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i I � i Geological Tecwcs/a. Page 5 Groundwater Monitoring Report Project No. 989.2 January 21,2002 ' • Low concentrations of MTBE werep resent in MW-4 MW-5 and MW-6. The levels are consistent with previous monitoring events. MW-4 and MW-6 show a slight decrease ' since the June 2001 monitoring event. MW-5 shows a slight increase since the June 2001 monitoring event. ' • MTBE was non-detect in wells near the former tank area, MW-1, MW-2 and MW-3. This has been consistent during the previous four quarterly monitoring events. • A plot of TPH-gasoline versus groundwater elevation for MW-1 shows that ' concentrations of TPH-gasoline fluctuate with groundwater elevation. Laboratory Data Sheets are included in Appendix C. The data is summarized in Table I of ' Appendix A. Chart I is a plot of TPH-gasoline versus groundwater elevation for MW-1. During purging of the monitoring wells, field measurements of the oxidation-reduction ' potential of the water were measured using a YSI meter. These measurements are summarized in Table 3 of Appendix A and the field logs in Appendix B. The results suggest that MW-1, 2, 3, & 4 are near the center of the plume. MW-5 and MW-6 appear to 1 now be in,contact with the margins of the reactive water. 4.0 CONCLUSIONS AND RECOMMENDATIONS ' The following conclusions have been drawn from the data generated from this site investigation work: ' Conclusions 1. The highest levels of BTEX and TPH-gasoline are present in MW-I & 4, as would be expected. ' ❑ MW-i is closest to the location of the former UST L3 MW-4 is the nearest down gradient well to the former UST 2. Since MTBE is present only in MW-4, MW-5 and MW-6, and not in the wells near the former USTs, the source is not clear. 3. Since March 1996 very low levels of MTBE have only been detected twice in wells near the location of the former UST. According to Wm. J. Hunter & Associates, the MTBE 1 detected in MW-1 during the July 2000 monitoring event is suspect. 4. Changes in TPH-gasoline concentrations are associated with groundwater elevation. ' Recommendations 1. Further define the lateral extent of the plume: Install two monitoring wells along Oak Street; one to the north and one near the northwest corner of the Property. 2. Further define the vertical extent of the plume: Install a deep monitoring well near the • former the UST.