ARCHIVED REPORTS_XR0008370 - Laserfiche WebLink

Home Browse Search

of monitonng, groundwater depth at the site was approximately 82 feet The depth to groundwater has nsen nearly 4 feet since the October monitoring event This is consistent with the recent rise in groundwater observed elsewhere in the county, and shows a reversal from falling groundwater dunng the summer months The present gradient is 0 001 ft/ft, oriented N 14° E (Figure 3) Within the margin of error of measurement, this gradient is ' identical to the gradient in September 1993, although it has rotated 40° to the east Well MW-3 remains down-gradient of the former UST cavity ' 4.2 Groundwater Contamination Benzene was detected in MW-2, MW-3 and MW-4 at concentrations of 13 ppb, 6 2 ppb and ' 3 4 ppb, i espectively TPH as gasoline was detected only in the sample from MW-3 at 51 ppb No ethylbenzene or xylenes were detected in any of the water samples The results are summarized in Table 3 One or more chlorinated hydrocarbons were also detected in each ' well The laboratory report and chain-of-custody are included in Appendix A 5.0 CONCLUSIONS ANID RECOMMENi]MONS 5.1 Groundwater Contamination 1 Low concentrations of benzene have been detected in allsam roundwater les collected g P during four consecutive monitonng events performed by GeoAudrt since January 1993 Low concentrations of other aromatic compounds, gasoline-range hydrocarbons, and chlorinated hydrocarbons have occasionally been detected as well ' Since the installation of MW-3 and MW-4 down-gradient from the former UST tank cavity, the groundwater gradient has remained relatively constant, but has rotated to the east. The gradient continues to be very flat, which can easily account for moderate or even large ' vanations in flow direction The next quarterly monitor ing should be scheduled by April of 1994 GeoAudrt recommends ' continued quarterly monitonng concurrent with intenm soil remediation ' 5.2 Soil Contamination As reported previously, soil contamination was detected in monitoring well MW-1 near the UST cavity This contamination has not been mitigated, and therefore poses a nsk of further groundwater contamination In the October 1993 Quarterly Report, we reiterated our I recommendation that a vadose-zone well for soil remediation be installed The procedures and specifications for this well were included in paragraphs 3-11 of the Intenm Remedial Work Plan, submitted in August 1993 This well will be terminated 10 feet above the present groundwater table or to the maximum depth of soil contamination, whichever is shallower � �A.,kSry M-6—P-F-e .QRn W i 35