U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2013–1190

Prepared in cooperation with the U.S. Army Corps of Engineers, New Mexico Interstate Stream 

Commission, and New Mexico Environment Department

Knowledge and Understanding of Dissolved Solids in the Rio 

Grande–San Acacia, New Mexico, to Fort Quitman, Texas, 

and Plan for Future Studies and Monitoring
 
Knowledge and Understanding of Dissolved 

Solids in the Rio Grande–San Acacia, New 

Mexico, to Fort Quitman, Texas, and Plan 

for Future Studies and Monitoring

By Douglas L. Moyer, Scott K. Anderholm, James F. Hogan, Fred M. Phillips, 

Barry J. Hibbs, James C. Witcher, Anne Marie Matherne, and Sarah E. Falk

Prepared in cooperation with the U.S. Army Corps of Engineers, New Mexico 

Interstate Stream Commission, and New Mexico Environment Department

Open-File Report 2013–1190

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

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

Suggested citation:

Moyer, D.L., Anderholm, S.K., Hogan, J.F., Phillips, F.M., Hibbs, B.J., Witcher, J.C., Matherne, A.M., and Falk, S.E., 

2013, Knowledge and understanding of dissolved solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, 

Texas, and plan for future studies and monitoring: U.S. Geological Survey Open-File Report 2013–1190, 55 p., 

http://pubs.usgs.gov/of/2013/1190/. 

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iii

Contents

Executive Summary ......................................................................................................................................1

Introduction ....................................................................................................................................................3

Purpose and Scope .............................................................................................................................6

Description of the Rio Grande Study Area ...............................................................................................6

Climate ...................................................................................................................................................6

Streamflow in the Rio Grande Study Area .......................................................................................6

Alluvial-Fill Basins ................................................................................................................................7

Water Use .............................................................................................................................................8

Factors Affecting Dissolved Solids ............................................................................................................9

Concentration .......................................................................................................................................9

Concentration and Load .....................................................................................................................9

Load ........................................................................................................................................................9

Spatial and Temporal Variability in Dissolved-Solids Transport .........................................................10

Streamflow ..........................................................................................................................................10

Spatial Variability in Streamflow ............................................................................................10

Temporal Variability in Streamflow ........................................................................................11

Summary of Streamflow Conditions ......................................................................................12

Dissolved-Solids Concentration ......................................................................................................13

Spatial Variability in Dissolved-Solids Concentration ........................................................15

Temporal Variability in Dissolved-Solids Concentration ....................................................17

Spatial and Temporal Variability in Ion Composition ..........................................................19

Summary of Dissolved-Solids Concentrations ....................................................................19

Dissolved-Solids Loads .....................................................................................................................21

Spatial Variability in Dissolved-Solids Loads .......................................................................22

Temporal Variability in Dissolved-Solids Loads ...................................................................23

Summary of Dissolved-Solids Loads .....................................................................................24

Dissolved-Solids Flow-Weighted Concentrations ........................................................................24

Data Gaps: Dissolved-Solids Concentrations and Loads ............................................................26

Dissolved-Solids Budgets ..........................................................................................................................28

Basic Budgets ....................................................................................................................................28

Complex Budgets ...............................................................................................................................30

Summary of Dissolved-Solids Budgets ..........................................................................................37

Data Gaps: Dissolved-Solids Budgets ............................................................................................37

Location of Areas with High Concentrations of Dissolved Solids ......................................................39

Socorro Basin .....................................................................................................................................39

San Marcial Basin .............................................................................................................................41

Engle Basin .........................................................................................................................................41

Palomas Basin ....................................................................................................................................41

Mesilla Basin ......................................................................................................................................41

Hueco Basin ........................................................................................................................................42

Future Studies and Monitoring Data .......................................................................................................43

Monitoring of Dissolved Solids ........................................................................................................43

Rio Grande and Agricultural Drain Monitoring ....................................................................43
iv

Groundwater/Surface-Water Interaction Investigation .....................................................44

Groundwater Monitoring .........................................................................................................44

Focused Hydrogeology Studies at Inflow Sources ......................................................................44

Helicopter Electromagnetic-Resistivity Data .......................................................................44

Hydrogeological and Tectonic Characterization at Inflow-Source Regions ..................45

Model Development for Dissolved-Solids Transport in the Rio Grande ...................................45

Fate and Transport of Dissolved Solids in Elephant Butte and Caballo Reservoirs .......45

Improved Mass-Balance Budgets for Rio Grande Dissolved Solids ...............................47

References Cited .........................................................................................................................................47

Appendixes 

1. Average annual and seasonal streamflow and dissolved solids concentration, 

flow-weighted concentration and load for monitoring stations along the Rio 

Grande between San Marcial, New Mexico and Fort Quitman Texas .............................53

2. Description of groundwater regions, in the Rio Grande study area, with unusually 

high concentration of dissolved solids and/or chloride ......................................................54

3. Description of gains and losses in Rio Grande streamflow and flux of dissolved 

solids from inflowing groundwater for each reach of the Rio Grande .............................55

Figures

1. Map showing the Rio Grande study area (white area) and the distribution of the 

six alluvial-fill basins underlying the Rio Grande: (1) Socorro, (2) San Marcial, 

(3) Engle, (4) Palomas, (5) Mesilla, and (6) Hueco Basins .....................................................5

2. Schematic hydrogeologic cross section of the Rio Grande Rift, parallel to the 

path of the river ............................................................................................................................7

3. Annual mean streamflow measured at selected monitoring stations along the 

Rio Grande from 1934 to 1963 ...................................................................................................11

4. Boxplot of streamflow data collected from the Rio Grande at San Marcial and 

El Paso (Courchesne Bridge) from 1897 to 1908 by Stabler (1911) ....................................12

5. Plot of annual streamflow measured in the Rio Grande at (A) San Marcial 

and (B) below Elephant Butte Dam (EB), below Caballo Dam (CAB), above 

Leasburg Dam (LEA), at El Paso (EP) and at Fort Quitman (FQ) from 1934 to 1963 ..........13

6. Boxplot of streamflow conditions during the nonirrigation (NON) and irrigation 

(IRR) season at selected sites in the Rio Grande study area from 1934 to 1999 .............14

7. Boxplot showing dissolved-solids concentration at selected sites in the Rio 

Grande study area from 1934 to 1999 .....................................................................................15

8. Plot of dissolved-solids concentration collected during the winter and summer 

2000–3 from the headwaters in Colorado to Fort Quitman, Texas .....................................16

9. Plot showing the locally weighted scatter plot smoothing curve from the Rio 

Grande at San Marcial, El Paso, and Fort Quitman ..............................................................17

10. Boxplot of dissolved-solids concentration during the nonirrigation (NON) and 

irrigation (IRR) seasons at selected sites in the Rio Grande study area from 

1934 to 1999 .................................................................................................................................18

11. Piper diagram of average decadal chemistry from the decades 1905–2000 for 

three Rio Grande stations: Otowi, San Marcial, and El Paso .............................................20
v

 12. Piper diagram of average decadal chemistry of water samples collected from 
vi

Tables

1. Mass balance for the monthly average dissolved solids transported in the Rio 

Grande between (1) San Acacia to San Marcial (SA to SM), (2) San Marcial to 

below Elephant Butte Dam (SM to EB), (3) below Elephant Butte Dam to below 

Caballo Dam (EB to CAB), and (4) below Caballo Dam to El Paso (Courchesne) 

(CAB to EP) for each decade from 1930–99 ...........................................................................38

2. Mass balance for annual average dissolved solids transported in the Rio Grande 

between El Paso and Fort Quitman during 1969–89 .............................................................39

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

acre 0.004047 square kilometer (km2

)

Volume

cubic foot (ft3

) 0.02832 cubic meter (m3) 

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

)

Flow rate

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

/s)

cubic foot per second (ft3

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

Mass

ton, short (2,000 lb) 0.9072 megagram (Mg) 

ton, long (2,240 lb) 1.016 megagram (Mg) 

ton per day (ton/d) 0.9072 metric ton per day

ton per day (ton/d) 0.9072 megagram per day (Mg/d)

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

°F=(1.8×°C)+32

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

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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

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

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

25 °C).

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

or micrograms per liter (μg/L).

Knowledge and Understanding of Dissolved Solids in the 

Rio Grande–San Acacia, New Mexico, to Fort Quitman, 

Texas, and Plan for Future Studies and Monitoring

By Douglas L. Moyer,1 Scott K. Anderholm,1 James F. Hogan,2 Fred M. Phillips,3 Barry J. Hibbs,4

James C. Witcher,5

 Anne Marie Matherne,1 and Sarah E. Falk1

Executive Summary

Both quantity and quality of water in the Rio Grande 

have long been a primary concern for water-resource 

managers. The transport and delivery of water in the basin 

has been engineered, using reservoirs, irrigation canals and 

drains, and transmountain-water diversions to ensure an 

adequate water supply to meet the agricultural, residential, 

and industrial demand. In contrast, despite the widespread 

recognition of critical water-quality problems, there have 

been minimal management efforts to improve water quality 

in the Rio Grande. Of greatest concern is salinization 

(concentration of dissolved solids approaching 1,000 

milligrams per liter [mg/L]), a water-quality problem that 

has been recognized and researched for more than 100 

years because of the potential to limit both agricultural and 

municipal use. 

In order to address the issue of salinization, waterresource managers need to (1) have a clear conceptual 

understanding of the sources of salinity and the factors 

that control storage and transport, (2) identify critical 

knowledge gaps in this conceptual understanding, and 

(3) develop a research plan to address these gaps and 

develop a salinity management program. As a result, the 

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

Corps of Engineers, New Mexico Interstate Stream 

Commission, and New Mexico Environment Department 

undertook this effort to summarize the current state of 

knowledge regarding the transport of dissolved solids in 

the Rio Grande between San Acacia, New Mexico, and 

Fort Quitman, Texas. This effort specifically focused on the 

following three questions:

1. What is the spatial and temporal variability present in the 

concentrations and loads of dissolved solids in the Rio 

Grande?

2. What is the source-specific budget for the mass of 

dissolved solids transported along the Rio Grande?

3. Where do new dissolved solids enter the Rio Grande?

Dissolved-solids concentration data provide a good 

indicator of the general quality of surface water and provide 

information on the factors governing salinization within 

the Rio Grande study area. The pattern in dissolved-solids 

concentrations along the Rio Grande is one of increasing 

concentration with increasing distance downstream from 

Elephant Butte and Caballo Reservoirs. The concentration of 

dissolved solids in the Rio Grande doubles (approximately 

500 to 1,000 mg/L) from below Elephant Butte Reservoir 

to El Paso and increases by more than a factor of 5 

(approximately 500 to 3,200 mg/L) from below Elephant 

Butte Reservoir to Fort Quitman. Studies that have focused 

on dissolved solids in the Rio Grande study area can be 

categorized into three major groups, which are: (1) identifying 

the sources of dissolved solids; (2) characterizing surfacewater processes that control the transport of dissolved solids, 

and (3) defining the role that groundwater processes play in 

controlling transport of dissolved solids.

Sources of dissolved solids have been investigated using 

three methods (1) synoptic sampling to identify locations 

where concentration increases, (2) spatial and temporal 

patterns within dissolved-solids loads, and (3) source 

determination through isotopic fingerprinting studies. During 

the past century, studies have investigated the hydrology/

hydrogeology and associated water-quality conditions 

along the Rio Grande and underlying alluvial basins from 

San Acacia to Fort Quitman. During these investigations, 

researchers have identified areas of surface water and(or) 

groundwater that contain unusually high concentrations of 

1

U.S. Geological Survey

2

Department of Hydrology and Water Resources, University of Arizona;

New Mexico Environment Department (current affiliation)

3

Department of Earth and Environmental Science, New Mexico Institute of 

Mining and Technology

4

Department of Geological Sciences, California State University

5

Witcher and Associates
2 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

dissolved solids or associated water-quality constituents. 

These areas have the potential to contribute significant 

amounts of dissolved solids to the Rio Grande and need to be 

considered for future investigations and(or) future locations 

of dissolved-solids mitigation efforts. Marked increases in the 

concentration of dissolved solids commonly coincide with 

contributions from agricultural drains, wastewater-treatment 

plants, regional groundwater, and upward-flowing saline 

groundwater. The locations of these areas containing elevated 

dissolved-solids concentration have been provided for the 

Socorro, San Marcial, Engle, Palomas, Mesilla, and Hueco 

Basins and include the (1) northern end of the Socorro Basins; 

(2) area surrounding Truth or Consequences, New Mexico; 

(3) southern end of the Palomas Basin through the northern 

end of the Mesilla Basin; (4) eastern and southern portions 

of the Mesilla Basin; and (5) area southeast of the El PasoHudspeth County line near Fabens. 

The greatest factor, from the surface-water system, in 

controlling dissolved solids in the Rio Grande is the amount 

of water that is being transported or stored. Annual mean 

streamflow in the Rio Grande decreased on average by 840 

cubic feet per second during 1934 and 1963, between San 

Marcial and Fort Quitman. Annual variation in streamflow 

is influenced primarily by climate (precipitation and 

evaporation) and management of Elephant Butte and Caballo 

Reservoirs (water storage and release cycles). Seasonal 

variation in streamflow within the Rio Grande study area is 

most evident at monitoring stations below Elephant Butte 

Reservoir. Streamflow conditions in this section of the river 

are categorized generally as irrigation (March–September) and 

nonirrigation (October–February) seasons. 

Streamflow in the Rio Grande is highest during the 

irrigation season and lowest during the nonirrigation season. 

As a result, dissolved-solids concentrations vary from season 

to season with the concentration of dissolved solids in the 

Rio Grande between Caballo Dam and El Paso commonly 

twice as high during the nonirrigation season as compared 

with concentrations during irrigation season. Dissolved-solids 

loads during the irrigation season decrease by approximately 

1,000 tons per day in the Rio Grande between Leasburg 

and Fort Quitman. These decreases in load are attributed 

primarily to irrigation diversions and losses to the underlying 

alluvial aquifer. Conversely, dissolved-solids loads during 

the nonirrigation season increase by nearly 900 tons per day 

between Caballo Dam and Fort Quitman. These increases 

in load are attributed to the inflow of dissolved solids 

from agricultural drains, wastewater-treatment plants, and 

groundwater with elevated concentrations of dissolved solids.

Seasonal variability in dissolved-solids loads also 

provides information on the critical role that the shallow 

groundwater system plays in the transport of dissolved solids 

in the Rio Grande in the study area. During the irrigation 

season dissolved-solids loads generally decrease between 

Leasburg and Fort Quitman primarily as a result of water 

being diverted from the Rio Grande to meet agricultural 

water-supply needs. Much of the dissolved-solids load carried 

by the diverted water infiltrates the shallow alluvial aquifer 

and subsequently is intercepted by agricultural drains and 

returned to the Rio Grande. However, in areas of extensive 

groundwater pumping, these dissolved solids are drawn deeper 

into the alluvial aquifer system and threaten the quality of 

the groundwater resource. During the nonirrigation season, 

dissolved-solids loads increase between Leasburg and Fort 

Quitman because of inflow from saline groundwater (Leasburg 

to El Paso) and freshwater dissolution of evaporite beds 

(El Paso to Fort Quitman). It is essential for water-resource 

managers to understand how groundwater transport processes 

collectively govern the transport of dissolved solids in the Rio 

Grande and how these processes influence the potential for 

salinity-mitigation efforts. 

Many studies have mass-balance budgets that account 

for the mass of dissolved solids transported along the Rio 

Grande. Two types of budgets for dissolved-solids transport 

in the Rio Grande have been developed since the early 

1900s. Basic budgets define the relation between the mass of 

dissolved solids transported by the Rio Grande into a specified 

reach to the mass of dissolved solids transported out of the 

specified reach. Complex budgets attempt to account for all 

sources (such as tributaries, agricultural drains, municipal 

wastewater effluent, mineral dissolution, and groundwater 

discharge) and sinks (e.g. irrigation canals, groundwater 

recharge, and mineral precipitation) of dissolved solids, such 

that mass balance between the inflows to and outflows from 

a specified reach of the Rio Grande equals zero. Results 

from the two types of budgets developed for dissolved solids 

indicate that (1) the inflow of saline groundwater, inflow of 

regional groundwater, and chemical reactions between mineral 

phases are the primary sources controlling dissolved solids in 

the Rio Grande, and (2) groundwater pumping and mineral 

precipitation are causing a net storage of dissolved solids in 

the Leasburg to El Paso and El Paso to Fort Quitman reaches 

of the Rio Grande. 

Historical dissolved-solids data in the Rio Grande study 

area provide good information for determining the associated 

spatial and temporal variations and defining preliminary 

budgets; however, these data also facilitate the determination 

of data and knowledge gaps. Primary data gaps are the lack of 

coupled long-term streamflow and water-quality monitoring 

in the Rio Grande and major agricultural drains and limited 

groundwater seepage data (groundwater and surface-water 

interactions) outside of the Mesilla Basin. The initiation 

and continuation of these monitoring data are essential for 

(1) improving the current understanding of dissolved-solids 

transport in the Rio Grande study area; (2) establishing 

water-quality goals; (3) building tools/models for waterresource managers to more effectively manage water-quality 

conditions; and (4) assessing changes in water-quality 

conditions in the Rio Grande resulting from salinity mitigation 

efforts. Critical knowledge gaps exist in (1) understanding 

the hydrologic controls that govern the transport of elevated 

dissolved solids from known groundwater sources to the Rio 

Grande and how these controls influence the potential for 
Introduction 3

interception or other mitigation efforts and (2) understanding 

the linkage between the surface-water, irrigation, and 

groundwater in the shallow alluvial aquifer systems and how 

changes in water-management and(or) climate may influence 

the quality of groundwater and surface water in the Rio 

Grande study area. 

Looking forward, multiple water-resource managers 

from state and local agencies in New Mexico and Texas as 

well as many federal agencies have united to form the Rio 

Grande Salinity Management Coalition. The unifying goal for 

the Coalition is to reduce the amount of dissolved solids that 

are transported and stored in the Rio Grande study area; thus, 

ensuring that the Rio Grande water resources are of the quality 

that promotes the integrity and vitality of the agricultural, 

municipal, and ecological communities. The recommendations 

for additional monitoring for focused hydrogeology studies 

of the source of inflowing groundwater with elevated 

concentrations of dissolved-solids and model development for 

dissolved-solids transport will assist the Coalition in planning 

for, implementing, and evaluating mitigation efforts for 

dissolved solids in the Rio Grande. These recommendations 

are as follows: 

• Monitoring:

• Couple water-quality and streamflow monitoring in 

the Rio Grande and agricultural drains; undertaking 

this effort will further improve the current 

understanding of dissolved-solids transport and 

allow for (1) establishment of water-quality goals, 

(2) improved quantification of dissolved-solids 

loads, and (3) determination of long-term trends of 

dissolved-solids concentrations and dissolved-solids 

loads.

• Perform groundwater-seepage investigations in the 

Rio Grande and major agricultural drains; the result 

of this effort will be the ability to quantify the flux 

of dissolved solids being delivered to and from the 

underlying alluvial aquifer.

• Monitor groundwater water-quality conditions in the 

Mesilla and Hueco Basins; supporting this effort will 

allow for (1) quantification of current water-quality 

conditions, (2) evaluation of temporal and spatial 

changes in water-quality conditions, and (3) the 

potential to forecast future water-quality conditions 

based on changes in municipal and agricultural water 

demands within the Mesilla and Hueco Basins.

• Focused Hydrogeology Studies at Inflow Sources:

• Map dissolved-solids concentrations in the Rio 

Grande and underlying alluvial aquifer using 

technology such as helicopter electromagnetic 

resistivity data; undertaking this effort will provide 

high-resolution 3-dimensional maps defining the 

spatial extent of areas containing unusually high 

concentrations of dissolved solids.

• Perform hydrogeologic characterization of 

subsurface areas containing unusually high 

concentrations of dissolved solids; undertaking 

this type of study will provide critical information 

regarding subsurface-flow paths and the underlying 

geology that governs the movement of dissolved 

solids. Additionally, this type of study will provide 

information on how the underlying geologic 

structure and flow paths may influence the potential 

to intercept and mitigate the inflowing saline 

groundwater.

• Modeling of Dissolved Solids: 

• Develop models to simulate the transport and 

storage of dissolved solids in both surface-water 

and groundwater systems; undertaking this effort 

will provide models to evaluate the impacts that 

surface-water management, groundwater pumping, 

and climate variability have on dissolved-solids 

transport in the Rio Grande and underlying alluvial 

basins. Additionally, information provided by these 

newly developed models and the data-collection 

effort listed above will be used to refine the current 

mass-balance budgets for dissolved-solids transport 

in the Rio Grande.

Introduction

Availability of water in the Rio Grande Basin has 

long been a primary concern for water-resource managers. 

The transport and delivery of water in the basin has been 

engineered using reservoirs, irrigation canals and drains, 

and transmountain-water diversions to meet agricultural, 

residential, and industrial water-supply needs. Annual delivery 

of water to surrounding agricultural, residential, and industrial 

users is critical to ensure the associated social and economic 

vitality of these communities (Jackson and others, 2001). The 

quantity and quality of the water supply are factors that often 

limit the ability of water-resource managers to meet the evergrowing water-supply requirements. 

The quantity of surface water available to meet various 

water-supply demands is influenced by many factors, 

including climate, population growth, and agricultural 

cropping patterns. Runoff from annual snow accumulation 

and summer monsoons serves as the primary source of water 

in the Rio Grande Basin; however, during extended periods of 

drought, runoff usually is inadequate to fully meet allocated 

water-supply needs (Booker and others, 2005). Added pressure 

to the quantity of surface water available for water supply 

is applied through population growth in Albuquerque, Las 

Cruces, El Paso, and Ciudad Juarez, as well as the replacement 

of agricultural crops, such as chilies, with crops that have 

greater water requirements, such as pecans. Nearly all of the 

water transported down the Rio Grande from the headwaters 
4 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

in Colorado is evaporated, consumed by the various watersupply demands, or lost to the underlying alluvial aquifer 

by the time the river reaches Fort Quitman, Texas (Rister 

and others, 2011). The combined effect of dry climate, 

population growth, and changes in agricultural cropping 

pattern causes the surrounding surface-water-users to become 

increasingly dependent on groundwater to meet the growing 

water demand. 

Water quality also is a primary factor that can limit the 

availability of water for use within the Rio Grande Basin. The 

concentration of dissolved solids is a common measurement 

variable used to assess the general quality of water in riverine 

systems and provides a measure for the amount of dissolvedorganic and inorganic compounds that are present in the water 

column. The majority of the dissolved-solids concentration in 

riverine systems consists of major ions, such as bicarbonate, 

calcium, chloride, magnesium, potassium, silica, sodium, 

and sulfate (Hem, 1992; Anning and others, 2007). These 

major ions occur naturally and are essential for plant and 

animal growth (Anning and others, 2007). However, elevated 

dissolved-solids concentrations may be detrimental to plant 

and animal species within an aquatic ecosystem and can result 

in reduced productivity of agricultural crops and increased 

costs for municipal and residential water treatment and use 

(Anning and others, 2007).

Concentrations of dissolved solids in riverine systems 

increase through concentrative or additive processes. 

