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08 February 2012 AGE-NC Project No. 95-0106 Page 3 of 4 Approximately 28 feet of piping (header pipe), oriented east-west will extend out from the eastern wall of the residence across the crawl space. Three sets of piping will intersect the header pipe and extend north-south across the crawl space; • The header pipe will be routed to the exterior of the residence and connected to a vertical PVC vent riser secured to the exterior of the residence and terminating at the roof line. A four-inch diameter hole will be drilled in the eastern wall of the residence, just below the floor of the residence to connect the header pipe to the vertical vent riser; • The vertical vent riser will be equipped with a Fantech low profile inline fan (HP190SL) to generate a lower pressure within the crawl space. The Fantech HP190SL is rated at a maximum flow rate of 157 cubic feet per minute (CFM). However, the proposed optimum flow rate for the mitigation system design is 67 CFM. The header pipe and vertical vent riser will be connected by the fan. The header pipe will connect horizontally to the inlet collar on the fan and the vent riser will connect vertically to the outlet collar on the fan. Additionally, the fan will have a dedicated power circuit. Installation instructions and a specification sheet for the Fantech HP190SL are presented in Appendix B. Detailed plans are attached and presented in Appendix C depicting the design and specifications of the vapor intrusion mitigation system. 2.3. COLLECTION AND ANALYSIS OF AIR SAMPLES AGE proposes semi-annual indoor air sampling to evaluate the effectiveness of the vapor intrusion mitigation system. Indoor air samples should be collected prior to the start-up of the vapor mitigation system and then semi-annually thereafter to determine the efficiency of the vapor mitigation system to abate soil gas intrusion within the crawl space. Initially, AGE proposes to collect indoor air samples and ambient air samples as proposed in the AGE-prepared, Indoor Air Investigation Work Plan dated 30 December 2011. Indoor air samples and ambient air samples should then be collected every 6 months after start- up of the vapor intrusion mitigation system. All air samples will be collected in six-liter Summa canisters using passive integrated sampling procedures. Each canister's initial vacuum will be measured and recorded to ensure the initial vacuum is greater than 25 inches of mercury (in hg). The sampling inlet on the canisters will be connected to a mass flow controller containing a particulate filter and calibrated to 3.8 milliliters/minute (ml/min). Air samples will be collected over a period of approximately 24 hours based on the calibrated flow of 3.8 ml/min. Advanced CcoEnvironmental,Inc.