HomeMy WebLinkAboutCosmos Hills Feasibility Study 2011Geotechnical Investigation Kogoluktuk River
Hydropower Site
Cosmos Hills Hydroelectric
Feasibility Study
Prepared for:
Alaska Village Electric
Cooperative (AVEC) & NANA
Regional Corporation
December 14, 2011
Prepared by:
WHPacific, Inc.
300 W. 31st. Avenue
Anchorage, AK 99503
WHPaCifiC
WHP Project 008228
WHP Project 008228
Geotechnical Investigation Kogoluktuk River
Hydropower Site
Cosmos Hills Hydroelectric
Feasibility Study
Prepared for:
Alaska Village Electric
Cooperative (AVEC) & NANA
Regional Corporation
December 14, 2011
Prepared by:
WHPacific, Inc.
300 W. 31st. Avenue
Anchorage, AK 99503
WHPac1fiC
Prepared for:
Title:
Project:
Prepared by:
WHP Project 008228
Brent Petrie, Manager, Community Development
Alaska Village Electric Cooperative
4831 Eagle Street
Anchorage, AK 99503
and
Sonny Adams, Project Manage
NANA Regional Corporation
I 00 I E. Benson Boulevard
Anchorage, AK 99508
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
WHPacific, Inc.
300 W. 31st Avenue
Anchorage, Alaska 99503
Contact: Steve Buckley, CPG
Geologist
Phone: 907-339-6533
Fax: 907-339-5327
E-mail address: sbuckley@whpacific.com
Table of Contents
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
1 Introduction .......................................................................................................................................... 1
2 Site Description ..................................................................................................................................... 2
3 Geotechnical Investigation ................................................................................................................... 4
3.1 Slope Stability I Seismic Activity ................................................................................................... 4
3.2 Bedrock Character at Intake and Outtake/Structural Mapping .................................................... 4
4 Kogoluktuk River Geotechnical Investigation: .................................................................................... 11
4.1 TestPits ....................................................................................................................................... 11
Lower Reach ........................................................................................................................................ 11
Upper Reach ........................................................................................................................................ 19
Figure 1: Project Location Map, Kogoluktuk Geotechnical Evaluation, Study Area ..................................... 6
Figure 2: Kogoluktuk Geotechnical Evaluation, Full Extent .......................................................................... 7
Figure 3: Kogoluktuk Geotechnical Investigation, Lower Extent .................................................................. 8
Figure 4: Kogoluktuk Geotechnical Investigation, Upper Extent.. ................................................................ 9
Figure 5: Surficial Deposit Types ................................................................................................................. 10
Photo 1: Bedrock Controlled Nickpoint ........................................................................................................ 2
Photo 2: Typical Shallow Wetland Soil .......................................................................................................... 3
Photo 3: Bedrock at proposed intake dipping north .................................................................................... 5
Photo 4: WPT 89 ......................................................................................................................................... 11
Photo 5: WPT 90 ......................................................................................................................................... 11
Photo 6: WPT 91 ......................................................................................................................................... 12
Photo 7: WPT 92 ......................................................................................................................................... 12
Photo 8: WTP 93 ......................................................................................................................................... 13
Photo 9: WTP 94 ......................................................................................................................................... 13
Photo 10: WTP 94 ....................................................................................................................................... 14
Photo 11: WTP 94 ....................................................................................................................................... 14
Photo 12: WTP 95 ....................................................................................................................................... 15
Photo 13: WTP 95 ....................................................................................................................................... 15
Photo 14: WTP 96 ....................................................................................................................................... 16
Photo 15: WTP 98 ....................................................................................................................................... 16
Photo 16: WTP 99 ....................................................................................................................................... 17
Photo 17: WTP 100 ..................................................................................................................................... 17
Photo 18: WTP 100 ..................................................................................................................................... 18
Photo 19: WTP 101 ..................................................................................................................................... 18
WHP Project 008228
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
Photo 20: WTP 111 ..................................................................................................................................... 19
Photo 21: WPT 126 ..................................................................................................................................... 19
Photo 22: WPT 126 ..................................................................................................................................... 20
Photo 23: WPT 126 ..................................................................................................................................... 20
Photo 24: WPT 127 ..................................................................................................................................... 21
Photo 25: WPT 128 ..................................................................................................................................... 21
Photo 26: WPT 129 ..................................................................................................................................... 22
Photo 27: WPT 129 ..................................................................................................................................... 22
Photo 28: WPT 130 ..................................................................................................................................... 23
Photo 29: WPT 131 ..................................................................................................................................... 23
Photo 30: WPT 132 ..................................................................................................................................... 24
Photo 31: WPT 133 ..................................................................................................................................... 24
Photo 32: WPT 133 ..................................................................................................................................... 25
Photo 33: WPT 134 ..................................................................................................................................... 25
Photo 34: WPT 135 ..................................................................................................................................... 26
Photo 35: WPT 137 ..................................................................................................................................... 26
Photo 36: WPT 138 ..................................................................................................................................... 27
Photo 37: WPT 139 ..................................................................................................................................... 27
Photo 38: WPT 140 ..................................................................................................................................... 28
WHP Project 008228 ii
A. Introduction
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
This report contains the results of WHPacific's geotechnical assessment of the Kogoluktuk River
Hydropower Study near Kobuk, Alaska. It includes the geological and geotechnical investigation for a
proposed small hydroelectric project in the Kogoluktuk (Kugluktuq} River near the Village of Kobuk. The
data includes field reconnaissance collected between August 30, 2011 and September 1, 2011 for a
portion of the Kogoluktuk River shown in Figure 1. Two reaches of the Kogoluktuk River were evaluated
for geotechnical considerations. This included bedrock geologic mapping and structural mapping, along
with shallow soil probing and a review of stream and slope stability.
