WORK PLANS FILE 1 - Laserfiche WebLink

Home Browse Search

Stantec August 15,2013 Page 2 of 8 On October 30, 2001, three groundwater monitoring wells (MW-5, MW-6, and MW-7) were installed to 20 feet bgs. TPHg, benzene, toluene, ethylbenzene, xylenes (BTEX), and MtBE in soil were not detected above laboratory reporting limits, except for 0.006 mg/kg total xylenes (MW-7@20'). Selected halocarbons also present in the soil samples indicated possible dry cleaner plume contributions (IT Corporation, 1999). On August 14, 2003, one deep groundwater monitoring well (MW-8) and one soil boring (SB-1) were advanced onsite. SECOR International Inc. (SECOR) summarized this assessment in the February 27, 2004 Additional Site Assessment Report and Fate and Transport Model, which also presented calculations of the lateral migration of dissolved MtBE in groundwater. Per the request of the San Joaquin County Environmental Health Department (SJCEHD), groundwater monitoring and sampling was coordinated with a former Exxon site (currently a Shell Gasoline station) immediately east of the 7-Eleven site. On July 22, 2004, SECOR submitted a proposal for a Field Test Program for Evaluation of Oxidation Capacity of Groundwater to the California Regional Water Quality Control Board (CRWQCB). The CRWQCB conditionally approved the proposal in a letter dated October 4, 2004. On July 27, 2004, SECOR submitted a Work Plan for Additional Offsite Assessment to the SJCEHD. The work plan was approved by the SJCEHD in a letter dated August 23, 2004. The work plan proposed installing two groundwater monitoring wells (MW-9 and MW-10) and advancing six soil borings (GP-1 through GP-3 and CPT-1 through CPT-3). Between April 26 and April 28,&Wg�, SECOR supervised the installation of oxygen injection well ,-1-and the advancement of soil borings GP-1, GP-2, and CPT-1 through CPT-3 by Gregg Drilling and Testing. With the exception of 4.0 micrograms per liter (pg/L) of MtBE in CPT-3 (CPT-3-70') the lateral extent of deep groundwater contamination was defined to the northeast and east. The lateral limits of shallow contamination in soil and groundwater was defined to the north, west, and southwest of the site. Proposed groundwater monitoring well MW-10 could not be installed due to the presence of underground utilities around the proposed location. Access to install proposed well MW-9 was not granted by USA Gas, therefore MW-9 was not installed. SECOR submitted the Additional Site Assessment and Site Conceptual Model report to the SJCEHD on September 30, 2005 summarizing the additional assessment activities. On December 2 and 16, 2005, SECOR conducted oxygen capacity testing into well 1-1 as outlined in the July 22, 2004 Field Test Program for Evaluation of Oxidation Capacity of Groundwater. On May 9, 2006, Results of Oxygen Injection Feasibility Pilot Study was submitted to the CRWQCB. On June 15, 2007, SJCEHD requested the submittal of a Correction Action Plan (CAP). The CAP was submitted to the SJCEHD on October 12, 2007. The SJCEHD requested a CAP addendum in a letter dated January 4, 2008. SECOR submitted the CAP Addendum to the SJCEHD on March 19, 2008. The SJCEHD approved the CAP Addendum on July 9, 2008. On June 1, 2008, SECOR International Inc. became Stantec Consulting Corporation (now Stantec Consulting Services Inc. [Stantec]). V:\1857\active\7- E leve n\active\185750063_711_14117\05_report_del iv\reports\14117_2013_08_15_closure_repo rt.doc