Understanding and managing the stressed Mexico-USA transboundary Hueco bolson aquifer in the El Paso del Norte region as a complex system

Zhuping Sheng · Jeff Devere

Abstract As the latest drought has swept over the Resum´ e´ Alors que la derniere` secheresse« a atteint toute la southwestern United States, most local and regional water partie Sud-Ouest des Etats-Unis, la plus part des distribu- providers have had to rely on ground water to meet their teurs d’eau, locaux et regionaux,« doivent s’approvisionner water demands as surface water supplies have diminished. en eau souterraine des« lors que les niveaux des eaux de sur- In areas near major population centers this situation has face ont diminues.« Dans les zones proches des grands cen- continued to put strain and stress on already over-drafted tres densement« peuples,« cette situation a continuee« a alter« ee« regional aquifers. Metropolitan centers throughout the des aquiferes` dej« a` surexploites.« Les centres metropolitains« southwestern United States, as exemplified by Las Vegas, du Sud-Ouest des Etats-Unis (Las Vegas dans le Nevada, Nevada; Phoenix and Tucson, Arizona; and El Paso, Texas, Phoenix et Tucson dans l’Arizona, El Paso au Texas) sont have a history of over drafting their available ground connus historiquement pour surexploites« leurs ressources water resources. How these stressed aquifers should be en eaux souterraines. Il devient urgent de definir« un mode managed is an urgent issue. In El Paso, Texas long-term de gestion de ses aquiferes` surexploites.« A El Paso dans groundwater mining in the transboundary Hueco bolson le Texas, le minage de l’aquifere` transfrontalier engen- aquifer has resulted in large water level drawdowns within dre un rabattement important dans le bassin, et plus the basin, particularly in several well fields. This situation particulierement` autour des zones de captage. Cette sit- has promoted the intrusion of brackish water into fresh uation a induit l’intrusion d’eaux saumatresˆ dans des zones water zones, and consequently reduced the volume of fresh d’eaux douces, et a par consequent« reduit« le volume d’eau water stored in the aquifer. Management of this aquifer is douce stockee« et exploitable dans l’aquifere.` La gestion de made more complex as the water resources of the region cet aquifere` est par ailleurs complexifiee« par la situation are shared across the United States/Mexico boundary and transfrontaliere,` d’autant que la zone frontaliere` connaˆõt the transboundary region continues to grow rapidly. This une croissance rapide. Cet article decrit« la situation actuelle paper describes the current situation within the Hueco dans la vallee« fermee« du Hueco, due au sur-rabattement et bolson due to over drafting and continued reliance on the a` l’exploitation continue des eaux douces, et decrit« com- fresh water in storage and describes how understanding ment la comprehension« de l’aquifere,` vu comme un systeme` the dynamics of the aquifer as a complex system can offer complexe, peut offrir des perspectives de gestion amenant a` managerial perspectives that can be used to establish oper- des procedures« operationnelles« et a` des programmes a` long ational procedures and programs for bringing drawdowns terme permettant de ramener al’` equilibre« la baisse des into equilibrium, increasing the longevity of the aquifer, niveaux d’eau. Ainsi la longevit« e« de l’aquifere` sera mieux gradually restoring water quality, and offering the hope of garantie, la qualite« de l’eau sera graduellement restauree« et utilization of the resource in a sustainable manner. l’utilisation de l’eau respectera le souci de developpement« durable. Received: 10 September 2003 / Accepted: 22 February 2005 / Published online: 21 June 2005 Resumen A medida que la ultima« sequ«õa ha pasado lig- eramente sobre el suroeste de Estados Unidos la mayor«õa
C Springer-Verlag 2005 de abastecedores locales y regionales de agua han tenido Z. Sheng (
) que depender del agua subterranea« para satisfacer sus de- Texas A&M University, Agriculture Research and Extension mandas de agua debido a que las fuentes de agua super- Center, 1380 A&M Circle, El Paso, TX 79927, USA ficial han disminuido. En areas« cerca de centros poblados e-mail: [email protected] Tel.: (915)-859-9111 principales esta situacion« ha continuado ejerciendo presion« Fax: (915)-859-1078 en los ya sobre explotados acu«õferos regionales. Los cen- tros metropolitanos en todo el suroeste de Estados Unidos, J. Devere por ejemplo Las Vegas, Nevada; Fenix« y Tucson, Arizona; Director Community and Economic Development, Town of y El Paso, Texas tienen una historia de sobre explotar los Rangely, 209 E Main, Rangely, CO 81648, USA e-mail: [email protected] recursos de agua subterranea« disponibles.

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 814 La gestion« de estos acu«õferos estresados constituye un regional water resources planner, has invested heavily in problema urgente. En El Paso, Texas el minado de agua the management of the Hueco bolson aquifer. Over the past subterranea« a largo plazo en el acu«õfero transnacional several years, a series of projects have been undertaken Hueco bolson« ha resultado en varios campos de pozos. to gain a more accurate knowledge of the current hydro- Esta situacion« ha promovido la intrusion« de agua salobre geological conditions within the aquifer. This recently hacia zonas con agua fresca y reducido consecuentemente obtained information has been used to formulate improved el volumen de agua fresca almacenado en el acu«õfero. El management strategies to prolong the useful “life” of manejo de este acu«õfero se hace mas« complejo debido a que the groundwater resource for future generations and los recursos h«õdricos de la region« son compartidos a traves« drought contingency. Recent successes include a deeper del l«õmite Estados Unidos/Mexico« y la region« transnacional understanding of current groundwater storage volumes continua« creciendo rapidamente.« Este art«õculo describe la and flow conditions in the aquifer, and development of a situacion« actual dentro del Hueco bolson« debido a la sobre set of potential strategies for preventing further brackish explotacion« y continua dependencia en el agua fresca alma- groundwater intrusion. These insights have been gained in cenada y describe como el entendimiento de la dinamica« part from the results of groundwater modeling conducted del acu«õfero como un sistema complejo puede ofrecer per- in a bi-national cooperation program with El Paso, Texas spectivas de gestion« que pueden utilizarse para establecer and Juarez, Mexico through the International Boundary procedimientos operacionales y programas que conduzcan and Water Commission (IBWC) and the United States al equilibrio de los descensos, aumentando la longevidad Geological Survey (USGS) (Heywood and Yager 2003). It del acu«õfero, gradualmente restaurando la calidad del agua, is expected that challenges in the management of the Hueco y ofreciendo la esperanza de utilizar el recurso de manera bolson can be resolved by integrating resource protection sostenible. with responsible utilization of the aquifer in conjunction with proactive management by all agencies within the Keywords Transboundary aquifer . Hueco bolson . region. Systems management of groundwater . Groundwater model . Brackish water intrusion Hydrogeology of the Hueco bolson aquifer Introduction The Hueco bolson aquifer is an unconfined and a semi- For nearly a century, El Paso and Ciudad Juarez in the El confined aquifer within a long, sediment-filled trough hav- Paso del Norte region, comprised of El Paso, Texas and ing a length of some 322 km (200 miles) and an average Las Cruces, New Mexico in the United States and Ciudad width of 40 km (25 miles) that lies between the Franklin, Juarez in Mexico (Fig. 1) have relied on the groundwater Organ, and San Andres Mountain ranges (west side) and the resources of the Hueco bolson as its major drinking water Quitman, Malone, Finlay, Hueco, and Sacramento Moun- source (Sayre and Livingston 1945; Ashworth and Hopkins tain ranges (east side). Hill (1900) first defined the Hueco 1995; White et al. 1997; Hibbs et al. 1997). Ciudad Juarez bolson as the whole basin including the Tularosa Basin presently fully depends on the Hueco bolson ground water as shown in Fig. 1. However, Richardson (1909) divided as its sole drinking water supply, as do several small the bolson into two parts: the Tularosa Basin to the north communities in New Mexico and U.S. Army Air Defense and the Hueco bolson to the south. The Hueco bolson and Artillery Center and Fort Bliss (Fort Bliss), El Paso, Texas. the Tularosa Basin are hydraulically connected to each El Paso continues to withdraw ground water from the other (Wilkins 1986) and have been combined into the Hueco bolson to provide 30 to 40% of its total water supply. Hueco-Tularosa aquifer (Hibbs et al. 1997). In this pa- This use of the aquifer amounts to mining the resource as per, Hill’s definition for the Hueco bolson will be used the Hueco bolson only receives a limited amount of natural to define the boundary of the aquifer, while the ground- and artificial recharge, all of which is much less than the water model only covers the southern part the Hueco current pumpage from the Hueco bolson (Ashworth and bolson. Hopkins 1995; Hibbs et al. 1997). As a result of such long- The Hueco bolson aquifer consists of unconsolidated term groundwater mining in the region, large water level to slightly consolidated deposits, composed of fine- to drawdown cones, as well as deterioration of water quality, medium-grained sand with interbedded lenses of clay, silt, have been observed and recorded over the last four decades gravel and caliche. Sediments in the bolson are fluvial, (Hibbs et al. 1997). Management of the aquifer has included evaporitic, alluvial fan, and aeolian in origin and have a reduction in pumpage and artificial aquifer recharge. The maximum thickness of 2,743 m (9,000 feet) (Mattick 1967; bulk of these activities have been implemented by the El Cliett 1969; Abeyta and Thomas 1996). Paso Water Utilities/Public Service Board (EPWU/PSB) in The basin fill can be classified into four hydrogeologic accordance with its overall water resource planning. These facies on the basis of their depositional processes and re- operational actions have been implemented to reduce water sulting sedimentary structures (Heywood and Yager 2003), level drawdowns, and decrease the rate of deterioration namely fluvial, alluvial-fan, recent alluvial and lacustrine- of water quality. EPWU/PSB, as a Texas State-recognized playa facies.

