10-10-1988 - Agenda Packet City Council - regular meeting

Home Browse Search

3.3.2 Ground Water Contamination Monitoring wells MW-10 and MW- I 1 are free of EPA 601/602 parameters. Monitoring well MW-10 had a detectable concentration of 1.1 microgram per liter (ug/1) of benzene. This low concentration is suspect due to the ubiquitous nature of this compound in our environment. Monitoring well MW-12 contained very low concentrations of xylenes, I,1-dichloroethylene, 1, 1 -dichloroethane, and toluene. The concentrations of these parameters are all below recommended allowable limits for drinking water. Sample analytical results from MW-10, MW-11, and MW-12 are provided in Appendix C. 4.1 Hvdro¢eolo¢v The water table of the unconfined aquifer at the site generally occurs eight to ten feet below the ground surface. Flow in this surficial aquifer is toward the south-southeast as discussed in our December 23, 1987 report. Monitoring wells MW-4D, MW-10, and MW- I I are all screened at the same approximate elevation and are 25 feet below the ground surface. Together, these wells show that flow in the 20 to 25 foot interval is toward the north-northwest. This apparent reversal in flow direction is suspected to be due to the influence of the drainage trench and buried sewer line along the eastern edge of the WSI property line, between monitoring wells MW-10, MW-11, and monitoring well MW-413 and therefore is thought to be very localized (Figure 2). We believe that shallower wells would reflect this same pattern and that ground water flow in the 20-25 foot intervai is similar to shallow ground water flow observed across the site. 4.2 Extent of Soil and Ground Water Contamination Soil and ground water contamination are primarily restricted to the area between monitoring wells MW- 2 and MW-4. Contaminant conditions identified in this area are discussed in our December 23, 1987 report. The aerial extent of soil and grot.nd water contamination is outlined in Figure 3. The vertical extent of VOC co^tamination is restricted to the upper 25 feet or the site. Boring logs of monitoring well MW-41) (Delta's May 24, 1987 report) show the presence of a sand unit between 21 and 24 feet. It is likely that the contaminants are moving through sand lenses such as this one. Our objective for remediation will be to intersect as many of these sand lenses as possible with the recovery trench.