Michael R. Walsh, Edwin J. Chamberlain, Karen S. Henry, September 1996

Donald E. Garfield and Ed Sorenson

SPECIAL REPORT 96-22

Dredging in an Active Artillery

Impact Area

Eagle River Flats, Alaska
Abstract: Remediation of sediments in permanently

ponded areas at Eagle River Flats, a salt marsh contaminated with white phosphorus (WP), may re-quire

dredging. Because the Flats were used as a

firing range impact area for over 40 years by the U.S.

military, there is much unexploded ordnance, which

will require that any dredging equipment be remotely

controlled. To treat the sediment pumped from dredged

areas, a spoils retention basin was designed, conHow to get copies of CRREL technical publications:

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structed, and tested. This basin contains several innovations, including a natural peaty-silt liner and a geofabric

barrier to inhibit reintroduction of WP into the environment, and is designed for the natural remediation of the WP. The dredging system was deployed in

October of 1994, with sampling indicating that WP-contaminated areas were removed from the dredged area.

An early snowfall curtailed operations shortly after initiation.
Special Report 96-22

U.S. Army Corps

of Engineers

Cold Regions Research &

Engineering Laboratory

Michael R. Walsh, Edwin J. Chamberlain, Karen S. Henry, September 1996

Donald E. Garfield and Ed Sorenson

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

Approved for public release; distribution is unlimited.

Dredging in an Active Artillery

Impact Area

Eagle River Flats, Alaska
PREFACE

This report was prepared by Michael R. Walsh, Mechanical Engineer, Engineering Resources Branch, Technical Resources Center, U.S. Army Cold Regions Research and Engineering Laboratory (CRREL), Hanover, New Hampshire; Edwin J.

Chamberlain, Research Civil Engineer, Applied Research Division, Research and

Engineering Directorate, CRREL; Karen S. Henry, Research Civil Engineer, Civil

and Geotechnical Engineering Research Division, Research and Engineering Directorate, CRREL; Donald E. Garfield, Mechanical Engineer, Engineering Resources

Branch, Technical Resources Center, CRREL; and Ed Sorenson, Civil Engineer,

Hydraulics and Hydrology Section, Civil Works Branch, Engineering Division, U.S.

Army Corps of Engineers, Alaska District.

Funding for this work was provided by the U.S. Army Environmental Center,

Aberdeen Proving Ground, Maryland, through the U.S. Army Alaska, Fort

Richardson, William Gossweiler, Army Remedial Project Manager.

Technical review of the manuscript was provided by Leonard Zabilansky and

Jeffrey Stark of CRREL. Susan Hunnewell assisted with the filter fabric work. Dennis Lambert and Troy Arnold helped with the dredging operation. Charles Collins

is the Science Coordinator for the Eagle River Flats Program and assisted with data

collection and surveying. Laurie Angell and Bill Smith, Fort Richardson Directorate of Public Works—Environmental, provided critical administrative and logistical support. Travis Barber, Mike Hamilton, John McKiernan, and George Boice and

his co-workers are much appreciated for their construction, excavation, and technical support throughout this program.

The contents of this report are not to be used for advertising or promotion purposes. Citation of brand names does not constitute an official endorsement or approval of the use of such commercial products.

ii
iii

CONTENTS

Page

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

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

Feasibility study ..................................................................................................... 1

Dredge specifications ............................................................................................ 2

Environmental considerations ..................................................................... 2

Ordnance ......................................................................................................... 3

Safety ............................................................................................................... 3

Transportability .............................................................................................. 3

Basin investigations ............................................................................................... 4

Settlement times ............................................................................................. 4

Laboratory sediment tests ............................................................................ 5

Weir flow ......................................................................................................... 8

Supernatant filtering ..................................................................................... 11

Site characterization ...................................................................................... 13

Site preparation ...................................................................................................... 24

Instrumentation and sampling ............................................................................ 27

Dredging activity ................................................................................................... 29

Results ..................................................................................................................... 31

Analysis of spoils samples ........................................................................... 31

Data from stations ......................................................................................... 31

Estimated dredged material quantity ......................................................... 31

Discussion ............................................................................................................... 32

Literature cited ....................................................................................................... 34

Appendix A: Dredging survey information package ....................................... 35

Appendix B: Retention basin model ................................................................... 37

Appendix C: Spoils sample collection, storage, and shipment SOP .............. 43

Appendix D: Decanted supernatant sample collection, storage,

and shipment SOP ......................................................................................... 45

Abstract ................................................................................................................... 47

ILLUSTRATIONS

Figure

1. Results of preliminary sedimentation tests ............................................. 5

2. Montgomery tube used for sedimentation tests .................................... 6

3. Sedimentation test results in Montgomery tube .................................... 7

4. Drop inlet structure, showing adjustable weir ....................................... 8

5. Instantaneous flow over a rectangular weir ........................................... 9

6. Instantaneous weir flow rates for various heads ...................................... 10

7. Basin drainage times as a function of weir length ................................. 11

8. Confirmation of integral relationship ...................................................... 12

9. Drainage times for 4.5- to 7.5-m weirs ..................................................... 12

10. Permeability of sediment in column ........................................................ 14

11. Results of Proctor tests of peaty silt .......................................................... 15

12. Results of laboratory permeability tests .................................................. 17

13. Hydraulic conductivity barrel test cells on the EOD pad ..................... 17

14. Schematics of barrel tests on EOD pad .................................................... 18

15. Results of barrel infiltration tests for unaltered and sedimented pad 20

16. Results of barrel infiltration tests for sludge on peaty silt .................... 20

17. Retention basin barrel infiltration and permeability test locations ..... 21

18. Barrel infiltration test cell in retention basin ........................................... 22
Page

19. Results of barrel infiltration tests for sediment on peaty silt liner ...... 23

20. Composite of lab and field permeability test results for peaty silt ...... 23

21. Retention basin berms ................................................................................ 24

22. Spoils line outlet pads ................................................................................ 25

23. Dredge traverse system.............................................................................. 26

24. Ordnance retention receptacle .................................................................. 27

25. Dredge spoils sampling station ................................................................ 28

26. Retention basin instrumentation station ................................................. 28

27. Cessation of dredging activities ................................................................ 30

28. Comparative chromatograms for spoils analysis................................... 31

29. Data from instrumentation stations ......................................................... 32

30. Pumping contaminated spoils from the Flats ......................................... 33

TABLES

Table

1. Settling times for spoils in fresh water .................................................... 4

2. Laboratory sedimentation test results following the Montgomery

(1978) procedures .................................................................................. 6

