HomeMy WebLinkAboutShallow Temperature Survey Naknek Electric Association
SHALLOW
TEMPERATURE
SURVEY
NAKNEK
GEOTHERMAL
SOURCES,
ALASKA
HDL 07-303
February 8, 2008
Lorie M.
Principal G
Dilley, PE/CPG
eologist
3335 Arctic Blvd., Ste. 100
Anchorage, AK 99503
Phone: 907.564.2120
2 Fax: 907.564.212
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page i
TABLE OF CONTENTS
EXECUTIVE SUMMARY..................................................................................... 1
1.0 INTRODUCTION....................................................................................... 3
2.0 BACKGROUND AND PREVIOUS FINDINGS.......................................... 3
2.1 LOCATION....................................................................................................... 3
2.2 CLIMATE.......................................................................................................... 4
2.3 GEOLOGICAL EVALUATION ....................................................................... 5
3.0 SHALLOW TEMPERATURE PROBE METHOD...................................... 6
4.0 SHALLOW TEMPERATURE SURVEY RESULTS .................................. 7
5.0 THERMAL MODELING .......................................................................... 10
5.1 ASSUMPTIONS AND RESULTS .................................................................. 11
6.0 CONCLUSIONS...................................................................................... 12
7.0 LIMITATIONS .........................................................................................13
8.0 BIBLIOGRAPHY .....................................................................................14
LIST OF FIGURES
Figure 1 Vicinity Map
Figure 2 Site Map
Figure 3 Map Legend
Figure 4 Absolute Temperatures on Topo Map
Figure 5 Deviatoric Temperatures on Landsat Map
Figure 6 Deviatoric Temperatures on Aeromagnetic Anomaly Map
LIST OF APPENDICES
Appendix A Photo Log
Appendix B Geochemistry Report for Lynx Road Spring Water
Appendix C Thermal Modeling
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 1
EXECUTIVE SUMMARY
Naknek Electric Association in Naknek, Alaska generates power to meet the demand of
3 megawatts (MW) in the winter with an increase to 7.3 MW during the summer months
due to the canneries and fish processing. The communities of Naknek and King Salmon
have a population of 1120 according to the 2000 census. The regional power peak
demand is approximately 8.4 MW in the winter and 13.1 MW in the summer, and
includes the load from 23 local communities. The production of a regional geothermal
facility has the potential to displace the use of 3.5 million gallons of diesel fuel annually.
The cost of diesel in 2007 ranges from $2.20 to $4.46 per gallon in the area. NEA
envisions as many as 30 local communities could eventually benefit from a geothermal
power project, starting with a 25-megawatt plant and expanding the capacity in 12.5 MW
increments as additional communities are connected and demand increases. Financial
feasibility of this project depends on the existence of an economically viable resource in
the Naknek area.
No direct evidence of an economically feasible resource in the Naknek area has been
found to date (HDL, 2007). However, previous work has found several overlapping
datasets of interest in the Naknek-King Salmon area, pointing to a region for further
consideration. Linear magnetic anomalies indicate the possibility of crossing faults in the
King Salmon area, which could provide a mechanism for deeper, warmer fluids to rise.
Remote sensing work by LAPP, Inc. indicates thermally anomalous surface areas.
Geothermometry on fluids from the bottom of a well drilled to 255 feet near King Salmon
indicated that the fluids may have at some point and at some unknown depth been at
about 90°C (190°F).
To further investigate this region of interest, a shallow temperature survey was
undertaken in November, 2007. One hundred temperature measurements were made
at a depth of 2 meters (6 feet) below the ground surface. Results were corrected for
basic differences in soil type and solar exposure by taking the average for each group of
measurements and then finding the deviation of each temperature from this average.
Sources of error in these deviatoric measurements may come from microclimates,
shallow groundwater flow and soil moisture, and differences in vegetation.
This survey points to three regions worthy of further study. An apparent temperature
anomaly was noted near a spring off of Lynx Road in Naknek. A geochemical
assessment of the water of the spring indicates anomalous silica suggesting a small
percentage of admixed deep thermal water. A number of probe locations returned
anomalous temperature readings in the area around King Salmon, especially near the
Air Force base. Although this may be due to the heat island effect of the town (paved
areas and heated buildings may be contributing to the heat in the ground), it is
interesting that this apparent anomaly occurs near the crossing of two roughly linear
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 2
aeromagnetic lows. A couple of anomalous temperatures were measured about 3 miles
northeast of King Salmon. This area also corresponds with aeromagnetic lows and a
possible temperature anomaly noted by Lapp, Inc in a remote sensing study. Denser
probing in each location would help investigate the possible anomalies. Geochemical
investigation and investigation of the local temperature gradient by deeper drilling (to
greater than 20 meters) may also assist in determining the existence of thermal
anomalies.
