Prepared in cooperation with 

FALLON PAIUTE-SHOSHONE TRIBE

Characterization of Surface-Water Quality in the S-Line 

Canal and Potential Geochemical Reactions from Storage

of Surface Water in the Basalt Aquifer near Fallon, Nevada

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2005–5102
COVER: View looking north of the top of Rattlesnake Hill. Photograph taken by Douglas K. Maurer, 2001. 
Characterization of Surface-Water Quality in the S-Line 

Canal and Potential Geochemical Reactions from Storage

of Surface Water in the Basalt Aquifer near Fallon, Nevada

By Alan H. Welch, Douglas K. Maurer, Michael S. Lico, and John K. McCormack

Prepared in cooperation with the

FALLON PAIUTE-SHOSHONE TRIBE

Scientific Investigations Report 2005–5102

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Carson City, Nevada: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

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endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

For additional information contact:

Director

USGS, Nevada Water Science Center

333 W. Nye Lane, Room 203

Carson City, NV 89706-0866

email: GS-W-NVpublic-info@usgs.gov

http://nevada. usgs.gov
iii

Contents

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

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

Purpose and Scope ............................................................................................................................. 5

Acknowledgments............................................................................................................................... 5

Methods Used ............................................................................................................................................... 5

Water Sampling Methods................................................................................................................... 5

Geochemical and Mineralogic Analytical Methods ...................................................................... 5

Physical Setting ............................................................................................................................................ 6

Hydrogeologic Setting ........................................................................................................................ 6

Recent Geologic History............................................................................................................ 6

Description of Aquifers.............................................................................................................. 7

Chemistry and Mineralogy of the Basalt Aquifer......................................................................... 12

Characterization of Surface Water in the S-Line Canal ....................................................................... 15

Geochemical Modeling of Recharge....................................................................................................... 18

Modeling Approach........................................................................................................................... 18

Model Scenarios and Limitations ................................................................................................... 20

Model Results..................................................................................................................................... 22

Summary and Conclusions........................................................................................................................ 25

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

Appendixes .................................................................................................................................................. 29

Figures

Figure 1. Map showing geographic features of Carson Desert hydrographic area and

Carson River basin....................................................................................................................... 2

Figure 2. Map showing geographic features of Lahontan Valley and location of irrigated 

land, phreatophytes, and discharging playas. ........................................................................ 3

Figure 3. Map showing lateral extent of basalt aquifer and location of wells drilled into 

basalt aquifer................................................................................................................................ 4

Figure 4. Oblique view of basalt aquifer, looking toward northeast..................................................... 8

Figure 5. Photograph showing scoriaceous cinders near the top of Rattlesnake Hill..................... 9

Figure 6. Photograph showing vesicular basalt flows on the southern flank of 

Rattlesnake Hill .......................................................................................................................... 10

Figure 7. Photograph showing fractured, vesicular basalt from well DB-1 recovered from

a depth of 441–442 ft below land surface. ............................................................................ 11

Figure 8. Optical microscope micrograph of Type 1 basalt from well DB-1 at 545 ft with 

crossed polarizers and uncrossed polarizers....................................................................... 13

Figure 9. Optical microscope micrograph of Type 2 basalt from well DB-1 at 441 ft with

crossed polarizers and uncrossed polarizers....................................................................... 14

Figure 10. Scanning electron microscope micrograph of vug-filling material from well 

DB-1 at a depth of 625 ft showing phillipsite........................................................................ 15
iv

Tables

Table 1. Bulk chemical composition of the basalt aquifer encountered at test hole DB-1 ........ 12

Table 2. Concentration of elements released from basalt rock samples following:

 A. Cation exchange using ammonium chloride ................................................................. 17 

 B. Anion exchange using potassium nitrate ...................................................................... 17

 C. Extraction of carbonate minerals by sodium acetate and acetic acid. .................... 17

 D. Extraction of iron and manganese oxides by hydroxylamine hydrochloride and 

 acetic acid 17

Table 3. Mean bulk density and porosity of basalt samples ............................................................ 19

Table 4. Surface complexation constants for carbonate adsorption on ferrihydrite .................. 19

Table 5. Initial conditions and reactions used for geochemical modeling of injection

 and infiltration of surface water and its subsequent recovery. ....................................... 21

Figure 11. Scanning electron microscope micrograph of vug-filling material from well 

 B-7 at a depth of 72 ft showing dolomite rhomboids above phillipsite rhomboids

and phillipsite prisms on surface of adularia ........................................................................ 16

Figure 12. Graph showing arsenic and dissolved organic carbon concentrations in S-Line

 Canal and mean daily flow in the Carson River below Lahontan Reservoir ................... 19

Figure 13. Graphs showing results of geochemical simulation of injection well model of 

 recharge into the basalt aquifer ............................................................................................ 23

Figure 14. Graphs showing results of geochemical simulation of basin-infiltration model of 

 recharge into the basalt aquifer ........................................................................................... 24
v

Conversion Factors and Datums

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi)

liter

square foot per pound (ft2/lb)

1.609

33.82

0.00278

kilometer (km)

ounce

square meters per gram (cm2/g)

Flow rate

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3/yr)

foot per year (ft/yr) 0.3048 meter per year (m/yr)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Water quality and other units used in this report:

g/μg gram per microgram mg/kg milligram per kilogram

g/cm3 gram per cubic centimeter mg/L milligram per liter

g/mol gram per mol mol/mol mole per mole

 g/L gram per liter mol/L mole per liter

 μm micrometer mm millimeter 

μg/L microgram per liter nm nanometer

μS/cm microsiemens per centimeter at 25°C pCi/L picocuries per liter

mg/g milligram per gram 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, 

formerly called “Sea-Level Datum of 1929”), which is derived from a general adjustment of the 

first-order leveling networks of the United States and Canada.
vi
Abstract

The Fallon basalt aquifer serves as the sole source of 

municipal water supply for the Lahontan Valley in westcentral Nevada. Principal users include the City of Fallon, 

Naval Air Station Fallon, and the Fallon Paiute-Shoshone 

Tribe. Pumpage from the aquifer increased from about 

1,700 acre-feet per year in the early 1970’s to more than 

3,000 acre-feet per year in the late 1990’s, and has been 

accompanied by declines in water levels and changes in 

water quality. Storage of surface water in the basalt may 

mitigate the effects of pumpage, but may cause undesirable 

changes in water chemistry. In May 2001, the U.S. Geological 

Survey began a study, in cooperation with the Fallon PaiuteShoshone Tribe, to characterize the surface-water quality of 

the S-Line Canal, a likely source of water for augmenting 

recharge. Because arsenic concentrations in ground water 

of the basalt aquifer exceed drinking water standards, the 

potential for arsenic release to artificial recharge was explored 

by using geochemical modeling. Model results suggest that 

arsenic release may increase concentrations to levels that could 

limit the use of artificial recharge. Field-based experiments are 

needed to evaluate the underlying model assumptions. 

Introduction

A basalt aquifer near Fallon, Nevada, in the Carson 

Desert Hydrographic Area, is the sole source of water for 

municipal supply to the City of Fallon, Naval Air Station 

Fallon, and the Fallon Paiute-Shoshone Tribe (fig. 1). The 

Carson Desert is the terminus of the Carson River and also 

receives surface-water flow from the Truckee River through 

the Truckee Canal (fig. 1). The basalt that forms the basalt 

aquifer crops out at Rattlesnake Hill, an eroded volcanic cone, 

about a mile northeast of Fallon. The water-producing part of 

the basalt is buried beneath sediments deposited by the Carson 

River and ancient Lake Lahontan to depths of 600 feet near its 

edges (figs. 2 and 3). In three dimensions, the basalt is a mushroom-shaped body of highly permeable volcanic rock. Viewed 

from above the aquifer is oval-shaped, about 4 miles wide and 

10 miles long (fig. 3). 

Pumpage from the basalt aquifer increased from about 

1,700 acre-ft/yr in the early 1970’s to over 3,000 acre-ft/yr in 

the late 1990’s, causing water levels in the aquifer to decline as 

much as 12 ft over the same time period (Maurer and Welch, 

2001, p. 30). Increased pumpage also is thought to have 

caused changes in water quality; Maurer and Welch (2001) 

reported the concentration of dissolved chloride in water 

pumped from the basalt by Navy and City of Fallon wells has 

increased from the 1970’s to the late 1990’s. Although chloride concentrations are still below the drinking-water standard 

of 250 mg/L, these changes have caused concern over the 

continued viability of the basalt aquifer as a source of water as 

development in the area continues. Concentrations of arsenic 

in the aquifer are about 0.1 mg/L, exceeding the drinkingwater standard of 0.01 mg/L (Federal Register, 2001). Arsenic 

concentrations apparently did not change between the early 

1970’s and the late 1990’s, although changes in analytical and 

sampling methods could mask actual changes (Maurer and 

Welch, 2001, p. 10 and 48). 

Declining water levels and changing water quality might 

be mitigated by storing treated surface water in the basalt 

aquifer for subsequent use. Treated surface water could be 

injected directly into the basalt aquifer or infiltrated through 

surface ponds on Rattlesnake Hill. The combined use of 

ground-water and surface-water resources often is called 

conjunctive use, and potentially could slow ground-water level 

declines and decrease chloride and arsenic concentrations. 

However, study is needed to evaluate the potential for arsenic 

release from the basaltic rock to the recharged water. 

With this objective in mind, in April 2001, the U.S. 

Geological Survey (USGS), in cooperation with the Fallon 

Paiute-Shoshone Tribe, began a study to characterize the water 

quality of the S-Line Canal near Rattlesnake Hill (fig. 3), a 

likely source for surface water, and to determine the potential 

for this water to cause arsenic release from the basalt.

Characterization of Surface-Water Quality in the S-Line 

Canal and Potential Geochemical Reactions from Storage 

of Surface Water in the Basalt Aquifer near Fallon, 

Nevada

By Alan H. Welch, Douglas K. Maurer, Michael S. Lico, and John K. McCormack
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Figure 1. Geographic features of Carson Desert hydrographic area and Carson River basin.

2 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
NAS

Fallon

4,000

4,000

4,000

4,000

4,000

5,000

5,000

5,000

4,000

4,000

5,000

4,200

4,200

4,200

Roads and hydrology from U.S. Geological Survey digital data,

1:100,000, 1979-80. Hypsography and water bodies from U.S. Geological Survey digital data, 1:250,000, 1971

Universal Transverse Mercator Projection, Zone 11

0 5 10 MILES

0 5 10 KILOMETERS

STILLWAT

E

R

RANGE

5,000

5,000

STILLWATER

WILDLIFE

MANAGEMENT

AREA

Carson

Lake

Stillwater

HOT

SPRINGS

MOUNTAINS

LAHONTAN

MOUNTAINS

BUNEJUG

MOUNTAINS

L A H O N T A N

UPSAL HOGBACK

RATTLESNAKE

HILL

Soda Lake

Stillwater Point

Reservoir

River

MARSH

STILLWATER

S ALT

WEL LS

BASI N

WH ITE T H RON E

M OU N TAI N S

Salt Wells

Fallon

Stillwater

HOT

SPRINGS

MOUNTAINS

LAHONTAN

MOUNTAINS

BUNEJUG

MOUNTAINS

L A H O N T A N

UPSAL HOGBACK

RATTLESNAKE

HILL

Soda Lake

Carson

River

Stillwater Point

Reservoir

River

MARSH

STILLWATER

S ALT

WEL LS

BASI N

WH ITE T H RON E

M OU N TAI N S

Carson

Lake

Salt Wells

CARSON SINK

Lyon Co

119°00' 118°45' 118°30'

39°45'

39°30'

39°15'

R. 27 E. R. 28 E. R. 29 E. R. 30 E. R. 31 E. R. 32 E.

T.

22

N.

T.

21

N.

T.

20

N.

T.

19

N.

T.

18

N.

T.

17

N.

T.

16

N.

Fallon

Carson

River

NAS

Fallon

STILLWATER

WILDLIFE

MANAGEMENT

AREA

EXPLANATION

Discharging playa—From Glancy and Katzer (1975, pl. 1)

Phreatophytes—From Glancy and Katzer (1975, pl. 1)

Irrigated land, 1984-90—From Bureau of Reclamation

digital data (Charles Johnson, Bureau of Reclamation,

1993)

Hydrographic-area boundary—From Rush (1968)

Topographic contour—Shows altitude of land surface.

