2006-10-19_REVISION - M1995035

• Permit No: M1995035
• IBM Index Class Name: Revision
• Doc Date: 10/19/2006
• Doc Name: Response to Inspection report dated March 28 2006
• From: Applegate Group Inc
• To: DRMS
• Type & Sequence: TR1
• Media Type: D
• Archive: No

Ms. Erica Crosby.
RE: Connell Resources, Inc. Wellington Downs Pit Technical Revision -_
October 13, 2006
Page 2 of 4
The State Pit site is located north of the- Wellington Downs site and Weitzel Pit groundwater '
lakes. A small portion of the State Pit site (approximately 3. acres) was reclaimed in -2005 and
eazly 2006 with abelow-grade clay liner and additional backfill material. During the 2005 and
eazly 2006 reclamation activities, pit dewatering flows from the State Pit were discharged, with
landowner permission, into the southeast groundwater lake on the Weitzel Pit site.
Local groundwater conditions at the three sites (State, Weitzel, and Wellington Downs) suggest
a flow. generally from the northwest to the southeast. Available published information (United
States Geological Survey Hydrologic Investigations Atlas 746B) suggests the groundwater
gradient across the site is approximately 0.003 (0.3 feet decline per 100 feet of horizontal
distance) from. northwest to southeast. The hydraulic conductivity for the aquifer was also
estimated from local, published pump-test data (Colorado Water Conservation Board Ground-
water Circular 11). Using the available data, estimated bulk hydraulic conductivity for the
alluvium is between 170 feeUday and 330 feetlday. This value is within the range of published
hydraulic conductivity values for unconsolidated clean to silty sands and gravels. In addition,
although specific measurements aze not available, published estimates of porosity for the alluvial
material in the saturated thickness (sand and gravel) range from 20 to 30 percent.
According to observations during mining, the saturated thickness of the alluvial aquifer is
generally less than 10 feet and varies with season. The normal water table ranges from 4 to
6 feet below the ground surface, but also varies with season. These observations aze consistent
with available .published information (United States Geological Survey Hydrologic
Investigations Atlas 746B).
The information collected suggests an alluvial groundwater system that has a relatively low
gradient and high transmissivity and porosity. Although specific modeling was not performed
for the groundwater conditions in this azea, Applegate Group, Inc. has been involved with
several modeling, investigations for mining and below-grade reservoir projects in the Cache la
Poudre River and South Platte River basins. These projects occurred in alluvial aquifer systems
with similaz groundwater conditions. Results have indicated that groundwater mounding and
shadowing is greatest immediately adjacent to azeas with sealed pits or compacted backfill.
Modeling has predicted mounding and shadowing around isolated sealed pits creating
approximately 2-foot differences in baseline groundwater table elevations, with~the affects
decreasing'rapidly with distance from the backfill.
Based on the site conditions and modeling results from similaz projects, it is not likely that the
liners and additional backfill used for reclamation of the mining sites will negatively affect the
sites or adjacent property owners. Potential increases in the groundwater table from mounding
affects would not likely expose groundwater at the normal ground level due to the estimated
baseline groundwater depth below the surface. Additionally, potential increases in water levels
of the Weitzel Pit groundwater lakes would most likely be temporary and seasonal and not likely
be distinguishable from normal seasonal fluctuations.
During the' Mazch 28, 2006 Division site inspection, water was observed flowing from the
southeast Weitzel Pit groundwater lake, over a low point in its southern bank, and onto the