3. Results of GC analysis for WP in water column above simulated

dredge spoils.......................................................................................... 8

4. System filtering efficiencies using Texel GEO 9 filtering fabric ........... 13

5. Laboratory hydraulic conductivity tests on sediment .......................... 14

6. Laboratory compaction test results for peaty silt ................................... 15

7. Laboratory hydraulic conductivity tests for the peaty silt liner

material ................................................................................................... 16

8. Field percolation tests................................................................................. 21

9. Field compaction test results for peaty silt .............................................. 21

10. Field infiltration tests in basin liner ......................................................... 23

11. Retention basin model results summary ................................................. 24

iv
INTRODUCTION

Ongoing investigations into the waterfowl dieoffs and the persistence of the causal agent, white

phosphorus, in Eagle River Flats, an estuarine salt

marsh and military impact area, indicate that any

remediation strategy will have to include consideration of removal and controlled processing of

contaminated sediments. Contaminated areas that

are constantly flooded, such as the deeper ponded

areas, do not allow natural drying of the soil and

subsequent sublimation of the residual white

phosphorus (WP) particles. Some of these permanently flooded areas are interconnected over large

areas and would be impractical to address through

pond draining. These areas, which are generally

vegetated and heavily used by affected dabbling

ducks and swans, have been found to be contaminated even after five years in which no WP rounds

have been fired into the Flats. Although some areas of the Flats have shown evidence of natural

remediation due to drying cycles, the ponded areas still pose a substantial risk to waterfowl.

The objective of this project is to investigate the

feasibility of using a small, remote-controlled

dredge to remove sediments from contaminated

ponded areas and treating the spoils in an open

retention basin. The treatment method will be

natural drying via atmospheric exposure consequently resulting in the sublimation of the contaminant, white phosphorus. Spoils are to be monitored prior to deposition in the retention basin,

and studies initiated to determine the fate of the

contaminated sediments undergoing treatment in

the basin.

Dredging was chosen as a method of remediation because of the positive displacement of the

contaminated material and the ability to treat the

material in a controlled environment. Using a

small dredge, limited areas can be addressed and

transport of the contaminated material (spoils) to

a retention basin for treatment can be quickly and

efficiently conducted. Environmental impact, although not negligible, can be minimized through

a careful dredging strategy and specific design

criteria.

This report describes the preparations for

dredging carried out during the spring and summer of 1994, and the short dredging operations

conducted in mid-October of that same year. A

detailed description of the retention basin design

and performance is included. This project was a

joint effort between the U.S. Army Cold Regions

Research and Engineering Laboratory (CRREL),

the U.S. Army Corps of Engineers, Alaska District

(COE-AK), and the Environmental Division of the

U.S. Army, Alaska, Directorate of Public Works

(DPW).

FEASIBILITY STUDY

Before dredging could be considered as a

remediation strategy, a feasibility study needed to

be conducted to ensure that dredging was a viable option. This was conducted by Walsh and

Garfield. Dredging in Eagle River Flats is unique

for one major reason: the potential presence of

large quantities of unexploded ordnance (UXOs).

Other factors that will affect dredging include the

seasonal high tides, elevating the spoils to the

holding pond on the explosive ordnance disposal

(EOD) pad, the presence of vegetation and driftwood, the long pumping distances, and, of course,

the white phosphorus. The feasibility study was

conducted in two phases. The first was a review

of available basic literature on dredging followed

by a more specific literature search. The second

phase involved contacting and visiting manufacturers of small dredges to brief them on the unique

situation at Eagle River Flats (ERF) and to discuss

the feasibility of the pilot project, as well as to solicit their ideas on how it could be done.

Due to the short amount of time available for

Dredging in an Active Artillery Impact Area

Eagle River Flats, Alaska

MICHAEL R. WALSH, EDWIN J. CHAMBERLAIN, KAREN S. HENRY,

DONALD E. GARFIELD AND ED SORENSON
this study, both the initial research as well as the

literature search were quite limited. The literature

search topic was amphibious dredges, as this was

the initial thrust of the study. Unfortunately, very

little relevant information could be found on this

subject. Concurrently, several basic texts and conference proceedings on dredging were reviewed.

Also, all the current pertinent reports on the phosphorus contamination problem at the Flats were

reviewed. With this background information, we

investigated possible dredge manufacturer contacts through the Thomas Registers and personnel at CRREL who had worked with small dredges

in the past. The objective was to determine

whether a small dredge capable of the special requirements of operating in the Flats was available

or could be easily modified from existing equipment.

A set of preliminary specifications was assembled and a list of prospective contacts was

compiled and the companies contacted. A brief

explanation of the situation and the preliminary

specifications were sent to each contact. We requested information on their product lines and

asked about visiting their facilities in the future to

discuss the project in more detail and to get a better feel for their capabilities and strengths. A short

list of five manufacturers was assembled and appointments to visit them were made. An information packet (Appendix A) was then assembled to

be given to each manufacturer during the visit.

Samples of the ERF sediments consisting of pond

bottom and shore material were bottled for the

manufacturers to give them a better feel of the

material to be dredged. We then visited with each

of the five manufacturers to discuss the feasibility

of the pilot project.

All the manufacturers visited felt the job was

feasible. Their major concern, of course, had to do

with the UXOs. There were many questions that

needed to be answered before any of the manufacturers would be able to design a complete system for the pilot project and estimate both price

and productivity. These questions needed to be

addressed to the extent possible in the dredge

specifications if the Project Manager decided to

pursue the dredging option. A write-up of the

study, including methodology and conclusions,

the information packet given to the manufacturers, unresolved questions, contacts, notes on the

meetings, background information on each company, and impressions of the visits and the companies’ capabilities by the two interviewers, was

given to the Project Manager.

Our opinion from this feasibility study was that

dredging is feasible at the Flats. To obtain reasonable production rates, the job will require a larger

machine (20- to 25-cm pump) than originally estimated. Rather than design a machine specifically

for the job, we felt we should try to use as standard a machine as practical to keep down costs

and facilitate repairs and replacement parts. A

modular design would be ideal. We moved more

towards the use of a cable/capstan-propelled and

guided floating dredge rather than an amphibious unit, as a floating unit would be more readily

available, less expensive, easier to operate, and

could be delivered sooner. Overall, if sufficient logistical and construction support from the Directorate of Public Works at Fort Richardson would

be available and procurement of the equipment

would not be delayed, conducting a demonstration project to confirm the feasibility of dredging

as a form of remediation in the summer of 1994

would be achievable.