Concentrative processes remove water from a riverine 

system but leave behind dissolved solids, which results in 

an increased concentration. Evaporation and transpiration 

are concentrative processes that increase dissolved-solids 

concentrations. Additive processes transport additional 

dissolved solids into a riverine system and can be categorized 

into three groups: (1) cyclical and surficial salts, (2) inflow 

of saline groundwater, and (3) anthropogenic salt inputs 

(Phillips and others, 2003; Anning and others, 2007; Hogan 

and others, 2007). Cyclical and surficial salts are delivered to 

riverine systems through atmospheric precipitation (rainfall 

and snowfall) and subsequent dissolution of salts accumulated 

on the land surface and in the soil. Saline groundwater 

contains elevated concentrations of dissolved-solids that 

originate from geothermal or nongeothermal sources. Saline 

groundwater can be derived from the dissolution of evaporite 

deposits, such as ancestral playa beds (Hibbs and Merino, 

2007) and gypsum and calcite (Witcher and others, 2004; 

Bastien, 2009), sedimentary brines of connate or diagenetic 

origin (Phillips and others, 2003; Witcher and others, 2004; 

Hogan and others, 2007), or geothermal processes (Bothern, 

2003; Witcher and others, 2004). Anthropogenic salt inputs 

are derived from a number of sources in agricultural, 

residential, and industrial areas of the basin. Examples of 

anthropogenic sources include fertilizers, residential water 

softeners, road salt, and industrial processes. These salts 

are often delivered to riverine systems through industrial 

water treatment, municipal wastewater treatment, or surface 

runoff.

The concentration of dissolved solids in the Rio Grande 

increases by nearly two orders of magnitude as water is 

transported from the headwaters in Colorado to Fort Quitman, 

Texas (Moore and Anderholm, 2002; Phillips and others, 

2003). During the past century, dissolved solids in the Rio 

Grande Basin have been intensively studied. Early studies 

focused on identifying the spatial and temporal variability 

present in dissolved-solids concentrations and whether these 

concentrations would limit the supply of water to developing 

agricultural communities (Stabler, 1911; National Resources 

Committee, 1938). Studies also focused on quantifying the 

mass of dissolved solids transported from one reach of the 

Rio Grande to the next to determine whether salts were 

accumulating in agricultural soils (Wilcox, 1957; Wilcox, 

1968; Williams, 2001). A major focus for studies during 

the past two decades is identifying factors that contribute 

to the increase in dissolved-solids concentration and loads 

measured along the Rio Grande (Moore and Anderholm, 

2002; Mills, 2003; Phillips and others, 2003; Witcher and 

others, 2004; Hibbs and Merino, 2007; Moore and others, 

2008). Researchers have been able to identify the dominant 

sources of added salts into the Rio Grande using a variety of 

hydrogeological, geophysical, and hydrochemical analyses. 

These sources include saline groundwater, wastewatertreatment plants, and mineral dissolution in the alluvial 

aquifer. 

In order to address the issue of salinization, waterresource managers need to (1) have a clear conceptual 

understanding of the sources of salinity and the factors that 

control storage and transport, (2) identify critical knowledge 

gaps in this conceptual understanding, and (3) develop a 

research plan to address these gaps and develop a salinity 

management program. In 2009, the U.S. Geological Survey 

(USGS) in cooperation with the U.S. Army Corps of Engineers 

(USACE), New Mexico Interstate Stream Commission 

(NMISC), and New Mexico Environment Department 

(NMED) initiated a project to summarize the current state 

of knowledge regarding the transport of dissolved solids in 

the Rio Grande between San Acacia, New Mexico, and Fort 

Quitman, Texas (fig. 1). Sources of dissolved solids in the 

portion of the watershed located in Mexico were not assessed. 

The primary objective is to provide hydrologic information 

pertaining to three questions: 

1. What is the spatial and temporal variability present in the 

concentrations and loads of dissolved solids in the Rio 

Grande? 

2. What is the source-specific budget for the mass of 

dissolved solids transported along the Rio Grande? 

3. Where do additional dissolved solids enter the Rio 

Grande? 

In addition to addressing these three questions, secondary 

objectives were to provide information regarding gaps in the 

current state of knowledge and suggestions for future studies 

and monitoring data. 
Introduction 5

(1)

(2)

(3)

(4)

(5)

(6)

10

25

10

Elephant Butte

Reservoir

Caballo

Reservoir

Rio Grande

0 20 40 60 MILES

0 20 40 60 KILOMETERS

CHIHUAHUA

NEW MEXICO

TEXAS

UNITED STATES

MEXICO

OTERO COUNTY

CATRON

COUNTY

SOCORRO COUNTY

CHAVES COUNTY

LINCOLN COUNTY

SIERRA COUNTY

GRANT

COUNTY

LUNA COUNTY

TORRANCE COUNTY

HUDSPETH COUNTY

DONA ANA

COUNTY

EL PASO

COUNTY

El Paso

Socorro

Leasburg

Las Cruces

San Acacia

San Marcial

Fort

Quitman

Fabens

Polvadera

Ciudad

 Juarez

Truth or 

Consequences

108°00' 107°30' 107°00' 106°30' 106°00' 105°30' 105°15'

34°15'

34°00'

33°45'

33°30'

33°15'

33°00'

32°45'

32°30'

32°15'

32°00'

31°45'

31°30'

31°15'

31°00'

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 13

North American Datum of 1983

EXPLANATION

Alluvial-fill basin underlying the Rio Grande—

 Boundaries are approximate

 Socorro

 San Marcial

 Engle

 Palomas

 Mesilla

 Hueco

TEXAS

COLORADO

OKLAHOMA ARIZONA

NEW MEXICO

UNITED STATES

MEXICO

ALBUQUERQUE

BASIN

San Antonio

Albuquerque

Area

enlarged

Rio Grande

surficial drainage area

in the United States

Figure 1. Map showing the Rio Grande study area (white area) and the distribution of the six alluvial-fill basins underlying the Rio 

Grande: (1) Socorro, (2) San Marcial, (3) Engle, (4) Palomas, (5) Mesilla, and (6) Hueco Basins. Boundaries of the six alluvial-fill basins 

are approximated from Wilkins (1986). 
6 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

Purpose and Scope

This report addresses the current state of knowledge 

regarding the transport of dissolved solids in the Rio Grande 

and associated alluvial-fill basins between San Acacia, New 

Mexico, and Fort Quitman, Texas. This current state of 

knowledge is a synthesis of existing studies that addressed 

various aspects of the transport of dissolved solids in the 

Rio Grande study area. This report includes discussions of 

(1) spatial and temporal variability associated with streamflow, 

dissolved-solids concentration, and dissolved solids load in 

the Rio Grande, (2) dissolved-solids budgets for six reaches 

along the Rio Grande study area, and (3) the locations of 

groundwater and surface-water containing high concentrations 

of dissolved solids. Also included is a plan of study with 

recommendations for future studies and monitoring data 

that will result in a better understanding of the transport of 

dissolved solids in the Rio Grande. 

Description of the Rio Grande Study 

Area

The Rio Grande is the fourth longest river system in the 

United States and extends from the southern part of Colorado 

to the Gulf of Mexico. The portion of the Rio Grande that 

will be discussed in this report extends from San Acacia, New 

Mexico, to Fort Quitman, Texas (fig. 1). Climate, surfacewater flows, geology, water use, and water management all 

play important roles in the transport of water and solutes 

through the Rio Grande study area. Many of the studies that 

addressed the sources of dissolved solids in the Rio Grande 

study area have determined that the geology and hydrology 

of the underlying alluvial aquifers and the structure and 

management of the surface-water system have the greatest 

influence on dissolved-solids concentration in the Rio Grande 

(Phillips and others, 2003; Hogan and others, 2007; Moore 

and others, 2008). This section provides a brief overview 

of each of these physical features and the role they play in 

influencing the hydrology and water quality of the Rio Grande. 

Climate

The climate of the Rio Grande study area and areas of 

the Rio Grande Basin that extend north of San Acacia, New 

Mexico, influences the hydrology and associated water quality 

through precipitation and evaporation. The average total 

annual precipitation that is delivered to the Rio Grande Basin 

is highly variable. In the northern mountainous areas of the 

Rio Grande Basin, average annual precipitation exceeds 50 

inches, whereas average annual precipitation delivered to the 

Rio Grande study area typically is less than 10 inches (Ellis 

and others, 1993). The concentration of dissolved solids in 

precipitation and associated runoff and infiltration typically 

are low and considered a minor contributor of dissolved solids 

in the Rio Grande Basin. Dissolved-solids concentrations in 

precipitation range from less than 0.5 to 3.0 milligrams per 

liter (mg/L) (Anning and others, 2007).

Most precipitation delivered to the Rio Grande Basin is 

lost to the atmosphere through evaporation and transpiration. 

Phillips and others (2003) determined that approximately 75 

percent of the water in the Rio Grande at the Colorado-New 

Mexico border is lost to the atmosphere through evaporation 

and transpiration by the time the river reaches El Paso, 

Texas. Evaporation and transpiration produce an approximate 

fourfold increase in concentration of dissolved solids in the 

Rio Grande between the headwaters in Colorado and Fort 

Quitman, Texas (Phillips and others, 2003; Hibbs and Merino, 

2007; Hogan and others, 2007). 

Streamflow in the Rio Grande Study Area

Streamflow in the Rio Grande study area decreases as 

water flows from San Acacia, New Mexico, to Fort Quitman, 

Texas, and exhibits considerable variability from year to year. 

The decrease in streamflow is a result of water withdrawals 

and streamflow losses, which exceed inflows (Wilcox, 1957). 

The majority of water in the Rio Grande as it enters the 

study area originates from mountainous regions of southern 

Colorado and northern New Mexico. Elevated streamflow 

conditions as a result of snowmelt runoff typically occur 

from May to August. Local runoff associated with summer 

monsoon rainfall also contributes water to the Rio Grande in 

the study area. Rainfall runoff from the mountainous regions 

in the Rio Grande study area is transported through a network 

of ephemeral channels; however, many of these ephemeral 

channels have flood-control dams that slow runoff, thus 

promoting increased seepage and evaporation. Groundwater 

discharge from the alluvial aquifers located within the Rio 

Grande study area also contributes to streamflow in the 

Rio Grande study area (Ellis and others, 1993). Additional 

contributions to streamflow occur through discharge from 

agricultural drains and municipal wastewater-treatment plants. 

Despite these contributions, streamflow decreases along the 

continuum of the Rio Grande study area because of losses 

through evaporation and transpiration (Phillips and others, 

2003), irrigation diversions (Wilcox, 1957), losses to the 

underlying alluvial aquifer (Wilson and others, 1981), and 

surface-water and groundwater withdrawals for municipal 

water supply (West, 1995; Hibbs and others, 2003; Witcher 

and others, 2004; Eastoe and others, 2007). 

The majority of the water in the Rio Grande that enters 

the study area is stored in Elephant Butte and Caballo 

Reservoirs (fig. 1). Elephant Butte and Caballo Reservoirs 

were constructed at the beginning of the 20th century as part 

of the Bureau of Reclamation’s Rio Grande Project (Autobee, 

1994). The primary purpose of these reservoirs is to store 

and release water for irrigation of agricultural crops in the 

Palomas, Mesilla, and Hueco Basins. Water is not released 
Description of the Rio Grande Study Area 7

from these two reservoirs from October through February; 

consequently, flow in the Rio Grande below Caballo Reservoir 

during this period is small and water in the Rio Grande is 

derived primarily from groundwater discharge, agricultural 

drains, and municipal wastewater-treatment plants. Water 

is released from these reservoirs during March through 

September to supply water to irrigation districts throughout the 

study area. An additional part of the Bureau of Reclamation’s 

Rio Grande Project was to construct a network of diversion 

dams and unlined irrigation canals to deliver Rio Grande water 

to irrigate agricultural crops (Autobee, 1994). Diversion dams 

route water from the Rio Grande to the irrigation canals, which 

route water to the agricultural fields. Approximately half of the 

surface water diverted for irrigation is transpired by vegetation 

or evaporated, whereas the remaining half infiltrates to the 

subsurface either through canal seepage or on-farm return 

flow to the alluvial aquifer system (Anderholm, 2002; Bastien, 

2009). Shortly after the completion of the Rio Grande Project 

surface-water distribution system, groundwater levels rose 

and resulted in saturated and salt-enriched soils. A network 

of agricultural drains was constructed during the 1920s and 

1930s to mitigate this problem. The purpose of the agricultural 

drains is to maintain the elevation of the groundwater table 

several feet below the surface of the fields by intercepting and 

draining shallow groundwater. Water in the agricultural drains 

typically returns directly to the Rio Grande. 

The concentration of dissolved solids in the agricultural 

drains is typically 2 to 5 times greater than the concentration 

of dissolved solids in the irrigation canals and Rio 

Grande (Anderholm, 2002; Bastien, 2009). The increased 

concentration of dissolved solids in the drains has been linked 

to (1) evaporation and transpiration within the agricultural 

fields (Hibbs and Boghici, 1999; Phillips and others, 2003; 

Bastien, 2009), (2) mineral dissolution (Witcher and others, 

2004; Bastien, 2009), and (3) inflow of sedimentary brine 

groundwater (Moore and others, 2008). Thus, the irrigation 

canal and agricultural-drain network integrates processes that 

exchange high-volume, low dissolved-solids-concentration 

Rio Grande water with low-volume, high dissolved-solidsconcentration groundwater. 

Alluvial-Fill Basins

The Rio Grande in New Mexico and west Texas flows 

through a series of alluvial-fill basins in the Rio Grande Rift. 

The Rio Grande Rift extends from southern Colorado through 

central New Mexico to near El Paso, Texas, and was formed 

approximately 30 million years ago as part of the widespread 

extension of the western United States (Keller and Baldridge, 

1999). The Rio Grande Rift is described as a series of northsouth trending downdropped basins (grabens and half grabens) 

that are connected end to end (Thorn and others, 1993). These 

basins are bordered on the east and west sides by areas of 

uplift, which commonly consist of Precambrian crystalline or 

Paleozoic sedimentary bedrock (Phillips and others, 2003). 

These series of connected basins are filled with alluvial and 

lacustrine sediment and range in depths from 13,000 feet 

(ft) to less than 100 ft (Wilson and others, 1981; Anderholm, 

2002; Phillips and others, 2003). The north-south boundaries 

between each of the alluvial-fill basins are formed by 

convergence of the eastern and western structural boundaries 

or regional uplift, which brings the underlying bedrock close 

to the surface (fig. 2; Thorn and others, 1993). Bryan (1938, 

p. 198) simply describes the relation between the Rio Grande 

Figure 2. Schematic hydrogeologic cross section of the Rio Grande Rift, parallel to the path of the river (from Phillips and others, 2003; 

used with permission). 
8 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

and underlying alluvial-fill basins as “a stream flowing from 

one sand-filled tub to another through narrow troughs.” Six 

alluvial-fill basins within the Rio Grande study area directly 

underlie the Rio Grande – the Socorro, San Marcial, Engle, 

Palomas, Mesilla, and Hueco Basins (fig. 1; Wilkins, 1998). 

Detailed descriptions of the geologic structure of the alluvialfill basins can be found in Chapin (1971), Hawley (1978), 

Riecker (1979), Hawley and Kennedy (2004), Hawley and 

others (2005), and Hutchinson (2006).

Recharge to the alluvial-fill basins occurs as a 

combination of (1) mountain-front recharge, (2) inflow 

from adjacent aquifers, (3) infiltration of water from the Rio 

Grande, and (4) infiltration of irrigation water applied to 

agricultural areas (Ellis and others, 1993; Anning and others, 

2007). Mountain-front recharge commonly is considered to 

be the primary mechanism for natural groundwater recharge 

in the alluvial-fill basins (Frenzel and others, 1992; Heywood 

and Yager, 2003; Anning and others, 2007). Mountain-front 

recharge is the infiltration of runoff from near basin margins 

(Frenzel and others, 1992; Heywood and Yager, 2003). This 

runoff originates in the uplifted and mountainous regions of 

the alluvial-fill basins and is subsequently transported through 

ephemeral channels. These ephemeral channels consist of 

porous substrate that facilitates the infiltration of runoff. In 

addition, most major ephemeral channels in the study area 

have flood-control dams, which further promote the infiltration 

of storm runoff. However, recent studies have found that a 

significant portion of the water that recharges alluvial-fill 

basins originates from the Rio Grande and irrigation network 

(Sanford and others, 2004; Witcher and others, 2004; Eastoe 

and others, 2007). The general flow paths that the regional 

groundwater follows in the alluvial-fill basins extend from 

basin margins toward the Rio Grande and southward from 

one alluvial-fill basin to the next (Ellis and others, 1993). The 

travel time for regional groundwater in the alluvial aquifer 

to move from groundwater recharge areas to groundwater 

discharge is on the order of 10,000 years (Anderholm and 

Heywood, 2003; Eastoe and others, 2007). Saline groundwater 

originates from geothermal or nongeothermal sources 

separate from the regional groundwater system, likely from a 

groundwater flow system in the bedrock underlying the basin, 

and seeps upward and mixes with the regional groundwater 

in the alluvial aquifer (Mills, 2003, Hogan and others, 2007, 

Moore and others, 2008).

Discharge from the alluvial-fill basins occurs 

through (1) direct discharge to the surface-water system, 

(2) evapotranspiration, (3) flow to adjacent alluvial aquifers, 

and (4) groundwater pumpage (Ellis and others, 1993). Direct 

discharge to the surface-water system occurs directly to the 

Rio Grande and through interception by agricultural drains. 

Groundwater discharge to the surface-water system is most 

pronounced at the distal end of each alluvial-fill basin (Wilson 

and others, 1981; Ellis and others, 1993; Phillips and others, 

2003; Hogan and others, 2007). This discharge occurs because 

of the decreased cross-sectional area of the alluvial-fill basin 

resulting from the convergence of the eastern and western 

structural boundaries (Ellis and others, 1993). The direct 

discharge of groundwater to the surface-water system has 

been identified as a significant mechanism for increasing 

the concentration and mass of dissolved solids in the Rio 

Grande (Wilson and others, 1981; Anderholm, 2002; Phillips 

and others, 2003; Witcher and others, 2004; Hibbs and 

Merino, 2007; Hogan and others, 2007; Moore and others, 

2008).

During predevelopment times, the amount of recharge 

that occurred in the alluvial-fill basins approximately equaled 

the amount of discharge. However, the development of 

groundwater resources in each of the alluvial-fill basins during 

the past half century to meet municipal and agricultural watersupply needs has shifted the groundwater balance such that 

discharge exceeds recharge (Ellis and others, 1993; Anning 

and others, 2007). Groundwater is used to meet the municipal 

water-supply needs for the cities of Las Cruces, Santa Teresa, 

El Paso, and Ciudad Juarez, as well as to supply irrigation 

water and supplement surface-water irrigation supplies during 

periods of drought. The primary impacts of groundwater 

pumpage are localized reduction in groundwater levels and 

the reversal of groundwater-flow paths, from flow paths that 

historically flowed southward along the Rio Grande to flow 

paths that now carry water perpendicularly away from the 

Rio Grande (Wilson and others, 1981; West, 1995; Hibbs and 

others, 2003; Witcher and others, 2004). A secondary impact 

of groundwater pumping is the reduction of groundwater 

discharge to drains, which is especially evident during periods 

of drought.

Water Use

The majority of water use in the Rio Grande study area is 

attributed to three general categories – agricultural, municipal, 

and reservoir evaporation. These three categories account 

for greater than 95 percent of the water used in five counties 

within the Rio Grande study area – Socorro, Sierra, and Dona 

Ana Counties in New Mexico (Longworth and others, 2008), 

and El Paso and Hudspeth Counties in Texas (Texas Water 

Development Board, 2007). Of these three water uses, water 

supplied for irrigating agricultural crops accounts for 93, 30, 

and 89 percent of the total water used in Socorro, Sierra, and 

Dona Ana Counties in New Mexico, respectively (Longworth 

and others, 2008), and 50 and 99 percent of the total water 

used in El Paso and Hudspeth Counties in Texas, respectively 

(Texas Water Development Board, 2007). The Rio Grande 

is the primary source of irrigation water in the study area; 

however, groundwater often is used during periods of drought 

to ensure that the irrigation requirement for the various 

agricultural crops is met (Frenzel and others, 1992; Ellis and 

others, 1993). 

The main population centers in the Rio Grande study 

area are Socorro (population 9,100), Las Cruces (population 

75,000), El Paso (600,000), and Ciudad Juarez (1,300,000). 

Groundwater is the primary source of drinking water for the 

residents of these population centers. Municipal water supply 
Factors Affecting Dissolved Solids 9

accounts for 1.7, 1.5, and 7.7 percent of the total water used 

in Socorro, Sierra, and Dona Ana Counties in New Mexico, 

respectively (Longworth and others, 2008), and 45, and 

0.3 percent of the total water used in El Paso and Hudspeth 

Counties in Texas, respectively (Texas Water Development 

Board, 2007). However, El Paso now uses both groundwater 

and Rio Grande water for municipal water supply (Hibbs and 

others, 2003). 

The loss of water through evaporation from reservoirs 

accounts for 4 percent of the total water used in Socorro 

County and 67 percent of the total water used in Sierra 

County. The two primary reservoirs within these two counties 

are Elephant Butte and Caballo Reservoirs. In 2005, the 

total amount of water evaporated from Elephant Butte and 

Caballo Reservoirs was estimated to be nearly 102,000 

acre-ft (Longworth and others, 2008). For comparison, the 

total amount of water consumed by the residents of El Paso 

in 2005 was estimated to be 136,000 acre-ft (Texas Water 

Development Board, 2007). Regardless of whether Rio 

Grande water is lost through evaporation from Elephant Butte 

or Caballo Reservoirs or from agricultural fields, the effect is a 

relative increase in the concentration of dissolved solids.

Factors Affecting Dissolved Solids 

Several processes influence the concentration and load 

of dissolved solids in the Rio Grande in the study area. 

Concentration is a measurement that describes the amount 

of dissolved solids that are present in a specified volume of 

water. The units for the concentration of dissolved solids 

are commonly milligrams per liter (mg/L). However, the 

concentration of dissolved solids does not provide information 

on the quantity of dissolved solids that are being transported 

along the continuum of the Rio Grande study area. Load is 

a measurement that describes the mass of dissolved solids 

that are mobilized per unit of time. Examples of the units that 

are used to define the load of dissolved solids are kilograms 

per day (kg/d) and tons per day (tons/d). Information on the 

loads of dissolved solids is essential for the development of 

mass-balance budgets. The processes that influence dissolved 

solids in the Rio Grande study area can be grouped into three 

categories – those that alter concentration only, those that 

influence concentration and load, and those that influence only 

load.

Concentration

The loss of water from the Rio Grande through 

evaporation, agricultural transpiration, and riparian 

transpiration are dominant processes that affect only the 

concentration of dissolved solids in the Rio Grande. The 

concentration of dissolved solids is increased as a result 

of evaporation and transpiration; however, the increase in 

concentration is proportional to the loss of water such that 

the dissolved-solids load remains nearly constant (Moore 

and Anderholm, 2002; Anning and others, 2006). Many 

studies have investigated the extent that evaporation and 

transpiration have on the pattern of increasing dissolved-solids 

concentration along the length of the Rio Grande study area. 

These investigations used hydrogen and oxygen isotopes 

to estimate the total water lost through evaporation and to 

indirectly quantify the water lost through transpiration and 

found that the loss of water through these processes governs 

the increase in dissolved-solids concentration observed along 

the length of the Rio Grande study area (Phillips and others, 

2003; Hogan and others, 2007; Eastoe and others, 2007; 

Moore and others, 2008). However, the increase in dissolvedsolids concentration along the Rio Grande is too large to be 

produced through evaporation and transpiration alone (Phillips 

and others, 2003; Hogan and others, 2007). 

Concentration and Load

Several processes affect dissolved solids in the Rio 

Grande study area by increasing both the concentration and 

load. These processes include (1) groundwater discharge, 

(2) tributary inflow, (3) industrial and municipal discharges, 

and (4) mineral dissolution, all of which involve the transport 

of additional dissolved solids into the Rio Grande. Several 

studies, using the ratio between chloride and bromide, have 

found that evaporation and transpiration alone cannot account 

for all of the increase in the concentration of dissolved solids 

observed along the length of the Rio Grande study area and 

that new sources of dissolved solids are needed to obtain the 

observed increase in both concentration and load (Phillips 

and others, 2003; Hibbs and Merino, 2007; Hogan and others, 

2007; Eastoe and others, 2007; Moore and others, 2008). 

