ARCHIVED REPORTS_SITE INVESTIGATION 2003 FINAL RPT

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3.1.4. Geophysical Clearance A private geophysical company, will investigate each proposed exploratory trench and boring location to evaluate potential buried utilities or other subsurface anomalies. There are limitations to performing geophysical clearances at landfill and burn dumps due to interference associated with buried metallic debris. Trench and boring locations will be adjusted, as necessary, if subsurface utilities or anomalies are identified. 3.1.5. Air Monitoring Support CIWMB staff, as necessary, will implement an air -monitoring program, during trenching activities. Air monitoring equipment will be maintained and calibrated daily before starting work. Air monitoring activities will be performed in accordance with the SHSP and likely include direct - reading air monitoring for lower explosive limit, oxygen, carbon monoxide, and hydrogen sulfide. Volatile organic compounds (VOCs) and particulates such as dust may be monitored during trench -related activities. 3.1.6. Trench and Boring Locations Proposed trench and boring locations were based on review of previously prepared documents, particularly site inspection reports, historic aerial photographs, and review of the topographic maps indicating locations/suspected locations of the former gravel pits (Figure 5). The proposed boring and trench locations are intended to provide the most information possible regarding the types and distribution of buried wastes. The actual number and locations of exploration points may be modified in the field, as necessary, based on earlier obtained field data. Only a portion of the McNalley property, the area corresponding to the suspected locations of the former gravel pit(s)/dredge tailings will be evaluated during this investigation. Authoritative protocol may be used to allow the investigator the flexibility to move sampling locations, as necessary, to accommodate unforeseen field conditions and to take into account information obtained as the investigation continues. At this time, CIWMB staff anticipates that approximately 50 to 55 sampling locations will be required to generally define the horizontal and vertical extents of the majority of buried wastes (Figure 5). Field activities are proposed to begin with excavating potholes/trenches in areas within the former gravel pits (areas suspected to contain the deepest buried wastes) to evaluate whether the total depths of buried wastes can be obtained using this method of exploration. These trenches will be at or in the vicinity of the proposed borings. If trench excavations cannot be advanced to the total depths of buried refuse, then borings will be drilled in these areas to attempt to obtain the vertical extent of buried wastes. Trench excavating is preferred because this method of exploration generally is able to advance through the buried wastes, buried wastes and subsurface lithologies can be directly observed in the trench excavations, a larger area is explored, and the actual depths of buried wastes and other materials can be directly observed and recorded. Borings also have the disadvantage of often not being able to be advanced to the desired depths due to refusal associated with encountering buried wastes such as metal, asphalt, and concrete debris, which can not be penetrated with conventional drilling methods. Areas of proposed borings will therefore first be potholed by trenching and if the vertical extent of wastes can be determined, these areas will not be drilled. 3.1.7. Trench Excavations An experienced, 40 -hour, HAZWOPPER trained, excavating subcontractor will use a track excavator to excavate subsurface materials at each location. They will provide an assistant to help with directing the excavations, handling excavated materials, and controlling dust, as 3-20