1

Geological and Geophysical

Investigations of the Hydrogeology

of Fort Wainwright, Alaska

Part I: Canol Road Area

Daniel E. Lawson, Jeffrey C. Strasser, Jodie D. Strasser,

Steven A. Arcone, Allan J. Delaney and Christopher Williams May 1996

CRREL REPORT 96-4
Abstract: The hydrogeology of Fort Wainwright, Alaska,

is extremely complex because of the relatively impermeable discontinuity of permafrost, which controls the

distribution and dimensions of the aquifer. Aquifers

occur above, below and adjacent to permanently frozen

materials, as well as within thaw zones surrounded by

permafrost. This complexity makes it difficult to predict

the direction and rate of ground water flow, as well as

its seasonal and annual variability. Considerable problems exist in locating suspected contaminant plumes,

identifying source areas, defining transport paths and

evaluating contaminant fate. This report summarizes

the results of ongoing investigations of the permafrost

and ground water conditions within the northwestern

part of the Fort Wainwright cantonment area, north of the

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Cover: Two examples of ground-penetrating radar profiles of permafrost and ground water on Fort Wainwright,

Alaska. The data are deconvolved 100-MHz profiles of transects G5 (top) and G7 acquired in September 1993.

Distance is along the x-axis (280 m for G5 and 120 m for G7). The y-axis represents 500 ns for both transects.

The profiles show a discontinuous response within the first 100 ns to the permafrost table, and a continuous response

at approximately 100–400 ns to the subpermafrost water. Areas that have no permafrost are indicated.

Chena River. Data from ground-penetrating radar, drilling, ground water flow sensors, aerial photographs and

ground observations were used to delineate aquifer distribution and develop a conceptual physical model of

hydrogeological conditions. Ground water seepage velocity and direction, which were measured during early to

mid-winter 1994–95, reflect the role of local water

sources and permafrost distribution in determining ground

water flow patterns. Other factors, including the vertical

and lateral extent of permafrost, a bedrock aquifer, and

the alluvial origins of unfrozen sediments and landforms,

are apparently more important than the subregional

aquifer in determining ground water conditions during

winter. Contaminant migration will be strongly affected by

these factors as well.
CRREL Report 96-4

Geological and Geophysical

Investigations of the Hydrogeology

of Fort Wainwright, Alaska

Part I: Canol Road Area

Daniel E. Lawson, Jeffrey C. Strasser, Jodie D. Strasser,

Steven A. Arcone, Allan J. Delaney and Christopher Williams May 1996

Prepared for

U.S. ARMY ENGINEER DISTRICT, ALASKA

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Dr. Daniel E. Lawson, Research Physical Scientist,

Jeffrey C. Strasser, Physical Scientist, Jodie D. Strasser, Physical Scientist, Geological Sciences Division, Dr. Steven A. Arcone, Geophysicist, Allan J. Delaney, Physical Science Technician, Snow and Ice Division, and Christopher Williams, Electronics Engineer, Engineering Resources Branch, U.S. Army Cold Regions Research and Engineering Laboratory.

The investigations described in this report were conducted through the U.S.

Army Engineer District, Alaska, for the Environmental Resources Department,

Public Works Directorate, U.S. Army, Alaska, under two projects: Geological and

Geophysical Analyses of Permafrost and Ground Water Conditions, Fort Wainwright,

Alaska, and Site-specific, In Situ Ground Water Flow Analyses at Fort Wainwright,

Alaska. The authors thank Cristal Fosbrook, Chief, Environmental Restoration

Branch, and Douglas Johnson, Chief, Environmental Resources Department,

USARAK, Fort Richardson, Alaska, for their continued support, encouragement

and assistance in many aspects of the work on Fort Wainwright.

The authors also thank the personnel in the Alaska District’s Geotechnical

Branch for obtaining and evaluating subsurface data by drilling the ground-truth

boreholes that are an essential element in interpreting and applying the groundpenetrating radar transect data. In particular they thank Jerry Raychel, Chief, Soils

and Geology, Del Thomas, Chief, Geotechnical Branch, and the many members of

the District’s field crews responsible for logging and sampling each hole, including James Sauceda, Chuck Wilson, Joni Sue Minor and Jeff Hitch. The Alaska

District’s drill crew, and the contracted drill crew for Ambler, Inc., particularly

driller Dan Finnegan, are to be commended for drilling and obtaining borehole

information even under the most trying of field conditions and weather.

The contents of this report are not to be used for advertising or promotional

purposes. Citation of brand names does not constitute an official endorsement or

approval of the use of such commercial products.

ii
CONTENTS

Page

Preface ................................................................................................................................ ii

Introduction ........................................................................................................................ 1

General background................................................................................................... 1

Surficial and bedrock geology .................................................................................. 4

Site descriptions .......................................................................................................... 4

Methods of investigation .................................................................................................. 6

Ground-penetrating radar......................................................................................... 6

Boreholes ..................................................................................................................... 6

Monitoring wells................................................................................................................ 6

Automated ground water flow system ................................................................... 9

Analysis and interpretation ............................................................................................. 9

Permafrost distribution ............................................................................................. 9

Aquifers ....................................................................................................................... 12

Ground water flow patterns ............................................................................................ 14

Seepage measurements ..................................................................................................... 15

Conclusions ........................................................................................................................ 21

Recommendations ............................................................................................................. 22

Literature cited ................................................................................................................... 22

Appendix A: Ground-penetrating radar operation and theory ................................. 23

Abstract ............................................................................................................................... 25

ILLUSTRATIONS

Figure

1. OU-3 sites north of the Chena River, including the Tank Farm,

Truck Fill Stand, Canol Road pipeline and Test Grid ................................ 2

2. Stacked, three-dimensional representations of upper and lower surfaces

of permafrost in the Canol Road “Test Grid” .............................................. 2

3. Aerial photograph of the discontinuous permafrost region generally

north of the Chena River ................................................................................ 3

4. Aerial photograph mosaic of the region generally north of the

Chena River from 9 September 1949............................................................. 4

5. Assemblages of alluvial deposits distinguished by the trends of the

point bars, swales, former channels, and levees north of

the Chena River................................................................................................ 5

6. GPR transects in the OU-3 area north of the Chena River ............................. 6

7. Ground-truth boreholes located on GPR transects ......................................... 7

8. Current locations of monitoring wells with CRREL prototype flow

 systems installed ............................................................................................. 7

iii
Figure Page

9. Ground water flow monitoring system ............................................................ 8

10. Preliminary maps of the Canol Road area ........................................................ 10

11. Cross section A-A′ illustrating the relationship between areas of

permafrost that extend into bedrock and the rapid transition from

unfrozen to frozen materials .......................................................................... 12

12. Depths to the bottom of permafrost from boreholes in the Canol Road

area ..................................................................................................................... 13

13. Preliminary map of the depth to bedrock from borehole data in the

Canol Road area ............................................................................................... 13

14. Potential near-surface flow paths depicted for two scenarios ....................... 14

15. Potential deep aquifer flow paths depicted for two scenarios ...................... 15

16. Potential interaction and flow directions between a subpermafrost

aquifer and an unfrozen zone, such as a former swale or channel .......... 16

17. Idealized subpermafrost and suprapermafrost flow patterns associated

with an aquifer within the bedrock in Birch Hill ........................................ 16

18. Monthly mean flow vectors calculated from daily flow system measurements during the October 1994 to March 1995............................................ 18

19. Mean flow directions for October 1994 to March 1995 ................................... 20

TABLE

Table

1. Seepage velocity and direction data .................................................................... 17

iv
In this report, we summarize the initial results

of ongoing hydrogeological investigations of the

ground water and permafrost conditions in the

northwestern corner of the cantonment of Fort

Wainwright. Our work has included developing

Ground-Penetrating Radar (GPR) to define the

spatial and vertical extent of permafrost. Our investigations are part of continuing site characterization for remedial investigations and treatability studies of contaminant problems on Fort

Wainwright (Fig. 1). This facility was placed on

the Comprehensive Environmental Response,

Compensation, and Liability Act (CERCLA) National Priorities List (NPL) in August 1990. The

Canol Road area contains two sites within one of

the five Operable Units (OU-3) established for

investigation and remediation under the Federal

Facilities Agreement (FFA) of 1992, which sets

guidelines for Fort Wainwright on contaminant

remediation under CERCLA.

General background

The three-dimensional distribution of permanently frozen ground exerts considerable control

on ground water flow in regions of discontinuous

permafrost. Transitions from unfrozen to frozen

conditions may be abrupt and without surface

expression. Further complicating our attempts to

define this distribution are several factors: the

current environment, past climatic conditions, terrain characteristics, vegetation cover, historic use

and surface disturbances (Hopkins et al. 1955,

Williams 1970).

Permafrost exists at various depths throughout the Fairbanks and Fort Wainwright area. The

top of the permafrost ranges from 0.5 to over 15

m deep, with the thickest thawed zones beneath

INTRODUCTION

Within interior Alaska, and, in particular, the

cantonment area of Fort Wainwright, the permanently frozen and unfrozen materials that contain

ground water aquifers are complexly and discontinuously distributed. Ground water may occur above, below and adjacent to those materials,

as well as in thawed zones that are within, or

penetrate through, the permafrost. The permafrost controls the movement of ground water because of its impermeability.

