ARCHIVED REPORTS_XR0005912 - Laserfiche WebLink

Home Browse Search

' 22 December 2003 AGE-NC Project No 98-0433 ' Page 4 of S ' are included in Appendix B The distribution of dissolved hydrocarbons is depicted on Figure 4 ' 4.0. SUMMARY AND CONCLUSIONS Based upon the data collected during the third and fourth quarters 2003 monitoring event, AGE ' concludes • Ground water at the site was encountered at approximately 26-27 feet below the casing tops ' The prevailing ground water flow direction from the former UST area was generally toward the northwest at a gradient of 0 002 ft/ft • The highest concentration of TPH-g was in the area of monitoring wells MW-1 and MW-9 ' located adjacent to the former UST area and well MW-6 approximately 300 feet east of the former UST area TPH-g concentrations in ground water decreased in the samples from wells MW-1, MW-2 and MW-6 The samples from MW-8 showed an increase in TPH-g ' concentrations TPH-diesel concentrations decreased in all wells on the site excluding MW-6 (Table 1) TPH concentrations in ground water decreased drastically in the samples collected ' from wells MW-1 and MW-2 since the last monitoring event C Benzene was detected in the sample from well MW-6 at a concentration of 18 µg/1, above the DHS'Maximum Contaminant Level(MCL) MTBE was detected in wells MW-1,MW-8 and ' MW-9 at concentrations as great as 2,000 µg/1, significantly above the DHS' primary MCL 0 The lateral extent of TPH-g, BTEX in well MW-6 and lack of MTBE indicates an older ' release, while the distribution of MTBE near the former UST area, indicates recent release The lateral extent of TPH-g,BTEX was previously defined in the former-U area, owever concentrations have reduced over the past three quarters of sampling ' The lateral extent of dissolved MTBE is generally defined by the current well network, including the wells sampled at the Ripon Farm Service site directly The vertical extent of ' MTBE at the former UST area is not defined below a depth of 40 feet bsg ' 5.0. RECOMMENDATIONS Based on the results of this investigation, AGE recommends ' Continued quarterly monitoring at the site,the next monitoring event should be scheduled for February 2003 Coordinate the ground water monitoring activities of Jimco Truck Plaza and ' the adjacent Ripon Farm Service (22871 South Highway 99) to occur concurrently e Due to the lowest water table level recorded at the site since the initiation of ground water monitoring, the majority of the petroleum impacted soil is within the vadose zone thus Advanced GeoEnvironrnentai,Inc