In cooperation with the International Boundary and Water Commission; National Park Service; 

Texas Commission on Environmental Quality; Secretaría de Medio Ambiente y Recursos 

Naturales, Mexico; Área de Protección de Flora y Fauna Cañón de Santa Elena, Mexico;

and Área de Protección de Flora y Fauna Maderas del Carmen, Mexico 

Quality of Water and Sediment in Streams Affected by 

Historical Mining, and Quality of Mine Tailings, in the 

Rio Grande/Río Bravo Basin, Big Bend Area of the 

United States and Mexico, August 2002 

Scientific Investigations Report 2008–5032 

U.S. Department of the Interior 

U.S. Geological Survey 
Front cover: Mine tailings piles in front of Study Butte Mine in Rough Run Draw near Study Butte, Texas, 

February 2002. 

Back cover:

Top, Ted Small, U.S. Geological Survey hydrologist (1923–2007), on top of bluff at La Clocha primitive 

campground sample site, Big Bend National Park, Texas, August 2002. 

Lower left, U.S. Geological Survey hydrologic technician collecting water-quality sample from Rio 

Grande/Río Bravo, August 2002. 

Lower right, Mine processing debris and tailings from mercury retort furnaces in Terlingua Creek 

watershed near Terlingua, Texas, February 2002. 
Quality of Water and Sediment in Streams 

Affected by Historical Mining, and Quality 

of Mine Tailings, in the Rio Grande/

Río Bravo Basin, Big Bend Area of the 

United States and Mexico, August 2002

By Rebecca B. Lambert, Christine M. Kolbe, and Wayne Belzer

In cooperation with the International Boundary and Water Commission; National 

Park Service; Texas Commission on Environmental Quality; Secretaría de Medio 

Ambiente y Recursos Naturales, Mexico; Área de Protección de Flora y Fauna 

Cañón de Santa Elena, Mexico; and Área de Protección de Flora y Fauna 

Maderas del Carmen, Mexico

Scientific Investigations 2008–5032

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

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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:

Lambert, R.B., Kolbe, C.M., and Belzer, Wayne, 2008, Quality of water and sediment in streams affected by historical mining, and quality of mine tailings, in the Rio Grande/Río Bravo Basin, Big Bend area of the United States and 

Mexico: U.S. Geological Survey Scientific Investigations Report 2008–5032, 45 p. 
iii

Contents

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

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

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

Previous Investigations .......................................................................................................................5

Acknowledgments ...............................................................................................................................6

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

Geologic Setting ...................................................................................................................................6

Historical Mining Areas ......................................................................................................................6

Chisos/Rainbow Mines ..............................................................................................................8

Mariposa (California Mountain) Mine .....................................................................................8

Study Butte (Big Bend, Texas-Almaden) Mine ......................................................................8

Two-Forty-Eight (Flecha) Mine .................................................................................................8

Waldron (Colquitt-Tigner) Mine ..............................................................................................10

Contributors of Flow, Sediment, Mercury, and Other Trace Elements .............................10

Methods ........................................................................................................................................................10

Quality of Stream Water ............................................................................................................................14

Salinity and Suspended Solids ........................................................................................................14

Trace Elements ...................................................................................................................................16

Quality of Streambed Sediment ................................................................................................................23

Quality of Mine Tailings ..............................................................................................................................28

Trace Elements ...................................................................................................................................28

Leaching Potential .............................................................................................................................31

Summary .......................................................................................................................................................31

References ..................................................................................................................................................33

Figures

1–2. Maps showing: 

1. Regional parks and protected areas in the Big Bend area of the United 

States and Mexico (study area) .......................................................................................3

2. Locations of sites sampled August 2002 in the Big Bend area of Texas, 

United States, and Chihuahua and Coahuila, Mexico ..................................................4

3. Photographs showing examples of mine and mine-tailing sample sites at 

(A) Study Butte Mine, (B) Chisos Mine, (C) Mariscal Mine, (D) La Linda Mine/

processing plant, (E) La Esperanza (San Carlos) Mine, and (F) Boquillas Mine 

(tailings) .........................................................................................................................................9

4. Boxplots showing distribution of concentrations of calcium, sulfate, chloride, 

dissolved solids, total suspended solids, and volatile suspended solids in water 

samples collected August 6–9, 2002, in the Big Bend area of the United States 

and Mexico .................................................................................................................................15
iv

5–6. Graphs showing: 

5. Concentrations of calcium, sulfate, and chloride in water samples 

collected August 6–9, 2002, from Rio Grande/Río Bravo main-stem (MS) 

and tributary (TR) sites (downstream order) in the Big Bend area of the 

United States and Mexico ...............................................................................................16

6. Concentrations of dissolved solids, total suspended solids, and volatile 

suspended solids in water samples collected August 6–9, 2002, from Rio 

Grande/Río Bravo main-stem (MS) and tributary (TR) sites (downstream 

order) in the Big Bend area of the United States and Mexico ..................................17

7. Boxplots showing distribution of concentrations of aluminum, barium, copper, 

mercury, nickel, selenium, and zinc in water samples collected August 6–9, 2002, 

in the Big Bend area of the United States and Mexico .......................................................18

8–12. Graphs showing: 

8. Concentrations of aluminum and barium in water samples collected 

August 6–9, 2002, from Rio Grande/Río Bravo main-stem (MS) and tributary 

(TR) sites (downstream order) in the Big Bend area of the United States 

and Mexico ........................................................................................................................19

9. Concentrations of copper and nickel in water samples collected August 6–9, 

2002, from Rio Grande/Río Bravo main-stem (MS) and tributary (TR) sites 

(downstream order) in the Big Bend area of the United States and Mexico .........20

10. Concentration of mercury in water samples collected August 6–9, 2002, 

from Rio Grande/Río Bravo main-stem (MS) and tributary (TR) sites 

(downstream order) in the Big Bend area of the United States and Mexico ........21

11. Relation of concentrations of total recoverable mercury to total suspended 

solids for water samples collected August 6–9, 2002, from Rio Grande/Río 

Bravo main-stem and tributary sites in the Big Bend area of the United 

States and Mexico ...........................................................................................................21

12. Concentrations of selenium and zinc in water samples collected August 6–9, 

2002, from Rio Grande/Río Bravo main-stem (MS) and tributary (TR) sites 

(downstream order) in the Big Bend area of the United States and Mexico .........23

13. Boxplots showing distribution of concentrations of antimony, arsenic, beryllium, 

cadmium, and chromium in streambed-sediment samples collected August 6–9, 

2002, in the Big Bend area of the United States and Mexico .............................................24

14–15. Graphs showing: 

14. Concentrations of antimony and arsenic in streambed-sediment samples 

collected August 6–9, 2002, from Rio Grande/Río Bravo main-stem (MS) and 

tributary (TR) sites (downstream order) in the Big Bend area of the United 

States and Mexico ............................................................................................................24

15. Concentrations of beryllium, cadmium, and chromium in streambed-sediment 

samples collected August 6–9, 2002, from Rio Grande/Río Bravo main-stem 

(MS) and tributary (TR) sites (downstream order) in the Big Bend area of the 

United States and Mexico ...............................................................................................25

16. Boxplots showing distribution of concentrations of copper, mercury, and nickel 

in streambed-sediment samples collected August 6–9, 2002, in the Big Bend area 

of the United States and Mexico .............................................................................................26

17. Graph showing concentrations of copper, mercury, and nickel in streambedsediment samples collected August 6–9, 2002, from Rio Grande/Río Bravo 

main-stem (MS) and tributary (TR) sites (downstream order) in the Big Bend area 

of the United States and Mexico .............................................................................................26
v

18. Boxplots showing distribution of concentrations of lead, manganese, and zinc in 

streambed-sediment samples collected August 6–9, 2002, from Rio Grande/Río 

Bravo main-stem and tributary sites in the Big Bend area of the United States 

and Mexico .................................................................................................................................27

19–22. Graphs showing: 

19. Concentrations of lead, manganese, and zinc in streambed-sediment 

samples collected August 6–9, 2002, from Rio Grande/Río Bravo main-stem 

(MS) and tributary (TR) sites (downstream order) in the Big Bend area of the 

United States and Mexico ...............................................................................................28

20. Detectable concentrations of arsenic, cadmium, and chromium in minetailing samples collected August 5–15, 2002, from abandoned mine and 

mine processing sites (downstream order) in the Big Bend area of the United 

States and Mexico ............................................................................................................29

21. Detectable concentrations of copper, mercury, and nickel in mine-tailing 

samples collected August 5–15, 2002, from abandoned mine and mine 

processing sites (downstream order) in the Big Bend area of the United 

States and Mexico ............................................................................................................30

22. Detectable concentrations of lead, manganese, silver, and zinc in minetailing samples collected August 5–15, 2002, from abandoned mine and 

mine processing sites (downstream order) in the Big Bend area of the 

United States and Mexico ...............................................................................................30

Tables

1. Information on abandoned mines and mine processing areas sampled August 

5−15, 2002, in the Big Bend area of the United States and Mexico .....................................7

2. Locations of stream and abandoned mine and mine processing sites sampled 

August 5−15, 2002, in the Big Bend area of the United States and Mexico .....................11

3. Criteria and screening levels used to assess surface-water quality in segment 

2306 of the Rio Grande/Río Bravo ...........................................................................................12

4. Water-quality data from samples collected August 6–9, 2002, in the Big Bend 

area of the United States and Mexico ...................................................................................36

5. Streambed-sediment data from samples collected August 6–9, 2002, in the Big 

Bend area of the United States and Mexico .........................................................................39

6. Mine-tailing data from samples collected August 5–15, 2002, in the Big Bend 

area of the United States and Mexico ...................................................................................43

7. Toxicity Characteristic Leaching Procedure leaching potential (concentrations) 

for mine-tailing samples collected August 5–15, 2002 (table 6) in the Big Bend 

area of the United States and Mexico ...................................................................................45
vi

Conversion Factors and Datum

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

mile (mi) 1.609 kilometer (km)

Flow

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

/s)

Mass

pound avoirdupois (lb avdp) 0.4536 kilogram (kg)

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

°C=(°F-32)/1.8

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

°F=(1.8×°C)+32

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

25 °C).

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

or micrograms per liter (μg/L). 

Concentrations of chemical constituents in streambed sediment are given in milligrams per 

kilogram (mg/kg). For sediment screening, micrograms per gram (μg/g) = mg/kg.

Datum

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

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

International Boundary and Water Commission—U.S. and 

Mexican Sections, the National Park Service, the Texas Commission on Environmental Quality, the Secretaría de Medio 

Ambiente y Recursos Naturales in Mexico, the Área de 

Protección de Flora y Fauna Cañón de Santa Elena in Mexico, 

and the Área de Protección de Flora y Fauna Maderas del Carmen in Mexico, collected samples of stream water, streambed 

sediment, and mine tailings during August 2002 for a study to 

determine whether trace elements from abandoned mines in 

the area in and around Big Bend National Park have affected 

the water and sediment quality in the Rio Grande/Río Bravo 

Basin of the United States and Mexico. Samples were collected from eight sites on the main stem of the Rio Grande/

Río Bravo, four Rio Grande/Río Bravo tributary sites downstream from abandoned mines or mine-tailing sites, and 11 

mine-tailing sites. Mines in the area were operated to produce 

fluorite, germanium, iron, lead, mercury, silver, and zinc during the late 1800s through at least the late 1970s. Moderate 

(relatively neutral) pHs in stream-water samples collected at 

the 12 Rio Grande/Río Bravo main-stem and tributary sites 

indicate that water is well mixed, diluted, and buffered with 

respect to the solubility of trace elements. The highest sulfate 

concentrations were in water samples from tributaries draining the Terlingua mining district. Only the sample from the 

Rough Run Draw site exceeded the Texas Surface Water Quality Standards general-use protection criterion for sulfate. All 

chloride and dissolved solids concentrations in water samples 

were less than the general-use protection criteria. Aluminum, 

copper, mercury, nickel, selenium, and zinc were detected 

in all water samples for which each element was analyzed. 

Cadmium, chromium, and lead were detected in samples less 

frequently, and silver was not detected in any of the samples. 

None of the sample concentrations of aluminum, cadmium, 

chromium, nickel, selenium, and zinc exceeded the Texas 

Surface Water Quality Standards criteria for aquatic life-use 

protection or human health. The only trace elements detected 

in the water samples at concentrations exceeding the Texas 

Surface Water Quality Standards criterion for human health 

(fish consumption use) was lead at one site and mercury at 10 

of 12 sites. Relatively high mercury concentrations distributed 

throughout the area might indicate sources of mercury in addition to abandoned mining areas. Streambed-sediment samples 

were collected from 12 sites and analyzed for 44 major and 

trace elements. In general, the trace elements detected in 

streambed-sediment samples were low in concentration, 

interpreted as consistent with background concentrations. 

Concentrations at two sites, however, were elevated compared 

to Texas Commission on Environmental Quality criteria. Concentrations of antimony, arsenic, cadmium, lead, silver, and 

zinc in the sample from San Carlos Creek downstream from 

La Esperanza (San Carlos) Mine exceeded the Texas Commission on Environmental Quality screening levels for sediment. 

The sample from Rough Run Draw, downstream from the 

Study Butte Mine, also showed elevated concentrations of 

arsenic, cadmium, and lead, but these concentrations were 

much lower than those in the San Carlos Creek sample and 

did not exceed screening levels. Elevated concentrations of 

multiple trace elements in streambed-sediment samples from 

San Carlos Creek and Rough Run Draw indicate that San 

Carlos Creek, and probably Rough Run Draw, have been 

adversely affected by mining activities. Fourteen mine-tailing 

samples from 11 mines were analyzed for 25 major and trace 

elements. All trace elements except selenium and thallium 

were detected in one or more samples. The highest lead 

concentrations were detected in tailings samples from the 

Boquillas, Puerto Rico, La Esperanza (San Carlos), and Tres 

Marias Mines, as might be expected because the tailings are 

from lead mines; the concentrations greatly exceeded the 

screening level for lead. Application of the Toxicity Characteristic Leaching Procedure to 14 samples from 11 abandoned 

mine and mine processing sites indicate that, in general, the 

leaching potential (concentration) was less than the Toxicity Characteristic Leaching Procedure limit. Cadmium and 

Quality of Water and Sediment in Streams Affected by 

Historical Mining, and Quality of Mine Tailings, in the 

Rio Grande/Río Bravo Basin, Big Bend Area of the 

United States and Mexico, August 2002

By Rebecca B. Lambert, Christine M. Kolbe1, and Wayne Belzer2 

1

 Texas Commission on Environmental Quality, Austin, Tex.

2

 U.S. Section, International Boundary and Water Commission, El Paso, 

Tex.
2 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

lead concentrations in the mine-tailings sample from San 

Carlos Mine exceeded the Toxicity Characteristic Leaching 

Procedure screening level for cadmium and lead, and the lead 

concentration in the mine-tailings sample from Boquillas Mine 

exceeded the screening level for lead.

Introduction 

The Rio Grande/Río Bravo (RG/RB) forms the boundary in the Big Bend area between Texas in the United 

States and Coahuila and Chihuahua in Mexico (fig. 1). The 

RG/RB is the primary source of water in the Big Bend area 

of the United States and Mexico (study area) and a source of 

habitat for wildlife and endangered species. Parks and protected areas in the study area include Big Bend National Park 

(BBNP), Big Bend Ranch State Park, and Black Gap State 

Wildlife Management Area in the United States, and Cañón 

de Santa Elena and Maderas del Carmen Protected Areas in 

Mexico (fig. 1). All of these parks and protected areas are 

downstream from the confluence of the Rio Conchos and the 

RG/RB. The Rio Conchos is the primary source of freshwater 

inflow to the RG/RB in the Big Bend area, and this inflow historically has dominated flow in the RG/RB during the summer 

rainy season (Davis, 1980). 

The National Parks Conservation Association, a parks 

advocacy group, listed BBNP as one of the 10 most endangered national parks in the United States, in part because of 

the decreasing quantity and quality of the RG/RB (National 

Parks Conservation Association, 2001). One of the possible 

sources of contaminants that might adversely affect the quality 

of the RG/RB upstream from, and in, the BBNP and Mexican 

Protected Areas (fig. 1) is drainage from areas in the basin 

where mining for fluorite, germanium, iron, lead, mercury, 

silver, and zinc has occurred. Tailings from abandoned mines 

have been found along Terlingua Creek and Fresno Creek 

(BBNP) in the United States and along San Carlos Creek 

in the Cañón de Santa Elena Protected Area and Arroyo del 

Fortino in the Maderas Del Carmen Protected Area in Mexico 

(International Boundary and Water Commission, 2004) 

(fig. 2).

Mercury was produced primarily from cinnabar ore (mercury sulfide) in the Big Bend area, and most of the historical 

production in the United States came from the Terlingua mining district west of BBNP (figs. 1, 2) (Swanson, 1995). Mining 

for mercury began at Terlingua in 1894, and the mines were 

worked continuously until 1946 (Swanson, 1995). Numerous abandoned mercury mines remain in the Terlingua Creek 

watershed (fig. 2). Gold, lead, and silver have been mined 

from the Shafter mining district on the flanks of the Chinati 

Mountains near Presidio (fig. 1). The locations of all abandoned mines are not shown on the available maps of the study 

area. Mine tailings from abandoned mines, some of which are 

shown on figure 2, and other mines not shown on the available maps of the area, might contribute trace elements (metals) 

such as lead and zinc to San Carlos Creek and Arroyo del Fortino (fig. 2) and other tributaries downstream from abandoned 

mining areas (fig. 2). Flow from watersheds that drain into the 

RG/RB upstream from BBNP (figs. 1, 2) might transport sediment with trace elements from the abandoned mining areas to 

the RG/RB. 

The presence of trace elements that might adversely 

affect water and sediment quality (arsenic, cadmium, chromium, copper, lead, selenium, silver, and thallium) has been 

documented in segment 2306 of the RG/RB; upward trends 

in mercury and zinc concentrations have been noted (International Boundary and Water Commission, 1997; Texas Natural 

Resource Conservation Commission, 1994). Elevated concentrations of these elements can be toxic to animals and humans; 

some of the trace elements are carcinogenic and mutagenic 

(Pais and Jones, 1997). There is increasing concern among 

park managers that elevated selenium and mercury concentrations present in prey species, including the endangered 

peregrine falcon, might affect the reproductive success of this 

species in BBNP (National Park Service, 2006). 

The U.S. Geological Survey (USGS), as part of the 

National Stream Quality Accounting Network (NASQAN) 

program, conducted a study in cooperation with the International Boundary and Water Commission—U.S. and Mexican 

Sections (USIBWC and CILA), the National Park Service 

(NPS), the Texas Commission on Environmental Quality (TCEQ), the Secretaría de Medio Ambiente y Recursos 

Naturales (SEMARNAT) in Mexico, the Área de Protección 

de Flora y Fauna (APFF) Cañón de Santa Elena in Mexico, 

and the APFF Maderas del Carmen in Mexico. The study in 

August 2002 was done to characterize the quality of water, 

streambed sediment, and mine tailings in the RG/RB and its 

tributaries in the Big Bend area because of the potential for 

adverse effects of trace elements from abandoned mines on the 

water and sediment quality in the RG/RB Basin. 

Purpose and Scope

This report summarizes results from the August 2002 

collection of samples for analysis of quality of stream water, 

streambed sediment, and mine tailings and relates the sampling results to abandoned mines and mine processing activities in the study area. Samples from 23 locations that include 

eight main-stem RG/RB sites, four RG/RB tributary sites, and 

11 mine-tailing sites were analyzed for concentrations of trace 

elements commonly associated with mining activities. Water 

samples also were analyzed for field properties (pH, specific 

conductance, temperature, dissolved oxygen, and alkalinity); major ions; dissolved solids (DS), total suspended solids 

(TSS), and volatile suspended solids (VSS); and nutrients. 

