HomeMy WebLinkAboutAllison Creek Hydropower Pre-feasibility Study - Feb 2008 - REF Grant 2195390February 2008
The Energy Company
February 11, 2008
H-327730
Robert A. Wilkinson, CEO
Copper Valley Electric Association
P.O. Box 45
Glennallen, AK 99588-2832
Dear Robert Subject: Allison Lake Hydroelectric Project
Pre-Feasibility Study
We are pleased to submit herewith our Pre-Feasibility Study for the Allison Lake Hydroelectric Project.
The development of this study has been performed as Task Order 01 under our Professional Services
Contract for General Services between the Copper Valley Electric Association, Inc. (CVEA) and Hatch
Acres Corporation.
The report presents our analysis of the hydroelectric potential of the Allison Lake basin. Following the
review of previous studies and a helicopter / field reconnaissance of the project site, three options for
hydropower development of Allison Lake were identified for the present study as follows:
An intake and diversion tunnel from Allison Lake to the Solomon Gulch Reservoir in
order to allow increased generation at the existing Solomon Gulch powerhouse.
An independent development of Allison Lake including an intake, tunnel, power
conduit and a new powerhouse near tidewater on Allison Creek.
An independent development of Allison Lake including a low dam at the outlet of
Allison Lake, a siphon intake, a surface power conduit and a new powerhouse near
tidewater on Allison Creek.
These three options are evaluated on the basis of their ability to contribute to the CVEA load, the
potential cost of power and the environmental / regulatory issues associated with their development.
All three options demonstrate technical, economic and environmental feasibility. Accordingly,
notwithstanding the apparent long-term advantages identified for the independent tunnel / power
conduit / powerhouse alternative, the report includes the recommendation that CVEA submit a FERC
Preliminary Permit Application to study the three above defined arrangements in further detail upon
the expiration of the existing FERC permit for the site.
We greatly appreciate the opportunity to work with you on this interesting project. If you have any
questions regarding the subject report, be sure to give us a call.
Yours very truly,
A. Richard Griffith, P.E.
Project Manager
Hatch Acres Corporation
6 Nickerson Street, Suite 101, Seattle, WA 98109 USA
Tel: 206-352-5730 • Fax: 206-352-5734 • www..hatchacres.com
Hatch Acres Corporation i
Table of Contents
1.Introduction............................................................................................................................................1
2. Field Reconnaissance ..............................................................................................................................5
3. Alternative Project Arrangements...........................................................................................................7
3.1 General..........................................................................................................................................7
3.2 Alternative 1 Allison Lake Diversion to Solomon Gulch Project, FERC P-2742 (Alt 1).................7
3.2.1 General................................................................................................................................7
3.2.2 Lake Tap ..............................................................................................................................8
3.2.3 Tunnel & Pipeline Structures................................................................................................9
3.2.4 Energy Dissipater................................................................................................................10
3.2.5 Access Road.......................................................................................................................10
3.2.6 Ecological Return Flow Facility...........................................................................................10
3.3 Alternative 2 Allison Lake Tap with Powerhouse on Allison Creek (Alt 2) .................................11
3.3.1 General..............................................................................................................................11
3.3.2 Lake Tap ............................................................................................................................11
3.3.3 Tunnel & Surface Penstock.................................................................................................11
3.3.4 Powerhouse .......................................................................................................................11
3.3.5 Access Road.......................................................................................................................12
3.3.6 Ecological Return Flow Facility...........................................................................................12
3.4 Alternative 3 Allison Lake Siphon Intake with Powerhouse on Allison Creek (Alt 3)..................12
3.4.1 Embankment Dam at Allison Lake......................................................................................12
3.4.2 Siphon Intake.....................................................................................................................13
3.4.3 Forebay Structure...............................................................................................................14
3.4.4 Penstock.............................................................................................................................14
3.4.5 Powerhouse .......................................................................................................................14
3.4.6 Access Road.......................................................................................................................14
3.4.7 Ecological Return Flow Facility...........................................................................................14
4. Power Studies........................................................................................................................................15
4.1 AUTOVista Model: System Loads and Resources .........................................................................15
4.2 AUTOVista Model: Allison Lake Hydropower Development........................................................15
4.3 Hydrology....................................................................................................................................17
4.4 Reservoir Characteristics ..............................................................................................................18
4.5 Hydro Equipment Characteristics .................................................................................................19
4.6 AUTOVista Results....................................................................................................................... 19
5. Project Construction Cost and Schedule...............................................................................................22
5.1 Construction Cost Estimates .........................................................................................................22
5.2 Cost Comparison with Previous Studies .......................................................................................22
5.3 Economic Analysis.......................................................................................................................25
6. Environmental and Regulatory Considerations......................................................................................28
6.1 Regulatory Requirements Associated with All Alternatives ...........................................................28
6.2 Alt 1 Allison Lake Tap Diversion to Solomon Gulch Project, FERC P-2742...............................29
6.3 Alt 2 Allison Lake Tap Hydro Project ........................................................................................31
6.4 Alt 3 Allison Lake Siphon Project..............................................................................................31
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7. Conclusions and Recommendations......................................................................................................33
7.1 Conclusions.................................................................................................................................33
7.2 Recommendations .......................................................................................................................36
8. References.............................................................................................................................................37
Appendices
Appendix A Photographs
Appendix B Reservoir Operation
Appendix C System Dispatch
Tables
Table 4.1 AUTO Vista Model Elements
Table 4.2 AUTO Vista Hydrologic Years
Table 4.3 Annual Generation, Existing Condition
Table 4.4 Annual Generation, Alt 1
Table 4.5 Annual Generation, Alt 2
Table 4.6 Annual Generation, Alt 3
Table 4.7 Annual Generation Benefits
Table 5.1 Allison Hydropower Development, Total Construction Cost (Bid 1/2008)
Table 5.2 Comparison of Tunnel Cost Estimates with Previous Studies (2008 Dollars)
Table 5.3 Comparison of Powerhouse Cost Estimates with COE Study (2008 Dollars)
Table 5.4 Basic Assumptions for Economic Analyses
Table 5.5 First Year Cost of Power (2008 Dollars)
Table 7.1 Alt 1 Pros and Cons
Table 7.2 Alt 2 Pros and Cons
Table 7.3 Alt 3 Pros and Cons
Figures
Figure 1.1 Allison Lake Hydroelectric Project Location
Figure 1.2 Alt 1 General Arrangement
Figure 1.3 Alt 2 General Arrangement
Figure1.4 Alt 3 General Arrangement
Figure 3.1 Alt 1 and Alt 2 Lake Tap
Figure 3.2 Alt 1 Diversion Tunnel and Pipeline
Figure 3.3 Alt 3 Siphon Intake Facilities
Figure 4.1 AUTO Vista Model Elements: Existing Project
Figure 4.2 AUTO Vista Model Elements: Alt 1
Figure 4.3 AUTO Vista Model Elements: Alt 2 and Alt 3
Figure 4.4 Allison Lake Annual Inflow, 1951-1989
Figure 4.5 Allison Lake Reservoir Storage
Figure 4.6 Allison Powerhouse Unit Characteristics
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1. Introduction
The purpose of this present Pre-Feasibility Study is to evaluate the economic viability of alternative
arrangements for the addition of the Allison Lake drainage to the generating resources within the
existing Copper Valley Electric Association (CVEA) electric system. The Allison Lake Hydroelectric
Project (Project) is located adjacent to Prince William Sound immediately south of Valdez, Alaska as
shown in Figure 1.1.
Figure 1.1
Allison Lake Hydroelectric Project Location
Previous investigations of the Project by HDR Engineering, Inc. (HDR) in 1992 and by the Army
Corps of Engineers (COE) in 1982 evaluated potential project configurations for maximizing the
Allison Lake resource. In the HDR study, recommendations were made to develop a 12,000-ft-long
tunnel and deep lake tap of Allison Lake for diversion to Solomon Lake. Under this project
configuration, water could be diverted during the winter months for use through the Solomon Gulch
turbine units. In the COE study, which was completed prior to the construction of the Solomon
Gulch Project, the COE recommended a stand alone hydro project from a deep lake tap in Allison
Lake for conveyance via tunnel and penstock to a powerhouse (8 MW) on Allison Creek at Tailwater
El. 100 ft. More recently, a preliminary permit application was filed for a shallower lake tap on
Allison Lake and a downsized powerhouse (5 MW) on Allison Creek at Tailwater El. 150 ft.
Allison
Lake
Allison
Lake
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Currently, CVEAs primary source of power is from the Solomon Gulch Hydroelectric Project, a 12-
megawatt hydroelectric facility owned by the Four Dam Pool Power Agency (FDPPA) and operated
under contract by the CVEA. Due to the seasonal pattern of the power production from this
resource, CVEA must also rely on other resources during the winter months. Most important of these
is a 5.2-megawatt cogeneration facility where exhaust heat is recovered and sold to and used by
Petro Star for refining purposes. Diesel-fueled reciprocating gensets are also operated and
maintained by CVEA for supplemental power requirements and for reserve purposes.
