ARCHIVED REPORTS XR0009921 - Laserfiche WebLink

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Corrective Action Plan Page 38 groundwater pumping These wells will then be sampled at monthly intervals for three months Thereafter, these wells will be regularly sampled once every three months Momtonng to Confirm the Areal Limits of Contamination To confirm that the areal extent of the plume of contaminated groundwater and the rate of its migration does not unexpectedly change, and to check for the arrival of any hydrocarbon fuel contamination migrating from up-gradient or co-gradient locations, samples will be recovered from monitoring wells NAV 2, NAV 5, NAV 6, NAV 7 and NAV 8 These wells are located around the perimeter of the plume and analyses of samples recovered from them have consistently shown them to be free of detectable concentrations of contaminants Consistent with the program established by the Groundwater Sampling Plan 152 Fast - 1 lth. Street, Tracy, California (Ref 8) that has been approved by the SJCPHS, sampling rounds that include the plume-perimeter wells will be performed twice per year - once during the annual wet season (February) and once during the dry season (September) Determination of Cimundwater Elevations Prior to each round of groundwater sampling, the depth from the top of the casing to the water table will be measured in all monitoring and recovery wells installed for the 152 East 11th Street site These data will be used to compute the groundwater table elevations relative to the local datum that has been established on the top of the casing of Well ULT 7, which was assigned a nominal elevation of 50 00 ft The computed groundwater-table elevations will be used to produce contour maps of the groundwater table and deterimne the direction and magnitude of the groundwater-flow gradient Sampling Procedure Prior to each round of sampling„ each monitoring well to be sampled will be purged of a minimum of 10 casing volumes The purge water be temporarily held in a 50-gallon steel drums before it is pumped to the groundwater treatment system for disposal Samples will be recovered from each monitoring well to be sampled using a dedicated bailer which will be suspended in the well casing when not in use Water brought to the surface in the bailers will be decanted so as to completely fill clean glassware supplied by the laboratory The sample vials will then be tightly closed, labeled for identification, entered into chain-of-custody control and packed on chemical ice for transport to the laboratory within 24 hours Following completion of sampling, the depth to groundwater in each monitoring well sampled will be re-measured and checked against the depth measured prior to the start of well purging This will provide information on well-recovery rates and indicate whether or not representative samples of groundwater are being recovered