Geochemical Trends and Natural Attenuation of RDX, Nitrate ...2. Hazardous Test Area, Open Burn/Open Detonation (OB/OD) site, and monitoring sites, White Sands Missile Range, New Mexico.....4

U.S. Department of the InteriorU.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


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 InteriorU.S. Geological Survey

U.S. Department of the InteriorDIRK KEMPTHORNE, Secretary

U.S. Geological SurveyMark 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 ...........................................................................................................................................................1Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2Description of the Study Area ............................................................................................................2

Geology and Hydrology ...............................................................................................................6Anthropogenic Compounds .......................................................................................................6

Previous Studies ...................................................................................................................................8Study Methods ......................................................................................................................................8Acknowledgments ..............................................................................................................................14

Geochemical Trends of RDX, Nitrate, and Perchlorate in the Fractured-Granite Aquifer ..............14Fracture Flow in the Fractured-Granite Aquifer ............................................................................14Contaminant Variability at the Open Burn/Open Detonation Site ...............................................18Downgradient Contaminant Variability ...........................................................................................22Water Level and Contaminant Relation ...........................................................................................28

Natural Attenuation in the Fractured-Granite Aquifer ..........................................................................28Tritium-Helium Age Dating and Dilution ..........................................................................................30Ground-Water Composition ..............................................................................................................30

Dilution ........................................................................................................................................30Degradation and Changes to Carbon Forms .........................................................................33Natural Attenuation and Chloride ...........................................................................................34

Stable Isotopes....................................................................................................................................35Reduction-Oxidation Sequence .......................................................................................................38Summation of Natural Attenuation Indicators ...............................................................................38

Summary........................................................................................................................................................41Selected 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 litermg/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

AbstractA 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 perchlo-rate 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 characteris-tics 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 down-gradient from the pits. Strong and moderate correlation of


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/con-taminant 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 well-oxygenated 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

IntroductionIn 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 (NO

3-

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 con ductivity 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 fractured-granite 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 vis-ible across the surface of the pediment. Vegetation consists mostly of perennial grasses, woody brushes, yucca, prickly

Introduction 3

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34

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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).


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 maxi-mum 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 HydrologyThe study area is surrounded by the San Andres Moun-

tains 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 environ-ment (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 weather-ing 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 com-position 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 CompoundsSince 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 con centrations 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

RattlesnakeRidge

Mineral Hill

Black PrinceCanyon

San AugustinMountains

San AndresMountains

7 0

Orga

n M

ount

ains

Fau

lt

3,000

4,000

5,000

6,000

7,000

MILES

8,000

0 1 2 3 4 5

ELEV

ATIO

N, I

N F

EET

C

C’

C

C’

OB/OD pits

Blac

k Pr

ince

Fau

lt Zo

ne

Bear Peak Fold and Thrust Zone

106° 32' 106° 30' 106° 28'

32º28'

32º30'

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 soil2 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 faultsin this area (Seager, 1981)

Precambrian granite pluton with diorite dikes

!

Normal fault—bar and ball on downthrown sideThrust fault—saw teeth on upthrown side

Base from U.S. Geological Survey National Elevation Dataset,1/9 arc second, 1:24,000, 2007Universal Transverse Mercator Zone 13N, NAD 83Faults, 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.


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 eas-ily 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 per-chlorate to chlorate (ClO

3–) and chlorite (ClO

2–) (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 moni-toring 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 evalu-ating 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 characteris-tics 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 tritium-helium 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 9Ta

ble

1.

Open

Bur

n/Op

en D

eton

atio

n Si

te a

nd H

azar

dous

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a st

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te in

form

atio

n.—

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inue

d

[USG

S, U

.S. G

eolo

gica

l Sur

vey;

NA

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3, N

orth

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eric

an D

atum

of

1983

; NA

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88,

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th A

mer

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tical

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um o

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ava

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sign

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gs. 2

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)

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199

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39.3

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199

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2032

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2432

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1632

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2935

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2932

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2732

2927

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4332

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2913

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2132

2933

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132

29

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Nov

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

ble

1.

