2890

2910

2920

2880

28702860

2900

2930

2940

2950

2960

2970

2980

2990

3000

3010

3050

3040

3030

3020

2912

2912 2914

2903 2901

2912

2956

2961 2983

3029

2992

2985

2994 2995 3049

3024

3011

3037

3046 3021

2884

2906 2897

2911

2953

2994

2938

2980

3022

3025

2895

2887

2898 2859

2884 2906

3051

Sand

Hollow

Reservoir

(showing stage

equal to 3058)

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5057

Prepared in cooperation with the Washington County Water Conservancy District

Assessment of Managed Aquifer Recharge at 

Sand Hollow Reservoir, Washington County, Utah, 

Updated to Conditions in 2012

Assessment of Managed Aquifer Recharge 

at Sand Hollow Reservoir, Washington 

County, Utah, Updated to Conditions in 2012

By Thomas M. Marston and Victor M. Heilweil

Prepared in cooperation with the Washington County Water Conservancy District

Scientific Investigations Report 2013–5057

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Marston, T.M. and Heilweil, V.M., 2013, Assessment of managed aquifer recharge at Sand Hollow Reservoir, 

Washington County, Utah, updated to conditions in 2012: U.S. Geological Survey Scientific Investigations Report 

2013–5057, 43 p. 
iii

Contents

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

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

Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir ........................................ 4

Data Collection Methods and Results ............................................................................................. 4

Production-Well Withdrawals ................................................................................................. 4

Drain Discharge .......................................................................................................................... 5

Groundwater-Level Data and Reservoir Altitude ................................................................. 5

Surface-Water Inflow to and Outflow from Sand Hollow Reservoir ................................. 7

Meteorological Data .................................................................................................................. 9

Reservoir Water Temperature ................................................................................................ 16

Estimates of Managed Aquifer Recharge from Sand Hollow Reservoir.................................. 16

Changes in Reservoir Storage................................................................................................ 17

Reservoir Evaporation ............................................................................................................. 17

Estimates of Managed Aquifer Recharge from Sand Hollow Reservoir......................... 18

Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the 

Navajo Sandstone......................................................................................................................... 20

Data Collection Methods.................................................................................................................. 21

Water-Quality Results ....................................................................................................................... 21

Field Parameters ...................................................................................................................... 21

Laboratory Water Chemistry .................................................................................................. 33

Dissolved Inorganic Ions ............................................................................................... 33

Dissolved Organic Carbon, Tritium, and Dissolved Gases ....................................... 34

Evaluating the Arrival of Managed Aquifer Recharge at Monitoring Wells ............................ 37

Summary ...................................................................................................................................................... 39

References Cited ........................................................................................................................................ 40

Figures

1. Map showing location of the Sand Hollow study area, Washington County, Utah .............. 2

2. Map showing location of wells, the weather station, drains, and reservoir sampling 

sites in Sand Hollow, Utah ......................................................................................................... 3

3. Graph showing Washington County Water Conservancy District production-well withdrawals in Sand Hollow, Utah, 2004–11 .................................................................................. 4

4. Graph showing monthly reported discharge from the North Dam drain, West Dam 

drain, and West Dam Spring drain in Sand Hollow, Utah, 2003–11 .................................... 5

5. Graph showing water-level altitude in selected wells and Sand Hollow Reservoir, 

Sand Hollow, Utah, 1995–2011 .................................................................................................. 6

6. Map showing potentiometric surface of the Navajo aquifer in January 2012, Sand 

Hollow, Utah ................................................................................................................................. 8

7. Graph showing monthly precipitation at Sand Hollow, Utah, 1998–2011 ................................ 9

8. Graph showing daily water temperature at various depths in Sand Hollow Reservoir, 

Utah, 2003–11 ............................................................................................................................. 16
iv

9. Graph showing monthly estimated evaporation, recharge, and reservoir altitude, 

Sand Hollow Reservoir, Utah, 2002–11 .................................................................................. 18

10. Graph showing monthly calculated recharge rates beneath Sand Hollow Reservoir, 

Utah, 2002–11 ............................................................................................................................. 19

11. Graph showing estimated annual inflow, evaporation, and recharge from Sand 

Hollow Reservoir, Utah, 2002–11 ............................................................................................ 20

12. Graph showing total dissolved-gas pressure in groundwater from selected 

monitoring wells in Sand Hollow, Utah, 2001–2012 ............................................................. 22

13. Graphs showing specific conductance of reservoir water and groundwater from 

selected monitoring wells in Sand Hollow, Utah, 1999–2012 ............................................. 27

14. Graph showing major-ion chemistry from selected surface water and groundwater 

sites in Sand Hollow, Utah ....................................................................................................... 32

15. Graph showing chloride-to-bromide ratios of reservoir water and groundwater 

from selected monitoring wells in Sand Hollow, Utah, 2001–12 ....................................... 33

16. Map showing tritium concentrations of reservoir water and groundwater from 

selected monitoring wells in Sand Hollow, Utah, February 2012 ...................................... 35

17. Map showing CFC–12 concentrations of reservoir water and groundwater from 

selected monitoring wells in Sand Hollow, Utah, February 2012 ...................................... 36

Tables

1. Reservoir data, evaporation, and calculated recharge from Sand Hollow Reservoir, 

Utah, 2002–11 ............................................................................................................................. 10

2. Field water-quality parameters, dissolved organic carbon, tritium, chlorofluorocarbons, sulfur hexafluoride, and neon excess in groundwater and surface 

water from Sand Hollow, Utah ................................................................................................ 23

3. Major and minor chemical constituents in groundwater and surface water from 

selected sites in Sand Hollow, Utah ...................................................................................... 28

4. Summary of tracer peaks showing year of arrival for reservoir recharge at selected 

monitoring wells in Sand Hollow, Utah ................................................................................. 38
v

Conversion Factors, Datums, and Abbreviated Water-Quality Units

Inch/Pound to SI

Multiply By To obtain

Length

inch (in) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

acre 0.004047 square kilometer (km2

)

square foot (ft2

) 929.0 square centimeter (cm2)

square foot (ft2

) 0.09290 square meter (m2)

square inch (in2

) 6.452 square centimeter (cm2)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

acre-foot (acre-ft) 1,233 cubic meter (m3

)

Flow rate

acre-foot per day (acre-ft/d) 0.01427 cubic meter per second (m3

/s)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Density

pound per cubic foot (lb/ft3

) 16.02 kilogram per cubic meter (kg/m3)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

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

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

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

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

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

micrograms per liter (μg/L).

Stable isotope concentrations are reported as per mil, which is equivalent to parts per thousand. 

Tritium units (TU) are used to report tritium concentration, where one TU equals tritium concentration 

in picoCuries per liter divided by 3.22. 

Chlorofluorocarbon concentrations are reported as picomoles per kilogram (pmol/kg). 

Sulfur hexafluoride concentrations are reported as femtomoles per kilogram (fmol/kg). 
vi

Acronyms and Abbreviations

CFCs chlorofluorocarbons

Cl chloride

Cl:Br chloride to bromide ratio

DO dissolved oxygen

DOC dissolved organic carbon

R2 coefficient of determination

SF6 sulfur hexafluoride

SHSP Sand Hollow State Park

TDG total dissolved gas

USGS U.S. Geological Survey

WCWCD Washington County Water Conservancy District 
Assessment of Managed Aquifer Recharge at Sand 

Hollow Reservoir, Washington County, Utah, Updated to 

Conditions in 2012

By Thomas M. Marston and Victor M. Heilweil 

interdisciplinary, cooperative investigations of groundwater 

hydrology and geochemistry since 1999. Previous Sand Hollow reports document pre-reservoir vadose-zone and groundwater conditions prior to March 2002 (Heilweil and Solomon, 

2004; Heilweil and others, 2006; Heilweil and others, 2007; 

Heilweil and McKinney, 2007; Heilweil and others, 2009b), 

pond and trench infiltration studies adjacent to the reservoir 

(Heilweil and others, 2004; Heilweil and Watt, 2011), and 

post-reservoir groundwater conditions, water budgets, and 

estimates of groundwater recharge from the reservoir from 

March 2002 through December 2009 (Heilweil and others, 

2005; Heilweil and Susong, 2007; Heilweil and others, 2009a; 

Heilweil and Marston, 2011). These reports also contain 

monitoring-well and production-well completion information, as well as historical water-quality and precipitation data. 

The objectives of this report are to present and interpret (1) 

groundwater levels, reservoir altitude, well withdrawals, drain 

discharge, meteorological data, reservoir water temperature, 

and inflows/outflows from March 2002 through December 

2011 for estimating monthly amounts of managed aquifer 

recharge from Sand Hollow Reservoir to the Navajo Sandstone, and (2) groundwater and surface water chemical data 

collected prior to the construction of the reservoir through 

March 2012 for evaluating groundwater flow paths and travel 

times of this managed aquifer recharge. This study is a cooperative effort by the Washington County Water Conservancy 

District (WCWCD) and the U.S. Geological Survey (USGS). 

Support for this work was provided by both the USGS and the 

WCWCD.

From 2002 through 2011, total surface-water diversions of 

about 199,000 acre-ft to Sand Hollow Reservoir have allowed 

the reservoir to remain nearly full since 2006. Groundwater 

levels in monitoring wells near the reservoir rose through 2006 

and then fluctuated more recently because of variations in 

reservoir water-level altitude and nearby pumping from production wells. Between 2004 and 2011, a total of about 19,000 

acre-ft of groundwater was withdrawn by these wells for 

municipal supply. In addition, a total of about 21,000 acre-ft of 

shallow seepage was captured by French drains adjacent to the 

North and West Dams (fig. 2) and used for municipal supply, 

irrigation, or returned to the reservoir.

Abstract

Sand Hollow Reservoir in Washington County, Utah, 

was completed in March 2002 and is operated primarily for 

managed aquifer recharge by the Washington County Water 

Conservancy District. From 2002 through 2011, surfacewater diversions of about 199,000 acre-feet to Sand Hollow 

Reservoir have allowed the reservoir to remain nearly full 

since 2006. Groundwater levels in monitoring wells near the 

reservoir rose through 2006 and have fluctuated more recently 

because of variations in reservoir altitude and nearby pumping from production wells. Between 2004 and 2011, a total 

of about 19,000 acre-feet of groundwater was withdrawn by 

these wells for municipal supply. In addition, a total of about 

21,000 acre-feet of shallow seepage was captured by French 

drains adjacent to the North and West Dams and used for 

municipal supply, irrigation, or returned to the reservoir. 

From 2002 through 2011, about 106,000 acre-feet of 

water seeped beneath the reservoir to recharge the underlying Navajo Sandstone aquifer. Water quality was sampled 

at various monitoring wells in Sand Hollow to evaluate the 

timing and location of reservoir recharge as it moved through 

the aquifer. Tracers of reservoir recharge include major and 

minor dissolved inorganic ions, tritium, dissolved organic 

carbon, chlorofluorocarbons, sulfur hexafluoride, and noble 

gases. By 2012, this recharge arrived at four monitoring wells 

located within about 1,000 feet of the reservoir. Changing 

geochemical conditions at five other monitoring wells could 

indicate other processes, such as changing groundwater levels 

and mobilization of vadose-zone salts, rather than arrival of 

reservoir recharge.

Introduction

Sand Hollow Reservoir (fig. 1) in Washington County, 

Utah, was completed in March 2002 and is operated primarily for managed aquifer recharge by the Washington County 

Water Conservancy District. The reservoir is an off-channel 

facility that receives water diverted from the Virgin River near 

the town of Virgin, Utah. Sand Hollow has been the subject of 
2 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Figure 1. Location of the Sand Hollow study area, Washington County, Utah.

Hurricane Fault

Virgin River

Virgin River

Sand

Hollow

Reservoir

 Quail

Creek

Reservoir

15

9

15

Base from U.S. Geological Survey digital data, 1:100,000, 1980

Universal Transverse Mercator projection, Zone 12

R. 14 W.

0 2 4 MILES

0 2 4 KILOMETERS

R. 13 W.

Utah

Location of

map area

T. 42 S.

T. 43 S.

Sand Hollow

Boundary

of study area

Hurricane

Treatment 

Plant

T. 41 S.

Virgin River

diversion to

Sand Hollow

Reservoir

approximately

3 miles east

La Verkin

113°15' 113°22' 30''

37°07'30"

37°15'

St George

approximately

10 miles

southwest

Sand

Hollow

Resort
Introduction 3

Figure 2. Location of wells, the weather station, drains, and reservoir sampling sites in Sand Hollow, Utah.

0 0.5 1 1.5 MILES

0 0.5 1 1.5 KILOMETERS

Base from State of Utah 25-cm aerial imagery, 2006

Universal Transverse Mercator projection, Zone 12

North American Datum of 1983

EXPLANATION

Monitoring well—Dot indicates nested wells

Production well

Surface-water site

Weather station

Drains (approximate location)

North Dam drain

West Dam drain

West Dam spring drain

113°23'45" 113°22'30" 113°21'15"

37°8'45"

37°7'30"

37°6'15"

WCWCD pump

station

Inflow/outflow pipeline

North Dam 3A 

WD 17

WD 18

WD 19

WD RJ WD 20

WD 1

WD 2

WD 4

WD 5

WD 9

WD 12

WD 13

WD 14

WD 15

WD 3

WD 6

WD 7

WD 8

WD 10

WD 11

WD 16

Well 2

Well 1

Well 4 Well 3

WCWCD

weather

station

NRCS

SCAN

station

Well 8

Well 9

Well 17

Well 18

Well 19

Well 20

Well 21

Well 22

Well 23

SH1-18

Boat Ramp

North Dam

West Dam

Haul Road

Sand

Hollow

Reservoir

Washington County Water Conservancy District (WCWCD)

Natural Resources Conservation Service (NRCS)

Soil Climate Analysis Network (SCAN)
4 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Assessment of Managed Aquifer 

Recharge from Sand Hollow Reservoir

Many different types of data have been collected to 

investigate recharge processes, to quantify recharge from Sand 

Hollow Reservoir, and to evaluate hydraulic and geochemical 

changes in the underlying Navajo Sandstone aquifer. These 

data include production-well withdrawals near the reservoir, 

amounts of pumpage from drains capturing shallow groundwater discharge adjacent to the reservoir, reservoir and monitoring-well water levels, meteorological parameters, reservoir 

water temperatures, and inflows and outflows through the 

pipeline connecting Sand Hollow Reservoir with the Virgin 

River and Quail Creek Reservoir and treatment plant (fig. 1). 

Data Collection Methods and Results

Data collection methods are described in detail in Heilweil 

and others (2005) and briefly summarized in the following 

sections. 

Production-Well Withdrawals

The WCWCD has 13 production wells completed in the 

Navajo Sandstone available to capture both pre-existing 

groundwater (natural recharge) in Sand Hollow and recharge 

from Sand Hollow Reservoir (fig. 2). The WCWCD and other 

water users have withdrawn natural recharge in Sand Hollow 

for many years. The WCWCD groundwater withdrawals are 

recorded monthly from in-line magnetic flow meters installed 

at each well. Since August 2004, monthly withdrawals by the 

WCWCD have generally exceeded 150 acre-ft, except for 

several months during the winters of 2004–05, 2005–06, and 

2008–09 (fig. 3). The majority of this pumping has been from 

Wells 8 and 9 (fig. 2), both located adjacent to the North Dam. 

From 2004 through 2006, there were minimal withdrawals 

from these wells during the winter. Since 2006, withdrawals have been more constant year-round. Combined monthly 

withdrawals from these two production wells averaged about 

220 acre-ft from March 2006 through December 2011. Greater 

amounts of pumping from Well 19 began during the summer 

of 2010 and remained near constant through 2011 at about 70 

acre-ft per month. Smaller amounts have been withdrawn from 

Wells 1, 2, 17, and 21. A total of about 19,000 acre-ft were 

pumped from the WCWCD production wells from January 

2004 through December 2011. Through 2011, withdrawals by 

the WCWCD at Sand Hollow have been permitted by the Utah 

Division of Water Rights as natural recharge in Sand Hollow. 

These withdrawals are governed by different water rights than 

recharge from Sand Hollow Reservoir; withdrawal rights for 

this artificial recharge have not yet been exercised.

Figure 3. Washington County Water Conservancy District production-well withdrawals in Sand Hollow, Utah, 2004–11.

0

50

100

150

200

250

300

Total monthly pumping, in acre-feet

Jan-04Jan-05Jan-06Jan-07Jan-08Jan-09Jan-10Jan-11Jan-12

Well 8 and Well 9

All well withdrawals
Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir 5

Drain Discharge

Because of the steep gradients associated with the hydraulic connection between the reservoir and the underlying 

Navajo aquifer, some land-surface areas downgradient of the 

North and West Dams became saturated following construction of the reservoir. In response, three French drains (North 

Dam drain, West Dam drain, and West Dam Spring drain) 

were constructed for capturing this shallow groundwater 

(fig. 2). Timing of excavation and spatial dimensions for the 

three drains can be found in Marston and Heilweil (2011).

Amounts of discharge pumped from these drains are measured with a Sparling Instruments Tigermag totalizing flow 

meter. Discharge to the North Dam drain has been pumped 

relatively consistently since September 2003 (fig. 4). About 

6,000 acre-ft were pumped from the North Dam drain between 

2003 and 2011. Initially, all of this water was returned to the 

reservoir, but since 2007, the majority of water, along with 

an additional 5,800 acre-ft of outflow from Sand Hollow 

Reservoir, has been used by Sand Hollow Resort (fig. 1) to 

meet irrigation demands. About 1,500 acre-ft of water were 

pumped from the West Dam drain back into the reservoir from 

2005 through 2011. Beginning in October 2006, pumping of 

discharge from the West Dam Spring drain was initiated and 

largely has replaced the need for pumping of the West Dam 

drain; from 2006 through 2011, about 13,500 acre-ft were 

pumped from the West Dam Spring drain for municipal use. 

While drainage to the West Dam Spring drain likely does not 

vary greatly, pumping from this drain has been intermittent. 

The intermittent pumping schedule results in high variability 

in the monthly reported discharge from the West Dam Spring 

drain (fig. 4).

Groundwater-Level Data and Reservoir Altitude 

Groundwater levels measured in an extensive monitoringwell network surrounding Sand Hollow Reservoir were used 

to document changes in the potentiometric surface associated 

with recharge from Sand Hollow Reservoir. The WCWCD 

measures water levels monthly in 21 monitoring wells completed in the Navajo Sandstone (fig. 2). These wells were 

constructed with either 1- or 2-in diameter pvc casing, with 

perforations along the bottom 5- to 20-ft length of the casing. 

Figure 4. Monthly reported discharge from the North Dam drain, West Dam drain, and West Dam Spring drain in Sand Hollow, Utah, 

2003–11.

Aug-03Nov-03

Feb-04

May-04

Aug-04Nov-04

Feb-05

May-05

Aug-05Nov-05

Feb-06

May-06

Aug-06Nov-06

Feb-07

May-07

Aug-07Nov-07

Feb-08

May-08

Aug-08Nov-08

Jan-09

May-09

Jul-09

Oct-09

Jan-10

Apr-10

Jul-10

Oct-10

Jan-11

Apr-11

Jan-12

Jul-11

Oct-11

0

100

200

300

400

500

600

2,990

3,010

3,000

3,020

3,040

3,030

3,050

3,060

3,070

Reservoir altitude, in feet

Drain pumping, in acre-feet

Reservoir altitude

North Dam drain

West Dam drain

West Dam Spring drain
6 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Three locations have nested pairs of water district (WD) 

monitoring wells: WD 15 and WD 16, WD 17 and WD 18, 

and WD 19 and WD 20. The vertical distance between well 

screens for the nested-pair wells are 243 ft, 79 ft, and 227 ft, 

respectively. Wells measured by the WCWCD had annual 

independent check measurements performed by USGS personnel for quality assurance to ensure accuracy of equipment used 

to measure water levels (electric-tape water-level indicators). 

Daily reservoir water-level altitude was recorded from 

January 2005 through December 2011 by using a pressure 

transducer installed by the WCWCD in the reservoir along 

the North Dam. Because of periods of transducer malfunction 

from 2005 through 2007, and from August 2011 to December 

2011, daily reservoir altitude was interpolated on the basis of 

monthly measurements recorded at the boat ramp by WCWCD 

and Sand Hollow State Park (SHSP) personnel, and then 

correlated with trends from the transducer data. From 2008 

through mid-2011, the transducer data were within 0.25 ft of 

the intermittent boat ramp measurements; thus, for this more 

recent period, the daily reservoir altitude recorded by the pressure transducer was used.

