ARCHIVED REPORTS_XR0002376 - Laserfiche WebLink

Home Browse Search

Wright performed a soil and groundwater investigation both in the vicinity of the former tanks and in the assumed downgradient direction (see Wright report dated April 21, 2000) That study revealed low concentrations of apparently degraded petroleum contaminants near the former tank pits, however, an elevated dissolved contammant concentration was observed at exploratory Bonng Three (B-3) After a review of this report, the PHS EHD has required installation of at least one groundwater monitoring well at the B-3 location Field Methods E�plorat=Drilling and Sam�g One exploratory boring was drilled at the site (see Figure 1) The boring was positioned at the Boring B-3 location, and adjusted as required given utility proximity Drilling and well installation permits were secured from the PHS EHD, and all utilities were cleared prior to doing the field work The boring was advanced to define the uppermost water bearing strata as in the previous borings, and advanced to the contact of the underlying local confining strata immediately below the uppermost water bearing strata The borehole was drilled with truck mounted hollowstem auger drilling equipment All drilling equipment and sampling tools were cleaned prior to arriving, and before leaving the site The augers were advanced to the desired sampling depth interval, and a drive split spoon sampler was driven ahead of the drill bit The sampler was retrieved and dissembled, and the soil filled brass liners were opened and logged The borehole was logged using the Unified Soil Classification System under the supervision of a registered geologist Additional hthologic information was collected to describe the subsurface geology Upon completion of the borehole drilling and information collection, one monitoring well was installed in the borehole Monitgang Well I,.n514llatnon One monitoring well was installed using Sch 40 PVC casing, threaded together, glues were not be used The slotted interval used a 0 020 inch slot and the annular space around the slots was backfilled with a 2112 size sand Previous experience has shown this to be a reliable well design in fine grained and stratified depositional environments The final well design was modified to the site specific conditions encountered in the borehole during drilling Once the aquifer strata interval was defined, the casing was lowered to the bottom of the borehole, leaving a slotted interval above the occurrence of groundwater to observe for floating product The sand pack was placed to a point about two feet above the slots The sandpack was surged to emplace the sandpack at the desired location prior to bentonite placement A bentonite seal was placed atop the sand pack, and a cement grout seal placed atop the bentonite using a trerrue line, filling from the bottom to top of the borehole A traffic rated well head access box and security device completed the wellhead Monitonng Well Sam�li g and Development The monitoring well was developed to remove the drilling muck, grade the sand pack and provide a more complete hydraulic connection to the aquifer A well development log was kept of the well volumes removed until the water cleared and the amount of sand pumped was minimal The well was allowed to recover for at least 72 hours prior to sampling Well Casing Elevation Survey The monitoring well casing elevation was surveyed by Triple "F' Engineering to a known elevation datum so accurate groundwater elevations and flow gradient can be measured Page 2