ARCHIVED REPORTS_XR0010643 - Laserfiche WebLink

Home Browse Search

32 Drilling/Soil Sampling/Grab Groundwater Sampling • On December 5, 6, and 9, 1994, Spectrum Drilling of Stockton, California, drilled seven exploratory soil boreholes, B-1 through B-7, under the supervision of a Wright field geologist (Figure 2) The soil boreholes were drilled utilizing a truck-mounted drill ng equipped with an 8-inch hollow-stem auger to depths ranging from approximately 9 5 to 20 feet below ground surface (bgs) All sampling equipment lowered into the bore hole was cleaned between sampling events according to the Wright Soil Sampling Protocol (Appendix B) The field geologist maintained a log of the materials encountered during the drilling using the Unified Soil Classification System Soil from the boreholes was placed between plastic sheeting to await characterization for disposal Following the Wright Soil Sampling Protocol, soil samples were collected at approximately five- foot intervals and at noticeable lithologic changes using a 2 5 inch outside diameter (O D ) split- spoon sampler, lined with three 2-inch-diameter by 6-inch long brass sample tubes The sampler was driven 18 inches ahead of the augers at each sample point Soil samples were field screened with a Hanbv Test Kit and a combustible gas indicator, GasTech-Tank-Tector (CGI) Fourteen samples collected for laboratory analyses were sealed with Teflon, capped, labeled, placed on ice in an insulated container The samples were accompanied by a chain-of-custody document and delivered to a state-certified laboratory Reconnaissance (grab) groundwater samples were collected from boreholes B-3 and B-5 to determine placement of the groundwater monitoring wells The grab groundwater samples were collected by completing the borehole to approximately 15 to 2 feet into first encountered water The hollow-stem augers were pulled back up to allow flow of groundwater into the borehole A clean, disposable bailer was lo«Bred down each borehole to collect the samples The samples were labeled and placed on ice in an insulated container for 0delivery to a State-certified laboratory, accompanied b,, chain-of-custody documents Upon completion, boreholes B-1, 13-3, B-4, and B-5 were backfilled with a grout seal using the augers as tremie lines 33 Monitoring Well Installation After completion of drilling, soil boreholes B-2, B-6, and 13-7 were converted to groundwater monitoring wells MW-1, MW-2, and MW-3, respectively The monitoring wells were constructed of 2-inch diameter, schedule 40 PVC casing with flush threads, and 0 020-inch-slot well screen The well screens were approximately 10 to 13 feet in length, installed to depths ranging from 17 to 20 feet bgs A sand filter pack was placed around the well screen to a height of approximately 1 foot above the top of the screen The wells were completed with a 1-foot bentonite seal and a neat-cement seal to within 1-foot of the surface and then a wellhead was set in concrete to grade The wellhead was protected by a locking cap and a traffic-rated street box with a water-tight bolted lid Well construction details are presented on the Boring logs (Appendix C) The monitoring well seals were witnessed by a representative of the PHS/EHD 34 Monitoring Well Development The monitoring wells were developed on December 14, 1994 by Blaine Tech Services of San Jose, California, using the surge and purge method The field technician used a surge block to agitate and set the sand pack around the annulus of the well The fine-grained sediments were then removed by either hand bailing or mechanically pumping until the well water was visibly clear This technique provides an even sand pack and improves the hydraulic, conductivity between the well and the natural formation The development water was placed in Department of Transportation-approved 55-gallon drums and left onsite pending characterization for disposal