SITE INFORMATION AND CORRESPONDENCE FILE 2

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ILE- C apy woe ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY 2•. �� .2Unit Supervisors Donna K.Heran,R.E.H.S. Carl Bor an,R.E.H.S. Director 304 East Weber Avenue, Third Floor Mike Huggins,R.E.H.S.,R.D.I. •. l� Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. c9�iFoa �v Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. Laurie A.Cotulla,R.E.H.S. Fax: (209) 464-0138 Robert McClellon,R.E.H.S. Program Manager Mark Barcellos,R.E.H.S. QM 2 2 2892 TOSCO MARKETING COMPANY BP OIL COMPANY 1380 LEAD HILL RD STE 120 295 SW 41ST ST ROSEVILLE CA 95661 RENTON WA 98055 RE: TOSCO-76/former BP#11192 SITE CODE: 1995123 1403 Country Club Blvd. RO#:0000087 Stockton, CA., 95204 San Joaquin County Environmental Health Department(EHD)has reviewed the"Updated Corrective Action Plan" (CAP)dated June 26, 2002 as submitted by Gettler-Ryan Inc(GRI)on July 8, 2002 and has the following comments. In correspondence dated April 23, 2002, EHD expressed a concern with the high concentration of TBA in MW-3 and MW-7 and requested confirmation sampling to verify the presence of this newly emerging contaminant. On May 9, 2002, EHD received a GRI report confirming the TBA concentrations in MW-3 and MW-7 at over 200,000 µg/I. GRI concluded that the decline in concentrations of MtBE in the groundwater samples from these two monitoring wells and the subsequent rise of TBA concentrations were due to the degradation of MtBE to TBA and was not from a new release at the site. Although this may well prove to be the case, EHD is not ready to accept this conclusion at this point for the following reasons: GRI hypothesizes that MtBE rapidly degraded to TBA in response to elevated dissolved oxygen concentrations. EHD is not aware of any research demonstrating this phenomenon and would appreciate any applicable documentation. EHD is aware of research showing reaction pathways for ozone degradation of MtBE, but not for rapid, partial degradation in the presence of dissolved oxygen. GRI has presented no documentation in the various CAPs or quarterly monitoring reports that dissolved oxygen concentrations increased as a result of the short-term operation of the DPE unit. There has been no presentation of data indicating that biodegradation of any gasoline components has occurred on the site or that site conditions are suitable for selective, biodegrading bacteria to propagate. high TBA concentrations was abrupt and indicates a The shift from high MtBE concentrations to significant composition change that permeated the local subsurface at a rate that intuitively appears to be more rapid than normal groundwater velocity, diffusion rates of dissolve oxygen, and initiation and completion of a phase of biological processes that hitherto appeared to have been dormant. An alternative explanation for the observed changes of contaminant concentrations can be made. Presupposing an ongoing release at a rate below the tightness test minimum release rate or from an area not subjected to a tightness test, a change of fuel formulation from MtBE to TBA as an oxygenate could action eventually couldcause the bserved changes.have memo ed the local MtBE-impacted grondwater rundwater and and the more, such as the recently TBAk test and - DPE test TBA- impacted groundwater over to the test area.