Recently measured (January 2008 through December 2011) 

and previously reported (Heilweil and others, 2005; Heilweil 

and Susong, 2007; Heilweil and others, 2009; Heilweil and 

Marston, 2011) groundwater levels and reservoir water-level 

altitude are shown in figure 5. The reservoir altitude rose from 

about 2,980 ft at the beginning of March 2002 to a maximum 

of about 3,060 ft in May 2006, when the reservoir was first 

filled to capacity. The reservoir altitude receded to about 

3,040 ft in December 2007 as a result of reduced inflows and 

evaporative losses, and then fluctuated between about 3,040 

and 3,060 ft from 2008 through 2011. The topographically 

lowest part of the reservoir bottom, near the North Dam, was 

the first region to be inundated with surface water in 2002 

and 2003. Therefore, the monitoring wells nearest the northern side of the reservoir were the first to show water-level 

responses and hydraulic connection with the reservoir. As the 

reservoir continued to fill from 2004 through 2006, the extent 

of stored water increased toward the south, roughly perpendicular to the North Dam. Water levels in WD 1, 2, 6, and 9 

rose rapidly beginning in the spring of 2002. Water levels in 

WD 3 and WD 11, located farther south along the western side 

of the reservoir, began to rise rapidly in November 2002 and 

January 2003, respectively. Water levels in WD 10 and WD 12 

(located on the eastern side of the reservoir) and in WD 7 and 

WD 8 (located along the southern side of the reservoir) began 

rising in the latter half of 2003. From 2004 through 2011, measured water levels in monitoring wells closer to the reservoir 

(WD 3, 7, 8, 9, 10, 11, 12) generally fluctuated with reservoir 

altitude. Exceptions to this were water levels in the monitoring wells near the North Dam (WD 1, 2, 6), which all had 

sharp rises during the winters of 2003–04, 2004–05, 2005–06, 

2008–09, 2009–10, and 2010–11 associated with the temporary cessation of pumping at nearby wells 8 and 9. Drawdown induced by pumping Well 19 from mid-2010 through 

2011 is apparent in monitoring wells located farther north of 

the North Dam (WD 4, 19, 20). At monitoring wells farther 

from the reservoir (WD 4, 5, RJ, 13, 14), water levels generally displayed a more subdued rise in response to recharge 

beneath the reservoir. Water levels have been measured only 

since May 2009 in WD 15, 16, 17, 18, 19, and 20. Changes 

in water levels from those observed in 1995 (Heilweil and 

others, 2000) indicate that much of the drawdown induced by 

irrigation pumping to the north of the reservoir has recovered. 

Figure 5. Water-level altitude in selected wells and Sand Hollow Reservoir, Sand Hollow, Utah, 1995–2011. Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08

Jan-09Jan-10Jan-11Jan-12

2,940

2,960

2,980

3,000

3,020

3,040

3,060

3,080

2,880

2,900

2,920

Water-level altitude, in feet 

WD 1

WD 3

WD 5

WD 6

WD 8

WD 10

WD 12

WD 14

WD 16

WD 18

WD 20

WD 2

WD 4

WD RJ

WD 7

WD 9

WD 11

WD 13

WD 15

WD 17

WD 19

Reservoir altitude
Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir 7

Yearly water-level measurements from a long-term monitoring 

well (C-42-14)12dbb-1, located 1.4 mi north of Sand Hollow 

Reservoir, show water levels returning to altitudes observed in 

the mid-1970s (Burden and others, 2012) by 2011. 

Based on water-level measurements in 21 monitoring 

wells, altitudes of the groundwater near Sand Hollow Reservoir during January 2012 ranged from 2,901 to 3,051 ft 

(fig. 6). The reservoir altitude during this same period was 

about 3,058 ft. The lines on figure 6 show the estimated potentiometric contours in the aquifer (lines of equal groundwaterlevel altitude), and the arrows indicate the generalized direction of horizontal groundwater flow away from the reservoir. 

Horizontal hydraulic gradients, calculated by dividing the 

difference in water-level altitudes between two points by the 

distance separating these locations, indicate the potential horizontal direction of groundwater flow. The steepest horizontal 

hydraulic gradients are beneath the North and West Dams and 

generally decline with increasing distance from the reservoir. The steep gradients beneath the dams are the combined 

result of low-conductivity materials at the core of the dams 

and pumping in wells and drains at the base of both dams. 

For example, the horizontal hydraulic gradient between Sand 

Hollow Reservoir (reservoir altitude of 3,058 ft) and WD 1 

(groundwater altitude of 2,971 ft) in 2011 was 0.132 ft/ft, 

whereas the gradient between WD 6 (groundwater altitude of 

2,957 ft) and WD 19 (2,903 ft) was 0.013 ft/ft. In 2011, the 

broader regional gradient between WD 9 (3,046 ft altitude) 

and WD RJ (2,914 ft altitude) was 0.021 ft/ft. In comparison, 

the hydraulic gradient between these same two wells in 2004 

was 0.017 ft/ft (fig. 7 of Heilweil and others, 2005). In general, 

groundwater, moves laterally away from the reservoir in all 

directions (fig. 6). The flow paths shown to the south, east, 

and west of the reservoir, however, likely curve around toward 

the north farther away from the reservoir. A syncline with an 

axis and plunge oriented in a northeasterly direction underlies 

Sand Hollow and controls the direction of all natural groundwater discharge from Sand Hollow. This natural discharge is 

primarily as seepage to the Virgin River to the north (fig. 1; 

Heilweil and others, 2000). In addition, the erosional extent of 

the Navajo Sandstone to the south and west of Sand Hollow, 

and the Hurricane Fault to the east, act as flow boundaries for 

the system. 

Surface-Water Inflow to and Outflow from Sand 

Hollow Reservoir

Surface water is pumped into and flows out of Sand Hollow Reservoir through a 60-in diameter pipeline that enters 

through an inlet structure at the North Dam (fig. 2). This 

pipeline is part of a network of pipelines that connect the 

Virgin River, Sand Hollow Reservoir, Quail Creek Reservoir, 

and the Quail Creek Reservoir Water Treatment Facility. The 

WCWCD has the capability to move water within this network 

of pipelines by using gravity-induced flow and inline pumping. Sand Hollow Reservoir is currently managed to maximize 

groundwater recharge and little surface water has been 

removed from the reservoir. Monthly surface-water inflow to 

and outflow from Sand Hollow Reservoir is shown in table 1. 

The “Monthly pump station inflow or outflow” column in this 

table is the amount of Sand Hollow Reservoir surface water 

coming in from the Virgin River or going out to Quail Creek 

Reservoir, the Quail Creek Water Treatment Plant, or other 

facilities (fig. 1). These data were collected at the WCWCD 

pump station located about 1 mi north of the North Dam. Five 

pumps, each with Sparling Tigermag totalizing flow meters, 

are linked to a computer system that combines and records 

total daily discharge in gallons. The flow meters have electronic modules on which calibration diagnostics are performed 

monthly by the WCWCD. Each module is removed annually 

for factory recalibration.

A wetter period during 2004 and 2005 resulted in above 

average snowpack in the Virgin River watershed, allowing the 

WCWCD to divert larger amounts of surface water to Sand 

Hollow Reservoir from the Virgin River and fill the reservoir 

to nearly full storage capacity by February 2006. Because 

2006 was a dry year (only 2.1 in of total rainfall recorded at 

Sand Hollow compared to the annual average of 7.0 in from 

1998 through 2011), very little water was diverted from the 

Virgin River to the reservoir. Larger amounts of precipitation 

during the latter half of 2007 through early 2011 allowed for 

increased diversions and storage in the reservoir.

The “Monthly drain and spring return flow to reservoir” 

column in table 1 is the portion of discharge to the three 

drains that is pumped back into Sand Hollow Reservoir. The 

“Monthly outflow to Sand Hollow Resort” column is the 

amount of water required by the resort that cannot be met by 

discharge to the North Dam drain and is fulfilled by outflow 

of stored water from Sand Hollow Reservoir. Therefore, the 

“Monthly total inflow or outflow to/from reservoir” column is 

a sum of the pump station inflow/outflow, the drain and spring 

return flow, and the outflow to Sand Hollow Resort (table 1). 

The “Monthly pump station inflow or outflow” column is 

unchanged from Heilweil and Marston (2011) and is comparable to the “Total surface-water inflow or outflow” column 

in table 7 of Heilweil and others (2005) from March 2002 to 

August 2004, the “Monthly surface-water inflow or outflow” 

column in table 2 of Heilweil and Susong (2007) from September 2004 to August 2006, and the “Monthly net surfacewater inflow/outflow” column in table 2 of Heilweil and others 

(2009) from September 2006 to December 2007. 

As in Heilweil and Marston (2011), both “Monthly drain 

and spring return flow to reservoir” and “Monthly outflow 

to Sand Hollow Resort” are included in calculations of total 

inflow to and outflow from the reservoir. These amounts are 

added to the “Monthly pump station inflow or outflow” and 

summed in the “Monthly total inflow or outflow to/from 

reservoir” column. Monthly total inflow/outflow amounts 

from March 2002 through December 2011 ranged from about 

-5,000 acre-ft to 6,600 acre-ft. Approximately 199,000 acre-ft 

of total net inflow were pumped into Sand Hollow Reservoir 

from the Virgin River from 2002 through 2011.
8 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

2890

2910

2920

2880

2870

2860

2900

2930

2940

2950

2960

2970

2980

2990

3000

3010

3050

3040

3030

3020

2912

2912 2914

2903 2901

2912

2956

2961

2983

3029

2992

2985

2994 2995 3049

3024

3011

3037

3046

3021

2884

2906 2897

2911

2953

2994

2938

2980

3022

3025

2895

2887

2898

2859

2884 2906

3051

Sand

Hollow

Reservoir

(showing stage

equal to 3058)

2 MILES

2 KILOMETERS

0 1

0 1

37°5'

37°12'30"

113°25' 113°20'

Base from State of Utah 25-cm aerial imagery, 2006

Universal Transverse Mercator projection, Zone 12

North American Datum of 1983

EXPLANATION

Monitoring well—With calculated 

water-level altitude, in feet, January 

2012. Black well symbol is for wells 

not in monitoring network. Dot

indicates nested wells

Potentiometric contour—Shows 

altitude at which water level would 

have stood in tightly cased wells, 

January 2012. Contour interval 10 

feet, dashed where inferred

Arrow showing direction of 

groundwater flow 

3040

2895

2912

Figure 6. Potentiometric surface of the Navajo aquifer in January 2012, Sand Hollow, Utah.
Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir 9

Meteorological Data

Meteorological data have been collected at the WCWCD 

weather station (fig. 2) in Sand Hollow since January 1998. 

Beginning in 2010, data from a Soil Climate Analysis Network 

(SCAN) Sand Hollow weather station operated by the Natural 

Resources Conservation Service (NRCS) replaced the collection of data by the WCWCD weather station. The NRCS Sand 

Hollow SCAN station is located south of the reservoir within 

Sand Hollow basin in proximity to the WCWCD station 

(fig. 2). Data from both weather stations have been used for 

evaluating evaporation and precipitation, which are required 

for calculating monthly recharge from Sand Hollow Reservoir. 

Parameters measured include air temperature, wind speed, 

wind direction, precipitation, relative humidity, and incoming 

solar radiation. Instrumentation includes a temperature and 

relative humidity probe, a wind direction and speed monitor, 

a tipping bucket rain gage, and a solar radiometer. Sensors 

collect data every minute, and average hourly and daily values 

are computed and stored on a data logger (with the exception 

of precipitation, which is summed rather than averaged). The 

solar radiation and temperature data were used for calculating 

evaporation (using the version of the Jenson and Haise method 

found in McGuinness and Bordne, 1971; see following). The 

other data were collected to permit calculations of evaporation 

using other methods.

From January 13, 1998, to December 30, 2011, daily 

average air temperature ranged from -5 to 37 °C. The coldest 

temperatures during the year typically were in December and 

January, when minimum air temperatures occasionally were 

below -8°C. The warmest temperatures were typically in July, 

when maximum air temperatures occasionally approached 

45°C. Daily average solar radiation ranged from 34 to 840 

calories per square centimeter per day. The minimum daily 

averages are typically in December and January, and the maximum daily averages are typically in June and July. 

Monthly precipitation has been recorded at Sand Hollow weather station continuously from January 1998 through 

December 2011, except for two periods when malfunctioning 

instrumentation resulted in data loss: December 26, 2008 to 

January 3, 2009, and September 28 to November 16, 2009. 

Precipitation amounts during these two periods were estimated 

on the basis of data from the nearby St. George Southgate 

Golf Course weather station (#427516; http://www.wrcc.dri.

edu/cgi-bin/cliMAIN.pl?ut7516). From January 1998 through 

December 2011, monthly precipitation ranged from 0 to about 

4.3 in (fig. 7) and averaged about 0.6 in. Average annual precipitation during the 14-year period from 1998 through 2011 

was 7.0 in. Annual precipitation was about 10.2 in, 10.6 in, 

and 15.7 in during 2004, 2005, and 2010, respectively, indicative of wetter-than-normal conditions at Sand Hollow. 

Figure 7. Monthly precipitation at Sand Hollow, Utah, 1998–2011.

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Monthly precipitation, in inches

Jan-98Jan-99Jan-00Jan-01Jan-02Jan-03Jan-04Jan-05Jan-06Jan-07Jan-08Jan-09Jan-10Jan-11Jan-12
10 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

[Reservoir altitude and Reservoir storage: value is from the last day of each month; Reservoir surface area: value is an average of the daily values for each month; 2ơ, 2 sigma; —, no 

data available]

Month

Reservoir 

altitude

(feet)

Reservoir 

storage

(acre-feet)

Monthly pump 

station inflow 

(+) or outflow (-) 

(acre-feet)

Monthly drain 

and spring 

return flow to 

reservoir

(acre-feet)

Monthly outflow 

(-) to Sand Hollow Resort 

(acre-feet)

Monthly total 

inflow (+) or 

outflow (-) to/

from reservoir 

(acre-feet)

Monthly 

reservoir storage change 

(acre-feet)

Reservoir 

surface area 

(acres)

Monthly evaporation rate 

(feet)2

Mar.–02 3,001 3,090 6,620 0 0 6,620 3,090 260 0.24

Apr.–02 3,003 3,500 3,690 0 0 3,690 410 280 0.46

May–02 3,001 3,090 2,450 0 0 2,450 -410 260 0.68

June–02 2,999 2,480 0 0 0 0 -610 230 0.91

July–02 2,997 2,050 0 0 0 0 -430 210 0.90

Aug.–02 2,995 1,650 0 0 0 0 -400 180 0.81

Sept.–02 2,994 1,300 0 0 0 0 -350 140 0.47

Oct.–02 2,995 1,500 790 0 0 790 200 160 0.26

Nov.–02 3,006 4,220 3,590 0 0 3,590 2,720 320 0.11

Dec.–02 3,012 7,000 3,930 0 0 3,930 2,780 400 0.05

Jan.–03 3,017 9,760 4,580 0 0 4,580 2,760 590 0.09

Feb.–03 3,019 10,670 2,850 0 0 2,850 910 570 0.10

Mar.–03 3,020 10,930 1,930 0 0 1,930 260 580 0.24

Apr.–03 3,019 10,680 540 0 0 540 -250 570 0.37

May–03 3,018 9,930 0 0 0 0 -750 540 0.66

June–03 3,010 6,040 -3,120 0 0 -3,120 -3,890 390 0.89

July–03 3,002 3,200 -2,020 0 0 -2,020 -2,840 240 0.92

Aug.–03 2,999 2,540 0 0 0 0 -660 230 0.75

Sept.–03 2,997 2,100 0 30 0 30 -440 220 0.58

Oct.–03 2,996 1,850 0 20 0 20 -250 170 0.36

Nov.–03 2,994 1,560 0 20 0 20 -290 200 0.09

Dec.–03 3,007 4,700 3,590 10 0 3,600 3,140 330 0.06

Jan.–04 3,013 7,600 3,990 30 0 4,020 2,900 480 0.06

Feb.–04 3,016 8,840 2,320 40 0 2,360 1,240 600 0.08

Mar.–04 3,019 10,400 2,400 50 0 2,450 1,560 630 0.38

Apr.–04 3,025 15,070 5,620 60 0 5,680 4,670 750 0.42

May–04 3,026 15,830 2,050 0 0 2,050 760 780 0.72

June–04 3,025 14,400 0 70 0 70 -1,430 750 0.87

July–04 3,023 13,000 0 60 0 60 -1,400 680 0.94

Aug.–04 3,021 11,670 0 50 0 50 -1,330 680 0.78

Sept.–04 3,019 11,260 3600 30 0 630 -410 630 0.53

Oct.–04 3,019 11,040 3630 30 0 660 -220 610 0.25

Nov.–04 3,022 12,650 32,300 40 0 2,340 1,610 630 0.10

Dec.–04 3,023 13,390 31,400 0 0 1,400 740 670 0.06

Jan.–05 3,027 16,200 33,500 60 0 3,560 2,810 740 0.07

Feb.–05 3,032 20,280 35,200 70 0 5,270 4,080 780 0.11

Mar.–05 3,037 25,030 6,530 90 0 6,620 4,750 880 0.24

Apr.–05 3,041 29,220 6,180 60 0 6,240 4,190 960 0.39

May–05 3,044 32,370 5,140 90 0 5,230 3,150 1,020 0.70

June–05 3,048 35,750 6,100 110 0 6,210 3,380 1,080 0.75

July–05 3,049 37,280 3,600 90 0 3,690 1,530 1,120 0.97

Aug.–05 3,050 38,670 3,390 80 0 3,470 1,390 1,140 0.75

Sept.–05 3,051 39,580 3,010 160 0 3,170 910 1,160 0.54

Table 1. Reservoir data, evaporation, and calculated recharge from Sand Hollow Reservoir, Utah, 2002–11. 
Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir 11

[Reservoir altitude and Reservoir storage: value is from the last day of each month; Reservoir surface area: value is an average of the daily values for each month; 

2ơ, 2 sigma; —, no data available]

Month

Monthly

evaporation

(acre-feet)

Monthly precipitation

(acre-feet)

Monthly groundwater recharge

(acre-feet)

Monthly groundwater recharge 

uncertainty, 2σ

(percent) 

Monthly groundwater recharge 

uncertainty, 2σ

(acre-feet)

Groundwater 

recharge rate 

(feet/day)

Average bottom 

water temperature 

(degrees Celsius)

Mar.–02 60 — 3,470 6.7 232 0.430 10

Apr.–02 130 — 3,150 5.9 187 0.383 16

May–02 180 — 2,680 6.6 176 0.330 22

June–02 210 — 400 12.6 50 0.058 22

July–02 190 — 240 13.1 31 0.040 23

Aug.–02 150 — 250 12.7 32 0.044 24

Sept.–02 70 — 280 11.7 33 0.070 21

Oct.–02 40 — 550 6.6 36 0.110 15

Nov.–02 30 — 840 7.2 61 0.090 9

Dec.–02 20 — 1,130 7.1 80 0.090 6

Jan.–03 50 — 1,770 7.0 123 0.097 5

Feb.–03 60 — 1,880 6.4 121 0.118 7

Mar.–03 140 — 1,530 6.5 99 0.085 10

Apr.–03 210 — 580 9.4 55 0.034 16

May–03 360 — 390 13.2 52 0.023 22

June–03 350 — 420 8.4 35 0.036 22

July–03 220 — 600 8.4 51 0.081 23

Aug.–03 170 — 490 12.0 59 0.069 24

Sept.–03 130 — 340 12.3 42 0.052 21

Oct.–03 60 — 210 11.9 25 0.040 15

Nov.–03 20 — 290 10.6 31 0.048 9

Dec.–03 20 — 440 7.4 32 0.043 6

Jan.–04 30 — 1,090 7.2 78 0.073 5

Feb.–04 40 — 1,080 6.9 74 0.064 6

Mar.–04 240 — 650 7.7 50 0.033 11

Apr.–04 310 — 700 7.6 53 0.031 15

May–04 560 — 730 8.6 63 0.030 18

June–04 650 — 850 13.1 112 0.038 21

July–04 640 — 820 13.1 108 0.039 23

Aug.–04 530 — 850 12.8 109 0.040 24

Sept.–04 330 — 710 10.2 73 0.038 22

Oct.–04 150 — 730 8.4 61 0.039 18

Nov.–04 70 — 660 7.3 48 0.035 12

Dec.–04 40 — 620 7.0 43 0.030 7

Jan.–05 50 — 700 7.3 51 0.031 6

Feb.–05 80 130 1,240 7.3 91 0.057 8

Mar.–05 210 100 1,760 7.4 130 0.065 11

Apr.–05 370 130 1,810 7.5 136 0.063 13

May–05 710 40 1,410 7.9 112 0.045 15

June–05 810 20 2,040 7.8 160 0.063 19

July–05 1,080 10 1,090 8.8 96 0.031 22

Aug.–05 850 40 1,270 8.5 108 0.036 22

Sept.–05 630 20 1,650 8.1 133 0.047 23

Table 1. Reservoir data, evaporation, and calculated recharge from Sand Hollow Reservoir, Utah, 2002–11. 
12 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

