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9.0 introduction This hydrologic report has been updated from the September 2011 report per comments by Regional Water Quality Control Board, Central Valley. This report describes the proposed finish grade drainage collection of the Extension of Closure Cap, Corral Hollow Sanitary Landfill in San Joaquin County,California. This hydrologic report is for a limited area of the Corral Hollow Sanitary Landfill (CHSL). This hydrologic report defines the project objectives, identifies the design criteria and methods,and summarizes the engineering design itself. Appendices attached to the report contain NOAA precipitation data and Auto CAD Hydroflow results calculations. j 9.9 Location and Characteristics The CHSL is located at 31130 South Corral Hollow Road, in southern San Joaquin County, approximately 5 miles south of the City of Tracy, at the intersection of Interstate 580 and Corral Hollow Road. CHSL is located in Township 3 South, Range 5 East of Section 18 of the Mount Diablo Meridian. 1 i CHSL is a closed, unlined Class III landfill. The landfill property includes approximately , 58 acres, 43 acres having been permitted for refuse receipt. The remaining area is comprised of ' access roads, storm water retention ponds, setbacks for environmental monitoring, and E firebreaks. Land within 1,000 feet of the facility is used for interstate freeway, associated easements and agriculture. C CHSL ceased receiving waste in 1991. The existing final cover was constructed in the fall of 1995 in compliance with Regional Water Quality Control Board (RWQCB), Central Valley Region Order No. 94-259. The closure cover consists of a 2 to 6-foot thick foundation layer { under a 1-foot minimum thick, low-permeability soil layer,with a 1-foot thick vegetative surface layer. The closure cap extension will be a 2-foot vegetative soil layer underlain by geosynthetie clay liner. 9.2 Design Overview The proposed finish grades of the closure cap extension are designed to promote.runoff to two proposed ditches. The proposed perimeter ditch adjacent to the easterly site perimeter access road has an approximate drainage area of 16.98 acres. The perimeter V- shaped earthen ditch shall have erosion control matting placed prior to hydroseeding for erosion control. The remainder of the stormwater runoff from the cap extension shall be captured by a proposed Caltrans V-shaped concrete lined ditch. The Caltrans ditch drainage area is approximately 4.33 acres. The Caltrans drainage area also incorporates stormwater runoff from the adjacent Caltrans I-580 right-of-way and a portion of Corral Hollow Road right-of-way as illustrated in Figure 1. The Caltrans ditch flow line pathway was designed to reroute the stormwater flow line SHAW ENV/ omfENTAL,INc. SfCme1MAOvePra,,MSmJ,,gV C.,1yU43515.2011.111111,raeCw9Mt*vM,',*eMJJ4ydcJ.Rept Rev.1,4/19/12