 2001, 2004, and 2007–14............................................13

 5. Concentration of Na and SO4 versus Cl in injectate over time, based on Hawai‘i State Department of 

Health records.............................................................................................................................................15

 6. Concentration of several major chemical species in the injectate over time, based on Hawai‘i State 

Department of Health records.....................................................................................................................16

 7. Concentration of gas species in the noncondensable gas line over time, based on Hawai‘i State 

Department of Health records for 1995, 1998, 2000, 2001, 2004, and 2007–14........................................16

 8. Concentration of six chemical species relative to Cl............................................................................................17

 9. Expanded view of figure 8 highlighting results from particular wells ....................................................................18

10. Temperature and concentration of several major species in MW-2 over time based on Hawai‘i State 

Department of Health records.....................................................................................................................21

11. Data for thermal groundwater wells added to data of figure 8, concentrations of selected chemical 

species versus Cl........................................................................................................................................22

12. Stable isotope results...........................................................................................................................................23
iv

Tables

1. Location and type of features sampled and results of on-site measurements ...........................5

2. Concentrations of major and minor dissolved species in milligrams per liter ........................... 6

3. Concentrations of trace metals, NH3, and H2S, in milligrams per liter, and stable isotopes 

of water, in per mil ........................................................................................................................8

4. Composition (in volume percent) of gas bubbles in samples collected from the Puna 

Geothermal Venture steam and injectate lines .....................................................................10

5. Concentrations of dissolved hydrocarbons in micromoles per kilogram for all samples 

containing a hydrocarbon larger than methane....................................................................11

6. Volatile organic compounds measured in water samples ............................................................14

Conversion Factors

International System of Units to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Volume

liter (L) 0.2642 gallon (gal)

Flow rate

meter per day (m/d) 3.281 foot per day (ft/d)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound, avoirdupois (lb)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as °C = (°F – 32) / 1.8.

Datum

•	 Vertical coordinate information is referenced to the North American Vertical Datum of 1983 (NAD83).

•	 Horizontal coordinate information is referenced to the North American Vertical Datum of 1983 (NAD83).

•	 Altitude, as used in this report, refers to distance above the vertical datum. 

Supplemental Information

•	 Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C).

•	 Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L), micrograms 

per liter (μg/L), or micromoles per kilogram (μmol/kg), where a kilogram of water is nearly equal to a liter.

•	 Concentrations of chemical constituents in gas are given in either volume percent or in parts-per-million by 

volume.

•	 Results for measurements of stable isotopes of water are expressed as the relative difference in parts per 

thousand (per mil) in the ratio of the number of the less abundant isotope (D or 18O) to the number of the more 

abundant isotope (H or 16O) with respect to Vienna Standard Mean Ocean Water (VSMOW).
v

Acknowledgments

Jim Kauahikaua (former U.S. Geological Survey [USGS] Scientist-In-Charge of the 

Hawaiian Volcano Observatory) encouraged us to undertake this study. Jeff Melrose (consultant 

for the County of Hawai‘i) was influential in moving the study forward and in arranging

logistics. Kawika Uyehara and Keith Okamoto (County Department of Water Supply [DWS]) 

helped arrange sample collection at public-supply wells, including the Kapoho Shaft, and 

provided the DWS records of water chemistry. Mark Prescott and Sam Martoni arranged 

sample collection at the private wells. Mike Kaleikini (Ormat) provided helpful information 

about the Puna Geothermal Venture plant, fluid flowpaths, additives used, and spreadsheets of

monitoring data, and also arranged for our sample collection at the plant, which relied heavily 

on assistance from Gary Dahl (Ormat). Bob Whittier (Hawai‘i State Department of Health 

[HDOH], Safe Drinking Water Branch) provided a huge amount of background information on 

past and present monitoring programs; Norris Uehara and staff in that office patiently scanned

hundreds of HDOH analytical records and sent them as pdf files. Don Thomas (University of

Hawai‘i) and Thomas Travis provided helpful feedback on the study objectives, as did Steve 

Gingerich and Jennifer Lewicki (USGS). Mark Huebner (USGS) transcribed hard-copy data 

into electronic spreadsheets and conducted the anion analyses. Steve Ingebritsen (USGS) and 

Don Thomas (University of Hawai‘i) provided helpful reviews of the draft report.

Groundwater Chemistry in the Vicinity of the Puna 

Geothermal Venture Power Plant, Hawai‘i, After Two 

Decades of Production

By W.C. Evans, D. Bergfeld, A.J. Sutton, R.C. Lee, and T.D. Lorenson

Abstract

We report chemical data for selected shallow wells 

and coastal springs that were sampled in 2014 to determine 

whether geothermal power production in the Puna area over 

the past two decades has affected the characteristics of regional 

groundwater. The samples were analyzed for major and minor 

chemical species, trace metals of environmental concern, 

stable isotopes of water, and two organic compounds (pentane 

and isopropanol) that are injected into the deep geothermal 

reservoir at the power plant. Isopropanol was not detected in 

any of the groundwaters; confirmed detection of pentane was

restricted to one monitoring well near the power plant at a low 

concentration not indicative of source. Thus, neither organic 

compound linked geothermal operations to groundwater 

contamination, though chemical stability and transport velocity 

questions exist for both tracers. Based on our chemical analysis

of geothermal fluid at the power plant and on many similar

results from commercially analyzed samples, we could not 

show that geothermal constituents in the groundwaters we 

sampled came from the commercially developed reservoir. 

Our data are consistent with a long-held view that heat moves 

by conduction from the geothermal reservoir into shallow 

groundwaters through a zone of low permeability rock that 

blocks passage of geothermal water. The data do not rule out 

all impacts of geothermal production on groundwater. Removal 

of heat during production, for example, may be responsible for 

minor changes that have occurred in some groundwater over 

time, such as the decline in temperature of one monitoring well 

near the power plant. Such indirect impacts are much harder 

to assess, but point out the need for an ongoing groundwater 

monitoring program that should include the coastal springs 

down-gradient from the power plant.

Introduction

The lower East Rift Zone (LERZ) of Kīlauea volcano

on the island of Hawai‘i (fig. 1) hosts a geothermal reservoir

at depths near 2 km, and the hot fluids have been exploited

for power generation since 1981 (Thomas, 1990). An early 

and on-going concern about geothermal development is the 

potential impact on local groundwater (for example, Iovenitti, 

1990). To address this concern, a major scientific effort was

carried out in the early days of well drilling and development 

to characterize existing hydrologic conditions in the region and 

delineate potential vulnerabilities (Iovenitti, 1990; Ingebritsen 

and Scholl, 1993; Sorey and Colvard, 1994; Janik and others, 

1994; Gingerich, 1995; Scholl and others, 1995). The basaltic 

lava flows from Kīlauea and its rift zone vents provide highly

permeable flow paths for groundwater, but vertical dikes

within the upper rift zone constitute effective barriers. Thus, 

groundwater north of the rift zone flows northeast toward

the ocean. Groundwater within the rift zone flows generally

down rift toward Cape Kumukahi, but some outflow into the

permeable lava flows to the south is suspected along the lower

part of the rift where the concentration of impermeable dikes 

decreases (Takasaki, 1993; Gingerich, 1995). Several shallow 

groundwater wells in the LERZ are tens of degrees warmer 

than ambient temperatures, and brackish springs along the 

southeast coast of the island, down the hydraulic gradient from 

the LERZ, are several degrees warmer than background. Thus, 

some type of hydrologic connection between the geothermal 

and groundwater systems is indicated. On the other hand, the 

warm groundwaters lack some of the distinctive features in 

the chemical composition of the deep geothermal water. This 

fact and other information from drill cores and temperature 

profiles in deep wells led many investigators to conclude that

direct leakage of water from the geothermal reservoir into 

groundwater was insignificant (Janik and others, 1994; Sorey

and Colvard, 1994). The warm temperatures in groundwater 

wells and coastal springs were commonly attributed to 

conductive heat transfer. Although some direct leakage of 

reservoir steam and sulfur-rich gas was proposed to account for 

the elevated temperatures and sulfate concentrations in shallow 

monitoring wells in the LERZ (Janik and others, 1994; Sorey 

and Colvard, 1994), a discharge pathway for hot water from the 

reservoir was not identified.

The large-scale scientific investigations of the

hydrogeology and groundwater chemistry at Kīlauea and the
2 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

LERZ in the early 1990s established the baseline geochemical 

conditions at about the time that Puna Geothermal Venture 

(PGV) began producing power from new wells in place 

of the original HGP-A well that had been used throughout 

most of the 1980s. A follow-up monitoring program was 

recommended (Sorey and Colvard, 1994) for detection of 

any impacts from producing the hot reservoir fluids or from

injecting the cooled water back into the deep reservoir. As a 

condition of the underground injection control permit (UH1529), PGV must conduct a hydrologic monitoring program. 

Under this program, several shallow wells, thermal and 

nonthermal, were sampled quarterly for chemical analysis,

and the results reported to the State of Hawai‘i Department of 

Health (HDOH) from 1991 through 2000. Beginning in 2001, 

the number of wells sampled each round by PGV was reduced 

to two thermal wells near the power plant, MW-2 and either 

MW-1 or MW-3, which are adjacent wells that tap similar 

depths. The County of Hawai‘i Department of Water Supply 

(DWS) routinely monitors nonthermal wells that are used for 

public supply. Coastal springs have gone largely unmonitored, 

and thus the full, cumulative impact of over 20 years of 

geothermal production/injection on this large groundwater 

system is unknown. These springs, sometimes referred to as 

anchialine pools, are brackish and unsuitable for drinking or 

agricultural use, but are recognized as important habitats in the 

near-shore environment (Foote, 2005). Recently (September 

2013), a local public health assessment study group headed by 

Dr. Peter S. Adler recommended that the County commission 

a study to re-evaluate the effects of geothermal operations on 

local groundwater and the near-ocean environment (Adler, 

2013). Our study was proposed in response to a County of 

Hawai‘i request.

The work was planned to be a pilot study of fairly 

limited scope: collect enough samples to obtain representative 

coverage of the various types of groundwater (for example, 

deep geothermal water, warm saline spring water, publicsupply water) rather than attempt to sample every available 

feature. The results could then be used to help determine 

the need for a bigger, more comprehensive study. None of 

the water-supply wells currently in use are obviously downgradient from the PGV plant, but some have static water levels 

at lower elevations than those reported for the geothermal 

wells. Thus, sample coverage extended nearly 10 km away 

from PGV to help detect any impact of development. Some 

of the intended target wells down-gradient from PGV were 

found unsuitable for sampling because of access issues or 

nonfunctional pumps. Thus more emphasis was placed on 

sampling the coastal springs to characterize ground-water 

most likely to be impacted by geothermal operations.

Sites sampled in April–May 2014 included a pair of 

public supply wells on either side of the LERZ, three private 

water-supply wells north of the LERZ, six coastal springs 

Figure 1. Map of study area 

showing sample locations and 

features of interest. Sample 

numbers simplified from table 

1 (for example, PG14-01 is 1). 

Coastal springs and ponds are 

shown as stars, and wells are 

shown as circles (in red for 

the production/injection wells 

at Puna Geothermal Venture). 

The lower East Rift Zone 

(LERZ) of Kīlauea volcano 

lies between the dashed lines 

(after Janik and others, 1994). 

18

10 PGV 11

13

14 12

24

17

5, 20 6

16, 21, 22

15, 25

3,4

8, 9

1, 2, 23

19

7

PACIFIC OCEAN

Pāhoa

Pohoiki

130

130

132

132

137

Cape

Kumukahi

Lower East Rift Zone

19°30’

19°25’

154°55’ 154°50’

0

0

1 2 3

1 2 3

MILES 

KILOMETERS 

Coastal springs and ponds

Wells

Production/injection wells

at Puna Geothermal Venture

EXPLANATION
Methods 3

and pools, and the three warm monitoring wells near the 

power plant. The steam and residual brine from a geothermal 

production well (KS-5), and the combined injectate stream (at 

Pad A) were also sampled. Additional samples were collected 

in December 2014 from two public supply wells (one unused) 

within or adjacent to the LERZ, and four coastal springs, two 

of which had been sampled previously in April–May 2014. 