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 815

Fig. 1 Location of the Hueco bolson aquifer in the El Paso del Norte region

1. Fluvial facies. The ancestral Rio Grande meandered 2. Alluvial-fan facies. Alluvial fans originated from the south along the east side of the Franklin Mountains and present day Organ and Franklin Mountains and Sierra deposited a thick sequence of fluvial sediments consist- Juarez, which consists of poorly sorted gravel and ing of fine- to coarse-grained channel sand interbedded coarse-to-fine grained sand. Deposits of this facies in- with silt and clay over-bank deposits. The predominant terfinger with the fluvial deposits of the Rio Grande. geologic formation in this facies is the Camp Rice For- 3. Lacustrine-playa facies. Thick deposits of clay and silt mation (Strain 1969) of Tertiary and Quaternary age. exist in the east and southeast parts of the Hueco bolson Electric logs of 101 wells in the El Paso area indicate and at depth beneath the fluvial and alluvial-fan facies. that the fraction of clay interbeds within the fresh water These fine-grained sediments were deposited in a low- portion of this facies is approximately one third (Hey- energy environment, possibly a lake of mid-Cenozoic wood and Yager 2003). age that formed a terminal deposit for the ancestral Rio

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 816 Grande (Strain 1969). The predominant geologic forma- and Yager 2003). The bottom part of the Hueco bolson tion of this facies is the Tertiary Fort Hancock Forma- is primarily clay and silt. Therefore, only the top several tion. hundred meters of the aquifer produce good-quality water. 4. Recent alluvial facies. Deposition of the fluvial, alluvial- Production wells are generally installed in known high- fan and lacustrine-playa facies and subsequent ero- permeability zones, such as alluvial-fan and fluvial facies sion resulted in formation of the topographic mesa that in the Hueco bolson. Even though the Hueco bolson has presently lies east and north of El Paso (Langford 2001). been divided into 10 layers for modeling purposes, it is con- About 0.67 million years ago, the Rio Grande breached sidered as a single, continuous hydrogeological unit with the El Paso Narrow, the gap separating the present-day all its layers interconnected. Mullican and Senger (1992) Franklin Mountains from the Sierra de Juarez (Fig. 1). suggested that groundwater from Cretaceous and Permian The Rio Grande eroded the topographic mesa, forming strata from the Diablo Plateau, southeast of the Hueco bol- the present-day lower El Paso Valley. Approximately 30 son, are connected to Cretaceous strata underneath the bol- to 60 m thick of late Pleistocene to recent sediments son. associated with the modern Rio Grande have been de- The Hueco bolson aquifer is recharged by mountain- posited in the Valley. front recharge; seepage from the Rio Grande and canals, lower valley agricultural irrigation, and deep-well injection Over most of the bolson, groundwater occurs under un- (Knorr and Cliett 1985; Land and Armstrong 1985; White confined conditions. In the El Paso lower valley, however, et al. 1997). Mountain-front recharge is the seepage of groundwater is unconfined in the Rio Grande alluvium and surface run-off into the aquifer after rainfalls. EPWU is partially confined where sands occur in the underling bol- has injected treated wastewater into its NE well fields to son deposits (Davis and Leggat 1965; Gates et al. 1980). increase recharge into the aquifer since 1985. Before its Along the Rio Grande flood plain between downtown El development and consequent heavy pumping, water in Paso and Ysleta, the water in the bolson deposits is un- the aquifer discharged naturally to the Rio Grande. After der slightly artesian pressure. The area was defined as the pumping caused water levels to decline, the Rio Grande city artesian area (Davis and Leggat 1965), which was began to lose water into the aquifer. Unlined irrigation envisioned only as a locality where groundwater passes canals and laterals also leak water into the aquifer; how- beneath lower permeability strata and is confined under ever, the water quality varies within the area of interest. pressure. The clay beds in the deposits of the northern part The major discharge of the aquifer is the municipal and of the bolson, however, are discontinuous lenses; conse- industrial pumping. The shallow aquifer also discharges quently, there is no single confined bed in the city artesian downstream through drains. area. The increase in pressure with depth in the lower val- Water quality in the Texas part of the Hueco bolson tends ley may be as much a result of the upward movement of to be asymmetrical with better quality water concentrated groundwater and low vertical permeability of overlying to the west rather than to the east, although there are pock- strata as it is a result of the water passing beneath confining ets of good-quality water in the eastern part of the bolson beds. (Gates et al. 1980). North of the Texas-New Mexico bor- The horizontal boundaries between the fluvial and der, water tends to have total dissolved solids (TDS) greater lacustrine-playa facies are believed to interfinger with each than 1,000 mg/l except near mountain fronts where there other, resulting in gradational changes in hydraulic conduc- is active recharge (Hibbs et al. 1997). The upper part of tivity at the scale of the groundwater flow model (Heywood the aquifer tends to be fresher with TDS ranging between