DREDGE SPECIFICATIONS

There were many factors to take into account

when developing the specifications for the dredge

to be used in the pilot study at the Flats. Among

these were environmental impact, the presence of

ordnance, personnel safety, and equipment

transportability. No single dredge that we had seen

was able to address all these factors as they relate

to the Flats, so a specific set of criteria was drawn

up for this application. In an attempt to minimize

the cost of the system, the specifications were kept

as close to standard as possible. However, some

deviation from normal was necessary.

Environmental considerations

The first factor addressed was the dredge’s impact on the environment. Eagle River Flats is an

important migration route stopover, and as little

permanent damage as possible should be done in

the process of remediation. A small dredge will

enable us to conduct the dredging process in a

more controlled, limited manner. The dredgehead

is specified as a shrouded, center-feeding auger

that minimizes the dispersal of resuspended sediment, therefore reducing the risk of redeposition

of WP particles on the surface of the pond bottom

(Sherman 1984). The small size also makes it airtransportable by helicopter, thereby negating the

need to channelize the Flats to move the dredge

from one area to another. The strategy developed

2
for the overall remediation of contaminated

ponded areas was to address small, one-hectare

sites each year, reducing the impact of any one

dredging season and allowing previously dredged

sites to begin recuperating during operations in

the out years. Finally, we had to plan for the worst:

a detonation of a large caliber UXO by the dredge.

Specifications were written such that a loss of a

fixed volume of hydraulic fluid would trigger an

automatic shutdown of the system. In addition,

the fluid used is biodegradable and nontoxic, so

spills should not adversely affect the environment.

The dredge power supply, a diesel generator set,

is located on shore to minimize problems caused

by petroleum, oil, and lubricant (POL) spills.

Ordnance

The presence of UXOs is the other major design consideration. Using a defect rate of 5%, an

estimated 10,000 unexploded rounds may be

present in the Flats in various degrees of decay

and sensitivity. There is no safe way of getting even

a rough estimate on distribution and densities of

these UXOs. Therefore, the dredge was specified

to minimize the structural and financial impact of

the detonation of a round during operations. The

dredge was specified as modular in design to facilitate repair and replacement of damaged or destroyed components. High value assemblies, such

as the pump and power system, are required to

be far away from the dredgehead to reduce damage due to detonation. Spare parts and a complete

spare unit were specified to reduce downtime in

case of a catastrophic explosion.

As mentioned previously, the power system

was designed to minimize the effects of a UXO

detonation while dredging. The hydraulic system

uses a nontoxic, biodegradable fluid (Mobil EAL

224H). System fluid loss will be limited due to a

pump shutdown circuit that senses the hydraulic

reservoir level. To eliminate the possibility of contaminating the Flats with diesel fuel, the power

source for the dredge is located on shore and

power is supplied via electric cable.

Safety

The issue of ordnance brought up another important design consideration: safety. The system

was specified to be remotely controlled from an

armored control cab. This cab, composed primarily of 13-mm-thick welded steel and 31-mm-thick

ballistic polycarbonate (Lexan) windows, was

blast tested in two separate tests using 105-mm

high-explosive (HE) rounds at a distance of about

37 m. The structure sustained only minor damage

due to shell fragmentation during the tests (Walsh

and L’Heureux 1995). In the test where damage

occurred, the round was placed on a wooden crate

approximately 0.6 m above water level, with the

back of the round pointed directly at the cab. This

was considered a worst-case scenario by Captain

Paul Arcangeli of the 176th EOD Detachment at

Fort Richardson, who supervised testing.

Minimum distance to the dredge during active

operations is 40 m. Therefore, to allow the operator to observe the dredging operation, a remote

high-resolution wireless CCD video system is to

be incorporated. Transmitted along with the video

signal are the output of vital operating sensors,

such as the various process pressures. This will

allow the dredge operator to conduct operations

as if he were onboard the vessel.

Separate from the dredge, a Health and Safety

Plan (HASP) was required by the Fort Richardson

Safety Office due to the hazards involved in the

dredging operation. This document includes several pages of material specific to the dredging operation. Before the commencement of active dredging activities, the HASP was approved by a representative of DPW and the chief of the Fort

Richardson Safety Office.

Transportability

Transport of the dredge is a critical design factor. To avoid adverse environmental impact resulting from channeling the Flats in the process of

moving the dredge between contaminated areas,

the unit needs to be air transportable. The options

for transport by helicopter are the UH-1 (Huey),

the UH-60 Blackhawk, and the CH-47 Chinook.

Load capacity and operating cost per hour increase

with each model, while availability decreases. The

load capacity of the Huey, at 680 kg, is too low for

practical consideration. The Blackhawk had a capacity of 3600 kg (upgraded to 4100 kg) and the

Chinook has a capacity of 5400 kg. Therefore, the

specifications were written such that the dredge

should not weigh over 3600 kg unless a waiver is

granted by the Program Manager. In that case,

maximum weight is to be 5400 kg. Other features

were specified to assist in movement and handling

of the dredge.

Due to procurement difficulties, purchasing the

dredge equipment was not possible in the time

frame available, so a lease contract for the equipment was pursued. The contracting office of the

U.S. Army, Alaska (USARAK) was tasked with the

responsibilities of writing, bidding and awarding

3
a contract for equipment lease, support and maintenance for a dredging system for the Flats. A formal set of technical specifications was written up

by CRREL and used by USARAK’s Contracting

Office in its request for bids.

Using the specifications as guidelines, CRREL

engineers reviewed the technical portion of the

bids received by the Contracting Office. These reviews were used in the overall evaluation of the

bids and the contract was awarded to the entity

deemed most appropriate by the Contracting Office: ChemTrack Services Group of Anchorage,

Alaska. The dredges to be used are from Liquid

Waste Technology, Inc., of Somerset, Wisconsin.

BASIN INVESTIGATIONS

Two of the most difficult issues to resolve during the pilot project were where and how the spoils

are to be contained during treatment. The most

obvious choice for a basin site is the EOD pad, a

6.3-ha gravel pad used until 1990 for the burning

and detonation of dated, faulty or excess ordnance.

