COMPLIANCE INFO_1990-1998 - Laserfiche WebLink

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ENVIRONMENTAL SETTING CLIMATE The average annual precipitation at the landfill is approximately 9.5 inches. Precipita- tion falls primarily between the months of October through April. SOILS/GEOLOGY Soils at the site consist of two units of the Capay Clay soil series. These soils occur on very gentle slopes ranging from 0 to 2 percent and are naturally wet due to the presence of a shallow seasonal water table ranging from 2 to 4 feet in depth. The establishment of subsurface drains has lowered the local water table to a depth of 4 to 6 feet. Field observations and laboratory analyses of physical and chemical properties docu- menting representative soil profiles of the proposed land application site indicate that the site is suitable for the long-term application of sludge at agronomic rates. The sludge application schedule must be based on crop utilization of nutrients, principally nitrogen. The site is underlain by alluvial deposits consisting of unconsolidated silts, clays, and sands of Pleistocene to Recent age. These materials originated from marine sedimen- tary rocks of the Coast Range. Below the alluvial deposits lies the Tulare Formation, which is composed of unconsolidated and semiconsolidated beds and lenses of clay, sand, and gravel. Within this formation is the Corcoran Clay layer, which acts as a confining bed for deeper groundwater in this portion of the San Joaquin Valley. GROUNDWATER As noted above, the Corcoran Clay layer separates the upper and lower aquifers in this portion of the San Joaquin Valley. The upper aquifer naturally extends to within 2 to 4 feet of the ground surface. However, no shallow groundwater was encountered to a depth of 8 to 10 feet during field investigations. Groundwater may rise to within 4 to 6 feet of the ground surface during the growing season when fields are being irrigated. Generally, groundwater moves in a northeasterly direction across the proposed appli- cation site toward the San Joaquin River. Local variation in this direction of ground- water movement may be caused by irrigation, drainage, and groundwater pumping. GROUNDWATER QUALITY Groundwater located above the Corcoran Clay layer is considered to be of relatively poor quality. Past studies have indicated that shallow groundwater contains high concentrations of dissolved solids, chloride, sulfate, nitrate, and boron. sAr./1'97ro81.51