One of the public supply wells north of the LERZ was also 

resampled. The water samples were analyzed for a suite of 

inorganic constituents including several heavy metals, but a 

unique feature of our study was the high sensitivity analysis

of pentane and isopropanol. These two organic compounds are 

added to the injectate stream within the power plant and could 

serve as definitive tracers of the geothermal fluid. Although

degradation of natural organic matter in any aquifer can

release a wide range of organic compounds into groundwater, 

especially at elevated temperatures, neither pentane nor 

isopropanol should be present at more than trace levels in 

groundwaters that are uncontaminated by PGV injectate. 

Current groundwater monitoring protocol does not include 

analysis of these compounds.

This report presents chemical analyses of the samples 

discussed above. Selected chemical data gathered during 

the past ~20 years of monitoring conducted or overseen by 

the HDOH and DWS are also presented, and the combined 

dataset is evaluated to assess the likelihood that geothermal 

development is affecting the regional groundwater.

Geothermal Development and 

Operations

Exploratory drilling in the 1960s established the 

existence of hot water within the LERZ to the south and 

east of the community of Pāhoa (Thomas, 1987). The first

productive well (HGP-A) was completed in 1976 to a depth 

of nearly 2 km. After a series of tests, this well was used for 

power production beginning in 1981 and ending in 1989 

(Thomas, 1987, 1990). During the 1980s and early 1990s, 

PGV or its predecessor companies drilled the nearby Kapoho 

State wells (KS series), some reaching depths in excess of 

2.5 km, and began producing power in May 1993 (Sorey 

and Colvard, 1994). The PGV plant has been in operation 

since that time and has continued well drilling operations; for 

example, KS-13 in 2005 (Teplow and others, 2009)

Unlike the HGP-A installation, the PGV plant does not 

use infiltration ponds for liquids or engineered abatement

for the produced gases under normal conditions, though 

abatement of H2S is carried out during emergencies that cause 

steam release to the atmosphere. The plant does incorporate a 

steam flash process where steam and gases separate from the

residual boiled water (brine). The high-pressure steam drives 

a turbine in the generating system, but condensation of the 

steam takes place downstream in a heat exchanger where the 

heat is used to boil liquid pentane. The condensed steam, and

ultimately the noncondensable gases such as CO2, H2, N2, and 

H2S, are mixed back into the brine flow, and the recombined

fluid is injected in its entirety back into the deep geothermal

reservoir. The pentane vapor from the heat exchanger drives 

an additional turbine, is condensed back to liquid, and is

ultimately returned to the heat exchanger. Thus, according to 

plant design, no geothermal gases or fluids are intentionally

released to the environment, and the pentane circulates 

through the plant in a closed loop that is separate from the 

water and steam. In practice, a small amount of pentane does 

enter the flow stream and is injected into the reservoir.

Because steam and gas separate from the residual brine 

upstream from the sampling ports, both the steam and brine 

pipelines were sampled in order to completely characterize 

the reservoir fluid tapped by the plant. Our sample from the

injectate pipeline was collected downstream from the point 

where steam, gas, and brine are recombined and just prior to 

the point of injection back into the reservoir. The injectate 

sample is particularly important to this study because it 

contains all the gases and dissolved species that are present 

in the produced reservoir fluid. It would also contain any

additives (for example, isopropanol) and other compounds 

derived from plant operations that enter the flow system.

Geothermal water that enters the local groundwater system, 

either through permeable flowpaths out of the reservoir or

through leaks in the well casings, would most likely resemble 

the injectate in terms of chemistry. Distinguishing the 

composition of the injectate from that of other thermal fluid(s)

long known to be present in the warm groundwaters and 

coastal springs is an important part of evaluating connectivity 

between the developed geothermal system and groundwater, a 

key step in assessing impact. 

Methods

The location of each sampled feature was determined 

to within a few meters with a hand-held global positioning 

system (GPS). Water temperature, specific conductance, pH,

and dissolved oxygen (DO) were measured on-site using handheld meters. At springs, the measurements were made near 

the water surface. For wells, a continuous flow of pumped

water from the wellhead was directed into a plastic container 

housing the measuring probes. In all cases, the pH meter was 

calibrated with buffer solutions at the temperature of the water. 

Water samples were collected using standard methods 

that have been described in detail elsewhere (Bergfeld and 

others, 2013). Briefly, water collected for chemical analysis

was filtered on-site into plastic bottles using a plastic syringe

and 0.45-micrometer (μm) filters. The bottle for cation analysis

was acidified to pH 2 with nitric acid. Glass bottles were filled

with unfiltered water for alkalinity determinations, and analysis

of stable isotopes of hydrogen and oxygen. Water was collected 

for pentane analysis by two different methods. In one method, 

water was drawn up into a 140-cubic centimeter (cc) syringe 

and injected into a pre-evacuated glass bottle (DIC bottle) 
4 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

through a septum port, leaving a headspace volume of about 

15–25 cc in the bottle. A description of these bottles is provided 

in Evans and others (2002). The second method made use of 

200-cc serum bottles, which were filled from the bottom by

flowing in water through flexible tubing. After allowing 600 cc

of water to overflow and flush the bottle, the tubing was slowly

withdrawn and a rubber septum was inserted into the top of 

the bottle and crimped in place with a metal band. Samples 

for isopropanol analysis were collected in triplicate into 40-cc 

amber glass bottles fitted with screw-on septa caps. Bottles

were filled to exclude any bubbles as described in Wilde and

others (2004). Isopropanol samples were refrigerated or stored 

on ice between collection and analysis.

Sampling of geothermal fluids from the pipelines requires

precooling to prevent extensive loss of steam and gas as the 

hot fluids are depressurized. Cooling was accomplished at

the PGV plant by collecting the samples through a cooling 

jacket flushed by a steady stream of cold water, that resulted

in collection temperatures of about 30 °C. Gas solubility 

increases as temperature decreases, and for sampling the brine 

pipeline, this level of cooling was sufficient to produce a flow

of bubble-free water at the collection point. Bubble-free water 

was initially obtained from the injectate pipeline but could not 

be maintained throughout sampling due to the added gases in 

the injectate. The small bubbles that formed in the sampling 

line were captured into an inverted funnel and collected in a 

pre-evacuated glass bulb. As anticipated, the steam line was 

so gas rich that the water flow contained a steady stream of

bubbles that were also collected into a glass bulb. Two other 

special sampling procedures (Presser and Barnes, 1974) were 

used on the geothermal fluids: water filtered into glass bottles

was preserved for H2S analysis with zinc acetate and sodium 

hydroxide, and aliquots of the brine and injectate were fielddiluted with deionized water to prevent polymerization of silica 

prior to analysis.

Samples collected for alkalinity and H2S were titrated at the 

end of each sampling day. Standardized solutions of H2SO4 (for 

alkalinity) and Na2S2O3 (for total sulfide) were used following

the electrometric and iodometric procedures, respectively, 

described in Presser and Barnes (1974). Other water samples 

and gases were analyzed at several U.S. Geological Survey 

(USGS) laboratories. Chemical analyses were conducted 

at USGS in Menlo Park, Calif. Gas samples from the PGV 

plant were analyzed on gas chromatographs in two different 

USGS labs following published methods for free gases (Evans 

and others, 1981) and headspace gases (Bergfeld and others, 

2011). One gas chromatograph was equipped with a thermal

conductivity detector (TCD) responsive to all gas species; the 

other had an additional flame ionization detector (FID), highly

sensitive but only responsive to flammable gas species, in this

case, hydrocarbons. Water samples were analyzed for anions 

by ion chromatography and for cations by argon plasma optical 

emission spectrometry. Stable isotope analyses of the waters were 

performed by mass spectrometry at the USGS Reston Stable 

Isotope Laboratory (Revesz and Coplen, 2008a,b). Isopropanol 

analyses were conducted at the USGS National Water Quality 

Laboratory in Denver Colo. using a volatile organic compound 

(VOC) heated purge and trap method on Schedule 4437 that 

detects 37 other VOCs. The VOC analysis was performed on 

samples from PG14-01 to PG14-19 and PG14-24.

Dissolved pentane samples were also analyzed at 

two different USGS labs in Menlo Park, Calif. Pentane 

samples collected in DIC tubes were analyzed on a gas 

chromatograph equipped with both a TCD and a FID using a

slight modification of the headspace gas method of Bergfeld

and others (2011). This method yields results for a large suite 

of nonhydrocarbon and hydrocarbon gas species, including 

pentane. The gas in the equilibrated headspace was expanded

to a pre-evacuated inlet system and injected into the gas 

chromatograph. From the known volumes of the headspace 

and inlet system, and the measured injection pressure, the 

concentrations of the gases that were originally dissolved in 

the water sample can be calculated from their individual Henry 

law solubilities (Wilhelm and others, 1977; Chapoy and others, 

2008). Samples collected in serum bottles were analyzed by 

equilibrating 100 cc of water with 40 cc of helium and injecting

the equilibrated gas into a gas chromatograph equipped with

an FID. This method, adapted from McAuliffe (1971), has 

excellent sensitivity for many alkanes including pentane.

Results

Water Chemistry

Sampled features are listed in table 1 with GPS locations 

and results of measurements made at the time of sampling. 

Many of these features were also sampled in the early 1990s by 

Janik and others (1994), who included chemical analyses from 

even earlier studies in their data tables. For features listed in 

Janik and others (1994), the ID number used by those authors, 

the number of analyses they report, and the years spanned by 

those analyses are given. Specific conductance increases with

ionic strength and is a qualitative measure of salinity. Water

supply wells all have values below 1,200 microsiemens per 

centimeter (mS/cm); coastal springs and geothermal fluids

have much higher values due to the greater influence of

seawater, which for reference has a specific conductance of

about 50,000 mS/cm. Dissolved oxygen in active water supply 

wells is at or near concentrations expected for local rainwater, 

showing that dissolved oxygen is largely conserved in the 

shallow groundwater from recharge to withdrawal. Dissolved 

oxygen is somewhat depleted in warm waters, such as the 

monitoring wells and most springs. The PGV fluids were all

expected to be oxygen-free; the tiny amounts of dissolved 

oxygen detected may reflect the fact that air could not be

completely excluded from the container housing the pH and 

oxygen probes. Note that the temperature reported for well 

samples is that of the water in the collection container, not 

actual down-hole temperature.
Results 5

Table 1. Location and type of features sampled and results of on-site measurements. Last 4 columns give the site ID number used in 

Janik and others (1994), the number of samples they report for each site, and the years spanned by those samples. 

[SW, supply well; MW, monitoring well; IW, injection well; PW, production well; B, brine pipeline; S, steam pipeline; °C, degrees Celsius; μS/cm, microsiemens per

centimeter at 25 degrees Celsius; DO, dissolved oxygen; mg/L, milligrams per liter; nm, not measured]

Sample

number Location Date Type Temp,in °C

Sp. Cond.