The fate of contaminants in ground water is

thereby linked to both the distribution of permafrost and the movement of the ground water within the adjacent unfrozen sediments. Prior to the

work discussed in this report, permafrost and

aquifer distributions across Fort Wainwright were

incompletely described and known only in general terms. Therefore, the complex hydrogeological

conditions led to considerable problems for those

trying to locate suspected contaminants, to identify source areas, to define transport paths, and to

evaluate the fate of contaminant plumes, including their migration off-site. Physical hydrogeological models of ground water flow in this permafrost terrain are therefore essential to remediating

contamination.

Permafrost may be present or absent because of

a number of factors, including human and natural

disturbances to the terrain and vegetation, and its

distribution may therefore be chaotic. Identifying

areas of permafrost and, conversely, unfrozen aquifers within permafrost areas is therefore extremely

difficult. Standard techniques such as drilling or

terrain analyses cannot readily locate frozen or

unfrozen zones except in the most obvious of cases.

Geological and Geophysical Investigations of the

Hydrogeology of Fort Wainwright, Alaska

Part I: Canol Road Area

DANIEL E. LAWSON, JEFFREY C. STRASSER, JODIE D. STRASSER,

STEVEN A. ARCONE, ALLAN J. DELANEY AND CHRISTOPHER WILLIAMS
swales or former stream channels, roads, buried

pipelines, building excavations and other areas

cleared of vegetation (Lawson et al. 1993). The

bottom surface of the permafrost commonly

ranges from 10 to over 50 m deep, with a minimum thickness of a few meters adjacent to thawed

areas, and maximum thicknesses over 80 m in

areas that may be some of the geologically oldest surficial materials on

Fort Wainwright. The top and bottom

surfaces of the permafrost also have

highly irregular relief and can substantially influence ground water

movement (Fig. 2).

Ground water flow within the cantonment area of Fort Wainwright (Fig.

1) is necessarily complex. This complexity reflects not only the presence

or absence of permafrost but also the

structure and stratigraphy of the surface sediments, the thickness of unfrozen materials above the permafrost,

the total thickness and depth to the

bottom of permafrost, and the immediate sources of ground water. These

sources include the Chena–Tanana

River system and more local aquifers

such as Birch Hill (Péwé 1958, Williams 1970, Shannon and Wilson, Inc.

1992, Lawson et al. 1993).

Two types of ground water systems

exist: a laterally discontinuous, nearsurface system above the permafrost

(suprapermafrost), and a deeper one

beneath the permafrost (subpermafrost) (Lawson et al. 1993). The suprapermafrost and subpermafrost aquifers are linked where the frozen

ground is perforated by isolated thaw zones (surrounded by permafrost, but unfrozen to bedrock),

and in more extensive unfrozen zones, typically

within former stream channel or swale deposits.

Isolated thaw zones (taliks) may be areas where

the subpermafrost aquifer discharges or recharges,

exhibiting either upward or downward vertical

Figure 2. Stacked, threedimensional representations of upper and lower

surfaces of permafrost in

the Canol Road “Test

Grid.” Permafrost is absent in those areas of the

figure where the upper

surface appears to be at a

lower elevation than the

bottom surface.

Figure 1. OU-3 sites north of the Chena River, including the Tank

Farm, Truck Fill Stand, Canol Road pipeline and Test Grid.

Shannon Park

Subdivision

Test Grid

Quarry

N

0 200 400 m

Road

Railroad

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Truck Fill

Stand

B i r c h

H i l l R o a d

Bir c h H i l l R o a d

Ft. Wainwright Boundar y

C a n o l Ro a d

P i p e l i n e

R i v e r R o a d

Trainor Gate Road

C h e n a R i v e r

School

2
gradients. The near-surface systems may also be

confined spatially by permafrost, with little or no

connection to a subpermafrost aquifer. Water levels, flow rates and flow directions in such a

perched aquifer may vary seasonally and diurnally in ways that are significantly different from

the general trends in the regional aquifer. This

may happen where the active layer or annual

depth of thaw is shallow (less than 1.0 m). The

subpermafrost aquifer can also be locally confined or isolated by areas of materials that are

permanently frozen into the underlying bedrock.

Figure 3. Aerial photograph of the discontinuous permafrost region generally north of the Chena River. Photo

taken 20 May 1993.

3
Figure 4. Aerial photograph mosaic of the region generally north of the Chena River from 9 September 1949. The

approximate area of the Truck Fill Stand is outlined.

Surficial and bedrock geology

Unconsolidated deposits of the Chena River

and its smaller tributaries make up most of the

surficial materials south of Birch Hill (Péwé et al.

1976). These deposits are mainly former point

bars, swales, channels or sloughs, and related

overbank deposits resulting from alluvial processes. Drilling has revealed that most of the

surficial deposits on Fort Wainwright consist of

gravels and sands, with sporadic silt layers and

lenses (U.S. Army Engineer District, Alaska, unpublished borehole records). There is a layer of

silt, usually less than 1 m thick, typically just

below a surface layer of organics.

The unconsolidated materials of the Chena

River floodplain lie unconformably above dark

pelitic schists of the Yukon–Tanana Complex

(King 1969), formerly identified as the Birch Creek

Schist (Péwé et al. 1976). This metamorphic unit

is generally of lower greenschist facies, and the

age, although controversial, is thought to be preJurassic (Péwé et al. 1976). Birch Hill, which

bounds the northern part of the cantonment, is

also composed of this highly fractured and foliated schist. In most areas of Birch Hill, the bedrock is overlain by eolian silt with thicknesses

that may exceed 3 m or more. Various processes

have moved weathered bedrock and silt downslope off Birch Hill, forming heterogeneous deposits of mixed grain sizes, colluvium, peripheral

to its base.

Site descriptions

The OU-3 sites that are under investigation in

the Canol Road area include the Tank Farm, the

Truck Fill Stand and the Canol Road pipeline

4
Figure 5. Assemblages of alluvial deposits distinguished by the trends of the point bars, swales, former

channels, and levees north of the Chena River. Cross-cutting relationships of these features indicate the relative

ages of the surficial deposits.

River Rd

0 100 200 m

N

Ft. Wainwright Boundary

Boundary Separating

Assemblages of Surficial

Alluvial Sediments

Approximate Trends

to Former Swales,

Channels and Levees

Quarry

Building

1173

Canol Road

Birch Hill

(Fig. 1 and 3). The Tank Farm is located on the

south–southwest slope of Birch Hill where permafrost is probably absent owing to its southern

exposure. Drilling shows that the Tank Farm area

is generally blanketed by accumulations of eolian

silt (loess). This silt overlies a 1- to 3-m-thick zone

of moderately to highly weathered schist, which

grades into unweathered schistose bedrock at

depth. The Truck Fill Stand lies south of the Tank

Farm in an area of alluvial deposits.

Arcuate patterns or meander scrolls on 1949

aerial photographs confirm the alluvial origins of

the sediments, and cross-cutting relationships provide evidence on relative ages of different deposits (Fig. 4). The most prominent features within

the site reflect a meandering channel migrating

towards the northeast, with the youngest deposits existing in the outer-most loop, which encircles

most of the site. Paleocurrents were presumably

in a counter-clockwise direction around this loop.

Cross-cutting the earliest deposits of this sequence,

however, are the north–south trending swales near

the western post boundary, indicating possibly

secondary channel cut-offs or sloughs. The youngest sediments within this area, however, are those

bordering River Road (Fig. 5) and within the Test

Grid area. As is discussed in a later section, there

is no clear relationship between the ages of sediments and the extent of permafrost development,

which further complicates predictions of locations

and extents of frozen zones. Prominent sloughs,

however, tend to be zones of partial or complete

thaw and may therefore be significant pathways

of groundwater flow.

Canol Road and the adjacent pipeline extend

southeast towards the Chena River within a

cleared right-of-way (Fig. 1). There is significant

thaw beneath the road and pipeline, with the top

of permafrost generally at depths of 7 to 13 m

(Lawson et al. 1993). The pipeline crosses the river

at the railroad bridge and terminates at the Rail

Off-Load Facility (ROLF), an area of point bar

and swale deposits within a convex, northward

loop in the Chena River (Fig. 1). More detailed

descriptions of each site and historical accounts

of contaminant sources are given by Ecology and

Environment (1994).

5
METHODS OF

INVESTIGATION

We have used several methods to

develop an understanding of permafrost distribution, ground water distribution and movement, and the area’s

hydrogeology. These data are coupled

to in-situ, site-specific measurements

of ground water flow direction and velocity in monitoring wells.

