ARCHIVED REPORTS XR0011668 - Laserfiche WebLink

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LEMSM ILL•HERKENFICWF. INC. Analysis of groundwater samples from MW1 , MW2, and MW3 indicates that the petroleum hydrocarbon contamination in the soils of the former tank excavation has migrated through the clay confining layers and has impacted the groundwater beneath the site. The highest contamination appears in which is down , gradient of the.-former tank excavati n (see Section 4.5 Groundwater ow) indica ung that leakage in the former tank excavation is probably the source of both the soils and the groundwater contamination beneath the site. As discussed in Section 3.3 Geologic Cross-Section, it appears that the groundwater aquifer beneath the site is not hydraulically connected to the sea channel located adjacent to the site. This was evidenced by the 20-foot differential in water levels between the two waters. This concept is further evidenced by the total dissolved solids (TDS) concentrations found in the two waters. As shown in Table 3, the TDS concentrations for the groundwater beneath the site ranges from 620 to 720 mg/L. Analysis of a sample collected directly 1 from the sea channel adjacent to the site indicated that the TDS concentration S� of the sea channel water i s 510 mg/L, 1 ower than -that of the groundwater aqui fer. 4. 5 GROUNDWATER FLOW +'J.:,t It �I,ti>7«-? The groundwater wells on the project site were installed not only to provide an indication of whether or not groundwater contamination exists beneath this site, ! • but also to determine specific hydrogeologic information such as direction and gradient of groundwater flow. ' Groundwater appears to be present in a semi-confined sandy clay layer below a depth of approximately 37 feet from ground surface. A clay layer above a depth of approximately 37 feet with little to no sand is confining the groundwater. This is evidenced primarily by the dryness of the clay as evidenced in the soil borings down to a depth of approximately 37 feet, the presence of a saturated sandy clay layer below a depth of 37 feet, and water rising to a potentiometric level of approximately 33 feet in the soil borings and monitoring wells that penetrated the confining layer. Reference point (RP) elevations were established to within 0.01 feet for each of the monitoring wells. All groundwater measurements and subsequent calculations are based on these RP's. Representative groundwater level measurements were obtained for each of the monitoring wells. Table 4 presents this data. 20 1.