μS/cm

DO

in mg/L pH EastingNAD 83

Northing

NAD 83 Janik ID

No. of 

samplesEarliest Latest

PG14-01 Keonepoko Nui Well #2 04/28/14 SW 19.6 118 9.1 7.76 293816 2158979

PG14-02 Keonepoko Nui Well #1 04/28/14 SW 19.4 121 9.0 7.80 293816 2159010 3188-01 2 1991 1992

PG14-03 Keauohana #1 04/28/14 SW 23.1 348 8.8 8.24 295002 2147670 2487-01 8 1972 1992

PG14-04 Keauohana #2 04/28/14 SW 23.3 598 8.6 8.10 295012 2147673 2487-02 1 1974 1974

PG14-05 Pohoiki Pond 04/29/14 Spring 35.0 13270 6.5 7.66 306493 2152557 2780-S1 5 1974 1992

PG14-06 Allison Spring 04/29/14 Spring 31.7 17720 5.5 7.28 307173 2153020 2780-S2 1 1974 1974

PG14-07 Hawaiian Shores Well 04/29/14 SW 21.4 202 8.4 7.68 297887 2159638 3185-02 2 1972 1974

PG14-08 Hawaiian Beaches 

Well #1

04/29/14 SW 21.9 159 8.6 7.61 297480 2159231 3185-01 4 1962 1992

PG14-09 Hawaiian Beaches 

Well #2

04/29/14 SW 22.7 169 8.5 7.65 297498 2159247

PG14-10 10-P-5 (MW-1) 04/30/14 MW 39.5 620 4.8 7.45 301459 2155283 2983-01 6 1991 1992

PG14-11 10-P-7 (MW-3) 04/30/14 MW 40.4 622 4.8 7.44 301421 2155350 2883-02 1 1992 1992

PG14-12 MW-2 04/30/14 MW 29.7 2770 0.7 8.08 301994 2154441 2883-07 7 1991 1993

PG14-13 Pad A (Injectate) 04/30/14 IW 32.8 22800 0.4 4.05 301606 2154684

PG14-14B KS-5 Brine 04/30/14 PW_B 24.6 26100 0.7 6.59 301407 2154528

PG14-14S KS-5 Steam 04/30/14 PW_S 24.1 72 0.0 4.03 301407 2154528

PG14-15 Vacation Land Roney 05/01/14 Spring 29.7 10040 6.2 7.59 308750 2156177 2979-S1 1 1991 1991

PG14-16 Ahala Nui County Park 05/01/14 Spring 34.1 14890 5.1 7.33 307667 2153731

PG14-17 Keahialaka Pond 05/01/14 Spring1 28.6 8990 6.9 7.24 306132 2152069

PG14-18 Lighthouse Spring 05/01/14 Spring 26.6 7920 8.6 7.36 310185 2158715 3178-S1 2 1991 1992

PG14-19 Kapoho Shaft 12/09/14 SW2 25.6 1086 2.6 6.87 307280 2157350 3080-02 5 1974 1975

PG14-20 Pohoiki Pond 12/09/14 Spring 35.7 13970 nm 7.32 306495 2152557 2780-S1 5 1974 1992

PG14-21 Ahala Nui County 

Park north

12/09/14 Spring 34.0 15400 nm 7.29 307669 2153740

PG14-22 Ahala Nui County 

Park south

12/09/14 Spring 34.3 18020 nm 7.24 307655 2153722

PG14-23 Keonepoko Nui Well #2 12/10/14 SW 19.9 120 8.3 6.92 293816 2158986

PG14-24 Pāhoa Well #2 12/10/14 SW 23.3 133 7.7 7.73 295977 2155842

PG14-25 Vacation Land Roney 12/10/14 Spring 31.0 10390 6.5 7.97 308750 2156177 2979-S1 1 1991 1991

1

Keahialaka Pond had no visible point of water inflow.

2

No longer in use.
6 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

Table 2. Concentrations of major and minor dissolved species in milligrams per liter (mg/L). Total alkalinity is expressed as 

HCO3; NO3 expressed as N; PO4 expressed as P. Balance is calculated as 2(C–A)/(C+A) in percent, where C represents the 

cations and A represents the anions in milliequivalents per liter (meq/L). 

[nm, not measured]

Sample

number Location Bmg/L

Ba

mg/L

Br

mg/L

Ca

mg/L

Cl

mg/L

F

mg/L

HCO3

mg/L

K

mg/L

Li

mg/L

PG14-01 Keonepoko Nui Well #2 0.009 0.002 <0.01 7.07 4.02 0.16 56 2.6 <0.001

PG14-02 Keonepoko Nui Well #1 0.008 0.002 <0.01 7.31 4.16 0.17 56 2.5 <0.001

PG14-03 Keauohana #1 0.028 0.003 0.24 8.78 75 0.21 32 3.7 0.005

PG14-04 Keauohana #2 0.039 0.004 0.49 12.4 150 0.24 34 6.2 0.004

PG14-05 Pohoiki Pond 1.17 <0.025 14.5 112 4,210 1.0 52 103 0.10

PG14-06 Allison Spring 1.50 <0.025 19.0 136 5,500 1.0 55 140 0.13

PG14-07 Hawaiian Shores Well 0.013 0.002 0.11 5.24 33.2 0.21 38 3.6 0.001

PG14-08 Hawaiian Beaches Well #1 0.012 0.002 0.06 4.73 20.6 0.22 40 3.4 0.001

PG14-09 Hawaiian Beaches Well #2 0.013 0.002 0.07 5.14 23.0 0.22 38 3.5 0.002

PG14-10 10-P-5 (MW-1) 0.28 0.007 0.06 27.4 22.0 0.38 30 12.1 0.025

PG14-11 10-P-7 (MW-3) 0.28 0.006 0.06 26.8 23.0 0.38 32 12.0 0.024

PG14-12 MW-2 0.29 0.014 2.62 41 750 0.27 52 22.8 0.02

PG14-13 Pad A (Injectate) 4.6 3.7 27.0 173 7,950 1.0 nm 893 2.0

PG14-14B KS-5 Brine 6.0 3.0 30.0 147 9,120 1.0 8 1,030 2.2

PG14-14S KS-5 Steam 0.126 0.006 0.04 0.38 14.1 0.01 nm 2.0 0.003

PG14-15 Vacation Land Roney 0.95 <0.013 11.0 90 3,130 1.0 48 83.4 0.08

PG14-16 Ahala Nui County Park 1.41 <0.025 16.5 134 4,840 1.0 49 135 0.15

PG14-17 Keahialaka Pond 0.75 <0.013 9.5 66 2,800 0.50 49 62.7 0.04

PG14-18 Lighthouse Spring 0.68 <0.013 8.3 78 2,410 0.75 46 58.7 0.05

PG14-19 Kapoho Shaft 0.081 0.007 0.35 75 128 0.23 429 8.2 <0.002

PG14-20 Pohoiki Pond 1.50 <0.041 15.5 121 4,450 0.95 64 104 0.065

PG14-21 Ahala Nui County Park north 1.78 <0.041 18.0 141 5,200 1.0 59 136 0.13

PG14-22 Ahala Nui County Park south 1.72 <0.041 20.5 152 5,850 1.0 61 146 0.14

PG14-23 Keonepoko Nui Well #2 0.012 0.002 <0.01 6.9 4.1 0.18 59 2.5 <0.001

PG14-24 Pāhoa Well #2 0.023 0.002 0.010 4.2 4.8 0.29 54 3.4 0.001

PG14-25 Vacation Land Roney 1.17 <0.021 11.5 101 3,220 1.2 58 87 0.10

Concentrations of the major and minor dissolved species 

are reported in table 2. Sodium is the dominant cation in all 

of the waters and chloride the dominant anion in the coastal 

springs and PGV fluids, reflecting the influence of seawater.

Bicarbonate (HCO3) is the dominant anion in some of the 

water supply wells. Several species, such as B, K, Li, Rb, and 

SiO2, are notably enriched in the PGV injectate and brine, 

while Mg is nearly absent. This pattern is a nearly universal 

characteristic of high-temperature geothermal systems 

worldwide. SiO2 values in field-diluted PGV samples were

within 5 percent of the nondiluted values, indicating that 

polymerization had not reduced SiO2 concentrations in the 

undiluted samples. The charge balance between cations and 

anions is a qualitative measure of analytical error and is less

than 5 percent for most of the samples. The balance exceeds 

10 percent only for the steam condensate, which is very dilute 

and subject to larger analytical errors.

Trace elements, including several metals of 

environmental concern, the stable isotopes of water, and NH3

and H2S concentrations in the PGV samples are reported in 

table 3. In general, trace metal levels are low in all of the 

waters, including the PGV fluids, as pointed out by Thomas

(1990). Concentrations of arsenic in the PGV fluids and in

some springs exceed the drinking water standard but are 

actually low in comparison to geothermal fluid compositions

worldwide, which often contain more than 1 milligram 

per liter (mg/L). The iodometric sulfide titration measures

all reduced sulfur species (HS-, S2O3

-

, etc.), but the nearly 
Results 7

Table 2. —Continued.

Sample

number Location Mgmg/L

Na

mg/L

NO3

mg/L

PO4

mg/L

Rb

mg/L

SiO2

mg/L

SO4

mg/L

Sr

mg/L

TDS

mg/L

Balance

%

PG14-01 Keonepoko Nui Well #2 4.66 9.78 0.25 0.08 <0.01 53 4.5 0.029 135 7.3

PG14-02 Keonepoko Nui Well #1 4.80 9.89 0.26 0.07 <0.01 52 4.7 0.030 139 8.6

PG14-03 Keauohana #1 3.99 50.4 0.27 0.08 <0.01 50 14.1 0.046 239 3.3

PG14-04 Keauohana #2 7.90 86.5 0.24 0.05 <0.02 51 23.7 0.080 367 –2.1

PG14-05 Pohoiki Pond 253 2,370 1.5 <0.5 <0.25 89 610 1.63 7820 –0.2

PG14-06 Allison Spring 321 3,080 1.5 <0.5 <0.25 88 780 2.05 10,100 –1.0

PG14-07 Hawaiian Shores Well 5.66 23.4 0.26 0.06 <0.01 56 7.8 0.031 174 5.3

PG14-08 Hawaiian Beaches Well #1 4.12 18.1 0.25 0.07 <0.01 58 6.4 0.025 156 4.2

PG14-09 Hawaiian Beaches Well #2 4.42 19.6 0.25 0.06 <0.01 59 6.7 0.026 160 8.9

PG14-10 10-P-5 (MW-1) 14.6 67.4 0.26 <0.02 0.027 106 218 0.095 511 –2.0

PG14-11 10-P-7 (MW-3) 14.5 68.0 0.20 <0.02 0.026 106 220 0.096 513 –2.9

PG14-12 MW-2 29.3 460 <0.01 <0.01 <0.05 62 136 0.34 1560 0.9

PG14-13 Pad A (Injectate) 0.2 4,420 7.0 1.0 2.36 597 17.0 5.17 14,100 –0.3

PG14-14B KS-5 Brine 0.1 5,180 2.0 <1 2.74 714 25.0 4.40 16,300 0.5

PG14-14S KS-5 Steam 0.004 9.4 <0.01 <0.01 <0.01 2 0.5 0.010 29 16.5

PG14-15 Vacation Land Roney 188 1,770 1.0 <0.5 <0.13 73 515 1.27 5,910 –1.1

PG14-16 Ahala Nui County Park 277 2,740 1.5 <0.5 <0.25 97 675 1.90 8,970 0.6

PG14-17 Keahialaka Pond 172 1,580 1.5 <0.25 <0.13 61 408 1.01 5,210 –0.5

PG14-18 Lighthouse Spring 152 1,380 0.50 <0.25 <0.13 60 393 1.05 4,590 1.3

PG14-19 Kapoho Shaft 40 94.8 2.4 0.09 <0.02 60 16.4 0.29 854 3.0

PG14-20 Pohoiki Pond 263 2,430 1.5 <0.5 <0.41 91 640 1.71 8,180 –2.9

PG14-21 Ahala Nui County Park north 293 2,850 1.5 <0.5 <0.41 97 715 2.01 9,510 –2.6

PG14-22 Ahala Nui County Park south 340 3,150 0.50 <0.5 <0.41 92 815 2.25 10,600 –3.7

PG14-23 Keonepoko Nui Well #2 4.55 9.4 0.22 0.06 <0.01 52 4.5 0.027 143 0.2

PG14-24 Pāhoa Well #2 3.10 16.5 <0.01 0.05 <0.01 57 12.2 0.020 155 –1.7

PG14-25 Vacation Land Roney 204 1,840 1.0 <0.5 <0.21 81 525 1.40 6,130 1.3

complete partitioning of reduced sulfur into the steam and gas 

phase—510 mg/L versus 9 mg/L in the brine—shows that the 

primary reduced sulfur species is H2S.

Gas Chemistry

The gas bubbles collected from the PGV steam and 

injectate lines are somewhat similar in bulk composition (table 

4). This is expected, given that between these two sampling 

ports PGV pumps the gas from the steam line into the injectate 

line. Major constituents in both samples include H2, CO2 and 

H2S, all of which are commonly found in geothermal systems. 

The N2 and Ar are likely derived from the atmosphere, in part 

from air dissolved in rainwater or seawater that ultimately 

recharges the geothermal reservoir. The presence of oxygen 

at low levels indicates that only a small amount of air 

contamination occurred during sample collection.