Open

Bur

n/Op

en D

eton

atio

n Si

te a

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te in

form

atio

n.—

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d

[USG

S, U

.S. G

eolo

gica

l Sur

vey;

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atum

of

1983

; NA

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th A

mer

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tical

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, Haz

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rea;

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/O

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n/O

pen

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ion;

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, not

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e]

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de

sign

atio

n (fi

gs. 2

and

5)

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te

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tific

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de

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e (N

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l dep

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es

2532

2943

1063

1050

132

29

43N

106

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Dec

embe

r199

9Y

es

2632

2940

1063

0510

132

29

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0PV

C18

0-20

0D

ecem

ber1

999

Yes

2932

2944

1063

1160

132

29

44N

106

31 1

6W5,

725.

515

8PV

C13

4-15

4D

ecem

ber1

999

Yes

3032

2939

1063

0570

132

29

39N

106

30 5

7W5,

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ecem

ber1

999

Yes

3132

2902

1063

0220

132

29

02.4

8N10

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23.

94W

5,25

1.7

85PV

C65

-85

Janu

ary

2002

Yes

3232

2924

1063

0260

132

29

24.0

5N10

6 30

28.

27W

5,34

3.8

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C55

-75

Janu

ary

2002

Yes

3332

2848

1063

0550

132

28

48.4

2N10

6 30

56.

83W

5,36

8.8

107

PVC

87-1

07Ja

nuar

y 20

02Y

es

3432

2943

1063

1280

132

29

43.4

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6 31

29.

88W

5,79

4.9

103

PVC

83-1

03Ja

nuar

y 20

02Y

es

3532

2704

1062

9060

132

27

04.6

1N10

6 29

08.

01W

4,61

8.4

159

PVC

139-

159

Janu

ary

2002

No

3632

2702

1062

9440

132

27

02.7

1N10

6 29

46.

23W

4,79

8.5

97PV

C77

-97

Janu

ary

2002

No

3732

2639

1062

9470

132

26

39.5

2N10

6 29

49.

2W4,

695.

913

8PV

C11

8-13

8Ja

nuar

y 20

02N

o

3832

2624

1063

0020

132

26

24.8

2N10

6 30

04.

01W

4,72

3.9

119

PVC

99-1

19Ja

nuar

y 20

02N

o

3932

2612

1062

9490

132

26

12.4

8N10

6 29

50.

73W

4,64

9.4

149

PVC

129-

149

Janu

ary

2002

No

4032

2609

1062

9140

132

26

09.2

6N10

6 29

15.

93W

4,51

3.6

199

PVC

179-

199

Janu

ary

2002

No

4132

2731

1062

8190

132

27

31.7

2N10

6 28

21.

12W

4,50

2.1

125

PVC

105-

125

Janu

ary

2002

Yes

4232

2837

1062

9430

132

28

37.3

3N10

6 29

44.

64W

4,99

3.5

137

PVC

117-

137

Janu

ary

2002

Yes

4432

2745

1063

0020

132

27

45.7

5N10

6 30

04.

4W4,

938.

313

9PV

C11

9-13

9Ja

nuar

y 20

02N

o

47A

3228

2710

6280

101

32 2

8 27

.04N

106

28 0

3.31

W4,

491.

718

4PV

C16

0-18

0Fe

brua

ry 2

003

No

4832

2538

1062

8570

132

25

37.8

4N10

6 28

58.

55W

4,40

6.4

159

PVC

139-

159

Janu

ary

2002

No

4932

2508

1062

9100

132

25

08N

106

29 1

1.62

W4,

411.

841

9PV

C38

9-41

9D

ecem

ber2

001

Yes

5032

2834

1062

7320

132

28

33.6

4N10

6 27

33.

38W

4,36

6.4

516

PVC

486-

516

Janu

ary

2002

Yes

5132

2901

1062

9010

132

29

00.9

3N10

6 29

03.

39W

4,83

4.8

145

PVC

122-

142

Febr

uary

200

3N

o

Introduction 11Ta

ble

1.

