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3-9 1101 South Littlejohn's Creek is labeled as "Zone A0, (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 further expansion of the northern portion (Austin Road Unit) of the landfill. The 7,600 -foot reach 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 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 Forward Unit of the landfill. From the FIRM map (Map No. 06077C Panels 0635F and 0630F), the existing South Fork is labeled as "Zone A0, (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 result, will not inundate or potentially erode the adjacent creek or cover the landfill. The predicted elevations from the 500 -year flood event range from 40.5 feet on the southwest edge to 43 feet on the east edge of the landfill along Austin Road and this level is only one to two feet higher than the toe of existing landfill slopes. The existing South Fork was designed to channel the 100 -year flood flow of 1,550 cfs within its banks and an additional one foot of freeboard. In the event that a 500 -year flood occurs (1,700 cfs, according to FEMA Flood Flows), the excess flow will spill over the southerly bank and into the adjacent area, rather than impact the Forward Landfill. The South Fork alignment is also a very flat gradient, 0.0006 feet per foot; therefore, erosion is not a significant concern. Rainfall intensities for a 1,000 -year storm event near Stockton, California are presented in Table 6. Figure 7 represents the regional 100 -year floodplain map. 3.7 Hydro eology 3.7.1 Regional Hydrogeology The Water Quality Control Plan for the Sacramento River Basin and the San Joaquin River Basin (Basin Plan) places the site in the Duck -Littlejohn Hydrologic Area (31.40) of the San Joaquin River Basin. As a major regional aquifer system, the San Joaquin hydrologic basin is used for industrial, domestic, and agricultural purposes. Most of the production wells in the area are constructed to depths on the order of 500 feet and produce water from the Laguna Formation. Although there are no regionally significant fine-grained intervals, by the heterogeneous nature of the Laguna Formation, some localized confinement of groundwater may be present, though typically, groundwater is unconfined or locally semi -confined. It is Forward Landfill SWT Engineering Joint Technical Document - April 2014 z:\projects\allied waste\forward\five year permit rvw 2013\itd-5 yr pr 2013\text\sec 3_final.doc