The original plan was to clear vegetation from the

pad and use as much of the pad as practical. A

low berm would be constructed and the spoils

from the dredging operation allowed to drain

through the pad. However, the presence of contaminants in the EOD pad has resulted in the area

being declared a Resource Conservation and Recovery Act (RCRA) site, thus requiring more thorough investigations into the use of the pad as a

treatment site. Although this is an uncapped site,

the Remedial Project Managers (RPMs) involved

with the project felt that water filtering through

the pad from spoils drainage was not acceptable

and should be minimized.

Permission was granted for construction of a

small, 0.8-ha retention basin with a controlled decanting structure at one end, contingent upon results of field and laboratory tests of the basin and

pad characteristics. The Alaska District of the U.S.

Army Corps of Engineers was tasked with design

of the structure based on testing performed by

CRREL. They were also responsible for overseeing the construction of the structure. Actual construction was carried out by the Roads and

Grounds Office of the Directorate of Public Works

(DPW) at Fort Richardson. CRREL engineers conducted the investigations into the basin and pad

surface hydrology and acted as technical consultants throughout the effort.

Settlement times

Initial design studies focused on settlement

times for the spoils. The treatment strategy was to

pump the material into a retention basin, allow

the solids to settle, and decant the supernatant over

a weir, a strategy similar to that advocated by

Poindexter (1984) and Palermo (1984). The drained

sediments would then be allowed to dry naturally,

and, climatological conditions permitting, the WP

would sublimate. Settlement times are important

in determining the dredge cycle as well as how

much water will percolate through the bottom of

the basin.

The objective of the settlement studies was to

determine settlement rates and times for a oneday dredge cycle: 8–10 hours of dredging at 380

m3/hour. The sediment cutoff size was ø 0.1 mm,

the minimum WP particle size thought to be problematic in the waterfowl die-offs (Walsh 1994).

Initial models using sediment particle sizes from

previous analyses (Lawson and Brockett 1993) in

freshwater indicated that settlement times for a

3/4-ha site would be on the order of days (Table

1). This model was based on Stoke’s Law:

v = g(ρ1 – ρ)d2/18μ (1)

Table 1. Settling times for spoils in fresh water.

Retention Settling Settling Silt WP Dredge

pond Particle velocity:silt velocity:WP Pond depth settling settling cycle

size (ha) size (cm) (cm/s) (cm/s) (cm) time (hr) time (hr) (days)*

0.75 0.01 7.0E-1 3.6E-1 40.53 0.02 0.03 0.3

0.75 0.001 7.0E-3 3.6E-3 40.53 1.61 3.14 0.5

0.75 0.0003† 6.3E-4 3.2E-4 40.53 17.89 34.88 1.8

*8-hour dredging plus retention time. No decanting time included.

†Median particle size (Lawson and Brockett).

4
where

v = particle settling velocity (cm/s: freshwater)

g = gravitational constant (980 cm/s2)

ρ1 = particle density (g/cm3)

ρ = fluid density (g/cm3)

d = particle diameter (cm)

μ = fluid viscosity (dyne-s/cm2).

The Reynolds Number

R = vρd/μ (dimensionless) (2)

is used to determine if settling is laminar or turbulent.

Settling times in Table 1 are given for both white

phosphorus and silt particles. Times are a function of particle size and depth of ponded water.

Note that the cycle time does not take into consideration the decanting time for removing the supernatant after settling is complete.

Laboratory sediment tests

The relatively long settlement times in Table 1

would adversely affect the dredging and filling

operations. Several days of calm water in the settling basin would be required before relatively

clear supernatant could form and be decanted over

a weir. However, data indicate that the water in

the Flats area is brackish. Tidal invasion of the Flats

regularly introduces seawater, which mixes with

freshwater from the Eagle River and groundwater sources. Salinity measurements in the region

where the dredging is proposed indicated the salinity of the water was between 5 and 7 ppt (normal seawater has a salinity of about 36 ppt). Because settlement rates can be much higher in water that contains salts in solution (Thackson et al.

1984, Palermo et al. 1978) than in freshwater, settlements times on the order of hours rather than days

were postulated after we recognized the impact

of salts in the sediment–water solution. The electrolytes in saline sediments reduce the repulsive

forces between soil particles. If the concentration

of electrolytes is strong enough, particle repulsive

forces will be neutralized. Particle attraction forces

will then dominate and particle aggregation will

become more common. The larger aggregations

of particles will settle more quickly than the

smaller individual particles. Only small salinity

levels in the range of 2–6 ppt are required for the

flocculation process to be effective (Praudic 1970).

Preliminary laboratory sedimentation tests with

samples from ERF (Fig. 1) showed that settling

times would be less than one hour, not the several

1000

800

600

400

200

0 20 40 60 80 100

Elapsed Time (min)

Sample No. 3

No. 4

No. 1

No. 2

Sediment Height on cm Scale 3

Figure 1. Results of preliminary sedimentation tests.

5
Water

Sludge

Silt

Gravel

Porous Stone

h

Sampling Ports

Hsludge

Hsilt

Hgravel

Hstone

Figure 2. Montgomery tube used for sedimentation tests.

Table 2. Laboratory sedimentation test results following the Montgomery (1978) procedures.

Dose #1 Dose #1R Dose #2 Dose #3

Elapsed Interface Percent Elapsed Interface Percent Elapsed Interface Percent Elapsed Interface Percent

time height settled time height settled time height settled time height settled

(min) (cm) (%) (min) (cm) (%) (min) (cm) (%) (min) (cm) (%)

