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1 EMO 1 Mr James L Barton 1 July 27, 2005 Page 9 1 Recommendations As stated above, vapor samples are collected from selected vapor extraction wells on a quarterly basis The highest concentration of TPI-Ig collected in a soil vapor sample from the second quarter sampling event was 2 9 pg/L at VEW-3 The samples were collected on 1 May 26u' while the water table was experiencing a seasonal low depth and is representative of a period when the extraction well screens are more exposed than during winter months As a ' result of repeated low concentrations of petroleum hydrocarbons in soil vapor samples, ENSR requests reducing the SVE well summa canister sampling to an annual event and requests that the sampling occur during the second quarter of each year ENSR will continue to monitor the ' AS and SVE wells on a quarterly basis with field instruments In the Vapor Intrusion Pathway Evaluation included as Appendix G of this report, ENSR ' suggests removing the following wells from the sampling program because they have no constituent concentrations above screening levels 10 O MW-5 • MW-15 © MW-22S © MW-28 o MW-7 ® MW-17 o MW-22D o MW-29 ® MW-9 9 MW-18 o MW-23S • MW-30 • MW-10 ® MW-19S a MW-23D • MW-31 • MW-10A a MW-19D a MW-25S • MW-32 ' • MW-13 • MW-21 S • MW-27 • AS-26 • MW-14A • MW-21D Additionally, based on this evaluation, it is recommended that monitoring cease for the following constituents with no concentrations above screening levels for the groundwater-to-indoor air pathway ' • n-Butylbenzene • sec-Butyibenzene • 1,2-Dichloroethane p �fh%#IK n- 'anc �U Ir • Isopropylbenzene (cumene) • Methyl-tertiary butyl ether (MTBE) • n-Butylbenzene e Toluene * 1,3,5-Tnmethylbenzene • Xylenes Qa Celebrating 35 Years of Excellence in Environmental Services