U.S. Department of the Interior

U.S. Geological Survey

Data Series 678

Prepared in cooperation with the Middle Pecos Groundwater Conservation District, 

Pecos County, City of Fort Stockton, Brewster County, and Pecos County Water Control 

and Improvement District No. 1

Data Collection and Compilation for a Geodatabase of 

Groundwater, Surface-Water, Water-Quality, Geophysical, 

and Geologic Data, Pecos County Region, Texas, 1930–2011
Cover left. The historical topographic map is a closeup of the City of Fort Stockton, Pecos County, Texas,

Fort Stockton quadrangle (U.S. Geological Survey, 1923, scale 1:62,500). The map also shows 

Comanche Springs, which is one of the sampling sites in this study.

Cover right. Water-quality sampling by U.S. Geological Survey, San Solomon Springs, Balmorhea, Texas 

(photograph by T. L. Sample, U.S. Geological Survey).
Data Collection and Compilation for a 

Geodatabase of Groundwater, SurfaceWater, Water-Quality, Geophysical, and 

Geologic Data, Pecos County Region, 

Texas, 1930–2011

By Daniel K. Pearson, Johnathan R. Bumgarner, Natalie A. Houston, 

Gregory P. Stanton, Andrew P. Teeple, and Jonathan V. Thomas

Prepared in cooperation with the Middle Pecos Groundwater Conservation 

District, Pecos County, City of Fort Stockton, Brewster County, and 

Pecos County Water Control and Improvement District No. 1

Data Series 678

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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:

Pearson, D.K., Bumgarner, J.R., Houston, N.A., Stanton, G.P., Teeple, A.P. and Thomas, J.V., 2012, Data 

collection and compilation for a geodatabase of groundwater, surface-water, water-quality, geophysical, 

and geologic data, Pecos County region, Texas, 1930–2011: U.S. Geological Survey Data Series 678, 67 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................1

Description of Study Area ...................................................................................................................3

Hydrogeologic Setting .........................................................................................................................3

Methods...........................................................................................................................................................7

Water-Quality Methods........................................................................................................................7

Water-Quality Sample Collection..............................................................................................7

Groundwater Sampling......................................................................................................7

Surface-Water Sampling.................................................................................................10

Spring Sampling................................................................................................................10

Analytical Methods ...................................................................................................................10

Geochemical Quality Assurance.............................................................................................11

Geophysical Methods ........................................................................................................................25

Surface Geophysical Methods ...............................................................................................25

Time-Domain Electromagnetic Soundings ............................................................................25

Audiomagnetotelluric Soundings............................................................................................29

Inverse Modeling of Surface Geophysical Results..............................................................29

Borehole Geophysical Methods..............................................................................................30

Electromagnetic Induction Logs .............................................................................................30

Natural Gamma Logs.................................................................................................................30

Electric Logs ...............................................................................................................................30

Caliper Logs ................................................................................................................................30

Fluid Resistivity and Temperature Logs..................................................................................31

Optical Borehole Imaging.........................................................................................................31

Acoustic Borehole Imaging ....................................................................................................31

Electromagnetic Flowmeter.....................................................................................................31

Geophysical Data Quality Assurance and Formats .............................................................32

Geodatabase Compilation ..........................................................................................................................32

Geodatabase Design..........................................................................................................................32

Data Input.............................................................................................................................................33

Geodatabase Data Quality Assurance............................................................................................33

Metadata..............................................................................................................................................33

References Cited..........................................................................................................................................35

Glossary.........................................................................................................................................................39

Appendix 1. Time-Domain Electromagnetic Resistivity from Field 

Measurements as a Function of Time and Inverse Modeling Results 

(Smooth and Layered-Earth Models)..........................................................................................41

Appendix 2. Inverse Modeling Results of Audio-Magnetotelluric Soundings 

as a Function of Resistivity and Depth........................................................................................47

Appendix 3. Digital Database Resources.............................................................................................61

Appendix 4. Federal Geographic Data Committee-Compliant Metadata Record..........................63
iv

Figures

1. Map showing location of study area and Pecos County region, 

Texas, 2011.....................................................................................................................................2

2. Map showing extent of the major aquifers (Pecos Valley, 

Edwards-Trinity [subcrop], and Edwards-Trinity [outcrop]) and minor 

aquifers (Igneous, Dockum, Rustler, and Capitan Reef Complex), 

Pecos County region, Texas, 2011..............................................................................................6

3. Map showing site locations of field-collected geochemical data, 

Pecos County region, Texas, 2010–11 .......................................................................................8

4. Site locations of field-collected geophysical data, including 

borehole logging and surface geophysical sites, Pecos County region, 

Texas, 2009–11.............................................................................................................................26

5. Diagram showing simplified geodatabase data model for hydrogeologic 

data for the Pecos County region, Texas, 2011......................................................................34

Tables

1. Hydrostratigraphic section in the Pecos County region, Texas............................................4

2. Geochemical data-collection sites in the Pecos County region, 

Texas, 2010–11...............................................................................................................................9

3. Helium-4 measured in groundwater samples collected in the Pecos 

County region, Texas, 2010–11..................................................................................................10

4. Results of major ion, trace element, and nutrient analyses from 

equipment blanks and field blanks collected in association with 

geochemical samples collected in the Pecos County region, 

Texas, 2010–11.............................................................................................................................12

5. Relative percent differences between sequential replicate and 

environmental samples analyzed for major ions, trace elements, and 

elemental isotopes collected in the Pecos County region, Texas, 2010–11......................22

6. Time-domain electromagnetic geophysical sounding sites, Pecos 

County region, Texas, 2009–11..................................................................................................27

7. Audio magnetotelluric geophysical sounding sites, Pecos County region, 

Texas, 2009–11.............................................................................................................................27

8. Borehole geophysical data-collection sites, Pecos County region, 

Texas, 2009–11.............................................................................................................................28
v

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

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

°F=(1.8×°C)+32

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

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

or micrograms per liter (μg/L).

Data Collection and Compilation for a Geodatabase 

of Groundwater, Surface-Water, Water-Quality, 

Geophysical, and Geologic Data, Pecos County 

Region, Texas, 1930–2011

By Daniel K. Pearson, Johnathan R. Bumgarner, Natalie A. Houston, Gregory P. Stanton, 

Andrew P. Teeple, and Jonathan V. Thomas 

Abstract

The U.S. Geological Survey, in cooperation with Middle 

Pecos Groundwater Conservation District, Pecos County, 

City of Fort Stockton, Brewster County, and Pecos County 

Water Control and Improvement District No. 1, compiled 

groundwater, surface-water, water-quality, geophysical, and 

geologic data for site locations in the Pecos County region, 

Texas, and developed a geodatabase to facilitate use of this 

information. Data were compiled for an approximately 

4,700 square mile area of the Pecos County region, Texas. 

The geodatabase contains data from 8,242 sampling 

locations; it was designed to organize and store field-collected 

geochemical and geophysical data, as well as digital database 

resources from the U.S. Geological Survey, Middle Pecos 

Groundwater Conservation District, Texas Water Development 

Board, Texas Commission on Environmental Quality, and 

numerous other State and local databases. The geodatabase 

combines these disparate database resources into a simple data 

model. Site locations are geospatially enabled and stored in a 

geodatabase feature class for cartographic visualization and 

spatial analysis within a Geographic Information System. The 

sampling locations are related to hydrogeologic information 

through the use of geodatabase relationship classes. The 

geodatabase relationship classes provide the ability to perform 

complex spatial and data-driven queries to explore data stored 

in the geodatabase.

Introduction

The U.S. Geological Survey (USGS), in cooperation 

with the Middle Pecos Groundwater Conservation District 

(MPGCD), Pecos County, City of Fort Stockton (COFS), 

Brewster County, and Pecos County Water Control and 

Improvement District No. 1, developed a geodatabase 

of available groundwater, surface-water, water-quality, 

geophysical, and geologic data for site locations in the Pecos 

County region, Texas (fig. 1). Digital data resources from 

existing databases and previous publications were identified 

and assessed for inclusion into the geodatabase based on 

data quality and completeness. Data were gathered from 

various Federal, State, and local databases including USGS, 

MPGCD, COFS, Texas Water Development Board (TWDB), 

Texas Commission on Environmental Quality (TCEQ), 

Texas Railroad Commission (TXRRC), U.S Environmental 

Protection Agency (USEPA), and the University of Texas 

Land System (UTLD). In addition to downloadable data 

sources, geochemical and geophysical data collected by the 

USGS during 2009–11 were included into the geodatabase. 

The geodatabase contains data from 8,242 sampling 

locations (sites) in the study area. Data from groundwater, 

surface-water, and water-quality sampling sites are included. 

Geophysical data and driller log files were compiled for 626 of 

the groundwater sites, along with the geologic data associated 

with those logs.

Purpose and Scope

This report documents data collection, compilation, 

and geodatabase design for a geodatabase of groundwater, 

surface-water, water-quality, geophysical, and geologic 

data collected from more than 8,000 sampling locations in 

the Pecos County region, Texas. Data were compiled from 

existing digital databases, previously published reports, and 

USGS field-collected data. The geodatabase compiled for 

this report will be used by the cooperating agencies as a data 

clearinghouse for obtaining groundwater, surface-water, 

water-quality, geophysical, and geologic data. Following 

a description of the study area, the methodologies used for 

field-collected data acquisition and the compilation of existing 

digital database resources and previously published reports in 

the geodatabase are described. The geodatabase compilation 

processes section includes an explanation of the geodatabase 

design, data input steps, and quality-assurance controls. The 

geodatabase provides detailed information regarding site 

locations and associated groundwater, surface-water, waterquality, geophysical, and geologic information.
2 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

HTEPS DUH

COUNTY

WINKLER

COUNTY ECTOR

COUNTY

MIDLAND

COUNTY

GLASSCOCK

COUNTY

STERLING

COUNTY

CULBERSON

COUNTY

COKE

COUNTY

REEVES

COUNTY

LOVING

COUNTY

WARD

COUNTY CRANE

COUNTY UPTON

COUNTY

REAGAN

COUNTY

IRION

COUNTY

PECOS 

COUNTY

JEFF DAVIS

COUNTY CROCKETT COUNTY

PRESIDIO

COUNTY

BREWSTER

COUNTY

NOTTUS

COUNTY

SCHLEICHER

COUNTY

TERRELL

COUNTY

VAL VERDE

COUNTY

Wink

Monahans

Pecos

Crane

Rankin

Big Lake Mccamey

Van Horn

Fort

Stockton Iraan

Ozona

Alpine

Marfa

Sanderson

Presidio

Grandfalls

Girvin

Pecos River

Pecos River

E D W A R D S P L A T E A U PECOS VALLEY

MEXICAN HIGHLAND

H I G H P L A I N S

B A R I L L A 

M O U N T A I N S

G L A S S 

M O U N T A I N S

MARATHON

BASIN

TOYAH 

BASIN

Río Grande

Río Grande

31°30' 31°30'

30°0' 30°0'

102°0'

102°0'

103°30'

103°30'

TEXAS

Study area

LOCATION MAP

EXPLANATION

Pecos County regionStudy areaBasin and range boundaryGreat plains boundary

0 20 40 MILES 10

20 40 KILOMETERS 0 10

Base modified from U.S. Geological Survey 1:2,000,000-scale digital dataAlbers Equal Area Projection, Texas State Mapping SystemNorth American Datum of 1983

Physiographic division data from 

Fenneman and Johnson, 1946

Figure 1. Location of study area and Pecos County region, Texas, 2011.
Introduction 3

Description of Study Area

The study area (fig. 1) includes the western part of the 

MPGCD management area (Pecos County) and extends 

beyond Pecos County to include the extent of the fieldcollected data gathered for this project. The study area was 

modified from the TWDB Groundwater Availability Model 

(GAM) of the Edwards-Trinity and Pecos Valley aquifers 

extent (Anaya and Jones, 2009). The northeastern boundary 

of the project study area was set at the Pecos River, while 

the southeastern and northwestern boundaries were aligned 

to the data cells of the GAM model and set to the extent of 

the geodatabase contents. The southwestern boundary was 

modified using the “active” part of the GAM model as a 

template for editing the final study area boundary. Geospatial 

data were compiled for the Pecos County region of West Texas 

including parts of Pecos, Reeves, Jeff Davis, Brewster, Terrell, 

Crane, Ward and Crockett Counties. 

The study area is located in the Pecos Valley, Edwards 

Plateau, and High Plains sections of the Great Plains 

Physiographic Province and the Mexican Highland section 

of the Basin and Range Province (Fenneman and Johnson, 

1946; fig. 1). West of the Pecos River, the Edwards Plateau 

section of the Great Plains Physiographic Province (Fenneman 

and Johnson, 1946) is defined by the boundary of the major 

geographic features in the area: (1) the Pecos River; (2) the 

Toyah Basin; (3) the Marathon Basin, characterized by ridges 

and isolated buttes and mesas; (4) the Glass Mountains; and 

(5) the Barilla Mountains (Small and Ozuna, 1993, fig. 1).

Hydrogeologic Setting

The geologic setting contributed to the formation of two 

major and four minor aquifers in the study area. The major 

aquifers include the Pecos Valley and the Edwards-Trinity, 

and the minor aquifers include the Igneous, the Dockum, 

the Rustler, and the Capitan Reef Complex (also called the 

Capitan Reef) aquifers (table 1, fig. 2). The Pecos Valley 

aquifer is composed of Cenozoic-age alluvium consisting of 

unconsolidated silt, sand, gravel and clay (Small and Ozuna, 

1993). In the northern part of the study area the Pecos Valley 

aquifer uncomformably overlies the Cretaceous-age 

Edwards-Trinity aquifers, Triassic-age Dockum aquifer, 

and Permian-age Rustler aquifer. The Igneous aquifer is a 

minor aquifer that is composed of Tertiary-age volcanic and 

volcaniclastic rocks. Located southwest of the study area, 

the Igneous aquifer uncomformably overlies the Cretaceousage Edwards-Trinity aquifer. The Edwards-Trinity aquifer 

is composed of lower Cretaceous-age rocks of limestone, 

marl, and clay of the Washita Group; limestone of the 

Fredericksburg Group; and sand, limestone, and shale of the 

Trinity group (table 1). The Edwards part of the aquifer is 

composed of rocks of the Washita and Fredericksburg Groups, 

which locally are referred to as the Edwards and Sixshooter 

Groups (Brand and DeFord, 1958; Small and Ozuna, 1993; 

Smith and others, 2000). The Fort Lancaster Formation, the 

Burt Ranch Member, and the Fort Terrett Formation make up 

the Edwards Group and occur in the eastern part of the study 

area (Rose, 1972; Smith and Brown, 1983; Small and Ozuna, 

1993). The Boracho Formation, the University Mesa Marl, 

which is a facies change equivalent of the Boracho Formation, 

and the Finlay Formation make up the Sixshooter Group and 

occur in the western part of Pecos County (Brand and DeFord, 

1958; Small and Ozuna, 1993; Smith and others, 2000). The 

Buda Limestone, which overlies the Boracho Formation, is 

present east of Fort Stockton. Regionally, the Buda 

Limestone, the Fort Lancaster Formation, and the Burt 

Ranch Member form the Washita Group. The Fort Terrett 

Formation forms the Fredericksburg Group. The Trinity 

group is composed of the Maxon Sand, the Glen Rose 

Formation, and the Basal Cretaceous Sand (Anaya and Jones, 

2009). The individual formations in the Trinity Group are not 

separated for the purposes of this report. Locally the Trinity 

Group is known as the Trinity Sands (Small and Ozuna, 

1993; Rees and Buckner, 1980). 

The Dockum aquifer is a minor aquifer and is composed 

of Triassic-age rocks of shale, sand, sandstone, and 

conglomerate of the Dockum Group (Bradley and Kalaswad, 

2003). The stratigraphic nomenclature of the Dockum Group 

has been updated and regionalized in the literature as better 

information became available (Lehman, 1994a,b; Bradley 

and Kalaswad, 2003). In Pecos County, a sand unit within the 

Dockum aquifer is recognizable in some geophysical logs, 

but the individual formations of the Dockum Group are not 

separated for the purposes of this report. Locally, the Dockum 

aquifer is also known as the Santa Rosa aquifer (Small and 

Ozuna, 1993).

The Rustler and Capitan Reef aquifers are minor 

aquifers composed of Permian-age rocks. The Rustler 

aquifer is composed of mostly dolomite, anhydrite, and some 

limestone of the Rustler Formation. A basal unit consists of 

sand, conglomerate, and some shale (Small and Ozuna, 1993; 

LBG-Guyton, 2003). The Capitan Reef aquifer consists of 

reef, fore-reef, and back-reef facies of dolomite and limestone 

of the older Capitan Limestone.
4 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Table 1. Hydrostratigraphic section in the Pecos County region, Texas.

