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STATE OF CALIFORNIA - Environmental Protlen Agency • PETE WILSON, Governor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION F :g s 3443 Routier Road, Suite A Sacramento, CA 95827-3098 PHONE: (916) 255-3000 FAX: (916) 255-3015 14 February 1995 FE3 x ;; 1995 Mr. Nick Nickerson Unocal Environmental Remediation & Technology ENVIRONMENTAL HEALTH 2000 Crow Canyon Road, Suite 450 PERMIT/SERVICES San Ramon, CA 94583 FORMER PUREGROIBREA FACILITY, BROADWAY AVE, STOCKTON: REQUEST FOR ADDITIONAL INVESTIGATION AND DEVELOPMENT OF REMEDIAL ALTERNATIVES Thank you for submitting the Fourth Quarter 1994 Monitoring Report for the former PureGro/Brea facility on Broadway Ave. After reviewing the report, I have the following comments: 1. If only one well volume of water is purged for a well, please discuss the reason and show how it was determined that formation water was collected for analysis. 2. The "Daily Work Activities Log" states that corrective maintenance is required for monitoring wells N1-4. Please complete this as soon as possible. 3. In order to maintain the quarterly monitoring schedule, the wells should be sampled again in March. I would prefer that they are sampled as early in the month as possible, while the groundwater is still at the high elevation brought on by the January rains. The report covering the First Quarter 1995 sampling should be submitted by the end of April. The two off-site wells have now been sampled twice, and both times elevated levels of 1,2- Dichloropropane, nitrate, chloroform, and bromochloromethane have been detected. While I am not certain whether the volatiles are coming from the PureGro property, the data collected to date shows that a plume of 1,2-DCP and nitrate originates on the PureGro property and has moved off-site to the west or southwest. Unocal will be required to finish defining the extent of the plume, and to clean up the groundwater to the extent economically and technologically feasible. To that end, Unocal is requested to submit a workplan containing the following items: 1. A plan to define the extent of the 1,2-DCP and nitrate plume. Hydropunch or BAT probes may be used; however, at least one more permanent monitoring well will be required. You have mentioned the desire to sample existing monitoring wells at gas stations to the north and south of the facility. Although these wells are not downgradient, if you still wish to sample them, I will do my best to help you get access. Please send me a copy of the access letter that the Central Coast Regional Board used at one of your other sites.