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 3
SHALLOW TEMPERATURE SURVEY
NAKNEK GEOTHERMAL SOURCES, ALASKA
1.0 INTRODUCTION
This study presents the results of our shallow temperature probe survey in the Naknek
region of the Alaska Peninsula. The purpose of this survey was to map areas of
elevated temperature at the depth of 6 feet below the ground surface as a preliminary
tool for geothermal prospecting in the Naknek region. This report is based on the
literature review conducted, HDL field work, and information presented in a previous
HDL report entitled ‘Preliminary Geological Evaluation, Naknek Geothermal Sources’
dated September 13, 2007. This is a preliminary survey to indicate locations of thermal
anomalies that may be associated with a geothermal source.
2.0 BACKGROUND AND PREVIOUS FINDINGS
2.1 LOCATION
Naknek is located on the Alaska Peninsula in the Bristol Bay Borough, Alaska. The area
is located at Latitude at 58°44′23″N, Longitude 156°58′18″W. Naknek is located on the
north bank of the Naknek River, close to where the river runs into the Kvichak Bay arm
of the northeastern end of Bristol Bay. A vicinity map is presented in Figure 1 and
topographic site map in Figure 2. Naknek is accessible by air and sea, and connects to
King Salmon via a 15.5-mile road. The Tibbetts Airport in Naknek has a lighted 1,700
foot long by 60 foot wide gravel runway. The State-owned Naknek Airport is located one
mile north of Naknek. It has a 1,950 foot long by 50 foot wide lighted gravel runway and
a 2,000 foot float plane landing area. Jet services are available at King Salmon.
The closest zones of known geothermal resource are associated with the volcanic
centers in Katmai about 70 miles to the southeast and at Ukinrek Maars and gas rocks
about 70 miles to the south. The hottest thermal springs in the Katmai Cluster are
measured at 167°C (333°F) on Mount Mageik according to the Geothermal Resources of
Aleutian Arc. The most recent temperature measurement of the surface waters at
Ukinrek Maars is 16°C (61°F). Gas Rocks is located a little over a mile north of the
Maars. These have a measured surface temperature of 39°C (102°F), with a reservoir
temperature of 108°C (226°F) listed in the Geothermal Resources of Aleutian Arc.
The occurrence and behavior of faults is important in geothermal exploration.
Geothermal potential is related to open fractures and faults which may provide pathways
for geothermally heated fluids to migrate in the crust, and the movement of faults in the
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 4
presence of friction provides a mechanism for heat generation. The Bruin Bay Fault cuts
through Katmai National Park to the east of Naknek and can be mapped for 330 miles
from Mt. Susitna to the south shore of Becharof Lake. This is the closest mapped fault
to Naknek, but there may be faults buried beneath the deep glacial sediments that
overlie the Naknek area.
2.2 CLIMATE
Naknek is located in a marine climate. Precipitation at the King Salmon airport averages
almost 20 inches, with 45 inches of snowfall annually (AEDIS). Highest amounts of
precipitation are generally in the months of July through October. Average maximum
summer temperature is 63.5°F (17.5°C), average minimum winter temperature is 7.7°F
(-13.5°C), average yearly temperature is about 34.5°F (1.4°C).
Recent analysis of air temperature data for the King Salmon station shows that the area
is experiencing a warming trend. The following graph from the Alaska Climate Research
Center at the University of Alaska Fairbanks (2007) shows the increase in the mean
annual temperature from 1949 to 2006. In King Salmon the trend is an increase of 4.3°F
(2.4°C) or 0.08 °F (.04°C) per year for the 57 year period, See Figure 2.2.1.
Figure 2.2.1 Mean Annual Temperatures for King Salmon from 1949 to 2006, with 5-year
moving average in red and trend line in black.
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 5
2.3 GEOLOGICAL EVALUATION
A previous report has been provided by HDL entitled ‘Preliminary Geological Evaluation,
Naknek Geothermal Sources’ and dated September 13, 2007. The information that
follows is a summary of some of the relevant data from that report.
Aeromagnetic Anomalies
Aeromagnetic data on the Alaska Peninsula shows both positive and negative anomalies
in the near vicinity of Naknek. There are apparent northeast to southwest linear trends
in both the high and low magnetic anomaly areas, as well as a more “blobby” structure.
Glacial sediments tend to be non-magnetic. Magnetic anomalies could represent
underlying rocks with a more magnetic signature, such as buried volcanic flows or
intrusions or sedimentary rocks with magnetic components. Magnetic lows or high
gradients in the magnetic anomalies (such as abrupt changes from high to low) may
correspond to fault traces.