Ground-penetrating

radar (GPR)

Ground-penetrating radar profiles

were made along transects established

on existing trails in the Canol Road

area, some of which were cleared of

recent vegetation by hydro-ax. Their

locations were subsequently surveyed

(Fig. 6). We profiled each transect by

dragging antennas along the ground

behind a tracked vehicle at a constant

velocity of about 1 m/s. The antennas

were situated approximately 6–7 m behind the vehicle. Event markers were

placed artificially on the records at 10-

m intervals. Scan durations, which are

related to depth, were set to encompass the features of interest. Generally,

we used 600 to 1200 ns for profiles

with both 50- and 100-MHz antennas. The 1200-

ns range penetrates approximately 40 m through

frozen ground, yielding data from the bottom

surface of permafrost. Scan durations of up to

2000 ns were used with the 50-MHz antennas in

areas with much deeper (60-m) permafrost.

The radar system consisted of a Geophysical

Survey Systems, Inc., SIR Model 4800 control unit,

assorted antennas, cables, a GSSI DT6000 digital

tape recorder, and a power supply. Appendix A

gives a more complete description of GPR methods and theory.

Boreholes

We identified subsurface material types and

permafrost horizons by drilling boreholes in 1993

and 1994. Drill sites (Fig. 7) were chosen according to the GPR data and preliminary interpretations of the site’s geomorphic features based upon

ground observations and aerial photography. Geologic logs provided data necessary to quantify

GPR records, which provide vertical depths in

terms of times of signal returns in nanoseconds,

Figure 6. GPR transects in the OU-3 area north of the Chena River.

Cross section A–A’ is illustrated in Figure 11.

rather than true depths. Borehole and GPR records

were subsequently combined to develop interpretive cross sections of permafrost and aquifer

distribution. Piezometric surface measurements

were also obtained from suprapermafrost, subpermafrost and unfrozen zone aquifers encountered

by the drilling. Geologic logging of each borehole

followed standard procedures.

Monitoring wells

Monitoring wells, generally in clusters of three

at depths of about 10, 20 and 30 m, were drilled,

logged and developed for use with a ground water flow system (see following section). Each monitoring well cluster is located within thawed, permafrost-free zones. Additional wells were drilled

to below permafrost into the subpermafrost aquifer and pressurized to prevent their closure by ice

growth (Fig. 8). Data from GPR surveys, borehole

logs and geomorphic features, and other geological data were used to select monitoring well locations and provide representative ground water

flow data.

Shannon Park

Subdivision

Quarry

N

0 200 400 m

XX (XX) GPR Transect No./Year

GPR Transect

Road

Railroad

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Bir c h H i l l R o a d

R i v e r R d

School

94 (94)

77 (94)

4 (93)

62 (94)

88 (94)

31 (93)

63 (94)

89 (94)

97 (94)

1 (93)

6 (93)

7 (93)

57 (94)

56 (94)

90 (94)

96 (94)

100 (94)

53 (94)

5 (92)

2 (93)

3 (92)

69 (94)

64 (94)

70 (94)

34 (93)

81 (94)

65 (94)

25 (93)

98 (94)

51 (94)

52 (94)

50 (94)

27 (93)

11 (93)

79 (94)

65 (94)

88 (94)

5 (93)

8 (93)

13 (93)

9 (93)

75 (94)

55 (94) 58 (94)

59 (95)

95 (94) 11 (93)

7 (93)4 (93)

5 (93)

8 (93)

6 (93) 10 (93)

9 (93)

12 (93)

13 (93)

Trainor Gate Road

Ft. Wainwright Boundar y

C h e n a R i v e r

54 (94)

A A'

6
Figure 7. Ground-truth boreholes located on

GPR transects.

Figure 8. Current locations of monitoring

wells with CRREL prototype flow systems

installed.

GPR Transect

Road

Railroad

1993 Borehole Location

1994 Borehole Location

Note: Borehole numbers mea-

 sure depth in meters.

0 200 400 m

Shannon Park

Subdivision

Quarry

N

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Bir c h H i l l R o a d

Trainor Gate Road

School

River Road

C h e n a R i v e r

Shannon Park

Subdivision

Quarry

N

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Bir c h H i l l R o a d

Ft. Wainwr gi ht Boundary School

Completed Subpermafrost Wells

Completed Shallow

Monitoring Well Cluster

Sampling Well

Picket Well

GPR Transect

Road

Railroad

C-12

C-5 C-2

P-2 C-3 C-4 C-6

P-10

P-4

C-1

Birch Hill Road

R i v e r R o a d

Test Grid C h e n a R i v e

T

r

rainor Gate Road

0 200 400 m

C a n o l Ro a d

P i p e l i n e

7
b. Electronic circuitry and data logger of the flow system.

Figure 9. Ground water flow monitoring system.

a. CRREL-modified flow sensor.

Monitoring wells above and below the permafrost were installed and developed following standard procedures. Each monitoring well was

drilled to a specified depth, at which a 3-m length

of well screen was installed. All monitoring wells

have a well screen, evaluated by laboratory testing at CRREL, that minimizes the restrictions to

water movement, keeps finer sediment from infiltrating the well, and permits in-situ measurements

with a prototype ground water flow system (Fig.

9). The well screen is ~2-in. (5 cm) i.d., continuous

wire wrap, stainless steel with 0.060-in. (15-mm)

8
slot size. A filter sock with a mesh of 120- to 150-

μm covers the outside of the screen (Fig. 9). After

we installed the wells, each hole was allowed to

collapse around the screen as a way to maintain

minimally disturbed conditions. Monitoring wells

drilled through permafrost were screened at a

depth beginning 3 m below the bottom of the

permafrost. During drilling through permafrost,

we followed standard procedures to stop ground

water from the suprapermafrost aquifer from

flowing down into the hole.

Automated ground water

flow system

CRREL’s prototype ground water flow system

uses the thermal tag and trace technique (e.g.,

Chapman and Robinson 1962, Hess 1982) to measure flow direction and seepage velocity in the

monitoring wells in the Canol Road area (Fig. 8).

This system employs a sensor that closely follows

the configuration of a commercial probe, which

had limited applicability to permafrost areas. Extensive work has developed a more refined system for accurately measuring the direction and

magnitude of slowly flowing ground water (Williams et al. 1995).

The prototype system uses a sensor with four

pairs of platinum Resistive Temperature Devices

(RTDs) in steel tynes that are arrayed in a circular

pattern around a point source heater (Fig. 9a).

Heat is transferred preferentially by ground water flow from the heater to the RTD’s. Conductive

heat transfer occurs through glass beads in which

the RTD tynes are imbedded.

Temperature fluctuations between paired RTDs

relative to background levels are recorded. This

temperature differential is then used to calculate

the direction of flow and seepage velocity. Each

sensor should be calibrated in a flume filled with

materials representative of those surrounding each

particular well screen to obtain absolute velocity

measurements. A constant displacement pump is

used to regulate seepage rates from 1 to 10 ft/day

(0.3 to 3 m/day).

Flow sensors are suspended from steel rods

lowered and locked into position in each well

after orientation to magnetic north. The suspension system was designed at CRREL to ensure

minimum slack in connections and precise orientation of the sensor at depth (Williams et al. 1995).

The direction and velocity of seepage are measured hourly, with system functions controlled

by a Campbell CR10XT data logger. Signals are

transmitted and received through a CRREL-designed circuit board (Fig. 9b). In addition, a pressure transducer (Druck PDCR-35D) is also installed in each well and hourly fluctuations in the

water level (piezometric surface) are recorded.

Data stored within the logger are subsequently

downloaded into a portable computer for analysis and graphical display.

As mentioned, flow sensors are calibrated

within a flume. For this study it was filled with a

commercially available sand mixture (sieve no.

8–12) that is generally representative of materials

in each well screen interval. This calibration provides an empirical relationship between the sensor readings and seepage velocity, as well as direction. A more precise and accurate velocity

measurement can be obtained by calibrating each

sensor to the actual materials surrounding each

well screen. The calibration used in this study

produces a relative velocity that is considered

accurate to within ±0.6 ft/day (±0.15 m/day).

ANALYSIS AND

INTERPRETATION

We have developed preliminary maps of the

permafrost distribution and hydrogeology of the

Canol Road area that are based upon interpretation of the GPR records, borehole logs, terrain

analyses and related data (e.g., Lawson et al. 1993,

Ecology and Environment 1994) on the surficial

geology and ground water conditions.

Permafrost distribution

Permanently frozen and unfrozen sediments

in the Canol Road area are complexly distributed,

with highly variable annual depths of thaw and

depths to the bottom of permafrost. The spatial

distribution of deep and shallow unfrozen zones,

including the active layer above permafrost, are

depicted in Figure 10a, while a second map (Fig.

10b) portrays the occurrence of unfrozen sediments beneath permafrost. Both maps show the

locations of zones that are completely unfrozen

but surrounded by permafrost.

Deep thaw zones—typically less than 3 to over

15 m deep—are commonly associated with disturbed terrain (e.g., roads and clearings), while

shallower active layers of less than 3-m depth

characterize undisturbed permafrost terrain (Fig.

10a). Areas with thin active layers (1.0 m or less)

are commonly associated with thick permafrost

that extends into bedrock. Areas or zones that are

unfrozen from the surface to bedrock are com9
Unfrozen areas of former sloughs and swales are

commonly vegetated by large birch and aspen or

poplar.