Open

Bur

n/Op

en D

eton

atio

n Si

te a

nd H

azar

dous

Tes

t Are

a st

udy

area

mon

itorin

g-si

te in

form

atio

n.—

Cont

inue

d

[USG

S, U

.S. G

eolo

gica

l Sur

vey;

NA

D 8

3, N

orth

Am

eric

an D

atum

of

1983

; NA

VD

88,

Nor

th A

mer

ican

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tical

Dat

um o

f 19

88; l

s, la

nd s

urfa

ce; P

VC

, pol

yvin

yl c

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HTA

, Haz

ardo

us T

est A

rea;

OB

/O

D, O

pen

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n/O

pen

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onat

ion;

NA

, not

ava

ilabl

e]

Site

de

sign

atio

n (fi

gs. 2

and

5)

USG

S si

te

iden

tific

atio

n nu

mbe

r

Latit

ude

(NA

D 8

3)Lo

ngitu

de

(NA

D 8

3)

Land

-sur

face

al

titud

e (N

AVD

88)

Wel

l dep

th

(fe

et b

elow

ls

)

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ng

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eria

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(fee

t be

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30 0

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0PV

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embe

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es

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Win

dmill

3223

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101

32 2

8 24

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6 50

52W

5,21

4.7

NA

NA

NA

NA

Mar

kham

Spr

ing

3229

5210

6314

401

32 2

9 52

.32N

106

31 4

5.99

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2N

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AN

AN

AY

es

Bon

ney

Spri

ng

Min

e

Win

dmill

3229

3810

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106

29 1

0.67

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Stee

lN

AN

AN

o

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cox

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dmill

3227

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106

29 0

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037

NA

NA

NA

No


346

45

43

2827

23

20

1816

14

1224

19

13

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!

!!! !

!

!

!

!

!

!

!

5

!

!

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4,800

5,0005,1

00

4,600

5,200

5,300

5,40

0

5,600

5,700

6,00

0 5,500

4,700

5,80

05,900

4,900

106º

31'

3 0°

2 8'

00.

5K

ILO

ME

TER

00.

5M

ILE

3 2°

2 9'

3 2°

30'

106º

30'

106º

29'

5,600

EXPL

ANAT

ION

Open

bur

n/op

en d

eton

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n (O

B/OD

) pit

Pave

d ro

ad

Topo

grap

hic

cont

our—

cont

our i

nter

val 1

00 fe

et, d

atum

is N

AVD

88

Dirt

road

Mon

itorin

g si

te a

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l tra

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A

A’B

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t are

a

23

20

16

14

12

24

13

11

16D

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!!

!

!

!

! !

!

!

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A

B

19

AA’

Base

from

U.S

. Geo

logi

cal S

urve

y di

gita

l dat

a, 1

994,

1:1

00,0

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iver

sal T

rans

vers

e M

erca

tor Z

one

13N

, NAD

83

B’!

OB/O

D si

te

east

pit

wes

t 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) DescriptionMethod/Lab

codeAnalytical precision

Contaminant and field data collected from 1996–2006:

ExplosivesExplosive compounds1, including

RDX and its degradates, analyzed by HPLC1

SW846 83302 0.05 to 0.25 µg/L

Nitrate NO3 and NO

2 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, CO

2, He, N

2, O

2

Gas chromatography with thermal conductivity detector (Ar, He, N

2, O

2) and flame ionization

detector (CH4, CO

2)

±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

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

Water isotopes 2/1H, 18/16OUSGS 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 sulfateUSGS 1951 (Carmody and others, 1997; Glesemann

and others, 1994)±0.4 ‰ as δ34S

Trace elementsAg, 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

1RDX; 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 perpen-dicular 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 tempo-ral 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 contami-nant concentrations between wells to identify source locations, transport characteristics, and possible natural attenuation of contaminants. All non-detect values (less than method detec-tion level) were assigned zero values. The Wilcoxon rank-sum 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’ con-centrations were analyzed for correlation strength. With the assumption that changes in ground-water flow and contami-nant 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 explo-sive-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 rank-ings 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-