Fig. 2 Schematic east-west geologic cross-section showing estimated groundwater withdrawals from the Hueco bolson in 2001 (location shown in Fig. 1)

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 817 500 and 1,500 mg/l, with an average of about 640 mg/l in consideration of the arid climatic condition in the (Ashworth and Hopkins 1995). Water quality in the shal- Chihuahua Desert. The aquifer also receives artifi- low part of the aquifer along the Rio Grande in the alluvium cial/induced recharge from seepage of the river, canals has degraded because of leakage of poor-quality irrigation- and laterals induced by groundwater pumping, infiltration return flow into the aquifer. Water quality beneath Ciudad from agricultural irrigation, usually with high salinity, and Juarez is generally less than 1,000 mg/l TDS (Hibbs et al. the injection of reclaimed wastewater by El Paso Water 1997), however, water-quality deterioration has been ob- Utilities. However, groundwater pumpage is much larger served in wells along the border and in the downtown area. than all the natural and artificial recharge combined. As a Water quality deterioration further reduces the availability result, groundwater storage is being depleted continuously, of fresh water from the aquifer in spite of measures that and thus native fresh water has been mined for the last have been implemented to reduce the rate of deterioration, several decades. In addition, lining canals will further including reduction of pumpage and artificial recharge into reduce the induced recharge. Infiltration from agricultural the aquifer. Water quality in the aquifer has been affected application could be potentially reduced due to drought by the large water-level declines that have induced flow of or retirement of agricultural land as result of urbanization poor-quality brackish water into areas of fresh water. Brack- and water rights transfer. Of key concern is that reduction ish water intrusion into the fresh water zone increases the in infiltration could add to the problem of brackish water concentration of TDS, chloride and sulfate in some areas to intrusion into the fresh water zone. Additional fresh water the extent that exceeds the safe drinking water standards. storage is projected to be dramatically affected because The rate of groundwater quality deterioration in some wells of brackish water intrusion, the poor quality of infiltrated has accelerated with time due to continuous mining of the water, and the current array of well fields, most of which aquifer. are located near the center of the native fresh water zone. In addition, groundwater pumping has changed the groundwater flow pattern across the Stateline with New Challenges in management of the stressed Hueco Mexico and the international border with Mexico, which bolson aquifer further complicated the management of fresh water re- sources in the aquifer. Along the Texas-New Mexico bor- The Hueco bolson has been strained by long-term pumping der, ground water generally flows from north to south. Prior stress because it significantly exceeds natural and artificial to large scale municipal pumping by EPWU/PSB in the recharge. In other words, the fresh groundwater storage in early 1960s, the average annual groundwater underflow the aquifer has been mined. As the Paso Del Norte region from New Mexico to Texas was approximately 7.4 mil- readies itself for the challenges lying ahead in terms of lion m3 (6,000 acre-feet) based on the groundwater model population growth and increasing water demands to meet simulation (Fig. 3). Increased groundwater pumpage from future water supply adequately, several key issues need to the City of El Paso has created an even larger hydraulic be addressed so the Hueco bolson groundwater resources gradient, which more recently corresponds to a greater rate can be managed in a long-term and sustainable manner. of groundwater underflow. Since the early 1960s, the rate of groundwater underflow has increased to approximately 22.2 million m3 (18,000 acre-feet) per year. This amount Diminishing fresh water resources includes both fresh and brackish waters. The Hueco bolson has historically been pumped at a rate Between the State of Texas and the Republic of Mexico, greater than natural and artificial aquifer recharge. Figure 2 in the shallow portion of the aquifer, ground water generally shows different user groups and estimated groundwater pumpage from the Hueco bolson in 2001 based on their historical water usage. Ciudad Juarez, the largest 50 single groundwater user in the Hueco bolson, pumped 3 Underflow across US (Texas) approximately 155 million cubic meters (m ) (125,660 40 /Mexico borderline acre-feet) of water, while the City of El Paso pumped 62.21 (+) flow from US to MX million m3 (50,438 acre-feet) in 2001. Total groundwater (-) flow form MX to US withdrawals from the aquifer amounted to about 312 30 million m3 (253.121 acre-feet) in the year 2001. However, the mountain front recharge and artificial recharge were es- 20 3 Underflow from New timated at approximately 9.6 million m (7,800 acre-ft) per Mexico to Texas year (Meyer 1976; Paso del Norte Water Task Force 2001; Annual flow Heywood and Yager 2003). Induced seepage from the (million cubic meters) 10 Rio Grande and irrigation canals and irrigation infiltration provide additional recharge to the shallow aquifer in the 0 lower valley. Much of this water is probably subsequently 1900 1920 1940 1960 1980 2000 discharged by evapotranspiration and intercepted by irrigation drains. For the whole aquifer, natural fresh -10 Year water recharge is limited to the mountain front recharge Fig. 3 Simulated underflows across the political boundaries

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 818

flows away from the river, or toward the center of the estab- 1,400 1.40 lished depression cones in Juarez. In the deeper part of the aquifer, the flow direction of ground water is also toward the 1,200 1.20 centers of the established cones of depression with an over- 1,000 1.00 all southward flow direction. Figure 3 shows the simulated net groundwater underflow across the borderline, where a 800 0.80 negative value means a net flow from Mexico to the United States, and a positive value means a net flow from the 600 0.60

United States to Mexico. In the early years, the net under- Water quality in mg/l flow was from Mexico to the United States, and reached its 400 0.40 3 maximum up to 7.6 million m in 1940 due to the greater 200 0.20 pumping rate on the El Paso side (Fig. 3). Since 1960 the Annual pumpage in million cubic meters direction of net underflow was reversed with an increasing 0 0.00 groundwater pumping rate in Juarez. The amount of the net 1979 1981 1983 1985 1987 1989 1991 underflow from the United States to Mexico has been con- Cl SO4 TDS Pumpage tinuously increased and is currently up to 44 million m3 per Fig. 4 Measured water quality changes with groundwater pumping year. for the EPWU Well #84 (JL-49-22-125)

