SITE INFORMATION AND CORRESPONDENCE

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Mr. Carl Navarra 7500 W. Eleventh Street Page 2 of 3 With the possible exceptions of the last two items, EHD generally concurs with these conclusions. EHD considers more time an analysis of data trends are necessary to fully evaluate the last two conclusions. The extent of the plume of impacted. groundwater,is approximately 800 feet in the down-gradient direction and approximately 350 feet in width. Intuitively, impacted groundwater and the contaminants will preferably migrate along paths of least resistance, i.e., along sand, gravel and in clean silt units compared to clayey fine- grained units. Groundwater in the deeper sand units of MW-3A, MW-3B and MW-12A apparently has not been impacted, which TSJCI attributes to intervening clayey units sufficiently retarding the migrations of the hydrocarbon contaminants. This demonstrates the vertical extent of impacted groundwater onsite and near the suspected source area. After three monitoring events since their installation, free product has not been detected in any of the wells installed to assess and monitor free product on the 7501 W. Eleventh Street site and has not been detected recently in monitoring well MW-7. This suggests that free product, if currently present on the 7501 W. Eleventh Street site, is not likely,to be present as a large plume of great mass. As fuel hydrocarbon contaminants have not been detected, in any of the six monitored potable water supply wells in the immediate area of the release, EHD concurs with the conclusion that the wells have not been impacted. SJCI recommended: • Collection of field data necessary to.evaluate the site capacity to sustain natural attenuation of the contaminants in the subsurface. • Closure of monitoring wells MW-3A, MW-3B and MW712A. • Cessation of the monitoring program for the six potable water supply wells. The issues noted above were discussed qt the 18 January 2005 meeting at EHD. In addition, the need to update the 1,2-dichloroethane (1,2-DCA), ethylene dibromide (EDB), methanol and ethanol data was discussed. Although previously assessed, the detection limits for 1,2-DCA,and EDB were too high for closure concurrence at this,time and should be reassessed utilizing a detection limit of 0.5 micrograms-per liter (pg/1) if possible. If adequate data with acceptable detection limits has been obtained that demonstrates methanol and/or ethanol are not chemicals of concern for your release, provide reference r to the data and the compound(s) will not need to be reassessed. Based on the results and interpretations presented in the Report and OMR, and on the points discussed at the 18 January 2005 meeting, EHD will not direct any additional site assessment at this time. EHD will evaluate a proposed .reduction of the monitoring program and reduction of sampling of the potable water, supply wells. The proposed monitoring program should provide the rational for the proposed monitoring frequency and show how the revised schedule will meet all monitoring objectives. It should be kept in mind that if monitored natural attenuation is selected as the most appropriate remedial option, adequate data must be collected to demonstrate that the method is effective and reducing the contaminants to background .conditions in a reasonable time frame. EHD