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conditions of a 25 year 24-hour rainstorm event, and (4) the projected volume and matter of runoff associated with a 25-year 24-hour rainstorm event [14 CCR 18220(m)]. The physical conditions at the Compost Facility site are described in detail in the following section. The specific items noted in the Permit Desk Manual requirements are summarized below. (1) The Forward site is located near the geographic center of the Great Valley of California. Original ground surface elevations at the site range from approximately 35 to 45 NGVD, sloping generally to the west. Regional topography is shown in Figure 1.1. The Great Valley is an asymmetrical structural trough filled with a thick sequence of flat-lying marine and continental sediments. The surface soils are mainly composed of two soil types typical of Victor Formation sediments, as shown in Figure 2.3. The two soils, as mapped by the Soil Conservation Service, are known as Clear Lake clay (CL) and Jacktone clay (ST). These soils are similar in composition; they were formed from alluvium. The permeability of both these soils are low, the available water-holding capacity is moderate, the shrink-swell potential is high, and the water erosion potentials are low. The general water bearing char- acteristics of the surface soils, separated into clay, silt, and sand components are presented in Table 2.1. Typical uses of these soil type include irrigated cropland, orchards, vineyards, and sometimes irrigated pasture and urban development. Table 2.1 Regional Hydrogeologic Characteristics Hydraulic Permeability Conductivity Specific Storage Porosity Material (k) cm2 (k) cm/sec (s) m' (n) % Sand 10-5 - 10'9 101 - 10.1 10-3 - 10'5 25 - 50 Silt 1W - 10-12 10'3 - 107 10-2 - 104 35 - 50 Clay 1012 - 10-15 10-7 - 1010 10-2 - 10-4 40 - 70 (2) The Forward site is located in the San Joaquin hydrologic basin. Based on q groundwater elevation contours published by the San Joaquin County Flood Control and Water Conservation District, the regional groundwater in the vicin- ity of the site was -20 to -30 feet NGVD (approximately 60 to 70 feet below ground surface (gbs)) and appeared to be flowing north-northeast in Spring, 1990. wa10029M4.wp5/37 9/28/94 37