Water quality deterioration recoveries in some areas where pumping has been stopped, Naturally occurring brackish or slightly saline (1,000Ð although EPWU has reduced annual pumping from 86.35 3,000 mg/l TDS) waters surround the thin freshwater zone million m3 (70,000 acre-feet) to 61.68 million m3 (50,000 of the Hueco bolson aquifer (Hibbs et al. 1997). The fresh acre-feet) since 1990. Despite the reduced pumpage, the water section thins to less than 30 m (100 feet) toward the rate of deterioration in water quality has not been mea- Hueco Mountains. Brackish water underlies the fresh water surably reduced because depression gradients still induce zone. Groundwater in the Rio Grande alluvium in the El the migration of brackish water into the fresh water zones. Paso lower valley is predominantly slightly saline/brackish This situation cannot be rapidly eliminated. Even totally water in El Paso County, and moderately saline or of poor eliminating pumping still leaves lingering cones of de- quality in Hudspeth County (Alvarez and Buckner 1980; pression that induce brackish water intrusion for many Gates et al. 1980). In the city artesian area (downtown of years. El Paso to Ysleta) at the northern end of El Paso lower Water quality continues to deteriorate in spite of mea- valley, the water in the Rio Grande alluvium is of poorer sures that have been implemented to reduce the rate of de- quality than the water in the underlying bolson deposits, terioration, including reduction of pumpage, and artificial but at many locations down the valley, the water in the recharge into the aquifer. Figure 4 is a composite graph that alluvium is of better quality than the water underlying shows measured groundwater quality changes at EPWU the bolson deposits. Soluble material in the fine-grained, well # 84 (Texas State Well No.: JL-49-22-125). With an predominantly playa-lake bolson deposits, and the lack of increase of groundwater pumping after 1979, TDS concen- groundwater circulation at depth probably accounts for the trations increased from about 800 mg/l to 1,200 mg/l after poor-quality water in the basin fill in the El Paso lower 10 years of pumping. Chloride and sulfate concentrations valley. Brackish water intrusion into the freshwater zone is were also increased. They all exceeded the Secondary Safe due to leakage from mud interbeds and artesian-confining Drinking Water Standards. The rate of groundwater quality beds, cascading waters along well casings and screens, lat- deterioration in some wells has accelerated with time due eral brackish water encroachment, potential upconing of to the continuous mining of the fresh water storage in the underlying brackish water, and movement of high salinity aquifer. drain water in the lower valley. With continuous pump- ing from both Juarez and El Paso, both cities have expe- rienced water quality degradation due to lateral brackish water intrusion into the fresh water zones in addition to the Limited data for model configuration large water level drawdowns. Heavy pumping decreases hy- The Hueco bolson aquifer is a trans-boundary aquifer. Data draulic heads at or near centers of pumpage, which induces sharing among the different entities that share the water the movement of surrounding brackish water into the fresh resources of the aquifer is essential for a successful man- water zone. In addition, brackish water intrusion from irri- agement of this aquifer, however data is limited in some gation return flow drains continues to expand laterally and areas due to lack of historical data collection. vertically, thereby degrading water quality in the shallow Most well data and hydraulic data are only available for alluvium aquifer along the Rio Grande. Due to the mining the portion of the aquifer within the well fields and ad- of the water resources of the Hueco bolson, several cones ditional data is needed for a better configuration of hy- of depression have been observed. The cones of depres- drogeological boundary conditions. Water quality data is sion continue to deepen within the pumping centers with very limited outside of the City of El Paso and Ciudad

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 819 Juarez. This makes it challenging to delineate the fresh wa- Multiple legal frameworks and complexity of local ter boundary. Lack of data for certain areas of the bolson issues for management of the shared water may limit modeling capabilities and applicability of the resources of the Hueco bolson model. The Hueco bolson is an aquifer at the crossroads of El Over the past 20 years there have been five models con- Paso, TX, and southern New Mexico on the US side, and structed or modified for the Hueco bolson aquifer system Ciudad Juarez on the Mexican side. As such, three differ- (Meyer 1976; Knowles and Alvarez 1979; Wilson 1986; ent legal approaches are involved when devising strategies Groschen 1994; Heywood and Yager 2003). Until recently, for managing the remaining fresh water resources of the the models were completed to determine flow conditions Hueco bolson. This area is known as the El Paso del Norte with little or no emphasis being placed on water quality region. It extends from the Elephant Butte Dam in New modeling. These flow models attempted to predict water Mexico (215 river kilometers upstream of El Paso), to Fort level declines that would result from continued pumping Quitman in Texas (133 km downstream), forming a sin- of El Paso municipal well fields. In 1994, the USGS com- gle hydrological and ecological sub-basin (Fig. 1). Even pleted a water quality model that predicted significant wa- though nature does not have boundaries, water laws and ter quality degradation in the Airport wellfield by the year water management regulations vary among the different 2000 (Groschen 1994). The simulation results indicated jurisdictions. Consequently, there is not an interstate and that changes in salinity were greater in the top layers than international management agreement for the Hueco bolson. in the lower layers of the aquifer, and that the greatest Historically, water in transboundary aquifers is appropri- potential for contamination of freshwater zones was more ated by those who have the largest pumps. When El Paso likely to occur due to the horizontal movement of brackish was approached to be part of the Bureau of Reclamation’s water at or near the water surface, rather than from vertical irrigation scheme in the 1920s, the need for surface water groundwater movement. was not envisioned. Early City developers, on both sides of To simulate steady state and transient groundwater flow the border, did not imagine a time when the construction in the Hueco bolson aquifer and to evaluate strategies build-out and the population growth that has characterized for obtaining the most beneficial use of the Hueco bol- this area for the last 80 years would outstrip the ground- son aquifer system, the USGS Hueco bolson groundwater water supply. In a similar time frame of 80 or so years the model was developed using MODFLOW-96, and calibrated fresh groundwater resources (less than to 1,000 mg/l TDS) with MODOFLOWP and UCODE (Heywood and Yager may be depleted as the current pumping trend continues, 2003). Unconsolidated deposits ranging from 138 to 693 m and the remaining brackish water resources will be heav- thick above an altitude of 600 m above mean sea level are ily mined and desalinated. This will occur alongside the represented with 10 model layers, of which each consists reallocation of surface water to such a point that no room of 165 rows and 100 columns of cells with a width of 500 will be left for population expansion let alone a drought. or 1,000 m on either side. Each of the top nine layers is How the shortcomings of institutional arrangements and the 30 m thick and the bottom layer (10th) varies in thickness long periods it takes for negotiation of treaties, agreements from 0 to 276 m. Parameter values of aquifer properties and and water transfers, not to mention social development, boundary conditions were resolved through nonlinear re- will cope with these factors are intimately tied to how the gression in a transient-state simulation with 96 annual time Hueco bolson water resources are managed in the present steps. The final model approximated 4,352 water levels and near future. It is a problem that requires a pragmatic obtained from measurements in 292 wells between 1912 response in a holistic manner. Management of the Hueco and 1995, three seepage-loss rates from a reach of the bolson water resources requires not only interstate and in- Rio Grande from 1979 to 1981, three seepage-loss rates ternational legal frameworks that can rapidly adjust to a from a reach of the Franklin Canal, which extends south- multitude of factors, but it also requires managerial and eastward from downtown El Paso to the lower El Paso operational parameters that can meet the changes of a fluid valley over the Rio Grande alluvium as shown in Fig. 1, social system and a desiccating environment due to climate from 1990 to 1992, and 24 seepage-loss rates into irriga- change (Manabe et al. 2004). tion drains from 1961 to 1983. Once the calibrated model As part of the legal mechanism established for long- was produced, the optimal parameter set was used to cre- term management of groundwater in Texas the state has ate an equivalent MODFLOW-96 simulation with monthly developed a system for designating Priority Groundwater temporal discretization to improve estimates of seepage Management Areas (PGMAs). These reasonably new reg- from the Rio Grande and to define the flow field through ulations could have a profound effect on water use and a chloride-transport simulation that factors water quality management. Unfortunately these regulations are silent on trends within the modeled area, and sets conditions for de- the policy ramifications of transboundary situations. It is lineating the boundary between fresh and brackish water. this lack of a comprehensive holistic approach that under- Boundary conditions were made flexible for reconfigura- mines such efforts. Establishment of PGMAs and ground- tion as changes from well pumpage, agricultural drainage, water conservation districts across the state are isolated and channel changes of the Rio Grande needed to be repre- activities that in and of themselves present a challenge for sented and thus make the model as representative of reality the management of the Hueco bolson water and do noth- as possible. ing realistic for the aquifer since restrictions on pumpage