Major ions and DS are discussed as components of salinity. 

Salinity, as used in this report, is the amount of dissolved salts 

in water and is indicated by DS. A procedure designed to 

simulate the leaching of contaminants in landfills was applied 

to determine the leaching potential for 10 trace elements from 
Introduction 3

")

")

Big Bend Ranch State Park

Big Bend National Park

Black Gap State Wildlife

Management Area

 Área de Protección 

de Flora y Fauna

Cañón de Santa Elena Área de Protección de Flora y Fauna

Maderas del Carmen

CHINATI

MOUNTAINS

PRESIDIO COUNTY

BREWSTER COUNTY

PECOS 

COUNTY

TERRELL 

COUNTY

VAL VERDE 

COUNTY

CROCKETT COUNTY

CHIHUAHUA

COAHUILA

M E X

341

M E X

16

M E X

29

M E X

2

M E X

93

Study area

Del  Rio

Alpine

Presidio

Sanderson

Marfa

Shafter

Terlingua

90 £¤

67 £¤ 385

£¤

277

£¤

285

£¤

377

£¤

67 £¤

377

£¤

385

£¤

277 £¤

RIO GRANDE

Maravillas Creek

Perdiz Creek

Dry Creek

Blue Creek

Buck Creek

Dagger Flat Draw

Long Draw

Alamito Creek

Cienega Creek Terneros Creek

Goat Creek

Calamity Creek

Terlingua Creek

Nine

Point Dr.

Tornillo Creek

Fresno Creek

San Francisco

Creek

l uyau G e keer C

ae B keer Cr

Maxon

Creek

Sanderson Creek

Downie Draw

Pecos River

Langtry Creek

Devils River

Johnson Draw

Do al

n Creek

Amistad

International

Reservoir

RIO

GRAND

E

R

OÍ

BRAVO

DEL 

NOR

TE

Rio Conchos

Escobillas

El Chu

ap

dero

El Burro

El Nopal

El Infante

Escondido

San Rodrigo

El Orégano

Las gI

es l

ias

El 

Tecolote

San Carlos

aP

ol m sa

United States base modified from U.S. Geological Survey digital dataScales 1:250,000 (county boundaries) and 1:100,000 (hydrography)Mexico base data modified from ESRI Data & Maps 2003 Scales 1:200,000 (roads) and 1:300,000 (hydrography)Universal Transverse Mercator Zone projection, Datum NAD 83Zone 13

End segment2306

Begin segment2306

103°45' 102°30' 101°15'

28°45'

30°0'

0 20 30 40 MILES 10

EXPLANATION

U.S. National Park Texas State Park or Management AreaMexican Protected AreaShafter mining districtTerlingua mining districtRio Grande Wild and Scenic River

TEXAS

MEXICO

UNITED 

 ST

ATES

COAHUILA CHIHUAHUA

PresidioCounty Brewster

County

Figure 1. Regional parks and protected areas in the Big Bend area of the United States and Mexico (study area). 
4 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

Figure 2. Locations of sites sampled August 2002 in the Big Bend area of Texas, United States, and Chihuahua and Coahuila, Mexico. 

!

La Linda

!

StudyButte !

Lajitas

United States base modified from U.S. Geological Survey digital dataScales 1:250,000 (county boundaries) and 1:100,000 (hydrography)Mexico base data modified from ESRI Data & Maps 2003 Scales 1:200,000 (roads) and 1:300,000 (hydrography)Universal Transverse Mercator Zone projection, Datum NAD 83Zone 13

")

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Terlingua

Shafter

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Panther Junction National Weather Service station

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!(Arroyo del Fortino

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!

!

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!!

!

!

!

!

Big Bend Ranch 

State Park

Big Bend 

National Park

Black Gap 

State Wildlife

Management

Area

 Área de Protección 

de Flora y Fauna Cañón de Santa Elena

Área de Protección 

de Flora y Fauna Maderas del Carmen

El B ru or

l E

hC upade or

Escobillas

La Pasta De Las Yegu sa

l A ma ito Creek

B al ck Hi ll s Creek

Terneros Creek

Terlingua Creek

Blue Creek

Fresno Creek

Tornillo Creek

Nine

Point Draw

Chalk Draw

ke re Crae B

Maravillas Creek

uyau G Cel er ek

RIO GRANDE

RÍO BRAVO DEL NORTE

Smo yk e

r C ek A mal o Creek

Fresno Creek

Glen Draw

San Carlos

38

£¤5

P l a mo as

Draw

Long

The

Mariscal 

Canyon

Hot Springs 

Canyon

Rio Grande Village

Boquillas

Canyon

1

11

10

2

14

9

15

17

12 16

21

19

22a,b23

8 6 7a,b 5a,b

Castolon

Santa

Elena

Canyon

4

3

20 18

13 Tres Marias Mine14 Rio Grande at Woodson’s Campground15 Rio Grande at Solis Campground16 Mariscal Mine17 Rio Grande at La Clocha Campground18 Boquillas Mine/processing area19 Rio Grande upstream of Boquillas Canyon20 Puerto Rico Mine

21 Arroyo del Fortino below Puerto Rico Mine

 La Linda Mine/processing plant23 Rio Grande at La Linda

13

22a,b

 Site no. Site name Site no. Site name

1 Rio Grande above Lajitas2 Rio Grande at Santa Elena Canyon Trailhead3 Waldron Mine4 Mariposa Mine

Chisos/Rainbow Mines

6 Two-Forty-Eight Mine

7a,b Study Butte Mine

8 Rough Run Draw at Study Butte9 Terlingua Creek at Terlingua Abaja

10 La Esperanza (San Carlos) Mine11 San Carlos Creek below La Esperanza Mine12 Rio Grande at Santa Elena Crossing

5a,b

103°52'15" 103°22' 102°51'45" 102°21'30"

28°59'

29°29'15"

0 20 30 40 MILES 10

EXPLANATION

U.S. National ParkTexas State Park or 

Management Area

Mexican Protected AreaTerlingua mining district

Sampled main-stem or tributary stream site and site numberSampled abandoned mine and mine-tailings site and 

2!

Abandoned mine and mine-tailings site (not sampled)

!

"

3

site number
Introduction 5

14 samples collected at 11 abandoned mine and mine-tailing 

sites in the United States and Mexico. Summary statistics and 

graphical data analysis were computed or prepared for data 

from the main-stem and tributary sites and the mine-tailing 

sites. Results were compared to applicable standards and 

screening levels. Information on the abandoned mines in 

the study area was compiled. More specifically, this report 

(1) provides information on abandoned mines and mine 

processing areas in the Big Bend area of the United States 

including the ores and minerals mined throughout the study 

area at the major mining districts and individual mines; 

(2) statistically compares the results of trace elements and 

other constituent concentrations in stream-water, streambedsediment, and mine-tailing samples with criteria and screening 

levels established by TCEQ for segment 2306 of the RG/RB 

in the Big Bend area of the United States and Mexico; and 

(3) uses summary tables, truncated boxplots, scatterplots, and 

bar graphs to show constituent concentrations and summarize 

data distributions for samples collected in the Big Bend area of 

the United States and Mexico. 

Previous Investigations

Several reports have been published that discuss the 

geology and mining activities in the Big Bend area. Yates and 

Thompson (1959) summarized the results of several geologic 

reconnaissances of the Terlingua mining district and described 

the occurrence of mercury deposits in specific mines in the 

mining district. Chester (1965) provided additional information on the history and production of mercury in West Texas 

in the Terlingua and other mining districts. Sharpe (1980) 

discussed the development of the mercury mining industry in 

the Trans-Pecos region of Texas (west of the Pecos River) and 

described some of the major mercury mines that were sampled 

during this study. Ragsdale (1976) wrote a history of the town 

of Terlingua and the history of the Chisos Mining Company, 

the largest historical producer of mercury in West Texas. 

Recent studies completed in and near BBNP and ongoing monitoring programs provide some insight into existing 

water-quality conditions as well as identify some water-quality 

issues. Van Metre and others (1997) documented an increase 

in concentrations of arsenic, chromium, copper, lead, mercury, 

nickel, vanadium, and zinc from 1969 to 1994 in sediment 

core samples collected from the RG/RB arm of Amistad 

Reservoir. An analysis of historical (1970s to 1994) riverbed 

sediment data for the RG/RB Basin indicated upward trends 

in mercury and selenium concentrations in the region between 

the Pecos River and Amistad Reservoir (Lee and Wilson, 

1997). Sources of these metals might include point and nonpoint sources associated with historic mining activities, as well 

as atmospheric deposition from fossil-fuel combustion and 

solid-waste incineration (Lee and Wilson, 1997). 

Water-quality and suspended-sediment data were collected during 1999–2007 as part of the USGS NASQAN 

program at two sites on the RG/RB—Rio Grande below Rio 

Conchos near Presidio, Tex. (station 08374200), and Rio 

Grande at Foster Ranch near Langtry, Tex. (station 08377200) 

(U.S. Geological Survey, 2006). Horowitz and others (2001) 

analyzed the suspended-sediment flux in the RG/RB using 

the NASQAN sediment-quality dataset for the 1996–98 water 

years (October 1, 1995–September 30, 1998) and determined 

that the majority (more than 70 percent) of trace elements, 

including aluminum, arsenic, barium, chromium, copper, iron, 

manganese, nickel, phosphorus, and zinc, are transported 

predominantly in association with the movement of suspended 

sediment. They found that the transport of strontium seems 

to be dominated by the dissolved phase, although the transport of lithium and total organic carbon seems to be equally 

divided between the suspended sediment and dissolved 

phases. Horowitz and others (2001) concluded that suspendedsediment fluxes in the RG/RB Basin are highly localized and 

extremely “flashy.”

Gutierrez (2000) conducted a study in the lower Rio 

Conchos Basin in Chihuahua, Mexico, documenting trace 

element concentration patterns in stream sediment. Using a 

two-step sequential extraction method, Gutierrez studied the 

distribution of boron, chromium, copper, lead, nickel, and 

vanadium in stream sediment in the lower Rio Conchos Basin. 

By correlating trace element concentrations in stream sediment and water, Gutierrez was able to differentiate between 

trace elements retained by sediment in the Rio Conchos and 

those not retained. Chromium, copper, and nickel concentrations in water showed statistically significant correlations with 

stream sediment, and boron, lead, and vanadium did not, indicating that some trace elements are stored longer in the stream 

sediment and others apparently are released more quickly into 

the water.

The TCEQ has identified several trace elements of concern in the RG/RB upstream from BBNP including arsenic, 

cadmium, chromium, copper, lead, mercury, selenium, silver, 

thallium, and zinc (International Boundary and Water Commission, 1997; Texas Natural Resource Conservation Commission, 1994). The TCEQ has established Texas Surface Water 

Quality Standards (TSWQS) for segment 2306 of the RG/

RB, a 313-mile reach from the inflow to Amistad Reservoir 

upstream to the confluence with the Rio Conchos near Presidio (Texas Commission on Environmental Quality, 2000). 

The uses designated for segment 2306 include public 

water supply, contact recreation, human health (fish consumption), and high aquatic life use (Texas Commission on Environmental Quality, 2000). This segment generally supports 

the designated uses. However, in the upper 25 miles of this 

reach, ambient sediment and water toxicity occasionally has 

exceeded the criteria for the protection of aquatic life. The suspected cause of the toxicity is the salinity in the reach of the 

RG/RB downstream from El Paso. As of 2004, there was no 

evidence to support trace elements as the cause of the toxicity 

(Texas Commission on Environmental Quality, 2004). 

Gray and others (2006) studied the speciation and microbial transformation of mercury from mine waste at selected 

mines in BBNP and the adjacent Terlingua mining district. 
6 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

Results of their study indicate that methyl mercury concentrations in mine waste correlate positively with concentrations 

of mercury, organic carbon, and sulfur, which are substances 

that influence processes of mercury cycling and methylation. They concluded that although the concentrations of total 

mercury and methyl mercury are locally high in some of the 

mine wastes, there is little offsite movement of mercury from 

the mines into stream sediment primarily because of the arid 

climate and lack of precipitation and mine runoff in the region. 

On the basis of the work by Horowitz and others (2001), 

movement of mercury from the mines into stream sediment is 

primarily in response to extreme runoff events. 

Acknowledgments

The study was a binational cooperative effort by personnel from multiple agencies from both the United States and 

Mexico. The study participants included 

United States Mexico

Gilbert Anaya, USIBWC, El Paso 

(lead)

Javier Aceves Monarrez, CILA, 

Ciudad Juarez (lead)

Daniel Borunda, USIBWC, El Paso Pablo Dominguez, SEMARNAT, 

Coahuila

Carlos Duarte, USIBWC, El Paso Carlos A Sifuentes, APFF Maderas 

del Carmen

Wayne Belzer, USIBWC, El Paso

Rebecca Lambert, USGS, San Antonio 

(lead)

Brian Petri, USGS, San Antonio

Michael Nyman, USGS, San Antonio

Jason Faith, USGS, San Antonio

Ted Small, USGS, San Antonio

Christine Kolbe, TCEQ, Austin (lead)

Roger Miranda, TCEQ, Austin

Carol Purchase, NPS–BBNP (lead)

Vidal Davila, NPS–BBNP

The authors thank the many property owners who provided access to the mining areas and also assisted in the data 

collection. Also, the authors thank the many individuals from 

all agencies in the United States and Mexico who worked 

together to make the sampling a success. Finally, the memory 

of Ted Small (1923–2007) is honored. Ted was a very humble 

man and a great friend who worked for more than 50 years 

in the region and whose knowledge of the Big Bend area was 

unparalleled. He was always willing to share his thoughts and 

to graciously answer questions. He was a mentor and source 

of information for many of the geologists who have worked in 

this region.

Physical Setting

The Big Bend area is a rugged, arid area in West Texas in 

the United States and in Coahuila and Chihuahua in Mexico 

(fig. 1). Located in the northern part of the Chihuahuan Desert, 

the Big Bend area generally receives little precipitation during 

the year. The normal annual precipitation (1971–2000) at the 

Panther Junction National Weather Service station in BBNP 

is 14.24 inches (National Climatic Data Center, 2005) (fig. 2). 

The lower altitudes along the RG/RB banks, where many of 

the abandoned mines are, generally receive less precipitation 

than that received at stations in higher altitudes, such as the 

Panther Junction weather station.

Geologic Setting

The Big Bend area is noted for its variety of geologic 

formations and structural features. These formations include 

thick sections of marine and continental Cretaceous deposits, 

bedded continental deposits, and Tertiary volcanic deposits 

and igneous intrusions (Maxwell and Dietrich, 1965). The 

deposition of these geologic units and the structural deformation and igneous activity that occurred during the Tertiary 

Period produced most of the ore deposits that have been mined 

in this area of the United States and Mexico, which in turn 

yields most of the trace elements that occur in streambed 

sediment. 

The geologic formations in the Big Bend area range in 

age from early Paleozoic to Tertiary, although almost all the 

stratified rocks exposed in the Terlingua mining district are of 

Cretaceous age (Yates and Thompson, 1959). Magmatic activity during the Tertiary (48 to 20 million years ago) deposited 

thick sections of volcanic tuff across the region and intruded 

the Cretaceous-age limestones as shallow dikes, sills, laccoliths, and stocks (Sharpe, 1980). The structure of the Terlingua mining district is dominated by large domes and grabens 

(Yates and Thompson, 1959). 

On a smaller scale, the rocks also have been irregularly 

deformed by intrusion, offset by innumerable faults, and 

pierced by breccia pipes (Yates and Thompson, 1959). Breccia 

pipes and other features that contain economic quantities of 

trace elements are formed by secondary solution and precipitation of solutes. There are three main types of solution 

features—open limestone caverns, filled caverns or cave-fill 

zones, and breccia pipes (Yates and Thompson, 1959), and two 

types of the open limestone caverns—vertical caves developed 

mainly along fractures and horizontal caves developed mainly 

along bedding planes.

Historical Mining Areas

Mines in the Big Bend area were operated from the late 

1800s through at least the late 1970s (table 1). Fluorite, lead, 

mercury, silver, and zinc are the most common types of mines 

in the area. The mines in the United States produced mainly 

mercury, while the mines in Mexico produced fluorite, lead, 

silver, and zinc. The most productive historical mercury mines 

are aligned from west to east in a narrow zone of fracturing 

along the axis of the Terlingua monocline, a steep, southwarddipping fold exposed along the south flank of the Terlingua 

uplift (Chester, 1965). These geologic structures have further 
Physical Setting 

7

Table 1. Information on abandoned mines and mine processing areas sampled August 5−15, 2002, in the Big Bend area of the United States and Mexico.[--, not available or not applicable; U.S., United States; >, more than; Mex., Mexico; BBNP, Big Bend National Park] 

Site 

no. 

(fig. 2)

Mine name

(alternate name)

Mining district Location Adjacent drainage Material mined Operator Approximate dates of operation1 Volume produced

3 Waldron Mine 

(Colquitt-Tigner)

Terlingua Near Lajitas, 

Brewster Co., Tex., U.S.

Comanche 

Creek2

Mercury Waldron Quicksilver Co. ? to 1914

1934 to 31940s 

Several hundred 

flasks4

4 Mariposa Mine 

(California 

Mountain)

Terlingua Near Lajitas, 

Brewster Co., Tex., U.S.

Comanche 

Creek2

Mercury Various owners including Esperado 

Mining Co.3

Esperado Mining Co.

1894 to 1,3,51918 1933 to 19451945–546

>32,000 flasks1

5a Chisos Mine portion 

of Chisos/Rainbow Mine

Terlingua Terlingua, 

Brewster Co., Tex., U.S.

Terlingua 

Creek

Mercury Chisos Mining Co.

Esperado Mining Co.

1901 to 19411941 to 1946

Estimated 100,000 

flasks4

5b Rainbow Mine 

portion of Chisos/Rainbow Mine

Terlingua Terlingua, 

Brewster Co., Tex., U.S.

Terlingua 

Creek

Mercury

Paulsel Mining Co.

pre-1935 to 19421951 to 1952

>8,000 flasks 4

6 Two-Forty-Eight 

Mine (Flecha)

Terlingua Between Study 

Butte and Terlingua, Tex., U.S.

Terlingua 

Creek

Mercury Esperado Mining Co. 1940 to 1946 > 600 flasks4

7a,b Study Butte Mine 

(Big Bend, TexasAlmaden)

Terlingua Terlingua, 

Brewster Co., Tex., U.S.

Rough Run 

Draw

Mercury Texas-Almaden Mercury Co.

Big Bend Mining Co.

1905 to 19441940 to 1944

>14,000 flasks4

10 La Esperanza (San 

Carlos) Mine

-- Chihuahua, Mex. San Carlos 

Creek

Iron, lead, 

silver, zinc

-- 1970s --

13 Tres Marias Mine -- Chihuahua, Mex. San Carlos 

Creek

Germanium, 

lead, silver, zinc

--

-- --

16 Mariscal Mine 

(Viviana, Ellis, 

Lindsey)

BBNP, Brewster 

Co., Tex., U.S.

Fresno 

Creek

Mercury --

Viviana Mining Co.Bob’s Mining Co.

1917 to 19231942 to 19431945

> 900 flasks1

18 Boquillas Mine/ 

processing area

-- Coahuila, Mex. Rio Grande Iron, lead, 

silver, zinc

--

-- --

20 Puerto Rico Mine -- Coahuila, Mex. -- Fluorite, lead, 

silver

--

-- --

22a,b La Linda Mine/ 

processing plant

-- Coahuila, Mex. Rio Grande Fluorite

--

-- --

1 Chester (1965). 3 Yates and Thompson (1959). 5 Swanson (1995).2 Not shown on map. 4 Sharpe (1980).
8 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

been modified by faults, en echelon fracture zones, and collapse features. The majority of faults are normal faults that 

bound downthrown grabens (Chester, 1965).

