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AL KLEINFELDER The disadvantage of this option is that the imported soil wedge will fill a good portion of the pit area. 3. Reinforced Soil Slope - This is similar to slope buttressing except that a geogrid and geotextile would be used to construct the soil wedge supporting the steep soil face. The advantage to this approach is that the soil wedge can be made steeper, something on the order of 1:1 or greater. This reduces the space taken up by the soil wedge in the pit area. Drawing 2A (cross-section A-A') shows how the geosynthetic liner would be placed in the pit area if the reinforced soil slope approach is used. As shown in this cross-section, the liner on the face of the reinforced soil slope would be too steep to cover with soil and would be covered with a second,protective geomembrane. Detail 1 on Drawing 2A shows this configuration. 2. Page 19, Section H.1.5 (Drainage) - To demonstrate adequacy of final drainage design, a discussion of the impacts of recent high rainfall events and seasons should be provided and compared with the design event. In addition, the effect of proposed FML installation in the pit area on drainage should be assessed. During the last rainy season (July 1, 1994 through June 30, 1995) the total precipitation at the Stockton was 17.81 inches (National Weather Service). Average annual precipitation in Stockton (as measured at the Stockton Fire Station 4, DWR Station B00-8530-0) is 14.35 inches (112 year period of record). The following table provides the calculated maximum precipitation (in inches) for a specified duration based on climatologic data from the Stockton Fire Station. Return Period 1 Day 1 Month 1 Year ears 2 1.49 5.05 13.92 5 1.99 6.86 17.63 10 2.31 7.96 19.76 20 2.61 8.96 21.64 25 2.70 9.27 22.20 40 2.74 9.89 23.34 50 2.98 10.18 1 23.86 100 3.25 11.05 25.42 Source:California Department of Water Resources Average annual pan evaporation in the Stockton area (as measured at the Mowry Bridge in Stockton, DWR Station Number B90-856200) is 67.4 inches. Using a pan coefficient of 0.7, the corrected value for evaporation is 47.2 inches. Rainwater from approximately 6.2 acres will drain into the pit area. Presently, some rainwater runoff collects in the pit during the rainy season but it usually evaporates completely during the summer. Since the present cap is a compacted soil intermediate cover, there is probably a significant portion of rainfall that is absorbed into the soil and does not travel to the pit area as runoff. Installation of the final cap (using a geomembrane) will effectively cut infiltration and most of the rainwater will end up in the pit area. The pit area itself will act as a stormwater impoundment. Runoff will collect in the impoundment and will either remain there for evaporation during the summer or will be pumped to the drainage Swale adjacent to the western boundary of the site. The amount of pumping that will occur during winter will of course depend upon the amount of rain. In this preliminary design, the pit area will be lined on all sides to an elevation of approximately 0 feet MSL (approximately 13 feet above the bottom of the pit). Once stormwater reaches within two or three feet of 0 feet MSL, it will be pumped to the 23-481399-A00/TL960001 Page 2 of 5 January 4, 1996 Copyright 1996 Kleinfelder,Inc.