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 820 on the Texas portion of the Hueco bolson alone will not the dynamic of the new state of complexity. The aquifer stop the depletion of the remaining fresh water storage in needs to be understood as a complex system whereby the the aquifer or brackish water intrusion. The Texas Com- behavior of the whole necessitates understanding the parts, mission of Environmental Quality (former Texas Natural however understanding the parts independently is not suf- Resources Conservation Commission) has acknowledged ficient to understand the whole. When interpreting what that stopping or reducing pumpage in the Texas portion of the aquifer “is”, as part of an understanding of the com- the Hueco bolson is not going to, by itself, resolve both plex system, it is important to include the dynamic so- issues: reduction in water quantity and deterioration in wa- cial, economic and other relevant institutional aspects as ter quality of the aquifer (TNRCC 1998). These factors part of the complex system. A political decision to expand coupled to the relentless pressure the aquifer is under dur- pumping has profound implications. It can have hydrogeo- ing periods of drought, when pumpage restrictions will be logical, social, and economic consequences. Management lifted in the face of political pressure and practical neces- requires understanding the complexity of the system in its sity, expose that these regulations at best provide an em- entirety and modeling more than the dynamic pumping phasis for more planning and at worst an artificial sense of and hydrogeological aspects of the aquifer. Any objectives security. of resource protection in one specific area may not fully For example, both the State of Texas through the Far achieve resource protection in another area that is being West Texas Water Planning Group and the State of New exploited. Therefore, water resource management must be Mexico are currently developing and revising their water viewed in the context of the whole system. This requires a plans for this region. However, lack of coordination in the paradigm shift away from traditional resource utilization, development of such regional water plans leads to a set which has most often been to construct wells in response of uncoordinated expectations, which result in practices to municipal and regional growth without entirely under- that are not aligned to the realities of long-term ground- standing the underlying aquifer system. To manage the water management. Forces outside regulatory agencies put challenges mentioned in the previous sections, a systems- intense political pressure on the resource as short term based management approach, premised on an understand- economic considerations outrank the need for long-term ing of the aquifer as a complex system, can be used to sustainability. Therefore, water planning is largely an exer- develop a set of strategies for long-term management of cise that attempts to incrementally change policy while the the resource. Utilizing this perspective of the Hueco bol- forces drawing on the resource expand faster than the im- son as a complex system has indicated that the following plementation of planning practices put forth to manage the strategies will result in better management of the regional situation. This puts all planning, whether it is on a regional aquifer and offer some hope of long-term sustainability if or local basis, in a reactive mode. Given the scale of the the broader resource questions of additional sources can problem, the most likely scenario is that the water resources be adequately managed. And just as it requires that the of the Hueco bolson will continue to be depleted and the aquifer be understood as a complex system, the aquifer social order in the United States will turn to technology for has to be included as part of the complex system of water a solution while in Mexico the degree of social injustice resource use within the El Paso del Norte region. Based (access to clean potable water) will increase. While tech- on these considerations the following management strate- nology is a necessary operational ingredient, that must be gies recognize key aspects of the aquifer as a complex included in all future resource management considerations, system. a regional solution is necessary to address the environmen- tal and humanitarian situation. The need for broad scale implementation of market adjustment for the cost of water, Safeguard the groundwater resources the need for social reallocation of the water resources, and Fresh water and brackish water, which are the two major the need to readjust the use of water based on a set of en- components of the water resource in the aquifer system, vironmental and humanitarian needs, may be as important interact with each other along their interface and will both a set of considerations for the sustainability of the aquifer continue to be mined. Past management has emphasized as are the operational aspects of how the water resource is fresh water exploitation, and considered brackish water as going to be mined. waste water with little or no value. Therefore not enough emphasis has been placed on managing the aquifer as a complete resource. This has led to a perception that the Future management strategies for the Hueco resource is diminished. In actuality, only the fresh water bolson aquifer resource is diminished. This perception belies another prob- lem, which has to do with the rise in the cost of water. Social Analysis of the conditions of the Hueco bolson and the hu- and political forces have been remiss in recognizing this man dynamics driving resource exploitation has led to the fact, and rather have sought to ignore the consequences, as conclusion that this large diversified regional water source in the case of Juarez, or attempted to continue exploitation has to be understood as a complex system. A system that of fresh water at the expense of the resource (as this is the in a natural state would be under a far different set of hy- cheapest source) in the case of El Paso. In 1991 in recogni- drological dynamics than it is today. In order to understand tion of the need for additional water resources supplies and the dynamics of the new system one has to understand the inability for the aquifer to provide a sustainable source,

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 821 EPWU/PSB implemented a water resource management immediately points to the fact that over a mid-term horizon plan which called for a reduction in pumping and aquifer the cost of water will continue to expand as the activi- storage and recharge (ASR) to protect the Hueco bolson ties in one section adjust to the realities in another. When water for future use. This plan was silent on the complexi- John Muir (1911) pointed out that “when we try to pick ties of the transboundary legal and regulatory frameworks out anything by itself, we find it hitched to everything else or the use of brackish water. While EPWU/PSB has a long in the Universe”, he was also pointing to the quintessen- and impressive history involving desalination, large scale tial reason for understanding things in a holistic manner, plants have been a less attractive option in most cases be- which is to say as a complex system. The best course of cause this would necessitate a rise in the price of water. For action for the Hueco bolson water and water resources in these and other reasons, the mining of the cheaper fresh wa- general as well as regional development is to implement ter has continued, the cones of depression have deepened the combined set of engineering tactics discussed in this and the brackish water has begun to intrude into the fresh paper and adjust them to the emerging changes within the water zones. While reduced pumping and ASR strategies system, without regard to national institutions and in a man- have had some success the brackish water intrusion contin- ner of real sharing of water resources across all types of ues to threaten the fresh water resources. borders. In response to, and as part of understanding of the aquifer as a complex system requiring a comprehensive manage- ment approach, multiple tactics are being explored to pre- vent further brackish water intrusion, and to protect the Optimization of the use of water resources remaining fresh water. Regional water providers have ex- To fully utilize water resources of the whole aquifer sys- plored and will continue to explore alternative pumping tem, the brackish water will be pumped and treated through scenarios to optimize the operation of the existing well desalination and blending with fresh water. Using the best fields, thereby reducing stress to the most heavily impacted quality water first has often been the preferred method of areas of the aquifer, and reducing intrusion of brackish groundwater production. However, by blending marginally water. Water users have also been progressively plugging poorer quality water with fresh water supplies, while keep- abandoned wells and administering wellhead protection ing TDS and chloride concentrations within Safe Drink- programs to prevent contamination from surface waste dis- ing Water Act Standards for TDS, chloride, and sulfate at posal or spills. An inventory of wellhead protection areas secondary maximum contamination levels, regional water is being updated to identify potential contamination sites providers can enhance their production capacity. using GPS receivers. This program is sponsored by the Brackish water constitutes a major component of the po- Environmental Alliance Senior Involvement (EASI), and tential water resource in the El Paso area. Our preliminary conducted by volunteer retirees. TA&MU staff works with estimates indicate a large volume of brackish water exists the staff of Texas Commission on Environmental Quality (approximately 24.7 billion m3 or 20 million acre-feet) in in data processing and analysis in this project to gain a the Hueco bolson within El Paso County. However, the better understanding of wellhead protection areas. In some thickness of brackish water zones varies within the bolson stressed areas, such as the El Paso Airport area, more com- and its recovery rate will change spatially. For the portions prehensive measures, such as an injection barrier and an of the Hueco bolson in New Mexico and Mexico, there is interception trench combined with a desalination plant, are insufficient data to make such an estimate of brackish water being considered. A key factor in effective implementation storage, but it is believed that these quantities are large and of these tactics is for all stakeholders to coordinate with should be explored. Regional water providers have actively each other in the development of a comprehensive water investigated the option of desalination. The desalinated wa- resource management strategy. This should include the im- ter will be blended with natural brackish ground water of mediate construction of vast desalination water treatment marginal water quality to maximize the use of the existing plants to supplement fresh water withdrawal and to pro- resource by production of potable water. The strategy of tect fresh water through the use of brackish water. This blending desalinated water in this manner further reduces would also begin the necessary readjustment of the cost the cost of this activity as it leverages the desalination structure for the water to reflect the need to adopt and im- process. Based on a preliminary evaluation, it was con- plement new technologies to properly manage the water cluded that the desalination wellfield could serve the dual resources. purposes of a desalination site and a pumping trough. This Even if this policy is pursued and cost adjustment is ac- reduces the intrusion of brackish water into the fresh water complished, this tactic would not address the transboundary zone by creating a brackish water cone of depression while resource question, where two sets of values and approaches establishing an additional potable water resource that is to human justice are followed. In Mexico, the economic re- drought resistant. Figure 5 illustrates the application of an sources are just not available in the same manner as in interception trench created by the brackish water pumping, the United States. Unless a common transboundary water which can be further enhanced by an injection barrier to utility is developed, where the humanitarian issues are bal- control brackish water intrusion. However it is not clear anced alongside those of the environment, success in cost how the fresh water storage and groundwater flow may valuation will not stop eventual water depletion in another be altered by mining of brackish water. Additional studies area. An understanding of the aquifer as a complex system would be needed to optimize the utilization of both brack-