Permafrost extends from about 7 m depth near

the base of Birch Hill to over 35 m south of the

Truck Fill Stand and west of Canol Road (Fig. 12).

Permafrost generally thickens, and depths to its

base increase, with distance south of Birch Hill.

Where unfrozen materials occur above bedrock,

we presume that the bedrock is unfrozen at depth

as well. The depth to bedrock ranges from several

meters to over 40 m in the same area (see Fig. 13).

mon within former channels, swales or sloughs,

resulting in an arcuate pattern that reflects the

past alluvial activity in this area (Fig. 10). Thaw

depths adjacent to such unfrozen areas are deeper,

but often become shallow rapidly with distance

away from them (Fig. 11).

Vegetation can tell us the approximate range

of thaw depth in some areas. Stunted black spruce,

for example, are usually growing on an active

layer that is less than 1 m thick. Larger, healthy

spruce, sometimes mixed with birch, may grow

within areas having deeper annual thaw zones.

a. Characteristic depths of thaw and the locations of zones that are unfrozen from the surface into

bedrock. Small, shallow drainageways and gullies are not identified on this map. These areas may

locally exceed thaw depths by two or three times the cited depths. Completely thawed areas have

peripheral shallow and deep thaw zones, which, unless quite wide, are omitted from the map to

reduce clutter.

Figure 10. Preliminary maps of the Canol Road area. Maps made from unrectified aerial photographs taken on 20 May 1993. Interpretations are based upon GPR and borehole data and ground

observations.

?

?

C

a

n

o l R

o

a d

? Based Upon

Limited Data

Active Layer Above

Permafrost (≤1.0 m)

Unfrozen Deep Thaw Above

Permafrost (>3.0 m)

Shallow Thaw Above

Permafrost (>1.0-3.0 m)

100 m

Ft. Wa ni wr gi ht Boundary

N

?

?

? ?

?

?

?

?

?

?

10
Because of its lateral extent, this area forms a nearly

impenetrable barrier to deeper ground water migration from the east and south of the Truck Fill

Stand, where there is a subpermafrost aquifer in

unfrozen materials beneath the permafrost.

The data on bedrock depth indicate the existence of a buried valley trending northeast to southwest across the site in an area of discontinuous

permafrost (Fig. 13). Because much of the Truck

Fill Stand area is characterized by unfrozen sediments beneath permafrost, the bedrock valley appears to provide a connection for ground water in

b. Presence or absence of unfrozen

materials below the permafrost.

Aquifers are usually present

within the unfrozen materials. In

the first unfrozen classification, the

following applies—sediments

thawed to bedrock; water bearing;

bedrock presumed thawed. In the

second classification, the following

applies—sediments thawed between permafrost and bedrock;

subpermafrost aquifer present. In

the third classification, the following applies—water not encountered during drilling through

weathered bedrock surface; locally

sporadic and discontinuous thaw

zones may be present at the sediment/bedrock interface, especially

near thaw zones and adjacent to

subpermafrost aquifer.

Figure 10 (cont’d).

Thus, there are large areas where sediments are

perennially frozen an unknown depth into the

underlying bedrock (Fig. 10b). Such areas laterally confine unfrozen and deeply thawed areas

from one another, thereby affecting ground water

flow. In other locations, permafrost thickness is

less than the depth to bedrock; underlying sediments are unfrozen, as is the bedrock beneath

them, and they generally contain ground water.

A particularly extensive area where bedrock is

relatively shallow and sediments are frozen into it

lies south and east of the Tank Farm (Fig. 10b).

S t e e s e H i g h w a y

F t . W a i n w r i g h t B o u n d a r y

T r a i n o r G a t e R d

Tank Farm

Permafrost Present to

an Unspecified Depth

Unfrozen

Permafrost Generally Extends

Through Sediments into Bedrock

at an Unspecified Depth

N

C

a

n

o l R

o

a

d

R i v e r Ro a d

? ? ?

? ?

? ? ?

?

?

?

?

?

?

?

?

100 m

11
0 50 100 150 200 250 300 350

Truck Fill Stand

0

10

20

30

40

50

Depth (m)

Canol

Road BH

Slough

BH BH BH

?

?

?

?

?

?

Distance (m)

A

East

A'

West

Permafrost Unconsolidated Alluvium

(silt, sand and gravel)

Weathered Schist Bedrock Schist Bedrock

Figure 11. Cross section A-A’ (survey line 62 (94), Fig. 6) illustrating the relationship

between areas of permafrost that extend into bedrock and the rapid transition from

unfrozen to frozen materials.

site (Fig. 10a and b) limits the potential interaction of both supra- and subpermafrost aquifers in

the study area with the aquifer further to the east.

It will thereby also affect the hydraulic gradient

within the site and may result in directions of

flow that respond to more local ground water

sources. Birch Hill may influence ground water

flow, given its elevation and the potential effects

of water influx at its surface. Exposures of schist

within quarries on the south side of Birch Hill

reveal numerous fractures from which water commonly seeps. Such fractures may therefore be

zones of highly localized ground water flow

within Birch Hill and beneath the Chena River

flood plain, creating localized piezometric gradients in the suprapermafrost and subpermafrost

aquifers that are difficult to predict.

The subpermafrost aquifer, however, will also

be in communication with ground water further

south in the Chena River area (Fig. 10b). This area

is more likely to be controlled by the subregional

flow system, which numerous studies have shown

to have a general west to northwest gradient (e.g.,

Williams 1970, Péwé et al. 1976, Ecology and Environment 1994). Therefore, both local and subregional ground water controls may determine flow

patterns and velocities within the subpermafrost

aquifer of the immediate site. Flow within the

unfrozen channel aquifers may be affected because

of their communication with the subpermafrost

aquifer.

Birch Hill with the subpermafrost aquifer south of

the site.

In addition, the trend and location of the buried valley align reasonably well with a gully

present on the hillside within the Tank Farm (Fig.

10b). We speculate that this ravine and the buried

valley are related, and that both follow a fracture

zone within the bedrock. This fracture zone may

also be sufficiently permeable to transmit ground

water within the bedrock.

Aquifers

Unfrozen sediments of former channels in the

Canol Road area represent aquifers through which

there may be significant flow of ground water

(Fig. 10a). These aquifers evidently merge near

the Truck Fill Stand and are continuous, with

more extensive unfrozen zones near the Steese

Highway. They are also probably continuous with

the subpermafrost aquifer south and west of the

site (Fig. 10b). Unfrozen colluvial sediments at

the base of Birch Hill may also represent a significant shallow aquifer, providing a route for ground

water migration parallel to the top of the slope.

Deeply thawed areas beneath Canol Road and

the Truck Fill Stand support a suprapermafrost

aquifer. Unfrozen channel deposits provide a direct connection between this suprapermafrost

aquifer and the subpermafrost aquifer.

The large area of permafrost frozen to bedrock

with a thin active layer east and southeast of the

12
Figure 12. Depths to the bottom of permafrost from boreholes in the Canol Road area.

Figure 13. Preliminary map of the depth to

bedrock from borehole data in the Canol

Road area; contour interval is 1.5 m.

R i v e r R o a d

Shannon Park

Subdivision

Quarry

N

0 200 400 m

Road

Railroad

Permafrost Depth (m)

Bedrock Depth (m)

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Truck Fill

Stand Bir c h H i l l R o a d

Trainor Gate Road

C h e n a R i v e r

School

36.9

23.2

31.7

26.4 25.0

31.7

35.7 36.6

39 42.1 >42.7

40.0

44.8

11.0

31.1

32.9 32.6

26.5

39

37.8

26.2

13.1

15.2

19.8 20.7 19.5

38.7

37.2

40.2 42.7

18.3

21.0

17.423.8

21.6 22.3

20.7

42.7

46.6 45.7

38.4 >38.4

27.7 32.3

26.2

23.5

19.5

23.2

25.9

27.1

26.2

22.5

36.6

36.3

36.6

34.4

31.1

15.2 21.3

19.2 21.3

24.7

19.2

22.3

20.7

>19.5

0

0

0

0

0

0

20.1

20.4 23.2

>20.4

>44.5

>44.8

>27.4

8.5

12.8 22.9

14.9

14.3 20.7 18.0

20.4

22.5

17.7

7.6

27.7

31.7

30.5

32.9

25.6

29.3

29.6 22.5

14.3

11.0

17.7

27.9

23.5

23.5 22.3

18.6

13.7

14.6 14.9

14

16.5

14.9

17.4 13.4

20.4

20.4

23.5 16.8

19.2

21.6

22.3

20.4

23.2

Shannon Park

Subdivision

Test Grid

Quarry

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

R i v e r R o a d

Trainor Gate Road

C h e n a R i v e r

School

22.6

8.4

>8.2

125

38.1

38.1

30.4

22.8

15.2

7.6

7.6

19.5

23.0

25.7 27.1

26.1

19.2

26.4

23.2

20.4

23.5

23.2 21.3

24.1

23.5

16.7

20.4

19.5

19.0

22.0

20.6

17.3 13.4

20.3

23.1

36.5 36.6 36.2

34.3

21.0 14.8

14.0

14.8

21.8

17.6

16.2

23.5 30.8

22.1

21.8

17.4

25.0

23.2

16.2

8.5

19.5

27.7

19.2

37.2

30.5

>39.9

32.0

>31.4

>31.4

>39.6 >39.6

>33.5

>29.3

>30.5

>32.9

>25.9

30.2

14.0 16.5

13.1

5.8 7.3 5.5

14.0

>44.5

40.2

>20.1

>33.5

43.3

>45.7

46.0

38.6

1.5

1.5

>9.4

3.4

4.6

40.5

21.6

34.3

>39.6

60.0

26.2

27.7 32.3

23.8

21.6 22.3

20.7

45.7 47.2

43.9

>45.7 >39.6

>44.5

>44.8

>42.7 >43.3

>41.1 >47.9

>51.8

>35.1

20.1

1.5

>9.4

7.6

GPR Borehole

E&E Soil Boring

E&E Monitoring

CRREL Microwell

Bedrock Depth below Surface

Bedrock Depth Greater than

Bottom of Drill Hole

Contour

Contour Interval (m)

