2011-02-24_PERMIT FILE - M2010049 ‎(2)‎

• Permit No: M2010049
• IBM Index Class Name: PERMIT FILE
• Doc Date: 2/24/2011
• Doc Name: Reply to Preliminary Adequacy Review
• From: Varra Companies, Inc.
• To: DRMS
• Email Name: MAC
• Media Type: D
• Archive: No

Varra Companies, Inc.
Office of Special Projects
8120 Gage Street Frederick, Colorado 80516 Telephone [phone] Fax[phone]
to the elevation of any proposed spillways and lake shore embankments. The
flood control plan should address mitigation measures including pit side
armoring, river site armoring and outflow channels, or other appropriate
measures.
The potential for berms around gravel pits to be damaged during flooding is
discussed in detail in the 1987 Urban Drainage and Flood Control District
(UDFCD) Publication "Technical Review Guidelines for Gravel Mining Activities
within or Adjacent to 100-year Floodplains." Strips of native ground or
constructed fill between the stream and the gravel pit, and generally aligned
with the flow direction of the stream are referred to in the UDFCD document as
riverside berms. Strips of native ground or constructed fill between the adjacent
pits and generally perpendicular to the stream are referred to as lateral berms.
The Western Sugar Reclamation Land Development Project is located outside of
the political boundaries of the UDFCD, but technical floodplain factors that led to
the formulation of the UDFCD guidance document still apply.
The Division has concerns about the lateral berms and riverside berms. There
is the potential the berms may erode and become unstable during a flood. If the
pits are excavated and dewatered, or if the pits are reclaimed but the water
levels in the ponds are low, floodwaters spilling into the pits could result in
erosion, rapid down-cutting, and potentially failure of the berms with exposure
and damage to the gas pipelines which are located within the lateral berms on
the site. For this reason, the Division will require further analysis of the
proposed riverside and lateral berms and a design mitigation that will ensure
stability during a 100 year flood event.
Alternatively, the Applicant may mine to the berm crest widths (100 ft.)
proposed in their permit application for the riverside berm with installation of
any of the numerous mitigation designs included in the UDFCD guidance
document. To mine within 100 feet of the river, reinforced berm cores, armored
side channel spillways, or bank stabilization methods are required by the
standard designs in order to leave a lateral berm of 100 feet crest width.
Following the UDFCD guidelines would save the Applicant the time and expense
involved with site specific hydrologic investigations and designs. Please provide
the Division with a comprehensive flood analysis and flood control plan to justify
the proposed setback distance from the river and the widths of the lateral and
riverside berms, or revise the Reclamation Plan to incorporate the guidelines in
the UDFCD document.
Varra Companies, Inc. correspondence of 23 February 2011 to the Colorado Office of Mined Land Reclamation 7
(OMLR) in reply to OMLR correspondence of 4 October 2010 - Western Sugar Reclamation Land
Development Project- M-2010-049.