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 822

Fig. 5 Schematic cross-section of potential control of brackish water intrusion using interception trench by brackish water pumping and enhanced injection

ish and fresh waters. The El Paso County Water Authority comparison of water resource management plans across the is currently providing drinking water for the nearby City international border. of Horizon and neighboring communities from a 15,142 The model includes the groundwater flow model (MOD- cubic meters per day (4 MGD) desalination plant using the FLOW, Harbaugh and McDonald 1996; Heywood and Hueco bolson brackish water. Another desalination plant Yager 2003) and associated tool packages for Geographic of 104,098 cubic meters per day (27.5 MGD) using the Information System (GIS) displays. It covers a larger area Hueco bolson brackish water is under design by EPWU than that of previous models, which included El Paso, Texas and Fort Bliss (Fig. 1). A pilot research desalination plant and the southern part of New Mexico, and Juarez on the at a capacity of 18,927 cubic meters per day (5 MGD) Mexico side. The groundwater flow model was designed to using Tularosa Basin brackish water is also under way in provide information required in dealing with the following Alamogordo, New Mexico (Fig. 1). key resources management issues:

Ð Assess water storage in the aquifer; Rigorous pursuit of information Ð Provide guidelines for optimization of pumping scenar- ios; One of the major components of systems management of Ð Evaluate the impacts of new production wells; water resources is the evaluation of the past resource use Ð Explore alternatives for control of brackish water intru- practices, review of current use practices and consideration sion; of projected future water demands. Data acquisition is a vi- Ð Assess the impacts of the Aquifer Storage and Recharge tal component of water resource management. El Paso has system, and; executed a routine field-monitoring program, and admin- Ð Provide information needed for the regional water re- istered cooperative programs with the USGS to measure sources planning with New Mexico and Mexico. water levels and water quality. EPWU has been drilling additional exploration holes and collecting more hydroge- It is expected that new features can be added to models ological information within the Texas portion of the Hueco to meet regional water providers’ expanded aquifer man- bolson. agement needs, and data exchange can be maintained and EPWU, JMAS (Junta Municipal De Agua Y Saneamiento enhanced by the bi-national programs through IBWC. The De Ciudad Juarez), the USGS, IBWC and CILA (Comi- model has been modified by the CDM consulting company, sion Internacional de Limites Y Aguas), and Fort Bliss El Paso, TX to simulate the effects of groundwater pump- have cooperated in the development of a comprehensive ing for the desalination plant to be constructed within the groundwater model for the Hueco bolson. This cooperative Montana/Airport wellfield in eastern El Paso (Fig. 1). program has also established a precedent for bi-national co- Texas A&M University and New Mexico State Univer- ordination with Mexico through the IBWC. Components of sity are developing a database and GIS program for the El this coordination include the exchange of scientific infor- Paso Del Norte Watershed, currently sponsored by EPWU mation, such as aquifer properties and pumping data, and and by the US Army Corps of Engineers. This program

