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102 Wilson Site <br /> Page 2 <br /> Several different oxygenates,blending agents and fuel additives have been documented to be present at the <br /> site in groundwater for an extended period of time. Samples collected for analyses by a state certified <br /> laboratory must include TPHg, BTEX, MtBE, EtBE, DIRE, TAME, TBA, McOH, EtOH, 1,2-DCA and <br /> EDB. EPA Method 8260B is recommended. Discrete high quality groundwater samples must also be <br /> collected in the saturated zone as you investigate the vertical distribution of hydrocarbons particularly in <br /> layers of observed high hydraulic conductivity [coarse grained deposits (preferential flow paths)]. More <br /> lateral definition should be performed at similar or greater depths in the event preferential flow paths or <br /> vertical groundwater flow/hydraulic communication is observed. <br /> At this time a RBCA or Fate and Transport model is premature as the plume is currently undefined. <br /> However, data compilation for these approaches can and should occur during each phase of field data <br /> collection. No detailed description of the model (mathematical or computer coded) is included in the <br /> workplan. In the event you choose to perform these types of assessments PHS/EHD should be provided <br /> with a complete site conceptual model,transport model and mathematical formula including the input fields <br /> in order to begin to determine site specific data collection which will be required to enter into the model. <br /> Please consider that these approaches require extensive site specific hydrogeological and biological data <br /> sets and substantial scrutiny in the model validation processes. <br /> PHS/EHD recommends that the responsible parties aggressively pursue engineered remediation and <br /> enhancement of the SVE system particularly at this site where approximately 50% of the previously <br /> estimated contaminant mass remains. Please provide PHS/EHD with a proposal for modifications to the <br /> SVE system. PHS/EHD has recently communicated with the USTCF regarding continuation of operation <br /> for the on-site SVE,some degree of cost pre-approval has been granted as of March 20,2000. <br /> PHS/EHD provides the directives above, an amended workplan must be submitted before May 8, <br /> 2000. <br /> Should you have questions regarding this correspondence please contact Ron Rowe at(209)468-0342. <br /> Donna Heran,RENS,Director <br /> Environmental Health Division <br /> Ronald Rowe,Sr. REHS M/arggaaretlagono,REHS <br /> LOP/Site Mitigation Unit Supervisor <br /> Cc: CVRWQCB—Marty Hartzell <br /> Ground Zero Analyses Inc.—Gregory Stahl <br />