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Description
As San Diego County continues to search for a suitable landfill site, persistent groundwater contamination is occurring at the Ramona Landfill. Crystalline granitic rocks dominate the area around the Ramona Landfill, and groundwater flows primarily through a secondary fracture network which has developed via tectonic forces and/or stresses associated with plutonic intrusion. Field mapping has revealed faults which transect the landfill and may significantly influence the flow of groundwater. A groundwater monitoring program which began in 1986, and now involves 17 wells around the site, has provided insight into both the spatial and temporal trends which exist in regards to water quality degradation. Downgradient groundwater has been impacted with high concentrations of the major ions and volatile organic constituents. Vadose zone gas sampling, has revealed elevated levels of carbon dioxide, methane and other volatile gases. Landfill gas is a significant by-product of landfill waste decomposition, along with landfill leachate. Off-site cultural activities which have occurred adjacent to the site, have contributed to groundwater contamination. Aquifer pump-tests were analyzed to determine groundwater and contaminant flow velocities. In the process, interpretations made by a private environmental consulting company were found to be flawed. Recent alluvial deposits residing in drainages, help to create hydraulic conductivity heterogeneities in the subsurface. In order to derive more reliable conclusions, additional monitoring wells need to be completed in locations with distinctly higher hydraulic conductivities (i.e. fractures). Two geochemical tests were carried-out as part of this research in hopes of defining zones of varying redox potentials within the groundwater. Groundwater samples were analyzed for nitrite and kjeldahl nitrogen (reduced), and neutralized against the standard nitrate-nitrite (oxidized) analyses. Results revealed a very minor reducing environment being generated by the landfill which correlates with the same trends set forth by the other major leachate indicators. Samples were also analyzed for arsenic speciation at extremely low detection levels using the hydride generation technique. Results revealed that the subsurface environment around the landfill is well-oxidized. The delineation of distinct redox zones was not possible at the Ramona Landfill.