[Water-yielding properties: yields (gallons per minutes) - small less than 50, moderate 50 to 500, large is more than 500; Classification of water 

dissolved-solids concentration (milligrams per liter) - fresh less than 1,000, slightly saline 1,000 to 3,000, moderately saline 3,000 to 10,000]

Era System Series or group Stratigraphic unit

Approximate 

maximum 

thickness (feet)

Cenozoic

Quaternary and 

Tertiary Alluvium 1,150

Tertiary Volcanic Rocks, Undivided 1,000+

Mesozoic

Cretaceous

Gulfian 

Series

Terlingua 

Group Boquillas Formation

250

Western Pecos 

County

Eastern Pecos 

County

Comanchean Series

Washita 

Group

Western Pecos County Eastern Pecos County 100 200 Sixshooter Group*

Buda Limestone

Boracho 

Formation*

Edwards 

Group**

Fort Lancaster 

Formation*** 410 350 University 

Mesa Marl***

Burt Ranch 

Member**

Fredericksburg 

Group

Finlay 

Formation*

Fort Terrett 

Formation** 165 200

Trinity Group Trinity Sands

Maxon Sands  300** **

Glen Rose Formation  200+** **

“Basal” Sand  100** **

Triassic Dockum Group

Middle 600

Lower 70

Paleozoic

Permian

Ochoan Series

Dewey Lake Red Beds 600

Southern 

Pecos 

County

Northern Pecos County

Southern 

Pecos 

County

Northern 

Pecos 

County

Tessey 

Limestone

Rustler Formation

1,050

450

Salado Formation 2,200

Castile Formation 2,300

Guadalupian 

Series

Whitehorse 

Group

Gilliam 

Limestone Capitan Limestone Guadalupian Formations; undivided 870 1,650 1,900

Lower Guadalupian Formations; undivided 2,000

Lower Permian Formations; undivided 10,000

Pennsylvanian Pennsylvanian Formations; undivided 6,000

* — Brand and DeFord, 1968

** — Rose, 1972

*** — Smith and Brown, 1983

**** — Rees and Buckner, 1980
Introduction 5

Character of rocks Water yielding properties

Hydrostratigrphic 

unit

Unconsolidated silt, sand, gravel, clay, boulders, caliche, gypsum, and 

conglomerate

Yields range from small to large quantities of 

fresh to moderately saline water Pecos Valley

Lavas, pyroclastic tuffs, volcanic ash, tuff breccias, fragmental breccias, 

agglomerates; few thin beds of conglomerates, sandstones, and 

freshwater limestones

Yields small quantities of freshwater Igneous

Brown to red flaggy limestone interbedded with shale Not known to yield water

Soft nodular limestone, marl, and thin-bedded hard granular limesone

Does not yield water in most of the study 

area; however, may yield small quantities 

in Reeves County

Edwards-Trinity

Hard massive limestone, thin-bedded limestone, and soft nodular 

limestone with some clay Yields small quantities of water

Soft nodular limestone, marl, and hard massive ledge-forming limestone Yields small quantities of water

Massive ledge-forming limestone and soft nodular limestone Yields small quantities of fresh to 

moderately saline water

Crossbedded, fine- to coarse-grained, poorly to well-cemented quartz 

sand with some silt, shale, and limestone

Yields small to moderate quantities of fresh 

to slightly saline water

Reddish-brown to gray coarse-grained sandstone Yields small to moderate quantities of fresh 

to slightly saline water Dockum

Red shale and siltstone Not known to yield water

Sand, shale, gypsum, and anhydrite Not known to yield water

Southern Pecos County Northern Pecos County Southern Pecos 

County Northern Pecos County

Limestone and dolomite

Red shale, sandstone, anhydrite, dolomite, 

limestone, conglomerate, and halite

Not known to 

yield water

Yields small to large 

quantities of slightly to 

moderately saline water

Rustler

Mostly halite, with anhydrite and some dolomite Not known to yield water

Mostly calcareous anhydrite, with halite and 

associated salts and some limestone Not known to yield water

Limestone , 

dolomite, 

and sandstone

Limestone, 

dolomite, 

and reef 

talus

Dolomite, limestone, anhydrite, shale, and sandstone

Yields freshwater 

to a few wells 

in the Glass 

Moutains

Yields moderate to large 

quantities of moderately 

saline water

Capitan Reef

Dolomite, dolomitic limestone, limestone, and siliceous shale Yields small to large quantities of moderately 

saline water

Shale, siliceous shale, limestone, dolomitic limestone, sandstone, 

and basal conglomerate Yields small quantities of water

Limestone, sand, sandstone, shale chert, and conglomerate Yields small quantities of water
6 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

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Pecos River

Pecos River

Fort

Stockton

REEVES

COUNTY

WARD

COUNTY

CRANE

COUNTY UPTON COUNTY

PECOS 

COUNTY

JEFF DAVIS

COUNTY

BREWSTER

COUNTY

TERRELL

COUNTY

CROCKETT

COUNTY

31°0'

30°30'

102°30'

103°0'

103°30'

Major aquifer (clipped to study boundary)

Pecos Valley

 Edwards-Trinity (subcrop) Edwards-Trinity (outcrop)Minor aquifer (clipped to study boundary) Igneous Dockum Rustler Capitan Reef ComplexStudy area boundary

EXPLANATION

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l

ll

0 10 20 KILOMETERS 5 150 10 15 20 MILES 5 Base modified from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal Area Projection, Texas Mapping SystemNorth American Datum of 1983

Aquifer data modified from Ashworth 

and Hopkins, 1995

Figure 2. Extent of the major aquifers (Pecos Valley, Edwards-Trinity [subcrop], and Edwards-Trinity [outcrop]) and minor aquifers (Igneous, Dockum, Rustler, and Capitan Reef Complex), Pecos County region, Texas, 2011.
Methods 7

Methods

The geodatabase contains data gathered in support of this 

project using two different data collection strategies. First, 

new (data collected during the study period) geochemical and 

geophysical data were collected in the field in 2009, 2010, and 

2011 by USGS. Second, existing data from Federal, State and 

local agencies that manage and store groundwater, surfacewater, water-quality, geophysical, and geology information 

were gathered and compiled into the geodatabase. These data 

were downloaded using internet portal, through direct connect 

with the native database using secured access, or gathered 

from published reports or other hardcopy sources.

Water-Quality Methods

Geochemical data were collected in 2010 and 2011 at 

44 data-collection sites (fig. 3, table 2). Final results were 

reviewed for completeness and accuracy and, with the 

exception of data for one constituent, uploaded to the USGS 

National Water Information System (NWIS) for warehousing 

(U.S. Geological Survey, 2011a). Helium–4 (4He) data were 

the only data collected that are not available from NWIS; 

these data are presented in table 3.

Water-Quality Sample Collection

Geochemical samples were collected in 2010–11 from 

38 wells screened in the Pecos Valley, Edwards-Trinity, 

Dockum, Rustler, and Capitan Reef aquifers, from 4 springs, 

and from 2 Pecos River surface-water sites (fig. 3, table 2) 

(Wilde and others, variously dated). Almost all of the data can 

be accessed using the USGS NWIS at http://waterdata.usgs.

gov (U.S. Geological Survey, 2011a). Those data that were 

not uploaded to the USGS NWIS web are included herein. 

Physicochemical properties (water temperature, dissolved 

oxygen, specific conductance, pH, turbidity, and alkalinity), 

barometric pressure, and depth to water were measured 

in the field at the time of sample collection. All samples 

were analyzed for major ions, nutrients, trace elements, 

and isotopes (hydrogen [hydrogen–2/hydrogen–1 (2H/1H)], 

oxygen [oxygen–18/oxygen–16 (18O/16O)], and strontium 

[strontium–87/strontium–86 (87Sr/86Sr)]). Samples collected 

from select sites were analyzed for pesticide compounds, 

tritium (3H), dissolved gases, and 4He.

Groundwater Sampling

Groundwater samples were collected using procedures 

described in the USGS National Field Manual for the 

Collection of Water-Quality Data (U.S. Geological Survey, 

variously dated), the USGS Chlorofluorocarbon Laboratory, 

Reston, Virginia (U.S. Geological Survey, 2011b), and 

the USGS Stable Isotope Laboratory in Reston, Va. 

(U.S. Geological Survey, 2011c). Groundwater-quality 

samples, physicochemical properties, and water-level data 

were collected once from each site (fig. 3) during 2010–11. 

Water levels in wells were measured manually at the time 

of sampling, when possible, by using an electric tape or 

steel tape. 

Observation wells were pumped using an electric, 

portable, submersible, positive displacement pump 

(Grundfos Redi–flo2, Redi–flo–3) constructed of stainless 

steel and Teflon. Water was pumped from domestic and 

municipal wells using existing pumps, and samples were 

collected at the wellhead prior to installation of any pressure 

tanks or filtering or other treatment devices. Prior to any 

treatment, a connection was made for purging and sampling 

by using a brass connector with compression fitting to 

refrigeration-grade copper tubing. 

Prior to sample collection, one to three casing volumes 

were purged from the well, depending on well type, either 

observation or supply. For wells that are continuously pumped 

(or pumped regularly every few hours) such as those used for 

public supply, domestic supply, or industrial purposes, purging 

less than three casing volumes is permissible (U.S. Geological 

Survey, variously dated, chapter A4). The purge procedure 

removes stagnant water in the well, reduces chemical artifacts 

of well installation or well construction materials, or mitigates 

effects of infrequent pumping. After purging was complete, 

the physicochemical properties dissolved oxygen, pH, specific 

conductance, and water temperature were measured until 

readings were stable (Wilde, variously dated). Once readings 

stabilized, water samples were collected through Teflon tubing 

in new, precleaned bottles. Water samples were collected 

and processed onsite to minimize changes to the watersample chemistry or contamination from the atmosphere. To 

prevent degradation of water samples and maintain the initial 

concentration of compounds between the time of sample 

collection and laboratory analyses, samples were preserved 

with the appropriate acid (when required) or chilled to 4 

degrees Celsius (oC) according to the laboratory protocols 

and shipped overnight to the analyzing laboratories.

At each site after sample completion, sampling 

equipment was cleaned according to established protocols 

prior to use at the next site (Wilde, 2004). All samples 

were stored on ice in coolers following collection and 

during shipping. Samples were shipped overnight to the 

analyzing laboratories.
8 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

08427500

08437000

08441500

08444500

08446500

08446600

303222103263701

303342103064001

303852102432902 303941103175001

304006103315601

30402010302520

3

2

04117102560101

304605103444601 304646103013401

304715103263501 304802103003901

304805103013301

304807103025301

304950103013401 305112102265901 305132103015701

305140102521101

305331103020501

305354102373501 305419102545301 305502103504101

305509103510101 305529102560601 305531103474201 305559103154101

305836102131701 305859102571001

305949102552301

310136102311601

310625103175201

310718102484801 310806103171901

310949103090401

311235103000901

311422102555101 311602102400601 311602102400901

311610103050901

Pecos River

Pecos River

REEVES

COUNTY

WARD

COUNTY

CRANE

COUNTY

UPTON

COUNTY

PECOS 

COUNTY

JEFF DAVIS

COUNTY

BREWSTER

COUNTY

TERRELL

COUNTY

CROCKETT

COUNTY

Fort Stockton

Grandfalls

Girvin

31°0'

30°30'

102°30'

103°0'

103°30'

EXPLANATION

Study area boundaryGeochemical sampling siteGroundwater well and station numberSpring and station numberU.S. Geological Survey  streamflow-gaging station and station numberGeodatabase site

08427500

310625103175201

08441500

Base modified from U.S. Geological Survey 1:2,000,000-scale digital dataAlbers Equal Area Projection, Texas State Mapping SystemNorth American Datum of 1983

0 10 20 MILES 5 15

0 10 20 KILOMETERS 5 15

Figure 3. Site locations of field-collected geochemical data, Pecos County region, Texas, 2010–11.
Methods 9

Table 2. Geochemical data-collection sites in the Pecos County region, Texas, 2010–11.

[USGS, U.S. Geological Survey; dd, decimal degrees; --, not applicable]

USGS station number Station name or State well number Latitude (dd) Longitude (dd) Site type Contributing 

aquifer

08427500 San Solomon Springs 30.94292 -103.78824 Spring --

08437000 Santa Rosa Spring 31.26743 -102.95828 Spring --

08441500 Pecos River below Grandfalls, Tex. 31.28348 -102.74265 Stream --

08444500 Comanche Springs 30.88628 -102.87495 Spring --

08446500 Pecos River near Girvin, Tex. 31.11320 -102.41764 Stream --

08446600 Diamond Y Springs 31.00190 -102.92358 Spring --

302955103451101 PS-52-34-303 30.49860 -103.75300 Well Igneous

303222103263701 BK-52-29-8xx (Brewster County ET Well) 30.53950 -103.44346 Well Edwards-Trinity

303342103064001 US-52-07-502 30.93779 -103.18711 Well Edwards-Trinity

303852102432902 US-53-19-7xx (PC QW) 30.64799 -102.72470 Well Rustler

303941103175001 US-52-22-8xx (Farm Well 3) 30.66139 -103.29720 Well Edwards-Trinity

304006103315601 PS-52-20-601 30.66827 -103.53216 Well Edwards-Trinity

304020103025202 US-52-24-501 30.67295 -103.05601 Well Rustler

304117102560101 US-53-17-501 30.68806 -102.93361 Well Edwards-Trinity

304605103444601 PS-52-11-702 30.77100 -103.74800 Well Igneous

304646103013401 US-52-16-910 30.77931 -103.02615 Well Edwards-Trinity

304715103263501 US-52-13-801 30.78740 -103.44343 Well Edwards-Trinity

304802103003901 US-52-16-611 30.80088 -103.01110 Well Edwards-Trinity

304805103013301 US-52-16-609 30.80129 -103.02618 Well Rustler

304807103025301 US-52-16-504 30.80241 -103.04844 Well Capitan Reef

305112102265901 US-53-13-208 30.85341 -102.44965 Well Dockum

305132103015701 US-52-16-3xx (S-21) 30.85899 -103.03244 Well Edwards-Trinity

305140102521101 US-53-09-306 30.87393 -102.88229 Well Edwards-Trinity

305331103020501 US-52-08-909 30.89210 -103.03516 Well Edwards-Trinity

305354102373501 US-53-03-9xx 30.89825 -102.62647 Well Edwards-Trinity

305419102545301 US-53-01-907 30.90560 -102.91610 Well Edwards-Trinity

305502103504101 PS-52-02-404 30.91737 -103.84518 Well Pecos Valley

305509103510101 PS-52-02-4xx (Balmerea) 30.91911 -103.85027 Well Edwards-Trinity

305529102560601 US-53-01-5xx (Apache 3) 30.92470 -102.93490 Well Rustler

305531103474201 WD-52-02-507 30.92539 -103.79511 Well Edwards-Trinity

305559103154101 US-52-06-603 30.93305 -103.26194 Well Dockum

305836102131701 US-53-07-105 30.97667 -102.22139 Well Edwards-Trinity

305859102571001 US-53-01-210 30.98293 -102.95271 Well Edwards-Trinity

305949102552301 US-53-01-208 30.99718 -102.92291 Well Dockum

310136102311601 US-45-60-903 31.02670 -102.52102 Well Edwards-Trinity

310625103175201 WD-46-62-201 31.10685 -103.29777 Well Pecos Valley

310718102484801 US-45-58-2xx 31.12162 -102.81354 Well Edwards-Trinity

310806103171901 WD-46-54-901 31.13502 -103.28796 Well Rustler

310949103090401 US-46-55-9xx (Weatherby Ranch) 31.16341 -103.15103 Well Dockum

311235103000901 US-46-56-309 31.20974 -103.00262 Well Edwards-Trinity

311422102555101 US-45-49-203 31.23974 -102.93097 Well Capitan Reef

311602102400601 US-45-43-807 31.26942 -102.67609 Well Pecos Valley

311602102400901 US-45-43-8xx (PA 1) 31.26934 -102.68214 Well Pecos Valley

311610103050901 US-46-48-701 31.26959 -103.08683 Well Dockum
10 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Surface-Water Sampling

Streamflow velocities at the Pecos River surfacewater sites were below 1.5 feet per second (ft/s) and, 

therefore, samples were collected using the multi-vertical 

grab sampling method (U.S. Geological Survey, variously 

dated). A sample was collected at each site using a 1-liter 

Teflon bottle with a 5/16- inch (in.) nozzle. The grab sample 

was then composited in a Teflon churn and dispensed into 

appropriate containers.

At each site after sample completion, sampling 

equipment was cleaned according to established protocols 

prior to use at the next site (Wilde, 2004). All samples 

were stored on ice in coolers following collection and 

during shipping. Samples were shipped overnight to the 

analyzing laboratories. 

