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ADDITIONAL ASSESSMENT WORKPLAN COLBERG BOAT WORKS APRIL 2001 PROPOSED FIELD ACTIVITIES Geoprobe Investigation To further define the vertical and horizontal extent of impacted groundwater, six geoprobes will be installed at locations shown on Figure 2. Geoprobes use a"direct push"technique to collect discreet soil and water samples with a minimum of impact to the surface and no production of drill cuttings, as with conventional auger drilling methods. Based on information from past subsurface investigations at the site, the proposed geoprobes will be pushed to approximately 15-feet bgs with discreet groundwater samples taken at approximately 10 to 15-feet bgs to evaluate the extent of petroleum hydrocarbon and fuel oxygenates in the groundwater at the site. In addition, at least one soil sample will be selected for analyses from each geoprobe location. Geoprobe sampling activities will be reviewed by a California Registered Geologist or Civil Engineer. Soil and groundwater samples will be screened in the field with a photo ionization detector(PID)or flame ionization detector(FID) organic vapor analyzer. Upon completion, each geoprobe boring will be sealed to complete depth with a neat/bentonite (<5%) grout. All work will be performed in accordance with the County regulations. Monitoring Well Installation `+ Upon completion of the geoprobe investigation, the data will be analyzed and recommendations will be provided to the County for the location of one to two groundwater monitoring wells to monitor the horizontal extent of impacted groundwater. The wells will also provide additional information on the gradient and direction of groundwater flow. Drilling and well installation activities will be reviewed by a California Registered Geologist or Civil Engineer. The wells will be drilled to approximately 25-feet bgs using a continuous flight hollow stem auger drill rig using 10-inch augers. The groundwater wells will be screened from approximately 10- feet below static ground water to 5-feet above, to allow for seasonal fluctuations in water levels. The wells will be completed with 2-inch diameter, flush threaded, Schedule 40 PVC 0.020-inch perforated and blank casing. A threaded end cap will be placed at the bottom of the PVC casing, �. which will be set through the augers. A#3 sand or equivalent sand pack will be placed in the annular space between the slotted casing and the boring wall, and will extend approximately 1-foot above the top of the screened interval. The well annulus from the top of the sand pack to at least 2-feet above the pack will be sealed t. with hydrated bentonite chips. 4