Although the Solomon Gulch Project operates year round, during winter months the Solomon Gulch
Project operates at reduced levels and CVEA must rely heavily on the above listed fossil resources to
meet system load. The objective for pursuing potential development of Allison Lake is to fill this gap
with additional hydropower generation. The general configuration of the three arrangements under
consideration consist of:
Alternative 1, which includes an intake and diversion tunnel to the Solomon Gulch Reservoir in
order to allow generation at the existing Solomon Gulch powerhouse during dry period
conditions (Alt 1).
Alternative 2, which includes an independent development of Allison Lake including an intake,
tunnel, power conduit and a new powerhouse near tidewater on Allison Creek (Alt 2).
Alternative 3, which also includes an independent development of Allison Lake including and a
low dam at the outlet of Allison Lake, a siphon intake, a surface power conduit and a new
powerhouse near tidewater on Allison Creek (Alt 3).
The general arrangement for Alt 1, Alt 2 and Alt 3 is shown in Figures 1.2, 1.3 and 1.4 respectively.
Figure 1.2
Alternative 1 General Arrangement
ALTERNATIVE 1
Diversion to Solomon GulchAllison Lake
ALTERNATIVE 1
Diversion to Solomon GulchAllison LakeAllison Lake
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Figure 1.3
Alternative 2 General Arrangement
Figure 1.4
Alternative 3 General Arrangement
ALTERNATIVE 2 Tunnel &
Penstock to Powerhouse @ Allison
CreekAllison Lake
ALTERNATIVE 2 Tunnel &
Penstock to Powerhouse @ Allison
CreekAllison Lake
ALTERNATIVE 3 Siphon Intake w/
Penstock to Powerhouse @ Allison CreekAllison Lake
ALTERNATIVE 3 Siphon Intake w/
Penstock to Powerhouse @ Allison CreekAllison LakeAllison Lake
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The scope of work for the Pre-Feasibility Study includes the following activities:
1. Data collection.
2. Field reconnaissance of Allison Lake area.
3. Development of general arrangement details of each alternative consistent with the purposes
of this study.
4. Analysis of Allison Lake hydrology and hydropower potential in relation to the existing
Valdez electric system.
5. Preliminary layout and cost estimate of hydroelectric project features.
6. Economic evaluation of the three above described alternatives.
7. Environmental review of the three above described alternatives.
8. Preparation of this Pre-Feasibility Report including the resulting conclusions and
recommendations.
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2. Field Reconnaissance
On October 9 2007, Hatch Acres representatives Mr. Steve Hart and Mr. Don Bowes accompanied
Mr. Steve Bushong of CVEA on a site reconnaissance of the Solomon Gulch and Allison Lakes
watersheds via helicopter. The morning of the trip was clear with high visibility. Flying up the basin
by helicopter, it appeared that the glaciers above the lakes drainage amounted to less than 5% of the
area (Photos 1 & 2)1 . Because of the basins physical similarity, we concluded that Solomon Gulch
streamflow could be used as a basis for the hydrology used within this Report.
The site condition at Allison Lake was void of any tree cover and consisted of light groundcover over
boulders left over from glacial retreat. The lake outlet was broad (Photos 3 & 4) with low flows in
Allison Creek. The northern reservoir rim showed only one rock outcrop (Photo 5) that appeared
reasonable for a lake tap, which appeared to be at the location that the U.S. Army Corps of Engineers
(COE) selected in its study of the Allison Lake Hydroelectric Project. The remaining length of the
northern reservoir rim was comprised of material from old debris slides from the upper slope. From
our observation, it seems that there is a high probability that some amount of this rocky debris exists
on the submerged slope of the proposed lake tap portal. The amount of this material covering the
rock outcrop will need to be investigated to better establish the construction cost for removing this
material from the site.
When the helicopter landed, it was apparent that the entire valley floor was covered in bouldery
moraine, which would make the installation of a buried pipeline costly, especially for the HDR
pipeline diversion scheme as described below.
The construction of a rockfill dam for raising Allison Lake pool was considered viable so long as the
structures height was limited. Normal construction of a dam requires a sound bedrock foundation,
which would not be practical since bedrock is over 100 feet below the lake outlet. The lake was
believed to be sealed through sealing this moraine deposit with glacial silt, which later investigation
of existing data substantiated. Glacial silt near the outlet was measured by others to be greater than
90 cm deep at three different lake locations, inclusive of near the lake outlet. Such siltation would
exist throughout the lake bottom.
Allison Creek continued to flow on the surface, but it appeared that some amount of groundwater
flow beneath the surface was possible. During our site visit, we did not observe any stream flow into
the creek below the lake outlet. There was some creek inflow into Allison Lake from glacial melt.
Later, when we visited the powerhouse site, Mr. Don Bowes observed that creek flow appeared
greater than at the lake outlet, which would seem to indicate some amount of groundwater inflow
from the lower watershed below the lake outlet. However, the amount of flow increase would need
to be substantiated through stream gauging data.
During our site visit, we observed an active gauge about 1,000 meters downstream of the lake outlet
(Photo 6). We assume that this gauge had been installed by the current permittee. The site was
appropriate and would appear to provide a reasonable estimate of lake inflow, provided that the data
was corrected for the actual drainage at the lake outlet versus the drainage at the gauging location. If
CVEA were to pursue a future preliminary permit license, we would recommend that gauging
stations be established at both the powerhouse site and at the existing gauging station near the lake
outlet.
1 See Appendix A
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In previous study analysis, site access to the tunnel portals for Allison Lake Hydro alternative was
assumed to be by helicopter only. In our review, constructing an access road would be difficult and
costly, but possible. We believe that the most promising route, if an access road were to be
constructed to Allison Lake, would be from across an upper bench just west of the Solomon Gulch
dam structure (Photo 7). This bench would also provide a suitable tunneling adit for the Allison Lake
diversion to Solomon Lake. Assuming that the access road could reach this bench from the existing
Solomon Gulch dam access road, we reasoned that the road alignment would continue in an easterly
direction (Photo 8) toward the top of a ridge that flanks Allison Creek to its west and that the road
could be constructed at less than a 5% grade.
The proposed alignment of the penstock (Alt 2 and Alt 3) that descends down the ridge to the
proposed powerhouse site, as identified in the current preliminary permit application appears
suitable and appropriate for a surface penstock design.
When we visited the powerhouse site, the soil cover approaching the site appeared suitable for
trenching the penstock for the short distance to the powerhouse site. The powerhouse site appeared
to be suitable and did not appear to present much difficulty. It was noted by Steve Bushong that
property issues would need to be reviewed, but that the alignment of a dirt trail to the powerhouse
site that was flagged by the current permittee appeared suitable for a new access road alignment off
the existing road used to access the Alyeska Pipeline.
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3. Alternative Project Arrangements
3.1 General
The level of conservatism varies in the preparation of the HDR, COE and the current preliminary
permit design alternatives and associated cost estimates. Accordingly, based on the observations
from the field reconnaissance and our review of these designs, we have prepared modified versions
of each for consideration of a possible development. The resulting configuration for each alternative
is described below.
3.2 Alternative 1 Allison Lake Diversion to Solomon Gulch Project,
FERC P-2742 (Alt 1)
3.2.1 General
Under this scheme, the water from the Allison Lake would be diverted during the low-flow winter
months to replenish the storage in Solomon Lake for hydro generation through the Solomon Gulch
power plant at times when the hydro plant is under utilized or shut down due to lack of water.
Then, when the Solomon Gulch Plant is normally at full output during the spring runoff, Allison Lake
would be refilled.
The recently collected bathymetry for a Northern Arizona University students masters thesis verifies
that the previously estimated storage from the COE and HDR studies are valid and justifies the
construction of a deep lake tap, such as has been performed for other Alaska hydro installations (e.g,
Tyee Lake).
From previous investigations, Allison Lake storage extraction was accomplished from a lake tap near
the bottom of the lake via a tunnel that would be excavated near the lake within a zone of sound
rock. From this tunnel, a more cavernous tunnel with rock traps would be excavated to provide
sufficient volume for the final shot rock that extends from the tunnel to the lake. A rock trap is
generally an over-excavated pit within the tunnel below the tunnel conveyance grade line and is
designed to ensure all loose rock is retained within the rock trap and does not pass into the
conveyance stream where loose rock could cause damage to the turbine runner equipment.
The two previous studies by the COE and HDR provide slightly different approaches in this lake tap
design as follows:
The COE lake tap design considered a drawdown of 100 feet in Allison Lake. The HDR
design assumed that the lake tap could be extended deeper to permit a 117-foot drawdown.
The proposed HDR lake tap was located about 6,000 feet from the Allison Lake outlet, while
the COE proposed lake tap was located about 2,500 feet closer. HDR rationalized that the
upper lake tap location was preferable to avoid debris deposits. They noted in their review
of existing geotechnical data near the lake outlet, that there was considerable debris on the
lake bottom. However, from our site reconnaissance and review of bathymetry data, we
believe that the COE intake site for a lake tap is preferable. The COE evidently had also
performed some bathymetry near its proposed lake tap entrance, because their drawing of
the lake cross section matches closely with the Northern Arizona University bathymetry.