The noticeable differences in composition between the 

steam and injectate samples (table 4) mainly reflect variation

in the solubility of the individual gas species and the volume 

ratio between gas bubbles and water in the sampling line. 

More soluble gases like H2S and CO2 are less able to partition 

into the small bubbles that form in the injectate sampling 

line; they remain in solution and are therefore at lower 

concentrations in the injectate gas sample relative to the steam 

sample. Less soluble gases like H2, Ar, and N2 get concentrated 

in those small bubbles; for example, N2 is nearly a factor of 2 

higher in the injectate gas sample.
8 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

Table 3. Concentrations of trace metals, NH3, and H2S, in milligrams per liter (mg/L), and stable isotopes of water, in per mil. NH3

values expressed as N; H2S values are total reduced S expressed as H2S.

[nm, not measured]

SAMPLE # Location Al

mg/L

As

mg/L

Cd

mg/L

Co

mg/L

Cr

mg/L

Cu

mg/L

Fe

mg/L

Mn

mg/L

PG14-01 Keonepoko Nui Well #2 <0.002 0.001 <0.001 <0.001 0.003 0.001 <0.003 <0.001

PG14-02 Keonepoko Nui Well #1 0.002 <0.001 <0.001 <0.001 0.003 <0.001 <0.003 <0.001

PG14-03 Keauohana #1 0.006 0.001 <0.001 <0.001 <0.001 <0.001 0.004 <0.001

PG14-04 Keauohana #2 <0.004 <0.002 <0.002 <0.002 <0.002 <0.002 <0.006 <0.002

PG14-05 Pohoiki Pond <0.05 <0.025 <0.025 <0.025 <0.025 <0.025 <0.075 <0.025

PG14-06 Allison Spring <0.05 0.03 <0.025 <0.025 <0.025 <0.025 <0.075 <0.025

PG14-07 Hawaiian Shores Well <0.002 0.001 <0.001 <0.001 0.001 0.002 <0.003 <0.001

PG14-08 Hawaiian Beaches Well #1 <0.002 <0.001 <0.001 <0.001 0.002 <0.001 <0.003 <0.001

PG14-09 Hawaiian Beaches Well #2 0.002 0.001 <0.001 <0.001 0.001 0.003 <0.003 <0.001

PG14-10 10-P-5 (MW-1) 0.003 <0.001 <0.001 <0.001 <0.001 <0.001 0.013 0.002

PG14-11 10-P-7 (MW-3) 0.003 0.001 <0.001 <0.001 <0.001 <0.001 0.015 0.005

PG14-12 MW-2 <0.01 <0.005 <0.005 <0.005 <0.005 <0.005 0.018 0.04

PG14-13 Pad A (Injectate) 0.18 0.053 <0.05 <0.05 <0.05 <0.05 0.17 0.3

PG14-14B KS-5 Brine 0.24 0.069 <0.05 <0.05 <0.05 0.065 <0.15 0.6

PG14-14S KS-5 Steam 0.007 <0.001 <0.001 <0.001 <0.001 <0.001 0.02 0.022

PG14-15 Vacation Land Roney <0.026 0.02 <0.013 <0.013 <0.013 <0.013 <0.039 <0.013

PG14-16 Ahala Nui County Park <0.05 <0.025 <0.025 <0.025 <0.025 <0.025 <0.075 <0.025

PG14-17 Keahialaka Pond <0.026 0.01 <0.013 <0.013 <0.013 <0.013 <0.039 <0.013

PG14-18 Lighthouse Spring <0.026 0.01 <0.013 <0.013 <0.013 <0.013 <0.039 <0.013

PG14-19 Kapoho Shaft <0.01 <0.02 <0.002 <0.002 <0.002 0.002 <0.006 <0.002

PG14-20 Pohoiki Pond <0.2 <0.04 <0.04 <0.04 <0.04 <0.04 <0.12 <0.04

PG14-21 Ahala Nui County Park north <0.2 <0.04 <0.04 <0.04 <0.04 <0.04 <0.12 <0.04

PG14-22 Ahala Nui County Park south <0.2 <0.04 <0.04 <0.04 <0.04 <0.04 <0.12 <0.04

PG14-23 Keonepoko Nui Well #2 <0.005 <0.01 <0.001 <0.001 0.003 0.002 <0.003 <0.001

PG14-24 Pāhoa Well #2 <0.005 <0.01 <0.001 <0.001 0.001 0.006 <0.003 <0.001

PG14-25 Vacation Land Roney <0.1 <0.21 <0.2 <0.2 <0.2 <0.2 <0.06 <0.2

The gases contain trace amounts of numerous 

hydrocarbons, from methane to compounds as large as 

pentane. Pentane and other hydrocarbons were clearly 

detectable on the TCD detector used to quantify major

constituents, even though this detector is not highly sensitive 

to hydrocarbons. The more precise values obtained from the 

FID are used in further discussion, but either set of results 

would produce the same conclusions.

The alkane hydrocarbon concentrations (as parts-permillion by volume) are shown in figure 2. Alkanes up to

butane, which has two isomers, are enriched about two-fold 

in the injectate relative to the steam sample. This enrichment 

likely reflects their low aqueous solubilities, similar to those

of Ar and N2, which show comparable enrichments (table 4). 

Thus, no in-plant source is required to explain the fact that

these alkane concentrations are higher in the injectate than 

in the produced steam. Pentane, in contrast, shows a sixfold enrichment in the injectate relative to the steam (fig. 2),

consistent with an in-plant source. 

The alkane hydrocarbons consist mainly of methane, and 

both samples show successively decreasing amounts of ethane, 

propane, and butane (fig. 2). This is the pattern expected in

virtually any natural gas, whether from a sedimentary basin 

or a geothermal system, where alkanes form from the thermal 

breakdown of organic matter (for example, kerogen) in the 

reservoir (Darling, 1998; Tassi and others, 2007). Successively 

higher molecular weight alkanes like pentane and hexane 

normally continue the trend of decreasing abundance. The 

PGV samples instead show a conspicuous increase in pentane, 

again consistent with an artificial source. The gas in the
Results 9

Table 3. —Continued.

SAMPLE # Location Mo

mg/L

Ni

mg/L

Se

mg/L

Zn

mg/L

NH3

mg/L

H2S

mg/L

δD

per mil

δ18O

per mil

PG14-01 Keonepoko Nui Well #2 <0.001 <0.001 <0.005 0.006 nm nm –22.1 –4.43

PG14-02 Keonepoko Nui Well #1 <0.001 <0.001 <0.005 0.006 nm nm –23.5 –4.51

PG14-03 Keauohana #1 <0.001 <0.001 <0.005 0.005 nm nm –15.0 –3.61

PG14-04 Keauohana #2 <0.002 <0.002 <0.01 0.005 nm nm –14.6 –3.58

PG14-05 Pohoiki Pond <0.025 <0.025 <0.125 <0.05 nm nm –9.9 –2.54

PG14-06 Allison Spring <0.025 <0.025 <0.125 <0.05 nm nm –9.1 –2.36

PG14-07 Hawaiian Shores Well <0.001 <0.001 <0.005 0.007 nm nm –13.7 –3.50

PG14-08 Hawaiian Beaches Well #1 <0.001 <0.001 <0.005 0.004 nm nm –13.9 –3.50

PG14-09 Hawaiian Beaches Well #2 <0.001 <0.001 <0.005 0.007 nm nm –15.0 –3.46

PG14-10 10-P-5 (MW-1) 0.002 <0.001 <0.005 0.004 nm nm –12.1 –3.18

PG14-11 10-P-7 (MW-3) 0.002 <0.001 <0.005 0.084 nm nm –12.7 –3.30

PG14-12 MW-2 <0.005 <0.005 <0.025 <0.01 nm nm –12.1 –3.20

PG14-13 Pad A (Injectate) <0.05 <0.05 <0.25 <0.1 < 0.04 122 –8.1 –1.55

PG14-14B KS-5 Brine <0.05 <0.05 <0.25 <0.1 < 0.04 9 –5.6 –0.80

PG14-14S KS-5 Steam <0.001 <0.001 0.01 <0.002 < 0.04 510 –6.1 –3.00

PG14-15 Vacation Land Roney <0.013 <0.013 <0.065 <0.026 nm nm –8.3 –2.51

PG14-16 Ahala Nui County Park <0.025 <0.025 <0.125 <0.05 nm nm –8.3 –2.32

PG14-17 Keahialaka Pond <0.013 <0.013 <0.065 <0.026 nm nm –10.9 –2.80

PG14-18 Lighthouse Spring <0.013 <0.013 <0.065 <0.026 nm nm –10.5 –2.91

PG14-19 Kapoho Shaft <0.002 <0.002 <0.01 <0.004 nm nm –15.4 –3.44

PG14-20 Pohoiki Pond <0.04 <0.04 <0.2 <0.08 nm nm –9.0 –2.31

PG14-21 Ahala Nui County Park north <0.04 <0.04 <0.2 <0.08 nm nm –7.4 –2.14

PG14-22 Ahala Nui County Park south <0.04 <0.04 <0.2 <0.08 nm nm –7.9 –2.04

PG14-23 Keonepoko Nui Well #2 <0.001 <0.001 <0.005 0.015 nm nm –20.7 –4.42

PG14-24 Pāhoa Well #2 0.001 <0.001 <0.005 0.062 nm nm –14.1 –3.75

PG14-25 Vacation Land Roney <0.2 <0.2 <0.1 <0.04 nm nm –8.7 –2.44

injectate stream also contains a significant amount of pentene

(table 4), a compound not detected in the produced steam. 

The PGV gases contain no hexane, which would likely be 

detectable if all of the other hydrocarbons derived from natural 

degradation of organic matter in the reservoir.

Thermal degradation of large hydrocarbons into smaller 

ones is a complex process (Darling, 1998). Although a full 

explanation of the hydrocarbon abundance patterns in the 

PGV gases cannot be provided, several assertions can be 

supported. The working fluid used by PGV is nearly pure

pentane (99.2 percent according to the material safety data 

sheet supplied by PGV). At some point in the plant, perhaps 

in the heat exchanger, pentane enters the flow system.

Some degradation to pentene must occur upstream from 

the injectate sampling port (table 4). Such a rapid reaction 

is possible in this case because H2S is known to catalyze 

hydrocarbon degradation under certain conditions (Xia 

and others, 2014). The pentene apparently breaks down 

into smaller hydrocarbons after injection into the reservoir, 

because it is not present in the produced steam (table 4). 

The injected pentane may also continue to break down 

into smaller hydrocarbons, but enough survives within the 

reservoir that it exceeds the abundance of butane (both 

isomers) in the produced steam. It is not possible with 

existing data to precisely distinguish hydrocarbons generated 

by thermal breakdown of organic matter in the reservoir from 

those produced by pentane degradation. Although some of 

the pentane may come from natural sources in the reservoir, 

it is clear from the data that the geothermal plant must be an 

important source.
10 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

Table 4. Composition (in volume percent) of gas bubbles in samples 

collected from the Puna Geothermal Venture steam and injectate lines. 