Remote Sensing
A remote sensing study was undertaken by Lapp Resources, Inc. They used airborne
digital multispectral video to visually search for evidence of natural linear trends in the
region that could be significant geologic features such as faults. They also used the
visual colored images to search for anomalous or unusual looking areas. These areas
may represent altered sediments or stressed vegetation, and could be caused by
hydrocarbon or geothermal “microseepage”. Three larger areas of these anomalies are
identified near the Naknek River in the vicinity of King Salmon. These areas also seem
to nearly correspond with the location of the crossing area of two linear aeromagnetic
lows.
Geothermal Potential
The regional temperature gradient in the whole Alaska Peninsula away from volcanic
centers seems to be in the range of 2°F or slightly less per 100 feet (or about 36°C per
kilometer). This is corroborated by bottom hole temperatures from wells drilled in the
area for oil exploration. To utilize this regional temperature gradient to produce
geothermal power in Naknek, wells of about 10,700 feet (3,260 meters) deep would be
needed, given that the starting ground temperature at the surface is around 36°F (2.2°C)
and that traditional geothermal power plants have needed fluids in excess of around
250°F (120°C) to operate in a commercially viable way.
Natural enhancements to this background geothermal gradient would increase the
geothermal viability of the area. Faults, for example, that allow deeper, hotter, fluids to
rise towards the surface or laterally from a source near the volcanic centers could
provide this enhancement. Although no faults have yet been mapped in the Naknek
area, and no direct evidence for an enhanced geothermal gradient exists, possible
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 6
thermally anomalous areas and linear (fault-like) features have been identified in the
region of Naknek by remote sensing (Lapp Resources, Inc, 2006). Particularly intriguing
are the correspondence of the linear magnetic anomaly lows in the vicinity of the NEA
drilling sites and the three large (possibly thermal) anomalies noted by Lapp Resources,
Inc. A northeast to southwest-trending linear magnetic low appears to cross one
trending northwest to southeast in this region. These lows could indicate the presence
of crossing faults in this area. Additionally, the shallow test well drilled by NEA this year
at the gravel pit site confirmed the presence of shallow bedrock and fluids at depth, and
geothermometry indicated the possibility of warm source fluids. The region
encompassing these anomalies and the gravel pit site were therefore chosen for a
shallow temperature probe survey to investigate local thermal anomalies.
3.0 SHALLOW TEMPERATURE PROBE METHOD
Shallow temperature measurements from 1 to 2 meters below the ground surface have
been used successfully to find and delineate blind geothermal resources in other areas
(e.g. Coolbaugh et al, 2007; Leshack et al, 1979). These results can be used without
much correction in ideal locations such as in the arid southwestern United States, where
soil types are relatively uniform and soil moisture and shallow ground water are not
much of a factor (Coolbaugh, 2007). In areas with less ideal conditions, an estimate of
soil diffusivity (or conductivity) and knowledge of shallow groundwater flow can help
correct the raw data and provide data that adequately matches temperature gradient
anomalies provided by deeper drilling (Leshack et al, 1979). Despite these caveats,
shallow temperature probing can be a good geothermal prospecting tool, allowing
relatively cheap and rapid reconnaissance of an area, and provide an indication of
locations of temperature anomaly.
Fieldwork was conducted between November 12 and 17, 2007. November was
considered a good time to do field work, as the ground was still soft enough to permit
easy penetration of the probes, and precipitation and infiltration of surface water into the
subsurface is minimal. A photo log of the field work is presented in Appendix A, showing
many of the procedural steps to the survey. One hundred test probe locations were
driven to a depth of 2 meters (6 feet) by two teams of two workers. One-quarter-inch
inside diameter steel pipe probes were driven into the ground approximately 2 meters (6
feet) deep. A Resistance Temperature Detector (RTD) was inserted into the probe, and
after the subsurface was allowed to stabilize the soil temperature was recorded.
Probes were driven daily from November 12 until November 17. Temperatures were
measured in the bottom of the probes from November 13 through 17. Probes were
generally left in the ground over night and temperatures were measured the next day.
On the final day of fieldwork, some temperatures were measured after the probe had
been in the ground for an hour, which is considered enough time for temperature
equilibration of the steel probe with the ground.
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 7
Probe emplacement on tundra away from roads and trails was hampered by the rough
and sometimes soft nature of the ground, and by impassable streams and lakes. For
this reason, most probes were driven within about 30 meters of a road or trail to get
good initial coverage of the area. See Figure 4 for probe locations.
Two recording stations were set up to monitor hourly changes in temperature at two
probe locations on opposite ends of the investigated area. Both of these stations were
in areas with trees. Daily effects were not expected at the probe depth, and seasonal
effects were also expected to be very small. No detectable changes were noted in the
temperatures at the recording stations over the 5 days that temperatures were recorded.