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 823 will enhance data sharing and management of the regional focused its efforts on helping American countries become water resources, which will provide additional data and involved in carrying out the programme’s tasks. Among the information for regional water managers to gain a bet- most important steps of the programme is the collection of ter understanding of aquifer behavior and continue to de- data on transboundary aquifers. Through preliminary ques- velop additional management and development strategies tionnaires sent to the countries, the two organizations have of groundwater resources. With more data collection and assessed the prevalence of transboundary aquifers in the upgrading of the model with new features such as solute Western Hemisphere in order to identify critical case stud- transport to assess brackish water intrusion, surface wa- ies while creating a comprehensive Transboundary Aquifer ter and groundwater interaction to assess their conjunctive Inventory of the Americas. Nine transboundary aquifers in- uses, and optimization assessment for management alter- cluding the Hueco bolson have been identified as possible natives, the model will serve as a powerful tool for long- case studies. The aquifers were selected on the basis of term management and planning of transboundary water their hydro-geological characteristics, amount of informa- resources. tion, agreements among country representatives, and other criteria. Priority case studies will be implemented follow- Coordination of stakeholders to achieve advanced ing the ISARM methodology; they will provide a compre- regional resources management hensive understanding of the aquifers as well as guidance for the actions to be taken in other aquifers with similar Another component of the systems management of the characteristics and the adoption of the more appropriate aquifer is legal and regulatory frameworks. As is the case sustainable management mechanisms. with many common resources that often overlap political boundaries, management of the Hueco bolson aquifer re- quires development of a regional management approach that includes all the relevant stakeholders. Because of the Systems based management approach bi-national and tri-state use of the resource, a unique regu- A systems based approach should be followed in order to latory framework is needed to adequately address the wa- manage the various strategies. From this perspective the ter resource needs of the region. Regional water providers systems based approach is a form of adaptive manage- are promoting the creation of a conjunctive regional wa- ment that involves understanding the complexity of the ter resources management district under the cooperation of aquifer and associated resource activities as an intercon- Texas, New Mexico and Mexico. Long-term planning re- nected system, which is composed of multiple subsystems quirements are forcing regional water providers to consider that should be managed to operate in harmony and bal- new regulatory situations and variances for brine disposal ance. This groundwater system consists of fresh and brack- and water quality, and to adopt management perspectives ish water, within geological formations exhibiting various that can facilitate construction of desalination plants and characteristics. Fresh water is interconnected with brack- other management options. ish water. Groundwater is also interconnected through the The management of the groundwater resources of the shallow aquifer with surface water in the canals and the Rio Hueco bolson requires a conjunctive coordination of all Grande. Well systems are a component affecting the whole the stakeholders. Consequently, forums such as the Paso system when they are in operation. By understanding the Del Norte Water Task Force and Paso Del Norte Watershed inherent interactions and interrelationships within the sys- Council have been created to address the most economi- tem, regional water providers can both exploit and extend cally efficient and environmentally friendly forms to use the longevity of the aquifer while utilizing a sequence of and manage the water resources of the region. As regional priorities to maintain harmony and balance. water resources managers understand the regional aquifers Additionally, the regional water providers must under- as interconnected systems that require system management stand themselves, their relationships, their cultural differ- approaches, forums such as the Paso Del Norte Water Task ences, and water use traditions in an honest manner so that Force, and the Paso Del Norte Watershed Council will play operational practices are aligned with the management need an important role in the regional coordination of the man- to maximize use and longevity of the groundwater resource. agement of the water resource. A premium will be added to the cost of water resources the The UNESCO/OAS ISARM-Americas Programme was longer it takes all segments of society to wake up to the launched at the IAH-ALHSUD Congress in 2002 in Mar problems being faced within the agencies directly manag- del Plata, Argentina as part of the worldwide ISARM ing the resources. Whole segments of society, whether it Programme (UNESCO/OAS 2004). The Internationally is because of disenfranchisement or because of short term Shared Aquifer Resources Management—ISARM Pro- economic perspectives, have really not become stakehold- gramme aims at improving understanding of scientific, ers in the problem. By not having everyone involved and socio-economic, legal, institutional, and environmental is- not understanding the critical nature of the problem and sues related to the management of transboundary aquifers. the need to manage it in a comprehensive fashion, sus- The Programme operates through a joint coordination tainability of the water resources is often not prioritized committee of experts from UNESCO-IHP, IAH, FAO as they would be if the long-term consequences were truly and UNECE. As the leading agency in coordinating the understood. A proactive program of developing water op- UNESCO/OAS ISARM-Americas Programme, OAS has tions before a crisis is upon a community is going to have

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 824 to become standard operating practice if communities are artificially conceived boundaries that have very real world going to successfully manage the humanitarian necessities consequences. of the world. Resource exclusion of some across a trans- The approaches and strategies outlined in this paper are boundary will result in a complex system response. This those determined to best suit this new vision of management response will be a chaotic system prone to unmanageable for the stressed aquifer. These tools provide the informa- shifts where long-term sustainability is compromised. tion and technology necessary for operational management One of the alternatives to reduce the depletion of fresh of the aquifer. When these tools are coupled to an under- ground water is to convert surface water from agricultural standing of the aquifer alone as a complex system within an use to municipal and industrial uses by lining irrigation even more complex system involving water resource man- canals and laterals, improving irrigation efficiency and re- agement, they provide the necessary options for sustainable tiring some irrigated land. Currently, the water from the Rio management. When they are used in isolation without re- Grande is used mainly for agricultural irrigation. Regional gard to the order of complexity in which they are employed water providers are pursuing this option through the devel- the result is the traditional exploitation model where com- opment of the El Paso—Las Cruces Regional Sustainable munity, states, regions, and nations are put at risk. Key tools Water Project (IBWC and EPWU 2000). The Regional Sus- identified to implement the perspectives discussed in this tainable Water Project is a very promising step towards the paper include: implementation of environmentally friendly and economi- Ð The use of the groundwater flow model (MODFLOW) cally efficient alternatives to supply the El Paso area, Las that allows for simulation and configuration of the Cruces, New Mexico (72 km north of El Paso) and other aquifer, for assessment of impacts of continuous pump- communities with adequate and sufficient water resources ing and for evaluation of alternative management strate- for the next 30 years. Juarez may also convert part of the gies. With new data and upgrading of the model with new Mexico’s share of the Rio Grande surface water allotment features, especially optimization assessment for manage- from agricultural application to municipal and industrial ment alternatives, the model will serve as a powerful tool uses. In addition, conjunctive uses of surface and ground for long-term management and planning of transbound- waters will help extend the aquifer’s useful life and pre- ary water resources. serve fresh ground water for drought contingency. As one Ð The conjunctive use of surface and ground water will component of the regional sustainable project, the Aquifer extend the longevity of the aquifer, as fresh groundwater Storage and Recovery (ASR) system will be used to store will be primarily used for drought contingency. The El surplus treated surface water during wet years and lower Paso—Las Cruces Regional Sustainable Water Plan pro- demand periods, and to recover previously treated surface vides a great framework to implement conjunctive use of water during the peak demand periods and during droughts. both resources. With water conservation by lining canals The ASR system will not only augment the water supply, and laterals and retirement of lands, the salvaged surface but also in part replenish the strained aquifer in the early water can then be used to meet increasing municipal and years of the project implementation if sufficient surface industrial water demand or to meet environmental needs. water is available. Water conservation by lining canals and The ASR system stores excess water during low demand laterals and retirement of lands can salvage surface water or wet periods and provides water supply to meet peak to be used to meet increasing municipal and industrial wa- demands. It is recommended that additional studies be ter demand or to meet environmental needs. At the same conducted to assess potential impacts on the aquifer fresh time less recharge into the aquifer as a result of canal lin- water storage as a result of the altered recharge. ing and retirement of irrigated lands and implementation Ð The desalination of brackish water provides supplemen- of the ASR system will alter fresh water storage. Potential tary water resources for the region, especially for drought impacts on the aquifer storage should be taken into account contingency. Regional water providers are actively pur- with regard to long-term groundwater availability. suing alternative water supplies to progressively reduce extraction of fresh water from the Hueco bolson. How- Conclusions ever, it is not clear how mining of brackish water may alter fresh water storage and groundwater flow. If the Challenges in management of the Hueco bolson water well field and its operation are designed right, the re- have forced regional water managers and planners to de- sulting trough in the piezometric surface should help velop new perspectives on water resources management preserve the fresh water storage. It is recommended that and broaden their scope to incorporate new options. By the impacts of brackish water development on the fresh integrating a large set of technical and managerial tools groundwater storage be further assessed to achieve opti- into the administration of the Hueco bolson water with mal utilization of both brackish and fresh waters. a recognition for its complexity, it is anticipated that the Ð The development of cooperative approaches that ac- transboundary aquifer can be preserved and maintained for knowledge the transboundary groundwater flow and im- an extended, if not sustainable, period in the Texas portion pacts that are caused by extensive pumping along the of the system. Long term management of the resource will US-Mexico and New Mexico-Texas boundaries. These require understanding the aquifer as a complex transbound- pumping impacts indicate the dire need for coordinat- ary system, made even more complex by the scale of our ing regional management of the water resource. New

