SITE INFORMATION AND CORRESPONDENCE

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0 0 Intervals between sand zones generally silt, locally clay-but not always present, little indication of forming a laterally continuous barrier to vertical migration of impacted groundwater. Locally, aquifer zones may in fact be continuous vertically. The extraction wells EW 1, EW2 and EW4 through EW 10 appear to just penetrate the main sand body of the second water zone by approximately 2 to 5 feet (30 to 35 feet bsg); therefore extraction through these wells may have had an influence on the second water zone and facilitated migration of MTBE-impacted groundwater to MW-8A. The New West pumping test yielded a calculated hydraulic conductivity of 2.49 x 10-4 to 3.5 x 10-5 ft/day, storativit�y of 21% and 11%,ROI of 204 to 360 feet, and transmissivity of 1524 ft/day to 215.7 ft /day. The Flag City Chevron pumping test yielded calculated The nearly instantaneous cleanup of MW-2 following initiation of the GWE system and the rapid rebound in MW-2 following cessation of GWE suggests that impacted groundwater did not migrate very far past MW-2 prior to initiation of GWE; active extraction from the GWE system quickly cleaned up the area with inferred induced westward plume migration. With MW-2 on the margin of the GWE area, residual contamination didn't have far to go to `rebound'. The GWE wells have been sampled only once since the GWE operation ceased, leaving little data to analyze any potential relationship to the rebound in MW-2. The MTBE impact to MW-8A is a puzzler. For a two-year period,while GWE was in operation,it was ND for all analytes of concern, then it began to be continuously impacted by MTBE in the mid-hundreds ppb. It is not known if first water above MW-8A is impacted. MW-19B and MW-20B toward and near New West Shell were initially impacted but their MTBE concentrations have rapidly declined. Possible reason: differing hydraulic conductivities in the area proximal to the New West area and the MW-8A area. This may tie into the relatively rapid migration of MTBE to MW-613 Recommend that NFA consideration be delayed at least two quarters to: • Collect additional data from MWs and GMWs to assess for a significant rebound in the pumping area and compare to MW-2 data • Collect grab water or new MW(preferred)data a short distance down-gradient of MW-2 (Approx. 15 to 20 feet) and in the current down gradient direction from MW-8A • Monitor the site concurrently with the New West Shell site • Give AGE, and hopefully Apex, opportunity to review and model data and present a technical model or explanation for MW-8A and MW-2 data. • Check monitoring wells on both sites with level-loggers and record pumping times at the CSA wells to check for an indication of a pumping influence. • Give EHD time to reevaluate pumping test data from both sites and calculate hydraulic properties of tested zones and calculate seepage velocity and possible distance traveled by plume in various plume geometries.