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Remo Canepa Page 2 of 2 6230 Pacific Ave. 08 Oct 2009 Stockton, CA groundwater most likely to yield useful data would be from the shallow, first water zone, which can be monitored by the SVE wells , hence the directive to monitor these wells, annually in the 17 April 2009 letter, semiannually in the 21 July 2009 letter. The EHD does not believe that the SVE wells duplicate the data obtained from W-1 ; the boring log for MW- 1 and AGE's Table 1 of Quarterly Report — Fourth Quarter 200„ dated 09 February 2009 , both indicate that MW-1 is actually screened from 50 to 70 feet bsg, not 25 to 45 feet bsg , and therefore monitors a distinctly deeper portion of the saturated zone compared to the SVE wells . If only one well is to be monitored , the EHD believes it should be SV-4, with its long monitoring history, as opposed to SV-1 recommended by AGE , unless AGE can provide a technical justification for the switch . The EHD mapped the total petroleum hydrocarbons quantified as gasoline (TPHg) obtained from the SVE wells circa September 2005. The data exhibited a normal plume-like distribution at that time. Such data for heptanes and butanes may help demonstrate a post-1993 release of the compounds and pinpoint the release point. The EHD recommends that you sample the SVE wells for all the chemicals of concern for your site and for heptanes and butanes; the directive for routine monitoring of the SVE wells , except for SV-4 , can be reevaluated after analysis of the data obtained from an initial monitoring of the SVE wells. In the WP , AGE proposes to advance five borings to 5 feet bsg and three borings to 30 feet bsg to obtain soil gas samples to evaluate the potential for vapor intrusion into on-site structures. The 5-foot sampling depths are standard for soil gas surveys; the proposed locations are approved as adequate and necessary [Health & Safety Code (H &S) Section 25299. 37(c)(3)] . There was no technical justification provided for the three proposed 30-foot sampling depths but it appears to the EHD that vapor potentially released from the capillary fringe and saturated zone is the point of interest. The EHD regards the shallow sampling depth as the critical sampling points for evaluating the potential for vapor intrusion , and therefore the three proposed 30-foot depth sampling points are not approved . Please submit to the EHD a well permit application and $434. 00 permit and inspection fee by 02 November 2009. The work should be completed by 20 November 2009 and a report of the work submitted to the EHD by 20 January 2010 . Also on that date submit the previously directed feasibility study and lateral assessment work plan . If you have any questions or comments regarding the issues in this letter, please contact Nuel Henderson , PG , at (209) 468-3436; other concerns with your site should be directed to Frank Girardi, Senior Registered Environmental Health Specialist, at (209) 953-7868. AA 0t Yjt/�vi)tA atA� � �0 Frank Girardi , REHS Nuel C . Henderson, Jr. , PG Senior Environmental Health Specialist Engineering Geologist C : James Barton , RWQCB, 11020 Sun Center Dr. #200 , Rancho Cordova , CA 95670 Robert Marty, AGE, 837 Shaw Road , Stockton , CA 95215 Comment and WP Approval Letter 1009