U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2008–5157

Prepared in cooperation with the U.S. Army, White Sands Missile Range

Geochemical Trends and Natural Attenuation of RDX, 

Nitrate, and Perchlorate in the Hazardous Test Area 

Fractured-Granite Aquifer, White Sands Missile 

Range, New Mexico, 1996–2006
Geochemical Trends and Natural 

Attenuation of RDX, Nitrate, and 

Perchlorate in the Hazardous Test Area 

Fractured-Granite Aquifer, White Sands 

Missile Range, New Mexico, 1996–2006

By Jeff B. Langman, Andrew J. Robertson, Jamar Bynum, and 

Fredrick E. Gebhardt

Prepared in cooperation with the U.S. Army, White Sands Missile Range

Scientific Investigations Report 2008–5157

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

This and other USGS information products are available at http://store.usgs.gov/

U.S. Geological Survey

Box 25286, Denver Federal Center

Denver, CO 80225

To learn about the USGS and its information products visit http://www.usgs.gov/

1-888-ASK-USGS

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

U.S. Government.

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

Langman, J.B., Robertson, A.J., Bynum, J., and Gebhardt, F.E., 2008, Geochemical trends and natural attenuation of 

RDX, nitrate, and perchlorate in the Hazardous Test Area fractured-granite aquifer, White Sands Missile Range, New 

Mexico, 1996–2006: U.S. Geological Survey Scientific Investigations Report 2008-5157, 45 p.
iii

Contents

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

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Description of the Study Area ............................................................................................................2

Geology and Hydrology...............................................................................................................6

Anthropogenic Compounds .......................................................................................................6

Previous Studies ...................................................................................................................................8

Study Methods ......................................................................................................................................8

Acknowledgments..............................................................................................................................14

Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer..............14

Fracture Flow in the Fractured-Granite Aquifer............................................................................14

Contaminant Variability at the Open Burn/Open Detonation Site...............................................18

Downgradient Contaminant Variability ...........................................................................................22

Water Level and Contaminant Relation...........................................................................................28

Natural Attenuation in the Fractured-Granite Aquifer ..........................................................................28

Tritium-Helium Age Dating and Dilution..........................................................................................30

Ground-Water Composition ..............................................................................................................30

Dilution ........................................................................................................................................30

Degradation and Changes to Carbon Forms .........................................................................33

Natural Attenuation and Chloride ...........................................................................................34

Stable Isotopes....................................................................................................................................35

Reduction-Oxidation Sequence .......................................................................................................38

Summation of Natural Attenuation Indicators...............................................................................38

Summary........................................................................................................................................................41

Selected References...................................................................................................................................42

Figures

1–5. Maps showing:

 1. Location of White Sands Missile Range, New Mexico, and 

the study area ........................................................................................................................3

 2. Hazardous Test Area, Open Burn/Open Detonation (OB/OD) site, and 

monitoring sites, White Sands Missile Range, New Mexico.........................................4

 3. Example of relative stability of contaminant concentrations in ground water 

at the Open Burn/Open Detonation (OB/OD) site, White Sands Missile Range, 

New Mexico, 2000 and 2006. ...............................................................................................5

 4. Geologic characteristics of the fractured-granite pluton at the Hazardous 

Test Area, White Sands Missile Range, New Mexico.....................................................7
iv

 5. Location of the study’s monitoring-site transects at the Hazardous Test Area, 

White Sands Missile Range, New Mexico......................................................................12

6. Photograph of borehole image and drilling log from construction of well 

28 at the Hazardous Test Area, December 1999....................................................................15

7. Diagram of fracture orientation in the granite pluton at boreholes in the 

Open Burn/Open Detonation pits and for selected wells downgradient 

from the pits.................................................................................................................................16

8. Map showing potentiometric-surface contours and ground-water flow paths 

in the Hazardous Test Area fractured-granite aquifer, New Mexico, 

October 2006................................................................................................................................17

9–26 Diagrams showing:

 9. Vertical profile of topography and potentiometric surface at the 

Hazardous Test Area, transect B–B’, October 2006.......................................................19

 10. Mean-daily water level for select wells and daily precipitation total at 

well 15, Hazardous Test Area, January 2003 to January 2006 .....................................19

 11. Spatial variability of RDX in ground water from wells in transect A–A’ 

at the Hazardous Test Area, 1996–2006 ...........................................................................20

 12. Temporal variability of RDX in ground water from wells in transect A–A’

at the Hazardous Test Area................................................................................................20

 13. Spatial variability of nitrate plus nitrite as nitrogen in ground water from 

wells in transect A–A’ at the Hazardous Test Area, 1996–2006 ...................................21

 14. Temporal variability of nitrate plus nitrite as nitrogen in ground water 

from wells in transect A–A’ at the Hazardous Test Area..............................................21

 15. Spatial variability of perchlorate in ground water from wells in 

transect A–A’ at the Hazardous Test Area, 1996–2006..................................................23

 16. Temporal variability of perchlorate in ground water from wells in 

transect A–A’ at the Hazardous Test Area......................................................................23

 17. Spatial variability of RDX in ground water from wells in transect 

B–B’ at the Hazardous Test Area, 1996–2006..................................................................24

 18. Temporal variability of RDX in ground water from wells in transect 

B–B’ at the Hazardous Test Area......................................................................................24

 19. Spatial variability of nitrate plus nitrite as nitrogen in ground water 

from wells in transect B–B’ at the Hazardous Test Area, 1996–2006 .........................25

 20. Temporal variability of nitrate plus nitrite as nitrogen in ground water 

from wells in transect B–B’ at the Hazardous Test Area..............................................25

 21. Spatial variability of dissolved oxygen in ground water from wells in 

transect B–B’ at the Hazardous Test Area, 1996–2006..................................................26

 22. Spatial variability of perchlorate in ground water from wells in 

transect B–B’ at the Hazardous Test Area, 1996–2006..................................................26

 23. Temporal variability of perchlorate in ground water from wells in 

transect B–B’ at the Hazardous Test Area......................................................................27

 24. Perchlorate concentrations in ground water from well 20 near the 

Open Burn/Open Detonation site and ground water from wells 16 

and 16D approximately 0.15 mile downgradient.............................................................27

 25. Piper diagram of major ion composition of ground water collected 

from monitoring sites in the Hazardous Test Area, October 2005 ...............................31

 26. Spatial distribution of dissolved-solids concentrations in the 

fractured-granite aquifer near the Open Burn/Open Detonation Site 

in the Hazardous Test Area, October 2005 ......................................................................32
v

27. Strontium and calcium concentrations in ground water from monitoring sites in the 

Hazardous Test Area, October 2005. .............................................................................................................33

28–32. Diagrams showing:

 28. Nitrate plus nitrite as nitrogen and dissolved nitrogen gas concentrations 

in ground water from selected wells in transect B–B’ at the Hazardous 

Test Area, October 2005......................................................................................................34

 29. Perchlorate (ClO4) and chloride (Cl) relations in ground water from 

selected wells in the Hazardous Test Area, October 2005 ...........................................35

 30. δ2hydrogen and δ18oxygen for ground water collected from selected wells 

in the Hazardous Test Area, October 2005 ......................................................................36

 31. δ15nitrogen and δ18oxygen values of nitrate in ground water from 

selected wells in the Hazardous Test Area, October 2005 ...........................................37

 32. Sulfate concentrations and δ34sulfur values for sulfate in ground 

water from selected wells in the Hazardous Test Area, October 2005 ......................37

33. Map showing possible reduction-oxidation conditions (relative electron 

potential values) for ground water at the Hazardous Test Area, 

Electro-Magnetic Radiation Energy area, and northern Main Post area, 

October 2005................................................................................................................................39

34. Map showing spatial pattern of contamination of the Hazardous Test Area 

fractured-granite aquifer near the Open Burn/Open Detonation site and 

indicators of natural attenuation that reduce contaminant concentrations 

in the downgradient direction, October 2005.........................................................................40

Tables

1. Open Burn/Open Detonation Site and Hazardous Test Area study area 

monitoring-site information.........................................................................................................9

2. Sample analytes and laboratory analysis methods..............................................................13

3. Kendall’s tau correlation coefficients for water level and RDX, nitrate, and 

perchlorate in ground water from wells in transect A–A’ at the Hazardous 

Test Area, 1996–2006..................................................................................................................29

4. Kendall’s tau correlation coefficients for water level and RDX, nitrate, and 

perchlorate in ground water from wells in transect B–B’ at the Hazardous 

Test Area, 1996–2006..................................................................................................................29

5. Kendall’s tau correlation coefficients for RDX and nitrate in ground water 

from wells in transect A–A’ at the Hazardous Test Area, 1996–2006.................................29

6. Kendall’s tau correlation coefficients for RDX and nitrate in ground water 

from wells in transect B–B’ at the Hazardous Test Area, 1996–2006.................................29

7. Ground-water ages for selected wells at the Hazardous Test Area, October 2005 ........31
vi

Conversion Factors and Datums

Multiply By To obtain

inch 2.540 centimeter (cm)

foot (ft) 0.3048 meter (m)

yard (yd) 0.9144 meter (m)

mile (mi) 1.609 kilometer (km)

acre 4,047 square meter (m2)

gallon (gal) 3.785 liter (L)

foot per day (ft/d) 0.00035 centimeters per second (cm/s)

foot per year (ft/yr) 9.7xl0-7 centimeters per second (cm/s)

gallons per minute (gal/min) 0.0038 cubic meters per minute (m3/min)

Temperature in degrees Celsius (oC) can be converted to degrees Fahrenheit (oF) as follows: 

oF = (1.8 x oC) + 32

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).

Abbreviations

DS Dissolved solids

EMRE Electro-Magnetic Radiation Energy

Ga Billion years before present

HTA Hazardous Test Area

Ma Million years before present

μg/L Micrograms per liter

mg/L Milligrams per liter

Nitrate Nitrate plus nitrite as nitrogen

OB/OD Open Burn/Open Detonation

RCRA Resources and Conservation Recovery Act

redox Reduction-oxidation

USGS U.S. Geological Survey

WSMR White Sands Missile Range

‰ Per mil
Abstract

A fractured-granite aquifer at White Sands Missile Range 

is contaminated with the explosive compound RDX, nitrate, 

and perchlorate (oxidizer associated with rocket propellant) 

from the previous use of the Open Burn/Open Detonation 

site at the Hazardous Test Area. RDX, nitrate, and perchlorate ground-water concentrations were analyzed to examine 

source characteristics, spatial and temporal variability, and 

the influence of the natural attenuation processes of dilution 

and degradation in the Hazardous Test Area fractured-granite 

aquifer. Two transects of ground-water wells from the existing 

monitoring-site network—one perpendicular to ground-water 

flow (transect A–A ́) and another parallel to ground-water flow 

(transect B–B ́)—were selected to examine source characteristics and the spatial and temporal variability of the contaminant 

concentrations. Ground-water samples collected in 2005 from 

a larger sampling of monitoring sites than the two transects 

were analyzed for various tracers including major ions, trace 

elements, RDX degradates, dissolved gases, water isotopes, 

nitrate isotopes, and sulfate isotopes to examine the natural 

attenuation processes of dilution and degradation.

Recharge entrains contaminants at the site and transports 

them downgradient towards the Tularosa Basin floor through 

a poorly connected fracture system(s). From 1996 to 2006, 

RDX, nitrate, and perchlorate concentrations in ground water 

downgradient from the Open Burn/Open Detonation site have 

been relatively stable. RDX, nitrate, and perchlorate in ground 

water from wells near the site indicate dispersed contaminant 

sources in and near the Open Burn/Open Detonation pits. 

The sources of RDX and nitrate in the pit area have shifted 

with time, and the shift correlates with the regrading of the 

south and east berms of each pit in 2002 and 2003 following 

closure of the site. The largest RDX concentrations were in 

ground water about 0.1 mile downgradient from the pits, the 

largest perchlorate concentrations were in ground water about 

0.15 mile downgradient from the pits, and the largest nitrate 

concentrations were in ground water about 0.25 mile downgradient from the pits. Strong and moderate correlation of 

Geochemical Trends and Natural Attenuation of RDX, 

Nitrate, and Perchlorate in the Hazardous Test Area 

Fractured-Granite Aquifer, White Sands Missile Range, 

New Mexico, 1996–2006

By Jeff B. Langman, Andrew J. Robertson, Jamar Bynum, and Fredrick E. Gebhardt

water level and the contaminant concentrations near the source 

areas and low correlation outside and downgradient from the 

source areas indicates a diminishing of the water level/contaminant relation with downgradient flow.

Ground water was not progressively older at all locations 

downgradient from the Open Burn/Open Detonation site 

indicating multiple recharge areas. Major ion and strontium 

concentrations and δ2H and δ18O values identified similar 

sources of recharge waters comprising the aquifer except 

along the basin periphery where recharge water may be 

influenced by dissolution of mineral assemblages associated 

with ore deposits that are present along the basin margins. 

Ground-water ages, dissolved-solids concentrations, and 

calcium-strontium concentrations indicate limited or 

partial connectivity between fractures and contributions of 

uncontaminated recharge water downgradient from the site 

that dilutes contaminant concentrations. Changes in RDX 

and nitrate concentration patterns, the presence of methane, 

changes in carbon dioxide concentrations and δ15N and δ34S 

values, and variable reduction-oxidation conditions suggest 

degradation of contaminants in the downgradient direction. 

Estimated values of electron potential were assigned to ground 

water collected in October 2005 from all monitoring sites 

at the Hazardous Test Area. Moderate to strong reducing 

conditions were present upgradient from the Open Burn/

Open Detonation site, at the site, and at various locations 

downgradient from the site, but the aquifer contained welloxygenated water between many of the reducing areas. The 

spatial variability of reduction-oxidation conditions in the 

aquifer exemplifies the partial connectivity of the fracture 

system(s). Dilution of the contaminants is likely dominant 

where oxidizing conditions are present and degradation likely 

assists in naturally attenuating the contaminants in areas of 

reducing conditions. Substantial contaminant transport beyond 

the existing areal extent of the contaminants appears unlikely 

given the relative “stability” of contaminant concentrations 

from 1996 to 2006 and the ongoing processes of dilution and 

degradation that produce this concentration stability.
2 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

Introduction

In 2007, the U.S. Geological Survey (USGS), in 

cooperation with U.S. Army White Sands Missile Range 

(WSMR), conducted an analysis of ground-water geochemical 

data collected at the Hazardous Test Area (HTA). The goal 

was to evaluate the temporal and spatial variability of the 

anthropogenic compounds of RDX (explosive compound 

associated with C-4), nitrate, and perchlorate (oxidizer 

associated with rocket propellant) contaminating the 

fractured-granite aquifer at the Open Burn/Open Detonation 

site (OB/OD site) at HTA, to evaluate source characteristics, 

and to examine possible natural attenuation mechanisms that 

may have stabilized contaminant concentrations. 

The Hazardous Test Area is located in southern New 

Mexico (fig. 1), about 25 miles (mi) east of Las Cruces and 

10 mi north of WSMR Main Post. The OB/OD site is located 

in the northwest part of HTA (fig. 2) and consisted of two 

open detonation pits. The pits were excavated from native 

soil in 1953, and berms were constructed with native soil 

on all sides, except for vehicle access points. The west pit 

measured approximately 100 by 180 feet (ft), and the east pit 

was approximately 170 by 180 ft. The pits were used for the 

demolition of ordnance including explosives and propellants 

(Black and Veatch Waste Science, Inc., 1995). Most 

demolitions at the OB/OD site were conducted in the east pit, 

and the site was officially closed December 31, 2000. In 2002 

and 2003, earthen berms along the southern and eastern sides 

of each OB/OD pit were pushed into the pits and the area 

regraded to the present topographic slope. 

White Sands Missile Range and the USGS have been 

monitoring an expanding monitoring-site network at HTA 

(fig. 2) since 1996 under the guidance of the State of New 

Mexico and the guidelines of the Resources Conservation and 

Recovery Act (RCRA). Sampling of the HTA monitoring-site 

network has detected three main anthropogenic compounds: 

RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), nitrate (NO3

-

plus NO2

-

, reported as nitrogen), and perchlorate (ClO4

-

). RDX 

and nitrate have been detected in ground water from wells at 

the OB/OD site since regular monitoring began in 1996 and 

perchlorate has been detected since 1999 when monitoring of 

this compound began. Wells have been added to the network 

during the period of study to better define the areal extent of 

the contamination and improved analytical capabilities have 

provided better concentration resolution, but during the entire 

history of monitoring at HTA, the contaminant concentrations 

have remained relatively stable across the area (fig. 3). 

An analysis of hydraulic conductivities in fractures 

penetrated by monitoring wells in the OB/OD site area in 

2003 (wells 10A–29) indicated a median hydraulic 

conductivity of 2 feet per day (ft/d) and a likely 

1,000 feet per year (ft/yr) average (Ralph Wilcox, U.S. 

