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'IMP <br /> INN% <br /> April 7, 1992 <br /> ARCO Station No. 2168,Stockton, California <br /> ADDITIONAL WORK <br /> On the basis of results of previous work and at the request of ARCO, RESNA proposes to <br /> conduct the work outlined below to evaluate the extent of hydrocarbons in soil and initially <br /> investigate ground water. The work will be conducted according to field methods included <br /> in our Work Plan dated May 17, 1991, which describes the site history, local geology, <br /> proximity to wells and utilities, soil borings, soil sampling methods, and vapor-well <br /> construction. Our previous Work Plan also includes the Site Safety Plan and Emergency <br /> Route to the Hospital, examples of the field boring logs, the Unified Soil Classification <br /> System, and Logs of Borings. <br /> We are modifying our vapor-extraction well construction: the screened portion of the wells <br /> will consist of factory-Ierforated casing with 0.1-inch-wide slots and pea gravel will be place <br /> in the annular space opposite the screen. We have include,' :he following attachments to <br /> this addendum: a description of ground-water monitoring .,ell installation, a schematic <br /> ground-water well design, and a modified schematic vapor-recovery well design. <br /> We understand from ARCO that Groundwater Technology Inc. (GTI) has requested and <br /> been granted authorization from ARCO to install a ground-water well south of the existing <br /> gasoline tank cavity. Work conducted 'oy GTI is in conjunction with a subsurface <br /> investigation at the Texaco station south of the site. According to correspondence from <br /> GTI, the local direction of ground-water flow is to the east. <br /> We propose the following tasks to conduct the subsurface investigation. <br /> 0 Locate underground storm drains beneath the site. <br /> 0 Acquire a drilling permit from the SJCPHS-FHD. <br /> Contact Underground Service Alert at least 48 hours before drilling to <br /> delineate public utility lines at the site. <br /> 0 Drill one 8-inch-diameter soil boring adjacent to boring B-1 to ground water <br /> to delineate residual hydrocarbons in soil vertically. <br /> 0 Drill four 8-inch-diameter soil borings to ground water or when two <br /> consecutive soil samples with photoionization detector (PID) readings below <br /> 10 parts pe- million by volume are collected in soils from below 25 feet. <br /> Three of the four borings will be converted to 4-inch-diameter vapor- <br /> 30094W <br /> 1-1 Mom 'M 0 %mm Nomp=I 10 <br />