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WASTE DISCHARGE REQUIREMENTS ORDER R5-2015-0058-01 -8- SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS FOOTHILL SANITARY LANDFILL, INC. FOOTHILL LANDFILL SAN JOAQUIN COUNTY 34. Designated waste can be discharged only at Class I WMUs or at Class II WMUs which comply with Title 27 and have been approved by the Central Valley Water Board for containment of the particular waste to be discharged. 35. Title 27 requires full containment of liquid designated wastes in Class II surface impoundment WMUs, double lined, with a leachate collection and removal system (LCRS), and which considers siting and geologic conditions (Title 27, § 20210). SITE DESCRIPTION 36. The topography in the site area consists of low, rolling hills vegetated with native grass and areas of exposed soil/bedrock. Surface elevations at the site range from about 240 feet MSL in the southeast corner to about 360 feet MSL in the northeast corner of the site. The area grade is generally about 2% toward the west. One mile to the east the terrain becomes more hilly like foothill terrain. 37. Land uses within one mile of the site include agriculture, livestock grazing, dairies, industrial, and rural residential. 38. A 2014 Department of Water Resources (DWR) well survey identified at least 8 supply wells within a one-mile radius of the site, including one agricultural well and seven domestic wells. The wells ranged in depth from about 230 to 340 feet while static water levels measure in the wells ranged from 75 to 200 feet below ground surface (bgs). Estimated well pumping rates ranged from 35 to 200 gallons per minute (gpm). One offsite domestic well (Well No. 39-587) was identified within 1,000 feet of the landfill facility boundary. One onsite industrial supply well (LW-1) was also identified. See Attachment C: Site Map. GEOLOGY 39. The regional geology in the area represents a transition between the Cretaceous - Quaternary age alluvial deposits of the Great Valley flood plain and the Jurassic age metamorphic rocks of the Sierra Nevada foothills. Valley deposits thin out within about a mile east of the site beyond which the surface geology is dominated by dissected alluvial uplands and exposed, uplifted bedrock characteristic of foothill terrain. 40. Valley deposits in the vicinity of the site include mid-to-late Pleistocene Modesto and Riverbank, Pliocene and early Pleistocene Laguna, and Miocene Mehrten deposits. The Mehrten occurs at the surface throughout the landfill property, except for the northeast corner which is mapped as Laguna. The Laguna soils generally consist of sand and gravel with minor silt and are typically weakly cemented with low to moderate permeability. The Mehrten soils consist of reworked volcanic mudflow deposits containing moderately cemented agglomerate, conglomerate, tuffaceous sandstone, and siltstone. Permeability is generally low. The Mehrten Formation also contains some andesitic mudflow breccias, which are also known as lahars. Both the Laguna and Mehrten can also contain expansive clay soil at the surface. Modesto and Riverbank formation deposits are found at the surface north and west of the site and adjacent to Mormon Slough. 41. The results of soil boring investigations conducted in 1985 and 1990 confirm that the