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w POM Bic�si ste n15 Page 15 August 10, 1985 Job No. 211-71-6 _ After the screened portion of the well casing was backfilled with filter sand, the hole was sealed from possible surface water contamination with a 2-foot thick bentonite 1'lug and then backfilled to within a few inches of the surface with cement grout containing about 5 percent bentonite. The grouting of the wells was witnessed by a representative of the County of San Joaquin Local Health District. Monitoring weli;m—w 15 thrw,gh MW-25 were finished with watertight, security traffic boxes and locking steel cc-ers set in concrete or lacking well caps. The traffic boxes were typica IIy set about an inch above the existing ground surface Io help divert surface water away from the well. Each weli ;s equipped with a watertight cap. Well Development and Water Sam lin The monitoring wets(2 inch in diameter)were developed by using a 1.7-inch O.D.stainless steel bailer to surge the water around the screened interval and remove fine particles from the vicinity of the screen casing. The water was purged from the wells until the water was relatively free of turbidity. All well development equipment was steam-cleaned between wells. The water obtained . from well development was placed in ]wf-.eled 55-9allor, drums for temporary storage or-site. Prior to purging, each well was measured using an.interface probe and then sampled with a clear teflon bailer in order to • observe the possible presence of floating hydrocarbons. The welts were purged using a 1.7-inch O.D. stainless steel ba;'er until pH and conductivity measurements p stabilized. This typically resnIted in the removal of 3 to 5 welt volumes of water. Prior to each sampling the bailer was washed with acetone or methanol,and then a triso(4ium phosphate soNtion, and finally rinsed with potable water. New bailer line was used for each sampling. Samples recovered from each well were decanted into two appropriately prepared 40-m! vol,tie organic analysis(VOA) bottles. Care was taken to avoid the presence of a headspace:n any of the sample bottles. The sample bottles were immediately plzced in an ice chest and maintained at 4°C for delivery to the State of California licensed Trace Analytical laboratory(Hayward). Routine chain- of-custody procedures were employed. Groun3-Wr.ter Gradient Determination 1 The most recent static water leve!elevations from the monitoring wells were obtained an Jure 19, 1989. Top of casing elevations and ground surface elevations were surveyed (to the nearest 0.01 foot) for MW-1 through MVI--25 by Liu Pont Biosystems. The datum survey used was a City of Lodi brass disc benchmark(51.70 feet MSL)located on the curb of South Cheroke..e bane,near the southwest corner of the property(see the Site Pin,Figure 2).. The depth to water was measured - using a Solinst electric immersion probe and/or an interface probe. i