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The liquids contained on the site in the lined evaporation pond shall consist of runoff from the wood storage and yard waste comoostina area. This liquid will be reused in the composting operation and will be allowed to evaporate. The pond is designed to contain the 100 -year annual precipitation and the 100- year/24-hour storm event and will evaporate dry by the end of the summer months. Implementation of these mitigations will reduce the potential impacts to surface waters to a less - than -significant level. Impact 4.5-2 Degradation or impairment of groundwater resources may result from contaminants entering the ground water system over the life of the project as a result of lack of or failure of impervious surfaces and liners in working areas. Contamination of a public water supply could occur. There is a potential that the project will substantially degrade ground water resources. The project site is located at the bottom of a pit in highly permeable gravel -rich soils. Waste products and contaminants routinely handled at the site may occasionally be spilled onto the ground. The "tipping floor' is to be periodically washed down to reduce dust and control nuisance odors. Leachate may be generated from the waste products. Wash water, leachate. and contaminants have the potential to infiltrate into the soil and ultimately into the ground water. The aquifer must be protected from impact resulting from infiltration of leachable chemicals vertically and horizontally through the highly permeable soils and geologic strata. There is a potential that wash waters from the "truck wash" area, and spilled petroleum products or hydraulic fluids from the "fueling" area may infiltrate into soils, and migrate downward into the ground water. It is recommended that a minimal ground water monitoring program be instituted at the project site, in order to maintain documentation of ground water quality and potential contamination moving from the site into ground water. Such a ground water monitoring program would allow establishment of baseline water quality information, and thus would be in the best interests of the project operators. Contaminants migrating from off site could be identified and potentially tracked as to source, so that the project is not deemed responsible for contaminants originating from other sources. Similarly. because the site is located in highly permeable, gravel -rich sediments, an adequate ground water monitoring program would also detect movement of contaminants that originate on the materials recovery and transfer facility. Monitoring wells that provide information on ground water levels, -gradient, and water quality can be effective in detecting contaminants that originate on the site, as well as detecting contaminants that originate off the site. Monitor wells are effective in disputes over the sources of migrating contaminants. From a CEQA standpoint, the monitor wells would not serve to mitigate any potential environmental impacts occurring at this time. However, monitor wells would allow timely recognition of contaminants potentially migrating from the facility in the future. 4.5-2 All mitigation measures implemented under Mitigation 4.5-1 to mitigate potential impact to surface waters will also serve to mitigate the potential impacts to ground water. If ground water quality protection standards are exceeded, the project applicant will implement a corrective action program to remediate the affected ground water. 0 1 ER -93-1 -70- (9-27-93)