ARCHIVED REPORTS_JULY 2014 FINAL RCSI

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3-10 Forward Composting Facility SWT Engineering Report of Composting Site Information - July 2014 z:\projects\allied waste\forward\resource recovery facility\5 yr permit rvw 2013-14\rcsi 2014\text\sec 3.doc (NGVD) (California Department of Water Resources, 1981). This precipitation station was selected due to its long and reliable period of record and its proximity to the project site. The precipitation depth-duration-frequency data for the site was obtained from the Stockton Weather Station Number B00-8560 (except where noted): ♦ 100-year, 24-hour storm intensity of 3.58 inches* ♦ 1,000-year, 24-hour storm intensity of 4.92 inches* ♦ 100-year annual precipitation of 25.42 inches ♦ Annual mean precipitation of 14.27 inches *Source: Non-Water Corrective Action Plan for Forward Landfill, GeoLogic Associates, November 2011. From the late 1980s to the early 1990s as well as recently, California is experiencing a severe drought. Although the precipitation data available during this period may not represent the statistical minimum precipitation that could occur at the project site, the likely minimum precipitation range anticipated during the service life and post-closure period of the landfill can be estimated. Table 9 presents monthly average total precipitation recorded for the Stockton Area, for a period of 62 years, between 1950 and 2012. During this period, the average annual precipitation recorded for the Stockton area was approximately 17.87 inches. Considering the drought conditions experienced during that period, a minimum annual average precipitation of 17.87 inches during the service life and post-closure period of the landfill site was estimated. As shown in Figure 8, the Forward site is located between the North Fork and the South Fork of the South Littlejohn’s Creek. Based on the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRMs) for the San Joaquin Valley, Forward Landfill is located within four FIRM Panels: 0490F; 0495F; 0630F; and, 0635F. From the FI RM Legend, the majority of the landfill (including the RRF and Composting Facility) is located within “Zone X”, which are areas determined to be outside the 0.2 percent annual chance of being in a floodplain. The area east of Austin Road at the North Fork of South Littlejohn’s Creek is labeled as “Zone AO, (Depth 1)”, which are areas with flood depths of one to three feet. This information was factored into the North Fork realignment of the South Littlejohn’s Creek relocation design. The North Fork of South Littlejohn’s Creek was relocated to allow continued development of the Forward Landfill. The 7,600-foot reach of the creek relocation was designed to channel the 100-year flood-flow of 1,025 cubic feet/second (cfs) within its banks with an additional one foot of freeboard. In the event that a 500-year flood occurs (1,100 cfs, according to FEMA Flood Flows), the excess flow will spill over the northern bank and into the adjacent farm land, rather than affecting Forward Landfill. Based on the realignment of the North Fork of South Littlejohn’s Creek, the landfill property is not located within the predicted elevation of the 500-year flood zone. Therefore, the existing realignment does not require an assessment for potential erosion or saturation of the landfill. The South Fork of South Littlejohn’s Creek runs south of and adjacent to the southern perimeter of the refuse footprint of the landfill. From the FIRM map (Map No. 06077C Panels 0635F and 0630F), the existing South Fork of South Littlejohn’s Creek is labeled as “Zone AO, (Depth 1)”, indicating depths of one foot, and Zone AE, indicating base flood elevations within the creek. These current flows are very slow and non-erosive and as a