Spring Sampling

Spring water was sampled as close to a spring orifice 

as possible. Otherwise, spring water was sampled from 

the bottom of the pool or nearest to the primary discharge 

location based on anecdotal evidence. Spring-water samples 

were collected using a peristaltic pump and flexible Teflon 

diaphragm head by immersing Teflon tubing below the water 

surface into or near the spring orifice, avoiding contact with 

the atmosphere and standing surface water. San Solomon 

Springs (8427500) was sampled from the main discharge 

point. Comanche Springs (08444500) was sampled at the 

Government Spring discharge point, which is the primary 

discharge orifice of the springs. A spring orifice could not be 

located at the Diamond Y Springs (08446600) or Santa Rosa 

Spring (08437000) sites, so the samples were taken from the 

spring pools.

At each site after sample completion, sampling 

equipment was cleaned according to established protocols 

Table 3. Helium-4 measured in groundwater samples collected in the Pecos County region, Texas, 2010–11.

[USGS, U.S. Geological Survey; cc/g, cubic centimeter per gram; H2O, water; STP, standard temperature and pressure]

 USGS station number Date Sample start time Helium-4 (cc/g of H2O at STP x 10-9)

305509103510101 9/1/2010 16:00 81

311602102400901 8/17/2010 21:00 164

302955103451101 9/2/2010 11:00 55

304715103263501 8/28/2010 14:00 230

305140102521101 8/10/2010 17:00 261

305502103504101 8/15/2010 19:00 53

304006103315601 6/23/2011 11:00 3,877

305531103474201 6/22/2011 11:00 573

304605103444601 6/22/2011 14:00 68

prior to use at the next site (Wilde, 2004). All samples 

were stored on ice in coolers following collection and 

during shipping. Samples were shipped overnight to the 

analyzing laboratories.

Analytical Methods

Samples collected and analyzed for major ions, nutrients, 

trace elements, and pesticide compounds were analyzed by the 

USGS National Water Quality Laboratory (NWQL), Denver, 

Colorado, using published methods. Methods for major ions 

are published in Fishman and Friedman (1989), Fishman 

(1993), and American Public Health Association (1998). 

Nutrients methods are published in Patton and Kryskalla 

(2003) and Fishman (1993). Trace element methods are 

published in Fishman and Friedman (1989), Garbarino and 

others (2006), and Garbarino (1999). Pesticide compound 

methods are published in Zaugg and others (1995), Lindley 

and others (1996), Madsen and others, (2003), and Sandstrom 

and others (2001). Samples for analysis of oxygen and 

hydrogen isotopes were analyzed at the USGS Stable Isotope 

Laboratory in Reston, Va. 18O/16O analytical methods are 

described in Révész and Coplen (2008a) and 2H/1H methods 

are described in Révész and Coplen (2008b). Samples for 

analysis of strontium isotopes were analyzed at the Menlo 

Park Isotope Laboratory in Menlo Park, California. Samples 

for the analysis of tritium were shipped to the Menlo Park 

Tritium Laboratory in Menlo Park, Calif. Analytical methods 

for 3H are documented in Ostlund and Warner (1962) and 

Thatcher and others (1977). Samples for the analysis of 

dissolved gases and 4–helium were shipped to the USGS 

Dissolved Gas Laboratory in Reston, Va., and analyzed 

by methods described in Busenberg and others (1993) and 

Busenberg and others (2001). Samples for the analysis of 

3–helium were analyzed by the Noble Gas Laboratory of 
Methods 11

concentration of 3.8 mg/L was greater than the measured zinc 

concentrations in 11 of the environmental samples. All of 

these detections of concern were measured in the field blank 

collected on August 28, 2010, except the lead concentration 

of 0.24 mg/L, which was measured in the field blank collected 

on August 12, 2010, and the filtered ammonia concentration 

of 0.011, which was measured in the field blank collected on 

June 22, 2011.

The cause of the low-level contamination of several 

metals in the field blank collected on August 28, 2010, 

and the detected concentrations of lead in three of the field 

blanks collected on August 12, 18, and 28, 2010, is currently 

(February 2012) unknown. The corresponding metals data 

from samples associated with these blanks were censored in 

the database.

Sequential replicate samples were collected to measure 

the variation in results originating from sampling and 

analytical methods. Sequential replicate sample results are 

included in table 5. Inorganic constituent replicates were 

collected with a new, preconditioned capsule filter. Capsule 

filters were replaced prior to collecting the sequential replicate 

in case of filter loading, which might reduce the effective pore 

size of the filter (Horowitz and others, 1996).

Replicate samples were compared with associated 

environmental samples to assess the variability of the 

measured concentrations by computing the relative percent 

difference (RPD) for each constituent with equation 1:

RPD = |C1 – C2|/((C1 + C2)/2) × 100, (1)

where

C1 is constituent concentration, in milligrams per 

liter, from the environmental sample; and

C2 is constituent concentration, in milligrams per 

liter, from the replicate sample.

RPDs of 10 percent or less indicate good agreement 

between the paired results if the concentrations are sufficiently 

large compared to their associated LRL (Oden and others, 

2011). An RPD was not computed for a replicated constituent 

if the paired results were censored as estimated or less than 

their associated LRL.

There was generally good agreement between the 

environmental and replicate samples with a few exceptions. 

Several of the replicate metal concentrations measured on 

January 25, 2011, and June 23, 2011, were greater than 10 

percent different (table 5). All but one of these samples with 

greater than 10 percent differences were detected at or near 

the detection limit so that small variability in the analysis 

caused large RPDs. The one exception was the detected lead 

concentration in the June 23, 2011, sample and, because 

of issues with lead concentrations in the blanks, these were 

already censored. The causes of the greater than 10 percent 

differences between some of the environmental and replicate 

samples are unknown.

Lamont-Doherty Earth Observatory of Columbia University, 

Palisades, New York, using methods described in Schlosser 

and others (1988).

The USGS uses two reporting conventions for the 

analytical data from the National Water Quality Laboratory, 

the laboratory reporting level (LRL) and the long-term 

method detection level (LT-MDL). The LRL is two times the 

LT-MDL, and concentrations measured between the LRL and 

LT-MDL are reported as estimated concentrations (Childress 

and others, 1999).

Geochemical Quality Assurance

Quality-control data were collected to assess the 

precision and accuracy of sample-collection procedures and 

laboratory analyses (U.S. Geological Survey, variously dated). 

Quality-control samples consisted of two equipment blank 

samples, four field blank samples, four sequential replicate 

samples, and environmental matrix-spike samples. 

Equipment blanks were collected annually in a controlled 

environment to determine if the cleaning procedures for 

sample containers and the equipment for sample collection and 

sample processing were sufficient to produce contaminant-free 

samples. Field blank samples were collected and processed 

at a sampling site prior to environmental samples to ensure 

equipment cleaning conducted in the field between sites was 

adequate, and that the collection, processing, or transporting 

procedures in the field did not contaminate the samples. 

Equipment blank results indicate the sampling equipment 

did not introduce appreciable amounts of the constituents of 

interest to the samples and, with a few exceptions, equipment 

blank results were less than the reporting limits (table 4). 

Field blank results indicate the sample collection and handling 

procedures did not introduce appreciable contamination of 

the constituents of interest to the environmental samples, 

with a few exceptions, and provided another indication that 

representative samples were collected. Analytes detected in 

the field blanks included ammonia, barium, calcium, chloride, 

cobalt, copper, fluoride, lead, magnesium, manganese, 

molybdenum, nickel, sodium, strontium, sulfate, thallium, 

total nitrogen, and zinc (table 4). Because most of the 

concentrations measured in the field blanks were low, with 

a few exceptions, the environmental results do not show a 

bias except for some of the metal concentrations measured 

in the field blank samples collected on August 28, 2010, and 

the lead concentrations in some of the blank samples. The 

detected copper concentration of 1.5 mg/L was greater than the 

measured copper concentrations in 23 of the environmental 

samples. The detected filtered lead concentrations of 0.24 

mg/L and 0.23 mg/L were greater than the measured lead 

concentrations in 21 of the environmental samples. The 

detected molybdenum concentration of 0.77 mg/L was greater 

than the measured molybdenum concentrations in five of the 

environmental samples. The detected nickel concentration of 

0.48 mg/L was greater than the measured nickel concentrations 

in 19 of the environmental samples. The detected zinc 
12 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011 Table 4. Results of major ion, trace element, and nutrient analyses from equipment blanks and field blanks collected in association with geochemical samples collected in the Pecos County region, Texas, 2010–11. [USGS, U.S. Geological Survey; mg/L, milligrams per liter; μg/L, micrograms per liter; --, no data; <, less than; E, estimated; M, presence verified but not quantified; U, analyzed for but not detected at a concentration equal to or greater than the long-term method detection level] USGS station number Station name or State well number Date Sample start time Sample type Calcium, water, filtered (mg/L) Magnesium, water, filtered (mg/L) Potassium, water, filtered (mg/L) Sodium, water, filtered (mg/L) Bromide, water, filtered (mg/L) Chloride, water, filtered (mg/L) Fluoride, water, filtered (mg/L) Hydrogen sulfide, water, unfiltered (mg/L) 302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank <0.04 <0.016 <0.06 <0.10 <0.02 <0.12 <0.08 -- 302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- -- 311610103050901 US-46-48-701 08-12-2010 10:05 Field blank <.04 <.016 <.06 <.10 <.02 <.12 <.08 -- 304805103013301 US-52-16-609 08-18-2010 15:05 Field blank <.04 <.016 <.06 <.10 <.02 <.12 <.08 -- 304715103263501 US-52-13-801 08-28-2010 13:05 Field blank .11 .026 <.06 E.10 <.02 .14 E.05

U

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank .03 <.008 <.02 <.06 <.01 <.06 <.04 --

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Silica, 

water, 

filtered as 

SiO2 (mg/L)

Sulfate, 

water, 

filtered (mg/L)

Ammonia 

plus organic 

nitrogen, 

water, filtered 

as nitrogen 

(mg/L)

Ammonia 

plus organic 

nitrogen, 

water, 

unfiltered 

as nitrogen 

(mg/L)

Ammonia, 

water, 

filtered 

as NH4

(mg/L)

Ammonia, 

water, 

filtered as 

nitrogen 

(mg/L)

Ammonia, 

water, 

unfiltered 

as NH4

(mg/L)

Ammonia, 

water, 

unfiltered as 

nitrogen 

(mg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank <0.06 <0.18 <0.10 -- -- -- <0.052 <0.04302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- E0.07 -- -- <.052 <.04311610103050901 US-46-48-701 08-12-2010 10:05 Field blank <.06 <.18 -- -- <0.026 <0.020 -- --304805103013301 US-52-16-609 08-18-2010 15:05 Field blank <.06 <.18 -- -- <.026 <.020 -- --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank <.06 E.12 -- -- <.026 <.020 -- --305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <.03 <.09 -- -- .014 .011 -- --
Methods 13

UUSGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Nitrate 

plus nitrite, 

water, 

filtered as 

nitrogen 

(mg/L) 

Nitrate, 

water, 

filtered 

(mg/L)

Nitrate, 

water, 

filtered as 

nitrogen 

(mg/L) 

Nitrite, 

water, 

filtered 

(mg/L)

Nitrite, 

water, 

filtered 

(mg/L) as 

nitrogen

Organic 

nitrogen, 

water, 

filtered 

(mg/L)

Organic 

nitrogen, 

water, 

unfiltered 

(mg/L)

Orthophosphate, 

water, filtered 

(mg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank <0.04 -- -- -- -- -- -- <0.025302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank <.04 <0.177 <0.040 <0.007 <0.002 -- <0.07 .080311610103050901 US-46-48-701 08-12-2010 10:05 Field blank <.04 <.177 <.040 <.007 <.002 <0.10 -- <.025304805103013301 US-52-16-609 08-18-2010 15:05 Field blank <.04 <.177 <.040 <.007 <.002 <.10 -- <.025304715103263501 US-52-13-801 08-28-2010 13:05 Field blank <.04 <.177 <.040 <.007 <.002 <.10 -- <.025305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <.02 <.089 <.020 <.003 <.001 <.04 -- <.012

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Orthophosphate, 

water, 

filtered as 

phosphorus 

(mg/L) 

Phosphorus, 

water, 

filtered as 

phosphorus 

(mg/L) 

Phosphorus, 

water, 

unfiltered as 

phosphorus 

(mg/L) 

Total 

nitrogen 

(nitrate + 

nitrite + 

ammonia 

+ organicN), water, 

filtered, 

analytically 

determined 

(mg/L)

Total 

nitrogen, 

water, 

filtered 

(mg/L)

Total 

nitrogen, 

water, 

unfiltered 

(mg/L)

Aluminum, 

water, 

filtered 

(μg/L)

Barium, water, 

filtered (μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank <0.008 <0.006 -- -- <0.14 -- <3.4 <0.14302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank .026 E.03 E0.03 -- -- <0.11 -- --311610103050901 US-46-48-701 08-12-2010 10:05 Field blank <.008 -- -- <0.10 -- -- <3.4 <.14304805103013301 US-52-16-609 08-18-2010 15:05 Field blank <.008 -- -- <.10 -- -- <3.4 <.14304715103263501 US-52-13-801 08-28-2010 13:05 Field blank <.008 -- -- E.10 -- -- <3.4 M305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <.004 -- -- <.05 -- -- 339 <.07
14 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011 USGS station number Station name or State well number Date Sample start time Sample type Beryllium, water, filtered (μg/L) Cadmium, water, filtered (μg/L) Chromium, water, filtered (μg/L) Cobalt, water, filtered (μg/L) Copper, water, filtered (μg/L) Copper, water, unfiltered, recover- able (μg/L) Iron, water, filtered (μg/L) Lead, water, filtered (μg/L) 302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- <0.02 <0.12 -- <1.0 -- <6 <0.03 302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- <1.4 -- -- 311610103050901 US-46-48-701 08-12-2010 10:05 Field blank <0.01 <.02 <.12 <0.01 <1.0 -- <6 .24 304805103013301 US-52-16-609 08-18-2010 15:05 Field blank <.01 <.02 <.12 <.01 E.92 -- <6 .10 304715103263501 US-52-13-801 08-28-2010 13:05 Field blank <.01 <.02 <.12 .02 1.5 -- <6 .23 305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <.01 <.02 <.06 .35 <.50 -- <3 .05 USGS station number Station name or State well number Date Sample start time Sample type Lead, water, unfiltered, recoverable (μg/L) Lithium, water, filtered (μg/L) Manganese, water, filtered (μg/L) Molybde- num, water, filtered (μg/L) Nickel, water, filtered (μg/L) Silver, water, filtered (μg/L) Strontium, water, filtered (μg/L) Thallium, water, filtered (μg/L) 302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- <0.3 -- <0.12 <0.01 <0.40 -- 302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank <0.06 -- -- -- -- -- -- -- 311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- <0.4 <.3 <0.03 <.12 <.01 <.40 E0.02

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- <.4 <.3 .05 E.08 <.01 <.40 <.02304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- <.4 E.2 .77 .48 <.01 .53 <.02305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank -- <.2 .7 <.01 <.09 <.01 <.20 <.01Table 4. Results of major ion, trace element, and nutrient analyses from equipment blanks and field blanks collected in association with geochemical samples collected in the Pecos County region, Texas, 2010–11.—Continued[USGS, U.S. Geological Survey; mg/L, milligrams per liter; μg/L, micrograms per liter; --, no data; <, less than; E, estimated; M, presence verified but not quantified; U, analyzed for but not detected at a concentration equal to or greater than the long-term method detection level]
Methods 15

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Vanadium, 

water, 

filtered 

(μg/L)

Zinc, 

water, 

filtered 

(μg/L)

Zinc, water, 

unfiltered, 

recoverable 

(μg/L)

Antimony, 

water, 

filtered 

(μg/L)

Arsenic, 

water, 

filtered 

(μg/L)

Boron, 

water, 

filtered 

(μg/L)

Selenium, 

water, 

filtered 

(μg/L)

1-Naphthol, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable (μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- <2.8 -- -- <0.04 <3 -- --302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- <2.0 -- -- -- -- --

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank <0.16 <2.8 -- <0.05 <.04 <3 <0.04 --

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank <.16 <2.8 -- <.05 <.04 <3 <.04 --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank <.16 3.8 -- <.05 <.04 <3 <.04 --

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <.08 <1.4 -- .03 <.02 <3 <.03 <0.036

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

2,6-Diethylaniline, 

water, 

filtered (0.7 

micron glass 

fiber filter), 

recoverable 

(μg/L)

2-Chloro-2’,

6’-diethylacetanilide, 

water, 

filtered, 

recoverable 

(μg/L)

2-Chloro4-isopropylamino6-amino-striazine, 

water, 

filtered, 

recoverable 

(μg/L)

