2003-03-03_HYDROLOGY - M2002004 - Laserfiche WebLink

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Memorandum to Paul Seby, Carolyn Burr February 7, 2003 Page 2 Therefore the wells must either be permitted or plugged and abandoned within one year of installation. The Dakota production well (DW -1) was drilled by Layne - Western using a reverse mud rotary drilling rig and a 17.5 -inch diameter drill bit. At the completion of drilling, geophysical surveys were conducted to more accurately determine the formation depths and identify the most porous sandy units for well screen placement. The Dakota Production Well was completed with 10 -inch inside diameter (ID) mild steel casing and stainless steel wire wrap well screen. The well screen was intermittently placed from 504 to 614 feet (90 feet of screen). A 20 -foot long sump (10 -inch ID) was attached to the base of the well screen. The annulus between the borehole wall and well screen was filled with 8 -16 mesh Colorado Silica Sand that extended from 50 above the well screen to the bottom of the well. The remainder of annulus was filled to the surface with neat cement. After the cement seal had cured, the well was developed for 24 hours using conventional airlifting techniques. The Dakota and Cheyenne monitor wells were installed to collect water level data during aquifer testing. The Cheyenne monitoring wells were installed by Layne - Western. Hier Drilling Co. of Castle Rock, Colorado installed the Dakota monitoring wells. The boreholes were advanced using a combination of air rotary and conventional mud rotary drilling techniques. The second Cheyenne monitoring well (CMW -2) was geophysically logged. The monitoring wells were completed with either 6 or 8 -inch ID mild steel casing that extended from the surface to the top of either the Dakota or Cheyenne aquifer. The casing was sealed in the borehole with neat cement. An open borehole then extended from the top of the sandstone into the top of the underlying formation. At the conclusion of drilling, the wells were developed using standard airlifting techniques. Geology A schematic of the geologic units encountered during drilling is presented in Attachment B. The Dakota aquifer was encountered from approximately 500 feet to 612 feet below ground surface. The aquifer consists of two fine- grained sandstones layers that were separated by approximately 50 feet of claystone. The total thickness of the sandstone layers was estimated to be 65 feet. The lower Dakota sandstone was underlain by the Kiowa Shale, which extended from approximately 612 feet to 666 feet below the ground surface. The Kiowa Shale was underlain by the Cheyenne Aquifer, which extended from approximately 666 to 800 feet. The Cheyenne Aquifer consisted fine- grained sandstones that were interbedded with claystone and siltstone lenses. The total sandstone thickness was estimated to be 106 feet. The Morrison Formation was encountered below the Cheyenne Aquifer. ;90066:2;