Studies also have employed various geochemical and isotopic 

analyses to characterize and identify the multiple sources and 

processes that add dissolved solids to the Rio Grande. Results 

from these studies indicate that the dominant processes that 

increase dissolved solids in the Rio Grande are the discharge 

of saline groundwater (Anderholm, 2002; Mills, 2003, Phillips 

and others, 2003; Witcher and others, 2004; Hogan and 

others, 2007; Moore and others, 2008) and mineral dissolution 

(Anderholm, 2002; Hibbs and Merino, 2007; Bastien, 2009).

Load

Dissolved-solids loads in the Rio Grande can be 

increased and decreased without changing associated 

dissolved-solids concentrations. Processes that decrease the 

dissolved-solids load without changing the concentration 

are those that remove water and associated water-quality 

constituents in equal proportions. These processes include 

(1) irrigation diversions, (2) municipal and industrial 

diversions, and (3) groundwater recharge. Processes that 

increase the dissolved-solids load without changing the 

dissolved-solids concentration are those that transport water 
10 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

having the same concentration of dissolved solids as the 

Rio Grande to the Rio Grande. Potential processes include the 

discharge of water from tributaries, agricultural drains, and 

industrial or municipal effluent. 

Spatial and Temporal Variability in 

Dissolved-Solids Transport

Dissolved solids in the Rio Grande are influenced by 

many factors such as climate, water-management operations, 

groundwater and surface-water interactions, and various 

contributing sources. In order to better manage dissolved 

solids in the Rio Grande, water-resource managers need to 

understand the extent of the spatial and temporal variability 

present in dissolved-solids conditions and the associated 

processes that govern transport and storage. In the following 

sections, the spatial and temporal variability associated 

with dissolved solids in the Rio Grande are described. 

Understanding the spatial variability associated with dissolved 

solids along the Rio Grande will allow managers and 

researchers to determine the sources of dissolved solids and 

where these dissolved solids are entering the Rio Grande. 

Understanding the temporal variability exhibited in dissolved 

solids provides information on the effect that factors, such 

as climate and water-management operations, have on the 

dissolved solids over extended time periods along the Rio 

Grande. Data collected by Wilcox (1968) from 1934 to 1963 

at Rio Grande at San Marcial, New Mexico (San Marcial); Rio 

Grande below Elephant Butte Dam, New Mexico (Elephant 

Butte); Rio Grande below Caballo Dam, New Mexico 

(Caballo); Rio Grande above Leasburg Dam, New Mexico 

(Leasburg); Rio Grande at El Paso (Courchesne Bridge), 

Texas (El Paso); and Rio Grande at Fort Quitman, Texas (Fort 

Quitman), were the primary sources of data used to evaluate 

spatial and temporal variability in dissolved solids along the 

Rio Grande study area. 

Streamflow

Variability in streamflow is a primary factor that affects 

dissolved-solids transport in the Rio Grande study area. The 

concentration of dissolved solids is affected by streamflow 

through dilution or evaporation, or as the contributions from 

other sources and flow paths vary as a result of changes 

in water-resource management practices. Additionally, 

dissolved-solids loads are a function of streamflow and 

vary as streamflow changes from year to year and season to 

season. Therefore, it is important to first examine the spatial 

and temporal patterns in streamflow in order to determine 

how these variations influence the resulting patterns in 

dissolved-solids concentrations and loads. Streamflow data 

and associated statistics are specific to the 1934 to 1963 time 

period; however, the temporal and spatial patterns observed in 

streamflow during the 1934 to 1963 period are related to more 

current data when applicable. 

Spatial Variability in Streamflow 

Annual streamflow in the Rio Grande study area indicates 

that streamflow decreased on average by 840 cubic feet per 

second (ft3/s) between San Marcial and Fort Quitman during 

the 1934 to 1963 period (fig. 3). Annual mean streamflow 

measured in the Rio Grande at San Marcial was 1,041 ft3/s. 

Management of Elephant Butte and Caballo Reservoirs and 

numerous irrigation canals and drains control streamflow in 

the Rio Grande between Leasburg and Fort Quitman (Moore 

and Anderholm, 2002). The effect of flow control by Elephant 

Butte and Caballo Reservoirs can be seen in the reduced 

variability in annual streamflow conditions for all stations 

below San Marcial (fig. 3). Annual mean streamflow measured 

in the Rio Grande at Leasburg between 1934 and 1963 was 

901 ft3/s. Approximately 300 ft3/s was lost annually from 

the Rio Grande between Leasburg and El Paso (fig. 3). The 

depletion of streamflow from this reach of the Rio Grande was 

caused primarily by agricultural transpiration depletions of the 

surface water applied for irrigation (Phillips and others, 2003). 

Additional depletion of streamflow can be attributed to losses 

through municipal groundwater pumping at the Las Cruces 

and Cañutillo (located about 15 miles upstream from El Paso) 

well fields (Wilson and others, 1981), agricultural groundwater 

pumping (Wilcox, 1968; Wilson and others, 1981), and loss 

of water from the Rio Grande to the alluvial aquifer through 

seepage (Wilson and others, 1981; Newton and others, 2002). 

Mean annual streamflow measured in the Rio Grande at El 

Paso was 597 ft3/s (fig. 3). An additional 400 ft3/s, on average, 

was lost each year from the Rio Grande between El Paso and 

Fort Quitman. Much of the streamflow loss from this section 

has been attributed to municipal groundwater withdrawals 

for El Paso and Ciudad Juarez (Miyamoto and others, 1995; 

Hibbs, 1999; Hibbs and others, 2003) and evapotranspiration 

(Miyamoto and others, 1995; Phillips and others, 2003; Eastoe 

and others, 2007). 

Losses in the annual mean streamflow from the 

Rio Grande between San Marcial and El Paso have been 

documented in other studies. Stabler (1911) measured 

streamflow in the Rio Grande at San Marcial and El Paso from 

1897 to 1908 (fig. 4) and found that the average difference in 

annual streamflow was 430 ft3

/s. The time period that Stabler 

(1911) monitored streamflow conditions was prior to the 

construction of Elephant Butte and Caballo Dams. Moore 

and Anderholm (2002) showed that during 1995 to 1997 the 

annual loss from the Rio Grande between San Marcial and 

Leasburg was 790 ft3/s and that an additional 180 ft3/s was lost 

between Leasburg and El Paso. One variable that confounds 

the direct comparison of annual streamflow conditions from 

time periods before and after the construction of Elephant 

Butte and Caballo Dams is the influence of storage and 

release of streamflow in these reservoirs. However, the 
Spatial and Temporal Variability in Dissolved-Solids Transport 11

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

ANNUAL MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

EXPLANATION

Percentile - Percentage of

values equal to or less than

indicated value

10th

25th

50th

75th

outlier

mean

90th

San Marcial below Elephant

Dam

below Caballo

Dam

above Leasburg

Dam

El Paso Fort Quitman

(30)

(30)

(30) (30)

(30)

(30)

(30) number of 

observations

Figure 3. Annual mean streamflow measured at selected monitoring stations along the Rio Grande from 1934 to 1963 (data from 

Wilcox, 1968).

fact remains that as water is transported in the Rio Grande 

between San Marcial and El Paso, significant losses occur as 

a result of agricultural and riparian transpiration, evaporation, 

and seepage from the Rio Grande to the shallow alluvial 

aquifer (Stabler, 1911; Wilson and others, 1981; Moore and 

Anderholm, 2002). 

Temporal Variability in Streamflow

Annual variation in the amount of streamflow that is 

transported down the Rio Grande is influenced by climate and 

the management of Elephant Butte and Caballo Reservoirs 

(fig. 5). Time-series data for annual mean streamflow for 

the Rio Grande at San Marcial shows a mix of wet and dry 

years between 1934 and 1963 (fig. 5A). The largest annual 

streamflow measured at San Marcial was 3,907 ft3

/s in 1941, 

and the lowest annual streamflow of 151 ft3/s occurred in 

1951. The influence that management of the Elephant Butte 

and Caballo Reservoirs has on streamflow in the Rio Grande 

is evident in the time-series records for the stations monitored 

by Wilcox (1968) below Elephant Butte Reservoir (fig. 5B). 

Streamflow that passed San Marcial during wet years was 

used to increase water stored in Elephant Butte and Caballo 

Reservoirs, and a lesser amount was passed to downstream 

locations. Conversely, during dry years more water was 

released to downstream locations than the amount that 

entered Elephant Butte and Caballo Reservoirs. The 

extended drought period that occurred during the mid-1950s 

had substantial impacts on the water resources in the Rio 

Grande study area. The drought caused shortfalls in the 

amount of surface water available for irrigation in the Mesilla 

Basin and, as a result, many wells were drilled in an attempt 

to use groundwater to meet the irrigation demand (Leggat 

and others, 1962; Frenzel and others, 1992). Additionally, 

West (1995) hypothesized that increased reliance on 

groundwater to meet water-supply needs in the Mesilla Basin 

resulted in increased stress on the underlying alluvial aquifer, 

which subsequently decreased the storage coefficient. This 

increased stress has resulted in a decrease in the annual flows 

below the reservoirs through an increase in the river and canal 

losses to the underlying alluvial aquifer (Helm, 1984; West 

1995). 
12 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

San Marcial

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

ANNUAL MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

El Paso

(12)

(12)

EXPLANATION

Percentile - Percentage of

values equal to or less than

indicated value

10th

25th

50th

75th

mean

90th

(30) number of 

observations

Figure 4. Boxplot of streamflow data collected from the Rio Grande at San Marcial and El Paso (Courchesne Bridge) from 1897 to 1908 

by Stabler (1911). 

Seasonal variation in streamflow in the Rio Grande in 

the study area, primarily a function of water management, 

is most evident at monitoring stations below Elephant Butte 

Reservoir (fig. 6). Two distinct water-management periods 

influence streamflow conditions in the Rio Grande study area. 

These seasons are generally categorized as irrigation and 

nonirrigation seasons (Wilcox, 1968). The irrigation season 

extends from March through September (roughly two-thirds 

of the year) and represents the period when water is being 

released from Elephant Butte and Caballo Reservoirs to supply 

water for the irrigation of agricultural crops. During this time 

period, streamflow in the Rio Grande between Elephant Butte 

Reservoir and El Paso is increased. Reductions in streamflow 

caused by evapotranspiration, surface-water diversions for 

irrigation, and leakage to the shallow alluvial aquifer occur 

in the Rio Grande between Leasburg and Fort Quitman. The 

nonirrigation season extends from October through February 

(roughly one-third of the year) and represents the time period 

when little to no water is released from the reservoirs. During 

this period, streamflow in the Rio Grande below Elephant 

Butte Reservoir is primarily inflow from agricultural drains 

(Wilcox, 1968), wastewater-treatment plants (Mills, 2003; 

Moore and others, 2008), and groundwater discharge (Wilson 

and others, 1981; Ellis and others, 1993). 

Summary of Streamflow Conditions

The spatial and temporal patterns in streamflow 

conditions provide information on the factors that govern 

streamflow along the Rio Grande study area. The management 

of Elephant Butte and Caballo Reservoirs is the primary factor 

that controls the spatial and temporal variability in Rio Grande 

streamflow conditions between Elephant Butte and El Paso. 

Additionally, losses have been attributed to evaporation from 

Elephant Butte and Caballo Reservoirs. Spatially, marked 

decreases in annual streamflow (approximately 700 ft3/s) 

occur between Leasburg and Fort Quitman (Appendix 1). 

These losses have been attributed to agricultural and riparian 

transpiration, municipal withdrawals, and seepage from the 

Rio Grande to the shallow alluvial aquifer. A strong temporal 

pattern is present in streamflow conditions along the Rio 

Grande. During the irrigation season, streamflow conditions 

between San Marcial and Leasburg are similar; however, 

streamflow decreases by a factor of seven in the Rio Grande 
Spatial and Temporal Variability in Dissolved-Solids Transport 13

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

ANNUAL MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

SM

1930 1935 1940 1945 1950 1955 1960 1965

0

500

1,000

1,500

2,000

2,500

3,000

ANNUAL MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

EB

CAB

LEA

EP

FQ

(A)

(B)

Figure 5. Plot of annual streamflow measured in the Rio Grande at (A) San Marcial and (B) below Elephant Butte Dam (EB), below 

Caballo Dam (CAB), above Leasburg Dam (LEA), at El Paso (EP) and at Fort Quitman (FQ) from 1934 to 1963 (Wilcox, 1968).

between Leasburg and Fort Quitman. This sevenfold decrease 

in streamflow has been primarily attributed to irrigation 

diversions, agricultural and riparian transpiration, and 

municipal withdrawals. During the nonirrigation season, 

streamflow entering Elephant Butte and Caballo Reservoirs is 

stored and not released to the downstream reaches. The pattern 

of increasing streamflow at stations downstream from Caballo 

Reservoir is a result of agricultural return flows, inflow of 

groundwater to the Rio Grande, and releases from wastewatertreatment facilities. 

Dissolved-Solids Concentration

Dissolved-solids concentration data provide a good 

indicator of the general quality of surface water in the Rio 

Grande in the study area. Spatial and temporal patterns in 

dissolved-solids concentration data provide information 

pertaining to the potential sources and processes contributing 

to changes in concentrations. However, concentration data 

alone do not provide information on the mass of dissolved 

solids being transported downstream 
14 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

NON IRR

0.1

1

10

100

1,000

10,000

MONTHLY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

NON IRR NON IRR NON IRR NON IRR NON IRR

San Marcial below Elephant

Dam

below Caballo

Dam

above Leasburg

Dam

El Paso Fort Quitman

(310)

(434)

(325)

(455)

(118)

(590)

(312)

(435)

(330)

(462)

(330)

(462)

EXPLANATION

Percentile - Percentage of

values equal to or less than

indicated value

10th

25th

50th

75th

outlier

mean

90th

(330) number of 

observations

Figure 6. Streamflow conditions during the nonirrigation (NON) and irrigation (IRR) season at selected sites in the Rio Grande study 

area from 1934 to 1999 (Wilcox, 1968; Williams, 2001).
Spatial and Temporal Variability in Dissolved-Solids Transport 15

Spatial Variability in Dissolved-Solids 

Concentration

The concentration of dissolved solids in the Rio Grande 

in the study area increases with distance downstream from 

Elephant Butte and Caballo Reservoirs (Lippincott, 1939; 

Moore and Anderholm, 2002; Phillips and others, 2003; 

Hogan and others, 2007; Moore and others, 2008; fig. 7). The 

range of dissolved-solids concentrations is similar for the Rio 

Grande at San Marcial, Elephant Butte, Caballo, and Leasburg. 

Average dissolved-solids concentration measured at the four 

stations from San Marcial to Leasburg ranged from 512 mg/L 

at Elephant Butte to 660 mg/L at Leasburg (fig. 7). Maximum 

dissolved-solids concentrations for these four stations ranged 

from 1,146 mg/L at Caballo to 1,861 at San Marcial (fig. 7). 

A marked increase in dissolved-solids concentration occurred 

in the Rio Grande between Leasburg and Fort Quitman. 

Average dissolved-solids concentration increased to 1,053 

mg/L by the time the Rio Grande reaches El Paso and to 

3,275 mg/L by the time the Rio Grande reached Fort Quitman 

(fig. 7). Maximum dissolved-solids concentrations in the Rio 

Grande at El Paso and Fort Quitman were 3,831 mg/L and 

10,738 mg/L, respectively. Essentially, the concentration of 

dissolved solids in the Rio Grande (considering both irrigation 

and nonirrigation seasons) doubles from Elephant Butte to 

El Paso and increases by more than a factor of five from 

Elephant Butte to Fort Quitman. The increases in dissolvedsolids concentration between Elephant Butte and El Paso 

have been attributed to the inflow of saline groundwater at 

the distal end of the Palomas Basin (Wilson and others, 1981; 

Anderholm, 2002) and Mesilla Basin (Wilson and others, 

1981; Phillips and others, 2003; Witcher and others, 2004). 

The increase in dissolved-solids concentration between El 

Paso and Fort Quitman has been attributed to the inflow of 

saline groundwater near the El Paso-Hudspeth County line 

(Hibbs and Merino, 2007).

The variation in dissolved-solids concentration in the 

Rio Grande in the study area has been documented since the 

early 1900s. Stabler (1911) showed that the average dissolvedsolids concentrations in the Rio Grande between 1905 and 

1907, prior to the construction of the Elephant Butte and 

Caballo Dams, were 404 mg/L and 681 mg/L at San Marcial 

100

1,000

10,000

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

San Marcial below Elephant

Dam

below Caballo

Dam

above Leasburg

Dam

El Paso Fort Quitman

(542)

(542)

(502)

(540)

(729)

(683)

EXPLANATION

Percentile - Percentage of

values equal to or less than

indicated value

10th

25th

50th

75th

outlier

mean

90th

(502) number of 

observations

Figure 7. Dissolved-solids concentration at selected sites in the Rio Grande study area from 1934 to 1999 (Wilcox, 1968; Williams, 2001).
16 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

and El Paso, respectively. Water-quality data collected by 

Stabler (1911) show that the maximum dissolved-solids 

concentrations measured at San Marcial and El Paso were 

1,930 mg/L and 3,880 mg/L, respectively. Lippincott (1939) 

indicated that the concentration of dissolved solids in the Rio 

Grande was 427 mg/L at the head of Elephant Butte Reservoir, 

832 mg/L at El Paso, and 2,120 mg/L at Fort Quitman. 

Monthly dissolved-solids concentration data collected by 

Moore and Anderholm (2002) during 1993–95 revealed that 

the concentration of dissolved solids increased by 200 mg/L 

between Leasburg and El Paso. 

Starting in 2000, researchers from the Sustainability 

of Semi-Arid Hydrology and Riparian Areas (SAHRA) 

National Science Foundation Science and Technology Center 

(http://www.sahra.arizona.edu/) started a water-quality 

monitoring program to evaluate changes in water-quality 

conditions and identify contributing sources at a fine spatial 

scale along the Rio Grande from the headwaters in Colorado 

to Fort Quitman, Texas (Phillips and others, 2003; Hogan 

and others, 2007). Water-quality monitoring was performed 

twice a year, once during winter (nonirrigation season) and 

once during the summer (irrigation season). Results from this 

monitoring effort indicated that dissolved-solids concentration 

in the Rio Grande increased by nearly two orders of magnitude 

from the headwaters in Colorado to Fort Quitman, Texas 

(fig. 8). Dissolved-solids concentration increased noticeably 

at the upstream end of the Rio Grande study area at San 

Acacia (655 km). The largest increase in dissolved-solids 

concentration occurred just above El Paso (1,015 km) and 

continued to Fort Quitman (fig. 8). Additionally, marked 

increases in the concentration of dissolved solids commonly 

coincide with contributions from agricultural drains, municipal 

wastewater-treatment plants, and direct groundwater discharge 

at the distal ends of the alluvial-fill basins (Mills, 2003; 

Phillips and others, 2003; Lacey, 2006; Hogan and others, 

2007; Bastien, 2009). Other studies have found that the 

concentration of dissolved solids in the agricultural drains is 

commonly two to three times greater than the dissolved-solids 

concentration in the Rio Grande (Anderholm, 2002; Bastien, 

2009). 

0

500

1,000

1,500

2,000

2,500

3,000

DISTANCE, IN KILOMETERS (km), DOWNSTREAM FROM THE HEADWATERS

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER 

Summer 2000

Summer 2001

Summer 2002

Winter 2001

Winter 2002

Winter 2003

0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200

San 

Acacia

655 km

San 

Marcial

731 km

below

Elephant

Butte Dam

801 km

below

Caballo

Dam

841 km

above

Leasburg

Dam

920 km

El Paso

1,015 km

Fort Quitman

1,149 km

Figure 8. Plot of dissolved-solids concentration collected during the winter and summer 2000–3 from the headwaters in Colorado to 

Fort Quitman, Texas (Phillips and others, 2003; Hogan and others, 2007).
Spatial and Temporal Variability in Dissolved-Solids Transport 17

Temporal Variability in Dissolved-Solids 

Concentration

Annual variation in the concentration of dissolved solids 

in the Rio Grande is influenced by changes in the Rio Grande 

hydrology (Yuan and Miyamoto, 2004) and the contributions 

from the various sources of dissolved solids. Year-to-year 

changes in the concentration of dissolved solids in the Rio 

Grande were identified by applying a smooth-fit curve 

analytical technique (locally weighted scatter plot smoothing 

(LOWESS); Helsel and Hirsch, 1992) to data collected by 

Wilcox (1968) and compiled by Williams (2001) at San 

Marcial, El Paso, and Fort Quitman (fig. 9). The LOWESS 

curve follows the trend in the observed data. The extended 

drought period of the 1950s can be identified by elevated 

dissolved-solids concentrations at all three stations (fig. 9). 

Similar temporal patterns in dissolved-solids concentrations 

occurred at San Marcial and El Paso; conversely, the patterns 

in dissolved-solids concentration were considerably different 

between El Paso and Fort Quitman (fig. 9). The LOWESS 

curves for San Marcial and El Paso also indicate that the 

concentrations of dissolved solids at these two sites have been 

decreasing since the drought period of the 1950s; similarly, 

dissolved-solids concentrations at Fort Quitman have been 

decreasing since the late 1970s.

Seasonal variation in dissolved-solids concentration 

in the Rio Grande is influenced primarily by the amount of 

water that is transported. Concentration of dissolved solids 

are considerably elevated in the Rio Grande at Caballo and 

El Paso during the nonirrigation season (fig. 10). During the 

nonirrigation season, streamflow is the lowest; as a result, 

dissolved solids in water transported from agricultural drains, 

direct groundwater discharge, and municipal wastewatertreatment plants are not diluted (Moore and others, 2008; 

fig. 10). Conversely, during the irrigation season, dissolvedsolids concentrations at these same stations are maintained at 

a considerably lower level because the increased streamflow 

levels in the Rio Grande dilute the concentration of dissolved 

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

San Marcial

El Paso

Fort Quitman

Figure 9. Locally weighted scatter plot smoothing curve from the Rio Grande at San Marcial, El Paso, and Fort Quitman
18 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

100

1,000

10,000

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

NON IRR NON IRR NON IRR NON IRR NON IRR NON IRR

San Marcial below Elephant

Dam

below Caballo

Dam

above Leasburg

Dam

El Paso Fort Quitman

(214)

(328)

(225)

(317)

(86) (416)

(218) (322)

(302)

(427)

(280)

(403)

EXPLANATION

Percentile - Percentage of

values equal to or less than

indicated value

10th

25th

50th

75th

outlier

mean

90th

(427) number of 

observations

Figure 10. Dissolved-solids concentration during the nonirrigation (NON) and irrigation (IRR) seasons at selected sites in the Rio 

Grande study area from 1934 to 1999 (Wilcox, 1968; Williams, 2001).
Spatial and Temporal Variability in Dissolved-Solids Transport 19

solids inflowing from agricultural drains, direct groundwater 

discharge, and municipal wastewater-treatment plants (Moore 

and others, 2008; fig. 10). Conversely, seasonal variability 

in dissolved-solids concentration at San Marcial and Fort 

Quitman is minimal and is related to the relatively minor 

seasonal variability in streamflow exhibited at both of these 

stations compared to other stations. 

