By Miranda S. Fram, Joshua K. Berghouse, Brian A. Bergamaschi, Roger Fujii, Kelly D. Goodwin, and Jordan F. Clark
U.S. GEOLOGICAL SURVEY
Open-File Report 02-102
Sacramento, California 2002
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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 three cycles of injection, storage, and recovery tests to evaluate the feasibility of artificially recharging ground water in the Lancaster area of Antelope Valley, California. During the third cycle (March 1998 through April 1999), the tests included investigations of the formation and fate of trihalomethanes in the aquifer. Trihalomethanes are disinfection by-products formed by reaction between natural dissolved organic carbon that is present in water and chlorine that is added during the drinking-water-treatment process. This report includes a discussion of the design of the investigation; descriptions of the sampling, analytical, and experimental methods used in the investigation; and a presentation of the data collected.
During the third cycle, 60 million gallons of chlorinated water was injected into the aquifer through well 7N/12W-27P2 in the Los Angeles County Department of Public Works well field in Lancaster between April 15 and June 16, 1998. One hundred fifty million gallons of water was extracted from the same well between June 30, 1998, and April 29, 1999. Water-quality samples were collected during the entire cycle from the well and from a nearby set of nested piezometers, and were analyzed for residual chlorine, dissolved organic carbon, trihalomethane, major anion, and dissolved solid concentrations; ultraviolet absorbance spectra; and a number of field water-quality parameters. A statistical analysis was done to evaluate the analytical precision of the residual chlorine, dissolved organic carbon, trihalomethane, and ultraviolet absorbance measurements on these samples. The formation of trihalomethanes in the injection water was examined in laboratory experiments: Trihalomethane concentrations in samples of injection water were monitored during a storage period, and trihalomethane formation potential in the presence of excess chlorine was measured. The role of mixing between injection water and ground water and the conservative or non-conservative behavior of trihalomethanes was studied by adding a conservative tracer, sulfur hexafluoride, to the injection water and monitoring its concentration in the extraction water. The potential for biodegradation of trihalomethanes by aquifer bacteria was assessed in laboratory experiments: Microcosms containing ground water or extraction water and sediment or concentrated bacteria were spiked with trihalomethanes, and the amount of trihalomethanes was monitored during an incubation period. The potential for sorption of trihalomethanes to aquifer sediments was assessed in laboratory experiments: Mixtures of sediment and water were spiked with trihalomethanes, and then the trihalomethane concentrations were measured after an equilibration period.
Abstract
Introduction
Purpose and Scope
Project Design
Site Description
Injection and Extraction Chronology for the Third Cycle
Acknowledgments
Water-Quality Monitoring at Wells
Sampling Methods
Statistical Method for Assessment of Quality-Control Data
Analytical Methods
Free and Total Residual Chlorine Analysis
Ultraviolet Absorption Analysis
Dissolved Organic Carbon Analysis
Trihalomethane Analysis
Results
Injection Water
Ground Water
Extraction Water
Water from the Nested Piezometers
Studies of the Formation and Fate of Trihalomethanes
Formation of Trihalomethanes from Injection Water
Experimental Methods
Storage Experiment Method
Trihalomethane-Formation-Potential Method
Results
Storage Experiment
Trihalomethane-Formation-Potential Experiment
Tracing the Injection Water with Sulfur Hexafluoride
Experimental Methods
Results
Biodegradation of Trihalomethanes by Aquifer Bacteria
Experimental Methods
Sediment Microcosm Method
Water Enrichment Method
Trihalomethane Addition and Analysis Methods
Bacterial Counting Method
Results
Sediment Microcosm Experiments
Water Enrichment Experiments
Bacterial Densities
Sorption of Trihalomethanes to Aquifer Sediments
Experimental Method
Results
Summary
References Cited
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