Geological Survey, written commun., 2003). The largest 

contaminant concentrations are spatially static (same wells 

continue to contain the largest contaminant concentrations), 

but the contaminants have been detected downgradient 

with addition of new wells (Ralph Wilcox, U.S. Geological 

Survey, written commun., 2003). Natural attenuation likely 

is decreasing contaminant concentrations with downgradient 

flow, and this decrease is balanced by a continued input of 

the contaminants from recharge interacting with contaminant 

sources in and around the pits (Ralph Wilcox, U.S. Geological 

Survey, written commun., 2003). Natural attenuation 

consists of physical, chemical, or biological processes that 

reduce contaminant concentrations in soil or ground water 

(U.S. Environmental Protection Agency, 1999). These 

processes can include biodegradation, dispersion, dilution, 

sorption, volatilization, or radioactive decay. The processes 

of biodegradation (degradation by microorganisms) and 

dispersion/dilution (dilution) are the most applicable to the 

nonvolatile and nonradioactive compounds of RDX, nitrate, 

and perchlorate.

Purpose and Scope

The purpose of this report is to examine geochemical 

trends and investigate the possibility of natural attenuation 

controlling the downgradient migration of large concentrations 

of the contaminants that enter the HTA fractured-granite 

aquifer at the OB/OD site. For purposes of this report, 

examination of natural attenuation processes is focused on 

dilution and degradation that would decrease the concentration 

of each contaminant with downgradient transport. This report 

describes the temporal and spatial concentration variability of 

the anthropogenic compounds of RDX, nitrate, and perchlorate 

as they react to recharge, ground-water flow, and likely natural 

attenuation processes. Data from 1996–2006 were compiled 

for 18 wells composing two transects extending across 

HTA from the existing monitoring-site network. Additional 

data including—water levels, dissolved oxygen, pH, RDX 

degradates (hexahydro-1-nitroso-,3,5-dinitro-1,3,5-triazine 

(MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine 

(DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX)), 

dissolved gases, major ions, trace elements, ground-water 

ages, stable isotopes of water, nitrogen and oxygen isotopes 

of nitrate, and sulfur isotopes of sulfate—for ground water 

at additional monitoring-site locations were used to better 

understand dilution and degradation processes affecting RDX, 

nitrate, and perchlorate concentrations in the HTA fracturedgranite aquifer.

Description of the Study Area

The OB/OD site is located near the western edge of the 

Tularosa Basin (fig. 1) at an altitude of approximately 5,700 ft 

on the pediment slope of the San Augustin and San Andres 

Mountains. A thin soil profile consisting mostly of granite 

wash covers much of the terrain, but granite outcrops are visible across the surface of the pediment. Vegetation consists 

mostly of perennial grasses, woody brushes, yucca, prickly 
Introduction 3

Las

Cruces

WHITE

SANDS

MISSILE

RANGE

El Paso

Lincoln County

Socorro County

Sierra County

Doña Ana County

Otero County

Rio Grande

Alam ogordo

S ocorro

Rio Grande

Ele p ha nt

Butte

Re se rvo ir

Oscura Mountains

NE W ME X IC O

NE W ME X IC O

ME X IC O

T E X AS

5 4

3 8 0

7 0

5 4

2 5

Organ Mtns

Jarilla Mtns

B

A

S I N

T

U L A

R

O

S

A

Sacramento Mountains

JIC AR IL L A

MTNS

San Andres Mountains

Franklin Mtns

3 4 °

0 0  ́

3 3 °

0 0  ́

3 2 ° 0 0  ́

1 0 7 °0 0  ́ 1 0 6 °0 0  ́

0

0

10

10

2 0 MIL E S

2 0 K IL O ME T E R S

Holloman

Air Force

Base

San Augustin

 Mtns

Fort Bliss

Military

Reservation

Main Post

STUDY

AREA

Map location

New Mexico

Texas

10

25

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

Figure 1. Location of White Sands Missile Range, New Mexico, and the study area. 
4 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

3

4

EMRE1

EMRE2

50

49

48

46

45

44

43

42

41

40 39

38

37

36 35

33

32

28

27

25

23 22

29

51

Halcox Windmill

Markham Spring

Bonney Spring Mine windmill

5,000

4,700

4,600

4,500

4,400

4,300

4,200

4,100

5,300

5,50

5

0

6, 00

5,700

5,800

5,900

6,000

4,800

4,900

5,400

5 1, 00

5 2, 00

20

17

5,600

32o

26'

0 2 KILOMETERS

Base from U.S. Geological Survey digital data, 1994, 1:100,000 0 2 MILES

Universal Transverse Mercator Zone 13N, NAD 83

Fault, fault zone, and fold and thrust zone from Seager, 1981

EXPLANATION

Paved road

Dirt road

Topographic contour—contour interval

100 feet, datum is NAVD 88

I

(

.

!

I 34

Monitoring well and designation, used as part of the 1996–2006 transect analysis

Monitoring well and designation, used as part of the October 2005 analysis 

Windmill (open well) and designation, used as part of the October 2005 analysis

Production well and designation, used as part of the 1996–2006 transect analysis

Spring and designation, used as part of the October 2005 analysis

!

 24

!

 13

16D

 16

!

!

 15

 14

 11

 10A

 12

 21

!

!

 31

!

 30

 18

19

!

 26

!

!

32o

28'

32o

30'

106° 32' 106° 30' 106° 28' 106° 26'

San Andres Mountains

Highway 70

White Sands Missile Range

Main Post 1.5 miles

Antelope Hill

OB/OD site

Mineral Hill

Bear Peak Fold and Thrust Zone

Black Prince Fault Zone

Hazardous Test Area

Black Mountain

!

!

!

!

!

Normal fault—bar and ball on 

downthrown side

(

5

Ephemeral channel

47A

San Augustin Pass San Augustin Mountains

HTA

Windmill

!

!

!(

!(

! !

!

!

!

!

!

! !

!!

!.

!

!

!

! !

!

!

! !

!

!

!

!

!

!

!

!

!

!(

! !

!(

!

Organ Mountains Fault

HTA access road

Monitoring sites (table 1)

40

43

5

3

Markham

 Spring

Figure 2. Hazardous Test Area, Open Burn/Open Detonation (OB/OD) site, and monitoring sites, White Sands Missile Range, 

New Mexico.
Introduction 5

3 46

28

27

23

20

12 16

24

19

11

! !

!

!

!

!

!

!

!

!

5,200

106o 31'

 29'

106o 30'

2006

 32°

 30'

5,300

5,400

5,500

5,600

5,700

5,800

5,900

6,000

!

 32°

3

28

27 23

20

12 16

24

19

11

! !

!

!

!

!

!

!

!

5,200

106o 31'

 29'

106o 30'

2000

3

46

28

27

23

20

12 16 24

19

11

! !

!

!

!

!

!

!

!

!

5,200

106o 31'

 29'

106o 30'

2006

 32°

 30'

5,300

5,500

5,400

5,600

5,700

5,800

5,900

6,000

!

 32°

 32°

 30'

5,300

5,500

5,400

5,600

5,700

5,800

5,900

6,000

!

 32°

3

28

27 23

20

12 16

24

19

11

! !

!

!

!

!

!

!

!

5,200

106o 31'

 29'

106o 30'

2000

 32°

 30'

5,300

5,400

5,500

5,600

5,700

5,800

5,900

6,000

!

 32°

3

28

27 23

20

12 16

24

19

11

! !

!

!

!

!

!

!

!

5,200

106o 31'

 29'

106o 30'

2000

3 46

28 27

23

20

12 16 24

19

11

! !

!

!

!

!

!

!

!

!

5,200

106o 31'

 29'

106o 30'

2006

 32°

 30'

5,300

5,400

5,500

5,600

5,700

5,800

5,900

6,000

!

 32°

 32°

 30'

5,300

5,500

5,400

5,600

5,700

5,800

5,900

6,000

!

 32°

1

10

0.1

10

 1

0.1 0.1

10

5 5

OB/OD site OB/OD site

OB/OD site OB/OD site

OB/OD site OB/OD site

0.2

0.2

10

20

0.2

10

5

Extension of plume

from additional 

wells in 2002

0.2

Well 46 added

in 2002

Base from U.S. Geological Survey digital data, 1994, 1:100,000

Universal Transverse Mercator Zone 13N, NAD 83

OB/OD site is the Open Burn/Open Detonation site

EXPLANATION

Topographic contour—contour interval 100 feet, datum is NAVD 88

Isoconcentration contour—contour interval indicated in italic bold, 

dashed where approximated

5,700

Paved road

0 1 KILOMETER

0 1 MILE

! Monitoring site and designation

(table 1)

Selected wells shown

for spatial reference

HTA access road

HTA access road

HTA access road

HTA access road

HTA access road

HTA access road

RDX, in micrograms per liter

Perchlorate, in milligrams per liter

Perchlorate, in milligrams per liter

RDX, in micrograms per liter

Nitrate plus nitrite as nitrogen, 

in milligrams per liter

Nitrate plus nitrite as nitrogen, 

in milligrams per liter

46

Figure 3. Example of relative stability of contaminant concentrations in ground water at the Open Burn/Open 

Detonation (OB/OD) site, White Sands Missile Range, New Mexico, 2000 and 2006 (modified from Ralph Wilcox, U.S. 

Geological Survey, written commun., 2003 and 2006).
6 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

pear, and barrel cactus. A series of nearly parallel ephemeral 

drainage channels extend east-southeast across the OB/OD 

site and continue through the HTA area to the valley floor 

of the Tularosa Basin (major ephemeral drainages shown in 

figure 2). The climate of the Tularosa Basin is semiarid, the 

basin averages less than 10 inches of precipitation per year for 

the interior of the basin, and average minimum and maximum temperatures range from 40 to 78°F (Western Regional 

Climate Center, 2007). The mountains bounding the basin 

average greater annual precipitation, and the eastern flank of 

the Organ, San Augustin, and San Andres Mountains typically 

receive 10 to 16 inches of precipitation per year (Waltemeyer, 

2001). 

Geology and Hydrology

The study area is surrounded by the San Andres Mountains to the north, San Augustin Mountains to the west, the 

Organ Mountains to the south, and the floor of the Tularosa 

Basin to the east (figs. 1 and 4). The San Augustin Mountains 

represent a transition from the Organ Mountains’ granite 

batholith to the tilted and faulted, Paleozoic marine strata of 

the San Andres Mountains (Seager, 1981). The Hazardous 

Test Area is located on a pediment composed of a granite 

pluton of Precambrian age bounded on the north by the Bear 

Peak Fold and Thrust Zone, the Black Prince Fault Zone to 

the west, the Organ Batholith to the south, and the Organ 

Mountains Fault to the east (Seager, 1981) (fig. 4). The granite 

pluton is an eroded part of an ancient mountain or rift system 

formed 1.45 to 1.35 Ga that was followed by a subsequent 

Precambrian extensional event that emplaced diorite-diabase 

dikes in the area (Seager, 1981; Raatz, 2002; New Mexico 

Bureau of Geology and Mineral Resources, 2003). Movement 

of the pluton occurred during the Laramide Orogeny (80 and 

40 Ma) and Rio Grande Rift deformation (35 Ma to present), 

and the pluton was likely rotated to its present configuration 

with movement along the Organ Mountains Fault, the Bear 

Peak Fold and Thrust Zone, and the Black Prince Fault Zone 

(Seager, 1981). Structural relations between the Precambrian 

granite pluton, the Bear Peak Fold and Thrust Zone, and the 

Black Prince Fault Zone indicate that Laramide deformation 

produced vertical uplift in a regional compressional environment (Seager, 1981). This uplift produced the current slope 

and configuration of this pediment basin that drains east to 

southeast to the floor of the Tularosa Basin. 

In the study area, a thin veneer (5 to 10 ft) of well-mixed, 

weathered-granite alluvium and a larger-clast, granite wash 

overlie the weathered, upper layer of the Precambrian granite 

pluton (fig. 4). The surface exposure of the pediment granite 

of the HTA basin is densely jointed, and a combination of 

granular disintegration, exfoliation, and spherical weathering produces outcrops of rounded boulders, knobs, and hills 

(Seager, 1981). The pluton consists of two types of granite—

one is gray/brown with a somewhat porphyritic texture and the 

other is bright red and contains abundant coarse-grained, pink, 

orthoclase feldspar. Diorite dikes are common in the granite 

outcrops, the dikes trend east to northeast at the surface, and 

typically range from 1 to 11-ft thick but can be as much as 

100-ft thick (Seager, 1981). The principal minerals in the dikes 

are green amphibole and plagioclase feldspar, ranging in composition from labradorite to oligoclase (Dunham, 1935). The 

diorite origin is unknown but may have been emplaced in the 

Precambrian when diorite-diabase intrusions formed during an 

extensional environment (Raatz, 2002) or may be associated 

with the andesitic volcanism during emplacement of the Organ 

Batholith during the Eocene (Maciejewski, 1996). 

The fractured-granite aquifer at HTA is almost entirely 

within the granite pluton. Paleozoic marine strata—including 

sandstone, dolomite, shale, and limestone formations—are 

adjacent to the Precambrian granite along the northern 

perimeter across the Bear Peak Fold and Thrust Zone (Seager, 

1981). Aquifer recharge likely occurs along the pediment/

mountain-front interface and possibly in the ephemeral 

channels (Risser, 1988). Ground-water flow paths are 

probably tortuous because flow paths are controlled by the 

geometry of hydraulically conductive fractures. Boreholes 

drilled for installation of monitoring wells did not produce 

water until such a fracture(s) was penetrated, but the extent 

and distribution of the fractures in the study area are poorly 

understood. Fracture orientation is highly variable at the OB/

OD site—orientation and dip of fractures were distinctly 

different between fractures penetrated during exploratory 

drilling in the east and west pits and also variable in the HTA 

area (Ralph Wilcox, U.S. Geological Survey, written commun. 

2003). 

Anthropogenic Compounds

Since 1996, contamination of ground water at HTA 

has been evident (Ralph Wilcox, U.S. Geological Survey, 

written commun., 2003). The largest concentrations have 

remained near and around the OB/OD pits, and contaminant 

concentrations in ground water at all monitoring wells have 

remained relatively stable (Ralph Wilcox, U.S. Geological 

Survey, written commun., 2003) (fig. 3). Detection of 

the contaminants in ground water at the site prompted 

WSMR personnel to authorize an investigation of soil 

and rock samples from the surface and subsurface in and 

around the OB/OD pits in 1999. RDX and other explosive 

compounds (1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX); 

2,4,6-dintrotoluene (246-DNT); 4-amino-2,6-dinitrotoluene 

(426-DNT); 2,4,6-trinitrotoluene (246-TNT); and tetryl) were 

detected in pit-soil samples. The largest concentrations were 

of RDX, and HMX was the most prevalent (Ralph Wilcox, 

U.S. Geological Survey, written commun., 2003). The largest 

explosives concentrations were in surface samples collected 

from the west pit, particularly along the southwestern border 

(Ralph Wilcox, U.S. Geological Survey, written commun., 

2003). Nitrate was detected in 72 of 96 soil/rock samples in 

the pits and 38 of 43 samples around the pits and ranged from 

0.1 to 18.5 milligrams per kilogram; concentrations were 

larger in the west pit than the east pit (Ralph Wilcox, U.S. 
Introduction 7

Black Mountain

Rattlesnake

Ridge

Mineral Hill

Black Prince

Canyon

San Augustin

Mountains

San Andres

Mountains

7 0

Organ Mountains Fault

3,000

4,000

5,000

6,000

7,000

MILES

8,000

0 1 2 3 4 5

ELEVATION, IN FEET

C

C’

C

C’

OB/OD pits Black Prince Fault Zone

Bear Peak Fold and Thrust Zone

106° 32' 106° 30' 106° 28'

32o

28'

32o

30'

Mountain front interface

(no layering shown)

Pediment block—unweathered, fractured granite pluton and diorite dikes

and highly variable orientation of fractures and dikes

(Ralph Wilcox, U.S. Geological Survey, written commun. 2003)

Layers are not to scale

1

2

3

1 Thin (generally 5 to 10 feet) veneer of gravelly soil

2 Granite wash—angular, coarse-grained rock debris, 

 highly variable thickness (range of 0 to 35 feet at the OB/OD pits)

3 Weathered granite—rind of weathered granite, upper competent

 layer of the pluton, highly variable thickness (range of 10 to 100

 feet) at the OB/OD site

(Ralph Wilcox, U.S. Geological Survey, written commun. 2003)

Black Prince fault zone,

likley steep normal faults

in this area (Seager, 1981)

Precambrian granite pluton with diorite dikes

!

Normal fault—bar and ball on 

downthrown side

Thrust fault—saw teeth on 

upthrown side

Base from U.S. Geological Survey National Elevation Dataset,

1/9 arc second, 1:24,000, 2007

Universal Transverse Mercator Zone 13N, NAD 83

Faults, fault zones, and fold and thrust zones from Seager, 1981

Paleozoic strata

Open Burn/Open Detonation (OB/OD) pits

Figure 4. Geologic characteristics of the fractured-granite pluton at the Hazardous Test Area, White Sands Missile Range, New Mexico.
8 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

Geological Survey, written commun., 2003). Perchlorate was 

less prevalent than the explosives but was found in and around 

the OB/OD pits in surface and subsurface samples. Pieces 

of solid rocket fuel containing perchlorate have been found 

at the surface in and around the OB/OD pits (Ralph Wilcox, 

U.S. Geological Survey, oral commun., 2005). The source 

of contamination appears to be focused within the pits, but 

ordnance demolition also has scattered the source materials 

outside of the pits.