Road

Railroad

N

0 200 400 m

Bir ch Hill Ro ad

13
GROUND WATER

FLOW PATTERNS

The movement of ground water in the Canol

Road area will reflect the confining and bounding

conditions imposed by the permafrost and bedrock. Permafrost constraints on

ground water flow include 1) the

extensive area east and southwest of the site where permafrost extends into the bedrock,

2) the zone of permafrost that is

frozen to bedrock within the upper half of the Truck Fill Stand

area, 3) the relatively limited occurrence and configuration of

unfrozen zones above bedrock,

4) the shallow depth of annual

thaw over areas immediately adjacent to the Tank Farm, Truck

Fill Stand and Canol Road pipeline, and 5) the depth and thickness of the subpermafrost aquifer peripheral to the site (Fig.

10a and b). Surface and nearsurface flows are also influenced

by the topography, including

such factors as the steep ravine

and slope of Birch Hill, the morphology of former swales and

channels that cross the area, and

active layer thickness, which will

affect the volume and rate of surface runoff (Fig. 10a).

We considered two scenarios

of the Canol Road area hydrogeology to be possible. The

first assumes that localized aquifers within Birch Hill and local

climatic events (e.g., precipitation, spring runoff) are the predominant water sources determining ground water flow

patterns and rates. The second

assumes that the subregional

aquifer associated with the

Chena River is the most important control on site-specific flow

patterns. As will be discussed

briefly later, the interaction of

both systems probably determines ground water conditions

north of the Chena River.

Potential pathways for nearsurface ground water movement and the possible

connections into unfrozen zones, and thus the

subpermafrost aquifer, are shown relative to the

shallow characteristic depths of thaw on Figure

14. The near-surface ground water system is located above permafrost where the thaw zone is

Figure 14. Potential near-surface flow paths depicted for two scenarios: a

hydraulic gradient dominated by the subregional aquifer and a more local

system dominated by Birch Hill. The resultant direction and velocity of flow

for each scenario differ significantly in both the subpermafrost aquifer and

in unfrozen zones linked to it. Map made from unrectified aerial photographs taken on 20 May 1993. Interpretations are based upon GPR and

borehole data and ground observations.

S t e e s e H i g h w a y

F t . W a i n w r i g h t B o u n d a r y

T r a i n o r G a t e R d

Tank Farm

Permafrost Present to

an Unspecified Depth

Unfrozen

Permafrost Generally Extends

Through Sediments into Bedrock

at an Unspecified Depth

N

C

a

n

o l R

o

a

d

R i v e r Ro a d

? ? ?

? ?

? ? ?

?

?

?

?

?

?

?

Subregional Aquifer Dominance

––––––––––––––––––––––––––

Subsurface

Subpermafrost

Birch Hill Aquifer Dominance

––––––––––––––––––––––––

Subsurface

Subpermafrost

100 m

?

14
sufficiently thick to permit a continuous to mostly

continuous aquifer. Thin active layers of 1.0 m or

less are unlikely to support a continuous ground

water aquifer, although sporadic, isolated ones

may exist in topographic lows. Thus, water may

move through a suprapermafrost aquifer within

the Truck Fill Stand area, the suprapermafrost

thaw bulb below Canol Road, and the narrow

unfrozen zone above bedrock along the base of

Birch Hill in the Tank Farm area (Fig. 15). The

flow direction responds to a gradient generated

mainly by local conditions, including seepage

through the near-surface materials and weathered bedrock of Birch Hill, and by runoff associated with precipitation or snowmelt.

The near-surface, perched ground water communicates with the subpermafrost aquifer through

the unfrozen zones of the former channel deposits (Fig. 14). Once within these unfrozen zones,

local gradients, hydraulic conductivities and sedimentary–stratigraphic properties determine seepage direction and velocity. The impermeable nature of the permafrost confines the aquifers within

these deposits, possibly directing lateral movements (Fig. 16). Areas with a downward gradient

will result in movement into the subpermafrost

aquifer.

The subpermafrost aquifer may respond to hydraulic gradients produced by either the subregional aquifer within the Chena and Tanana rivFigure 15. Potential deep aquifer flow paths depicted for two scenarios: a hydraulic gradient

dominated by the subregional aquifer and a more local system dominated by Birch Hill. The

resultant direction and velocity of flow for each scenario differ significantly in both the

subpermafrost aquifer and in unfrozen zones linked to it. Map made from unrectified aerial

photographs taken on 20 May 1993. Interpretations are based upon GPR and borehole data

and ground observations.

?

n

a

o l R

o

a d

C

? Based Upon

Limited Data

Subregional Aquifer

Dominance

Active Layer Above

Permafrost (≤1.0 m)

Birch Hill Aquifer

Dominance

100 m

Deep Thaw Above

Permafrost (>3.0 m)

Shallow Thaw Above

Permafrost (>1.0-3.0 m)

Unfrozen

Ft. Wa ni wr gi ht Boundary

N

?

? ?

?

?

?

? ?

?

15
Figure 16. Potential interaction and flow directions between a subpermafrost aquifer and an unfrozen zone, such as a former swale or channel.

Figure 17. Idealized subpermafrost and suprapermafrost flow

patterns associated with an aquifer within the bedrock in Birch

Hill. Flow below the permafrost responds to the hydraulic

gradient of Birch Hill. Flow that trends E–W is the result of

permafrost confinement in unfrozen former channels.

Pf Pf

Near Surface Flow

Subsurface Flow

ers’ alluvium or a bedrock aquifer associated with

Birch Hill (Fig. 15). In either case, the constraints

of permafrost are relevant. Barriers caused by permafrost extending into bedrock will affect flow

patterns for both scenarios, resulting in mainly a

north–south trend, the actual direction responding to the local gradient. A system dominated by

flow from water within the bedrock in or below

Birch Hill (referred to hereafter as the localized

aquifer within Birch Hill) would result in subsurface flow that generally parallels the direction of

slope, resulting in upward directed flow after

passing beneath permanently frozen materials

(Fig. 17). Also relevant to this scenario are the

down-gradient water table fluctuations that respond to stage fluctuations in the Chena River,

thus affecting the ultimate baseline and hydraulic

gradient between the Canol Road OU-3 sites and

the Chena River in the downtown Fairbanks area.

We consider it probable that both the subregional Chena and Tanana river system aquifer

and the localized aquifer within Birch Hill significantly affect ground water flow directions and

seepage velocities in the Tank Farm and Truck

Fill Stand area. Moreover, the dominance of one

system over the other may vary seasonally in

response to changes in runoff and infiltration of

snowmelt or rain. We expect seasonal periods of

little to no flow within the unfrozen channel deposits, as well as in deep thaw zones above the

permafrost.

In addition, the effects of the subregional aquifer on subpermafrost flow may vary seasonally,

in some cases raising water levels within the Canol

Road area and perhaps inducing reversals in flow

direction. Changes will be most pronounced

within the unfrozen channel deposits that are surrounded by permafrost, and include both east–

west and north–south trending features. Subregionally controlled directions will be mostly

northward in the north–south unfrozen zones

south of the Truck Fill Stand, while mostly north–

northeast in the subpermafrost aquifer (Fig. 14).

We anticipate southerly flow in these unfrozen

zones and southwesterly in the subpermafrost

aquifer if the localized aquifer within Birch Hill

controls the local hydraulic gradient. This scenario of interacting aquifers in determining flow

patterns is consistent with deep (30 m) flow measurements made during the early winter period

of 1994–95.

SEEPAGE MEASUREMENTS

Limited measurements of ground water flow

with the CRREL prototype system suggest that

patterns within the study area for the early to

mid-winter period of October 1994 to January

1995 mainly respond to locally generated hydraulic gradients interacting with the impermeable

permafrost (Table 1).