Cinnabar, the primary ore from which mercury is derived, 

was mined primarily from Cretaceous-age limestones (Sharpe, 

1980). Cinnabar commonly occurs as a secondary replacement 

mineral in argillaceous breccia matrix or as vein fillings in, or 

near, volcanic rocks and hot springs. After mining and crushing, the mercury then was extracted from the ore concentrates 

by heating the ore in retorts, or furnaces, in the presence of 

air (oxygen) to release the metal as a vapor that when cooled 

condensed to liquid mercury. The liquid mercury, also called 

quicksilver, was bottled for distribution in 76-pound steel 

cylinders called flasks. 

The Terlingua mining district and adjacent smaller 

districts in Brewster and Presidio Counties in Texas produced 

more than 150,000 flasks of mercury from 1899 to 1970 

(Sharpe, 1980). The total reported output of mercury from 

Texas from 1897 to 1960 was more than 147,200 flasks, or 

about 9 percent of the new mercury produced in the United 

States during the same period (Chester, 1965). The major mercury-producing mines or groups of mines in Texas that were 

sampled for this study include the Chisos/Rainbow Mines, 

Mariposa (California Mountain) Mine, Study Butte (Big Bend, 

Texas-Almaden) Mine, Two-Forty-Eight (Flecha) Mine, and 

Waldron (Colquitt-Tigner) Mine. More than 90 percent of 

the mercury in the Terlingua mining district was produced 

from the Mariposa, Chisos/Rainbow, and Study Butte Mines 

(figs. 2, 3) (Sharpe, 1980). A number of other mines, including 

the La Esperanza (San Carlos), Tres Marias, Boquillas, Puerto 

Rico, and La Linda Mines in Mexico, were mined for fluorite, 

lead, silver, and zinc, but there is little information available 

for these mines (figs. 2, 3).

Chisos/Rainbow Mines 

The Chisos Mine (fig. 2; table 1), one of the oldest mines 

and the most productive mercury mine in the Terlingua mining district, is at the middle part of The Long Draw (Sharpe, 

1980). The Chisos Mine was the only mine in the Terlingua 

mining district that economically produced cinnabar from 

calcite veins (Sharpe, 1980). The Chisos Mine connects with 

the adjoining Rainbow Mine, one of the deepest and most 

productive mines in the Terlingua mining district at a reported 

shaft depth of 670 feet (Yates and Thompson, 1959). The shaft 

follows a fault zone for much of its extent. The ore that was 

mined was obtained from altered limestones and clays, with 

high-grade cinnabar occurring along fractures and in irregular 

replacements.

Mariposa (California Mountain) Mine

The Mariposa Mine (fig. 2; table 1) ranks second in 

production of mercury in the Terlingua mining district 

(Yates and Thompson, 1959). Between 1895 and 1945, the 

Mariposa Mine produced more than 32,000 flasks of mercury 

(Chester, 1965). Ore from the Mariposa Mine was produced 

from cave-fill zones that are typical of the limestone-clay 

contact deposits in the Terlingua mining district (Yates and 

Thompson, 1959). The principal ore mineral is cinnabar, but 

there also are appreciable quantities of native mercury and 

other rare mercury minerals. The cinnabar occurs as disseminations and as solid masses in the clay matrix of the cavefill, and to a lesser extent, as veinlets and disseminations in 

limestone (Yates and Thompson, 1959). Most of the ore was 

produced before 1911, but some was mined during World War 

I and again from 1933 to 1945. By March, 1945, no appreciable ore reserves remained and the mine was closed (Yates 

and Thompson, 1959).

Study Butte (Big Bend, Texas-Almaden) Mine

About the same time that mercury was discovered in the 

Terlingua area, it also was found farther east in the area of 

the Study Butte Mine and the Two-Forty-Eight Mine (fig. 2; 

table 1) (Yates and Thompson, 1959). The Study Butte Mine 

was the third largest producer of mercury in the Terlingua 

mining district and essentially marks the eastern end of the 

Terlingua mining district about 5 miles east of Terlingua. 

Cinnabar was discovered early in 1902 and was actively mined 

as early as 1905, although substantial production did not begin 

until World War I (Yates and Thompson, 1959). The Study 

Butte Mine consists of two adjacent properties, the Big Bend 

and the Texas-Almaden, which historically have been worked 

either individually or as a single unit. The mine structure 

includes four principal shafts with many associated minor 

shafts, and more than 3 miles of horizontal workings on four 

main and numerous sublevels (Yates and Thompson, 1959). 

The workings of the Study Butte Mine are almost entirely in 

the Study Butte quartz soda syenite intrusion, which forms 

the hill that gives the mine its name (Yates and Thompson, 

1959). Cinnabar occurs in association with igneous rocks in 

several places in the Terlingua mining district, but the Study 

Butte Mine was the only economic producer from this type of 

mercury source (Sharpe, 1980). 

Two-Forty-Eight (Flecha) Mine

The Two-Forty-Eight (Flecha) Mine consists of a breccia 

pipe with a mine shaft greater than 600 feet deep that has 

produced cinnabar (Yates and Thompson, 1959). The TwoForty-Eight Mine (fig. 2; table 1) is 2 miles east of Terlingua 

and is named for section 248 where it is located (Yates and 

Thompson, 1959). Cinnabar was discovered before 1902, but 

by 1934 only 700 feet of subsurface workings had been driven 

(Yates and Thompson, 1959). In the 1940s, the Esperado 

Mining Company extended the mine workings to more than 

7,000 feet with 13 different levels that extended from the 

main shaft at irregular intervals (Yates and Thompson, 1959). 

The mercury deposits from the Two-Forty-Eight Mine can be 
Physical Setting 9

Figure 3. Examples of mine and mine-tailing sample sites at (A) Study Butte Mine, (B) Chisos Mine, (C) Mariscal Mine, (D) La Linda 

Mine/processing plant, (E) La Esperanza (San Carlos) Mine, and (F) Boquillas Mine (tailings). 

(A)

(C)

(E)

(D)

(B)

(F)
10 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

divided into two groups—the first and more important group 

includes deposits in marginal fissures of the breccia pipe and 

within the breccia pipe. The second group comprises fillings 

along fractures outside of, and away from, the breccia pipe. 

The most productive breccia pipes in the Terlingua mining district were from the Chisos and Two-Forty-Eight Mines (fig. 2).

Waldron (Colquitt-Tigner) Mine

The Waldron Mine (fig. 2; table 1) is northeast of the 

Mariposa Mine, and consists of about 900 feet of horizontal 

or near-horizontal passageways (Sharpe, 1980). The principal workings of the mine run approximately parallel to 

complementary fracture planes in a steep zone of brecciated 

and altered limestone (Sharpe, 1980). The Waldron mine is a 

“solution cavern” type of mine where calcite in small crystals 

coats some of the breccia and coarser calcite bands and, in 

part, fills vugs in the limestone (Yates and Thompson, 1959). 

Contributors of Flow, Sediment, Mercury, and 

Other Trace Elements

In the upper part of the study area, runoff from the 

Waldron Mine, Mariposa Mine, Chisos/Rainbow Mines, and 

Two-Forty-Eight Mine contributes flow and sediment to the 

Terlingua Creek watershed (fig. 2). The Study Butte Mine contributes flow and sediment to the adjacent Rough Run Draw, 

which is a subwatershed of the Terlingua Creek watershed. 

All of these mines are part of the Terlingua mining district 

and have the potential to contribute mercury and other trace 

elements associated with mercury deposits and mining to 

Terlingua Creek and also to the upper part of the RG/RB in 

the study area. The San Carlos Mine and the Tres Marias Mine 

produced lead, silver, and zinc and can contribute these trace 

elements and runoff to San Carlos Creek and to the upper part 

of the RG/RB (fig. 2). The Mariscal Mine in BBNP contributes flow and sediment from mercury deposits to Fresno 

Creek, a tributary of the RG/RB. The Boquillas Mine/processing area can contribute lead, silver, and zinc in flow and sediment directly to the RG/RB upstream from Boquillas Canyon 

(fig. 2). The Puerto Rico Mine in Coahuila can contribute lead 

and fluorite to the Arroyo del Fortino. Farther downstream, 

the La Linda mine/processing plant can contribute fluorite 

and other trace elements directly to the RG/RB near La Linda, 

Mexico (fig. 2).

Methods

Water, streambed-sediment, and mine-tailing samples 

were collected in August 2002 from eight RG/RB main-stem 

sites, four RG/RB tributary sites downstream from abandoned mines or mine tailings, and 11 mine-tailing sites, one 

of which also is a specific-source site (holding tank) (fig. 2; 

table 2). Summary statistics (minimum, maximum, average, 

median, and standard deviation) were computed for data from 

RG/RB main-stem and tributary sites and mine-tailing sites. In 

addition to scatterplots and bar graphs, truncated boxplots with 

whiskers drawn to 90th and 10th percentiles of the data set 

were used to summarize the distribution of data for selected 

constituents (Helsel and Hirsch, 1992). In all cases where boxplots were prepared to visually display the data distribution, 

the number of data points was eight or greater. 

The Texas Surface Water Quality Standards (TSWQS), 

Title 30, Chapter 307 of the Texas Administrative Code, are 

written by TCEQ with the authority of Section 303(c) of the 

Clean Water Act and Section 26.023 of the Texas Administrative Code. The standards establish specific water-quality goals 

for specific stream segments, lakes, and reservoirs throughout 

Texas. The standards are established to maintain the quality 

of water in Texas consistent with public health and recreation 

uses and also to protect aquatic life (Texas Commission on 

Environmental Quality, 2006). The TSWQS include specific 

numerical criteria for 39 toxic contaminants, maximum allowable in-stream concentrations for specified constituents, and 

criteria needed to protect aquatic life. Concentrations that 

exceed the criteria are considered indicators of potential shortterm (acute) and long-term (chronic) effects on aquatic life. 

Human consumption of fish and drinking water is protected by 

numerical criteria for 65 toxic contaminants. Concentrations 

that exceed the criteria indicate a long-term exposure risk and 

represent a potential human health hazard if untreated water or 

fish from a water body are consumed on a regular, long-term 

basis (table 3). 

In-stream concentrations of nutrients, toxic substances 

in sediment, and salinity are used to identify water-quality 

issues. Numerical criteria for these constituents have not been 

established in the TSWQS. The screening levels for these 

constituents establish targets that can be directly related to 

in-stream data. The screening levels are statistically derived 

from long-term monitoring data (for example, nutrients) or are 

based on published levels of concern (for example, sediment). 

For this study, these criteria and screening levels are only used 

as tools to screen the data for assessment purposes. A larger 

data set would be required to determine if a particular reach 

supports the designated water-quality standards using these 

criteria (Texas Commission on Environmental Quality, 2006).

Where applicable, water-quality and sediment-quality 

data were compared with TSWQS criteria and screening levels 

(table 3) for selected constituents as a measure of the effect 

of the abandoned mines. The use of criteria and screening 

levels to assess water-quality conditions is documented in the 

"Guidance for Assessing and Reporting Surface Water Quality in Texas" (Texas Commission on Environmental Quality, 

2006). Analytical data from the sample collected from the 

specific-source site (holding tank) was included in the report 

for informational purposes only regarding the chemical composition of similar sites that might exist elsewhere in the study 

area. The data from the specific-source site was not included 

in the analysis of main-stem and tributary water and sediment 

quality.
Methods 11

Table 2. Locations of stream and abandoned mine and mine processing sites sampled August 5−15, 2002, in the Big Bend area of the 

United States and Mexico.

[ddmmss, degrees minutes seconds; MS, main stem; SW, stream-water quality; BS, streambed-sediment quality; MT, mine-tailing; LP, leaching potential; TR, 

tributary; BBNP, Big Bend National Park; SS, specific source]

Site 

no. 

(fig. 2)

Site name and general location Sample identifier Site

type

Type of 

analysis 

or sample 

medium

Latitude

(ddmmss)

Longitude

(ddmmss)

1 Rio Grande above Lajitas, Texas, United States MS-Lajitas MS SW/BS 29°"15'54.9" 103°46'59.8"

2 Rio Grande at Santa Elena Canyon Trailhead, 

BBNP, United States

MS-Santa Elena 

Canyon

MS SW/BS 29°09'51.1" 103°36'55.8"

3 Waldron Mine, Texas, United States Waldron MT Rock/LP 29°19'39" 103°40'42"

4 Mariposa Mine, Texas, United States Mariposa MT Rock/LP 29°18'56.2" 103°41'53.9"

5a,b Chisos/Rainbow Mine, Texas, United States Chisos 1, 2 MT Rock/LP 29°19'00” 103°37'15"

6 Two-Forty-Eight Mine, Texas, United States 248 MT Rock/LP 29°19'34.5" 103°34'04"

7a, b Study Butte Mine, Texas, United States Study Butte 1, 2 MT Rock/LP 29°19'16.6"

29°19'22.4"

103°31'37.8"

103°31'37.1"

8 Rough Run Draw at Study Butte, Texas, United 

States

TR-Rough Run TR SW/BS 29°19'15.3" 103°31'33.1"

9 Terlingua Creek at Terlingua Abaja, BBNP, 

United States

TR-Terlingua 

Creek

TR SW/BS 29°11'59" 103°36'19"

10 La Esperanza (San Carlos) Mine, Chihuahua, 

Mexico

San Carlos MT Rock/LP 29°07'35.2" 103°38'16.8"

11 San Carlos Creek below La Esperanza Mine, 

Chihuahua, Mexico

TR-San Carlos 

Creek

TR SW/BS 29°07'3.2" 103°37'48.5"

12 Rio Grande at Santa Elena Crossing, BBNP, 

United States

MS-Santa Elena 

Crossing

MS SW/BS 29°07'20.8" 103°31'25.2"

13 Tres Marias Mine, Chihuahua, Mexico Tres Marias MT Rock/LP 29°08'25.48" 103°39'47.2"

14 Rio Grande at Woodson’s Campground, BBNP, 

United States

MS-Woodson’s MS SW/BS 29°00'22.9" 103°17'43.8"

15 Rio Grande at Solis Campground, BBNP, 

United States

MS–Solis MS SW/BS 29°02'39.1" 103°06'18.9"

16 Mariscal Mine, BBNP, United States Mariscal MT Rock/LP 29°05'40.5" 103°11’20.9"

17 Rio Grande at La Clocha Campground, BBNP, 

United States

MS-La Clocha MS SW/BS 29°08'54.9" 103°00'27.9"

18 Boquillas Mine/processing area, Coahuila, 

Mexico

Boquillas MT Rock/LP 29°11'18.3" 102°56'6.3"

19 Rio Grande upstream of Boquillas Canyon, 

BBNP, United States

MS-Boquillas 

Canyon

MS SW/BS 29°11'57.2" 102°55'04.7"

20 Puerto Rico Mine, Coahuila, Mexico Puerto Rico MT Rock/LP 29°10'55.4" 102°49'9.3"

21 Arroyo del Fortino below Puerto Rico Mine 

near Boquillas, Coahuila, Mexico

TR-Arroyo del 

Fortino

TR SW/BS 29°12'21.4" 102°53'21.1"

22a,b La Linda Mine/processing plant near La Linda, 

Coahuila, Mexico

SS-La Linda 1, 2 SS1 (MT) SW/Rock/

LP/BS

29°27'06" 102°49'04"

23 Rio Grande at La Linda, Coahuila, Mexico MS-La Linda MS SW/BS 29°26'57.5" 102°49'22.8"

1

 Sample of stream water (site 22, table 4) collected from holding tank at mine-tailing site; sample of streambed sediment (site 22, table 5) collected from 

creek downstream from processing plant; samples of mine tailings (site 22a,b, tables 6–7) collected from mine tailings at processing plant 1, 2.
12 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

Water-quality samples were collected during August 6–9, 

2002, at each RG/RB site as a single grab sample from the 

part of the river with the greatest volume of flow at an approximate depth of 1 foot below the water surface. Flow of the 

RG/RB at the IBWC streamflow-gaging station Rio Grande 

at Johnson Ranch near Castolon, Tex., and Santa Elena, 

Chihuahua (08-3750.00), during the 4-day sampling period 

averaged 802 cubic feet per second, which is about 66 percent 

of the long-term (1936–2007) average flow of 1,216 cubic feet 

per second at the station (International Boundary and Water 

Commission, 2007) but about 150 percent of the average flow 

during the past 15 years (October 1992–September 2007) of 

Table 3. Criteria and screening levels used to assess surface-water quality in segment 2306 of the Rio Grande/Río Bravo (Texas 

Commission on Environmental Quality, 2006).

[μg/L, micrograms per liter; mg/L, milligrams per liter; mg/kg, milligrams per kilogram; μg/g, micrograms per gram; TCLP, Toxicity Characteristic Leaching 

Procedure; --, not applicable; °C, degrees Celsius; DO, dissolved oxygen; DS, dissolved solids]

Constituent

Aquatic life-use protection1

(μg/L)

Human health criteria2

(μg/L) General-use 

protection 

criteria3

Screening levels4 TCLP 

screening 

limit6

(mg/L)

Acute 

criteria 

Chronic 

criteria 

Fish consumption usePublic water 

supply use

Nutrients 

(mg/L)

Sediment5 

(mg/kg)

pH (units) -- -- -- -- 6.5–9.0 -- -- --

Temperature (oC) -- -- -- -- 32.2 -- -- --

DO (mg/L) -- -- -- -- 5 -- -- --

Chloride (mg/L) -- -- -- -- 300 -- -- --

Sulfate (mg/L) -- -- -- -- 570 -- -- --

DS (mg/L) -- -- -- -- 1,500 -- -- --

Phosphorus -- -- -- -- -- 0.69 -- --

Orthophosphorus -- -- -- -- -- .37 -- --

Nitrite + nitrate -- -- -- -- -- 2 -- --

Ammonia -- -- -- -- -- .33 -- --

Aluminum 991 -- -- -- -- -- -- --

Antimony -- -- -- -- -- -- 25 1

Arsenic 360 190 -- 50 -- -- 33 5

Barium -- -- -- 2,000 -- -- -- 100

Beryllium -- -- -- -- -- -- -- .08

Cadmium 92.1 2.1 -- 5 -- -- 4.98 1

Chromium (0, III 

and VI)

1,162 377 100 100 -- -- 111 5

Copper 43.7 26.9 -- -- -- -- 149 --

Lead 233 8.1 4.98 -- -- -- 128 5

Mercury 2.4 1.3 .0122 -- -- -- 1.06 .2

Nickel 3,073 341 -- -- -- -- 48.6 70

Selenium 20 5 50 -- -- -- -- 1

Silver .8 -- -- -- -- -- 2.2 5

Zinc 248.8 227.1 -- -- -- -- 459 --

1

 Includes acute and chronic criteria for metals and organics in water, DO, toxicity in water and sediment, sediment contaminants, biological communities, and 

in-stream habitat.

2

 Established in Texas Surface Water Quality Standards (TSWQS), designed to prevent contamination of drinking water, fish, and other aquatic life, to ensure 

safe use for human consumption.

3

 Water-quality criteria established in TSWQS to safeguard general water quality, rather than protection of specific use; DO criterion is the exception and is 

related to aquatic life-use protection (Texas Commission on Environmental Quality, 2000). 

4

 Statistically derived from 10 years of surface-water-quality monitoring data using 85th percentile; used in the absence of established criteria to denote a 

concern.