The other distinctive design differences of the HDR and COE lake tap schemes is with the intake
gating and water conveyance lining, which is the lining that retains the internal water pressure within
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the tunnel and minimizes or eliminates leakage from the tunnel and prevents instability of the
surrounding rock, especially near the outlet portal where the rock cover is minimal. The COE design
is more conservative than for the HDR design, but both designs fall within good engineering
practice. They are briefly described as follows:
The COE design included an intake gate shaft with an access tunnel to the intake gate hoist
equipment contained within an underground vault. The gate shaft included two hydraulic
slide gates in sequence leading into a circular concrete lined tunnel with an inside diameter
of 6 feet. The tunnel was designed to be a pressure tunnel with some sections left unlined in
zones of sound rock. Other sections would be concrete-lined in zones of less competent
rock or low rock cover, and a steel-lined section near the outlet portal would be provided for
the prevention of hydrojacking. The tunnel grade was set at 0.5% for the majority of its
length; a short steeply inclined tunnel set at 45% is shown near the intake to protect the
tunnel against negative hydraulic transients.
The HDR intake design did not include a gate shaft and access tunnel to the gate operator.
Instead, two 42-inch-diameter butterfly inlet valves in series were to be located at a
Bellmouth intake within the tunnel just downstream of the lake tap. Our design indicates
that 24-inch valves would be suitable. From the two inlet valves, a 24-inch diameter steel
pipe would be constructed on cradles throughout the entire length of the tunnel to an outlet
energy dissipation valve. The HDR tunnel construction grade was set at approximately 5%,
which eliminates the requirement for a steeply inclined tunnel section, but also would
provide greater difficulty for construction. Rubber-tired vehicles would be required for
hauling out excavation material (muck) rather than rail mucking cars. A potential
drawback of this design is the lack of good access to the butterfly inlet valves. Access would
occur at the downstream portal and would require a 2-mile hike up the tunnel by
maintenance personnel to the valves. The primary maintenance requirement is replacement
of the seal to one of the valves with the other valve (the upstream of the two) providing the
shutoff to allow maintenance.
3.2.2 Lake Tap
The less costly HDR scheme was adopted for Alt 1 as well as for Alt 2 to be discussed later. From
our site trip, our field observations showed a prominent rock outcrop at the location of the COE site
that we believe provided the most promise of a suitable intake location. Following the review of the
bathymetry, we also believe that the depth of the lake tap selected by COE is also appropriate, which
is located above the lake bottom (approximately El. 1180 ft). The lake bottom along the rim of the
lake on the north shore is likely characterized with colluvial material from rock debris slides. We
would expect a possibility of some removal of this rocky/gravelly debris from a barge in the vicinity
of the lake tap prior to the excavation of the lake tap. The barge components could be flown to the
lake if an access road were not constructed to the lake tap and assembled on the shore of the lake.
Backhoe equipment would be used to remove the rocky debris up to a certain limiting depth. The
balance of debris, would then be removed with draglines to remove the majority of material from
where the lake tap is to be located. Neither the COE nor HDR accounted for such debris excavation
in their cost estimates due to lack of subsurface information to substantiate such a construction
requirement.
The lake tap to be constructed under this alternative is assumed to include two large rock trap zones
from which to collect the rocky rubble once the final rock mass to the Allison Lake is drilled and
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shot. The concrete plug for the intake structure would include a double door water-tight hatch for
containment of the rocky rubble. The intake structure would be protected with ice blocks prior to
the final blasting. The basic lake tap scheme can be seen in Figure 3.1.
Figure 3.1
Alt 1 and Alt 2 Lake Tap
3.2.3 Tunnel & Pipeline Structures
To reduce the cost of construction, the proposed tunnel alignment for Alt 1 would be different from
the HDR selected alignment. First we selected a grade of approximately 3%, which is the maximum
generally used for rail car usage in the tunneling mucking operation. The rate of tunnel excavation is
always dependent on the removal rate of excavated rock and the use of rails provides the most
efficient and rapid means of tunneling. The tunnel portal area from where rock is removed generally
requires a favorable work staging area. From our review of possible sites, where we could still
maintain a maximum tunneling grade of no more than about 3%, we identified a suitable portal
location at a low saddle above the Solomon Lake at about El. 940 ft. From this location the length of
the tunnel to the preferred lake tap location is about 2,000 feet less than the HDR selected
alignment, or about 10,000 feet.
Within the tunnel, a 24-inch-diameter steel pipe would be constructed as shown in Figure 3.2 over
the entire tunnel length to the energy dissipation structure located just outside of the tunnel near the
lake shore. Two 24-inch-diameter butterfly shutoff valves would be installed in series behind the
upstream concrete plug. This would permit inspection and repair to the water conveyance pipeline.
The second valve is provided as a backup to the main valve and allows for replacement of seals to
the principal valve. To facilitate the required maintenance of the butterfly valve seals, the tunnel
would be enlarged in this area and require an overhead hoist to permit seal replacement. A control
cabinet for the valve operation would be located to one side of the valves.
–El 1367.0 Max Pool
–El 1267.0 Min Pool
El 1250.0 Lake Tap
Rock TrapsConcrete Plug
Control Valves
Air Vent
Rockslide Deflector
Active Storage =
1367 – 1267 = 100’
–El 1367.0 Max Pool
–El 1267.0 Min Pool
El 1250.0 Lake Tap
Rock TrapsConcrete Plug
Control Valves
Air Vent
Rockslide Deflector
Active Storage =
1367 – 1267 = 100’
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Figure 3.2
Alt 1 Diversion Tunnel and Pipeline
3.2.4 Energy Dissipater
Unless a hydro plant is constructed to recover the
energy between Allison Lake and Solomon Lake
(1367 685 = 682 feet), an energy dissipating,
control valve is needed for releasing the diverted
water into Solomon Lake. The HDR report assumed
that a valve house would be constructed just above
Normal Maximum pool El. 685 ft and would contain
Bailey Polyjet dissipating valves or equivalent. In
this scheme, the dissipated energy would be
released into a wet well, with water overflowing a weir and running down the reservoir side
embankment in a 60-inch-diameter outlet pipe to below the Minimum Solomon Gulch Reservoir El.
616.6 ft.
With the outlet tunnel portal of Alt 1 located well above Solomon Lake, our preferred alternative
assumed that a fixed-cone valve energy dissipater would be used and directed into an outlet chute
that would free-discharge the released flow into Solomon Lake via a man-made falls. The falls would
be established by excavating loose and weathered rock in directing the flow down to the reservoir
below.
3.2.5 Access Road
The access to the tunnel outlet portal would make use of the existing access road to the Solomon
Gulch dam site (about El. 680 ft). From there, a new access road would be extended up to the portal
area at El. 940 ft. In limiting this new road to a 10% grade, the length would need to be about 2,600
feet.
We have assumed that all of the tunneling work would be performed from this portal. The
ventilation shaft to be constructed above the valve chamber at the upstream end of the tunnel would
be constructed with either helicopter or float plane access to Allison Lake.
3.2.6 Ecological Return Flow Facility
Unlike other alternatives where an outlet can be provided at the diversion weir for providing
minimum ecological flows in the bypass reach, this will not be possible due to the lake drawdown
below the natural lake outlet. The previous HDR study assumed that the minimum water flow
requirement would be collected at the Solomon Gulch powerhouse tailrace outlet and pumped back
to Allison Creek via the highway to the oil terminal near its outlet to the tidal waters.
Because this mixing of water may generally not be preferred, it may be that a return flow conduit,
which returns ecological flows back to the Allison Creek channel as high up in the creek basin as
possible, should originate from the 24-inch steel pipeline at the tunnel outlet through a high-pressure
pipeline. This pipeline would terminate at about Allison Creek elevation 150 feet, which represents
the location of an anadromous fish barrier.
88
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3.3 Alternative 2 Allison Lake Tap with Powerhouse on Allison Creek (Alt 2)
3.3.1 General
Alt 2 is essentially the same design concept as that presented by the COE, but modified to
incorporate similar lake tap design as for Alt 1. The COE assumed that two 4-MW Pelton turbine-
generators would be housed in the powerhouse. However, we have reduced the installation to a
single 4 MW unit. In this study, we have not yet considered a staged design that would allow the
incorporation of a second phase 4-MW addition.
3.3.2 Lake Tap
The location, the depth of lake drawdown and the inlet design of the proposed lake tap for Alt 2 are
the same as described for Alt 1.
3.3.3 Tunnel & Surface Penstock
The horizontal alignment of the Alt 2 tunnel is the same alignment as presented for the COE
preliminary design . The grade of the tunnel would be about 2% to eliminate the requirement of the
steeply-inclined tunnel section near the lake tap as proposed by the COE design scheme. Disposal of
rock material from the tunneling operation would generally be performed per the COE
recommendation on the east side of the portal by means of mechanically operated railroad gondola
cars.