Contour interval, 1,000 feet, with supplemental contour

at 4,200 feet. Datum is sea level

Wetlands

4,200

5,000

4,000

Churchill Co

4,000 42

95

50

50

50

95

South

Branch

V A L L E YV A L L E Y

Carson

South

Branch

Figure 2. Geographic features of Lahontan Valley and location of irrigated land, phreatophytes, and discharging playas.

Introduction 3
NAS, Fallon

A-Line

Canal

Harmon Reservoir

Harmon Drain

Oles

Pond

Fallon

L A H O N T A N

V A L L E Y

RATTLESNAKE

HILL

Carson

Indian

Lakes

Diagonal Canal

50

50

95

95

Fallon

L A H O N T A N

V A L L E Y

RATTLESNAKE

HILL

S-Line Reservoir S-Line Reservoir

Oles

Pond

S-Line Canal

Schottner

Drain

Indian

Lakes

Diagonal Canal

Naval Air Station

Fallon

S-5

Canal

Wade Drain

S-Line Canal

L-Line

Canal

Carson

River

0 3 KILOMETERS

0 3 MILES

EXPLANATION

Roads and hydrology from U.S. Geological Survey digital data, 1:100,000, 1979-80

Universal Transverse Mercator Projection, Zone 11

Water bodies from U.S. Geological Survey digital data, 1:250,000, 1971

Political boundaries and canal names from U.S. Geological Survey, 1:24,000, 1969-87;

1:100,000, 1979-80

B-3 Well location and well number

Sampling site on S-Line Canal

Approximate extent of basalt at depth of 600 feet

below land surface—From Glancy (1986)

R28E R29E R30E

T

19

N

T

18

N

T

20

N

118°50'

39°34'

39°30'

39°26'

118°45' 118°40'

B-3

DB-2

DB-3

DB-1

Figure 3. Lateral extent of basalt aquifer and location of wells drilled into basalt aquifer.

4 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
Purpose and Scope

The purpose of this report is to present results of waterquality analyses of surface water in the S-Line Canal near 

Rattlesnake Hill and geochemical analyses of samples of 

basaltic rock and associated coatings. Results of modeling 

potential geochemical reactions within the basalt aquifer during recharge also are presented. Nine samples of surface water 

were obtained from the S-Line Canal from May 2001 through 

October 2002 and analyzed for major ions, trace metals, 

nutrients, radioactive constituents, dissolved and total organic 

carbon, pesticides and polychlorinated biphenyls, dissolved 

and total mercury, and selected wastewater indicators. Five 

samples of basaltic rock collected from surface outcrops on 

Rattlesnake Hill and from cores taken during drilling of the 

basalt were analyzed for the chemical composition of minerals 

making up the basalt, and of coatings on fractures and within 

vesicles of the basalt. Basalt samples also were subjected to 

chemical extractions to evaluate the cation and anion exchange 

capacity and the composition of carbonate and iron oxide. 

Results of the water-quality and rock analyses were used to 

simulate geochemical reactions that could affect arsenic concentrations using the computer program PHREEQC (Parkhurst 

and Appelo, 1999). 

Acknowledgments

The authors thank Blair Jones and Daniel Webster, 

USGS, Reston, Virginia, for their X-ray diffraction work; Paul 

Lechler, University of Nevada, Reno, for whole-rock analyses; 

Rikkert Vos, BC Research Inc., Vancouver, British Columbia, 

Canada, for chemical extractions; and Lawrence Feinson, 

USGS, for simulations using PHREEQC. Richard Sanzalone, 

USGS, provided valuable insight into the use and interpretation of chemical extractions. Keith Halford, USGS, provided 

spreadsheet assistance.

Methods Used

Water Sampling Methods

Water samples were collected from S-Line Canal (fig. 

3) during 2000–2002 (site 1031221902 in Berris and others, 

2003). Samples were collected monthly or bimonthly when the 

canal was flowing, typically from April-May to about October (see Appendix 1). Water samples were obtained using the 

equal-width-increment method described by Wilde and Radtke 

(1998). A DH-81 handheld sampler fitted with a Teflon nozzle 

and a 1-L bottle was used to obtain water at each vertical in 

the cross section and these samples were composited into 3-L 

Teflon bottles. The samples were split into subsamples using 

an all-Teflon cone splitter described by Capel and Larson 

(1996). Each subsample was treated with the appropriate 

preservation method as outlined by Wilde and Radtke (1998). 

Sample processing was done using techniques described by 

Wilde and Radtke (1998). Specific conductance and pH were 

measured on a split of the raw sample. Alkalinity was determined in the field using incremental titration with sulfuric acid 

on an aliquot of filtered water. Dissolved oxygen and temperature were measured directly in the canal. 

Ground-water samples were collected from well B-3 

(fig. 3; Appendix 1) located near a potential recharge basin on 

the eastern flank of Rattlesnake Hill. Well B-3 is a 71-ft deep, 

2-in. PVC, monitoring well. The well is screened just below 

the water table. The basalt aquifer is encountered at 

32 ft below land surface at the well, and accordingly, the 

water quality at well B-3 is believed to be representative 

of the water beneath the site of a potential recharge basin. 

Ground-water samples were collected and processed 

following protocols described by Wilde and Radtke (1998). 

Before water samples were collected, the water level in the 

well was measured, the well was purged of at least three wellbore volumes of water, and field parameters (pH, specific conductance, temperature, and dissolved oxygen) were measured 

in a flow-through chamber until they were stable (Wilde and 

Radtke, 1998). An all stainless steel and Teflon pump system 

was used to obtain water samples from wells. Water samples 

that required filtration were filtered with in-line 0.45-μm poresize capsule filters. Whole-water samples were filled directly 

from the discharge line of the pump. Water samples were 

preserved following methods outlined in Wilde and Radtke 

(1998). Alkalinity was determined in the field using incremental titration with sulfuric acid on an aliquot of filtered sample.

Geochemical and Mineralogic Analytical 

Methods

Water samples were analyzed at the USGS National 

Water Quality Laboratory in Lakewood, Colorado and the 

USGS Stable Isotope Laboratory in Reston, Virginia. Major 

cations and most trace elements were analyzed using inductively coupled plasma mass spectrometry (Fishman, 1993; 

Fishman and Friedman, 1989; Garbarino, 1999; Struzeski and 

others, 1996). Arsenic and selenium were analyzed by graphite 

furnace atomic absorption spectrometry as described by Jones 

and Garbarino (1999). Nutrient species were analyzed by the 

methods described in Fishman (1993), Fishman and Friedman 

(1989), and Patton and Truitt (2000). Pesticides were extracted 

from the water samples with C-18 solid-phase extraction and 

analyzed using capillary-column gas chromatography with 

mass spectrometry (Madsen and others, 2003; Zaugg and 

others, 1995). Wastewater indicators were analyzed by polystyrene-divinylbenzene solid-phase extraction and capillarycolumn gas chromatography with mass spectrometry (Zaugg 

and others, 2002). The stable isotopes of water were determined using methods described by Coplen and others (1991) 

for hydrogen and those described by Epstein and Mayeda 

(1953) for oxygen. Gross alpha and beta radioactivity were 

determined using alpha and beta counting methods described 

in Thatcher and others (1977).

Methods Used 5
The mineralogy of the basalt and coatings were determined by X-ray diffraction by Daniel Webster, USGS, Reston, 

Virginia, and by optical microscopy. Basalt samples and 

vug-filling material were examined by SEM/EDS (scanning 

electron microscopy/energy dispersive spectrometry) using a 

JEOL model 840A with KEVEX EDS/imaging programming. 

The EDS is capable of qualitative identification of elements 

having an atomic weight of 12 or greater. Samples were airdried, mounted on metal tabs, and coated with a thin layer of 

gold. Images can be taken simultaneously with EDS analyses. 

Whole rock analyses of cuttings retrieved during drilling of 

test hole DB-3 (fig. 3) were made under the supervision of 

Paul Lechler, Nevada Bureau of Mines and Geology, using 

X-ray fluorescence. Results of the mineralogical examination 

expand on the work of Lico and Seiler (1994), who provide a 

description of the mineralogy of cuttings from a well owned 

by the Fallon Paiute-Shoshone Tribe on the west side of 

Rattlesnake Hill (fig. 3).

Chemical extraction methods, which also are known as 

partial solution techniques, have been developed to obtain 

information about the chemistry of heterogeneous earth materials, such as rocks and soils. Under ideal conditions, sequential extractions can provide information on the association of 

elements with various minerals within a rock or soil. Reactions involving exchangeable ions, carbonate minerals, and 

iron oxide are of particular concern in the Fallon area because 

of potential release of arsenic from rocks and soils into the 

ground water. Commonly, extraction solutions are applied 

in order from the least to most chemically aggressive. For 

instance, a sequence of extractions could attempt to determine 

solutes that are progressively released by exchange, followed 

by dissolution of carbonate minerals, organic material, and 

sulfide minerals. Extractions for organic material and sulfide 

minerals were not used in this study.

Basalt obtained by drilling and the surface samples 

taken from rock outcrops were selected for sequential extraction using the methods of Sumner and Miller (1996) and 

Tessier and others (1979). The extractions were performed 

in duplicate on samples weighing about 50 g. The samples 

were approximately 3⁄4-in. by 3⁄4-in. pieces of drill core or 

outcrop and were not crushed prior to extraction. This size 

was selected to approximate the actual rock surface area of 

vesicular and fractured basalt within the aquifer. Details of the 

analytical steps are presented in Appendix 3.

Physical Setting

Carson River water and diversions from the Truckee 

River are stored in Lahontan Reservoir and used to irrigate 

about 56,000 acres of land in Lahontan Valley, the name commonly applied to the irrigated part of the Carson Desert (fig. 2; 

Maurer and Welch, 1996, p. 4). Irrigated lands form the Carson Division of the Newlands Project, constructed from 1902 

to 1915. Canals provide water to agricultural land, including 

the S-Line and L-Line Canals that flow south and east of 

Rattlesnake Hill (fig. 3). Surface water not used for irrigation 

drains north to the Carson Sink, northeast to wetlands of the 

Stillwater Marsh, and south to the Carson Lake wetlands 

(fig. 2).

Alfalfa is the main irrigated crop in the valley along with 

pasture, other forage crops, and some cereal and vegetable 

crops. Cottonwood is abundant near homes and ranches in the 

irrigated part of the valley, willows line many of the canals, 

and cattails are present in many drains. Except for the Carson 

Sink, which is largely barren, non-irrigated areas are sparsely 

vegetated with greasewood, rabbitbrush, saltgrass, and marsh 

grasses.

The city of Fallon is the major and growing population 

center in the area. The population of Fallon has increased from 

about 3,000 in the early 1970’s (Glancy, 1986, p. 27) to 8,800 

in 2000 with about 15,000 additional people living in the surrounding unincorporated parts of the county (http://factfinder.

census.gov). Agriculture is a major economic base in the area, 

along with employment at the Naval Air Station Fallon. 

The floor of Lahontan Valley is a relatively flat plain, 

sloping from about 3,960 ft above sea level near Fallon to 

about 3,870 ft near the Carson Sink (fig. 2). Several low-lying 

mountain ranges rising to about 5,500 ft in altitude surround 

the valley on the north, south, and west. The Stillwater Range, 

rising to 8,800 ft in altitude, bounds the valley on the east. 

Lahontan Valley is in the rain shadow of the Sierra Nevada 

and received an average 5.3 in. of annual precipitation from 

1960 to 1991 (Owenby and Ezell, 1992, p. 15). Summer temperatures reach an average maximum of about 90o

F in July and 

August, and average minimum temperatures are about 18oF 

in December and January (Owenby and Ezell, 1992, p. 11). 

Open-water evaporation is about 5 ft/yr (Bureau of Reclamation, 1987, p. 1–7).

