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CONDOR EARTH TECHNOLOGIES INC <br /> 188 Frank West Circle Suite I <br /> °+ Stockton CA 95206 <br /> Phone 209.234.0518 <br /> FAX 209.234.0538 <br /> CONDOR www.condorearth.com <br /> December 7, 2004 <br /> Michael Lozano <br /> Department of Toxic Substances Control <br /> School Property Evaluation and Cleanup Division <br /> 8800 Cal Center Drive <br /> Sacramento, CA 95826-3200 <br /> Subject: Supplemental Site Investigation Addendum: Additional Soil Gas Survey for the Proposed <br /> Pittman Elementary School, Stockton, California <br /> Dear Mr. Lozano: <br /> This is an addendum to the Supplemental Site Investigation (SSI) scope to describe additional soil gas <br /> and groundwater sampling to be conducted at the proposed Pittman Elementary School in downtown <br /> Stockton, California. <br /> The soil gas results of the SSI confirmed the presence of the constituent of concern 1,3-butadiene at the <br /> northeast comer of the Site, in soil gas borings SG-1 and SG-2. Based on these results and <br /> recommendations from the Department of Toxic Substances Control at the team meeting on December 6, <br /> 2004, Condor Earth Technologies,Inc. (Condor)proposes advancing an additional 10 borings for soil gas <br /> sample collection at three depths.The soil gas sampling depths will be at approximately 8, 13, and 24 feet <br /> below ground surface (bgs), or other depths to be determined in consultation with DISC. In addition, two <br /> borings will be advanced to the groundwater interface, anticipated to be approximately 40 feet bgs, for the <br /> purpose of collecting two groundwater grab samples. The additional soil gas borings will be advanced in <br /> the following locations: one boring between SG-1 and SG-2, one boring between SG-1 and VB2, two <br /> borings between SG-1 and SG4, two borings between SG-2 and SG-3, one boring north of SG-2 off-site, <br /> one boring east of SG-2, and two borings upgradient of SG-1 and SG-2 to be advanced off-site. One of <br /> the two off-site borings and one of the borings in the vicinity of SG-1 will be advanced to groundwater <br /> depth for collection of groundwater grab samples. The proposed locations of the additional borings are <br /> indicated on the attached figure. <br /> In addition to the 24 soil gas samples to be collected from the borings, two duplicate soil gas samples, one <br /> ambient air blank sample, one steam tunnel sample (if accessible), and one equipment blank sample will <br /> be collected for quality assurance/quality control (QA/QC) purposes. The duplicate samples will be <br /> collected at the same time as the collection of the primary samples using a certified-clean tee splitter and <br /> will not be identifiable as a duplicate sample to the laboratories. The equipment blank sample will be <br /> collected by running purified nitrogen gas through the sampling equipment and into the 6-liter Summa <br />