RDX is a highly energetic cyclic nitroamine and is a 

commonly used military explosive. It is soluble in water 

(about 38–100 mg/L possible), and sorption of RDX to soil 

material is variable but typically low (Seth-Smith and others, 

2002). Degradation of RDX in ground water mainly occurs 

under anaerobic conditions and is facilitated by certain 

bacteria (McCormick and others, 1981; Kitts and others, 1994; 

Speitel and others, 2001). RDX will sequentially degrade to 

MNX, DNX, and TNX, and may undergo further degradation 

with cleavage of the ring formation to produce basic carbon 

and nitrogen compounds such as carbon dioxide, methane, 

nitrate, and ammonia (McCormick and others, 1981; Hawari 

and others, 2000). RDX also can degrade in oxygenated water 

and in the presence of select bacteria and fungus (Fournier 

and others, 2002; Seth-Smith and others, 2002; Thompson and 

others, 2005). Aerobic bacteria utilizing RDX as a nitrogen 

source may cause ring cleavage to produce 2,4-diazabutanal, 

ammonia, nitrous oxide, formaldehyde, and carbon dioxide 

(Fournier and others, 2002). However, other bacteria are 

capable of using RDX as a carbon and nitrogen source and 

may produce 2,4-diazabutanal, nitrate, and formaldehyde 

(Thompson and others, 2005).

Nitrate is stable in a range of environments, is highly 

soluble, and moves readily with the flow of water (Hem, 

1989). The biodegradation of nitrate (denitrification) by 

microorganisms is most efficient in anaerobic conditions 

and produces nitric oxide, nitrous oxide, and nitrogen gas 

(Wendland and others, 1994). Degradation of nitric oxide and 

nitrous oxide will produce nitrogen gas as the final byproduct. 

Denitrification occurs readily in anaerobic conditions because 

nitrate is the dominant electron acceptor when oxygen is 

deficient (Wendland and others, 1994; Chapelle, 1993). 

Although the available free energy from the reduction of 

nitrate is similar to that of oxygen, the reduction of oxygen is 

more thermodynamically favorable. Additionally the activity 

of the denitrifying enzyme, nitrate reductase, is inhibited by 

the presence of molecular oxygen (Chapelle, 1993). 

Perchlorate is used as a rocket propellant because of its 

strong oxidizing properties (Brown and Baohua, 2006). It is 

highly soluble in water (maximum of 185 grams per liter) 

and generally will not adsorb to soil material (Urbansky and 

Brown, 2002). These characteristics allow perchlorate to easily move with ground-water flow. Many bacteria in aqueous 

environments can use perchlorate as a reducing compound to 

oxidize other compounds, leading to the degradation of perchlorate to chlorate (ClO3

–

) and chlorite (ClO2

–

) (Coates and 

Achenbach, 2004). Further degradation results in the release of 

chloride and oxygen (Van Ginkel and others, 1996). 

Previous Studies

No published documents are available that describe the 

HTA fractured-granite aquifer. From 1996–2006, the USGS 

provided quarterly data reports of HTA ground-water monitoring to WSMR for submission to the State of New Mexico 

under RCRA guidelines. All annual ground-water-level data 

and ground-water-quality data collected by the USGS in the 

HTA area from 1996–2006 are available in the USGS National 

Water Information System (NWISWeb at http://waterdata.

usgs.gov/usa/nwis).

Study Methods

Contaminant data were compiled for 18 (table 1 and 

fig. 5) of 47 sites in the existing monitoring-site network 

for the period of record (1996–2006). Dissolved oxygen, 

pH, and water level for ground water at these wells were 

collected during sampling and are included in the analysis 

where applicable. In addition to contaminant and field data, 

ground-water tracer data were compiled for monitoring sites 

sampled in October 2005. The tracer data includes dissolved 

solids, trace elements, major ions, tritium-helium dating, RDX 

degradates (MNX, DNX, and TNX), dissolved gases, stable 

isotopes of water, nitrogen and oxygen isotopes of nitrate, 

and sulfur isotopes of sulfate (table 2). Of these tracers, only 

dissolved-solids and trace-element concentrations are available 

for all sites in the HTA monitoring network for October 2005; 

selected sites were sampled for analysis of the remaining 

tracer data. The October 2005 data represent a “snapshot” 

of the ground-water characteristics for interpretation of the 

natural attenuation processes of dilution and degradation. 

The selected tracer constituents are applicable for evaluating ground-water flow paths and geochemical processes such 

as water-rock interaction and changes in reduction-oxidation 

conditions. Dissolved-solids, major-ion, and trace-element 

concentrations can provide general compositional characteristics and are indicators of water-rock interactions and possible 

reduction-oxidation conditions (Hem, 1989). Ground-water 

age can be determined through the analysis of radioactive 

isotopes, such as tritium that is incorporated into precipitation 

and carried to an aquifer through recharge. A more accurate 

method of dating than simply using tritium is the tritiumhelium method, which mass balances the helium isotopes to 

determine the amount of 3He derived from radioactive decay 

of 3H in the water sample (Schlosser and others, 1989). The 

application of water isotopes (2/1H as δ2H and 18/16O as δ18O) 

allows constraint of hydrologic flow paths because of the 

variation in isotopic composition of precipitation that may 

discriminate recharge areas (Genereux and Hooper, 1998). 

Nitrogen and oxygen stable isotope ratios of nitrate (15/14N as 

δ15N and 18/16O as δ18O) and sulfur stable isotopes of sulfate 
Introduction 

9

Table 1. Open Burn/Open Detonation Site and Hazardous Test Area study area monitoring-site information.—Continued[USGS, U.S. Geological Survey; NAD 83, North American Datum of 1983; NAVD 88, North American Vertical Datum of 1988; ls, land surface; PVC, polyvinyl chloride; HTA, Hazardous Test Area; OB/OD, Open Burn/Open Detonation; NA, not available]

Site 

designation 

(figs. 2 and 5)

USGS site 

identification 

number

Latitude 

(NAD 83)

Longitude 

(NAD 83)

Land-surface 

altitude 

(NAVD 88)

Well depth 

(feet below 

ls)

Casing 

material

Screen 

interval (feet 

below ls)

Installed Dedicated 

pump

Transect A–A’: monitoring sites perpendicular to ground-water flow—well line is southwest to northeast immediately downgradient from east pit (fig. 5)

23 322935106311801 32 29 35.22N 106 31 17.48W 5,681.9 135 PVC 110-130 December 1999 Yes13 322938106311601 32 29 37.13N 106 31 15.84W 5,692.1 120 PVC 95-115 March 1998 Yes14 322939106311701 32 29 39.31N 106 31 16.69W 5,697.9 110 PVC 90-110 July 1995 No10A 322941106311502 32 29 39.82N 106 31 15.08W 5,690.1 80 PVC NA June 1995 Yes11 322941106311301 32 29 40.74N 106 31 15.04W 5,693.4 85 PVC 60-80 March 1991 Yes20 322943106311401 32 29 42.75N 106 31 13.30W 5,701.5 100 PVC 75-95 March 1998 Yes24 322947106311101 32 29 46.61N 106 31 10.95W 5,694.1 163 PVC 139-159 December 1999 No

Transect B–B’: monitoring sites parallel to ground-water flow—well line is northwest to southeast from upgradient from the OB/OD pits to the SE corner of the HTA area (fig. 5)

12 322943106312301 32 29 43.21N 106 31 23.61W 5,757.4 155 PVC 130-150 March 1991 Yes10A 322941106311502 32 29 39.82N 106 31 15.08W 5,690.1 80 PVC NA June 1995 Yes16 322937106310901 32 29 37.77N 106 31 08.50W 5,643.3 103 PVC 78-98 March 1997 Yes16D 322937106310902 32 29 37.50N 106 31 08.16W 5,640.1 160 PVC 134-154 March 1998 Yes19 322935106310301 32 29 34.69N 106 31 02.79W 5,597.0 147 PVC 122-142 March 1998 Yes18 322932106305601 32 29 31.24N 106 30 54.71W 5,538.7 130 PVC 105-125 March 1998 Yes27 322927106305101 32 29 26.86N 106 30 51.19W 5,496.6 179 PVC 159-179 December 1999 No28 322923106304601 32 29 23.50N 106 30 46.38W 5,453.4 149 PVC 120-140 December 1999 Yes3 322910106303601 32 29 11.68N 106 30 37.13W 5,357.9 160 PVC 60-150 Feburary 1984 Yes46 322906106300301 32 29 06.27N 106 30 02.51W 5,159.2 145 PVC 120-140 January 2002 Yes43 322857106292801 32 28 57.00N 106 29 27.85W 4,956.9 99 PVC 77-97 January 2002 Yes45 322823106283501 32 28 23.34N 106 28 34.57W 4,637.7 139 PVC 78-138 January 2002 Yes

Monitoring sites used for the snapshot analysis of data from October 2005 (fig. 2)

4 322913106301801 32 29 13.95N 106 30 20.58W 5,269.5 72 Steel NA NA Yes5 322756106311601 32 27 55.67N 106 31 15.74W 5,360.0 122 Steel NA NA No15 322938106310801 32 29 38N 106 31 08W 5,645.1 102 PVC 77-97 July 1996 Yes17 322936106311001 32 29 36N 106 31 10W 5,643.6 110 PVC 85-105 March 1991 Yes21 322933106310901 32 29 33N 106 31 09W 5,621.5 110 PVC 85-105 November1999 Yes
10 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico Table 1. Open Burn/Open Detonation Site and Hazardous Test Area study area monitoring-site information.—Continued [USGS, U.S. Geological Survey; NAD 83, North American Datum of 1983; NAVD 88, North American Vertical Datum of 1988; ls, land surface; PVC, polyvinyl chloride; HTA, Hazardous Test Area; OB/ OD, Open Burn/Open Detonation; NA, not available] Site designation (figs. 2 and 5) USGS site identification number Latitude (NAD 83) Longitude (NAD 83) Land-surface altitude (NAVD 88) Well depth (feet below ls) Casing material Screen interval (feet below ls) Installed Dedicated pump 22 322924106310501 32 29 24N 106 31 05W 5,559.3 110 PVC 85-105 December1999 Yes 25 322943106310501 32 29 43N 106 31 06W 5,645.7 120 PVC 95-115 December1999 Yes 26 322940106305101 32 29 40N 106 30 51W 5,533.7 200 PVC 180-200 December1999 Yes 29 322944106311601 32 29 44N 106 31 16W 5,725.5 158 PVC 134-154 December1999 Yes 30 322939106305701 32 29 39N 106 30 57W 5,570.2 200 PVC 176-196 December1999 Yes 31 322902106302201 32 29 02.48N 106 30 23.94W 5,251.7 85 PVC 65-85 January 2002 Yes 32 322924106302601 32 29 24.05N 106 30 28.27W 5,343.8 75 PVC 55-75 January 2002 Yes 33 322848106305501 32 28 48.42N 106 30 56.83W 5,368.8 107 PVC 87-107 January 2002 Yes 34 322943106312801 32 29 43.48N 106 31 29.88W 5,794.9 103 PVC 83-103 January 2002 Yes 35 322704106290601 32 27 04.61N 106 29 08.01W 4,618.4 159 PVC 139-159 January 2002 No 36 322702106294401 32 27 02.71N 106 29 46.23W 4,798.5 97 PVC 77-97 January 2002 No 37 322639106294701 32 26 39.52N 106 29 49.2W 4,695.9 138 PVC 118-138 January 2002 No 38 322624106300201 32 26 24.82N 106 30 04.01W 4,723.9 119 PVC 99-119 January 2002 No 39 322612106294901 32 26 12.48N 106 29 50.73W 4,649.4 149 PVC 129-149 January 2002 No 40 322609106291401 32 26 09.26N 106 29 15.93W 4,513.6 199 PVC 179-199 January 2002 No 41 322731106281901 32 27 31.72N 106 28 21.12W 4,502.1 125 PVC 105-125 January 2002 Yes 42 322837106294301 32 28 37.33N 106 29 44.64W 4,993.5 137 PVC 117-137 January 2002 Yes 44 322745106300201 32 27 45.75N 106 30 04.4W 4,938.3 139 PVC 119-139 January 2002 No 47A 322827106280101 32 28 27.04N 106 28 03.31W 4,491.7 184 PVC 160-180 February 2003 No 48 322538106285701 32 25 37.84N 106 28 58.55W 4,406.4 159 PVC 139-159 January 2002 No 49 322508106291001 32 25 08N 106 29 11.62W 4,411.8 419 PVC 389-419 December2001 Yes 50 322834106273201 32 28 33.64N 106 27 33.38W 4,366.4 516 PVC 486-516 January 2002 Yes 51 322901106290101 32 29 00.93N 106 29 03.39W 4,834.8 145 PVC 122-142 February 2003 No
Introduction 11

Table 1. Open Burn/Open Detonation Site and Hazardous Test Area study area monitoring-site information.—Continued[USGS, U.S. Geological Survey; NAD 83, North American Datum of 1983; NAVD 88, North American Vertical Datum of 1988; ls, land surface; PVC, polyvinyl chloride; HTA, Hazardous Test Area; OB/OD, Open Burn/Open Detonation; NA, not available]

Site 

designation 

(figs. 2 and 5)

USGS site 

identification 

number

Latitude 

(NAD 83)

Longitude 

(NAD 83)

Land-surface 

altitude 

(NAVD 88)

Well depth 

(feet below 

ls)

Casing 

material

Screen 

interval (feet 

below ls)

Installed Dedicated 

pump

EMRE1 322804106301701 32 28 04N 106 30 17W 5,045.2 180 PVC 155-175 December1999 YesEMRE2 322800106300901 32 28 00N 106 30 09W 4,996.1 100 PVC 76-95 December1999 YesHTA Windmill 322310106305101 32 28 24N 106 50 52W 5,214.7 NA NA NA NAMarkham Spring 322952106314401 32 29 52.32N 106 31 45.99W 6,062.2 NA NA NA NA YesBonney Spring 

Mine Windmill

322938106291101 32 29 37.58N 106 29 10.67W 5,042.1 62 Steel NA NA No

Halcox Windmill 322711106290401 32 27 11.33N 106 29 05.98W 4,642.0 37 NA NA NA No
12 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

3

46

45

43

28

27

23

2 0

18

16

14

12

24

19

13

11

16D

10A !!

!

!

! !!

!

!

!

!

!

!

!

5

!

!

!

4,800

0, 5 0 0

5 1, 0 0

4 6, 0 0

5,200

5 3, 0 0

5 ,4 0 0

5 6, 0 0

5 7, 0 0

6 ,0 0 0

5 5, 0 0

7, 4 0 0

5 ,8 0

9, 5

0

0 0

4 9, 0 0

106o 31'

3 0°

2 8'

0 0.5 KILO ME TE R

0 0.5 MILE

3 2°

2 9'

3 2°

30'

106o 30' 106o 29'

5,600

EXPLANATION Paved road

Open burn/open detonation (OB/OD) pit Topographic contour—contour interval 100 feet, datum is NAVD 88

Dirt road Monitoring site and designation ! 45 Well transect

A

A’

B

B’

Inset area

23

20

16

14

12

24

13

11

16D

10A

!

!

!

!

!

!!

!

!

A’

!

A

B

19

A A’ Base from U.S. Geological Survey digital data, 1994, 1:100,000 Universal Transverse Mercator Zone 13N, NAD 83

!

B’

OB/OD site

east pit

west pit

Figure 5. Location of the study’s monitoring-site transects at the Hazardous Test Area, White Sands Missile Range, New Mexico. 
Introduction 13

Table 2. Sample analytes and laboratory analysis methods.