5

 Assessed in support of aquatic life-use protection (Texas Commission on Environmental Quality, 2006); mg/kg = μg/g.

6

 Any metal greater than limit does not pass TCLP test; any metal less than limit passes TCLP test (Federal Register, 2007). For this study, used as screening 

tool; TCLP applies to hazardous waste. 
Methods 13

536 cubic feet per second. Flow conditions during the sampling period are difficult to characterize relative to long-term 

conditions, as long-term conditions might be changing. Field 

properties of specific conductance, pH, temperature, dissolved 

oxygen, and alkalinity were measured at each RG/RB site. 

The water-quality samples were collected and field properties were measured in accordance with the TCEQ “Surface 

Water Quality Monitoring Procedures, Volume 1: Physical 

and Chemical Monitoring Methods for Water, Sediment, and 

Tissue” (Texas Commission on Environmental Quality, 2003). 

These procedures are outlined in the Texas Clean Rivers Program (CRP) Rio Grande Basin Monitoring Quality Assurance 

Project Plan (International Boundary and Water Commission, 

2001). 

The water-quality samples were analyzed by the 

USIBWC CRP contract laboratories for selected constituents 

that include major ions; DS, TSS, and VSS; nutrients; and 

trace elements. Analytical methods used to analyze these 

constituents are documented by the Texas Commission on 

Environmental Quality (2003, Appendix D). Calcium was analyzed using U.S. Environmental Protection Agency (USEPA) 

method 200.7, and magnesium was analyzed using USEPA 

method 242.1. Chloride and sulfate concentrations were 

analyzed using USEPA method 300.0. DS, TSS, and VSS 

were analyzed using USEPA methods 160.1, 160.2, and 160.4, 

respectively. Nitrite plus nitrate was analyzed using USEPA 

method 353.3. Nitrogen, as ammonia, was analyzed using 

USEPA method 350.1. Total phosphorus was analyzed using 

USEPA method 365.3, and orthophosphorus was analyzed 

using USEPA method 300.0. The water-quality samples for 

trace elements were collected using clean techniques with 

pre-cleaned bottles, equipment, and instructions provided 

by the USIBWC CRP contract laboratory following USEPA 

methods 1669 and 1631c (Albion Environmental, 2003a, b, 

c; U.S. Environmental Protection Agency, 1995b). Concentrations of aluminum, barium, cadmium, chromium, copper, 

nickel, lead, silver, and zinc were analyzed by inductively 

coupled plasma-mass spectrometry according to USEPA 

methods 1638/200.8 (Albion Environmental, 2003c; U.S. 

Environmental Protection Agency, 1995a). Mercury concentrations in water were analyzed using USEPA methods 1669 

and 1631C (Albion Environmental, 2003a; U.S. Environmental Protection Agency, 2001); selenium concentrations were 

analyzed using USEPA method 1632 (Albion Environmental, 

2003b; U.S. Environmental Protection Agency, 1996). Speciation was not determined for any trace elements and all trace 

element concentrations were total dissolved values, with the 

exception of mercury and selenium. In the case of mercury 

and selenium, the water samples were analyzed for total recoverable concentrations.

Field blank samples for trace elements were collected 

from three sites (table 4, at end of report). Most of the constituents analyzed in the field blanks were less than the laboratory 

reporting level (LRL). Although the field blank collected from 

the Rio Grande at Santa Elena Crossing site had a detectable 

mercury concentration of 0.0003 microgram per liter (μg/L), 

the concentration was less than the LRL of 0.0005 μg/L and 

likely does not indicate contamination of mercury analyses 

from the sampling procedure (Albion Environmental, 2003a). 

Zinc was detected in the field blank samples collected from 

the Rio Grande above Lajitas and Rio Grande at Santa Elena 

Crossing sites. The zinc concentration in the Lajitas field 

blank, 3.58 μg/L, was greater than the concentration measured 

in many of the environmental samples (table 4). This high 

field blank concentration indicates that the other samples with 

zinc concentrations less than 18 μg/L might have been biased 

because of potential contamination during sampling (Albion 

Environmental, 2003c). Two duplicate samples were collected 

from main-stem sites and one duplicate sample was collected 

from a tributary site. Results of duplicate sampling are listed 

in table 4.

Streambed-sediment-quality samples were collected 

from the RG/RB main-stem and tributary sites following 

guidelines established for the USGS National Water-Quality 

Assessment Program (Shelton and Capel, 1994) (table 5, at 

end of report). Fine-grained surficial sediment samples were 

collected and composited from two to five wetted natural 

depositional zones along the river bank at each selected site 

to yield a representative sample. The fine-grained surficial 

sediment was collected using a Teflon spoon, scoop, or spatula 

and latex-free synthetic polymer gloves to minimize contamination. Once collected, these samples were composited 

and sieved through a 63-micrometer mesh nylon-sieve cloth 

held in a plastic frame to obtain a sample composed of the silt 

fraction with particles that were less than 63 micrometers in 

diameter. The samples then were stored in air-tight containers 

and chilled until analysis. The streambed-sediment-quality 

samples were analyzed for 44 major and trace elements by the 

USGS Geologic Discipline in Denver, Colo., using the analytical methods discussed in Arbogast (1996), Briggs and Meier 

(1999), and Taggart (2002). The predominant major ions (calcium, magnesium, potassium, sodium), as well as phosphorous 

and aluminum, are reported by the USGS Geologic Discipline 

in percent of total bottom material, whereas most other trace 

elements are reported in micrograms per gram. Duplicate 

samples were collected from two main-stem sites and results 

are listed in table 5.

Mine-tailing-quality samples were collected from areas 

in and adjacent to accessible abandoned mines and mine processing areas (table 6, at end of report). Similar to the procedures used to collect streambed-sediment samples, two to five 

mine-tailing samples were collected at each site using Teflon 

scoops and latex-free synthetic polymer gloves and then 

composited to form a representative sample from each minetailing site. Samples were collected from unweathered tailings 

beneath the surface of the tailings pile. The mine-tailing 

samples were analyzed by the TCEQ Environmental Laboratory in Houston, Tex., for 25 inorganic ions and trace elements 

using USEPA Method 200.7 (U.S. Environmental Protection Agency, 2002). The TCEQ laboratory that analyzed the 

samples reported all constituents in milligrams per kilogram, 

including the predominant major ions (calcium, magnesium, 
14 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

potassium, sodium) as well as phosphorous and aluminum. For 

quality assurance, laboratory method blanks were analyzed 

with environmental mine-tailing samples. All method blanks 

for the mine tailings yielded constituent concentrations less 

than the LRLs. Laboratory method blank surrogates also were 

analyzed with the environmental samples. The actual recoveries for all the analytes ranged from 99.7 to 104 percent, which 

is within the laboratory-reported acceptable range of 85 to 115 

percent. 

The Toxicity Characteristic Leaching Procedure (TCLP), 

using USEPA SW–846 analytical method 1311, was designed 

to simulate the leaching of contaminants in landfills (Environment, Health and Safety Online, 2007; U.S. Environmental 

Protection Agency, 1992). The TCLP was applied to determine the leaching potential for 10 trace elements from 

14 samples collected at 11 abandoned mine and mine-tailing 

sites in the United States and Mexico (fig. 2, table 7, at end 

of report). The TCLP extraction is done by subjecting the 

material to a simulated landfill leachate; concentrations in the 

simulated leachate are reported in milligrams per liter. Acetic 

acid is used as the extraction fluid because it is the major 

component of typical municipal landfill leachates. After 

extraction, the resulting liquid from the study samples were 

analyzed for antimony, arsenic, barium, beryllium, cadmium, 

chromium, lead, nickel, selenium, and silver (table 7). For 

screening purposes only, the results were compared with 

TSWQS criteria and screening levels to indicate how readily 

metals contained in the mine tailings might be leached into the 

surrounding area (table 3). The higher the TCLP concentration, the higher the potential for that particular constituent to 

be leached from its source. 

Quality of Stream Water

The water chemistry of 12 samples collected from the 

RG/RB main-stem and tributary sites in the study area provides insight into the salinity and solute transport of major 

ions and trace elements in the RG/RB and its tributaries. The 

water chemistry also can provide information on the relative 

effects of the abandoned mines and mine processing sites on 

the water in the basin. Ions and trace elements, if present in 

sufficient concentrations, might have an adverse effect on the 

quality of water needed to maintain human health and protect aquatic life. A number of constituents sampled for were 

detected at fairly low concentrations, many less than the LRL, 

indicating a relatively low probability for adversely affecting 

the water quality in the region. Other constituents that were 

detected frequently at relatively high concentrations throughout the study area are discussed in the following sections.

Salinity and Suspended Solids

Salinity differs from one watershed to another and is 

highly dependent on the underlying rock type. Arid areas in 

the region tend to concentrate salts in the soil because of the 

high rate of evaporation. Runoff from these areas carries salts 

into streams or reservoirs. Salinity commonly is increased by 

irrigation return flows or by domestic wastewater discharges. 

Reduced flows and high evaporation during drought conditions 

also can increase salinity. Increased salinity can make a water 

body unsuitable for aquatic species not tolerant of brackish 

water, for use in agriculture (livestock and crops), and for use 

as a drinking-water source.

Elevated salinity in streams, especially in the more arid 

parts of the region, results from both natural and human activities. In general, rainwater has a very low salinity. However, as 

runoff flows over land, the slightly acidic nature of rainwater 

can dissolve and release ions from soil and rock, causing an 

increase in the salinity (Hem, 1992). The most common ions 

(inorganic salts) are bicarbonate, calcium carbonate, chloride, 

magnesium, potassium, sodium, and sulfate. The relative 

contribution of these ions to the salinity in a solution can be 

determined directly by analysis of the water for these constituents or DS, or indirectly by field measurements of specific 

conductance, pH, and alkalinity (Hem, 1992).

Calcium concentration can be an important factor in 

the water chemistry of streams as it forms chemical bonds 

with carbonates. If sufficient quantities of calcium carbonate 

are present in minerals, such as limestones, the acidic water 

derived from mine openings and tailings can be buffered by 

calcium carbonate. Calcium concentrations ranged from 67 to 

490 milligrams per liter (mg/L), with a median concentration 

of 290 mg/L (fig. 4; table 4). The lowest calcium concentrations were in samples collected from the tributary sites (fig. 5). 

The highest calcium concentrations were in samples collected 

from RG/RB main-stem sites from Santa Elena Crossing 

downstream to La Linda, a section of the river known for 

perennial springs that contribute ground water to the base 

flow of the river. The higher calcium concentrations in the 

main-stem samples indicate that flow in the RG/RB is diluting 

runoff from the tributaries and buffering the river from more 

acidic water.

Sulfate is a common constituent in mine drainage. 

The sulfate concentrations from the RG/RB main-stem and 

tributary sites ranged from 102 to 796 mg/L, with a median 

concentration of 268 mg/L (fig. 4; table 4). The TSWQS 

general-use protection criterion for sulfate, 570 mg/L (table 3), 

was exceeded only at the Rough Run Draw site (fig. 5) in the 

upper part of the study area. The lowest sulfate concentrations 

were in samples from the San Carlos Creek and Arroyo del 

Fortino sites in Mexico, both of which are spring-fed creeks. 

In general, relatively high sulfate concentrations were in the 

upper part of the study area from the Lajitas to Woodson’s 

sites, with the highest sulfate concentrations from tributaries 

draining the Terlingua mining district (figs. 2, 5). The higher 

sulfate concentrations in the upper part of the basin might be 

an indication of dissolution of minerals such as cinnabar (mercury sulfide) from mercury mining areas. 

Chloride concentrations ranged from 3 to 225 mg/L, 

with a median concentration of 51 mg/L (fig. 4; table 4). 
Quality of Stream Water 15

All concentrations were less than the TSWQS general-use 

protection criterion for chloride of 300 mg/L (table 3). Except 

for the samples collected at the Lajitas and Woodson’s sites, 

the chloride concentrations at all other sites were 80 mg/L 

or less and were fairly consistent throughout the study area 

(fig. 5).

The DS concentration is used as an indication of salinity. 

Consistent with previous USGS reports, in this report freshwater is defined as water with DS concentration of 1,000 mg/L 

or less, slightly saline water is defined as water with DS 

concentration between 1,000 to 3,000 mg/L, and saline water 

is defined as water with DS concentration equal to or greater 

than 3,000 mg/L (Winslow and Kister, 1956; Nickerson, 

2006). All water samples were fresh to slightly saline, with DS 

concentrations ranging from 255 to 1,350 mg/L and a median 

concentration of 710 mg/L (fig. 4; table 4). The TSWQS 

general-use protection criterion for DS in segment 2306 is 

1,500 mg/L (table 3). DS concentrations of all water samples 

were less than the TSWQS criterion.

The higher DS concentrations (slightly saline) were in 

samples collected from the Lajitas, Rough Run Draw, and 

Terlingua Creek sites in the upper part of the study area 

downstream from the Terlingua mining district (figs. 2, 6). The 

lowest DS concentration (the freshest water) was at the Santa 

Elena Crossing site. The lower concentration might indicate 

a freshwater source, possibly ground-water seepage from 

springs to the main-stem RG/RB in this area, that is diluting 

DS concentrations.

CALCIUM SULFATE CHLORIDE DISSOLVED

SOLIDS

TOTAL

SUSPENDED

SOLIDS

VOLATILE

SUSPENDED

SOLIDS

1

10

100

1,000

10,000

CONCENTRATION, IN MILLIGRAMS PER LITER

(12) (12) (12) (10) (12) (8)

(12)

50th percentile

25th percentile

75th percentile

90th percentile

10th percentile

EXPLANATION

Number of samples

Figure 4. Distribution of concentrations of calcium, sulfate, chloride, dissolved solids, total suspended solids, and volatile suspended 

solids in water samples collected August 6–9, 2002, in the Big Bend area of the United States and Mexico.
16 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

TSS is a measure of both organic and inorganic suspended solids in water (Texas Commission on Environmental 

Quality, 2003). TSS concentrations were highest in water 

samples collected from the main-stem RG/RB and lowest in 

samples collected from the tributaries (fig. 6; table 4). The 

TSS concentration ranged from 5 to 5,550 mg/L with a median 

concentration of 2,265 mg/L. The highest TSS concentrations were in the samples collected from the Solis, La Clocha, 

and Boquillas Canyon main-stem RG/RB sites. Higher TSS 

concentrations correspond to lower DS concentrations in the 

main-stem RG/RB section from the Santa Elena Crossing site 

downstream to the La Linda site. During flows higher than 

those during August 6–9, 2002, there is probably a greater 

input of TSS and sediment from the tributaries. 

VSS is the portion of TSS that is lost after the sample is 

ignited (Texas Commission on Environmental Quality, 2003, 

Appendix B, Glossary). The VSS represents the organic portion of the TSS that is volatilized. VSS concentrations were 

variable, ranging from 3 to 920 mg/L, with a median concentration of 310 mg/L (fig. 6; table 4). Similar to the results 

for TSS, the higher VSS concentrations were from main-stem 

RG/RG samples and probably are related to the higher 

sediment load carried by the river. In the lower part of the 

study area from the Woodson’s site to Boquillas Canyon site, 

the main-stem VSS concentrations were similar to the DS 

concentrations.

Trace Elements

For most mining areas, water released from the mines, 

dumps, or mine tailings tends to carry high trace element 

concentrations at the source that are roughly in proportion to 

acidity of the water. Such waters evolve to a higher pH and 

lower trace element concentrations as mine waters are diluted 

and neutralized by natural processes in streams (Nash, 2003). 

The pH of water determines the solubility (amount that can be 

dissolved in the water) and the biological availability (amount 

that can be used by aquatic life) of chemical constituents and 

trace elements. In the case of trace elements, the degree to 

which they are soluble determines their toxicity. Metals tend 

to be more toxic at lower pH values because they are more 

soluble. All sample pHs were moderate (relatively neutral), 

ranging from 7.3 to 8.3, with a median of 7.5 (table 4). The 

pHs were within the range of 6.5 to 9.0 specified by the 

TSWQS general-use protection criterion for segment 2306 

(Texas Commission on Environmental Quality, 2006). The 

Figure 5. Concentrations of calcium, sulfate, and chloride in water samples collected August 6–9, 2002, from Rio Grande/Río Bravo 

main-stem (MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. 

0

100

200

300

400

500

600

700

800

900

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's 

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MILLIGRAMS PER LITER

Sulfate

Chloride

Calcium

Texas Surface Water Quality Standard - sulfate

Texas Surface Water Quality Standard - chloride
Quality of Stream Water 17

majority of pH values measured in segment 2306 of the 

RG/RB during 1999–2004 were in the specific range, which 

is typical of surface-water bodies in this part of Texas (C.M. 

Kolbe, Texas Commission on Environmental Quality, written commun., 2006). The pH of 8.3 in the sample from San 

Carlos Creek downstream from La Esperanza (San Carlos) 

Mine probably is the result of a greater proportion of ground 

water in the flow, as San Carlos Creek is partially spring-fed. 

The moderate pHs indicate that waters in the RG/RB and its 

tributaries are well mixed, diluted, and buffered with respect to 

the solubility of trace elements from mining areas. 

Aluminum is a trace element that is commonly in rocks in 

the Big Bend area and that can be toxic to plants and aquatic 

life (Pais and Jones, 1997). The TSWQS acute criterion for the 

protection of aquatic life for aluminum is 991 μg/L (table 3). 

Aluminum concentrations in the water samples ranged from 

2.2 to 545 μg/L, with a median concentration of 126 μg/L 

(fig. 7; table 4). The higher aluminum concentrations were 

measured in the main-stem RG/RB sites in the upper part of 

the watershed that drains the Terlingua mining district in the 

United States and the San Carlos Creek in Mexico (figs. 2, 8). 

All aluminum concentrations were less than the TSWQS acute 

criterion. 

Barium is a common trace element in the Earth’s crust 

and frequently found in combination with sulfate and carbonate (Pais and Jones, 1997). Although generally chemically 

inactive, it can become highly toxic to animals and humans 

when combined to form soluble salts such as barium sulfate. 

The barium in water samples ranged from 47.7 to 172 μg/L 

with a median concentration of 110 μg/L (fig. 7; table 4). All 

barium concentrations were less than the 2,000 μg/L TSWQS 

human health criterion for public water supply use (table 3). 

The higher barium concentrations were in the main-stem 

RG/RB samples as compared to the tributary samples (fig. 8). 

Cadmium is a naturally occurring element in the earth’s 

crust and usually is found combined with other elements as 

a mineral (Pais and Jones, 1997). All soils and rocks, as well 

as coal and other fossil fuels and mineral fertilizers, contain 

Figure 6. Concentrations of dissolved solids, total suspended solids, and volatile suspended solids in water samples collected August 

6–9, 2002, from Rio Grande/Río Bravo main-stem (MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United 

States and Mexico. 

0

1,000

2,000

3,000

4,000

5,000

6,000

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's 

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MILLIGRAMS PER LITER

Dissolved solids

Total suspended solids

Volatile suspended solids

 Texas Surface Water Quality Standard - total dissolved solids
18 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002 CONCENTRATION, IN MICROGRAMS PER LITER

0.0001

0.001

0.01

0.1

1

10

100

1,000

10,000

ALUMINUM BARIUM COPPER MERCURY NICKEL SELENIUM ZINC

EXPLANATION

50th percentile

25th percentile

75th percentile

90th percentile

10th percentile

(11) (11) (11) (12) (11) (12) (11)

(11) Number of samples

some trace amounts of cadmium (Pais and Jones, 1997). 