As with Alt 1, a steel pipeline would be installed on concrete cradles within the tunnel. The
diameter of the pipeline would be 33-inch-diameter for the proposed 4 MW installation. To allow
for a later 4-MW expansion a second inlet with a bulkhead could be constructed within the concrete
plug at the tunnel headworks. We have assumed that the low-pressure pipeline within the tunnel
could use less costly HDPE pipe throughout the 10,500-foot length of the tunnel, but steel pipe
material would be used outside of the tunnel as the penstock extends to the powerhouse structure.
At the tunnel outlet portal, a surface penstock would continue down the nose of the ridge on the
right side of Allison Creek, then continue to the powerhouse site. The penstock would be entirely
above ground and constructed on concrete cradles (or piers) along the rocky nose ridge. The
concrete piers would be at 40-foot intervals. At the bottom of the ridge, the penstock would
transition to a buried conduit.
3.3.4 Powerhouse
The powerhouse site would be near creek El. 150 ft. This site is the same as currently being
proposed in a preliminary permit application that is scheduled to expire in March 2008. It was
selected because the plant discharge would occur near an anadromous fish barrier and would allow
salmon and other anadromous fish to still make use of the stream habitat below the fish barrier.
The powerhouse would be sited above Allison Creek such that its service bay is located above the
500-year-return period flood level. As the Pelton unit operates with free-discharge into the
atmosphere, it may need to be located above the 100-year-return period flood level to permit
operation of the unit.
For the base-scheme alternative, the powerhouse would contain a single 4-MW synchronous
generator with a 2-nozzle horizontal Pelton turbine unit. The surface powerhouse would include a
15-ton bridge crane and all other equipment required for operation and maintenance of the
powerhouse. Remote control of the powerhouse would be from the Solomon Gulch powerhouse.
The tailrace flow would be released back into the Allison Creek.
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3.3.5 Access Road
While the COE assumed that helicopters would be used to transport equipment, material and
personnel to the tunnel portal during construction, we have assumed that a contractor would
construct an access road to the tunnel outlet portal despite the difficult terrain. The existing Solomon
Gulch access road to its dam would be used and then be extended generally as described for Alt 1 to
the saddle location above the west side of the dam. Contractor requirements for access road
construction would include reinforcing the existing Bailey Bridge to the dam crest sufficiently to
carry the highest loading that the contractor might impose upon the bridge during construction of
structures in the upper Allison Creek basin.
From the saddle location above Solomon Lake, the access road would then continue at a less than
10% grade in a westerly direction to the tunnel portal outlet. A second road would make use of the
existing access road for the Valdez Oil Marine terminal that extends in a southerly direction on the
east side of Allison Creek. From this road a 0.4-mile-long road would be constructed to the
powerhouse site.
As the surface penstock gradient to the powerhouse structure is too steep for access road
construction, the construction contractor will likely need to make use of a high-liner to facilitate its
construction.
Access to the outlet control valves is assumed to occur via the tunnel similar to Alt 1.
3.3.6 Ecological Return Flow Facility
Due to the deep lake tap and drawdown, it would not be possible to release ecological flows at the
lake outlet. Instead, the ecological flow releases would occur into Allison Creek in the vicinity of the
tunnel outlet portal. The penstock would have a diversion tap that would branch out to Allison
Creek and deliver about 5% of mean annual discharge (MAD), or whatever flow is eventually
negotiated with the fishery resource agencies.
3.4 Alternative 3 Allison Lake Siphon Intake with Powerhouse on
Allison Creek (Alt 3)
Alt 3 is similar to one of the alternatives described in the HDR study that makes use of a siphon
intake and a low-level rockfill embankment dam in developing 55-feet of lake storage rather than
100-feet of storage of Alt 1 and Alt 2. Because of negative transient pressure concerns, the discharge
from the pipeline would occur into a forebay structure downstream at about El. 1300 ft. A forebay is
an established small pond from which the penstock originates in conveying water to the power plant
for hydroelectric generation. From the forebay, the penstock would cross over to the ridge line of
the Alt 2 penstock alignment then descend down to the powerhouse structure, which houses the 4-
MW Pelton turbine equipment.
The 55-foot-drawdown of the lake is comprised of 20 foot of siphon withdraw, 15-feet of additional
lake rise, and 20 feet of trenching below current lake level.
3.4.1 Embankment Dam at Allison Lake
The embankment dam would be a rockfill structure and include a spillway at normal maximum pool
El. 1379 ft, or approximately 12 feet above the current normal Allison Lake El. 1367 ft, as established
in the COE study. The lake outlet is characterized of a deep boulders left during the last glacial
retreat. The glacial silt has sealed the lake, which was verified by core samplings made recently by
the Northern Arizona University study. Such siltation is characteristic of many alpine lakes in Alaska.
Copper Valley Electric Association, Inc. - Allison Lake Hydroelectric Project
Pre-Feasibility Study
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Construction of a low-level dam, while not ideal, is within industry practice. It simply is not feasible
to provide for a bedrock foundation. Instead, the existing moraine outlet becomes a part of the
embankment structure. The rockfill embankment is assumed to have a clay core and sandy transition
zones between the clay core and rockfill zones. The clay core would connect with the existing silt
layer of the lake outlet moraine.
Additional testing and analysis is needed to establish whether a gravel cover over the silt lining the
moraine is needed to prevent possible washout during the lake drawdown operation cycles.
While the upstream slope is assumed to be 1.5H: 1.0V, the downstream slope is assumed to be
3.0H: 1.0V. This flatter slope would incorporate the spillway chute structure, which in the vicinity of
the creek bed would be grouted and concrete lined. Additional hydrologic and hydraulic analysis
would need to occur in future studies, if it was decided to pursue this alternative for development.
3.4.2 Siphon Intake
To establish the maximum possible drawdown of the lake without the use of a tunnel, a deep trench
about 24-feet below normal lake El. 1360 ft, would be excavated to the centerline of the proposed
dam axis. This trench would then contain the siphon outlet pipe, which would then need to
continue to the forebay pool to permit effective use of the siphon, once it has been primed by
appropriate equipment. The siphon piping into the lake would need to be flexible piping, probably
HDPE and extend about 330 feet out into the lake to a depth of about 1310 feet to permit lake
drawdown to El. 1320 ft.
Due to the fairly thick silt layer that lies on the lake bottom, the intake to the siphon pipe would
include a raised platform with concrete footings to secure the intake to the bottom and prevent the
suction of silt into the intake.
The siphon equipment would be located inside a deep concrete vault at the downstream end of the
clay core. The top of the vault would be at about El .1380 ft and El. 1320 ft at the bottom. A
cofferdam into the lake would be needed to help facilitate the construction of the siphon inlet and
the completion of the dam where the trench excavation continues at 1335 feet into the lake.
The schematic drawing of the intake is shown in Figure 3.3.
Figure 3.3
Alt 3 Siphon Intake Facilities
Active Storage =
1 3 7 9 – 1 3 2 7 = 5 2 ’
–El 1379.0 New Max Pool
El 1367.0 Existing Max Pool
–El 1327.0 Min Pool
Existing Ground
Buried Pipeline
Pump House
Submerged
Screened Intake
Rock Fill Dam
Siphon Operation = 20 feet
12
20
Active Storage =
1 3 7 9 – 1 3 2 7 = 5 2 ’
–El 1379.0 New Max Pool
El 1367.0 Existing Max Pool
–El 1327.0 Min Pool
Existing Ground
Buried Pipeline
Pump House
Submerged
Screened Intake
Rock Fill Dam
Siphon Operation = 20 feet
12
20
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3.4.3 Forebay Structure
The forebay structure for Alt 3 is comprised of a concrete-gravity diversion weir to be constructed at
about Allison Creek El. 1300 ft. The diversion weir would be sufficiently high for providing sufficient
submergence to the penstock intake structure. The intake structure would have a Bellmouth
entrance and would have trashracks for screening out debris.
3.4.4 Penstock
The penstock is assumed to be an above ground, 33-inch-diameter, steel pipeline supported on
concrete cradles. The penstock follows a westerly alignment to the site of the tunnel portal location
of Alt 2, then follows the ridge nose down to the powerhouse site below.
3.4.5 Powerhouse
The powerhouse site would be near the creek El. 150 ft, or the same as described for Alt 2. It was
selected because the plant discharge would occur near an anadromous fish barrier and would allow
salmon and other anadromous fish to still make use of the stream habitat below the fish barrier.
The powerhouse would contain a single 4-MW synchronous generator with a 2-nozzle horizontal
Pelton turbine unit. The surface powerhouse would include a 15-ton bridge crane and all other
equipment required for operation and maintenance of the powerhouse. Remote control of the
powerhouse would be from the Solomon Gulch powerhouse. The tailrace flow would be released
back into the Allison Creek.
3.4.6 Access Road
While the COE assumed that helicopters would be used to transport equipment, material and
personnel to the tunnel portal during construction, we have assumed that a contractor would
construct an access road to the proposed forebay dam and to the Allison Lake outlet dam despite the
difficult terrain. The existing Solomon Gulch access road to its dam would be used and then be
extended generally as described for Alt 1 to the saddle location above the west side of the dam. The
road would then continue at a less than 10% grade in a westerly direction to the tunnel portal outlet.