[μg/L, micrograms per liter; mg/L, milligrams per liter; μmol/L, micromoles per liter; USGS, U.S. Geological Survey; ‰, per mil]

Constituent(s) Description Method/Lab 

code

Analytical 

precision

Contaminant and field data collected from 1996–2006:

Explosives

Explosive compounds1, including 

RDX and its degradates, analyzed 

by HPLC1

SW846 83302 0.05 to 0.25 μg/L

Nitrate NO3 and NO2 as N MCAWW 353.23 0.02 mg/L

Perchlorate ClO4 TestAmerica DEN LC-0024 (SW68602) 0.01 μg/L

Field values Dissolved oxygen, pH YSI 550A (+0.3 mg/L), Orion 250A+ (±0.02 pH) ±0.3 mg/L, ±0.02 pH

Tracer data collected in October 2005:

Dissolved gases Ar, CH4, CO2, He, N2, O2

Gas chromatography with thermal conductivity 

detector (Ar, He, N2, O2) and flame ionization 

detector (CH4, CO2)

±0.1 μmol/L

Major ions Br, Cl, F, SO4, Ca, Mg, Na, K MCAWW 300.0A3, SW846 6010B2 0.1 to 1 mg/L

Tritium-helium 

dating 3

H/3He USGS 1033 (Schlosser and others, 1989) ±0.5 years

Water isotopes 2/1H, 18/16O USGS 1142 (Coplen and others, 1991; Epstein and 

Mayeda, 1953)

±2 ‰ as δ2H and 

±0.2 ‰ δ18O

Nitrate isotopes 15/14N and 18/16O of nitrate USGS 2899 (Sigman and others, 2001) ±0.5 ‰ as δ15N and as δ18O

Sulfate isotopes 34/32S of sulfate USGS 1951 (Carmody and others, 1997; Glesemann 

and others, 1994) ±0.4 ‰ as δ34S

Trace elements

Ag, Al, As, B, Ba, Be, Cd, Co, Cr, 

Cu, Fe, Li, Mn, Mo, Ni, Pb, Sb, 

Se, Si, Sr, Tl, U, V, Zn

SW846 6010B2, SW846 60202 0.01 to 2 μg/L

1

RDX; HMX; tetryl; 2-amino-4,6-dinitrotoluene; 4-amino-2,6-dinitrotoluene; 1,3-, 2,4-, and 2,6-dinitrotoluene; nitrobenzene; 2-, 3-, and 

 4-nitrotoluene; 1,3,5-trinitrobenzene; and 2,4,6-trinitrotoluene by high-performance liquid chromatography.

2

 U.S. Environmental Protection Agency, 1983.

3

 U.S. Environmental Protection Agency, 1986.

(

34/32S as δ34S) can be indicators of possible nitrate or sulfate 

sources and biodegradation of nitrogen and sulfur-containing 

compounds (Kendall, 1998 and Canfield, 2001).

The 18 wells selected for analysis of 1996–2006 data 

represented two transects at the OB/OD site—one perpendicular to ground-water flow (transect A–A ́) and one parallel 

to ground-water flow (transect B–B ́). Transect A–A ́ (about 

0.25 mi in length) is located immediately downgradient from 

the OB/OD pits and was used to examine spatial and temporal variability of the contaminants coming from the OB/OD 

site. Transect B–B ́ (about 3.25 mi in length) is parallel to the 

direction of ground-water flow with an origin upgradient from 

the OB/OD pits and an endpoint downgradient from the pits 

where contaminants have not been detected. Trend analysis 

consisted of graphical and statistical comparison of contaminant concentrations between wells to identify source locations, 

transport characteristics, and possible natural attenuation of 

contaminants. All non-detect values (less than method detection level) were assigned zero values. The Wilcoxon ranksum test was used to test for differences in the contaminant 

concentration distributions between wells. This nonparametric 

test assesses whether two sets of non-normal data come from 

the same distribution (population) or not (Ott, 1993). 

To examine aquifer properties that affect contaminant 

movement, a well’s water level and the contaminants’ concentrations were analyzed for correlation strength. With the 

assumption that changes in ground-water flow and contaminant concentrations are related, correlation analysis was used 

to test the hypothesis that changes in flow are the cause of the 

small temporal variability of contaminant concentrations. In 

addition to correlation between water level and contaminant 

concentrations, RDX and nitrate concentrations were analyzed 

for strength of correlation to examine the relation of the explosive-based contaminant sources. The nonparametric Kendall’s 

tau rank correlation coefficient (Kendall, 1938) was used to 

evaluate the strength of correlation between any two variables. 

This method measures the degree of correlation between rankings of two groups to assess the strength of the relation.

This study implemented USGS study methods described 

by Lapham and others (1997), and ground-water sample col-
14 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

lection followed USGS guidelines established by Wilde and 

Radtke (2005). Water levels were measured below a known, 

fixed altitude prior to well purging using either an electric tape 

or steel tape. Ground-water samples were collected from all 

monitoring wells using dedicated bladder pumps or a portable 

submersible pump. A minimum of 20 gallons was purged from 

each monitoring well prior to sampling. Bladder pumps were 

operated using compressed nitrogen during well purging and 

sampling. All samples were analyzed by TestAmerica, Inc., 

in Arvada, Colorado, except for dissolved gas and isotope 

samples collected in October 2005. The October 2005 dissolved-gas and isotope samples were analyzed by the USGS 

Dissolved Gas Laboratory (dissolved gases), Lamont-Doherty 

Earth Observatory at Columbia University (tritium-helium 

age dating), and the USGS Reston Stable Isotope Laboratory 

(hydrogen, oxygen, nitrogen, and sulfur stable isotopes). 

Quality-assurance procedures were implemented for 

water-level measurements and to collect and process waterquality samples. Prior to purging, water levels were repeatedly 

measured with an electric tape to ensure stability and accuracy. 

During purging, specific conductance, water temperature, 

dissolved oxygen, and pH were measured in a flowthrough 

chamber and allowed to stabilize prior to sample collection. 

Stable field measurements were used to determine sufficient 

purge amounts for sampling formation water. After purging 

20 gallons, field measurements were deemed stable if three or 

more sequential measurements during a minimum 10-minute 

period were within the following ranges: specific conductance, 

+0.3 percent; temperature, +0.2°C; dissolved oxygen, +0.3 

mg/L, and pH, +0.1 standard unit (Wilde and Radtke, 2005).

Four types of quality-control samples were collected 

in the field: equipment blanks, replicates, matrix spikes, and 

trip blanks. One field-equipment blank was collected during 

each sampling round to determine the adequacy of cleaning 

procedures of the portable submersible pump. Two sequential 

replicate samples were collected at randomly selected wells 

to evaluate laboratory precision. One matrix-spike and one 

matrix-spike duplicate samples were collected to ascertain 

matrix interference. Trip blanks were included in all RDX 

sample shipments to TestAmerica, Inc. for examination of 

potential contamination from volatile organic compounds 

during transport. In addition, all laboratories used internal 

quality-assurance and quality-control practices including the 

analysis of laboratory-control and method-blank samples 

with submitted samples. Analysis of quality-control data did 

not indicate any issues with the quality of the data. Overall, 

concentrations in equipment and trip blanks were less than 

laboratory reporting levels, concentrations in replicates were 

within 10 percent of the environmental-sample concentrations, 

and matrix-spike and matrix-spike duplicate recoveries were 

within laboratory guidelines. 

Acknowledgments

The cooperation of many individuals and organizations 

was essential for completion of this study. The authors 

acknowledge the support and help of the Environmental 

Compliance Unit at WSMR. In particular, Jose Gallegos 

who helped guide this study and provided useful insight for 

completion of study goals.

Geochemical Trends of RDX, Nitrate, 

and Perchlorate in the FracturedGranite Aquifer

Contaminant trends in the fractured-granite aquifer at 

HTA can provide information concerning source location(s), 

transport, and natural attenuation of the contaminants. Differences in concentrations along transect A–A ́ (fig. 5) were used 

to identify wells closest to contaminant sources (or the largest 

contaminant sources) and provide information concerning the 

lateral dispersal of the sources. Ground-water data from wells 

along transect B–B ́ were used to evaluate downgradient transport and possible natural attenuation of the contaminants. 

Fracture Flow in the Fractured-Granite Aquifer

Ground-water flow in the HTA fractured-granite aquifer 

likely occurs only in discrete fractures that intersect the upper 

surface of the pluton where recharge may occur. Ground water 

was not produced during drilling until a substantial fracture or 

diorite dike was penetrated during installation of all monitoring wells (Ralph Wilcox, U.S. Geological Survey, written 

commun., 2003). The pluton body is mostly competent with 

a limited amount of dikes and fractures in the vertical profile 

(figure 6 provides an example of the vertical profile of the 

upper pluton). Typically only a few water-producing fractures 

were identified in each borehole during drilling. Greater depth 

of drilling did not always penetrate an increasing number of 

fractures, such as well 28 (fig. 6), where an additional 125 ft 

of vertical penetration did not intersect any additional waterproducing fractures beyond the deepest water-producing 

fracture at 178.5 ft below land surface. Fractures in the granite 

pluton dip in all directions, but the predominant orientation 

generally ranges from south to northeast (fig. 7). The angle of 

fracture dip also is variable, but clusters of fractures do appear 

to have similar dip angles (fig. 7). Connectivity between fractures or fracture systems is unknown, but some connectivity 

is assumed given the relatively smooth potentiometric surface 

(discussed in the following paragraph) found across HTA 

(fig. 8). As part of another investigation, an aquifer test in well 

11 produced a small response (about 2 inches of drawdown) 

in the adjacent well 10A that suggests some fracture connectivity in this area (Andrew Robertson, U.S. Geological Survey, 

oral commun., 2008). 
Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer 15

 0

 10

20

30

40

50

60

70

80

90

100

110

120

130

Soil with weathered granite 

fragments

Weathered granite

Granite, slight moisture

Diorite, slight moisture 

at 25 to 27.5 feet

Granite, soft

Granite, harder than above layer, 

moist zone

Possilbe pegmatite, fracture zone

Granite, dry except for slight 

moisture at 84 to 86 feet

and at 98 feet

Minor water-producing fracture

Granite, dry, except some moisture

at 103 feet

Granite, some moisture

Granite, fractured, iron staining, 

some moisture airlift discharge at 

123 feet of 1 gallon per minute

Granite, hard, 

fracture at 132.5 to 133 feet

with abundant iron staining

140

150

160

170

180

190

200

210

220

230

240

250

260

270

280

290

Granite, hard

Diorite

Granite, small amount of 

iron staining

Diorite, some iron staining, airlift 

discharge measured at 178.5 feet 

of 3.5 gallons per minute

Granite, no iron staining, airlift 

discharge at 195 feet was the 

same as at 178.5, no additional

water

Granite, airlift discharge

measured at 243 feet was same

as at 178.5 feet, no additional

water

No additional water-producing

fractures penetrated in the 

bottom 120 feet of the borehole

No data

BOREHOLE IMAGE

DRILLING LOG DRILLING LOG

Scale

(feet) S W N E S

Scale

(feet)

Scale in feet and represents

depth below land surface

BOREHOLE IMAGE

S W N E S

Variable fracture 

orientation indicated by

different fracture shapes

shown in the unwrapped

borehole image

Figure 6. Borehole image and drilling log from construction of well 28 at the Hazardous Test Area, December 1999.
16 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

WEST PIT EAST PIT 16D 19 18 27 28

 0

 10

 20

 30

 40

 50

 60

 70

 80

 90

100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250

260

270

280

290

300

310

 25

 50

 75

100

vector mean

N

percent

Direction of fracture dips: each 10-degree-wide slice of the rose diagram shows the percent of fractures dipping within ±45 degrees of the center of the slice.

0 90 0 90 0 90 0 90 0 90 0 90 0 90

Tadpoles indicate a fracture location,head location is 

degree of dip on the horizontal scale (0 to 90), and tail

points in the azimuth direction of dip.

BOREHOLE BOREHOLE WELL WELL WELL WELL WELL

DEPTH BELOW LAND SURFACE, IN FEET

Figure 7. Fracture orientation in the granite pluton at boreholes in the Open Burn/Open Detonation pits and for selected wells 

downgradient from the pits.
Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer 17

, 4 0 6 0

, 4 5 5 0

, 4 5 6 0

, 4 0 7 0

, 4 5 8 0

4 7, 5 0

4 9, 0 0

4 9, 5 0

5 2, 5 0

4 8, 0 0

5 0, 0 0

5 2, 0 0

5 0, 5 0

5 1, 0 0

5 1, 5 0

5 3, 5 0

5 4, 5 0

5 4, 0 0

5, 5 0 0

5 6, 5 0

5 7, 0 0

, 5 0 6 0

5 6, 0 0

5 3, 0 0

5 5, 5 0

5 6, 5 0

5 ,2 9 0

5 8 5.0

5 ,2 8 9 .0

5 ,2 3 9 .2

4 ,9 4 5 .4

4 ,9 3 6 .7

5 ,0 7 4 .4

4 ,5 6 1 .0

4,88 5.8

4 ,9 2 8 .0

5 ,7 4 4 .6

5 ,3 0 9 .8

5,311 .1

5,2 0 8 .8

5 ,4 7 6 .8

5 ,63 0.1

5 ,3 9 2 .6 4

5 ,4 3 1 .5 5

5

,5 5 8 .8

5 ,5 9 0 .0

5 ,4 6 3 .8

5 ,5 5 1 .2

5 ,5 5 7 .3

1

4 ,7 4 8 .7

5 ,3 7 3 .8

!

(

!

!

!

! !

!

!

! !

!

!

!

!

!

!

!

5

!

!

!

!

!

!

!

!

!

(

!

!

(

(

!

!

, 4 08 0

0, 5 00

5 1, 00

, 4 06 0

, 5 02 0

5 3, 00

5 4, 00

5 6, 00

5 7, 00

6 0, 00

5 5, 00

7, 4 00

5

8, 0

9, 5

0

00

, 4 09 0

32o

30'

106 ̊ 31' 106 ̊ 30' 106 ̊ 29'

5,011.0

32o

29'

32o

28'

, 4 06 0

, 4 55 0

6, 4 05

, 4 07 0

, 4 58 0

, 4 57 0

4 9, 00

4 9, 50

5 2, 50

, 4 08 0

5 0, 00

5 2, 00

5 0, 50

5 1, 00

5 1, 50

, 5 53 0

5 4, 50

, 5 04 0

5, 5 00

, 5 56 0

, 5 07 0

, 5 06 0

, 5 06 0

, 5 03 0

5 5, 50

, 5 56 0

5,290.0

5,585.0

5,289.0

5,239.2

4,945.4

4,936.7

5,074.4

4,560.9

4,885.8

4,928.0

5,744.6

5,309.8

5,311.2

5,208.8

5,476.8

5,630.1

5,392.6

5,431.5

5,558.8

5,590.0

5,463.8

5,551.2

5,557.3

4,748.7

5,164.6

5,422.2

5,373.8

4,600

0 0.5 KILOMETER

0 0.5 MILE

EXPLANATION Open burn/open detonation 

(OB/OD) pit locationPaved road

Dirt road

Topographic contour—countour interval 100 feet, datum is NAVD 88

Well and potentiometric-surface elevation ! ( 5 Possible fault of unknown strike and slip

5,600

Black Mountain

5,600 Potentiometric contour—shows altitude of water level in cased well, October 2006. 

Dashed where approximated. Contour interval 50 feet. Datum is NAVD 88.

5,623.1

5,617.6

5,623.1

5,617.6

5,553.9

5,585.0

5,659.5

5,466.0

Base from U.S. Geological Survey digital data, 1994, 1:100,000Universal Transverse Mercator Zone 13N, NAD 83

Hazardous Test Area

OB/OD site

5,585.0

Ground-water flow direction

Figure 8. Potentiometric-surface contours and ground-water flow paths in the Hazardous Test Area fractured-granite aquifer, 

New Mexico, October 2006.
18 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

The potentiometric surface of the fractured-granite 

aquifer in October 2006 is parallel to the topographic 

gradient, and the gradient of both surfaces is about 7 percent 

(fig.8). Ground-water flow at the local scale will follow 

fracture orientation. Regional fracture connectivity would 

allow ground-water flow perpendicular to the potentiometric 

contours, which is southeastward away from the OB/OD 

site and towards the valley floor of the Tularosa Basin. 

Ground water in the fractures penetrated by monitoring 

wells does not have sufficient hydraulic head to reach land 

surface (fig. 8), but is pressurized (confined or semi-confined 

aquifer) and rises above the water-producing fractures in all 

wells. A divergence between land surface and the fracturedgranite aquifer’s potentiometric surface about 0.25 to 0.5 mi 

downgradient from the pits (fig. 9) may be an indicator of 

recharge variability at the mountain-front interface and OB/

OD pits and disconnection of fractures penetrated by the 

monitoring wells. The potentiometric surface and depth to 

water-producing fractures were similar in this location (fig. 9). 

The past use of the demolition pits possibly altered fracture 

patterns and recharge in the pit area (Ralph Wilcox, U.S. 

Geological Survey, written commun., 2003). Recharge at the 

OB/OD pits is demonstrated by the presence of RDX and 

perchlorate in downgradient ground water, and recharge may 

have been enhanced from construction of the pits that formed 

catchment basins.

The potentiometric-surface irregularity at the OB/OD 

pits near the 5,650 and 5,600 potentiometric-surface contours 

is caused by a minor fault that extends through the southern 

part of the OB/OD site (fig. 8). Fault gouge was observed at a 

depth of 89 to 99 ft in the east pit (fig. 5) during exploratory 

drilling in 1998 (Ralph Wilcox, U.S. Geological Survey, written commun., 2003). The strike of the fault was inferred to run 

northwest to southeast from the east pit to a location between 

wells 10A and 14. The fault also may be a factor in the divergence of land surface and potentiometric surface downgradient 

of the pits (fig. 9) and also a factor in the variability of fracture 

orientation in the local area (fig. 6). Fault orientation and 

movement are unknown, but the lower potentiometric surface 

to the southwest of the fault may indicate a dip-slip direction 

of the fault (lower block to the southwest). The effect of the 

fault on the potentiometric surface does not appear to extend 

beyond the OB/OD site, although the lower density of wells 

south of the OB/OD pits inhibits detection of any influence. 

