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0 <br /> .a <br /> _y <br /> LEEDSkIti•NEitK€kHOFF,IkC. - <br /> Analysis of groundwater samples from MWl, MW2, and MW3 indicates that the <br /> _ petroleum hydrocarbon contamination in the soils of the former tank excavation <br /> has migrated through the clay confining layers and has impacted the groundwater <br /> beneath the site. The highest contamination appears in 3 which is down <br /> -- gradient of the former tank excavation (see Section 4.5 Greun water ow} <br /> /ind�ng that leakage in t e armer tank excavation is probably the source o <br /> both the soils and the groundwater cont f <br /> lt. amination beneath the site. <br /> As discussed in Section 3.3 Geologic Cross-Section, it appears that the <br /> groundwater aquifer beneath the <br /> located site is not hydraulically connected to the sea <br /> channel adjacent to the site. This was evidenced by the 20-foot <br /> differential in water levels between the 'two waters. This concept is further <br /> evidenced by the total dissolved solids (T0S) concentrations found i <br /> n thelwo <br /> waters. As showy in Table 3 the TOS concentrations for the groundwater beneath <br /> the site ranges from 620 Y:o'720 mg/L. Analysis of a sample collected directly <br /> from the sea channel adjacent to the site indicated <br /> of the sea channel water is 510 mg/L, lower thanthat the FDS concentration <br /> e at of thQgroundwater aquifer. J � <br /> c.., . <br /> 4.5 GROUNDWATER FLOW �4;JC1 <br /> f " The groundwater wells on the project site wAre installed not onl•y,t9 provide an <br /> ; - infication of whether or not groundwater contamination exist <br /> bvs beneath this site, <br /> t also to determine specific hydrogeologic inf <br /> s. gradient of groundwater flow. armaticn such as direction and <br /> Groundwater appears to be present in a semi-confined sandy clay layer below a <br /> depth of approximately 37 feet <br /> ,r^m ground sut-face.. A clay layer above a depth <br /> of approximately 37 feet with .l.ittle to no sand is confining the groundwater. <br /> This is evidenced primarily by'the dryness of the clay as evidenced in the soil <br /> borings down to a depth of approximately 37 feet, theres } <br /> a sandy clay layer below a depth of 37 feet, and water risingto a potentiometric <br /> level of approximately 33 Feet in the soii borings and monitoring wells that. <br /> Penetrated the confining layer. <br /> Reference point (RP) elevations :,are established to within O.U1 feet for each of <br /> the monitoring wells. All groundwater measurements and subsequent calculations <br /> are based on these RP's. Representative groundwater level measurements werejog <br /> obtained for each of the monitoring Wells. Table 4 <br /> presents this data, <br /> f <br /> 20 <br /> is <br /> f <br />