A second road would make use of the existing access road for the Valdez Oil Marine terminal that
extends in a southerly direction on the east side of Allison Creek. From this road a 0.4-mile-long
road would be constructed to the powerhouse site.
As the surface penstock gradient from the forebay dam to the powerhouse structure is too steep for
access road construction, the construction contractor will likely need to make use of a high-liner to
facilitate its construction.
3.4.7 Ecological Return Flow Facility
Due to the deep lake tap and drawdown of the siphon option, it would not be possible to release
ecological flows at the lake outlet. Instead, the ecological flow releases would occur at the forebay
dam on Allison Creek. We have assumed that ecological flow releases would be equivalent to about
5% of MAD, or whatever flow is eventually negotiated with the fishery resource agencies.
Copper Valley Electric Association, Inc. - Allison Lake Hydroelectric Project
Pre-Feasibility Study
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4. Power Studies
AUTOVista was used to evaluate the generation benefits of various upgrade configurations under
consideration for the Project. AUTOVista is one of the several components of a decision support
system, Vista, which was developed by Hatch Acres for use by system dispatchers and engineering
operations staff, to assist them in short- and long-term scheduling to achieve maximum value for the
generation system. In this case, the AUTOVista component was used as an analysis tool to evaluate
the economic value of alternative project configurations and methods of operation. It considers plant
characteristics, water, pricing, and constraints in its calculations.
The following is a description of the program and a discussion of the use of AUTOVista on this
project.
4.1 AUTOVista Model: System Loads and Resources
The AUTOVista model operates on an hourly time step to meet system loads in the most cost
effective manner using available system resources as a function of their respective cost of production.
For the present study, the system load was based on CVEA data for 2006. The system resources
considered for the existing case included the combined diesel plant facilities in Valdez and
Glennallen, the combined cycle unit as operated under the contract with Petro Star, and the existing
hydropower facilities at the Solomon Gulch Project. The proposed development included the
additions as discussed in Section 2 above as well as retirement of the existing thermal generation
resources to the extent possible in each respective case under consideration.
4.2 AUTOVista Model: Allison Lake Hydropower Development
The AUTOVista model for the Project includes the drainage basins for both the existing Solomon
Gulch Hydroelectric Project and Allison Lake. It is comprised of a series of arcs and nodes with each
element having its set of characteristics. These basic elements and typical data associated with each
are summarized in Table 4.1.
Table 4.1
AUTO Vista Model Elements
Element Typical Characteristics
Arcs
Inflow Hourly inflow at discrete points within drainage basin
Spillway Spillway rating curves / discharge requirements
Open Channel (Streams) Minimum flows / ramping rates
Closed Conduits (Penstocks) Head loss coefficients
Nodes
Reservoirs Area-capacity data / elevation & discharge constraints
Powerhouse Units Efficiency data / maximum & minimum flows
The graphical model for the existing system Alt 1, Alt 2 and Alt 3 as expressed in these terms is
shown below in Figures 4.1, 4.2 and 4.3. Major features of the AUTOVista model are briefly
described below.
Copper Valley Electric Association, Inc. - Allison Lake Hydroelectric Project
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Figure 4.1
AUTO Vista Model Elements: Existing Project
Figure 4.2
AUTO Vista Model Elements: Alt 1
SLGR
(Solomon Gulch Reservoir)
SLGQ
(Solomon Gulch Inflow)
SLGP
(Solomon Gulch Power)
SLGT
(Solomon Gulch TWL)
S_SINK
(Source_Sink)
ALSQ
(Allison Lake Inflow)
A_SINK
(Source_Sink)
SINS
(Solomon
Instream Flow)
SLGS
(Solomon Gulch Spill)
ALSS
(Allison Lake Spill)
SLGINS_RJ
(Solomon Gulch INS Junc)
SLGS_RJ
(Solomon Gulch SPWY Junction)
ALSSPWY_RJ
(Allison SPWY TWL)
ALSR
(Allison Lake)
SLGR
(Solomon Gulch Reservoir)
SLGQ
(Solomon Gulch Inflow)
SLGP
(Solomon Gulch Power)
SLGT
(Solomon Gulch TWL)
S_SINK
(Source_Sink)
ALSQ
(Allison Lake Inflow)
A_SINK
(Source_Sink)
SINS
(Solomon
Instream Flow)
SLGS
(Solomon Gulch Spill)
ALSS
(Allison Lake Spill)
SLGINS_RJ
(Solomon Gulch INS Junc)
SLGS_RJ
(Solomon Gulch SPWY Junction)
ALSSPWY_RJ
(Allison SPWY TWL)
ALSR
(Allison Lake)
SLGR
(Solomon Gulch Reservoir)
SLGQ
(Solomon Gulch Inflow)
SLGP
(Solomon Gulch Power)
SLGT
(Solomon Gulch TWL)
S_SINK
(Source_Sink)
ALLQ
(Allison Reservoir Inflow)
S_SINK
(Source_Sink)
SINS
(Solomon
Instream Flow)
SLGS
(Solomon Gulch Spill)
ALLS
(Allison Reservoir Spill)
SLGINS_RJ
(Solomon Gulch INS Junc)
SLGS_RJ
(Solomon Gulch SPWY Junction)ALLS_RJ
(Allison SPWY Junc)
ALLR
(Allison Reservoir)
ATPS
(Allison Lake Tap)
SLGR
(Solomon Gulch Reservoir)
SLGQ
(Solomon Gulch Inflow)
SLGP
(Solomon Gulch Power)
SLGT
(Solomon Gulch TWL)
S_SINK
(Source_Sink)
ALLQ
(Allison Reservoir Inflow)
S_SINK
(Source_Sink)
SINS
(Solomon
Instream Flow)
SLGS
(Solomon Gulch Spill)
ALLS
(Allison Reservoir Spill)
SLGINS_RJ
(Solomon Gulch INS Junc)
SLGS_RJ
(Solomon Gulch SPWY Junction)ALLS_RJ
(Allison SPWY Junc)
ALLR
(Allison Reservoir)
ATPS
(Allison Lake Tap)
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Figure 4.3
AUTO Vista Model Elements: Alt 2 and Alt 3
4.3 Hydrology
The hydrology used for the prefeasibility is based on the work done by the COE in 1982 as part of
their evaluation of the potential project configurations for maximizing the Allison Lake resource. The
correlations developed from that study results in a 39-year period of average daily flows from 1950
through 1989. The annual inflow for each of the 39 years is shown on Figure 4.4.
Figure 4.4
Allison Lake Annual Inflow, 1951 - 1989
ALSR
(Allison Lake)
ALSQ
(Allison Lake
Inflow)
A_SINK
(Source_Sink)
ALSS
(Allison Lake Spill)
ALSP
(Allison Lake
Power)
ALST
(Allison Lake TWL)
SLGR
(Solomon Gulch Reservoir)
SLGQ
(Solomon Gulch Inflow)
SLGP
(Solomon Gulch Power)
SLGT
(Solomon Gulch TWL)
S_SINK
(Source_Sink)
SINS
(Solomon
Instream Flow)
SLGS
(Solomon Gulch Spill)
SLGINS_RJ
(Solomon Gulch INS Junc)
ALSSPWY_RJ
(Allison SPWY TWL)
ALSR
(Allison Lake)
ALSQ
(Allison Lake
Inflow)
A_SINK
(Source_Sink)
ALSS
(Allison Lake Spill)
ALSP
(Allison Lake
Power)
ALST
(Allison Lake TWL)
SLGR
(Solomon Gulch Reservoir)
SLGQ
(Solomon Gulch Inflow)
SLGP
(Solomon Gulch Power)
SLGT
(Solomon Gulch TWL)
S_SINK
(Source_Sink)
SINS
(Solomon
Instream Flow)
SLGS
(Solomon Gulch Spill)
SLGINS_RJ
(Solomon Gulch INS Junc)
ALSSPWY_RJ
(Allison SPWY TWL)
20,000
25,000
30,000
35,000
40,000
45,000
50,000
55,000
1950 1955 1960 1965 1970 1975 1980 1985 1990
Year
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Figure 4.5
Allison Lake Reservoir Storage
A statistical analysis of this period of record was performed to establish a representative smaller
group of 7 years for use within the present AUTOVista. The set of 7 years was chosen on the basis of
balancing the low to dry conditions of annual inflow to the two basins. The specific years chosen are
indicated by the large red dots in Figure 4.4 and the associated representative inflow conditions are
summarized in Table 4.2.
Table 4.2
AUTO Vista Hydrologic Years
4.4 Reservoir Characteristics
The minimum and maximum reservoir elevations
and storage characteristics for the Solomon Gulch
Reservoir were taken from the existing
information for the project as included in the
Supplemental Technical Information document as
prepared in support of the FERC Part 12 Safety
Inspection process for the project.
In the case of Allison Lake, stage relationships were taken from the previously referenced COE and
HDR studies as appropriate for Alt 1, Alt 2 and Alt 3. The available storage relationships, however,
were found through a recent study as performed by the Northern Arizona University as part of a
research of the receding of glaciers. The image taken from the web site that includes a description
and photographs of the research program and the resulting reservoir storage relationships are shown
on Figure 4.5.