[Reservoir altitude and Reservoir storage: value is from the last day of each month; Reservoir surface area: value is an average of the daily values for each month; 2ơ, 2 sigma; —, no 

data available]

Month

Reservoir 

altitude

(feet)

Reservoir 

storage

(acre-feet)

Monthly pump 

station inflow 

(+) or outflow (-) 

(acre-feet)

Monthly drain 

and spring 

return flow to 

reservoir

(acre-feet)

Monthly outflow 

(-) to Sand Hollow Resort 

(acre-feet)

Monthly total 

inflow (+) or 

outflow (-) to/

from reservoir 

(acre-feet)

Monthly 

reservoir storage change 

(acre-feet)

Reservoir 

surface area 

(acres)

Monthly evaporation rate 

(feet)2

Oct.–05 43,052 440,960 2,960 180 0 3,140 41,380 41,190 0.28

Nov.–05 3,055 44,310 5,160 210 0 5,370 4

3,350 1,230 0.11

Dec.–05 3,056 46,120 3,380 240 0 3,620 1,810 1,250 0.05

Jan.–06 3,059 49,590 4,660 290 0 4,950 3,470 1,290 0.08

Feb.–06 3,059 49,840 1,200 250 0 1,450 250 1,320 0.12

Mar.–06 3,058 48,700 60 210 0 270 -1,140 1,310 0.18

Apr.–06 3,059 49,450 2,060 100 0 2,160 750 1,300 0.45

May–06 3,060 51,280 3,650 110 0 3,760 1,830 1,320 0.76

June–06 3,059 49,520 10 130 0 140 -1,760 1,330 0.92

July–06 3,058 47,920 30 140 0 170 -1,600 1,310 0.88

Aug.–06 3,056 46,220 0 140 0 140 -1,700 1,280 0.80

Sept.–06 3,055 44,610 10 90 0 100 -1,610 1,260 0.52

Oct.–06 3,054 43,390 30 120 0 150 -1,220 1,230 0.22

Nov.–06 3,053 42,360 0 100 0 100 -1,030 1,220 0.07

Dec.–06 3,055 45,100 4,430 70 0 4,500 2,740 1,230 0.04

Jan.–07 3,058 48,230 4,190 100 0 4,290 3,130 1,270 0.05

Feb.–07 3,057 47,630 30 60 0 90 -600 1,290 0.13

Mar.–07 3,057 47,660 1,210 70 0 1,280 30 1,290 0.33

Apr.–07 3,057 46,720 50 80 0 130 -940 1,280 0.45

May–07 3,055 44,880 0 0 -110 -110 -1,840 1,220 0.74

June–07 3,054 43,390 0 0 -220 -220 -1,490 1,240 0.93

July–07 3,053 41,740 120 0 -200 -80 -1,650 1,210 0.92

Aug.–07 3,051 40,040 60 0 -210 -150 -1,700 1,180 0.81

Sept.–07 3,050 38,040 5

-750 0 -210 6-910 -2,000 1,160 0.57

Oct.–07 3,046 34,280 5

-2,660 0 -120 6-2,780 -3,760 1,120 0.32

Nov.–07 3,045 32,480 5

-750 0 -100 6-850 -1,800 1,060 0.16

Dec.–07 3,044 31,680 90 10 0 100 -800 1,040 0.05

Jan.–08 3,044 31,470 0 20 0 20 -210 1,030 0.06

Feb.–08 3,046 34,490 3,240 20 0 3,260 3,020 1,050 0.13

Mar.–08 3,050 38,460 4,420 0 -70 4,350 3,970 1,110 0.29

Apr.–08 3,053 42,670 4,950 0 -160 4,790 4,210 1,180 0.45

May–08 3,055 44,410 3,260 0 -120 3,140 1,740 1,230 0.61

June–08 3,053 42,540 0 0 -220 -220 -1,870 1,230 0.93

July–08 3,052 41,080 0 0 -180 -180 -1,460 1,180 0.95

Aug.–08 3,047 34,600 7

-5,000 0 -180 -5,180 -6,480 1,140 0.82

Sept.–08 3,045 32,960 0 0 -140 -140 -1,640 1,070 0.61

Oct.–08 3,044 31,890 0 0 -70 -70 -1,070 1,050 0.36

Nov.–08 3,043 31,160 0 0 -10 -10 -730 1,040 0.16

Dec.–08 3,046 34,490 4,100 40 0 4,140 3,330 1,050 0.06

Jan.–09 3,046 33,830 0 70 0 70 -660 1,080 0.09

Feb.–09 3,049 37,770 4,630 50 0 4,680 3,940 1,110 0.14

Mar.–09 3,052 41,320 4,800 0 -30 4,770 3,550 1,190 0.30

Apr.–09 3,055 44,030 3,920 0 -70 3,850 2,710 1,220 0.44

May–09 3,053 42,180 180 10 -170 20 -1,850 1,220 0.78

Table 1. Reservoir data, evaporation, and calculated recharge from Sand Hollow Reservoir, Utah, 2002–11.—Continued 
Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir 13

[Reservoir altitude and Reservoir storage: value is from the last day of each month; Reservoir surface area: value is an average of the daily values for each month; 

2ơ, 2 sigma; —, no data available]

Month

Monthly

evaporation

(acre-feet)

Monthly precipitation

(acre-feet)

Monthly groundwater recharge

(acre-feet)

Monthly groundwater recharge 

uncertainty, 2σ

(percent) 

Monthly groundwater recharge 

uncertainty, 2σ

(acre-feet)

Groundwater 

recharge rate 

(feet/day)

Average bottom 

water temperature 

(degrees Celsius)

Oct.–05 4330 60 1,490 7.6 113 0.040 18

Nov.–05 140 40 1,920 7.2 138 0.052 15

Dec.–05 60 20 1,770 6.9 122 0.046 8

Jan.–06 100 10 1,390 7.3 101 0.035 8

Feb.–06 160 30 1,070 7.3 78 0.029 7

Mar.–06 240 60 1,230 11.4 140 0.030 9

Apr.–06 580 40 870 8.7 76 0.022 12

May–06 1,000 0 930 8.7 81 0.023 17

June–06 1,220 10 690 14.1 97 0.017 21

July–06 1,160 30 640 14.1 90 0.016 25

Aug.–06 1,020 0 820 13.8 113 0.021 27

Sept.–06 650 10 1,070 12.8 137 0.028 24

Oct.–06 270 30 1,130 11.6 132 0.030 19

Nov.–06 90 0 1,040 10.8 112 0.028 14

Dec.–06 60 10 1,710 7.0 120 0.045 8

Jan.–07 60 10 1,110 7.2 80 0.028 4

Feb.–07 170 30 550 11.9 65 0.015 4

Mar.–07 430 0 820 9.0 73 0.021 8

Apr.–07 580 50 540 13.4 73 0.014 12

May–07 900 0 830 13.3 110 0.022 15

June–07 1,150 0 120 14.4 17 0.003 19

July–07 1,110 110 560 13.5 76 0.015 22

Aug.–07 960 60 650 13.3 87 0.018 26

Sept.–07 660 80 510 10.8 55 0.015 25

Oct.–07 360 0 620 8.6 53 0.018 18

Nov.–07 170 100 880 9.3 82 0.028 14

Dec.–07 50 90 940 10.0 94 0.029 8

Jan.–08 60 50 220 11.9 26 0.007 4

Feb.–08 140 100 200 7.7 15 0.007 4

Mar.–08 320 10 70 7.8 5 0.002 8

Apr.–08 530 0 50 8.0 4 0.001 11

May–08 750 50 700 8.5 59 0.018 15

June–08 1,140 10 520 13.8 72 0.014 19

July–08 1,120 110 270 14.2 38 0.007 22

Aug.–08 940 10 370 8.7 32 0.010 17

Sept.–08 650 20 870 12.8 111 0.027 19

Oct.–08 370 60 690 12.5 86 0.021 19

Nov.–08 160 80 640 11.6 75 0.021 14

Dec.–08 60 50 800 7.4 59 0.025 9

Jan.–09 100 50 680 11.2 76 0.020 5

Feb.–09 150 60 650 7.5 49 0.021 7

Mar.–09 360 0 860 7.7 66 0.023 9

Apr.–09 530 20 630 8.0 50 0.017 11

May–09 950 0 920 12.9 119 0.024 13

Table 1. Reservoir data, evaporation, and calculated recharge from Sand Hollow Reservoir, Utah, 2002–11.—Continued 
14 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Table 1. Reservoir data, evaporation, and calculated recharge from Sand Hollow Reservoir, Utah, 2002–11.—Continued 

[Reservoir altitude and Reservoir storage: value is from the last day of each month; Reservoir surface area: value is an average of the daily values for each month; 2ơ, 2 sigma; —, no 

data available]

Month

Reservoir 

altitude

(feet)

Reservoir 

storage

(acre-feet)

Monthly pump 

station inflow 

(+) or outflow (-) 

(acre-feet)

Monthly drain 

and spring 

return flow to 

reservoir

(acre-feet)

Monthly outflow 

(-) to Sand Hollow Resort 

(acre-feet)

Monthly total 

inflow (+) or 

outflow (-) to/

from reservoir 

(acre-feet)

Monthly 

reservoir storage change 

(acre-feet)

Reservoir 

surface area 

(acres)

Monthly evaporation rate 

(feet)2

June–09 3,052 40,600 210 0 -130 80 -1,580 1,190 0.73

July–09 3,050 38,700 220 0 -170 50 -1,900 1,170 0.96

Aug.–09 3,049 36,960 210 0 -150 60 -1,740 1,140 0.80

Sept.–09 3,047 35,380 200 0 -150 50 -1,580 1,110 0.58

Oct.–09 3,046 33,940 200 10 -80 130 -1,440 1,090 0.30

Nov.–09 3,045 32,960 180 10 -20 170 -980 1,070 0.16

Dec.–09 3,044 32,320 200 40 0 240 -640 1,050 0.05

Jan.–10 3,044 31,890 0 50 0 50 -430 1,040 0.07

Feb.–10 3,044 31,470 0 40 0 40 -420 1,040 0.10

Mar.–10 3,047 35,490 5,100 90 -50 5,140 4,020 1,070 0.23

Apr.–10 3,050 38,930 5,280 70 -110 5,240 3,440 1,130 0.36

May–10 3,053 41,810 4,650 90 -160 4,580 2,880 1,180 0.56

June–10 3,054 43,660 3,890 80 -190 3,780 1,850 1,220 0.81

July–10 3,053 42,300 570 100 -240 430 -1,360 1,220 0.91

Aug.–10 3,051 40,240 0 80 -220 -140 -2,060 1,190 0.77

Sept.–10 3,050 38,350 0 80 -210 -130 -1,890 1,160 0.60

Oct.–10 3,049 37,310 0 100 -90 10 -1,040 1,140 0.29

Nov.–10 3,048 36,620 0 90 -40 50 -690 1,120 0.13

Dec.–10 3,051 40,240 4,290 90 -10 4,370 3,620 1,150 0.06

Jan.–11 3,054 43,960 5,650 60 -10 5,700 3,720 1,200 0.09

Feb.–11 3,057 47,750 4,540 40 -30 4,550 3,790 1,260 0.11

Mar.–11 3,059 50,270 3,780 20 -30 3,770 2,520 1,310 0.26

Apr.–11 3,058 49,110 0 10 -140 -130 -1,160 1,310 0.43

May–11 3,057 47,460 0 10 -150 -140 -1,650 1,290 0.59

June–11 3,056 45,680 0 80 -190 -110 -1,780 1,270 0.89

July–11 3,054 43,710 0 10 -200 -190 -1,970 1,240 0.89

Aug.–11 3,053 41,990 0 10 -190 -180 -1,720 1,220 0.93

Sept.–11 3,052 40,600 0 20 -150 -130 -1,390 1,190 0.61

Oct.–11 3,051 39,910 0 30 -70 -40 -690 1,170 0.35

Nov.–11 3,054 43,490 3,980 30 -30 3,980 3,580 1,200 0.15

Dec.–11 3,058 48,010 4,990 20 -10 5,000 4,520 1,260 0.07

Total — — — — — 199,110 — — —

1 Negative (-) values indicate flows out of Sand Hollow to Quail Creek Water Treatment Plant or to Quail Creek Reservoir. 

2 Monthly evaporation rate from February 2007 through December 2009 was calculated with a correction factor to account for higher solar radiation measurements with new instrument. 

3 Because of problems with monitoring equipment, inflows from September 2004 through February 2005 are estimated based on previous inflow history and changes in reservoir altitude. 

4 Revised value based on refined reservoir altitude estimate for October 2005. 

5 Monthly pump station outflow was increased from amount reported in Heilweil and others (2009a) based on reservoir altitude relations. 

6 Monthly total outflow was increased from amount reported by Washington County Water Conservancy District based on reservoir altitude relations. 

7 Monthly pump station outflow was increased from previously reported amount (Heilweil and others, 2009a) based on reservoir altitude relations. 

8 Sand Hollow rain gauge not functioning; values of 0 based on lack of precipitation from St. George precipitation station #427516. 
Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir 15

1 Negative (-) values indicate flows out of Sand Hollow to Quail Creek Water Treatment Plant or to Quail Creek Reservoir. 

2 Monthly evaporation rate from February 2007 through December 2009 was calculated with a correction factor to account for higher solar radiation measurements with new instrument. 

3 Because of problems with monitoring equipment, inflows from September 2004 through February 2005 are estimated based on previous inflow history and changes in reservoir altitude. 

4 Revised value based on refined reservoir altitude estimate for October 2005. 

5 Monthly pump station outflow was increased from amount reported in Heilweil and others (2009a) based on reservoir altitude relations. 

6 Monthly total outflow was increased from amount reported by Washington County Water Conservancy District based on reservoir altitude relations. 

7 Monthly pump station outflow was increased from previously reported amount (Heilweil and others, 2009a) based on reservoir altitude relations. 

8 Sand Hollow rain gauge not functioning; values of 0 based on lack of precipitation from St. George precipitation station #427516. 

Table 1. Reservoir data, evaporation, and calculated recharge from Sand Hollow Reservoir, Utah, 2002–11.—Continued 

[Reservoir altitude and Reservoir storage: value is from the last day of each month; Reservoir surface area: value is an average of the daily values for each month; 

2ơ, 2 sigma; —, no data available]

Month

Monthly

evaporation

(acre-feet)

Monthly precipitation

(acre-feet)

Monthly groundwater recharge

(acre-feet)

Monthly groundwater recharge 

uncertainty, 2σ

(percent) 

Monthly groundwater recharge 

uncertainty, 2σ

(acre-feet)

Groundwater 

recharge rate 

(feet/day)

Average bottom 

water temperature 

(degrees Celsius)

June–09 870 10 800 12.9 103 0.022 14

July–09 1,120 10 840 13.1 110 0.023 15

Aug.–09 910 0 890 12.8 114 0.025 16

Sept.–09 650 0 980 12.3 120 0.029 19

Oct.–09 320 8

0 1,320 11.1 147 0.039 18

Nov.–09 170 8

0 1,050 10.6 111 0.033 12

Dec.–09 60 100 920 9.6 88 0.028 7

Jan.–10 80 150 550 11.2 62 0.017 6

Feb.–10 110 220 570 11.5 65 0.018 7

Mar.–10 250 190 1,060 7.6 80 0.032 9

Apr.–10 400 40 1,440 7.6 109 0.041 11

May–10 660 10 1,050 8.0 84 0.029 14

June–10 990 0 940 8.6 81 0.025 16

July–10 1,100 0 690 12.7 88 0.018 17

Aug.–10 920 60 1,060 13.0 138 0.029 17

Sept.–10 690 0 1,070 12.7 136 0.030 18

Oct.–10 320 280 1,010 12.0 121 0.029 19

Nov.–10 150 80 670 11.6 78 0.019 14

Dec.–10 70 410 1,090 7.5 82 0.031 9

Jan.–11 100 10 1,890 7.1 135 0.051 7

Feb.–11 140 170 790 7.5 60 0.020 6

Mar.–11 340 110 1,020 7.7 79 0.025 8

Apr.–11 560 90 560 13.1 73 0.014 11

May–11 760 50 800 13.1 105 0.020 13

June–11 1,130 10 550 13.9 76 0.014 14

July–11 1,110 10 680 13.6 92 0.018 15

Aug.–11 1,130 20 430 13.9 60 0.011 16

Sept.–11 720 50 590 13.3 79 0.016 17

Oct.–11 420 120 350 13.4 47 0.010 18

Nov.–11 180 40 260 7.7 20 0.007 13

Dec.–11 90 50 440 7.5 33 0.011 7

Total 49,780 — 105,790 — — — —
16 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Reservoir Water Temperature

Continuous water-temperature measurements were made 

in Sand Hollow Reservoir and used for evaluating effects of 

water viscosity changes on seepage rates beneath the reservoir. A string of five thermistors was installed in January 2003 

in the deepest part of Sand Hollow Reservoir, about 300 ft 

from the North Dam. These thermistors were attached to a 

floating buoy at depths of about 0.3 ft (R1), 3 ft (R2), 10 ft 

(R3), 15 ft (R4), and 30 ft (R5). A sixth thermistor (R6) was 

added on May 6, 2008, at a depth of 50 ft (or at the bottom of 

the reservoir, if shallower). The thermistors (Onset® Hobo®

TidbiT Water Temperature Data Loggers) are reported to have 

an accuracy of better than 0.5oC over the temperature range 

of 0 to 35oC. Water temperature from January 2003 through 

December 2011 ranged from about 1 to 30oC. Both the previous (January 2003 through December 2007) and current (January 2008 through December 2011) temperature data are shown 

in figure 8. Water temperature data at the following locations 

were not recorded for periods exceeding 30 days because of 

problems with the thermistors, buoy, or both: R1 at the 0.3-ft 

depth, January 1 to June 4, 2008 and March 31 to August 4, 

2010; R2 at the 3-ft depth, March 11 to June 5, 2008; R3 at the 

10-ft depth, March 11 to July 29, 2008; R4 at the 15-ft depth, 

Figure 8. Daily water temperature at various depths in Sand Hollow Reservoir, Utah, 2003–11.

March 11 to May 5, 2008, August 27 to October 3, 2009, and 

September 8 to December 31, 2011; R5 at the 30-ft depth, 

June 5 to July 29, 2008; and R6 at the 50-ft depth, June 5 to 

July 29, 2008. 

Estimates of Managed Aquifer Recharge from 

Sand Hollow Reservoir

Substantial amounts of surface water from Sand Hollow Reservoir infiltrate through the underlying sediments to 

recharge the Navajo Sandstone aquifer. This recharge either 

is captured by production wells for municipal supply, or it 

moves northward through the aquifer towards the Virgin River. 

Through 2011, withdrawals from production wells operated 

by the WCWCD at Sand Hollow have been permitted for the 

capture of natural recharge in Sand Hollow. These withdrawals 

are governed by different water rights than those associated 

with managed aquifer recharge from Sand Hollow Reservoir; 

withdrawal rights for this artificial recharge have not yet been 

exercised.

Recharge from Sand Hollow Reservoir is calculated as the 

residual with the following water-budget equation (modified 

from Heilweil and others, 2005):

0

5

10

15

20

25

30

35

40

Water temperature, in degrees Celsius

Thermistor number and depth

R1: 0 ft

R2: 3 ft

R3: 10 ft

R4: 15 ft

R5: 30 ft

R6: 50 ft

May-02

Sep-02

Jan-03

May-03

Sep-03

Jan-04

May-04

Sep-04

Jan-05

May-05

Sep-05

Jan-06

May-06

Oct-06

Feb-07

Jun-07

Oct-07

Feb-08

Jun-08

Oct-08

Feb-09

Jun-09

Oct-09

Feb-10

Jun-10

Oct-10

Feb-11

Jun-11

Oct-11

Feb-12

Jun-12
Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir 17

R = I

sw + Idr – Osw + P ± ΔS – E (1)

where 

R is recharge, 

Isw is surface-water inflow,

Idr is drain return flow,

Osw is surface-water outflow, 

P is the amount of precipitation falling directly on 

the reservoir, 

ΔS is change in surface-water storage, and 

E is evaporation.

All the variables in equation 1 are in units of acre-ft. 

