HYDROGEOLOGIC STUDIES OF TERRESTRIAL GROUNDWATER INPUTS TO NEW WETLANDS ON THE SHORES OF THE RETREATING SALTON SEA, CA

New wetlands have appeared near the north shore of Salton Sea, Bombay Beach area, California. The wetlands have developed atop semi-perching confining units formed from deposits of “Ancient Lake Cahuilla.” This lake had various periods of filling over the last 2000 years, and the lake eventually disappeared around year 1580. Several factors are responsible for appearance of the new wetlands along the retreating shorelines of Salton Sea, including drought, reduction of seepage from irrigation canals due to canal lining, more efficient agriculture, and short term transfers of Colorado River project water to southern California cities. Wetlands are appearing at locations around the retreating Salton Sea where there is a significant source of terrestrial water. On the north shore, lining of the Coachella Canal in 2006 is responsible for ending a significant input of canal seepage of Colorado River project water. Other terrestrial water inputs along the north shore are not especially common, except from temporary winter and local monsoonal rains. At Bombay Beach, the perennial source of terrestrial water comes from a thermal artesian aquifer that supplies water to recreational spas and a fish farm via artesian wells. Waste flows from the thermal spas and fish farm provide input to several local channels that drain into the new wetlands, providing a constant perennial source of water. The artesian wells tapping the thermal aquifer are completed from 110 to 300 m deep, with temperatures reaching 55 to 80 degrees C at the wellheads. The higher temperatures are associated with the deeper wells. Salinity of groundwater issuing from these artesian wells is in the 4100 to 5200 mg/L TDS range, with a consistent sodium-chloride hydrochemical signature. The thermal groundwater is apparently old, with no tritium detected and carbon-14 near 3.5 PMC. Water isotopes tested in the thermal artesian water is consistent with a slightly cooler period, and a locally derived source (-71 del D and -8.7 del O18) with no evidence of any imported Colorado River water. The provenance of the thermal, pluvial groundwater is probably to the north of Salton Sea, and will be investigated further.