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CPA0057 Sites RECEIVE 27 April 2016 � West Charter Way and Lincoln Street Stockton, San Joaquin County MAY 020 2016 v ENVIRONMENTAL HdEALT�-1 DEPARTMENT b. Delineation in the B zone is neede sou hwest of well CMW-5A on the former Chevron property to delineate the extent of benzene detected at 519 ug/L in CMW-5A, in the 4Q15 report. c. Delineation in the B Zone is also need to the west of SLMW-7S and SLVE-1 where benzene has been reported at 11,000 ug/L and 4,300 ug/L, respectively, on the former Dolly Madison property. d. Delineation in the C zone is needed to the east of SMW-28C is needed to characterize the extent of benzene detected at 140 ug/L in 2015. Central Valley Water Board staff recommend completing delineation of petroleum impacts using depth discrete grab groundwater sampling or use of temporary well installations. Please submit a Work Plan Addendum to complete horizontal and vertical delineation of petroleum constituents to the WQO by 30 June 2016. A proposal for the installation of monitoring wells will be expected once the extent of pollution is defined, to confirm pollutant concentrations are stable to decreasing. 5. Benzene in the D zone wells SLMW-1 OD and SMW-29D is currently detected at 2,500 ug/L and 5,000 ug/L, respectively, and is not delineated to the southeast. Wells SMW-36D and SMW-35D are proposed to be installed down-gradient, to the south and east, of SLMW-1 OD and SMW-29D however, the proposed distances seem excessively far from the reported petroleum impacts (about 180 to 200 feet down-gradient). SMW-34E is proposed to be located up-gradient of SLMW-10D. I am concerned the data obtained from these locations may not provide useful data on the distribution of contaminants or effectiveness of cleanup operations. Please move SMW-35D and SMW-34E to a location down-gradient about 100 feet of SLMW-1 OD, and move SMW- 36D to within 100 feet of existing well SMW-29D. An additional E zone well should be co-located with proposed well SMW-36D and a third E zone well should be proposed to allow for calculation of the groundwater flow direction in the E zone. Please confirm relocation of proposed wells SMW-34 E, SMW-36D and SMW-35D; and the addition of a third E zone well in the Work Plan Addendum due 30 June 2016. 6. We understand there are some difficulties in securing access to the wells on the Dolly Madison property. Wells DMW-6, DMW-8, DMW-9 and DMW-15 were supposed to be transferred to the commingled plume case in 2011 when the Dolly Madison underground storage tanks case was closed. As shown in the 4Q15, table 2, these wells do not appear to have been sampled since 2013. In addition to concerns for the lack of groundwater monitoring data from these wells, no well construction details are provided for DMW-6, DMW-8, DMW-9 or DMW-15. It is unclear if these wells adequately characterize the horizontal and vertical extent of petroleum impacts detected on the BBU property, specifically, the extent of benzene detected at SLMW-7S, screened from 55-63 ft. bgs, and from CPT-2, collected at 87 ft. bgs, at concentrations of 11,000 ug/L and 4,600 ug/L, respectively. Please provide well construction details for and collect groundwater samples from well DMW-6, DMW-8, DMW-9 and DMW-15 to confirm the extent of petroleum impacts to the south and south east of the BBU property in the Semi-Annual Groundwater Monitoring report due 30 June 2016.