0 38.0 0.0 1 51.0 0.0 0 68.3 0.0 0 74.7 0.0

2 37.5 1.8 2 51.0 0.0 1 68.0 0.9 2 74.5 0.9

3 37.3 2.7 3 50.9 0.4 3 67.7 1.7 5 74.4 1.3

5 37.0 3.6 5 50.8 0.9 5 67.3 2.8 10 73.8 4.0

7 36.8 4.5 6 50.5 1.8 7 66.8 4.3 15 73.1 7.1

10 36.0 7.2 10 50.0 3.6 10 66.2 6.0 20 72.5 9.8

20 34.0 14.5 15 49.5 5.4 15 65.3 8.5 30 71.1 16.0

30 32.5 19.9 20 48.8 7.9 20 64.5 10.8 45 69.6 22.7

48 30.0 29.0 30 47.7 11.9 30 63.0 15.1 60 68.3 28.4

60 28.5 34.4 45 45.8 18.8 45 61.2 20.2 75 66.9 34.7

77 26.8 40.8 60 44.4 23.8 62 59.5 25.0 90 65.5 40.9

90 25.3 46.2 78 42.7 30.0 75 58.4 28.1 110 63.8 48.4

105 23.8 51.6 90 41.5 34.3 90 56.9 32.4 120 62.9 52.4

120 22.0 58.0 105 40.0 39.7 105 55.5 36.4 132 61.9 56.9

135 20.8 62.5 120 38.4 45.5 120 54.1 40.3 172 58.3 73.1

150 20.3 64.3 135 36.8 51.3 132 53.1 43.2 180 57.5 76.4

165 20.0 65.2 150 35.0 57.8 180 48.3 56.8 195 55.0 87.6

180 19.8 66.1 165 33.8 62.1 195 46.9 60.8 221 53.3 95.1

205 19.5 67.0 180 33.4 63.5 210 45.0 66.2 240 52.8 97.3

240 19.0 68.8 221 32.6 66.4 240 43.0 71.9 270 52.2 100.0

243 18.6 70.3 240 32.3 67.5 245 42.8 72.4

246 18.4 71.0 245 32.0 68.6 250 42.6 73.0

255 18.1 72.1 251 31.6 70.0 255 42.5 73.3

270 17.7 73.6 255 31.5 70.4 260 42.3 73.9

285 17.3 75.0 260 31.4 70.8 270 42.1 74.4

300 17.0 76.1 270 31.1 71.8 285 41.8 75.3

330 16.3 78.6 285 30.7 73.3 295 41.6 75.9

360 15.8 80.4 300 30.3 74.7 1380 33.1 100.0

390 15.5 81.5 315 30.0 75.8 1410 33.1 100.0

420 15.0 83.3 330 29.7 76.9

1380 10.4 100.0 360 29.1 79.1

1440 10.4 100.0 390 28.5 81.2

405 28.3 81.9

1380 23.3 100.0

6
days required for freshwater sediments. More rigorous laboratory settlement tests following the

method of Montgomery (1978) confirmed the preliminary tests. These sedimentation tests were conducted in a 15-cm-diameter polycarbonate tube

with a length of about 1.8 m. The tube had a porous stone and drainage port in its base (see Fig.

2). Water was prepared at a salinity of 5 ppt and

mixed with sediment at a ratio of four parts water

to one part wet sediment by volume (70% water

content by weight). The water content for the sediment was obtained from an estimate of the water

content in the sediments that the dredge would

pump into the settling pond. The sediment was

thoroughly mixed to its initial water content in a

laboratory blender (in contrast to hand mixing in

the preliminary tests) and then mixed in a barrel

with the saline water using a stirring agitator. It

was then quickly poured into the sediment tube.

The elevation of the interface at the top of the sediments was then monitored for at least 24 hours. A

definite interface formed within a few minutes,

the water above the interface being relatively transparent. Table 2 and Figure 3 show the test results.

In all cases, 50% of the total settlement occurred

in about two hours. In the preliminary tests, 50%

of the total settlement occurred in about 15 minutes. The difference between these results is probably related to the size of the soil aggregates used

in the two tests and the quality of the mixing. The

aggregates were much coarser in the hand-mixed

test than the machine-mixed tests, thus settling

more quickly. The two cases probably bracket the

range of results that would be achieved in the

dredging operation.

These tests confirmed our preliminary study

and gave us confidence that we could readily conduct the dredging, filling and decanting operations

in daily cycles. However, we had to be assured

that any white phosphorus in suspension would

drop from suspension in the two-hour window of

time. We conducted a fourth sedimentation test,

this time with white phosphorus particles in suspension. We spiked the sediment with white phosphorus particles obtained from the Flats by

Marianne Walsh of CRREL. White phosphorus

particles of the size considered to affect the health

of the waterfowl were used (≈ ø 0.1 mm [Walsh

personal communication*]). Water samples were

taken through ports located at 15-cm intervals in

100

80

60

40

20

0

100

80

60

40

20

0

Sediment Height (cm)

Percent Settlement

Dose No. 3

2 hrs.

100 200 300 400 500

Elapsed Time (min)

100

80

60

40

20

0

100

80

60

40

20

0

Sediment Height (cm)

Percent Settlement

50% Settlement

2 hrs.

Dose No. 1

0 0

Dose No. 1R

100

80

60

40

20

0

100

80

60

40

20

0

Sediment Height (cm)

Percent Settlement

2 hrs.

100 100

0 0

500 1000 1500

Elapsed Time (min)

100

80

60

40

20

0

100

80

60

40

20

0

Sediment Height (cm)

Percent Settlement

Dose No. 2

2 hrs.

a. Dose #1.

b. Dose #1R.

Figure 3. Sedimentation test results in Montgomery

tube.

c. Dose #2.

d. Dose #3.

*M.E. Walsh, Applied Research Division, U.S. Army

Cold Regions Research and Engineering Laboratory,

Hanover, New Hampshire.

7
the side of the sedimentation tube starting after

one hour of settling. The results, shown in Table 3,

indicate that no WP particles were found in suspension. All of the WP particles placed in suspension appeared to have settled in one hour or less.

Concentrations are indicative of dissolved WP.

Weir flow

After the sediment has settled sufficiently to enTable 3. Results of GC analysis for WP in water column above simulated dredge spoils.

Hour Label Peak ht. WP mass (μg)* Calibration

1 S-1 185 0.0082 Standard (70 μg/L)

1 S-2 175 0.0077 Peak Ht.

1 S-3 200 0.0088 4994

1 S-4 263 0.0116 4433

1 S-5 180 0.0080 5201

1 S-6 0 ND† 4893

2 S-1 0 ND 4799

2 S-2 0 ND 4694

2 S-3 0 ND 4188

2 S-4 0 ND 4765

2 S-5 0 ND Average = 4745.875

2 S-6 0 ND RF [peak ht/mg/L)] = 67.8

4 F-1 0 ND

4 F-2 0 ND

4 F-3 0 ND

4 S-1 0 ND

4 S-2 0 ND

4 S-3 0 ND

4 S-4 0 ND

4 S-5 0 ND

4 S-6 0 ND

*34-mL aliquot of water extracted with 3.0 mL isooctane.

†Not detected; detection limit 0.006 μg.

sure that WP particles in the target range are no

longer suspended in the water column (≈ two

hours), the supernatant must be decanted. To do

this, a drop inlet structure in the corner of the

retention basin opposite the spoils inlet was

designed. Decantation of the supernatant from the

basin is to be done over an adjustable weir

(Fig. 4).