Hydrogeologic Setting

Recent Geologic History

During the Pleistocene Epoch [about two million years 

before present (Ma) to ten thousand years before present (ka)], 

lakes formed in the Carson Desert, expanded, and shrank to 

complete dryness several times under the influence of changing glacial climates (Axelrod, 1956; Morrison, 1964). During 

high stands, the lakes coalesced to form ancient Lake Lahontan having a depth of more than 500 ft near Fallon (Davis, 

1978, p. 2; Morrison, 1991, p. 288). High stands of Lake 

Lahontan were from 1.2 Ma to 850 ka, 650 to 600 ka, 400 to 

130 ka, and 25 to 10 ka (Benson, 1991; Benson and others, 

1990, p. 241). During high stands of Lake Lahontan, thick clay 

beds were deposited in the deeper parts of Lake Lahontan, 

deltas were formed on the western side of the valley where the 

Carson River entered the lake, and sand and gravel beaches 

6 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
and bars were formed by wave action along the shorelines 

(Morrison, 1964, p. 28–71). During interglacial periods when 

Lake Lahontan was dry, large sand-dune and sand-sheet 

complexes covered much of the valley floor and the Carson 

River meandered across the valley floor forming river channels 

which are now buried. As lake levels rose and fell, these depositional environments moved back and forth across the valley 

floor, creating a complex mixture of Quaternary sediments, 

locally reaching a thickness greater than 2,500 ft (Maurer and 

Welch, 1996, p. 11).

Also during the Pleistocene Epoch, isolated volcanic 

activity produced Rattlesnake Hill, an eroded volcanic cone 

about 1 mi in diameter and about 200 ft high with a shallow crater at the center (Morrison, 1964, p. 23). The cone 

was formed by repeated basalt flows, issuing radially from 

Rattlesnake Hill for 2 to 7 mi. (fig. 2) to produce the mushroom-shape basalt aquifer described by Glancy (1986, p. 14). 

A sample of the basalt from the high point of Rattlesnake Hill 

was dated by whole-rock potassium-argon analysis to be 1.03 

± 0.05 Ma (Evans, 1980, p. 20), and argon-argon dates from 

the upper surface of the basalt near its western and southern 

extent range from 2.5 ± 0.3 Ma to 1.3 ± 0.2 Ma (Maurer and 

Welch, 2001, p. 16). Stratigraphic evidence shows that the 

basalt is older than the early high stands of Lake Lahontan 

(Morrison, 1964, p. 23) which indicates that the basalt was 

present during the entire history of Lake Lahontan.

Holocene Epoch deposits in the Carson Desert (less than 

10 ka) are eolian, alluvial, fluvial, deltaic, and shallow-lake 

sediments deposited after the last high stand of Lake Lahontan. An extremely dry, windy period followed the last high 

lake stand from 7 to 4 ka, and shallow lakes were formed in 

the Carson Desert during the last 5 to 4 ka (Davis, 1978; Morrison, 1964, p. 8). The last of the shallow lakes dried up just 

before non-native Americans entered the area in the 1800’s 

(Davis, 1978, p. 8).

Description of Aquifers

The basalt aquifer was first described in detail by Glancy 

(1986), who also defined three basin-fill aquifers that envelope the basalt. Glancy (1986, p. 41) defined a shallow aquifer 

extending from the water table, generally 5 to 10 ft below 

land surface, to a depth of 50 ft below land surface. Below the 

shallow aquifer, an intermediate aquifer extends to depths of 

500 to 1,000 ft, the approximate range of sediments bearing 

fresh water near the basalt aquifer (Glancy, 1986, p. 51). The 

intermediate aquifer contains fresh water beneath much of the 

southern Carson Desert. A deep aquifer extends beneath the 

intermediate aquifer to depths of several thousand feet, and is 

thought to be mainly non-potable because of a high dissolvedsolids content (Glancy, 1986, p. 51 and 60).

Glancy (1986) delineated the extent of the basalt aquifer 

using lithologic descriptions from driller’s logs and surface 

electrical resistivity soundings. He described it as an asymmetrical, mushroom-shaped body of basalt exposed at Rattlesnake 

Hill with the bulk of the basalt enveloped by the sedimentary 

aquifers (Glancy, 1986, p. 13–14). Drillers' logs show the 

basalt is 400–600 ft below land surface near its southwestern 

extent about 2 mi southwest of Rattlesnake Hill, and about 

200–300 ft below land surface near its northeastern extent 

5–7 mi northeast of Rattlesnake Hill (fig. 4). Electrical 

resistivity data indicates that at depths greater than 1,000 ft 

below land surface, the basalt narrows to a thin neck approximately centered beneath Rattlesnake Hill. Seismic-reflection 

profiles presented by Maurer and Welch (2001, pgs.16 and 19) 

largely confirm the lateral extent of the basalt described by 

Glancy (1986). The seismic profiles indicate the presence of 

a secondary vent in the northern part of the basalt that is not 

exposed at land surface (fig. 4).

Exposed basalt consists of loosely consolidated 

scoriaceous cinders near the top of Rattlesnake Hill (fig. 5) 

and vesicular flows along the flanks of Rattlesnake Hill (fig. 

6). Recent drilling at test hole DB-1, near the southern extent 

of the aquifer (fig. 3), penetrated about 300 ft of very porous 

and fractured basalt alternating with more massive zones 

(Maurer, 2002). Core material from test hole DB-1 (fig. 7) is 

similar in appearance to cuttings from other test wells drilled 

near the southern half of basalt aquifer and to the vesicular 

flows along the flanks of Rattlesnake Hill. To the north, test 

hole DB-2 penetrated about 340 ft of low permeability, brecciated and massive basalt (Maurer, 2002).

Water quality in the basalt aquifer generally is uniform 

over its lateral extent and is suspected to be a blend of fresh 

water and water with a higher dissolved solids content. The 

observed increase in dissolved chloride over the past 30 years 

indicates that more saline water may be migrating into the 

basalt aquifer. Maurer and Welch (2001, p. 48) suggest the 

source of the more saline water may be near the southern 

edge of the basalt from depths greater than 300 ft below land 

surface. Recent drilling (Maurer, 2002) shows that water quality within the basalt, near its southern extent, is fairly uniform 

through its entire thickness of about 290 ft, and that ground 

water in the underlying intermediate aquifer contains chloride 

concentrations of nearly 2,000 mg/L. Thus, the underlying 

aquifer could be a source for the increasing chloride concentrations. Maurer and Welch (2001, p. 42 and 43) suggest the 

basalt is recharged by a mixture of water from the shallow 

aquifer near Rattlesnake Hill, water from the intermediate 

aquifer on the southwest, west, and northwest side of the 

basalt, and more saline water from depths greater than 300 ft 

below land surface.

Physical Setting 7
Figure 4. Oblique view of basalt aquifer, looking toward northeast. Modified from figure 8B in Maurer and Welch (2001).

MILES

MILES

0

2

12

4

2

4

6

8

10

6

8

10

�����������

����������������������������������������� Vertical exaggeration approximately 8X 300

8 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
Figure 5. Scoriaceous cinders near the top of Rattlesnake Hill. 

Bottle is 10-inches high, used for scale.

Physical Setting 9
Figure 6. Vesicular basalt flows on the southern flank of Rattlesnake Hill. 

Wallet is used for scale.

10 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
Figure 7. Fractured, vesicular basalt from well DB-1 recovered from a depth of 441–442 ft below land surface. 

Physical Setting 11
Chemistry and Mineralogy of the Basalt Aquifer

The mineralogy of unweathered basalt is dominated by 

fine-grained plagioclase and augite, as determined by X-ray 

diffraction. The plagioclase and augite are partially altered to 

illite and chlorite. Optical microscopy reveal a classic olivine 

basalt: plagioclase, clinopyroxene, olivine, and opaque minerals in a fine-grained groundmass. Olivine and iron-bearing 

minerals (ilmenite or magnetite) are present in minor amounts 

(Lico and Seiler, 1994). Plagioclase occurs as finer groundmass and as somewhat larger phenocrysts. The plagioclase 

composition varies over the relatively narrow range of An50-

55 (labradorite to andesine-labradorite). Plagioclase exhibits 

both normal concentric zoning (more calcic cores) and oscillatory zoning. Clinopyroxenes are smaller and are typically 

subhedral groundmass materials, with few coarse phenocrysts. 

EDS analyses of the clinopyroxenes indicate that they are 

diopsidic because they contain very low aluminum and iron 

and abundant calcium and magnesium. Olivine typically forms 

larger grains, is subhedral, and colorless. EDS analyses of the 

olivine indicates a forsteritic composition because the olivine 

contains relatively small amounts of iron. EDS analyses of 

the opaque minerals indicate that most are ilmenitic (Fe-rich 

titanium oxides), but some contain significant chromium. The 

opaque minerals are not significantly magnetic.

Even though mineralogy of the basalts is consistent 

throughout the sections, they fall into two subtypes based 

on relative plagioclase and opaque mineral contents. Type 

1 is defined here as containing significantly less plagioclase 

and more opaque minerals than type 2. Typical images of 

both types are shown in figures 8 and 9. Comparison of these 

figures demonstrates the higher plagioclase and lower opaque 

mineral content of type 2 compared to type 1 basalt.

Despite a difference in plagioclase and opaque mineral 

concentrations between the two basalt types, plagioclase composition is very similar in both types, indicating they originated from similar, if not the same, parent magma. Several 

samples of both basalts are visibly argillized and chloritic. 

The high Loss-On-Ignition (LOI; table 1) indicates that these 

samples were weathered and altered, and probably include 

zeolite and clay materials. This alteration also may explain 

why the aluminum and potassium content of these samples is 

significantly higher than in most basalts. Conversely, the magnesium content is significantly lower than in most basalts. The 

low titanium values compared to typical basalts (table 1), and 

the olivine character of these samples indicates that they are a 

mid-ocean ridge type basalt. Arsenic concentrations for four 

basalt samples recovered from depths of 399–730 ft below 

land surface ranged from 0.66 to 1.2 mg/kg (table 1).

Table 1. Bulk chemical composition of the basalt aquifer encountered at test hole DB-1. 

[Symbol: --, not available]

Parameter, in weight 

percent except 

as noted

Sample depth, in feet Typical basalt1

390

to

399

433 482 730 Mean Standard 

deviation

SiO2 49.5 49.2 50.4 51.2 50.06 3.65

TiO2 1.92 1.54 1.87 1.66 1.86 1.1

Al2O3 16.9 17.4 18 17.4 15.99 2.58

Fe, as Fe2O3 8.93 7.01 8.79 8.15 11.38 --2

MnO .17 .11 .14 .017 -- --

MgO 5.42 3.05 3.28 4.69 6.96 2.97

CaO 8.53 9.78 7.93 8.55 9.66 1.91

Na2O 3.33 3.68 3.94 3.27 2.97 0.91

K2O 2.17 2.62 2.13 2.19 1.12 0.75

P2O5 .78 .7 .065 0.71 -- --

Loss On Ignition 2.26 4.38 2.26 2.26 -- --

Total 100.57 99.47 98.805 100.097 100 --

As3 .66 1.00 .8 1.17 -- --

1

 Values are based on 3,594 analyses (Le Maitre, 1976).

2

 Le Maitre (1976) presents standard deviations for Fe2O3 and FeO ( 2.17 and 2.5, respectively) individually rather than for total iron.

3

 Concentrations in mg/kg.

12 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
Figure 8. Optical microscope micrograph of Type 1 basalt from well 

DB-1 at 545 ft with (A) crossed polarizers and (B) uncrossed polarizers. Field of view is 6 mm. These images show the bimodal size 

distribution of plagioclase, and typical size and form of olivine and 

clinopyroxene grains. The uncrossed view plainly shows the opaque 

mineral content.

A

B

Olivine

Clinopyroxene

Plagioclase

Opaque minerals

(black areas)

Physical Setting 13
Figure 9. Optical microscope micrograph of Type 2 basalt from 

well DB-1 at 441 ft with (A) crossed polarizers and (B) uncrossed 

polarizers. Field of view is 6 mm. These photographs are taken at 

the same magnification of those in figure 8 and clearly show the 

higher plagioclase and lower opaque mineral content of Type 2 

basalt relative to Type 1.