[TCD, results from the gas chromatograph equipped with a thermal conductivity

detector; FID, results from the gas chromatograph equipped with a flame ionization

detector; nm, not measured]

Sample

 Method

PG14-14S

steam line

PG14-13

injectate line

TCD FID TCD FID

Bulk gas analysis

Helium He <0.01 nm <0.01 nm

Hydrogen H2 33.0 nm 42.2 nm

Argon Ar 0.276 nm 0.412 nm

Oxygen O2 0.346 nm 0.120 nm

Nitrogen N2 15.4 nm 27.2 nm

Carbon Dioxide CO2 27.8 nm 21.4 nm

Hydrogen Sulfide H2

S 25.2 nm 10.5 nm

Carbon Monoxide CO <0.001 nm <0.001 nm

Hydrocarbons

Methane CH4 0.226 0.193 0.421 0.372

Ethylene C2

H4 0.0003 0.0003 0.0003 0.0003

Ethane C2

H6 0.017 0.0148 0.029 0.0267

Propylene C3

H6 0.003 0.0027 0.003 0.0025

Propane C3

H8 0.006 0.0068 0.012 0.0131

Butane n-C4

H10 0.001 0.0016 0.003 0.0036

Isobutane i-C4

H10 0.002 0.0025 0.004 0.0056

Pentene C5

H10 <0.001 <0.0002 0.014 0.0086

Pentane C5

H12 0.005 0.0060 0.031 0.0398

Hexane C6

H14 <0.01 <0.003 <0.01 <0.004

0 

100 

300 

400 

200 

Alkane hydrocarbon concentrations,

in parts-per-million by volume

Produced Steam (PG14-14S)

Injectate (PG14-13)

methane/10 ethane propane butane

EXPLANATION

isobutane pentane

Figure 2. Concentration of alkane 

hydrocarbons (in parts-per-million 

by volume) in gas samples from 

the steam (blue) and injectate (red) 

pipelines at Puna Geothermal 

Venture. Concentration of methane 

divided by 10.
Results 11

Table 5. Concentrations of dissolved hydrocarbons in micromoles per kilogram (μmol/kg) for all samples containing a hydrocarbon 

larger than methane. DIC and serum bottle samplers discussed in text.

 [nm, not measured]

Sample PG14-14S

Steam

PG14-13

Injectate1

PG14-14B

Brine

PG14-12

MW-2

PG14-01

Keonepoko Nui #2

PG14-19

Kapoho Shaft

PG14-24

Pāhoa #2

Method (DIC) (serum) (serum) (DIC) (serum) (DIC) (serum) (DIC) (serum) (DIC) (serum) (DIC) (serum)

CH4 1.6 1.1 3.9 0.03 0.02 0.34 1.2 0.004 0.002 0.04 0.008 0.04 0.006

C2

H4 <0.01 nm nm 0.007 nm <0.01 nm <0.01 nm <0.01 nm <0.01 nm

C2

H6 0.18 0.11 0.35 0.007 0.002 0.01 0.01 0.008 <0.001 0.005 <0.001 0.008 <0.001

C3

H6 0.08 nm nm 0.009 nm <0.01 nm <0.01 nm 0.02 nm <0.01 nm

C3

H8 0.05 0.01 0.06 <0.01 0.001 0.01 0.01 <0.01 <0.001 0.007 <0.001 <0.01 <0.001

n-C4

H10 0.01 0.005 0.02 <0.01 0.0003 0.01 0.005 0.007 <0.001 <0.01 <0.001 <0.01 <0.001

i-C4

H10 0.01 0.004 0.03 0.004 <0.001 0.003 0.001 <0.01 <0.001 <0.01 <0.001 <0.01 <0.001

C5

H10 <0.01 nm nm 0.02 nm <0.01 nm <0.01 nm <0.01 nm <0.01 nm

C5

H12 0.03 0.01 0.14 <0.01 <0.001 <0.01 0.001 0.008 <0.001 <0.01 <0.001 <0.01 <0.001

C6

H14 <0.05 <0.001 <0.001 <0.05 <0.001 <0.05 <0.001 <0.05 <0.001 <0.05 <0.001 <0.05 <0.001

1

DIC bottle broken in shipment

Pentane in Water Samples 

For the purpose of this study, a criterion is needed to 

identify a PGV-related hydrocarbon component in groundwater 

that might also contain hydrocarbons from natural sources. An 

excess of pentane relative to total butane is an obvious criterion 

to apply, given the gas sample results discussed above, but for 

thoroughness the water samples collected for pentane analysis 

were analyzed for the full hydrocarbon abundance patterns as 

was done for the gas samples. Traces of methane were found at 

every site, but this is a common gas that can be formed through 

microbial activity in many groundwaters. The results for every 

site where a hydrocarbon larger than methane was detected are 

shown in table 5.

Two caveats about these data must be acknowledged. 

Collection and analysis of water samples containing these 

highly insoluble gases involves several steps where gas 

concentrations can be altered. For example, the tiny bubbles 

that frequently form during collection can result in significant

depletion or enrichment of gas within the actual water sample. 

Thus even duplicate samples analyzed by the same method 

can show large differences. A particular concern for this 

sample set is the low concentration of most hydrocarbons. The 

original goal of the study was to attain a detection limit for 

pentane of 1 microgram/kilogram of water, which equates to

0.014 micromoles/kilogram (μmol/kg). The method using the

DIC bottles attained this detection limit, while the serum bottle 

method achieved a much lower detection limit of 0.001 μmol/kg.

For completeness, a value is reported in table 5 for every case 

where an identifiable peak was seen in the chromatogram,

even in cases where the concentration was below the stated 

detection limit. The identity of the compound is fairly certain; 

however, for the many values near the respective detection 

limits, the concentration carries a large uncertainty.

Despite the uncertainties, pentane exceeds total butane 

in the steam (using both sampling methods) and especially in 

the injectate (table 5). Because visible gas loss occurred during 

collection of these samples (bubbles in the collection tubing), 

these values are minimum concentrations. The brine sample is 

gas poor by comparison, having lost nearly all of its gas to the 

steam phase. A few hydrocarbons are detectable at low levels, 

mainly alkenes which are more soluble than alkanes. Several 

hydrocarbons were detected by both methods in MW-2 near the 

plant, including a trace of pentane in the serum bottle.

Hydrocarbons larger than methane were only detected at 

three other sites (table 5) and, in each case, only detected in 

the DIC bottles at levels close to the detection limits of that 

method. The April DIC sample from Keonepoko Nui well #2 

showed several alkane peaks, including pentane, but neither of 

the two serum bottles from that well showed any hydrocarbons 

other than methane. This well was resampled in December, 

and no hydrocarbons (other than methane) were detected by 

either method. Thus the alkane detects for the one DIC sample, 

all of which are less than 0.01 mmol/kg, may reflect low-level

contamination of that sample bottle during initial evacuation 

or analysis. Pentane was not detected at any other site, but DIC 

bottles from Kapoho Shaft and the Pāhoa supply well showed

some trace hydrocarbons larger than methane. Serum bottles 

from these wells showed only methane, so perhaps the results 

from these DIC bottles also reflect low-level contamination in

the bottles. However, such hydrocarbons can also be produced 

from organic matter (for example, pipe grease) within well 
12 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

plumbing systems and be flushed out intermittently as the well

pumps are cycled on and off. Samples collected only minutes 

apart could reflect this variation, and thus the data should not be

automatically disregarded.

Alkane abundances are shown in figure 3 for the sites

where pentane was detected. The abundances in MW-2 (PG14-

12) do not show the pentane enrichment pattern seen in the 

injectate, and instead show a steady decrease in abundance 

with increasing molecular size. If these alkanes originated 

as pentane from the PGV injectate, thermal degradation of 

that pentane has proceeded to the point where the abundance 

pattern is indistinguishable from that expected to result from 

degradation of natural organic matter. The alkane abundances 

in the Keonepoko Nui #2 (PG14-01) DIC sample from April 

2014 look nothing like the pattern in the injectate, MW-2, 

or any typical groundwater, and are considered unlikely to 

represent the groundwater feeding this well. Thus there was 

no clear evidence for PGV-derived pentane in any of the 

groundwater features we sampled.

Isopropanol 

Isopropanol (isopropyl alcohol) is a component of the 

additive ChemTreat GG442 used by PGV to control corrosion 

in pipelines at the plant. The concentration range of isopropanol 

in the additive is listed as 1–5 percent by weight in the material 

safety data sheet obtained from PGV, and a more precise figure

could not be obtained from the manufacturer. PGV records for 

the month of April 2014 show that, on an average day, 52 gallons

of additive are mixed into 5 million gallons of injectate, a mixing 

ratio of about 10 mg of additive per liter of injectate, ignoring 

density differences between the two fluids. Isopropanol should

thus constitute between 100 and 500 micrograms per liter (μg/L)

of the injectate. The measured isopropanol concentration in the 

sample of injectate (PG14-13) was 496 mg/L, consistent with 5

percent isopropanol in the additive.

Unlike pentane, isopropanol is quite soluble in water, so that

partitioning into gas bubbles during sample collection at ambient 

temperature is not a significant concern. At high temperatures,

volatility does become important, and most of the injected 

isopropanol that survives transport through the reservoir to the 

production well partitions into the steam line. The isopropanol 

concentration in PG14-14S was 60.5 mg/L; that in PG14-14B 

was 3.8 mg/L. Interestingly, the ratio of isopropanol concentration 

in injectate to that in steam is 8.2:1, not too different from the 

pentane ratio for injectate to steam, which is 6.4:1 based on the 

average pentane concentration in the two steam samples in table 

5. Either the two compounds degrade at comparable rates in 

the reservoir, or they degrade very little and the concentration 

ratios reflect the reservoir dilution factor. Isopropanol was

below detection (<0.8 mg/L) in all samples, except for the three 

collected from the plant, and thus provided no evidence for PGVderived fluid in the groundwaters.

Isopropanol analysis also yielded results for 37 other 

VOCs. The complete list of these compounds, representative 

detection limits, and instances of detection are shown in 

table 6. In nearly every instance, concentrations are near the 

detection limits, and the reported concentrations should be 

viewed with caution unless confirmed by future sampling. The

single exception is the reported concentration of isopropyl 

acetate in the injectate sample. This compound may be an 

impurity in the ChemTreat GG442 additive or a reaction 

product derived from isopropanol in the piping system. 

Apart from isopropanol and possibly isopropyl acetate, the 

compounds in table 6 are not known to be contaminants 

specifically related to geothermal production.

0 

0.2 

0.3 

0.4 

0.1 

Alkane hydrocarbon concentration, in micromoles per kilogram

methane/10 ethane propane butane isobutane pentane

Injectate (PG14-13)

MW-2 (PG14-12)

Keonepoko Nui #2 (PG14-01*)

Figure 3. Concentration of alkane EXPLANATION

hydrocarbons (in μmol/kg) in both 

wells where pentane was detected, 

MW-2 (PG14-12) and Keonepoko Nui 

#2 (PG14-01—*DIC sample only). 

Red bars show concentrations in 

the injectate sample (PG14-13) for 

comparison. Concentration of methane 

divided by 10.
Injectate Composition Over Time 13

Injectate Composition Over Time

Direct leakage of deep geothermal water or gas into 

shallow groundwater would likely first be detected at sites

nearest to the plant, in this case the three monitoring wells. 

Contaminant transport in shallow groundwater to remote 

locations like the coastal warm springs 5–10 km away would 

be controlled by groundwater velocity from the LERZ down to 

the coast. Scholl and others (1996) used tritium data to estimate 

residence times of 18–25 years for the groundwater feeding 

these springs, though some of this time could include periods 

of slow flow through dike-impounded zones within the LERZ.

Hydraulic conductivity between the rift and the coastal warm 

springs is thought to be in the range of 1–6 km/d (Imada, 1984; 

Takasaki; 1993; Gingerich, 1995). Given the hydraulic gradient 

and effective porosity south of the rift zone (Gingerich, 1995), 

groundwater flow expressed as particle velocity relevant to

contaminant transport is likely to range from about 3 to 30 m/d 

(Sorey and Colvard, 1994). Thus it might require several years

for any contaminant derived from the PGV plant to appear at 

the springs. Evaluation of contamination in these features also 

requires some knowledge of geothermal fluid composition in

previous years.

The injectate is sampled on a regular basis to satisfy 

conditions of the operating permit. Bimonthly samples 

are analyzed for a suite of inorganic species similar to 

that presented in tables 2 and 3. Samples of gas from the 

noncondensable gas line, taken just before it flows into the

injectate stream, are also analyzed. Additional samples of the 

injectate are collected twice a year for specialized analyses 

that include a large suite of organic compounds, but not 

isopropanol. The records are extensive, and we obtained a 

partial set from the HDOH that provided inorganic chemistry 

and gas composition for 2008–14 and selected prior years.

Pentane and Isopropanol

Analyses of pentane in injectate apparently began on 

November 3, 2000, when it constituted 0.632 percent of the 

noncondensable gas. Values since that time have generally been 

an order of magnitude lower, and in the samples collected just 

before and after our sampling were near 0.02 percent (fig. 4).

