Determination of Specific Yield and Water-Table Changes Using Temporal Microgravity Surveys Collected During the Second Injection Storage and Recovery Test at Lancaster, Antelope Valley, California, November 1996 through April 1997

By James F. Howle, Steven P. Phillips, Roger P. Denlinger, and Loren F. Metzger



Water-Resources Investigations Report 03-4019

Sacramento, California 2003

Prepared in cooperation with the Los Angeles County Department of Public Works and

Antelope Valley-East Kern Water Agency

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To evaluate the feasibility of artificially recharging the ground-water system in the Lancaster area of the Antelope Valley, California, the U.S. Geological Survey, in cooperation with the Los Angeles County Department of Public Works and the Antelope Valley-East Kern Water Agency, conducted a series of injection, storage, and recovery tests between September 1995 and September 1998. A key component of this study was to measure the response of the water table to injection, which was difficult because the water table averaged 300 feet below land surface. Rather than install many expensive piezometers, microgravity surveys were conducted to determine specific yield and to measure the development of a ground-water mound during the injection of about 1,050 acre-feet of fresh water into an alluvial-aquifer system. The surveys were done prior to, during, and near the end of a 5-month injection period (November 12, 1996, to April 17, 1997). Results of the surveys indicate increases in gravity of as much as 66 microgals between a bedrock reference station and 20 gravity stations within a 1-square-mile area surrounding the injection site. The changes were assumed to have been caused by changes in the ground-water elevation.

Gravity and ground-water levels were measured simultaneously at an existing well (7N/12W-34B1). The coupled measurements were used to calculate a specific yield of 0.13 for the alluvial aquifer near the well. To determine the gravitational effect of the injection mound on the gravity measurements made near well 7N/12W-34B1, a two-dimensional gravity model was used. Results of the model simulation show that the effect on gravity associated with the mass of the injection mound was minor and thus had a negligible effect on the calculation of specific yield. The specific yield of 0.13, therefore, was used to infer water-level changes at other gravity stations within the study area. The gravity-derived water-level changes were compared with simulated water-table changes.




Description of Study Area

Description of Injection Wells

Previous Microgravity Studies

Microgravity Surveys

Determination of Specific Yield

Effect of Injection Mound on the Calculated Specific Yield

Gravity-Derived Water-Level Changes

Comparison of Gravity-Derived Accumulated Mass and Injected Volume

Discussion of General Applicability and Limitations of Temporal Microgravity


Summary and Conclusions

References Cited

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