CORRESPONDENCE_2007 (1/07 - 6/07)

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• Abandonment of the temporary borings C All field work will be in conformance with a Health and Safety Plan that will be prepared prior to mobilization of the drill rig. A technical specification prepared in Construction Standard Institute (CSI) format is contained in Appendix A that describes the field work in detail. 2.2.1 Exploratory Soil Boring (HydroPunch or Equivalent) Prior to the start of drilling, the drill rig and all down -hole equipment will be decontaminated Exploratory borings will be drilled by a hollow stem auger drill rig. The hollow stem auger (HSA) drill rig will use 4.25" inner diameter (ID) by 8.25" outer diameter (OD). Soil samples will be taken every 5 feet by split -spoon sampler. A field geologist will log the borehole during drilling in accordance with the American Standard for Testing and Materials (ASTM) Method D2488-00, Description and Identification of Soils, Visual -Manual Procedure (ASTM, 2000). Additionally, the geologist will observe and note the soil color, relative density or stiffness, moisture content, odor (if any), and any contamination (if present). Auger cuttings will be collected and observed. The field geologist will be supervised by a California professional geologist. Volatile hydrocarbons detected by the PID will be reported in parts per million. The geologist will record all observations on the geologic boring log that will be included in the well installation report. Soil cuttings from the well borings will be dispersed on the ground next to the boring location. Drill cuttings from borings located outside of CHSL will be transported back to the landfill and disposed in an area agreed upon with landfill personnel. Soil samples will be field -monitored for total volatile hydrocarbons using a hand-held photoionization detector (PID). Samples will be sealed in a plastic baggie and left for approximately 15 minutes, which is generally sufficient for volatiles to escape from the soil. The temporary soil borings will be drilled to about 75 feet, or 5 feet below first encountered water, which ever comes first. 2.2.2 Permanent Groundwater Monitoring Well Installation Monitoring well (MW -8) will be installed in the exploratory boring at the CSHL The soil boring that will be used to install permanent monitoring wells MW -8 and -9 will be drilled to 15 feet below encountered groundwater in the shallow aquifer, wherever it may be Corral Hollow EMP WPlan Rev2Mar 22-07.DOC 2-3 March 20, 2007