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Ar.vt r - €wONE The closest surface water to the site is the Mokelumne River, approximately one-half mile to the northeast. The river in this location flows generally to the northwest and is subject to periodic flooding, The regional groundwater flow is generally towards the Mokelumne River to the north. Groundwatp-r beneath the site occurs at a depth approximately 12 feet below grade and flows southwest. of 2.3 Proximity of private, municipal and irrigation wells: A survey of all water wells within a one half mile radius of the site was conducted based on information received from the California Department of Water Resources. The closest well to the site is a municipal supply well approximately 90 feet north of the site. This well has screened intervals from 135-150 feet, 160-•185 feet, and 225-•235 feet below grade. It is sealed to a depthofgroundwater feet contain natiis not expected to be impacted by Numc -ous monitoring and industrial wells of various depths exist, at several local. canneries along the Southern Pacific Railroad tracks, approximately 1000 feet east of the site. The approximate locations of known water wells are plotted on Figure 2. 2.4 Locations of nearby septic tanks and underground utilities: The location of the septic tank and leach line in the vicinity of underground tank and product line are plotted in Figure 3. No underground utilities have been located on- site. The location of the septic tank and leach line are approximate, based on verbal communication from Bruno Maury of the Thornton Fire Department. e 3,0 FIELD INVESTIGATION On November lst, 1590, WaterWork personnel advanced three soil borings (MWI, mW2, MW3) to depths ranging from 27 to 28 feet below grade at the project site to accomplish the following: 1) define the lateral and vertical extent of petroleum hydrocarbon soil contamination; 2) determine soil stratigraphy; and 3) install groundwater monitoring wells within the uppermost aquifer in order to assess groundwater quality. The boring/well locations are plotted in Figure 3. Boring/wall locations were chosen based on an assumed southwest groundwater gradient direction. 3,1 Soil Sampling Drilling was conducted by Spectrum Exploration, Inc. (C57 512289) utilizing a hollow stem auger drill rig. A field geologist continuously logged all drill cuttings and cored soil samples utilizing theDescriptionsl ofClassification soil types System (Appendix II) . ction intervals are included an encountered and sample colle 2