The aquifer in the study area is not highly reactive to 

possible recharge events such as large storms (fig. 10). Mean 

daily-water levels did not indicate any substantial, sudden 

increases following such events from 2003–06. Aquifer 

recharge appears to be moderated by unsaturated-zone flow 

paths and possibly fracture geometry and density, including 

accessible entry points. Large precipitation accumulations in 

2004 and 2006 appear to have reversed declining water levels 

(fig. 10). The larger response to large precipitation accumulations in well 10A suggests that most recharge likely occurs 

near the mountain-front interface and the response is moderated downgradient (limited recharge away from the mountain 

front). The lack of water-level increase in well 15 suggests 

limited connectivity of fractures penetrated by this well with 

fractures penetrated by the other wells shown in figure 10. 

Contaminant Variability at the Open Burn/Open 

Detonation Site

RDX has been detected in ground water in all wells in 

transect A–A ́ (median concentrations of 2 to 60 μg/L), but the 

largest source appears to be located upgradient from wells 14 

and 10A (fig. 11). The main source of RDX is likely within 

the pits but a dispersed source also is present outside of the 

immediate pit area. Demolition of RDX-containing material 

likely dispersed some of the material outside of pit boundaries. 

RDX concentrations along transect A–A ́ during 1998, 2000, 

2003, and 2006 indicate a shift in peak RDX concentrations 

(fig. 12). From 1998 to 2006, peak concentrations shifted from 

well 14 to well 11 (about 100 yards between wells). This shift 

occurred in 2003 and is a result of the removal of the south 

and east berms of each pit in 2002 and 2003 where the berm 

material was pushed into the pits and the area regraded. Previous soil sampling in and around the pits detected RDX within 

the pits, particularly along the southwestern border (berm) of 

the west pit (Ralph Wilcox, U.S. Geological Survey, written 

commun., 2003).

Background concentrations of nitrate in ground water at 

HTA probably range from about 1 to 4 mg/L (Ralph Wilcox, 

U.S. Geological Survey, written commun., 2003). Median 

nitrate concentrations in ground water from wells 13, 14, 10A, 

11, and 20 in transect A–A ́ range from 7 to 8 mg/L (fig. 13). 

The elevated nitrate concentrations in ground water at the OB/

OD site originate from degradation of nitrogen-based explosives. A larger spread of nitrate concentrations across transect 

A–A ́ suggests a more dispersed source than RDX (fig. 13). 

Differences in fate and transport of RDX and the other source 

explosives in the natural environment can explain the differences in RDX and nitrate concentrations and spatial patterns in 

transect A–A ́. In ground water, RDX tends to be more mobile 

than nitroaromatics such as TNT because of less sorption to 

soil particles (Xue and others, 1995; Yamamoto and others, 

2004). Differences in soil retention could produce different 

rates of degradation and entrainment in ground water. HMX 

was the most prevalent explosive detected in soil samples collected in and around the pits (Ralph Wilcox, U.S. Geological 

Survey, written commun., 2003), but HMX has rarely been 

detected in ground water at HTA from 1996–2006 and only 

in wells close to the pits (10A, 11, 14, 16, 16D, and 20). This 

lack of HMX detection in ground water suggests degradation 

of HMX to nitrate prior to entrainment or prior to entering the 

fractures penetrated by the monitoring wells.

Between 1998 and 2006, the largest nitrate concentrations 

in transect A–A ́ shifted from well 13 to 10A, and this 

shift corresponds with moving of the berms in 2002 and 

2003 (fig. 14). This shift corresponds to the shift in RDX 

concentrations that also occurred with berm regrading. The 
Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer 19

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

TRANSECT SURFACE DISTANCE, IN MILES

4,500

4,750

5,000

5,250

5,500

5,750

6,000

ELEVATION, IN FEET ABOVE NAVD 88

Land surface

Aquifer potentiometric surface

Vertical exaggeration = 11:1

NA = not available

B B’

Mountain-front interface (well 12)

10A 16 19 18 27 28

Open Burn/Open Detonation pits

Well designation and location:

Fault location, oblique to B−B’

3 46 43 45 

Location of uppermost water-producing

fracture during drilling

NA

NA

NA

Figure 9. Vertical profile of topography and potentiometric surface at the Hazardous Test Area, transect B–B’, October 2006.

Figure 10. Mean-daily water level for select wells and daily precipitation total at well 15, Hazardous Test Area, January 2003 to 

January 2006.

1/1/2003 7/28/2003 2/22/2004 9/17/2004 4/14/2005 11/8/2005 6/5/2006 12/31/2006

85.0

82.5

80.0

77.5

75.0

72.5

70.0

9

8

7

6

5

4

3

2

1

WATER LEVEL, IN FEET BELOW LAND SURFACE

DAILY PRECIPITATION TOTAL, IN INCHES

WELL 15 DAILY PRECIPITATION TOTAL

0

 10

67.5

87.5

Well 43

Well 10A

Well 28

Well 45

Well 15

Gaps are missing data
20 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

Figure 11. Spatial variability of RDX in ground water from wells in transect A–A’ at the Hazardous Test Area, 1996–2006.

Figure 12. Temporal variability of RDX in ground water from wells in transect A–A’ at the Hazardous Test Area.

23 13 14 10A 11 20 24

A WELL DESIGNATION AND TRANSECT A’

0

20

40

60

80

100

RDX CONCENTRATION, IN MICROGRAMS PER LITER

1.5 times the interquartile

range or less

75th percentile

50th (median)

25th percentile

1.5 times the interquartile

range or less

Outlier

Outlier

Pits were directly upgradient

 from these well locations

Sample size 28 27 36 38 44 34 28

23 13 14 10A 11 20 24

A WELL DESIGNATION AND TRANSECT A’

0

20

40

60

80

100

RDX CONCENTRATION, IN MICROGRAMS PER LITER

October 1998

October 2000

October 2003

October 2006

Location of peak concentrations shifted with time

because of pit berm removal

Pits were directly upgradient

 from these well locations
Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer 21

Figure 13. Spatial variability of nitrate plus nitrite as nitrogen in ground water from wells in transect A–A’ at the Hazardous Test Area, 

1996–2006.

Figure 14. Temporal variability of nitrate plus nitrite as nitrogen in ground water from wells in transect A–A’ at the Hazardous Test Area.

23 13 14 10A 11 20 24

A WELL DESIGNATION AND TRANSECT A’

0

5

10

15

NITRATE PLUS NITRITE AS NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

1.5 times the interquartile

range or less

75th percentile

50th (median)

25th percentile

1.5 times the interquartile

range or less

Outlier

Outlier

Pits were directly upgradient

 from these well locations

Sample size 28 27 36 38 44 34 28

23 13 14 10A 11 20 24

A WELL DESIGNATION AND TRANSECT A’

0

5

10

15

NITRATE PLUS NITRITE AS NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

October 1998

October 2000

October 2003

October 2006

Location of peak concentrations likely shifted

with time because of pit berm removal

Pits were directly upgradient

 from these well locations
22 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

similarity of nitrate and RDX concentrations reacting to the 

berm regrading indicates similar sources or similar source 

locations. This shift in peak source contribution is less 

pronounced and traveled less distance compared to the RDX 

peak source. The less pronounced shift in nitrate source and 

the larger relative differences for RDX compared to nitrate 

probably is a result of the greater dispersed source of nitrate 

compared to RDX.

The perchlorate source location(s) appears to be more 

concentrated compared to RDX and nitrate sources. In transect 

A–A ́, peak concentrations of perchlorate were detected in 

ground water from well 20, and the next largest concentrations were in ground water from wells 11, 10A, and 14; 

median concentrations for all wells ranged from 0.1 to 19 

mg/L (fig. 15). Additionally, the source of perchlorate has not 

shifted during the period of record as was observed with RDX 

and nitrate indicating that a perchlorate source was not located 

at the south and east berms of each pit that were regraded in 

2002 and 2003 (fig. 16). Peak concentrations across transect 

A–A ́ have decreased, possibly indicating a decreasing amount 

of source material.

Downgradient Contaminant Variability

Concentrations of RDX along the downgradient transect 

(B–B ́) sharply decline in the direction of ground-water flow 

(fig. 17). From well 10A at the pits to well 19 (about 0.25 mi), 

concentrations decreased from a median of 60 μg/L to less 

than 0.2 μg/L. From 1998 to 2006, this downgradient decline 

in RDX has been stable, and the larger concentrations of 

RDX have not moved downgradient with ground-water flow. 

Recharge water continued to entrain RDX from the sources 

at and near the pits, but a concentrated mass of RDX has not 

migrated with ground-water flow during the period of study 

(fig. 18). The spatial stability of RDX concentrations is not 

a reflection of the lack of downgradient transport of RDX, 

because ground water in well 46 (about 1.5 mi downgradient 

from the pits) has contained very small concentrations of 

RDX since installation of the well in 2002. The apparent 

lack of downgradient transport of RDX likely results from 

natural attenuation (dilution and (or) degradation) that reduces 

concentrations within a short distance of the OB/OD site. 

Nitrate concentrations indicate a mixed pattern in the 

downgradient direction, and concentrations are largest in 

ground water from well 19 (about 0.25 mi downgradient 

from the OB/OD pits) (fig. 19) where RDX concentrations 

are small (fig. 18). This downgradient pattern of nitrate 

has remained stable since 2000 and only small changes in 

concentrations at each well have been observed (fig. 20). The 

pattern of nitrate concentrations along transect B–B ́ is similar 

to the pattern of dissolved-oxygen concentrations (fig. 21). 

This pattern suggests that changes to reduction-oxidation 

(redox) conditions are influencing nitrate concentrations, 

particularly concentrations in ground water from wells 27 and 

46. Ammonia has been detected at small concentrations (less 

than 0.1 mg/L) in only a few wells at HTA (Ralph Wilcox, 

U.S. Geological Survey, written commun., 2003), although if 

converted to ammonium (protonation of ammonia) adsorption 

of NH4

+

 can be substantial (Appelo and Postma, 2005) and can 

reduce the presence of ammonium in solution. Denitrification 

because of changes in redox conditions in certain fracture 

systems may be producing the variable downgradient pattern 

of nitrate at HTA, which suggests disconnected or limited 

connectivity between fractures radiating from the OB/OD 

site. The different downgradient patterns of RDX and nitrate 

suggest natural attenuation instead of vertical migration of the 

contaminants beyond the depths of the monitoring wells.

Perchlorate concentrations in ground water from wells in 

transect B–B ́ indicate increasing and then decreasing concentrations in the downgradient direction (fig. 22). Perchlorate 

concentrations were largest in ground water from wells 16 

(median of 19.3 mg/L) and 16D (median of 21.0 mg/L); both 

wells are about 0.15 mi downgradient from the OB/OD site. 

Concentrations further downgradient sharply decreased with 

median concentrations of 0.06 and 0.95 mg/L at wells 27 and 

28 (about 0.5 mi downgradient from the OB/OD site), respectively. Perchlorate was present in ground water from all downgradient wells and concentrations generally ranged from 1 to 

40 μg/L at wells furthest from the OB/OD site (3, 46, 43, and 

45). Perchlorate concentrations were stable in ground water 

along transect B–B ́ from 1999 to 2006 with minor concentration fluctuations likely from variable recharge (fig. 23).

The larger perchlorate concentrations typical of ground 

water from wells 16 and 16D were not detected in ground 

water from wells closer to the OB/OD site except for ground 

water from well 20. A possible link between ground water 

from well 20 and ground water from well 16 or 16D is difficult to ascertain (fig. 24). Perchlorate trends at these locations were similar but also indicated sufficient differences to 

question a possible relation. The Wilcoxon rank-sum test was 

used to compare the data distributions of perchlorate in ground 

water at well 20 with perchlorate data for wells 16 and 16D. 

Test results indicate no relation between perchlorate in ground 

water from the shallower, downgradient well 16 and well 20 

(p-value of 0.55), but a likely relation between perchlorate in 

ground water from the deeper, downgradient well 16D and 

the OB/OD well 20 (p-value of 0.02). These results suggest 

possible fracture connectivity downgradient from the OB/OD 

pits (wells 16D and 20), but also downgradient fractures that 

are not connected or have limited connectivity with fractures 

penetrated by wells near the OB/OD pits (comparing wells 

16 and 20). Ground water in wells 16 and 16D have the same 

potentiometric-surface elevation (fig. 8) that suggests recharge 

from the same elevation where the contaminants are entrained 

and no vertical hydraulic gradient between shallow and deeper 

fractures at this location.

Small concentrations of perchlorate (less than 10 μg/L) in 

ground water from HTA could or could not be from anthropogenic sources. The anthropogenic use of perchlorate is as 

a strong oxidizer in rocket propellants, explosives, and flares. 

Perchlorate has been detected in ground water in the Rio 
Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer 23

Figure 15. Spatial variability of perchlorate in ground water from wells in transect A–A’ at the Hazardous Test Area, 1996–2006.

Figure 16. Temporal variability of perchlorate in ground water from wells in transect A–A’ at the Hazardous Test Area.

23 13 14 10A 11 20 24

A WELL DESIGNATION AND TRANSECT A’

0

10

20

30

PERCHLORATE CONCENTRATION, IN MILLIGRAMS PER LITER

1.5 times the interquartile

range or less

75th percentile

50th (median)

25th percentile

1.5 times the interquartile

range or less

Outlier

Outlier

Pits were directly upgradient

 from these well locations

Sample size 28 25 30 25 31 30 28

23 13 14 10A 11 20 24

A WELL DESIGNATION AND TRANSECT A’

0

10

20

30

PERCHLORATE CONCENTRATION, IN MILLIGRAMS PER LITER

October 1999

October 2000

October 2003

October 2006

No peak shift with time

Pits were directly upgradient

 from these well locations
24 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

Figure 17. Spatial variability of RDX in ground water from wells in transect B–B’ at the Hazardous Test Area, 1996–2006.

Figure 18. Temporal variability of RDX in ground water from wells in transect B–B’ at the Hazardous Test Area.

12 10A 16 16D 19 18 27 28 3 46 43 45

B WELL DESIGNATION AND TRANSECT B’

0

20

40

60

80

100

RDX CONCENTRATION, IN MICROGRAMS PER LITER

1.5 times the interquartile

range or less

75th percentile

50th (median)

25th percentile

1.5 times the interquartile

range or less

Outlier

Outlier

45 39 37 29 44 40 42 39 44 39 12 Sample

size 39

0

20

40

60

80

100 RDX CONCENTRATION, IN MICROGRAMS PER LITER

October 1998

October 2000

October 2003

October 2006

No downgradient shift in peak concentrations

but some variability in peak concentrations with time

12 10A 16 16D 19 18 27 28 3 46 43 45

B WELL DESIGNATION AND TRANSECT B’
Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer 25

Figure 19. Spatial variability of nitrate plus nitrite as nitrogen in ground water from wells in transect B–B’ at the Hazardous Test Area, 

1996–2006.

Figure 20. Temporal variability of nitrate plus nitrite as nitrogen in ground water from wells in transect B–B’ at the Hazardous Test Area.

0

10

20

30

NITRATE PLUS NITRITE AS NITROGEN, IN MILLIGRAMS PER LITER

12 10A 16 16D 19 18 27 28 3 46 43 45

B WELL DESIGNATION AND TRANSECT B’

1.5 times the interquartile

range or less

75th percentile

50th (median)

25th percentile

1.5 times the interquartile

range or less

Outlier

Outlier

44 38 37 29 35 35 28 27 13 14 12 Sample

size 26

0

5

10

15

20

25

NITRATE PLUS NITRITE AS NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

October 1998

October 2000

October 2003

October 2006 No downgradient shift in peak concentrations

but some variability in peak concentrations with time

12 10A 16 16D 19 18 27 28 3 46 43 45

B WELL DESIGNATION AND TRANSECT B’

No data
26 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

Figure 21. Spatial variability of dissolved oxygen in ground water from wells in transect B–B’ at the Hazardous Test Area, 1996–2006.

Figure 22. Spatial variability of perchlorate in ground water from wells in transect B–B’ at the Hazardous Test Area, 1996–2006.

0

2

4

6

8

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

12 10A 16 16D 19 18 27 28 3 46 43 45

B WELL DESIGNATION AND TRANSECT B’

1.5 times the interquartile

range or less

75th percentile

50th (median)

25th percentile

1.5 times the interquartile

range or less

Outlier

Outlier

34 24 34 27 37 35 28 28 18 21 20 Sample

size 34

0

5

10

15

20

25

30

PERCHLORATE CONCENTRATION, IN MILLIGRAMS PER LITER

12 10A 16 16D 19 18 27 28 3 46 43 45

B WELL DESIGNATION AND TRANSECT B’

1.5 times the interquartile

range or less

75th percentile

50th (median)

25th percentile

1.5 times the interquartile

range or less

Outlier

Outlier

28 23 29 23 29 29 27 27 13 19 16 Sample

size 16
Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer 27

Figure 23. Temporal variability of perchlorate in ground water from wells in transect B–B’ at the Hazardous Test Area.