During early to mid-winter, water levels were

slowly falling while seepage directions and velocities remained relatively constant to slowly falling (Table 1). Seepage velocities, based upon the

calibration to a no. 8–12 sand mixture, typically

ranged from 0.5 to 1 m/day, with maximum values of 1.7 to 2.6 m/day measured in two 10-mdeep wells (Table 1). These isolated higher values

may reflect localized controls on water movement,

or perhaps inaccuracies for a particular well atEquipotential

Lines

Pf Pf Pf

Bedrock

Near Surface Flow

Subsurface Flow

Birch

Hill

1173

16
Table 1. Relative seepage velocity and direction data in monitoring wells.

October–January

Well October November December January averages

Well depth Avg dir Std dev Avg vel Std dev Avg dir Std dev Avg vel Std dev Avg dir Std dev Avg vel Std dev Avg dir Std dev Avg vel Std dev Dir Vel

number (ft) (m) (°) (°) (ft/day) (m/day) (ft/day) (m/day) (°) (°) (ft/day) (m/day) (ft/day) (m/day) (°) (°) (ft/day) (m/day) (ft/day) (m/day) (°) (°) (ft/day) (m/day) (ft/day) (m/day) (°) (ft/day) (m/day)

MWC-1 100.3 (30.6) 167.65 5 1.51 (0.46) 0.1( 0.03) 162.00 8 1.50 (0.46) 0.10 (0.03) 113.00 23 2.00 (0.61) 0.8 (0.24) 120.00 3 3.60 (1.10) 0.2 (0.06) 140.66 2.15 (0.65)MWC-1A 60.0 (18.3) 82.38 2 2.08 (0.63) 0.1 (0.03) 82.00 2 2.10 (0.64) 0.10 (0.03) 85.00 2 2.10 (0.64) 0.1 (0.03) 86.00 2 2.20 (0.67) 0.1 (0.03) 83.85 2.12 (0.64)MWC-1B 30.0 (9.1)MWC-2 90.5 (27.6) 215.03 5 1.56 (0.48) 0.1 (0.03) 217.00 4 1.50 (0.46) 0.10 (0.03) 201.00 9 1.70 (0.52) 0.5 (0.15) 198.00 3 2.50 (0.76) 0.1 (0.03) 207.76 1.81 (0.55)MWC-2A 60.0 (18.3) 127.11 2 2.55 (0.78) 0.1 (0.03) 125.00 2 2.50 (0.76) 0.10 (0.03) 120.00 3 2.50 (0.76) 0.1 (0.03) 122.00 3 2.30 (0.70) 0.1 (0.03) 123.53 2.46 (0.75)MWC-2B 30.0 (9.1) 216.83 2 3.44 (1.05) 0.1 (0.03)MWC-3 90.0 (27.4) 240.30 3 1.59 (0.49) 0 245.00 3 1.60 (0.49) 0.10 (0.03) 245.00 2 1.50 (0.46) 0.1 (0.03) 245.00 4 1.50 (0.46) 0.1 (0.03) 243.83 1.55 (0.47)MWC-3A* 60.0 (18.3) 124.18 2 4.78 (1.46) 0.2 (0.06) 131.00 6 5.50 (1.68) 0.70 (0.21) 144.00 2 7.50 (2.29) 0.4 (0.12) 149.00 1 7.90 (2.41) 0.2 (0.06) 137.04 6.42 (1.96)MWC-3B 30.5 (9.3) 37.37 2 2.29 (0.70) 0.1 (0.03)MWC-4 85.5 (26.1) 200.26 9 3.00 (0.91) 0.2 (0.06) 195.00 14 2.80 (0.85) 0.20 (0.06) 213.00 18 2.60 (0.79) 0.2 (0.06) 217.00 2 2.40 (0.73) 0.1 (0.03) 206.31 2.70 (0.82)MWC-4A 60.5 (18.4) 156.33 7 2.91 (0.89) 0.2 (0.06) 157.91 1 2.90 (0.88) 0.10 (0.03) 157.00 2 2.90 (0.88) 0.1 (0.03) 156.00 1 3.00 (0.91) 0.1 (0.03) 156.81 2.93 (0.89)MWC-4B 30.5 (9.3) 39.00 4 1.87 (0.57) 0.1 (0.03)MWC-5 90.5 (27.6) 206.36 10 1.11 (0.34) 0.1 (0.03) 179.00 28 1.50 (0.46) 0.50 (0.15) 140.00 3 2.10 (0.64) 0.1 (0.03) 158.00 11 2.30 (0.70) 0.1 (0.03) 170.84 1.75 (0.53)MWC-5A 60.5 (18.4) 161.62 2 2.98 (0.91) 0.2 (0.06) 162.56 1 2.95 (0.90) 0.10 (0.03) 163.00 2 3.00 (0.91) 0.2 (0.06) 162.39 2.97 (0.91)MWC-5B 29.5 (9.0) 320.59 5 7.64 (2.33) 0.3 (0.09) 305.00 1 8.00 (2.44) 0.10 (0.03) 308.00 1 8.10 (2.47) 0.1 (0.03)MWC-6 30.0 (9.1) 44.86 6 1.36 (0.42) 0.1 (0.03)MWC-7 90.0 (27.4) 200.00 3 2.50 (0.76) 0.30 (0.09) 200.00 3 2.70 (0.82) 0.2 (0.06) 195.00 3 2.70 (0.82) 0.2 (0.06) 198.33 2.63 (0.80)MWC-7A 60.0 (18.3) 81.87 2 4.10 (1.25) 0.1 (0.03) 80.00 1 4.10 (1.25) 0.10 (0.03) 79.00 1 4.20 (1.28) 0.1 (0.03) 78.00 2 4.20 (1.28) 0.1 (0.03) 60.97 4.15 (1.27)MWC-7B 30.0 (9.1) 174.93 14 1.88 (0.57) 0.8 (0.24)MWC-8 59.5 (18.1) 269.71 146 1.06 (0.32) 0.1 (0.03) 335.00 8 1.10 (0.34) 0.10 (0.03) 339.00 16 1.10 (0.34) 0.1 (0.03) 299.00 7 1.30 (0.40) 0.1 (0.03) 310.68 1.14 (0.35)MWC-8A 29.5 (9.0)MWC-9 59.5 (18.1)MWC-9A 29.5 (9.0)MWC-11 119.0 (36.3)MWC-11A 89.0 (27.1)MWC-11B 59.2 (18.0) 111.22 11.55 1.61 (0.49) 1.58 (0.48) 113.95 7.43 1.42 (0.43) 0.12 (0.04) 100.00 38 0.90 (0.27) 0.2 (0.06) 108.39 1.31 (0.40)MWC-11C 29.5 (9.0)MWC-12 29.5 (9.0) 114.23 3.92 1.93 (0.59) 0.17 (0.05) 113.00 8.00 1.50 (0.46) 0.20 (0.06) 132.00 14 1.30 (0.40) 0.1 (0.03) 119.74 1.58 (0.48)*Velocities reflect electronic failure and not true velocity increase.
River Rd

Shannon Park

Subdivision

Quarry

N

0 200 400 m

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Birch Hill Rd

B i r ch Hi l l R oad

Ft. Wainwr gi ht Boundary

C a n o l Ro a d

P i p e l i n e

Trainor Gate Road

C h e n a R i v e r

School

C-2

C-4 C-3

C-1

C-6

C-8 P-3

C-7 C-9

P-5

P-9

P-18

P-7

P-0

P-10

P-4

C-11

P-2

C-5 P-1

C-12

Ground Water

Flow Vectors

Completed Subpermafrost Well

Completed Shallow

Monitoring Well Cluster

Picket Well

Railroad

October

November

December

Road

River Rd

Shannon Park

Subdivision

Quarry

N

0 200 400 m

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Birch Hill Rd

B i r ch Hi l l R oad

Ft. Wainwr gi ht Boundary

C a n o l Ro a d

P i p e l i n e

Trainor Gate Road

C h e n a R i v e r

School

C-2

C-4 C-3

C-1

C-6

C-8 P-3

C-9

C-7

P-5

P-9

P-18

P-7

P-0

P-10

P-4

C-11

P-2

P-1

P-14A

C-12

C-5

Ground Water

Flow Vectors

Completed Subpermafrost Well

Completed Shallow

Monitoring Well Cluster

Picket Well

Railroad

October

November

December

Road

b. 20-m wells.

Figure 18. Monthly mean flow vectors calculated from daily flow system measurements

during the October 1994 to March 1995.

a. 10-m wells.

18
ity is apparently a function of the confining effect

of permafrost. Certain wells, notably MWC-12, had

a reversal in flow direction within this period.

The flow data from early to mid-winter indicate that seepage directions and velocities vary

with well depth, this variability apparently reflecting the proximity and geometry of the permafrost. Surrounding and confining permafrost,

which extends from about 25 to 35 m below the

surface, locally controls flow directions, while interaction with the subpermafrost aquifer of the

area may induce highly variable horizontal and

vertical gradients and seepage rates. Directions

of flow may therefore deviate greatly from the

subregional pattern of flow (e.g., MWC-12, MWC1, Table 1). The variability in the 10- and 20-m

well data are consistent with their location within

thaw zones bounded by permafrost. In contrast,

the more consistent flow pattern of the 30-m-depth

wells probably reflects the overall flow pattern of

the deeper aquifer in this area because measurements are close to the bottom of the permafrost.

