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1.i .� April 10, 1998 Page 2 Site Problem Assessement Old Delta-99 Sixth Street Project No. 98-4509-T, PHS-EHD Site Code 2183 Up to six exploratory borings will be drilled at the locations shown on Figure 1. The borings will be drilled under the approved PHS-EHD permits. Drilling and well installation permits will be secured prior to doing the field work. The boreholes will be drilled with hand auger tools and truck mounted hollowstem auger drilling equipment. All drilling equipment and sampling tools will be cleaned prior to arriving, and before leaving the site. The augers will be advanced to the desired sampling depth interval, and a drive split spoon sampler will be driven ahead of the drill bit. Each borehole will be advanced into the aquifer a orarily cased. he water entering the borehole will be sampled using a clean bailer, and carefully pour in o the appropriate laboratory prepared container with minimum cavitation. The sampler will then be retrieved and dissembled, and the soil filled brass liner will be sealed with TeflonS paper and plastic endcaps, labeled, logged onto chain-of-custody forms and place in a chilled ice chest. The boreholes will be logged using the Unified Soil Classification System under the supervision of a registered geologist. Additional lithologic information will be collected to describe the subsurface geology. The samples will be collected at five-foot intervals, at intervals of obvious contamination and at stratigraphic features of interest. Upon completion of the borehole drilling and collection of information, the boreholes not selected for monitoring well installation will be backfilled with grout, placed from the bottom to top of the borehole leaving room to replace asphalt or concrete surfaces as required. Monitoring Well Installation After the locations of the groundwater monitoring wells are selected from the borings noted above the following well installation procedure will be used. Monitoring wells will be installed at the locations selected and will be cased with Sch. 40 PVC casing, threaded together; glues will not be used. The slotted interval will be a 0.020 inch slot and the annular space around the slots will be backfilled with a 2/12 size sand. Previous experience has shown this to be a reliable well design in fine grained and stratified depositional environments. Final well design will be modified to the site specific conditions encountered in the borehole during drilling. Once the aquifer strata has been defined, the casing will be lowered to the bottom of the borehole, leaving a slotted interval above the occurrence of groundwater to observe for floating product. The sand pack will be placed to a point about two feet above the slots. A bentonite seal will be placed atop the sand pack, and a cement grout seal placed atop the bentonite using a tremie line, filling from the bottom to top of the borehole. A traffic rated well head access box and security device will complete the well. The installations will be done under the required PHS-EHD permits and sealing requirements. Well Head Survev All monitoring wells will be surveyed to mean sea level using a known datum. This will allow accurate measurements and groundwater gradient to be calculated. Monitoring Well Sampling and Development All monitoring wells will be developed to remove the drilling muck, grade the sand pack and provide a more complete hydraulic connection to the aquifer. The well volume will be calculated and a number of those volumes will be removed until the water becomes clear and the amount of sand pumped is minimal. The well will be allowed to recover for at least 72 hours prior to sampling. A log of the development will be kept for each well.