Figure 24. Perchlorate concentrations in ground water from well 20 near the Open Burn/Open Detonation site and ground water from 

wells 16 and 16D approximately 0.15 mile downgradient.

0

5

10

15

20

25

PERCHLORATE CONCENTRATION, IN MILLIGRAMS PER LITER

October 1999

October 2000

October 2003

October 2006

No downgradient shift in peak concentrations

but some variability in peak concentrations with time

12 10A 16 16D 19 18 27 28 3 46 43 45

B WELL DESIGNATION AND TRANSECT B’

4/1/1999 4/27/2000 5/24/2001 6/20/2002 7/17/2003 8/12/2004 9/8/2005 10/6/2006

10

15

20

25

30

PERCHLORATE CONCENTRATION, IN MILLIGRAMS PER LITER

well 16

well 16D

well 20
28 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

Grande Valley of New Mexico (Plummer and others, 2006) 

(ranging from 0.12 to 1.8 μg/L) and in northwestern Texas 

(Jackson and others, 2003) (concentrations generally were less 

than 5 μg/L) where no known anthropogenic source(s) exists. 

Further investigation of perchlorate in northwestern Texas and 

eastern New Mexico produced evidence that perchlorate was 

from a natural source (Rajagopalan and others, 2006). Atmospheric processes such as the interaction of chloride and ozone 

can produce perchlorate naturally (Dasgupta and others, 2005). 

With wet or dry deposition, perchlorate can accumulate in soil 

and be transported to an aquifer by recharge. The increasing 

analytical capability to detect perchlorate at small concentrations (0.1 μg/L or greater) has allowed the identification of 

naturally occurring perchlorate in arid and semiarid climates 

where it may accumulate in the soil (Rajagopalan and others, 

2006; Rao and others, 2007). In October 2006, perchlorate was 

detected at HTA in ground water from many of the monitoring 

wells in the larger monitoring network beyond the general OB/

OD area at small concentrations (1 to 2 μg/L or less). Many 

of these wells probably are not connected to ground-water 

flow paths that originate from the OB/OD site (many wells 

are located in areas not potentiometrically downgradient), and 

perchlorate at these locations may be naturally occurring.

Water Level and Contaminant Relation

Changes in water level may correlate with contaminant 

(RDX, nitrate and perchlorate) concentrations as an increase 

or decrease in recharge either dilutes or concentrates entrained 

contaminants. Nonparametric (Kendall’s tau) correlation 

coefficients and the associated p-values for comparison of 

water levels and the three contaminants at each well indicate 

limited correlation, except for a few wells (tables 3 and 4). 

For this study, strong correlation is a tau greater than ±0.8, 

moderate correlation is greater than ±0.5, and low correlation 

is less than ±0.5 (±1 is considered perfect correlation and 0 

indicates no correlation). For transect A–A ́, water level and 

RDX were positively and strongly correlated for well 14 

(tau of 0.81, p-value of 0.00) and moderately and negatively 

correlated for well 23 (tau of -0.53, p-value of 0.00). Well 

14 penetrates a fracture(s) that contains ground water with 

the some of the largest RDX concentrations, and well 23 

penetrates a fracture(s) that contains ground water with 

some of the smallest RDX concentrations for transect A–A ́

(fig. 11). Additionally, a positive and moderate correlation 

(tau of 0.51, p-value of 0.00) was present for perchlorate and 

water level in well 20, which contained ground water with 

the largest perchlorate concentrations for wells in transect 

A–A ́ (fig. 15). For transect B–B ́, water level and all three 

contaminant concentrations were not strongly correlated 

(table 4). Correlation coefficients for water level and nitrate, 

which indicated low correlation strengths for all wells in 

transect A–A ́, indicated positive and moderate strength of 

correlation for wells 3, 12, and 16 in transect B–B ́. Strong and 

moderate correlation of water level and the contaminants near 

the source areas and low correlation outside and downgradient 

from the source(s) suggests a diminishing of the water level/

contaminant relation with downgradient flow. The lessening of 

these relations may be a result of natural attenuation that alters 

contaminant concentrations and changes the relation with 

water level.

The correlation of RDX and nitrate concentrations was 

examined for similarities in contaminant sources and entrainment and transport of the two contaminants. Movement of 

these two contaminants in the aquifer may be similar because 

of their likely similar anthropogenic source (explosives). 

Correlation coefficients for RDX and nitrate indicate low 

correlation laterally (transect A–A ́) and in the downgradient 

direction (transect B–B ́) (tables 5 and 6). This lack of correlation suggests differences in source locations and possibly differences in solubility and degradation of the source explosives 

and nitrate within the aquifer. Nitrate is very soluble, mobile, 

and easily degraded under reducing conditions (Hem, 1989). 

RDX is more environmentally persistent compared to other 

explosives such as TNT (trinitrotoluene) (Spalding and Fulton, 

1988). RDX and TNT were detected in soil samples collected 

at the OB/OD site in 1999 (Ralph Wilcox, U.S. Geological 

Survey, written commun., 2003). Elevated nitrate concentrations are likely a result of entrainment and degradation of 

the explosive compounds detected in soil and core samples 

collected in and around the OB/OD pits that included RDX, 

HMX, DNT, TNT, and tetryl (Ralph Wilcox, U.S. Geological 

Survey, written commun., 2003). The recurrent detection of 

RDX in ground water at HTA compared to the rare detection 

of other explosives highlights the greater persistence of RDX 

compared to other explosive compounds that are present at 

the site. The differences in source locations, degradation, and 

solubility of the explosive compounds explain the low correlation between RDX and nitrate

Natural Attenuation in the FracturedGranite Aquifer

Results of the previous section suggest natural attenuation 

of the contaminants in the fractured-granite aquifer. The loss 

of the contaminants because of vertical migration beyond 

the depths of the monitoring wells is unlikely. Monitoring of 

shallow and deeper parts of the aquifer at a single location 

(well 16 (shallow) and well 16D (deep)) produced equal 

or larger contaminant concentrations in the shallow well 

compared to the deeper well, and reveal that the contaminants 

are present throughout the vertical column and no vertical 

concentration gradient is present downgradient from the pits 

(figs. 17, 19, and 22). Additionally, no vertical hydraulic 

gradient is present at this location (same ground-water 

elevation in both wells). The sharp decreases in contaminant 

concentrations (figs. 18, 20, and 23) and changes to dissolved 

oxygen (fig. 21) suggest that natural attenuation, through 

dilution and degradation, is occurring downgradient from 
Natural Attenuation in the Fractured-Granite Aquifer 29

Table 3. Kendall’s tau correlation coefficients for water level and RDX, nitrate, and perchlorate in ground water from wells 

in transect A–A’ at the Hazardous Test Area, 1996–2006.

[A correlation coefficient of 1 indicates a perfect, positive correlation, a coefficient of -1 indicates a perfect, negative correlation, and coefficient 

of 0 indicates no correlation; for this study, strong correlation is greater than 0.8, moderate correlation is greater than 0.5, and low correlation is 

less than 0.5; moderate and strong correlations are in bold]

Correlation with 

water level

Well number

23 13 14 10A 11 20 24

RDX: tau -0.53 0.18 0.81 -0.18 -0.12 -0.43 -0.39

p-value 0.00 0.19 0.00 0.12 0.23 0.00 0.00

Nitrate: tau 0.38 0.48 0.29 -0.43 0.07 0.24 0.37

p-value 0.00 0.00 0.03 0.00 0.52 0.04 0.00

Perchlorate: tau 0.16 0.26 0.27 -0.01 0.21 0.51 0.37

p-value 0.22 0.07 0.02 0.94 0.09 0.00 0.01

Table 4. Kendall’s tau correlation coefficients for water level and RDX, nitrate, and perchlorate in ground water from wells 

in transect B–B’ at the Hazardous Test Area, 1996–2006. 

[A correlation coefficient of 1 indicates a perfect, positive correlation, and a coefficient of -1 indicates a perfect, negative correlation; NA, not 

applicable—no detections of the constituent at this well; for this study, strong correlation is greater than 0.8, moderate correlation is greater than 

0.5, and low correlation is less than 0.5; moderate and strong correlations are in bold]

Correlation with 

water level

Well number

12 10A 16 16D 19 18 27 28 3 46 43 45

RDX: tau NA -0.18 0.15 0.02 -0.28 -0.13 -0.41 NA NA -0.57 NA NA

p-value NA 0.12 0.20 0.85 0.01 0.14 0.00 NA NA 0.00 NA NA

Nitrate: tau 0.59 -0.43 0.63 0.44 0.33 -0.47 -0.05 -0.25 0.52 0.21 -0.12 -0.05

p-value 0.00 0.00 0.00 0.00 0.00 0.00 0.69 0.06 0.00 0.20 0.57 0.84

Perchlorate: tau NA -0.01 0.23 0.11 -0.33 -0.54 -0.04 -0.46 -0.47 0.19 -0.06 -0.34

p-value NA 0.94 0.07 0.42 0.01 0.00 0.78 0.00 0.00 0.21 0.72 0.06

Table 6. Kendall’s tau correlation coefficients for RDX and nitrate in ground water from wells in transect B–B’ at the 

Hazardous Test Area, 1996–2006. 

[NA, not applicable; A correlation coefficient of 1 indicates a perfect, positive correlation, and a coefficient of -1 indicates a perfect, negative 

correlation; NA, not applicable—no detections of the constituent at this well]

Kendall’s tau 

correlation

Well number

12 10A 16 16D 19 18 27 28 3 46 43 45

RDX/nitrate NA 0.29 0.05 0.03 -0.13 0.08 -0.07 NA NA -0.02 NA NA

p-value NA 0.01 0.65 0.81 0.25 0.33 0.55 NA NA 0.92 NA NA

Table 5. Kendall’s tau correlation coefficients for RDX and nitrate in ground water from wells in transect A–A’ at the 

Hazardous Test Area, 1996–2006. 

[A correlation coefficient of 1 indicates a perfect, positive correlation, a coefficient of -1 indicates a perfect, negative correlation, and coefficient of 

0 indicates no correlation]

Kendall’s tau 

correlation

Well number

23 13 14 10A 11 20 24

RDX/nitrate -0.23 0.48 0.26 0.29 0.36 -0.13 -0.41

p-value 0.06 0.00 0.03 0.01 0.00 0.28 0.00
30 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

the pits, but the effect of dilution and (or) degradation of the 

contaminants is difficult to ascertain because of the possible 

limited connectivity between fractures within the aquifer. To 

help evaluate the effect of natural attenuation and discriminate 

dilution from degradation of the contaminants, ground-water 

samples from select wells in the HTA monitoring network 

collected in October 2005 were analyzed for selected 

geochemical tracers (table 2). 

All wells in fractures with ground water containing the 

contaminants have received recharge that has passed through 

the OB/OD site because of the presence of the contaminants, 

but uncontaminated recharge also is occurring outside of the 

OB/OD site and is likely mixing with contaminated water 

downgradient from the pits. This mixing of contaminated 

and uncontaminated water downgradient from the OB/

OD site would dilute the contaminants and attenuate large 

downgradient concentrations. This mixing and decrease of 

contaminant concentrations were possibly indicated in figures 

18, 20, and 23 where contaminant concentrations quickly 

declined after peak concentration locations. The presence 

of the contaminants throughout the OB/OD site and into the 

larger fractured-granite aquifer indicates that contaminant 

transport is occurring throughout the HTA, but the large 

concentrations (large concentrated mass) of contaminants 

near the OB/OD pits have not migrated with this overall 

contaminant transport. Decrease of the contaminant masses 

in solution through sorption is unlikely given the mobility 

of the contaminants (Anthropogenic Compounds section), 

so the mass is likely decreased by dilution through mixing 

with uncontaminated water originating outside of the OB/OD 

site or degradation of the contaminants such as microbially 

induced reduction of nitrate under hypoxic or anoxic 

conditions. Effects on the contaminant masses by these two 

processes will be further explored through an analysis of 

geochemical tracers.

Tritium-Helium Age Dating and Dilution

In October 2005, the apparent age of ground water from 

selected wells at HTA was estimated using the tritium-helium 

method developed by Schlosser and others (1989). Ground 

water in the fractured-granite aquifer is young (less than 25 

years from the OB/OD pits to 3.25 mi downgradient), which 

suggests that contaminated recharge should have transported 

the contaminants throughout the downgradient aquifer. Given 

that the concentrations quickly decline with downgradient 

transport, it appears that natural attenuation processes, such 

as dilution, are decreasing downgradient concentrations. 

Within the fractured-granite aquifer, ground water was not 

progressively older at all downgradient locations (table 7). 

Younger water was present in downgradient wells (28 and 

45) compared to upgradient wells (wells 19, 31, 43, and 

51). Younger water in wells 28 and 45 suggests recharge is 

closer to these locations than upgradient wells. Fractures 

penetrated by wells 28 and 45 possibly receive recharge (or 

more recharge) from nearby ephemeral channels or mix with 

uncontaminated water recharged along the mountain-front 

interfaces along Black Mountain to the north or Mineral 

Hill to the south (fig. 2). Ground water in wells 28 and 45 

did not contain large concentrations of the contaminants 

(Downgradient Contaminant Variability section). Ground 

water in these wells has mixed with younger, uncontaminated 

water and diluted contaminant concentrations and decreased 

ground-water ages. 

Ground-Water Composition

The chemical composition of ground water 

(hydrochemical facies) is a response to water-rock interactions 

and atmospheric and anthropogenic inputs (Bullen and 

Kendall, 1998). Longer contact time of ground water with 

rock minerals will increase solute concentrations in response 

to dissolution reactions that are variable because of kinetic 

and thermodynamic properties of ground-water flow and 

formation minerals (Bullen and Kendall, 1998). Except 

for ground water along the periphery of the basin (wells 5, 

40, 48, 49, and Bonney Spring Mine windmill) (fig. 2), the 

chemical composition of the fractured-granite aquifer at HTA 

was similar for most wells (mixed cation and mixed anion 

composition) and indicated similar water-rock interactions 

and recharge pathways (fig. 25). The different chemical 

composition of ground water in wells 5, 40, 48, 49, and the 

Bonney Spring Mine windmill is related to water interacting 

with different mineral assemblages. Ore deposits are present 

along the basin margins (fault zones and batholith contacts), 

and are particularly prevalent at San Augustin Pass (fig. 2) 

and northward where most of the mining in the area occurred 

(Seager, 1981). The Bonney Spring Mine windmill is located 

along the contact of the metamorphosed sedimentary rocks 

of the San Andres Mountains and the HTA granitic pluton 

in the Bear Peak Fold and Thrust Zone (fig. 4). This zone is 

known for zinc-lead-silver mineralization where a shale layer 

provided a barrier to the movement of ore fluids and mineral 

precipitation occurred (Seager, 1981). 

Dilution 

Dissolved-solids (DS) concentrations in ground water 

from the HTA fractured-granite aquifer in October 2005 

ranged from 348 to 710 mg/L for the entire HTA monitoring 

network and ranged from 458 to 683 mg/L in the OB/OD site 

area (fig. 26). Variation in DS concentrations was a result of 

variable water-rock interaction (mineral differences and time 

of dissolution (age of water)), mixing of recharge sources, and 

contaminant inputs. The largest DS concentrations were northnortheast of the pits (wells 24, 25, and 29), and the smallest 

concentrations were south and southeast of the pits (wells 23 

and 27) (fig. 26). Changes in DS concentrations across transect 

A–A ́ (wells 23, 13, 14, 10A, 11, 20, and 24) suggest differences in recharge upgradient from and at the OB/OD pits. 
Natural Attenuation in the Fractured-Granite Aquifer 31

Percent Calcium

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20 

 40 

 60 

 80 

 100 

Sodium plus Potassium

Chloride plus Fluoride

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 

Bicarbonate

 100 

 80 

 60 

 40 

 20 

 0 

Sulfate

 0 

 20 

 40 

 60 

 80 

 100 

Sulfate plus Chloride

 0 

 20 

 40 

 60 

 80 

 100 

Calcium plus Magnesium

 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

Percent

Percent

49

5

5

Bonney

Bonney

40

40

48

48

49

5

48 40

EXPLANATION

Monitoring site designation

for outlier values

Monitoring site designation

49

Figure 25. Piper diagram of major ion composition of ground water collected from monitoring sites 

in the Hazardous Test Area, October 2005.

Table 7. Ground-water ages for selected wells at the Hazardous Test Area, October 2005. 

[Ground-water age determined by tritium-helium method (Schlosser and others, 1989); NA, not available]

Downgradient direction 

Well 12 11 16 19 28 31 43 51 45 41

Approximate age 

(years) NA 3.0 ±0.1 7.4 ±0.1 13.6 ±0.5 6.2 ±0.3 19.7 ±0.6 22.0 ±5 23.8 ±0.9 17.2 ±0.9 NA

Tritium units 1.43 8.59 9.82 2.93 1.41 1.56 2.17 1.04 0.84 0.71

Only RDX peaked in concentration near the pits (fig. 18), 

but the peak RDX concentrations are at the microgram per 

liter scale and would not substantially contribute to the DS 

milligrams per liter concentrations. Nitrate concentrations 

peaked near well 19 and perchlorate concentrations peaked 

near well 16 and 16D, and DS concentrations in this area are 

larger than DS concentrations in ground water from wells 

along the eastern and southern boundaries of the OB/OD pits. 

