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R10/71-51-1C 4.0 INVESTIGATIVE METHODS ' As part of the SI Work Plan, a Sampling and Analysis Plan (SAP) was developed The SAP provided the guidelines for the field investigation The field investigation for Shop 10 ' Sl included soil drilling, installation of groundwater monitoring wells, and sampling of soil and groundwater based on the SI Work Plan prepared earlier for Caltrans All field investigations were conducted in Level D protection according to the Health and Safety ' Plan in the Work Plan Field monitoring of the breathing zone of the drillers was done by using a Foxboro Organic Vapor Analyzer (OVA) The same instrument was used to monitor the samples for volatile organics Eleven borings were completed to a maximum ' depth of 94 feet Six of these borings were converted into groundwater monitoring wells The locations of five soil borings and six monitoring wells are shown in Figure 'I (see Appendix A) 1 The purpose of the field investigation is to determine the horizontal and vertical extent of hydrocarbon soil and groundwater contamination due to leaking underground fuel Itanks or past practices from vehicle maintenance operation on the site Collection and chemical analyses of soil and groundwater samples will provide information on the levels of suspected contamination in these matrices 41 SOIL AND GROUNDWATER SAMPLING Five soil boring locations and six groundwater monitoring well locations were established ed during the pre-work site visit and are shown in Figure 2 (see Appendix B) During the field investigation, the following changes were made o MW16- The location was changed to the new location indicated in Figure 1 (Appendix A) This was done in order to cover an area where two previously installed wells (MW8 and MW9) had dried up An attempt 1 was made to revive MW8 but to no avail o SB21- Originally planned to be a slant borehole, this was not drilled as the drill rig was not capable of drilling slant boreholes An attempt was made to drill a vertical borehole inside the steam room This was not successful either as there was not enough vertical clearance The concrete core cut on the floor inside the steam room was abandoned by plugging it with bentonite seal and resurfacing it with concrete 11