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1 <br /> GEOMATRIX <br /> PHS/EHD In addition, the groundwater samples from two existing wells and three new <br />' monitoring wells were analyzed for nitrate and sulfate using U S EPA Method 300 and <br /> dissolved iron and manganese using U S EPA Method 6010B <br />' 4.0 DATA EVALUATION <br />' The results of this assessment are described in the following sections These results and the <br /> data obtained from previous site investigations are used to evaluate the lithology (Section 4 1), <br />' hydrogeology (Section 4 2), and the extent of petroleum hydrocarbons in soil (Section 4 3) <br /> and groundwater(Section 4 4) at the site Based on these evaluations, a site conceptual model <br /> on the release and migration of petroleum hydrocarbons is presented in Section 4 5 <br /> 4.1 SITE LITHOLOGY <br />' The boring logs for B3-14, MW3-4, MW3-5, and MW3-6 are included in Appendix A The <br /> shallow soil from the ground surface to about 10 feet bgs at the site generally comprises sand, <br />' silt, and clay The shallow soil beneath the paved areas at the site, including the former UST <br /> area, is mostly fill sand Underlying the shallow soil is a layer that comprises mostly clay <br /> and/or silt to a depth of about 20 to 32 feet bgs This 10- to 24-foot thick clay/silt layer is <br /> continuous and laterally extensive beneath the site The interval beneath the clay/silt layer to <br /> the maximum depths of the soil borings at the site generally comprises sandy soil, including <br /> silty sand and poorly-graded sand This soil consists mostly of fine sand with some medium <br /> sand The stratigraphy of the site is shown on Figures 3 and 4 <br />' The soil from about 10 feet bgs to the maximum depth of the soil borings at the site is <br /> g P g <br />' generally dark greenish gray in color, indicating reducing conditions <br /> 4.2 SITE HYDROGEOLOGY <br />' When advancing the soil borings for the new monitoring wells, first groundwater was <br /> encountered in the sandy interval starting at approximately 20 5 to 22 feet bgs (Figures 3 <br />' and 4) After the new monitoring wells were completed, depth to water measured in the new <br /> wells ranged from about 10 toll 5 feet bgs (Table 2) This indicates that the clay/silt layer <br /> overlying the sandy interval is a confining layer <br />' Depth to water measured in the existing monitoring wells at the site has ranged from about <br /> 9 to 13 feet bgs (Table 2) Horizontal groundwater flow has vaned in all directions (Table 3) <br /> 11PROJEC1VOWA6437 00016437-08 c1m 9 <br />