SITE INFORMATION AND CORRESPONDENCE

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Main Street Investors/Villas de Amistad Page 2 of 3 601 East Main Street September 16, 2014 Stockton, California 95202 "One six-liter Summa canister will be utilized for purging and soil-vapor samples will be collected in one-liter Summa canisters (TO-15) and four-liter sorbent tubes (TO-17). Based on the EHD letter dated 11 March 2014 and the phone conference held between AGE and EHD personnel on 07 May 2014, a duplicate TO-15 and a replicate TO-17 soil- vapor sample will be collected during the investigation. The sampling and purge canisters will be connected together with a dedicated and serialized sampling inlet manifold. The sampling inlet manifold will consist of a vapor-tight valve; a particulate filter; a calibrated flow restrictor, calibrated to 200 milliliters per minute (ml/min); a stainless steel tee-fitting; two vacuum gauges at either end of the flow controller and connections for both purge and sampling canisters (manifold assembly). The manifold assembly will be attached to the Teflon tubing from the vapor implants; for the duplicate TO-15 sample, a tee-fitting will be used to attach the tubing to two separate manifold assemblies. The purge canister will be attached to the end of the sampling manifold while the sample canisters will be attached to the tee-fitting between the tubing and purge container." "A manifold assembly will not be used for sorbent tube sample collection. The inlet of the sorbent tube will be attached directly to the Teflon tubing and a low-flow pump will be attached to the outlet of the sorbent tube. The low-flow pump will be calibrated to approximately 100 ml/min and will (be) used to extract soil-vapor through the tubing and into the sorbent tube. Approximately four liters of soil-vapor will be collected into each sorbent tube. This step will (be) repeated for collection of a replicate TO-17 soil-vapor sample." "Upon achieving a successful leak test and allowing for 120 minutes of equilibration time, the purge canister valve will be opened for a calculated period of time to allow for three calculated volumes of air to be purged. The purge canister vacuum gauge will be monitored to ensure a proper decrease of vacuum ensuring flow and purging. The purge volume will be determined by calculating the internal volume of the tubing, vapor implant and the volume of sampling void." "The samples will be transported under chain-of-custody procedure to a CDPH-certified laboratory. Each sample canister and tube will be labeled with sample designation, time, date and sampler's initials and analyzed for the constituents listed in Section 2.3. Additionally, sorbent tubes will be placed in a chilled container for transport and include a trip blank for TO-17." By email dated 16 June 2014, AGE provided documentation that the soil-gas-sample-collection materials proposed in the revised Work Plan have been applied at a different site and the materials have not interfered or contributed to the detection of contaminants of concern. Therefore, the EHD is rescinding the directive to submit a material blank. The EHD approves the addendum to Site Assessment and Vapor Intrusion Investigation Work Plan as presented above with the following conditions: