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Page 3 Ms. Vicki McCartney, RUTS February 20, 2004 j samples were collected for analysis. This CPT. investigation indicated that the lateral extent of impacted groundwater is largely contained within the Earthgiain's property boundaries. Results from this investigation were reported in PSC's May 1999 Subsurface Investigation and Groundwater Monitoring Report. An additional air sparging and soil venting pilot test was performed in June 2000 using VW- I as ` the vent well. This test was conducted in general accordance with procedures described in PSC's May 15, 2000 Pilot Testing Work Plan. Once again, pilot test results indicated that this technology would be an effective method of treating :petroleum hydrocarbon impact at the site. b� Test results and designs for an air sparging and soil venting remediation system are contained in L PSC's August 31, 2000 Remedial Action Work Plan. Operation of a full scale air sparging and soil venting remediation system was initiated on April 25, 2001.. Installation of a new air sparging well (SP -A) was performed on March 14, 2002. The remediation system was disengaged in December 2002 to evaluate whether petroleum concentrations in groundwater samples would remain stable. Prior to disengagement, PSC had noted significant decreases in petroleum concentrations in groundwater samples (Table 2) PSC submitted the April 14, 2003 Remedial Action Completion Report that presented an SCM and requested that EHD review site conditions and consider granting case closure for this UST site. EHD responded in their January 9, 2004 letter, which directed additional work to be performed including: 1. Estimating the contaminant mass in the vadose zone; 2. Assessing the vertical extent of impacted groundwater; 3. Collecting a groundwater sample from.a nearby irrigation well; 4. Testing for 1,2 -DCA and EDB; and, 5. Reinitiating quarterly groundwater monitoring. PROPOSED SCOPE OF WORK Procedures to implement EHD directed work are proposed in the following sections. Vadose Zone Assessment EHD expressed concern that there is a lack of data characterizing the magnitude of impact within the vadose zone around the source of the release. There is some soil data available that provides an indication of the extent of impacted soil in the vadose zone. Table 1 includes analytical results of soil samples collected from borings 90-1, 90-2, MW -1, MW -2, MW -5 and MW -7, located around the perimeter of the release, that typically contain non-detectable or relatively low KLEINFELDER 3077 Fite Circle, Sacramento, CA 95827-1815 (916) 366,-1701. (916) 366-7013 fax A