Spatial and Temporal Variability in Ion 

Composition

In addition to the spatial and temporal variations 

in dissolved solids, the concentrations of the individual 

solute species that comprise the dissolved solids also vary 

spatially and temporally. The piper diagram (Piper, 1944) is 

a useful tool to evaluate the major-ion composition of water 

samples. Bastien (2009) used the piper diagram to describe 

the major-ion composition of the Rio Grande at Otowi, New 

Mexico (Otowi); Rio Grande at San Marcial, New Mexico 

(San Marcial); and Rio Grande at El Paso, Texas (El Paso). 

Bastien (2009) showed how the ion composition of the Rio 

Grande water evolves as it is transported from Otowi to El 

Paso and how this ionic transformation varied during the 

past century. The ion composition of the Rio Grande evolves 

from calcium-bicarbonate water near the Colorado and New 

Mexico border (Otowi) to sodium-sulfate-chloride water near 

El Paso (fig. 11). The chemical composition of the water in 

the Rio Grande at Otowi is influenced primarily by the water 

delivered by headwater tributaries; whereas, the chemical 

compositions of the water in the Rio Grande at San Marcial 

and El Paso are influenced primarily by the inflow of saline 

groundwater (Bastien (2009). Sodium-sulfate-chloride water 

is an evolved hydrochemical facies that typically is found in 

saline groundwater. 

 The ionic composition of the water in the Rio Grande at 

El Paso has varied over time (fig. 12). The ionic composition 

of the water in the Rio Grande at El Paso prior to the 

construction of the Elephant Butte Dam (Stabler, 1911) 

closely matches the ionic composition of the water in the Rio 

Grande at San Marcial (Bastien, 2009; fig. 11). Following 

the construction of Elephant Butte Dam, the composition of 

calcium and carbonate in the Rio Grande was reduced because 

of carbonate mineral precipitation in Elephant Butte Reservoir 

(Bastien, 2009; fig. 12). Additionally, the concentration of 

sulfate, chloride, and sodium increased in the Rio Grande 

below Elephant Butte Reservoir because of increased inflow 

from saline groundwater accompanied by precipitation of the 

more reactive ions (calcium, magnesium, and bicarbonate) 

under agricultural fields (Bastien, 2009; fig. 12). During the 

most recent decades, the composition of the anions (chloride, 

sulfate, bicarbonate plus carbonate) in the Rio Grande at 

El Paso has been shifting closer to the anion composition 

observed by Stabler (1911) prior to Elephant Butte (Bastien, 

2009; fig. 12). Additional information on the ion composition 

of surface water and groundwater within the Rio Grande study 

area can be found in Wilson and others (1981) and Frenzel and 

others (1992). 

Summary of Dissolved-Solids Concentrations

The spatial and temporal patterns exhibited in dissolvedsolids concentration data provide information on the factors 

that influence salinity in the Rio Grande. Spatial patterns 

exhibited in dissolved-solids concentration data indicate that 

concentrations increase with increasing distance downstream 

from San Acacia, New Mexico (Appendix 1). This pattern 

of increasing concentration is apparent in dissolved-solids 

concentration data extending as far back as the early 1900s. 

The most dramatic increase in dissolved-solids concentrations 

occurs in the Rio Grande between Leasburg and Fort Quitman 

where average concentrations increase by a factor of five 

(612 to 3,275 mg/L). The locations where dissolved-solids 

concentrations increase most noticeably (San Acacia, San 

Marcial, Elephant Butte, Leasburg, and El Paso) coincide with 

the distal ends of the associated underlying alluvial basins 

where the inflow of saline groundwater is the primary factor 

influencing dissolved-solids concentration. 

Temporal patterns in dissolved-solids concentration 

data along the Rio Grande between 1934 and 1999 reveal 

much information regarding the impact of climate and watermanagement operations on dissolved-solids concentration. 

Above Elephant Butte Reservoir, dissolved-solids 

concentrations are similar for the irrigation and nonirrigation 

seasons, which indicates that streamflow and contributing 

sources of dissolved solids are consistent from season to 

season (Appendix 1). From Elephant Butte to El Paso, 

dissolved-solids concentrations exhibit significant temporal 

variation. During the nonirrigation season when streamflow is 

substantially reduced, dissolved-solids concentrations nearly 

triple (from about 500 to 1,500 mg/L); this increase has been 

attributed primarily to the inflow of groundwater containing 

elevated dissolved-solids concentration and municipal 

wastewater-treatment facilities. During the nonirrigation 

season when streamflow is increased, dissolved-solids 

concentrations are comparable (about 500 to 600 mg/L) and 

substantially reduced compared to concentrations during the 

nonirrigation season. The increased streamflow during this 

period serves to dilute the dissolved solids delivered through 

the inflow of groundwater and municipal wastewater-treatment 

facilities. Therefore, the primary factors that control dissolvedsolids concentrations in the Rio Grande between Elephant 

Butte and El Paso are water-management operations and the 

inflow of saline groundwater. Below El Paso, dissolved-solids 

concentrations in the Rio Grande increase to an average 

concentration of 2,500 mg/L by the time the water reaches 

Fort Quitman during both the irrigation and nonirrigation 

seasons. The primary factor influencing dissolved-solids 

concentrations in the Rio Grande between El Paso and Fort 

Quitman is inflow of saline groundwater near the El PasoHudspeth County line.
20 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

Figure 11. Piper diagram of average decadal chemistry from the decades 1905–2000 for three Rio Grande stations: Otowi, San Marcial, 

and El Paso (Bastien, 2009; used with permission). 
Spatial and Temporal Variability in Dissolved-Solids Transport 21

Figure 12. Piper diagram of average decadal chemistry of water samples collected from the Rio Grande at El Paso for the decades 

1905–2000 (Bastien, 2009; used with permission). 

Dissolved-Solids Loads

Dissolved-solids load data provide important information 

pertaining to the mass of dissolved solids that are transported 

down the Rio Grande. Load, or burden, is defined as the mass 

of a given water-quality constituent transported during a 

given time period. Therefore, the load of a given constituent 

is a function of both concentration and flow. Dissolved-solids 

loads will only increase when new mass of dissolved solids is 

added through sources, such as direct groundwater discharge, 

tributary inflow, and discharge from municipal wastewatertreatment plants (Moore and Anderholm, 2002). Dissolvedsolids loads will only decrease when mass is removed from 

the system through pathways, such as irrigation diversions, 

groundwater recharge (seepage), or by precipitation of 

relatively insoluble minerals (Moore and Anderholm, 2002). 

The calculation of loads for dissolved solids in the 

Rio Grande in the study area is a critical step for the 

establishment of a budget for dissolved-solids transport. 

Various methods have been used to calculate dissolved-solids 

loads. Instantaneous loads are calculated by multiplying 

the concentration from a single water-quality sample by the 

streamflow that occurred when the sample was collected. 

Instantaneous loads are particularly useful for developing a 

detailed mass-balance of solute transport for a single point 

in time. Mills (2003), Phillips and others (2003), and Hogan 

and others (2007) used instantaneous loads to determine the 

mass balance for chloride transport in the Rio Grande from 

the headwaters in Colorado to Fort Quitman, Texas, during 

winter and summer hydrologic conditions. Time-integrated 

loads (for example, daily, monthly, annual, and decadal) 

are calculated using one of two methods: (1) multiplying an 
22 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

average water-quality concentration for a given time period 

by the total streamflow that occurred during that time period 

and a unit conversion factor (Wilcox, 1968; Bastien, 2009); 

or (2) applying a multiple linear-regression model to relate 

a water-quality constituent to a given streamflow condition 

(Moore and Anderholm, 2002). The benefit of using timeintegrated loads is that they account for variations in flow 

and water-quality conditions. The discussion on loads in the 

Rio Grande study area will focus solely on time-integrated 

loads calculated by Wilcox (1968) and Moore and Anderholm 

(2002).

Spatial Variability in Dissolved-Solids Loads

Dissolved-solids loads in the Rio Grande study area 

generally increase from San Marcial to Leasburg and decrease 

from Leasburg to Fort Quitman (Witcher and others, 2004; 

fig. 13). The mean daily load for dissolved solids during 

1934-63 was 1,295 tons/d at San Marcial and 1,364 tons/d 

at Leasburg (an increase of 69 tons/d). Both streamflow and 

dissolved-solids concentrations increase between San Marcial 

and Leasburg, indicating that the increase in load is caused 

by inflow of saline groundwater (Phillips and others, 2004; 

Hogan and others, 2007). The average daily load decreased 

by 196 tons in the Rio Grande between Leasburg and El Paso 

during 1934–63 (Wilcox, 1968). Between Leasburg and El 

Paso, annual streamflow is reduced, on average, by nearly 

40 percent; however, the annual load for dissolved solids, on 

average, is reduced by only 13 percent. The minor reduction 

of dissolved-solids load relative to the losses in streamflow 

between Leasburg and El Paso reflects the increased 

dissolved solids derived from the discharge of agricultural 

drains, municipal wastewater-treatment plants, and saline 

groundwater within this reach (Mills, 2003; Moore and 

others, 2008). More recent data from this reach (Moore and 

Anderholm, 2002) indicates that during 1993–95, the mean 

daily load in the Rio Grande between Leasburg and El Paso 

increased by 138 tons/d even though streamflow decreased 

by 213 ft3/s. Between El Paso and Fort Quitman, the mean 

daily load in the Rio Grande decreased by 252 tons/d (Wilcox, 

1968). Within this reach of the Rio Grande, approximately 70 

percent of the streamflow was lost between El Paso and Fort 

Quitman; however, the mean daily load was only reduced by 

22 percent (Wilcox, 1968). If the reduction in dissolved-solids 

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

DISSOLVED SOLIDS, IN TONS PER DAY

San Marcial below Elephant

Dam

below Caballo

Dam

above Leasburg

Dam

El Paso Fort Quitman

(30) (30)

(30) (30)

(30)

(30)

EXPLANATION

Percentile - Percentage of

values equal to or less than

indicated value

10th

25th

50th

75th

outlier

mean

90th

(30) number of 

observations

Figure 13. Boxplot of dissolved-solids annual mean daily loads for selected stations along the Rio Grande study area during 1934–63 

(Wilcox, 1968). 
Spatial and Temporal Variability in Dissolved-Solids Transport 23

loads was a result of the loss in streamflow, then the total 

reduction in dissolved solids would be nearly 70 percent. 

However, the dissolved-solids load is only decreased by 22 

percent, which indicates that a source of water with elevated 

concentrations of dissolved solids is contributing dissolved 

solids to the Rio Grande between El Paso and Fort Quitman. 

Hibbs and Merino (2007) determined that inflowing saline 

groundwater near the El Paso-Hudspeth County line is the 

dominant source of dissolved solids between El Paso and Fort 

Quitman. 

Temporal Variability in Dissolved-Solids Loads 

Annual variation in the mass of dissolved solids that are 

transported down the Rio Grande is influenced by climate and 

the management of Elephant Butte and Caballo Reservoirs 

(fig. 14). Investigation of time-series data for the annual mean 

load of dissolved solids transported in the Rio Grande at San 

Marcial shows the influence that climate had on the transport 

of dissolved solids during 1934–63 (fig. 14A). During wet 

years the load of dissolved solids in the Rio Grande at San 

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

DISSOLVED SOLIDS, IN TONS PER DAY

SM

1930 1935 1940 1945 1950 1955 1960 1965

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

DISSOLVED SOLIDS, IN TONS PER DAY

EB

CAB

LEA

EP

FQ

(A)

(B)

Figure 14. Plot of dissolved-solids annual mean loads measured in the Rio Grande at (A) San Marcial and (B) below Elephant Butte 

Dam (EB), below Caballo Dam (CAB), above Leasburg Dam (LEA), at El Paso (EP), and at Fort Quitman (FQ) from 1934 to 1963 (Wilcox, 

1968).
24 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

Marcial increased, and during drier years the load decreased. 

The influence of management of the Elephant Butte and 

Caballo Reservoirs on the load of dissolved solids in the Rio 

Grande is evident in the time-series records for the stations 

monitored by Wilcox (1968) below Elephant Butte Reservoir 

(fig. 14B). In general, most of the load of dissolved solids 

that passes San Marcial during wet years is stored in Elephant 

Butte and Caballo Reservoirs and a lesser amount is passed to 

downstream locations. Conversely, during drier years, more 

water and associated dissolved-solid load are released to 

downstream locations than enter Elephant Butte and Caballo 

Reservoirs. The influence of the extended drought during 

the 1950s on dissolved-solids load in the Rio Grande below 

Elephant Butte Reservoir is evident in figure 14B; dissolvedsolids loads were considerably reduced in the Rio Grande 

at El Paso and Fort Quitman. The downstream reduction in 

dissolved-solids loads in the Rio Grande is primarily a result 

of the storage of dissolved solids in the irrigated soils and(or) 

underlying alluvial aquifer (Miyamoto and others, 1995; 

Moore and Anderholm, 2002).

Seasonal variation in dissolved-solids loads in the Rio 

Grande is influenced primarily by the amount of water that 

is being transported. The management of Elephant Butte and 

Caballo Reservoirs has a major influence on the seasonal 

variation of the downstream transport of dissolved solids. 

These reservoirs store dissolved solids during the nonirrigation 

season, and a portion of these dissolved solids is released 

during the irrigation season. Dissolved-solids loads in the 

Rio Grande are greatest during the irrigation season. During 

the irrigation season, the load of dissolved solids increases 

between San Marcial and Leasburg (fig. 15). This increase in 

load during the irrigation season can be attributed to dissolved 

solids that are transported into the study area by snowmelt 

runoff and released from Elephant Butte and Caballo 

Reservoirs. Additional increases in dissolved-solids loads in 

the Rio Grande between San Marcial and Leasburg have 

been attributed to the inflow of regional groundwater with 

increased concentrations of dissolved solids (Cox and Reeder, 

1962; Anderholm, 2002). During the nonirrigation season, 

dissolved-solids loads in the Rio Grande below Elephant 

Butte Reservoir are reduced considerably because of limited 

streamflow; however, the pattern of increasing loads along 

the Rio Grande between Caballo and El Paso during the 

nonirrigation season has been attributed to contributions from 

agricultural drains, municipal wastewater-treatment plants, 

and discharge of saline groundwater (Mills, 2003; Moore and 

others, 2008; fig. 15).

Summary of Dissolved-Solids Loads

The value of understanding the spatial and temporal 

patterns in dissolved-solids loads is that these data provide 

a direct measure of the mass of dissolved solids that is 

transported or stored within a given reach of the Rio Grande. 

Spatially, dissolved-solids loads exhibit two distinct patterns 

(Appendix 1). The first pattern is one of slightly increasing 

loads between San Marcial and Leasburg. This pattern 

indicates that there is a net downstream flux of dissolved 

solids (that is, the mass of dissolved solids being transported 

exceeds the mass being stored), and that the mass of new 

load (for example, groundwater discharge) entering the 

reach exceeds the mass of load being stored (for example, 

groundwater recharge). The second pattern is one of 

decreasing dissolved-solids load in the Rio Grande between 

Leasburg and Fort Quitman. This pattern indicates that more 

dissolved solids are being stored through processes, such as 

irrigation diversions, groundwater recharge, municipal water 

supply, and mineral interactions, than are being transported 

downstream. Annual variations in dissolved-solids loads 

at monitoring stations above and below Elephant Butte 

Reservoir show that climate and management of Elephant 

Butte Reservoir considerably influence the downstream flux of 

dissolved solids. During wet years, Elephant Butte Reservoir 

typically stores dissolved solids along with streamflow; 

whereas, during dry years, Elephant Butte Reservoir releases 

stored dissolved solids to downstream reaches. During the 

irrigation season, dissolved-solids loads are high because 

of increased streamflow and show a negative trend from 

Leasburg to Fort Quitman because of increased storage by 

processes that include irrigation diversions, municipal water 

supply, and agricultural and riparian transpiration. During 

the nonirrigation season, dissolved-solid loads are lower 

because of decreased streamflow and show a positive trend 

from Caballo to Fort Quitman. This positive trend is a direct 

result of new dissolved solids entering the Rio Grande from 

the inflow of saline groundwater, agricultural drains, and 

wastewater-treatment plants. 

Dissolved-Solids Flow-Weighted 

Concentrations

Flow-weighted concentrations have been used by the 

Colorado River Salinity Management Program to establish 

water-quality goals and evaluate progress in meeting those 

goals (Colorado River Basin Salinity Control Forum, 2008). 

The flow-weighted concentration is an estimate of the mean 

annual concentration in a total volume of water flowing past 

a specific location during a specific time period, such as 

a month or a year (Langland and others, 2006). The flowweighted concentration (milligrams per liter) is calculated by 

dividing the total monthly or annual load by the total monthly 

or annual flow. The Colorado River Project (Colorado River 

Basin Salinity Control Forum, 2008) established water-quality 

criteria for dissolved-solids concentration at three monitoring 

stations along the Colorado River (fig. 16). The established 

criteria for dissolved-solids concentration at each monitoring 

station is based on a flow-weighted concentration. The annual 

flow-weighted concentration at each station is used to evaluate 

progress towards the goal of reducing dissolved-solids loads in 

the Colorado River. 
Spatial and Temporal Variability in Dissolved-Solids Transport 25

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

DISSOLVED SOLIDS LOADS, IN TONS PER DAY

NON IRR NON IRR NON IRR NON IRR NON IRR NON IRR

San Marcial below Elephant

Dam

below Caballo

Dam

above Leasburg

Dam

El Paso Fort Quitman

(214)

(328)

(225)

(317)

(86)

(416)

(218)

(322)

(302)

(427)

(280)

(403)

EXPLANATION

Percentile - Percentage of

values equal to or less than

indicated value

10th

25th

50th

75th

outlier

mean

90th

(427) number of 

observations

Figure 15. Boxplot of dissolved-solids annual mean loads during the nonirrigation (NON) and irrigation (IRR) season at selected sites in 

the Rio Grande study area from 1934 to 1999 (Wilcox, 1968; Williams, 2001).
26 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

Figure 16. Time series for annual flow-weighted dissolved-solids (TDS) concentration, in milligrams per liter (mg/L), and associated 

water-quality criteria at three monitoring stations along the Colorado River (from Colorado River Basin Salinity Control Forum, 2008). 

Flow-weighted concentrations of dissolved solids at Rio 

Grande stations monitored by Wilcox (1968) from 1934 to 

1963 show a pattern of increasing concentration as the Rio 

Grande passes from San Marcial to Fort Quitman (fig. 17). 

The annual median flow-weighted concentrations of dissolved 

solids in the Rio Grande are as follows: San Marcial, 507 

mg/L; Caballo, 504 mg/L; Leasburg, 559 mg/L; El Paso, 

731 mg/L; and Fort Quitman, 2,105 mg/L. Data collected by 

Wilcox (1968) could be used to establish initial water-quality 

criteria for monitoring stations along the Rio Grande in the 

study area. However, data collection and the calculation of 

annual dissolved-solids loads would have to be reinstituted 

in order to evaluate current conditions for flow-weighted 

concentrations and to evaluate progress toward dissolvedsolids reduction goals.

Data Gaps: Dissolved-Solids Concentrations and 

Loads

The primary data gaps associated with dissolved-solids 

concentration and loads are the availability of observed 

dissolved-solids concentration data, the comparability of loads 

data, and accuracy and completeness of streamflow data. 

Following the data-collection effort that occurred between 

1934 and 1963 (Wilcox, 1968), extensive gaps in observed 

water-quality data have occurred (Williams, 2001; Mills, 2003; 

Lacey, 2006; Bastien, 2009). Large amounts of water-quality 

data were collected from the Rio Grande at San Acacia, San 

Marcial, below Elephant Butte Dam, below Caballo Dam, 

above Leasburg Dam, El Paso, and Fort Quitman from 1934 

to 1963. During this period, several water-quality constituents, 

including dissolved solids and major cations and anions, were 

monitored. These data allowed the computation of dissolvedsolids loads and the identification of spatial and temporal 

trends in water-quality conditions along the Rio Grande. Since 

1963, water-quality data have been collected only sporadically. 

Water-quality data collected since 1963 have not been 

collected frequently enough to allow for detailed computations 

of dissolved-solids loads. The extensive gaps in water-quality 

data and inconsistency in data available from site to site limit 

the ability to evaluate long-term changes in water-quality 

conditions and the ability of water-resource managers to make 

informed decisions based on current water-quality conditions.

Spatial gaps in the availability of dissolved-solids 

concentration and load is most evident for the many irrigation 

drains that transport dissolved solids to the Rio Grande. The 

drains play an important role in transporting intercepted 

shallow groundwater and infiltrating irrigation water and 

associated dissolved solids to the Rio Grande. Dissolved 
Spatial and Temporal Variability in Dissolved-Solids Transport 27

1930 1935 1940 1945 1950 1955 1960 1965

300

400

500

600

700

800

900

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

SM

1930 1935 1940 1945 1950 1955 1960 1965

400

500

600

700

800

900

1,000

CAB

LEA

EP

1930 1935 1940 1945 1950 1955 1960 1965

0

1,000

2,000

3,000

4,000

5,000

FQ

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

(A)

(B)

(C)

Figure 17. Time series for annual flow-weighted concentration of dissolved solids in the Rio Grande (A) at San Marcial, (B) below 

Caballo Dam and above Leasburg Dam at El Paso, and (C) at Fort Quitman for the period 1934–63. 
28 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

solids are monitored in many of the irrigation drains within 

the study area; however, the infrequency of data collection in 

these drains and the absence of water-quality data in others 

prevent the computation of the dissolved-solids loads being 

transported by these drains. The absence of dissolved-solids 

load data for the irrigation drains is a major data gap that 

limits the understanding of dissolved-solids transport within 

the Rio Grande study area. 

The comparability of calculated loads is another data 

gap that exists in the current literature. Several studies 

have calculated loads to address questions related to the 

transport and mass balance of dissolved solids along the Rio 

Grande. Various methods and time steps have been used for 

the computation of dissolved-solids loads. Wilcox (1968) 

multiplied the total monthly streamflow by the monthly 

average concentration of dissolved solids to calculate loads. 

Moore and Anderholm (2002) used multiple linear-regression 

techniques to compute monthly and annual loads. Mills (2003) 

calculated instantaneous loads at multiple stations along the 

continuum of the Rio Grande during winter and summer flow 

regimes. The question remains, with multiple techniques being 

employed to describe the downstream flux of dissolved solids, 

are the resulting loads fully comparable?

Dissolved-Solids Budgets

The ability to account for the mass of dissolved solids 

transported along the Rio Grande is essential for both 

researchers who seek to understand the sources and sinks 

of dissolved solids and for managers who strive to preserve 

the quality of terrestrial and water resources within the Rio 

Grande Basin. Two types of budgets for dissolved-solids 

transport in the Rio Grande have been developed since the 

early 1900s. The first type of budget defines the relation 

between the mass of dissolved solids transported, typically 

monthly or annually, by the Rio Grande into a specified reach 

to the mass of dissolved solids transported out of the specified 

reach. If the mass of dissolved solids entering a particular 

reach of the Rio Grande exceeds the mass of dissolved solids 

exiting the reach, the mass balance for dissolved solids is 

considered adverse because dissolved solids are being stored 

in the agricultural soils or in the shallow alluvial aquifer rather 

than being transported farther downstream (Wilcox, 1957; 

Williams, 2001). The first type of dissolved-solids budget is 

referred to as a basic budget because it defines the balance 

between the mass of dissolved solids in river inflow and 

outflow for a defined reach of the Rio Grande. The second 

type of budget, referred to as a complex budget, accounts for 

all sources (such as, tributaries, agricultural drains, municipal 

wastewater effluent, mineral dissolution, and groundwater 

discharge) and sinks (such as, irrigation diversions, municipal 

diversions, groundwater recharge, and mineral precipitation) 

of dissolved solids such that the mass balance between the 

inflows to and outflows from a specified reach of the Rio 

Grande equals zero. The development of complex budgets 

has been made more possible during the past decade 

because newly developed hydrogeological, geophysical, 

and hydrochemical analyses allow for the quantitative 

identification of significant contributing sources (Mills, 2003; 

Phillips and others, 2003; Hogan and others, 2007; Eastoe and 

others, 2007; Moore and others, 2008).

