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22 Constant Discharge Pumping Test--The consta t discharge pumping test will involve pumping groundwater at a constant rate fron. the extraction well while monitoring water levels in the extraction well and existinz monitoring wells. The pumping rate will be measured with an in-line flow meter ind will be dependent on the :;result of the step-drawdown test, the flow-through rate of the GAC filters, and the tank storage capacity. Water levels will be measured periodically during the test with a water level probe. Duration of the constant discharge pumping test is expected to ';be about 72 hours. Groundwater levels in the extraction well and existing monitoring wells will be measured periodically for 36 hours following the constant discharge ;pumping test or until water levels have recovered to the pre-pumping test levels. Groundwater Sampling--A groundwater sample will be collected from thej pipeline hose bib at the wellhead at the end of each step of the step-drawdown pumping test and periodically from the pipeline hose bib on the downstream side of the GAC filters. The purpose of these samples is to onitor the effectiveness of the portable GAC treatment system before proceeding with the constant discharge pumping. test. During the constant discharge pumping test, groundwater samples will be 11collected approximately every 12 hours from the pipeli a hose bibs at the wellhead and on the downstream side of the GAC filters. This data will help estimate what might be expected during operation of the final remedial system. Sample bottles will be filled to the brim dir ctly from the hose bib. A teflon-lined cap will be placed on the bottles, and the bottles will be checked to determine that no air bubbles remain within. All water samples will be labeled, stored, and transported, as described in the soil sampling section above. The water samples will be submitted to Eureka Laboratories, Inc., for analysis of BTX by EPA Method 602. Installation of Off-Site Groundwater Monitoring Wells This section describes the methods for monito 'ng well construction, developirient, and sampling. ARCO will be responsible for the proper well abandonment when the' Regional Board and/or the County determine that monitoring groundwater quality is no longer 4 necessary. Borehole Drilling. BC will supervise the drilling of four off-site soil boreholes and the installation of groundwater monitoring wells in all four boreholes (see Figure 3). The boreholes will be drilled using a truck-mounted d 'lling rig equipped with 8-inch-outside- diameter, hollow-stem augers. Borehole depths are expected to be 75 feet. .:Borehole cuttings will be contained in 55-gallon drums and temporarily stored at Station 434. The disposal of these drill cuttings is the responsibility f ARCO. Soil Sampling. Soil samples for lithologic -lassification will be collected;j,at 5-foot intervals using a 1.5-foot-long by 2-inch-diameter split-spoon drive sampler. The sampler will be driven into undisturbed soil ahead of the augers. The boreholes will be logged by an experienced field geologist working under the direct supervision of a !iregistered geologist. u