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. URS V Ms Vicki McCartney, REHS Page 3 San Joaquin Environmental Health Department January 7, 2004 The geology of the Sacramento Valley consists mainly of Holocene to younger Oligocene continental sedimentary and volcanic deposits. These deposits unconformably overlie thick sequences of inter- fingered Eocene to Cretaceous sediments. The Eocene to Cretaceous sediments unconformably overlie the Mesozoic intrusive felsic (granitic)basement rocks of the Sierra Nevada Batholith(and associated Paleozoic metasediments and metavolcanics). Based on observations during drilling activities,the site vicinity is underlain primarily by silt with inter- bedded clay.The silty zone is underlain by a sandy zone composed of sand and silty sand. A second silty zone is beneath the sandy zone and a second sandy zone is beneath the second silty zone. Depth-to-water measurements at the site have ranged from approximately 34 to 59 feet below ground surface (bgs). Monitoring data from June 9, 2003 indicates that the dominant inferred groundwater flow directions are east-northeast, with average hydraulic gradients of 0.01 feet per foot. Historical data shows groundwater direction and hydraulic gradient to be variable. The direction of flow and gradient will change between sampling intervals. PROPOSED SCOPE OF WORK Task l —SVE/AS System Design Prior to initiation of field activities, URS will obtain all necessary permits for installation of this SVE/AS system from San Joaquin Valley Unified Air Pollution Control District(SJVUAPCD) and the �e r�+I —City of Stockton. Remedial system design plans, including remedial piping layouts and equipment �Il }"r' specifications, will be completed and forwarded to SJVUAPCD prior to system installation. The SVE Gt rG #�vm Vis-GI-14`.tY system will be used to control possible vapor migration induced by the AS system and to enhance n�f.Z�-N airflow and subsequent hydrocarbon destruction in the shallow water-bearing zone, capillary fringe,and (ON the vadose zone. URS will prepare a site-specific Health and Safety PIan(HASP)prior to field activities. The HASP will be reviewed by field staff and contractors and will be present on site during field activities. A site pian showing proposed well locations and piping runs is included as Figure 2. Task 2—SVE/AS System Installation,Troubleshooting,and Startup Upon receipt of approved permits from SJVUAPCD and the City of Stockton, system installation will begin. URS currently estimates system installation and completion by the end of March 2004. A project schedule for SVE/AS system installation is included as Figure 3. Upon completion of system installation, the system will be operated to verify the correct operation of all process equipment and controls, and to troubleshoot and repair any component of the system that is not operating correctly. KAWprocessU5 BP ARCO%02186\SVE System(new)UI86 Workplan 03.doc