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r � Navarra Property: Recomm ations for Closure Page 1 wells, except that in Monitoring Well MW-7, have been reduced to zero or very low to trace concentrations. The historic water-quality data is consistent with the finding from the fully-scoped natural attenuation evaluation conducted in March 2005 that aerobic bioremediation processes were actively remediating affected groundwater at all locations except in the vicinity of Monitoring Well MW-7. Natural bioremediation was also acting on the groundwater in that area but the processes were anaerobic in nature. Non-aqueous phase liquids were detected in Monitoring Well MW-7 over the period December 2001 to November 2003 with thicknesses up to 0.58 ft. but, subsequently, LNAPL has been absent except in very small volumes. No LNA.PL has been observed in Monitoring Well MW-7 since July 2007. Consistent with that observation, recently measured concentrations of diesel and components of gasoline in samples of groundwater recovered from Monitoring Well MW-7 have followed a generally declining trend. This suggests that anaerobic processes of bioremediatiun are now active in that arca oftlw site. Aerobic bioremediation processes remediate groundwater contamination at an accelerated rate compared to anaerobic processes. ISO C�� fr�G� �FV Cost Benefit Considerations 7"j The area where concentration of diesel and components of gasoline in groundwater remain high is of a limited extent and, because it is located under the East I Ith Street right-of-way and a very small portion of an adjacent parking lot, it does not raise any health risk concerns. I fully expect that processes of natural bioremediation will act over the next several years to fully remediate the subsurface. Therefore, a strong case can be made that expenditure of an estimated $44,000, excluding continuing monitoring costs, to pursue active remediation of the area around Monitoring Well MW-7 would not be a justifiable use of public funds because the natural processes of bioremediation of contaminants will, in time, fully remediate that area of the site. Recommendation for Closure Based on the present condition of the 7500 West Eleventh Street site, I recommend that it be"closed" without undue delay and that the extant monitoring wells be destroyed. If, for some reason, additional.monitoring should be required I believe that consideration should be given to the fact that the past several years of groundwater-quality data acquisition has not substantially added to understanding of the characteristics of the plume of affected groundwater. That being the case, any further monitoring should be limited to recovery of samples from Monitoring Well MW-7 and Monitoring Well MW- 19, which is located at the down-gradient limit of the plume. Monitoring of those two wells should be performed no more than once per year - in July, at which time groundwater elevations at the site are at their highest and, historically, contaminant concentrations have been at their seasonal highs If you concur with my proposals for closing the site, I. will inform the State Water sic