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gC010gib(Technics Inc. Page s Groundwater Monitoring Report •� Project No. 1030.2 September 30, 2002d-: d-: ' The test results showed the following: • MW-1 has a high level of alkalinity compared to MW-2 and MW-3. Elevated levels of ' alkalinity are an indicator of benzene biodegradation, either aerobic or anaerobic. • The average nitrate as nitrogen constituent in MW-2, 3 and 4 is 15.7 mg/L. MW-1 has 10.1 mg/L indicating nitrate depletion, which is consistent with biodegradation in an ' anaerobic environment. • Redox potential has been consistently lowest in MW-1 suggesting MW-1 is near the center of the plume (Table 4). ' ❑ Redox potential measured over three years may suggest the site conditions are in an anaerobic state. ❑ Redox potential measurements from the last two quarters suggest that there is reaction between groundwater and the halo of the plume near MW-2, MW-3 and MW-4. The groundwater temperature at the site ranges between 680 and 72°F. • The measured pH at the site ranges between 6 and 8. The test results showed the following trends when comparing the contaminated zone to background conditions. • Alkalinity of the contaminated zone was enriched compared to background M • Nitrate of the contaminated zone was depleted compared to background • Sulfate and total iron was inconclusive ' • Oxidation reduction potential of the contaminated zone is lower compared to background pH data was inconclusive ' • Temperature was slightly elevated in the impacted area Site Characteristics • The plume is defined vertically by MW-101 and laterally by MW-2 and MW-3. • MW-4 appears to define the head of the plume. ' 0 The clay layer at 19 feet bgs provides a significant barrier to vertical plume migration. • Groundwater slope is gradual (<0.005 ft/ft)_which impedes the migration of the plume. ' • The average concentration of TPH-G is 288 • Purge water has been removed from site. • Soil disposal is scheduled by mid-October. ' 3.0 RECOMMENDATIONS • GTI recommends that this site be considered for closure after the next monitoring event if the results are consistent with previous test results. • Upon closure, the monitoring wells should be properly abandoned. 0 Dispose of purge water stored on site.