These data also indicate that the hydraulic gradient is controlled locally by an aquifer within or

north of Birch Hill.

tributable to the current probe calibration in a

standard no. 8–12 sand mixture.

The 30-m-deep wells have fairly consistent

seepage velocities and directions of flow, while

the 20-m-deep wells exhibit slightly greater variability in direction from month to month (Fig.

18). Velocities remain fairly constant but at a

rate greater than those of the 30-m depth. The

20-m well data exhibit a mostly south–southeast

flow pattern within thaw zones that trend

mainly northwest to southeast (Fig. 18b). Eastern trending directions of flow (e.g., MWC-1,

MWC-12) are consistent with well locations within

thaw zones that trend mainly east to west (Fig. 15

and 18c).

Data from the 30-m-depth monitoring wells

exhibit a south to southwest pattern with velocities ranging from about 0.5 to 1 m/day (Fig. 18c

and 19c). These data vary little from month to

month. Their consistency in direction and rate

probably reflects their location at or below the

base of the permafrost.

The patterns exhibited by the 10-m wells are of

much greater variability (Table 1) than those at

either 20 or 30 m (Fig. 18c and 19c). This variabilc. 30-m wells.

River Rd

Shannon Park

Subdivision

Quarry

N

0 200 400 m

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Birch Hill Rd

B i r ch Hi l l R oad

Ft. Wainwr gi ht Boundary

C a n o l Ro a d

P i p e l i n e

Trainor Gate Road

C h e n a R i v e r

School

Ground Water

Flow Vectors

Completed Subpermafrost Well

Completed Shallow

Monitoring Well Cluster

Picket Well

Railroad

October

November

December

Road

C-2

C-4 C-3

C-1

C-6

C-8 P-3

C-9

C-7

P-5

P-9

P-18

P-7

P-0

P-10

P-4

C-11

P-2

P-1

C-12

C-5

Figure 18 (cont’d).

19
River Rd

Shannon Park

Subdivision

Quarry

N

0 200 400 m

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Birch Hill Rd

B i r ch Hi l l R oad

Ft. Wainwr gi ht Boundary

C a n o l Ro a d

P i p e l i n e

Trainor Gate Road

C h e n a R i v e r

School

0 1

Completed Subpermafrost Well

Completed Shallow

Monitoring Well Cluster

Picket Well

Road

Railroad

Ground Water Flow Vector

Measuring Velocity (m/day)

C-2

C-4 C-3

C-1

C-6

C-8 P-3

C-9

C-7

P-5

P-9

P-18

P-7

P-0

P-10

P-4

C-11

P-2

C-5

C-12

P-1

River Rd

Shannon Park

Subdivision

Quarry

N

0 200 400 m

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Birch Hill Rd

B i r ch Hi l l R oad

Ft. Wainwr gi ht Boundary

C a n o l Ro a d

P i p e l i n e

Trainor Gate Road

C h e n a R i v e r

School

C-2

C-4 C-3

C-1

C-6

C-8 P-3

C-7 C-9

P-5

P-9

P-18

P-7

P-0

P-10

P-4

C-11

P-2

C-5

C-12

P-1

0 1

Completed Subpermafrost Well

Completed Shallow

Monitoring Well Cluster

Picket Well

Road

Railroad

Ground Water Flow Vector

Measuring Velocity (m/day)

Figure 19. Mean flow directions for October 1994 to March 1995.

b. 20-m wells.

a. 10-m wells.

20
CONCLUSIONS

Hydrogeological conditions are extremely complex within the Canol Road

area because of the complex distribution of aquifers within the discontinuous permafrost. Aquifers occur within

the unfrozen materials above (suprapermafrost), below (subpermafrost) and

within (intrapermafrost) the impermeable, permanently frozen alluvial

sediments. Zones that are completely

unfrozen from the surface into the bedrock interconnect the supra- and subpermafrost aquifers. Near-surface flow generally takes place in suprapermafrost

aquifers within deeply thawed, disturbed areas, where the top of permafrost lies at depths ranging from a few

meters to over 15 m, as well as within

unfrozen former swales or channels. In

addition, areas where materials are

deeply frozen and possess only thin active layers interrupt the continuity of

the subpermafrost aquifer, as well as

confine or isolate suprapermafrost aquifers from unfrozen zones. In particular,

a zone to the east and southeast of the

site severely limits communication of

ground water with the aquifer further

south near the Chena River.

Seepage measurements with flow sensors in

monitoring wells for the period of October 1994

to January 1995 indicate that flow directions at

the 30-m depth were consistently to the south–

southwest. At the 10- and 20-m depths, flow is

much more variable in orientation and velocity.

This variability reflects the effects of permafrost

and its configuration. Seepage data suggest that

the local gradient is responding to a hydraulic

gradient north of the site, including Birch Hill.

These limited data suggest that ground water

movement within the Canol Road area is mainly

controlled by local water sources and hydraulic

gradients. The overall directions of flow are therefore not the same as the subregional pattern of

westerly to northwesterly flow. Rather, they trend

mainly south to southwest in the subpermafrost

aquifer. Directions may vary greatly from site to

site within unfrozen zones surrounded by permafrost. Northeast–southwest trending zones tend to

have a southwesterly flow, while east–west trending zones show mainly easterly flow directions.

These results are critical to predicting ground

water movement and the fate and transport of

contaminants. Simple water table elevation

measurements from wells across the area that are

commonly taken quarterly or monthly at some

sites cannot be used to develop a hydraulic

gradient and predict site-specific flow patterns.

Site-specific flow patterns often differ significantly from the general subregional flow pattern.

Therefore, measurements that consider the effects

of permafrost provide accurate data on ground

water movement and site specific movements and

should be used to analyze contaminant fate or

migration.

Potential pathways for contaminant migration

include 1) unfrozen former channels trending both

east–west and north–south across the site, 2) the

subpermafrost aquifer above bedrock where it is

interconnected with the unfrozen zones and the

unfrozen southern slope of Birch Hill, and 3) nearsurface, suprapermafrost aquifers within disturbed areas of Canol Road, Lazelle Road, Birch

Hill Road, the Tank Farm and the Truck Fill Stand.

Our initial data suggest that the migration of conRiver Rd

Shannon Park

Subdivision

Quarry

N

0 200 400 m

ROLF

Birch Hill

S t e e s e H i g h w a y

Tank Farm

Birch Hill Rd

B i r ch Hi l l R oad

Ft. Wainwr gi ht Boundary

C a n o l Ro a d

P i p e l i n e

Trainor Gate Road

C h e n a R i v e r

School

0 2

Completed Subpermafrost Well

Completed Shallow

Monitoring Well Cluster

Picket Well

Road

Railroad

Ground Water Flow Vector

Measuring Velocity (m/day)

C-2

C-4 C-3

C-1

C-6

C-8 P-3

C-7 C-9

P-5

P-9

P-18

P-7

P-0

P-10

P-4

C-11

P-2

C-5

C-12

P-1

c. 30-m wells.

Figure 19 (cont’d).

21
taminants is controlled locally and varies seasonally, including reversals in transport direction.

Although we cannot yet predict the directions

and rates of ground water movement within the

Canol Road area with certainty, continued analyses of the distribution of frozen and unfrozen

materials that are coupled to flow measurements

in monitoring wells, including new subpermafrost

wells, will allow us to develop a much clearer

picture of the overall patterns above, within and

below the permafrost. Moreover, long-term data

acquisition will reveal whether flow parameters

change seasonally or annually, and will give us

insight into the dominant aquifer controlling the

ground water system of the Canol Road area.

RECOMMENDATIONS

Ground water flow patterns require further

analysis to define potential contaminant migration pathways in the discontinuous permafrost

within the Tank Farm, Truck Fill Stand and Canol

Road areas. Preliminary data are insufficient to

model ground water flow accurately, particularly

the role of local (Birch Hill) or subregional aquifers in ground water movement. Monitoring wells

should be installed in Birch Hill to define the

local hydraulic gradients. Water quality parameters should also be analyzed for wells at various

depths in each aquifer within and external to the

study area to further define water sources affecting site-specific ground water flow. Year-round

flow system measurements are required to identify seasonal variability in direction and seepage

velocity.

LITERATURE CITED

Chapman, H.T. and A.E. Robinson (1962) A thermal flowmeter for measuring velocity of flow in a

well. U.S. Geological Survey Water Supply Paper, 544-E.

Ecology and Environment (1994) Remedial investigations report, Operable Unit 3, Fort Wainwright, Alaska, Volumes 1, 2, and 3. Prepared for

the U.S. Army Engineer District, Alaska.

Hess, A.E. (1982) A heat pulse flowmeter for measuring low velocities in boreholes. U.S. Geological Survey Open File Report, 82-699.

Hopkins, D.M., T.N.V. Karlstrom and others

(1955) Permafrost and ground water in Alaska.