From a health perspective, cadmium is a carcinogen and is 

introduced into the atmosphere from mining, industry applications, and burning of coal and household waste (International 

Boundary and Water Commission, 2004). Sources of cadmium 

in water are the metal plating industry, industrial effluent, and 

municipal wastewater treatment plant effluent. Cadmium does 

not break down in the environment and can be persistent in 

water. Cadmium often bioaccumulates in tissue, thus contributing to a high potential for acute and chronic toxicity to 

aquatic life (International Boundary and Water Commission, 

2004).

There were few detectable cadmium concentrations in the 

water samples (table 4). Only the samples collected from San 

Carlos Creek and Arroyo del Fortino had detectable cadmium 

concentrations. San Carlos Creek drains the San Carlos Mine, 

and Arroyo del Fortino drains the Puerto Rico Mine (fig. 2). 

The remaining samples contained less than the LRL for 

cadmium of 0.1 μg/L, and all samples contained less than the 

TSWQS criterion for aquatic life-use protection and for human 

health (table 3). 

Chromium is a naturally occurring element in rocks, 

plants, animals, volcanic dust, and gases (Pais and Jones, 

1997). The chemistry of chromium is complex, and its toxicity 

Figure 7. Distribution of concentrations of aluminum, barium, copper, mercury, nickel, selenium, and zinc in water samples collected 

August 6–9, 2002, in the Big Bend area of the United States and Mexico. 
Quality of Stream Water 19

is based on its valence state, which affects its solubility and 

reactivity. Chromium (III) occurs naturally and is an essential nutrient required by humans, and chromium (VI) and 

chromium (0) generally are produced by industrial processes 

(International Boundary and Water Commission, 2004). In 

addition, the deposition of airborne chromium also can be an 

important nonpoint source of chromium in surface water. 

Chromium is both a carcinogen and a mutagen (Pais 

and Jones, 1997). A small amount dissolves in water, and the 

remainder settles to the bottom of the stream channel. Soluble 

chromium compounds can remain in water for years before 

settling to the bottom. Chromium does not accumulate in fish 

tissue but is very persistent in water. Chromium is more toxic 

in soft water than in hard water. Chromium (III) has a moderate acute toxicity and high chronic toxicity to aquatic life, and 

chromium (VI) has high acute and chronic toxicity to aquatic 

life (International Boundary and Water Commission, 2004). 

The absorption of chromium is influenced by the presence of 

chelating agents and metals, particularly zinc and iron (Pais 

and Jones, 1997). 

Detectable chromium concentrations were only in water 

samples from the Lajitas, Terlingua Creek, and Arroyo del 

Fortino sites (table 4). The samples from Lajitas and Terlingua Creek drain the Terlingua mining district. The Arroyo del 

Fortino site receives drainage from the area of the Puerto Rico 

Mine. Similar to cadmium, all samples had chromium concentrations less than the TSWQS criterion for acute and chronic 

aquatic life-use protection and for human health (table 3).

Copper is common in rocks and soils but generally is 

fairly immobile in soils (Pais and Jones, 1997). Rainfall might 

be a substantial source of copper to the aquatic environment 

in industrial and mining areas (International Boundary and 

Water Commission, 2004). Copper can easily be precipitated 

and readily interacts with both organic and inorganic substances (Pais and Jones, 1997). Van Metre and others (1997) 

documented an upward trend in copper concentrations in a 

sediment core in the RG/RB arm of Amistad Reservoir. Copper also is an essential micronutrient that can become toxic to 

plants when the tissue concentration exceeds 20 to 30 milligrams per kilogram (mg/kg) (Pais and Jones, 1997). 

Copper concentrations also were relatively low with little 

variation among samples for all sites, ranging from 1.11 to 

3.03 μg/L, with a median concentration of 1.56 μg/L (fig. 7; 

table 4). The highest copper concentrations were in samples 

from the tributary sites, Rough Run Draw and Arroyo del 

Fortino (fig. 9), that drain the Study Butte Mine and the Puerto 

Figure 8. Concentrations of aluminum and barium in water samples collected August 6–9, 2002, from Rio Grande/Río Bravo main-stem 

(MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. 

0

100

200

300

400

500

600

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's 

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MICROGRAMS PER LITER

Aluminum

Barium

NA Not analyzed

NA NA
20 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

Rico Mine, respectively. All copper concentrations were less 

than the TSWQS criterion for acute and chronic aquatic lifeuse protection (table 3).

Nickel, one of the most common trace elements, is in 

all soils and can occur from weathering of rocks, deposition 

from precipitation, and surface-water runoff (Pais and Jones, 

1997). Nickel is a common trace element in air and is removed 

from the atmosphere by rain or snow. Most nickel becomes 

attached to soil or sediment particles. Common sources of 

nickel include the burning of coal and other fossil fuels, electroplating, and smelting. Nickel is a known carcinogen with 

a high acute toxicity and high chronic toxicity in aquatic life, 

although it is not known to bioaccumulate in fish tissue (International Boundary and Water Commission, 2004). 

Similar to copper concentrations, nickel concentrations were relatively low, ranging from 2 to 3.62 μg/L with 

a median concentration of 2.62 μg/L (table 4). The highest 

nickel concentrations were in samples from Lajitas to Woodson’s main-stem sites and from Rough Run Draw tributary site 

(fig. 9). All nickel concentrations were less than the TSWQS 

criterion for acute and chronic aquatic life-use protection 

(table 3). 

Mercury can occur naturally in the environment, or can 

be introduced in runoff from urban and industrial sources and 

municipal and industrial discharges. Mercury also can enter 

the environment through atmospheric deposition. Mercury 

occurs in several forms, ranging from elemental to dissolved 

organic and inorganic. Certain microorganisms have the ability to convert the organic and inorganic forms to highly toxic 

methyl and dimethyl mercury (Pais and Jones, 1997; Texas 

Commission on Environmental Quality, 2006). This methylation process has made all forms of mercury highly hazardous 

to the environment (International Boundary and Water Commission, 2004). 

Mercury was detected in all water samples collected 

from the RG/RB main-stem and tributary sites. The mercury 

concentration ranged from 0.0007 to 0.198 μg/L, with a 

median concentration of 0.0975 μg/L (fig. 7; table 4). Mercury 

concentrations in all samples, except those from the tributary 

sites at Terlingua Creek and Arroyo del Fortino, were greater 

than the TSWQS human health criterion for fish consumption (0.0122 μg/L), but all concentrations were considerably 

less than the criteria for acute and chronic aquatic life-use 

protection (table 3). The highest mercury concentrations were 

measured in samples from the Lajitas, Woodson’s, Solis, 

La Clocha, and Boquillas Canyon main-stem sites (fig. 10). 

The concentrations were lowest in samples from the tributary 

sites and from the Santa Elena Canyon and Santa Elena 

Crossing main-stem sites. The relatively low mercury concentration at the Santa Elena Crossing site might be the result of 

mixing of RG/RB water with ground water from springs in the 

area. 

Most of the higher mercury concentrations can be 

related linearly to the TSS concentration (fig. 11); two of the 

Figure 9. Concentrations of copper and nickel in water samples collected August 6–9, 2002, from Rio Grande/Río Bravo main-stem 

(MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. 

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's 

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MICROGRAMS PER LITER

Copper

Nickel

NA Not analyzed

NA NA
Quality of Stream Water 21

Figure 10. Concentration of mercury in water samples collected August 6–9, 2002, from Rio Grande/Río Bravo main-stem (MS) and 

tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. 

0

0.05

0.10

0.15

0.20

0.25

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's 

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MICROGRAMS PER LITER

Mercury, total recoverable

Figure 11. Relation of concentrations of total recoverable mercury to total suspended solids for water samples collected August 6–9, 

2002, from Rio Grande/Río Bravo main-stem and tributary sites in the Big Bend area of the United States and Mexico. 

R 2 = 0.77123

0

0.050

0.100

0.150

0.200

0.250

0 1,000 2,000 3,000 4,000 5,000 6,000

CONCENTRATION OF TOTAL SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

CONCENTRATION OF TOTAL RECOVERABLE MERCURY, 

IN MICROGRAMS PER LITER
22 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

samples (Lajitas and Woodson’s) appear to be outliers, that is, 

exceptionally high concentrations relative to the corresponding TSS concentrations. The high mercury concentrations in 

these two samples might indicate that the sites are receiving 

mercury from a nearby source. The source of mercury in water 

throughout the study area, however, does not seem to be solely 

abandoned mines and mine-tailing areas. Gray and others 

(2006) reported that the hot, arid climate in the area limited 

the process of mercury methylation and the transference of 

mercury and methyl-mercury from the Study Butte mine site. 

During hot and dry periods, offsite movement of mercury into 

streams might be minimal. Mobilization processes associated with extreme runoff events could be important transport 

mechanisms for mercury mobilization (Horowitz and others, 

2001). During extreme runoff events, offsite movement of 

mercury into streams and remobilization of sediment and tailings previously transported to stream channels might be substantial. Relatively high mercury concentrations are not only 

in the upper part of the basin near the Terlingua mining district 

where expected, but they also are distributed throughout the 

study area. The presence of relatively high concentrations 

throughout the study area might indicate multiple sources of 

mercury in water. Possible sources include point sources in the 

abandoned mining areas, nonpoint sources from the erosion of 

bedrock that provides trace elements to the stream sediment, 

and nonpoint-source atmospheric deposition of mercury from 

human activities (Van Metre and others, 1997). 

Lead is carcinogenic and teratogenic (causes fetal 

malformation) and is considered a major contaminant (Pais 

and Jones, 1997; International Boundary and Water Commission, 2004). The USEPA has included lead in the list 

of probable human carcinogens (Group B2) (U.S. Environmental Protection Agency, 2004). Lead is a major constituent 

of more than 200 minerals, of which only three are sufficiently 

abundant to form mineral deposits (International Boundary 

and Water Commission, 2004). Lead is the least mobile 

of the metals, accumulating primarily on the land surface. 

Lead is introduced to the environment through atmospheric 

deposition by precipitation and fallout of lead dust, urban runoff, and industrial and municipal wastewater treatment plant 

discharges (International Boundary and Water Commission, 

2004). The availability of lead in the soil is influenced 

by pH—an increase in pH of soil decreases the solubility of 

lead (Pais and Jones, 1997). Lead is not readily soluble in 

water and generally, concentrations in sediment are relatively 

low. 

The dissolved lead concentrations generally were relatively low in all water samples except the San Carlos Creek 

sample, which had a concentration of 21 μg/L (table 4). 

Concentrations in five samples were less than the LRL of 

0.10 μg/L, and concentrations in the remaining samples 

from Lajitas, Santa Elena Canyon, Santa Elena Crossing, 

Boquillas Canyon, and Arroyo del Fortino ranged from 

0.12 to 0.26 μg/L. The most probable source of the high 

lead concentration in the San Carlos Creek sample is the 

nearby San Carlos Mine and associated tailings. The San 

Carlos Mine, upstream in the San Carlos Creek watershed, 

was mined for economic quantities of iron, lead, silver, and 

zinc (table 1). The lead concentration detected in the San 

Carlos Creek sample was greater than the TSWQS chronic 

criterion for the protection of aquatic life (8.1 μg/L) and the 

human health criterion for fish consumption (4.98 μg/L) 

(table 3). Although the lead concentration was elevated, the 

high pH of 8.3 associated with alkaline soils in the area might 

result in relatively low solubility of lead from the mine tailings 

and thus minimize the amount of lead that is transported 

offsite. 

Selenium generally is unaffected by water and increases 

in concentration when there is an associated increase in the 

clay content of a soil (Pais and Jones, 1997). The solubility 

of selenium generally is relatively low. However, on poorly 

drained or calcareous soils and arid soils where selenium 

concentrations in the soil are high, selenium might accumulate to sufficient levels in plants to pose a substantial hazard 

to grazing animals (Pais and Jones, 1997). The selenium 

concentration in the water samples ranged from 0.25 to 3.26 

μg/L, with a median concentration of 0.98 μg/L (fig. 7; table 

4). The higher selenium concentrations were measured in 

samples from the tributary sites Rough Run Draw and Terlingua Creek, downstream from the Terlingua mining district 

(fig. 12; table 4). Selenium concentrations for all analyzed 

samples were less than the TSWQS criteria for the protection 

of aquatic life and human health (table 3). 

There were no detectable concentrations of dissolved 

silver in any of the water samples. Silver concentrations in all 

samples were less than the TSWQS criterion for the protection 

of aquatic life of 0.8 μg/L (table 3). 

Zinc is one of the most common trace elements and 

occurs in air, soil, and water (Pais and Jones, 1997). Zinc is an 

essential dietary element present in all foods. Zinc, which is 

readily transported in most river systems, can be introduced to 

the environment by natural processes and by human activities such as mining, steel production, waste incineration, and 

burning of coal or other fossil fuels (International Boundary 

and Water Commission, 2004). Zinc is one of the most readily 

soluble of all the trace elements in soils (Pais and Jones, 1997) 

and is not a known carcinogen but can accumulate in fish and 

other organisms. Zinc has a fairly high bioaccumulation index 

and the mechanism of zinc toxicity to aquatic primary producers is an interference with phosphorylation reactions (Bates 

and others, 1982). The dissolved zinc concentration in the 

water samples varied greatly. The zinc concentrations in most 

samples were between 0.89 and 3.12 μg/L. Highest concentrations of 18.6 μg/L or greater were in the samples from the San 

Carlos Creek, Santa Elena Crossing, and Arroyo del Fortino 

sites (fig. 7; table 4). A possible explanation for the high zinc 

concentration at the three sites is abandoned mine areas. The 

San Carlos Creek sample was collected downstream from the 

San Carlos Mine tailings, and the Arroyo del Fortino sample 

was collected downstream from the Puerto Rico Mine (fig. 2). 

All zinc concentrations were less than the TSWQS acute and 

chronic criteria for the protection of aquatic life (table 3).
Quality of Streambed Sediment 23

Quality of Streambed Sediment

The chemistry of streambed sediment is important 

because of its relation to the chemistry of water in the stream 

and, in turn, the effects of water chemistry on aquatic life. 

Streambed sediment is assessed in support of the aquatic lifeuse protection in Texas (Texas Commission on Environmental 

Quality, 2006). The aquatic life-use protection includes criteria 

for toxicity in water and sediment, sediment contaminants, 

biological communities, and in-stream habitat.

The percentages or concentrations of aluminum, antimony, arsenic, beryllium, bismuth, and cadmium were low 

at most sites throughout the study area, except for antimony, 

arsenic, and cadmium in streambed-sediment samples from 

the San Carlos Creek and Rough Run Draw sites (table 5). The 

percentage of aluminum in the streambed-sediment samples 

ranged from 1.7 to 6.7 for all samples, with a median of 5.9 

(table 5). There was greater variability in the concentrations 

from the tributary sites. There is no TCEQ screening level for 

aluminum in sediment. 

The antimony concentration ranged from 0.60 to 420 

micrograms per gram (μg/g), with a median of 0.80 μg/g 

(fig. 13; table 5). All samples had detectable antimony concentrations. The highest concentrations were measured in the 

samples from Rough Run Draw and San Carlos Creek, which 

are downstream from the Study Butte Mine and the La Esperanza (San Carlos) Mine tailings, respectively (fig. 14). The 

San Carlos Creek sample concentration exceeded the TCEQ 

sediment screening level of 25 mg/kg (μg/g) used to evaluate trace elements that can have an adverse ecological effect 

(table 3). 

Arsenic is released to the environment from natural 

sources (volcanoes, erosion from mineral deposits) and also 

from anthropogenic sources (metal smelting, chemical production and use, coal and other fossil fuel combustion, waste disposal) (International Boundary and Water Commission, 2004). 

Arsenic is a carcinogen, dissolves in water, changes from one 

form to another, is persistent in water, and can accumulate in 

fish and shellfish tissue. Certain forms have high acute and 

chronic toxicity in aquatic life. 

All samples had detectable arsenic concentrations, with 

concentrations ranging from 5.7 to 450 μg/g and a median of 

8.3 μg/g (fig. 13; table 5). Similar to antimony, the highest 

arsenic concentrations were measured in samples from San 

Carlos Creek downstream from the San Carlos Mine and 

from Rough Run Draw downstream from the Study Butte 

Mine (fig. 14). Most of the arsenic concentrations, except 

in samples from San Carlos Creek and possibly Rough Run 

Draw, probably are representative of background sediment 

concentrations. The concentration of the San Carlos Creek 

sample (450 μg/g), however, is more than an order of magnitude greater than the other sample concentrations and likely 

is the result of mining activities in the area. The San Carlos 

Creek sample concentration exceeded the TCEQ screening 

level of 33 mg/kg (μg/g) used to evaluate trace elements that 

can have an adverse ecological effect (table 3). The arsenic 

concentrations at all other sites were well below the screening 

level.

Figure 12. Concentrations of selenium and zinc in water samples collected August 6–9, 2002, from Rio Grande/Río Bravo main-stem 

(MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. 

0

5

10

15

20

25

30

35

40

45

50

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's 

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MICROGRAMS PER LITER

Selenium

Zinc

NA Not analyzed

NA
24 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

Figure 13. Distribution of concentrations of antimony, arsenic, beryllium, cadmium, and chromium in streambed-sediment samples 

collected August 6–9, 2002, in the Big Bend area of the United States and Mexico. CONCENTRATION, IN MICROGRAMS PER GRAM

ANTIMONY ARSENIC BERYLLIUM CADMIUM CHROMIUM

EXPLANATION

50th percentile

25th percentile

75th percentile

90th percentile

10th percentile

0.1

1

10

100

1,000

(12) (12) (12) (12) (12)

(12) Number of samples

Figure 14. Concentrations of antimony and arsenic in streambed-sediment samples collected August 6–9, 2002, from Rio Grande/Río 

Bravo main-stem (MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. 

0.1

1

10

100

1,000

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson’s

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MICROGRAMS PER GRAM

Arsenic

Antimony
Quality of Streambed Sediment 25

The beryllium concentration in the streambed-sediment 

samples ranged from 0.87 to 2.5 μg/g, with a median of 

2.0 μg/g (fig. 13; table 5). The highest beryllium concentrations were in samples from Lajitas, Terlingua Creek, and 

Solis (fig. 15). The beryllium concentrations vary over a fairly 

narrow range throughout the study area (fig.15) and probably 

are representative of regional background beryllium concentrations in streambed sediment. There is no TCEQ screening 

level for beryllium in streambed sediment. 

The cadmium concentration ranged from 0.16 to 240 

μg/g, with a median of 0.3 μg/g (fig. 13; table 5). Excluding 

the highest concentration, 240 μg/g in the San Carlos Creek 

sample, the sample concentrations ranged from 0.16 to 1.4 

μg/g (fig. 15). The next highest concentration (1.4 μg/g) was 

from Rough Run Draw, downstream from the Study Butte 

Mine. The cadmium concentration in the San Carlos Creek 

sample exceeded the TCEQ screening level for cadmium of 

4.98 mg/kg (μg/g) (table 3). All other sample concentrations 

were less than the screening level. 

Chromium concentrations ranged from 14 to 46 μg/g, 

with a median of 31 μg/g (fig. 13; table 5). The highest chromium concentrations were in the samples from Lajitas and 

Rough Run Draw and the lowest in the sample from San 

Carlos Creek (fig. 15). Concentrations at all sites were less 

than the TCEQ sediment screening level for chromium of 

111 mg/kg (μg/g) (table 3). 

The copper concentration ranged from 12 to 49 μg/g, 

with a median of 17 μg/g (fig. 16; table 5). The highest concentration was measured in the San Carlos Creek sample and 

the lowest concentration in the Santa Elena Canyon sample 

(fig. 17). All sample concentrations were less than the TCEQ 

sediment screening level for copper of 149 mg/kg (μg/g) 

(table 3).

