PERMFILE121731

• Permit No: M2000156
• IBM Index Class Name: Permit File
• Doc Date: 3/15/2001
• Doc Name: ADEQUACY REVIEW COULSON EXCAVATING CO INC BONSER PIT FN M-2000-156
• From: DMG
• To: COULSON EXCAVATING CO INC
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
131 }Sherman SL, Room '_ I S
Denver, Colorado 80203
Phone. [phone]
FAS: 1303) 83'8106
DATE: March 13, 2001
~~
DIVISION OF
MINERALS
GEOLOGY
R E C L A M A T I O N
MINING•SAf ET7
TO: Gregg Squire RIB Owem
Grnernor

FROM:
Allen Sorenson ~ GrrR E. lValrhrr
E.ecun.r D~rrao.
Michael B. EnnF

RE:
Reclamation Permit Application to Construct a Lined Gravel Pit, Drvmm~ D~recior
Coulson Excavating Company, Inc., Bonser Pit, File No. M-2000-156
I have reviewed the above referenced gravel pit application and have identified the following issues to
be addressed prior to recommending approval of the proposed plan for reclamation. The scope of this
review is limited to consideration of hydrologic and pit liner installation issues.
1. Possible Flooding_Imnacts
The proposed operation would mine gravel within approximately 100 feet of the Big Thompson River
and at approximately 1300 feet upstream of the I-25 Bridge. The Division is concerned with the
potential for off-site impacts if the river down cuts the pit banks during a flood and temporarily or
permanently alters the course of the river's mainstem. Down cutting that may result if the proposed
pit captures the river could result in both upstream and downstream impacts, possibly including
impacts to the 1-25 Bridge abutments. The Division suggests that a review of the Flood Insurance
Rate Maps (FIRM) for the pit location may provide useful information on the potential for flooding
impacts.
• Where are the floodplain and floodway boundaries in the area of the proposed pit?
• What is the anticipated depth, velocity, and flow direction of flood waters relative to the pit?
It maybe that the pit area becomes a placid backwater during a flood due to channel constrictions at
the I-25 crossing. This condition would be much less of a concern than if the pit area is subject to
deep, high velocity flooding, in which case the Applicant may consider installation of spillways to
pass floodwaters safely through the pit, or may consider increasing the mining setback distance from
the river. These types of mitigation measures are described in Urban Drainage and Flood Control
District publication "Technical Review Guidelines for Gravel Mining Activities," (December 1987)
and in the Division of Minerals and Geology Publication "In-Stream Aggregate Extraction and
Reclamation Guidance Document;' (August 1998). Flooding mitigation measures, if needed, may
also be designed based on the results of site specific floodplain modeling studies that consider the
location and shape of the proposed pit. The documents cited above are available for purchase from