Total Inflow
Year Percentile A cre-Feet
1969 10% 28,900
1984 25% 30,800
1954 25% 30,900
1961 50% 33,200
1957 75% 36,100
1977 75% 37,900
1989 90% 42,800
Average 34,400
1,100
1,150
1,200
1,250
1,300
1,350
1,400
0 5,000 10,000 15,000 20,000 25,000 30,000 35,000
Storage (Acre-Ft)
Alternative 3
Storage =12,100 Ac-Ft
Alternatives 1 & 2
Storage = 19,500 Ac-Ft
El. 1267
El. 1367El. 1379
El. 1327
1,100
1,150
1,200
1,250
1,300
1,350
1,400
0 5,000 10,000 15,000 20,000 25,000 30,000 35,000
Storage (Acre-Ft)
1,100
1,150
1,200
1,250
1,300
1,350
1,400
0 5,000 10,000 15,000 20,000 25,000 30,000 35,000
Storage (Acre-Ft)
Alternative 3
Storage =12,100 Ac-Ft
Alternatives 1 & 2
Storage = 19,500 Ac-Ft
El. 1267
El. 1367El. 1379
El. 1327
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4.5 Hydro Equipment Characteristics
The performance curves for the Solomon Gulch Powerhouse have been included as provided by the
CVEA. The new units at the proposed Allison Lake Powerhouse for Alt 2 and Alt 3 are based on
Hatch Acres in-house generic data for Pelton units. A plot of the characteristics used in this analysis
is shown in Figure 4.6.
Figure 4.6
Allison Powerhouse Unit Characteristics
All elements of the conduit system components for each alternative have been assumed to perform in
accordance with published engineering data.
4.6 AUTOVista Results
Representative plots of the annual operation of the Solomon Lake and Allison Lake Reservoirs are
included in Appendix B. The two primary observations from these plots for Alt 1 are that this
alternative attempts to conserve the storage in the Solomon Gulch Reservoir as long as possible and
that the Solomon Gulch Powerhouse is slightly undersized. In the case of Alt 2 and Alt 3, the plots
suggest a parallel operation of the two basins and demonstrate a reasonable balance between
reservoir storage and powerhouse capacity.
In addition, stacked bar charts indicating the most efficient dispatch of system resources as required
to meet the system load are included in Appendix C for the existing condition and Alt 2. The first
charts compare the existing condition and Alt 2 for the 1961 water year, which is the 50% year as
indicated in Table 4.2. Also included for comparative purposes are the charts for 1954 and 1977
water years which represent 25% and 75% water years respectively. Finally, a chart is included that
expands the scale to show a typical weekly dispatch from 1961.
The annual generation for each of the 7 years included in the analysis for the existing and Alt 1, Alt 2
and Alt 3 cases are shown in Tables 4.3, 4.4, 4.5 and 4.6 below.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 10 20 30 40 50 60Discharge (cfs)Efficiency (%)0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Power (MW)Efficiency
Power
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 10 20 30 40 50 60Discharge (cfs)Efficiency (%)0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Power (MW)Efficiency
Power
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Table 4.3
Annual Generation – Existing Condition
Table 4.4
Annual Generation – Alt 1
Table 4.5
Annual Generation – Alt 2
Year SG 1 SG 2 Allison Diesel Cogen Total
1969 32,500 19,700 NA 11,200 22,900 86,400
1984 34,100 22,000 NA 7,500 22,800 86,400
1954 31,400 22,700 NA 9,300 23,000 86,400
1961 34,800 23,500 NA 6,800 21,300 86,400
1957 35,200 24,800 NA 6,200 20,200 86,400
1977 36,500 25,300 NA 3,400 21,100 86,400
1989 35,200 26,700 NA 4,800 19,700 86,400
Average 34,200 23,500 NA 7,000 21,600 86,400
Generation (MW h)
Year SG 1 SG 2 Allison Diesel Cogen Total
1969 41,900 34,800 NA 1,900 7,800 86,400
1984 42,200 36,500 NA 1,600 6,100 86,400
1954 41,600 33,600 NA 200 11,000 86,400
1961 42,000 36,700 NA 300 7,400 86,400
1957 42,000 36,500 NA 300 7,600 86,400
1977 42,400 38,300 NA 100 5,600 86,400
1989 42,300 37,400 NA 200 6,600 86,400
Average 42,100 36,300 NA 700 7,400 86,400
Generation (MWh)
Year SG 1 SG 2 Allison Diesel Cogen Total
1969 37,400 19,000 26,600 400 2,900 86,400
1984 37,200 20,500 25,400 300 3,000 86,400
1954 35,700 20,600 23,500 600 6,000 86,400
1961 37,500 21,800 23,500 400 3,200 86,400
1957 37,500 20,700 23,300 700 4,100 86,400
1977 38,900 22,600 23,200 400 1,300 86,400
1989 37,700 21,100 23,700 900 3,000 86,400
Average 37,400 20,900 24,200 500 3,400 86,400
Generation (MW h)
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Table 4.6
Annual Generation – Alt 3
The annual general benefits from the AUTOVista Analyses can then be summarized as shown in
Table 4.7 in terms of the incremental hydropower generation and associated reduction on thermal
power as required to satisfy the system load for each of the three alternatives under consideration.
Please note that the minor differences between the hydro and thermal generation values for each
alternative are due to rounding within the AUTOVista modeling.
Table 4.7
Annual Generation Benefits
Year SG 1 SG 2 Allison Diesel Cogen Total
1969 35,700 17,400 26,000 300 7,100 86,400
1984 36,200 17,100 26,500 300 6,300 86,400
1954 33,800 16,200 24,700 600 11,000 86,400
1961 35,800 15,500 27,400 300 7,400 86,400
1957 35,500 16,400 26,700 300 7,500 86,400
1977 36,800 15,100 29,100 500 5,000 86,400
1989 35,900 15,300 28,300 300 6,700 86,400
Average 35,700 16,100 27,000 400 7,300 86,400
Generation (MW h)
Existing Alternative 1 Alternative 2 Alternative 3
Hydro 57,700 78,400 82,500 78,800
Fossil 28,600 8,100 3,900 7,700
Total 86,300 86,500 86,400 86,500
Benefit NA 20,500 24,700 20,900
Generation (MWh)
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5. Project Construction Cost and Schedule
Section five has been removed from this report. As of September 2008, no preferred alternative
has yet been identified for the three alternatives under review. The report contained the
following range of information
*Total capital required $27-$45 million
First year cost of power ($/kWh) $.138-$.181
Energy output (MWH’s) 20,500-24,700
Under the current plan of work it is anticipated a preferred alternative will be identified
following the 2008 field study season. Following that decision, a refined economic analysis and
final feasibility will be determined.
The pre-feasibility study concluded that any of the three proposed alternatives would produce
energy at a cost lower than the incremental cost of a diesel kWh which, as of September 2008, is
$.26 per kWh.
*Assumes 100% commercial financing at an interest rate of 7%
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6. Environmental and Regulatory Considerations
Three potential development options have been identified and discussed in the engineering and
economic analyses of developing the power potential at Allison Lake performed for Copper Valley
Electric Association, Inc. (CVEA):
Allison Lake Tap Diversion to Solomon Gulch Lake that would enhance generation at the
existing Solomon Gulch Project, FERC No. P-2742 (Alt 1)
Allison Lake Tap Hydro Project, a stand-alone project with a new powerhouse at tidewater
(Alt 2)
Allison Lake Siphon Hydro Project, a stand-along project with a new powerhouse at
tidewater (Alt 3)
This section of the report to CVEA includes a preliminary identification of regulatory &
environmental issues and a proposed work plan to clarify these issues and provide recommendations
for further analysis under the proposed Preliminary Permit to study options and develop an
Application for License. At this time, we are evaluating the issues and required studies that would
support an application to the Federal Energy Regulatory Commission (FERC). We are also
monitoring development of a State Hydro Licensing Program currently under consideration by the
Regulatory Commission of Alaska (RCA) that would, if approved by the RCA and FERC, transfer
licensing of projects of 5 MW or less from federal jurisdiction to the State of Alaska. Because the
study requirements under either FERC or State jurisdiction are essentially equal, the proposed work
plan would serve either regulatory option.
6.1 Regulatory Requirements Associated with All Alternatives
The FERC hydropower licensing process requires applicants to identify all interested resource
agencies, Tribes, and other interested persons and organizations and provide opportunities for
participation by all participants throughout the pre-filing preparation of the application and the post-
filing activities during the FERC staff processing of the application. The proposed State process
would include similar requirements.
Each of the three alternatives considered would require preparation of applications to the FERC. The
general timeframe for preparing the application and the FERC staff processing would be similar:
Consultations with resource agencies and other participants; identification of necessary field
and office studies to support an application to the FERC; performance of field and office
studies and report preparation; and preparation of the application document would require 2
to 3 years.
