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E C O R Work Plan for Soil and Groundwater lfiestigation Former ARCO Service Station#0760 December 13,2006 Page 3 Quarterly groundwater sampling has been conducted since October 2002. A summary of the historic groundwater data is included in Table 1. Well construction information is presented in Table 2. SENSITIVE RECEPTORS The sensitive receptor survey conducted by URS identified three wells within a '/2 mile radius of the site. Only one water supply well location was identified approximately'/4 mile north of the site. City of Lodi municipal well #1 R is located approximately 812 feet east of the site. SITE GEOLOGY AND HYDROGEOLOGY Soil encountered generally consisted of sand,silty sand,sandy silt,and silt. Based on quarterly water level measurements from October 2002 through July 2006,the groundwater flow direction varies from the southeast to southwest at an average gradient of 0.02 feet/foot. A summary of the historic groundwater gradients is included in Table 3. PROPOSED SCOPE OF WORK The proposed scope of work includes: • Drilling and installation of three groundwater monitoring wells to approximately 70 feet bgs. • Installation of three soil vapor probes. • Collecting soil samples during the drilling of the monitoring wells. • Development and sampling of the newly installed monitoring wells. • Surveying each of the newly installed groundwater wells and vapor probes. • Collection of soil vapor samples from newly installed vapor probes. Details for the activities associated with completion of the scope of work outlined above are provided below. Health and Safety Plan 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 fieldwork. Subcontractors performing field activities will also be provided a copy of the HASP prior to initiating work. Permitting Permits for the installation of the monitoring wells and vapor probes will be obtained from the San Joaquin County Environmental Health Department (SJCEHD) prior to initiating field work. Borehole Clearance Activities Prior to initiating field activities, the boring locations will be marked and Underground Service Alert (USA)will be notified at least 48 hours prior to the initiation of field work. In addition, a private utility locator will be contacted to determine whether the proposed boring locations are clear of potential subsurface obstructions. After clearance is verified by USA and the utility locator,the borings will be air knifed to a depth of approximately five feet bgs to further minimize the risk of encountering utility lines. ARCO 00760 Soil and Groundwater Investigation WP.doc