A

B

Olivine Clinopyroxene

Plagioclase

Opaque minerals

(black areas)

14 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
X-ray diffraction and SEM/EDS analysis of material 

from sites DB-1 and B-7 (fig. 10 and 11) show that fracture 

surfaces and vesicles (vugs) in the basalt contain coatings 

that include phillipsite, dolomite, calcite, clay minerals, and 

iron oxide. These minerals are important from the standpoint 

of water chemistry because they can dissolve or have easily 

exchangeable ions, which can alter the chemical quality of the 

injected water. For example, phillipsite is a zeolite with cationexchange sites that can react with injected water. Vug-filling 

materials in samples from other sites were very similar to the 

materials shown in figure 10 and no other mineral phases were 

identified. 

Sequential chemical extractions of basalt aquifer material indicates the presence of exchangeable cations and anions, 

calcite, and iron oxide (table 2). The presence of calcite and 

exchangeable cations is important because calcite dissolution and cation exchange can alter the water chemistry. The 

presence of iron oxide is particularly important because it 

can adsorb or release arsenic. The results of the chemical 

extractions can be used in geochemical models to predict the 

behavior of arsenic during recharge and withdrawal of water 

from the basalt aquifer.

Characterization of Surface Water in 

the S-Line Canal

 Analytical results for surface-water samples from the 

S-Line Canal are presented in Appendixes 1 and 2. Water used 

for irrigation and maintenance of wildlife areas in Lahontan 

Valley originates as runoff from the Sierra Nevada. Water 

from the Carson River and water imported from the Truckee 

River via the Truckee Canal are stored in Lahontan Reservoir. 

The S-Line Canal is one of the principal delivery canals in 

the extensive network of canals that transports water through 

Lahontan Valley. During a typical year, water released from 

Lahontan Reservoir maintains flow in the S-Line Canal from 

April to October. 

Water in the S-Line Canal (Appendix 1) is a Na-CaHCO3

 type water, with pH ranging from 7.7 to 8.2, and totaldissolved solids concentrations of about 195 mg/L. Sulfate 

concentrations have a narrow range of about 30–48 mg/L. 

Nitrogen and phosphorus concentrations generally are low, 

none exceeding 0.45 mg/L as N or 0.2 mg/L as P. 

Figure 10. Scanning electron microscope micrograph of 

vug-filling material from well DB-1 at a depth of 625 ft showing phillipsite. Phillipsite was identified by the occurrence, 

morphology, and EDS compositional analyses which identified 

abundant silica, aluminum, potassium, and sodium with no 

other cations present.

Characterization of Surface Water in the S-Line Canal 15
Figure 11. Scanning electron microscope micrograph of vug-filling 

material from well B-7 at a depth of 72 ft showing (A) dolomite rhomboids above phillipsite rhomboids and (B) phillipsite prisms on surface 

of adularia. Dolomite identified by morphology and EDS analyses, 

which identified calcium. Adularia identified by its vug-filling secondary occurrence, and EDS analyses which identified potassium, silica, 

and aluminum.

A

B

16 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
Table 2A. Concentration of elements released from 

basalt rock samples following cation exchange using 

ammonium chloride. 

[Concentrations are in mg/kg, milligram per kilogram]

Sample

identifier Calcium Potassium Magnesium

DB-1 442A 184 135 37

DB-1 442B 393 155 46

RSHCA 1,580 303 78

RSHCB 2,190 227 124

RSHO 173 16.5 4.1

Table 2B. Concentration of elements released from 

basalt rock samples following anion exchange using 

potassium nitrate.

[Concentrations are in mg/kg, milligrams per kilogram]

Sample

identifier Chloride Phosphorus Arsenic

DB-1 442A 11.4 36 0.08

DB-1 442B 6.7 37.1 0.08

RSHCA 35.3 33.9 0.08

RSHCB 15.4 36.6 0.04

RSHO 7.4 36.2 0.04

Table 2C. Concentrations of elements released from basalt rock samples following extraction of carbonate minerals by 

sodium acetate and acetic acid.

 [Concentrations are in mg/kg, milligram per kilogram. Symbol: <, less than]

Sample

identifier

Aluminum Arsenic Calcium Iron PotassiumMagnesiumManganesePhosphorus Lead Silica Sulfate

DB-1 442A <4 4 992 35.9 1,620 81.6 2.4 11 0.69 153 2,280

DB-1 442B <4 3.2 4,620 28 2,150 167 16.7 20.1 11.2 187 3,930

RSHCA 42.7 2.3 1,770 26.4 5,160 89.3 5 286 1.8 241 3,570

RSHCB 34.3 2.7 4,780 20.2 4,780 373 12 236 32.2 343 3,990

RSHO <4 1.8 742 26.4 618 8.2 0.41 27.2 <.4 154 3,170

Table 2D. Concentration of elements released from basalt rock samples following extraction of iron and manganese oxides by hydroxylamine hydrochloride and acetic acid. 

[Concentrations are in mg/kg, milligram per kilogram]

Sample 

identifier1

Aluminum Arsenic Calcium IronPotassiumMagnesiumManganesePhosphorus Silica Sulfate

DB-1 442A 71.4 0.2 1,070 103 163 153 29.6 144 223 20.4

DB-1 442B 157 0.42 3,060 167 209 251 50.2 162 403 20.9

RSHCA 544 1.7 2,170 112 272 214 88.3 816 482 214

RSHCB 311 0.97 2,200 91.2 96.6 708 103 616 622 193

RSHO 72.1 0.82 1,100 99.9 61.8 61.8 18.5 547 220 61.8

1

 Sample identifiers: RSHCA, RSHCB, RSHO represent Rattlesnake Hill cinder sample A, B, and vesicular outcrop sample, respectively. DB-1 442A and 442B are basalt core samples from a depth of 442 feet below land surface from well DB-1. 

Characterization of Surface Water in the S-Line Canal 17

1

1 1
Trace-element concentrations and radionuclide activities 

generally were low and, except for arsenic, did not exceed 

drinking-water standards. For arsenic, all but one sample 

exceeded the 10 μg/L Nevada drinking-water standard. The 

one sample with a low arsenic concentration (1.5 μg/L) was 

collected in May 2001 (fig. 12) when the flow in the Carson 

River below Lahontan Reservoir was 790 ft3/s. These limited 

data indicate that diverting flow from the S-Line Canal during 

high flow could minimize the arsenic concentrations in water 

from the basalt aquifer. Chloride concentrations in the canal 

were less than 22 mg/L in all the samples collected during this 

study (Appendix 1), compared with average chloride concentrations in the basalt aquifer that exceed 100 mg/L (Appendix 

1 in Maurer and Welch, 2001). Dissolved organic carbon 

(DOC) concentrations ranged from 2.5 to 5.8 mg/L in the six 

water samples analyzed for carbon. DOC concentrations in 

water used for artificial recharge are important because DOC 

reacts with chlorine to form carcinogenic disinfection-byproducts and because metabolism of DOC by bacteria can 

indirectly mobilize arsenic in an aquifer. DOC concentrations 

are lowest during spring runoff (Appendix 1), indicating that 

artificial recharge using water during high flow in the Carson 

River would have the additional benefit of minimizing the 

DOC content.

Analyses of water samples for pesticides and other 

anthropogenic organic compounds show very little contamination of S-Line Canal water with these chemicals. A few 

pesticides (Atrazine, EPTC, Prometon, and Simizine) were 

detected at very low levels (<0.01 μg/L) in the water samples 

but were not common (Appendix 2). Several consumer chemicals, including Bisphenol A, caffeine, cholesterol, and DEET, 

were detected at very low concentrations, indicating the presence of wastewater in the canal water. 

Geochemical Modeling of Recharge

Modeling Approach

Artificial recharge of the basalt aquifer with surface water 

could mitigate declining water levels and increasing chloride 

concentrations. However, the chemistry of the surface water 

could change following recharge, which raises the concern 

that arsenic may exceed standards in recovered ground water. 

Ground water in the basalt aquifer has a high pH (Appendix 

1), which is characteristic of high-arsenic ground water elsewhere in the United States (Welch and others, 2000). Because 

high pH values can promote arsenic desorption (Stollenwerk, 

2003), reactions that increase the pH of recharged water could 

increase the arsenic concentrations. An overall reaction that 

could increase the pH involves cation exchange and calcite 

dissolution as indicated by the following reaction:

CaCO3 + Na2-X + H2O ↔ 2 Na+ + HCO3

−

 + Ca-X + OH− (1)

Where -X represents exchange sites.

The relatively low calcium and magnesium concentrations compared to the sodium concentration in the basalt 

aquifer are consistent with this exchange reaction.

Calcite containing phosphorus and arsenic has been 

identified in the basalt aquifer (as indicated by the chemical extraction data in table 2C). Dissolution of calcite in the 

basalt could directly lead to higher arsenic concentrations by 

freeing adsorbed arsenic. Welch and others (2003), suggest 

that dissolution of calcite present in the basalt aquifer results 

in an increase in aqueous phosphorus. Because phosphate and 

arsenic compete for adsorption sites on a variety of adsorbants 

(Stollenwerk, 2003), phosphate released from the calcite may 

result in higher arsenic concentrations by competitively inhibiting adsorption of the arsenic.

Geochemical reactions that may result from recharge of 

water from S-Line Canal were simulated using the computer 

program PHREEQC (Parkhurst and Appelo, 1999), which has 

been widely used for modeling chemical reactions. Of particular importance for the recharge simulations is the capability of 

PHREEQC to include adsorption, precipitation, and dissolution reactions along with transport of the water. Modeling 

adsorption of arsenic requires knowledge of the amount and 

chemical character of the adsorbent in the aquifer. One common and important adsorbent in aquifers is iron oxide, particularly in ground water containing dissolved oxygen (Welch and 

others, 2000). The modeling presented below only includes 

iron oxide because it is present in the basalt aquifer and an 

internally consistent set of adsorption constants is available for 

arsenic and other potentially competing ions. The exclusion of 

other phases that could contribute arsenic to recharged water 

could lead to an underestimate of the potential for arsenic 

release. 

Surface complexation modeling requires that the site density, the specific area of the surface, and the mass of the adsorbant be specified. Following the approach of Dzombak and 

Morel (1990), a site density of 0.2 mol/mol and a surface area 

of 600 m2/g were used in the adsorption model for iron oxide. 

These values are applicable for hydrous ferric oxide (HFO), 

which may overestimate the surface area and site density for a 

system like the basalt aquifer. Extracted arsenic and iron concentrations, along with values for porosity and density (table 

3), were used to estimate the iron oxide content and adsorbed 

arsenic associated with sampled ground water. Following the 

approach of Welch and Lico (1998), the laboratory values for 

extracted arsenic and iron were converted to mol/L of water by 

using the following general equations:

18 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
DOC, in milligrams per liter 

Arsenic, in micrograms 

 per liter 

Discharge

DATE

CONCENTRATION

DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

NOV

DEC

FEB

APR

JUNE

AUG

DEC

FEB

APR

JUNE

JAN

MAR

MAY

OCT

AUG

OCT

JULY

SEP

NOV

JAN

MAR

MAY

JULY

SEP

2000 2001 2002

0

200

400

600

800

1,000

0

5

10

15

20

Figure 12. Graph showing arsenic and dissolved organic carbon (DOC) concentrations in S-Line Canal and daily 

mean flow in the Carson River below Lahontan Reservoir.

G = M x D x (1-Φ) x (1000 cm3/L) x (10-6 g/μg) / (Φ)

 and C = G/W

 Where G = concentration, in g/L

 M = mass of arsenic or iron extracted, in

 μg/g of aquifer material

 D = aquifer material density, in g/cm3

 Φ = porosity, dimensionless

 C = concentration, in mol/L

 W = gram-formula weight of arsenic 

 (74.92 g/mol) or iron (55.85 g/mol) 

Competitive adsorption in the simulations uses the ‘best 

fit’ models for iron oxide from Dzombak and Morel (1990). 

More recently, the adsorption of carbonate on iron oxide, 

both HFO (Appelo and others, 2002) and goethite (Van Geen 

and others, 1994), has been discussed. The effect of carbonate adsorption on arsenic concentrations was included in the 

modeling using the adsorption parameters in table 4.

Table 3. Mean bulk density and porosity of basalt samples 

(Brian Andraski, USGS, 2003, written commun.)

