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94128/1999 11:68 29983751%52 WRIGHT ENVIRONMENTAL PAGE 66 Engineered fill consisting of Class 11 base rack will be placed from 1.5 feet bp to .5 feat bgs pnor to restoring the concrete paved surface.its the area of excavating and surrounding areas by excavation equipment. field Activities-Exploratory Soil Boring and Well Construction One exploratory soil boring will be advanced_ to shallow occur=g groundwater for monitoring well MW-1 replacement installation (see Figure 1). The boring will be drilled vdth a hollowstem flight auger dnll rig under approved permits of the PHS-EHD. The boring,%vill be sampled to collect lithologic data;, for aquifer contact identiScat k m and screen placement! The i drilling and sampling will be done using the attached Wnght soil and groundwater sampling protocols. All drilling and litltologic logging wdl be done under the supervision of a certified ertgawering geologist using the Unified Soil Classification System and geologic observati ms. Keplacement Monitoring Well Installation One monitoring well will be installed using the attached Wright Protocol. The well vrM be cased with Sch 40 FVC casing, threaded together; glues will not be used. the slotted it terval will be a 0.020 inch slot and the annular space around the slots will be backfilled with x;'2/12 size sand. Previous experience has shown this to be a reliable well design in fine V arced and/or stratified depositional envirvranents. ,Final well design will be modified to tt 4 site specific conditions encountered in the borehole during drilling. Once the aquifer stra is 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 v1 be placed to a point about two feet above the top of the slots. A bentonite semi will be place'liatop the sand pack, and a cement grout seal placed atop the bentonite using a.tremie line, Cluing from the bottom to top of the borehole. A traffic rated well head access box and security device will complete the well Well Head Survev All wells will be surveyed to mean sea level using the site datum. This will allow ac:urate I measurements and groundwater gradient to be calculated. Morntoring,Well Sampling and Development The monitoring well 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 A:ill be calculated and a number of those volumes will be removed until the water becomes cie.l and the amount of sand pumped is mammal '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 weal. Groundwater Samulirtg The monitoring well will be sampled_ A brief summary of the .procedures follows: :,'Each borehole will be advanced into the aquifer and temporarily cased. The water enterer g the borehole will be saaspled using a clean bailer; arid'carefully poured iiiio the apprapriatae laboratory prepared container with minimum cavitation. Each monitoring weEl will be purged using calculated well volumes based upon the depth to water in each casing. DejAh to groundwater measurements will be made to the nearest one-one hundredth of one foo¢; and also checked for the presence of separate phase product. As each purge volume is removed, meamurements of pH, electrical ,