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• stratigraphy at the site is characterized by horizontal distributary channel and overbank deposits of mainly silty sand and sandy silt with subordinate clayey silts Soil at the site has developed on the Quaternary Modesto Formation These sediments were derived predominantly from igneous and metamorphic rocks of the Sierra Nevada and deposited in a westward-thickening wedge towards the axis of the Great Valley Province Elevation at the site is approximately 6 5 ft above mean sea level Groundwater is present in an onsite well at approximately 21 5 ft below ground surface, or approximately 15 ft below mean sea level The deeper, regional groundwater aquifer is assumed to be approximately 90 to 100 ft below ground surface at the site Shallow groundwater beneath the site is expected to have very little gradient, but may slope in a northwesterly or southeasterly direction PROPOSED SUBSURFACE INVESTIGATION To delineate the vertical and lateral extent of soil contamination, the lateral extent of groundwater contamination, and to evaluate alternative remedial solutions at the site, Walsh proposes to drill a minimum of three soil borings to total depths of approximately 35 ft below grade (approximately 14 ft below the groundwater surface) and install groundwater monitoring wells in each of the borings The proposed locations of these soil borings/monitoring wells have been selected to represent groundwater in the assumed upgradient and downgradient directions (Figure 3) Drilling will be performed using a drilling rig equipped with 8-in hollow-stem augers The augers will be steam cleaned prior to drilling each boring to prevent downhole or cross-boring contamination If any of these borings indicate evidence of soil or groundwater contamination, a truck- or skid- mounted geoprobe will be used to delineate the lateral extent of groundwater contamination by sampling and analyzing geoprobe groundwater samples A minimum of nine groundwater probes will be installed The purpose of groundwater sample screening is to identify locations for soil boring and groundwater monitoring well sampling that will fully delineate the extent of contamination at the site Soil Borings Soil samples will be collected at approximately 5-ft intervals and at changes in lithology encountered in the borings using a California-modified split spoon sampler containing three clean brass sleeves The open ends of the lower sleeve will be covered with aluminum foil, plastic end caps and made airtight with duct tape This sleeve will be labelled and placed in iced storage Approximately one-half the contents of the middle sleeve will be place in a sealable plastic bag, after 3 to 4 min, the probe of an organic vapor meter (OVM) will be inserted into the bag and the meter reading will be recorded The remaining contents of the middle sleeve will be used for descriptive purposes which will be recorded on the log of the borings Contents of the upper sleeve will be regarded as sluff material and will be added to the drill cuttings Drill cuttings will be place in Department of Transportation(DOT)-approved 17-H drums and stored onsite pending the results of laboratory analyses Disposal of this soil is the responsibility of the site owner, &W 9114193 4 1685-630 scw & Associates, Inc Environmental scientists and Engineers