2007-06-29_PERMIT FILE - C1981022A ‎(2)‎

• Permit No: C1981022A
• IBM Index Class Name: Permit File
• Doc Date: 6/29/2007
• Section_Exhibit Name: 2.05 Operation and Reclamation Plans
• Media Type: D
• Archive: Yes

Sctzurt ~ 2.05.6
Detailed discussions of specific potential impacts and proposed control and mitigation measures are
. presented in the following sections.
Overview of Hydrologic Environment -The hydrologic environment in the nwre permit and
adjacent areas is described and charatterized in some detail in Sections 2.04.5, General Description of
Geology and Hydrology, and 2.04.7, Hydrologic Description. Relevant hydrologic features are
mapped on the Regional Geology and Hydrology Map (Map 2.04-M2) and the Surface Water and
Ground Water Hydrology Maps (Maps 2.04•M3 and M4). The following summary statements,
condensed from Sections 2.04.5 and 2.04.7, aze provided as a framework for understanding the
discussion of hydrologic consequences and protection measures.
The semi-arid climate of this area limiu overall precipitation and there is a significant variation in
precipitation between the lowland valley areas to the west (approximately 5 inches per yeaz) and the
high mountain peaks to the east (approximately 20 inches per year). Average annual precipitation in
the immediate mine vicinity is approximately 17 inches per yEaz. Because it is relatively dry, most of
the precipitation that does «cur infiltrates quickly into the relatively coarse, unconsohdated surface
materials and is rapidly lost to evaporation and transpiration. Very little runoff «ctus except doting
spring snowmelt and major thunderstorm events, and the limited runoff that does «cur resulu in
brief, high vel«ity flows m the smaller drainages due to the steep terrain.
The North Fork of the Gunnison River h pan of the larger Colorado River system and begins just
downstream of Paotria Reservoir where Anthracite Creek joins Muddy Creek The mine permit area
and the Town of Somerset are on the north side of the river approximately 5 miles downstream from
this point. The Noah Fork flows to the southwest approximately 23 miles from the Town of
Somerset, where it joins the Gunnison River west of the Town o{ Hotchkiss. From this confluence,
the Gunnison River flows approxitna[ely 70 miles to the northwest joining the Colorado River near
• the Town of Fruita. The North Fork of the Gunnison River exhibiu a perennial flow pattern, with
flows varying due [o upstream control of discharge from Paotria Reservoir, seasonal climatic Factors,
and extensive downstream agricultural withdrawals of water for irrigation.
The watershed of the North Fork is generally charatterized by relatively steep mountain slopes and
high mountain parks which are intersected by numerous steep, narrow, drainage valleys. Smaller area
drainages typically demonstrate an ephemeral flow panem, flowing only in response to spring
snowmelt or major thunderstomrs. larger drainages may drain significant sub-watershed areas and
carry intemtittent or perennial flows. The valley ass«iated with the North Fork u generally narrow
and v-shaped with a broad, deeply incised flow channel and limited floodp]ain. Relatively thick
deposits of coarse alluvial/colluvial material occur along the ntatgins of the narrow floodplain as
remnant terraces or pediments ass«iated with previotss river levek as the river cut iu way downward.
As the Nonh Fork flows to the west, the valley widens and the steep mountains traruition into high
mesas with a progression of narrow ridges and steep drainages on their flanks.
Surface water quality is generally fair to good with a calciturrbicarbonate/sulfate chemistry, neutral to
slightly alltaline pH, and relatively low dissolved solids. Natural suspended solids levels can be high,
particularly during snowmelt runoff and major thunderstorm evenu, due to the steep tersain and
relatively high runoff and flow velocities. Relatively high sediment loads often accompany high flow
ve]«ities, In addition, suspended solids levels in the North Fork are directlyinfluenced by discharges
from Paonia Reservoir, upstream Paonia Reservoir was constructed primarily for irrigation storage,
but also acts to reduce [he extremely high natural sediment loads in Muddy Creek Discharges from
Paonia Reservoir may carry elevated levek of suspended solids depending on time of yrar and
discharge rate.
The intermittent high-vel«ity flows limit sediment deposition in the upper reaches of the drainages
but often result in significant sediment deposition in lower valley areas to the west where flow
gradienu flanen. Dissolved metals concentrations are characteristically low but total metak
concentrations can be higher and are generally ass«iated with the elevated suspended solids. Water
PR04 2.05-74 Revised August 2000