The influx of contaminants appears to have increased DS 

concentrations downgradient from the pits, but a diluting influence is evident downgradient from well 19. DS concentrations 

in ground water from well 18, 27, and 28 are substantially 

lower than DS concentrations in ground water from wells 15, 

16, 16D, 17, and 19. This decrease in DS concentrations is 

likely because of dilution from another recharge source that 

was suggested by the decrease in contaminant concentrations 

(Downgradient Contaminant Variability section) and groundwater ages. 

A linear trend of calcium and strontium concentrations 

indicates differences in mineral dissolution and mixing of 
32 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

!

!

!

!

!

!

!

!

!

!

!

!

!

!

5,300

5,500

5,600

5,700

5,400

20

655

5,600

0 1 KILOMETER

Base from U.S. Geological Survey digital data, 1994, 1:100,000 0 0.5 MILE

Universal Transverse Mercator Zone 13N, NAD 83

EXPLANATION

Open Burn/Open Detonation (OB/OD) pit

Paved road

Dirt road

!34

574

Monitoring site and designation (circled) with total dissolved-solids

concentration in milligrams per liter, October 2005

!

659 

24

 13 548 ! !

!

15 658

645

12

!

!

!

30

498

19

656

!

32o

30'

106° 30'

San Andres Mountains

Hazardous Test Area

Black Mountain

!

5,100

5,200

5,900

5,800

6,000

Topographic contour—contour interval 100 feet, datum is NAVD 88

32o

29'

106° 31'

6,100

6,200

616

26

16

662

18

575

31

604

28

548

27

475 32

575

3

526

!4

541

46

563

22

544 Overall flow direction but flow is contained in fracture systems 

that may or may not be connected

Most recharge likely occurs along the mountain-front interface

but the pits formed catchment basins that also focus recharge

21

587

683

29

25 665

17

663

23

458

Inset area

!12

645

!23

458

 13!

 548

 613 14!!10A 539

 11 !592

!20 655

!

659

24

!16 662

!16D 657

!17 663

!

658

15

OB/OD site

!32

575

!

683

29

Figure 26. Spatial distribution of dissolved-solids concentrations in the fractured-granite aquifer near the Open Burn/Open Detonation 

Site in the Hazardous Test Area, October 2005.
Natural Attenuation in the Fractured-Granite Aquifer 33

various recharge and flow paths (fig. 27). Ground water from 

wells 27, 45, 46, and 47A is influenced by dissolution of 

other mineral assemblages not representative of the granitediorite minerals that compose the granitic pluton. Larger 

concentrations of strontium relative to calcium can indicate 

dissolution of limestone (Bierman and others, 1998), which 

is abundant in the San Andres Mountains and at Black 

Mountain along the northern perimeter of the HTA fracturedgranite aquifer. Recharge water from this area appears to 

cross the Bear Peak Fold and Thrust Zone and merge with 

select fractures in the HTA fractured-granite aquifer. The 

strontium/calcium indicator of mixing of contaminated and 

uncontaminated water near well 27 agrees with interpretation 

of the ground-water ages and DS concentrations that suggested 

a similar influence by well 28.

Degradation and Changes to Carbon Forms

Biodegradation of organic compounds, such as RDX 

and other explosives, can affect ground-water physical and 

chemical properties (Fetter, 1999). The degradation of RDX 

and other explosives likely contributes various byproducts 

to ground water in the fractured-granite aquifer that may be 

visible at or downgradient from the large RDX concentrations, 

or the degradation of the RDX and other explosives may alter 

ground-water chemistry such as the change in dissolved oxygen visible in figure 21. Degradation of RDX and other explosives would consume oxygen and produce degradates (such as 

MNX, DNX, and TNX for RDX) or final byproducts (such as 

nitrate, methane, carbon dioxide, or nitrogen gas) (McCormick 

and others, 1981; Hawari and others, 2000). 

Some of the indicators of RDX degradation in the 

HTA fractured-granite aquifer include the presence of RDX 

degradates, RDX/nitrate/nitrogen-gas pattern, the presence 

of methane, and changes in carbon dioxide concentrations. 

Certain RDX degradates were detected in ground water 

collected in October 2005 from a few wells near and 

downgradient from the pits. MNX was detected in ground 

water from wells 10A, 11, and 29; DNX was detected in 

ground water from wells 23 and 46; and TNX was not 

detected. The presence of these compounds in the fracturedgranite aquifer indicates degradation of RDX near its source 

location(s) and downgradient from the pits. The lack of 

degradates further downgradient indicates degradation to 

simpler chemical forms such as nitrate or dilution. In the 

downgradient direction, the largest RDX concentrations 

were in ground water from well 10A (fig. 18) followed by 

downgradient decreases to near nondetection levels by well 19. 

This pattern was opposite of the downgradient nitrate pattern 

that indicated an increasing nitrate concentration from well 

12 to the largest nitrate concentration in ground water from 

well 19 (fig. 20). This inverse pattern from the OB/OD pits 

to well 19 suggests a contribution of nitrate to ground water 

from the degradation of RDX. The likely degradation of RDX 

Figure 27. Strontium and calcium concentrations in ground water from monitoring sites in the Hazardous Test Area, October 2005.

75 85 95 105 115

CALCIUM CONCENTRATION, IN MILLIGRAMS PER LITER

100

200

300

400

500

600

700

800

STRONTIUM CONCENTRATION, IN MICROGRAMS PER LITER

3 4

11

12

13

14

15

16 17

18

19

20 21

22

23

24

25

26

27

28

29

30

31

32

34

42

43

45

46

51

10A

16D

47A

Markham

27 45

46

Limestone influence

from Black Mountain

19 Monitoring-site identifier

Calcium/strontium trend in

granite-diorite fractures

in the Hazardous Test Area
34 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

Figure 28. Nitrate plus nitrite as nitrogen and dissolved nitrogen gas concentrations in ground water from selected wells in transect 

B–B’ at the Hazardous Test Area, October 2005.

can only account for a small part of the increase in nitrate, 

which suggests additional nitrate inputs. These other nitrate 

inputs may be related to the degradation of other explosive 

compounds—such as HMX, DNT, TNT, and teryl—that have 

been detected in soil samples in and around the pits but are 

rarely detected in ground water and only at wells near the 

OB/OD pits, including wells 10A, 11, 13, 14, 16, 16D, 20, 

and 24. It is possible that other fractures not represented by 

the upgradient wells are transporting nitrate from degraded 

explosives to this location.

During October 2005, ground-water samples from 

selected wells were analyzed for dissolved gases including 

nitrogen, methane, and carbon dioxide. An inverse relation 

was present for nitrogen gas and nitrate concentrations in 

ground water from wells in transect B–B ́, indicating denitrification and formation of nitrogen gas (fig. 28). Denitrification 

typically occurs under anaerobic conditions where nitrate is 

reduced by microbes to nitrogen gas (Stumm and Morgan, 

1996). Small dissolved-oxygen concentrations were present 

in ground water at wells 12, 27, and 46 (fig. 21), which corresponds to wells with the largest nitrogen gas concentrations 

and the smallest nitrate concentrations (fig. 28). 

Methane was detected in ground water from wells 26 and 

46 (2 of the 12 samples collected for gas analysis from wells 

in the OB/OD pits area or downgradient from the pits), but 

only the detection of methane in ground water from well 46 

appears to correlate with degradation that also has increased 

nitrogen-gas concentrations and decreased nitrate and oxygen 

concentrations in ground water at this location. The USGS 

geochemical model PHREEQC (version 2.13.1) was used to 

estimate carbon-dioxide concentrations (partial pressures) 

for ground water from selected wells where water temperature, pH, dissolved oxygen, and alkalinity were determined 

for the October 2005 samples. Results were cross validated 

against carbon dioxide concentrations measured as part of 

the dissolved gas analyses for selected wells. Carbon dioxide 

concentrations likely increased in ground water downgradient 

from the OB/OD pits from well 10A (0.33 millimoles per liter) 

to well 16D (0.62 millimoles per liter). This increase in carbon 

dioxide (CO2) over this distance corresponds to the decrease in 

RDX (C3H6N6O6) over this same distance (fig. 18). 

Natural Attenuation and Chloride

Chloride is considered a conservative element that 

may be used for tracing source waters and flow paths 

(Drever, 1997), but the addition of anthropogenic chloride 

to the aquifer from degradation of perchlorate adds to the 

uncertainty of the chloride source at each location. Perchlorate 

likely is degrading within the soil and ground water thereby 

producing artificially large and variable perchlorate and 

chloride concentrations in the aquifer downgradient from 

the OB/OD site. The relation of chloride to chloride plus 

perchlorate (in millimoles per liter) for ground water from 

12 16 19 18 27 28 46 43 45

WELL

0

5

10

15

20

25

NITROGEN CONCENTRATION, IN MILLIGRAMS PER LITER

Nitrate plus nitrite as nitrogen

Dissolved nitrogen gas
Natural Attenuation in the Fractured-Granite Aquifer 35

wells at and downgradient from the OB/OD site provides 

a means of visualizing the degradation of perchlorate and 

changes to chloride concentrations. The largest perchlorate 

concentrations relative to chloride concentrations were present 

in ground water from wells 11, 15, and 20 near the OB/OD 

pits (fig. 29). The larger chloride concentration in ground 

water from well 15 suggests an additional chloride input 

along with entrainment of perchlorate from the OB/OD site. 

Ground water in well 15 possibly represents entrainment of 

perchlorate from the OB/OD site but also the entrainment of 

additional chloride from the OB/OD site that may be a result 

of the degradation of additional perchlorate at the surface or 

in the vadose zone. Ground water from wells 11 and 20 near 

the pits indicates a relatively large input of perchlorate but no 

corresponding input of additional chloride, which indicates a 

different source pathway than ground water in well 15. 

Downgradient from the OB/OD pits, perchlorate concentrations decline in ground water from all wells as indicated 

by the increasing chloride to chloride-plus-perchlorate ratio 

(fig. 29), and this decline was strongly visible in transect B–B ́

(fig. 22). Chloride concentrations generally decline in the 

downgradient direction but concentrations are more variable 

because of the initial upgradient chloride contribution, which 

further highlights the likelihood of disconnected or partially 

connected fracture systems. Wells 15, 16, 16D, 18, 19, 27 and 

28 may represent a connected or partially connected fracture 

system and changes to perchlorate and chloride may provide 

insight to natural attenuation processes. The effect of degradation is unknown but dilution is visible in this system of wells. 

If this was a closed system that did not receive additional 

recharge, chloride concentrations would increase with the 

degradation of perchlorate but the opposite effect is visible. 

Chloride concentrations declined with decreasing perchlorate 

concentrations indicating dilution of chloride and either dilution and (or) degradation of perchlorate. 

Stable Isotopes

The δ2H and δ18O values for October 2005 samples 

collected from selected wells at HTA indicate similar isotope 

ratios (small range of δ2H and δ18O), although ground water 

from the southern part of the study area (wells 37, 40, 41, and 

45) did contain slightly less depleted values (fig. 30). Stable 

isotopes of water are temperature dependent and similar 

isotopic values indicate similar source waters (Eby, 2004). The 

slightly less depleted isotopic values in ground water from 

selected wells may be a result of different recharge elevations 

or seasonal differences. Seasonal differences are related to 

temperature effects such as differences in evaporation prior to 

recharge or different isotopic values when comparing winter 

or summer precipitation (Eby, 2004). Ground water in wells 

near the OB/OD site contained a slight variation of isotope 

ratios that may be a result of the mixing of waters from 

different recharge areas that have a slightly different isotopic 

Figure 29. Perchlorate (ClO4) and chloride (Cl) relations in ground water from selected wells in the Hazardous Test Area, October 2005.

0.85 0.90 0.95 1.00 Cl/(Cl + Cl04)

0.25

0.55

0.85

1.15

1.45

1.75

CHLORIDE, IN MILLIMOLES PER LITER

3

4

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26 27

28

29

30

31

32

34

42

43

45

46

10A

16D Possible downgradient relation of chloride and perchlorate in a connected or partially

connected fracture system that includes wells 15, 16, 16D, 18, 19, 27, and 28

15 Monitoring-site identifier
36 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

Figure 30. δ2hydrogen and δ18oxygen for ground water collected from selected wells in the Hazardous Test Area, October 2005.

value because of temperature effects. Ground water at the 

downgradient locations may receive a mix of recharge from 

the San Augustin Mountains and San Andres Mountains (wells 

41 and 45) or some local contributions such as from around 

Mineral Hill (wells 37 and 40), which may produce a slightly 

different isotopic signature than just San Augustin recharge. 

These results partially correspond to calcium/strontium results 

(fig. 27) where ground water from downgradient wells 27, 

45, and 46 indicated a likely limestone-water interaction. 

Limestone is only present in the San Andres Mountains 

(Black Mountain) in the study area.

Denitrification and sulfate reduction will increase (enrich 

the heavier isotope) δ15N and δ18O values for residual nitrate 

and δ34S values for residual sulfate as the lighter isotopes are 

more quickly reduced (Eby, 2004). The δ15N and δ18O values 

of nitrate were heaviest in ground water from wells 12 (upgradient from the pits), 26 (east of the pits), and 43 (downgradient from the pits) (fig. 31). The lightest nitrogen and oxygen 

isotope ratios of nitrate were in ground water from wells 19 

and 11 (near the OB/OD pits). Sulfate in ground water from 

wells 12 and 24, upgradient and north of the OB/OD pits, 

contained the lightest δ34S values, and sulfate in ground water 

from well 46, downgradient from the OB/OD pits, was the 

heaviest (fig. 32). 

The differences in δ15N and δ18O values in nitrate are 

probably the result of mixing of naturally occurring nitrate and 

nitrate derived from explosives at the OB/OD site along with 

the effect of denitrification of the mixed nitrate pool (overall 

mass available for geochemical reactions). Nitrate derived 

from natural organic material typically contains a δ15N greater 

than zero and as much as 9‰ (Fogg and others, 1998; Komor 

and Anderson, 1993). The δ15N values of nitrogen and oxygen 

in nitrate derived from RDX have not been determined, but 

nitrogen used in the production of explosives likely is similar 

to atmospheric nitrogen (0‰) given the atmospheric source 

for nitrogen-based explosives. Coffin and others (2001) determined δ15N values for TNT ranging from 3 to 6‰. The δ15N 

values for nitrate degraded from explosives may be smaller 

than δ15N of the source compound because the lighter isotope 

is preferentially removed from the explosive compound during 

degradation. For these reasons, δ15N of nitrate degraded from 

explosives likely is lighter (smaller) than δ15N of nitrate from 

natural organic sources. The lightest δ15N and δ18O values in 

ground water were located at wells 11 and 19 where some 

of the largest nitrate concentrations were measured. Ground 

water from well 12 (upgradient from the OB/OD site) contained the heaviest δ15N and δ18O values, which indicates a 

mostly natural source of nitrate. The heavier δ15N and δ18O 

values for ground water from wells 26 and 43 indicate denitrification of the mixed nitrate pool.

Biologically mediated sulfate reduction is considered a 

strong reduction indicator because the reduction of oxygen, 

-9.4 -9.2 -9.0 -8.8 -8.6 -8.4 -8.2 -8.0

-67.0

-65.5

-64.0

-62.5

-61.0

-59.5

-58.0

11

12

16

18

19 22

25

26

27

28

31

37

40

41

43

45

46

51

HTA ground water:

δ2

H = 6.4δ18O - 6.2

Overall small range of δ2

H and δ18O 

suggestive of similar source water 

in the Hazardous Test Area (HTA)

δ18O, IN PER MIL

δ2H, IN PER MIL 

Wells in the southern part of HTA 

Wells near or downgradient from the OB/OD site 

Global Meteoric Water Line (Craig, 1961)

δ2

H = 8δ18O + 10

15 Monitoring-site identifier
Natural Attenuation in the Fractured-Granite Aquifer 37

Figure 32. Sulfate concentrations and δ34sulfur values for sulfate in ground water from selected wells in the Hazardous Test Area, 

October 2005.

Figure 31. δ15nitrogen and δ18oxygen values of nitrate in ground water from selected wells in the Hazardous Test Area, October 2005.