2-Ethyl6-methylaniline, water, 

filtered, 

recoverable 

(μg/L)

3,4-Dichloroaniline, 

water, 

filtered, 

recoverable 

(μg/L)

3,5-Dichloroaniline, 

water, 

filtered, 

recoverable 

(μg/L)

4-Chloro2-methylphenol, 

water, 

filtered, 

recoverable 

(μg/L)

Acetochlor, 

water, filtered, 

recoverable 

(μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- --302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- --

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- --

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- --

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.006 <0.010 <0.006 <0.010 <0.004 <0.004 <0.005 <0.010
16 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011 USGS station number Station name or State well number Date Sample start time Sample type Alachlor, water, filtered, recoverable (μg/L) alpha-Endo- sulfan, water, filtered, recoverable (μg/L) Atrazine, water, filtered, recoverable (μg/L) Azinphos- methyl oxygen analog, water, filtered, recoverable (μg/L) Azinphos- methyl, water, filtered (0.7 micron glass fiber filter), recover- able (μg/L) Benflura- lin, water, filtered (0.7 mi- cron glass fiber filter), recover- able (μg/L) Carbaryl, water, filtered (0.7 micron glass fiber filter), recoverable (μg/L) Carbofuran, water, filtered (0.7 micron glass fiber filter), recoverable (μg/L) 302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- -- 302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- -- 311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- -- 304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- -- 304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- -- 305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.008 <0.006 <0.008 <0.04 <0.120 <0.014 <0.060 <0.060 Table 4. Results of major ion, trace element, and nutrient analyses from equipment blanks and field blanks collected in association with geochemical samples collected in the Pecos County region, Texas, 2010–11.—Continued [USGS, U.S. Geological Survey; mg/L, milligrams per liter; μg/L, micrograms per liter; --, no data; <, less than; E, estimated; M, presence verified but not quantified; U, analyzed for but not detected at a concentration equal to or greater than the long-term method detection level]
Methods 17

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Chlorpyrifos 

oxygen 

analog, 

water, 

filtered, 

recoverable 

(μg/L)

Chlorpyrifos, 

water, 

filtered, 

recoverable 

(μg/L)

cisPermethrin, 

water, 

filtered 

(0.7 micron 

glass fiber 

filter), 

recoverable 

(μg/L)

cisPropiconazole, 

water, 

filtered, 

recoverable 

(μg/L)

Cyanazine, 

water, 

filtered, 

recoverable 

(μg/L)

Cyfluthrin, 

water, 

filtered, 

recoverable 

(μg/L)

Cypermethrin, 

water, 

filtered, 

recoverable 

(μg/L)

DCPA, water, 

filtered 

(0.7 micron 

glass fiber 

filter), 

recoverable 

(μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- --302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- --

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- --

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- --

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.06 <0.004 <0.010 <0.008 <0.022 <0.016 <0.020 <0.008

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Desulfinylfipronil 

amide, 

water, 

filtered, 

recoverable 

(μg/L)

Desulfinylfipronil, 

water, 

filtered, 

recoverable 

(μg/L)

Diazinon, 

water, 

filtered, 

recoverable 

(μg/L)

Dichlorvos, 

water, 

filtered, 

recoverable 

(μg/L)

Dicrotophos, 

water, 

filtered, 

recoverable 

(μg/L)

Dieldrin, 

water, 

filtered, 

recoverable 

(μg/L)

Dimethoate, water, 

filtered 

(0.7 micron 

glass 

fiber filter), 

recoverable 

(μg/L)

Disulfoton 

sulfone, water, 

filtered, 

recoverable 

(μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- --302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- --

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- --

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- --

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.029 <0.012 <0.006 <0.04 <0.08 <0.008 <0.006 <0.01
18 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011 USGS station number Station name or State well number Date Sample start time Sample type Disulfoton, water, filtered (0.7 micron glass fiber filter), recoverable (μg/L) Endosulfan sulfate, water, filtered, recoverable (μg/L) EPTC, water, filtered (0.7 micron glass fiber filter), recoverable (μg/L) Ethion monoxon, water, filtered, recoverable (μg/L) Ethion, water, filtered, recover- able (μg/L) Ethoprop, water, filtered (0.7 micron glass fiber filter), recover- able (μg/L)Fenamiphos sulfone, water, filtered, recoverable (μg/L) Fenamiphos sulfoxide, water, filtered, recoverable (μg/L) 302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- -- 302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- -- 311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- -- 304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- -- 304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- -- 305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.04 <0.016 <0.006 <0.02 <0.008 <0.016 <0.054 <0.08 USGS station number Station name or State well number Date Sample start time Sample type Fenamiphos, water, filtered, recoverable (μg/L) Fipronil sulfide, water, filtered, recoverable (μg/L) Fipronil sulfone, water, filtered, recoverable (μg/L) Fipronil, water, filtered, recoverable (μg/L) Fonofos, water, filtered, recover- able (μg/L) Hexa- zinone, water, filtered, recover- able (μg/L) Iprodione, water, filtered, recoverable (μg/L) Isofenphos, water, filtered, recoverable (μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- --302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- --

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- --

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- --

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.03 <0.012 <0.024 <0.018 <0.005 <0.008 <0.014 <0.006

Table 4. Results of major ion, trace element, and nutrient analyses from equipment blanks and field blanks collected in association with geochemical samples collected in the Pecos County region, Texas, 2010–11.—Continued[USGS, U.S. Geological Survey; mg/L, milligrams per liter; μg/L, micrograms per liter; --, no data; <, less than; E, estimated; M, presence verified but not quantified; U, analyzed for but not detected at a concentration equal to or greater than the long-term method detection level]
Methods 19

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

lambdaCyhalothrin, 

water, 

filtered, 

recoverable 

(μg/L)

Malaoxon, 

water, 

filtered, 

recoverable 

(μg/L)

Malathion, 

water, 

filtered, 

recoverable 

(μg/L)

Metalaxyl, 

water, 

filtered, 

recoverable 

(μg/L)

Methidathion, 

water, 

filtered, 

recoverable 

(μg/L)

Methyl 

paraoxon, 

water, 

filtered, 

recoverable 

(μg/L)

Methyl 

parathion, 

water, 

filtered 

(0.7 micron 

glass 

fiber filter), 

recoverable 

(μg/L)

Metolachlor, 

water, filtered, 

recoverable 

(μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- --302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- --

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- --

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- --

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.010 <0.022 <0.016 <0.014 <0.012 <0.01 <0.008 <0.020

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Metribuzin, 

water, 

filtered, 

recoverable 

(μg/L)

Molinate, 

water, 

filtered (0.7 

micron glass 

fiber filter), 

recoverable 

(μg/L)

Myclobutanil, 

water, 

filtered, 

recoverable 

(μg/L)

Oxyfluorfen, 

water, 

filtered, 

recoverable 

(μg/L)

Pendimethalin, 

water, 

filtered 

(0.7 

micron 

glass fiber 

filter), 

recoverable (μg/L)

Phorate 

oxygen 

analog, 

water, 

filtered, 

recoverable 

(μg/L)

Phorate, 

water, 

filtered 

(0.7 micron 

glass 

fiber filter), 

recoverable 

(μg/L)

Phosmet oxygen 

analog, water, 

filtered, 

recoverable 

(μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- --302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- --

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- --

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- --

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.012 <0.004 <0.010 <0.006 <0.012 <0.03 <0.020 <0.05
20 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011 USGS station number Station name or State well number Date Sample start time Sample type Phosmet, water, filtered, recoverable (μg/L) Prometon, water, filtered, recoverable (μg/L) Prometryn, water, filtered, recoverable (μg/L) Propanil, water, filtered (0.7 micron glass fiber filter), recoverable (μg/L) Propar- gite, water, filtered (0.7 micron glass fiber filter), recover- able (μg/L) Simazine, water, filtered, recover- able (μg/L) Tebuthi- uron, water, filtered (0.7 micron glass fiber filter), recoverable (μg/L) Tefluthrin, water, filtered, recoverable (μg/L) 302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- -- 302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- -- 311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- -- 304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- -- 304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- -- 305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.140 <0.012 <0.006 <0.010 <0.02 <0.006 <0.03 <0.010 Table 4. Results of major ion, trace element, and nutrient analyses from equipment blanks and field blanks collected in association with geochemical samples collected in the Pecos County region, Texas, 2010–11.—Continued [USGS, U.S. Geological Survey; mg/L, milligrams per liter; μg/L, micrograms per liter; --, no data; <, less than; E, estimated; M, presence verified but not quantified; U, analyzed for but not detected at a concentration equal to or greater than the long-term method detection level]
Methods 21

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Terbufos 

oxygen 

analog 

sulfone, 

water, 

filtered, 

recoverable 

(μg/L)

Terbufos, 

water, filtered 

(0.7 micron 

glass fiber 

filter), 

recoverable 

(μg/L)

Terbuthylazine, 

water, 

filtered, 

recoverable 

(μg/L)

Thiobencarb, water, 

filtered 

(0.7 micron 

glass 

fiber filter), 

recoverable 

(μg/L)

transPropiconazole, 

water, 

filtered, 

recoverable 

(μg/L)

Tribuphos, 

water, 

filtered, 

recoverable 

(μg/L)

Trifluralin, 

water, 

filtered 

(0.7 micron 

glass 

fiber filter), 

recoverable 

(μg/L)

Organic 

carbon, water, 

unfiltered 

(mg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank -- -- -- -- -- -- -- E0.3302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank -- -- -- -- -- -- -- <.6

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank -- -- -- -- -- -- -- --

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank -- -- -- -- -- -- -- --304715103263501 US-52-13-801 08-28-2010 13:05 Field blank -- -- -- -- -- -- -- --

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <0.04 <0.02 <0.01 <0.016 <0.01 <0.018 <0.018 --

USGS station 

number

Station name or 

State well 

number Date

Sample 

start time Sample type

Uranium 

(natural), 

water, 

filtered 

(μg/L)

302009097405901 Austin Field Headquarters 03-15-2010 14:00 Equipment blank --302009097405901 Austin Field Headquarters 04-05-2010 12:30 Equipment blank --

311610103050901 US-46-48-701 08-12-2010 10:05 Field blank <0.01

304805103013301 US-52-16-609 08-18-2010 15:05 Field blank <.01304715103263501 US-52-13-801 08-28-2010 13:05 Field blank <.01

305531103474201 WD-52-02-507 06-22-2011 10:00 Field blank <.004
22 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Table 5. Relative percent differences between sequential replicate and environmental samples analyzed for major ions, trace 

elements, and elemental isotopes collected in the Pecos County region, Texas, 2010–11.

[USGS, U.S. Geological Survey; mg/L, milligrams per liter; μg/L, micrograms per liter; pCi/L, picocuries per liter; NTRU, Nephelometric Turbidity Ratio 

Unit; <, concentration was less than laboratory reporting level; --, RPD not calculated because the concentration for one or both samples in the pair was 

less than the laboratory reporting level]

USGS station 

number

Date Constituent Sequential 

replicate 

result

Environmental 

result

Relative 

percent 

differences

08437000 1/25/2011 Alkalinity, water, filtered inflection-point titration method 

(incremental titration method), field (mg/L as calcium 

carbonate)

254.0 232.0 9.05

08437000 1/25/2011 Aluminum, water, filtered (μg/L) 5.6 <5.1 --

08437000 1/25/2011 Ammonia, water, filtered (μg/L) .057 .060 5.13

08437000 1/25/2011 Arsenic, water, filtered (μg/L) 1.7 1.7 0

08437000 1/25/2011 Barium, water, filtered (μg/L) 20 20 0

08437000 1/25/2011 Beryllium, water, filtered (μg/L) .04 .04 0

08437000 1/25/2011 Bicarbonate, water, filtered, inflection-point titration 

method (incremental titration method), field (mg/L)

309 283 8.78

08437000 1/25/2011 Boron, water, filtered (μg/L) 1,010 1,020 0.99

08437000 1/25/2011 Bromide, water, filtered (mg/L) 2.33 2.37 1.70

08437000 1/25/2011 Cadmium, water, filtered (μg/L) .10 .05 66.67

08437000 1/25/2011 Calcium, water, filtered (mg/L) 447 462 3.30

08437000 1/25/2011 Carbonate, water, filtered, inflection-point titration method 

(incremental titration method), field (mg/L)

.3 .2 40.00

08437000 1/25/2011 Chloride, water, filtered (mg/L) 1,180 1,180 0

08437000 1/25/2011 Chromium, water, filtered (μg/L) .40 .43 7.23

08437000 1/25/2011 Cobalt, water, filtered (μg/L) .46 .36 24.39

08437000 1/25/2011 Delta deuterium, water, unfiltered (per mil) -46.70 -47.00 -0.64

08437000 1/25/2011 Delta oxygen-18, water, unfiltered (per mil) -6.57 -6.56 -0.15

08437000 1/25/2011 Dissolved solids dried at 180 degrees Celsius, water, 

filtered (mg/L)

4,530 4,520 0.22

08437000 1/25/2011 Fluoride, water, filtered (mg/L) 1.70 1.72 1.17

08437000 1/25/2011 Iron, water, filtered (μg/L) 15 <13 --

08437000 1/25/2011 Lead, water, filtered (μg/L) 0.11 <0.04 --

08437000 1/25/2011 Lithium, water, filtered (μg/L) 280 279 0.36

08437000 1/25/2011 Magnesium, water, filtered (mg/L) 176 180 2.25

08437000 1/25/2011 Manganese, water, filtered (μg/L) 12.8 12.5 2.37

08437000 1/25/2011 Molybdenum, water, filtered (μg/L) 13.7 13.7 0

08437000 1/25/2011 Nickel, water, filtered (μg/L) 2.0 1.9 5.13

08437000 1/25/2011 Nitrite, water, filtered (μg/L) .02 .02 0

08437000 1/25/2011 Nitrate plus Nitrite, water, filtered (mg/L) 2.97 2.95 0.68

08437000 1/25/2011 Orthophosphate, water, filtered (mg/L as phosphorus) .02 .02 0

08437000 1/25/2011 Potassium, water, filtered (mg/L) 21.1 21.6 2.34

08437000 1/25/2011 Selenium, water, filtered (μg/L) 5.4 5.6 3.64

08437000 1/25/2011 Silica, water, filtered (mg/L as SiO2) 32.4 32.8 1.23

08437000 1/25/2011 Silver, water, filtered (μg/L) <.01 .02 --

08437000 1/25/2011 Sodium, water, filtered (mg/L) 688 696 1.16

08437000 1/25/2011 Strontium, water, filtered (μg/L) 8,760 9,060 3.37

08437000 1/25/2011 Sulfate, water, filtered (mg/L) 1,550 1,550 0
Methods 23

08437000 1/25/2011 Thallium, water, filtered (μg/L) 0.28 0.26 7.41

08437000 1/25/2011 Total nitrogen, water, filtered (mg/L) 3.09 3.16 2.24

08437000 1/25/2011 Tritium, water, unfiltered (pCi/L) 1.9 1.8 5.41

08437000 1/25/2011 Uranium (natural), water, filtered (μg/L) 21.0 21.1 0.48

08437000 1/25/2011 Vanadium, water, filtered (μg/L) 6.3 6.5 3.13

304006103315601 6/23/2011 Alkalinity, water, filtered inflection-point titration method 

(incremental titration method), field (mg/L as calcium 

carbonate)

 330 336 1.80

304006103315601 6/23/2011 Ammonia, water, filtered (μg/L) .781 .780 0.13

304006103315601 6/23/2011 Antimony, water, filtered (μg/L) <.03 .13 --

304006103315601 6/23/2011 Arsenic, water, filtered (μg/L) 3.1 3.0 3.28

304006103315601 6/23/2011 Barium, water, filtered (μg/L) 40 40 0

304006103315601 6/23/2011 Beryllium, water, filtered (μg/L) .02 .02 0

304006103315601 6/23/2011 Bicarbonate, water, filtered, inflection-point titration 

method (incremental titration method), field (mg/L)

401 409 1.98

304006103315601 6/23/2011 Boron, water, filtered (μg/L) 1,120 1,110 0.90

304006103315601 6/23/2011 Cadmium, water, filtered (μg/L) .03 .03 0

304006103315601 6/23/2011 Calcium, water, filtered (mg/L) 26.8 27.0 0.74

304006103315601 6/23/2011 Carbonate, water, filtered, inflection-point titration method 

(incremental titration method), field (mg/L)

.7 .6 15.38

304006103315601 6/23/2011 Chloride, water, filtered (mg/L) 57.1 58.6 2.59

304006103315601 6/23/2011 Cobalt, water, filtered (μg/L) .07 <0.02 --

304006103315601 6/23/2011 Dissolved solids dried at 180 degrees Celsius, water, 

filtered (mg/L)