The following equation was developed to evaluate the 

uncertainty for each monthly recharge estimate:

CU= Σ[(|Ci|/Σ|Ci|)*Ui] (2)

where 

CU is the composite uncertainty fraction (two standard 

deviation, 2σ)

|Ci| is the absolute value of each component of the 

water budget (acre-ft), 

Σ|Ci| is the sum of absolute values of all the waterbudget components (acre-ft), and

Ui is the uncertainty fraction (2σ) for each individual 

water-budget component.

The smallest estimated uncertainty fraction is 0.05 

(5 percent) for Isw, IDr, and Osw because these flows are 

recorded using calibrated inline flow meters. The estimated 

uncertainty fraction for P is higher, at 0.10 (10 percent), 

because it is an indirect measurement made on the basis of 

nearby meteorological station data. Similarly, the estimated 

uncertainty fraction is also 0.10 (10 percent) for ΔS because 

changes in surface-water storage are based only on approximate reservoir water-level altitude/volume relations rather 

than direct measurements. The largest estimated uncertainty 

fraction is 0.20 (20 percent) for E, which is based on differences between alternative methods for estimating evaporation 

both at Sand Hollow and other areas (Heilweil and others, 

2007; Rosenberry and others, 2007).

The first two reports documenting monthly groundwater 

recharge beneath Sand Hollow Reservoir through August 

2006 (Heilweil and others, 2005; Heilweil and Susong, 2007) 

did not include precipitation falling directly on the reservoir. 

Beginning with the third report (Heilweil and others, 2009a), 

and continuing in this report, an additional term for precipitation falling directly on the reservoir (P) was included in 

equation 1. The monthly amount of precipitation falling on 

the reservoir is calculated by multiplying the total monthly 

precipitation recorded by the Sand Hollow weather station by 

the average reservoir surface area for that month (based on 

reservoir water-level altitude to area relations for the reservoir; RBG Engineering, written commun., 2002; Washington 

County Water Conservancy District, written commun., 2006). 

The precipitation term in equation 1, however, does not 

account for precipitation runoff to the reservoir. Because of 

high evaporation rates and permeable surficial soils, precipitation events seldom produce runoff that reaches the lower part 

of Sand Hollow (L. Jessop, Washington County Water Conservancy District, oral commun., 2001), where the reservoir is 

situated.

Monthly water-budget values for Sand Hollow Reservoir 

are given in table 1. Values are generally monthly averages 

or totals, except for reservoir altitude and storage, which are 

shown for the last day of each month. Values for “Monthly 

evaporation rate,” “Monthly evaporation,” and “Monthly 

groundwater recharge” from March 2002 through January 

2005 and from January 2008 through December 2011 are 

monthly averages; during February 2005 through December 

2007, however, the values are the sum of daily measurements. 

Summing of daily evaporation estimates was discontinued 

after 2007 because comparison of daily and average monthly 

calculations during 2008 and 2009 showed little difference, 

and the equation used for calculating evapotranspiration is 

more appropriate for calculating average evaporation over 

longer periods (McGuinness and Bordne, 1971). 

Changes in Reservoir Storage

Changes in reservoir storage were calculated from daily 

reservoir water-level altitudes reported by the WCWCD by 

using altitude to volume relations (RBG Engineering, written commun., 2002). Since inception of the reservoir in 2002, 

surface-water storage increased to a maximum of about 51,000 

acre-ft in May of 2006. From the latter half of 2006 through 

2007, surface-water storage decreased to about 32,000 acre-ft, 

and during 2008 through 2010, surface-water storage varied between about 31,000 and 44,000 acre-ft. Following the 

abnormally wet winter and spring of 2010–11, surface-water 

storage was kept at a high level during 2011, varying between 

40,000 to 50,000 acre-ft (table 1).

Reservoir Evaporation 

The McGuinness and Bordne (1971) version of the JensenHaise method was selected for calculating evaporation from 

Sand Hollow Reservoir during this study. A detailed comparison to results using other methods for estimating evaporation 

is given in Heilweil and others (2005). The McGuinness and 

Bordne (1971) version of the Jensen-Haise method is based on 

the relation: 

PET = {[((0.01Ta) – 0.37)(Qs)]0.000673}2.54 (3)

where

PET is potential evaporation, in centimeters per day, 

Ta is air temperature, in degrees Fahrenheit, and 

Qs is solar radiation, in calories per square centimeter 

per day.

The units for PET can be converted to feet per day by 

multiplying by 0.0328.
18 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

By using air temperature and solar radiation from the 

nearby weather station (fig. 2), monthly evaporation rates were 

calculated with equation 3. These estimated evaporation rates 

ranged from 0.04 to 0.97 ft/mo from March 2002 through 

December 2011 (table 1; Heilweil and others, 2005; Heilweil 

and Susong, 2007; Heilweil and others, 2009, Heilweil and 

Marston, 2011). Multiplying the estimated evaporation rates 

by average reservoir surface area yields monthly evaporation 

losses that ranged from about 20 to 1,200 acre-ft between 

March 2002 and December 2011.

Estimates of Managed Aquifer Recharge from 

Sand Hollow Reservoir

Monthly estimates of precipitation (P), evaporation (E), 

inflows (Isw and I

dr), outflows (Osw), and changes in surfacewater storage (ΔS) were used in equation (1) to calculate 

recharge to the Navajo Sandstone aquifer beneath Sand Hollow Reservoir. Monthly recharge from March 2002 through 

December 2011 ranged from about 50 to 3,500 acre-ft (fig. 

9), with two standard deviation (σ) composite uncertainties 

ranging from about 6 to 14 percent of the estimate (table 1). 

Higher composite uncertainties in the summer reflect the 

larger, weighted importance of evaporation losses, which have 

the highest uncertainty. Several monthly recharge values differ 

from previously reported values in Heilweil and others (2005), 

Heilweil and Susong (2007), and Heilweil and others (2009) 

because of the inclusion of both “Monthly drain and spring 

return flow to reservoir” and “Monthly outflow to Sand Hollow Resort” (both through the 60-in pipeline) in the current 

estimates of monthly recharge. Instances of differing values 

from previous reports are noted with an explanation of identified cause of error in table 1.

Estimated average monthly recharge rates beneath Sand 

Hollow Reservoir ranged from about 0.001 to 0.43 ft/d 

between March 2002 and December 2011 (fig. 10). Although 

the graph shows large monthly fluctuations, three general periods can be observed. Period 1 (March through June 2002) had 

very high initial rates and then a rapid decrease as the vadose 

zone of the Navajo Sandstone became saturated and a hydraulic connection between the reservoir and aquifer was established, causing an abrupt decrease in hydraulic gradient. This 

establishment of a saturated hydraulic connection is supported 

by measurements in monitoring wells closest to the reservoir, 

which show rapidly rising water levels beginning in late spring 

2002 near the southern end of the reservoir (fig. 5). Although 

consecutive monthly recharge rates occasionally fluctuate by 

more than 100 percent, Period 2 (mid-2002 through mid-2007) 

generally shows a gradual decline in recharge rates, while 

Period 3 (mid-2007 through 2011) demonstrates relatively 

constant, low recharge rates. 

Figure 9. Monthly estimated evaporation, recharge, and reservoir altitude, Sand Hollow Reservoir, Utah, 2002–11.

4,000

3,000

3,500

2,000

2,500

1,000

1,500

0

500

Volume, in acre-feet

3,080

3,060

3,020

3,000

2,960

2,980

3,040

Reservoir altitude, in feet 

Groundwater recharge volume

Evaporation volume

Reservoir altitude

Mar-02

Jun-02

Sep-02Dec-02

Mar-03

Jun-03

Sep-03Dec-03

Mar-04

Jun-04

Sep-04Dec-04

Mar-05

Jun-05

Sep-05Dec-05

Mar-06

Jun-06

Sep-06Dec-06

Mar-07

Jun-07

Sep-07Dec-07

Mar-08

Jun-08

Sep-08Dec-08

Mar-09

Jun-09

Sep-09Dec-09

Mar-10

Jun-10

Sep-10Dec-10

Mar-11

Jun-11

Sep-11Dec-11
Assessment of Managed Aquifer Recharge from Sand Hollow Reservoir 19

The general decline in observed recharge rates can be 

caused in part by (1) a decrease in the regional hydraulic 

gradient with rising water levels as managed aquifer recharge 

continues to increase groundwater storage in Sand Hollow 

basin, or (2) changes in permeability caused by trapped gas 

bubble exsolution or dissolution (Heilweil and others, 2009b), 

biofilm growth and decay, and silt accumulation or reduction, 

or both. A numerical simulation of managed aquifer recharge 

from Sand Hollow Reservoir to the surrounding Hurricane 

Bench area was utilized to assess the reservoir recharge 

boundary in relation to the regional hydraulic gradient. Initial 

use of a reservoir bed conductance similar to the hydraulic 

conductivity of the Navajo Sandstone yielded an overestimate 

of recharge relative to calculated values. The model required a 

reduced hydraulic conductivity beneath the reservoir to match 

nearby water levels and calculated monthly reservoir recharge 

rates (Marston and Heilweil, 2012). 

Monthly recharge rates, particularly during Period 2 

(fig. 10), indicate seasonal fluctuations that are likely not 

caused by changes in hydraulic gradient. Recharge rates are 

generally higher during the winter months (particularly evident in 2003 through 2007), even though infiltrating water is 

cooler and more viscous during that time of year. A previous 

study at Sand Hollow (Heilweil and others, 2009) suggested 

biofilm growth/dissipation and summer-time bubble formation 

from plant respiration/decay as possible mechanisms for this 

variability. Further studies are needed to evaluate if these seasonal fluctuations in recharge beneath Sand Hollow Reservoir 

are caused by (1) a seasonal die-off of the biofilm layer and a 

decrease in physical clogging as this biofilm layer is broken 

up, (2) dissipation of the silt layer in the shallower parts of 

the reservoir due to wave action associated with the increase 

in winter/spring winds, (3) a reduction of plant-respired gases 

and increased solubility of biogenic gas bubbles due to cooler 

water temperatures, and (or) (4) the dissolution of or physical 

reduction in the size of trapped gas bubbles due to cooler temperatures. Previous calculations using the ideal gas law have 

shown that a 25°C reduction in reservoir water temperature 

from summer to winter would cause an 8 percent reduction in 

the volume of entrapped-gas bubbles. Laboratory permeability 

testing showed that a 10-percent increase in saturation resulted 

in an order of magnitude increase (from 0.06 to 0.6 ft/d) in 

the hydraulic conductivity of sandstone cores (Heilweil and 

others, 2004). 

Figure 10. Monthly calculated recharge rates beneath Sand Hollow Reservoir, Utah, 2002–11.

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Average monthly recharge rate, in feet per day

Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12

Groundwater recharge rate
20 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Net annual inflow, evaporation, and groundwater recharge 

from Sand Hollow Reservoir from 2002 through 2011 are 

shown in figure 11. Total net inflow during this period was 

about 199,000 acre-ft, with annual inflow during this period 

ranging from about 800 acre-ft in 2007 to 56,000 acre-ft in 

2005. The general increase in reservoir water-level altitude 

and area from 2002 to 2007 resulted in a steady increase in 

the volume of annual evaporation from about 1,000 acre-ft in 

2002 to about 6,600 acre-ft in 2006, which then leveled off 

from 2007 through 2011. Total estimated evaporative losses 

from 2002 through 2011 were about 50,000 acre-ft. Annual 

recharge ranged from a low of about 5,000 acre-ft in 2008 to a 

high of about 18,000 acre-ft in 2005. Total estimated recharge 

from 2002 through 2011 was about 106,000 acre-ft, with a two 

standard deviation uncertainty of 9,200 acre-ft.

Evaluation of the Movement of 

Managed Aquifer Recharge and 

Geochemical Mixing in the 

Navajo Sandstone

As managed aquifer recharge from Sand Hollow moves 

into the underlying aquifer, it has an initial water-quality 

signature similar to the reservoir water, but this evolves as 

water moves through the shallow subsurface to the pre-reservoir water-table depth within the aquifer. This water-quality 

signature includes field parameters, major- and trace-ion 

chemistry, isotopes, and dissolved gases. Along its travel path, 

the managed aquifer recharge water initially moves from the 

reservoir through the organic-rich silt layer that has accumulated beneath the reservoir, and then through the pre-reservoir 

vadose zone (now saturated) where vadose-zone solutes had 

naturally accumulated and air was trapped prior to and during 

filling of the reservoir. This results in an overall managed aquifer recharge water-quality signature that is distinctly different 

than that of native groundwater. Water-quality data from Sand 

Hollow Reservoir and surrounding monitoring wells, therefore, are used to assess the movement of groundwater recharge 

from the reservoir through the Navajo Sandstone aquifer. 

These include both field water-quality parameters as well as 

water samples collected for laboratory chemical, isotopic, and 

dissolved-gas analysis. 

Figure 11. Estimated annual inflow, evaporation, and recharge from Sand Hollow Reservoir, Utah, 2002–11.

20,000

30,000

40,000

50,000

60,000

0

10,000

Volume, in acre-feet

Net annual inflow

Evaporation

Groundwater recharge

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 21

Field parameters were measured to provide an on-site 

indication of both surface- and groundwater quality. Field 

water-quality parameters included water temperature, specific 

conductance, pH, dissolved oxygen, and total dissolved-gas 

(TDG) pressure. TDG pressure is the combination of the 

partial pressures of all the dissolved gases in water. If dissolution of air is the primary source, these dissolved gases 

will be predominantly nitrogen, oxygen, and argon. Dissolved 

gases may also include carbon dioxide, methane, hydrogen 

sulfide (CO2,CH4, H2S), and other gases formed during plant 

respiration and microbial consumption (anaerobic and aerobic 

decay).While both dissolved oxygen and TDG pressure in the 

recharging reservoir water are initially in atmospheric equilibrium, these parameters can increase if this water circulates 

through porous media with trapped air bubbles, which can 

form as the vadose zone becomes saturated from the wetting 

front beneath the reservoir connecting with the underlying 

aquifer (Heilweil and others, 2005). As hydrostatic pressure 

increases with depth below the reservoir altitude, the trapped 

gas in the porous media is dissolved by the recharge water. In 

contrast, dissolved oxygen and TDG pressure can decrease 

through microbially-mediated reducing conditions associated 

with consumption of dissolved organic carbon.

Data Collection Methods

Field parameters were measured with a multi-parameter 

sonde placed within the screened interval at the bottom of 

each 2-in monitoring well, and in the reservoir at water depths 

of approximately 2 ft. The multi-parameter sonde was too 

large to enter the 1-in monitoring wells (North Dam 3A, WD 

1, WD 4, WD 5, WD RJ, and WD 12). Consequently, field 

measurements from these wells were made on site with a flowthrough chamber connected to the discharge lines from either 

a Waterra or peristaltic pump; no TDG pressure measurements 

were made at these sites. Additional details regarding field 

parameter methods are given in Heilweil and others (2005) 

and Heilweil and Susong (2007).

Laboratory water-quality analyses of surface water from 

Sand Hollow Reservoir and groundwater from the Navajo 

Sandstone aquifer included major and trace dissolved inorganic and organic constituents, tritium (3

H), and noble and 

industrial dissolved gases. The major inorganic ions included 

calcium, magnesium, sodium, potassium, bicarbonate, sulfate, 

chloride, fluoride, and nitrate. Trace ions included bromide, 

iron, manganese, arsenic, nitrite, ammonia, and orthophosphate. Organic constituents included dissolved organic carbon. 

Dissolved gases included chlorofluorocarbons (CFC–11, 

CFC–12, CFC–113), sulfur hexafluoride (SF6), and noble 

gases (He, Ne, Ar, Kr, Xe). 

Water-chemistry samples were collected from 2-in monitoring wells by using either a Grunfos or Bennett sample 

pump; 1-in wells were sampled with a Waterra hand pump; 

production wells were sampled utilizing installed turbine 

pumps. Prior to water-chemistry sample collection from 

monitoring wells, water was purged from each well until field 

parameters stabilized and a minimum of three casing volumes 

were removed. After purging each well, water was pumped 

into samples bottles and filtered as necessary. Since 2009, a set 

of replicates for all constituents has been separately analyzed 

annually at one randomly selected sampling site for quality 

assurance.

Samples for major and trace ions were filtered with 

0.45-micron disposable filters and collected in cleaned polyethylene bottles according to procedures described by Wilde 

and Radtke (1998); samples for cation analysis were preserved 

with 7.7-normal nitric acid. Tritium samples were collected 

in 500 milliliter (ml) polyethylene bottles with polyseal caps 

without head space. CFC and SF6

 samples were collected 

in 250-ml and 1-liter (L) glass bottles, respectively, according to procedures described at: http://water.usgs.gov/lab/. 

Noble gases were collected using diffusion sampler methods described by Sheldon (2002) and Gardner and Solomon 

(2009). 

Inorganic and organic chemical analyses (major ions, trace 

ions, dissolved organic carbon) were analyzed by the U.S. 

Geological Survey at the National Water Quality Laboratory 

in Denver, Colorado. CFCs and SF6 were analyzed by the U.S. 

Geological Survey at the Chlorofluorocarbon Laboratory in 

Reston, Virginia. Tritium and noble gases were analyzed by 

the University of Utah’s Dissolved Gas Service Center using 

quadrupole and sector-field mass spectrometers; tritium concentrations were determined by the in-growth method (Clarke 

and others, 1976).

Water-Quality Results

Field Parameters

Total dissolved-gas (TDG) pressures at the three 2-in 

monitoring wells closest to the reservoir (WD 6, WD 9, 

WD 11) have shown the arrival and passage of peak values 

associated with reservoir recharge. TDG pressures at these 

wells increased from background values of 700 to 850 millimeters of mercury (mm Hg) to values of 1,800 to more than 

2,250 mm Hg, or about two to three times atmospherically 

equilibrated concentrations. During 2011–2012, TDG pressures remained elevated at WD 6, but have declined at WD 9 

and WD 11 (fig. 12). The multi-parameter sonde used for TDG 

pressure measurements relies on a pressure transducer that 

cannot measure pressures greater than 2,250 mm Hg and is not 

within its linear calibration range above about 1,500 mm Hg. 

Measurements less than 1,500 mm Hg have an error of less 

than 5 percent. Because of this non-linearity of in-situ measurements greater than 1,500 mm Hg, analyses of noble gases 

collected with advanced diffusion samplers (Gardner and Solomon, 2009) have been used in selected monitoring wells for 

more accurate TDG pressures (see footnote 2 of table 2). Measured TDG pressure values at WD 9 (located 55 ft from the 
22 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

reservoir) exceeded 2,250 mm Hg during February and April 

2005, indicating peak arrival about 3 years after inception of 

the reservoir. TDG pressures at WD 9 have since declined to 

pre-reservoir conditions—the 2012 measurement of 720 mm 

Hg was only slightly higher than the measured reservoir TDG 

and local barometric pressure of about 700 mm Hg. TDG pressures measured at WD 11 (located 160 ft from the reservoir) 

exceeded 2,250 mm Hg from 2005 through 2008, so an exact 

peak-arrival date could not be determined. Since 2010, TDG 

pressures declined slightly, fluctuating between about 1,700 

and 1,900 mm Hg. TDG pressure measurements at WD 6 

(located 1,000 ft from the reservoir) reached a peak of about 

1,800 mm Hg in April 2009 and declined to 1,200 mm Hg in 

2010, but increased back up to 1,700 mm Hg in 2012. These 

fluctuations can be caused by changing hydraulic conditions 

associated with nearby pumping at Well 8. Of the monitoring 

wells drilled in 2008 (WD 15 through WD 20), elevated TDG 

pressures have only been measured at WD 15 (1,300–1,500 

mm Hg), located closer to the reservoir and screened shallower in the aquifer (where water-level changes have been 

larger) than WD16 through WD 20. These elevated TDG pressures were likely caused by rising water levels and entrapment 

of air bubbles in the shallow part of the aquifer at this location 

rather than signifying the arrival of reservoir recharge.

Dissolved-oxygen (DO) concentrations at the three 2-in 

monitoring wells closest to the reservoir (WD 6, WD 9, 

WD 11) showed the arrival and passage of peak values 

associated with reservoir recharge (table 2). Background 

native groundwater DO values were generally between 6.1 

and 8.7 mg/L. Similar to TDG pressure, DO reached elevated 

values, from about 18 to 26 mg/L (about 2 to 3 times atmospheric equilibration), in monitoring wells near the reservoir. 

DO at both WD 9 and WD 11 reached maximum values in 

April 2005; DO peaked at WD 6 in April 2009. While DO 

values have since declined at all three sites, WD 9 showed a 

much sharper decline, and had values of less than 0.5 mg/L 

in 2011 and 2012. These values were much less than DO 

measurements of reservoir water (ranging from 7 to 12 mg/L) 

and likely indicate biological consumption of oxygen in the 

shallow organic-rich sediments beneath the reservoir.

