GENERAL55781

• Permit No: C1981016
• IBM Index Class Name: General Documents
• Doc Date: 3/14/1983
• Doc Name: PROPOSED DECISION AND FINDINGS OF COMPLIANCE
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

-30-
The current Bear and Mt. Gunnison mining operations are adjacent to
Sylvester Gulch and Lone Pine Gulch, which are ephemeral streams flowing
directly to the North Fork. Characteristics of the drainages are given
in Table 5. No flow was observed in Lone Pine Gulch for a period of
several years. Sylvester Gulch is an ephemeral stream and has a drainage
area of 4.25 square miles. As indicated on Table 5, the hydrologic yield
of Sylvester Gulch is low compared to the other watersheds. This is due
to the fact that it drains an area which is lower in elevation and which
has gentler slopes.
The Mt. Gunnison life-of-mine area is drained by five tributaries to
Minnesota Creek. East Fork, Horse Creek, South Prong, Lick Creek, and
Dry Fork drain into Minnesota Creek from areas to be undermined by the
Mt. Gunnison No. 1 Mine. Their slopes are generally steeper and the
watersheds are at higher elevations than those tributary to the North
Fork. Based upon streamflows measured in water year 1978, the water
yields from these drainages are nearly an order of magnitude greater than
that from Sylvester Gulch.
Two reservoirs are located within the hlinnesota Creek drainage.
I~innesota Reservoir is located on Dry Fork. It has a decreed capacity of
1,285 acre-feet. The actual capacity may be closer to 500 acre-feet,
however. Beaver Reservoir is located on the East Fork of Minnesota Creek
and has an absolute decreed capacity of 1,620 acre-feet and a conditional
decree of 522 acre-feet. Both reservoirs store water for irrigation
purposes and are filled during spring runoff. They are usually drained
by late August or early September.
Water quality data has been collected at several sites throughout the
hlinnesota CreeK drainage. The data indicate that these waters are of a
calcium bicarbonate type with relatively low total dissolved solids
concentration.
There are over 100 springs located throughout the Mt. Gunnison
life-of-mine area. Measurements indicate that spring flows generally
decrease from a high in the early summer to a low in the fall. A number
of the springs are ephemeral, indicating that their sources are small
localizes aquifers (i.e. landslide deposits, colluvium, lenticular
sandstones, etc.). There are a total of 13 decreed spring water rights
on or near the Mt. Gunnison permit area.
Precipitation and kunoff
Only two precipitation stations exist for the watershed; one at Paonia
and one at Wilcox Ranch. Since these are located near the North Fork of
the Gunnison River, they may not be representative of the total
watershed. Isoliyetal lines can be used to show average precipitation
that falls on the watershed. Figure 5 represents mean annual
precipitation and Figure ti illustrates May to September precipitation of
the years 1931 to 1960. All values were obtained from maps drawn by the
U.S. Weather Bureau. Table 6 summarizes precipitaion data for both the
north and south sections of the watershed. Comparing these isohyetal
maps with Figure 7 shows that precipitation patterns are strongly
influenced by topography.