The temperature change detection limit of our equipment was about 0.25°C. Thus, no
correction was made to our measured temperature for seasonal changes. If additional
work is done, it will be necessary to drive one or two probes as near as possible to probe
locations from this survey to tie the two surveys together by correcting for seasonal
variations in ground temperature. Similarly, repeated measurements of temperature
must be made in these probe locations throughout the length of the survey to correct for
any seasonal variations during the survey.
4.0 SHALLOW TEMPERATURE SURVEY RESULTS
A first look at the data (below) reveals that at least two different populations are present
in the measurements. Areas of tundra devoid of trees generally had temperatures at 6
feet in depth between 1 and 3°C, with an average of about 2.2°C. Areas with trees or
brush (even if these trees were sparse or small) appear to belong to a separate
population with a range of about 3 to 6°C, with an average value near 4.7°C. The
difference in the average temperature observed between the tundra and tree area is
probably due to differences in the thermal diffusivities of the soils underlying the sites; to
shallow groundwater differences; and to the vegetation’s ability to trap heat. Areas of
tundra without any trees are likely underlain by poorly drained, fine grained soils and
organics. These areas may also be underlain by permafrost deeper than 6 feet, though
no probe locations in this survey found frozen ground at 6 feet in depth. Two other small
groups were separated off. Three probes were driven in gravel pits, and four were
identified to be in regions with southern exposure. Both of these areas were found to be
warmer than even the tree areas on average, as could be expected from enhanced solar
heating due to lack of ground cover or southern exposure.
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 8
Histogram of Recorded Temperatures by Ground
Type
0
5
10
15
20
25
30
35
11.522.533.54 55.566.577.5
Temperature Bins - Degrees CFrequency Tundra
Trees
South
Gravel
A legend to the maps showing temperature measurements is presented in Figure 3.
Figure 4 presents a map of the area with absolute temperature at probe locations
indicated by the color of the dot, as given in the map legend. No correction is made here
for the differing populations discussed above, and one is cautioned against drawing
conclusions from this map alone. Figures 5 and 6 present maps of the area where
deviations of temperature from the average for the population are plotted. These
deviations were calculated as follows: First the probe locations were divided up into the
four groups (tundra, trees, south facing, gravel pits). An average was obtained for each
of these four groups, and this average was subtracted off from each measurement in the
group to arrive at the temperature deviation. The absolute range of temperatures
measured is less than 7°C, after the above corrections, the range of deviation is about
5.5°C. This is not a large range, but shallow temperature probing of a known anomaly at
Upsal Hogback in Nevada had a temperature range of about 4°C. Upsal Hogback was
an unknown geothermal area until 1903, when a well being drilled for a survey camp hit
boiling water at about 60 feet in depth (Garside and Schilling, 1979).
Several explanations for temperature deviations on Figures 5 and 6 are possible. In
some cases, the probe locations may not have been put in the correct representative
group. For example, some tundra locations were small and near to tree locations, so
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 9
may have thermal characteristics at depth more closely resembling the tree areas (see
the Thermal Modeling section below). This example would result in an apparent “hot
spot” that may not be real, but instead is due to the incorrectly assumed thermal
characteristics. Variations in thermal diffusivity, sun exposure; soil moisture, ground
water presence and flow, measurement errors, microclimates, vegetative cover
differences, and precipitation and snow cover differences could all also cause erroneous
temperature deviations to be noted.
Given the above caveats, three areas appear worthy of further study at this time. An
apparent temperature anomaly was noted near a spring off of Lynx Road in Naknek
(Figures 5 and 6). A geochemical assessment of water sampled from the spring by Bill
Edwards of NEA was carried out in December of 2007 at the New Mexico Tech
Laboratory. The analysis by David Norman at New Mexico Tech is presented in
Appendix B and shows the water has low total dissolved solids and has a chemical
composition similar to rainwater. A high iron content suggests bog waters. The silica
content is slightly high, suggesting a small percentage of admixed deep thermal water.
Geothermometry is the process of using the chemistry of a fluid to indicate if the water
has had contact with higher temperature fluid. Using the silica content, a quartz
geothermometer puts the temperature at about 62°C (144°F). It is unknown at what
depth or at what point in the fluid’s history this temperature was achieved, and certain
assumptions are made in the calculation, including no mixing or boiling of the fluid. This
is slightly less than the geothermometry temperature result for the Naknek River water
from our previous report, ‘Preliminary Geological Evaluation, Naknek Geothermal
Sources’. Further shallow temperature probes nearby may indicate the nature and
extent of this possible anomaly.
