HR: 1340h
AN: H33E-1689    [Abstracts]
TI: Fate and Transport of Perchlorate at California's Stringfellow Superfund Site
AU: * Kenoyer, G J
EM: gkenoyer@kleinfelder.com
AF: Kleinfelder, 1220 Research Dr., Suite B, Redlands, CA 92374, United States
AU: Nuttall, H E
EM: enuttall@kleinfelder.com
AF: Kleinfelder, 8300 Jefferson NE, Suite B, Albuquerque, NM 87113, United States
AU: Paulson, R
EM: RPaulson@dtsc.ca.gov
AF: Dept. of Toxic Substances Control, Stringfellow Branch, 8800 Cal Center Dr., Sacramento, CA 95826, United States
AU: Wolfenden, A
EM: AWolfend@dtsc.ca.gov
AF: Dept. of Toxic Substances Control, Stringfellow Branch, 8800 Cal Center Dr., Sacramento, CA 95826, United States
AU: Aldern, J
EM: jaldern@kleinfelder.com
AF: Kleinfelder, 1220 Research Dr., Suite B, Redlands, CA 92374, United States
AB: Geologic conditions exert primary control over the fate and transport of perchlorate at the Stringfellow Superfund site. A buried valley filled with alluvium has been defined that extends from Pyrite Canyon, location of the former Stringfellow acid pits, down to near the Santa Ana River. The buried valley is cut into the underlying granitic bedrock, and appears to be a paleo-channel of the ancestral Pyrite Creek. The groundwater hydraulic gradient aligns closely with the buried valley, as does the perchlorate plume. The buried valley appears to be a preferential pathway for contaminant migration. Perchlorate concentrations in the downgradient portion of the plume have been slowly decreasing over time, suggesting that the groundwater extraction wells are effective at cutting off the source. Perchlorate degradation, however, appears to be minimal over most of the sandy aerobic aquifer, as concentrations of perchlorate persist over a 5-mile long plume. Scattered concentrations of perchlorate in the 1 to 12 ug/L range are widespread over a broad area adjacent to the plume and appear to be unrelated to the plume. Hydrogeologic analysis and perchlorate isotope analysis are being used to investigate whether these outlying concentrations may be related to the historic use of perchlorate- bearing mineral nitrate fertilizer. At the distal end of the plume, a marked change in the fate of perchlorate occurs beneath the Santa Ana River. Sampling of mini-piezometers installed into the river sediments shows that the perchlorate and nitrate concentrations fall to below detection as the aquifer environment changes from oxidizing to reducing conditions. In this local environment, it appears that anaerobic biodegradation reduces the perchlorate and nitrate. As a result of degradation of perchlorate, and possibly mixing of infiltrating river water beneath the losing portions of the river, perchlorate concentrations decrease to below 6 ug/L downgradient of the river. This presentation will show how geologic conditions and the geochemical environment affect the fate and transport of perchlorate at the Stringfellow site.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1899 General or miscellaneous
SC: Hydrology [H]
MN: 2007 Fall Meeting