This geotechnical investigation is part of a larger evaluation of the wetlands and fisheries of the
Kogoluktuk River conducted by WHPacific personnel including Steve Buckley, Philip Quarterman, Casey
Storey and James Mills. Steve Buckley, CPG, conducted the geotechnical aspects of the project; Phil
Quarterman's portion included the wetlands; Casey Storey did an aquatic analysis ofthe river; and
James Mills assisted in the labor process and drafting ofthe report. Lodging was provided by Nova Gold
at the Dahl Creek facility. Access to the study area included helicopter support. Hikes between the
upper and lower extent allowed access between helicopter drop-off and pick-up points.
The field reconnaissance included physical observations of the soil and an analysis of any geological
hazards, including evidence of landslide prone areas and major faults. Soil depth, condition and
consistency of soil, and wetland locations were mapped and photographed at 35 test pits. Reference
points were recorded via GPS and are identified in Figures 1 through 4.
WHP Project 008228
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
B. Site Description
The Kogoluktuk Hydropower Study area is approx. 4 miles northeast of Kobuk. Hydroelectricity is being
considered for seasonal supplementation ofthe current diesel generators in Kobuk and Shungnak. This
geotechnical investigation is part of a larger study, which includes wetland mapping and characterization
along with fisheries investigations of the Kogoluktuk River itself. Detailed descriptions of the site are
contained in the wetland and fisheries reports1 and are not repeated here.
The geotechnical investigation of the reach shows a variety of landforms associated with two main,
bedrock controlled cascade reaches.
Photo 1: Bedrock Controlled Nickpoint
Bedrock consists of very competent granitic gneiss with a shallow north dip in both reaches. This
bedrock controls upstream and downstream nick points in the river and most of the stream reach is
underlain by exposed bedrock. The most important structural fabric in the bedrock is a shallow north-
dipping foliation (20-30 degrees).
Shallow soils are developed both directly on bedrock and on thin deposits of glacial outwash and ice-
marginal deposits adjacent to the river. These deposits range from well-sorted cobble and gravel
1 Quarterman, Philip J, PWS, Reconnaissance Report: Wetlands and Other Waters of the United States: Kogoluktuk
River Study Area Cosmos Hills Hydroelectric Pre-Construction Program (FERC Preliminary Permit #13286) April 5,
2012, WHPacific.
Storey, Casey M, Reconnaissance Report: Fisheries and Water Quality Resources (Aquatic Resources): Kogoluktuk
River Study Area Cosmos Hills Hydroelectric Pre-Construction Program, April 25, 2012, WHPacific.
WHP Project 008228 2
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
alluvium, to fine-grained sandy outwash, to silty wind-blown loess . Organic-rich histosols soils are
developed directly on bedrock in some shallow wetlands.
Photo 2: Typical Shallow Wetland Soil
No evidence of permafrost was encountered to the maximum depth of excavation (approximately 2'}.
This may reflect the well-drained characteristics ofthe soils in the area in general, although some of the
wetland areas lack internal drainage.
WHP Project 008228 3
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
C. Geotechnical Investigation
Five main types of surficial deposits are found along this corridor of the Kogoluktuk River (Figure 5).
Brief descriptions are provided below and waypoint numbers refer to the location maps and photos
provided in section 4.0.
1. The most extensive type consists of thin alluvial deposits developed on bedrock ridges. These
are well-drained soils in moderately sorted fluvial gravels. They are typically found on high
spots, forming a thin cover over bedrock ridges. Examples of this type of soil cover are shown in
Figures 3 and 4, and in the photos of the test pits for way points# 89, 100, and 131.
2. A large part of the project area is covered by fine-grained, sandy, wind-blown loess. These soils
range from fine sand to silt and are the result of wind-blown deposition related to ice-marginal
glacial sediment. Examples of this type of soil are found in Figures 3 and 4, in waypoints # 99,
111, and 135.
