FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

v..w, advanced to the desired sampling depth interval, and a drive split spoon sampler was driven ahead of the drill bit. The soil samples were sealed with Teflon paper and plastic endcaps, labeled, logged onto chain-of-custody forms and place in a chilled ice chest on crushed ice for transport to a State certified analytical laboratory. The boreholes were logged using the Unified Soil Classification System under the supervision of a professional geologist. Additional lithologic information was collected to describe the subsurface geology. The soil samples were collected at five-foot intervals, and at intervals of obvious contamination and at stratigraphic features of interest. Soil samples were field screened with a portable photoionization detector (PID) for fuel hydrocarbons vapor and staining. Samples showing elevated PID readings were selected for chemical analysis. If field screening was inconclusive, soil samples were selected based upon possible staining, site stratigraphy and near the occurrence of groundwater. Upon completion of the borehole drilling and collection of soil samples, three (3) boreholes were converted to groundwater monitoring wells using the procedures discussed below. Borehole drill cuttings, decontamination water, cement mixing and cleanup water were placed into closed top drums, labeled and left at the Client specified location, Boyd Service Center. 4.0 Groundwater Monitoring Well Installation and Sampling 4.1 Monitoring Well Design and Installation Three 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 uses a 0.020-inch slot and the annular space around the slots was backfilled with#3-size sand. The sand pack was placed to a point 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 seal was placed atop the sand pack, and a cement grout seal (cement mix 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. 4.2 Monitoring Well Head Survey All wells were scheduled for a location and elevation survey to a known datum. The well survey was performed so that well location and elevation are plotted for inclusion for regulatory reporting. 4.3 Monitoring Well Sampling The wells were developed by a contract sampling company after waiting at least 72 hours for the well cement grout seals to set. Prior to sampling each monitoring well was purged using calculated well volumes based upon the depth to water in each casing. Depth to groundwater measurements were made to the nearest one-one hundredth of one foot from the top of casing, and also checked for the presence of separate phase product. As each purge volume was removed, measurements of pH, electrical conductivity, turbidity, and temperature were taken