FERC staff review of the filed application and preparation of a recommendation to the
Commission regarding issuance of a license, or in the case of Alt 1 an application for
amendment to the existing license: potential requests for additional information;
consultation with the state and federal resource agencies as required under the Federal
Power Act (FPA) and the FERC regulations; preparation of the FERC documents required
under the National Environmental Policy Act (NEPA) and related noticing and comment
periods; and preparation of the Order Issuing License or Order Approving License
Amendment would require 19 months to 2 years.
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Following issuance of any Commission Order, there is opportunity for any participant to
request rehearing of the Order time required for this would depend on issues raised by the
participants.
Once any requests for rehearing are addressed, CVEA would notify the FERC that it accepts
the license as issued.
Regulatory requirements of the above described licensing process include:
Request by CVEA to FERC to use one of three options for the FERC licensing process the
default is the Integrated Licensing Process that imposes strict timeframes for all activities; the
Alternative Licensing Process, a collaborative process, that allows greater flexibility, but
includes some FERC-required deadlines; and the Traditional Licensing Process that exposes
applicants to additional exposure to late-requested resource agency requirements.
Consultation process as required by the FERC regulations, including negotiations with
resource agencies, et. al., regarding required studies program.
Consultation with Alyeska Pipeline Service Company regarding Alyeskas existing water
rights at Allison Creek (#61345 for 108,000 gpd priority date 6/11/73 and #11813 for
95.21 AF/yr priority date 3/16/88).
Resource agency recommended and mandatory measures under their separate authorities
that shape the construction and operation of FERC-licensed projects includes fisheries,
wildlife, and historic/cultural resources.
Requests for protection, mitigation, and enhancement measures to address project-related
effects on natural and cultural resources.
6.2 Alt 1 Allison Lake Tap Diversion to Solomon Gulch Project, FERC P-2742
The regulatory issues for Alt 1 differ significantly from either stand-alone project option in that an
Amendment to the existing license for the Solomon Gulch Project would be required. Presently the
Solomon Gulch Project is licensed to the Four Dam Pool Power Agency (FDPPA). Ongoing
negotiations related to the divestiture of the four projects with the members of the FDPPA may result
in a transfer of this license to CVEA. This transfer is anticipated to be complete by the time an
amendment to license would be filed.
CVEA would need to receive approval of the FDPPA if CVEA determines to pursue Alt 1.
Implementation of Alt 1 would require modifications to the existing Solomon Gulch Project and
require amendment to that license. Section 6 of the Federal Power Act states, in part, that
Licenses may be altered only upon mutual agreement between the licensee and the Commission
after thirty days public notice.
While not subject to a ruling by the FERC, CVEA would need to reach agreement regarding payment
for the additional generation at Solomon Gulch that would occur with the diversion of water from
Allison Lake to Solomon Gulch Reservoir and conveyance through pipelines to the generation units
at Solomon Gulch. Presently generation at Solomon Gulch is addressed in an existing Long Term
Power Sales Agreement.2 CVEA is a Party to this Agreement and the Solomon Gulch Project is
included in the Initial Project covered by this agreement. Section 1(f) states that Electric Power
2 LONG-TERM POWER SALES AGREEMENT, FOUR DAM POOL INITIAL PROJECT OF THE ALASKA
POWER AUTHORITY, 11-12-85.
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sold pursuant to this Agreement is Power from the Initial Project as defined in this Agreement. The
Parties recognize that additional physical facilities may be constructed in the future and considered
for addition to the Initial Project, but the Parties agree that facilities not included in the Initial Project
as defined in this Agreement may not be added to the Initial Project for purposes of this Agreement
except by subsequent agreement of the Parties.
The license to operate Solomon Gulch was issued to CVEA in 1978; the license was transferred to
the State of Alaska in 1982 as part of the Energy Project for Alaska; and in January 2002 the license
was transferred to the FDPPA. CVEA operates the Solomon Gulch Project through a contract with
the FDPPA.
Regulatory and environmental issues include:
Potential impacts to the Valdez Fisheries Development Association (VFDA) hatchery
operations. In 1991 the Alaska Energy Authority (AEA), CVEA, and VFDA signed an
agreement regarding the use of water resources and maintenance of instream flows in
Solomon Gulch Creek (1991 Agreement). The 1991 Agreement recognizes that VFDA
needs predictable and reliable water year-round for hatchery operations. Issues that may
arise with an Amendment to transfer water from Allison Lake to Solomon Lake include:
-Potential impacts associated with Allison Lake water mixing with Solomon Lake on
hatchery operations water chemistry and potential pathogens and change in the scent
of release and potential confusion to returning hatchery fish.
-Renegotiation of the 1991 Agreement, including the current required 2 cfs instream flow
release. The VFDA is on record as requesting an increased release of 12 cfs (1-30-1996
Motion to Intervene). VFDA may also request revision to the energy water payment
clause.
-Potential mitigation requests by VFDA to improve its own piping within the hatchery
and other potential improvements.
Potential requests by the Alaska Department of Fish and Game (ADF&G), the US Fish and
Wildlife Service (USFWS), and the National Marine Fisheries Service (NMFS) for modifications to
the existing license articles that address fisheries concerns, including the 2 cfs minimum flow
release. The Amendment would constitute a material change in operations at Solomon Gulch
and these agencies could request additional Protection, Mitigation, and Enhancement (PM&E)
measures given the significant changes in their respective authorities from those in place at the
original license issuance. ADF&G now can request PM&E measures under Section 10(j) of the
Federal Power Act, and the USFWS and NMFS now enjoy mandatory conditioning authority.
Potential requests by ADF&G, USFWS, and NMFS for an instream flow release from Allison Lake
to compensate for the cross-basin transfer of flow currently available to Allison Creek.
The Amendment would re-open the existing Solomon Gulch License and all aspects of project
operation would be reviewed and could include additional requirements for recreation
enhancements.
Literature search and on-the-ground survey for potential project-related effects on any historic,
cultural, and archaeological resources eligible for listing on the National Register.
Correspondence from the SHPO on March 15, 2006 identified historic resources in the
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immediate vicinity of Solomon Lake which may have the potential to be adversely affected by
activities related to this [Allison Lake] project.
6.3 Alt 2 Allison Lake Tap Hydro Project
The regulatory issues for Alt 2 relate to a stand-alone project that would be licensed by either the
FERC or the State of Alaska and would not affect the existing Solomon Gulch license discussed above
at Alt 1. The studies program would be developed in consultation with the resource agencies and
other interested participants.
Regulatory and environmental issues include:
The proposed 90-foot drawdown of Allison Lake potential project-related effects on visual and
aesthetic resources at Allison Lake and reduced flow in the creek; and recreational access to and
use of the area, including Allison Creek downstream of the lake tap.
Potential need to release an instream flow between the lake tap and the powerhouse. FERC and
the resource agencies are currently requiring that an instream flow release be made to any
stream that would be dewatered due to hydro operations. The release from the lake tap/tunnel
scheme would need to be addressed could require pumping operations to ensure a minimum
flow.
Existing and potential geological and soil hazards in the project area potential landslides,
avalanche chutes, and seismic areas.
Use of the project area by mountain goats and potential project-related effects, in particular
spring kidding and rearing.
Bird study to determine whether there are any project-related effects on birds protected under
the Migratory Bird Treaty Act.
Habitat surveys for terrestrial and aquatic species in the project area.
Restoration of vegetation along the tunnel right-of-way.
Powerhouse operations and potential effects on fisheries, including effects of temperature
changes on spawning, rearing, and egg incubation, and emergence timing.
Literature search and on-the-ground survey for potential project-related effects on any historic,
cultural, and archaeological resources eligible for listing on the National Register.
6.4 Alt 3 Allison Lake Siphon Project
The regulatory issues for Alt 3 relate to a stand-alone project that would be licensed by either the
FERC or the State of Alaska and would not affect the existing Solomon Gulch license discussed above
at Alt 1. The studies program would be developed in consultation with the resource agencies and
other interested participants.
Regulatory and environmental issues include:
The proposed 50-foot drawdown of Allison Lake potential project-related effects on visual and
aesthetic resources at Allison Lake and reduced flow in the creek; and recreational access to
Allison Lake.
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Existing and potential geological and soil hazards in the project area potential landslides,
avalanche chutes, and seismic areas.
The proposed surface pipeline/penstock from Allison Lake to the powerhouse at tidewater
potential project-related effects on wildlife migration and recreational access along the pipeline
corridor.
Potential need to release an instream flow between the low dam at the outlet and the
powerhouse. FERC and the resource agencies are currently requiring that an instream flow
release be made to any stream that would be dewatered due to hydro operations.
Use of the project area by mountain goats and potential project-related effects, in particular
spring kidding and rearing.
Bird study to determine whether there are any project-related effects on birds protected under
the Migratory Bird Treaty Act.
Habitat surveys for terrestrial and aquatic species in the project area.
Powerhouse operations and potential effects on fisheries, including effects of temperature
changes on spawning, rearing, and egg incubation, and emergence timing.
Literature search and on-the-ground survey for potential project-related effects on any historic,
cultural, and archaeological resources eligible for listing on the National Register.