869 859 1.16

304006103315601 6/23/2011 Fluoride, water, filtered (mg/L) 1.22 1.23 0.82

304006103315601 6/23/2011 Iron, water, filtered (μg/L) 66 65 1.53

304006103315601 6/23/2011 Lead, water, filtered (μg/L) .02 1.21 193.50

304006103315601 6/23/2011 Lithium, water, filtered (μg/L) 198 199 0.50

304006103315601 6/23/2011 Magnesium, water, filtered (mg/L) 4.39 4.38 0.23

304006103315601 6/23/2011 Manganese, water, filtered (μg/L) 15.9 16.1 1.25

304006103315601 6/23/2011 Molybdenum, water, filtered (μg/L) 12.5 12.5 0

304006103315601 6/23/2011 Orthophosphate, water, filtered (mg/L as phosphorus) .019 .019 0

304006103315601 6/23/2011 Potassium, water, filtered (mg/L) 7.25 7.43 2.45

304006103315601 6/23/2011 Selenium, water, filtered (μg/L) .06 .06 0

304006103315601 6/23/2011 Silica, water, filtered (mg/L as SiO2) 20.7 21.1 1.91

304006103315601 6/23/2011 Sodium, water, filtered (mg/L) 266 265 0.38

304006103315601 6/23/2011 Strontium, water, filtered (μg/L) 1,020 1,030 0.98

304006103315601 6/23/2011 Sulfate, water, filtered (mg/L) 271 271 0

304006103315601 6/23/2011 Total nitrogen, water, filtered (mg/L) .85 .86 1.17

304006103315601 6/23/2011 Uranium (natural), water, filtered (μg/L) 22.4 22.4 0

304006103315601 6/23/2011 Vanadium, water, filtered (μg/L) .19 .21 10.00

Table 5. Relative percent differences between sequential replicate and environmental samples analyzed for major ions, trace 

elements, and elemental isotopes collected in the Pecos County region, Texas, 2010–11.—Continued

[USGS, U.S. Geological Survey; mg/L, milligrams per liter; μg/L, micrograms per liter; pCi/L, picocuries per liter; NTRU, Nephelometric Turbidity Ratio 

Unit; <, concentration was less than laboratory reporting level; --, RPD not calculated because the concentration for one or both samples in the pair was 

less than the laboratory reporting level]

USGS station 

number

Date Constituent Sequential 

replicate 

result

Environmental 

result

Relative 

percent 

differences
24 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

304006103315601 6/23/2011 Zinc, water, filtered (μg/L) 2.6 3.0 14.29

305331103020501 8/17/2010 Alkalinity, water, filtered inflection-point titration method 

(incremental titration method), field (mg/L as calcium 

carbonate)

230 235 2.15

305331103020501 8/17/2010 Arsenic, water, filtered (μg/L) .60 .56 6.90

305331103020501 8/17/2010 Barium, water, filtered (μg/L) 15 16 6.45

305331103020501 8/17/2010 Bicarbonate, water, filtered, inflection-point titration 

method (incremental titration method), field (mg/L)

280 286 2.12

305331103020501 8/17/2010 Boron, water, filtered (μg/L) 388.8 396.4 1.94

305331103020501 8/17/2010 Bromide, water, filtered (mg/L) 1.06 1.05 0.95

305331103020501 8/17/2010 Calcium, water, filtered (mg/L) 275 278 1.08

305331103020501 8/17/2010 Carbonate, water, filtered, inflection-point titration method 

(incremental titration method), field (mg/L)

.2 .2 0

305331103020501 8/17/2010 Chloride, water, filtered (mg/L) 760 758 0.26

305331103020501 8/17/2010 Cobalt, water, filtered (μg/L) .11 .11 0

305331103020501 8/17/2010 Delta deuterium, water, unfiltered (per mil) -50.50 -52.30 -3.50

305331103020501 8/17/2010 Delta oxygen-18, water, unfiltered (per mil) -7.41 -7.47 -0.81

305331103020501 8/17/2010 Dissolved solids dried at 180 degrees Celsius, water, 

filtered (mg/L)

2,770 2,770 0

305331103020501 8/17/2010 Fluoride, water, filtered (mg/L) 1.31 1.30 0.77

305331103020501 8/17/2010 Lead, water, filtered (μg/L) .19 .19 0

305331103020501 8/17/2010 Lithium, water, filtered (μg/L) 130 133 2.28

305331103020501 8/17/2010 Magnesium, water, filtered (mg/L) 107 109 1.85

305331103020501 8/17/2010 Molybdenum, water, filtered (μg/L) 14.2 14.5 2.09

305331103020501 8/17/2010 Nickel, water, filtered (μg/L) .88 .83 5.85

305331103020501 8/17/2010 Nitrate plus Nitrite, water, filtered (mg/L) 1.63 1.61 1.23

305331103020501 8/17/2010 Orthophosphate, water, filtered (mg/L as phosphorus) .016 .018 11.76

305331103020501 8/17/2010 Potassium, water, filtered (mg/L) 15.0 15.2 1.32

305331103020501 8/17/2010 Selenium, water, filtered (μg/L) 3.6 3.7 2.74

305331103020501 8/17/2010 Silica, water, filtered (mg/L as SiO2) 23.4 23.3 0.43

305331103020501 8/17/2010 Sodium, water, filtered (mg/L) 418 421 0.72

305331103020501 8/17/2010 Strontium, water, filtered (μg/L) 5,490 5,330 2.96

305331103020501 8/17/2010 Sulfate, water, filtered (mg/L) 912 908 0.44

305331103020501 8/17/2010 Thallium, water, filtered (μg/L) .87 .87 0

305331103020501 8/17/2010 Total nitrogen, water, filtered (mg/L) 1.61 1.61 0

305331103020501 8/17/2010 Tritium, water, unfiltered (pCi/L) 1.5 1.3 14.29

305331103020501 8/17/2010 Uranium (natural), water, filtered (μg/L) 8.76 8.90 1.59

305331103020501 8/17/2010 Vanadium, water, filtered (μg/L) 1.8 1.9 5.41

305509103510101 9/1/2010 Delta deuterium, water, unfiltered (per mil) -11.70 -11.50 -1.72

305509103510101 9/1/2010 Delta oxygen-18, water, unfiltered (per mil) -0.52 -0.61 -15.93

Table 5. Relative percent differences between sequential replicate and environmental samples analyzed for major ions, trace 

elements, and elemental isotopes collected in the Pecos County region, Texas, 2010–11.—Continued

[USGS, U.S. Geological Survey; mg/L, milligrams per liter; μg/L, micrograms per liter; pCi/L, picocuries per liter; NTRU, Nephelometric Turbidity Ratio 

Unit; <, concentration was less than laboratory reporting level; --, RPD not calculated because the concentration for one or both samples in the pair was 

less than the laboratory reporting level]

USGS station 

number

Date Constituent Sequential 

replicate 

result

Environmental 

result

Relative 

percent 

differences
Methods 25

Field spikes are used to assess bias and variability from 

degradation of organic constituent concentrations during 

sample processing, storage, and analysis. Field spikes are 

environmental replicate samples into which a known volume 

and concentration of target analytes are added. Analytical 

recoveries of the spiked target compounds are expressed 

as percentages of expected (theoretical) concentrations. 

Computed field-spike recoveries (equation 2) are compared 

to theoretical and laboratory recoveries to evaluate matrix 

interferences or degradation of organic compounds:

Recovery = [(Cspiked – Cunspiked) ÷ Cexpected] × 100, (2)

where

Cspiked is the measured concentration of analyte 

in the spiked environmental sample, in 

micrograms per liter; 

Cunspiked is the measured concentration of analyte in 

the unspiked environmental sample, in 

micrograms per liter;

Cexpected is the theoretical concentration of analyte 

in the spiked environmental sample, in 

micrograms per liter, and is computed as

Cexpected = Csolution × Vspike ÷ Vsample, (3)

where

Csolution is concentration of analyte in spiked 

environmental solution, in micrograms 

per liter;

Vspike is volume of spike added to environmental 

sample, in milliliters; and

Vsample is volume of environmental sample, in liters.

A mixture of target analytes was added to a replicate 

environmental sample (site 305419102545301 collected on 

August 6, 2010). The calculated spike recoveries in this report 

were compared to time-series graph of groundwater spike 

recoveries in appendix 3 of Martin and Eberle (2011). In 

2010, the spike recoveries in this report are within the range 

of spike recoveries shown by Martin and Eberle, indicating no 

bias in the results. For target analytes not included, the spiked 

recoveries of reagent water by the NWQL were reviewed for 

method performance, with methods appearing to be operating 

normally (U.S. Geological Survey, 2012). 

Geophysical Methods

Surface and borehole geophysical data were collected 

throughout the study area from 2009 to 2011 to supplement 

compiled historical data and to minimize data gaps. Timedomain electromagnetic (TDEM) soundings were collected at 

4 locations (fig. 4, table 6) and audio-magnetotelluric (AMT) 

soundings were collected at 13 locations (fig. 4, table 7) and 

borehole geophysical logs were collected at 44 locations 

(fig. 4, table 8). Site locations and associated information can 

be accessed using the USGS NWIS (U.S. Geological Survey, 

2011a) and archived geophysical database.

Surface Geophysical Methods 

Surface geophysical resistivity methods can be used to 

detect changes in the electrical properties of the subsurface 

(Zohdy and others, 1974). The electrical properties of soil and 

rock are determined by water content, porosity, clay content 

and mineralogy, and conductivity (or reciprocal of electrical resistivity) of the pore water (Lucius and others, 2007). 

Resistivity measurements can be used to construct graphical 

images of the spatial distribution of electrical properties of the 

subsurface which, in turn, can be used to identify stratigraphic 

units and describe subsurface hydrogeology. The two 

surface geophysical methods used to evaluate the subsurface 

stratigraphy and hydrogeology in the study area were TDEM 

and AMT. Comprehensive descriptions of the theory and 

application of surface geophysical resistivity methods, as 

well as tables of the electrical properties of earth materials, 

are presented in Keller and Frischknecht (1966) and Lucius 

and others (2007). 

Time-Domain Electromagnetic Soundings

Four TDEM soundings were collected at four different 

sites using the Geonics Protem 47 and 57 systems (Geonics 

Limited, 2006a,b). Each of the locations were near wells 

that had borehole geophysical logs collected by the USGS. 

Locations were selected so that the TDEM could be compared 

to the borehole geophysical logs to determine if this 

geophysical method would yield information to fill in data 

gaps associated with these sites.

The Geonics Protem 47 and 57 systems (hereinafter 

referred to as Protem 47 and 57, respectively) were used to 

collect TDEM soundings at each site. The Protem 47 and 57 

use a multiturn receiver (Rx) coil to measure electromagnetic 

fields in the center of the transmitter (Tx) loop. The effective 

area of the receiver relates to the sensitivity of the Rx coil. 

The 100 square meter (m2) Rx coil of the Protem 57 is able to 

measure smaller voltages than the 31.4-m2 coil of the Protem 

47. At each sounding, an integration time of 15 seconds (s) 

was used to measure six different data sets (the compilation 

of these data sets is referred to as a stack). The mean value of 

all the soundings collected over the integration time is stored. 

The values stored in the stack are averaged to ensure data 

quality and repeatability, and averaging is done prior to the 

inversion step, which is explained in the inverse modeling 

section of this report. 
26 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011 31°0' 30°30' 102°30' 103°0' 103°30'

Pecos River

Pecos River

REEVES

COUNTY

WARD

COUNTY

CRANE

COUNTY

UPTON

COUNTY

PECOS 

COUNTY

JEFF DAVIS

COUNTY

BREWSTER

COUNTY

TERRELL

COUNTY

CROCKETT

COUNTY

303717103214801

303852102432901

302630102503801

303948103205801

302125103022801

303718103214601

303824102285001

305042102595601

304620103015101

305110102533401

305234102504301

305548103161401

304551102361201

305055103110801

303503102303601

304134102312601

304711103003301

304715103263501 304728102304401

311434102384801

304622102312401

305357102172001 311244102451401

310041102152901

305627103071901 305715102571401

305323102530201 305416102184801

305336102361801

305404102512701

310806103171901

304210102443201

305740103110901

311124102302201

305706102095501

310238103191701

305835102134701

311100103080501

311235103000901

302122102504501

304153103090501

305604102581301

311625102403901

311615103035101

AMT#13

AMT#10

AMT#9

AMT#6

AMT#5

AMT#4

AMT#3

AMT#2

AMT#1

AMT#8

AMT#7

AMT#11

AMT#12

TDEM#4

TDEM#2 TDEM#1

TDEM#3

Fort Stockton

Grandfalls

Girvin

EXPLANATION

Study area boundaryGeochemical sampling site Borehole logging site and  station number Audio-magnetotelluric sounding  site and site identifier Time-domain electromagnetic sounding site and site identifierGeodatabase site

310238103191701

AMT#4

TDEM#3

Base modified from U.S. Geological Survey 1:2,000,000-scale digital dataAlbers Equal Area Projection, Texas State Mapping SystemNorth American Datum of 1983

0 10 20 MILES 5 15

0 10 20 KILOMETERS 5 15

Figure 4. Site locations of field-collected geophysical data, including borehole logging and surface geophysical sites, Pecos County region, Texas, 2009–11.
Methods 27

Table 6. Time-domain electromagnetic geophysical sounding sites, Pecos County region, Texas, 2009-11

[TDEM, time-domain electromagnetic; USGS, U.S. Geological Survey; dd, decimal degrees]

Sounding identification number USGS station number State well number Latitude (dd) Longitude (dd)

TDEM#1 305110102533401 US-53-09-301 30.85286 -102.89278

TDEM#2 305042102595601 US-53-09-106 30.84509 -102.99899

TDEM#3 304711103003301 US-52-16-909 30.69795 -103.15138

TDEM#4 303824102285001 US-53-21-703 30.64000 -102.48052

Table 7. Audio magnetotelluric geophysical sounding sites, Pecos County region, Texas, 2009-11.

[AMT, audio magnetotelluric; USGS, U.S.Geological Survey; dd, decimal degrees; --, sounding not collected at/near well site]

Sounding identification number USGS station number State well number Latitude (dd) Longitude (dd)

AMT#1 -- -- 30.57745 -103.28333

AMT#2 -- -- 30.51932 -103.30687

AMT#3 -- -- 30.71023 -103.52157

AMT#4 -- -- 30.88350 -103.38389

AMT#5 -- -- 30.80659 -103.48194

AMT#6 -- -- 30.60335 -102.78842

AMT#7 303824102285001 US-53-21-703 30.64000 -102.48052

AMT#8 302630102503801 US-53-34-401 30.44176 -102.84396

AMT#9 -- -- 31.06002 -103.13731

AMT#10 -- -- 30.94134 -102.55057

AMT#11 304622102312401 US-53-12-901 30.77304 -102.52379

AMT#12 310806103171901 WD-46-54-901 31.13502 -103.28796

AMT#13 -- -- 30.86516 -103.82792
28 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Table 8. Borehole geophysical data-collection sites, Pecos County region, Texas, 2009-11.

[USGS, U.S. Geological Survey; dd, decimal degrees]

USGS station number State well number Latitude (dd) Longitude (dd)

302122102504501 US-53-42-101 30.356 -102.8458611

302125103022801 BK-52-48-301 30.357 -103.0411306

302630102503801 US-53-34-401 30.4417611 -102.8439611

303503102303601 US-53-28-303 30.5842111 -102.5100694

303717103214801 US-52-30-107 30.62143889 -103.3638306

303718103214601 US-52-30-108 30.62181944 -103.3632389

303824102285001 US-53-21-703 30.64 -102.4805194

303852102432901 US-53-19-701 30.6479 -102.7247111

303948103205801 52-22-7xx 30.66344444 -103.3494444

304134102312601 US-53-20-603 30.69278889 -102.5239889

304153103090501 US-52-23-604 30.69795 -103.1513806

304210102443201 53-19-4xx 30.70269444 -102.7422778

304551102361201 US-53-12-701 30.76448056 -102.6038694

304620103015101 US-53-02-7xx (COFS 6) 30.7721 -103.0308

304622102312401 US-53-12-901 30.77303889 -102.5237889

304711103003301 US-52-16-909 30.78641944 -103.0093194

304715103263501 US-52-13-801 30.7874 -103.4434306

304728102304401 US-53-12-902 30.79098056 -102.5121611

305042102595601 US-53-09-106 30.84508889 -102.9989889

305055103110801 52-15-2xx 30.84863889 -103.1856667

305110102533401 US-53-09-301 30.8528611 -102.8927806

305234102504301 US-53-02-708 30.87618056 -102.8452111

305323102530201 US-53-01-908 30.88951944 -102.8839694

305336102361801 US-53-04-701 30.89363889 -102.6054

305357102172001 US-53-06-901 30.89923056 -102.2891194

305404102512701 US-53-02-710 30.9012 -102.8577

305416102184801 US-53-06-803 30.90458056 -102.3132694

305548103161401 US-52-06-604 30.9302 -103.2706

305604102581301 US-53-01-4xx (Apache 4) 30.93455 -102.9703

305627103071901 US-52-08-402 30.94075 -103.122

305706102095501 US-53-07-601 30.95175 -102.1653611

305715102571401 US-53-01-503 30.9542611 -102.9538194

305740103110901 US-52-07-201 30.9612 -103.1860806

305835102134701 US-53-07-106 30.9765 -102.2297694

310041102152901 US-45-62-901 31.0115611 -102.25855

310238103191701 US-46-62-801 31.0440111 -103.3213889

310806103171901 WD-46-54-901 31.13501944 -103.2879611

311100103080501 US-46-55-603 31.1834611 -103.1347389

311124102302201 US-45-52-602 31.19008056 -102.5065389

311235103000901 US-46-56-309 31.20973889 -103.0026194

311244102451401 US-45-50-302 31.21208889 -102.7539694

311434102384801 US-45-51-306 31.24468056 -102.6493

311615103035101 US-46-48-805 31.2708111 -103.0641611

311625102403901 US-45-43-806 31.27378889 -102.6778389
Methods 29

For each TDEM sounding collected, the voltages 

measured from the eddy currents were averaged and evaluated 

statistically by using preprocessing scripts (Joe Vrabel, U.S. 