Basic Budgets

Basic budgets, which describe whether dissolved 

solids are being stored or released from a specified reach 

in the Rio Grande in the study area, have been developed 

and described by Williams (2001) and Witcher and others 

(2004). Williams (2001) described the balance between the 

mass of dissolved solids in river inflow and outflow for the 

following reaches of the Rio Grande: (1) San Marcial to below 

Elephant Butte Dam, (2) below Elephant Butte Dam to below 

Caballo Dam, (3) below Caballo Dam to above Leasburg 

Dam, (4) above Leasburg Dam to El Paso (Courchesne 

Bridge), and (5) El Paso to Fort Quitman. The mass balance 

for the dissolved solids transported monthly in river inflow 

and outflow for each reach was determined by subtracting 

total monthly outflow from the total monthly inflow. If the 

inflow of dissolved solids is less than the outflow (negative 

values), the mass balance of dissolved solids generally is 

considered beneficial because dissolved solids are being 

released rather than stored or accumulated in the specified 

reach (Wilcox, 1957; Williams, 2001; Witcher and others, 

2004). A negative mass balance for dissolved solids can be a 

result of inflow of dissolved solids from tributaries, municipal 

wastewater effluent, mineral dissolution, and(or) groundwater 

discharge that occurs along the length of the specified reach. 

Conversely, if the inflow of dissolved solids is greater than 

the outflow (positive values), the mass balance of dissolved 

solids is considered adverse because dissolved solids are 

being stored in rather than released from the specified reach 

(Wilcox, 1957; Williams, 2001; Witcher and others, 2004). 

Dissolved solids can be stored through many transport and 

storage processes that include leakage of surface water and 

groundwater to the groundwater system, mineral precipitation, 

ion exchange, reservoir storage, and surface-water and 

groundwater withdrawals. The concern associated with the 

storage of dissolved solids is that their accumulation can lead 

to the degradation of agricultural soils and(or) groundwater 

resources.

The cumulative mass balances of dissolved solids for 

reaches along the Rio Grande in the study area, as described 

by Williams (2001) and Witcher and others (2004), are 

presented in figure 18. The cumulative mass balance for the 

reach from San Marcial to below Elephant Butte Dam shows 

that dissolved solids over the entire period were being stored; 

however, the temporal variation in the cumulative mass 

balance shows that the balance trends positive during highflow periods and trends negative during low-flow periods 
Dissolved-Solids Budgets 29

-2,000,000

-1,000,000

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

1934193619381940194219441946194819501952195419561958196019621964196619681970197219741976197819801982198419861988199019921994

DISSOLVED SOLIDS, IN TONS

SM - EB

EB-CAB

CAB - LEA

LEA - EP

EP - FQ

RELEASE

STORAGE

Figure 18. Cumulative mass balance for dissolved solids transported monthly in specified reaches along the Rio Grande study area 

(from Williams, 2001; used with permission). Specified reaches include San Marcial to below Elephant Butte Dam (SM – EB), below 

Elephant Butte Dam to below Caballo Dam (EB – CAB), below Caballo Dam to above Leasburg Dam (CAB – LEA), above Leasburg Dam to 

El Paso (Courchesne Bridge; LEA – EP), and El Paso to Fort Quitman (EP – FQ). 

(Williams, 2001) and is driven in large part by changes in 

storage in Elephant Butte Reservoir (Lacey, 2006). Witcher 

and others (2004) suggest that this temporal variation is a 

result of water and solutes being stored in Elephant Butte 

Reservoir during high-flow periods and subsequently released 

during low-flow periods. Other possibilities for the overall 

positive trend in mass balance are groundwater recharge 

and(or) mineral precipitation in the reservoir (Witcher and 

others, 2004). 

The cumulative mass balance for the reach below 

Elephant Butte Dam to below Caballo Dam indicates 

dissolved solids were being released, approximately 700,000 

tons during 1934–63 (fig. 18; Witcher and others, 2004). 

The negative mass balance for dissolved solids are attributed 

to tributary discharge to Caballo Reservoir during stormrunoff events or, more importantly, the discharge of saline 

groundwater of geothermal origin to the Rio Grande at Truth 

or Consequences, New Mexico (Cox and Reeder, 1962; 

Witcher and others, 2004). 

The cumulative mass balance for the reach from below 

Caballo Dam to above Leasburg Dam shows that dissolved 

solids were being released from this reach, approximately 

300,000 tons (fig. 18; Witcher and others, 2004). Witcher and 

others (2004) attribute this negative salt balance to mineral 

dissolution in the soils of the Rincon Valley. In addition to 

mineral dissolution, Anderholm (2002) suggests that discharge 

of regional groundwater contributes to the high dissolvedsolids concentration in the region of the Rincon Drain and at 

the distal end of the Palomas Basin. 

The cumulative mass balance for the reach from above 

Leasburg Dam to El Paso indicates considerable variability. 

The dissolved-solids balance for this reach was primarily 

negative (released dissolved solids) for the period 1934–51; 

however, the drought that occurred during the 1950s reversed 

the dissolved-solids balance to a primarily positive one (stored 

dissolved solids; fig. 18). Approximately 700,000 tons of 

dissolved solids were stored in this reach during 1955–63, and 

1,500,000 tons were stored during 1979–94. 
30 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

The cumulative mass balance for the reach from El Paso 

to Fort Quitman shows that dissolved solids primarily were 

stored, approximately 5,500,000 tons during 1934–75 (fig. 18; 

Witcher and others, 2004). The reversal of the cumulative 

mass-balance trend from positive to negative starting in 1986 

has been linked to spillway overflow and high-flow releases 

from Elephant Butte Reservoir that subsequently flushed 

accumulated salts, equivalent to 30 years of storage, in this 

reach of the river (Miyamoto and others, 1995; Witcher and 

others, 2004). 

The results of the cumulative mass-balance analysis for 

dissolved solids (Witcher and others, 2004) indicate long-term 

and continued storage of dissolved solids in the reaches from 

above Leasburg Dam to El Paso and from El Paso to Fort 

Quitman along the Rio Grande. One potential explanation 

for the increased storage in these reaches is loss of water and 

solutes from the Rio Grande to the underlying alluvial aquifer. 

West (1995) discussed the influences of the 1950s drought and 

increased dependence on groundwater supplies in the Mesilla 

Basin on streamflow. Increased groundwater diversions in 

the Mesilla Basin have reduced flow in the irrigation drains, 

thus reducing the amount of salts being flushed from the 

alluvial aquifer. Hibbs and Boghici (1999) also showed 

that the El Paso-Ciudad Juarez reach of the Rio Grande is 

a losing reach during all flow conditions, and the loss has 

been intensified since the 1970s as a result of groundwater 

pumping for municipal water supply. Wilson and others (1981) 

described the dissolved solids in the alluvial aquifer beneath 

the Mesilla Basin as having three unique zones—upper, 

middle, and lower—based on the associated concentration 

of dissolved solids. The upper zone generally has dissolvedsolids concentrations ranging from 1,000 to 3,000 mg/L. The 

middle zone generally has dissolved-solids concentrations 

that are less than 500 mg/L. The lower zone generally has 

dissolved-solids concentrations that are greater than 3,000 

mg/L. The large dissolved-solids concentrations in the upper 

zone of the alluvial aquifer beneath the Mesilla Basin may 

be a result of groundwater recharge from the Rio Grande 

and irrigation systems and concentration of these irrigation 

waters (Wilson and others, 1981; Witcher and others, 2004). 

Walton and others (1999) described that, in the Mesilla Basin, 

(1) irrigation and associated evaporation leads to increased 

dissolved-solids concentrations in the shallow alluvial aquifer; 

(2) the large dissolved-solids concentrations overlie the lower 

dissolved-solids concentrations in the intermediate depths; 

and (3) groundwater pumping for irrigation draws water with 

large dissolved-solids concentration water into the lowerconcentration water of the intermediate depths. 

There also is variation in the cumulative mass balances 

for the individual major ions, both temporally and spatially 

(Witcher and others, 2004). For example, the cumulative mass 

balance for major ions transported in the Rio Grande between 

Leasburg Dam and El Paso indicate two general patterns 

(fig. 19). Calcium, magnesium, sulfate, and bicarbonate 

all exhibit positive cumulative mass balance for the period 

1934–63 and 1980–94 (fig. 19). Conversely, sodium and 

chloride exhibit negative cumulative mass balance for the 

periods 1934–63 and 1980–94 (fig. 19); that is, more of 

these ions are leaving the basin at El Paso than entering at 

Leasburg. The storage of calcium, magnesium, sulfate, and 

bicarbonate in the reaches from Leasburg to El Paso and from 

El Paso to Fort Quitman can be attributed to the diversion of 

surface water for irrigation combined with a reduction in the 

drain flows (compounded by groundwater pumping), which 

otherwise would have transported irrigation return flows 

back to the Rio Grande, mineral precipitation, groundwater 

pumping, and(or) ion exchange (Witcher and others, 2004). 

The release of chloride along the Rio Grande has been 

investigated extensively during the past decade (Mills, 2003; 

Phillips and others, 2003; Lacey, 2006; Hibbs and Merino, 

2007; Hogan and others, 2007; Moore and others, 2008). 

These studies have found that discharge of saline groundwater 

(rich in chloride and sodium) to the Rio Grande is the primary 

source of dissolved solids in the Rio Grande study area. 

Complex Budgets

The goal for the development of complex solute budgets 

is to quantitatively represent all solute inflows and outflows 

such that the solute balance equals zero. Recent studies in 

the Rio Grande study area have focused on the development 

of complex budgets for solutes (Mills, 2003; Lacey, 2006; 

Bastien, 2009). The majority of the research focus was on 

developing complex budgets for chloride (Mills, 2003; Lacey, 

2006). Chloride was chosen because it is a conservative 

constituent that is not involved in chemical reactions with 

the surrounding environment. Results from these chloridebased investigations indicate that the dominant source 

contributing chloride to the Rio Grande is the discharge of 

saline groundwater to the Rio Grande; this discharge occurs 

primarily at the distal end of each alluvial-fill basin (Mills, 

2003; Phillips and others, 2003; Lacey, 2006; Hibbs and 

Merino, 2007; Hogan and others, 2007; Moore and others, 

2008). However, based on the cumulative mass-balance 

analysis for dissolved solids and major ions (Williams, 2001; 

Witcher and others, 2004), using complex budgets for chloride 

alone to describe the inflows and outflows of dissolved solids 

to the Rio Grande in the study area may not be completely 

representative. 

Mills (2003) developed complex budgets that represent 

chloride transport during both the irrigation (figs. 20, 21) 

and nonirrigation seasons (figs. 22, 23). These budgets 

represent the mass of chloride that is transported into and 

out of the Rio Grande from the headwaters in Colorado to 

Fort Quitman, Texas, during two snapshots in time – August 

2001 and January 2002. The structure of the pipe diagrams 

that represent chloride transport (figs. 20–23) shows (1) the 

flux of chloride being delivered by the Rio Grande in 

blue; (2) the inflows (gains) of chloride to the Rio Grande 

(tributaries, wastewater-treatment plants, agricultural drains, 
Dissolved-Solids Budgets 31

RELEASE

STORAGE

-800,000

-600,000

-400,000

-200,000

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1934193619381940194219441946194819501952195419561958196019621964196619681970197219741976197819801982198419861988199019921994

LOAD, IN TONS

DS

Ca

Mg

Na

SO4

Cl

HCO3

Figure 19. Cumulative mass balance for dissolved solids (DS), calcium (Ca), magnesium (Mg), sodium (Na), sulfate (SO4), chloride (Cl), 

and bicarbonate (HCO3) transported monthly in the reach of the Rio Grande above Leasburg Dam to El Paso (from Williams, 2001; used 

with permission). 

and groundwater seepage), which are represented on the 

left side of the pipe diagram; and (3) the outflows (losses) 

of chloride from the Rio Grande (irrigation diversions and 

seepage), which are represented on the right side of the pipe 

diagram. The flux of chloride for each source represented on 

the pipe diagram is based on (1) chloride concentration from 

a single water-quality sample and stream discharge obtained 

from the associated gaging stations; or (2) estimated chloride 

concentration and discharge based on previously published 

values. The pipe diagram for August 2001 (irrigation season) 

reveals that the chloride flux increases considerably below 

Elephant Butte Dam as a result of water and associated 

chloride released from Elephant Butte Reservoir (figs. 20, 

21). The flux of chloride leaving the Rio Grande (irrigation 

diversions and seepage) far exceeds the flux of chloride 

entering the Rio Grande. The flux of chloride in the Rio 

Grande below Elephant Butte Reservoir during the irrigation 

season is nearly completely removed by irrigation diversions 

by the time the Rio Grande reaches the El Paso-Hudspeth 

County line (river distance about 1,021 km from the 

headwaters). The flux then increases to levels greater than 

what were released originally from Elephant Butte Reservoir 

in the Rio Grande between the El Paso-Hudspeth County 

line and Fort Quitman, Texas (fig. 21). The pipe diagram 

for January 2002 (nonirrigation season) shows that the flux 

of chloride in the Rio Grande is diminished considerably 

compared to August 2001, which is a result of water and 

chloride being stored in Elephant Butte Reservoir (figs. 22, 

23). The chloride flux in the Rio Grande markedly increases 

near San Acacia (about 660 km from the headwaters), which 

is the area where the Rio Grande moves from the Albuquerque 

Basin to the Socorro Basin (fig. 22). The chloride flux is 

reduced considerably in the Rio Grande below Caballo Dam, 

but it steadily increases to the El Paso-Hudspeth County 

line and markedly increases between the El Paso-Hudspeth 

County line and Fort Quitman (fig. 23). Increases in the flux 

of chloride in the Rio Grande during January 2002 were 

attributed to the inflow of chloride from saline groundwater, 

agricultural drains, and wastewater-treatment plants (Mills, 

2003).
32 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

South Fork +

Goose Creek

Pinos Creek

Closed Basin Canal

Conejos River

Winograd (1959)

Embudo Creek

natural tribs + 

seepage (Winograd,1959)

Rio Chama + 

Santa Cruz River

Conveyance

Channel Newton and others (2002)

Newton and others (2002)

Percha diversions

Leasburg

diversions

Cochiti diversions

Angostura diversions

Jemez River + ag + Rio 

Rancho wastewater

Albuquerque 

wastewater + ag Isleta diversions + seepage 

(Papadopulos, 2002a)

Rio Puerco + 

San Juan Drain

San Acacia diversions +

seepage (Papadopulos, 2002a)

San Luis 

valley 

diversions

Elephant Butte reservoir

Caballo reservoir

Cochiti reservoir

Distance (km)

3.2

61.7

104.1

141.2

192.8

203.1

256.9

306.7

359.3

384.5

430.9

471.0

496.4

547.5

630.7

655.3

731.1

801.1

841.0

899.4

919.5

Garfield and

Hatch Drains

Legend

agricultural diversion/

return flow

wastewater outfall

riverbed seepage (source cited)

natural tributary

pipe width indicates Cl flux

scale 1 cm = 25,000 kg Cl /dy -

-

cm 0 1 2 6

kg/dy 25*103

50*103 150*103

Inputs are to the left of the main pipe; 

 outputs are to the right.

Position of input/output pipes does not 

 reflect actual geographic position.

main stem Rio Grande

reservoir (indicates transient

salt storage)

Figure 20. Pipe diagram of chloride burden of the Rio Grande, its modeled tributaries and diversions, August 2001 (kilograms per day; 

kg/d). River distance 3.2–919.5 kilometers (km) (figure from Mills, 2003; used with permission).
Dissolved-Solids Budgets 33

Las Cruces 

wastewater

Mesilla diversions

East Drain

Del Rio and

La Mesa Drains

Montoya Drain

El Paso wastewater

American Canal and 

Acequia Madre diversions

Ascarate Wasteway and 

Fabens Waste

Channel

944.7

955.1

987.6

1,013.8

1,021.6

1,149.0

919.5

Distance (km)

Wilson and others (1981)

Wilson and others (1981)

Wilson and others (1981)

Figure 21. Pipe diagram of chloride burden of the Rio Grande, its modeled tributaries and diversions, August 2001 (kilograms per day; 

kg/d). River distance 919.5–1,149.0 kilometers (km) (figure from Mills, 2003; used with permission).
34 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

South Fork +

Goose Creek

Pinos Creek

Closed Basin Canal

Conejos River

Winograd (1959)

natural tribs + 

seepage (Winograd,1959)

Embudo Creek

Santa Cruz River 

(Rio Chama gage frozen)

Jemez River + 

Rio Rancho wastewater

Albuquerque

wastewater + ag

Papadopulos (2002a)

Papadopulos (2002a)

San Juan Drain

Newton and others (2002)

Conveyance

Channel

Distance (km)

3.2

61.7

104.1

141.2

192.8

203.1

256.9

306.7

359.3

384.5

430.9

471.0

496.4

547.5

630.7

655.3

731.1

801.1

841.0

899.4

919.5

Cochiti reservoir

Elephant Butte reservoir

Caballo reservoir

Legend

agricultural diversion/

return flow

wastewater outfall

riverbed seepage (source cited)

natural tributary

pipe width indicates Cl flux

scale 1 cm = 25,000 kg Cl /dy -

-

cm 0 1 2 6

kg/dy 25*103

50*103 150*103

Inputs are to the right of the main pipe; 

 outputs are to the left.

Position of input/output pipes does not 

 reflect actual geographic position.

main stem Rio Grande

reservoir (indicates transient

salt storage)

Newton and others (2002)

Figure 22. Pipe diagram of chloride burden of the Rio Grande, its modeled tributaries and diversions, January 2002 (kilograms per day; 

kg/d). River distance 3.2–919.5 kilometers (km) (figure from Mills, 2003; used with permission).
Dissolved-Solids Budgets 35

Las Cruces wastewater

Wilson and others (1981)

Wilson and others (1981)

Wilson and others (1981)

Montoya Drain +

El Paso wastewater

East Drain

Del Rio and

La Mesa Drains

American Canal

Fabens Waste

Channel

944.7

955.1

987.6

1,013.8

1,021.6

1,149.0

919.5

Distance (km)

Figure 23. Pipe diagram of chloride burden of the Rio Grande, its modeled tributaries and diversions, January 2002 (kilograms per day; 

kg/d). River distance 919.5–1,149.0 kilometers (km) (figure from Mills, 2003; used with permission).
36 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

Mills (2003) computed the cumulative influence that 

each chloride source, identified during the August 2001 

sampling event, had on the associated total chloride load 

in the Rio Grande (fig. 24). The inflow of chloride from 

deep groundwater accounted for 37 percent of the total 

chloride load. The majority of the chloride delivered by 

deep groundwater occurred in the Rio Grande between 

Elephant Butte Reservoir and El Paso (approximately 

770 to 1,000 km). The inflow of chloride from natural 

tributaries and wastewater-treatment plants accounted for 

28 and 26 percent of the chloride load in the Rio Grande, 

respectively. Finally, 9 percent of the total chloride load in 

the Rio Grande was attributed to processes that occur within 

Elephant Butte Reservoir. The chloride contribution attributed 

to Elephant Butte Reservoir was defined as the difference 

between the inflow of chloride to Elephant Butte Reservoir 

and the amount of chloride discharged from Elephant Butte 

Dam. 

Chloride-flux information produced by Mills (2003) 

provides a detailed picture of the magnitude of fluxes of 

chloride entering and leaving the Rio Grande. The pipe 

diagrams for chloride flux clearly show where chloride is 

entering and leaving the Rio Grande; however, caution should 

be used when interpreting these figures. First, the chloride-flux 

information presented by Mills (2003; figs. 20–23) are based 

on two snapshots in time (August 2001 and January 2002) and 

probably do not reflect the variability inherent in the various 

long-term transport and storage processes. Second, many of 

the inflows and outflows of chloride are estimated based on 

values obtained from the literature and not directly measured. 

Finally, the pipe diagrams provide a detailed picture of 

chloride fluxes but do not account for the inflow and outflow 

of other dominant constituents contributing to the dissolved 

solids in the Rio Grande, such as sodium, calcium, sulfate, and 

bicarbonate.

Bastien (2009) developed complex budgets for dissolved 

solids and major ions for selected reaches in the Rio Grande 

study area between San Acacia and El Paso. The reaches of 

the Rio Grande that were included in the complex budget 

development are (1) San Acacia to San Marcial, (2) San 

Marcial to below Elephant Butte Dam, (3) below Elephant 

Butte Dam to below Caballo Dam, and (4) below Caballo 

Dam to El Paso (Courchesne Bridge). Bastien (2009) chose to 

develop complex budgets for dissolved solids as an average 

load for decadal time periods: 1930–39, 1940–49, 1950–59, 

1960–69, 1970–79, 1980–89, and 1990–99, given that the 

relation between inflow and outflows of dissolved solids 

varies temporally. Bastien (2009) represented three sources 

of dissolved solids to each reach of the Rio Grande: (1) Rio 

Grande inflow, (2) groundwater discharge to Rio Grande, 

and (3) brine. Rio Grande inflow represents the mass of 

dissolved solids that were transported by the Rio Grande 

into each specified reach in the study area. Much of the Rio 

Grande inflow data were obtained from Wilcox (1968) and 

Williams (2001). Groundwater discharge represents the mass 

of dissolved solids that are transported to the Rio Grande from 

the underlying alluvial aquifer. Data for groundwater discharge 

were based on published seepage studies for the volume of 

discharge and on Plummer and others (2004) for the quality 

of the discharge. Brine represents the discharge of saline 

groundwater to the Rio Grande. Data for the contribution of 

brines within each reach were based on published discharge 

and water-quality data from Newton (2005) and Moore 

and others (2008). Additionally, Bastien (2009) represents 

a category called “Rio Grande Inflow+,” which is the sum 

of the Rio Grande inflow, groundwater seepage, and brine 

categories. The “Rio Grande Inflow+” is the estimated amount 

of dissolved solids that would leave a given reach if the 

balance equaled zero. The actual outflow from each reach is 

represented by the “Rio Grande Outflow” category. 

Figure 24. Stacked graph of cumulative chloride addition by natural tributaries (nat), wastewater effluent (wwtp), deep groundwater 

(gw), and Elephant Butte Reservoir (res) dynamics, August 2001 (figure from Mills, 2003; used with permission).
Dissolved-Solids Budgets 37

Results from the complex budget development by 

Bastien (2009) are presented in table 1. As part of the 

evaluation of each complex budget for dissolved solids, the 

estimated inflow of dissolved solids (Rio Grande Inflow+) 

was compared to the measured outflow (Rio Grande Outflow). 

Discrepancies between the estimated inflow and measured 

outflow were attributed to chemical interactions with mineral 

phases, including aluminosilicate weathering reactions, 

dedolomitization, dissolution of minerals, and ion exchange 

interactions; each chemical interaction may act as a source or 

a sink for dissolved solids in irrigated or riparian areas 

(Bastien, 2009). The discrepancy between estimated inflow 

and measured outflow also could be attributed to groundwater 

and surface-water interactions and subsequent storage of 

dissolved solids in the underlying alluvial aquifer. Bastien 

(2009) concluded that dissolved-solids loads in the Rio 

Grande study area are controlled by three mechanisms. These 

mechanisms are groundwater seepage (discharge to Rio 

Grande), direct discharge of saline groundwater, and mineral 

interactions. 

