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File No. 8013-01 May 30, 1999 Page 4 A fairly low to moderate microbial population oQ680 col ny forming units/milliliter(CFUImI) of water was measured. For groundwater, mia 9-cool typically range from 100 to 100,000 CFUImI (Suthersan, 1997). Higher counts generally suggest a healthier population. Following insertion of the ORCO, a heterotrophic plate count conducted during follow up testing will determine whether an increase in colony forming units resulted from �- the increased subsurface oxygen. 5.0 CONCLUSIONS 5.1 Groundwater Flow Direction and Gradient The groundwater flow direction and gradient for March 1999 was calculated based on the static groundwater elevations measured in the four monitoring wells. The shallow groundwater was calculated to flow toward the northeast(N 10 E) at a gradient varying from approximately 0.0030 to 0.0050 Tuft. Figure 3 illustrates the groundwater contour map for March 1999. 5.2 Groundwater Contamination Groundwater contamination was detected in monitoring well MW-2. The groundwater contamination consisted of total petroleum hydrocarbons as gasoline, and associated volatile fuel components BTEX. No petroleum oxygenates were detected in well MW-2, and no contamination was detected in the other three wells. The groundwater contaminant plume in the vicinity of well MW-2 is inferred to extend down- gradient of well MW-2 approximately 60 feet. The plume is inferred to extend up-gradient and cross-gradient approximately 15 and 20 feet, respectively. Figure 4 illustrates the inferred limits ` of groundwater contamination for the March 1999 sampling. 6.0 RECOMMENDATIONS In accordance with the approved workplan, JJW Geosciences recommends the following: 1) In June 1999, evaluate the potency of the ORCO sock in well MW-2. If sufficient, the ORCO sock will be re-inserted for a second three-month period. If the sock is found to no longer be sufficient, it will be removed and disposed. '" 2) In June 1999, perform quarterly sampling of the three perimeter wells. The +� samples will be analyzed for total petroleum hydrocarbons as gasoline and the associated volatile fuel components BTEX. �. If, during task 1 above, the ORCO sock is found to no longer be sufficient, then quarterly sampling of well MW-2 will be included in this quarter. The sample from well MW-2 will be analyzed for the parameters above, plus petroleum oxygenates and biodegradation parameters. 3) In September 1999, a third and final quarter of groundwater sampling will be conducted (under this existing approved workplan). All four wells will be sampled and analyzed for total petroleum hydrocarbons as gasoline and the associated volatile fuel components BTEX. r JJW GEOSCIENCES Inc.