2008-01-23_REVISION - M2003016

• Permit No: M2003016
• IBM Index Class Name: REVISION
• Doc Date: 1/23/2008
• Doc Name: Surety reduction request
• From: SW Chambers LLC
• To: DRMS
• Type & Sequence: SR1
• Email Name: ACS
• Media Type: D
• Archive: No

~. i
CIVIL RES~URCES,LLC
ENGINEERS 8. PLANNERS
March 9, 2007
Mr. Carl Mount
Division of Reclamation ,Mines, and Safety
1313 Sherman Street, Room 215
Denver, Colorado 80203
RE: SW Chambers, LLC, Permit No. M-2003.016 - Heit Pit Resource; Technical Revision 3 -
Underdrain Design Memo to Prevent Groundwater "Mounding"
Dear Mr. Mount:
In accordance with Permit M-2003-016, SW Chambers, LLC, is submitting the following: l) $188 application
fee; 2) Technical Revision #3 (TR-3) underdrain Design Memo; and 3) construction drawings for the
proposed Heit Pit underdrain.
This memo is based on prior work and submittals by Wright Water Engineers (WWE) and requirements per
the DBMS:
1, Groundwater;°~vi~luation For Proposed Heit Aggregate Operation, Weld County, Colorado,
Prevention Plan, dated,March~2003: (WWE)
2. Groundwafer Monitoring for Hert Aggregate-Resource Operation, Weld County, Aquatic and
Wetland Nursery'and Coyle. Properties, dated.July 3?gi)3 (WIIV~)
3. Heit Pit Groundwater Monitoring Data, Larch 2004 theou~h January 2007.
4. Monitoring Well boring Logs from March 2, 3, aril 11, 2004. ~(WWE)
5. Request For Technical Revision for Mine Permit #M2003-016, SW, ..;Chambers, LLC,, dated
September 14, 2005. (WWE).
Slurry Wall -Groundwater Clislope Parameters
The Heit Pit area prevailing groundwater.flowdirection isnorth-northeast~tiiward the South Platte River.
Locally the groundwater levels and flow directions are also impacted by;1) the„groundwater °shadow effect"
from the slurry walled Koenig Pit immediately to the south of Weld County.Rtii~d"(WCR) 20 and the
proposed Heit Pit, and 2) the Little Dry Creek drainage which roughly parallels the west side of the Heit Pit
at distances ranging from 230 feet to 450 feet to the low flow channel.
The slurry wall around the Heit Pit could cause "mounding° of groundwater on the upstream side of the
proposed slurry wall based on modeling completed as part of TR-2, dated September 14, 2005, by Wright
Water Engineers, as stated below.
°A potential impact to groundwater will have occurred when post-mining groundwater
monitoring data show: l) a change in the average (growing ornon-growing season)
groundwater by more than 2-feet, or 2) a change in three or more consecutive readings by
more than 3-feet compared to data taken the same time of year prior to mining."
Per TR-2, an uderdrain system will eliminate upstream mounding. The underdrain design installs a
perforated pipe within the overlapping zones of the permitted two foot rise of average groundwater elevation
for the growing and non-growing seasons. The capacity of each underdrain was sized to convey the
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