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(FIRM) for San Joaquin County (Federal Emergency Management Agency, 1988). A flood with the probability of occurring once in every 100 years will inundate the 100 year floodzone, and once in every 500 years inundates the 500 year floodzone. The proposed quarry site is located outside the 500 year floodzone and would to be at least 1,000 feet from the river. Approximately 55 acres of the proposed quarry site is topographically higher than the surrounding relatively level farmland. On site drainage is currently provided by a single grass lined ditch located along the base of the bluffs roughly located on the west, south, and east site boundaries. This drainage terminates as a small pond on site. Adjacent to the drainage ditch, on the southeastern boundary of the proposed quarry site, is the Clements Drainage Pond which serves as a flood control structure for a portion of the town of Clements. The pond, owned by San Joaquin County, is designed to retain runoff from the 10 year storm event (Kelley, C., pers. comm.) and allows percolation to groundwater. If the capacity of the pond is exceeded, overflow passes through several culverts to the drainage ditch. Surface runoff from the drainage area encompassing the proposed quarry site has not developed a watercourse or fixed drainage pattern. An onsite field inspection revealed no drainage outlets directly to the Mokelumne River, although some agricultural runoff may reach the stream channel in the form of sheetflow. Drainage on the north side of the Mokelumne River (at the existing gravel processing facility) is also contained on site, allowing no runoff to the river. A series of ditches and ponds have been developed to store and recirculate water used in the aggregate processing operation. The natural river levee on the north bank is higher than the adjacent land, impounding any surface runoff and preventing an outlet to the river. Groundwater Within the deep water aquifer of the Eastern San Joaquin Basin, groundwater is found at approximately 40 foot depth in the vicinity of Clements (Hirata, 1988). However, the water table may be encountered closer to the ground surface at the proposed quarry site. This shallower groundwater may be perched above the less permeable substratum after heavy rains or application of irrigation water (USDA SCS, 1988). An exploration study performed for the project applicant in 1989, one-quarter mile north of Clements, consistently found groundwater between 15 and 20 foot depths 30