Geological Survey, written commun., 2010). These scripts use 

the raw field data (voltage data) to calculate the uncertainty of 

each time gate (measured voltage values at discreet intervals 

of time increasing after shutoff of the current) independently. 

After calculating the standard deviation of the voltage, the 

user can specify limits to trim the data set (remove outliers 

prior to inverse modeling). For this study, the data were 

initially filtered by using the mean of the six stacks collected. 

Outliers were evaluated by the program and any data that 

were more than 10 percent above or below other data points 

were removed. The averages of each time gate were saved 

as processed data files to be used in the inversion software 

(Interpex Limited, 1996). 

Audiomagnetotelluric Soundings

A total of 13 AMT soundings was collected and 

processed within the study area using the Stratagem EH4 

electrical conductivity imaging system developed by 

Geometrics, Inc. and Electromagnetic Instruments, Inc. 

(Geometrics, 2012), and in accordance with techniques 

described by Asch and Sweetkind (2010). Of the 13 soundings 

collected, 4 of these soundings were collected near wells that 

had borehole geophysical logs collected by the USGS. These 

locations were selected so that the AMT soundings could be 

compared to the borehole geophysical logs, which aid in the 

interpretation of the AMT soundings. The remaining nine 

sounding locations were selected in areas where little or no 

other compiled data were located. 

The Stratagem EH4 system was used to collect AMT 

data for each sounding location. The Stratagem EH4 system 

measures perpendicular arrays of electrical and magnetic 

fields labeled as X and Y directions within a range of 10 hertz 

(Hz) to 100 kilohertz (kHz) (Asch and Sweetkind, 2010). 

The electric field was measured by four stainless-steel 

electrodes placed into the earth with a 25-meter dipole (two 

electrodes separated by 25 meters) in the X direction and a 

25-meter dipole in the Y direction. A fifth electrode was 

used as a ground. The ambient magnetic field was measured 

with two induction magnetometer coils that were placed 

more than 3 meters away from the electrode dipoles and are 

placed level in a small trench and then covered with dirt to 

ensure there is no movement of the coil. The controlled 

source transmitter was a 400-watt transmitter to supplement 

the received electromagnetic signal in the frequency range 

from 900 Hz to 23,000 Hz. The X and Y directions were 

chosen on a site by site basis with the X and Y directions 

being approximately 45 degrees from visible anthropogenic 

sources (Geometrics, 2007).

Time-series datasets were analyzed and selected based 

on the optimal signal-to-noise ratio before calculations were 

performed on the datasets. The measured AMT time-series 

datasets at each location were converted to the frequency 

domain and processed to determine a two-dimensional (2D) 

impedance tensor of apparent resistivity and phase (Asch and 

Sweetkind, 2010). Poor quality (noisy) data were filtered out 

in the time-series datasets before the conversion was made 

and in the spectral and resistivity datasets after conversion. 

Apparent resistivity is the approximate ratio of the magnitude 

of the electric field to the magnitude of the magnetic field for a 

given frequency (Asch and Sweetkind, 2010). The impedance 

tensor was rotated to an angle that closely represented a 2D 

earth at each sounding location. This allows for the separation 

of the TE and TM modes, which can be used to identify lateral 

variation across the sounding site. 

Data were exported from Imagem, the Stratagem data 

acquisition program, into two files: a cross-power data 

file, which contained spectral conversion of the data and a 

magnetotelluric (MT) impedance data file, which contained 

the apparent resistivity and phase conversion of the data 

(Geometrics, 2007). These files were used during the 2D 

inversion modeling process. 

Inverse Modeling of Surface 

Geophysical Results

Apparent resistivity represents the resistivity of a 

completely uniform (homogenous and isotropic) subsurface 

(Keller and Frischknecht, 1966). Inverse modeling is the 

process of creating an estimate of the true distribution of 

subsurface resistivity (derived from the actual heterogeneous, 

anisotropic rocks) from the measured apparent resistivity 

(modeled as homogeneous, isotropic rocks). To estimate the 

resistivity of nonuniform earth material, inverse modeling 

software is used. The IX1Dv3 program, developed by 

Interpex Limited (1996), was used for inverse modeling of 

the TDEM soundings. The AMT sounding data were inverted 

using selected inversion algorithms within the Geotools 

MT software package used to process AMT and MT data 

(Geotools, 1998).

For this report, root mean square errors (RMSE) of 

10 percent or less were generally considered acceptable, 

and RMSEs of 5 percent were generally considered good.

The inverse modeling results of the TDEM data collected 

throughout the area had RMSEs of less than 4 percent for all 

soundings collected (appendix 1). The TDEM results were 

not able to resolve the depths needed to make geologic picks, 

so AMT was used to obtain deeper information.

The inverse modeling results of the AMT data 

collected throughout the area had acceptable errors between 

the measured field data and the calculated model data 

(appendix 2). There were two locations (AMT07 and 

AMT13, fig. 4) where anthropogenic noise distorted the 

signal sufficiently such that a poor inversion result was 

obtained. Four of the AMT soundings were located near wells 

from which geophysical logs were obtained, allowing the data 

quality to be assessed using borehole geophysical results.
30 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Borehole Geophysical Methods

Borehole geophysical data such as natural gamma, 

formation resistivity, and caliper are commonly used to 

characterize and identify stratigraphic units (Keys, 1997). 

Many of these data had been collected in some wells in 

the study area as parts of previous studies and petroleum 

exploration (Small, and Ozuna, 1993; Smith and others, 2000). 

Conventional borehole geophysical log data such as natural 

gamma, formation resistivity, fluid resistivity, temperature, 

and caliper were collected in 44 wells where additional 

geophysical data were most critical to supplement existing 

data. In addition to the conventional borehole geophysical 

methods, advanced borehole geophysical measurements of 

vertical flow (magnitude and direction), in the borehole were 

collected in six representative wells using the Electromagnetic 

(EM) flowmeter. These data can be evaluated to determine the 

relation of flow to the hydrostratigraphic units in each well. 

All borehole geophysical data were collected using a Century 

Geophysical Corporation System VI logging system conveyed 

by a 0.25-in. diameter 4-conductor wireline or a Mount Sopris 

Instruments Matrix logging system conveyed by a 0.1875-in. 

diameter single conductor wireline. Limitations, calibration 

procedures, and algorithms of the geophysical probes are 

available from the manufacturers (Century Geophysical 

Corporation, 2012; Mount Sopris Instruments, 2012).

Electromagnetic Induction Logs

Electromagnetic induction probes measure conductivity 

in air- or water-filled holes and perform well in open holes 

or polyvinyl chloride (PVC) cased holes. The measurement 

of conductivity commonly is reciprocated to provide logs 

with curves of resistivity and conductivity (Keys, 1997). 

Conductivity is affected by the salinity of borehole and 

formation fluids and the type of lithology encountered. 

Generally, pure carbonates, sands, and gravels have lower 

conductivity, thus higher resistivity, than clays or shales 

(Keys, 1997). A Century Geophysical Corporation 9510 or a 

Geonics EM39 induction conductivity probe was calibrated 

and was used to the manufacturer’s specifications (Century 

Geophysical Corporation, written commun., 2011; Mount 

Sopris Instruments, written commun., 2011). The EM 

induction conductivity measurements (commonly sensitive 

to metallic conductive objects) were affected at depths 

corresponding with metal objects such as centralizers and 

stainless steel screens. 

Natural Gamma Logs

Natural gamma logs provide a record of gamma 

radiation detected at depth in a borehole. Fine-grained 

sediments that contain abundant clay tend to be more 

radioactive than quartz-grain sandstones or carbonates 

(Keys, 1997). The natural gamma log was run in conjunction 

with the fluid resistivity log and was recorded in natural 

gamma counts per second simultaneously as the induction 

log was recorded in both cased and open boreholes. A 

Century Geophysical Corporation 8044 multiparameter 

probe or a Mount Sopris Instruments 2PGA–1000 natural 

gamma probe with a sodium iodide detector was calibrated 

and was used to the manufacturer’s specifications. The 

natural gamma and induction logs collectively can be useful 

in identifying lithologies and contact depths of the strata 

penetrated in the borehole. 

Electric Logs

Electric logs use a series of electrodes mounted on the 

downhole probe and a surface electrode in the ground to 

measure potential (or voltage) that varies with the electrical 

properties of fluids and rock materials. Electric logs require 

an uncased, fluid-filled hole to allow the current to flow 

into the formation. Electric logs include the following 

electrical methods measured in boreholes: normal resistivity, 

lateral resistivity, spontaneous potential, and single-point 

resistance. A Century Geophysical Corporation model 8044 

multiparameter E-log probe was used to measure normal 

resistivity, lateral resistivity, spontaneous potential, and 

single-point resistance. These geophysical methods are 

explained in detail in Keys (1990, 1997). 

Caliper Logs

Caliper logs provide a measurement of the diameter of 

the borehole and are useful in determining changes in borehole 

diameter that can be related to drilling techniques, cavernous 

formations, lithology, and well construction. The Century 

Geophysical Corporation model 7074 and the Mount Sopris 

Instruments 2PCA–1000, three-arm caliper probes were used 

in this study and recorded an average diameter measured 

by the three arms. The Century Geophysical Corporation 

7074 probe was run in the short or long arm configurations 

(depending on hole diameter) for boreholes from 2 to 24 and 

2 to 36 inches in diameter, respectively (Century Geophysical 

Corporation, 2012). The Mount Sopris Instruments 

2PCA–1000 can be used in boreholes from 2 to 17 inches in 

diameter (Mount Sopris Instruments, 2012). Other limitations 

and algorithms of the geophysical probes can be found at 

Century Geophysical Corporation (2012) and Mount Sopris 

Instruments (2012). The caliper logs were collected using the 

Century Geophysical Corporation System IV or Mount Sopris 

Instruments Matrix logging systems. The caliper was calibrated by performing a two-point calibration on short sections 

of pipe (rings) where diameters were larger and smaller than 

the borehole sizes that were expected to be encountered.
Methods 31

Fluid Resistivity and Temperature Logs

Fluid resistivity logs provide a record of the capacity 

of the borehole fluid to conduct electrical current (Keys, 

1990). Changes in fluid resistivity are measured by ring 

electrodes inside a housing that allows borehole fluid to 

flow through it. When feasible, fluid resistivity logs were 

run as the first logging run to record the ambient conditions 

before other probes have passed through the borehole and 

have vertically mixed the borehole fluid. Curve deflections 

on the fluid resistivity log can indicate horizontal or vertical 

flow, stratification of borehole fluid, or screened intervals 

in cased wells. The fluid resistivity values also can be used 

in calculations with other logs. Fluid resistivity and the 

reciprocal (fluid conductivity) are shown on the logs in this 

study for comparison to specific-conductance values collected 

at springs (appendix 1). 

The fluid conductivity values contained in the logs for 

this study are the values recorded at the ambient borehole 

temperature and are not corrected to a standard temperature. A 

Century Geophysical Corporation model 8044 multiparameter 

E-log probe or a Mount Sopris Instruments model 2PFA–1000 

probe was used to log fluid resistivity in uncased (open) 

boreholes and cased wells. Calibration of the fluid resistivity 

logging probes was done with solutions of known conductivity 

in a two-point calibration. Temperature logs record the 

temperature of the borehole fluid that the logging probe passes 

through as it is raised or lowered in the borehole. A Century 

Geophysical Corporation model 8044 multiparameter E-log 

probe or a Mount Sopris Instruments model 2PFA–1000 probe 

was used to log fluid temperature in uncased (open) boreholes 

and cased wells. All temperature logs were collected as the 

probe was lowered in the borehole to maximize the flow into 

the sensor housing at the bottom of the Century Geophysical 

Corporation model 8044 logging probe. Temperature logs can 

provide useful information on the movement of water through 

a water-well borehole, including the location of depth intervals 

that produce or accept water (Keys, 1990). 

Optical Borehole Imaging

The optical borehole imager (OBI) is an oriented logging 

device that can provide a high-resolution, 360-degree image 

or “cylindrical picture” of the circumference of the borehole 

that can be used to evaluate secondary porosity features 

such as fractures and solution openings. The OBI uses a 

digital scanning camera and conical mirror, which records a 

360-degree image of the borehole wall showing the texture, 

color, and fractures in air-filled or clear fluid-filled boreholes 

(Hearst and others, 2000). A cylindrical light ring between 

the camera and mirror illuminates the part of the borehole 

wall being imaged. An Advanced Logic Technology optical 

borehole imager or OBI40 was used to collect optical images 

of the surface wall of open and cased wells in both air and 

clear water (Advanced Logic Technology, 2012). The utility 

and analytical methods of optical imaging are explained in 

Keys (1997) and Hearst and others (2000).

Acoustic Borehole Imaging 

The acoustic borehole imager (ABI) is an oriented 

logging device that can provide a high-resolution, 360-degree 

image or cylindrical acoustic image of the circumference of 

the borehole that can be used to evaluate secondary porosity 

features such as fractures and solution openings. Acoustic 

borehole imaging tools generate an image of the borehole wall 

by transmitting ultrasonic pulses from a rotating sensor and 

recording the amplitude and traveltime of the signals reflected 

at the interface between the borehole fluid and borehole wall. 

Because of the need for sound waves to be transmitted to 

and from the borehole wall and rock formation, ABI tools 

can only be used in fluid-filled holes. An Advanced Logic 

Technology acoustic borehole imager or ABI40 was used to 

collect acoustic borehole images. These are multiecho systems 

that measure multiple echoes of amplitude and traveltime. 

The ABI image shows the borehole-fracture intersection by 

scattering acoustic energy and enabling the defined orientation 

and fracture aperture to be used to calculate the strike and dip 

of planar features such as fractures and bedding planes (Hearst 

and others, 2000; Keys, 1997; Paillet, 1991). 

Electromagnetic Flowmeter

The EM flowmeter measures the vertical flow rate 

and direction in a borehole using the principal of Faraday’s 

Law of EM Induction (Century Geophysical Corporation, 

written commun., 2006). The EM flowmeter probe consists 

of an electromagnet and two electrodes 180 degrees apart 

and oriented 90 degrees to the magnetic field inside a 

hollow cylinder or tube. The voltage induced by a conductor 

moving at right angles through the magnetic field is directly 

proportional to the velocity of the conductor (water) through 

the field (Century Geophysical Corporation, written commun., 

2006). Generally, when using the tool to measure low-velocity 

flow, rubber diverters direct the water flow through the tube, 

which is open at both ends, instead of around the tool. 

Because the diameter of the tube and voltage response is 

calibrated, the volume of flow is instantaneously recorded. 

The direction of water flow is determined by the polarity of 

the response; upward flow is positive and downward flow 

is negative. If there are vertical hydraulic head gradients 

within the aquifer adjacent to the borehole, then the ambient 

flow profile is subtracted from the flow profile during steady 

pumping to yield the estimated relative interval transmissivity 

(Paillet, 2001).
32 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Geophysical Data Quality Assurance 

and Formats

All logs collected during 2009–11 were collected 

according to the American Society of Testing and Materials 

(ASTM) borehole geophysical standard procedures: (1) 

ASTM Standard Guide for Planning and Conducting Borehole 

Geophysical Logging - D5753-05 (American Society of 

Testing and Materials, 2010), (2) ASTM Standard Guide 

for Conducting Borehole Geophysical Logging Mechanical 

Caliper - D6167 – 97 (American Society of Testing and 

Materials, 2004), and (3) ASTM Standard Guide for 

Conducting Borehole Geophysical Logging Electromagnetic 

Induction - D6726 – 01 (American Society of Testing and 

Materials, 2007). All logs were collected in digital format and 

were recorded in the proprietary format of the data acquisition 

equipment used to collect the logs. These proprietary data 

formats were converted to and stored as Log American 

Standard Code for Information Interchange (ASCII) Standard 

(Canadian Well Logging Society, 2011) tabular data and 

presented as chart logs in a portable document format (PDF) 

file (appendix 2). All surface geophysical data were collected 

in accordance with ASTM Standard Guide for Selecting 

Surface Geophysical Methods - D6429 (American Society of 

Testing and Materials, 1999).

