WORK PLANS - Laserfiche WebLink

Home Browse Search

f V Borehole drill cuttings, decontamination water, cement mixing and cleanup water were placed into closed top drums,labeled and left onsite at Boyd Service Center. 7.0 Groundwater Monitoring Well Installation and Sampling 7.1 Monitoring Well Design.and Installation Four monitoring wells were constructed using threaded Sch. 40 PVC casing; glues were not used. Final. well design was modified to the site-specific conditions encountered in.the borehole during drilling_ Once the aquifer strata are defined, the casing was lowered to the bottom of the borehole, leaving a short sand pack interval above the occurrence of groundwater to observe for floating product. The slotted interval used a 0.020-inch. slot and the annular space around the slots was backfilled with 2112-size sand. The sand pack was placed to a level about two feet above the slots. Previous experience has shown this to be a reliable well design in fine grained and stratified depositional environments in this area. A bentonite seat was placed atop the sand pack, and a cement grout sea] (cement mix witnessed and approved by the SJC/EHD representative in the field prior to sealing) was placed atop the bentonite using a tremie line, filling from the bottom to top of the borehole. A traffic-rated wellhead access box and security device completed each well. 7.2 Monitoringell Head Survey All wells were surveyed by the City of Tracy for location and top of casing elevation survey to a known datum. The well survey also provides well location and elevation are then plotted for inclusion for regulatory electronic reporting. 7.3 Monitoring Well Development and Sampling The wells were developed by a contract sampling company after waiting at least 72 hours for the grout well seals to set, and then. purged and sampled after development. Each monitoring well was purged using calculated well volumes based upon the depth to water in each casing. Development continued until the water became clear and/or sand pumping decreased, and notes were kept of the development_ Prior to sampling each monitoring well was purged by a contract sampling company using calculated well volumes based upon the depth to water in each casing. The depth to groundwater measurement was made to the nearest one-one hundredth of one foot, and the well was also checked for the presence of sheen or separate phase product. As each purge volume is removed, measurements of pH, electrical conductivity, turbidity, and temperature were taken until these parameters stabilized over two measurements, which are interpreted to indicate aquifer water entering the casing. The well water level was allowed to stabilize to about 80% of its initial water Level before collecting the sample. Each groundwater sample was carefully collected with a clean disposable PVC bailer and poured with minimum cavitation and minimum headspace into the appropriate laboratory prepared container. Each water sample was labeled, logged onto a chain-of�custody form, and placed in a chilled ice chest on crushed ice. Upon completion of well sampling„ each well was closed and Ptgc5of 14