Our gas sample, PG14-13, has a somewhat higher value, near 

0.04 percent, but this sample was collected from the injectate 

pipeline instead of the noncondensable gas line, where samples 

are normally obtained. The two-fold difference is probably due 

to solubility effects as discussed above.

Although the rate at which pentane enters the injectate 

stream continues to show variability (fig. 4), it seems

reasonable to assume that the measured concentration of 

dissolved pentane in our injectate sample, 0.14 mmol/kg 

(table 5), is representative of average conditions over the past 

six years. Given the detection limit of 0.001 mmol/kg by the 

serum bottle method, pentane could be detectable in springs 

and wells that contain as little as 1 percent injectate. Pentane 

would thus be a good indicator of leaks in the event of casing 

failure in an injection well. However, pentane concentrations 

in the deep reservoir are no doubt substantially less than 

those in the injectate due to degradation and (or) dilution. 

Furthermore, pentane could be lost to exsolution during 

groundwater flow over many kilometers from the PGV area,

so the absence of pentane in coastal springs, for example, does 

not in itself preclude contamination by geothermal fluid.

PGV use of isopropanol began in September 2013, so 

groundwater transport of this compound would not be expected 

to extend far (many kilometers) from the plant at the time of 

our sampling. Our motivation in measuring isopropanol in 

distal sites was mainly to obtain a complete picture of natural 

background levels, enhancing possible future use as a tracer. 

2000 2008

Pentane in noncondensable

gas line

Pentane in gas bubbles from

injectate line (April, 2014)

2004

EXPLANATION

2012 2016

Pentane, in volume percent

0.14

0.12

0.10

0.08

0.06

0.04

0

0.02

0.632%

Figure 4. Concentration of 11/03/2000

pentane (in volume percent) 

in the noncondensable gas 

line at Puna Geothermal 

Venture, as reported in 

Hawai‘i State Department 

of Health records for 2001, 

2004, and 2007–14. Value 

for initial report of November 

3, 2000, is off scale and 

shown by the arrow. Black 

diamond shows the pentane 

concentration we measured 

in gas bubbles from the 

injectate line.
14 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

Table 6. Volatile organic compounds (VOCs) measured in water samples. VOCs were below detection in all other 

samples.

[All samples measured in micrograms per liter; detections in bold]

PG14-01

Keonepoko 

Nui #2

PG14-02

Keonepoko 

Nui #1

PG14-12

Monitoring

Well 2

PG14-13

PGV

injectate

PG14-14S

PGV

steam

PG14-14B

PGV

brine

acrolein <0.24 <0.24 <0.325 <0.599 <0.471 <0.48

hexachlorocyclopentadiene <1.6 <1.6 <1.6 <1.6 <1.6 <3.2

isophorone <5 <5 <5 <5 <5 <10

nitrobenzene <0.6 <0.6 <0.6 <0.6 <0.6 <1.2

1,2-dichloropropane <0.004 <0.004 <0.004 <0.004 <0.004 <0.008

isopropyl acetate <0.01 <0.01 <0.01 0.17 <0.01 <0.02

propyl acetate 0.08 0.04 <0.032 <0.032 <0.032 <0.064

1-methoxy-4-(2-propenyl)benzene <0.6 <0.6 <0.6 <0.6 <0.6 <1.2

2-ethoxyethyl acetate <4.2 <4.2 <4.2 <4.2 <4.2 <8.4

2-propen-1-ol <5 <5 <5 <5 <5 <10

alpha-terpineol <6 <6 <6 <6 <6 <12

butanal <0.38 <0.38 <0.38 <0.38 0.2 0.2

crotonaldehyde <0.48 <0.48 <0.48 <0.48 <0.48 <0.96

acetonitrile <0.8 <0.8 <0.8 <0.8 <0.8 <1.6

isopropanol <0.8 <0.8 <0.8 496 60.5 3.8

methyl acetate <0.14 <0.14 <0.14 <0.14 <0.14 <0.28

1-butanol <0.8 <0.8 <0.8 <0.8 <0.8 <1.6

tert-butyl alcohol <0.24 <0.24 0.24 <0.248 0.5 <0.48

n-pentanal <0.054 <0.054 <0.054 <0.188 <0.428 0.04

2-nitropropane <0.12 <0.12 <0.12 <0.12 <0.12 <0.24

cyclohexanone <1.2 <1.2 <1.2 <1.2 <1.2 <2.4

4-methyl-2-pentanol <0.2 <0.2 <0.2 <0.2 <0.2 <0.4

5-methyl-2-hexanone <0.022 <0.022 <0.022 <0.0240 <0.0762 <0.044

2-methylpropyl acetate <0.028 <0.028 <0.028 <0.028 <0.028 <0.056

1-octanol <1.8 <1.8 <1.8 <1.8 <1.8 <3.6

2-ethyl-1-hexanol <2 <2 <2 <2 <2 <4

2,6-dimethyl-4-heptanone <0.032 <0.032 <0.032 <0.032 <0.032 <0.064

1,2,3-trichloropropane <0.006 <0.006 <0.006 <0.006 <0.006 <0.012

chloropicrin <0.018 <0.018 <0.018 <0.018 <0.018 <0.036

1,2-dibromoethane <0.004 <0.004 <0.004 <0.004 <0.004 <0.008

tert-butyl methyl ether <0.012 <0.012 <0.012 <0.012 <0.012 <0.024

n-nitrosodiethylamine <3.6 <3.6 <3.6 <3.6 <3.6 <7.2

1,1-dichloro-2-propanone <0.24 <0.24 <0.24 <0.24 <0.24 <0.48

dimethoxymethane <0.044 <0.044 <0.044 <0.044 <0.044 <0.088

1,4-dioxane <0.7 <0.7 <0.7 <0.7 1 <1.4

1,3-dioxolane <0.38 <0.38 <0.38 <0.38 <0.38 <0.76

ethyl acetate <0.06 <0.06 <0.06 <0.06 <0.06 <0.12

dibromochloropropane <0.02 <0.02 <0.02 <0.02 <0.02 <0.04
Injectate Composition Over Time 15

The aqueous solubility of isopropanol at low temperature

exceeds that of pentane by a factor of 105, suggesting that 

it would be much more likely to remain in solution during 

groundwater transport.

Water and Gas Composition of Injectate

Seawater is an important source of fluid for the

geothermal reservoir, and thus the chemical composition of 

PGV fluid has many of the characteristics of seawater. Rainfall

is abundant and infiltration rapid in the Puna area (Thomas,

1987; Takasaki, 1993; Ingebritsen and Scholl, 1993; Gingerich, 

1995; Scholl and others, 1995), and some of this infiltration

reaches the reservoir, causing variable dilution of the seawater 

component. Injectate monitoring records from HDOH show 

that NaCl content has nearly doubled since 1995, but that 

the rate of increase has slowed greatly over the last 15 years 

(fig.5). During the last six years the Na and Cl concentratio

have been reasonably constant and are near the concentration 

in our injectate sample, PG14-13. The Na/Cl ratio has followed 

the seawater dilution line. The injectate has always been low in 

sulfate, which is almost completely removed into solid phases 

or converted to reduced forms at the high temperatures in and 

adjacent to the reservoir. Interestingly, the fluid composition in

the HGP-A well showed a similar evolution during its years of 

production (Thomas, 1987; Janik and others, 1994), leveling 

off at about the same composition as present-day PGV fluid.

The concentrations of several major species over the past 

six years, including a sample collected two weeks after our 

injectate sample, are shown in figure 6. While some species

(Ca, total S) show significant short-term variability (fig. 6B), 

long-term trends are not readily apparent. 

Gas composition (in the noncondensable gas line) has also 

been reasonably stable over the past six years and even farther 

back into the late 1990s (fig. 7), although the minor gases CH4

and Ar have shown a long-term increases (fig.7B). The dominant 

gas species are typically H2 and CO2, with lesser amounts of N2

and H2S. Our gas sample from the injectate line is somewhat 

richer in H2 and N2 and depleted in CO2 and H2S, due to the 

0 

1,000 

3,000 

5,000 

1995

1998–2000

2001–2007

2008–2014

Injectate sample

EXPLANATION

Na SO4

2,000 

4,000 

6,000 

Na, in milligrams per liter

Cl, in milligrams per liter

SO4, in milligrams per liter

2,000 

1,600 

800 

0 

400 

1,200 

2,400 

0 2,000 4,000 6,000 8,000 10,000 

SO4 seawater dilution

Na seawater dilution

Figure 5. Concentration (in mg/L) of Na (blue) and SO4 (red) versus Cl in injectate over time, based 

on Hawai‘i State Department of Health records. The record is broken into four time increments: 1995 

(crosses); 1998–2000 (triangles); 2001–07 (diamonds); and 2008–14 (pluses). Filled circles show 

composition of our injectate sample on April 30, 2014. Solid and dashed lines are seawater dilution lines 

for Na and SO4

, respectively.
16 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

solubility effects discussed above, but is nevertheless similar in 

composition to the HDOH data from the last six years.

The stable chemical composition of the injectate during the

past six years provides a straightforward test for a component

of reservoir fluid in the groundwater, specifically by searching

for any trend in groundwater chemistry toward the injectate 

composition. We conduct the test using a series of plots that 

have the Cl on the x-axis and show dilution lines that would 

result from mixing a saline fluid (like seawater or injectate)

with pure water. The properties and benefits of such plots

were discussed in detail by Janik and others (1994). Using 

pure-water as an end member means that the dilution lines are 

independent of actual groundwater chemistry, helping to focus 

on the processes responsible for deviations of any particular 

groundwater from the dilution lines; for example, mineral 

solution reactions.

Groundwater Chemistry

Groundwater chemistry is plotted at different salinity 

scales, with figure 8 emphasizing results from springs and figure

9 focused on the less-saline groundwater wells. Seawater, with 

19,000 mg/L Cl, exceeds the range of the x-axis but is represented 

by a dilution line on all plots. For consistency with Janik and 

others (1994), we use the composition of seawater from Hem 

(1985). When the injectate value exceeds the range of the axes, an 

injectate dilution line is shown based on sample PG14-13.

The six species used in these plots (figs. 8 and 9) were

chosen for their contrasting behaviors in geothermal systems. 

In general, Na behaves as a conservative species that, like 

Cl, primarily reflects source waters; K and B have additional

mineral sources and tend to become enriched in water as 

temperature increases; Mg partitions out of solution into 

2008 20102009 2011 20132012 2014 2015

Concentration, in milligrams per liter

200

250

150

100

50

0

B

A

10,000

8,000

6,000

4,000

2,000

0

Cl

Na

K

SiO2

Ca

S

EXPLANATION

Figure 6. Concentration (in mg/L) of several major chemical species 

in the injectate over time, based on Hawai‘i State Department of Health 

records (open symbols). Filled symbols show concentrations of the same 

species in our injectate sample of April 30, 2014. A) Na (diamonds), 

K (red triangles), Cl (green circles), SiO2

 (squares); B) Ca (purple 

triangles), S (brown circles) which represent total sulfate and reduced 

sulfur as S.

