ARCHIVED REPORTS_XR0012015 - Laserfiche WebLink

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Mr Ron Rowe Page 5 The VES has removed a significant mass of contamination from accessible vadose soils since ' operation began in November 1997 During this period approximately 11,500 pounds of hydrocarbons have been removed from the subsurface The estimated total mass of soil contaminants prior to instituting vapor extraction was approximately 24,000 pounds, suggesting that ' approximately 50% of the total has been removed The remaining 50% is comprised for the most part of contaminated soil which is currently submerged due to high water levels This is not expected to become accessible to the VES for several years, if at all As discussed in the previous ' quarterly report, air sparging does not appear to be a viable technique for dealing with the saturated soil contamination Influent vapor concentrations to the VES are approaching asymptotic levels ' and water levels continue to rise and are threatening to submerge the screen in yet another vapor well We recommend that a cost/benefit analysis be conducted in the near future to provide guidance as to the point at which soil vapor extraction should cease Despite the rising water levels which have submerged many of the screens in the groundwater monitoring wells, it is abundantly clear that the plume of dissolved hydrocarbon contamination is stable The exception is the increasing concentrations of dissolved gasoline and MTBE beneath the southern portion of the property As discussed previously in this report, the source of this commingled contamination is offsite and most likely the adjacent ARCO facility Any additional efforts to define the limits and nature of increasing or migrating contamination should be borne by the party responsible for its release ' Pending development and agreement on the criteria and schedule for case closure we recommend the following ' VES Operation Based on estimated carbon usage Ground Zero recommends continuing with the thermal oxidizer as ' the more cost-effective offgas treatment method, even though the vapor extraction system efficiency appears to be approaching the asymptotic limit for hydrocarbon removal We recommend monitoring the VES on a weekly schedule and collecting vapor samples for laboratory analysis on ' a monthly basis QuarterIy Groundwater Monitoring and Sampling ' Ground Zero recommends continuing quarterly sampling to monitor the extent of gasoline hydrocarbons in groundwater Analysis for oxygenates should continue for wells MW1, MW3, MW4, MW 11, MW 12, and MW 13 for next quarter It would also be advisable to analyze samples ' from well MW7 for oxygenates due to its position downgradient of MTBE impacted wells MW3 and MW4 The next groundwater sampling event is scheduled for May 1999 Your office will be ' provided with 48-hours notice of any field work 1mk%q=\1 qmi 999