The weir was modeled to ensure that the deFigure 4. Drop inlet structure, showing adjustable weir.

8
sign would be sufficient to allow drainage of a

day’s dredging supernatant in a reasonable

amount of time, six to eight hours, without velocities that would resuspend the poorly consolidated

settled solids or damage the filtering fabric located

2 m behind the weir.

The following analysis of the drainage of the

Spoils Retention Basin, sited on the EOD at Eagle

River Flats, Alaska, uses the Francis Formula for

fluid flow over a rectangular, sharp-edged weir.

In a normal eight-hour dredge cycle, approximately 2400 m3 of water will be pumped into the

retention basin, assuming a 380-m3/hour production rate and a 4:1 ratio of water to spoils (by volume).

The initial analysis is of flow rates over a 3.2-m

weir for a given head. The height of the weir is

given as about 15 cm. Although the weir height

affects the flow rate, it will not be considered here,

as the effect is minimal for low heads (< 0.3 m).

We will be operating with heads of 0.1 m or less.

The reason for this is to minimize the turbulence

in the sheet flow towards the weir. Boundary conditions and the instantaneous flow rate equation

are given below:

H = 0.1, 0.098 ... 0.01 (Head, or height of

water above weir in meters)

P = 0.15, L = 3.2 (Height and length of weir

in meters)

g = 9.81 (gravitational constant, m/s2)

Q(H) = 2.54 [L – 0.2(H)] (H)1.5 (3600) (Flow rate,

m3/hour [Hicks 1972]). (3)

Figure 5 is a graph of the instantaneous flow rate

over a 3.2-m (10 ft) weir. The volume retained in

the 0.8-ha retention basin above the weir can be

expressed as

V(H) = AH = 2 (4047) H (m3). (4)

One of the primary concerns in the retention

pond design is the flow over the weir, which will

be impacting the silt fence located between the

weir and the basin outflow culvert. To get a

handle on this, we can analyze the effect of differing weir length for a given head on the flow rate,

in cubic yards per hour. This is an extension of

0.02 0.04 0.06 0.08 0.10

H, Head (m)

Q(H)

(m /hr) 3

10

20

30

40

50

0

Figure 5. Instantaneous flow over a rectangular weir.

9
the previous calculations:

H = 0.04, 0.05 ... 0.07 (m)

P = 0.15 (m), g = 9.81 (m/s2)

L = 1.2, 1.3 ... 9.7 (m)

Q(H) = (9144) [L – 0.2(H)] (H)1.5 (m3/hour).(3a)

The instantaneous effect of head on flow rates over

the weir is illustrated in Figure 6. This, of course,

is a linear relationship. We can now look at the

time-required-to-drain relationship for a given

weir length. The following relationships are used:

L = 3.05 (m)

Q(H) = 9144 [L – 0.2(H)] (H)1.5 (m3/hour) (3a)

V(H) = (8094) H (m3). (4a)

An integral was developed to derive the time

required to drain based on the flow (Q): volume

(V) relationship. It is integrated over the change

in head over the fixed weir:

 

t V H

Q H

dH H H

H = 



 

 ∫  1

2

1 ( )

( ) (hour). (5)

Now we can look at drainage times (in hours)

as a function of weir length:

L = 2.44, 3.94, ... 9.5 (m)

Q(H) = (9144) [L – 0.2(H)] (H)1.5 (m3/hour) (3a)

V(H) = (8094) H (m3) (4a)

 

t

H

V H

Q H = ∫ dH 



 



 1

0 005

0 076

.

. ( )

( ) (hours). (5a)

Evaluating this integral yields the graph in

Figure 7.

To confirm this analysis, we can look at Hicks’

analysis of the variation in head on a weir without inflow to the reservoir, essentially what we

have here. The formula used in Hicks (1972) is

t = [2A/CL] (1/h2

0.5 – 1/h10.5) (hours) (6)

where

t = drainage time (hours)

A = pond area (m2)

C = 1.83, the discharge coefficient

L = weir length (m)

2000

1600

1200

800

400

0

2 4 6 8 10

L, Weir Length (m)

Q(H,L)

(m /hr) 3

H = 0.07

0.06

0.05

0.04

Figure 6. Instantaneous weir flow rates for various heads.

10
h1, h2 = starting and ending heights of water

over the weir.

For the retention basin design, the following relationships will be used:

t = [2A/CL] (1/h2

0.5 – 1/h10.5) (hours)

A = 8094 m2

C = 1.83

L = 2.44, 3.94, ... 9.75

h1 = 0.076, h2 = 0.005 (m). (6)

Iteration of the above yields a curve (Fig. 8) very

similar to that from the above integration.

A weir of 3.6 m or more will be necessary to

ensure timely drainage of the retention pond. This

can be accomplished with two to four 4.9-m (8 ft)

weirs. A more detailed look at drainage times for

weirs between 4.5 m and 7.5 m is shown on the

next page (Fig. 9).

The curve was derived using the following relationships:

L = 4.88, 5.18, ... 7.32 (m)

Q(H) = 9144 [L – 0.2(H)] (H)1.5 (m3/hour) (3a)

V(H) = (8094) H (m3) (4a)

 

t

H

V H

Q H = ∫ dH 



 



 1

0 005

0 076

.

. ( )

( ) (hours). (5a)

A 6-m (20 ft) weir looked to be the most effective for the retention basin application, with drainage times between 4 and 4.5 hours. Note that draining is to 0.5 cm (0.2 in.) above the weir. Draining

to 0.25 cm (0.1 in.) above the weir increases total

draining times by 50%. Note also that in this analysis, an assumption is made that all of the suspended solids have settled out of solution. This is

definitely not going to be the case. Therefore, these

calculations should be quite conservative. The

above model indicates that the best procedure for

decanting may involve graduated draining of the

supernatant. If 0.3 m of water needs to be decanted,

it should be drained in three or four steps.

The weir used is rectangular and adjustable,

with adjustment made by removing 4-cm- (1 5/8

in.) thick boards. Two boards are to be removed at

a time from each of the three weir sections to ensure low flow turbulence in the pond.

Supernatant filtering

Settlement calculations were based on 0.1-mmdia. WP particles, as stated above. These criteria

were chosen because this particle size was sieved

from sediments by dabbling ducks. However, data

8

6

4

2 4 6 8 10

L, Length (m)

t(L)

(hrs)

Figure 7. Basin drainage times as a function of weir length.

