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S E C O R SJCEHD December 8,2006 Page 2 i i A pump and treat groundwater remediation system was.operated at the site from 1992 until 1996. 1 Post remediation groundwater monitoring showed increased methyl tent-butyl ether (MtBE) concentrations at MW-2 and AMW-5. Depth to groundwater at the site currently ranges from approximately 4.5 to 7 feet below ground surface (bgs). Groundwater flow direction in the shallow zone is to the northwest. UPDATED SENSITIVE RECEPTOR SURVEY Updated sensitive receptor information is included at Attachment C. The updated survey, dated December 12, 2005, supplements previous information. According to the December 12, 2005 survey there are two wells located within a % mile of the site. The wells are owned by the City of Tracy and are located 750 feet northeast'of the site and 1,250 feet southeast of the site. PROPOSED SCOPE OF WORK The proposed scope of work will consist of the installation of one groundwater ronitoring well to an approximate depth of 50 feet bgs in the area of the historically highest concentration of groundwater contaminants, near MW-3 (Figure 2). A summary of the planned field work is presented below. Field and laboratory procedures are provided in Attachment D. • Health and Safety Plan (HASP). As required by the Occupational Health and Safety Administration (OSHA),Standard "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910.120), and by they California Occupational Health and Safety Administration (Cal-OSHA)"Hazardous Waste Operations and Emergency Response"guidelines (CCR Title 8, Section 5192), SECOR will update the current site-specific HASP prior to the commencement of fieldwork. The HASP will be reviewed by the field staff and contractors before beginning field operations at the site. • Permitting. Included in this work plan as Attachment E is the monitoring well permit application and a check in the amount of$89 to cover appropriate fees. • Borehole Clearance Activities. Prior to initiating field activities, SECOR will mark the boring location, contact Underground Service Alert (USA),at least 48 hours prior to the initiation of field work, and will contract a private utility locator to determine whether the proposed boring location is clear of potential subsurface obstructions. After clearance is verified by USA and the utility locator;,the boring will be air knifed to a depth of approximately 5 feet bgs to further minimize the risk of encountering utility lines that are not anticipated at the location. • Groundwater Monitoring Well-installation. One soil boring will be advanced at the location shown on Figure 1 using hollow stem auger drilling equipment. During drilling activities, borings will be logged by a geologist using cuttings observed during the drilling process. Soil lithology will be logged every 5 feet to a depth of 20 feet and then continuously sampled using a California Split Spoon sampler to determine depths and thicknesses of any aquicludes at the site. Based on information from borings conducted at the Chevron northeast of the site, the area is underlain by silty clay to clayey silt mixtures to an approximate depth of 20 to 50 feet bgs. 'A 2-inch.well will be completed within a borehole I:1BP-ARC0105 SP-COP Sites1111941Work PIan111194 Vertical Delineation WP.doc