A budget for dissolved solids in the Rio Grande between 

El Paso and Fort Quitman was presented by Miyamoto and 

others (1995). The major inflows of dissolved solids in this 

reach of the Rio Grande were represented as Rio Grande 

inflow at El Paso and municipal wastewater effluent from El 

Paso (table 2). The major outflows for dissolved solids were 

represented as those dissolved solids lost through diversions 

to the American and Mexican Canals as well as Rio Grande 

outflow at Fort Quitman (table 2). The mass-balance analysis 

for dissolved solids indicated that, on average, 64,000 tons 

were accumulated annually in the reach from El Paso to Fort 

Quitman reach during 1969–89. The mass-balance result 

from Miyamoto and others (1995) is in agreement with the 

results from Williams (2001) and Witcher and others (2004), 

who showed that dissolved solids are being stored rather than 

released from this reach.

Summary of Dissolved-Solids Budgets

Results from existing basic and complex budgets 

for dissolved solids in the Rio Grande provide valuable 

information pertaining to the mass of dissolved solids that is 

transported and(or) stored in designated reaches as well as 

the dominant sources that deliver dissolved solids to the Rio 

Grande. Results from basic dissolved-solids budgets for each 

reach in the Rio Grande study area revealed that three of the 

five reaches typically store more dissolved solids than are 

released; these reaches are San Marcial to below Elephant 

Butte Dam, above Leasburg Dam to El Paso, and El Paso 

to Fort Quitman. Storage in the reach from San Marcial to 

below Elephant Butte Dam has been attributed to storage in 

Elephant Butte Reservoir and the associated shallow alluvial 

aquifer. Storage in the reaches from above Leasburg Dam 

to El Paso and El Paso to Fort Quitman has been attributed 

to groundwater recharge, surface-water and groundwater 

withdrawals, and mineral precipitation. The concern regarding 

storage in theses reaches is the potential for degradation of 

agricultural soils and(or) groundwater resources through 

increased salinization. The remaining two reaches, which 

are below Elephant Butte Dam to below Caballo Dam and 

below Caballo Dam to above Leasburg Dam, transport more 

dissolved solids out of each respective reach than what entered 

each reach. This increase in dissolved solids in these two 

reaches has been attributed primarily to the inflow of saline 

groundwater near Truth or Consequences, New Mexico, and 

at the distal end of the Palomas Basin. Results from complex 

budgets indicate that the primary sources of dissolved solids 

entering the Rio Grande are derived from the inflow of saline 

groundwater, inflow of regional groundwater, and chemical 

reactions between mineral phases. The implication of these 

results for water-resource managers attempting to mitigate 

salinization along the Rio Grande is that they will have to 

consider both the inflow of saline and regional groundwater 

to the Rio Grande and the water and dissolved solids from the 

Rio Grande that are stored in agricultural soils and the shallow 

alluvial aquifer. 

Data Gaps: Dissolved-Solids Budgets

The computation of detailed budgets for the transport 

of dissolved solids and associated water-quality constituents 

is essential for the management of the Rio Grande water 

resources. Advancements in geochemical and isotopic 

analyses have enabled researchers to determine that most 

of the dissolved solids in the Rio Grande are derived from 

groundwater sources, such as discharge of saline groundwater 

derived from geothermal and nongeothermal sources. 

However, the ability for researchers to accurately quantify the 

flux of dissolved solids from the various groundwater-derived 

sources currently is not possible. The values represented in 

the previously discussed complex budgets that describe the 

contribution of saline groundwater to the Rio Grande are 

derived from published values for general discharge rates 

and water-quality. Accurate and reach-specific computations 

for the load of dissolved solids derived from the various 

groundwater sources are essential for future dissolved-solids 

mitigation efforts. 

Another data gap associated with the development and 

representation of complex budgets for specified reaches 

along the Rio Grande in the study area is the lack of direct 

measurement, or quantification, of the amount of dissolved 

solids stored in the underlying alluvial aquifer or associated 

soils. Bastien (2009) discusses the losses of dissolved solids 

through chemical and mineral interactions. However, the 

presentation of detailed budgets to date show inflow fluxes 

of dissolved solids or chloride and do not show the outflow 

fluxes (losses) from the Rio Grande to the underlying alluvial 

aquifer. 
38 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

Table 1. Mass balance for the monthly average dissolved solids transported in the Rio Grande between (1) San Acacia to San Marcial 

(SA to SM), (2) San Marcial to below Elephant Butte Dam (SM to EB), (3) below Elephant Butte Dam to below Caballo Dam (EB to CAB), 

and (4) below Caballo Dam to El Paso (Courchesne) (CAB to EP) for each decade from 1930–99. Data from Bastien, 2009.

[Rio Grande Inflow+, sum of Rio Grande Inflow, Groundwater Seepage, and Brine Inflow; nd, no data; --, value listed as a zero in Bastien (2009)]

Source SA to SM

(tons per month)

SM to EB

(tons per month)

EB to CAB

(tons per month)

CAB to EP

(tons per month)

1930 to 1939

Rio Grande inflow nd 29,785 44,597 nd

Groundwater seepage 404 273 1,011 5,320

Brine inflow nd 4,161 -- --

Rio Grande inflow+ nd 34,219 45,608 nd

Rio Grande outflow 29,785 44,597 nd 49,687

1940 to 1949

Rio Grande inflow 47,302 41,288 47,132 51,508

Groundwater seepage 404 273 1,011 5,320

Brine inflow 1,122 3,079 2,364 5,009

Rio Grande inflow+ 48,827 44,641 50,507 61,837

Rio Grande outflow 41,288 47,132 51,508 57,945

1950 to 1959

Rio Grande inflow nd 41,366 27,998 30,133

Groundwater seepage 404 273 1,011 5,320

Brine inflow nd -- 1,090 --

Rio Grande inflow+ nd 41,639 30,099 35,453

Rio Grande outflow 41,366 27,998 30,133 21,577

1960 to 1969

Rio Grande inflow 39,671 54,497 26,772 28,494

Groundwater seepage 404 273 1,011 5,320

Brine inflow 4,983 -- 1,198 107

Rio Grande inflow+ 45,058 54,770 28,981 33,921

Rio Grande outflow 39,671 54,497 26,772 28,494

1970 to 1979

Rio Grande inflow 35,358 50,140 21,804 --

Groundwater seepage 404 273 1,011 5,320

Brine inflow -- -- -- 13,381

Rio Grande inflow+ 35,762 50,413 22,814 --

Rio Grande outflow 50,140 21,804 -- 56,241

1980 to 1989

Rio Grande inflow 37,433 52,694 39,431 41,539

Groundwater seepage 404 273 1,011 5,320

Brine inflow 3,839 129 2,013 3,687

Rio Grande inflow+ 41,676 53,097 42,455 50,546

Rio Grande outflow 52,694 44,777 41,539 53,052

1990 to 1999

Rio Grande inflow 33,306 44,425 39,851 41,877

Groundwater seepage 404 273 1,011 5,320

Brine inflow 4,385 190 1,762 59

Rio Grande inflow+ 38,095 44,888 42,624 47,256

Rio Grande outflow 44,425 39,851 41,877 37,241
Location of Areas with High Concentrations of Dissolved Solids 39

Table 2. Mass balance for annual average dissolved solids 

transported in the Rio Grande between El Paso and Fort Quitman 

during 1969–89. Data from Miyamoto and others, 1995.

[nd = no data ] 

Source Dissolved solids

(million tons per year)

Inflows

Rio Grande inflow – El Paso 0.425

Municipal sewage effluent – El Paso 0.042

Outflows

American Canal 0

Mexican Canal 0.051

Rio Grande outflow – Fort Quitman 0.352

Balance

Mass balance (inflow minus outflow) 0.064

Location of Areas with High 

Concentrations of Dissolved Solids 

Many studies have investigated the hydrogeology and 

associated water-quality conditions along the Rio Grande 

and underlying alluvial-fill basins. During these investigations, 

researchers have identified areas of surface water and(or) 

groundwater that contain unusually high concentrations of 

dissolved solids or associated water-quality constituents 

compared to the nearby water-quality conditions (Appendix 2). 

This section identifies areas that contain high concentrations 

of dissolved solids and discusses potential sources that 

contribute to this water-quality condition. These areas have 

the potential to contribute substantial amounts of dissolved 

solids to the Rio Grande and need to be considered for future 

investigations and(or) future locations of dissolved-solids 

mitigation efforts. The organizing features for this section are 

the alluvial-fill basins that underlie the Rio Grande from San 

Acacia, New Mexico, to Fort Quitman, Texas. The locations 

of areas containing high dissolved-solids concentration will 

be discussed for the Socorro, San Marcial, Engle, Palomas, 

Mesilla, and Hueco Basins. Detailed description of the spatial 

extent and hydrogeology of these alluvial-fill basins can be 

found in Wilkins (1986). 

Socorro Basin

The Socorro Basin underlies the Rio Grande from 

San Acacia to San Marcial. The hydrogeology and water 

quality of the Socorro Basin was extensively studied by 

Anderholm (1987). During this investigation, Anderholm 

(1987) identified two distinct regions of the Socorro Basin 

that have values of specific conductance and chloride 

concentrations that are larger than those in surrounding 

areas (Appendix 2; fig. 25). Detailed locations of groundwatermonitoring wells and associated water-quality conditions 

are provided in Anderholm (1987, pl. 4). The first region of 

elevated specific conductance and chloride is located in the 

northern part of the basin between San Acacia and Polvadera, 

New Mexico. Chloride concentrations approach 4,020 mg/L 

in this northernmost region. Elevated chloride concentrations 

in this part of the basin are likely from upward-flowing 

groundwater with elevated concentrations of dissolved 

solids derived from the distal end of the Albuquerque 

Basin (Anderholm, 1987; Wilkins, 1998; Mills, 2003; 

Hogan and others, 2007). The second region Anderholm 

(1987, pl. 4) identified as having elevated chloride is located in 

an area that extends from approximately 5 mi north and south 

of San Antonio, New Mexico. Chloride concentrations in this 

region are as high as 1,100 mg/L and most likely are from 

upward-flowing groundwater with elevated concentrations of 

dissolved solids or geothermal water that is leaking upward 

along the Capitan lineament (Anderholm, 1987). Results 

of seepage investigations performed by Newton and others 

(2002) during 2000–2002 indicate that the Rio Grande 

between San Acacia and San Marcial primarily is a losing 

reach (loss of Rio Grande water to the shallow alluvial 

aquifer; Appendix 3). However, during periods of elevated 

flow in the Rio Grande, Newton and others (2002) found 

that groundwater inflow to the Rio Grande occurs between 

Escondida and Highway 380 (Appendix 3). These seepage 

investigations coupled with the location of elevated 

dissolved solids identified by Anderholm, (1987) may 

provide information on where elevated dissolved solids 

enter the Rio Grande; however, additional hydrogeologic 

studies are needed to identify flow paths and underlying 

geologic structure that controls the flow of these dissolved 

solids to the Rio Grande and influence the potential for 

mitigation. 

Another area with large concentrations of dissolved solids 

and chloride is the Luis Lopez Drain A (Mills, 2003). The Luis 

Lopez Drain A, which drains agricultural fields exclusively, is 

9-km long and ultimately flows into the Socorro Drain (Mills, 

2003). The dissolved-solids concentration was found to be 

1,200 mg/L year round. The measured chloride concentration 

in the Luis Lopez A Drain was 232 mg/L, and the chloridebromide ratio was 839. Mills (2003) argued that with no salt 

source evident at the surface, high chloride-bromide ratios, 

and historically consistent concentration of dissolved solids, 

it is probable that this drain intercepts upward-flowings saline 

groundwater. 
40 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

(1)

(2)

(3)

(4)

(5)

(6)

10

25

10

Elephant Butte

Reservoir

Caballo

Reservoir

Rio Grande

0 20 40 60 MILES

0 20 40 60 KILOMETERS

CHIHUAHUA

NEW MEXICO

TEXAS

UNITED STATES

MEXICO

OTERO COUNTY

CATRON

COUNTY

SOCORRO COUNTY

CHAVES COUNTY

LINCOLN COUNTY

SIERRA COUNTY

GRANT

COUNTY

LUNA COUNTY

TORRANCE COUNTY

HUDSPETH COUNTY

DONA ANA

COUNTY

EL PASO

COUNTY

El Paso

Socorro

Leasburg

Las Cruces

San Acacia

San Marcial

Fort

Quitman

Fabens

Polvadera

Ciudad

 Juarez

Truth or 

Consequences

108°00' 107°30' 107°00' 106°30' 106°00' 105°30' 105°15'

34°15'

34°00'

33°45'

33°30'

33°15'

33°00'

32°45'

32°30'

32°15'

32°00'

31°45'

31°30'

31°15'

31°00'

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 13

North American Datum of 1983

EXPLANATION

Alluvial-fill basin underlying the Rio Grande—

 Boundaries are approximate

 Socorro

 San Marcial

 Engle

Area containing unusually high concentrations

 of dissolved solids

 Palomas

 Mesilla

 Hueco

TEXAS

COLORADO

OKLAHOMA ARIZONA

NEW MEXICO

UNITED STATES

MEXICO

ALBUQUERQUE

BASIN

San Antonio

Albuquerque

Area

enlarged

Rio Grande

surficial drainage area

in the United States

Figure 25. The Rio Grande study area (white area) and the approximate location of areas containing unusually high concentrations 

of dissolved solids (in shaded black polygons) within each of the six alluvial-fill basins underlying the Rio Grande: (1) Socorro, (2) San 

Marcial, (3) Engle, (4) Palomas, (5) Mesilla, and (6) Hueco Basins. Boundaries of the six alluvial-fill basins are approximated from Wilkins 

(1986).
Location of Areas with High Concentrations of Dissolved Solids 41

San Marcial Basin

The San Marcial Basin is the next basin south of the 

Socorro Basin. The Rio Grande flows southwest through the 

San Marcial Basin from San Marcial, New Mexico, to the 

upstream end of Elephant Butte Reservoir (Wilkins, 1986). 

Virtually no published information is available regarding the 

hydrogeology (Wilkins, 1986) and associated water quality of 

the San Marcial Basin. 

Engle Basin

The Engle Basin is the next downstream alluvial-fill 

basin that underlies the Rio Grande (Wilkins, 1986). The Rio 

Grande flows through the Engle Basin from the upstream 

end of Elephant Butte Reservoir to just south of Truth or 

Consequences, New Mexico. The groundwater conditions in 

the Engle Basin were evaluated by Cox and Reeder (1962), 

who found that an area of thermal artesian groundwater, from 

the Magdalena group of Pennsylvanian and Permian age, 

discharges to the Rio Grande at Truth or Consequences, New 

Mexico. The thermal artesian groundwater, based on samples 

collected from well 14.4.4.211, has a sulfate concentration 

of 96 mg/L, a chloride concentration of 1,300-1,400 mg/L, a 

specific conductance of 4,450 microsiemens per centimeter 

(μS/cm), and a temperature of 104 °F (Cox and Reeder, 

1962). Cox and Reeder (1962) delineate the area of thermal 

groundwater as water in wells and springs in the S1/2 sec. 

33, T. 13 S., R. 4 W., and the N1/2 sec. 4, T. 14 S., R. 4W., 

within the limits of the town of Truth or Consequences 

north of the ridge of Precambrian rocks upon which Carrie 

Tingley Hospital is located (fig. 25). Based on two seepage 

investigations, performed November 30, 1960, and January 

20, 1961, Cox and Reeder (1962) concluded that discharge 

increased by approximately 25 ft3

/s (1.1 ft3/s /mile) from 

below Elephant Butte Dam to the upstream end of Caballo 

Reservoir (Appendix 3). Coupled water-quality data and 

seepage results indicate that the inflow of saline groundwater 

of geothermal origin occurs between Truth or Consequences 

and Williamsburg (located about 3 miles downstream from 

Truth or Consequences) (Cox and Reeder, 1962). 

Processes governing the transport and storage of 

dissolved solids in Elephant Butte Reservoir are not 

completely understood. In a recent study, Lacey (2006) 

developed a model to simulate the water and chloride mass 

balance in Elephant Butte Reservoir. During this investigation, 

Lacey (2006) found strong evidence that suggests saline 

groundwater is discharging to Elephant Butte Reservoir and 

subsequently transported downstream. Lacey (2006) suggests 

that the discharge of saline groundwater into Elephant Butte 

Reservoir is minimized when the reservoir storage is high, 

such as during the 1979–93 period; conversely, the discharge 

of saline groundwater increases during periods when storage 

in Elephant Butte Reservoir is substantially reduced, such as 

during 1993–2004. Additional information is needed to better 

identify and quantify the processes that govern the transport 

and storage of dissolved solids into and out of Elephant Butte 

Reservoir.

Palomas Basin

The Palomas Basin is the next downstream basin from 

the Engle Basin that underlies the Rio Grande (Wilkins, 

1986). The Rio Grande flows southeast through the Palomas 

Basin from just south of Truth or Consequences, New 

Mexico, to Selden Canyon north of Leasburg (Wilkins, 1986; 

Anderholm, 2002). The surface-water quality, quality of 

the groundwater in the shallow alluvial aquifer, and factors 

affecting water quality in the Palomas Basin were investigated 

and described by Anderholm (2002). Anderholm (2002) 

found that the concentrations of dissolved solids in the Rio 

Grande, agricultural drains, and groundwater in the shallow 

alluvial aquifer increased toward the southern end of the 

basin. The concentrations of dissolved solids in agricultural 

drains were always higher than the concentration of dissolved 

solids in the Rio Grande. Dissolved-solids concentrations 

double along the length of both the Hatch and Rincon Drains. 

Dissolved-solids concentrations in the Hatch Drain increased 

from approximately 650 mg/L to approximately 1,000 mg/L 

over a distance of 9 mi. Dissolved-solids concentrations in 

the Rincon Drain increased from approximately 800 mg/L 

to approximately 1,300 mg/L over a distance of 6 mi. The 

largest concentrations of dissolved solids were measured 

in groundwater wells completed in the shallow alluvial 

aquifer (well numbers 25, 26, 27, and 29) between the town 

of Rincon, New Mexico, and the discharge point of the 

Rincon Drain (fig. 25). Dissolved-solids concentrations in 

these groundwater wells ranged from 1,350 to 3,630 mg/L 

(Anderholm, 2002). Anderholm (2002) attributed the high 

concentrations of dissolved solids in the southern section 

of the Hatch and Rincon Drains and in the groundwater in 

the shallow alluvial aquifer near the distal end of the basin 

to inflow of regional groundwater. A major pathway for the 

movement of regional groundwater has been identified as 

groundwater transported from the Jornada del Muerto Basin 

eastward into the Palomas Basin (King and others, 1971). 

Results from seepage investigations show that groundwater 

inflow dominates the reach of the Rio Grande from below 

Caballo Dam to above Leasburg Dam (Appendix 3; 

Anderholm, 2002). Groundwater enters the Rio Grande for 

24 mi below Caballo Dam and between the Hatch and Rincon 

Drains. Anderholm (2002) also showed that Rincon Drain 

intercepts considerable inflow of regional groundwater. 

Mesilla Basin

The Mesilla Basin is the next downstream alluvial-fill 

basin from the Palomas Basin (Wilkins, 1968). The Rio 

Grande enters the Mesilla Basin as it flows through Selden 

Canyon at Leasburg, New Mexico, and continues flowing 
42 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

southeast to a narrow section of alluvial fill formed by the 

near-surface bedrock at El Paso, Texas. The water resources 

of the Mesilla Basin have been extensively studied for the past 

century. Detailed descriptions of the groundwater chemistry 

and the factors affecting groundwater chemistry are provided 

by Frenzel and others (1992) and Witcher and others (2004). 

Dissolved solids in the Mesilla Basin portion of the Rio 

Grande are controlled primarily by inflow of geothermal 

groundwater along the eastern portion of the Mesilla Basin 

and inflow of saline groundwater at the distal end of the 

Mesilla Basin (Frenzel and others, 1992; Witcher and others, 

2004; Moore and other, 2008). 

The inflow of geothermal groundwater has been 

identified as a major contributing source of dissolved solids 

in the Mesilla Basin portion of the Rio Grande (Frenzel 

and others, 1992; Witcher and others, 2004). Frenzel and 

others (1992, pl. 2) showed that the inflow of geothermal 

groundwater is not confined to a small area; rather, geothermal 

inflow of groundwater occurs along faults that underlie much 

of the eastern side of the Mesilla Basin (fig. 25). Frenzel and 

others (1992) identified two groundwater wells, 25S.3E.6.212 

and 23S.2E.25.321, that characterize the chemistry of the 

geothermal groundwater. Another area of inflow of geothermal 

groundwater occurs southeast of the I–10 and I–25 interchange 

at Las Cruces, New Mexico (Witcher and others, 2004). 

Additionally, the East Drain, which runs along the eastern side 

of the Mesilla Basin from Anthony to Mesquite, is believed to 

intercept inflowing geothermal groundwater (Conover, 1954; 

Frenzel and others, 1992).

Inflow of saline groundwater also has been identified 

as a major contributing source of dissolved solids in the 

Mesilla Basin portion of the Rio Grande (Mills, 2003; 

Hogan and others, 2007; Moore and others, 2008). Most 

of the saline groundwater, termed brines in several of the 

references, flow upward at the distal end of the Mesilla Basin 

(fig. 25). It is in this area where the underlying geology 

forces saline groundwater at depth towards the surface and 

Rio Grande. Water chemistry in groundwater wells along the 

southern end of the Montoya Drain and above the narrow 

section at El Paso is indicative of upward-flowing saline 

groundwater. Concentrations of dissolved solids (4,010 

mg/L), chloride (1,320 mg/L), sulfate (1,150 mg/L), and 

sodium plus potassium (1,310 mg/L) are elevated in well 

number JL-49-12-106 (Frenzel and others, 1992, pl. 5), 

located along the Montoya Drain north of the city limits 

of El Paso. Further south along the Montoya Drain, well 

number 29S.4E.6.243 (Frenzel and others, 1992, pl. 5) has 

even higher concentrations of chloride (4,000 mg/L), sulfate 

(3,600 mg/L), and sodium plus potassium (3,622 mg/L). In 

addition, the New Mexico Interstate Stream Commission and 

New Mexico Environment Department operate a monitoringwell network in the southern Palomas and Mesilla Basins. 

Results from quarterly monitoring of the groundwater 

network, during 2006–7, indicated that elevated dissolved 

solids and associated constituents extend from Santa Teresa, 

New Mexico (wells ISC-6 and ISC-7), to the region just 

southeast of the confluence of the Montoya Drain and the Rio 

Grande (wells ISC-4, ISC-5 and El Paso Electric wells EPE-9, 

EPE-17, EPE-20, EPE-21; Daniel B. Stephens & Associates, 

Inc., 2008). Concentrations of dissolved solids (30,000 

mg/L), chloride (18,000 mg/L), sulfate (6,200 mg/L), and 

sodium (7,700 mg/L; Moore and others, 2008) are elevated in 

groundwater well ISC-4 near the confluence of the Montoya 

Drain and the Rio Grande. Groundwater in the ISC-4 well 

commonly is used to represent the water chemistry of the 

upward-flowing saline groundwater (Mills, 2003; Moore and 

others, 2008; Bastien, 2009). 

Seepage investigations have been conducted annually 

(1988–2008) by the USGS along a 62.4-mi reach of the Rio 

Grande that extends from below Leasburg Dam to El Paso 

(Courchesne Bridge) (http://nm.water.usgs.gov/projects/

mesilla/). Results from these seepage investigations show that 

considerable gains to the Rio Grande (groundwater inflow) 

occur (1) from below Leasburg Dam to Shalem Bridge 

and (2) from Sunland Park Bridge to Courchesne Bridge 

(Appendix 3). Conversely, these seepage investigations also 

show that considerable losses occur (1) from Shalem Bridge 

to below Mesilla Dam and (2) from Vinton Bridge to Sunland 

Park Bridge. 