Geodatabase Compilation

Groundwater, surface-water, water-quality, geophysical, 

and geologic information were downloaded from existing 

database resources hosted by various Federal, State, and 

local agencies. The geodatabase comprises data accessed 

and downloaded from enterprise database resources that 

warehouse environmental data, such as USGS NWIS, USEPA 

Modernized Storage and Retrieval Repository (STORET), 

TWDB Groundwater Database, TCEQ Surface Water Quality 

Information System (SWQMIS), and others. 

The USGS groundwater, surface-water, and water-quality 

data were obtained from NWIS and include measurements 

taken as part of routine sampling and project-specific 

sampling in the Texas Water Science Centers (U.S. Geological 

Survey, 2011a). In addition, field-collected geochemical 

and geophysical data reported in the sections above were 

included with the downloaded data obtained from NWIS. The 

USEPA data were obtained from the Modern STORET and 

include mostly surface water-quality data supplied by State 

and local agencies (U.S. Environmental Protection Agency, 

2011). Data from the TWDB Groundwater Database include 

well information, water quality, and water levels reported 

to TWDB from Federal, State, and local entities (Texas 

Water Development Board, 2011). The TCEQ SWQMIS 

data were obtained using direct connection with the database 

(Texas Commission on Environmental Quality, 2011). This 

information includes mostly surface-water information 

focused on water quality for sites throughout Texas. Local 

database resources were used from the City of Fort Stockton 

and Middle Pecos Groundwater Conservation District. 

Additional data were mined from published reports and other 

hardcopy data resources in the geodatabase. In most cases, 

these data were acquired directly from the source agency and 

accessed through the publishing agency’s website or online 

libraries. Appendix 3 provides detail about the database 

resources used in the final geodatabase product. 

Many of the data resources compiled into the geodatabase 

came from databases or other digital files with vastly different 

file formats, contents, structure, and function. The compilation 

process included a qualitative and quantitative analysis of 

each individual data source to identify relevant, authoritative 

data to include in the geodatabase. Data were extracted 

from the native data source using custom queries and export 

functions, and then loaded into the geodatabase using import 

functions and structured query language (SQL) code. This 

process incorporates data from many disparate databases into 

a single compilation and may result in duplicate records in 

the geodatabase because of redundant data reported between 

unique databases.

The first step of this process was to compile all 

geographic site locations from independent database 

resources into a single master site file for the geodatabase. 

Site locations were provided in a compatible geospatial data 

format (geodatabase feature class or shapefile format) or 

latitude/longitude coordinates were identified in the tabular 

information. The final master site file was then related to 

the groundwater, surface-water, water-quality, geophysical, 

and geologic data stored in data tables in the geodatabase. 

Groundwater levels and geologic data were combined into 

a single table for all available sources, while groundwater, 

surface-water, and water-quality data were stored in separate 

tables in the geodatabase and organized by source agency. 

Geodatabase Design

A geodatabase is a spatially enabled database that contains spatial and tabular data and allows users to associate 

tabular data with physical and spatial components (Shah 

and Houston, 2007). It is capable of handling volumes 

of data efficiently through the use of a relational database 

management system. The geodatabase can be explored 

interactively using a GIS or accessed through traditional 

database queries. Using a GIS, the spatial data can be viewed 

in combination with other relevant geospatial data layers 

(aerial imagery, surface geology, administrative boundaries, 

and so forth) to analyze distribution patterns, data gaps, spatial 

relationships, and to create cartographic representations of the 

geodatabase contents.
Geodatabase Compilation 33

The geodatabase is comprised of database objects: 

feature classes, relationship classes, and attribute tables. 

Feature classes store geospatial data objects of similar 

geometry type (point, line, or polygon). A collection of feature 

classes are stored and managed in a feature dataset, which uses 

a single, defined geographic or projected coordinate system for 

all data stored within the database object. Relationship classes 

link geospatial data stored in the feature classes with related 

tabular information stored in attribute tables. Relationship 

classes allow the end user to query data by establishing 

connections between geospatial data stored in 

the feature classes with related tabular information stored 

within the geodatabase attribute tables (Zeiler, 1999). 

The geodatabase designed for this study was based on an 

Environmental Systems Research Institute (ESRI) ArcGIS 

10.0 personal geodatabase platform. ArcGIS personal 

geodatabases store database information as Microsoft 

Access (97–2003) files (Zeiler, 1999). 

Figure 5 shows the simplified geodatabase model 

used for this project. Figure elements are shaded to 

highlight the distinction between data sources, data 

elements used to store geographic information and those 

used to store related tabular information. Compiling data, 

entering data into the geodatabase, ensuring data quality, and 

documenting the associated metadata were the primary steps 

in creating the geodatabase.

Data Input

Digital data were imported and select hardcopy data 

were entered manually into the geodatabase. Data were 

extracted from the native data resources using custom queries 

and basic data export functions and then were loaded into 

the geodatabase using import functions and SQL code within 

Microsoft Access. Whenever possible, SQL code was used 

to automate the creation of tables within the geodatabase 

and to load data into specified database elements within the 

geodatabase. Traditional geodatabase import/export functions 

within ArcGIS were used for the final compilation for 

geospatial components. The Microsoft Access table and query 

design wizards also were used for data input. In addition, 

ESRI ArcCatalog was used to create tables and upload data 

into the geodatabase attribute tables using the “Simple Data 

Loader.” This efficient tool allows the end-user to load both 

spatial and tabular data, stored in various native data formats, 

into a geodatabase feature class or attribute table. 

Geodatabase Data Quality Assurance

Database schemas and data formats from the various 

source agencies are incongruent, so the final database schema 

was simplified to capture only essential information needed 

for the geodatabase. Using database imports functions and 

SQL code, the disparate data were loaded into the generalized 

schema for geographic locations (sitefile) and attribute tables 

that store water-level and water-quality data. Simple crosschecks were performed to ensure the number of records from 

the native data resources were consistent with the number of 

records imported into the geodatabase after loading. 

In some cases, data from one source agency were 

reported in one or more of the unique database sources used 

in this project. For example, some of water-level altitudes 

collected by the USGS and stored in NWIS were also stored 

in the TWDB Groundwater Database. Based on the design 

of the geodatabase, native database resources uploaded into 

the geodatabase reside in independent attribute tables and 

are linked to the sitefile through relationship classes linked 

by the unique identifier for each record. The design of the 

geodatabase operates under the assumption that data might be 

duplicated between source agencies. 

Additional quality assurance methods can be applied 

after querying the geodatabase to ensure a higher level of data 

quality. This may include a search for duplicate geographic 

site locations using a tolerance established by the end-user. 

Shah and Maltby (2010) used a 30-meter horizontal buffer to 

identify site locations near each other and then used additional 

fields (for example, source agency) to eliminate duplicate 

information where possible. Additionally, tabular information 

can be reviewed post-query using a combination of key fields, 

such as source agency, date/time, site type, parameter name or 

result values, to help identify potential duplicates. While these 

steps can help eliminate duplicate data, the possibility that 

duplicate data exist in the post-query results is still high based 

on the inability to precisely identify all duplicate data because 

of data rounding, incongruent database schemas, and other 

data handling errors present in each database resource. 

Metadata

Federal Geographic Data Committee (FGDC) compliant 

metadata were created for each spatial data layer in the 

geodatabase. Metadata describe the “who, what, when, where, 

why, and how” for each spatial data layer. FGDC metadata 

include data categories such as title, abstract, publication date, 

and sourcing information. In addition, the metadata record 

describes the geographic setting for each spatial data layer, 

including the geographic or projected coordinate system 

and vertical/horizontal datum. Lastly, the metadata record 

describes the attribute label definitions and domain values for 

fields in the attribute table of the spatial data layer. A detailed 

listing of metadata contents can be found at http://www.fgdc.

gov/metadata (Federal Geographic Data Committee, 2012). 

The metadata record for the sitefile feature class can be found 

in appendix 4.
34 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

D

B

S

A

T

X

R

R

C

B

R

A

C

S

U

S

G

S

Sitefile

Drillers Logs

Geophysical Logs

U

T

L

D

Geology

E

P

A

M

P

G

C

D

T

C

E

Q

T

X

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R

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D

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Water Level

Water Sample

E

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Water Result

Sitefile

GEODATABASE DATA MODEL - Water Level and Water Sample/Result

GEODATABASE DATA MODEL - Drillers/Geophysical Logs and Geology

Simplified Data Model ElementsData Source—Digital or hardcopy data informationused in the geodatabase compilationGeodatabase Feature Class—Spatial data, features stored as polygons, lines or pointsGeodatabase Attribute Table—Information/datastored in rows and columns, generally related to feature classGeodatabase Relationship Class—Links spatialinformation and tabular data

Texas Water 

Development Board

Texas Railroad 

Commission

Texas Commission on 

Environmental Quality

U.S. Environmental

 Protection Agency

City of Fort Stockton

Middle Pecos Groundwater

Conservation District

U.S. Geological Survey

University of Texas Lands

Daniel B. Stephens 

and Associates 

TWDB Brackish Resources 

Aquifer Characterization 

System 

Data Source Digital  HardcopyGeodatbase Feature Class  Attribute Table Relationship Class

EXPLANATION

Figure 5. Simplified geodatabase data model for hydrogeologic data for the Pecos County region, Texas, 2011.
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Glossary 39

Glossary

Acronyms and terms used throughout the report

ABI acoustic borehole imager

AMT audio-magnetotelluric

ASCII American Standard Code for Information Interchange

ASTM American Society of Testing and Materials

COFS City of Fort Stockton

EM electromagnetic

ESRI Environmental Systems Research Institute

FGDC Federal Geographic Data Committee

GAM groundwater availability model

GIS geographic information system

LRL laboratory reporting level

MPGCD Middle Pecos Groundwater Conservation District

MT magnetotelluric

NWIS National Water Information System

OBI optical borehole imager

Ohm Unit of measure of electrical resistance (International System)

Ohm-meters Unit by which resistivity is measured; it is derived from the following equation:

 R = rA/L

 where 

 R is resistivity, in ohm-meters; 

 r is resistance measured, in ohms; 

 A is cross-sectional area, in meters squared; and 

 L is length of the resistor, in meters.

PDF Portable Document Format

RMSE root mean square error

RPD relative percent difference

SQL Structured Query Language

STORET Storage and Retrieval Repository

SWQMIS Surface Water Quality Monitoring Information System

TCEQ Texas Commission on Environmental Quality

TDEM time-domain electromagnetic

TE transverse electric

TM transverse magnetic

TWDB Texas Water Development Board

TXRRC Texas Railroad Commission

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

UTLD University of Texas System Lands

Appendix 1. 41

Appendix 1. Time-Domain Electromagnetic Resistivity from Field 

Measurements as a Function of Time and Inverse Modeling Results 

(Smooth and Layered-Earth Models)

Measured apparent resistivity data as a function of time are presented in appendix 1. Apparent resistivity values are 

calculated from the raw voltage values measured for each sounding, When plotted in time, these apparent resistivity values 

yield a decay curve representing the subsurface electrical stratigraphy. Data points that deviated appreciably (in the judgment of 

the authors) from the decay curve (and, therefore, represented suspect data) were deleted before inverse modeling. Appendix 1 

includes the decay curve for each sounding as well as the inverse modeling results calculated from the curve.

A smooth inverse model (a multilayered model that holds the depth values fixed and allows the resistivities to vary during 

inversion) was then fit to the data using Occam’s inversion principle (Constable and others, 1987). The inversion process uses a 

series of iterations to create a model that closely fits the data. Iterations were continued until the root mean square error (RMSE) 

between measured and calculated apparent resistivity changed less than 0.1 percent between iterations. To better represent the 

electrical stratigraphy of each sounding, layered-earth models were then generated. The layered-earth models are simplified 

to represent geologic units with depth. Throughout the area, the layered-earth models range from 4 to 6 layers, depending on 

observed inflections in the apparent resistivity decay curve and smooth model inversions. Graphs of the smooth and layeredearth models for each sounding site are in appendix 1. The graphs show the raw apparent resistivity data and the inversion 

results. The smooth (green line), layered-earth (red line), and error or bounds of layered equivalent models (grey shaded area 

around depth profiles) are shown in the plots. 
42 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 1.1 Sounding site TDEM#1, Pecos County, Texas. A, 80-meter time-domain electromagnetic sounding data (apparent resistivity from field measurements) as a function of time. B, 80-meter layered and equivalent inverse modeling results (models of true resistivity as a function of depth).

10 0 10 2 10 4

0

100200300400500600700800900

1,000

Resistivity, in ohm-meters

Depth below land surface, in feet

10 −3 10 −2 10 −1 10 0 10 1 10 2

10 1

10 210 3

Time- in milli-seconds

Apparent resistivity, in ohm-meters

EXPLANATION

A B

Boundary of layered equivalence modelsSmooth inverse modelLayered inverse modelMeasured resistivity

Number of smooth model layers: 20Smooth model root mean square: 3.11 percentNumber of layered model layers: 5Layered model root mean square: 3.15 percent
Appendix 1. 43 Figure 1.2 Sounding site TDEM#2, Pecos County, Texas. A, 80-meter time-domain electromagnetic sounding data (apparent resistivity from field measurements) as a function of time. B, 80-meter layered and equivalent inverse modeling results (models of true resistivity as a function of depth).

10 −3 10 −2 10 −1 10 0 10 1 10 2

10 1

10 210 3

Time, in milli-seconds

Apparent rResistivity, in ohm-meters

10 0 10 1 10 2

0

100200300400500600700800900

1,000

Resistivity, in ohm-meters

Depth below land surface, in feet

EXPLANATION

Number of smooth model layers: 20Smooth model root mean square: 2.49 percentNumber of layered model layers: 4Layered model root mean square: 2.89 percent

A B

Boundary of layered equivalence modelsSmooth inverse modelLayered inverse modelMeasured resistivity
44 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 1.3 Sounding site TDEM#3, Pecos County, Texas. A, 80-meter time-domain electromagnetic sounding data (apparent resistivity from field measurements) as a function of time. B, 80-meter layered and equivalent inverse modeling results (models of true resistivity as a function of depth).

10 −3 10 −2 10 −1 10 0 10 1 10 2

10 110 210 3

Time, in milli-seconds

Apparent resistivity, in ohm-meters

A B

10 0 10 1 10 2 10 3

0

100200300400500600700800900

1,000

Resistivity, in ohm-meters

Depth below land surface, in feet

EXPLANATION

Number of smooth model layers: 20Smooth model root mean square: 1.61 percentNumber of layered model layers: 5Layered model root mean square: 1.52 percent

Boundary of layered equivalence modelsSmooth inverse modelLayered inverse model

Measured resistivity
Appendix 1. 45 Figure 1.4 Sounding site TDEM#4, Pecos County, Texas. A, 80-meter time-domain electromagnetic sounding data (apparent resistivity from field measurements) as a function of time. B, 80-meter layered and equivalent inverse modeling results (models of true resistivity as a function of depth).

10 −3 10 −2 10 −1 10 0 10 1 10 2

10 1

10 210 3

Time, in milli-seconds

Apparent resistivity, in ohm-meters

10 0 10 1 10 2 10 3

0

100200300400500600700800900

1,000

Resistivity, in ohm-meters

Depth below land surface, in feet

EXPLANATION

A B

Number of smooth model layers: 20Smooth model root mean square: 3.91 percentNumber of layered model layers: 3Layered model root mean square: 3.80 percent

Boundary of layered equivalence modelsSmooth inverse modelLayered inverse model

Measured resistivity

Appendix 2. 47

Appendix 2. Inverse Modeling Results of Audio-Magnetotelluric Soundings 

as a Function of Resistivity and Depth

Inverse modeling of the best fit for the transverse magnetic (TM) curve for the audio-magnetotelluric (AMT) sounding 

data is the best choice when approximating a three-dimensional structure beneath a centrally located point as demonstrated by 

Wannamaker and others (1984). However, the depths to the base of electrical units in the model may not be well constrained 

because TM data are relatively insensitive to the depth extent of a subsurface body (Eberhart-Phillips and others, 1995). Using 

a mixed mode analysis (modeling the mixed mode analysis of transverse magnetic and transverse electric response [TMTE] 

mode) can aid in the interpretation of elongated geologic structures from the modeling results.

