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\(rink Southwest, ]uric. was placed in the boring holes above the bentonite seal to approximately 1 foot bgs. The wellheads were secured with locking well caps and completed with 12-inch-diameter Emco- Wheaton traffic lids installed in minimum 24-inch square concrete pads. Well construction details are included on the boring logs in Appendix A. 8.2 GROUNDWATER SAMPLING AND MONITORING Following installation, the wells were developed using a vacuum truck on October 16, 2003. A dedicated clean stinger constructed of 1'/z-inch Schedule 40 PVC was inserted into each well. Prior to purging and sampling, depth to groundwater in the monitoring wells was measured to 0.01-foot accuracy from the top of the well casings using an electronic oil/water interface probe. A minimum of three to four well volumes of water was purged from each of the monitoring wells prior to sampling using the vacuum truck. The wells were allowed to recharge to at least 80% of the static head prior to sample collection. A groundwater sample was collected from each well by lowering a disposable bailer approximately 2 feet into the water column. The bailer was recovered and the water decanted into appropriate laboratory-supplied containers. The containers were labeled, then placed immediately into a chilled cooler and maintained at approximately 4 degrees centigrade for delivery to a CDHS-certified laboratory for analyses. Strict chain-of-custody protocol was followed throughout field and laboratory procedures. The samples were analyzed for NH3-N by EPA Method 350.2 by the analytical testing laboratory and for pH using a calibrated field instrument. In a similar manner, existing Port of Stockton groundwater wells MW 3-4 and MW 3-6, located east and southeast of the tank farm, were sampled and analyzed for NH3-N by EPA Method 350.2 and pH using a calibrated field instrument. The static depth of groundwater water was found to range from 11.87 to 13.98 feet bgs. The local groundwater gradient appeared to be a nose that channels water from northwest to northeast with gradients varying from 0.0043 ft/ft to 0.0065 ft/ft (averaging 0.0050 ft/ft in a generally northern direction). The groundwater gradient is depicted on Figure 4. 725.PRI.00 Page 6 December 4,2003