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construction details are presented on Figure 4. The monitoring wells will be constructed and developed in accordance with the Winzler& Kelly's Standard Operating Procedures (SOPS) for Soil Boring and Monitoring Well Installation and Development(Appendix B). The new wells will be developed a minimum of 72 hours after installation of the sanitary seal. The proposed soil gas sampling points will be advanced no deeper than 55 feet bgs. Soil gas samples will be collected after sufficient time elapses for soil gas equilibration; the sample points will be purged and sampled using a Summa canister. 2.3 SOIL AND GROUNDWATER SAMPLING AND ANALYSIS Winzler& Kelly proposes to collect soil samples from the monitoring well and soil borings at 5- foot intervals. Soil samples may also be retained at changes in lithology,zones of obvious hydrocarbon impact,and from the vadose zone. Soil sampling and handling will be completed in accordance with the Winzler&Kelly's SOP for Soil and Water Sampling from a Boring with VOCs(Appendix B). A maximum of two(2) soil samples for chemical analyses will be retained from each of the four monitoring wells and soil borings. The soil samples will be submitted to Analytical Sciences Laboratory, (a State-certified laboratory)under proper chain-of-custody procedure for the following analysis: • TPH-G by EPA Test Method 8015M/8260B; • BTEX, 5-oxygenates: MTBE,Tert-amyl methyl ether(TAME), Tert-butyl alcohol (TBA), Di- isoproply ether(DIPE), and Ethyl tertiary butyl ether(ETBE), 1,2-DCA, and EDB by EPA Test Method 8260B; • TPH-D with silica gel cleanup by EPA Test Method 8015M; • Total recoverable hydrocarbons (TRPH)by SM 5520F/Silica Gel; and • Total lead by EPA Test Method 6010. 2.4 MONITORING WELL DEVELOPMENT The new groundwater monitoring wells will be developed in accordance with Winzler& Kelly's SOP for Soil Boring and Monitoring Well Installation and Development(Appendix B). Well development occurs to remove fine-grained sediment from the well casing and filter pack. The well will be alternately surged and bailed, and then pumped with a 1.5-inch stainless steel electric pump, until extracted water became mostly clear or a minimum of 10 well volumes have been purged. Total volumes of water removed during well development will be recorded on the field forms,along with the field parameters of dissolved oxygen,pH,temperature, and conductivity. 2.5 SOIL GAS PROBE INSTALLATION Soil gas probes will be either advanced using a hand operated rotary-hammer drill with attached direct- push tooling or using a limited access direct push drill rig, following the guidelines presented in the Draft Advisory-Active Soil Gas Investigations,provided by the Department of Toxic Substances Control (DTSC), dated March 2010 (DTSC Guidelines). A copy of the DTSC Guidelines is provided in Appendix C. In accordance with this advisory,borings will be advanced to approximately 5_feet bgs or first encountered groundwater,whichever occurs first. The depth was selected as it will provide the most relevant data for the proposed human health risk evaluation. Additionally, 5 feet bgs is the minimum 03009-10016-37020 4 WINZLER&KELLY August 2011