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Section 1 Introduction and Background 1.1 INTRODUCTION The Lockeford Community Services District's(Lockeford CSD)wastewater treatment and disposal facility (WWTF) is located within San Joaquin County,Lockeford, California. The purpose of this workplan is to address inadequacies in the existing groundwater monitoring network,pursuant to the Central Valley Regional Water Quality Control Board's (Regional Board)February 21, 2006 letter request. Implementation of this workplan should provide adequate monitoring of both background grou dwater quality and groundwater down gradient of wastewater treatment, storage, and disposal fa ilities. Accordingly,the following sections summarize site soils, geology, and the methods and materials used to construct groundwater monitoring wells, consistent with both State and County Well Standards. 1.2 SITE SOILS, GEOLOGY, AND OYDROGEOLOGY 1.2.1 GEOLOGY AND SOILS The California Department of Mines and Geology (CDMG) Geologic Map of the Sacramento Quadrangle indicates that the project area is located in Pleistocene (deposited from about 2 to 0.01 million years ago)alluvial deposits west f the Sierra Nevada Foothills and within the Central Valley of California. According tot is source,the underlying geology at the WWTF consists of the Modesto-Riverbank formation and is comprised of an arkosic (feldspar rich and generally derived from the rapid disintegratio of granite or granitic rocks) alluvium of gravel, sand, silt, and clay. In addition to available geologic information for the site, available soils coverage provides increased resolution of near surface soils/sediment in the vicinity of the WWTF. Georeferenced soils coverage data were obtained from the United States Department of Agriculture (USDA)National Resources Conservation Service(MRCS). According to this source, soils underlying the WWTF are composed predominantly of the Burella,Exeter, Hicksville, and San Joaquin soil types. Of th se soils,both the Exeter(Figure 4,#157) and San Joaquin(Figure 4, #239 and#240)are noted as having an approximate 4 to 17-inch thick duripan (siliceous cemented hardpan) at approximate 20 to 40 inches below ground surface. This duripan also represents the limiting layer with respect to saturated hydraulic conductivity and is reported as essentially non conductive (San Joaquin Soil Survey). The limiting saturated hydraulic conductivity (within approximately the upper 40 inches of the soil profile)of the remaining Burella and Hicksville soil types was reported as 4.2 x 10-5 and 1.4 x 10"4 cm/second, March 2006 Lockeford CSD �_ Groundwater Monitoring Well Installation Workplan