U.S. Geological Survey Professional Paper 264-F.

King, P.B. (1969) Tectonic map of North America

(1:5,000,000). U.S. Geological Survey Map.

Lawson, D.E., S.A. Arcone, J.C. Strasser, A.

Delaney, C. Williams and D. Albert (1993) Geological and geophysical analyses of permafrost

and ground water conditions, Fort Wainwright,

Alaska. Progress Report prepared for the U.S.

Army 6th ID and U.S. Army Engineer District,

Alaska.

Péwé, T.L. (1958) Geologic map of the Fairbanks

D-2 Quadrangle, Alaska. U.S. Geological Survey

Geology Quadrangle Map GQ-110.

Péwé, T.L., J.W. Bell, R.B Forbes and F.R. Weber

(1976) Geologic map of the Fairbanks D-2 SE

Quadrangle, Alaska. U.S. Geological Survey Miscellaneous Investigations Series Map I-942.

Shannon and Wilson, Inc. (1992) Potential offsite

ground water contaminant migration, west

boundary, Fort Wainwright, Alaska. Prepared

for the U.S. Army Engineer District, Alaska.

Williams, J.R. (1970) Ground water in the permafrost regions of Alaska. U.S. Geological Survey

Professional Paper, 696.

Williams, C.R., J.S. Morse, D.E. Lawson, D.E.

Garfield, J.D. Strasser and T. Tantillo (1995) An

automated monitoring system for site-specific,

in situ ground water flow analyses, Fort Wainwright, Alaska. Interim Draft Report for U.S.

Army Alaska, Directorate of Public Works, and

U.S. Army Engineer District, Alaska.

22
General operation

A Geophysical Survey Systems, Inc., SIR Model

4800 radar control unit, assorted antennas, cables,

a GSSI DT6000 digital tape recorder, and a power

supply were used in this study. The control unit

keys the transmitter on and off at 50 kHz (synchronized with the receiver), sets the scan rate

(rate at which echo scans are compiled, generally

25.6 scans/s), scan time range and the time range

gain to be applied to the scans. The transmit antenna radiates a broadband pulse that lasts from

only a few to tens of nanoseconds (ns). A separate, identical receive antenna is employed because echoes can return from near-surface targets

before the transmit antenna has stopped radiating. The received signals are converted by sampling into an audio frequency facsimile for filtering, amplification and recording.

Field procedures

Transects were established along trails in the

Canol Road area and profiled by dragging the

antennas along the ground, about 6–7 m behind a

tracked vehicle. All surveys were done with the

antennas polarized perpendicular to the transect

direction so that the more intense, but unorthodox, H-plane pattern was in the line of the transect.

Event markers were placed artificially on the

records at measured intervals, generally every 10

m. Scan durations were set to encompass the features of interest, which always occurred within

the depth of the noise floor visible on the oscilloscope incorporated in the control unit. Generally,

we used 500 to 1000 ns for profiles with both the

50- and 100-MHz antennas as the deeper sections

of water beneath permafrost usually occurred between 400 and 600 ns into the records. Scan durations up to 2000 ns for the 50-MHz antennas were

used in areas with much deeper (to 60 m) permafrost.

Data recording

and processing

All data were recorded at a scan rate of 25.6/s,

and a scan sampling density of 512 or 1024 eightbit words. The slow dragging speed resulted in a

recorded scan about every 4 cm. All data were

stacked five-fold, which marginally affected detail as the stacked horizontal data density was

about one scan per 20 cm. Data recorded when

antenna movement was stalled were deleted from

the total record. After editing, the lengths of the

APPENDIX A: GROUND-PENETRATING RADAR OPERATION AND THEORY

records between distance markers were equalized (i.e., “justified”) to compensate for changes

in towing speed. Later processing reduced background ringing (e.g., from surface meltwater), alleviated overall gain variations resulting from

inconsistent antenna–ground coupling, and enhanced vertical resolution using deconvolution.

Data were displayed as echo-time-of-return vs.

profile distance using either wiggle trace or line

intensity format. Individual scans are easily retrieved with the software.

Data interpretation is generally based on the

simple echo delay formula

d = ct/2n (A1)

where d is the depth of a reflector in centimeters, t

is the echo time delay in nanoseconds and c is the

speed of electromagnetic waves in a vacuum (30

cm/ns). The quantity n is often replaced by ε1/2,

where ε is the dielectric constant (approximately

5.3–6 for frozen alluvium). The factor of 2 in eq

A1 accounts for the round-trip propagation path

of the pulse and applies only to reflections from

horizontally flat interfaces extending several insitu wavelengths, or to scattering from point

sources. Equation A1 can be applied to several

layers successively if n is known for each layer

and the delay times to each layer interface are

easily picked off the record. Measurements made

during the summer, when conditions had remained dry for over 6 weeks, reveal that a roundtrip propagation time of 100 ns corresponds to a

depth of about 6.5 m in permafrost, and 24 ns

corresponds to 1 m of surface thaw.

Proper translation of echo time of return into

depth requires a complicated process known as

migration. Successful migration requires detailed

knowledge of the subsurface velocity structure.

Our knowledge of permafrost and thaw velocity

comes from correlations between GPR and borehole data, along with previous studies of refraction in the Canol area. Migration is not necessary

when subsurface interfaces are fairly horizontal,

as they are in this study. In viewing the GPR

profiles it must be remembered that there is a

very large compression in the horizontal direction.

Antennas and radiation

All antennas used are resistively loaded dipoles that radiate a pulse containing about 2 to

23
2.5 cycles. The 50-MHz surveys were performed

with a pair of unshielded (metallic shielding mitigates back radiation) strings of resistors. The transmit and receive antennas were separated by 3.3 m

to prevent overloading the receiver by the 800-W

peak power transmitter. The transmitter keyed

the receiver along a fiber optic cable to reduce

cable noise.

The 100-MHz antennas were commercially obtained (Model 3207, GSSI, Inc.) flared dipoles with

a tapered resistive loading. The antennas were

backshielded and housed in separate units placed

2 m apart. The transmitter is rated at 800 W peak

power. All waveforms had a 3-dB bandwidth of

about 35%. The received pulse waveforms of the

100-MHz antennas were similar to those of the 50

MHz.

Theoretical transmit radiation patterns for point

dipoles are nonuniform, with nulls and lobes in

planes parallel (E-plane) and perpendicular (Hplane), respectively, to the antenna axis. These

features occur in the angular directions ψ = ±sin–1

(1/n) measured from vertical, where n is the real

part of the refractive index of the propagation

medium. For frozen alluvium with n = 2.3, ψ = ±26°.

The effective transmit–receive directivity patterns are for a horizontal, unshielded, finite-size

radar antenna operating monostatically on the

ground. The H-plane pattern is perpendicular to

the antenna axis and, therefore, along our profile

directions. This orientation helps to ensure that

we were profiling the ground directly beneath us

rather than to the sides. These patterns are not

affected significantly by the finite separation of

transmit and receive antennas, which is much

less than the ground water depths investigated.

The patterns are more directive than for a single

transmit antenna owing to multiplication of the

identical transmit and receive directivities. The

patterns may be considered to be the response to

an isotropic, polarization-insensitive, nondispersive point target.

24
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VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

May 1996

Geological and Geophysical Investigations of the Hydrogeology of Fort

Wainwright, Alaska: Part I. Canol Road Area.

Daniel E. Lawson, Jeffrey C. Strasser, Jodie D. Strasser, Steven A. Arcone,

Allan J. Delaney and Christopher Williams

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road CRREL Report 96-4

Hanover, New Hampshire 03755-1290

U.S. Army Engineer District, Alaska

for the Environmental Department, Public Works

Directorate, U.S. Army Alaska

Fort Wainwright, Alaska

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

32

Alluvium Ground penetrating radar Hydrogeology

Conceptual model Ground water Permafrost

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

The hydrogeology of Fort Wainwright, Alaska, is extremely complex because of the relatively impermeable

discontinuity of permafrost, which controls the distribution and dimensions of the aquifer. Aquifers occur

above, below and adjacent to permanently frozen materials, as well as within thaw zones surrounded by

permafrost. This complexity makes it difficult to predict the direction and rate of ground water flow, as well as

its seasonal and annual variability. Considerable problems exist in locating suspected contaminant plumes,

identifying source areas, defining transport paths and evaluating contaminant fate. This report summarizes

the results of ongoing investigations of the permafrost and ground water conditions within the northwestern

part of the Fort Wainwright cantonment area, north of the Chena River. Data from ground-penetrating radar,

drilling, ground water flow sensors, aerial photographs and ground observations were used to delineate

aquifer distribution and develop a conceptual physical model of hydrogeological conditions. Ground water

seepage velocity and direction, which were measured during early to mid-winter 1994–95, reflect the role of

local water sources and permafrost distribution in determining ground water flow patterns. Other factors,

including the vertical and lateral extent of permafrost, a bedrock aquifer, and the alluvial origins of unfrozen

sediments and landforms, are apparently more important than the subregional aquifer in determining ground

water conditions during winter. Contaminant migration will be strongly affected by these factors as well.