[Abbreviation: g/cm3, grams per cubic centimeter] 

Sample type 

Number

of

samples

Average bulk

 density

(g/cm3)

Average 

porosity

Surface outcrop, cinders 2 1.14 0.48

Surface outcrop, flow 2 2.52 .09

Vesicular basalt 4 2.25 .16

Table 4. Surface complexation constants for carbonate adsorption 

on ferrihydrite. Data from Appelo and others (2002)..

Reaction Log K

Hfo_wOH + CO3

2- + H+

 = Hfo_wOCO2

-

 + H2O 12.78 ± 0.48

Hfo_wOH + CO3

2- + 2H+

 = Hfo_wOCO2

-

 H + H2O 20.37 ± 0.20

Geochemical Modeling of Recharge 19
Model Scenarios and Limitations

Surface water can be injected directly into ground water 

through wells or recharged through the unsaturated zone 

beneath infiltration basins. Simulation of chemical reactions 

during direct injection and basin spreading are termed ‘wellinjection’ and ‘basin-infiltration’ models, respectively. Both 

models considered only advective, or plug flow; that is, dispersion and mixing were not considered. Chemical equilibrium 

was assumed during each reaction step. The well-injection 

model consists of reacting water with the basalt aquifer as 

summarized in table 5. The basalt aquifer was discretized into 

10 reaction cells in the saturated zone. The surfaces of the 

aquifer material prior to injection was assumed to be in chemical equilibrium with basalt-aquifer water. The surfaces were 

subsequently equilibrated with the recharge water. Withdrawal 

then was simulated by changing the flow direction and the 

invading basalt-aquifer water was equilibrated with the chemically altered surfaces of the aquifer material. 

The basin-infiltration model added two reaction cells to 

the well-injection model to simulate initial reactions in the 

unsaturated zone prior to reactions in the saturated zone (table 

5). The first reaction cell simulated reactions with the surface 

cinder and the second simulated reactions with the vesicular 

basalt. Simulation of chemical reactions during injection and 

withdrawal in the saturated zone used the same approach as 

described for the well-injection model. 

The ability of any numerical model to accurately simulate 

the outcome of a process such as the chemistry resulting from 

artificial recharge is limited for a variety of reasons. These 

limitations fall into three broad categories. The first involves 

formulation of the underlying mathematical approaches for 

simulation of chemical and physical processes. The second 

involves the adequacy and applicability of the information 

required to perform a simulation. The third involves how 

closely a modeled scenario and the actual recharge approach 

correspond. These limitations are discussed in turn. 

The PHREEQC computer code includes an aqueous 

model that calculates the chemical activities of the aqueous 

species. The underlying mathematical approach and thermodynamic data used for the aqueous model are considered fully 

adequate for the simulations. Ground water with high iron and 

organic carbon concentrations could be important if organicrich water were recharged and produced because interaction 

between arsenic (V) and organic matter can affect aqueous 

arsenic activities (Redman and others, 2002). The PHREEQC 

database does not account for this phenomenon. This interaction only appears to be important in water with high iron concentrations (>600 mg/L); thus, this interaction is not expected 

to be important for the simulations discussed here. 

Adsorption of arsenic was simulated using a surfacecomplexation model (Dzombak and Morel, 1990; Parkhurst 

and Appelo, 1999). This approach allows the simulation of 

arsenic adsorption in complex natural environments (Grossl 

and Sparks, 1995). Laboratory experiments and field studies 

(Jain and Loeppert, 2000; Swedlund and Webster, 1999) 

demonstrate that arsenic adsorption by iron oxide is affected 

by other anions, including phosphate and silica, at concentrations found in many ground-water systems. Competitive 

adsorption between arsenic and other anions for the same 

adsorption sites on a solid also was simulated using the 

surface-complexation model in PHREEQC. Competitive 

adsorption is more complex than is represented by the surfacecomplexation model of Dzombak and Morel (1990). Recent 

laboratory investigation into the adsorption of As(V) and 

phosphate on goethite (α-FeOOH) produced results that are 

incompatible with a surface-complexation model (Hongshao 

and Stanforth, 2001). Of particular importance is the observation that goethite contains a non-exchangeable fraction for 

As(V) and phosphate, which means that sequential addition of 

the adsorbents results in a different aqueous composition than 

is obtained when the adsorbents are introduced concurrently. 

Consequently, the mathematical approach used in the simulations may result in higher aqueous arsenic concentrations 

being predicted than would be expected on the basis of the 

laboratory studies (see Hongshao and Stanforth, 2001; Manning and Goldberg, 1996). 

Data used to simulate the water quality during recharge 

include temperature, chemistry of the recharge water, mineralogy and chemistry of the aquifer materials, and aquifer porosity. The chemical information on the aquifer material is limited 

to analyses of a few samples. 

If all the oxygen in the recharge is consumed by oxidation of DOC, then iron and manganese oxides can dissolve. 

The reaction of dissolved oxygen with organic carbon commonly is written as:

 CH2O + O2 → CO2 + H2O (2)

The stoichiometry of this reaction indicates that ground 

water with 8 mg/L of dissolved oxygen can oxidize about 3 

mg/L of organic carbon. Although not all of the DOC will 

necessarily react with oxygen, the amount of DOC in some 

samples collected from the S-Line Canal is large enough 

(Appendix 1) that it could consume all of the dissolved oxygen 

and then react with iron and manganese oxides. The reaction 

of DOC with these oxides could produce undesirable concentrations of iron and manganese in addition to releasing other 

trace inorganic constituents that commonly are contained 

within and on the surface of these oxides. The simulations 

assume that the recharge contains enough dissolved oxygen 

that iron and manganese oxides will not dissolve. Most of the 

S-Line Canal water sampled has sufficient dissolved oxygen to 

oxidize all the particulate and dissolved organic carbon, which 

makes this assumption reasonable for most of the samples.

Changes in water chemistry resulting from an actual 

project to artificially recharge the basalt likely will differ 

to some degree from the results of simulations made here. 

Although the basalt is largely homogenous, the mineralogy 

and chemistry of the basalt at an actual project location may 

differ from what was used in the simulations. Similarly, the 

chemical composition of the S-Line Canal changes during the 

year and the chemical composition of water used during actual 

artificial recharge may be different from what was used in the 

simulations. 

20 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
Table 5. Initial conditions and reactions used for geochemical modeling of injection and infiltration of surface water and its subsequent recovery.

Description of simulation Influent water composition

Aquifer material

composition Reactions

Well injection

W1. Equilibrate aquifer material 

with native ground water to 

set initial conditions.

Native ground water from site 

B-3 (sampled 06-30-99; 

Appendix 1).

Total number of cation exchange 

sites and iron-oxide surface 

from extraction of basalt core 

samples DB-1 442A and B.

Equilibrate native ground water 

with the aquifer material in 

reaction cells.

W2. Injection of surface water. S-Line Canal water (sampled 

05-14-01; Appendix 1).

Composition produced in simulation W1.Inject surface water into reaction 

cells. Equilibrate with calcite, 

cation exchange, and iron 

oxide (closed with respect to 

CO2).

W3. Withdrawal of injected 

water.

Native ground water from site 

B-3 (sampled 6-30-99; 

Appendix 1).

Composition produced in simulation W1.Withdraw injected water from 

reaction cells and replace with 

native ground water. Equilibrate with calcite, cation exchange, and iron oxide (closed 

with respect to CO2).

Basin infiltration

B1. Cell one, equilibrate recharge with cinder.S-Line Canal water (sampled 

05-14-01; Appendix 1).

Total number of cation exchange 

sites and iron-oxide surface 

from extraction of cinder 

outcrop samples RSHCA and 

RSHCB (table 2D).

Equilibration with atmospheric 

CO2 (pCO2 = -3.5 atmospheres) to simulate exposure 

to the atmosphere. React water 

with cinder.

B2. Cell two, equilibrate with 

water reacted with basalt 

cinder.

Water from previous reaction in 

cell one.

Cation exchange sites and ironoxide surface from extraction 

results of vesicular outcrop 

sample RSHO (table 2D).

Equilibrate water from cell one 

with vesicular outcrop. Equilibration with atmospheric CO2

(pCO2 = -3.5 atmospheres) 

to simulate exposure to the 

atmosphere.

B3. Cells three through ten,

initial aquifer and recharge 

composition.

Ground water from site B-3 

(sampled 06-30-99; 

Appendix 1).

Total number of cation exchange 

sites and iron-oxide surface 

from extraction of basalt core 

samples DB-1 442A and B.

Equilibrate water with the basalt 

composition in reaction cells.

B4. Cells three through ten,

infiltration into the basalt 

aquifer. 

Composition after reaction in 

cell two.

Total number of cation exchange 

sites and iron-oxide surface 

from extraction of basalt core 

samples DB-1 442A and B.

Inject surface water into reaction 

cells. Equilibrate with calcite, 

cation exchange and iron 

oxide (closed with respect to 

CO2).

B5. Cells three through ten, 

withdrawal.

Ground water from site B-3 

(sampled 06-30-99; 

Appendix 1).

Composition produced in B3. Withdraw injected water with 

inflow of B-3 water into reaction cells three through ten. 

Equilibration with calcite, cation exchange and iron oxide 

(closed with respect to CO2).

Geochemical Modeling of Recharge 21
Another way actual results may differ from simulated 

results is that the modeling approach assumes that lateral flow 

does not affect the ground-water quality of recovered water. 

Lateral flow would move the injected/infiltrated water away 

from the recharge site, replacing it with native ground water. 

This would decrease the removal of arsenic because of reequilibration of arsenic in the ground water with the exchange 

sites. Factors which increase the amount of lateral flow, such 

as higher lateral-flow rates and longer times between recharge 

and withdrawal can lead to less efficient removal of arsenic. 

Model Results

The chemical modeling involved reaction cells to simulate water chemistry during recharge and withdrawal. During 

the recharge phase in the well-injection model, surface water 

is injected into the first cell, displacing the native ground 

water from cell one to cell two. Following equilibration with 

the aquifer material, additional surface water is injected into 

cell one, displacing the now modified surface water from cell 

one to cell two. This sequence was repeated for 10 reaction 

steps until all 10 cells contained injected surface water. During the withdrawal phase, the process is reversed and water 

is removed from cell one and sequentially replaced by water 

from cells two through ten. Withdrawal continues until 

native ground water has replaced injected surface water in 

the 10 cells.

The results shown in figure 13 are the simulations for the 

first cell of the well-injection model, with the first cell representing a single well that both injects and withdraws water. 

Simulated pH, and arsenic and chloride concentrations during 

a single cycle of injection and withdrawal are shown in figure 

13A and following multiple cycles are shown in figure 13B. 

Modeling injection of water with a chemical composition 

similar to that of the S-Line Canal into the basalt aquifer and 

then withdrawing the water suggests that arsenic concentrations in the withdrawn water will be higher than in the injected 

water (fig. 13A). The results in cell one shown on figure 13A 

represent the composition of the water that moves into the next 

cell as outlined in table 5. The results for cell one represent 

the composition of the recovered water during the withdrawal 

cycle. The injection and withdrawal can be discussed in terms 

of three periods. During the first period, as water is being 

injected into the aquifer, chloride concentrations drop and pH 

increases to nearly 10 during the first reaction step. During 

reaction steps 2–10, arsenic concentrations jump as arsenic 

desorbs from the basalt and then decreases as the arsenic is 

transported out of the reaction cells. During the second period, 

as the injected water is withdrawn for the following 10 reaction steps, arsenic concentrations increase as injected water 

that had moved away from the well head now returns. In the 

third period, starting at reaction step 20, chloride concentrations jump sharply, indicating the return of native basaltaquifer water. The pH in the withdrawn water returns to that 

normally found in the basalt aquifer after a few reaction steps 

during this last period. The lower pH causes an abrupt arsenic 

decrease, followed by a gradual increase to a value close to 

that normally found in the basalt aquifer over the next 30 reaction steps. 

A second model consisted of simulating a series of 

injection and withdrawal cycles. An important difference 

between this model and that described above is that more 

water is injected than withdrawn, with withdrawal being 

limited to retrieval to the point where native basalt-aquifer 

water reaches cell two, but not cell one. Accordingly, the 

chloride concentrations in cell one always remain equal to 

the concentration in the injected water (fig. 13B). The pH 

and arsenic values during the first injection-withdrawal cycle 

are the same as described for the first two periods described 

above. During subsequent injection-withdrawal cycles, the 

arsenic and pH values show the same patterns with a progressive decrease with each succeeding cycle. The decreasing pH, 

which causes the lower arsenic concentrations, is a result of 

progressively less calcite dissolution. The decreasing calcite 

dissolution is a result of reduced exchange of calcium for 

sodium, which promotes calcite dissolution, as shown by 

reaction (1). 