Prior to inception of Sand Hollow Reservoir in March 

2002, specific-conductance values of native groundwater 

ranged from 130 μS/cm at WD 6 to 560 μS/cm at WD RJ 

(table 3, fig. 13). Elevated specific-conductance values at four 

monitoring wells (North Dam 3A, WD 6, WD 9, and WD 11) 

indicate the arrival of reservoir recharge. At these sites, 

specific-conductance values all peaked at values greater than 

those of the reservoir, then declined to values similar to the 

reservoir. This higher peak is attributed to the mobilization of 

natural salts that accumulated in the vadose zone prior to the 

inception of the reservoir and were incorporated into the leading edge of the reservoir recharge. These peak arrivals indicate 

Figure 12. Total dissolved-gas pressure in groundwater from selected monitoring wells in Sand Hollow, Utah, 2001–2012.

Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13

500

1,000

1,500

2,000

2,500

Total dissolved-gas pressure, in millimeters of mercury

WD 9 (55 feet from reservoir)

WD 11 (160 feet from reservoir)

WD 6 (1,000 feet from reservoir)
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 23

[Analyzing agency: Dissolved organic carbon at U.S. Geological Survey (USGS) National Water Quality Laboratory in Denver, Colorado; Tritium at University of Utah. Dissolved 

Gas Laboratory in Salt Lake City, Utah; CFC-11, CFC-12, CFC-113, SF6

 at USGS Chlorofluorocarbon (CFC) Laboratory in Reston, Virginia. Water temperature: °C, degrees Celsius; Specific conductance: μS/cm, microsiemens per centimeter at 25 degrees Celsius; Dissolved oxygen, dissolved organic carbon: mg/L, milligrams per liter; Total dissolved-gas 

pressure: mm Hg, millimeters of mercury; Tritium, Tritium precision: TU, tritium units; CFC-11, CFC-12, CFC-113: pmol/kg, picomoles per kilogram; SF6

: fmol/kg, femtomoles 

per kilogram; —, no data available; E, estimated; >, greater than; <, less than]

Site name Date

sampled

Water temperature

(°C)

Specific 

conductance

(μS/cm)

pH

(standard 

units)

Dissolved 

oxygen 

(mg/L)

Total dissolved-gas 

pressure 

(mm Hg)

Dissolved 

organic 

carbon 

(mg/L) 

Tritium 

(TU)

Tritium 

precision 

(TU)

CFC-11 

(pmole/

kg)

CFC-12 

(pmole/

kg)

CFC-113 

(pmole/

kg)

SF6

(fmol/

kg)

Neon 

excess 

(percent)

Native groundwater

North Dam 3A 10/8/2002 15.9 4,430 8.0 5.0 — — 2.71 0.14 — — — — —

12/18/2002 14.7 2,830 8.0 10.8 — — — — — — — — —

6/10/2003 21.5 1,330 7.8 — — — — — — — — — —

10/9/2003 — 1,230 7.8 — — — — — — — — — —

1/8/2004 16.0 1,220 8.2 — — — — — — — — — —

9/21/2004 18.4 980 7.7 11.0 — — — — — — — — —

10/29/2004 15.9 910 7.9 11.1 — — — — — — — — —

2/10/2005 15.3 960 7.7 13.5 — — — — — — — — —

4/5/2005 16.5 960 7.8 12.6 — — — — — — — — —

1/19/2006 — 840 8.0 — — — — — — — — — —

2/15/2007 15.2 840 7.9 7.5 — — 2.53 0.31 — — — — —

3/14/2008 14.8 820 7.7 4.0 — — 3.45 0.44 — — — — —

4/30/2009 — 850 7.2 — — — 3.03 0.11 — — — — —

3/16/2010 22.8 860 7.6 1.3 — 1.91 3.05 0.12 0.54 2.0 0.10 — —

3/10/2011 20.3 830 7.4 0.8 — 1.93 2.87 0.12 0.60 1.93 0.09 — —

2/6/2012 11.3 820 7.8 — — 2.00 3.46 0.41 — — — — —

WD 4 4/2/1999 21.0 360 8.2 — — — 0.22 0.10 — — — — —

12/18/2002 18.7 350 7.7 8.1 — — — — — — — — —

1/19/2006 — 350 8.0 — — — — — — — — — —

2/15/2007 19.0 340 7.9 8.7 — — — — — — — — —

3/13/2008 22.6 350 7.8 7.8 — — 0.25 0.10 — — — — —

10/23/2008 21.2 360 8.0 — — — 0.13 0.10 0.62 0.61 0.09 0.44 —

4/28/2009 — 350 7.8 — — — 0.15 0.07 0.54 0.52 0.07 0.45 —

11/24/2009 18.7 340 7.8 9.5 — 0.43 0.09 0.03 0.42 0.54 0.07 — —

3/15/2010 19.7 360 7.7 9.5 — E0.37 0.06 0.03 0.62 0.60 0.09 — —

3/10/2011 19.7 360 7.4 10.5 — 0.40 0.12 0.03 1.04 0.79 0.13 0.73 —

2/8/2012 19.5 550 7.3 8.9 — 2.25 0.00 0.15 1.26 1.07 0.30 1.19 —

WD 5 4/3/1999 15.0 540 8.3 — — — 0.19 0.03 — — — — —

12/17/2002 17.6 530 7.8 6.6 — — — — — — — — —

1/18/2006 — 530 7.9 — — — — — — — — — —

2/15/2007 18.3 530 7.8 8.3 — — — — — — — — —

3/13/2008 20.0 540 7.8 7.0 — — 0.05 0.10 — — — — —

10/23/2008 21.0 540 8.2 — — — 0.07 0.10 0.12 0.08 0.01 0.13 —

4/30/2009 — 520 7.5 — — — 0.02 0.06 — — — — —

11/24/2009 16.9 510 8.5 7.2 — 0.45 0.09 0.05 0.20 0.07 0.02 — —

3/15/2010 21.0 540 7.7 8.1 — E0.44 0.09 0.10 0.19 0.10 0.03 — —

3/10/2011 19.5 510 7.4 8.0 — 0.72 0.00 0.03 0.12 0.07 0.03 0.10 —

WD RJ 4/2/1999 18.0 560 8.2 — — — 0.02 0.05 — — — — —

12/17/2002 18.2 530 7.7 6.4 — — — — — — — — —

1/18/2006 — 550 7.7 — — — — — — — — — —

2/15/2007 19.0 530 7.7 8.1 — — — — — — — — —

3/12/2008 19.3 540 7.3 6.8 — — 0.03 0.10 — — — — —

4/28/2009 — 550 7.5 — — — 0.04 0.02 — — — — —

3/15/2010 19.6 560 7.6 8.0 — 0.84 0.06 0.03 0.25 0.13 0.07 — —

3/9/2011 19.6 540 7.3 7.5 — — 0.00 0.03 0.34 0.15 0.06 — —

Table 2. Field water-quality parameters, dissolved organic carbon, tritium, chlorofluorocarbons, sulfur hexafluoride, and neon excess 

in groundwater and surface water from Sand Hollow, Utah. 
24 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

[Analyzing agency: Dissolved organic carbon at U.S. Geological Survey (USGS) National Water Quality Laboratory in Denver, Colorado; Tritium at University of Utah. Dissolved 

Gas Laboratory in Salt Lake City, Utah; CFC-11, CFC-12, CFC-113, SF6

 at USGS Chlorofluorocarbon (CFC) Laboratory in Reston, Virginia. Water temperature: °C, degrees Celsius; Specific conductance: μS/cm, microsiemens per centimeter at 25 degrees Celsius; Dissolved oxygen, dissolved organic carbon: mg/L, milligrams per liter; Total dissolved-gas 

pressure: mm Hg, millimeters of mercury; Tritium, Tritium precision: TU, tritium units; CFC-11, CFC-12, CFC-113: pmol/kg, picomoles per kilogram; SF6

: fmol/kg, femtomoles 

per kilogram; —, no data available; E, estimated; >, greater than; <, less than]

Site name Date

sampled

Water temperature

(°C)

Specific 

conductance

(μS/cm)

pH

(standard 

units)

Dissolved 

oxygen 

(mg/L)

Total dissolved-gas 

pressure 

(mm Hg)

Dissolved 

organic 

carbon 

(mg/L) 

Tritium 

(TU)

Tritium 

precision 

(TU)

CFC-11 

(pmole/

kg)

CFC-12 

(pmole/

kg)

CFC-113 

(pmole/

kg)

SF6

(fmol/

kg)

Neon 

excess 

(percent)

WD 6 5/15/2001 — 130 7.6 — — — 4.77 0.24 — — — — —

8/28/2001 19.7 190 7.7 6.1 710 — 6.88 0.34 — — — — -0.2

9/9/2002 19.4 290 7.7 — 850 — — — — — — — 13.5

12/17/2002 19.0 400 7.6 9.3 920 — — — — — — — —

3/19/2003 19.2 424 7.5 10.9 1,150 — — — — — — — —

5/7/2003 19.3 450 7.5 — 1,220 — — — — — — — —

6/9/2003 19.6 390 7.8 14.0 1,260 — — — — — — — —

8/4/2003 19.3 350 7.5 11.9 1,280 — — — — — — — —

10/6/2003 19.6 400 7.6 12.0 1,160 — — — — — — — —

5/3/2004 19.4 700 7.4 15.2 1,357 — — — — — — — —

9/20/2004 19.6 820 7.7 15.0 1,266 — — — — — — — 75.8

10/28/2004 19.0 810 7.6 13.5 1,240 — — — — — — — —

2/9/2005 19.2 450 7.9 14.6 1,460 — — — — — — — 83.6

4/5/2005 19.2 460 7.6 15.5 1,490 — — — — — — — 88.0

1/19/2006 18.9 680 7.6 17.7 1

1,700 — — — — — — — —

2/15/2007 19.1 1,110 7.6 17.2 1

1,600 — — — — — — — —

3/13/2008 19.2 1,300 7.5 14.4 1

1,590 — 2.11 0.14 — — — — 125.3

4/29/2008 19.3 1,290 7.7 17.1 1

1,590 — — — — — — — 124.0

6/3/2008 19.4 1,330 7.6 16.5 1

1,590 — — — — — — — 124.3

10/24/2008 19.0 1,190 — 16.3 1

1,540 — 2.55 0.13 2.8 1.3 0.15 0.72 —

4/30/2009 19.2 1,050 7.7 22.0 1

1,810 — 2.66 0.14 3.2 1.5 0.16 0.73 161.7

11/23/2009 18.9 970 7.9 15.3 1

1,650 1.71 2.93 0.23 1.7 1.8 0.17 — 140.8

3/15/2010 19.2 920 7.5 14.4 1,200 1.68 3.15 0.15 1.7 1.6 0.19 — 88.5

3/9/2011 19.1 900 7.5 11.2 2

1,410 1.56 1.54 0.10 2.64 1.73 0.20 0.65 125

(replicate) 3/9/2011 19.1 870 7.9 — — 1.59 2.83 0.13 2.64 1.73 0.20 0.72 —

2/7/2012 19.1 810 7.3 15.6 1

1,700 1.70 2.88 0.31 2.23 1.67 0.18 0.87 199

WD 8 5/21/2001 — 300 7.7 — — — 4.13 0.38 — — — — —

9/12/2001 18.7 305 7.7 9.6 890 — 2.98 0.15 — — — — 58

9/9/2002 18.9 305 7.9 -- 840 — 3.89 0.19 — — — — 23

3/20/2003 18.7 335 7.6 7.8 910 — — — — — — — —

5/8/2003 18.6 340 7.5 4.6 880 — — — — — — — —

10/16/2003 — 360 7.4 — — — — — — — — — —

2/7/2012 18.5 250 7.1 20.8 22,300 0.75 3.36 0.33 1.93 1.71 0.16 — 322

WD 9 5/23/2001 19.5 300 7.7 8.0 800 — 0.00 0.01 — — — — —

9/14/2001 19.4 280 7.4 — 790 — 0.20 0.15 — — — — 49.5

9/11/2002 19.5 350 7.9 — 980 — — — — — — — 28.1

5/7/2003 19.7 320 7.8 — 1

>2,250 — — — — — — — —

6/9/2003 19.5 350 7.7 24.4 1

>2,250 — — — — — — — 158.8

8/5/2003 19.7 720 7.5 19.3 1

1,800 — — — — — — — —

10/7/2003 19.6 740 7.5 17.9 1

1,600 — — — — — — — —

1/6/2004 19.4 630 7.7 16.7 1

1,700 — — — — — — — —

5/3/2004 19.4 530 7.4 25.7 1

>2,250 — — — — — — — —

9/20/2004 18.5 750 7.8 22.6 1

>2,250 — — — — — — — —

10/28/2004 18.5 760 7.6 20.7 1

2,210 — — — — — — — —

2/9/2005 18.4 880 7.7 20.2 1

>2,250 — — — — — — — 246.2

4/5/2005 18.5 820 7.4 23.2 1

>2,250 — — — — — — — —

1/18/2006 18.0 1,230 7.9 15.0 1

1,900 — — — — — — — —

2/14/2007 17.3 790 7.4 4.6 1

1,600 — — — — — — — —

Table 2. Field water-quality parameters, dissolved organic carbon, tritium, chlorofluorocarbons, sulfur hexafluoride, and neon excess 

in groundwater and surface water from Sand Hollow, Utah.—Continued
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 25

[Analyzing agency: Dissolved organic carbon at U.S. Geological Survey (USGS) National Water Quality Laboratory in Denver, Colorado; Tritium at University of Utah. Dissolved 

Gas Laboratory in Salt Lake City, Utah; CFC-11, CFC-12, CFC-113, SF6

 at USGS Chlorofluorocarbon (CFC) Laboratory in Reston, Virginia. Water temperature: °C, degrees Celsius; Specific conductance: μS/cm, microsiemens per centimeter at 25 degrees Celsius; Dissolved oxygen, dissolved organic carbon: mg/L, milligrams per liter; Total dissolved-gas 

pressure: mm Hg, millimeters of mercury; Tritium, Tritium precision: TU, tritium units; CFC-11, CFC-12, CFC-113: pmol/kg, picomoles per kilogram; SF6

: fmol/kg, femtomoles 

per kilogram; —, no data available; E, estimated; >, greater than; <, less than]

Site name Date

sampled

Water temperature

(°C)

Specific 

conductance

(μS/cm)

pH

(standard 

units)

Dissolved 

oxygen 

(mg/L)

Total dissolved-gas 

pressure 

(mm Hg)

Dissolved 

organic 

carbon 

(mg/L) 

Tritium 

(TU)

Tritium 

precision 

(TU)

CFC-11 

(pmole/

kg)

CFC-12 

(pmole/

kg)

CFC-113 

(pmole/

kg)

SF6

(fmol/

kg)

Neon 

excess 

(percent)

WD 9 3/11/2008 17.0 820 7.3 1.5 1,080 — 2.61 0.22 — — — — 138.4

4/27/2009 16.6 830 7.4 1.8 840 — 2.99 0.12 1.2 2.2 0.19 2.15 91.4

3/15/2010 16.4 840 7.3 1.7 920 1.23 3.20 0.14 0.8 2.2 0.21 — 103.4

(replicate) 3/15/2010 16.4 840 7.3 1.7 920 1.17 2.90 0.12 0.8 2.2 0.18 — —

3/8/2011 16.1 900 7.3 0.5 900 1.36 3.34 0.16 1.33 2.10 0.17 — 77

2/7/2012 16.3 830 7.1 0.4 720 1.77 3.56 0.28 0.76 1.85 0.13 — 29

WD 11 6/14/2001 18.5 420 7.8 8.1 860 — — — — — — — —

9/14/2001 18.5 450 7.7 8.6 900 — 0.53 0.08 0.53 0.24 — — 70.9

9/12/2002 18.5 465 7.6 — 873 — — — — — — — 26.8

12/16/2002 18.2 455 7.6 8.1 890 — — — — — — — —

5/7/2003 18.4 620 7.7 — 1

1,770 — — — — — — — —

6/9/2003 18.4 650 7.9 22.5 1

1,600 — — — — — — — 87.9

8/5/2003 18.6 700 7.8 12.4 1

1,520 — — — — — — — —

10/7/2003 18.5 800 7.8 19.4 1

1,700 — — — — — — — —

5/3/2004 18.4 680 7.7 21.5 1

1,900 — — — — — — — —

9/20/2004 18.0 920 8.2 23.5 1

>2,250 — — — — — — — —

10/28/2004 18.0 990 7.9 22.8 1

2,080 — — — — — — — —

2/9/2005 18.0 960 8.1 22.1 1

2,200 — — — — — — — 162.5

4/5/2005 17.8 930 7.9 25.2 1

>2,250 — — — — — — — —

1/18/2006 17.6 980 7.9 23.0 1

>2,250 — — — — — — — —

2/14/2007 17.1 820 7.6 19.0 1

>2,250 — — — — — — — —

3/11/2008 17.0 840 7.6 14.9 1

>2,250 — 2.30 0.14 — — — — 319.1

4/30/2008 17.0 840 7.7 17.4 1

>2,250 — — — — — — — —

6/2/2008 17.1 850 7.7 18.9 1

>2,250 — — — — — — — 213.8

10/22/2008 16.7 840 8.0 15.9 1

>2,250 — 2.36 0.11 — — — — —

4/30/2009 15.9 840 7.7 19.4 1

2,160 — 3.06 0.14 2.0 3.0 0.34 3.5 291.3

11/23/2009 16.3 840 7.9 13.2 1

2,160 1.46 2.75 0.12 0.8 3.0 0.30 — 293.7

3/15/2010 16.2 840 7.7 10.3 2

1,700 1.35 2.81 0.13 0.8 2.9 0.30 — 76.1

3/8/2011 16.0 890 7.7 9.9 2

1,940 1.45 2.76 0.14 1.24 2.76 0.24 — 336

2/7/2012 15.4 800 7.4 9.5 2

1,850 1.57 2.52 0.21 0.76 2.60 0.18 — 324

WD 12 4/30/1999 — 330 — — — — 0.53 0.38 — — — — —

9/12/2002 — 335 7.9 — — — 0.02 0.06 — — — — —

12/16/2002 — 330 7.8 7.0 — — — — — — — — —

3/9/2011 19.9 1,670 7.1 13.4 — 2.17 0.96 0.06 2.34 2.20 0.25 0.68 —

2/8/2012 19.3 2,100 7.2 9.2 — 3.81 1.01 0.13 2.27 2.04 0.28 1.10 —

WD 15 10/25/2008 18.8 720 — 14.2 1,300 — — — — — — — —

4/28/2009 18.9 710 8.0 17.6 1,490 — 0.77 0.04 2.3 1.9 0.23 1.4 92.9

11/23/2009 18.8 730 8.3 14.5 1,410 2.47 0.68 0.05 1.0 1.9 0.22 — 88.5

3/16/2010 19.1 730 7.9 11.5 1,320 2.49 0.72 0.05 1.2 2.1 0.25 — 73.7

3/8/2011 19.1 820 8.0 12.5 1,400 2.50 0.55 0.06 2.56 2.27 0.28 1.56 90

2/7/2012 19.1 820 8.0 18.8 2

1,450 3.15 0.15 0.13 2.36 2.14 0.27 1.48 112

WD 16 10/25/2008 18.7 470 8.0 7.7 780 — — — — — — — —

4/27/2009 18.7 440 7.7 8.7 970 — 0.02 0.02 0.28 0.13 0.04 0.43 27.0

11/24/2009 18.7 450 7.7 7.1 760 <0.66 0.03 0.04 0.12 0.01 0.01 — 10.6

3/16/2010 18.7 440 7.6 5.1 770 <0.66 0.03 0.02 0.13 0.04 0.01 — 5.6

3/8/2011 18.5 480 7.7 4.1 770 <0.15 0.04 0.03 0.07 0.01 0.02 0.2 21

Table 2. Field water-quality parameters, dissolved organic carbon, tritium, chlorofluorocarbons, sulfur hexafluoride, and neon excess 

in groundwater and surface water from Sand Hollow, Utah.—Continued 
26 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

[Analyzing agency: Dissolved organic carbon at U.S. Geological Survey (USGS) National Water Quality Laboratory in Denver, Colorado; Tritium at University of Utah. Dissolved 

Gas Laboratory in Salt Lake City, Utah; CFC-11, CFC-12, CFC-113, SF6

 at USGS Chlorofluorocarbon (CFC) Laboratory in Reston, Virginia. Water temperature: °C, degrees Celsius; Specific conductance: μS/cm, microsiemens per centimeter at 25 degrees Celsius; Dissolved oxygen, dissolved organic carbon: mg/L, milligrams per liter; Total dissolved-gas 

pressure: mm Hg, millimeters of mercury; Tritium, Tritium precision: TU, tritium units; CFC-11, CFC-12, CFC-113: pmol/kg, picomoles per kilogram; SF6

