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OMAN ., SAE ASSESSMENT WMK PLAN Shell Station 420 W. Kettleillan Lane Lodi, California Aegis Project No. 89-013 page 10 4.1.3 Soil said le screenin : Portable Photoionization Detector Method Soil samples placed in sealed bags will be allowed to outgas for approximately two minutes. The head space of the soil sample will be screened with a portable ionization detector (HNu) calibrated to Methane for direct reading in part per million volume (ppmv) . The aluminum probe tip will be inserted into the sample bag headspace and the highest level indicated will be recorded. 4.2 Ground Water, Monitoring Wells Groundwater monitoring wells will be constructed of 4-inch diameter PVC schedule #40 pipe. Machine slotted screen will extend from a screw on cap at total depth to 10 ,teet above the water table; :a: total: of,20 feet-of 'slotted ..screen. Schedule 1140 PVC blank pipe.will extend from ..the.screened interval to a traffic grade monument box located at ground level. Sand filter l pack will extend from total depth to two feet above the top of ~� the screened interval. Two feet of bentonite pellets will be emplaced above the sand filter pack to form a sanitary seal. The . pellets will be wetted and allowed to hydrate. cement and Bentonite grout will extend from the bentonite seal to land f f surface. The well head will be completed with a lockable, expansive bung. The locking well cap will be secured in a traffic grade manhole box flush-mounted in concrete. The well ' head will be clearly labeled with well number, elevation, and r measuring point. A typical groundwater monitoring well is :shown in figure S. 4.2.3 Monitoring well Gravel Pack and Blot sizeSelection. The. size of the gravel pack that will be placed adjacent to the well screen will be determined by the project manager, based on i an estimation of tha distribution of grain size in the formation E Which :is likely to be encountered within the uppermost saturated zone at the site. Available geologic information will be utilized in the sele+:Lion of the grain size. The gravel pack will be selected such that it will permit the development of a � . zone ofhigher hydraulic conductivity ad,'..t=ent to the well screen but will not"•allow piping of the finer-grained formation into the well 'bore. The slot size_ of the well.--screen_wa 11-be-selecte3 ------- -. -- such-that'.Y.t-will_retain a minimum of 95$ of the gravel pack -- - ------ - — ---- -- material. Slotte3 ;screen of .010-inch -width and filter pack sand ~I� of, Lone-Star designation 0/30 is projected to be emplaced in the : r.E