The basin-infiltration model differs from the wellinjection model in that it includes two additional cells that 

represent the cinder and vesicular basalt in the unsaturated 

zone above the water table. The third cell represents the 

saturated zone below the infiltration basin. Results for this 

third cell are shown in figure 14 and describe the water quality 

at a withdrawal well tapping ground water below the basin. 

Simulations of water infiltrating through the unsaturated zone 

indicate potential for high arsenic concentrations in withdrawn 

ground water (fig. 14). Two scenarios are represented in figure 

14 and differ in the amount of arsenic present in the iron oxide 

in the unsaturated zone. The first model represents iron oxide 

with no initial arsenic (fig. 14A). The second model assumes 

the iron oxide has equilibrated with a water composition like 

that of the infiltrating water except containing 10 μg/L of 

arsenic (fig. 14B). The results show similar patterns, although 

the arsenic concentrations in the recovered water are higher 

for the model represented in figure 14B because of the greater 

amount of arsenic in the unsaturated zone, particularly during 

the first scenario. 

Because the amount of carbon dioxide in the unsaturated 

zone affects carbonate solubility, it also could affect arsenic 

concentrations. The simulation results shown in figures 13–14 

used atmospheric concentrations of carbon dioxide (pCO2 of 

10-3.5). However, similar arsenic and pH results were obtained 

using a higher pCO2 of 10-2.5, which is similar to observed 

pressures in the soil zone (data not shown). 

The model results indicate the potential for unacceptably high arsenic concentrations in recovered ground water; 

however, simulated arsenic concentrations in the recovered 

water may overestimate concentrations during real recharge 

operations. First, the models do not consider the effect of 

22 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
Average arsenic 

concentration in 

basalt aquifer

Average arsenic 

concentration in 

basalt aquifer

Arsenic

Chloride

pH

Injection Withdrawal

pH

7.50

7.75

8.00

8.25

8.50

8.75

9.00

9.25

9.50

9.75

10.00

10.25

pH

7.50

7.75

8.00

8.25

8.50

8.75

9.00

9.25

9.50

9.75

10.00

10.25

0

20

40

60

80

100

120

140

160

180

200

0

20

40

60

80

100

120

140

160

180

200

CONCENTRATION CONCENTRATION

REACTION STEP

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

0 5 10 15 20 25 30 35 40 45 50

A

B

Figure 13. Results of geochemical simulation of injection well model of recharge into the basalt aquifer. Model 

scenarios are for a (A) single cycle and (B) multiple cycles. Concentration units are μg/L for arsenic and mg/L for 

chloride. Black and blue horizontal lines at top of graphs represent injection and withdrawal cycles.

Geochemical Modeling of Recharge 23
Average arsenic 

concentration in 

basalt aquifer

Arsenic concentration = 1,700 micrograms per liter at reaction step 1

Arsenic

Chloride

pH

Average arsenic 

concentration in 

basalt aquifer

Injection Withdrawal

Injection Withdrawal

pH

CONCENTRATION

pH

CONCENTRATION

REACTION STEP

0 10 15 20 25 30 35 40

7.50

7.75

8.00

8.25

8.50

8.75

9.00

9.25

9.50

9.75

10.00

10.25

0

20

40

60

80

100

120

140

160

180

200

7.50

7.75

8.00

8.25

8.50

8.75

9.00

9.25

9.50

9.75

10.00

10.25

0

20

40

60

80

100

120

140

160

180

200

Iron oxides in unsaturated zone have equilibrated with water 

 containing 10 micrograms per liter arsenic

B 

A Iron oxides in unsaturated zone have equilibrated with water 

 containing 0 micrograms per liter arsenic

5

Figure 14. Results of geochemical simulation of basin-infiltration model of recharge into the basalt aquifer. 

Model scenarios are for iron oxide equilibrated with water containing (A) no arsenic and (B) 10 μg/L arsenic. 

Concentration units are μg/L for arsenic and mg/L for chloride. Black and blue horizontal lines at top of graphs 

represent injection and withdrawal cycles, respectively.

24 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
lateral flow of ground water between injection and recovery. 

Second, released arsenic may be less because the model uses 

adsorption parameters for HFO that may overestimate the 

amount of arsenic released to ground water. The retention of 

arsenic in iron oxide is an important factor when considering 

a long-term recharge effort. The transformation of freshly precipitated iron oxide into a more crystalline form needs to be 

considered. Field (Mettler, 2002) and laboratory (Ford, 2002) 

studies suggest that this process may occur at a rate that can be 

important for long-term recharge projects. Laboratory aging of 

HFO coprecipitated with As(V) shows a half-life for transformation into goethite of about 300 days at 25o

C in the presence 

of dissolved oxygen (Ford, 2002). The transformation was not 

accompanied by a release of arsenic into solution. The applicability of these laboratory experiments to field settings has not 

been well studied.

The effects of flushing of constituents such as chloride and sulfate that may be present in the unsaturated zone 

beneath Rattlesnake Hill were not considered in the basininfiltration model. These and other soluble salts may have 

been added to the basalt exposed at Rattlesnake Hill during the 

dessication of Lake Lahontan and subsequently by rainfall and 

dust. Flushing of these solutes may be important during the 

early phase of a recharge effort and could decrease as they are 

leached out of the unsaturated zone. 

Summary and Conclusions

The Fallon basalt aquifer serves as the sole source of 

municipal water for Lahontan Valley in west-central Nevada. 

The principal users include the City of Fallon, Naval Air Station Fallon, and the Fallon Paiute-Shoshone Tribe. Increased 

pumpage from the aquifer has been accompanied by declines 

in water levels and changes in water quality. Storage of surface water in the basalt may mitigate the effects of increased 

pumpage, but may cause undesirable changes in water chemistry. Water-quality samples of the S-Line Canal, a likely source 

of water for augmentation of recharge, indicates that with the 

exception of arsenic, the water is acceptable for water supply. Because the arsenic in ground water of the basalt aquifer 

exceeds drinking water standards, the potential for arsenic 

release to artificial recharge was explored by using geochemical modeling. Model results inidcate that arsenic release from 

the basalt may increase its concentrations in ground water to 

levels that could limit the use of artificial recharge. Model 

results for well injection indicate that arsenic concentrations 

may initially increase following artificial recharge, but decline 

with repeated cycles of injection and withdrawal. Field based 

experiments are needed to evaluate the underlying model 

assumptions. 

Arsenic concentrations in withdrawn water following 

artificial recharge could be limited by increasing adsorption 

onto the basalt aquifer. Field and laboratory experiments show 

that a combination of increasing the iron oxide content of the 

basalt aquifer and lowering the pH of the ground water could 

decrease arsenic concentrations (Welch and others, 2003). The 

short- and long-term effects of artificial recharge on arsenic 

concentrations could be evaluated through similar experimental approaches described by these authors.

Surface infiltration has several advantages over well 

injection and the high permeability of scoriaceous cinders near 

the top of Rattlesnake Hill could make this a good location 

from the standpoint of allowing rapid infiltration. Clay and 

larger size particles in recharge water that often reduce the 

infiltration and injection rates can be mechanically removed 

from the surface of an infiltration basin. In contrast, rehabilitating a well clogged by the clay particles in recharge water 

may be very expensive or impossible. Nonetheless, the cinders 

have a large reactive surface area that could lead to undesirable 

geochemical reactions. In such a case, surface infiltration may 

not be a desirable approach. Additional field-based experiments are needed to evaluate which approach is the best.

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APPENDIXES
Appendix 1. Field measurements and concentrations of major ions, nutrients, trace elements, radionuclides, and organic carbon in water sample

Cemetery Bridge and USGS basalt well B-3 collected from October 1997 to October 2002. [Abbreviations and symbols: oC, degrees Celsius; E, estimated concentration; ft3/s, cubic feet per second; ft, feet; mm, millimeters; M, presence verified but not quantified; liter; nm, nanometer; pCi/L, picoCuries per liter; UV, ultraviolet; μS/cm, microsiemens per centimeter at 25 oC; μg/L, microgram per liter; <, less than; --, not determined concentrations were determined on filtered samples unless otherwise noted.]

Site

 (fig. 3)

U.S. Geological 

Survey 

Site identifier Date Time

Well 

depth

Daily 

mean 

stream 

discharge

(ft3/s)

pH 

(units)

Air

temperature

(

oC)

Water 

temperature 

(

oC)

Dissolved 

oxygen

(mg/L)

Specific 

conductance

(uS/cm)

Surface Water

S-Line Canal 1031220115 05-14-01 1120 -- 23 8.5 27.5 15.6 7.8 275 

06-19-01 1045 -- 16 8.5 28.5 19.8 8.0 288 07-25-01 1050 -- .06 31 21.2 7.6 290 08-21-01 925 -- .05 7.6 28.5 19.8 8.2 301 10-17-01 1015 -- 18 9.1 20.5 14.4 8.0 320 04-08-02 1015 -- .38 9.0 18.5 12.6 8.2 371 06-25-02 1015 -- .11 7.7 -- 19.0 7.9 283 08-27-02 1045 -- 28 7.4 -- 19.8 7.9 293 10-18-02 1115 -- 17 9.4 -- 13.8 7.7 297 

Ground Water

Well B-3 392914118442701

10-20-97 1500 71 -- 9.1 -- 22.5 .9 1,110 06-30-99 1000 71 -- 9.3 -- 22 .4 1,120 
Appendix 1. Field measurements and concentrations of major ions, nutrients, trace elements, radionuclides, and organic carbon in water samples 

Cemetery Bridge and USGS basalt well B-3 collected from October 1997 to October 2002—Continued 

Site

(fig. 3) Date

Calcium

(mg/L 

as Ca)

Magnesium

(mg/L 

as Mg)

Sodium

(mg/L

 as Na)

Potassium

(mg/L 

as K)

Bicarbonate

(mg/L as 

HCO3

)

Carbonate

(mg/L 

as 

CO3

)

Alkalinity(mg/L 

 as

 CaCO3

)

Sulfate

(mg/L

 as SO4

)

Chloride

(mg/L 

as Cl)

Bromide

(mg/L

as Br)

Fluoride

(mg/L

 as F)

Iodi

(mg

 as 

Surface Water

S-Line Canal 05-14-01 21.1 5.86 25.8 3.39 98 0 81 29.6 14.0 -- .2 -- 

06-19-01 23.6 6.46 26.4 3.48 99 0 81 36.5 14.1 -- .3 -- 07-25-01 22.2 6.12 27.4 3.61 99 0 81 36.0 13.3 -- .2 -- 08-21-01 24.0 6.53 26.7 3.62 109 0 90 38.0 13.6 -- .2 -- 10-17-01 23.1 6.57 28.3 3.72 111 0 91 43.1 16.1 -- .3 -- 04-08-02 27.4 7.83 38.0 4.05 126 0 104 48.4 21.7 -- .3 -- 06-25-02 22.2 6.34 26.4 3.23 95 0 78 35.3 15.4 -- .15 -- 08-27-02 22.7 6.25 26.3 3.42 101 0 83 36.3 12.3 -- .25 -- 10-18-02 22.3 6.44 28.7 3.65 97 0 80 36.8 13.8 -- .22 -- 

Ground Water

Well B-3 10-20-97 1.72 .904 236 7.8 245 30 251 102 130 .21 .8 .0

06-30-99 1.67 .651 232 7.92 250 45 280 100 127 .22 .9 -- 
Appendix 1. Field measurements and concentrations of major ions, nutrients, trace elements, radionuclides, and organic carbon in water sample

Cemetery Bridge and USGS basalt well B-3 collected from October 1997 to October 2002—Continued

Site

(fig. 3) Date

Nitrate

plus

nitrite

(mg/L as 

N)

Nitrite

(mg/L as 

N)

Ammonia

(mg/L 

as N)

Ammonia

plus

organic

nitrogen

(mg/L 

as N)

Ammonia

plus

organic

nitrogen,

total

(mg/L 

as N)