The mercury concentration ranged from 0.02 to 0.68 

μg/g, with a median of 0.04 μg/g (fig. 16; table 5). The highest 

mercury concentrations were in samples from the Rough Run 

Draw tributary site downstream from the Terlingua Mining District and from the main-stem RG/RB La Linda site 

(fig. 17). The mercury concentrations at all other sites were 

0.06 μg/g or less. The mercury concentrations at all sites were 

less than the TCEQ sediment screening level for mercury of 

1.06 mg/kg (μg/g) (table 3). 

The concentrations of molybdenum, nickel, selenium, 

and silver were relatively low in most samples (table 5). 

All nickel concentrations were less than the TCEQ sediment screening level of 48.6 mg/kg (μg/g) (table 3). The one 

exception to the relatively low concentrations was the silver 

concentration in the San Carlos Creek sample of 24 μg/g that 

Figure 15. Concentrations of beryllium, cadmium, and chromium in streambed-sediment samples collected August 6–9, 2002, from Rio 

Grande/Río Bravo main-stem (MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. 

0.1

1

10

100

1,000

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MICROGRAMS PER GRAM

Beryllium

Cadmium

Chromium
26 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

Figure 16. Distribution of concentrations of copper, mercury, and nickel in streambed-sediment samples collected August 6–9, 2002, in 

the Big Bend area of the United States and Mexico. 

Figure 17. Concentrations of copper, mercury, and nickel in streambed-sediment samples collected August 6–9, 2002, from Rio Grande/

Río Bravo main-stem (MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. CONCENTRATION, IN MICROGRAMS PER GRAM

COPPER MERCURY NICKEL

EXPLANATION

50th percentile

25th percentile

75th percentile

90th percentile

10th percentile

0.01

0.1

1

10

100

(12) (12) (12)

(12) Number of samples

0.01

0.1

1

10

100

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MICROGRAMS PER GRAM

Copper

Mercury

Nickel
Quality of Streambed Sediment 27

exceeded the TCEQ sediment screening level for silver of 2.2 

mg/kg (μg/g) (table 3).

The lead concentration in streambed-sediment samples 

ranged from 13 to 9,500 μg/g (figs. 18, 19; table 5). Most 

lead concentrations were between 13 and 19 μg/g, although 

the concentration at Rough Run Draw was 59 μg/g and at San 

Carlos Creek was 9,500 μg/g. Lead concentrations, except for 

the Rough Run Draw and San Carlos Creek samples, probably 

represent regional background concentrations. Only the San 

Carlos Creek sample concentration exceeded the TCEQ sediment screening level for lead of 128 mg/kg (μg/g) (table 3). 

The high lead concentration in the sample from San 

Carlos Creek indicates that some of the mining activities or 

mine tailing debris from the San Carlos Mine or other mines 

in the area have an effect on the sediment quality (fig. 19). 

The source of the elevated lead probably is the San Carlos 

Mine and tailings in the upper part of the San Carlos Creek 

watershed because of the large volume of mine tailings present 

and the size of the mining operation. Elevated concentrations 

of the same order of magnitude were not measured in any 

other samples collected in the study area. Because lead is the 

least mobile of the trace elements, however, there is probably 

not much movement of lead away from the mining site. The 

lead concentration in the Rough Run Draw sample is higher 

than the concentrations measured in the other samples but not 

nearly as high as the concentration measured in the San 

Carlos Mine sample. The Study Butte Mine is upstream 

from the Rough Run Draw sample site and is the likely lead 

source.

Manganese is one of the most abundant trace elements in 

the lithosphere and exists in soil over a wide range of oxidation states (Pais and Jones, 1997). The manganese concentration ranged from 460 to 20,000 μg/g (fig. 18; table 5). Except 

for the concentration of 20,000 μg/g in the sample from San 

Carlos Creek, concentrations in all other samples ranged from 

460 to 580 μg/g (fig. 19). The source of the elevated manganese most likely is the San Carlos Mine and mine tailings. 

There is not a TCEQ sediment screening level for manganese.

Thallium, tin, and vanadium were detected in several 

samples. The thallium concentration was less than the LRL of 

1 μg/g at all sites except the San Carlos Creek site, where the 

thallium concentration was 2 μg/g (table 5). Tin concentrations 

also were fairly low, ranging from 1 to 3 μg/g in all samples 

except the San Carlos Creek sample (27 μg/g). The vanadium 

concentrations ranged from 47 to 97 μg/g, with a median of 

83 μg/g. There is not a TCEQ sediment screening level for 

thallium, tin, or vanadium.

The zinc concentration in the streambed-sediment 

samples ranged from 62 to 12,000 μg/g (fig. 18; table 5). Most 

streambed-sediment concentrations were similar in value 

(fig. 19) and less than 90 μg/g in all samples except the Rough 

Run Draw sample (140 μg/g) and San Carlos Creek sample 

(12,000 μg/g). The San Carlos Creek zinc concentration was 

several orders of magnitude greater than the other samples 

and was the only sample concentration that exceeded the 

TCEQ sediment screening level for zinc of 459 mg/kg (μg/g) 

(table 3). The elevated zinc concentration at the San Carlos 

Creek site could be an issue because zinc has a fairly high 

Figure 18. Distribution of concentrations of lead, manganese, and zinc in streambed-sediment samples collected August 6–9, 2002, 

from Rio Grande/Río Bravo main-stem and tributary sites in the Big Bend area of the United States and Mexico. CONCENTRATION, IN MICROGRAMS PER GRAM

1

10

100

1,000

10,000

100,000

LEAD MANGANESE ZINC

EXPLANATION

50th percentile

25th percentile

75th percentile

90th percentile

10th percentile

(12) (12) (12)

(12) Number of samples
28 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

bioaccumulation index and interferes with phosphorylation 

reactions (Bates and others, 1982).

The uranium concentration in the streambed-sediment 

samples ranged from 2.3 to 7.5 μg/g, with a median of 2.7 

μg/g (table 5). The highest concentration was measured in 

the sample from San Carlos Creek. All other sample concentrations ranged from 2.3 to 3.0 μg/g, a range that probably 

represents background conditions in the region. 

The elevated concentrations of multiple trace elements 

in samples from the San Carlos Creek and Rough Run Draw 

sites indicate that San Carlos Creek, and probably Rough Run 

Draw, have been adversely affected by mining activities.

Quality of Mine Tailings

Trace Elements

All 25 major and trace elements analyzed, except selenium and thallium, were detected in one or more of the minetailing samples collected during the study (fig. 2; table 6). 

The aluminum concentration ranged from 4,920 mg/kg at 

the Study Butte Mine 2 site to 25,100 mg/kg at the Chisos/

Rainbow Mine 2 site, with a median of 9,425 mg/kg (table 6). 

Detectable antimony concentrations were measured in only 

three of 14 mine-tailing samples—Waldron, La Esperanza 

(San Carlos), and Boquillas Mines. These concentrations 

ranged from 43 to 109 mg/kg, and all exceeded the TCEQ 

sediment screening level for antimony of 25 mg/kg (table 3). 

Arsenic was detected in 13 of 14 samples at concentrations 

ranging from 19 to 1,250 mg/kg (Boquillas) (fig. 20). Arsenic was not detected in the sample from Study Butte Mine 2. 

Detected arsenic concentrations exceeded the TCEQ sediment 

screening level for arsenic of 33 mg/kg (table 3) in all but two 

of the 13 samples. 

Cadmium was detected at four sites, and detectable 

concentrations ranged from 24 to 409 mg/kg (table 6). All 

samples with detectable concentrations exceeded the TCEQ 

sediment screening level for cadmium of 4.98 mg/kg (table 3). 

The highest cadmium concentrations were in the samples from 

San Carlos, Tres Marias, and Puerto Rico Mines in Mexico. 

Chromium was detected in all samples but at much 

lower concentrations than detected cadmium concentrations; 

chromium concentrations ranged from 2 to 23 mg/kg with 

a median of 11 mg/kg. The highest concentrations were in 

the Chisos samples in the Terlingua mining district and the 

Figure 19. Concentrations of lead, manganese, and zinc in streambed-sediment samples collected August 6–9, 2002, from Rio Grande/

Río Bravo main-stem (MS) and tributary (TR) sites (downstream order) in the Big Bend area of the United States and Mexico. 

1

10

100

1,000

10,000

100,000

MS - Lajitas

MS - Santa Elena Canyon

TR - Rough Run

TR - Terlingua Creek

TR - San Carlos Creek

MS - Santa Elena Crossing

MS - Woodson's

MS - Solis

MS - La Clocha

MS - Boquillas Canyon

TR - Arroyo del Fortino

MS - La Linda

SAMPLE IDENTIFIER

CONCENTRATION, IN MICROGRAMS PER GRAM

Lead

Manganese

Zinc
Quality of Mine Tailings 29

Mariscal sample in BBNP (fig. 20). None of the samples 

exceeded the TCEQ sediment screening level for chromium of 

111 mg/kg (table 3).

Copper concentrations were detected in 13 of 14 minetailing samples and ranged from 4 to 2,310 mg/kg (table 6). 

The highest copper concentrations were measured in Tres 

Marias (119 mg/kg), Boquillas (1,780 mg/kg), and Puerto 

Rico (2,310 mg/kg) mine-tailings samples (fig. 21; table 6). 

The samples from Boquillas and Puerto Rico Mines in the 

lower part of the study area exceeded the TCEQ sediment 

screening level for copper of 149 mg/kg (table 3). 

Mercury concentrations were detected in all mine-tailing 

samples and varied widely, ranging from 0.08 to 966 mg/kg 

with a median of 120 mg/kg. The highest mercury concentrations were from the Mariposa, Two-Forty-Eight, and Study 

Butte 2 samples collected in the Terlingua mining district in 

Texas and from the Tres Marias sample in Chihuahua. Mercury concentrations in samples from 10 of 14 sites exceeded 

the TCEQ sediment screening level for mercury of 1.06 mg/kg 

(table 3). 

Nickel was detected in nine of 14 mine-tailing samples, 

with concentrations ranging from 3.5 to 39 mg/kg. The highest concentrations were measured in the Chisos and Mariscal 

samples (fig. 21). All nickel concentrations were less than the 

TCEQ sediment screening level for nickel of 48.6 mg/kg.

Lead was detected in seven of 14 mine-tailing samples. 

The detectable lead concentrations ranged from 7 to 67,900 

mg/kg (fig. 22; table 6). The highest concentrations were 

measured in the Boquillas, Puerto Rico, San Carlos, and 

Tres Marias samples, as might be expected because the tailings 

are from lead mines. The concentrations at these sites greatly 

exceeded the TCEQ sediment screening level for lead of 

128 mg/kg (table 3). 

The manganese concentration ranged from 120 to 18,600 

mg/kg. Concentrations in most samples ranged from 120 to 

440 mg/kg, but concentrations in the Boquillas, Puerto Rico, 

and San Carlos samples were 700 mg/kg or greater. The highest concentration was measured in the San Carlos sample. 

Silver was detected in the San Carlos, Boquillas, and 

Puerto Rico samples. All detectable concentrations exceeded 

the TCEQ sediment screening level for silver of 2.2 mg/kg 

(table 3). 

Zinc was detected in all mine-tailing samples and ranged 

in concentration from 28 to 90,400 mg/kg (fig. 22; table 6). 

Concentrations in 10 of 14 samples were 181 mg/kg or less. 

Concentrations in the four remaining samples (San Carlos, 

Tres Marias, Boquillas, and Puerto Rico sites) ranged from 

15,000 to 90,400 mg/kg, greatly exceeding the TCEQ screening criterion for zinc of 459 mg/kg (table 3). 

There were between 14 and 21 detectable concentrations 

of the 25 major and trace elements that were analyzed for 

in each of the mine-tailing samples (table 6). The most detections were in the samples from Boquillas Mine (21 of 25) 

and Study Butte Mine site 1 (20 of 25). The highest concentrations of calcium, beryllium, and molybdenum were in the 

sample from La Linda Mine/processing plant 2. The highest 

Figure 20. Detectable concentrations of arsenic, cadmium, and chromium in mine-tailing samples collected August 5–15, 2002, from 

abandoned mine and mine processing sites (downstream order) in the Big Bend area of the United States and Mexico. 

1

10

100

1,000

10,000

Waldron

Mariposa

Chisos 1Chisos 2

248

Study Butte 1Study Butte 2

San Carlos

Tres Marias

Mariscal

Boquillas

Puerto Rico

La Linda 1

La Linda 2

SAMPLE IDENTIFIER

CONCENTRATION, IN MILLIGRAMS PER KILOGRAM

Arsenic

Cadmium

Chromium

ND Not detected

 

NDNDNDNDNDNDNDNDNDNDND
30 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

Figure 21. Detectable concentrations of copper, mercury, and nickel in mine-tailing samples collected August 5–15, 2002, from 

abandoned mine and mine processing sites (downstream order) in the Big Bend area of the United States and Mexico. 

Figure 22. Detectable concentrations of lead, manganese, silver, and zinc in mine-tailing samples collected August 5–15, 2002, from 

abandoned mine and mine processing sites (downstream order) in the Big Bend area of the United States and Mexico. 

0.01

0.1

1

10

100

1,000

10,000

CONCENTRATION, IN MILLIGRAMS PER KILOGRAM

Copper

Mercury

Nickel

ND Not detected

NDNDNDNDNDND

Waldron

Mariposa

Chisos 1

Chisos 2

248

Study Butte 1

Study Butte 2

San Carlos

Tres Marias

Mariscal

Boquillas

Puerto Rico

La Linda 1La Linda 2

SAMPLE IDENTIFIER

1

10

100

1,000

10,000

100,000

CONCENTRATION, IN MILLIGRAMS PER KILOGRAM

Lead

Manganese

Silver

Zinc

ND Not detected

NDNDNDNDNDNDNDNDNDNDNDNDNDNDNDND

ND

ND

Waldron

Mariposa

Chisos 1Chisos 2

248

Study Butte 1

Study Butte 2

San Carlos

Tres Marias

Mariscal

Boquillas

Puerto Rico

La Linda 1

La Linda 2

SAMPLE IDENTIFIER
Summary 31

concentrations of potassium, arsenic, lead, silver, and zinc 

were in the sample from Boquillas Mine. The highest concentrations of magnesium, antimony, cobalt, iron, and manganese 

were in the sample from San Carlos Mine. The highest aluminum and nickel concentrations were in the sample from 

Chisos/Rainbow Mine 2. The highest cadmium and copper 

concentrations were in the sample from Puerto Rico Mine; 

the highest mercury concentration was from Mariposa Mine; 

the highest sodium concentration was from Two-Forty-Eight 

Mine; and the highest barium concentration was from Waldron 

Mine.

Trace element concentrations generally were higher in 

streambed-sediment samples from San Carlos Creek than 

from any other main-stem or tributary site. Unlike the other 

mine sites, the tailings from the San Carlos Mine lie across the 

headwaters of San Carlos Creek, dominating the area. The tailings at San Carlos Mine generally were finer and less consolidated than those at the other mine sites. These characteristics 

likely facilitate the transport of mine tailings into San Carlos 

Creek. Few of the other mine sites were as close to the perennial streams that were sampled during this study. Other mine 

sites generally were adjacent to ephemeral streams that dry 

quickly following storms. San Carlos Creek is one of the few 

perennial tributaries in the area. Mine tailings also were visible 

in San Carlos Creek downstream from the tailings; they appear 

to be a dominant part of the streambed sediment. These factors 

probably account for the appreciably higher trace element 

concentrations in the San Carlos Creek streambed-sediment 

sample compared to concentrations in sediment samples from 

other sites. The relative concentrations of arsenic, cadmium, 

lead, manganese, silver, and zinc in the streambed-sediment 

sample from San Carlos Creek are similar to those in the 

mine-tailing sample from San Carlos Mine. To a lesser extent, 

this relation also applies to relative concentrations of those 

trace elements in the sediment sample from Rough Run Draw 

and in tailings samples from Study Butte Mine. 

Leaching Potential

The potential for leaching of antimony, arsenic, barium, 

beryllium, chromium, nickel, selenium, and silver from the 

mine tailings was less than the TCLP screening limit (table 3) 

for all samples collected during this study (table 7). The only 

trace elements with a leaching potential equal to or greater 

than the TCLP limit were cadmium and lead. The TCLP 

cadmium concentration for San Carlos Mine was 6.50 mg/L, 

exceeding the TCLP limit for cadmium of 1.0 mg/L; and the 

TCLP cadmium concentration for Tres Marias Mine was 1.00 

mg/L, which equaled the TCLP screening limit. TCLP lead 

concentrations were detected in four of 14 samples; the highest TCLP lead concentrations were in tailings from San Carlos 

Mine (15.5 mg/L) and Boquillas Mine/processing area (120 

mg/L). Both concentrations exceeded the TCLP screening 

limit for lead of 5 mg/L. 

Overall, the relatively low TCLP concentrations for most 

trace elements indicate that the potential for leaching because 

of weathering and other climatic effects is minimal. The 

higher leaching potentials for cadmium and lead might be the 

result of more recent mine activity or the volume of mine tailings that remain at some sites. Many of the mines in the upper 

part of the study area in the United States have been inactive 

for several decades. 

Summary

This report characterizes the quality of water, streambed 

sediment, and mine tailings in the Rio Grande/Río Bravo (RG/

RB) Basin in the Big Bend study area of Texas in the United 

States and Chihuahua and Coahuila in Mexico. Mines in the 

area were operated from the late 1800s through at least the late 

1970s. Mercury mines and mine processing areas that were 

sampled include the Waldron Mine, Mariposa Mine, Chisos/

Rainbow Mine, Two-Forty-Eight Mine, and Study Butte Mine 

in the Terlingua mining district and Mariscal Mine in Big 

Bend National Park in the United States. The fluorite, germanium, iron, lead, silver, and zinc mines that were sampled in 

Mexico include La Esperanza (San Carlos) Mine, Tres Marias 

Mine, Boquillas Mine/processing area, Puerto Rico Mine, and 

La Linda Mine/processing area. 

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

the International Boundary and Water Commission—U.S. and 

Mexican Sections, the National Park Service, the Texas Commission on Environmental Quality, the Secretaría de Medio 

Ambiente y Recursos Naturales in Mexico, the Área de Protección de Flora y Fauna Cañón de Santa Elena in Mexico, and 

the Área de Protección de Flora y Fauna Maderas del Carmen 

in Mexico, collected water-quality, bed-sediment, and minetailing samples during August 2002 for a study to determine 

whether trace elements from abandoned mines in the area in 

and around Big Bend National Park have adversely affected 

water and sediment quality in the RG/RB Basin. Samples were 

collected from eight sites on the main stem of the RG/RB, 

four RG/RB tributaries downstream from abandoned mines 

or mine-tailing sites, and 11 mine-tailing sites, one of which 

also is a specific-source site (holding tank). The water-quality 

samples collected at the 12 RG/RB main-stem and tributary 

sites were analyzed for selected constituents including major 

ions; dissolved solids, total suspended solids, and volatile suspended solids; nutrients; and trace elements. Field properties 

also were measured—pH, specific conductance, temperature, 

dissolved oxygen, and alkalinity. The water-quality results 

were compared to the Texas Surface Water Quality Standards 

(TSWQS) written by the Texas Commission on Environmental 

Quality (TCEQ) to determine whether concentrations meet 

standards for human health and recreation uses, and also for 

the protection of aquatic life.

Calcium concentrations can be a measure of the capacity of the river system to buffer acidic mine drainage. The 

lowest calcium concentrations were measured in samples from 

the tributary sites, and the highest calcium concentrations 

were measured in samples from main-stem sites from Santa 
32 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002

Elena Crossing downstream to La Linda. The higher calcium 

concentrations might be related to ground-water inflow from 

perennial springs that contribute ground water to base flow of 

the river. 