A number of probe locations returned anomalous temperature readings in the area
around King Salmon, especially near the Air Force base. Although this may be due to
the heat island effect of the town (paved areas and heated buildings may be contributing
to the heat in the ground), or to some other effect of being a populated area, it is
interesting that this apparent anomaly occurs near the crossing of two roughly linear
aeromagnetic lows (Figure 6). These magnetic lows may indicate the presence of faults,
and crossing high-angle faults commonly provide the pathway for warm fluids to rise
toward the surface in areas of geothermal activity. This area could be investigated by a
denser arrangement of probes to help delineate the apparent temperature anomaly and
investigate whether it follows populated areas or the aeromagnetic lows more closely. It
may be especially useful here to drive probes on the south side of the Naknek River
near this location and in the LAPP feature anomaly (Figure 5).
A couple of anomalous temperatures were measured about 3 miles northeast of King
Salmon (labeled Area 3 on Figures 5 and 6). This area also corresponds with
aeromagnetic lows and a possible temperature anomaly noted by Lapp, Inc in a remote
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 10
Sinusoidal Temperature Change
Spring
Summer – max avg. air
temperature
Winter – min avg. air
temperature
Fall Avg. annual air temperature
sensing study. Denser probing around the two probes with the highest deviatory
temperature in this location would help investigate this possible anomaly.
If further shallow temperature probing is conducted, it is recommended that it be
performed in the winter when the Naknek River is frozen to permit easy access to the
south side with equipment, and sufficient snow covers the ground to make travel on the
tundra easier. Probes should still be drivable even when the ground is frozen.
5.0 THERMAL MODELING
To investigate the effect of varying soil properties and other conditions on measured
subsurface temperatures, a simple thermal model was conducted for the Naknek area
using TEMPW, a finite element program. The program generates a three dimensional
(x, y, and time) thermal model based on the climate, soils, starting temperatures, thermal
conductivity, heat capacity, and unfrozen water content. The cross-sections shown in
Appendix C, have two basic regimes based on the assumed subsurface conditions. The
‘tundra’ type noted above is modeled as moist, silty soils overlain by a meter of peaty
material. The ‘tree’ type is modeled as better drained, less moist, gravelly soils, again
overlain by a meter of organic/peaty soil. The cross-section is divided into a series of
elements and each corner of the element (typically a rectangle) is assigned an initial
condition. The initial condition is assumed based on the local climate. TEMPW uses the
fundamental laws of thermodynamics to predict ground temperature changes with
changes in boundary conditions, and includes the effects from latent heat transfer during
the phase change from ice to water. The program was used to estimate the effect of
differing soil types and other conditions on the subsurface temperatures.
In order to predict how the subsurface
temperatures change with the seasons and to
arrive at more accurate subsurface
temperatures than those applied as initial
conditions; a boundary function is applied at the
model’s ground surface. Four temperature
points were input to simulate the sinusoidal
temperature distribution. These four points are
the average annual air temperature for “spring”
and “fall” and the minimum average air
temperature for “winter” and maximum average
air temperature for “summer”. The program
interpolates between these four points to create
a sinusoidal air temperature boundary function
that matches the actual air temperatures. See
Section 2.2, Climate, for temperature
information used in the model. The model is
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 11
set to run in time steps for 40 years, and arbitrary length chosen to allow the model time
to thermodynamically model the interaction of differing subsurface soils with the same
surface climate. Snap-shots of the temperature profile may be viewed in any of the four
seasons. In this case, we present the results for fall, to correspond most closely to the
November fieldwork time-span.
Two models were developed for the thermal analysis:
1) Base Model: Half silt (tundra) and half gravel (tree)
2) Base Model plus Water Body: includes a small water body in the silt area
5.1 ASSUMPTIONS AND RESULTS
Thermal conductivities and volumetric heat capacities were estimated for each material
type except ice, which is fixed within certain temperature limits. Thermal conductivity
defines how much heat is transferred from one soil unit to the next. Thermal conductivity
is dependent upon the soil type (coarse grain, fine grain, or organic), unit weight, and
moisture content of the material. The thermal conductivities used in the model were
based on properties of typical silts and gravels and may vary significantly from those
found in the study area.
Variations in soil types and moisture contents in the study area, the effects of snow
cover, topography, shade, and moving shallow ground water, among other things, may
reduce the accuracy of our models for predicting subsurface temperatures.
