PERMFILE134266

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: EXHIBIT 70 REFUSE PILE EXPANSION
• Media Type: D
• Archive: No

REFUSE PILE EXPANSION
~F
HLA personnel were onsite October 2 - 4, 1995, to
conduct the geologic engineering mapping of the
proposed RPE and [he proposed topsoil and subsoil
storage areas for materials removed during RPE
development activities. She area of primary focus
during the mapping investigation was the lower slope
of the Wes[ Flatiron, where the majority of the RPE
development is proposed. The generaleleva[ion(s)of
the slope is 6200 to 6400 feet MSL.
A geologic engineering map of the proposed RPE
area (see Figure J-1), showing landslides, hummocky
terrain, rockslides, and springs was developed during
this investigation. Surveyingwas not used during this
mapping effort, rather geomorpholoeic features were
located by compass, altimeter, and using power poles
and major topographic features as references. Field
map features were correlated to aerial photographs
and photogrammetric maps (Nichols & Associates,
1996).
5.3.3 Geologic/Hydrologic Features
The following sections provide a discussion of the
field mapping activities as shown on Figure J-l.
Relevant comments are made regarding preliminary
construction, development, and staging of the
proposed RPE.
5.3.3.1 North Side of Highway 133
The north side of Highway 133 was initially
proposed as a staging and storage area for subsoil and
topsoil materials removed prior to construction of the
RPE. The area originally determined to be
approximately 2.75 acres in size, is bordered by the
North Fork of the Gunnison River to the north, and
Highway 133 to [he south. The location is relatively
flat with an overhead power line oriented parallel to
the highway which will be avoided during
construction.
Geologic features identified in this area included a
shallow soil failure I'_'" to 18" in depth associated
with a steep slope located on the western edee of the
s[agine and storage area. This soil failure will not
affect or be affected by the soil stockpile operations.
The lamest hydrologic feature in this area is the North
.;~ Fork of the Gunnison River. Field investigation of
the river embankments revealed a 15 to 20 foot high,
smooth, but steep transition between the bench and
the active river. No undercuttingor hone}•combingof
the river embankments was apparent. Two minor
ephemeral drainages were also identified in this area
and will be avoided.
5.3.3.2 Sylvester Gulch Corridor
The area identified as the Sylvester Gulch corridor
extends from the 6260 foot elevation to the water line
of the North Fork of the Gunnison River at a general
elevation of 6070 feet above MSL as shown in the
southwest corner of Figure J-I. Streamflow through
Sylvester Gulch is routed under Highway 133 through
a large box culvert.
Geologic features identified along the course of
Sylvester Gulch include two small mudflows and one
shallow soil failure, all located on the east flank of
Sylvester Gulch. These features are being generated
by loose colluvial clay and silt eroding with the flow
of surface water associated with snowmelt and rain.
All three geologic features are shallow in depth (12"
to 23"), sinuous or scarped, and lenticular in form.
Field examination of the stream embankments along
the Sylvester Gulch indicate some minor undercutting
and honeycombing.
The only hydrologic feature discovered in this area
during the field investigation was a spring on the east
flank of Sylvester Gulch. This spring is associated
with one of the mudflows previously mentioned. At
some past time, the spring was developed to provide
water for a now abandoned stock watering tank. The
spring is located below the proposed Sylvester Gulch
haul road grossing and will not affect the road
stability.
5.3.3.3 Lower RPE Area
The Lower RPE Area is a relatively flat region
located below the north slope of the lower portion of
[he West Flatiron. The lower RPE area extends
northward to Highway 133 and includes a low lying
arch shaped depression, which is a wetland. The area
is bordered to the west by the Sylvester Gulch
corridor, and to the east by the mouth of the unnamed
drainase between Box Canyon and Sylvester Gulch.
In this flat area, the major portion of the RPE
foundation will be constructed. A sediment control
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Harding Lawson Associates 5