The AMT sounding data were inverted using the computer algorithm RLM2DI (Mackie and others, 1997; Rodi and 

Mackie, 2001) from Geotools MT (Geotools, 1998). The forward modeling computer algorithm PW2D (Wannamaker and 

others, 1987) then used the inversion results from RLM2DI as the initial input model to perform a sensitivity analysis on the 

conductive units. The RLM2DI algorithm uses Maxwell’s equations governing magnetotellurics within a finite-difference 

network to calculate the forward model and minimizes the objective function using a nonlinear conjugate gradient optimization 

approach for the inverse modeling results (Asch and Sweetkind, 2010). The PW2D algorithm simulates transverse electric and 

magnetic fields using a linear basis for each finite element. RLM2DI ran approximately 25 iterations in order to reduce the 

root mean square error (RMSE) to a reasonable value between the measured field data and the calculated data. PW2D ran the 

necessary number of iterations of forward modeling for a sensitivity analysis of conductive units based on how complex the 

inversion results were from RLM2DI. Graphs of the AMT inversion results for each sounding site (figs. 2.1–2.13) show modeled 

resistivity with warmer colors (red, orange, and yellow) representing higher values and cooler colors (green, blue, and violet) 

representing lower values measured in ohm-meters. The graphs show the inversion results for the TMTE mode for all sounding 

locations. For sites where there appeared to be a three-dimensional change, the TM and transverse electric (TE) modes were 

separated in order to get a better understanding of what is present at that site. 
48 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 2.1 Sounding site AMT#1, Pecos County, Texas. Resistivity of mixed mode transverse magnetic and transverse electric responses.

1

1.62.5

4

6.3

1016

254063

100

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0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters
Appendix 2. 49

Figure 2.2 Sounding site AMT#2, Brewster County, Texas. A, Resistivity of mixed mode transverse magnetic and transverse electric 

responses. B, Resistivity of transverse electric response. C, Resistivity of transverse magnetic response.

3.2

1032

100320

1,00

10

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1032

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1,000

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0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters

A B C

Resistivity, in ohm-meters Resistivity, in ohm-meters
50 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 2.3 Sounding site AMT#3, Jeff Davis County, Texas. A, Resistivity of mixed mode transverse magnetic and transverse electric 

responses. B, Resistivity of transverse electric response. C, Resistivity of transverse magnetic response.

1

1.62.5

4

6.3

1016254063 100

1

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1016254063

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1,000

AMT#3

0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters

A B C

Resistivity, in ohm-meters Resistivity, in ohm-meters
Appendix 2. 51

Figure 2.4 Sounding site AMT#4, Pecos County, Texas. A, Resistivity of mixed mode transverse magnetic and transverse electric 

responses. B, Resistivity of transverse electric response. C, Resistivity of transverse magnetic response.

1

3.2

1032

100320

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3.2

1032

100320

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3.2

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AMT#4

0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters

A B C

Resistivity, in ohm-meters Resistivity, in ohm-meters
52 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 2.5 Sounding site AMT#5, Pecos County, Texas. Resistivity of mixed mode transverse magnetic and transverse electric responses.

1

3.2

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AMT#5

0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters
Appendix 2. 53

Figure 2.6 Sounding site AMT#6, Pecos County, Texas. A, Resistivity of mixed mode transverse magnetic and transverse electric 

responses. B, Resistivity of transverse electric response. C, Resistivity of transverse magnetic response.

1

3.2

1032

100320

1,000

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3.2

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0

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Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters

A B C

Resistivity, in ohm-meters Resistivity, in ohm-meters
54 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 2.7 Sounding site AMT#7, Pecos County, Texas. A, Resistivity of mixed mode transverse magnetic and transverse electric 

responses. B, Resistivity of transverse electric response. C, Resistivity of transverse magnetic response.

1

3.2

1032

100320

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3.2

1032

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3.2

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0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters

A B C

Resistivity, in ohm-meters Resistivity, in ohm-meters
Appendix 2. 55

Figure 2.8 Sounding site AMT#8, Pecos County, Texas. A, Resistivity of mixed mode transverse magnetic and transverse electric 

responses. B, Resistivity of transverse electric response. C, Resistivity of transverse magnetic response.

1

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100320

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Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters

A B C

Resistivity, in ohm-meters Resistivity, in ohm-meters
56 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 2.9 Sounding site AMT#9, Pecos County, Texas. Resistivity of mixed mode transverse magnetic and transverse electric responses.

1

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625

650

675

700

725

750

775

800

825

850

875

900

925

950

975

1,000

AMT#9

0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters
Appendix 2. 57

Figure 2.10 Sounding site AMT#10, Pecos County, Texas. Resistivity of mixed mode transverse magnetic and transverse electric responses.

1

1.62.5

4

6.3

1016254063 100

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

425

450

475

500

525

550

575

600

625

650

675

700

725

750

775

800

825

850

875

900

925

950

975

1,000

AMT#10

0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters
58 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 2.11 Sounding site AMT#11, Pecos County, Texas. A, Resistivity of mixed mode transverse magnetic and transverse electric 

responses. B, Resistivity of transverse electric response. C, Resistivity of transverse magnetic response.

1

3.2

1032

100320

1

3.2

1032

100320

1

3.2

1032

100320

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

425

450

475

500

525

550

575

600

625

650

675

700

725

750

775

800

825

850

875

900

925

950

975

1,000

AMT#11

0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters

A B C

Resistivity, in ohm-meters Resistivity, in ohm-meters
Appendix 2. 59

Figure 2.12 Sounding site AMT#12, Reeves County, Texas. A, Resistivity of mixed mode transverse magnetic and transverse electric 

responses. B, Resistivity of transverse electric response. C, Resistivity of transverse magnetic response.

1

1.62.5

4

6.3

1016254063 100

1

1.62.5

4

6.3

1016254063 100

1

3.2

1032

100320

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

425

450

475

500

525

550

575

600

625

650

675

700

725

750

775

800

825

850

875

900

925

950

975

1,000

AMT#12

0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters

A B C

Resistivity, in ohm-meters Resistivity, in ohm-meters
60 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Figure 2.13 Sounding site AMT#13, Jeff Davis County, Texas. Resistivity of mixed mode transverse magnetic and transverse 

elctric responses.

1

1.62.5

4

6.3

1016254063

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

425

450

475

500

525

550

575

600

625

650

675

700

725

750

775

800

825

850

875

900

925

950

975

1,000

AMT#13

0

Resistivity, in ohm-meters

Depth below land surface, in feet

91.7583.50

75.25

67.00

58.75

50.5042.2534.00

25.75

17.50

9.25

Resistivity, in ohm-meters
Appendix 3. 61

Appendix 3. Digital Database Resources

Source: U.S. Environmental Protection Agency STORET Modern

Processing: Created sample table. Created unique site identifier by prefixing site_id assigned by sourcing agency with site_abv. 

Data Origination: Downloadable data- http://www.epa.gov/storet/

Water-Quality Date Range: 8/15/1996 – 6/15/2011

Number of sites: 7

Source: Middle Pecos Groundwater Conservation District 

Processing: Created unique site identifier by prefixing site_id assigned by sourcing agency with site_abv. 

Data Origination: File transfer protocol or other direct access

Water-Quality Date Range: no data available

Number of Sites: 33

Source: Texas Commission on Environmental Quality , Surface Water Quality Information System

Processing: Created sample table. Created unique site identifier by prefixing site_id assigned by sourcing agency with site_abv. 

Data Origination: File transfer protocol or other direct access

Water-Quality Date Range: 9/5/1968 – 8/24/1992

Number of Sites: 13

Source: Texas Railroad Commission

Processing: Created unique site identifier by prefixing site_id assigned by sourcing agency with site_abv. 

Data Origination: Downloadable data- http://www.rrc.state.tx.us/data/online/oilgasrecords.php 

(Texas Railroad Commission, 2011)

Water-Quality Date Range: no data available

Number of Sites: 6220

Source: Texas Water Development Board Groundwater Database (GWDB)

Processing: Created sample table. Created unique site identifier by prefixing site_id assigned by sourcing agency with site_abv. 

Data Origination: Downloadable data- http://www.twdb.state.tx.us/groundwater/data/gwdbrpt.asp

Water-Quality Date Range: 10/2/1930–4/30/2009

Number of Sites: 1065

Source: U.S. Geological Survey, National Water Information System

Processing: Created unique site identifier by prefixing site_id assigned by sourcing agency with site_abv. 

Data Origination: File transfer protocol or other direct access

Water-Quality Date Range: 4/7/1932–6/23/2011

Number of Sites: 81

Source: University of Texas System Lands

Processing: Created unique site identifier by prefixing site_id assigned by sourcing agency with site_abv. 

Data Origination: Downloadable data- http://www.utlands.utsystem.edu/WellSearchInfo.aspx 

(University of Texas System Lands, 2011)

Water-Quality Date Range: no data available

 Number of Sites: 823
62 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Source: City of Fort Stockton Well Locations (Domestic and Municipal)

Processing: Created unique site identifier by prefixing site_id assigned by sourcing agency with site_abv. 

Data Origination: File transfer protocol or other direct access

Water-Quality Date Range: no data available

 Number of Sites: 281

Source: Daniel B. Stephens and Associates (Capitan Reef Study)

Processing: Data compiled from digital media included previously published geologic formation picks

Data Origination: File transfer protocol or other direct access

Water-Quality Date Range: no data available

Number of Sites: 153

Source: Texas Water Development Board Brackish Resources Aquifer Characterization System

Processing: Data compiled from digital media included previously published geologic formation picks

Data Origination: File transfer protocol or other direct access (Meyer and others, 2011)

Water-Quality Date Range: no data available

Number of Sites: 153
Appendix 4. 63

Appendix 4. Federal Geographic Data Committee-Compliant Metadata Record

Identification_Information

 Citation:

 Citation_Information:

 Originator: U.S. Geological Survey

 Publication_Date: 20111101

 Title: Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011 

 Region, Texas, 2011

 Geospatial_Data_Presentation_Form: vector digital data

 

Description:

 Abstract: The U.S. Geological Survey, in cooperation with the Middle Pecos Groundwater Conservation 

District, Pecos County, City of Fort Stockton, Brewster County, and Pecos County Water Control 

and Improvement District No. 1, developed a geodatabase of available groundwater, surface-water, 

water-quality, geophysical, and geology data for site locations in the Pecos County region, Texas. 

Data were compiled for an approximately 4,700 square mile area of the Pecos County region, Texas. 

The geodatabase, designed to warehouse field-collected geochemical and geophysical data, as well as 

digital database resources from the U.S. Geological Survey, Middle Pecos Groundwater Conservation 

District, Texas Water Development Board, Texas Commission on Environmental Quality, and numerous 

other State and local databases, contains 8,242 unique sampling locations. The geodatabase was used 

to combine these disparate database resources into a simple data model. Site locations are geospatiallyenabled and stored in a geodatabase feature class for general mapping purposes and more rigorous 

spatial analysis. The sampling locations are related to the hydrogeologic information through the use 

of geodatabase relationship classes. The geodatabase relationship classes provide the ability to perform 

complex spatial and data-driven queries to explore data stored in the geodatabase. 

 Purpose: The purpose of this report is to provide information on data acquisition and geodatabase 

compilation of hydrogeologic data, Pecos County region, Texas. Groundwater, surface-water, waterquality, geophysical, and geologic information for more than 8,000 sampling locations were compiled 

from various digital data sources in the study area. Digital data sources were gathered from existing 

databases, previously published reports, and field-collected data.
64 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Time_Period_of_Content:

 Time_Period_Information:

 Single_Date/Time:

 Calendar_Date: 2011

 Currentness_Reference: 1930–2011

 Status:

 Progress: On-going

 Maintenance_and_Update_Frequency: None Planned

 Spatial_Domain:

 Bounding_Coordinate:

 West_Bounding_Coordinate: -103.903888

 East_Bounding_Coordinate: -101.816520

 North_Bounding_Coordinate: 31.420552

 South_Bounding_Coordinate: 30.356220

Keywords:

 Theme:

 Theme_Keyword: hydrogeology

 Theme_Keyword: groundwater

 Theme_Keyword: surface water

 Theme_Keyword: water quality

 Theme_Keyword: geology

 Place:

 Place_Keyword: Pecos County region

 Place_Keyword: Trans-Pecos

 Place_Keyword: Pecos County

 Place_Keyword: Reeves County

 Place_Keyword: Jeff Davis County

 Place_Keyword: Brewster County

 Place_Keyword: Terrell County

 Place_Keyword: Crane County

 Place_Keyword: Ward County

 Place_Keyword: Crockett County
Appendix 4. 65

Use_Constraints: These data are for informational purposes only. These data have not received Bureau 

approval and as such are provisional and subject to revision. The data are released on the condition that 

neither the U.S. Geological Survey, its cooperators, nor the U.S. Government may be held liable for any 

damages resulting from its authorized or unauthorized use. Although these data have been processed 

successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied 

is made regarding the accuracy or utility of the data on any other system or for general or scientific 

purposes, nor shall the act of distribution constitute any such warranty. 

Native_Data_Set_Environment: Microsoft Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 

3; ESRI ArcGIS 10.0.0.2414

Data_Quality_Information:

 Lineage:

 Process_Step:

 Process_Description: Geographic locations of groundwater well sites, oil/gas well sites and surface- 

 water sites were gathered from various Federal, State, and local databases. These data were 

 compiled into a simplified feature class that maintains information related to: source agency, site 

 identifier, unique identifier, site code (type), and site name.

 Process_Date: 20111101

Spatial_Data_Organization_Information:

 Direct_Spatial_Reference_Method: Vector

 Point_and_Vector_Object_Information:

 SDTS_Terms_Description:

 SDTS_Point_and_Vector_Object_Type: Entity point

 Point_and_Vector_Object_Count: 8242

Spatial_Reference_Information:

 Horizontal_Coordinate_System_Definition:

 Geographic:

 Latitude_Resolution: 0.000000

 Longitude_Resolution: 0.000000

 Geographic_Coordinate_Units: Decimal degrees
66 Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011

Geodetic_Model:

 Horizontal_Datum_Name: North American Datum of 1983

 Ellipsoid_Name: Geodetic Reference System 80

 Semi-major_Axis: 6378137.000000

 Denominator_of_Flattening_Ratio: 298.257222

Entity_and_Attribute_Information:

 Detailed_Description:

 Entity_Type:

 Entity_Type_Label: sitefile

 Attribute:

 Attribute_Label: OBJECTID

 Attribute_Definition: Internal feature number.

 Attribute_Definition_Source: ESRI

 Attribute_Domain_Values:

 Unrepresentable_Domain: Sequential unique whole numbers that are automatically generated.

 Attribute:

 Attribute_Label: SHAPE

 Attribute_Definition: Feature geometry.

 Attribute_Definition_Source: ESRI

 Attribute_Domain_Values:

 Unrepresentable_Domain: Coordinates defining the features.

 Attribute:

 Attribute_Label: source_nm

 Attribute_Definition: Source name.

 Attribute:

 Attribute_Label: source_abv

 Attribute_Definition: Source abbreviation.

 Attribute:

 Attribute_Label: site_id

 Attribute_Definition: Native source identifier.

 Attribute:

 Attribute_Label: unique_id

 Attribute_Definition: Unique identifier is combination of source_abv and site_id fields.

 Attribute:

 Attribute_Label: site_cd

 Attribute_Definition: Site code.
Appendix 4. 67

 Attribute:

 Attribute_Label: site_nm

 Attribute_Definition: Site name.

Distribution_Information:

 Resource_Description: Downloadable Data

 Metadata_Reference_Information:

 Metadata_Date: 20111101

 Metadata_Contact:

 Contact_Information:

 Contact_Organization_Primary:

 Contact_Organization: U.S. Geological Survey

 Contact_Person: Public Information Officer

 Contact_Address:

 Address_Type: mailing and physical address

 Address: 1505 Ferguson Lane

 City: Austin

 State_or_Province: Texas

 Postal_Code: 78754

 Country: USA

 Contact_Voice_Telephone: 512–927–3500

 Contact_Facsimile_Telephone: 512–927–3590

 Contact_Electronic_Mail_Address: gs-w-txpublic-info@usgs.gov

 Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata

 Metadata_Standard_Version: FGDC–STD–001–1998

 Metadata_Time_Convention: local time

 Metadata_Extensions:

 Profile_Name: ESRI Metadata Profile

Prepared by the USGS Lafayette Publishing Service Center

Pearson and others—Data Collection and Compilation for a Geodatabase, Pecos County Region, Texas, 1930–2011—Data Series 678

ISBN 978-1-4113-3373-4

Printed on recycled paper 9 7 8141

1 3337 3 4