COMBINING AIRBORNE EM AND SURFACE-WATER ANALYSES TO IDENTIFY NATURAL AND OIL-FIELD SALINITY SOURCES THAT DEGRADE WATER QUALITY IN TWO TEXAS STREAMS
Increases in salinity loading in the upper Colorado River below Spence Reservoir occur along four segments of elevated apparent conductivity, each several kilometers long, identified from airborne geophysical survey data. Each segment encompasses areas of baseflow salinity contributions to the river from oil-field produced water (1 site) and natural dissolution of evaporite minerals from Paleozoic strata (3 sites). Significant increases in salinity load in Petronila Creek on the coast are also associated with shallow baseflow contributions along three segments of elevated apparent conductivity, each several kilometers long. The dominant mechanism contributing salinity within two upstream segments includes historic discharge of produced water into unlined drainage ditches, infiltration into exposed Pleistocene channel deposits, lateral migration as far as several kilometers, and discharge into the stream. Geophysical and chemical data suggest a mixture of oil-field and seawater salinity contributions at the most downstream Petronila Creek segment.