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C-PIT Hydrogeologic Investigations Technical Revision No. S 2: Site Analysis and Field Activities Mining Permit M-1977-208 2.3 Instrumentation of C-Pit and Monitoring Well CEM-001 On Maxch 9, 2007, leased In-Situ Multiparameter Troll 9500 data logger units were installed in both C-Pi[ and monitoring well CEM-001. The C-Pit unit was deployed below the water suxface in a 40-foot length of vertical PVC-plastic well casing with a 10-Foot screen, which was leaned against the northeast highwall of the pit. This arrangement provided access fox downloading data and performing maintenance and calibration of the recording unit. The data logger in monitoring well CEM-001 was installed after the well had been purged and sampling on March 9. CEM-001 is a 141.5-foot deep well located 800 feet southeast of the eastern wall of C-Pit. See Figure 2 and the cross-section shown on Figure 3. The 40-foot screen of CEM-001 runs approximately 10 feet above and below the Foxt Hays Limestone contacts with the adjacent shale units. The recording device was initially installed in the upper end of the empty well bore. The unit xecoxded the post-sampling water level in CEM-001 as it recovered and reached the elevation of the installed logger. It took another approximately 68 hours fox the water to cease rising as it reached an equilibrium elevation. This is an indication of the relatively low permeability of the bedrock monitored by CEM-001. The In-Situ Multiparameter Troll 9500 units recorded static water head, temperature, pH, conductivity, dissolved oxygen, and oxidation/reduction potential (OItP). Initial data collected by these units were used in the planning of the TR-8 hydrogeological investigations. The pit water elevation in C-Pit and water level in well CEM-001 were surveyed and xecoxded to deternune the initial conditions prior to Filling in the C-Pit ' water body. On March 17, 2007, the water elevation in C-Pit was 5.33 Eeet higher than the elevation measured on January 27, 2007. The January 2007 elevation 0195.13 above mean sea level, ox amsl) had been the highest elevation of C-Pit water observed by Brown and Caldwell since September 2005. The previously 1 recorded peak water elevation of 5192.7 amsl was observed on March 18, 2006, prior to the Apri12006 start up of pumping C-Pit water to the spray tower through summer 2006. CEMEX commenced pushing stockpiled fill material into the C-Pit water body on or around March 16, 2007. The Filling process displaced the water in C-Pit, as shown by the data collected by the installed data logger. Approximately 500,000 cubic yards of fill were placed in C-Pit from mid-Maxch until May 10, 2007, reducing the 4.3 acres of exposed water suxface down to less than one acre while raising the water level. Brown and I Caldwell and CEMEX staff regularly downloaded the accumulated data from the loggers in C-Pit and CEM- 001 during this time period. As the water level rose in C-Pit during the Filling process, an additional 10-foot length of PVC casing was added to the riser that housed the C-Pit data logger. The continuing increase of the ' C-Pit water surface elevation eventually made it necessary to move the data logger to another location to make it more accessible. On May 3, 2007, the battery that powered the data logger in CEM-001 failed. This lead to a disruption in ' data collection in this well until May 16, 2007 when the batteries were replaced in both units. On June 14, 2007, the two leased 5-channel data loggers were removed from C-Pit and CEM-001 and remmed to the vendor. Asingle-channel water pressure head recorder was reinstalled in C-Pit to continue monitoring water ~ elevation at that location, and remains there at present. 2.4 Piezometer and Well Installation Six piezometexs (P-001, P-002, P-003, P-004, P-005, and P-006) were installed at the Site to the west of C-Pit during April 2007. piezometexs P-001, P-002 and P-003 are located between the Boulder Feeder Canal and the Swede Ditch. See Figure 2. 2-7 Use of contents on this sheet is sublecuo the limitations spectlled et the end of Ahis document ABCDEN021projects\Dela\GEMGemealTR-8\Reporeng\CEMEX Repotl 0&31-O7.doc