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�t <br /> 1 <br /> October 9, 1997 Approval to modify VES, remove carbon units from system vent <br /> directly to atmosphere, less than 2 pounds per day of Total Petroleum <br /> Hydrocarbons and below laboratory detection limits for Benzene. <br /> October 31, 1997 Completion of Lincoln Village plume study. <br /> December 8, 1997 Start air sparging system in wells MW2 and MW 13. <br /> December 22, 1997 Oxygenants study found only MTBE in monitor well MWI 1 at 30 <br /> ug/L. <br /> Natural attenuation study indicates that biodegradation is occurring. <br /> July 2, 1998 Total removal of TPHg by vapor extraction and venting of MW8 <br /> 75,088 pounds (12,014 gallons). <br /> GROUNDWATER <br /> Primary MCL's have been achieved for monitor wells MWI, MW4, <br /> MW5, MW6, MW7, MW9, MW10 and MWI 1. Secondary MCL's <br /> have been achieved for monitor wells MWI, MW4, MW5, MW6, <br /> . MW7, MW9, and MWI 1. <br /> SOIL <br /> Soil has been remediated. <br /> GROUNDWATER MONITORING <br /> Depths to groundwater measurements were obtained from all monitor wells associated with this site <br /> (MWI, MW2, MW3, MW4, MW5, MW6, MW7, MW8, MW9, MWI 0, MW 11, MWI2 and MWI 3) <br /> on May 28, 1998. No vacuum influence was measured, the vapor extraction system had been non- <br /> operative for 44 days (vacuum pump malfunction) and the sparging system had been non-operative <br /> for five days, see Appendix A - Field Notes and Methods and Procedures. Figure 4 represents the <br /> groundwater gradient obtained from measurements obtained on May 28, 1998 and shows a <br /> groundwater low with a depressions at MW IO and a groundwater high at MW2 with localized <br /> gradient flowing to the east. <br /> Figure 5 is a Lithologic Fence Diagram and shows the historic high and low groundwater levels for <br /> this site. Top of screened interval has always been above the top of groundwater for the following <br /> wells MWI, MW2, MW3, MW4, MW5, MW6, MW7, MWS, and MW9 with the exception of this <br /> latest sampling (May 28, 1998) where the top of groundwater averaged 2.16 feet above the top of <br /> screened interval. The top of the screened interval at MW 10 has always been above top of <br /> 4 R603 Update##52/CLOSURE RV 7198 <br />