Laserfiche WebLink
Ms. Shelby Lathrop -2 - 14 June 2010 <br /> Former Tosco Bulk Terminal No. 1u-13 <br /> Central Valley Water Board staff also reviewed the 30 April 2010 Remedial Action Plan (RAP), <br /> which summarizes historical contaminant trends and the remedial technologies attempted at the <br /> Site, and presents an evaluation of five remedial alternatives. Based on (1) the previous use of <br /> pump and treat, (2) the current mobile oxygen injections, and (3) the significant historical <br /> reductions in COC concentrations, the RAP recommends continuing the oxygen injections until <br /> the fourth quarter of 2010. At that time, if the recent concentration trends are unchanged, <br /> ConocoPhillips proposes to initiate monitored natural attenuation (MNA) during the first quarter <br /> of 2011 until remedial objectives are met or until MNA parameters are projected to meet water <br /> quality objectives (WQOs) in a reasonable time. <br /> Our comments are presented below: <br /> 1 . ConocoPhillips' RAP must be amended to (1) specify the remedial objectives, (2) present <br /> background concentrations on which the proposed remedial objectives are based, <br /> (3) present a contingency plan should COCs rebound once the injections are discontinued, <br /> and (4) define the magnitude of the rebound that would trigger the contingency measures. <br /> By 21 July 2010, ConocoPhillips needs to submit a RAP addendum resolving these issues. <br /> 2. We concur with ConocoPhillips' conclusion that additional monitoring must be conducted to <br /> determine whether the presence of methanol is a byproduct of natural attenuation or is <br /> attributable to laboratory error. However, the Central Valley Water Board has established a <br /> toxicity WQO of 3,500 pg/L for methanol. We will require ConocoPhillips to clean up to this <br /> standard, where applicable, if future groundwater monitoring results show that this chemical <br /> persists. <br /> 3. In the 2009 Third QMR, ConocoPhillips estimated that it had injected a total of 3,740 pounds <br /> of oxygen, but the 2010 First QMR estimates 2,937 pounds and the RAP estimates <br /> 5,900 pounds. ConocoPhillips needs to explain these discrepancies. <br /> 4. The RAP contains a request to dismantle and remove the idle groundwater extraction <br /> system (GWETS) from the Site. This request was originally presented in ConocoPhillips' <br /> 18 November 2008 Work Plan for Continuation of Mobile Oxygen Injection and Installation of <br /> Additional Oxygen Injection Wells (Work Plan). Our response, presented in our <br /> 31 December 2008 letter, stated "...since the equipment and remediation compound are no <br /> longer being used for their intended purpose, the decision regarding whether or not to keep <br /> them on site is an internal matter that does not require the Regional Water Board staff's <br /> approval." Our current response to this request is unchanged from our previous response. <br /> In summary, by 21 July 2010, please submit a RAP addendum as described above and an <br /> explanation for the discrepancies in the amount of oxygen injected. If you have any questions <br /> regarding this letter, you may contact me at (916) 464-4811 or betaylor@waterboards.ca.gov. <br /> 1' p <br /> /4 <br /> (-6--BRIAN TAYLOR P.G. <br /> Engineering Geologist <br /> cc list on next page <br />