Nitrogen,

particulate

(mg/L 

as N)

Total

phosphorus

whole water

(mg/L 

as P)

Total

phosphorus

filtered

(mg/L 

as P)

Orthophosphate

filtered

(mg/L 

as P)

i

Surface Water

S-Line Canal 05-14-01 0.17 0.015 0.05 0.27 0.45 0.09 0.131 0.073 0.06 

06-19-01 .15 .007 <.04 .20 .40 .16 .131 .079 .07 07-25-01 .14 E.003 <.04 .20 .39 .32 .190 .094 .08 08-21-01 .12 <.006 <.04 .22 .43 .16 .164 .109 .09 10-17-01 .09 <.008 <.04 .21 .39 .19 .196 .113 .09 04-08-02 <.05 <.008 <.04 .21 .34 .12 .105 .081 .05 06-25-02 E.03 <.008 <.04 .14 .34 .18 .139 .085 .07 08-27-02 .05 <.008 <.04 .19 .31 .11 .141 .097 .09 10-18-02 <.06 <.008 <.04 .19 .33 .10 .162 .111 .08 

Ground Water

Well B-3 10-20-97 -- -- -- -- -- -- -- -- .27 

06-30-99 -- -- -- -- -- -- -- -- -- 
Appendix 1. Field measurements and concentrations of major ions, nutrients, trace elements, radionuclides, and organic carbon in water sample

Cemetery Bridge and USGS basalt well B-3 collected from October 1997 to October 2002—Continued

Site

(fig. 3) Date

Carbon,

organic,

dissolved

(mg/L

as C)

Carbon,

organic,

particulate

(mg/L

as C)

Aluminum

(μg/L 

As Al)

Antimony

(μg/L 

as Sb)

Arsenic

(μg/L 

as As)

Barium

(μg/L 

as Ba)

Beryllium

(μg/L 

as Be)

Boron

(μg/L as 

B)

Cadmium

(μg/L

as Cd)

Chromium

(μg/L as 

Cr)

Cobalt

(μg/L as 

Co)

Copper

(μg/L) as 

Cu

Surface Water

S-Line Canal 05-14-01 2.9 E.7 1 0.10 1.5 82 <.06 44 <.04 <.8 0.27 1.1 

06-19-01 2.5 1.3 2 .48 10.9 33 <.06 246 0.04 <.8 .11 2.1 07-25-01 5.8 2.0 2 .52 10.0 33 <.06 259 E.03 <.8 .12 1.9 08-21-01 3.7 1.2 1 .48 10.8 34 <.06 233 E.02 <.8 .10 2.5 10-17-01 -- 1.4 1 .47 10.4 33 <.06 259 <.04 <.8 .12 2.7 04-08-02 -- 1 .35 13.7 38 <.06 380 E.04 <.8 .16 2.2 06-25-02 -- 1.2 2 .49 10.2 34 <.06 242 E.03 <.8 .12 2.5 08-27-02 4.0 .7 2 .51 11.2 33 <.06 215 E.03 <.8 .10 2.9 10-18-02 5.4 .7 <2 .56 11.2 31 <.06 253 E.02 <.8 .11 2.4 

Ground Water

Well B-3 10-20-97 0.7 -- -- -- 135 -- -- -- -- -- -- -- 

06-30-99 -- -- -- -- 123 -- -- -- -- -- -- -- 
Appendix 1. Field measurements and concentrations of major ions, nutrients, trace elements, radionuclides, and organic carbon in water sample

S-Line Canal at Cemetery Bridge and USGS basalt well B-3 collected from October 1997 to October 2002—Continued

Site

(fig. 3) Date

Manganese

(μg/L

as Mn)

Mercury

(μg/L

as Hg)

Mercury,

Total

(μg/L

as Hg)

Molybdenum

(μg/L

as Mo)

Nickel

(μg/L as 

Ni)

Selenium

(μg/L

as Se)

Silver

(μg/L as 

Ag)

Strontium

(μg/L

as Sr)

Thallium

(μg/L

as Tl)

Vanadi

(μg/

as V

Surface Water

S-Line Canal 05-14-01 5.5 -- 0.24 1.5 0.5 0.4 <1 357 E0.04 3.6

06-19-01 4.2 -- -- 5.6 .29 <.3 <1 246 .07 6.6 07-25-01 3.9 -- .45 5.8 .29 <.3 <1 255 <.04 5.1 08-21-01 2.1 -- .34 6.3 <.06 E.2 <1 263 <.04 5.510-17-01 1.9 -- .42 6.3 .65 E.3 <1 256 <.04 5.304-08-02 9.4 0.01 .18 7.6 .61 <.3 <1 284 <.04 5.3 06-25-02 7.5 -- .19 5.0 .36 E.2 <1 228 .16 5.2 08-27-02 3.1 E.01 -- 5.5 1.69 <.3 <1 242 <.04 5.7 10-18-02 3.0 <.02 -- 5.2 1.02 <.5 <.20 229 E.03 5.0

Ground Water

Well B-3 10-20-97 <1.0 -- -- -- -- -- -- -- -- -- 

06-30-99 <3.0 -- -- -- -- -- -- -- -- -- 
Appendix 1. Field measurements and concentrations of major ions, nutrients, trace elements, radionuclides, and organic carbon in water samples 

etery Bridge and USGS basalt well B-3 collected from October 1997 to October 2002—Continued 

Site

(fig. 3) Date

Delta

deuterium

(per mil)

Delta

oxygen-18

(per mil)

Alpha

radioactivity

(pCi/L

as Th-230)

Alpha

radioactivity,

2-sigma

precision

estimate

(pCi/L

as Th-230)

Gross

beta

radioactivity

(pCi/L

as Cs-137)

Beta

radioactivity,

2-sigma

precision

estimate

(pCi/L

as Cs-137)

Radium-226

(pCi/L)

Radi

2-s

pre

est

(p

Surface Water

S-Line Canal 05-14-01 -85.7 -10.35 <3 1.3 5 1.6 0.04 

06-19-01 -89.1 -10.48 3 1.4 6 1.7 .05 07-25-01 -88.2 -10.36 3 1.2 8 2.0 .06 08-21-01 -84.5 -9.92 3 1.1 6 1.8 .04 10-17-01 -81.0 -9.23 3 1.2 7 1.9 .05 04-08-02 -84.2 -10.00 5 1.8 9 2.2 .23 06-25-02 -90.1 -10.90 3 1.4 5 1.5 .03 08-27-02 -86.7 -10.32 2 1.2 7 2.0 .06 10-18-02 -86.5 -10.00 3 1.3 7 1.9 .04 

Ground Water

Well B-3 10-20-97 -110 -13.89 -- -- -- -- -- 

06-30-99 -- -- -- -- -- -- -- 
Appendix 1. Field measurements and concentrations of major ions, nutrients, trace elements, radionuclides, and organic carbon in water samples from S-Line Canal at Cemetery Bridge and USGS basalt well B-3 collected from October 1997 to October 

2002—Continued

Site

(fig. 3) Date

Carbon,

inorganic plus

organic, total

(mg/L as C)

Carbon,

inorganic plus

organic,

particulate

(mg/L as C)

Carbon,

organic,

dissolved

(mg/L as C)

Carbon,

organic,

particulate

(mg/L as C)

Surface Water

S-Line Canal 05-14-01 0.7

M 2.9 E.7

06-19-01 1.3 <.1 2.5 1.307-25-01 2.0 <.1 5.8 2.008-21-01 1.3 <.1 3.7 1.210-17-01 1.4 <.1 -- 1.404-08-02 .6 -- -- --06-25-02 1.2 <.1 -- 1.208-27-02 .7 <.1 4.0 .710-18-02 .7 <.1 5.4 .7

Ground Water

Well B-3 10-20-97 -- -- .7 --

06-30-99 -- -- -- --
Appendix 2. Concentrations of organic compounds in water samples from S-Line Canal collected from Cemetery Bridge, May 2001 to October 2

[All samples were filtered unless otherwise noted by “Total”. Abbreviations and symbols: E, estimated value; M, presence verified, not quantified; --, not analyzed; <, less 

Date Time

1,4-Dichlorobenzene

(μg/L)

1-

Methylnaphthalene

(μg/L)

2,6-

Diethylaniline

(μg/L)

2,6-

Dimethylnaphthalene

(μg/L)

2-

Methylnaphthalene

(μg/L)

3-Beta

Coprostanol

(μg/L)

3-

Methyl1(H)-indole

(μg/L)

3-tertbutyl4-hydroxyanisole

(μg/L)

4-

Cumylphenol

(μg/L)

4-

Octy

phen

(μg/L

05-14-01 1120 -- -- <0.002 -- -- -- -- -- -- 06-19-01 1045 -- -- <.002 -- -- -- -- -- -- 08-21-01 925 -- -- <.002 -- -- -- -- -- -- 10-17-01 1015 <.5 <.5 <.002 <.5 <.5 <2 <1 <5 <1 <1 04-08-02 1015 <.5 <.5 <.006 <.5 <.5 <2 <1 <5 <1 <1 08-27-02 1045 <.5 <.5 <.006 <.5 <.5

M <1 <5 <1 <1 

10-18-02 1115 -- -- <.006 -- -- -- -- -- -- 

Date

Acetochlor

(μg/L)

Acetophenone

(μg/L)

Acetyl

hexamethyltetrahydronaphthalene

(μg/L)

Alachlor

(μg/L)

Aldrin,

Total

(μg/L)

Alpha

BHC

(μg/L)

Anthracene

(μg/L)

Anthraquinone

(μg/L)

Atrazine

(μg/L)

Benfluralin

(μg/L)

Benzo(a)-

pyrene

(μg/L)

Benzophenone

(μg/L)

Be

sitos

(μg

05-14-01 <.004 -- -- <.002 -- <.005 -- -- E.002 <.010 -- -- 06-19-01 <.004 -- -- <.002 -- <.005 -- -- E.002 <.010 -- -- 08-21-01 <.004 -- -- <.002 <.01 <.005 -- -- <.007 <.010 -- -- 10-17-01 <.004 E.1

M <.002 -- <.005 <.5 <.5 <.007 <.010 <.5 <.5 <2 

04-08-02 <.006 <.5 <.5 <.004 -- <.005 <.5 <.5 <.007 <.010 <.5 <.5 <2 08-27-02 <.006 E.1 <.5 <.004 <.01 <.005 <.5 <.5 <.007 <.010 <.5 <.5 <2 10-18-02 <.006 -- -- <.007 -- <.005 -- -- <.007 <.010 -- -- 
Appendix 2. Concentrations of organic compounds in water samples from S-Line Canal collected from Cemetery Bridge, May 2001 to October 2002—Co

Date

Bromoform

(μg/L)

Butylate

(μg/L)

Caffeine

(μg/L)

Camphor

(μg/L)

Carbaryl

Carbazole

(μg/L)

Carbofuran

(μg/L)

Chlor

dane,

Total

(μg/L)

Chlorpyrifos

(μg/L)

Cholesterol

(μg/L)

Cotinine

(μg/L)

Cyanazine

(μg/L)

DCPA

(μg/L)

De

atr

(μ

(μg/L) 

05-14-01 -- <.002 -- -- <.041 -- <.020 -- <.005 -- -- <.018 <.003 06-19-01 -- <.002 -- -- <.041 -- <.020 -- <.005 -- -- <.018 <.003 08-21-01 -- <.002 -- -- <.041 -- <.020 <.1 <.005 -- -- <.018 <.003 10-17-01 <.5 <.002 <.5 <.5 <1 <.5 <.020 -- <.5

M <1 <.018 <.003 

04-08-01 <.5 <.002

M <.5 <.041 <.5 <.020 -- <.005 <2 <1 <.018 <.003 

08-27-02 <.5 <.002 E.1 <.5 <.041 <.5 <.020 <.1 <.005 E1 <1 <.018 <.003 10-18-02 -- <.002 -- -- <.041 -- <.020 -- <.005 -- -- <.018 <.003 

Date

Diazinon

(μg/L)

Dieldrin

(μg/L)

Dieldrin,

Total

(μg/L)

Disulfoton

(μg/L)

D-Limonene

(μg/L)

Endosulfan I,

Total

(μg/L)

Endrin

(μg/L)

