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N%Wwl Catherine Quinn Page 5 June 27,2002 Task 2-Perform Field Investigation. CH2M HILL will perforin the field investigation activities as follows: • Day 1-Four to five temporary piezometers will be installed and sampled. The grab groundwater samples will be sent to a California State Certified laboratory for analysis. The water levels will be allowed to recover over night. • Day 2-The elevations for the temporary piezometers will be surveyed relative to a local benchmark and the water table elevation and gradient determined. • Day 3-Grab groundwater samples will be collected from additional locations,if necessary,based on the water table gradient determined from the temporary piezometers and the analytical results from the first day's grab groundwater samples. The grab groundwater samples will be sent to a California State Certified laboratory for analysis. The field investigation days will be spaced apart,as necessary, to allow sufficient time for the prior day's results to be analyzed and used in the subsequent day's field investigation activities. The number of temporary borings and groundwater samples will depend on conditions encountered in the field and results of the laboratory analyses. The following field and laboratory procedures will be implemented. • Soil Boring Logging. The temporary borings will be advanced using a Geoprobe rig and soils will be logged for lithology,depth-to-water,and presence of petroleum hydrocarbon contamination. The presence of any potential contaminants will be assessed in the field using visual observation,odor,and headspace screening with a photoionization detector(PID). • Groundwater Gradient Determination. The temporary piezometers will be constructed with small diameter(e.g.,1-inch)PVC casing lowered into the Geoprobe borehole. The PVC casing will be perforated and have an end cap at the bottom. Groundwater elevations will be allowed to reach equilibrium. Water level elevations will be determined by subtracting depth-to-water measured from the top of casing(TOC), which will be surveyed for elevation relative to a local benchmark. Accuracy will be to the nearest 0.01-inch. • Groundwater Sample Collection and Analysis. Groundwater samples will be collected in laboratory-supplied containers and submitted to a California State Certified analytical laboratory under chain-of-custody protocol. Sample container and laboratory analytical methods are specified in Table 1. Groundwater samples will be collected with a decontaminated bailer or factory clean disposable bailer. Each boring will be backfilled with cement grout in accordance with San Joaquin County requirements.