HR: 0800h
AN: H31C-1319    [Abstracts]
TI: Unusual Recharge Processes near Arroyos of the Rio Grande Aquifer, El Paso/Juarez Area
AU: * Merino, M
EM: m2merino@yahoo.com
AF: CEA-CREST California State University, Los Angeles, 5151 State University Dr, Los Angeles, CA 90032
AU: Hibbs, B J
EM: bhibbs@calstatela.edu
AF: CEA-CREST California State University, Los Angeles, 5151 State University Dr, Los Angeles, CA 90032
AU: Hogan, J
EM: jhogan@sahra.arizona.edu
AF: SAHRA University of Arizona, 1040 E 4th St., Tucson, AZ 85721
AU: Eastoe, C J
EM: eastoe@geo.arizona.edu
AF: SAHRA University of Arizona, 1040 E 4th St., Tucson, AZ 85721
AU: Druhan, J
EM: jenny@sahra.arizona.edu
AF: SAHRA University of Arizona, 1040 E 4th St., Tucson, AZ 85721
AB: The twin-cities of El Paso and Juarez share the water resources of the Hueco Bolson aquifer and overlying Rio Grande aquifer. Both aquifers span the international border between Mexico and the United States. Salinity in the Rio Grande aquifer varies widely, some parts of the shallow aquifer containing less than 1,000 mg/L total dissolved solids (TDS), other parts of the aquifer exceeding 5,000 mg/L TDS. One sizable part of the "Lower Valley" area, approximately 45 km below El Paso contains very dilute water near the outer edge of the floodplain. Historically it had been thought that the dilute waters in this location were derived from recharge from arroyos that drained proximal parts of the Hueco Bolson. Instead, our hydrogen and oxygen isotope data and carbon-14 data indicate that these dilute waters were derived from pre-dam infiltration of the Rio Grande. Relatively light and slightly evaporated pre-dam waters (-11.5 del O18) at the arroyos are also relatively young (60 to 90 percent modern carbon), tagging them as runoff waters from pre-dam snowmelt in Colorado. These isotopically light waters are found up to 110 meters beneath land surface. Prior to Rio Grande rectification and channelization of the mid-1930's, the Rio Grande flowed near the outer edge of the floodplain where these pre-dam, dilute waters are found at depth. Review of predevelopment drill stem tests indicated a permeable zone about 150 to 230 meters deep that had a lower hydraulic head than the overlying Rio Grande aquifer. The permeable zone acted as a predevelopment sink for flow that induced recharge from the Rio Grande and Rio Grande aquifer. Thus, we can account for local predevelopment recharge of the Rio Grande aquifer from infiltration of dilute water from the Rio Grande prior to the historic era of channel rectification, and not from recharge from flanking arroyos as had been postulated by previous researchers.
DE: 1829 Groundwater hydrology
SC: Hydrology [H]
MN: Fall Meeting 2005