: fmol/kg, femtomoles 

per kilogram; —, no data available; E, estimated; >, greater than; <, less than]

Site name Date

sampled

Water temperature

(°C)

Specific 

conductance

(μS/cm)

pH

(standard 

units)

Dissolved 

oxygen 

(mg/L)

Total dissolved-gas 

pressure 

(mm Hg)

Dissolved 

organic 

carbon 

(mg/L) 

Tritium 

(TU)

Tritium 

precision 

(TU)

CFC-11 

(pmole/

kg)

CFC-12 

(pmole/

kg)

CFC-113 

(pmole/

kg)

SF6

(fmol/

kg)

Neon 

excess 

(percent)

WD 18 4/28/2009 19.7 500 7.4 7.5 870 — 0.04 0.02 0.21 0.16 0.03 1.46 26.6

3/16/2010 19.3 470 7.4 4.9 740 E0.48 0.14 0.02 0.16 0.07 0.01 — 36.9

3/9/2011 19.2 480 7.3 7.8 750 0.70 0.03 0.03 0.08 0.02 0.02 — 19

WD 19 10/23/2008 18.9 1,070 — 9.2 910 — — — — — — — —

3/10/2011 19.1 2,030 7.5 9.8 920 4.61 2.70 0.10 3.25 2.03 0.31 — 39

2/7/2012 18.6 1,900 7.5 6.8 820 4.87 2.99 0.30 3.17 1.82 0.30 1.55 24

(replicate) 2/7/2012 — — — — — 5.65 2.84 0.29 3.21 1.85 0.29 1.54 30

WD 20 10/23/2008 19.1 340 — 7.9 740 — — — — — — — —

4/29/2009 19.7 330 7.5 6.7 760 — 0.06 0.01 0.10 0.02 0.01 0.01 -2.7

(replicate) 4/29/2009 19.7 330 7.5 6.7 760 — 0.06 0.01 0.12 0.02 0.01 0.06 —

3/17/2010 19.4 340 7.4 7.2 720 <0.66 0.03 0.04 0.11 0.04 0.01 — -2.4

3/10/2011 18.9 330 7.3 7.2 710 0.23 0.01 0.04 0.15 0.07 0.02 — 7

Sand Hollow Reservoir water

Haul road 9/10/2002 24.2 1,000 8.8 — — — 2.47 0.12 — — — — —

12/18/2002 7.9 860 8.4 10.2 670 — — — — — — — —

3/20/2003 11.1 830 8.2 8.4 680 — — — — — — — —

6/10/2003 23.6 850 8.2 8.8 680 — — — — — — — —

8/6/2003 26.0 930 7.6 — 690 — — — — — — — —

10/7/2003 21.9 910 8.4 — — — — — — — — — —

1/8/2004 7.1 870 8.4 11.7 720 — — — — — — — —

Boat ramp 5/5/2004 17.3 710 8.2 8.5 680 — — — — — — — —

9/22/2004 18.9 770 8.5 7.2 — — — — — — — — —

2/10/2005 8.3 860 8.4 11.3 — — — — — — — — —

1/18/2006 6.9 820 8.5 11.9 — — — — — — — — —

2/14/2007 5.1 760 8.1 11.6 — — — — — — — — —

3/13/2008 9.6 820 8.4 10.1 — — — — — — — — —

10/21/2008 18.3 820 8.7 8.9 700 — 3.59 0.18 2.3 1.5 0.22 1.49 —

4/29/2009 16.1 790 8.4 7.0 — — 4.61 0.20 3.1 2.0 0.32 1.94 —

8/10/2009 25.0 800 8.6 — — 2.85 — — — — — — —

11/24/2009 11.3 800 8.5 9.5 — 2.95 3.29 0.14 2.1 2.6 0.30 — —

3/16/2010 9.8 820 8.0 9.4 — 2.88 3.64 0.15 3.0 3.3 0.47 — —

3/9/2011 8.6 830 8.1 10.7 710 2.73 3.79 0.14 5.31 3.14 0.52 2.86 —

2/8/2012 6.1 820 8.2 9.2 700 2.70 3.23 0.30 5.37 2.98 0.52 2.91 —

SH 1-18 10/23/2008 18.0 820 8.7 9.1 690 — 4.60 0.34 2.5 1.6 0.23 1.16 —

4/29/2009 14.3 800 8.6 9.6 — — 2.55 0.22 3.4 2.1 0.26 1.98 —

8/10/2009 25.3 800 8.7 9.1 — 5.67 — — — — — — —

3/16/2010 9.6 820 8.0 9.6 — 2.87 3.68 0.13 3.0 3.2 0.44 — —

3/9/2011 8.1 820 8.2 10.7 700 2.66 3.52 0.13 5.47 3.19 0.50 — —

2/8/2012 5.9 800 8.0 10.7 670 2.76 3.49 0.53 5.45 3.05 0.52 — —

Table 2. Field water-quality parameters, dissolved organic carbon, tritium, chlorofluorocarbons, sulfur hexafluoride, and neon excess 

in groundwater and surface water from Sand Hollow, Utah.—Continued 

1

 Total dissolved-gas pressures greater than 1,500 mm Hg exceed the linear calibration of the multi-parameter sonde.

2

 Total dissolved-gas pressure determined with advanced diffusion sampler. 
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 27

Figure 13. Specific conductance of reservoir water and groundwater from selected monitoring wells in Sand Hollow, Utah, 1999–2012.

Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

Specific conductance, in microsiemens per centimeter

0

0

200

400

600

800

1,000

1,200

1,400

1,600

Specific conductance, in microsiemens per centimeter

A

Reservoir water

WD 9 (55 feet from reservoir)

WD 11 (160 feet from reservoir)

WD 6 (1,000 feet from reservoir)

WD 4 (2,600 feet from reservoir)

WD 5 (2,800 feet from reservoir)

WD RJ (5,200 feet from reservoir)

B

North Dam 3A (100 feet from reservoir)
28 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

[Specific conductance: mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; Temperature: °C, degrees Celsius; Cl:Br, chloride-to-bromide ratio; 

μg/L, micrograms per liter; <, less than; E, estimated; —, no data available; ft, feet; repl., replicate]

Site Name Date

Dissolved 

oxygen

(mg/L)

Specific

conductance

(μS/cm)

pH

(Standard 

units)

Temperature

(oC)

Total

dissolved 

solids (mg/L)

Calcium

(mg/L 

as Ca)

Magnesium 

(mg/L 

as Mg) 

Sodium

(mg/L 

as Na)

Potassium 

(mg/L 

as K)

Alkalinity as 

CaCO3

(mg/L)

Sulfate

(mg/L 

as SO4

) 

Native groundwater

WD 4 12/18/02 8.1 350 7.7 18.7 205 29 17 16 2.1 125 18.1

WD 4 11/24/09 9.5 338 7.8 18.7 197 28.7 16.6 15.1 2.1 121 20.6

WD 4 3/15/10 9.5 362 7.7 19.7 217 27.3 16.2 13.3 2.1 129 19.7

WD 4 3/10/11 10.5 361 7.4 19.7 208 31.2 18.3 15.2 2.2 125 21.8

1

WD 4 2/8/12 8.9 549 7.3 19.5 325 44.8 26.6 29.5 2.6 134 68.4

WD 5 12/17/02 6.6 530 7.8 17.6 311 45 22 29 1.8 138 46.8

WD 5 11/24/09 7.2 512 8.5 16.9 298 43.1 21.4 27.2 1.8 136 46.4

WD 5 3/15/10 8.1 543 7.7 21.0 313 43.3 22.2 24.9 2.0 136 45.8

WD 5 3/10/11 8.0 510 7.4 19.5 298 45.7 22.1 26.9 2.0 141 43.8

WD RJ 12/17/02 6.4 530 7.7 18.2 309 47 22 27 2.3 137 46

WD RJ 3/15/10 8.0 560 7.6 19.6 338 46.6 22.6 25.1 2.3 139 47.9

WD RJ 3/9/11 7.5 539 7.3 19.6 324 48.9 23.1 28 2.4 143 47.3

WD 6 9/9/02 — 290 7.7 19.4 167 37 3.4 12 1.6 93 24

WD 7 9/10/01 9.8 380 7.8 18.8 — 37 12 25 1.9 137 28

WD 8 9/9/02 — 305 7.9 18.9 173 37 10 8.9 2.3 116 15

WD 8 2/7/12 20.8 251 7.1 18.5 179 47.1 4.0 6.6 1.6 95 25.9

WD 9 9/11/02 — 335 7.9 19.5 189 36 7 22 1.6 120 18

WD 12 9/12/02 — 335 7.9 — 202 37 13 9.0 1.6 115 19

1

WD 12 3/9/11 13.4 1,670 7.1 19.9 1,150 132 57.3 150 3.0 116 440

1

WD 12 2/8/12 9.2 2,100 7.2 19.3 1,510 173 75.0 188 3.5 124 665

WD 13 8/30/01 — 275 8.1 19.9 — 24 16 8.4 1.5 109 12

WD 14 12/18/02 8.3 385 7.7 19.3 220 36 20 10 2.4 122 29

1

WD 15 4/28/09 17.6 707 8.0 18.9 414 41.0 35.9 48.0 2.1 191 71.4

1

WD 15 11/23/09 14.5 729 8.3 18.8 436 43.3 33.6 57.5 2.1 184 80.4

1

WD 15 3/16/10 11.5 734 7.9 19.1 458 42.0 33.8 51.6 2.1 188 84.7

1

WD 15 3/8/11 12.5 816 8.0 19.1 469 45.9 39.3 60.6 2.1 182 91.3

1

WD 15 2/7/12 18.8 821 8.0 19.1 473 42.2 38.2 67.8 2.1 169 102.0

WD 16 4/27/09 8.7 444 7.7 18.7 255 44.1 23.0 13.2 1.9 136 33.6

WD 16 11/24/09 7.1 449 7.7 18.7 260 42.3 21.9 13.7 1.7 129 33.8

WD 16 3/16/10 5.1 441 7.6 18.7 262 41.7 22.4 12.3 1.8 135 33.0

WD 16 3/8/11 4.1 478 7.7 18.5 241 45.4 23.0 13.6 1.9 135 32.0

WD 18 4/28/09 7.5 500 7.4 19.7 280 45.2 19.5 24.5 1.9 143 40.4

WD 18 3/16/10 4.9 467 7.4 19.3 296 43.7 19.2 21.3 1.8 155 37.9

WD 18 3/9/11 7.8 476 7.3 19.2 293 46.0 19.2 23.8 1.7 138 38.0

1

WD 19 3/10/11 9.8 2,030 7.5 19.1 1,120 120 41.6 216 2.8 210 282

1,2WD 19 2/7/12 6.8 1,900 7.5 18.6 1,150 123 43.1 181 2.9 246 349

WD 20 4/29/09 6.7 331 7.5 19.7 188 30.2 17.4 11.7 2.1 120 20.8

WD 20 3/17/10 7.2 344 7.4 19.4 214 28.0 16.1 10.5 1.9 120 19.6

WD 20 3/10/11 7.2 332 7.3 18.9 181 31.5 17.7 12.1 2.0 116 18.9

Well 1 at 890 ft 5/6/03 — 350 7.8 — 216 31 21 7.4 2.9 130 19

Well 2 at 400 ft 10/10/02 — 365 8.0 — 208 30 21 9.0 2.1 129 20

Well 2 at 615 ft 10/10/02 — 365 8.1 — 190 30 21 6.5 2.5 131 16

Well 2 at 750 ft 10/10/02 — 370 8.1 — 196 30 22 6.8 2.7 134 18

Well 4 8/29/01 — 480 8.0 20.1 — 36 19 38 2.0 128 58

Well 4 9/11/02 — 495 8.1 19.1 297 36 19 35 2.0 124 56

Well 8 at 245 ft 10/8/02 — 550 7.5 19.0 323 49 20 35 2.1 141 70

Well 9 8/30/01 — 285 7.9 20.7 179 27 16 7.0 1.9 115 13

Table 3. Major and minor chemical constituents in groundwater and surface water from selected sites in Sand Hollow, Utah. 
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 29

Table 3. Major and minor chemical constituents in groundwater and surface water from selected sites in Sand Hollow, Utah.—

Continued 

[Specific conductance: μS/cm, microsiemens per centimeter at 25 degrees Celcius; mg/L, milligrams per liter; μg/L, micrograms per liter; Temperature: °C, degrees Celcius; —, no 

data available; ft, feet; Cl:Br, chloride-to-bromide ratio; repl., replicate; E, estimate; <, less than]

Site Name

Chloride 

(mg/L 

as Cl) 

Fluoride 

(mg/L 

as F) 

Bromide 

(mg/L 

as Br) 

Cl:Br

Silica

(mg/L

as SiO2

)

Iron

(μg/L as Fe) 

Manganese 

(μg/L 

as Mn) 

Arsenic 

(μg/L as As) 

Nitrogen

(nitrite + nitrate) 

(mg/L as N) 

Nitrogen, 

nitrite

(mg/L as N) 

Nitrogen, 

ammonia 

(mg/L as N) 

Phosphorous 

(orthophosphate)

(mg/L as P)

Native groundwater

WD 4 18.8 0.23 0.08 235 14 <10 <2 13.2 2.35 <0.008 <0.04 0.02

WD 4 17.2 — 0.10 179 14.3 E3.8 <0.2 14.7 2.29 <0.002 <0.02 0.03

WD 4 17.9 0.25 0.10 184 15.7 <6 <0.2 14.4 2.29 <0.002 <0.02 0.03

WD 4 20.2 0.25 0.14 150 15.3 <3.2 0.19 13.7 2.25 <0.001 <0.01 0.03

1

WD 4 54.5 0.20 0.42 128 15.7 4.5 0.37 11.9 2.21 <0.001 <0.01 0.02

WD 5 44.8 0.29 0.16 280 13 <10 E1 9.1 4.18 <0.008 <0.04 E0.01

WD 5 37.9 0.27 0.23 168 13.4 <6 <0.2 9.6 4.61 <0.002 <0.02 0.02

WD 5 39.2 0.28 0.24 164 15 <6 <0.2 9.0 4.60 <0.002 <0.02 0.01

WD 5 38.2 0.31 0.21 179 14.3 <3.2 0.19 9.3 4.60 <0.001 <0.01 0.01

WD RJ 47.8 0.51 0.20 239 14 <10 <2 7.9 3.28 <0.008 <0.04 0.01

WD RJ 47.2 0.51 0.27 176 15.3 <6 <0.2 8.3 3.28 <0.002 E0.012 0.02

WD RJ 47.4 0.54 0.24 196 14.5 <3.2 0.18 8.54 3.34 <0.001 <0.01 0.01

WD 6 15.0 E0.08 0.16 94 13 <10 E2 2.0 E1.6 <0.008 <0.04 0.02

WD 7 18.0 0.3 0.13 139 14 <10 <3 6.0 3.80 <0.008 <0.04 0.02

WD 8 10.1 0.1 0.07 144 14 <10 <2 6.0 3.90 <0.008 <0.04 0.02

WD 8 13.6 0.1 0.08 173 13.8 7.4 0.99 11.5 3.33 <0.001 <0.01 0.02

WD 9 21.4 0.5 0.06 357 15 9 15 12.0 0.48 <0.008 <0.04 0.01

WD 12 20.0 0.2 0.08 250 15 <10 1 10.0 2.10 <0.008 <0.04 0.02

1WD 12 196 0.10 1.16 169 17.0 <3.2 0.35 8.24 1.89 <0.001 <0.01 0.0089

1WD 12 264 0.12 1.54 171 17.1 14.5 <0.32 7.33 1.92 <0.001 0.01 0.0077

WD 13 12.1 E0.1 0.05 258 12 <10 2 6.3 2.00 <0.006 <0.04 0.02

WD 14 28.3 0.25 0.11 257 13 <10 <2 15.6 2.18 <0.008 <0.04 0.02

1

WD 15 57.0 0.41 0.33 174 15 <4 0.7 28.3 3.32 E0.001 <0.02 0.02

1

WD 15 63.5 0.41 0.36 178 14 <6 0.1 28.9 3.46 <0.002 <0.02 0.02

1

WD 15 68.8 0.42 0.36 189 15 <6 <0.2 27.5 3.54 <0.002 <0.02 0.02

1

WD 15 77.0 0.40 0.43 180 14.5 <3.2 <0.16 27.6 3.78 <0.001 <0.01 0.02

1

WD 15 88.2 0.37 0.50 176 14.1 <3.2 2.08 26.7 4.32 <0.001 0.02 0.02

WD 16 29.1 0.25 0.17 170 14 <4 <0.2 6.2 4.48 E0.001 <0.02 0.01

WD 16 28.7 0.21 0.18 158 13 <6 <0.2 6.1 4.50 <0.002 <0.02 0.01

WD 16 29.9 0.22 0.18 169 13.8 <6 0.79 5.9 4.44 <0.002 <0.02 0.01

WD 16 29.4 0.28 0.18 166 13.6 <3.2 <0.16 6.0 4.43 <0.001 <0.01 0.01

WD 18 36.1 0.37 0.21 171 16 16 1 10.6 3.15 0.002 <0.02 0.01

WD 18 34.1 0.33 0.22 154 15.8 <6 <0.2 10.0 3.14 <0.002 <0.02 0.02

WD 18 35.1 0.36 0.22 163 15.3 <3.2 <0.16 10.2 3.12 <0.001 <0.01 0.01

1

WD 19 252 0.37 1.17 215 17.1 <3.2 <0.16 9.9 8.75 <0.001 <0.01 0.02

1,2WD 19 192 0.34 0.89 216 17.5 5.2 0.16 9.3 9.38 <0.001 <0.01 0.03

WD 20 16.4 0.28 0.09 178 14 53 1 7.7 2.41 E0.001 <0.02 0.02

WD 20 17.2 0.24 0.09 185 14.2 <6 0.53 8.0 2.40 <0.002 <0.02 0.02

WD 20 16.9 0.22 0.09 197 14.3 <3.2 <0.16 7.6 2.37 <0.001 <0.01 0.02

Well 1 at 890 ft 16.9 1.08 — — 11 11 19 9.1 3.37 0.008 0.03 0.01

Well 2 at 400 ft 17.8 0.2 — — 11 10 12 2.6 3.41 0.008 0.10 0.02

Well 2 at 615 ft 13.2 0.23 — — 11 27 6 4.6 3.73 0.004 <0.04 0.02

Well 2 at 750 ft 14.3 0.23 0.10 143 12 19 3 5.9 3.84 <0.008 0.03 0.02

Well 4 44.4 E0.1 0.20 218 13 <10 <3 7.1 1.50 <0.006 <0.04 0.02

Well 4 42.0 0.2 0.17 247 13 <10 <2 8.0 2.10 <0.008 <0.04 0.02

Well 8 at 245 ft 38.7 0.29 0.15 258 14 <10 5 16.6 1.72 0.03 0.18 0.01

Well 9 13.0 0.2 0.07 186 13 <10 <3 12.4 2.40 <0.006 <0.04 0.02
30 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

[Specific conductance: mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; Temperature: °C, degrees Celsius; Cl:Br, chloride-to-bromide ratio; 

μg/L, micrograms per liter; <, less than; E, estimated; —, no data available; ft, feet; repl., replicate]

Site Name Date

Dissolved 

oxygen

(mg/L)

Specific

conductance

(μS/cm)

pH

(Standard 

units)

Temperature

(oC)

Total

dissolved 

solids (mg/L)

Calcium

(mg/L 

as Ca)

Magnesium 

(mg/L 

as Mg) 

Sodium

(mg/L 

as Na)

Potassium 

(mg/L 

as K)

Alkalinity as 

CaCO3

(mg/L)

Sulfate

(mg/L 

as SO4

) 

