Laserfiche WebLink
h Mr Ron Rowe <br /> Page 5 of b <br /> I <br /> expected to become accessible to the VES for several years, if at all As discussed in previous <br /> reports, air sparging does not appear to be a viable technique for dealing with the saturated soil <br /> contamination Influent vapor concentrations to the VES are approaching asymptotic levels and <br /> water levels continue to rise We recommend that a cost/benefit analysis be conducted in the near <br /> ' future to provide guidance as to the point at which soil vapor extraction should cease <br /> Despite the rising water levels which have submerged many of the screens in the groundwater <br /> monitoring wells, it is abundantly clear that the plume of dissolved hydrocarbon contamination is <br /> stable The exception is the increasing concentrations of dissolved gasoline and MTBE beneath <br /> ' the southern portion of the property As discussed previously in this report, the source of this <br /> commingled contamination is offsite and most likely the adjacent ARCO facility Any additional <br /> efforts to define the limits and nature of increasing or migrating contamination should be borne by <br /> ' the party responsible for its release <br /> Pending development and agreement on the criteria and schedule for case closure we recommend <br /> ' the following <br /> VES Operation <br /> yBased on estimated carbon usage Ground Zero recommends continuing with the thermal oxidizer <br /> as the more cost-effective offgas treatment method, even though the vapor extraction system <br /> ' efficiency appears to be approaching the asymptotic limit for hydrocarbon removal We <br /> recommend monitoring the VES on a weekly schedule and collecting vapor samples for <br /> laboratory analysis on a monthly basis <br /> ' Quarterly Groundwater Monitoring and Sampling <br /> ' Ground Zero recommends continuing quarterly sampling to monitor the extent of gasoline <br /> hydrocarbons in groundwater Analysis for oxygenates should continue for wells MW 1, MW3, <br /> MW4, MW 11, MW 12, and MW 13 for next quarter It would also be advisable to analyze <br /> ' samples from well MW7 for oxygenates due to its position downgradient of MTBE impacted <br /> wells MW3 and MW4 The next groundwater sampling event is scheduled for August 1999 <br /> ' Your office will be provided with 49-hours notice of any field work <br /> 1 <br /> roeki999 <br />