The Montoya Drain drains a large area in the Mesilla 

Basin and has the largest flow and dissolved-solids load 

contribution to the Rio Grande of any other drains. The 

Montoya Drain accounts for more than half of the streamflow 

and dissolved-solids loads that are measured in the Rio 

Grande at El Paso (approximately 0.25 mi downstream from 

the Montoya Drain) during the nonirrigation season (Edward 

Nickerson, U.S. Geological Survey, written commun., June 

16, 2009). The Montoya Drain generally carries water with 

values of specific conductance that range from 3,000 to 

4,000 μS/cm and chloride concentrations that range from 

500 to 675 mg/L. Geochemical and isotopic investigations 

reveal that the water chemistry of the Montoya Drain is 

derived from a mix of saline groundwater from geothermal 

and nongeothermal origins and Rio Grande water (Moore and 

others, 2008; Bastien, 2009). Therefore, salinity-mitigation 

efforts that reduce the mass of dissolved solids in inflowing 

saline groundwater should result in improvement of the quality 

of water delivered by the Montoya Drain and other irrigation 

drains.

Hueco Basin

The Hueco Basin is located southeast of the Mesilla 

Basin. The Rio Grande enters the Hueco Basin at the narrow 

section at El Paso and flows southeast to Fort Quitman, Texas 

(Wilkins, 1986). Extensive research in the Hueco Basin has 

focused on characterizing the various aquifer systems and 

associated hydrogeology (Hibbs, 1999; Hibbs and others, 

2003; Anderholm and Heywood, 2003; Druhan and others, 

2007). According to Hibbs and Merino (2007), the dominant 

source of dissolved solids in the Rio Grande within the 

Hueco Basin is the dissolution and subsequent transport 
Future Studies and Monitoring Data 43

of buried evaporites. However, Hibbs and Merino (2007) 

warned that the continued use of groundwater with elevated 

concentrations of dissolved solids for irrigation purposes 

will lead to continued degradation of soil conditions. Hibbs 

and Merino (2007) identified artesian groundwater flow and 

subsequent dissolution of evaporites associated with “paleophreatic playa beds” in a region approximately 2 mi southeast 

of Fabens, Texas (fig. 25). Within this area, Hibbs and Merino 

(2007) found chloride concentrations of 15,000 mg/L and 

chloride-bromide ratios of 5,800 in groundwater from the 

alluvial aquifer from approximately 150 to 250 ft below the 

land surface. Dissolved solids derived from the dissolution 

of the evaporates in the buried playa beds and subsequent 

transport by upwelling artesian groundwater are intercepted 

by agricultural drains and subsequently transported to the Rio 

Grande at various locations (Hibbs and Merino, 2007). 

Municipal wastewater effluent from the Cities of El Paso 

and Fabens results in substantial dissolved-solids load to the 

Rio Grande in the Hueco Basin and needs to be evaluated. 

Miyamoto and others (1995) estimated that the average annual 

discharge of dissolved solids from the El Paso wastewatertreatment facility was 42,000 tons (approximately 10 percent 

of the load in the Rio Grande at El Paso) for the 1969–89 time 

period. Also, Mills (2003) showed that contributions from 

the Ascarate and Fabens waste channels deliver substantial 

amounts of chloride to the Rio Grande. Effluent from the 

wastewater-treatment facility in Fabens, Texas, discharges 

directly to the Fabens waste channel.

Future Studies and Monitoring Data

Looking forward, multiple water-resource managers 

from State and local agencies in New Mexico and Texas 

as well as many Federal agencies have united to form the 

Rio Grande Salinity Management Coalition (http://www.

nmenv.state.nm.us/swqb/LowerRioGrande/). The unifying 

goal for the Coalition is to reduce the amount of dissolved 

solids that are transported and stored in the Rio Grande study 

area, thus ensuring that the Rio Grande water resources are 

of the quality that promotes the integrity and vitality of the 

agricultural, municipal, and ecological communities that 

rely on this limited resource. The following section provides 

recommendations for data-collection efforts and development 

of tools that could assist the Coalition in planning for, 

implementing, and evaluating mitigation efforts for dissolved 

solids in the Rio Grande. These recommendations are grouped 

into three categories: (1) monitoring of dissolved solids, 

(2) focused hydrogeology studies at inflow sources, and 

(3) modeling of dissolved solids.

Monitoring of Dissolved Solids

The collection of water samples to measure the 

concentration of dissolved solids and associated constituents 

from the Rio Grande, irrigation and agricultural-drain 

network, and underlying groundwater system is imperative 

for water-resource managers to effectively manage the 

surface-water and groundwater resources of the Rio Grande 

study area. Collection of these data provide a foundation for 

(1) improving the current understanding of dissolved-solids 

transport in the Rio Grande study area; (2) establishing waterquality goals; (3) building tools for water-resource managers 

to more effectively manage water-quality conditions; and 

(4) assessing changes in water-quality conditions in the Rio 

Grande resulting from salinity-mitigation efforts. 

Rio Grande and Agricultural Drain Monitoring

The primary data-collection effort recommendation is 

to reestablish and(or) maintain monitoring of streamflow and 

water-quality conditions along the Rio Grande and major 

agricultural drains. Streamflow and water-quality monitoring 

data will be essential for the computation of dissolved-solids 

loads and the evaluation of long-term trends. The availability 

of annual load data is essential for determining the total 

amount of dissolved solids and associated water-quality 

constituents that are being transported or stored annually 

in the Rio Grande study area. These monitoring data also 

will allow for the evaluation of short- and long-term trends 

in water-quality conditions in the Rio Grande as a result of 

various dissolved-solids mitigation efforts. The computation of 

annual loads and evaluation of short- and long-term trends will 

provide water-resource managers with information regarding 

the influence dissolved-solids mitigation efforts are having on 

water-quality conditions. 

Streamflow and water-quality conditions need to be 

monitored along the Rio Grande and at the distal end of major 

agricultural drains. The Rio Grande monitoring stations should 

include (1) San Acacia, (2) San Marcial, (3) below Elephant 

Butte Dam, (4) below Caballo Dam, (5) above Leasburg Dam, 

(6) at El Paso (Courchesne Bridge), (7) at Fabens (El PasoHudspeth County line), and (8) Fort Quitman. The irrigationdrain monitoring stations should include (1) Socorro Drain, 

(2) Rincon Drain, (3) Montoya Drain, and (4) Fabens waste 

canal. Water-quality data need to be collected monthly from 

the above listed locations. Water-quality samples need to be 

analyzed for dissolved solids, major ions (chloride, sulfate, 

carbonate, bicarbonate, sodium, calcium, and magnesium), 

bromide, and selected isotopes (used by Phillips and others, 

2003; Hogan and others, 2007; Moore and others, 2008). 

Streamflow conditions need to be monitored continuously, 

such as 15-minute intervals, at each of the above locations; 

this monitoring will facilitate the computation of loads and 

evaluation of trends. A quality-assurance and quality-control 

plan needs to be developed and implemented to ensure that 

collected streamflow and water-quality data are of similar 

quality and are comparable among various collecting agencies 

and monitoring stations and over time.

The computation of water-quality constituent loads needs 

to be calculated and reported annually and employ a multiple 
44 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

linear-regression technique similar to the one used by Moore 

and Anderholm (2002). Examples of water-quality monitoring 

programs that incorporate multiple linear-regression analyses 

to compute loads and evaluate short- and long-term trends can 

be found for the Chesapeake Bay watershed (Langland and 

others, 2006) and the Mississippi River watershed (Aulenbach 

and others, 2007). 

Groundwater/Surface-Water Interaction 

Investigation

Groundwater-seepage investigations are a commonly 

used approach to determine if a specified reach of river is 

receiving groundwater discharge or is losing surface water 

to the underlying alluvial aquifer (Harvey and Wagner, 

2000; Rosenberry and LaBaugh, 2008). These investigations 

require the measurement of surface-water flow at the 

upstream and downstream locations of a specified reach and 

accounting for major surface inflows to and outflows from 

the reach. Differences in surface-water flow between two 

locations indicate whether groundwater (or other sources) is 

discharging to the surface-water system (gaining reach) or if 

surface water is being lost to the underlying alluvial aquifer 

(losing reach). The USGS has been performing fine-scale 

seepage investigations in the Rio Grande and contributing 

irrigation drains in the Mesilla Basin annually since 1988 

(http://nm.water.usgs.gov/projects/mesilla/). These seepage 

investigations are performed during the nonirrigation period 

in order to maximize the groundwater-discharge signal. 

Results from seepage investigations in the Mesilla Basin 

have identified the reaches of the Rio Grande in the Mesilla 

Basin that are “gaining” and “losing.” Additionally, the 

USGS quantifies the load of dissolved solids and associated 

constituents being gained or lost from each reach by collecting 

water-quality data in conjunction with each discharge 

measurement. 

Therefore, the implementation of groundwaterseepage investigations is recommended for the reaches of 

the Rio Grande that drain the Socorro, San Marcial, Engle, 

Palomas, and Hueco Basins with continued support of the 

seepage investigation in the Mesilla Basin. These seepage 

investigations need to be executed during both the highflow (irrigation season) and low-flow (nonirrigation season) 

periods. Seepage investigations during low-flow conditions 

best identify groundwater discharge to the surface-water 

system. Seepage investigations also need to be performed 

during high-flow conditions to quantify the volume of water 

and dissolved solids that are transported from the surfacewater system and subsequently stored in the alluvial aquifer. 

Water-quality samples also need to be collected and analyzed 

for dissolved solids, major ions (chloride, sulfate, carbonate, 

bicarbonate, sodium, calcium, and magnesium), bromide, and 

selected isotopes (used by Phillips and others, 2003; Hogan 

and others, 2007; Moore and others, 2008). By including the 

collection of water-quality data during seepage investigations, 

the flux of dissolved solids entering and leaving the Rio 

Grande can be calculated. 

Groundwater Monitoring

The results from the mass-balance analysis performed 

by Williams (2001) and Witcher and others (2004) indicate 

that substantial amounts of dissolved solids are being stored 

in the Mesilla and Hueco Basins. One mechanism that has 

been attributed to the loss of surface water and associated 

dissolved solids from the Rio Grande is groundwater pumping 

for agricultural and municipal purposes (West, 1995; Hibbs 

and Boghici, 1999). The concern is that groundwater pumping 

will facilitate the degradation of groundwater quality in the 

Mesilla and Hueco Basins by (1) transporting water with 

high concentrations of dissolved solids from the Rio Grande 

into the upper levels of the alluvial aquifer, and (2) mixing 

water having high concentrations of dissolved solids in 

the upper zone of the alluvial aquifer with water at great 

depths containing low concentrations of dissolved solids 

(Walton and others, 1999). Therefore, it is recommended 

that a groundwater-monitoring network be instrumented that 

allows for (1) monitoring of current water-quality conditions, 

(2) evaluation of temporal and spatial changes in waterquality conditions, and (3) the potential for forecasting future 

water-quality conditions based on changes in municipal and 

agricultural water demands within the Mesilla and Hueco 

Basins. 

Focused Hydrogeology Studies at Inflow 

Sources 

Recent studies have determined that the dominant sources 

controlling dissolved solids in the Rio Grande study area are 

derived from the inflow of two saline groundwater sources – 

groundwater with elevated concentrations of dissolved 

solids and geothermal groundwater (Phillips and others, 

2003; Hibbs and Merino, 2007; Hogan and others, 2007; 

Moore and others, 2008). As a result, focused hydrogeologic 

investigations are needed to (1) better define the spatial extent 

where elevated dissolved-solids concentrations have been 

identified, (2) identify locations and associated flow paths 

where dissolved solids and associated constituents are being 

discharged from the underlying alluvial aquifer to the Rio 

Grande, and (3) identify the influence that the underlying 

geology has on the transport of dissolved solids and potential 

for successful mitigation. 

Helicopter Electromagnetic-Resistivity Data

The USGS, in Austin, Texas, in cooperation with 

the U.S. Bureau of Reclamation, has collected helicopter 

electromagnetic resistivity (HEM) data along parts of the 

Rio Grande and Rio Grande study area. These HEM data 
Future Studies and Monitoring Data 45

provide a measure of the electrical resistivity of the underlying 

alluvial aquifer (Rosenberry and LaBaugh, 2008). Changes in 

resistivity of the underlying alluvial aquifer can be related to 

changes in the properties of the alluvium (for example, gravel 

or clay) or changes in water-quality conditions (for example, 

high concentrations of dissolved solids or low concentrations 

of dissolved solids). The resistivity data are related (“groundtruthed”) to measured subsurface properties and(or) waterquality conditions to obtain a three-dimensional framework for 

the specified property. Preliminary three-dimensional images 

for dissolved solids in the alluvial aquifer underlying the Rio 

Grande within the city limits of El Paso are now available 

(fig. 26). These images effectively identify the spatial extent 

of areas containing high concentrations of dissolved solids. 

HEM data for the distal end of the Mesilla Basin indicate that 

high-conductivity water with high concentrations of dissolved 

solids is in close proximity to the land surface in the area 

of the narrow section at El Paso (fig. 26). The spatial extent 

of these data is from levee to levee and reaches a depth of 

approximately 100 ft beneath the land surface.

HEM data need to be collected and processed for areas 

that currently are not covered by the work being performed 

by the USGS and U.S. Bureau of Reclamation. These HEM 

data could serve as a valuable tool for managing dissolved 

solids along the Rio Grande. By having a three-dimensional 

image of the spatial extent of dissolved solids in the alluvial 

aquifer, water-resource managers working with engineers 

and hydrologists, would be able to better identify areas of 

the Rio Grande where inflow of saline groundwater occurs. 

Additionally, HEM data could provide valuable information 

on the hydrogeologic framework for each of the alluvial-fill 

basins. This framework then could be incorporated into the 

groundwater model for each basin. 

Hydrogeological and Tectonic Characterization 

at Inflow-Source Regions

Considerable research has been performed on the 

characterization of the hydrogeological matrix of the Rio 

Grande study area and associated alluvial basin (Chapin, 1971; 

Hawley, 1978; Riecker, 1979; Hawley and Kennedy, 2004; 

Hawley and others, 2005). The spatial scale associated with 

these hydrogeological characterizations has been focused 

primarily on the basin scale (for example, Mesilla Basin and 

Tularosa-Hueco Basin). These investigations have provided 

valuable information that describes the structure of the 

underlying geology and physical properties and processes 

that govern the transport of water through the associated 

alluvial aquifer. However, these investigations do not 

provide information, primarily because of scale, pertaining 

to the geological structure and transport processes that are 

specific to the delivery of saline groundwater to the Rio 

Grande. Hydrogeological and tectonic characterizations are 

needed in each of the identified source areas containing high 

concentrations of dissolved solids and associated constituents. 

It is likely that saline groundwater from geothermal and 

sedimentary sources are being transported into the shallow 

alluvial aquifer and Rio Grande along structural features, 

principally faults. A detailed investigation of the geological 

structures in the areas of the saline water introduction would 

contribute significantly to any assessment of the feasibility of 

active salinity mitigation. 

Model Development for Dissolved-Solids 

Transport in the Rio Grande

Models are needed to simulate the transport and storage 

of dissolved solids in the Rio Grande and associated stream 

and irrigation network. These models would provide a tool for 

water-resource managers and researchers to (1) simulate and 

test the current conceptual model for the transport and storage 

of dissolved solids; (2) identify critical data and knowledge 

gaps that need to be filled in order to calibrate and improve 

the accuracy of the model to better understand solute transport 

in the Rio Grande; (3) evaluate the effect that variations 

in climate, land and water use, and water operations have 

on water quality in the Rio Grande; (4) develop a detailed 

budget for the transport and storage of dissolved solids and 

associated constituents; and (5) test the anticipated results 

of proposed salinity-mitigation projects. The models put in 

place to simulate dissolved solids in the Rio Grande study area 

ultimately will need to account for the role that surface water, 

groundwater, surface-water and groundwater interactions, 

water-management operations, irrigation, and groundwater 

withdrawals have in the transport and storage of dissolved 

solids. Several knowledge gaps exist within the current 

understanding of the transport and storage of dissolved solids 

in the Rio Grande study that need to be addressed as part of 

the model(s) development. These gaps are provided in the 

recommendations listed below. 

Fate and Transport of Dissolved Solids in 

Elephant Butte and Caballo Reservoirs

The processes that govern transport and storage of 

dissolved solids into and out of Elephant Butte and Caballo 

Reservoirs are not well understood. It is essential for waterresource managers to understand the influence that the 

physical structure and water operations of these reservoirs 

has on the downstream transport of dissolved solids. Lacey 

(2006) developed a model to simulate the water and chloride 

mass balance in Elephant Butte Reservoir; however, additional 

studies are needed to expand on this research. First, the annual 

delivery and associated variability of dissolved solids into 

Elephant Butte and Caballo Reservoirs need to be quantified. 

These sources include dissolved solids that are transported by 

the Rio Grande as well as the direct discharge of deep saline 

groundwater. Second, a complex budget for Elephant Butte 

and Caballo Reservoirs needs to be developed that represents 

the annual inflow, outflow, and storage of dissolved solids. 

This added information regarding the effect of Elephant Butte 
46 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

New Mexico

UNITED STATES

MEXICO

Don Ana County

Chihuahua

El Paso County

El Paso

Rio Grande

Texas

SECTION BELOW

3,515,000 3,520,000 3,525,000 3,530,000 3,535,000 3,540,000

335,000 340,000 345,000 350,000 355,000 360,000

EASTING, IN METERS

NORTHING, IN METERS

Helicoptor electromagnetic profile

EXPLANATION

Well location

0 2.5 5.0 7.5 KILOMETERS

0 1,000 1,900 3,000 >5,400

1,100

1,110

1,120

1,130

1,140

ALTITUDE, IN METERS ABOVE NAVD 88

<37

58

84

128

175

>492

Conductivity, in milliSeimens per meter

Don Ana County

Chihuahua

El Paso County

Rio Grande

0 3,400 8,200 >22,800

A

B

C

Dissolved solids, in milligrams per liter

Dissolved solids, in milligrams per liter

Figure 26. Images showing comparison of gridded dissolved solids (DS) measured from groundwater wells to gridded conductivity 

values measured from helicopter electromagnetic (HEM) data: (A) Map showing gridded DS at the study area and location of the HEM 

profile, (B) map showing gridded DS at the location of the HEM section, and (C) section showing gridded conductivity values from the 

HEM profile.
References Cited 47

and Caballo Reservoirs on dissolved solids will be essential 

for (1) developing improved mass-balance budgets for 

downstream reaches of the Rio Grande and (2) constructing 

water-quality model(s) for the Rio Grande in the study area. 

Improved Mass-Balance Budgets for Rio Grande 

Dissolved Solids

Continued improvement in the detail of the dissolvedsolids mass-balance budgets is recommended. Bastien (2009) 

developed the latest mass-balance budget for reaches between 

San Acacia, New Mexico, and El Paso, Texas, in which 

the inflow of regional groundwater and the inflow of saline 

groundwater were the dominant sources of dissolved solids. 

Additionally, Bastien (2009) established that the difference 

between the estimated inflow and measured outflow of 

dissolved solids were a result of chemical reactions with 

various mineral phases (mineral dissolution and precipitation 

reactions). Building upon the detailed mass-balance budgets 

established by Bastien (2009), three core processes need to be 

further resolved and refined for each reach in the Rio Grande 

study area. These processes are (1) direct quantification of the 

load of dissolved solids and major ions associated with the 

inflow of saline groundwater (geothermal and nongeothermal); 

(2) further quantification of the flux of dissolved solids that 

are derived from the dissolution of minerals from the soils 

beneath agricultural and riparian areas; and (3) identification 

and quantification of processes that store dissolved solids in 

each reach, such as mineral precipitation, ion exchange, and 

groundwater pumping. A major challenge that will have to 

be addressed is quantifying the balance between processes 

that act as sources (groundwater inflow) and sinks (mineral 

precipitation and groundwater storage) for dissolved-solids 

transport in each reach. Information provided by the tools 

and data collection recommended above will help to improve 

the accuracy and level of detail in the mass-balance budgets. 

Finally, the complex mass-balance budgets developed by 

Bastien (2009) only represent reaches in the Rio Grande 

study area that extend from San Acacia, New Mexico, to 

El Paso, Texas. A complex mass-balance budget for dissolved 

solids and major ions (chloride, sulfate, bicarbonate, sodium, 

potassium, and magnesium) is needed for the reach of the Rio 

Grande that extends from El Paso, Texas, to Fort Quitman, 

Texas. 

References Cited

Anderholm, S.K., 1987, Hydrogeology of the Socorro and 

La Jencia basins, Socorro County, New Mexico: U.S. 

Geological Survey Water-Resources Investigations Report 

84–4342, 62 p.

Anderholm, S.K., 2002, Water-quality assessment of the 

Rio Grande Valley, Colorado, New Mexico, and Texas—

Surface-water quality, shallow ground-water quality, 

and factors affecting water quality in the Rincon Valley, 

south-central New Mexico, 1994–95: U.S. Geological 

Survey Water-Resources Investigations Report 02–4188, 

117 p.

Anderholm, S.K., and Heywood, C.E., 2003, Chemistry and 

age of ground water in the southwestern Hueco Bolson, 

New Mexico and Texas: U.S. Geological Survey WaterResources Investigations Report 02–4237, 16 p.

Anning, D.W., Bauch, N.J., Gerner, S.J., Flynn, M.E., Hamlin, 

S.N., Moore, S.J., Schaefer, D.H., Anderholm, S.K., and 

Spangler, L.E., 2007, Dissolved solids in basin-fill aquifers 

and streams in the Southwestern United States: U.S. 

Geological Survey Scientific Investigations Report 2006–

5315, 336 p.

Aulenbach, B.T., Buxton, H.T., Battaglin, W.A., and 

Coupe, R.H., 2007, Streamflow and nutrient fluxes of the 

Mississippi-Atchafalaya River Basin and subbasins for the 

period of record through 2005: U.S. Geological Survey 

Open-File Report 2007–1080, available only online at 

http://pubs.usgs.gov/of/2007/1080/.

Autobee, Robert, 1994, Rio Grande Project, accessed August 

21, 2012 at http://www.usbr.gov/projects//ImageServer?img

Name=Doc_1305577076373.pdf.

Bastien, E.M., 2009, Solute budget of the Rio Grande above 

El Paso, Texas: Socorro, N. Mex., New Mexico Institute of 

Mining and Technology, M.S. thesis, 232 p.

Booker, J.F., Michelsen, A.M., Ward, F.A., 2008, Economic 

impact of alternative policy responses to prolonged and 

severe drought in the Rio Grande Basin: Water Resources 

Research, v.41 W02026, doi:10.1029/2004WR003486.

Bothern, L.R., 2003, Geothermal salt intrusion into the Mesilla 

basin aquifers and the Rio Grande, Dona Ana County, 

New Mexico: Las Cruces, N. Mex., New Mexico State 

University, M.S. thesis, 127 p.

Bryan, Kirk, 1938, Geology and ground-water conditions of 

the Rio Grande depression in Colorado and New Mexico, 

in National Resources Committee, 1938, Regional planning 

report part VI, The Rio Grande joint investigation in the 

upper Rio Grande Basin in Colorado, New Mexico, and 

Texas,1936–1937: Washington, D.C., U.S. Government 

Printing Office, p. 197–225.

Chapin, C.E., 1971, The Rio Grande Rift – part 1—

Modifications and additions, in James, H.L., ed., Guidebook 

of the San Luis Basin, Colorado: New Mexico Geological 

Society, 22nd Field Conference, p. 191–201.
48 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

Colorado River Basin Salinity Control Forum, 2008, 2008 

review, water quality standards for salinity, Colorado River 

system: Colorado River Basin Salinity Control Forum, 

October 2008, accessed June 15, 2009, at http://www.

coloradoriversalinity.org/docs/2008%20Review.pdf. 