Groundwater affected by reservoir recharge

North Dam 3A 10/8/02 5.0 4,430 8.0 15.9 3,020 150 160 590 2.0 148 1,020

North Dam 3A 12/18/02 10.8 2,830 8.0 14.7 1,890 110 110 340 3.6 155 584

North Dam 3A 3/16/10 1.3 864 7.6 22.8 554 65.8 38.0 51.2 3.0 177 187

North Dam 3A 3/10/11 0.82 834 7.4 20.3 538 68.0 36.7 59.0 3.40 170 181

North Dam 3A 2/6/12 — 820 7.8 11.3 523 64.8 35.9 58.0 3.36 180 174

WD 6 4/30/09 22.0 1,045 7.7 19.2 660 98.5 9.0 113 1.6 169 220

WD 6 11/23/09 15.3 968 7.9 18.9 629 93.6 8.7 101 1.5 161 210

WD 6 3/15/10 14.4 923 7.5 19.2 618 94.1 8.6 86.3 1.5 166 211

WD 6 3/9/11 11.2 896 7.5 19.1 577 106 11.5 73.4 1.49 157 208

WD 6 - repl. 3/9/11 — 867 7.9 19.1 590 106 11.5 72.5 1.47 153 208

WD 6 2/7/12 15.6 807 7.3 19.1 542 103 11.5 58.7 1.63 152 200

WD 9 4/27/09 1.8 832 7.4 16.6 549 78.2 30.9 53.7 3.4 157 200

WD 9 3/15/10 1.7 842 7.3 16.4 543 71.8 31.0 52.2 3.3 157 200

WD 9 - repl. 3/15/10 1.7 842 7.3 16.4 545 67.4 28.8 51.0 3.2 155 198

WD 9 3/8/11 0.5 902 7.3 16.1 531 73.8 33.9 60.9 3.58 161 188

WD 9 2/7/12 0.4 826 7.1 16.3 533 66.4 34.2 56.6 3.45 162 185

WD 11 5/3/04 21.5 677 7.7 18.4 440 69.0 31.6 68.1 1.7 187 90

WD 11 4/30/09 19.4 843 7.7 15.9 557 79.2 38.6 49.6 2.4 186 187

WD 11 11/23/09 13.2 835 7.9 16.3 553 74.0 35.7 49.4 2.2 171 191

WD 11 3/15/10 10.3 837 7.7 16.2 552 67.2 34.3 45.6 2.2 178 190

WD 11 3/8/11 9.9 891 7.7 16.0 533 75.2 36.6 51.2 2.15 186 179

WD 11 2/7/12 9.5 798 7.4 15.4 529 74.6 34.5 51.6 2.05 193 169

Well 9 9/11/02 — 740 8.2 19.5 458 53 28 52 2.3 124 126

Well 9 3/10/11 3.8 777 7.6 15.3 535 60.2 36.1 54.2 3.32 151 175

Sand Hollow Reservoir water

Haul road 9/10/02 — 1,000 8.8 24.2 669 63 43 71 5.3 92 300

Boat ramp 5/5/04 8.5 710 8.2 17.3 442 63 26 45 3.3 161 122

Boat ramp 4/29/09 7.0 790 8.4 16.1 503 54.3 37.4 53.7 4.0 147 189

Boat ramp 11/24/09 9.5 797 8.5 11.3 502 40.9 39.8 62.9 4.3 108 212

Boat ramp 3/16/10 9.4 817 8.0 9.8 534 43.5 38.4 57.6 4.6 120 211

Boat ramp 3/9/11 10.7 827 8.1 8.6 534 60.2 39.2 62.2 4.5 142 212

Boat ramp 2/6/12 9.2 821 8.2 6.1 534 53.6 39.8 61.3 4.3 138 213

SH 1-18 4/29/09 9.6 800 8.6 14.3 502 56.1 37.2 53.6 4.2 146 190

SH 1-18 8/10/09 9.1 800 8.7 25.3 501 42.6 38.3 60.5 4.3 110 —

SH 1-18 3/16/10 9.6 819 8.0 9.6 525 45.9 40.8 58.6 4.7 124 211

SH 1-18 3/9/11 10.7 820 8.2 8.1 528 60.1 39.6 61.2 4.43 140 210

SH 1-18 2/8/12 10.7 801 8.0 5.9 526 54.2 39.5 59.6 4.28 140 214

1

 High or increasing total dissolved solids but low Cl:Br ratio indicate groundwater is affected by flushing of naturally occuring solute accumulations in vadose zone prior to reservoir construction. 

2

 Replicate sample not reported because submersible pump was re-installed for replicate collection and total dissolved solids differed by more than 10 percent. 

Table 3. Major and minor chemical constituents in groundwater and surface water from selected sites in Sand Hollow, Utah.—

Continued 
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 31

[Specific conductance: μS/cm, microsiemens per centimeter at 25 degrees Celcius; mg/L, milligrams per liter; μg/L, micrograms per liter; Temperature: °C, degrees Celcius; —, no 

data available; ft, feet; Cl:Br, chloride-to-bromide ratio; repl., replicate; E, estimate; <, less than]

Site Name

Chloride 

(mg/L 

as Cl) 

Fluoride 

(mg/L 

as F) 

Bromide 

(mg/L 

as Br) 

Cl:Br

Silica

(mg/L

as SiO2

)

Iron

(μg/L as Fe) 

Manganese 

(μg/L 

as Mn) 

Arsenic 

(μg/L as As) 

Nitrogen

(nitrite + nitrate) 

(mg/L as N) 

Nitrogen, 

nitrite

(mg/L as N) 

Nitrogen, 

ammonia 

(mg/L as N) 

Phosphorous 

(orthophosphate)

(mg/L as P)

Groundwater affected by reservoir recharge

North Dam 3A 744 0.90 41.2 18 13 <30 <5 90.1 17.8 <0.008 0.03 0.03

North Dam 3A 476 0.79 2.44 195 14 <30 <5 63.9 14.3 <0.008 <0.04 0.03

North Dam 3A 55.2 0.43 0.06 882 16 <6 3.19 35.2 <0.04 E0.001 E0.01 0.03

North Dam 3A 58.3 0.45 0.06 936 15.5 <3.2 3.48 35.2 0.03 <0.001 0.07 0.03

North Dam 3A 55.4 0.39 0.07 778 16.3 12.6 17.3 34 0.07 <0.001 0.21 0.04

WD 6 92.5 0.32 0.31 295 13 <4 0.23 3.3 1.2 <0.002 <0.02 0.01

WD 6 80.3 0.30 0.28 286 12 <6 <0.2 3.3 1.06 <0.002 <0.02 0.01

WD 6 77.9 0.32 0.24 322 13 20.8 0.32 3.0 0.97 <0.002 <0.02 0.01

WD 6 63.5 0.30 0.14 457 13.5 6.3 0.4 2.82 0.71 <0.001 <0.01 0.01

WD 6 - repl. 63.3 0.32 0.14 455 13.6 6.1 0.31 2.78 0.70 0.001 <0.01 0.01

WD 6 54.8 0.22 0.08 684 13.9 17.6 0.75 2.33 0.47 <0.001 0.02 0.01

WD 9 53.4 0.27 0.06 900 12 5 4 5.8 0.09 <0.002 <0.02 0.01

WD 9 56.6 0.24 0.05 1,040 12 13.6 0.68 6.1 0.09 <0.002 <0.02 0.01

WD 9 - repl. 56.3 0.27 0.05 1,083 12 13.5 0.57 6.1 0.09 <0.002 <0.02 0.01

WD 9 58.7 0.28 0.04 1,310 11.6 6.7 0.47 6.14 0.05 0.002 <0.01 0.01

WD 9 55.6 0.27 0.06 927 11.3 26.3 2.53 5.87 0.06 <0.001 0.01 0.01

WD 11 49.8 0.40 0.25 199 15 <6 <0.8 15.3 3.06 <0.008 <0.04 0.02

WD 11 49.6 0.35 0.07 687 14 <4 <0.2 9.6 0.99 <0.002 <0.02 0.01

WD 11 49.8 0.31 0.07 711 13 <6 <0.2 10.3 0.67 <0.002 <0.02 0.01

WD 11 51.8 0.32 0.07 781 14 18.6 0.26 10.0 0.70 <0.002 <0.02 0.02

WD 11 53.6 0.31 0.07 811 14.7 4.4 0.26 9.57 0.48 0.001 <0.01 0.01

WD 11 53.3 0.26 0.07 733 15.3 11.4 0.34 9.16 0.48 <0.001 <0.01 0.01

Well 9 72.2 0.20 0.28 258 14 250 6 17.0 2.20 <0.008 <0.04 0.02

Well 9 53.8 0.33 0.08 706 11.7 13.5 2.61 13.8 0.56 <0.001 <0.01 0.01

Sand Hollow Reservoir water

Haul road 76.0 0.30 0.02 3,800 4.9 <10 <2 2.0 0.04 <0.008 <0.04 0.02

Boat ramp 50.0 0.21 0.01 5,000 7.3 <6 1.3 1.1 — — — —

Boat ramp 54.9 0.31 0.04 1,227 2.9 <4 0.3 1.4 0.04 0.002 <0.02 0.008

Boat ramp 60.4 0.28 0.05 1,313 1.5 <6 0.2 1.6 <0.04 <0.002 <0.02 0.008

Boat ramp 61.7 0.30 0.04 1,374 1.4 6.3 1.7 1.3 E0.033 <0.002 0.02 <0.008

Boat ramp 57.0 0.30 0.04 1,390 4.0 <3.2 2.0 1.13 0.10 0.004 0.03 <0.004

Boat ramp 58.3 0.27 0.05 1,108 4.2 <3.2 0.86 1.01 0.12 0.001 0.01 <0.004

SH 1-18 54.6 0.27 0.04 1,318 3.0 <4 0.4 1.4 0.04 0.003 0.13 0.008

SH 1-18 — 0.24 — — 1.3 3 0.3 1.6 <0.04 <0.002 <0.02 0.008

SH 1-18 61.6 0.30 0.04 1,417 1.2 6.2 1.8 1.4 E0.025 <0.002 0.02 <0.008

SH 1-18 57.2 0.30 0.04 1,546 3.9 <3.2 2.10 1.12 0.10 0.005 0.02 <0.004

SH 1-18 56.5 0.27 0.05 1,060 4.1 <3.2 1.31 1.04 0.09 0.001 0.02 <0.004

1

 High or increasing total dissolved solids but low Cl:Br ratioindicate groundwater is affected by flushing of naturally occuring solute accumulations in vadose zone prior to reservoir 

construction. 

2

 Replicate sample not reported because submersible pump was re-installed for replicate collection and total dissolved solids differed by more than 10 percent. 

Table 3. Major and minor chemical constituents in groundwater and surface water from selected sites in Sand Hollow, Utah.—

Continued 
32 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Figure 14. Major-ion chemistry from selected surface water and groundwater sites in Sand Hollow, Utah.

EXPLANATION

Sulfate (SO4) + Chloride (Cl)

Calcium (Ca) + Magnesium (Mg)

Milliequivalents per liter, in percent Milliequivalents per liter, in percent

CATIONS ANIONS

Calcium (Ca) Chloride (Cl)

Na+K HCO3 Ca + CO3 Cl

Mg SO4

80

60

40

20

80

60

40

20

Carbonate (CO3) + Bicarbonate (HCO3)

20 40 60 80

20

40

60

80

Sulfate (SO4)

Reservoir water

Reservoir at Boat ramp collected in 2012

Reservoir at SH1-18 collected in 2012

Native groundwater

Groundwater affected by reservoir recharge

North Dam 3A sample collected in 2012

WD 4 sample collected in 2012

WD 5 sample collected in 2011

WD 6 sample collected in 2012

WD RJ sample collected in 2011

80 60 40 20

20

40

60

80

Magnesium (Mg)

80

60

40

20

80

60

Sodium (Na) + Potassium (K)

40

20

40

60

80

20

40

60

80

20

WD 8 sample collected in 2012

WD 9 sample collected in 2012

WD 11 sample collected in 2012

WD 12 sample collected in 2012

WD 15 sample collected in 2012

WD 16 sample collected in 2011

WD 18 sample collected in 2011

WD 19 sample collected in 2012

WD 20 sample collected in 2011

Production well 9 sample collected in 2011
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 33

travel times of less than 1 year for reservoir recharge to reach 

North Dam 3A and about 2.5, 4, and 6 years to reach WD 11, 

WD 9, and WD 6, respectively. By 2012, specific conductance 

at all four of these monitoring wells declined to values measured in the reservoir (about 800 μS/cm). The specific conductance at WD 4 began rising slightly in 2012, possibly indicating the arrival of reservoir water in the near future. While 

specific conductance was also elevated at monitoring wells 

WD 12, WD 15, and WD 19, low chloride-to-bromide ratios 

(Cl:Br, discussed below) indicate that these increases could 

be caused by mobilization of natural vadose-zone salts near 

the well screen with rising water levels (discussed in Heilweil 

and Marston, 2011) rather than marking the arrival of reservoir 

water. The other monitoring wells (WD 5, WD RJ, WD 8, WD 

16, WD 18, WD 20) showed no substantial increase in specific 

conductance through 2012.

Laboratory Water Chemistry 

Dissolved Inorganic Ions

Major-ion chemical signatures can be used to identify 

the arrival of reservoir recharge from Sand Hollow Reservoir at downgradient monitoring wells. Figure 14 shows that 

groundwater at some sites in Sand Hollow has been affected 

by recharge from the reservoir, while other sites have not. 

The trilinear (Piper) diagram shows that native (background) 

groundwater in Sand Hollow is lower in chloride, magnesium, and sodium (plus potassium) and higher in calcium and 

bicarbonate than the infiltrating reservoir water. Groundwater 

influenced by reservoir recharge typically plots between native 

groundwater and reservoir water, indicating that groundwater 

at these sites has shifted from calcium bicarbonate- to sodium 

chloride-type water. Exceptions to this are seen in samples 

collected from WD 12 and WD 19, where a geochemical signature different than reservoir water could reflect the mobilization of vadose-zone salts.

Chloride-to-bromide ratios (Cl:Br) of water from Sand 

Hollow Reservoir are useful for tracing the movement of 

recharge from the reservoir through the aquifer. Cl:Br ratios 

in the reservoir fluctuated between 1,100 and 5,000 from 2003 

through 2006 because of leaching of surficial salts while the 

reservoir was being initially filled (fig. 15). Beginning in 2007, 

the ratios in Sand Hollow Reservoir gradually increased from 

about 1,000 to 1,400, then in 2012, declined to about 1,100. In 

contrast, Cl:Br ratios of native groundwater in Sand Hollow 

are much lower at about 90 to 280 (table 3). Cl:Br ratios in 

wells receiving recharge from the reservoir (North Dam 3A, 

WD 6. WD 9, WD 11) generally rose in recent years, indicating the arrival of reservoir recharge. Cl:Br ratios did not rise at 

four other monitoring wells (WD 4, WD 12, WD 15, WD 19) 

showing recent increases in specific conductance and chloride 

concentration, indicating a mobilization of natural vadosezone salts rather than the arrival of reservoir water.

Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13

Reservoir water

WD 9 (55 feet from reservoir)

North Dam 3A (100 feet from reservoir)

WD 11 (160 feet from reservoir)

WD 6 (1,000 feet from reservoir)

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

Chloride-to-bromide ratio

Figure 15. Chloride-to-bromide ratios of reservoir water and groundwater from selected monitoring wells in Sand Hollow, Utah, 2001–12.
34 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Dissolved Organic Carbon, Tritium, and Dissolved Gases

Dissolved organic carbon (DOC) is another potential tracer 

of reservoir recharge, and it has been included in Sand Hollow water-quality sampling since 2008. Measured values of 

DOC in Sand Hollow Reservoir water ranged from 2.7 to 5.7 

mg/L (table 2). In contrast, native groundwater at monitoring 

wells not yet affected by reservoir recharge (WD 5, WD RJ, 

WD 16, WD 18, WD 20) generally had relatively low DOC 

concentrations of 0.4 to 0.8 mg/L. Groundwater at monitoring 

wells North Dam 3A, WD 6, WD 9, and WD 11, all affected 

by reservoir recharge based on elevated Cl:Br ratios, had 

DOC concentrations of 1.2 to 2.0 mg/L. Elevated DOC (0.8 

to 5.7 mg/L) also was measured at wells WD 4, WD 8, WD 

12, WD 15, and WD 19, where rising or elevated concentrations of other parameters (specific conductance, tritium, CFCs, 

SF6) but low Cl:Br ratios, could indicate the mobilization of 

vadose-zone salts or local natural recharge rather than arrival 

of reservoir water. Although DOC could be an indicator of the 

arrival of reservoir recharge, further data collection is needed 

to evaluate other potential sources of DOC in groundwater 

within Sand Hollow. 

Tritium concentrations in reservoir water and groundwater 

have been measured sporadically since 1999. Like specific 

conductance, TDG pressure and dissolved industrial gases, 

surface-water tritium concentrations were generally higher 

than in groundwater, making it a useful tracer of reservoir 

recharge. Reservoir water has had tritium concentrations of 2.5 

to 4.6 TU, with values generally stable at about 3.5 TU since 

2009 (table 2). In contrast, native groundwater in monitoring 

wells, sampled either before the reservoir was constructed 

or those sampled more recently but away from the reservoir, 

has tritium concentrations generally less than about 0.5 TU 

(fig. 16), indicating that the majority of natural recharge 

infiltrated prior to the 1960s. The exception to this is WD 8, 

which had 3 to 4 TU prior to construction of the reservoir, 

indicating higher natural recharge rates through infiltration of 

precipitation. The monitoring wells already receiving reservoir 

recharge (North Dam 3A, WD 6, WD 9, WD 11) have had 

tritium concentrations of 2.1 to 3.6 TU since 2008. Because of 

low Cl:Br ratios (less than 250), the elevated tritium concentrations at WD 12 and WD 19 (about 1 to 3 TU) could indicate 

the arrival of modern natural recharge rather than reservoir 

recharge.

Chlorofluorocarbons (CFC–11, CFC–12, and CFC–113) 

and sulfur hexafluoride (SF6

) are trace atmospheric gases that 

have been sampled in Sand Hollow since 2008, as additional 

indicators of reservoir recharge. CFC–12 is considered the 

most stable of the three chlorofluorocarbons—both CFC–11 

and CFC–113 are more likely to be affected by microbial 

decay. Dissolved CFC–12 concentrations in surface water collected from Sand Hollow Reservoir gradually increased from 

about 1.5 to 3.0 pmol/kg between 2008 and 2010 (Heilweil 

and Marston, 2011), then remained relatively stable during 

2011–2012 (table 2; fig. 17). Monitoring wells sampled near 

the reservoir during 2011–2012 (North Dam 3A, WD 6, WD 

9, WD 11) had CFC–12 concentrations ranging from 1.7 to 

2.6 pmol/kg, signifying the arrival of reservoir recharge. Low 

CFC-12 concentrations (less than 0.2 pmol/kg) measured in 

2010 and 2011 at monitoring wells farther from the reservoir 

(WD 5, WD RJ, WD 16, WD 18, WD 20), indicate older 

native groundwater. During 2011–2012, higher CFC–12 concentrations (1.7 to 2.2 pmol/kg) were measured in the group of 

wells (WD 8, WD 12, WD 15, WD 19) having elevated tritium 

concentrations and low Cl:Br ratios, which are attributed to 

modern natural recharge, as discussed previously. The unique 

locations on the trilinear diagram (fig. 14) of samples from 

this group of wells is not easily explained. While it is conceivable that reservoir water has reached WD 8 and WD 12 (both 

located within 1,000 ft of the reservoir), it is unlikely that this 

has occurred at WD 15 and WD 19, located 2,400 to 5,000 ft 

from the reservoir and co-located with the deeper (WD 16, 

WD 20) monitoring wells showing no signs of the arrival of 

reservoir recharge. Rising specific-conductance values at all 

wells but WD 8 could instead be indicative of the mobilization 

of nearby vadose-zone salts associated with the rising regional 

water table. 

The measured SF6

 concentrations in surface water from 

the reservoir boat ramp, representing water equilibrated with 

modern atmospheric concentrations of the gas, increased from 

about 1.5 to 1.9 fmol/kg in 2008-2009 to about 2.9 fmol/kg 

in 2011–2012 (table 2). This is at least partly attributed to the 

increase in atmospheric SF6 concentrations of about 7 percent 

per year, or from about 6.5 to 7.8 pptv from 2008 to 2012 

(http://water.usgs.gov/lab/sf6/background/). During 2011–

2012, groundwater SF6 concentrations ranged from about 0.1 

to 1.5 fmol/kg. The locations of low and high groundwater 

SF6 concentrations were generally similar to the locations of 

CFC–12 concentrations. Like CFC-12, SF6 concentrations 

increased at WD 4 and WD 6 from 2008 to 2012. The increase 

at WD 6 was due to the increasing fraction of reservoir water 

at this location, consistent with increasing Cl:Br ratios and 

major-ion geochemical evolution (see fig. 14B of Heilweil 

and Marston, 2011). WD 4 is unique among all the monitoring wells, showing an increase in dissolved-gas concentrations 

(both CFCs and SF6

) during 2011–2012, but very low tritium 

concentrations (less than about 0.1 TU). Specific conductance 

of water from this well has recently increased to 550 μS/cm 

and its geochemical signature is evolving toward that of other 

groundwater sites affected by reservoir recharge. Because it 

is located about 2,600 ft from the reservoir (similar to WD 15 

and WD 5, which are not yet receiving reservoir recharge), 

this monitoring well could be affected by a combination of 

the mobilization of vadose-zone salts and recent water-table 

drawdown (fig. 5) associated with pumping at nearby Well 19. 

