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k 4. WORK PLAN This work plan proposes the installation of a groundwater monitoring well to assess the vertical extent of petroleum hydrocarbons in groundwater under the site of former Chevron SS 9-1918. The well will be drilled to a final depth, 10-15 feet into the first encountered groundwater,antic- ipated to be approximately 50 feet below the ground surface. It will be located near the former tank field(Figure 16) and will provide information about whether petroleum hydrocarbons leached downward as the groundwater level dropped over the last four years. It is assumed that the groundwater flow direction remains northeast and is generally unchanged from the gradient determined in July 1989. 4.1 DRILLING AND WELL INSTALLATION The proposed monitoring well will be installed by a licensed C-57 well driller with a rotary method using hollow-stem augers. If deeper groundwater under the site occurs under confining conditions at a depth beyond the range of the hollow-stem auger drilling method(which is about 100-120 feet),the dry borehole will be grouted and an air or mud rotary rig will have to be used to install the well. Well casing and screen will he installed to the required depth. A sand filter, Bentonite seal,and cement-Bentonite grout will be installed around the well screen and casing as Y the drilling pipe is gradually removed from the borehole. A log of the soil boring will be recorded by an EA geologist overseeing the drilling operations. The drill cuttings and soil samples will be monitored in the field for the presence of hydrocar- bons with an organic vapor analyzer(O`!A)that uses a flame ionization detector. The moisture content of the soil samples and the initial and static water levels will also be noted on the logs. All drill cuttings will be contained onsite in sealed 55-gallon drums within a locked fence. The drums will be labeled with the borehole number,owner's name,depth interval of soil contents, date,and monitoring equipment readings. The drill cuttings will be disposed of at proper facili- ties on the basis of soil sample analysis. Drill cuttings that are free of petroleum hydrocarbons will be disposed of onsite. 4.2 SOIL SAMPLING Soil samples will be collected at 5-foot intervals and at any substantial changes of soil type, beginning at 5 feet below ground surface. Soil samples will be collected to the total depth of the -- -- - - - borehole unless heaving sand occurs.._Every-attempt_will be made to collect a soil sample at the water table(expected at about 50 feet below ground surface). 7 1701918MI -