GENERAL50142

• Permit No: C1981038
• IBM Index Class Name: General Documents
• Doc Date: 7/15/1991
• Doc Name: ADDENDUM to FINDINGS OF COMPLIANCE FOR RN1
• From: For Alluvial Valley Floor
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

VI. ALLUVIAL VALLEY FLOORS (2.06.8. 4.24
The discussion of Alluvial Valley Floors can be found on pages 5-6, Section 2.06 of
Volume 1; in the AVF Appendix A, Volume 4 and in the Geo-Hydro Phase 2 studies.
Identification of Alluvial Valley Floors
The general azea in which the Orchard Valley Mine is situated contains several
deposits of alluvium. These alluvial deposits are derived from three sources: 1)
Flood-plain alluvium (Qal) along the North Fork of the Gnnn+~on River; 2) Valley-fill
deposits (Qvf) along a portion of Steven's Gulch; and 3) Alluvial gravel (Qag)
divided into three (3) age categories younger (Qagy) , middle (Qagm) and older
(Qago) . The valley 511 deposits aze located along the North Fork Valley side slopes.
Cyprus has identified alluvial/colluvial deposits in a second azea that is located along
Steven's Gulch in the W 1/2 NW 1/4 of Section l3, TL35, R92W. As identified in the
Phase 1 AVF Study, the area is approximately 20 acres in size and is composed of
valley-fill deposits (Qvf) . The mine has a well in this deposit that can pump 30, 000
GPD from the alluvium/colluvium. Depth to water varies from about 7 feet in May to
approximately 36 feet in February. The area is high and isolated, but has been used
for pasture-hay meadow. The azea is not flood irrigated, has not been flood
irrigated, and is too high in elevation to be flood irrigated (at this elevation, the
growing season is too short for the normal flood irrigated crops). Subirrigation is
limited to azeas along the stream channel itself. The azea is determined not to be an
Alluvial Valley Floor based on its lack of flood irrigation potential and lack of
significant subirrigation.
An additional azea along Steven's Gulch which lies within and to the south of the
mine permit azea, contains areas of alluvium. This azea includes alluvial gravel
deposits in Sections 24 and 25 (T735 , R92w) and the W 1/2 of Section 30 (TL35,
R91W) . Four sepazate deposits have been identified within this azea, as shown on
Map No. 2-2. The two lazger deposits, labeled Qagy and Qago, may meet the
geomorphic criteria of Alluvial Valley Floors, but do not meet the water availability
criteria for either flood irrigation or subirrigation. Due to the steep slopes, rocky
surface, and lack of sufficient water, these azeas can not be flood irrigated.
Regazding subirrigation potential, the 5eld investigation to detect subirrigated
species along Steven's Gulch did not identify any such species within these azeas.
Vegetation suggests subirri.gation does occur along portions of Steven's Gulch, but
these species aze confined to the extreme channel bottom azeas. Hared upon this
information, these two azeas are found not to meet the criteria for Alluvial Valley
Floors. These are older terraced deposits that have been dissected by stream
channels, such that the channels have completely cut through the deposit. These
areas aze found not to be Alluvial Valley Floors. The larger of the two azeas totals
ll.5 acres, but the residential access road that passes over the area reduces the
acreage to below 10 acres.
A third azea identified as having alluvial deposits is located along the North Fork of
the Gunnison River. These consist of floodplain and low terrace alluvial deposits and
aze identified as (Al) on Plate No. 2. This azea meets the geologic and hydrologic
criteria of an Alluvial Valley Floor in having unconsolidated stream-laid deposits with
water sufficient to sustain agriculture. Portions of the loadout facility and rail spur
have been part of the mine plan before August 3, 1977 therefore their construction
is grandfathered (see Alluvial Valley Floor Findings that follow) .