ARCHIVED REPORTS XR0009934 - Laserfiche WebLink

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a+ Extended Investigation of Groundwater Quality - 152 East 11th Street, Tracy Page 8 Street properties have been synthesized and used as the bans for an interpretation of the lateral and vertical extent to which the subsurface has been affected by hydrocarbons This interpretation is presented in the form of the plan view on Figure 3 and longitudinal and cross sections on Figures 4 through 6 A preliminary interpretation of the area of the subsurface that may have been affected by leakage of hydrocarbon fuels was previously made and was used to select the sites of monitoring wells NAV 5, NAV 6, NAV 7, and NAV 8 that were instaled on June 16th and 17th 1993 (Ref Workplan dor Further Soil And GrMdwater Assessment at 152 East 11 th StregLCaliform The San Joaquin Company Inc February 1993 ) The data obtained from these wells, and the results of the other investigations reported herein, broadly confirm the earner interpretation However, compared to the estimates made previously, the lateral extent'of the area affected of hydrocarbons is now interpreted to be more limited in the easterly and westerly directions along East 11th Streets due to the finding of no detectable concentrations of components of gasoline in airy of the sod or groundwater samples recovered from the new wells It is important to understand that the interpretations shown on Figures 3 through 6 are not intended to precisely define the exact boundaries of hydrocarbon fuel components affecting the subsurface Specifically, they should not be used for reaching a conclusion as to whether or not groundwater affected by hydrocarbons that may have been released into the subsurface on the 152 E 11th Street site has, or has not, coalesced with fuel components released into the subsurface on the Beacon Station site However, when taken together with the previously available data, the geotechnical, geochermcal and hydrological data reported herein support an interpretation that gasohne that leaked from underground tanks that were on the 152 East 11th Street property has moved downgadient from the point where those tanks were formerly located toward the East 11th Street frontage of the site and has probably migrated some distance northward under the street The data also indicates that the bulk of the hydrocarbons that were present in the subsurface at the Beacon Station at 153 East 11th Street was successfully removed by the remediation work that was conducted on that site in 1986 when the underground tanks were replaced and that any residual contamination of limited extent RECOMMENDATIONS FOR MODIFICATION OF SAMPLING PLAN The approved Groundwater Sampling Plan provides for modification of the specific wells to be sampled in future sampling rounds if information obtained during the progress of the Plan's implementation indicates that adjustments would be appropriate so as to best achieve the objectives of the Plan Although it is well positioned to monitor any downgradient or cogradient migration of contaminants, when the Plan was ongmally developed, Well ULT 8 was not included in the wells to be sampled m future rounds of sampling that are planned to follow the first, comprehensive sampling that was performed on July 8th 1993 This decision was based on available records that indicted this well had been "dry" since July 1991 However, as