FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

• SNOW, d The borehole was logged under the supervision of a professional geologist using the Unified Soil Classification System together with lithologic information to describe the subsurface geology. The soil samples were collected at about five-foot intervals, and at stratigraphic features of interest. Soil samples were field screened for fuel hydrocarbons vapor and staining. Upon completion of the borehole drilling and collection of soil samples,the borehole was converted to a groundwater monitoring well using the procedures discussed below. Borehole drill cuttings, decontamination water, cement mixing and cleanup water were placed into closed top drums, labeled and left on-site at the City specified location onsite. 4.0 Groundwater Monitoring Well Installation and Sampling 4.1 Monitoring Well Design and Installation One (1) monitoring well MWWES-1 was 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 through the hollowstem auger, leaving a short sand pack interval above the occurrence of groundwater to observe for floating product. The slotted interval used a 0.020- inch machine sawn slot and the annular space around the slots was backfilled with 2/12-size sand. The sand pack was placed to a point about two (2) feet above the slots. The driller surged the sandpack during installation to create amore complete hydraulic connection to the aquifer during sand pack filling. Previous experience has shown this to be a reliable well design in fine grained and stratified depositional environments in this region. A bentonite seal was placed atop the sand pack, and a cement grout seal (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 the well. 4.2 Monitoring Well Top of Casing Well Head Survey The top of well casing elevations were surveyed by the City of Tracy in January 2010 to the same known datum as existing monitoring wells MWHP-5, MWHP-6, MWHP-7 and MWHP-8. Wright has attached this information to the report. 4.3 Monitoring Well Development and Sampling The contract sampler developed the well on October 22, 2009 after waiting at least 72 hours for the well cement grout seals to set, and then purged and sampled after development. The monitoring well was first purged using calculated well volumes based upon the depth to water in each casing prior to sampling. Depth to groundwater measurements were made to the nearest one-one hundredth of one foot, and also checked for the presence of separate phase product. As each purge volume is removed, measurements of pH, electrical conductivity, turbidity, and temperature will be taken until these parameters stabilize over two measurements, which are interpreted to indicate aquifer water entering the casing. The well was allowed to stabilize to about 80%of its initial water level before sampling. Page 3 of 9