Concentration, in volume percent

B

1994 1998 2002 2006 2010 2014

0.6

0.8

0.4

0.2

0

A

60

50

40

30

20

10

0

EXPLANATION

CO2

H2

H2S

N2

Ar

CH4

Figure 7. Concentration (in volume percent) of gas species (other 

than pentane) in the noncondensable gas line over time, based on 

Hawai‘i State Department of Health records for 1995, 1998, 2000, 

2001, 2004, and 2007-14 (open symbols). Filled symbols show 

concentrations of the same species in our injectate sample of April 

30, 2014. A) CO2

 (diamonds), H2 (squares), H2S (green triangles), N2

(black circles); B) Ar (purple triangles), CH4

 (brown circles).
Groundwater Chemistry 17

0

400

200

800

600

1,000

0

2,000

1,000

4,000

3,000

5,000

0

60

30

120

90

150

0

200

100

400

300

500

0

80

40

160

120

200

0

2

1

4

3

5

Cl, in milligrams per liter

0 2,000 4,000 6,000 8,000 0 2,000 4,000 6,000 8,000 10,000

SO4, in milligrams per liter K, in milligrams per liter Ca, in milligrams per liter

Na, in milligrams per liter Mg, in milligrams per liter B, in milligrams per liter

A

C

B

D

E F

Water-supply wells

Kapoho Shaft

MW-1, MW-3

MW-2

Coastal springs

Injectate

Springs, pre-1993

Injectate avg. 2008–14

Seawater 

Injectate dilution

EXPLANATION

Figure 8. Concentration of six chemical species relative to Cl. Filled 

symbols are data from this study: water-supply wells, green circles; Kapoho 

Shaft, green square; MW-1 and MW-3, which co-locate at this scale, red 

triangles; MW-2, purple square; coastal springs, blue diamonds; injectate, 

black circle. Open black diamonds are spring data reported in Janik and 

others (1994). Open black circle is average injectate composition for 2008-

14 from Hawai‘i State Department of Health records. Solid lines extend to 

the composition of seawater at 19,000 mg/L Cl; dashed arrow in D extends 

to the composition of our injectate sample (893 mg/L K). 
18 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

0 

20

40

60

80

Ca, in milligrams per liter

Cl, in milligrams per liter

0.1

0 

0.2

0.3

0.4

0.5

B, in milligrams per liter

0 50 100 150 200 250 0 50 100 150 200 250 

10 

0 

20 

30 

40 

50 

Mg, in milligrams per liter

4

0 

8

12

16

20

K, in milligrams per liter

Seawater

Injectate

EXPLANATION

30 

0 

60 

90 

120 

150 

A B

C D

E F

50 

0 

100 

150 

200 

250 

Na, in milligrams per liter

SO4, in milligrams per liter

Average composition in combined 

DWS and HDOH records (1991–2014)

Range of MW-1 and MW-3

Range of Kapoho Shaft

Keauohana wells 1 and 2

Water-supply wells

MW-1 and MW-3

Kapoho Shaft

Figure 9. Expanded view of figure 8 highlighting results from particular wells. Filled symbols are data from this 

study, open symbols from Janik and others (1994). Keauohana wells 1 and 2, brown circles; all other active watersupply wells in table 1, green circles; MW-1 and MW-3, red triangles; Kapoho Shaft, green square. Large X’s show 

average composition in combined County Department of Water Supply and Hawai‘i State Department of Health 

(HDOH) records (1991-2014) for species analyzed at least five times: Keauohana #1 and #2, brown; Keonepoko 

Nui #1 and #2, and Pāhoa #2, green. Range of values for MW-1 and MW-3 from HDOH records during 1991-2014, 

red boxes; range for Kapoho Shaft from HDOH records during 1991-94, green boxes. Solid lines extend to the 

composition of seawater at 19,000 mg/L Cl; dashed arrows extend to the composition of our injectate sample.
Groundwater Chemistry 19

mineral phases as temperature increases, as does SO4, which 

can also be reduced to sulfide; Ca is typically dissolved

from minerals at low temperature but can also be soluble at 

high temperature, depending on reservoir conditions. These 

contrasting behaviors are clearly reflected in figure 8. The

injectate point lies on the seawater dilution line in the Na and 

Ca plots, and thus neither element can be used to distinguish 

reservoir fluid input from seawater input. The injectate plots

above the line in the K and B plots, and well below the line and 

near the x-axis in the Mg and SO4 plots.

Springs

The new spring data (fig. 8) extend to slightly higher

concentrations than the data of Janik and others (1994). We 

found the salinity of these ponded springs to vary from point 

to point within the pool (based on field-measured specific

conductance), and the difference in concentration ranges could 

reflect in part the exact sampling location. Temporal variation

in salinity with tidal conditions has also been noted. Janik 

and others (1994) sampled at low tide, whereas we collected 

samples at various tidal conditions and made an effort to cover 

a broad salinity range. Regardless, the overlap in the datasets 

is large and, most importantly, the new and old data fall on 

essentially the same trend lines. Thus, the main conditions 

controlling the chemistry of these springs appear to be 

unchanged over time. 

Janik and others (1994) proposed that the springs contain 

a component of heated seawater from a source region with a 

temperature near 165 °C. The actual salinity and temperature 

of this component are somewhat poorly constrained, because 

they depend, in part, on large extrapolations of trends like 

those in figure 8. Nevertheless, all trend lines radiate from

a dilute end-member resembling the well waters toward a 

saline end-member with thermal characteristics, such as Mg 

depletion and K enrichment, relative to the starting seawater 

composition. The thermal, saline end-member is thus variably 

diluted by cold groundwater during underground flow to the

springs.

Sorey and Colvard (1994) proposed that the source 

area for the thermal end-member is near the rift zone in 

a “conductive halo” around the commercially produced 

reservoir, where heated seawater can buoyantly rise through 

the overlying groundwater. They cite geophysical evidence 

(Kauahikaua, 1993) for outflow of saline thermal groundwater

from the rift zone to the coast. Sorey and Colvard (1994) and 

Janik and others (1994) note that thermal saline water with 

similar characteristics was encountered in wells between the 

rift zone and the coast (for example, Malama-Ki and Allison).

None of the spring trend lines deviate far from the 

seawater dilution lines (fig. 8), but the Mg, B, and K trends

fall toward the injectate side and could be consistent with a 

small admixture of reservoir fluid in the thermal, saline endmember. However, best-fit lines through the spring data (new

and old) yield different mixing ratios: 17 percent reservoir fluid

for Mg, 13 percent for B, and 5.6 percent for K. Furthermore, 

the SO4 data show no indication of reservoir fluid, nor do the

Ca data which, apart from one outlier in the older dataset that 

is likely spurious, plot on a trend parallel to the seawater and 

injectate dilution lines. The thermal end-member is apparently 

richer in Ca (relative to Cl) than both seawater and the PGV 

reservoir fluid. The major-ion chemistry data are not consistent

with significant leakage of reservoir fluid into this large

groundwater system. The concept of a conductively heated zone 

at a temperature above 60 °C, where Mg depletion typically 

begins (Seyfried and Bischoff, 1979; Sorey and Colvard, 1994), 

possibly as hot as 165 °C, is consistent with our data. 

Two more points about the springs should be made. Their 

location within or just above the tidal zone exposes them to 

direct seawater dilution, which is likely the reason that Janik 

and others (1994) sampled at low tide. However, trends in 

the Mg and K data actually deviate further from the seawater 

dilution line with increasing Cl concentration, so that direct 

seawater dilution is not apparent in the data. Groundwater 

flow modeling presented by Imada (1984) and discussed by

Sorey and Colvard (1994) implies that abundant rainfall and 

infiltration in the Puna area would rapidly dilute and erase

evidence of geothermal contamination during groundwater 

flow from the rift toward the coast. However, if the springs do

not mix with cold seawater at the coast, their Cl concentrations 

indicate that they still contain 10–30 percent of the heated 

seawater end-member (Cl ~19,000 mg/L). The corresponding 

70–90 percent dilution by dilute groundwater during flow

to the coast would not be so great as to completely erase 

contaminant signatures caused by leakage of reservoir fluids

into the “conductive halo”.

Groundwater Wells

Lower concentration ranges are plotted on figure 9 to

focus on the well chemistry. Dilution lines in all plots point 

to the composition of seawater and injectate, which plot far 

offscale. The active groundwater supply wells are plotted in 

two groups that distinguish the Keauohana wells from the 

other, more dilute wells. The results from our samples follow 

the same trends as the data of Janik and others (1994) except 

for a few outliers in the older data that are likely spurious. 

Monitoring records for several public wells are available 

from the State HDOH and (or) the County DWS, and these 

records fill the gap between our 2014 sampling and the pre1994 data reported by Janik and others (1994). The number 

of analyses for each well and each species varies greatly; for 

example, some wells have been analyzed frequently for Na

but never for B. For this study, we combined the records from 

the Keonepoko Nui and Pāhoa wells and calculated average

concentrations for each species of interest (fig. 9). We also

combined the records of the two Keauohana wells between 

1991and 2014 and denote the average concentrations on figure

9. Averages were not calculated unless the number of analyses 

in the combined HDOH and DWS records exceeded five.
20 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

The averages that were calculated plot within the respective 

groups of well data from our study and that of Janik and others 

(1994).

For species other than Mg, data trends fall along, or 

parallel to, the seawater dilution lines. Seawater is thus 

an important source of dissolved species even in this low 

concentration range. Additional Na, K, Mg, and Ca can be 

derived from mineral dissolution in the aquifer, so that the

wells generally plot above the seawater dilution lines. The Mg 

data for the Keauohana wells follow a trend subparallel to the 

injectate dilution line. These wells have long been considered 

to have a slight geothermal character (Iovenitti, 1990; Janik 

and others, 1994), but the trends in SO4, K, and B clearly differ 

from injectate-dilution trends, and therefore no component of 

reservoir fluid can be discerned. The geothermal component

in the Keauohana wells could be similar to the conductively 

heated seawater in the coastal springs, slightly depleted in 

Mg. Regardless, the older data from Janik and others (1994) 

include samples from the mid-1970s, prior to geothermal 

development, and the similarity over 40 years argues against 

any substantial impact on chemistry from PGV operations.

The Kapoho Shaft was originally used as a public-supply 

well but has not been pumped in decades. The small portable 

pump we used to bring up water was not capable of fully 

purging water from the well and bringing in fresh groundwater 

from the local aquifer. Perhaps as a result of this, our sample

differs somewhat from all previous analyses, but shows a 

general similarity in that it is rich in Mg, Ca, and HCO3 (table 

2; fig. 9). Janik and others (1994) attribute these characteristics

to mineral dissolution by dissolved CO2. The B concentration 

in this well plots on the injectate-dilution line, but the Mg, Ca, 

and SO4 concentrations provide no evidence for influence of

PGV injectate.

Thermal Wells

The new data for MW-1 and MW-3 are compositionally 

similar to the older data from Janik and others (1994), but 

slightly higher in several constituents (fig. 9). The data fall

within the range observed in ~75 samples collected from 

these two adjacent wells between 1991 and 2014 as part of the 

ongoing HDOH water monitoring program.

The unique chemistry of the water in these two wells is

attributed to absorption of H2S gas from an underlying steam 

zone, followed by oxidation to sulfuric acid, which dissolves 

cations from aquifer minerals (Janik and others, 1994; Sorey

and Colvard, 1994). Thus, the major anion is sulfate and cations 

are substantially elevated relative to the seawater dilution line. 

Steam absorption also explains the high concentrations of B, 

which becomes volatile at high temperatures. Variations in 

the relative proportions of rainfall recharge and steam upflow

likely cause some of the chemical variability over time but 

the absence of obvious long-term trends in water composition 

(fig.9) suggests that geothermal operations are not induci

major changes to these groundwaters.

Well MW-2, plotted in figure 8, shows a greater seawater

influence than MW-1 and MW-3, but also a clear depletion

in Mg and a small enrichment in SO4 relative to the seawater 

dilution lines. Some small component of H2S-laden steam 

may explain the SO4 enrichment, but this well is also located 

near the former HGP-A site, where SO4 from gas abatement 

procedures was allowed to infiltrate during the 1980s (D.M.

Thomas, University of Hawaii, Mānoa, personal commun.,

2015). The water chemistry is generally consistent with 

conductively heated seawater diluted by local groundwater. 

The long-term HDOH monitoring record (fig.10) shows a

high degree of chemical variability at MW-2 that must reflect

in part frequent changes in the mixing proportions of the

source fluids. The chemistry of our sample is within the range

of variability in the monitoring data. This well is equipped

with a small gas-lift pump, and the low flow rate we used for

sampling probably explains why our sample is several degrees 

cooler than is typical of the recent monitoring data. Despite 

this issue, the HDOH record shows clear long-term trends 

of declining temperature and increasing Mg concentration 

that are independent of source mixing and likely linked, 

given that Mg is more easily retained in solution at lower 

temperatures. These long-term trends may be an indirect 

impact of geothermal development, in that conductive heat 

transfer might decline with long-term extraction of heat from 

the reservoir, but any linkage to geothermal operations is 

speculative. A possible link between changes in temperature 

and chemistry in 1991–92, and a steam blowout at well KS-8 

was found unconvincing by Sorey and Colvard (1994), and the 

amplitude of variations in the record since that time (fig. 10)

make such a link even less likely.