11
14

12

10

8

6

4

2 4 6 8 10

L, Weir Length (m)

t(L)

(hrs)

Figure 8. Confirmation of integral relationship.

2.4

2.2

2.0

1.8

1.6

1.4

4.5 5.5 6.5 7.5

L, Weir Length (m)

t, Time (hrs)

Figure 9. Drainage times for 4.5- to 7.5-m weirs.

12
indicate that the sediment size ranges down to

0.001 mm and less, with 50% coarser than 0.003

mm (by weight) (Lawson and Brockett 1993). Settling out these fines in a reasonable time frame in

the area allotted is not possible, so a large number

of very fine particles may be decanted off along

with the supernatant. Along with these particles,

particles of larger size may become resuspended

during the decanting process. Concern over recontamination of the Flats by these larger particles was

expressed, so filtering investigations using sediments from the Flats were conducted at CRREL

(Henry and Hunnewell 1995, Henry et al. 1996).

After extensive testing using a modeling flume

built at CRREL, a candidate fabric was chosen that

effectively filters particles 0.1 mm and larger.

Filtering efficiency of the selected fabric is 73%,

and when the fabric was incorporated in a system

that allowed for sedimentation of the mixed spoils,

efficiencies approached 99.8% (Table 4). These efficiencies were attained even when scraping the

upstream side of the fabric to enhance flow rates.

Filtering efficiencies will vary according to settlement time, and attempting to filter particles with

diameters smaller than 0.1 mm is impractical due

to clogging of the fabric and low flow rates. One

important use of the silt fence is as a secondary

impoundment component in case the weir fails

(Fig. 4). This is important in ensuring that the Flats

do not become recontaminated in the case of catastrophic weir failure.

Site characterization

With the basics of the retention basin conceptualized and laboratory test results supporting our

design considerations, the surface hydraulic conductivity (permeability) at the site had to be characterized. To do this we conducted infiltration tests

both in the laboratory and in situ.

Laboratory tests

We hypothesized that the sediments from the

dredging operation would quickly clog the voids

in the gravel pad and significantly reduce the hydraulic conductivity. It was expected that the subsequent buildup of sediment would further reduce

the infiltration rate into the EOD pad. To gain additional insight on the sediment’s effect on infiltration, we conducted laboratory tests to determine the hydraulic conductivity of the sediment.

The following relationships were used in determining hydraulic conductivity:

Havg = Average height of sediment (cm)

∆t = Elapsed time (sec)

h1 = Initial head of water at t = 0 (cm)

h2 = final head of water at t = ∆t (cm)

.

 

k

H

t h

h

=

•

avg

∆ ln 1

2

(7)

These tests were performed in the sedimentation

tube (Fig. 2) on the sediments formed during the

previous laboratory sedimentation tests. The results are shown in Table 5 and Figure 10. In all

four tests, the hydraulic conductivity initially exceeded 1 × 10–4 cm/s in the first three or four hours

and gradually fell to about 2 × 10–5 cm/s within

eight to 24 hours. This confirmed our expectation

that the sediment itself might not reduce the hydraulic conductivity below the targeted 1 × 10–5

cm/s level.

Table 4. System filtering efficiencies using Texel GEO 9 filtering fabric (From

Henry and Hunnewell).

Final total Filtering Retained on

Flow rate suspended efficiency: #200 (74 μm)

Test # Geotextile [(m3/m2)/min] solids (mg/L) system (% ) sieve (%)

1 No DNM* 9249 95.3 DNM*

3 No DNM* 6360 96.8 1

7 No DNM* 14466 92.7 3

2 Yes 0.021 654 99.7 <0.1

4 Yes 0.046 1185 99.4 <0.1

6 Yes 0.028 1465 99.3 DNM*

*Did not measure.

13
Table 5. Laboratory hydraulic conductivity tests on sediment.

System Sediment

Elapsed Water Sediment hydraulic hydraulic

Test series time height height conductivity conductivity

number (min) (cm) (cm) (cm/s) (cm/s)

1 dose of sediment on porous stone

1 30 37.00 17.7 2.72E-04 2.64E-04

60 36.65 17.0 9.16E-05 8.87E-05

180 35.60 15.0 6.46E-05 6.23E-05

1200 31.80 10.4 2.34E-05 2.24E-05

1 dose of sediment on 13.7 cm of gravel

1R 20 49.90 31.4 3.70E-04 2.19E-04

60 49.30 30.3 1.55E-04 8.51E-05

120 48.60 29.1 1.22E-04 6.43E-05

165 48.20 28.3 8.78E-05 4.48E-05

1140 43.50 23.3 4.52E-05 2.06E-05

2 doses of sediment on 13.7 cm of gravel

2 20 67.70 42.3 2.09E-04 1.42E-04

55 67.50 41.6 5.91E-05 3.88E-05

190 67.00 38.3 3.67E-05 2.34E-05

1170 63.50 33.1 3.41E-05 2.09E-05

3 doses of sediment on 13.7 cm of gravel

3 334 79.00 41.2 1.01E-04 7.06E-05

1750 76.50 41.1 1.56E-05 1.00E-05

3351 73.70 41.1 1.60E-05 1.03E-05

Figure 10. Permeability of sediment in column.

10

Total

Sediment

Dose No. 1R

10– 3

10 –4

10– 5

10

Hydraulic Conductivity (cm/s)

– 6

3

Dose No. 1

10– 3

10 –4

10– 5

10– 6

Hydraulic Conductivity (cm/s)

3

10– 3

0 1000 2000 3000 4000

Elapsed Time (min)

Total

Sediment

10 –4

10– 5

10

Hydraulic Conductivity (cm/s)

– 6

Dose No. 3

10

Total

Sediment

Dose No. 2

10– 3

0 400 800 1200

Elapsed Time (min)

10 –4

10– 5

10

Hydraulic Conductivity (cm/s)

– 6

d. Dose #3.

a. Dose #1. b. Dose #1R.

c. Dose #2.

14
As a result we concluded that some type of liner

was required for the settling pond. We briefly investigated the feasibility of using a geosynthetic

liner, but cost and availability considerations led

us to explore other options to reduce the potential

infiltration into the EOD pad. We were made

aware of a peaty silt material that was available in

abundance near Fort Richardson. This material

appeared to have a very high organic content,

making it unsuitable for most engineering projects.

However, since this material was readily available,

we decided to evaluate its suitability as a liner for

the settlement pond.