Despite the simplicity of this model, it does reflect the gross differences seen between
the tundra and tree areas. The base model in Appendix C, Figure C1 predicts the
temperature at 2 meters depth to be 2.2°C in the silt far from the boundary with the
gravel soil, which is the average temperature measured in the tundra areas. It predicts
the temperature in the gravel soils to be 5.6°C at 2 meters depth, which is about a
degree above the average measured in the tree areas, perhaps because these soils are
not as accurately represented by the model gravel. They are very likely more silty than
modeled. The base model further predicts that temperatures near a boundary between
the two regimes may be measurably affected up to about 15 meters or more from the
boundary. Some of our measurements in the tundra areas were within several tens of
meters from tree areas, and higher temperatures measured may be explained by the
thermal effects of being in proximity to different soils. From this model, a maximum
temperature in silts near a boundary with gravels is about 4.8°C, or about 2.6°C above
the average. The effect in the gravels is less, with the temperature being a maximum of
about 0.6°C lower near a transition to silt.
The model including a small water body at the surface, presented in Appendix C, Figure
C2, shows a slight increase, by about 0.2°C, in the temperatures measured in the
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 12
neighborhood of such a body to those expected without such a body. The two-
dimensional, simulated water body is 3.5 meters deep and 5 meters across. A larger
body may be expected to have more of an effect. On visual inspection, there does not
seem to be a large correlation between bodies of water and large positive temperature
deviances from the mean in our data. These two models do show that thermodynamic
effects of varying subsurface soils and surface water bodies can have a measurable
effect on the temperature at 2 meters below the ground surface. The maximum amount
of these effects due to the conditions modeled is on the order of 3°C in the silts, less in
the gravelly soils.
6.0 CONCLUSIONS
Shallow temperature measurements have proven to be effective proxies for deeper
temperature gradient measurements in other areas, and can be very useful in targeting
an area for further geothermal exploration. Even when conditions are near perfect and
error sources such as shallow ground water flow are minimized, shallow temperature
results must eventually be born out by deeper drilling to verify the presence of a
geothermal resource.
At this time (December, 2007) a resource has not been confirmed. Further exploration
followed by a confirmation phase needs to be conducted prior to any decisions about
type of power plant and number of wells. We would recommend that further shallow
temperature probes be conducted in the areas of interest identified (near Lynx Road,
King Salmon, and Area 3 – Figures 5 and 6). We would also recommend that when
seismic data is available in the area, this data be examined to see if buried faults or
other features interpreted from the data correspond to other evidence of local anomalies.
We would recommend that two or more of the following exploration methods also be
conducted for assessing the local thermal and hydrological gradient:
1. Shallow temperature probes concentrated in the three areas of interest.
2. Accurately and uniformly characterize the chemistry of local springs and river
waters;
3. Conduct CO2 gas surveys to identify potential faults in select areas;
4. Conduct electric and/or magnetotelluric methods to identify argillic alteration
locations and to target potential well locations;
5. Develop a hydrological model of the region by reviewing existing literature and
studying deeper wells in the area.
Assuming that favorable conditions have been found (corresponding regions of shallow
temperature anomalies, geophysical evidence of faults, geochemical indications of
geothermal activity), we recommend as the next step the drilling of at least one regional
temperature gradient well (to at least 20 meters (60 feet); preferably to 70 meters (200
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 14
8.0 BIBLIOGRAPHY
AEDIS (Alaska Engineering Design Information System):
https://rsgis.crrel.usace.army.mil/aedis/
Coolbaugh, Mark F., Sladek, Chris, Faulds, James E., Zehner, Richard E., and Gary L.
Oppliger (2007) Use of Rapid Temperature Measurements at 2-Meter Depth to
Augment Deeper Temperature Gradient Drilling., Proceedings, 32nd Workshop on
Geothermal Reservoir Engineering.
Giggenbach, W. F. (1986) Graphical techniques for the evaluation of water/rock
equilibration conditions by use of Na, K, Mg, and Ca-contents of discharge waters:
Proceedings of the 8th New Zealand Geothermal Workshop, University of Auckland
Geothermal Institute, p. 37-43.
Garside, Larry J., and John H. Schilling (1979) Thermal Waters of Nevada, Bulletin 91,
Nevada Bureau of Mines and Geology.
Hanse, Cedric Nathanael. (2005) Factors Affecting Costs of Geothermal Power
Development. Geothermal Energy Association.
Henley, R.W., A.H. Truesdell & P.B. Barton, Jr. (1984) Fluid-Mineral Equilibria in
Hydrothermal Systems, Reviews in Economic Geology, V. 1, Society of Economic
Geologists.
Kienle, J. and S.E. Swanson (1983) Volcanism in the Eastern Aleutian Arc: Late
Quaternary and Holocene Centers , Tectonic Setting and Petrology. [In] B.H. Baker
and A.R. McBirney (eds.), Jour. of Volcanology and Geothermal Research 17:393-
432.
