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STATE OF CALIFORNIA - Environmental Pro ,on Agency PETE WILSON, Governor <br /> j CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD <br /> CENTRAL VALLEY REGION <br /> e 3443 Routier Road, Suite A <br /> Sacramento, CA 95827-3098 <br /> 3 PHONE: (916) 255-3000 <br /> FAX: (916) 255-3015 <br /> I <br /> I <br /> 1 June 1994 <br /> Mr. Nick Nickerson <br /> Unocal Corporate Environmental Remediation & Technology /905. & JW4,wy <br /> 2000 Crow Canyon Road, Suite 450 � H <br /> San Ramon, CA 94583 <br /> REVIEW OF WORKPLAN: FORMER PUREGRO/BREA FACILITY <br /> Thank you for meeting with me today to discuss the progress which has been made in <br /> delineating the nitrate and 1,2-DCP plumes in the groundwater beneath the former <br /> PureGro/Brea facility on Broadway Street in Stockton. I have reviewed your latest report, <br /> "Proposed Work Plan, Ground-Water Investigation", for the continued investigation at this <br /> facility. <br /> The workplan is approved, with the addition of the following: <br /> Section 3.2 describes concerns that the production well at the facility may be influencing the <br /> groundwater gradient. You should determine whether any of the other businesses nearby <br /> also have production wells, and whether they may also be influencing the gradient. <br /> Section 3.3 states that several monitoring wells exist near the facility. Some of these wells <br /> appear to have been installed as a result of leaking underground tanks. The Borad's ? <br /> Underground Tank unit usually requires that an EPA 624 scan (among others) be run on <br /> groundwater samples. Since 1,2-DCP is detected by the 624 scan, you may wish to search <br /> the Board's underground tank records for a better understanding of 1,2-DCP concentrations <br /> in the area. <br /> Section 3.5 discusses monitoring well installation. Unless a reason is given otherwise, the <br /> two new wells should be constructed in the same manner as the four existing wells. I find <br /> two differences: the existing wells have a screen slot size of 0.020, while it is proposed that <br /> the new wells will have a slot size of 0.010. In addition, the workplan states that the highest <br /> groundwater measured in the last two years was 75' bgs. This is untrue; when the four wells <br /> were drilled, groundwater was encountered at 70' bgs (Condor, 30 June 1993). The four <br /> wells have a 20' screen length because of the large fluctuation of elevations in the area, and <br /> are screened from about 65' to 85' bgs. Unless information is submitted justifying the <br /> difference in construction, the two new wells should have the same slot size and be screened <br /> at the same elevations as the existing wells. <br /> Section 3.7 states that the two off-site wells and the new monitoring wells will only be <br /> sampled once. However, the timeline (Table 2) implies that the new wells (as well as the old <br />