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� � I TASK DESCRIPTIONS BC - ARCO NORTHERN CALIFORNIA PROGRAM DRILLING Soil borings and installation of monitoring wells at sites involve the use of drilling equipment. The drilling of soil borings involves a mobile drill ria using a hollow stem auger, reverse air rotary, or dual-tube percussion. The collection of soil samples involves using a drop-hammer assembly. The borehole will be backfilled with cement and/or bentonite grout if no well is to be installed. The installation of a monitoring well involves the completion of the open boring with screened and blank casing, the placement of a filter pack, and installing a sanitary seal. Hazards involved with drilling consist of the same chemical hazards and physical hazards described under Hazard Analysis on pages 4 through 9. Other hazards associated with drilling include the following: Drilling Equipment Hazards Drilling involves the use of large and heavy pieces of equipment, especially augers. Special attention is needed when this equipment is pulled overhead. Loose clothing and other items may become entangled in the rigging and can result in injury. Traffic also presents a hazard to personnel involved in drilling. All field personnel must be aware of all drilling activities and general traffic at all times. Dust Hazards Drilling, especially with rotary drills using air percussion, can create high levels of airborne dust. Inhalation of dusts can result in increased exposures to soilbound chemicals and pneumoconiosis. Overexposure may occur when the dust becomes visible in the normal light. Signs of potential overexposure are congestion of the nasal passages and irritation of the eyes and respiratory system. GROUNDWATER SAMPLING Groundwater sampling is a required element of quarterly monitoring of most sites. Samples of groundwater may be obtained on or near the site from monitoring wells, existing production •(supply) wells, and from seeps or springs. Results of groundwater sample analyses not only provide an indication of water quality at the particular sampling points but taken together can provide an indication of the extent of contaminant plume movement due to subsurface groundwater transport. Groundwater sampling involves well evacuation (purging) using some form of submersible pump or bailer. Groundwater samples should be collected within 2 hours after the well has been evacuated to assure the sample is representative of aquifer conditions. When the recovery of the well exceeds 2 hours, the well should be evacuated to dryness once and then the well should be 07m"S W0t71MISMORTH"Co QMS•M=W