SITE INFORMATION AND CORRESPONDENCE

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Mr. Jeff Baker - 3 - 15 December 2008 Stockton Terminals Tech nicalamittee 4 b) specifically name all six monitored remedial observation wells (not just two) in which concentrations will be monitored and compared to historical levels, c) identify which well or combination of wells with concentration exceedances will trigger implementation of the contingency plan, d) add TBA to the list of monitored petroleum hydrocarbons, and e) calculate a median TBA threshold concentration for all remedial observation wells that will trigger the contingency plan. For the trigger wells we suggested that: a) TBA should be added to the list of constituents in the trigger wells at the water quality objective (WQO) of 12 pg/L, and b) a discrepancy should be cleared up between the four wells tabulated in the contingency plan (OW-2A, OW-2B, OW-4A, and OW-4B) and the two wells discussed in the text (OW-1A and OW-4A). On 7 November, Stantec responded on behalf of the STTC with a revised contingency plan that included some of the requested revisions. However, Stantec requested that (1) TBA be excluded as a constituent to trigger the contingency plan and (2) the threshold concentrations be exceeded for all constituents in all six remedial observation wells in order to trigger the contingency plan. In addition, the STTC's historical median TBA concentrations were higher than the median concentration calculated by the Regional Water Board staff for remedial observation (RO) wells PS/MW-18 and PS/WC-1M. Stantec proposed that these issues be discussed further during a meeting scheduled for 10 December 2008. On 14 November, Regional Water Board staff responded to Stantec via email and requested a resolution on the discrepancy between historical medians for RO wells PS/MW-18 and PS/WC-1 M. Our email also proposed that exceedances of threshold concentrations of all monitored constituents in any single RO well or trigger well be sufficient to trigger the contingency plan. We requested that the discrepancies be resolved before the meeting on 10 December. When Stantec did not respond to our 14 November email, Regional Water Board staff contacted Stantec on 20 November seeking a resolution on the outstanding issues. Stantec, on behalf of the STTC, stated that they concurred with our recommendation that exceedances of threshold concentrations of all monitored constituents in any single RO well or trigger well would be sufficient to trigger the contingency plan. They stated, however, that they stood by their calculations of the TBA historical mean concentrations and on 25 November emailed us a spreadsheet of the data. The spreadsheet included data for RO wells PS/MW-18 and PS/WC-1 M dating back to February 2001 and essentially was the same data Regional Water Board staff used to calculate the historical medians for these two wells. Our recalculation of the median concentrations using the data in the spreadsheet for RO wells PS/MW-18 and PS/WC-1M was substantially lower than Stantec's calculated historical mean concentrations of 602 and 57.4 pg/L, respectively. Regional Water Board staff replied to Stantec on the same day informing them about the results of our recalculation using the data in the spreadsheet and requested a resolution before the 10 December meeting.