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An 8-year bioremediation field study was conducted in a trichloroethene (TCE)-contaminated, highly indurated (i.e., hard), rechargelimited (i.e., contains little water) conglomerate where common remediation strategies, such as groundwater recirculation and direct push installation of a large well network, could not be used. A tracer test using isotopically distinct water from the Hetch Hetchy Reservoir indicated that remediation fluids mainly flowed through fractures and sand lenses in the conglomerate. This was confirmed during in situ bioremediation of the site, in which Dehalococcoides (from a bioaugmentation culture) and volatile fatty acids (from injection of lactate) were the most accurate indicators of transport between wells. Some contaminants were also displaced out of the area due to injection of tracer water. Despite these difficulties, dissolved contaminant mass decreased by an estimated 80% by the end of the test, reaching the lowest values ever recorded at this site. Furthermore, the persistence of ethene 4 years after bioaugmentation suggests that the dechlorinating capacity of the remaining microbial community is comparable to the matrix diffusion of TCE into the dissolved phase.

Esser et al. (2002) Nitrate Contamination in California GroundwaterPage 5 of 62 Executive Summary BACKGROUNDNitrate contamination of California drinking water supplies is pervasive-about 10% of California public drinking water supply wells produce water that exceeds the regulatory drinking water limit, and a much larger fraction produce water which approaches the limit. As the population of California increases by 50% over the next 20 years, water resources will be in critically short supply. If the State can develop acceptable methods to prevent nitrate contamination of susceptible groundwaters and to remediate contaminated groundwaters, then the volume of available "new" water will be a critical benefit to California's continuing growth and prosperity.Nitrate is commonly viewed as an intractable problem for three reasons. First, nitrate contamination is ubiquitous in both surface and groundwater -a substantial number of California public and especially private groundwater wells have nitrate levels that exceed or approach regulatory limits for drinking water, and a significant fraction of surface water supplies have nitrate concentrations that would preclude their use for groundwater recharge if draft DHS regulations were adopted.  Second, the activities that contribute anthropogenic nitrate to groundwater -animal operations, crop fertilization, wastewater treatment discharge, septic systems -are ongoing and essential to the industry and commerce of the State of California.  Finally, nitrate is expensive to remove from drinking water supplies, especially in public and private systems that rely on untreated groundwater and do not have the necessary water treatment infrastructure. These factors combine to make nitrate the number-one contaminant threat to California's drinking water supply and at the same time may represent an opportunity to make important strides in providing sufficient water to meet California's future growth. A working group at LLNL has surveyed the current approach to characterizing and managing groundwater nitrate contamination in California, and has identified specific opportunities for developing better characterization methods. SPECIFIC RECOMMENDATIONS FOR GROUNDWATER NITRATE MANAGEMENT Conduct a Groundwater Basin Assessment of Nitrate Inventories and ImpactsThe ultimate goal of the Groundwater Quality Monitoring Act of 2001 (AB599) is the implementation of a comprehensive monitoring program to allow groundwater basin assessment. Assessment is a broad term still being defined by the AB599 Interagency Task Force and Advisory Board, but encompasses assessing susceptibility of groundwater to contamination, characterizing current water quality in a basin, and predicting future water quality under different conditions. To meet these goals, basin assessment must consider the current inventory of nitrate in basin soils and waters, current and past source loading, groundwater recharge and transport, An LLNL Water Initiative White Paper (LLNL-TR-466420)Page 6 of 62 and nitrogen cycling in the so...

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