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i' ENVIRONMENTAL HEALTlrOEPARTMENT SAN JOAQUIN COUNTY Donna K.Heron,R1r.H . Unit W. s _Carl Bot man R E H.S. R.E.H.S. " -� Director 304 East Weber Avenue,Third Floor Mike Huggins,R.E.lf.5.,R-DI. M Olsen,RE.H.S. Stockton, California 95202-2708 Douglas W Wilson,R.E.H.s. Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. t+Foy Laurie A.Cotulla,RE.H.S. Program Manager Fax: (209)464-013$ Robert McClellan,R.E.li.$. Mark Barcellos,R.E H.S. ROB FISHBURN FEB o 6 2ool; ULTRAMAR INC 685 W THIRD STREET HANFORD CA 93230 RE: Beacon#3641 SITE CODE: 1125 1210 E. Hammer Lane ROM 000070 Stockton, CA San Joaquin County Environmental Health Department (EHD) has reviewed Results of Additional Subsurface Investigation and Site Conceptual Model(SCM) dated December 7, 2005, as submitted by your consultant, Horizon Environmental Inc, and has the following comments. This comprehensive report was requested by EHD in order to evaluate the subsurface conditions now that the investigation phase is complete, as determined by your consultant. The SCM included the installation of five monitoring wells from October 4 to 8, 2004, as well as a discussion of the history and status of the site. An evaluation of the residual mass, migratory potential, and vapor intrusion/migration to the surface was also included in the SCM. A remedial action status update was included and stated that during October 2005, the soil vapor extraction (SVE) and in-situ air sparging (IAS) was started at the site. In March 2003, EHD approved changes in the ground water sampling protocol as based on a request from your consultant. EHD approved an overall reduction in frequency and constituent analyses. With changes in the site status now, EHD will require modifications to the ground water sampling and reporting protocol. As the result of the newly activated remedial actions at the site, substantial changes in ground water petroleum concentrations are being noted in the laboratory data contained in the quarterly monitoring reports (QMR). In order to keep apprised of these changes, EHD will require the following modifications to the ground water sampling requirements of the wells located in the `core' area only(area most impacted by petroleum) to be enacted immediately. • MW-1, MW-5, and VW-7 are to be sampled and reported on a quarterly basis for TPHg, BTEX, and MtBE. Once a year, in the First quarter of the year as previously established, these wells shall be sampled for all Oxygenates, 1,2-DCA, and EDB by EPA Method 8260B and lead by EPA Method 6010.