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8 825

well-informed operational processes will demonstrate Hibbs BJ, Ashworth JB, Boghici RN, Hayes ME, Creel BJ, Hanson that successful cooperative efforts have a greater per- AT, Samani BA, Kennedy JF (1997) Trans-boundary aquifers of ceived viability. The use of additional information and the El Paso/Ciudad Juarez/Las Cruces region: report prepared by the Texas Water Development Board and New Mexico data that can be collected, to better configure and under- Water Resources Research Institute for the U.S. Environmental stand the aquifer and improve the model, offers further Protection Agency, Region VI under contract X 996343-01-0 cooperative opportunities. As part of this approach, suc- and X 996350-01-0 cess could be further achieved through the development Hill RT (1900) Physical geography of the Texas region: U.S. Geological Survey, Topographic Atlas, Folio No. 3 of a regional conjunctive management entity so trans- IBWC (International Boundary and Water Commission) and EPWU boundary water can be managed across political bound- (2000) Draft environmental impact statement, El Paso—Las aries. Cruces Regional Sustainable Water Project: Volume I Knorr D, Cliett T (1985) Proposed groundwater recharge at El Paso, Acknowledgment This project is supported in part by EPWU, Texas. In: Asano T (ed) Artificial recharge of groundwater, Texas Agriculture Experiment Station, Hatch Project of U.S.A. Butterworth, pp 425Ð480 Department of Agriculture, and the Cooperative State Research, Knowles TR, Alvarez HJ (1979) Simulated effects of ground-water Education, and Extension Service, U.S.A. Department of Agriculture pumping in portions of the Hueco bolson in Texas and Mexico under Agreement No. 2003-34461-13278. Authors would also like during the period 1973 through 2029: Texas Department of to thank Mr. Edmund G. Archuleta, General Manager of EPWU, Mr. Water-Resources Report LP-104 John Burkstaller, the former Chief Technical Officer of EPWU and Land LF, Armstrong CA (1985) A preliminary assessment of land- Dr. Ari Michelsen, Resident Director of the Agriculture Research surface subsidence in the El Paso area, Texas: U.S. Geological and Extension Center for their support in this project. Authors thank Survey Water Resource Investigations Report 85Ð4155 Mr. Charles E. Heywood of the USGS, Mr. Michael P. Fahy and Langford RP (2001) Segmentation of the Rio Grande alluvial surface Mr. William Hutchison of EPWU for their technical review and and evolution of the Rio Grnade rift [abs.]: Proceedings of the constructive comments. Authors are thankful to Mr. Roger Sperka 53rd annual meeting (April 29 to May 2, 2001) of the Rocky and Mr. Scott Reinert of EPWU, and Luis Santiago Aristizabal Mountain Section, Geological Society of America, Boulder, CO and Joshua Villalobos for their assistance in the preparation of this Manabe S, Wetherald RT, Milly PCD, Delworth TL, Stouffer RJ paper and data interpretation. The authors are in debt to Dr. Eduardo (2004) Century-Scale Change in Water Availability: CO2- Mestre, Dr. Shammy Puri, Dr. Karin Kemper and Mr. Robert Quadrupling Experiment. Climatic Change, Kluwer, May 2004, Schneider for their constructive review comments. The opinions and vol 64, iss 1Ð2, pp. 59Ð76(18) results presented are those of the authors and do not represent those Mattick RE (1967) A seismic and gravity profile across the Hueco of regional water providers such as EPWU/PSB, or regional water bolson, Texas: U.S. Geological Survey Professional Paper planning groups, such as Far West Texas Water Planning Group. 575-D. pp 85Ð91 Meyer WR (1976) Digital model for simulated effects of ground water pumping in the Hueco bolson, El Paso area, Texas, New Mexico, and Mexico: U.S. Geological Survey Water Resources References Investigations Report 58Ð75 Muir J (1911) My First Summer in the Sierra.Chapter 6, Houghton Abeyta C, Thomas CL (1996) Hydrogeology and groundwater Mifflin, Boston pp 110 quality of the chromic acid pit site, U.S. Army Air Defense Mullican WF III, Senger RK (1992) Hydrogeologic investigations of Artillery Center and Fort Bliss, El Paso, Texas: U.S. Geological deep ground-water flow in the Chihuahua Desert, Texas: Texas Survey Water-Resource Investigations Report 96Ð4035 Bureau of Economic Geology Report of Investigation No. 205, Alvarez HJ, Buckner AW (1980) Ground-water development in the 60 p El Paso region, Texas, with emphasis on the Lower El Paso Paso del Norte Water Task Force (2001) Water planning Valley: Texas Water Development Board Report R246 in the Paso del Norte: Toward Regional Coordination, Ashworth JB, Hopkins J (1995) Aquifers of Texas: Texas Water http://www.sharedwater.org Development Board Report 345 Richardson GB (1909) Geological atlas, El Paso Folio (No. 166): Cliett TE (1969) Groundwater occurrence of the El Paso area and U.S. Geological Survey its related geology. In: New Mexico Geological Society, Border Sayre AN, Livingston P (1945) Groundwater resources of the El Paso Region, Chihuahua, Mexico, and United States, Guidebook area, Texas: U.S. Geological Survey Water Supply Paper 919 20th Field Conference, pp 209Ð214 Strain WS (1969) Late Cenozoic strata of the El Paso area. In: Davis ME, Leggat ER (1965) Reconnaissance investigation of the Kottlowski EE, Lemone DV (eds) Border strategraphy sym- groundwater resources of the upper Rio Grande basin, Texas, in posium. Socorro, New Mexico Bureau of Mines and Mineral Reconnaissance investigations of the ground-water resources of Resources Circular 104, 123 p the Rio Grande basin, Texas: Texas Water Comm. Bull. 6502, TNRCC (1998) El Paso County priority groundwater management pp U1-U99 area report, TNRCC, Austin, Texas Gates JS, White DE, Stanley WD, Ackerman HD (1980) Availability White DE, Baker ET, Sperka R (1997) Hydrology of the shallow of fresh and slightly saline ground water in the basins of western- aquifer and uppermost semi-confined aquifer near El Paso, most Texas: Texas Department of Water Resources Report 256 Texas: U.S. Geological Survey, Water-Resources Investigations Groschen GE (1994) Simulation of ground-water flow and the Report 97Ð4263 movement of saline water in the Hueco bolson aquifer, El Paso, Wilkins DW (1986) Geohydrology of the southwest alluvial basins Texas, and adjacent areas: U.S. Geological Survey Open-File regional aquifer-systems analysis, parts of Colorado, New Report 92Ð171 Mexico, and Texas: U.S. Geological Survey, Water-Resources Harbaugh AW, McDonald MG (1996) User’s documentation for Investigation Report 84Ð4224 MODFLOW-96, an update to the U.S. Geological Survey Wilson L, Associates (1986) Technical report for the Hueco bolson modular finite-difference ground-water flow model: U.S. hearing, Prepared for El Paso Water Utilities/Public Service Geological Survey Open-File Report 96Ð485 Board Heywood CE, Yager RM (2003) Simulated ground-water flow in the UNESCO/OAS (2004) UNESCO/OAS ISARM Americas Hueco bolson: an alluvial-basin aquifer system near El Paso, Programme: Transboundary aquifers of the Americas, Texas: U.S. Geological Survey Water-Resources Investigation 1st Coordination Workshop, September 24Ð25, 2003 Report 02Ð4108 http://www.oas.org/usde/news/isarm report-jan16 eng.pdf

Hydrogeology Journal (2005) 13: 813Ð825 DOI 10.1007/s10040-005-0451-8