Conover, C.S., 1954, Ground-water conditions in the Rincon 

and Mesilla Valleys and adjacent areas in New Mexico: 

U.S. Geological Survey Water-Supply Paper 1230, 200 p.

Cox, E.R., and Reeder, H.O., 1962, Ground-water conditions 

in the Rio Grande valley between Truth or Consequences 

and Las Palomas, Sierra County, New Mexico: New Mexico 

State Engineer Technical Report 25, p. 45.

Daniel B. Stephens & Associates, Inc., 2008, Annual report 

for the lower Rio Grande water quality monitoring 

program, May 2006 through February 2007: Albuquerque 

and Los Alamos, N. Mex., Consulting report prepared for 

New Mexico Environment Department and New Mexico 

Interstate Stream Commission, June 30, 2008.

Druhan, J.L., Hogan, J.F., Eastoe, C.J., Hibbs, B.J., and 

Hutchison, W.R., 2007, Hydrogeologic controls on 

groundwater recharge and salinization: A geochemical 

analysis of the northern Hueco Bolson aquifer, Texas, USA: 

Hydrogeology Journal, v. 16, no. 2, p. 281–296.

Eastoe, C.J., Hibbs, B.J., Olivas, A.G., Hogan, J.F., Hawley, 

John, and Hutchison, W.R., 2007, Isotopes in the Hueco 

Bolson aquifer, Texas (USA) and Chihuahua (Mexico): 

Local and general implications for recharge sources in 

alluvial basins: Hydrogeology Journal, v. 16, no. 4, p. 737–

747.

Ellis, S.R., Levings, G.W., Carter, L.F., Richey, S.F., and 

Radell, M.J., 1993, Rio Grande Valley, Colorado, New 

Mexico, and Texas: Journal of the American Water 

Resources Association, v. 29, no. 4, p. 617–648.

Frenzel, P.F., Kaehler, C.A., and Anderholm, S.K., 1992, 

Geohydrology and simulation of ground-water flow in the 

Mesilla Basin, Dona Ana County, New Mexico, and El 

Paso County, Texas, with a section on water quality and 

geochemistry: U.S. Geological Survey Professional Paper 

1407–C, 105 p.

Harvey, J.W., and Wagner, B.J., 2000, Quantifying hydrologic 

interactions between streams and their subsurface hyporheic 

zones, in Jones, J.B., and Mulholland, P.J., eds., Streams 

and Ground Waters: San Diego, Calif., Academic Press, 

p. 3–44. 

Hawley, J.W., 1978, Guidebook to the Rio Grande Rift in New 

Mexico and Colorado: New Mexico Bureau of Mines and 

Mineral Resources Circular 163, 241 p.

Hawley, J.W., and Kennedy, J.F., 2004, Creation of a digital 

hydrogeologic framework model of the Mesilla Basin and 

southern Jornada del Muerto Basin: Las Cruces, N. Mex., 

New Mexico Water Resources Research Institute of New 

Mexico State University, Technical Completion Report 332, 

123 p.

Hawley, J.W., Kennedy, J.F., Ortiz, Marquita, and Carrasco, 

Sean, 2005, Digital hydrogeologic framework model of the 

Rincon Valley and adjacent areas of Dona Ana, Sierra and 

Luna Counties, NM: Las Cruces, N. Mex., New Mexico 

Water Resources Research Institute of New Mexico State 

University, addendum to Technical Completion Report 332, 

accessed October 22, 2009, at http://wrri.nmsu.edu/publish/

techrpt/tr332/cdrom/addendum.pdf.

Helm, D., 1984, Analysis of sedimentary skeletal deformation 

in a confined aquifer and the resulting drawdown, in

Rosenshein, J.S., and Bennett, G.D., eds., Groundwater 

Hydraulics: Washington, D.C., American Geophysical 

Union, Water Resources Monograph 9, p. 29–82.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: New York, N.Y., Elsevier, 529 p.

Hem, J.D., 1992, Study and interpretation of the chemical 

characteristics of natural water: U.S. Geological Survey 

Water-Supply Paper 2254, 263 p.

Heywood, C.E., and Yager, R.M., 2003, Simulated groundwater flow in the Hueco Bolson, an alluvial-basin aquifer 

system near El Paso, Texas: U.S. Geological Survey WaterResources Investigations Report 02–4108, 73 p.

Hibbs, B.J., 1999, Hydrogeologic and water quality issues 

along the El Paso/Juarez Corridor: An international case: 

Environmental and Engineering Geoscience, v. 5, no. 1, 

p. 27–39.

Hibbs, B.J., and Boghici, R.N., 1999, On the Rio Grande 

aquifer: Flow relationships, salinization, and environmental 

problems from El Paso to Fort Quitman, Texas: 

Environmental and Engineering Geoscience, v. 5, p. 51–59.

Hibbs, B.J., and Merino, Mercedes, 2007, Discovering 

a geologic salinity source in the Rio Grande aquifer: 

Southwest Hydrology, July/August 2007, v. 6, no. 4, 

p. 20–23.

Hibbs, B.J., Phillips, F.M., Hogan, J.F., Eastoe, C.J., Hawley, 

J.W., Kennedy, J.F., Nunez, Francisco, Granados, Alfredo, 

and Kretzschmar, Thomas, 2003, Binational study of the 

surface and ground water resources of the El Paso/Juarez 

International Corridor: Universities Council on Water 

Resources, Water Resources Update Issue 125, June 2003, 

p. 25–30.
References Cited 49

Hogan, J.F., Phillips, F.M., Mills, S.K., Hendrickx, J.M.H., 

Ruiz, Joaquin, Chesley, J.T., Asmerom, Yemane, 2007, 

Geologic origins of salinization in a semi-arid river: The 

role of sedimentary basin brines: Geology, v. 35, no. 12, 

p. 1063–1066.

Hutchison, W.R., 2006, Groundwater management in El 

Paso, Texas: El Paso, Tex., University of Texas, Ph.D. 

dissertation, 329 p.

Jackson, R.B., Carpenter, S.R., Dahm, C.N., McKnight, D.M., 

Naiman, R.J., Postel, S.L., and Running, S.W., 2001, Water 

in a changing world: Ecological Applications, v. 11, no. 4, 

p. 1027–1045.

Keller, G.R., and Baldridge, W.S., 1999, The Rio Grande Rift, 

a geological and geophysical overview: Rocky Mountain 

Geology, v. 34, no. 1, p. 121–130.

King, W.E., Hawley, J.W., Taylor, A.M., and Wilson, R.P., 

1971, Geology and ground-water resources of central and 

western Dona Ana County, New Mexico: New Mexico 

Bureau of Mines and Mineral Resources Hydrologic 

Report 1, 64 p.

Lacey, H.F., 2006, Quantification and characterization of 

chloride sources in the Rio Grande: Socorro, N. Mex., New 

Mexico Institute of Mining and Technology, M.S. thesis, 

166 p.

Langland, M.J., Raffensperger, J.P., Moyer, D.L., Landwehr, 

J.M., and Schwarz, G.E., 2006, Changes in streamflow and 

water quality in selected nontidal basins in the Chesapeake 

Bay watershed, 1985–2004: U.S. Geological Survey 

Scientific Investigations Report 2006–5178, 75 p.

Leggat, E.R., Lowry, M.E., and Hood, J.W., 1962, Groundwater resources of the lower Mesilla Valley, Texas and New 

Mexico: Texas Water Commission Bulletin 6203, 191 p.

Lippincott, J.B., 1939, Southwest border water problems: 

Journal of the American Water Works Association, v. 31, 

p. 1–28.

Longworth, J.W., Valdez, J.M., Magnuson, M.L., Albury, 

E.S., and Keller, Jerry, 2008, New Mexico water use by 

categories, 2005: New Mexico Office of the State Engineer 

Technical Report 52, 111 p.

Mills, S.K., 2003, Quantifying salinization of the Rio Grande 

using environmental tracers: Socorro, N. Mex., New 

Mexico Institute of Mining and Technology, M.S. thesis, 

397 p.

Miyamoto, Seiichi, Fenn, L.B., and Swietlik, D., 1995, Flow, 

salts, and trace elements in the Rio Grande: A review: Texas 

Water Resources Institute Technical Report 169, 30 p.

Moore, S.J., and Anderholm, S.K., 2002, Spatial and temporal 

variations in streamflow, dissolved solids, nutrients, 

and suspended sediment in the Rio Grande Valley study 

unit, Colorado, New Mexico, and Texas, 1993–95: U.S. 

Geological Survey Water-Resources Investigations Report 

02–4224, 52 p.

Moore, S.J., Basset, R.L., Liu, Beiling, Wolf, C.P., and 

Doremus, Dale, 2008, Geochemical tracers to evaluate 

hydrogeologic controls on river salinization: Ground Water, 

May–June 2008, p. 489–501.

Newton, B.T., 2005, Geologic controls on shallow 

groundwater in the Socorro Basin, New Mexico: Socorro, 

N. Mex., New Mexico Institute of Mining and Technology, 

M.S. thesis, 163 p.

Newton, B.T., Kuhn, S., Johnson, P., and Hathaway, D.L., 

2002, Investigation of flow and seepage conditions on a 

critical reach of the Rio Grande, New Mexico, in Summer 

Specialty Conference on Ground Water/Surface Water 

Interactions, Keystone, Colo., July 1–3, 2002, Proceedings: 

Keystone, Colo., American Water Resources Association, 

p. 581–586.

National Resources Committee, 1938, Regional Planning 

Report VI, Rio Grande joint investigation in the upper 

Rio Grande basin in Colorado, New Mexico, and Texas, 

1936–1937: Washington, D.C., U.S. Government Printing 

Office, 566 p.

Phillips, F.M., Hogan, J.F., Mills, S.K., and Hendrickx, 

J.M.H., 2003, Environmental tracers applied to quantifying 

causes of salinity in arid-region rivers: Results from the Rio 

Grande, southwestern USA, in Alsharhan, A.S., and Wood, 

W.W., eds., Water Resources Perspectives: Evaluation, 

Management and Policy: New York, Elsevier Science, 

p. 327–334.

Piper, A.M., 1944, A graphic procedure in the geochemical 

interpretation of water analyses: American Geophysical 

Union Transactions, v. 25, p. 914–923.

Plummer, L.N., Bexfield, L.M., Anderholm, S.K., Sanford, 

W.E., and Busenberg, Eurybiades, 2004, Geochemical 

characterization of ground-water flow in the Santa Fe group 

aquifer system, Middle Rio Grande Basin, New Mexico: 

U.S. Geological Survey Water-Resources Investigations 

Report 03–4131, 395 p.

Riecker, R.E., ed., 1979, Rio Grande Rift: Tectonics and 

magmatism: Washington, D.C., American Geophysical 

Union, 438 p.

Rister, M.E., Sturdivant, A.W., Lacewell, R.D., and Michelsen, 

A.M., 2011, Challenges and Opportunities for Water 

of the Rio Grande: Journal of Agricultural and Applied 

Economics, v. 43, p. 367–378.
50 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

Rosenberry, D.O., and LaBaugh, J.W., 2008, Field techniques 

for estimating water fluxes between surface water and 

ground water: U.S. Geological Survey Techniques and 

Methods 4–D2, 128 p.

Sanford, W.E., Plummer, L.N., McAda, D.P., Bexfield, L.M., 

and Anderholm, S.K., 2004, Hydrochemical tracers in 

the middle Rio Grande Basin, USA: 2. Calibration of a 

groundwater-flow model: Hydrogeology Journal, v. 12, 

p. 389–407.

Schmid, Wolfgang, Hanson, R.T., Maddock, Thomas, III, 

and Leake, S.A., 2006, User guide for the farm process 

(FMP1) for the U.S. Geological Survey’s modular threedimensional finite-difference ground-water flow model, 

MODFLOW–2000: U.S. Geological Survey Techniques and 

Methods 6–A17, 127 p.

Stabler, Herman, 1911, Some stream waters of the western 

United States: U.S. Geological Survey Water-Supply Paper 

274, 188 p.

Texas Water Development Board, 2007, 2005 Texas water 

use summary estimates: Texas Water Development Board, 

accessed June 15, 2009, at http://www.twdb.state.tx.us/data/

water_use/2005est/2005wus.htm.

Thorn, C.R., McAda, D.P., and Kernodle, J.M., 1993, 

Geohydrologic framework and hydrologic conditions in the 

Albuquerque Basin, central New Mexico: U.S. Geological 

Survey Water-Resources Investigations Report 93–44149, 

106 p.

Walton, John, Ohlmacher, Gregory, Utz, Dennis, and 

Kutianawala, Murtaza, 1999, Response of the Rio Grande 

and shallow ground water in the Mesilla Bolson to 

irrigation, climate stress, and pumping: Environmental and 

Engineering Geoscience, v. 5, no. 1, p. 41–50. 

West, Francis, 1995, The Mesilla Valley: A century of water 

resources investigations, in 40th Annual New Mexico Water 

Conference, Reaching the limits: Stretching the resources 

of the Lower Rio Grande, proceedings, October 1995: Las 

Cruces, N. Mex., New Mexico Water Resources Research 

Institute of New Mexico State University, p. 21–28.

Wilcox, L.V., 1957, Analysis of salt balance and salt-burden 

data on the Rio Grande, in Duisberg, P.C., ed., Problems 

of the Upper Rio Grande: An arid zone river: Socorro, 

N. Mex., U.S. Commission for Arid Improvement and 

Development Publication 1, p. 39–44.

Wilcox, L.V., 1968, Discharge and salt burden of the Rio 

Grande above Fort Quitman Texas, and salt-balance 

conditions on the Rio Grande project, Summary report for 

the 30-year period 1934–1963: U.S. Salinity Laboratory 

Research Report 113.

Wilkins, D.W., 1986, Geohydrology of the southwest alluvial 

basins regional aquifer-systems analysis, parts of Colorado, 

New Mexico, and Texas: U.S. Geological Survey WaterResources Investigations Report 84–4224, 61 p.

Wilkins, D.W., 1998, Summary of the southwest alluvial 

basins regional aquifer-system analysis in parts of 

Colorado, New Mexico, and Texas: U.S. Geological Survey 

Professional Paper 1407–A, 49 p.

Williams, J.H., 2001, Salt balance in the Rio Grande project 

area from San Marcial, New Mexico, to Fort Quitman, 

Texas: Las Cruces, N. Mex., New Mexico State University, 

M.S. thesis, 42 p.

Wilson, C.A., White, R.R., Orr, B.R., and Roybal, R.G., 1981, 

Water resources of the Rincon and Mesilla Valleys and 

adjacent areas, New Mexico: New Mexico Office of the 

State Engineer Technical Report 43, 514 p.

Witcher, J.C., King, J.P., Hawley, J.W., Kennedy, J.F., 

Williams, J., Cleary, M., and Bothern, L.R., 2004, 

Sources of salinity in the Rio Grande and Mesilla Basin 

groundwater: Las Cruces, N. Mex., New Mexico Water 

Resources Research Institute of New Mexico State 

University, Technical Report 330, 168 p.

Yuan, Fasong, and Miyamoto, Seiichi, 2004, Influence of the 

Pacific decadal oscillation on hydrochemistry of the Rio 

Grande, USA, and Mexico: Geochemistry, Geophysics, 

Geosystems, v. 5, no. 12, p. 1–10.
Appendixes 1–3

Appendix 1 53

Appendix 1. Average annual and seasonal streamflow and dissolved solids concentration, flow-weighted concentration and load for 

monitoring stations along the Rio Grande between San Marcial, New Mexico and Fort Quitman Texas. 

[ft3/s, cubic feet per second; mg/L, milligrams per liter]

Rio Grande 

monitoring station

Average 

annual 

streamflow 

(ft3

/s)1

Average monthly streamflow2 Average annual 

flow-weighted 

dissolved solids 

concentration 

(mg/L)1

Average annual 

dissolved solids 

concentration 

(mg/L)1

Non-irrigation 

season 

(ft3

/s)

Irrigation 

season 

(ft3/s)

At San Marcial, NM 1,041 784 1,396 528 586

Below Elephant Butte, NM 960 372 1,390 516 512

Below Caballo, NM 947 158 1,101 545 612

Above Leasburg, NM 901 149 1,436 591 660

At El Paso, TX 597 201 848 746 1,053

At Fort Quitman, TX 198 192 210 2,069 3,275

Rio Grande 

monitoring station

Average dissolved solids concentration2 Average annual 

dissolved 

solids load 

(tons/day)1

Average dissolved solids load2

Non-irrigation 

season 

(mg/L)

Irrigation 

season 

(mg/L)

Non-irrigation 

season 

(tons/day)

Irrigation 

season 

(tons/day)

At San Marcial, NM 563 602 1,296 917 1,557

Below Elephant Butte, NM 533 497 1,259 546 1,805

Below Caballo, NM 711 592 1,319 216 1,476

Above Leasburg, NM 801 559 1,364 309 2,186

At El Paso, TX 1,464 763 1,168 567 1,569

At Fort Quitman, TX 3,355 3,219 916 1,127 1,119

1

Data from Wilcox, 1968 (Dates represented 1934 through 1963).

2

Data from Wilcox, 1968; Williams, 2001 (Dates represented 1934 through 1968 (Wilcox, 1968) and 1969 through 1999 sporadically (Williams, 2001).

Appendix 1
54 Knowledge and Understanding of Dissolved Solids in the Rio Grande–San Acacia, New Mexico, to Fort Quitman, Texas

Appendix 2. Description of groundwater regions, in the Rio Grande study area, with unusually high concentration of dissolved solids 

and/or chloride. 

[mg/L, milligrams per liter; DS, dissolved solids; Alb. Albuquerque; gw, groundwater; SC, specific conductance]

Basin Location/

areal extent

Sample 

type

Chloride 

(mg/L)

DS

(mg/L)

Probable 

source(s)

Data 

source

Socorro Basin S. Albuquerque Basin and 

N. Socorro Basin between 

La Joya and Polvadera, NM

gw 270–4,020 Upward flow of gw 

brines from distal end 

of Alb. basin

Anderholm, 1987

5 miles north and south of San 

Antonio, NM

gw 260–1,100 Upward flow of gw 

brines/geothermal 

gw along Capitan 

lineament

Anderholm, 1987

Area 5.5 miles long near Luis 

Lopez Drain

gw 232 1,200 Upward flowing gw 

brines intercepted by 

drain

Mills, 2003

San Marcial 

Basin

No published information gw

Engle Basin Elephant Butte Reservoir, NM gw Discharge of gw brines Lacey, 2006

Truth or Consequences, NM gw 1,300; 1,400 SC = 4,450; 

TDS = 2,600

Geothermal gw from 

Magdalena group

Cox and Reeder, 

1962; Moore 

and others, 

2008

Palomas Basin Hatch Drain 9 mile long reach 

near Hatch,NM

drain 650 to 1,000 

along drain

Regional gw inflow 

from Joranada del 

Muerto Basin

Anderholm, 2002

Rincon Drain 6 mile long reach 

near Rincon, NM

drain 800 to 1,300 

along drain

Regional gw inflow 

from Joranada del 

Muerto Basin

Anderholm, 2002

Alluvial wells in area from 

Rincon, NM to Rincon Drain 

discharge point

shallow gw 1,350 to 3,630 Regional gw inflow 

from Joranada del 

Muerto Basin

Anderholm, 2002

Mesilla Basin Eastern Mesilla Basin (general) gw 940 Inflow of geothermal 

gw along faults 

underlying eastern 

Mesilla Basin

Frenzel and 

Kaehler, 1992; 

Witcher and 

others, 2004

Eastern Mesilla Basin - East 

Drain from Anthony, NM to 

Mesquite, NM

drain Upward gw flow 

intercepted by drain

Frenzel and 

Kaehler, 1992

Distal end of Mesilla Valley - 

near Montoya Drain and 

above El Paso, TX

gw well 4,000 Upward gw flow at 

distal end of basin

Frenzel and 

Kaehler, 1992

Distal end of Mesilla Valley near 

Montoya drain and confluence 

with Rio Grande

gw well 18,000 30,000 Upward flow of gw 

brines at distal end of 

basin

Moore and others, 

2008

Distal end of Mesilla Valley - 

Montoya Drain

drain 640 2,400 Upward flow of gw 

brines at distal end of 

basin

Moore and others, 

2008

Hueco Basin Downstream of El Paso 

Wastewater Treatment 

Facility

effluent 1,390 Wastewater effluent Miyamoto and 

others, 1995

Ascarate & Fabens waste 

channel

Wastewater effluent Mills, 2003

Area 2 miles SE of Fabens, TX gw 15,000 Artesian flow through 

evaporite deposits to 

the Rio Grande

Hibbs and Merino, 

2007

Appendix 2
Appendix 3 55

Appendix 3. Description of gains and losses in Rio Grande streamflow and flux of dissolved solids from inflowing groundwater for 

each reach of the Rio Grande.

[GW, groundwater; ft3/s/mile, cubic feet per second per mile; ~, approximately]

Reach Basin Source

Gains in 

Rio Grande 

streamflow from 

groundwater inflow

Losses in 

Rio Grande 

discharge to 

groundwater 

recharge

Flux of groundwater 

dissolved solids 

from seepage and 

brine inflow (Bastien, 

2009, for 1980–89) 

tons per month

San Acacia to San 

Marcial

Socorro and San 

Marcial

Newton and others, 

2002

From San Acacia to 

San Marcial during 

both Irrigation 

and nonirrigation 

periods

GW Seepage flux = 404; 

Brine flux = 3,839

San Acacia to San 

Marcial

Socorro and San 

Marcial

Newton and others, 

2002

Between Escondida 

and North Bosque 

Hwy 380 

San Marcial to 

below Elephant 

Butte

Engle GW seepage flux = 273; 

Brine flux = 129

Below Elephant 

Butte to Caballo 

Reservoir

Engle/ Palomas Cox and Reeder, 

1962

Between 

Williamsburg and 

Caballo Reservoir 

(~1.1 ft3

/s/mile) 

GW seepage flux = 1,011; 

Brine flux = 2,013

Below Caballo 

Reservoir to 

Above Leasburg

Palomas Anderholm, 2002; 

Wilson and others, 

1981

From Caballo to 24 

miles downstream 

(1.5 ft3

/s/mile)

Below Caballo 

Reservoir to 

Above Leasburg

Palomas Anderholm, 2002; 

Wilson and others, 

1981

Between Hatch and 

Rincon Drains 

(0.3 ft3/s/mile)

Below Caballo 

Reservoir to 

Above Leasburg

Palomas Anderholm, 2002 Rincon Drain 

(~0.5 ft3/s/mile)

Above Leasburg to 

El Paso

Mesilla http://nm.water.

usgs.gov/projects/

mesilla; Wilson 

and others, 1981

From below Leasburg 

dam to ~ 10 miles 

downstream near 

Shalem Bridge

Above Leasburg to 

El Paso

Mesilla http://nm.water.

usgs.gov/projects/

mesilla; Wilson 

and others, 1981

From Shalem Bridge 

(12.5 miles) to 

Below Mesilla 

Dam 

Above Leasburg to 

El Paso

Mesilla http://nm.water.

usgs.gov/projects/

mesilla; Wilson 

and others, 1981

From Vinton Bridge 

(14 miles) to 

Sunland Park 

Bridge

Above Leasburg to 

El Paso

Mesilla http://nm.water.

usgs.gov/projects/

mesilla

From Sunland 

Park Bridge to 

Courchesne Bridge

Bbelow Caballo 

Reservoir to 

El Paso

Palomas/Mesilla Bastien, 2009 GW seepage flux = 5,320; 

Brine flux = 3,687

El Paso to Fort 

Quitman

Hueco http://www.ibwc.

state.gov/Water_

Data/binational_

waters.htm

From El Paso/

Hudspeth County 

Line to Fort 

Quitman

Appendix 3
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