EPTC

(μg/L)

Ethalfluralin

(μg/L)

Ethoprop

(μg/L)

Fipronil

Degradate

RPA105048

(μg/L)

Fipronil

Sulfide

(μg/L)

Fipronil

Sulfone

(μg/L)

05-14-01 <.005 <.005 -- <.02 -- -- -- 0.011 <.009 <.005 -- -- -- 06-19-01 <.005 <.005 -- <.02 -- -- -- <.002 <.009 <.005 -- -- -- 08-21-01 <.005 <.005 <.006 <.02 -- <.02 <.01 <.002 <.009 <.005 -- -- -- 10-17-01 <.5 <.005 -- <.02 <.5 -- -- <.002 <.009 <.005 -- -- -- 04-08-02 <.005 <.005 -- <.02 <.5 -- -- <.002 <.009 <.005 -- -- -- 08-27-02 <.005 <.005 <.006 <.02 <.5 <.02 <.01 <.002 <.009 <.005 -- -- -- 10-18-02 <.005 <.005 -- <.02 -- -- -- <.002 <.009 <.005 <.009 <.005 <.005 
Appendix 2. Concentrations of organic compounds in water samples from S-Line Canal collected from Cemetery Bridge, May 2001 to October 2002—Co

Date

Fonofos

(μg/L)

Heptachlorepoxide,

Total

(μg/L)

Heptachlor,

Total

(μg/L)

Hexahydrohexamethylcyclopentabenzopyran

(μg/L)

Indole

(μg/L)

Isoborneol

(μg/L)

Isophorone

(μg/L)

Isopropylbenzene

(Cumene)

(μg/L)

Isoquinoline

(μg/L)

Lindane

(μg/L)

Lindane,

Total

(μg/L)

Linuron

(μg/L)

M

05-14-01 <.003 -- -- -- -- -- -- -- -- <.004 -- <.035 06-19-01 <.003 -- -- -- -- -- -- -- -- <.004 -- <.035 08-21-01 <.003 <.009 <.01 -- -- -- -- -- -- <.004 <.006 <.035 10-17-01 <.003 -- --

M <.5 <.5 E.3 <.5 <.5 <.004 -- <.035 

04-08-02 <.003 -- -- <.5 <.5 <.5 <.5

M <.5 <.004 -- <.035 

08-27-02 <.003 <.009 <.01 <.5 <.5 <.5 1.8 <.5 <.5 <.004 <.006 <.035 10-18-02 <.003 -- -- -- -- -- -- -- -- <.004 -- <.035 

Date

Metalaxyl

(μg/L)

Methoxychlor,

Total

(μg/L)

Methylazinphos

(μg/L)

Methylparathion

(μg/L)

Methylsalicylate

(μg/L)

Metolachlor

(μg/L)

Metribuzin,

(Sencor)

(μg/L)

Mirex

Total

(μg/L)

Molinate

(μg/L)

N,N,-Diethylmeta- Diethyltoluamide

(DEET)

(μg/L)

Naphthalene

(μg/L)

Napropamide

(μg/L)

D

05-14-01 -- -- <.050 <.006 -- <.013 <.006 -- <.002 -- -- <.007 06-19-01 -- -- <.050 <.006 -- <.013 <.006 -- <.002 -- -- <.007 08-21-01 -- <.020 <.050 <.006 -- <.013 <.006 <.006 <.002 -- -- <.007 10-17-01 <.5 -- <.050 <.006 <.5 <.5 <.006 -- <.002

M <.5 <.007 

04-08-02 <.5 -- <.050 <.006 <.5 <.013 <.006 -- <.002 E.1 <.5 <.007 08-27-02 <.5 <.020 <.050 <.006 <.5 <.013 <.006 <.006 <.002 E.1 <.5 <.007 10-18-02 -- -- <.050 <.006 -- <.013 <.006 -- <.002 -- -- <.007 
Appendix 2. Concentrations of organic compounds in water samples from S-Line Canal collected from Cemetery Bridge, May 2001 to October 200

Date

Monoethoxyoctylphenol

(μg/L)

p,p’-

DDE

Total

(μg/L)

p,p’-

DDD,

Total

(μg/L)

p,p’-

DDE,

Total

(μg/L)

p,p’-

DDT,

Total

(μg/L)

Paracresol

(μg/L)

Paranonylphenol

(μg/L)

Parathion

(μg/L)

PCB

Total

(μg/L)

Pebulate

(μg/L)

Pendimethalin

(μg/L)

05-14-01 -- <.003 -- -- -- -- -- <.007 <.002 <.010 06-19-01 -- <.003 -- -- -- -- -- <.007 <.002 <.010 08-21-01 -- <.003 <.007 <.006 <.009 -- -- <.007 <.1 <.002 <.010 10-17-01 <1 <.003 -- -- -- <1 <5 <.007 <.002 <.010 04-08-02 <1 <.003 -- -- -- <1 <5 <.010 <.004 <.022 08-27-02 <1 <.003 <.007 <.006 <.009 <1 <5 <.010 <.1 <.004 <.022 10-18-02 -- <.003 -- -- -- -- -- <.010 <.004 <.022 

Date

Phenanthrene

(μg/L)

Phenol

(μg/L)

Phorate

(μg/L)

Prometon

(μg/L)

Pronamide

(μg/L)

Propachlor

(μg/L)

Propanil

(μg/L)

Propargite

(μg/L)

Pyrene

(μg/L)

Simazine

(μg/L)

Stigmastanol

(μg/L)

Tebuthiuron

(μg/L)

05-14-01 -- -- <.011

M <.004 <.010 <.011 <.02 -- <.011 -- <.02 

06-19-01 -- -- <.011 <.01 <.004 <.010 <.011 <.02 -- E.002 -- <.02 08-21-01 -- -- <.011 <.01 <.004 <.010 <.011 <.02 -- <.011 -- <.02 10-17-01 <.5 E.3 <.011 <.5 <.004 <.010 <.011 <.02 <.5 <.011 <2 <.02 04-08-02 <.5 <.5 <.011 <.01 <.004 <.010 <.011 <.02 <.5 <.005 <2 <.02 08-27-02 <.5 E.4 <.011 <.01 <.004 <.010 <.011 <.02 <.5 <.005 <2 <.02 

10-18-02 -- -- <.011 <.01 <.007 <.010 <.011 <.02 -- <.005 -- <.02 
Appendix 2. Concentrations of organic compounds in water samples from S-Line Canal collected from Cemetery Bridge, May 2001 to October 200

Date

Tetrachloroethylene

(μg/L)

Thiobencarb

(μg/L)

Toxaphene,

Total

(μg/L)

Tri-

(2-chloroethyl)

phosphate

(μg/L)

Tri-

 (dichlorisopropyl)-

phosphate

(μg/L)

Triallate

(μg/L)

Tributylphosphate

(μg/L)

Triclosan

(μg/L)

Triethylcitrate

(μg/L)

Trifluralin

(μg/L)

Triphenylphosphate

(μg/L)

05-14-01 -- <.005 -- -- -- <.002 -- -- -- <.009 -- 06-19-01 -- <.005 -- -- -- <.002 -- -- -- <.009 -- 08-21-01 -- <.005 <1 -- -- <.002 -- -- -- <.009 -- 10-17-01 <.5 <.005 -- <.5 E.1 <.002 <.5 <1 <.5 <.009

M 

04-08-02 <.5 <.005 -- E.1 E.1 <.002 <.5 <1 <.5 <.009 <.5 08-27-02 <.5 <.005 <1

M

M <.002 <.5 <1 <.5 <.009 <.5 

10-18-02 -- <.005 -- -- -- <.002 -- -- -- <.009 -- 
Appendix 3. Reagents and analytical methods used for partial solution extractions

Water soluble and cation exchange capacity

Reagents, analytical steps, and analytes Reference

0.2 M NH4Cl: Dissolve 107 g of NH4Cl and make up to 10 L with deionized water.

1. Weigh each rock sample and record. Take the entire amount for the analysis.

2. Add the rock to a 1,000 mL beaker or erlenmeyer flask and add 300 mL of 0.2 M NH4Cl.

3. Shake gently on a gyaratory shaker for 1 hour. Slow the shaker speed so there is no attrition grinding.

4. Decant the supernatant into a 2,000 mL volumetric flask.

5. Add another 300 mL of 0.2 M NH4Cl and shake for 1 hour as before.

6. Decant the supernatant into the same 2,000 mL volumetric flask.

7. Repeat steps 5 and 6 three more times for a total of five cycles.

8. Make the final volume up to 2,000 mL. Filter an aliquot and analyze by ICP-ES (Na, K, Ca, Mg, Al, 

SiO2 and As). 

9. Save the rock samples for anion exchange capacity. 

Sumner and Miller (1996)

Anion exchange capacity

Reagents, analytical steps, and analytes Reference

0.2 M potassium nitrate 0.2 M KNO3: Dissolve 202 g of KNO3 and make up to 10 L with deionized 

water.

1. Wash the rock with 300 mL of DI water. Shake gently on the gyratory shaker for 1 hour and discard 

the wash water by decanting off.

2. Repeat step 1 two more times discarding the wash water each time.

3. Weigh the rock to determine the quantity of entrained liquid. Record.

4. Add 300 mL of 0.2 M KNO3 and shake for 1 hour. Decant the supernatant into a 2,000 mL 

volumetric flask.

5. Repeat Step 4 four more times for a total of 5 cycles.

6. Make up the final volume to 2,000 mL and submit a filtered aliquot to chemistry for ammonia, total P, 

chloride and arsenic analysis. 

7. Save the rock samples for determination of the carbonate minerals.

Sumner and Miller (1996)

42 Characterization of Surface-Water Quality and Potential Geochemical Reactions from Storage of Surface Water
Appendix 3. Reagents and analytical methods used for partial solution extractions—Continued

Carbonate minerals

Reagents, analytical steps, and analytes Reference

1 M sodium acetate, adjust to pH = 5.0 with acetic acid 1M sodium acetate: dissolved 410 g of NaC2H3O2

in 4 L of DI water. Adjust to pH 5.0 with glacial acetic acid. Makeup to a final volume of 5.0 L.

1. To each rock sample add 300 mL of pH 5 solution and shake slowly on a gyratory shaker for 6 hours. 

Check the pH after 3.0 hours. If it is >5.5 decant the solution. Pour the decant into a 2 L volumetric 

flask and analyze a small filtered aliquot for calcium. 

2. Add a fresh 300 mL aliquot to the rock and agitate overnight 16 hours. Analyze a small filtered aliquot 

for calcium and decant the remaining solution into a 2 L volumetric flask.

3. Repeat Step 2 for an additional 6-hours and 16-hour period, if required, until the quantity of calcium 

decreases indicating minimal carbonate dissolution. Save the rock samples for determination of the iron 

oxide fraction.

4. Makeup the combined extracts to a final volume of 1,000 or 2,000 mL depending on the number of 

extracts.

5. Analyze a filtered aliquot for Ca, Mg, total P, SiO2, Al and As.

6. Save the rock samples for determination of iron and manganese oxide fraction.

Tessier and others (1979)

Iron and manganese oxides

Reagents, analytical steps, and analytes Reference

Hydroxylamine hydrochloride in 25 percent (v/v) acetic acid 0.04 M hydroxylamine hydrochloride: 

dissolve 11.12 g of NH2OH.HCl and add 25 percent acetic acid (v/v) until the pH is ~2.0. Makeup to a 

final volume of 4.00 L.

1. To each rock sample add 300 mL of solution and shake slowly on a gyratory shaker for 6 hours. Decant 

the solution into a 2 L volumetric flask and analyze a small aliquot for iron. 

2. Add another 300 mL aliquot and again agitate for 16 hours. Analyze and save a small aliquot for iron 

analysis and decant the remaining solution into a 2 L volumetric flask.

3. Repeat Step 2 for an additional 6-hour and 16-hour period, if required, until the quantity of iron 

decreases indicating minimal oxide dissolution.

4. Analyze the first extract solution for SO4, Fe, Mn, total P, SiO2, Al and As.

Tessier and others (1979)

APPENDIX 3 43
Welch—Characterization of Surface-Water Quality in the S-Line Canal, Basalt Aquifer near Fallon, Nevada — Scientific Investigations Report 2005–5102