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IPROTOCOLS FOR QUARTERLY GROUNDWATER MONITORING • ' GROUNDWATER GAUGING Wells are opened prior to gauging to allow the groundwater Ievel in the wells to equilibrate with atmospheric pressure The depth to groundwater and depth to liquid-phase hydrocarbons,if present, are then measured to the nearest 0 01 feet using an electronic water level meter or optical interface probe The measurements are made from a permanent reference point at the top of the well casing If less than 1 foot of water is measured in a well,the water is bailed and,if the well does not recover, the well is considered "dry " Wells with a sheen or measurable liquid-phase hydrocarbons are generally not purged or sampled IWELL PURGING After the wells are gauged, each well is purged of approximately 3 well casing volumes of water to provide representative groundwater samples for analysis Field parameters of pH,temperature,and electrical conductance are measured during purging to ensure that these parameters have stabilized Ibefore groundwater in a well is sampled Groundwater parameters are considered stable when two consecutive readings indicate no greater than a 10 percent change from the previous reading for temperature and electrical conductance and no greater than a 0 1 pH units change from the previous reading for pH Groundwater in each well is purged using an inertial pump (WaTerra), an electric submersible pump, or a bailer After the well is purged,the water level is checked to ensure that the Iwell has recharged to at least 80 percent of its original water level GROUNDWATER SAMPLING After purging, groundwater in each well is sampled using dedicated tubing and an inertial pump (WaTerra) or a factory-cleaned disposable bailer Samples from extraction wells are typically I collected from sample ports associated with the groundwater remediation system Samples collected for volatile organic analysis are placed in Teflon septum-sealed 40-milliliter glass vials Samples collected for diesel analysis are placed in 1-liter amber glass bottles Each sample bottle is labeled I with the site name,well number, date, sampler's initials,and preservative The samples are placed in a cooler with ice for delivery to a state-certified laboratory The information for each sample is entered on a chain-of-custody form prior to transport to the laboratory I I I I i I IG 1PmiectsTxxonMobrllMaster•ExxonMobtl QMR templates\QMR protocols purge-waterra doc