Other thermal wells exist in the Puna area but are not 

pumped, and were therefore not suitable for our sampling protocol. 

Two of these wells, Malama-Ki and TH-3, were included in the 

HDOH monitoring program until the year 2000, and the resulting 

data are shown in figure 11 along with data from Janik and others

(1994). These wells, and the thermal Allison well, show a high 

degree of temporal variability, as seen in the large spread in data in 

every plot (fig. 11). Nevertheless, apart from a few outlying points,

the data do show some clustering and trends.

The trend along the seawater-dilution line is fairly 

clear for Na and Cl. In contrast to the coastal springs, the 

thermal wells show depletion in both Mg and SO4 relative to 

seawater dilution lines—a noted characteristic of the injectate. 

However, the trends through the data miss the injectate and 

indicate mixing between two source components, dilute 

local groundwater and seawater that has been extensively 

hydrothermally altered, greatly reducing its Mg and SO4

concentrations. A three-component mixture that includes an 

injectate component could also be consistent with the data. 

However, the HDOH monitoring data for Malama-Ki and 

TH-3 plot on and around the older data from Janik and others 

(1994), which includes analyses from the 1970s in Kroopnick 

and others (1978), suggesting that these wells were not 

changing in response to geothermal operations through the 

year 2000.
Groundwater Chemistry 21

Stable Isotopes

The isotopic composition of groundwaters in the Puna 

area was investigated in the 1970s by McMurtry and others 

(1977). Scholl and others (1996) established an extensive 

network of precipitation collectors in the region in the early 

1990s and found that rainfall on the southern part of the island 

plotted on a line with formula δD = 8.0 δ18O + 12. They 

defined this formula as the local meteoric water line (LMWL)

and noted that it matched the earlier findings of McMurtry and

others (1977). 

Scholl and others (1995), in their appendix 2, reported 

isotopic values for many of the springs and wells sampled in 

our study and averaged the values from 2-3 different samples 

of each feature with the earlier data from McMurtry and others 

(1977). In figure 12A, the isotopic data for our 2014 samples 

is compared with that in appendix 2 of Scholl and others 

(1995) for wells and springs in the Puna area. The two datasets 

show an overall similarity despite the fact that some sampling 

locations differ. However, the new spring data are clearly 

shifted upward (toward less negative δD values) relative to 

the older data. The springs puzzlingly plot on or near the 

LMWL of Scholl and others (1995), even though they contain 

a component of heated seawater. Closer inspection reveals that 

the new data from the groundwater wells plot slightly to the 

left of the LMWL; that is, the change in isotopic composition 

is not restricted to the springs.

The isotopic composition of precipitation, and hence 

groundwater, in a given area can shift over time in response 

to changing climatic conditions. A change in storm tracks 

or precipitation patterns that persists for some months could 

conceivably cause a temporary shift in the LMWL in a 

setting like the Puna area, where recharge and groundwater 

velocities are high. The 2014 data for supply and monitoring 

wells adhere to a line with a formula δD = 7.86 δ18O + 13.2 

(fig. 12B) With our limited number of sampling points, we 

cannot define a new LMWL, but we take our line of best fit to

reasonably characterize Puna groundwater in 2014. Relative 

to this line, the springs plot in the direction of seawater as 

expected. Isotope and Cl data combine (figs. 12C,D) to 

0

20

40

60

80

0

20

40

60

80

1991 1995 1999 2003 2007 2011 2015

Concentration, in milligrams per liter

Temperature, in degrees Celsius

B

A

0

300

600

900

1,200

Concentration, in milligrams per liter

EXPLANATION

Cl

Na

Ca

Mg

T

K

Figure 10. Temperature (T in °C) 

and concentration (in mg/L) of several 

major species in MW-2 over time 

based on Hawai‘i State Department 

of Health records (open symbols). 

Filled symbols show results for our 

sample of April 30, 2014. A) Na (blue 

diamonds), Cl (green circles); B) K 

(purple diamonds), Ca (squares), Mg 

(triangles), T (red circles).
22 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

Cl, in milligrams per liter

0

2,000

1,000

4,000

3,000

5,000

0

400

200

800

600

1,000

0

120

60

240

180

300

0

120

60

240

180

300

0

2

1

4

3

5

0

200

100

400

300

500

A B

C D

E F

0 2,000 4,000 6,000 8,000 0 2,000 4,000 6,000 8,000 10,000

SO4, in milligrams per liter K, in milligrams per liter Ca, in milligrams per liter

Na, in milligrams per liter Mg, in milligrams per liter B, in milligrams per liter

TH3

Malama-Ki

Allison

Injectate

Injectate dilution

Seawater dilution

EXPLANATION

Water-supply wells

Kapoho Shaft

MW-1, MW-3

MW-2

Coastal springs

Figure 11. Data for thermal groundwater wells 

added to data of figure 8, concentrations of selected 

chemical species versus Cl (note changes in scale for 

some species). TH 3, red circles; Malama-Ki, brown 

circles; Allison, purple circles. Open symbols from 

Janik and others (1994); filled symbols from Hawai‘i 

State Department of Health records 1991–2000.
Groundwater Chemistry 23

0 2,000 4,000 6,000 8,000 10,000

Cl, in milligrams per liter

-5 -4 -3 -2 -1 0

0 2,000 4,000 6,000 8,000 10,000

-5 -4 -3 -2 -1 0

δ18O, in parts per mil

δD, in per mil

–5

–10

–20

–15

–25

0

–30

–5

–10

–20

–15

–25

0

–30

δ18O, in per mil

–5

–4

–2

–3

–1

0

–5

–10

–20

–15

–25

0

–30

C D

A B

Groundwater wells 

including Kapoho Shaft

MW-1, MW-3

MW-2

EXPLANATION

Coastal springs

Injectate

SMOW

LMWL

Figure 12. Stable isotope results. Groundwater 

wells including Kapoho Shaft, green circles; MW-1 and 

MW-3, red triangles; MW-2, purple square; coastal 

springs, blue and black diamonds; injectate, black 

circle. Results from this study are shown as filled 

symbols; open symbols are data reported in appendix 

2 of Scholl and others (1995). Open black triangle 

represents standard mean ocean water (SMOW). A) 

δD versus δ18O (in per mil) with local meteoric water 

line (LMWL) of Scholl and others (1995). B) 2014 

results only with regression line for wells (dotted line). 

C) δ18O (in per mil) versus Cl (in mg/L). D) δD (in per 

mil) versus Cl (in mg/L). Solid black line in C and D

extends from the monitoring wells to the composition of 

seawater at 19,000 mg/L Cl.
24 Groundwater Chemistry in the Vicinity of the Puna Geothermal Venture Power Plant, Hawai‘i

support the inference that the springs are mixtures of heated 

seawater and local groundwater. This groundwater appears 

to be isotopically similar to that in the monitoring wells near 

PGV. An injectate component would not be recognizable on 

the basis of stable isotopes.

Some part of the change in the δD values of the springs 

over time, and the apparent shift to higher average salinity 

(fig. 12D), could reflect changing conditions at depth (for

example, in the conductive halo), which might include 

boiling and steam formation as hypothesized by Janik and 

others (1994). However, explanations for the small observed 

changes, and any linkage to geothermal development, are 

speculative at this point.

Conclusions

In response to concerns raised in the report by Adler 

(2013), our groundwater sampling program focused on 

water-supply wells and on thermal springs in the coastal 

environment. We were able to access, sample, and analyze 

nearly all of our intended targets for pentane and isopropanol, 

two tracer compounds that enter the fluid at the PGV power

plant and are injected into the deep geothermal reservoir. 

Isopropanol was not detected in any groundwaters. Traces of 

pentane were detected in one of the PGV monitoring wells 

(MW-2) and in one sample from Keonepoko Nui well #2. 

Replicate samples indicate that the “detect” at Keonepoko Nui 

is spurious. The pentane in MW-2 could be linked to PGV 

injectate, but alkane abundances are consistent with a natural 

source, such as buried organic matter that is degraded at the 

warm aquifer temperatures. Thus, neither tracer provided

meaningful evidence for contamination of groundwater by 

PGV fluids, although the recent onset of isopropanol use

(September 2013) would probably preclude its migration 

to sites far from the power plant prior to our sampling. 

Pentane was found to degrade in the hot H2S-rich geothermal 

fluids, and degradation of isopropanol cannot be ruled out.

Degradation complicates, but does not exclude, the use of 

these tracers to detect leakage of reservoir fluids into shallow

groundwater. They would certainly be of great value for local 

detection of direct leakage of injectate into groundwater due to 

well casing failure, for example.

Previous studies of groundwater chemistry in the Puna 

area (for example, Sorey and Colvard, 1994; Janik and others, 

1994) have invoked conductive heat flow from the geothermal

reservoir into saline groundwater that is consequently altered

from its original seawater composition. The postulated hot 

saline groundwater is diluted by shallow groundwater before 

emerging at the coastal springs or, after great dilution, being 

pumped from the Keauohana wells. Our new water chemistry 

data fit this general model.

The Puna area hydrology is characterized by 

rapid infiltration of rainfall, a thin freshwater lens, and

convective instabilities near the rift zone (Thomas, 1987; 

Ingebritsen and Scholl, 1993). These and other factors 

lead to temporal variations in mixing between dilute and 

saline end-member fluids and are likely responsible for

the short-term compositional variability that is a wellknown feature of many Puna groundwaters. This variability 

complicates the use of water chemistry in assessing 

geothermal impacts. However, long-term or abnormal 

changes in chemistry can still be recognized at features 

with a long history of sampling. For instance, our results 

reveal higher average salinity and a small but distinct 

shift in the isotopic composition of the coastal springs 

from values measured in the 1970s–1990s. We also find a

long-term drop in temperature and increase in Mg at well 

MW-2. These changes could be due in part to alteration 

of pressure gradients and heat flow at depth in response to

geothermal development, but direct linkage would be hard 

to substantiate. Apart from these changes, the similarity 

between our results, the results from mandated monitoring 

over the previous 20 years, and results from samples from 

the 1970s–1990s imply that geothermal production has not 

had a significant impact on groundwater chemistry.

Our sampling protocol was developed for flowing wells

or springs that discharge at the land surface. Sample coverage 

did not include any offshore vents of warm water, which exist 

in the area, and we point out that contaminant transport from 

the geothermal reservoir directly to such features could occur 

on timescales much different from those based on shallow 

groundwater velocities assumed in this report. We were 

also unable to sample any of the hot groundwater wells that 

lack pumps and are down-gradient from PGV. We reviewed 

the water chemistry data from HDOH records for samples 

collected downhole through the year 2000 at Malama-Ki and 

TH-3. These data do not show obvious evidence of longterm trends related to geothermal production, but do show 

significant scatter that might obscure such trends. Samples

suitable for pentane and isopropanol analysis could be 

obtained from such wells, but temporary installation of pumps 

would likely be required.

If any immediate follow-up to our study is desired, we 

recommend that it focus on the hot groundwater wells, using 

pumps to completely flush the wellbores, and on offshore

vents of warm water, using underwater sampling techniques

as necessary. Given that obvious geothermal impacts were 

not observed in the groundwaters we studied, we suggest 

only minor changes to the existing onshore monitoring 

program: (1) the analytical protocol for the Keauohana 

and Pāhoa public-supply wells near PGV should include

isopropanol on at least an annual basis; (2) a sampling 

program should be established for a representative group 

of coastal springs to ensure that comprehensive chemical 

analyses are performed annually or at least every few years 

(these analyses should include isopropanol and perhaps 

pentane); (3) isopropanol analyses should be performed 

on the monitoring wells (MW-1 through MW-3) at least 

annually, and more frequently if casing pressures in the

injection well show any indication of leakage.
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Produced in the Menlo Park Publishing Service Center

Manuscript approved for publication September 23, 2015

Edited by Katherine D. Jacques

Layout and design by Jeanne S. DiLeo
W.C. Evans and others—Groundwater Chemistry in the Vicinity of the Puna Geotherman Venture Power Plant— Scientific Investigations Report 2015–5139