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Active Groundwater Sampling Standard Operating Procedure SWE-FSOP-401;Revision 1 Ahtna Southwest Environmental Operations If NAPL (such as floating/heavier-than-water product) is suspected in the well, check for NAPL presence using an oil/water interface probe. If detected, record the presence and thickness of NAPL in the field notebook (SWE-FSOP-102. "Groundwater and NAPL Measurements"). Before groundwater purging and sampling, measure groundwater depths (and total depths if needed)to assess the site hydrogeologic conditions. Measure the depth to groundwater in each well to within 0.01 feet. Measurements can be performed as one activity or individually when combined with the sampling effort. Ideally, depth to water measurements should be taken within one day. In practice, measurements should be taken within a few days but not longer than one week. If fieldwork is performed outside this guideline, the PL shall instruct the FTL. Conditions that should trigger discussions are heavy rainfalls,tidal influences, excessive nearby groundwater extraction, or other unusual condition. 4.2 Representative Samples 4.2.1 Purging If left standing, the well's groundwater can become stagnant or change in ways that make it unrepresentative of the groundwater to be collected. Groundwater purging is a procedure that draws fresh groundwater from the surrounding formation into the well immediately prior to sample collection. When purging with a motorized pump, care should be taken to maintain the height of the groundwater table as measured by "depth to water." Excessive pumping pulls water from above and below the intended position for collecting samples. For low-flow sampling techniques, pumping rates from 100 mL/minute to 500 mL/minute (DTSC, 2008). Equipment-specific purging techniques are described in Sections 4.3 through 4.6. 4.2.2 Groundwater Parameters Groundwater quality parameters are collected for two reasons. To show that purging activites have conditioned the well water so that a representative sample can be collected at a specified well depth. To collect water quality measurements commonly used in engineering and science evaluations. Using low-flow sampling techniques, a well's groundwater is considered representative at the screened- interval of the well when successive measurements have met criteria. Note.Techniques other than low-flow may use three well volumes as the criteria for a representative sample (Sections 4.3-4.6). Using a calibrated multimeter, water quality parameters are measured. Depending upon the sampling technique, the multimeter probes will be connected to a flow-through cell or a manufacturer-supplied cup. During low-flow sampling, measurements are recorded at the onset of purging and then every three to five minutes. When three successive readings meet stability criteria listed below, the well water is ready for sampling.The final measurement is used for project evaluations and reporting. Page 8 of 14