SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Dopaco, Inc. - 2 - 14 April 2014 800 W. Church St., Stockton San Joaquin County activities proposed by GC in the Work Plan, including semi-annual monitoring for DMW-1, DMW-3, and DMW-4, but recommend the following offsite monitoring well additions to achieve closure in the most expeditious manner: 1. Additional shallow and deep groundwater sampling should be conducted on along Church Street and a third zone monitored near DMW-6, to confirm the groundwater plume is migrating N21 W as previously indicated during the first four quarters of monitoring or N53W as indicated during the first quarter of 2014. This transect has a better chance of confirming the downgradient and vertical extent of the groundwater plume. The grab groundwater sample results cited in the Report targeted groundwater at a depth of about 30 feet below ground surface in the first permeable zone (A zone) only. Note that additional monitoring wells may be necessary if the new wells do not provide adequate delineation of the horizontal and vertical extent of the groundwater pollution. 2. Figures showing before and after excavation soil isoconcentrations in map view and geologic cross sections, including soil concentration data from all sampling points outside of the excavation area for Toluene and Total Petroleum Hydrocarbons as diesel should be included in the Final Excavation Report. 3. All maps should include a North arrow on the Figure. 4. During the meeting on 5 February 2014 at the site, GC requested input from Central Valley Water Board staff concerning tasks necessary to get this case to closure. Our letter dated 10 February 2014 staff stated that to achieve closure of this case the following tasks must be completed; a. The horizontal and vertical extent of impacts from the toluene release (and any other chemicals comingled with the toluene) must be determined. b. A declining or stable concentration trend of all chemicals of concern must be established in groundwater. c. A determination that no sensitive receptors (water supply wells or surface water bodies) are threatened by the residual pollution must be made. d. The time for groundwater to reach water quality objectives should be predicted based on available data. e. Once groundwater monitoring demonstrates that the pollutant plume is stable, and a site conceptual model is deemed adequate for understanding the distribution of the soil and groundwater pollution, a 60-day public comment period must be completed. Owners and occupants of properties within 500 feet of the pollutant plume will need to be notified of the proposed closure. f. Finally, all monitoring and remediation wells will need to be properly destroyed prior to issuance of the No Further Action Required letter. Please submit the following: • The offsite well cluster(s) Work Plan by 30 April 2013. • The Final Excavation Report by 30 May 2014. • The April 2014 Monitoring Report and Offsite Monitoring Well Installation Report by 30 May 2014. • The monthly status updates by email.