SITE INFORMATION AND CORRESPONDENCE FILE 1

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08/24/2000 16:35 2095385` GEOLOGICAL TECHI�3 PAGE 07 C�eolagical Zecfinirs 2nc. Page 4 Valentine(Castle Motors) Vertical Def. WP August 23,2000 Ethers Detection Limits: _8020 8260 EDB 8260 80151x1 Water(�tg/L) Y0.3 T.3 20 2.3 Monitoring Well Construction As an option, we propose to install a deep, discretely screened monitoring well into this borehole. The depth of the screened interval and exact construction of the well would be determined in the field after the geology has been investigated and in consultation with Mr. Jeff Wong of San Joaquin County and Geological Technics personnel. A possible construction of this well is described below. However, it is recognized that information obtained during drilling may alter the construction. The deep monitoring well will be constructed using a pre-packed filter assembly in a 2.0-inch diameter PVC casing with flush threads and a screened section of 2.5-5 foot. Prior to installing the two to three foot weighted bentonite pellet seal, clean tap water is pumped down the casing and up the borehole to remove the drilling mud. The bentonite seal is then added and allowed to hydrate for a minimum of '/2 hour before pumping the neat cement grout(augmented with<4%bentonite)via a tremie tube. The final construction of the deeper well will be determined in the field depending on the geology encountered. See Figure 3 for a schematic of monitoring well construction. A table showing possible construction is included below, Well o. ra. D Screen of Fi1tcr Iac cans. Seal I Grout Seat re-pace i ter -sur ace After the well sealing materials have set (>24 hours) the wells will be developed (using mechanical surging and pumping methods) until a clear stream of water is obtained. The well will be purged and groundwater samples collected no sooner than 48 hours after well development. All development and purge water will be containerized in 55-gallon DOT approved containers and stored on site until their disposition can be arranged_ A licensed land surveyor will survey the top of casing measuring point for the well into the current elevation plane established for the site. 2.4 Groundwater Sampling Procedure The groundwater in the new wells will be sampled no sooner than 48 hours after Well development and from there after on a quarterly basis. The following is a procedure for the sampling of groundwater from the well: Before sampling is attempted, the wells that are screened across the water table will be sounded for depth to water and then a clear disposable bailer will be used to determine if floating product is present. The wells will be purged of at least 3 well volumes of stagnant water using either a submersible pump or a stainless steel bailer. Purging will continue until the temperature, conductivity, and pH of the groundwater has stabilized (<10% variation