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Mr. Mike Desso - 2 - 4 December 2006 2. Nestle's evaluation should include the horizontal and vertical extent of TCE vapor migration in the vicinity of borings SG-2 through SG-5, and the areas west and south of 320 Stockton Avenue. 3. Also, Nestle's evaluation of the horizontal and vertical extent of TCE vapor migration should include the residential areas northwest, west, and south of 519 S. Stockton Avenue. 4. Concentrations of TCE in soil vapor may present a future risk to human health if currently vacant properties near the Former Facility are developed. Nestle should notify the City of Ripon Building Department about this potential risk to human health, allowing the City to take appropriate interim administrative measures. 5. Until VOCs in soil gas near the Former Facility (i.e. soil boring SG-1 location) have been remediated to risk-appropriate concentrations for current and future buildings, Nestle should implement soil gas monitoring. This will require completion of several soil gas monitor wells/piezometers that will allow for periodic collection of samples from the same locations. Specific Comments on the Draft Report The following comments address specific issues within the Draft Report that Regional Water Board staff identified. 6. Sampling procedures utilized by Nestle for collecting soil vapor samples from 5 feet below ground surface (bgs) deviated from the procedures presented in the revised work plan dated September 15, 2006. The first four feet of each boring was advanced with a hand auger. The boring was then backfilled with the cuttings and the sampling probe was pushed through the cuttings and through one foot of soil where it was stopped at 5 feet bgs. Hand augering was apparently done to avoid puncturing subsurface utilities. When sampling probes are advanced in this manner, the soil vapor sample should be collected after 48 hours to allow time for soil vapor to equilibrate. However, Nestle collected the 5-foot soil vapor sample after only 20 minutes. The twenty-minute equilibration time was only appropriate for the samples collected at 10, 15, and 20 feet bgs. 7. The method used by Nestle to advance the soil vapor sample probe to 5 feet bgs should be described in more detail. If the probe was advanced by the drilling subcontractor, that should be indicated. 8. The first paragraph of Section 4, page 3 of the Draft Report indicates that the field notes are presented in Appendix B. However, they are not presented. They should be presented in the Final Report. 9. The results of leak testing with isopropyl alcohol, including photo ionization detector (PID) readings and PID calibration methods are not included in the Draft Report. They should be presented in the Final Report. The laboratory analyses specified for soil vapor samples did not include isopropyl alcohol. Laboratory analyses for isopropyl alcohol should be included in the Final Report. 10.The Draft Report indicates that the PID detection limit was 10 parts per million-volume (ppmv). The Regional Water Board staff notes that the Department of Toxic Substances Control document, entitled Advisory—Active Soil Gas Investigations, January 28, 2003 (Reference 5 of