SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

4, Mr. Welch `..i - 2 - 28 August 1997 Based on review of the Report, we concur with SECOR's recommendation that monitoring of dissolved oxygen be discontinued. As noted in our 9 June 1997 letter responding to the First Quarter 1997 Monitoring Report and SECOR's recommendations contained therein, we do not concur with discontinuing the monitoring for benzene, toluene, ethylbenzene, and xylenes (BTEX), on the basis that detections of some of those components continue to occur in one or more site wells, and that detection of benzene will serve as an early warning for additional releases or remobilizations. We will remove gasoline from the monitoring program when the program is revised in September. At that time we may consider reduction to semi-annual of monitoring for BTEX in some of the wells. 2. Proposed Risk-Based Corrective Action (RBCA)Analysis: In January 1997, SECOR proposed performing a Tier 1 RBCA Human Health Risk Screening Assessment for the site. The Report states (p.2)that SECOR is still awaiting approval of the proposed assessment from the Regional Board. As discussed with SECOR staff in August 1996 before the Tier 1 proposal was made, there is no Regional Board guidance or State of California guidance or regulations on performance of RBCA analyses; however,the ASTM approach may be used as a model provided that the chosen receptors and target constituents are appropriate for the site conditions and consistent with the water quality goals and objectives as expressed in the Region's Basin Plan. Protection of the groundwater resource must be considered. SECOR and Westrec do not need Regional Board permission to conduct a RBCA analysis of this site; however,based on site conditions and the above comments, staff does not consider that a Tier 1 analysis, if based on and limited to the concentrations used as examples (not standards) in the ASTM look-up tables, will prove to be sufficient. Any analysis of the site and proposal for action or for further reduction in the monitoring program should include information showing that the extent of the plume and residual contamination have been defined, or should show cause why this is not necessary. The analysis should consider the potential presence of certain known or suspected carcinogens that may be components of the hydrocarbons present; for example,benzene and polynuclear aromatic hydrocarbons such as napthalene, and should use these as target compounds. The enclosed document contains examples of constituents of concern that your consultants should consider including in the risk analysis. A proposal for continued monitoring without any other action should include evidence that the plume is stable and/or shrinking in extent. Staff encourages SECOR to proceed with a RBCA analysis or other approach to the determination and consideration of appropriate levels of response to the free product, soil contamination, and dissolved constituents at this site. If you have any questions, please call Gail Wiggett at(916)-255-3119 or Victor Izzo at (916)-255- 3059. el4t7A40154V , AIL WIGGETT Associate Engineering Geologist AST Pr gram enc. cc: San Joaquin County Public Health Services, Stockton Ms. Yvonne Mabee,Tower Park Marina,Lodi (w/o enclosure) Ms. Nancy Bond, SECOR, San Francisco (via facsimile)