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4.3 Field Investigation <br /> The scope of work for this project includes an underground utility location survey and the <br /> advancement of up to eight soil borings using direct-push sampling equipment. The utility <br /> surveys will be conducted using ground penetrating radar(GPR) and electromagnetic radio <br /> frequency survey equipment. <br /> 4.3.1 Underground Utility Location Survey <br /> An underground utility location survey will be conducted to assess the absence or presence of <br /> unreported underground utilities at each site. The geophysical surveys will clear utilities for the <br /> direct push boring locations. <br /> The surveys will be conducted using ground-penetrating radar(GPR) and radio frequency survey <br /> equipment. The approach for the geophysical surveys will be to initially conduct a GPR survey <br /> to locally investigate suspect magnetic anomalies. The GPR traverses will be spaced <br /> approximately 1.5 meters (5 feet) apart and oriented both parallel and perpendicular to the <br /> anomaly. A map showing GPR traverses and subsurface features located by the GPR will be <br /> produced. Based on the GPR survey results, electromagnetic radio frequency pipe locating <br /> equipment will be used to investigate possible underground utilities. <br /> 4.3.2 Drilling and Soil Sampling <br /> 4.3.2.1 Patterson Maintenance Station <br /> Up to six soil borings will be advanced using direct-push sampling equipment. Soil borings will <br /> be located in accordance with Caltrans' Task Order 10-OE7900-MZ. Figure 3 shows proposed <br /> boring locations. Four borings will be advanced to approximately 7 meters (23 feet)below <br /> ground surface (BGS). Two borings will be advanced to approximately 2 meters (6.6 feet)BGS. <br /> Discreet soil samples will be collected at 1.0-meter(3.3-foot) intervals. Soil samples will be <br /> collected using a 5-centimeter(2-inch) diameter sampler lined with a 1.3-meter(4-foot) long <br /> acetate sleeve. Soil samples will be field screened using a photo-ionization detector(PID). <br /> Groundwater samples will be collected from each deep boring using one or more of the methods <br /> described in Section 4.3.3. Drilling and sampling procedures are presented in Appendix A. <br /> Following sample collection, the borings will be backfilled with bentonite cement grout from the <br /> bottom of the borehole to ground surface. The surface material will be repaired with cold patch <br /> asphalt or concrete where applicable. Drill cuttings will be placed into a 208-liter(55-gallon) <br /> United Nations-approved drum. <br /> SACIDP-N. &hsplStockton&Patterson wp.doc 4_2 <br /> 513102 <br />