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Work Plan for Additional Assessment � - ARCO Service Station No. 548 Stockton, California Page 3 of 6 Well # 1 , located approximately 950 feet south-southeast of the site. This well produces approximately 800 gallons per minute (gpm ) and is screened at various intervals between 170 and 240 feet below ground surface (bgs) . The sensitive receptor survey did not identify any surface water bodies , child-care centers , schools , or wildlife habitats within 500 feet of the site (URS , 2004) . 1 ,2-DCA EVALUATION 1 , 2-DCA has historically been detected in AS- 1 , AS-21 AS-3 , MW- 1 , MW-2 , MW-5, MW-6, MW-7 , VW- 1 , VW-2 , VW-3 , VW-4 , VW-5S , and VW-5D , with the highest concentrations in VW-5D reported at 83 lag/L in December 2001 . 1 , 2-DCA was detected during the fourth quarter 2006 above reporting limits in MW-5, MW-7 , VW-2 , VW-3, and VW-4 , at a maximum concentration of 22 lag/L in VW-2 . The United States Environmental Protection Agency (USEPA) document title " Engineering Approaches to In Situ Bioremediation of Chlorinated Solvents : Fundamentals and Field Applications' http://www. epa . gov/tio/download/remed/engappinsitbio . pdf, excerpts in Attachment B) indicates that concentrations of 1 ,2-DCA may be reduced by biosparging . A biosparge feasibility test is currently being conducted at the site to monitor the effectiveness for remediating petroleum hydrocarbons . Concentrations of 1 , 2-DCA will also be monitored during the test to determine the effectiveness at reducing these concentrations . 1 , 2-DCA will be reevaluated following completion of the biosparging feasibility test. PROPOSED SCOPE OF WORK The scope of work outlined in this work plan includes the installation of additional groundwater monitoring wells to provide lateral definition of the groundwater contamination south and west of the site . The following sections describe the installation of three groundwater monitoring wells (MW-9 through MW- 11 ) . Task 1 - Preliminary Field Activities Prior to conducting the subsurface investigation , a site-specific Health and Safety Plan (HASP) for use by personnel during implementation of this work plan will be prepared . The HASP will address the proposed subsurface investigation activities, and a copy of the HASP will be available on-site during field work. Subcontractors performing field activities will also be provided a copy of the HASP prior to initiating work. The required monitoring well installation permits will be obtained from SJCEHD . All locations will be marked and Underground Service Alert (USA) will be notified at least 48 hours in advance of drilling . In addition , proposed boring locations will be cleared by a private utility locator and boring locations will be cleared by hand to approximately 5-feet bgs before machine drilling is initiated . Task 2 — Soil Boring Advancement, Soil Sampling and Groundwater Monitoring Well Installation In order to evaluate the current lateral extent of fuel-related hydrocarbons , MTBE , and 1 , 2-DCA three shallow zone (screen interval 25 to 40 feet bgs) are proposed at the approximate locations shown on Figure 3 . Locations of proposed wells may require modification due to field conditions (obstructions) . It is also possible that the locations of some wells may be moved for space constraints and/or to accommodate drilling equipment. Each boring will be advanced using a hollow-stem auger drill rig equipped with 8-inch diameter continuous flight augers . During advancement, soil samples for chemical analyses will be collected at five-foot intervals using a California-modified split-spoon sampler driven approximately 18 inches using a 140-pound hammer falling 30 inches (blow count) . Soil contained in the sampler will also be classified according to the Unified Soil Classification System (USCS) by a scientist under the direction of a State of California