In general, relatively high sulfate concentrations were in 

the upper part of the study area from the Lajitas to the Woodson’s sites, with the highest sulfate concentrations from tributaries draining the Terlingua mining district. The sample from 

the Rough Run Draw site was the only one in which the sulfate 

concentration exceeded the TSWQS general-use protection 

criterion of 570 mg/L. The lowest sulfate concentrations were 

in samples from the spring-fed San Carlos Creek and Arroyo 

del Fortino sites in Mexico. All chloride concentrations were 

less than the TSWQS general-use protection criterion. 

The water in the RG/RB and its tributaries was fresh to 

slightly saline. The higher dissolved solids concentrations 

(slightly saline) were from the Lajitas, Rough Run Draw, 

and Terlingua Creek sites in the upper part of the study area 

downstream from the Terlingua mining district. The lowest 

dissolved solids concentration (the freshest water) was at the 

Santa Elena Crossing site and could indicate a freshwater 

source, possibly ground-water seepage from springs into the 

main-stem RG/RB in this area, that is diluting dissolved solids 

concentrations. Dissolved solids concentrations of all samples 

were less than the TSWQS criterion of 1,500 mg/L. Total 

suspended solids concentrations were highest in samples collected from the main-stem RG/RB sites Solis, La Clocha, and 

Boquillas Canyon.

The pHs of all samples were moderate (relatively neutral) 

and met the TSWQS general-use protection criterion TCEQ 

has established for segment 2306 of the RG/RB. The moderate 

pHs indicate that waters in the RG/RB and its tributaries are 

well-mixed, diluted, and buffered with respect to the solubility 

of trace elements from mining areas. 

Aluminum, barium, copper, mercury, nickel, selenium, 

and zinc were detected in water samples for which each was 

analyzed. Cadmium, chromium, and lead were detected in 

samples less frequently, and silver was not detected in any 

of the samples. Cadmium was detected at San Carlos Creek 

and Arroyo del Fortino; chromium was detected at Lajitas, 

Terlingua Creek, and Arroyo del Fortino. Lead was detected 

in the Lajitas, Santa Elena Canyon, San Carlos Creek, Santa 

Elena Crossing, Boquillas Canyon, and Arroyo del Fortino. 

None of the sample concentrations for aluminum, cadmium, 

chromium, nickel, selenium, and zinc exceeded the TSWQS 

criteria for aquatic life-use protection or human health. The 

lead concentration in the San Carlos Creek sample exceeded 

the TSWQS chronic criterion for the protection of aquatic 

life and the human health criterion for fish consumption. The 

mercury concentration in water samples from all but two tributary sites exceeded the TSWQS criterion for human health 

(fish consumption use). Relatively high mercury concentrations are distributed throughout the study area, which might 

indicate sources in addition to abandoned mining areas; a 

previous study indicated atmospheric deposition as a potential 

source.

Streambed-sediment samples were collected from 12 

sites and analyzed for 44 major and trace elements. Streambed sediment is assessed by the TCEQ in support of aquatic 

life-use protection. Streambed-sediment trace element 

analytical results were compared to TCEQ sediment screening levels. In general, the trace elements that were detected in 

the streambed-sediment samples were low in concentration, 

interpreted as consistent with background concentrations and 

not the result of point-source contamination. Trace-element 

concentrations at two sites, however, were elevated compared 

to TCEQ screening levels or relative to concentrations at other 

sites. Concentrations of antimony, arsenic, cadmium, lead, 

silver, and zinc in the San Carlos Creek sample downstream 

from the San Carlos Mine exceeded the TCEQ screening levels for sediment. The sample from Rough Run Draw, downstream from the Study Butte Mine, also showed higher than 

background concentrations of arsenic, cadmium, and lead, 

but these concentrations were much lower than those in the 

San Carlos Creek sample and did not exceed TCEQ screening levels. Elevated concentrations of multiple trace elements 

in samples from the San Carlos Creek and Rough Run Draw 

sites indicate that San Carlos Creek, and probably Rough Run 

Draw, have been adversely affected by mining activities. 

Fourteen mine-tailing samples from 11 mines in the 

United States and Mexico were analyzed for 25 major and 

trace elements. All 25 trace elements except selenium and 

thallium were detected in one or more of the mine-tailing 

samples. Concentrations of the trace elements for which 

TCEQ has screening levels were compared to those levels. 

Antimony concentrations in tailings at the Waldron Mine, 

San Carlos Mine, and Boquillas Mine exceeded the TCEQ 

sediment screening level for antimony. Arsenic was detected 

in samples from all tailings sites except the Study Butte 2 site. 

Detected concentrations in all but two samples exceeded the 

TCEQ sediment screening level for arsenic. The highest arsenic concentrations were measured in the Boquillas tailings. 

Cadmium was detected at four sites, with the highest concentrations at the San Carlos, Tres Marias, and Puerto Rico 

sites. Cadmium concentrations at four sites exceeded the 

TCEQ sediment screening level for cadmium. Chromium 

was detected in all samples at concentrations less than the 

TCEQ sediment screening level. Copper was detected in 13 

of 14 samples, and concentrations in two of the samples 

(Boquillas and Puerto Rico) exceeded the TCEQ sediment 

screening level. Lead was detected in seven of 14 mine-tailing 

samples. The highest lead concentrations were measured in the 

Boquillas, Puerto Rico, San Carlos, and Tres Marias samples, 

as might be expected because the tailings are from lead mines. 

The concentrations at these sites greatly exceeded the TCEQ 

sediment screening level for lead. Mercury was detected in all 

mine-tailing samples and concentrations exceeded the TCEQ 

sediment screening level in 10 of 14 samples. The highest mercury concentrations were measured in the Mariposa, 

Tres Marias, Study Butte 2, and Two-Forty-Eight tailings 

samples. Nickel was detected in nine of 14 samples, and all 

concentrations were less than the TCEQ screening level. 
References 33

Silver was detected in the San Carlos, Boquillas, and Puerto 

Rico samples; all detected concentrations exceeded the TCEQ 

screening level. Zinc was detected in all mine-tailing samples, 

and the zinc concentrations greatly exceeded the TCEQ 

screening level in the Boquillas, Tres Marias, Puerto Rico, and 

San Carlos samples.

The Toxicity Characteristic Leaching Procedure (TCLP) 

was applied to 14 samples from 11 abandoned mine and mine 

processing sites to determine the leaching potential of antimony, arsenic, barium, beryllium, cadmium, chromium, 

lead, nickel, selenium, and silver. In general, results of the 

analyses indicate that the leaching potential (concentration) 

for most trace elements was less than the TCLP limit. The 

TCLP yielded detectable concentrations for at least one constituent at each mine. The highest TCLP concentrations were 

for cadmium in samples from San Carlos and Tres Marias 

Mines and for lead in samples from Boquillas and San Carlos 

Mines. Cadmium and lead TCLP concentrations in the San 

Carlos Mine tailings and the lead TCLP concentration in the 

Boquillas Mine tailings equaled or exceeded the TCLP limit.

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36 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002 Table 4. Water-quality data from samples collected August 6–9, 2002, in the Big Bend area of the United States and Mexico. [μS/cm, microsiemens per centimeter; °C, degrees Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; MS, main stem; Environ., environmental; TR, tributary; --, not analyzed for or not calculated; SD, standard deviation; SS, specific source; μg/L, micrograms per liter; E, estimated; <, less than] Site no. (fig. 2) Sample identifier1 Sample type Collection date Specific conductance 

(μS/cm 

at 25 °C)

pH 

(units)

Temperature, 

water 

(°C)

Dissolved 

oxygen 

(mg/L)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved 

(mg/L)

Alkalinity 

(mg/L as 

CaCO3

)

Sulfate, 

dissolved 

(mg/L)

Chloride, 

dissolved 

(mg/L)

Dissolved 

solids 

(mg/L)

Main-stem and tributary samples

1 MS-Lajitas Environ. 8/8/2002 1,750 7.7 26.5 6.3 290 34 153 389 225 1,1402 MS-Santa Elena Canyon Environ. 8/6/2002 1,050 7.3 28.0 6.2 290 20 274 264 80 7628 TR-Rough Run Environ. 8/7/2002 1,870 7.4 26.2 6.2 200 12 42 796 12 1,3509 TR-Terlingua Creek Environ. 8/6/2002 1,440 7.5 26.9 6.1 130 16 209 558 9 1,060

11 TR-San Carlos Creek Environ. 8/7/2002 495 8.3 26.4 6.7 67 16 144 102 3 --12 MS-Santa Elena Crossing Environ. 8/6/2002 937 7.5 27.0 6.4 340 24 165 526 47 25514 MS-Woodson’s Environ. 8/8/2002 1,330 7.9 30.4 6.4 290 27 141 352 175 --15 MS-Solis Environ. 8/7/2002 880 7.4 28.0 6.5 360 30 101 270 48 65317 MS-La Clocha Environ. 8/7/2002 881 7.6 29.0 6.1 370 32 105 265 57 64119 MS-Boquillas Canyon Environ. 8/7/2002 918 7.5 29.0 6.1 490 44 125 259 48 77221 TR-Arroyo del Fortino Environ. 8/8/2002 -- -- -- -- 82 25 221 157 54 55623 MS-La Linda Environ. 8/9/2002 936 7.5 27.0 5.8 390 36 133 262 58 657

. . . . . . . Minimum 495 7.3 26.2 5.8 67 12 42 102 3 255. . . . . . . Maximum 1,870 8.3 30.4 6.7 490 44 274 796 225 1,350

Summary statistics2 . . . . . . . Mean 1,135 7.6 27.7 6.3 275 26 151 350 68 785

. . . . . . . Median 937 7.5 27.0 6.2 290 26 143 268 51 710. . . . . . . SD 414 .3 1.34 .3 131 9.4 61.2 193 67 316

Specific-source and quality-assurance samples

22 SS-La Linda Environ. 8/8/2002 -- -- -- -- 63 2.1 105 16 11 185

1 MS-Lajitas Field blank 8/8/2002 -- -- -- -- -- -- -- -- -- --1 MS-Lajitas Duplicate 8/8/2002 -- -- -- -- -- -- -- -- -- --

11 TR-San Carlos Creek Field blank 8/7/2002 -- -- -- -- -- -- -- -- -- --11 TR-San Carlos Creek Duplicate 8/7/2002 -- -- -- -- -- -- -- -- -- --12 TR-Santa Elena Crossing Field blank 8/6/2002 -- -- -- -- -- -- -- -- -- --12 TR-Santa Elena Crossing Duplicate 8/6/2002 -- -- -- -- -- -- -- -- -- --

Table 4
Table 4 37

Table 4. Water-quality data from samples collected August 6–9, 2002, in the Big Bend area of the United States and Mexico—Continued. 

Site no. 

(fig. 2) 

Sample 

identifier1

Sample 

type

Suspended 

solids, 

total 

(mg/L)

Suspended 

solids, 

volatile 

(mg/L)

Nitrogen, 

nitrite plus 

nitrate, 

dissolved

 (mg/L)

Nitrogen, 

ammonia, 

dissolved 

(mg/L)

Phosphorus, 

total 

(mg/L)

Phosphorus, 

total 

orthophosphorus 

(mg/L)

Aluminum, 

dissolved 

(μg/L)

Barium, 

dissolved

(μg/L)

Cadmium, 

dissolved 

(μg/L) 

Main-stem and tributary samples

1 MS-Lajitas Environ. 2,630 330 -- 0.5 1.96 -- 545 172 <0.1

2 MS-Santa Elena Canyon Environ. 3E1,960 -- -- .2 .05 -- 458 128 <.1

8 TR-Rough Run Environ. 25 6 1.14 .2 <.06 <0.04 9.72 53.6 <.1

9 TR-Terlingua Creek Environ. 3E5 -- -- <.02 .06 -- 2.2 66.9 <.1

11 TR-San Carlos Creek Environ. 3E384 -- -- .2 .08 -- 11.4 47.7 1.56

12 MS-Santa Elena Crossing Environ. 3E2,880 -- -- .3 .07 -- 232 112 <.114 MS-Woodson’s Environ. 2,620 290 -- .4 1.97 -- 125 135 <.1

15 MS-Solis Environ. 4,220 770 1.14 .5 .68 <.04 -- -- --

17 MS-La Clocha Environ. 5,130 920 1.15 .7 4.45 <.04 126 106 <.1

19 MS-Boquillas Canyon Environ. 5,550 792 .79 .6 4.21 .24 195 111 <.1

21 TR-Arroyo del Fortino Environ. 20 3 -- .1 <.06 -- 34.7 51.7 .88

23 MS-La Linda Environ. 2,970 250 -- .4 2.52 -- 162 110 <.1

. . . . . . . Minimum 5 3 .79 <.02 <.06 <.04 2.2 47.7 <.1. . . . . . . Maximum 5,550 920 1.15 .7 4.45 .24 545 172 1.56

Summary statistics2 . . . . . . . Mean 2,370 420 1.06 .37 1.6 -- 173 99.4 1.22

. . . . . . . Median 2,265 310 1.14 .4 1.3 -- 126 110 1.22. . . . . . . SD 1,968 361 .2 .2 1.7 -- 181 39.9 .5

Specific-source and quality-assurance samples

22 SS-La Linda Environ. 94 7 -- <.02 <.06 -- <2 52.8 <.1

1 MS-Lajitas Field blank -- -- -- -- -- -- <2 <.5 <.1

1 MS-Lajitas Duplicate -- -- -- -- -- -- 151 175 <.1

11 TR-San Carlos Creek Field blank -- -- -- -- -- -- <2 <.5 <.1

11 TR-San Carlos Creek Duplicate -- -- -- -- -- -- 15.9 48.8 1.87

12 TR-Santa Elena Crossing Field blank -- -- -- -- -- -- <2 <.5 <.112 TR-Santa Elena Crossing Duplicate -- -- -- -- -- -- -- -- --
38 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002 Table 4. Water-quality data from samples collected August 6–9, 2002, in the Big Bend area of the United States and Mexico—Continued. Site no. (fig. 2) Sample identifier1 Sample type Chromium, dissolved 

(μg/L)

Copper, 

dissolved 

(μg/L)

Lead, 

dissolved 

(μg/L)

Mercury, 

total 

recoverable 

(μg/L)

Nickel, 

dissolved 

(μg/L)

Selenium, 

total 

recoverable 

(μg/L)

Silver, 

dissolved 

(μg/L)

Zinc, 

dissolved 

(μg/L)

Carbon, 

total 

organic 

(mg/L)

Main-stem and tributary samples

1 MS-Lajitas Environ. 1.6 1.96 0.26 0.198 3.62 0.95 <0.1 3.12 5.9

2 MS-Santa Elena Canyon Environ. <1 1.56 .24 .0688 3.13 .94 <.1 1.66 4.158 TR-Rough Run Environ. <1 3.03 <.1 .0125 3.53 3.26 <.1 1.35 5.79 TR-Terlingua Creek Environ. 1.73 1.11 <.1 .0063 2.39 3.07 <.1 .89 <2

11 TR-San Carlos Creek Environ. <1 1.21 21 .0359 2 .29 <.1 47.5 11.812 MS-Santa Elena Crossing Environ. <1 1.79 .16 .0819 2.8 1 <.1 41.4 3.7814 MS-Woodson’s Environ. <1 1.7 <.1 .176 3.25 .94 <.1 1.18 <215 MS-Solis Environ. -- -- -- .15 -- .96 -- -- 3.517 MS-La Clocha Environ. <1 1.54 <.1 .189 2.54 1.14 <.1 1.38 4.119 MS-Boquillas Canyon Environ. <1 1.51 .12 .192 2.62 1.19 <.1 1.14 10.321 TR-Arroyo del Fortino Environ. 1.09 2.85 .25 .0007 2.27 .25 <.1 18.6 <223 MS-La Linda Environ. <1 1.43 <.1 .113 2.43 1.05 <.1 1.06 7.4

. . . . . . . Minimum <1 1.11 <.1 .0007 2 .25 <.1 .89 <2. . . . . . . Maximum 1.73 3.03 21 .198 3.62 3.26 <.1 47.5 11.8

Summary statistics2 . . . . . . . Mean 1.47 1.79 3.67 .102 2.78 1.25 -- 10.8 6.29

. . . . . . . Median 1.6 1.56 .25 .0975 2.62 .98 -- 1.38 5.7. . . . . . . SD .3 .6 8.5 .1 .5 .9 -- 17.4 3

Specific-source and quality-assurance samples

22 SS-La Linda Environ. 1.64 .42 <.1 .0013 1.45 2.12 <.1 1.94 9.8

1 MS-Lajitas Field blank <1 <.3 <.1 <.0002 <1 <.1 <.1 3.58 --1 MS-Lajitas Duplicate 1.55 1.93 <.1 .135 3.44 1.09 <.1 1.83 --

11 TR-San Carlos Creek Field blank <1 <.3 <.1 <.0002 <1 <.1 <.1 <.5 --

11 TR-San Carlos Creek Duplicate 1.29 1.31 24.6 .0099 2 .28 <.1 51.6 --12 TR-Santa Elena Crossing Field blank <1 <.3 <.1 .0003 <1 <.1 <.1 .71 --12 TR-Santa Elena Crossing Duplicate -- -- -- .0828 -- 1.02 -- -- --

1 Site name and general location listed in table 2. 2 Only concentrations greater than laboratory reporting level used to compute mean, median, and standard deviation for all constituents.3 Four suspended sediment values flagged as estimated by laboratory because holding times on samples were exceeded prior to analysis (Wayne Belzer, International Boundary and Water Commission, written 

commun., 2008). 
Table 5 39

Table 5. Streambed-sediment data from samples collected August 6–9, 2002, in the Big Bend area of the United States and Mexico.[Bed sediment represents wet-sieved fraction less than 62.5 micrometers in diameter. μg/g, micrograms per gram; MS, main stem; Environ., environmental; TR, tributary; SD, standard deviation; SS, specific source; <, less than; --, not calculated]

Site no. 

