2012-04-30_HYDROLOGY - M1977208 (3)

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Limestone: Dark grayish brown (Munsell Color 10YR 4/2), moderately hard, platy, fossiliferous. The underlying Carlile Shale is described as follows: Sandy Shale: Very dark gray (Munsell Color Gley 1 3/), sandy, poor fissility, moderately hard, argillaceous, thin bedded, non calcareous, bordering on a very fine grained sandstone. For additional detail, the hand written log can be found in Attachment A to this report. Page3 of 4 `PACIFIC WESTERN TECHNOLOGIES, LTD. Well Construction Details: After the successful drilling of CEM -005 to 400 feet BGS, the details for the well construction were discussed first with Ingram drilling and then with the CEMEX Environmental Manager. It was desired by CEMEX that the well mimic, as closely as possible, previous well CEM -005. The goal was to have the screen fall into the Fort Hays Limestone and the underlying Carlile Shale Formation, with the goal of monitoring the groundwater that may be influenced by C -Pit. The total depth for the original compliance well, CEM -005 was 401 feet BGS, with the screened interval spanning from 388 feet to 398 feet BGS. The boring log from the previous contractor indicated the casing could not be placed to total depth, and showed a cobble symbol from 398 -401 feet BGS. It was presumed that the interval between 398 and 401 feet BGS was filled in with slough from the overlying lithology, that was caved in as the casing was run into the hole. For the replacement well, the 10 foot section of Schedule 80, 10 slot PVC screen was capped with a 6 -inch end cap. As a protective measure, 6 inches of filter pack sand was placed in the hole to provide a cushion layer on which the casing to sit. A PVC centralizer was added at the base of the screen, where the end cap was attached. The next centralizer was placed on the casing section 8 feet above the screen. Centralizers were placed every 20 feet up the hole at depths of 320 feet, 240 feet, 160 feet and 80 feet BGS. Upon placement of the casing to total depth, it was found that the casing could not be placed to total depth and that approximately 3 feet had caved in upon casing placement. This placed the new total depth at 397 feet BGS. With the 0.5 foot of cushion sand meant that the bottom of the hole was now at 396.5 feet. After subtracting 0.5 foot for the end cap, it meant that the screened interval would instead be from 386 -396 feet BGS. The corrective action of removing the casing, rewashing the hole and re- placing the casing was considered. Ingram indicated that they could do this but cautioned that the more you wash a shale hole and disturb with casing placement, the more friable the walls could become, making the cave -in worse, ultimately resulting in a lost hole. CEMEX was informed of the situation and agreed that placing the screened interval 2 feet higher than intended was acceptable, as long as the Fort Hays Limestone was still screened into the Carlile Shale. According to the well log, it would still be cased as desired and Ingram was directed to start with placement of the sand filter pack. The sand filter pack used 8/12 mesh sand. The previous well had sand placed from 378 to 388 feet BGS. Ingram indicated that, as a general practice, having only 10 feet above the screen was not advisable because this was not always enough to prevent grout intrusion into the screen. Ingram recommended a minimum of 20 feet of sand above a screen. Because the screened interval on the new well would be from 386 -396 feet BGS, 20 feet of sand would place the filter pack into the Smoky Hill Shale. Because monitoring the Smoky Hill Shale is not the intent of