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60 Lot B Underground Storage Tank—Monitoring11AE11 and Additional Delineation Work Plan 216 N.California Street,Stockton,California February 2,2010 Page 3 60 3.0 RATIONALE,PROPOSED LOCATIONS,AND SAMPLE INTERVALS ko. In order to better establish dissolved diesel concentrations in groundwater, a monitor well within the central contaminated soil mass is proposed. Due to the well-established east-northeast local groundwater gradient direction (Figure 8, Appendix A), additional monitor wells may only be necessary to delineate ` the extent of significant diesel groundwater impact. One groundwater monitoring well and two soil borings are proposed. The work will be completed in two phases. The first phase will include the installation of one monitoring well (MW1) within the central contaminated soil mass. The well will be ` advanced to a depth of 45 feet bgs near the location of CPT 1, in the landscaped area immediately east of the former UST. The well screen interval will be 20-45 feet bgs in order to accommodate fluctuating groundwater depths of 25 to 40 feet bgs. hn Soil samples will be collected at five-foot intervals starting at 10 feet bgs.The well will be developed and sampled as described in Section 4.4. If the laboratory analytical r Its indicate that groundwater sampled from MW 1 has a TPH-D concentration of 2,500 pg/L or ea er' en t e two additional ortng locations willinstead be use or two monitoring well insta ations. If additional monitoring wells are installed, then soil will be sampled at five foot intervals beginning at 10 feet bgs. The additional monitoring wells would be installed with the same methods and construction as described for MW 1. If the laboratory analytical results indicate that groundwater sampled from MW 1 has a TPH-D concentration of less than 2,500 pg/L, then the two additional boring locations will be used for CPT soil borings(Figures 2 and 3,Appendix A). Soil boring CPT4 will be installed approximately 80 feet east of MW 1 and near the northeast corner of the property (Figures 2 and 3, Appendix A). Soil boring CPT5 will be installed approximately 100 feet 61 southeast of MW 1 and near the southeast corner of the property. The purpose of CPT4 and CPT5 will be to provide data on the lateral distribution of sorbed and aqueous phase hydrocarbons east of MW 1 and the former UST area (see Figure 5, Appendix A). Soil samples will be collected at depths of 30 feet, 40 hm feet, 50 feet, and 60 feet bgs. A groundwater grab sample will be collected from the 30- to 34-foot interval or at the uppermost groundwater. The samples will be analyzed by the laboratory, as described below, for comparison to data previously collected from SB-5. A generalized soil boring construction `, diagram is included as Figure 7,Appendix A. 4.0 MONITORING WELL INSTALLATION FIELD PROCEDURES hn 4.1 SITE PREPARATION Condor will prepare an encroachment permit application for sidewalk closure from City of Stockton-Public ` Works Department. Condor will prepare a monitoring well and soil boring installation permit application for submittal to the SJCEHD. Condor will receive the permits prior to initiating any fieldwork. The proposed monitoring well and boring locations will be marked with white paint and Underground Service ` Alert (USA) will be notified at least 48 hours in advance of the fieldwork to locate and identify underground utilities in and near the work area. However,because companies contacted by USA may not identify utilities past private property lines and into the Site, a private utility line locator will survey Site utilities (if present). Prior to initiating fieldwork at the Site, all field personnel will familiarize themselves with the Site-Specific Health and Safety Plan (HASP). In addition, a tailgate safety meeting will be held prior to commencement of fieldwork. The HASP pertains to field activities and includes ' California Regional Water Quality Control Board,Screening For EnvironmentalConcerns at Sites with Contaminated Soil and Groundwa er I - Groundwater Environmental Screening Levels for TPH middle distilla Table F-1 a),November,2007 L. wAr�b LC-1vi YVOT Ccv�S!< t�vc�„c� p!!,4,1 /,/, z&vtAa,CONDOR 7'aL-'J�F-1C. '4- ,Go ►00 febTef4j (-hrn��.��(Q.r•c)