ABSTRACT
Groundwater levels in Lancaster, in the Mojave Desert of southern California, declined more than 60 m during the 20th century, resulting in depletion of this key water source and about 2 m of land subsidence in the alluvial aquifer system. Water managers are considering an aquifer storage and recovery (ASR) program to help meet future demand. A pilot ASR program was monitored by the U.S. Geological Survey, in cooperation with Los Angeles County and the Antelope Valley-East Kern Water Agency. Measurement of the groundwater response to injection was difficult because the water table averaged 100 m below land surface. Rather than install many expensive piezometers, microgravity surveys were used to determine the change in water mass beneath 19 gravity stations. Specific yield, estimated using coupled measurements of gravity and water-level change at one location, was used to convert the measured changes in water mass at 18 other stations to changes in water-table altitude.