3. Sandy loam soil is developed on fine-grained alluvial deposits adjacent to the river. These are
likely Holocene terrace remnants. Test pits at waypoints #90 and 92 are examples of sandy loam
soil.
4. Wetland soils are developed in shallow depressions, typically on bedrock. These depressions, in
many cases, lack internal drainage, and remain saturated throughout the year. These soils are
typified in test pits at waypoints #93 and 95.
5. Large bedrock slabs form colluvial deposits in some areas of the project area. They typically
occur near bedrock outcrops but contain large voids and are covered by moss and spruce trees.
These areas are characterized at waypoints #96 and 98.
Slope Stability I Seismic Activity
During the mapping and test pit investigation, any evidence of slope instability such as solifluction or
slumping, or hydrologic or vegetative evidence of slope instability was examined in the field and on air
photos. There are some shallow scarps developed along the immediate cutbanks of the river especially
on outside bends in alluvial reaches. Otherwise, slopes appear stable and there is no evidence of any
recent seismic activity such as fault scarps, slumps or landslides. The Kobuk Fault has been reported to
have been historically active. It trends east-west and is located 10-15 miles south of the project area.
The USGS Earthquake Database shows some minor earthquake activity in the region, though the relation
of the seismic activity to the Kobuk Fault is unclear.
Bedrock Character at Intake and Outtake/Structural Mapping
The bedrock at both the proposed Intake and Outtake is moderately foliated granite gneiss. The gneiss
consists of a medium-grained quartzo-feldspathic ground mass separated by foliation planes consisting
of fine-grained mica. The gneiss is highly competent, separated by thin foliation planes typically 6" -10"
apart. At the intake the gneiss has a consistent trend striking 130 degrees and dipping 20 degrees north.
WHP Project 008228 4
WHP Project 008228
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
Photo 3: Bedrock at proposed intake dipping north
5
WHPacific
WHP Project 008228
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
Project Location Map
Kogoluktuk Geothechnlcal Evaluation
Study Area
10/25/11
N
A
Figure 1
6
WHP Pro
Kogoluktuk Geotechnical Investigation
Full Extent
10127/2011
N
A
0 o.s
WHPacific
awes
Legend
• Sampte l.oc8tions
Figure 2
,wer Site
ity Study
97 •
0
WHP
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
Figure 3: Kogoluktuk Geotechnical Investigation, lower Extent
:. \ ... \ .•
0.125 0.25
\
.. \\
.. . \,
;. .\
\ >,
\
Legend
0.5 Miles
• Sample Locations
0
WHP Project 008228
Geotechnical Investigation Kogoluktuk River Hydropower Site
Cosmos Hills Hydroelectric Feasibility Study
Figure 4: Kogoluktuk Geotechnical Investigation, Upper Extent
0.125 0.25 o.5 Mites
Legend
WHP Project 008228
Figure 5: Surficial Deposit Types
0
I
0.125 0.25
I
0.5 Miles
I
+
Legend
--Faull
We nand
ILH Ple!slocene Terrace
I~.%;J AlluVIum
c:JBedmck
10
10
11
D. Kogoluktuk River Geotechnical Investigation:
Test Pits
Test pits were conducted throughout the study area at depths of 24 inches or less and were
selected for analyzing soil composition and seasonal permafrost trends.
Lower Reach
Photo: WPT 89
4" organic root matt over
alluvium composed of 70%
sand, 15% gravel (sub
grounded) and 15% silt.
Photo: WPT 90
Holocene Terrace with
glacial outwash/moraine
Silty sandy loam. WPT 090.
WHP Project 008228
Photo 4: WPT 89
Photo 5: WPT 90
11
Photo: WPT 91
Active floodplain, 3-5'
above bankfull stage.
Willow and 5' cottonwood
vegetation
Bare sandy soil.
Photo: WPT 92
Lower Holocene terrace 3-
5' above floodplain.
Sandy loam with 2" root
zone in A horizon over
fluvial sand.
WHP Project 008228
12
Photo 6: WPT 91
Photo 7: WPT 92
12
Photo: WPT 93
Bog/Wetland.
Photo: WPT 94
Bedrock outcrop with E-W
strike and 30oN dip.
Foliated granite/gneiss, K-
spar, quartz, biotite.
WHP Project 008228
13
Photo 8: WTP 93
Photo 9: WTP 94
13
Photo: WPT 94
Looking downstream
Photo: WPT 94
Looking upstream at
potential outlet site
WHP Project 008228
14
Photo 10: WTP 94
Photo 11: WTP 94
14
Photo: WPT 95
Wetland soil pit. 6-8"
histosol on bedrock
Photo: WPT 95
Characteristic open water
wetland developed on
shallow bedrock
WHP Project 008228
15
Photo 12: WTP 95
Photo 13: WTP 95
15
Photo: WPT 96
Foliated granite gneiss
with E-W strike and 20° N
dip.
