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SECTION 5 SAMPLING PROCEDURES AND ANALYSIS The following sampling procedures will be followed to ensure that water levels and quality can be reliably compared from well to well and from sampling event to sampling event and that the data are reproducible. This section also outlines the laboratory analyses required for each groundwater sample. 5.1 Sampling Protocols Prior to beginning sampling, field instruments will be calibrated following the manufacturers' instructions. Calibration information and results will be documented in the field notebook each time a field instrument is calibrated for use in this sampling effort. 5.1.1 Monitoring Wells MW-001A, MW-002, MW-003, and MW-004. Following is the protocol that will be followed for groundwater sampling at MW-OOlA, MW-002, MW-003, and MW-004. Note that MW-001A will be checked for water during each sampling event, and groundwater samples of this well will be taken only if there is water in the well. Measure the depth to groundwater from the top of the casing using an electric well probe and engineer's scale. Purge a minimum of three casing volumes. It is possible monitoring wells installed in the St. Charles alluvial aquifer will be purged dry prior to removing three well casing volumes. During dry seasons, well recharge rates may be slow and prevent sample collection following purging the well dry. To assure a sample is collected from each well during the sampling event, purge water from the first well volume removed will be collected in laboratory-prepared containers and stored until the purge is complete. If the well is purged dry and measurable recharge is not observed, the sample collected from the first well volume will be submitted for analysis. If groundwater is not detected at all, the total depth of the monitoring well will be treasured to confirm that the screened interval has not become filled with sediment or collapsed. When water is not available for analysis, observations of the well condition will be reported. ^ Purge the wells using a bailer or a peristaltic pump. The well purge water will be discharged and allowed to infiltrate into the soil ox flow in a nearby arroyo. ^ Record field water quality measurements in the field notebook at the start of purge and after removing the first, second, and thud casing volumes. Field water quality measurements include pH, specific conductance/electrical conductivity (SC/EC), and temperature. Collect the groundwater sample using a bailer or peristaltic pump and fill laboratory- prepared containers assigned to the well. • Submit the groundwater samples to an EPA-certified laboratory for analysis. P:\Dara\GEN\FS-P-T\12421\Permimng\Snpuladon Rcsponm\Groundnmr Suppling Plan\Gondiuon 1 Gmundwner Sampling Plan 3 14 03.d«