Screened about 80 to 90 ft below land surface, water levels 

in WD 4 rose from about 20 ft above the screened interval 

in 2002 to about 50 ft above the screened interval in 2010, 

likely mobilizing vadose-zone salts. Subsequent, pumping at 

Well 19 lowered the water level in WD 4 by about 20 ft by 

2012, likely bringing younger, higher salinity water toward 
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 35

Figure 16. Tritium concentrations of reservoir water and groundwater from selected monitoring wells in Sand Hollow, Utah, February 

2012.

0 0.5 1 1.5 MILES

0 0.5 1 1.5 KILOMETERS

Base from State of Utah 25-cm aerial imagery, 2006

Universal Transverse Mercator projection, Zone 12

North American Datum of 1983

EXPLANATION

113°23'45" 113°22'30" 113°21'15"

37°8'45"

37°7'30"

37°6'15"

Sand

Hollow

Reservoir

Tritium—In tritium units

Surface-water sites

2.5 – 3.5

Monitoring well sites; *sampled in 

February 2011

0 – 0.50

0.51 – 1.5

1.6 – 2.5 (no sites)

2.6 – 3.6

No data

(WD 5) 0.00*(WD 5) 0.00*

(WD 4) 0.15(WD 4) 0.15

(WD 19) 2.8

(WD 18) 0.03* (WD 20) 0.01*

(WD 16) 0.04*

(WD 15) 0.15(WD 15) 0.15

(WD 9) 3.6(WD 9) 3.6

(WD 11) 2.5(WD 11) 2.5

(WD 6) 2.9(WD 6) 2.9

(North Dam 3A) 3.5

(WD 12) 1.0(WD 12) 1.0

(SH1-18) 3.5

(Boat Ramp) 3.2

(WD 8) 3.4(WD 8) 3.4

(WD RJ) 0.00*
36 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Figure 17. CFC–12 concentrations of reservoir water and groundwater from selected monitoring wells in Sand Hollow, Utah, 

February 2012.

0 0.5 1 1.5 MILES

0 0.5 1 1.5 KILOMETERS

Base from State of Utah 25-cm aerial imagery, 2006

Universal Transverse Mercator projection, Zone 12

North American Datum of 1983

EXPLANATION

113°23'45" 113°22'30" 113°21'15"

37°8'45"

37°7'30"

37°6'15"

Chlorofluorocarbon–12—In picomoles per kilogram

Surface-water sites

 3.0 – 4.0

Monitoring wells; *sampled in February 2011

0 – 0.50

0.51 – 1.0

1.1 – 2.0

2.1– 3.0

3.1 – 4.0

No data

(WD 19) 1.9 (WD 18) 0.02* (WD 20) 0.07*

(WD 4) 1.1

(WD 9) 1.9

(WD 15) 2.1

(WD 16) 0.01*

(WD 5) 0.07*

(WD 6) 1.7

(WD 11) 2.6

(SH1-18) 3.1

(Boat Ramp) 3.0

Sand

Hollow

Reservoir

(WD 8) 1.7

(WD 12) 2.0

(North Dam 3A) 1.9*

(WD RJ) 0.15*
Evaluation of the Movement of Managed Aquifer Recharge and Geochemical Mixing in the Navajo Sandstone 37

the screened interval. While this pumping could explain the 

changing salinity and ages, the contradiction between modern 

dissolved gases and pre-modern tritium concentrations at this 

site requires further investigation.

As discussed in Heilweil and Marston (2011), water samples collected at selected monitoring wells were also analyzed 

for dissolved noble gases (helium, neon, argon, krypton, and 

xenon) to allow for the calculation of excess neon by using the 

closed system equilibrium (CE) model (Aeschbach-Hertig and 

others, 2000). Neon excess refers to the amount of dissolved 

neon in water above atmospherically equilibrated quantities. 

High neon-excess values in Sand Hollow indicate dissolution 

of air bubbles, either associated with the rapidly rising water 

table or air trapped directly beneath the reservoir as this region 

became saturated. Prior to the filling of Sand Hollow Reservoir, noble-gas measurements in monitoring wells indicated 

excess neon concentrations up to about 70 percent (table 2). 

In contrast, excess-neon values ranged from about 160 to 

340 percent in monitoring wells close to the reservoir. While 

neon excess in most monitoring wells near the reservoir has 

been increasing, values at WD 9 have rapidly decreased from 

about 250 percent in 2005 to 30 percent in 2012, indicating 

the dissolution of most of the initially trapped air beneath the 

reservoir.

Evaluating the Arrival of Managed Aquifer 

Recharge at Monitoring Wells

As described by Heilweil and Marston (2011), changes in 

values for selected field parameters (TDG pressure, DO, and 

specific conductance), dissolved chemical constituents (Cl:Br 

ratios, major-ion chemistry, organic carbon), tritium, and dissolved industrial and noble gases (CFC–12, SF6

, neon) at the 

monitoring wells were used to evaluate the movement of managed aquifer recharge through the Navajo Sandstone aquifer 

in Sand Hollow. While the various tracers showed recharge 

from Sand Hollow Reservoir had arrived at several monitoring wells close to the reservoir, they often indicated different 

peak arrival years for the same monitoring well (table 4). This 

is likely due to different behavioral characteristics of each 

of the tracers, such as adsorption and retardation, dispersion, 

and gas dissolution as recharge enters and moves through the 

aquifer. In general, these tracers indicated that recharge from 

the reservoir arrived earliest at the wells located closest to the 

reservoir (WD 9, North Dam 3A). North Dam 3A was initially 

a dry borehole in the vadose zone and received recharge from 

the reservoir in mid-2002, when it first became saturated, 

even though the peak Cl:Br ratio and DO concentration were 

not measured until 2004 and 2005, respectively. The recharge 

arrival year at WD 9 is less certain, with tracer peaks between 

2003 and 2011. At WD 11, most of the tracers indicated that 

the peak breakthrough of reservoir recharge was likely in 2005 

or 2006; the peak in neon excess could have been in 2011. 

At WD 6, the majority of the tracers indicated that recharge 

arrived between 2005 and 2009. Although CFC and SF6

concentrations were still rising at WD 6 in 2012, this could 

partially reflect their rising concentrations in the reservoir in 

recent years. It is not clear whether reservoir recharge was 

beginning to reach WD 8, WD 12, or WD 4 during 2012. All 

three of these wells showed some changes in field parameters 

(TDG pressure, dissolved oxygen, or specific conductance) 

and various other environmental tracers, but no increase in 

Cl:Br ratios was observed during 2012. While some tracers 

sampled at WD 15 and WD 19 were elevated above background levels, this could have been caused by the rising 

water table rather than the arrival of reservoir recharge. This 

interpretation is consistent with the fact that the wells are farther from the reservoir and had low Cl:Br ratios. This is also 

supported by environmental tracer concentrations at monitoring wells WD 16 and WD 20, deeper monitoring wells at the 

same sites as WD 15 and WD 19, respectively, that showed no 

indication of the arrival of reservoir recharge through 2012. 

Monitoring wells WD 5, WD RJ, and WD 18, similarly, did 

not show any indication of the arrival of reservoir recharge by 

2012.
38 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

Table 4. Summary of tracer peaks showing year of arrival for reservoir recharge at selected monitoring wells in Sand Hollow, Utah.

[Cl:Br, chloride-to-bromide ratio; —, no data available; ?, uncertain year of tracer peak; NMF, not meaningful]

Site

Distance from 

reservoir,

in feet

Total

dissolved-gas 

pressure

Dissolved 

oxygen

Specific conductance 1

Cl:Br Major-ion 

chemistry Tritium CFC-12 SF6 Neon excess

Dissolved 

organic 

carbon

WD 9 55 2003, 

2004–05?

2003, 

2004?

2006 2011 Prior to 

2009

Prior to 

2008

Prior to 

2008

Prior to 

2009

2004–05 Prior to 

2010

North Dam 3A 100 — 2005 2002 Rising 2002 2002 Prior to 

2008

— — Prior to 

2010

WD 11 160 2004, 

2005–08?

2004–05 2004 Rising? Prior to 

2009

Prior to 

2008

Prior to 

2009

Prior to 

2009

2011? Prior to 

2009

WD 8 500 2

Rising 2Rising No arrival No arrival No arrival 3NMF 2Elevated 2Elevated 2Rising No arrival

WD 6 1,000 2009 2009 2008 Rising Prior to 

2009

3

NMF 4Rising 4Rising Rising Prior to 

2009

WD 12 1,000 — 2

Elevated 2Elevated No arrival Changing 2Rising 2Elevated 2Elevated — 2Rising

WD 15 (shallow) 2,400 2

Rising 2Elevated 2Elevated No arrival Changing 2Elevated 2Elevated 2Elevated 2Elevated 2Rising

WD 16 (deep) 2,400 No arrival No arrival No arrival No arrival No arrival No arrival No arrival No arrival No arrival No arrival

WD 4 2,600 — — 2

Rising No arrival Changing No arrival 2Rising 2Rising — 2Rising

WD 5 2,800 — No arrival No arrival No arrival No arrival No arrival No arrival No arrival — No arrival

WD 19 (shallow) 5,000 No arrival No arrival 2

Elevated No arrival Changing 2Rising 2Elevated 2Elevated No arrival 2Rising

WD 20 (deep) 5,000 No arrival No arrival No arrival No arrival No arrival No arrival No arrival — No arrival No arrival

WD RJ 5,200 No arrival No arrival No arrival No arrival No arrival No arrival No arrival — — No arrival

WD 18 (deep) 5,900 No arrival No arrival No arrival No arrival No arrival No arrival No arrival — No arrival No arrival

1

 Based on data from both Table 3 of this report and Table 1 of Heilweil and others (2009). 

2

 Rising or elevated dissolved-gas pressure, dissolved oxygen, specific conductance, tritium, CFC-12, SF6, neon excess, or dissolved organic carbon during 2011–2012 may 

indicate local natural recharge and rising water table (dissolution of trapped air bubbles and chloride bulge) rather than reservoir recharge. 

3

 Not meaningful because of elevated tritium concentrations prior to reservoir construction. 

4

 Rising CFC-12 and (or) SF6 concentrations in the reservoir during 2008–2012 complicate the interpretation of peak arrival year. 
Summary 39

Summary

The objectives of this study were to both quantify amounts 

of recharge from Sand Hollow Reservoir and to evaluate its 

movement through the Navajo Sandstone aquifer, with conditions updated to 2012. This study follows previous USGS Scientific Investigations Reports 2005–5185 (Heilweil and others, 

2005), 2007–5023 (Heilweil and Susong, 2007), 2009–5050 

(Heilweil and others, 2009), and Heilweil and Marston (2011). 

Since its inception in 2002, diversions to the reservoir 

from the nearby Virgin River have resulted in generally rising 

reservoir altitude, from about 3,000 ft in 2002 to a maximum 

of about 3,060 ft in 2006, which then fluctuated between 

about 3,040 and 3,060 ft from 2008 through 2011. Similarly, 

groundwater levels in monitoring wells closest to the reservoir 

generally rose between 2002 and 2006, and then fluctuated 

with reservoir altitude and pumpage rate from nearby production wells. Water levels in monitoring wells farther from the 

reservoir were still rising during 2011.

About 19,000 acre-ft of groundwater were withdrawn from 

Sand Hollow Reservoir between 2004 and 2011, mostly from 

production wells located near the North Dam. French drains, 

installed to capture shallow seepage near the reservoir, are also 

pumped as they fill with water. About 6,000 acre-ft of groundwater were pumped from the North Dam drain between 2003 

and 2011. This water initially was returned to the reservoir, but 

since 2007 has been used by Sand Hollow Resort for irrigation. About 1,500 acre-ft of water were pumped from the West 

Dam drain back into the reservoir from 2005 through 2011. 

In 2006, the West Dam Spring drain was constructed and has 

largely replaced the function of the West Dam drain. From 

2006 through 2011 about 13,500 acre-ft have been pumped 

from this drain into the Washington County Water Conservancy District’s municipal supply system.

Total annual surface-water inflow to Sand Hollow Reservoir ranged from about 800 acre-ft in 2007 to 56,000 acre-ft in 

2005. Total inflow from 2002 through 2011 was about 199,000 

acre-ft. The general increase in reservoir water-level altitude 

and surface area from 2002 and 2007 resulted in a steady 

increase in the volume of annual evaporation from about 1,000 

in 2002 to about 6,600 acre-ft through 2006, which leveled 

off from 2007 through 2011. Total estimated cumulative 

evaporative loss from 2002 through 2009 was about 50,000 

acre-ft. During this same period, annual reservoir recharge to 

the underlying Navajo Sandstone aquifer fluctuated between 

about 5,000 and 18,000 acre-ft. Annual recharge for 2010 

and 2011was approximately 11,000 and 8,400 acre-ft, respectively. Total calculated reservoir recharge from 2002 through 

2011 was about 106,000 acre-ft with a two standard deviation uncertainty of 9,200 acre-ft. From 2002 through 2011, 

calculated monthly recharge volumes ranged from about 50 to 

3,500 acre-ft, and average daily recharge rates (calculated for 

each month) ranged from 0.001 to 0.43 ft. From March 2002 

through May 2002, there was a rapid decrease in rates as the 

vadose zone wetted up and the reservoir became hydraulically 

connected to the aquifer. From mid-2002 through 2007, there 

was a gentler decline in recharge rates, likely caused by both 

the decreasing hydraulic gradient in the aquifer and permeability reduction beneath the reservoir. From 2007 through 

2011, recharge rates generally remained low but were highly 

variable from month to month. 

Water quality was assessed at various monitoring wells in 

Sand Hollow to evaluate the timing and location of reservoir 

recharge moving through the aquifer. Tracers of reservoir 

recharge include major and minor dissolved inorganic ions, 

tritium, dissolved organic carbon, and dissolved industrial and 

noble gases, including chlorofluorocarbons, sulfur hexafluoride, and neon. The various tracers often have different peak 

arrival years at individual monitoring wells. This is likely due 

to different behavioral characteristics of each of the tracers, 

such as adsorption and retardation, dispersion, and gas dissolution as recharge enters and moves through the aquifer. By 

2012, reservoir recharge clearly arrived at four monitoring 

wells (North Dam 3A, WD 6, WD 9, WD 11) within about 

1,000 ft of the reservoir. Tracer concentrations at five other 

monitoring wells (WD 5, WD RJ, WD 16, WD 18, WD 20) 

indicated that reservoir recharge had not reached these sites. 

The low Cl:Br ratios but elevated or increasing environmental 

tracer concentrations at the remaining monitoring wells (WD 

4, WD 8, WD 12, WD 15, WD 19), are difficult to interpret; 

these changes could either be an early indication of the arrival 

of reservoir recharge or could be caused by other processes 

such as local mobilization of vadose-zone salts and incorporation of dissolved gases associated with rising groundwater 

levels. 
40 Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Updated to Conditions in 2012

References Cited

Aeschbach-Hertig, W., Peeters, F., Beyerle, U., and Kipfer, 

R.,2000, Paleotemperature reconstruction from noble 

gases in ground water taking into account equilibrium with 

trapped air: Nature, v. 405, p. 1040–1044.

Clarke, W.B., Jenkins, W.J., and Top, Z., 1976, Determination of tritium by mass spectrometric measurements of 3

He: 

International Journal of Applied Radiation Isotopes, v. 27, 

p. 515–522.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: PrenticeHall, Inc., Englewood Cliffs, New Jersey, 604 p.

Gardner, P., and Solomon, D.K., 2009, An advanced passive 

diffusion sampler for the determination of dissolved gas 

concentrations: Water Resources Research, v. 45, W06423.

 Heilweil, V.M., Freethey, G.W., Stolp, B.J., Wilkowske, C.D., 

and Wilberg, D.E., 2000, Geohydrology and numerical 

simulation of ground-water flow in the central Virgin River 

basin of Iron and Washington Counties, Utah: Utah Department of Natural Resources Technical Publication 116, 

182 p.

Heilweil, V.M., and Marston, T.M., 2011, Assessment of 

managed aquifer recharge from Sand Hollow Reservoir, 

Washington County, updated to conditions in 2010: U.S. 

Geological Survey Scientific Investigations Report 2011-

5142, 39 p.

Heilweil, V.M., and McKinney, T.S., 2007, Net-infiltration 

map of the Navajo Sandstone outcrop area in western Washington County, Utah: U.S. Geological Survey Scientific 

Investigations Map 2988.

Heilweil, V.M., McKinney, T.S., Zhdanov M.S., and Watt, 

D.E., 2007, Controls on the variability of net infiltration 

to desert sandstone: Water Resources Research, v. 43, 

W07431. DOI:10.1029/2006WR005113, 15 p.

Heilweil, V.M., Ortiz, G., and Susong, D.D., 2009a, Assessment of managed aquifer recharge at Sand Hollow Reservoir, Washington County, Utah, updated to conditions 

through 2007: U.S. Geological Survey Scientific Investigations Report 2009–5050, 19 p.

Heilweil, V.M. and Solomon, D.K., 2004, Millimeter- to 

kilometer-scale variations in vadose-zone bedrock solutes: 

implications for estimating recharge in arid settings, in

Phillips, F., Scanlon, B., and Hogan, J., eds., Ground-water 

recharge in a desert environment: the southwestern United 

States, Water Science and Application 9: Washington, D.C., 

American Geophysical Union, p. 49–67.

Heilweil, V.M., Solomon, D.K., and Gardner, P.M., 2006, 

Borehole environmental tracers for evaluating net infiltration and recharge through desert bedrock: Vadose Zone 

Journal, v. 5, p. 98–120.

Heilweil, V.M., Solomon, D.K., and Ortiz, G., 2009b, Silt 

and gas accumulation beneath an artificial recharge spreading basin, southwestern Utah, U.S.A: Boletin Geologico y 

Minero, v. 120, no. 2, p. 185–195.

Heilweil, V.M., Solomon, D.K., Perkins, K.S., and Ellett, 

K.M., 2004, Gas-partitioning tracer test to quantify trapped 

gas during recharge: Ground Water, v. 42, no. 4, p. 589–600.

Heilweil, V.M., and Susong, D.D., 2007, Assessment of 

artificial recharge at Sand Hollow Reservoir, Washington 

County, Utah, updated to conditions through 2006: U.S. 

Geological Survey Scientific Investigations Report 2007–

5023, 14 p.

Heilweil, V.M., Susong, D.D., Gardner, P.M., and Watt, D.E, 

2005, Pre- and post-reservoir ground-water conditions and 

assessment of artificial recharge at Sand Hollow, Washington County, Utah, 1995–2005: U.S. Geological Survey 

Scientific Investigations Report 2005–5185, 74 p.

Heilweil, V.M., and Watt, D.E., 2011, Trench infiltration for 

managed aquifer recharge to permeable bedrock: Hydrological Processes 25, DOI: 10.1002/hyp.7833, p. 141–151.

Hurlow, H.A., 1998, The geology of the central Virgin River 

basin, southwestern Utah, and its relation to ground-water 

conditions: State of Utah Water Resources Bulletin 26, 53 p.

Marston, T.M., and Heilweil, V.M., 2012, Numerical simulation of groundwater movement and managed aquifer 

recharge from Sand Hollow Reservoir, Hurricane Bench 

area, Washington County, Utah: U.S. Geological Survey 

Scientific Investigations Report 2012–5236, 34 p.

McGuinness, J.L., and Bordne, E.F., 1971, A comparison of 

lysimeter-derived potential evapotranspiration with computed values: U.S. Department of Agriculture Technical 

Bulletin 1472, Agricultural Research Service, Washington 

D.C., 71 p.

Rosenberry, D.O., Winter, T.C., Buso, D.C., and Likens, G.E., 

2007, Comparison of 15 evaporation methods applied to a 

small mountain lake in the northeastern USA: Journal of 

Hydrology, v. 340, p. 149–166.

Sheldon, A., 2002, Diffusion of radiogenic helium in shallow 

ground water: Implications for crustal degassing: Salt Lake 

City, Utah, University of Utah, Ph.D. Dissertation, 185 p.

Wilde, F.D., and Radtke, D.B., 1998, National field manual for 

the collection of water-quality data: Field measurements: 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 9, chap. A6, 233 p. 

Marston and Heilweil—Assessment of Managed Aquifer Recharge at Sand Hollow Reservoir, Washington County, Utah, Updated to Conditions in 2012—SIR 2013–5057