Photo: WPT 98
Large flat slabs of
bedrock/sub-crop with a
thin veneer of
moss/spruce. Rock is
foliated granite/gneiss.
WHP Project 008228
16
Photo 14: WTP 96
Photo 15: WTP 98
16
Photo: WPT 99
Grey/brown silty soil with
a 3" A horizon, 3" B
horizon and 4" mottled
brown/grey glacial silt.
Photo: WPT 100
Thin skiff of alluvial
gravel/cobble on top of
bedrock near proposed
inlet. 30% sand, 10%
cobble and 60% gravel
Photo 16: WTP 99
with little to no A horizon . ~~~
Photo 17: WTP 100
WHP Project 008228
17
17
Photo: WPT 100
Same as Photo 17 but
zoomed out. Philip
Quarterman is in the
background.
Photo: WPT 101
Same outwash feature as
above. Sample is a couple
hundred feet above inlet.
2" A horizon, outwash
Photo 18: WTP 100
sand and grey/tan mottled ~-~
sand .
Photo 19: WTP 101
WHP Project 008228
18
18
Photo: WPT 111
Wetland. Reduced sulfidic
soil in grey silty sand.
Upper Reach
Photo: WPT 126
Outlet site. Bedrock is
quartz-mica schist with K-
spar and foliation strikes
95° and dips 20° South .
WHP Project 008228
19
r•~•
Photo 20: WTP 111
Photo 21: WPT 126
19
Photo: WPT 126
Same as Photo 21, but
looking upstream.
Photo: WPT 126
Same as Photo 21, looking
downstream.
WHP Project 008228
20
Photo 22: WPT 126
Photo 23: WPT 126
20
Photo: WPT 127
Alluvial soil on hill slope .
Probably Pleistocene. 3" A
horizon composed of peat,
3" B horizon composed of
gray gravel soil with sand
and 4" C horizon
composed of brown
rounded cobble/gravel.
Photo: WPT 128
Soil sample has 1" A
horizon, 1" silty B horizon
and 6" gravel with silt C
horizon.
WHP Project 008228
21
Photo 24: WPT 127
Photo 25: WPT 128
21
Photo: WPT 129
Meadow: Sandy soil in
moderate depression with
well drained, slightly
reduced soil.
Photo: WPT 129
1" A horizon, 6" B horizon
sandy loam with some
gravel and C: 5" mottled
gray and tan sandy
alluvium.
WHP Project 008228
22
Photo 26: WPT 129
Photo 27: WPT 129
22
Photo: WPT 130
Moss bog A horizon 3" dk
brown peat over 16"
orange sphagnum moss.
Saturated but no standing
water in pit.
Photo: WPT 131
Thin skiff of alluvial gravel
on top of bedrock (quartz,
mica and schist). W' A
horizon.
WHP Project 008228
23
Photo 28: WPT 130
Photo 29: WPT 131
23
Photo: WPT 132
Soil above intake. 2" dark
brown A horizon, 2" dark
brown silty loam B horizon
and 6" mica schist bedrock C
horizon.
Photo: WPT 133
looking upstream at
proposed intake.
WHP Project 008228
24
Photo 30: WPT 132
Photo 31: WPT 133
24
Photo: WPT 133
Same as above but looking
down stream.
Photo: WPT 134
Foliated granite gneiss.
Strikes 130° and dips
20°North .
WHP Project 008228
25
Photo 32: WPT 133
Photo 33: WPT 134
25
Photo: WPT 135
Outwash ridge of windblown ·~·"'-"-~~~~~~~~)~~~~~M~
loess below a thin layer of
volcanic ash. 2" A horizon, 2"
gray ash, 3" brown B horizon
and 4" green/brown loess.
Photo: WPT 137
Soil sample has 2" A horizon,
3" buff silt with rock
fragments and 6" olive silt
with trace rock fragments.
Soil is well drained.
WHP Project 008228
Photo 34: WPT 135
Photo 35: WPT 137
26
26
Photo: WPT 138
Soil sample. A horizon has 2"
root zone. Sample was taken ~~~~~~~~,\~
from a possible moraine
along a steep hill slope.
Photo 36: WPT 138
Photo: WPT 139
..
Sandy loam in alluvial sand ·
with 2" A horizon, 5" grey
silty sand and 6" sandy
orange/brown sand. WPT
139.
WHP Project 008228
Photo 37: WPT 139
27
27
Photo: WPT 140
Sandy floodplain with
cottonwood, willow and
scattered spruce.
WHP Project 008228
28
Photo 38: WPT 140
28