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CALIFORNIA REGION*ATER QUALITY CONTROL BOARD Cal/EPA _--. CENTRAL VALLEY REGION 3443 Routier Road, Suite A -lrr Sacramento, CA 95827-3098 p� Phone(916)255-3000 Pete WiLsm,Governor FAX(916)255-3015 36 1 August 1997 Mr. Nick Nickerson Unocal 2000 Crow Canyon Place, Suite 470 San Ramon, CA 94583-0973 REVIEW OF FIRST QUARTER MONITORING REPORTAND TIME SCHEDULE, PUREGROIBREA, STOCKTON, SAN JOAQUINCOUNTY Thank you for submitting the First Quarter 1997 Quarterly Monitoring Report and the Proposed Completion Schedule for the former PureGroBrea Ag facility on North Broadway Street in Stockton. As you may recall, I collected split samples from three wells during the fust quarter monitoring event. Because several of the analytical results were highly variable, I met with the Board's laboratory and then requested both labs to review portions of their chromatograms. The labs have now completed their reviews, and each have made changes to their results. Therefore, Tables 4, 5, and 7 of the first quarter monitoring report need to be revised. Enclosed are copies of these tables with the necessary changes indicated. The outcome is that there is now less variability between the analytical results from the two laboratories. Because the chemicals EDB, DBCP and 1,2,3-trichloropropane were detected in March 1997, these chemicals need to be added to the list of analytes for fixture sampling events. In addition, the groundwater samples should be analyzed for ammonia instead of total Kjeldahl nitrogen. My comments about the proposed schedule are as follows: 1. I have not yet received the workplan for characterization of on-site soils. The schedule shows that this was to have been submitted in mid-June, so it appears that all the dates in the schedule are off by at least six weeks. 2. The schedule shows that the human health risk assessment (HRA)will be submitted as two separate documents: one for the groundwater and one for the soil. I believe that this approach will lead to confusion and may not provide for a complete assessment of all health risks. Therefore,the schedule must be revised to show the submittal of one workplan, one draft HRA, and one final HRA. The HRA will evaluate the risks to human health from the chemicals in both the soil and the groundwater. 3. The following tasks should be added to the schedule: obtaining a contract between the Department of Toxic Substances Control and Unocal for review of the HRA, final definition of the extent of groundwater contamination, and submittal of the quarterly monitoring reports.