Kienle, Juergen, Kyle, P. R., Self, Stephen, Motyka, R. J., and Lorenz, Volker (1980)
Ukinrek Maars, Alaska: I, April 1977 eruption sequence, petrology and tectonic
setting: Journal of Volcanology and Geothermal Research, v. 7, n. 1, p. 11-37.
Lapp Resources, Inc (2006) Remote Sensing Interpretation, for Naknek Electric
Association.
LeSchack, Leonard A., Lewis, John E., Chang, David C., Lewellen, Robert I., and
Norbert W. O’Hara (1979) Rapid Reconnaissance of Geothermal Prospects Using
Shallow Temperature Surveys, LeSchack Associates, LTD.
Magoon, L.B., C.M. Molenaar, T.R. Bruns, M.A. Fisher, and Z.C. Valin (1995) 1995
National assessment of United States oil and gas resources – Southern Alaska
Province (003), USGS
Miller, T. P., McGimsey, R. G., Richter, D. H., Riehle, J. R., Nye, C. J., Yount, M. E., and
Dumoulin, J. A. (1998) Catalog of the historically active volcanoes of Alaska: U.S.
Geological Survey Open-File Report OF 98-0582, 104 p.
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
February 8, 2008 Page 15
Motyka, R. J., Liss, S. A., Nye, C. J., and Moorman, M. A. (1993) Geothermal resources
of the Aleutian Arc: Alaska Division of Geological & Geophysical Surveys
Professional Report PR 0114, 17 p., 4 sheets, scale 1:1,000,000.
National Climatic Data Center (NCDC), (1988) Climatic Atlas of the Outer Continental
Shelf Waters and Coastal Regions of Alaska. Volume II: Bering Sea. USDOI Mineral
Management Service, Alaska Outer Continental Region, OCS Study, MMS 87-0012.
Paug-Vik Development Corp. and OASIS Environmental, Inc. (2000) Record of Decision
for Final Remedial Action, North Bluff (LF005) and South Bluff (LF014) (Groundwater
Zone 3 (OT029)), King Salmon Air Station, Department of the Air Force.
Rafferty, Kevin (2000) Geothermal Power Generation, a primer on Low-Temperature,
Small-Scale Applications: Fact Sheet by Department of Energy Geo-Heat Center.
Smith, R.P., V.J. S. Grauch, and D.D. Blackwell (2002) Preliminary Results of a High-
Resolution Aeromagnetic Survey To Identify Buried Faults at Dixie Valley, Nevada,
Geothermal Resources Council Transactions, Vol 26
Truesdell, A.H., and Hulston, J. R. (1980) Isotopic Evidence of Environments of
Geothermal Systems; in Handbook of Environmental Isotope Geochemistry, v. 1: P.
Fritz and J. Ch. Fontes, eds.
CHECKED BY:JOB NO.:
SHEET:DRAWN BY:DATE:
SCALE:
ENGINEERING
EARTH SCIENCE
PROJECT MANAGEMENT
PLANNING
(907) 564-2120
www.hdlalaska.com
SHALLOW TEMPERATURE SURVEY
NAKNEK GEOTHERMAL SOURCES
11/20/07NONE MMW
LMD 07-303
LEGEND
FIGURE:-
Absolute Temperatures at 6 feet
1.0 - 1.8 degrees C
1.8 - 2.6 degrees C
2.6 - 3.4 degrees C
3.4 - 4.2 degrees C
4.2 - 5.0 degrees C
5.0 - 5.7 degrees C
5.7 - 6.5 degrees C
6.5 - 7.3 degrees C
Temperature Deviation at 6 feet
-3.0 - 0.0 degrees C
0.0 - 0.5 degrees C
0.5 - 1.0 degrees C
1.0 - 1.5 degrees C
1.5 - 2.0 degrees C
2.0 - 2.5 degrees C
2.5 - 3.0 degrees C
3.0 - 3.6 degrees C
^_NEA Drill Sites
LAPP Features
Anomaly
Circular
Linear
LEGEND
Magnetic Anomaly
Low High
^_
^_
^_
Recording Station
Recording Station
NAKNEK
KING SALMON
Area 3
Lynx Rd.
South Side
Gravel Pit Site
Pikes Ridge Site
CHECKED BY:JOB NO.:
SHEET:DRAWN BY:DATE:
SCALE:
APPENDIX A
Photo Log
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
Appendix A-Photo Log Page A-1
Assembling field gear, including generators, drivers, and probes (pipes in bundles at lower right) -
probes are marked off at 6’ from closed end w/ paint pen prior to driving.
Driving a probe with the smaller driver on the tundra.
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
Appendix A-Photo Log Page A-2
Drilling out the hole at the top of the probe, which tends to get deformed by the driving.
