Sources of Salinity and Strategies for Salinity Mitigation, El Paso-Juarez Valley

The Rio Grande floodplain between El Paso/Juarez and Fort Quitman, Texas is impacted by high salinity.  Salinity of surface water and groundwater increases from 800-2000 mg/L total dissolved solids (TDS) near El Paso to 2500 to 5500 mg/L TDS near Fort Quitman approximately 115 km downstream.  Chloride (Cl) and Chloride/Bromide (Cl/Br) ratios increase downstream, with a marked increase in salinity about 45 km below El Paso.  Groundwater sampling of the Rio Grande aquifer extending from 35 to 60 km below El Paso identified two distinct water types.  The first water type is a relatively dilute groundwater containing 1000 to 2000 mg/L TDS, 250 to 600 mg/L Cl, and Cl/Br weight ratios of 550 to 900.  The second water type is a relatively saline groundwater containing 2000 to 6000 mg/L TDS, 900 to 3500 mg/L Cl, and Cl/Br weight ratios of 1200 to 3500.  Drilling of nested monitoring wells detected a silty-clay, halite-bearing aquitard at 45 to 80 m bgs, directly below the Rio Grande alluvial deposits.  This saline water bearing unit contains about 15,000 mg/L Cl and Cl/Br weight ratios of about 5800.  Halide mixing curves and chlorine isotopes establish this saline unit as a primary local source of salinity in the Rio Grande and Rio Grande aquifer.    

Dilute artesian water from deeper strata flows upward through the saline aquitard, reacting with halite and contaminating the Rio Grande aquifer.  Saline water in the Rio Grande aquifer then moves into drainage ditches feeding into the Hudspeth Regulating Reservoir, an important irrigation water supply in Hudspeth County.  A set of management strategies are proposed in this project to reduce saline inflow into Hudspeth Regulating Reservoir.  Strategies include capture of artesian water and reduction of artesian pressure to reduce leakage through the halite bearing aquitard, and re-configuration of the irrigation drainage network.