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CONESTOGA-ROVERS & ASSOCIATES May 4, 2009 3 Reference No. 632277 Actual depths may be changed in the field depending on the depth to water at the time of the field work. The borings will be continuously logged by CRA field personnel. The final locations of the borings will be based on site and utility constraints as evaluated in the field. To evaluate the vapor intrusion to indoor air pathway at the site, the four borings will be completed as soil vapor wells that will be used to collect soil vapor samples. A schematic diagram of the soil vapor probe construction is presented as Attachment D, Figure A. The soil vapor probes will also be constructed in general accordance with CRA's Standard Field Procedures (Attachment C) . One-quarter inch diameter Nylaflow® nylon tubing will be fitted with a 6-inch long 0.010-inch slotted polyvinyl chloride (PVC) filter screen. The tubing and screen will be placed into each open boring with the screen at approximately 4.5 fbg. Washed No. 2/16 silica sand will be placed from 4 to 5 fbg to create a filter pack around the PVC screen. A 3-inch layer of dry granular bentonite will be placed on top of the sand pack followed by hydrated bentonite powder to a few inches from the surface. The tubing exiting the bentonite will be capped, and the top of the vapor well will be protected by a traffic-rated vault. Soil and Soil Vapor Sampling: Unsaturated soil samples will be collected at approximately 3 fbg. Soil samples will be collected using a slide hammer and a drive-core barrel . Soil vapor samples will be collected no sooner than 72 hours after installation of the vapor wells to allow adequate time for accumulation of representative soil vapor. Soil vapor sample collection will not be scheduled until after a minimum of five consecutive significantly precipitation-free days (>0.5 inches of rain) . Service station manager will be asked to discontinue any onsite watering for five days prior to soil vapor sample collection. —generalized-scherriatitDjigurea Samples will be collected using a 1-liter SUMMATM canister connected to the sampling tubing at each vapor point. Prior to collecting soil vapor samples, the initial vacuum of the canister will be measured and recorded on the chain-of-custody (this should be approximately 30 inches of mercury) . The vacuum of the SUMMATM canister will be used to draw the soil vapor through the flow controller until a negative pressure of approximately 5 inches of mercury is observed on the vacuum gauge. This is the residual vacuum and this measurement should be recorded on the chain-of-custody. With the flow controller set at approximately 200 millimeters/ minute, sample collection should take approximately 5 minutes. Prior to sample collection, stagnant air in the sampling apparatus will be sufficiently removed by purging approximately 3 probe volumes using a purge pump (Attachment D, Figure B). The volume of the borehole will generally not be included in the volume calculation as it is assumed that the soil vapor concentrations in the probe and sand pack are equilibrated with the surrounding native soil. A minimum of one field duplicate will be collected for each day of sampling. A field duplicate will be collected by using a splitter connected to the soil vapor probe. After vapor sampling, the SUMMATM canisters will be properly labeled, packaged, and sent to a laboratory under chain-of-custody for analysis. Worldwide Engineering, Environmental, Construction, and IT Services