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7. Conclusions and Recommendations
The primary activities of the current pre-feasibility study have included the following:
a reconnaissance review of the project site,
identification of three potential physical means to develop the hydropower potential of
Allison Lake,
an evaluation of the power production capability of the selected arrangements,
cost estimates of each arrangement leading to the cost of power there from and
an evaluation of the environmental and regulatory issues involved with each arrangement.
The three potential configurations considered include:
A lake tap and tunnel diversion of Allison Lake inflow to the existing Solomon Gulch
Reservoir.
A lake tap and tunnel / penstock connecting to a new powerhouse on Allison Creek.
A low dam and siphon intake with an above ground penstock connecting to a new
powerhouse on Allison Creek.
The conclusions and recommendation resulting from the study of these alternatives are included
below.
7.1 Conclusions
The conclusion gained from the studies performed as a part of the present evaluation include:
The three project configurations studied all have the appearance of being technically
feasible. Arguments can be made on behalf of any of the three as being the best in this
regard, the truth is yet to be determined through detailed on the ground geotechnical
investigations.
The three project configurations would all appear to deliver power to the CVEA at a cost less
than the current cost of fossil generation on the basis of reasonably conservative assumptions
for construction cost estimating and financing arrangements.
All three configurations would benefit greatly from grant monies from the state or more
attractive financing arrangements as provided for under the recently enacted Federal Energy
Act.
Uncertainties exist in the area of environmental and regulatory process for each of the three
arrangements as follows:
-Alt 1 involves an amendment to the existing license for the Solomon Gulch Project.
The Amendment would be a Capacity Amendment and would potentially open the
terms of the existing license. Issues of concern include:
o Concerns raised by the VFDA regarding interest in increasing the current
minimum flow release from 2 cfs to 12 cfs and potential impacts on the
hatchery from trans-basin delivery of water from Allison Lake affecting
hatchery operations;
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o potential for the resource agencies to request an increase in the minimum
flow release and/or to require better management of the release given the
history of interruptions in delivery of the current 2 cfs release requirement;
and,
o potential for interested participants to request increased recreational access
and related improvements to the trail system. The VFDA raised issues related
to the minimum flow release in the previous license transfer proceedings. If
Alt 1 is selected, CVEA should consider how to address these concerns given
the proposed divestiture of the FDPPA and transfer of the Solomon Gulch
license to CVEA.
-Alt 2 and Alt 3 would introduce a drawdown in the current lake level at Allison
Lake and reduce the current flow from Allison Lake to Allison Creek and tidewater.
-Alt 2, the lake tap, would have the most significant drawdown of the Lake and the
release to Allison Creek may require pumping from the lake to a release to the
Creek.
-Alt 3, the siphon intake arrangement would have the most visual and terrestrial
impact to the area owing to the surface conduit arrangement.
The general pros and cons of the three alternatives are summarized in Tables 7.1, 7.2 and 7.3
respectively.
Table 7.1
Alt 1 Pros and Cons
Alt 1 Pros Alt 1 Cons
Low visual and terrestrial impact Requires FDPPA permission to generate at
Solomon Gulch Project P-2742
New generation facilities are not
required
Requires re-negotiation of power purchase
contract with FDPPA
No access to Allison Lake is
required
Amendment Opens existing Solomon Gulch
Project could result in additional
requirements
Provides opportunity for Phase 2
development of new powerhouse
at banks of Solomon Gulch
Reservoir
May require modification to existing 2 cfs
minimum flow release
Lowest initial cost of development
and incremental unit cost of power
May require re-negotiation of Agreement
with Valdez Fisheries Development
Association
Low exposure to elements Involves cross-basin transfer of water
change in chemistry and pathogens
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Alt 1 Pros Alt 1 Cons
Proposed100-foot drawdown visual effects
Requires release from Allison Lake down
Allison Creek additional facilities
Table 7.2
Alt 2 Pros and Cons
Alt 2 Pros Alt 2 Cons
No impact to current Solomon Gulch
FERC License or existing FDPPA
Power Sales Agreement
Higher unit cost of power than Alts 1 & 3
Higher amount of additional energy
than Alts 1 & 3
Proposed 100-foot drawdown visual
effects
Minimal exposure to elements Requires pumping from tunnel to release
minimum flow to upper reaches of Allison
Creek
No access required to Allison Lake
Tunnel reduces barrier to wildlife
movement and disturbance to
mountain goats during kidding &
rearing
Tunnel reduces overall effects on
terrestrial resources and visual effects
Table 7.3
Alt 3 Pros and Cons
Alt 3 Pros Alt 3 Cons
No impact to current Solomon
Gulch FERC License or existing
FDPPA Power Sales Agreement
Greater above-ground construction and
effects on terrestrial and visual resources
than Alts 1 & 2
Lower unit cost of power than Alt 2 Pipeline may provide barrier to mountain
goats and other terrestrial species
Proposed 52-foot drawdown less
visual effects than Alts 1 & 2
Greater exposure to elements than Alts 1 & 2
Copper Valley Electric Association, Inc. - Allison Lake Hydroelectric Project
Pre-Feasibility Study
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7.2 Recommendations
Based on the conclusions outlined above, CVEA would be well served to undertake the following:
Of three alternatives considered in this study, Alternative 2, the proposed lake tap and
tunnel/penstock with a new powerhouse on Allison Creek appears to provide the greater
long-term benefit to the CVEA system. However, to preserve any of the three options for
further investigation, we recommend that CVEA prepare an application for preliminary
permit for Allison Lake including the three alternatives stated in this report. CVEAs
Application for Preliminary Permit should be filed at the earliest date possible following
expiration of the permit in effect to Green Power.
During the first six-month period of the three-year preliminary permit term, narrow the range
of alternatives to focus on the best fit to meet CVEAs future demand for electric power.
Consult with the VFDA, ADF&G, NMFS, USFWS, and the Alaska Department of Natural
Resources (ADNR) water resources, land management and State Historic Preservation
Officer in preparing its Application for Preliminary Permit. The Application for Preliminary
Permit requires a detailed Work Plan be prepared and filed with the Application. These
resource agencies and the hatchery will shape the studies program to be conducted under
the terms of the Preliminary Permit.
Request approval to use the Alternative Licensing Process (ALP) instead of the required
default Integrated Licensing Process (ILP). The ALP allows greater flexibility in scheduling
activities and conducting studies. The ILP is better suited to a relicensing where issues are
related to continuing project operations.
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8. References
1. HDR Engineering, Inc., Allison Lake Reconnaissance Study, prepared for Alaska Energy
Authority, September 1992.
2. US Army Corps of Engineers, Electric Power for Valdez and the Copper River Basin, Interim
Feasibility Report and Final Environmental Impact Statement, March 1981.
3. Schiff, Caleb. Thesis: "Late-Holocene temperature of Prince William Sound, Southern
Alaska." 2006. Northern Arizona University.
<http://oak.ucc.nau.edu/cjs235/AlaskaClimate/allison.html>
Photo 1: Allison Lake Drainage – Looking South
Photo 2: Allison Lake Drainage – Looking North
Photo 3: Allison Lake Outlet – Looking West
Photo 4: Allison Lake Outlet Area – Looking South
Photo 6: Allison Creek – Existing Stream Gauge
Photo 5: Allison Lake Bank – Potential Lake Tap Area
Photo 8: Allison Lake Looking South
Alt 2 Tunnel Portal Area
Photo 7: Solomon Gulch Lake
Bench @ East Bank / Alt 1 Tunnel Portal Area
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul620610600590580670660650640630690680Elevation (feet)MonthAlt. 1Alt. 3Alt. 2ExistingAppendix B-1
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul620610600590580670660650640630690680Elevation (feet)Month7 Year Study RecordAppendix B-2
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul620610600590580670660650640630690680Elevation (feet)Month7 Year Study RecordAppendix B-3
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul620610600590580670660650640630690680Elevation (feet)Month7 Year Study RecordAppendix B-4
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul620610600590580670660650640630690680Elevation (feet)Month7 Year Study RecordAppendix B-5
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul1340132013001280126013601380Elevation (feet)Month7 Year Study RecordAppendix B-6
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul1340132013001280126013601380Elevation (feet)Month7 Year Study RecordAppendix B-7
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul1340132013001280126013601380Elevation (feet)Month7 Year Study RecordAppendix B-8
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJul2.06.08.010.04.012.014.0MonthGeneration (MW)SG 1SG 2AllisonCogenDieselAppendix C-1
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJulMonthGeneration (MW)2.06.08.010.04.012.014.0SG 1SG 2AllisonCogenDieselAppendix C-2
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJulMonthGeneration (MW)2.06.08.010.04.012.014.0SG 1SG 2AllisonCogenDieselAppendix C-3
Nov Dec Apr MayJan JunMarFeb Sep Oct NovAugJulMonthGeneration (MW)2.06.08.010.04.012.014.0SG 1SG 2AllisonCogenDieselAppendix C-4
Generation (MW)2.06.08.010.04.012.0Day 1 Day 6Day 5 Day 7Day 4Day 3Day 2SG 1SG 2AllisonCogenDieselAppendix C-5