(fig. 2)

Sample 

identifier1

Sample 

type

Collection 

date

Calcium, 

total in 

bottom 

material 

(percent)

Magnesium, 

total in bottom material 

(percent)

Potassium, 

total in 

bottom 

material 

(percent)

Sodium, 

total in 

bottom 

material 

(percent)

Phosphorus, 

total in 

bottom 

material 

(percent)

Aluminum, 

total in 

bottom 

material 

(percent)

Antimony, 

total in 

bottom 

material 

(μg/g)

Arsenic, 

total in 

bottom 

material 

(μg/g)

Barium, 

total in 

bottom 

material 

(μg/g)

Beryllium, 

total in 

bottom 

material 

(μg/g)

Main-stem and tributary samples

1 MS-Lajitas Environ. 8/8/2002 10 1.1 2.1 1.0 0.095 6.7 0.82 8.9 500 2.32 MS-Santa Elena Canyon Environ. 8/6/2002 12 .66 1.9 1.6 .064 5.3 .70 8.2 570 2.08 TR-Rough Run Environ. 8/7/2002 15 .88 1.8 .86 .063 5.9 3.5 13 320 1.49 TR-Terlingua Creek Environ. 8/6/2002 8.8 .85 1.6 1.6 .086 6.0 .60 7.4 520 2.5

11 TR-San Carlos Creek Environ. 8/6/2002 7.3 8.2 .19 .02 .039 1.7 420 450 160 .8712 MS-Santa Elena Crossing Environ. 8/6/2002 12 .67 1.6 1.2 .076 5.1 .80 8.0 660 1.714 MS-Woodson’s Environ. 8/8/2002 10 .74 1.8 1.5 .090 5.9 .70 7.4 540 2.015 MS-Solis Environ. 8/7/2002 9.5 .97 1.8 .90 .089 6.4 .80 9.1 440 2.217 MS-La Clocha Environ. 8/7/2002 11 .60 1.8 1.6 .069 5.6 .70 5.7 560 2.019 MS-Boquillas Canyon Environ. 8/7/2002 9.7 .73 1.9 1.2 .071 5.9 .70 8.4 560 1.921 TR-Arroyo del Fortino Environ. 8/8/2002 11 .98 1.9 .99 .077 6.6 1.2 8.0 450 2.023 MS-La Linda Environ. 8/9/2002 10 .74 1.7 1.2 .075 6.0 .80 8.4 540 1.7

. . . . . . . Minimum 7.3 .60 .19 .02 .039 1.7 .60 5.7 160 .87. . . . . . . Maximum 15 8.2 2.1 1.6 .095 6.7 420 450 660 2.5

Summary statistics2. . . . . . . Mean 10 1.36 1.7 1.17 .075 5.6 106 45 485 1.9

. . . . . . . Median 10 .74 1.8 1.2 .076 5.9 .80 8.3 530 2.0. . . . . . . SD 1.9 2.1 .50 .40 .015 1.3 209 127 132 .40

Specific-source and quality-assurance samples 

22 SS-La Linda Environ. 8/8/2002 35 .10 .24 .09 .023 .72 1.0 25 61 32014 MS-Woodson’s Environ. 8/8/2002 9.3 .70 1.6 1.4 .079 5.5 .7 5.8 530 1.919 MS-Boquillas Canyon Environ. 8/7/2002 9.2 .61 2.0 1.5 .065 5.8 .7 5.6 620 2.3

Table 5
40 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002 Table 5. Streambed-sediment data from samples collected August 6–9, 2002, in the Big Bend area of the United States and Mexico—Continued. Site no. (fig. 2) Sample identifier1 Sample type Bismuth, total in bottom material 

(μg/g)

Cadmium, 

total in 

bottom 

material 

(μg/g)

Cerium, 

total in 

bottom 

material 

(μg/g)

Chromium, 

total in 

bottom 

material 

(μg/g)

Cobalt, total in 

bottom 

material 

(μg/g)

Copper, 

total in 

bottom 

material 

(μg/g)

Europium, 

total in 

bottom 

material 

(μg/g)

Gallium, 

total in 

bottom 

material 

(μg/g)

Gold, 

total in 

bottom 

material 

(μg/g)

Holium, 

total in 

bottom 

material 

(μg/g)

Iron, 

total in 

bottom 

material 

(percent)

Main-stem and tributary samples

1 MS-Lajitas Environ. <1 0.35 65 38 9.3 19 1 16 <1 1 2.92 MS-Santa Elena Canyon Environ. <1 .26 70 26 8.5 12 1 14 <1 <1 3.2

8 TR-Rough Run Environ. <1 1.4 50 46 8.4 17 <1 14 <1 <1 2.8

9 TR-Terlingua Creek Environ. <1 .16 52 24 12 16 1 13 <1 <1 2.8

11 TR-San Carlos Creek Environ. 18 240 160 14 39 49 <1 5.4 <1 <1 23

12 MS-Santa Elena Crossing Environ. <1 .31 53 32 8.4 17 1 12 <1 <1 2.9

14 MS-Woodson’s Environ. <1 .26 60 25 9.0 16 1 14 <1 <1 2.9

15 MS-Solis Environ. <1 .35 70 37 10 19 1 16 <1 1 3.117 MS-La Clocha Environ. <1 .27 52 24 7.3 14 1 13 <1 <1 2.5

19 MS-Boquillas Canyon Environ. <1 .29 60 30 7.8 16 1 14 <1 <1 2.8

21 TR-Arroyo del Fortino Environ. <1 .41 59 37 8.8 19 1 15 <1 <1 2.8

23 MS-La Linda Environ. <1 .28 59 34 8.1 16 1 14 <1 <1 2.8

. . . . . . . Minimum <1 .16 50 14 7.3 12 <1 5.4 <1 <1 2.5

. . . . . . . Maximum 18 240 160 46 39 49 1 16 <1 1 23

Summary statistics2. . . . . . . Mean -- 19 68 31 11 19 -- 13 -- -- 4.5

. . . . . . . Median -- .3 60 31 8.7 17 -- 14 -- -- 2.9. . . . . . . SD -- 69 30 8.5 8.8 10 .1 3 -- -- 5.8

Specific-source and quality-assurance samples

22 SS-La Linda Environ. <1 .41 16 6.2 1.6 4.7 <1 3 <1 <1 .54

14 MS-Woodson’s Environ. <1 .28 58 25 8.9 16 1 14 <1 <1 2.8

19 MS-Boquillas Canyon Environ. <1 .26 60 26 7.5 14 1 14 <1 <1 3
Table 5 41

Table 5. Streambed-sediment data from samples collected August 6–9, 2002, in the Big Bend area of the United States and Mexico—Continued. 

Site no. 

(fig. 2)

Sample 

identifier1

Sample 

type

Lanthanum, 

total in 

bottom 

material 

(μg/g)

Lead, 

total in 

bottom 

material 

(μg/g)

Lithium, 

total in 

bottom 

material 

(μg/g)

Manganese, 

total in 

bottom 

material 

(μg/g)

Mercury, 

total in 

bottom 

material 

(μg/g)

Molybdenum, 

total in 

bottom 

material 

(μg/g)

Neodymium, total 

in bottom 

material 

(μg/g)

Nickel, 

total in 

bottom 

material 

(μg/g)

Niobium, 

total in 

bottom 

material 

(μg/g)

Scandium, 

total in 

bottom 

material 

(μg/g)

Selenium, 

total in 

bottom 

material 

(μg/g)

Main-stem and tributary samples

1 MS-Lajitas Environ. 34 18 37 520 0.04 1.6 30 20 30 11 0.62 MS-Santa Elena Canyon Environ. 37 13 20 580 .03 2.1 30 13 21 9.4 .58 TR-Rough Run Environ. 26 59 30 470 .68 1.3 22 21 19 10 .89 TR-Terlingua Creek Environ. 27 13 26 560 .03 1.6 24 16 16 8.4 .5

11 TR-San Carlos Creek Environ. 190 9,500 27 20,000 .06 3.1 23 13 9 3.4 .912 MS-Santa Elena Crossing Environ. 29 15 22 540 .03 2 24 16 22 8.6 .814 MS-Woodson’s Environ. 32 14 23 520 .03 1.5 28 14 27 8.6 .515 MS-Solis Environ. 36 17 35 570 .06 2 31 19 28 11 .617 MS-La Clocha Environ. 28 14 23 460 .02 1.4 24 13 24 7.6 .519 MS-Boquillas Canyon Environ. 32 16 26 490 .03 1.8 28 15 30 8.6 .421 TR-Arroyo del Fortino Environ. 31 19 34 510 .04 1.4 27 18 26 11 .523 MS-La Linda Environ. 32 16 26 470 .29 1.7 27 16 26 9.1 .5

. . . . . . . Minimum 26 13 20 460 .02 1.3 22 13 9 3.4 .4. . . . . . . Maximum 190 9,500 37 20,000 .68 3.1 31 21 30 11 .9

Summary statistics2. . . . . . . Mean 45 810 27 2,141 .11 1.8 27 16 23 8.9 .6

. . . . . . . Median 32 16 26 520 .04 1.7 27 16 25 8.9 .5. . . . . . . SD 46 2,737 5.5 5,624 .2 .50 3 2.8 6 2.1 .1

Specific-source and quality-assurance samples

22 SS-La Linda Environ. 9 19 13 170 .05 65 8 13 18 <2 .2

14 MS-Woodson’s Environ. 31 14 23 530 .03 1.4 28 14 21 7.8 .619 MS-Boquillas Canyon Environ. 32 15 24 530 .02 1.9 27 12 26 8.0 .5
42 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002 Table 5. Streambed-sediment data from samples collected August 6–9, 2002, in the Big Bend area of the United States and Mexico—Continued. Site no. (fig. 2) Sample identifier1 Sample type Silver, total in bottom material 

(μg/g)

Strontium, 

total in 

bottom 

material 

(μg/g)

Tantalum, 

total in 

bottom 

material 

(μg/g)

Thallium, 

total in 

bottom 

material 

(μg/g)

Thorium, 

total in 

bottom 

material 

(μg/g)

Tin, 

total in 

bottom 

material 

(μg/g)

Titanium, 

dry 

weight 

recoverable in 

bottom 

material 

(percent) 

Vanadium, 

total in 

bottom 

material 

(μg/g)

Ytterbium, 

total in 

bottom 

material 

(μg/g)

Yttrium, 

total in 

bottom 

material 

(μg/g)

Zinc, 

total in 

bottom 

material 

(μg/g)

Uranium, 

total in 

bottom 

material 

(μg/g)

Main-stem and tributary samples

1 MS-Lajitas Environ. 0.31 460 2 <1 10 2 0.40 88 2 21 88 3.02 MS-Santa Elena Canyon Environ. .20 600 1 <1 7 2 .73 97 2 20 80 2.38 TR-Rough Run Environ. .30 800 <1 <1 8 2 .28 81 2 15 140 2.69 TR-Terlingua Creek Environ. .20 570 <1 <1 7 1 .4 68 2 17 62 2.3

11 TR-San Carlos Creek Environ. 24 250 <1 2 3 27 .097 47 <1 10 12,000 7.5

12 MS-Santa Elena Crossing Environ. .20 630 1 <1 8 2 .57 89 2 18 76 2.6

14 MS-Woodson’s Environ. .30 580 1 <1 7 2 .54 83 2 19 73 2.415 MS-Solis Environ. .30 480 1 <1 10 3 .48 96 2 23 88 3.017 MS-La Clocha Environ. .30 600 <1 <1 7 2 .46 72 2 18 66 2.419 MS-Boquillas Canyon Environ. .30 470 <1 <1 9 2 .48 80 2 19 79 2.921 TR-Arroyo del Fortino Environ. .30 480 1 <1 9 3 .39 88 2 20 84 3.023 MS-La Linda Environ. .30 480 1 <1 9 2 .47 83 2 19 75 2.8

. . . . . . . Minimum .20 250 <1 <1 3 1 .10 47 <1 10 62 2.3

. . . . . . . Maximum 24 800 2 2 10 27 .7 97 2 23 12,000 7.5

Summary statistics2. . . . . . . Mean 2.2 533 -- -- 8 4 .44 81 2 18 1,076 3.1

. . . . . . . Median .30 525 -- -- 8 2 .47 83 2 19 80 2.7. . . . . . . SD 6.9 132 -- -- 2 7 .2 14 .2 3 3,440 1.4

Specific-source and quality-assurance samples

22 SS-La Linda Environ. .20 480 1 <1 2 1 .044 18 <1 9 64 5.8

14 MS-Woodson’s Environ. .30 590 <1 <1 8 2 .46 82 2 20 72 2.5

19 MS-Boquillas Canyon Environ. .30 460 <1 <1 8 3 .57 79 2 19 84 2.7

1 Site name and general location listed in table 2. 2 Only concentrations greater than laboratory reporting level used to compute mean, median, and standard deviation for all constituents.
Table 6 43

Table 6. Mine-tailing data from samples collected August 5–15, 2002, in the Big Bend area of the United States and Mexico. [mg/kg, milligrams per kilogram; <, less than; SD, standard deviation; --, not calculated]

Site no. 

(fig. 2)

Sample 

indentifier1

Collection 

date

Calcium, 

total 

(mg/kg)

Magnesium, 

total 

(mg/kg)

Potassium, total 

(mg/kg)

Sodium, 

total 

(mg/kg)

Aluminum, 

total 

(mg/kg)

Antimony, 

total 

(mg/kg)

Arsenic, 

total 

(mg/kg)

Barium, 

total 

(mg/kg)

Beryllium, total 

(mg/kg)

Cadmium, 

total 

(mg/kg)

Chromium, total 

(mg/kg)

Cobalt, 

total 

(mg/kg)

Copper, 

total 

(mg/kg)

3 Waldron 8/5/2002 273,000 1,440 1,190 198 9,900 46 125 4,190 2 <4 10 6 13

4 Mariposa 8/7/2002 171,000 1,930 2,800 445 15,500 <19 94 916 <.8 <3 16 5 75a Chisos 1 8/5/2002 205,000 3,340 2,800 343 19,400 <20 23 81 <.9 <3 23 5 245b Chisos 2 8/5/2002 226,000 3,050 2,890 313 25,100 <22 48 134 <.9 <3 22 5 216 248 8/5/2002 143,000 6,960 1,630 2,240 8,950 <17 52 44 <.7 <3 17 6 247a Study Butte 1 8/5/2002 22,900 348 1,390 679 5,570 <5 19 55 .78 <.8 2 1 107b Study Butte 2 8/5/2002 39,500 752 1,380 1,700 4,920 <6 <6 31 1.3 <.9 4 1 23

10 San Carlos 8/6/2002 95,400 93,100 <411 84 15,500 109 438 52 <2 280 12 39 6113 Tres Marias 8/15/2002 214,000 1,880 2,110 322 5,020 <22 811 7.35 <1 215 6.7 <2 119

16 Mariscal 8/8/2002 178,000 2,550 3,940 242 17,000 <24 45 107 3.6 <4 21 8 18

18 Boquillas 8/8/2002 86,200 3,250 5,640 2,100 16,500 43 1,250 2,800 <1 24 12 25 1,78020 Puerto Rico 8/8/2002 248,000 9,470 1,660 92.2 6,000 <40 365 245 <2 409 6.7 9 2,31022a La Linda 1 8/8/2002 189,000 1,200 2,460 1,390 7,480 <27 36 46 189 <4 9.1 <2 4

22b La Linda 2 8/8/2002 310,000 571 <328 535 7,170 <30 46 14 248 <4 4.9 <2 <4

 . . . Minimum 22,900 348 1,190 84 4,920 43 19 7 .78 24 2 1 4 . . . Maximum 310,000 93,100 5,640 2,240 25,100 109 1,250 4,190 248 409 23 39 2,310

Summary statistics2 . . . Mean 171,500 9,274 2,490 763 11,715 -- 258 623 89 232 12 10 339

 . . . Median 183,500 2,240 2,285 394 9,425 -- 52 68 4 248 11 6 23 . . . SD 85,470 24,260 1,280 758 6,377 -- 378 1,268 120 160 7 12 765

Table 6
44 Quality of Water and Sediment in Streams Affected by Historical Mining, United States and Mexico, August 2002 Table 6. Mine-tailing data from samples collected August 5–15, 2002, in the Big Bend area of the United States and Mexico—Continued. Site no. (fig. 2) Sample indentifier1 Iron, total (mg/kg) Lead, total (mg/kg) Manganese, total (mg/kg) Mercury, total (mg/kg) Molybdenum, total (mg/kg) Nickel, total (mg/kg) Selenium, total (mg/kg) Silver, total (mg/kg) Thallium, total (mg/kg) Tin, total (mg/kg) Vanadium, total (mg/kg) Zinc, total (mg/kg)

3 Waldron 24,900 <21 440 81 12 21 <27 <1.2 <38 <19 49 69

4 Mariposa 15,800 <15 170 966 <6 16 <19 <1.2 <27 <13 38 54

5a Chisos 1 13,800 <16 120 6.4 9.6 39 <21 <1.3 <29 <15 101 103

5b Chisos 2 14,700 <18 130 30 7.9 32 <23 <1.4 <32 <16 110 101

6 248 211,000 <14 260 136 12 31 <18 <1.1 <25 <12 106 86

7a Study Butte 1 40,400 8 150 53 9.6 3.5 <5.3 <.33 <7.5 3.9 5 57

7b Study Butte 2 35,100 7 340 173 6.5 <2 <6.1 <.38 <8.6 <4 7 62

10 San Carlos 216,000 10,000 18,600 .08 <13 <13 <38 28.8 <54 <27 43 15,00013 Tres Marias 67,200 3,070 200 176 23 <8 <22 <1.4 <32 <16 20 84,400

16 Mariscal 19,900 <19 440 47 <8 34 <24 <1.5 <34 <17 125 181

18 Boquillas 100,000 67,900 700 .14 195 28 <25 84.5 <35 <17 56 90,40020 Puerto Rico 24,300 52,700 1,200 11 <13 19 <40 39.6 <57 <28 19 75,10022a La Linda 1 5,200 22.3 200 .16 175 <10 <28 <1.7 <39 <20 20 54

22b La Linda 2 5,760 <24 350 .3 297 <11 <30 <1.9 <43 <21 25 28

 . . . . . Minimum 5,200 7 120 .08 7 3.5 -- 28.8 -- 3.9 5 28 . . . . . Maximum 216,000 67,900 18,600 966 297 39 -- 84.5 -- 3.9 125 90,400

Summary statistics2 . . . . . Mean 56,720 19,100 1,660 168 75 25 -- -- -- -- 52 18,978

 . . . . . Median 24,600 3,070 300 120 12 28 -- -- -- -- 41 94 . . . . . SD 71,170 28,700 4,880 38 107 11 -- -- -- -- 42 35,212

1 Site name and general location listed in table 2. 2 Only concentrations greater than laboratory reporting level used to compute summary statistics for all constituents.
Table 7 45

Table 7. Toxicity Characteristic Leaching Procedure leaching potential (concentrations) for mine-tailing samples collected August 5–15, 2002 (table 6) in the Big Bend area of the United States and Mexico. [mg/L, milligrams per liter; <, less than] 

Site no. 

(fig. 2)

Sample 

identifier1

Collection 

date

Antimony 

(mg/L)

Arsenic 

(mg/L)

Barium 

(mg/L)

Beryllium 

(mg/L)

Cadmium 

(mg/L)

Chromium 

(mg/L)

Lead 

(mg/L)

Nickel 

(mg/L)

Selenium 

(mg/L)

Silver 

(mg/L)

3 Waldron 8/5/2002 <0.052 0.211 0.552 <0.002 <0.008 0.006 <0.042 <0.019 <0.053 <0.0034 Mariposa 8/7/2002 <.052 .239 .175 <.002 <.008 <.004 <.042 <.019 <.053 <.0035a Chisos 1 8/5/2002 <.052 <.049 .131 <.002 <.008 <.004 <.042 <.019 <.053 <.0035b Chisos 2 8/5/2002 <.052 <.049 .116 <.002 <.008 <.004 <.042 <.019 0.056 <.0036 248 8/5/2002 <.052 <.049 .024 <.002 <.008 <.004 <.042 .025 <.053 <.0037a Study Butte 1 8/5/2002 <.052 <.049 .028 .003 <.008 <.004 <.042 <.019 <.053 <.0037b Study Butte 2 8/5/2002 <.052 <.049 .020 .006 <.008 <.004 <.042 <.019 <.053 <.003

10 San Carlos 8/6/2002 <.052 <.049 .019 <.002 6.50 <.004 15.5 .037 <.053 <.00313 Tres Marias 8/15/2002 <.052 <.049 .023 <.002 1.00 <.004 1.17 .023 <.053 <.00316 Mariscal 8/8/2002 <.052 .139 .262 <.002 <.008 <.004 <.042 <.019 <.053 <.00318 Boquillas 8/8/2002 .404 2.13 1.42 <.002 .187 <.004 120 .135 <.053 <.00320 Puerto Rico 8/8/2002 <.052 <.049 .600 <.002 .493 <.004 1.53 <.019 <.053 <.00322a La Linda 1 8/8/2002 <.052 .050 .233 <.002 <.008 <.004 <.042 <.019 <.053 <.00322b La Linda 2 8/8/2002 <.052 <.049 .136 <.002 <.008 <.004 <.042 <.019 <.053 <.003

1 Site name and general location listed in table 2. 

Table 7
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