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 dis-solved-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 water-quality 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 Fractured-Granite Aquifer

Contaminant trends in the fractured-granite aquifer at HTA can provide information concerning source location(s), transport, and natural attenuation of the contaminants. Differ-ences 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 trans-port 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 monitor-ing 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 water-producing 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 frac-tures 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 connec-tivity 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 feetand at 98 feet

Minor water-producing fracture

Granite, dry, except some moistureat 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 feetwith 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 additionalwater

Granite, airlift dischargemeasured at 243 feet was sameas at 178.5 feet, no additionalwater

No additional water-producingfractures penetrated in the bottom 120 feet of the borehole

No data

BOREHOLE IMAGEDRILLING LOG DRILLING LOG

Scale(feet)S W N E S

Scale(feet)

Scale in feet and representsdepth below land surface

BOREHOLE IMAGES W N E S

Variable fracture orientation indicated bydifferent fracture shapesshown in the unwrappedborehole image

Figure 6. Borehole image and drilling log from construction of well 28 at the Hazardous Test Area, December 1999.


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 75100

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 tailpoints in the azimuth direction of dip.

BOREHOLE BOREHOLE WELL WELL WELL WELL WELL

DEPT

H BE

LOW

LAN

D SU

RFAC

E, IN

FEE

T

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

4,600

4,550

4,650

4,700

4,850

4,750

4,900

4,950

5,250

4,800

5,000

5,200 5,0

505,1

00

5,150

5,350

5,450

5,400

5,500

5,650

5,700

5,600

5,600

5,300

5,550

5,650

5,2

90

585.

0

5,2

89.0

5,2

39.2

4,94

5.4

4,93

6.7

5,07

4.4

4,56

1.0

4,88

5.8

4,92

8.0

5,7

44.6

5,30

9.8

5,31

1.1

5,20

8.8

5,47

6.8

5,6

30.1

5,39

2.64

5,43

1.55

5,5

58.8

5,59

0.0

5,4

63.8

5,55

1.2

5,55

7.3

1

4,74

8.7

5,37

3.8

!

(

!

!

!

!!

!

!

!!

!

!

!

! !

!

!

5

!

!

!

!

!

!

!

!

!

(

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!

(

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4,800

5,0005,1

00

4,600

5,200

5,300

5,40

0

5,600

5,700

6,00

0 5,500

4,700

5,80

05,900

4,900

32º

30'

106˚

31'

106˚

30'

106˚

29'

5,01

1.0

32º

29'

32º

28'

4,600

4,550

4,650

4,700

4,850

4,750

4,900

4,950

5,250

4,800

5,000

5,200 5,0

505,1

00

5,150

5,350

5,450

5,400

5,500

5,650

5,700

5,600

5,600

5,300

5,550

5,650

5,29

0.0

5,58

5.0

5,28

9.0

5,23

9.2

4,94

5.4

4,93

6.7

5,07

4.4

4,56

0.9

4,88

5.8

4,92

8.0

5,74

4.6

5,30

9.8

5,31

1.2

5,20

8.8

5,47

6.8

5,63

0.1

5,39

2.6

5,43

1.5

5,55

8.8

5,59

0.0

5,46

3.8

5,55

1.2

5,55

7.3

4,74

8.7

5,16

4.6

5,42

2.2

5,37

3.8

4,60000.

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9.5

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from

U.S

. Geo

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urve

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a, 1

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1:1

00,0

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erca

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rdou

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nd-w

ater

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Figure 8. Potentiometric-surface contours and ground-water flow paths in the Hazardous Test Area fractured-granite aquifer, New Mexico, October 2006.


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 fractured-granite 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, writ-ten commun., 2003). The strike of the fault was inferred to run northwest to southeast from the east pit to a location betwe

Documents

Geochemical Trends and Natural Attenuation of RDX, Nitrate ...2. Hazardous Test Area, Open Burn/Open Detonation (OB/OD) site, and monitoring sites, White Sands Missile Range, New Mexico.....4