Driving a Shallow Temperature Probe with the Hilti driver
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
Appendix A-Photo Log Page A-3
A probe with its insulated cap. Wire sticking out is the lead from
the RTD (Resistance Temperature Detector).
Inserting RTD (Resistance Temperature
Detector) in probe at least one hour after
driving.
Reading the resistance of the RTD. This is
converted to temperature by a simple equation.
Naknek Electric Association Shallow Temperature Survey
HDL 07-303 Naknek Geothermal Sources, Alaska
Appendix A-Photo Log Page A-4
Removing a probe driven in Hermann's gravel pit. Removal was done either with a pipe
wrench or with a jack and wrench.
Removing a probe from an area with brush
and small trees - this would be considered a
'tree' area.
APPENDIX B
Geochemistry Report for
Lynx Road Spring Water
REPORT ON GEOTHERMOMETRY SAMPLE: Naknek Lynx Spring
The analysis shows the water has low TDS; it is almost rainwater. High Fe suggests bog waters. The silica
is anomalous, which suggests a small percentage of admixed deep thermal water. Admixed thermal
water is too small to show un Giggenbach’s diagrams. Aluminum is high for such a low TTDS sample. I
would disregard alkali geothermonetry on such a low TDS sample.
Analysis
pH 7.4
Conductivity (uS/cm) 74
TDS (ppm)
(calculation) 54
TDS (ppm)
(gravimetric)
ANALYSIS Conc. (mg/L) meq/L
Hardness (CaCO3) 22
Alkalinity
Carbonate (CO32-) 0.0000
Bicarbonate (HCO3-) 33 0.5409
Major Anions
Bromide (Br) <0.1 0.0000
Chloride (Cl-) 3.4 0.0959
Fluoride (F-) <0.1 0.0000
Nitrite (NO2-) <0.1 0.0000
Nitrate (NO3-) <0.1 0.0000
Phosphate (PO43-) <0.5 0.0000
Sulfate (SO42-) 1.9 0.0396
Major Cations
Sodium (Na) 4.5 0.1958
Potassium (K) 0.49 0.0127
Magnesium (Mg) 2.6 0.2139
Calcium (Ca) 4.5 0.2205
Total meq/L Cations 0.71
Total meq/L Anions 0.68
% Difference 2.34
ANALYSIS Conc. (mg/L) meq/L
Aluminum (Al) 0.14 0.0161
Antimony (Sb) <0.001
Arsenic (As) <0.001
Barium (Ba) 0.054
Beryllium (Be) <0.001
Boron (B) 0.004
Cadmium (Cd) <0.001
Chromium (Cr) <0.001
Cobalt (Co) <0.001
Copper (Cu) 0.001
Iron (Fe) 0.91 0.0486
Lead (Pb) <0.001
Lithium (Li) <0.001
Manganese (Mn) 0.008 0.0006
Molybdenum (Mo) <0.001
Nickel (Ni) <0.001
Selenium (Se) <0.001
Silica (SiO2) 19
Silicon (Si) 8.8
Silver (Ag) <0.001
Strontium (Sr) 0.025 0.0006
Thalium (Tl) <0.001
Thorium (Th) <0.001
Tin (Sn) 0.001
Titanium (Ti) 0.007
Uranium (U) 0.000
Vanadium (V) 0.002
Zinc (Zn) 0.001 0.0000
GEOTHERMOMERTY
Analysis Geothermometers
(ppm)
SiO2 19 Quartz ‐ no steam loss 62 C
Na 4.5 Quartz ‐ max. steam loss 67 C
K 0.49 Chalcedony 30 C
Ca 4.5 a‐Cristobalite 12 C
Mg 2.6 b‐Cristobalite ‐31 C
Amorphous silica ‐47 C
Na/K 225 C
Na‐K‐Ca beta = 4/3* 14 C
Na‐K‐Ca beta = 1/3 138 C
K‐Mg 21 C
* use if t<100C and (2.06+LOG10((Ca^0.5)/Na) > 0
(2.06+LOG10((Ca^0.5)/Na) = 1.73
APPENDIX C
Thermal Modeling
Fall- base, Green - Peat, Blue - Silt, Orange - Gravel
2.2 3 3.8 4.6 5.2
5.4 5.6
Length - meters
0 5 10 15 20 25 30 35 40Elevation - meters0
5
10
15
20
25
30
35
40
45
50
55
Fall- base w/ Water Body(Aqua), Green - Peat, Blue - Silt, Orange - Gravel
2 .4 3.4 3.4 4.8 5.4
5.6 5.8
Length - meters
0 5 10 15 20 25 30 35 40Elevation - meters0
5
10
15
20
25
30
35
40
45
50
55