4 5 6 7 8 9

-1

0

1

2

3

4

5

11

12

16

18

19

22 25

26

28

31

43

45

51

Natural nitrate

Dominantly nitrate derived

from explosives

Residual nitrate following mixing of anthropogenic 

and natural sources of nitrate and partial denitrification

δ18O OF NITRATE, IN PER MIL 

δ15N OF NITRATE, IN PER MIL

12 Monitoring-site identifier

120 140 160 180 200 220

SULFATE CONCENTRATION, IN MILLIGRAMS PER LITER

2

4

6

8

10

12

14

16

18

20

22

24

12

19

24

25

26

27

45 31

46

51 δ34S OF SULFATE, IN PER MIL

Likely reduction of sulfate and

enrichment of the 34S isotope

12 Monitoring-site identifier
38 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

nitrate, manganese, iron, and organic matter generally will 

occur prior to reduction of sulfate because of the increased 

energy necessary for the reduction reaction (inversely 

described by the electron activity of the solution) (Stumm and 

Morgan, 1996). Sulfur isotopes of sulfate were only measured 

in ground water from a few wells, but the limited results 

suggest an inverse relation between sulfate concentrations and 

δ34S values (fig. 32). This inverse relation likely is the result 

of sulfate reduction that decreased the sulfate concentration 

and increased the isotopic ratio for the residual sulfate. The 

likelihood of sulfate reduction suggests strong reducing 

conditions in parts of the aquifer. 

The aroma of hydrogen sulfide (reduced sulfur form) 

was detected by the authors in ground water from downgradient wells 23, 24, 36, 40, 46, and 48 during the study period 

of 1996–2006, which further suggests downgradient reducing 

conditions and likely degradation of the contaminants in the 

aquifer. Sulfate reduction is not a continuous process in the 

aquifer and likely fluctuates according to inputs and oxygen 

consumption. Hydrogen sulfide has been detected in ground 

water from well 24 but not during the October 2005 sampling. 

Sulfate concentrations and sulfur isotopes of sulfate in ground 

water from well 24 from the October 2005 sampling also do 

not indicate sulfate reduction compared to sulfur isotope data 

from the other wells (fig. 32). Additionally, hydrogen sulfide 

has been detected in ground water from well 34 but not well 

12. This difference in reducing conditions in the two upgradient wells (located within 200 yards of each other) suggests 

different fracture systems radiating from the mountain-front 

interface above the OB/OD site (assuming a closed fracture 

system and no loss of hydrogen sulfide gas if these two wells 

penetrated the same system).

Reduction-Oxidation Sequence

The introduction of anthropogenic organic compounds 

into a closed or semi-closed ground-water system can induce 

a sequence of redox reactions. This redox sequence is microbially mediated and results from the relative ease of certain 

compounds to provide energy to the microbes (Stumm and 

Morgan, 1996). The redox sequence generally consists of 

the following major reactions in order of increasing reducing 

conditions: oxygen consumption (respiration), denitrification, 

manganese reduction, fermentation (organic matter reduction), 

iron reduction, sulfate reduction, and methane fermentation 

(Stumm and Morgan, 1996). Contaminant concentrations and 

isotope ratios indicate that ground water at HTA is undergoing 

redox reactions, and ground water at specific wells is undergoing various reduction processes that can be used to indicate a 

position in the overall redox sequence. 

Using the redox sequence, estimated values of pe- (electron potential, log {e–

}) were assigned to ground water collected in October 2005 from all wells in the larger monitoring 

network that contained data for dissolved oxygen, nitrate, 

manganese, iron, sulfate, and bicarbonate. These values 

were used to estimate the strength of reducing and oxidizing conditions at HTA (fig. 33). Values of pe-

 were assigned 

using median values of the reduction processes over their 

known range as presented in Stumm and Morgan (1996). For 

example, a pe- value of +15 was assigned to ground water 

from a well that indicated aerobic conditions and no visible 

reduction indicators such as increased manganese or iron 

concentrations, as opposed to a pe- value of -7.5 where sulfate 

reduction is likely occurring as indicated by a smaller sulfate 

concentration. Seven possible pe- values were assigned: no 

apparent reduction in dissolved oxygen concentrations (+15), 

likely reduced oxygen concentrations (+10), reduced nitrate 

concentration (+7.5), increased manganese concentration (+5), 

increased iron concentration (-5), decreased sulfate concentration (-7.5), and increased bicarbonate concentration from carbon dioxide production (-10). Values assigned to ground water 

at the individual wells do not convey known electron potentials but are estimates of redox strength based on available data 

for comparison of ground water in and around HTA. 

Spatial variability of redox conditions at HTA (fig. 33) 

supports the conclusion of disconnected or partially connected 

fractures within the aquifer with variable hydraulic conductivities. Moderate to strong reducing conditions are present upgradient from the OB/OD site, at the OB/OD site, and at various 

locations downgradient from the pits, but well-oxygenated 

water also is located between many of the reducing locations. Such changes in redox conditions with downgradient 

flow in a connected aquifer system would require substantial 

re-oxidation of the ground water, which is unlikely given the 

mostly closed nature of the fractured-granite aquifer at HTA. 

The clustering of reducing conditions around the OB/OD pits 

also suggests biodegradation of the contaminants and the subsequent influence on redox conditions in ground water. Strong 

reducing conditions along the periphery of the basin (near 

Black Mountain, Antelope Hill, and Mineral Hill) may be an 

effect of sulfide-mineral dissolution in the mineralized zones 

described in the Ground-Water Composition section.

Summation of Natural Attenuation Indicators

Various indicators of natural attenuation described 

in this report present discrete evidence of dilution and 

degradation of the contaminants in the HTA fractured-granite 

aquifer. Individually, these indicators only suggest natural 

attenuation, but combined, a distinct and fully evident picture 

of natural attenuation is more apparent. Figure 34 spatially 

presents the major indicators for natural attenuation with 

downgradient ground-water flow from the OB/OD site. The 

spatial summation of natural attenuation indicators describes 

partially disconnected fracture systems and natural attenuation 

of the contaminants with downgradient flow. Dilution of the 

contaminants is dominant where oxidizing conditions are 

present as described in the Reduction-Oxidation Sequence 

section above. Degradation assists in naturally attenuating 

the contaminants in areas of reducing conditions given the 
Natural Attenuation in the Fractured-Granite Aquifer 39

Halcox Windmill

5,000

4,700

4,600

4,500

4,400

4,300

4,200

4,100

5,300

5,50

5

0

6, 00

5,700

5,800

5,900

6,000

4,800

4,900

5,400

5 1, 00

5 2, 00

5,600

32o

26'

0 2 KILOMETERS

Base from U.S. Geological Survey digital data, 1994, 1:100,000 0 2 MILES

Universal Transverse Mercator Zone 13N, NAD 83

EXPLANATION

Open burn/open detonation (OB/OD) pit

Paved road

Dirt road

Topographic contour—contour interval

100 feet, datum is NAVD 88

!

+15 Likely strong oxidizing conditions

+10

+7.5

+5

-5

-7.5

-10 Likely strong reducing conditions

!

! !

! !

!

!

!

!

32o

28'

32o

30'

106° 32' 106° 30' 106° 28' 106° 26'

San Augustin Mountains

San Andres Mountains

Highway 70

White Sands Missile Range

Main Post 1.5 mile

Antelope Hill

OB/OD site

Mineral Hill

Hazardous Test Area

!

!

!

!

!

!

!

!

!

Possible electron potential (peˉ)—indicator of

likely reduction-oxidation condition

!

! !

northern Main Post area

Electro-Magnetic 

Radiation Energy area

Black Mountain

!

!

!

! ! !

!

!

!

!

!!

!!

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

Figure 33. Possible reduction-oxidation conditions (relative electron potential values) for ground water at the Hazardous Test Area, 

Electro-Magnetic Radiation Energy area, and northern Main Post area, October 2005.
40 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

3

4

46

33

32 28

27

25

23

22

29

!(

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

5,300

5,500

5,600

5,700

5,400

20

17

5,600

0 1 KILOMETER

Base from U.S. Geological Survey digital data, 1994, 1:100,000 0 0.5 MILE

Universal Transverse Mercator Zone 13N, NAD 83

EXPLANATION

Paved road

Dirt road

(

34!

Monitoring site and designation

!

 24

13 ! 16/16D

!

!

15

 14

 11

 10A

12

21!

! 31

!

30

 18

19

!

 26

32o

30'

106° 30'

San Andres Mountains

OB/OD site

Hazardous Test Area

Black Mountain

!

!

!

5,100

5,200

5,900

5,800

6,000

Overall flow direction but flow is contained in fracture systems 

that may or may not be connected

Most recharge likely occurs at the mountain-front interface

Largest RDX concentrations and other explosives detected in ground water in this area

Largest nitrate and small RDX concentrations

and lightest nitrate isotope ratios

Large perchlorate and chloride concentrations

and increased carbon-dioxide and dissolved-solids concentrations 

Small RDX, nitrate, perchlorate, and oxygen concentrations, 

larger nitrogen gas concentrations, and reducing conditions

Small nitrate and oxygen concentrations, largest nitrogen 

gas concentrations, methane present, heaviest sulfur of 

sulfate isotope ratio, and reducing conditions

Largest perchlorate concentrations

Younger water than upgradient wells,

likely uncontaminanted water mixing

with contaminanted water from the

OB/OD site

Topographic contour—contour interval 100 feet, datum is NAVD 88

32o

29'

106° 31'

6,100

6,200

Methane present, reducing conditions

Smaller dissolved-solids concentrations from

source-water mixing

33

OB/OD pits

Figure 34. Spatial pattern of contamination of the Hazardous Test Area fractured-granite aquifer near the Open Burn/Open Detonation 

site and indicators of natural attenuation that reduce contaminant concentrations in the downgradient direction, October 2005.
Summary 41

greater likelihood of contaminant degradation under anaerobic 

conditions. Substantial contaminant transport beyond the 

existing areal extent of the contaminants appears unlikely 

given the relative “stability” of contaminant concentrations 

from 1996–2006 and the ongoing processes of dilution and 

degradation that produce this concentration stability.

Summary

In 2007, the U.S. Geological Survey, in cooperation with 

U.S. Army White Sands Missile Range, conducted a study of 

ground-water geochemical data collected at the Hazardous 

Test Area at White Sands Missile Range from 1996–2006 to 

evaluate temporal and spatial variability of RDX (explosive 

compound associated with C-4), nitrate, and perchlorate 

(oxidizer associated with rocket propellant) contaminating 

the fractured-granite aquifer. Contamination of the aquifer 

was a result of the use of the Open Burn/Open Detonation 

site at the Hazardous Test Area, and the goal of the analysis 

was to examine natural attenuation mechanisms that appear to 

have induced stability in the areal extent of the contaminant 

concentrations in ground water. 

The Hazardous Test Area is located in southern New 

Mexico, about 25 miles east of Las Cruces and 10 miles north 

of White Sands Missile Range Main Post. The Open Burn/

Open Detonation site is located in the northwestern part of 

the Hazardous Test Area and consisted of two open detonation pits. The pits were used for ordnance demolition, were 

closed in 2000, and partially regraded in 2002 and 2003. The 

Hazardous Test Area aquifer is almost entirely within a fractured, Precambrian-granite pluton that contains diorite dikes. 

Most aquifer recharge likely occurs along the mountain-front 

interface and in ephemeral channels. Two transects of groundwater wells from the existing monitoring-well network—

one perpendicular to ground-water flow (transect A–A ́) and 

another parallel to ground-water flow (transect B–B ́)—were 

selected to examine source characteristics and the spatial 

and temporal variability of the contaminant concentrations. 

Ground-water samples collected in 2005 from a larger sampling of wells than the two transects were analyzed for various 

tracers including major ions, trace elements, RDX degradates, 

dissolved gases, water isotopes, nitrate isotopes, and sulfate 

isotopes to examine the natural attenuation processes of dilution and degradation.

Ground water in the fractures penetrated by monitoring 

wells is pressurized in the closed or semi-closed system, and 

the potentiometric surface parallels land topography except 

immediately downgradient from the pits. An anomaly in the 

potentiometric surface near the Open Burn/Open Detonation 

site is caused by a minor fault that runs through the southern 

part of the site. Recharge entrains contaminants at the site 

and transports them downgradient towards the Tularosa Basin 

floor through a poorly connected fracture system(s). RDX in 

ground water from wells at the Open Burn/Open Detonation 

site indicates a source near the pits but also a dispersed source 

outside of the immediate pit area. The main source of RDX 

has shifted with time, and the shift in peak concentrations 

correspond with the regrading of the south and east berm areas 

of each pit in 2002 and 2003 following site closure. A larger 

dispersal pattern and larger nitrate concentrations compared 

to RDX indicate a larger source area of degrading explosive 

compounds that produce elevated nitrate concentrations in the 

aquifer. The dispersed nitrate source did shift with time and 

corresponded with berm regrading. The source of perchlorate 

appears to be more concentrated compared to RDX and nitrate 

sources, and the source location of perchlorate has not shifted 

with time. 

From 1996–2006, RDX, nitrate, and perchlorate concentrations in ground water downgradient from the Open Burn/

Open Detonation site have been relatively stable. Natural 

attenuation (dilution and (or) degradation) appears to be reducing contaminant concentrations within 0.5 mile downgradient 

from the site. Largest RDX concentrations were located within 

0.1 mile of the pits (wells 10A, 11, and 14). The largest nitrate 

concentrations were present in ground water about 0.25 mile 

downgradient from the pits (well 19). Perchlorate concentrations were largest in ground water from wells 16 and 16D 

(about 0.15 mi downgradient from the pits), and perchlorate 

concentrations quickly declined further downgradient. There 

is limited correlation between changes in water levels and 

contaminant concentrations and between the concentrations of 

the explosives-related contaminants of RDX and nitrate except 

at the largest contaminant concentration locations.

Ground water was not progressively older at all locations 

in the downgradient direction, and age-dating results may 

be evidence of disconnected or partially connected fractures 

and downgradient recharge and mixing of contaminant and 

uncontaminated waters. Dissolved-solids concentrations 

in ground water in the Open Burn/Open Detonation site 

area were largest north-northeast of the pits, concentrations 

increased immediately downgradient from the pits because 

of contaminant inputs, and concentrations then decreased 

likely because of dilution from downgradient flow mixing. 

Major ion and strontium concentrations and δ2H and δ18O 

values identified similar sources of recharge waters to the 

aquifer except along the basin periphery where recharge water 

may be influenced by dissolution of mineral assemblages 

associated with ore deposits that are present along the basin 

margins. Some recharge appears to be crossing the Bear 

Peak Fold and Thrust Zone from the San Andres Mountains 

and mixing within certain fractures as indicated by calcium, 

strontium, and δ2H and δ18O values. The RDX degradates of 

MNX and DNX were present in ground water in a few wells 

near and downgradient from the pits in October 2005. In the 

downgradient direction, the largest RDX concentrations were 

in ground water from well 10A followed by downgradient 

decreases to near nondetection levels by well 19. This pattern 

was opposite of the downgradient nitrate pattern that indicated 

an increasing nitrate concentration from well 12 to the largest 

nitrate concentration in ground water from well 19. This 
42 Geochemical Trends and Natural Attenuation of RDX, Nitrate, and Perchlorate in the Hazardous Test Area, New Mexico

inverse pattern from the Open Burn/Open Detonation pits 

to well 19 suggests a contribution of nitrate to ground water 

from the degradation of RDX. The likely degradation of RDX 

can only account for a small part of the increase in nitrate, 

which suggests additional nitrate inputs. These other nitrate 

inputs may be related to the degradation of other explosive 

compounds—such as HMX, DNT, TNT, and teryl—that have 

been detected in soil samples in and around the pits but are 

rarely detected in ground water and only at wells near the 

Open Burn/Open Detonation pits, including wells 10A, 11, 13, 

14, 16, 16D, 20, and 24. 

Nitrogen-gas and nitrate concentrations in ground water 

from downgradient wells showed an inverse relation and indicated degradation of nitrate at certain locations in the aquifer. 

The presence of methane and changes in likely carbon-dioxide 

concentrations in ground water from certain wells suggest 

reducing conditions and degradation of the contaminants. The 

perchlorate and chloride relation indicates perchlorate degradation at the Open Burn/Open Detonation pits and dilution 

of perchlorate and chloride downgradient from the pits. The 

lightest δ15N and δ18O values of nitrate in ground water were 

located at wells 11 and 19 where the largest nitrate concentrations were present. Ground water from the background well 

(12) contained the heaviest δ15N and δ18O values because of 

a natural nitrate source. The lighter δ15N and δ18O values for 

ground water in downgradient wells suggest denitrification of 

the mixed nitrate pool. Sulfate concentrations and δ34S values 

also indicate redox changes and reduction downgradient from 

the Open Burn/Open Detonation pits.

Estimated electron potential values were assigned to 

ground water collected in October 2005 from all wells at the 

Hazardous Test Area that contained data for dissolved oxygen, 

nitrate, manganese, iron, sulfate, and bicarbonate. Moderate to 

strong reducing conditions were present upgradient from the 

Open Burn/Open Detonation site, at the site, and at various 

locations downgradient from the site, even though the aquifer 

contained well-oxygenated water between many of the reducing locations. The spatial variability of reducing conditions 

in the aquifer exemplifies disconnected or partially connected 

fractures and natural attenuating conditions with downgradient 

flow. Dilution of contaminants is dominant where oxidizing 

conditions are present and biodegradation assists in naturally 

attenuating the contaminants in areas of reducing conditions. 

Substantial contaminant transport beyond the existing areal 

extent of the contaminants appears unlikely given the relative 

“stability” of contaminant concentrations from 1996–2006 and 

the ongoing processes of dilution and degradation that produce 

this concentration stability.

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