To do this we subjected samples of the peaty

silt to compaction and hydraulic conductivity tests

in the CRREL laboratories. The laboratory compaction (standard Proctor) and hydraulic conductivity tests were conducted according to ASTM

standard methods D 698 and D 5084, respectively.

The compaction water contents ranged from about

29% to about 46%, bracketing the initial in-situ (in

the borrow pit) water content estimate of about

38%. The results of the compaction tests are tabulated in Table 6 and shown in Figure 11. The optimum water content for the peaty silt material is

about 38%, the same as the expected in-situ water

content. This result appeared fortuitous, because

it meant that we might not have to make a special

effort to adjust the water content of the peaty silt.

Laboratory hydraulic conductivity tests were

conducted for the same water content regime as

the compaction tests. The tests were conducted for

effective stress levels of 7, 14 and 35 kPa (1, 2 and

5 psi) to determine the effectiveness of increasing

thickness (e.g., increasing stress) as the sediment

thickness increases during the dredging operations. The results are tabulated in Table 7 and illustrated in Figure 12. The two tests conducted at

38% and 46% (above optimum) water content

showed hydraulic conductivities less than

1 × 10–5 cm/s, the magnitude decreasing with inTable 6. Laboratory compaction test results for

peaty silt.

Water Dry

Sample content density

number (%) (g/cm3)

PS-3 28.8 1.116

PS-1 38.2 1.130

PS-2 46.4 1.087

creasing stress level. The results (Fig. 12c) for the

test specimen with a water content of about 29%

(9% below optimum) did not pass the 1 × 10–5 cm/

s litmus test. This was not unexpected, as according to Lambe and Whitman (1969) the hydraulic

conductivity for fine-grained soils significantly increases at water contents below the optimum level.

The importance of this finding is that the field

water content during compaction must be near or

above 38%. This appeared to be no problem as the

water content in the borrow pit was estimated to

be 38%.

Field tests

The first field tests were conducted in the natural gravel surface of the pad. The second tests were

conducted through a layer of sludge obtained from

the Eagle River Flats, and a third test through two

layers of sludge sediment. A fourth test was performed through a peaty silt layer compacted on

the gravel surface inside the test chamber (barrel).

Later tests were conducted directly in the peaty

silt once it was compacted in the retention basin.

The locations of these initial in-situ tests are shown

in Figure 13.

The site for the first series of tests was selected

to be representative of the EOD pad. Modified barrels were used for the test chambers. The bottoms

of 82.5-L steel barrels, 40 cm in diameter and 64

cm high, were removed and the barrels were set

into the test pad as illustrated in Figure 14. The

barrels were set into circular channels cut carefully

into the pad to about a 15-cm depth. The annular

space between the outer barrel walls and the gravel

was backfilled with a wet mixture of sand and

bentonite clay to prevent leaking of the water

placed in the barrel for the infiltration tests. The

interior annulus was refilled with a mixture of

20 30 40 60

Compaction Water Content (%)

1.4

1.2

1.0

0.8

Dry Density (g/cm ) 3

50

S = 100% for G = 2.35 s

In-situ

Water Content

Figure 11. Results of Proctor tests of peaty silt.

15
Table 7. Laboratory hydraulic conductivity tests for the peaty silt liner material.

Measured Corrected Avg. Avg.

Water Dry Effective hydr. Test hydr. hydr. effective

Sample content density stress Run cond. temp. cond. cond. stress

number (%) (Mg/m3) (kPa) number (cm/s) (°C) (cm/s) (cm/s) (kPa)

PS-1 38.2 1.090 9.1 1.00 7.09E-06 22.8 6.57E-06 6.588E-06 8.5

(optimum 7.9 2.00 7.33E-06 22.8 6.80E-06

water 8.6 3.00 7.12E-06 22.8 6.61E-06

content) 8.2 4.00 6.84E-06 22.6 6.37E-06

14.6 1 2.81E-06 22.7 2.61E-06 2.49E-06 14.6

14.6 2 2.72E-06 22.7 2.53E-06

14.6 3 2.48E-06 22.8 2.31E-06

14.5 4 2.67E-06 22.6 2.49E-06

33.6 1 1.40E-06 22.6 1.30E-06 1.14E-06 33.5

33.9 2 1.25E-06 22.6 1.16E-06

33.5 3 1.16E-06 22.6 1.08E-06

32.8 4 1.08E-06 22.6 1.01E-06

PS-2 46.4 1.064 6.4 1 5.26E-06 23.0 4.86E-06 3.66E-06 4.8

(optimum 4.7 2 3.53E-06 23.0 3.26E-06

water 4.0 3 3.70E-06 23.1 3.41E-06

content 4.0 4 3.38E-06 23.1 3.12E-06

+8.2%)

13.2 1 1.42E-06 23.3 1.30E-06 1.03E-06 13.8

13.3 2 1.29E-06 23.2 1.19E-06

14.4 3 9.50E-07 23.3 8.71E-07

14.3 4 8.15E-07 23.2 7.49E-07

35.5 1 3.29E-07 22.3 3.09E-07 2.35E-07 35.4

35.4 2 2.38E-07 22.5 2.23E-07

35.4 3 1.45E-07 22.6 1.35E-07

35.4 4 2.94E-07 22.6 2.74E-07

PS-3 28.8 1.077 5.4 1 2.46E-04 23.7 2.24E-04 2.41E-04 5.4

(optimum 5.4 2 2.63E-04 23.7 2.39E-04

water 5.4 3 2.59E-04 23.7 2.36E-04

content 5.4 4 2.93E-04 23.7 2.66E-04

–9.4%)

14.2 1 2.25E-04 23.7 2.04E-04 2.04E-04 14.2

14.2 2 2.27E-04 23.7 2.06E-04

14.2 3 2.37E-04 23.7 2.15E-04

14.2 4 2.11E-04 23.7 1.92E-04

36.1 1 1.09E-04 22.4 1.02E-04 9.70E-05 36.1

36.1 2 9.98E-05 22.4 9.35E-05

36.1 3 1.01E-04 22.4 9.46E-05

36.1 4 1.04E-04 22.4 9.76E-05

16
3

10– 3

10– 4

10– 5

10– 6

10– 7

10– 8

w.c. = 38.2%

γ = 1.090 Mg/m3 d

a. Optimum Water Content

c. Below optimum water content.

Figure 12. Results of laboratory permeability tests.

a. Optimum water content. b. Above optimum water content.

10– 3

b. Above Optimum Water Content (8.2%)

10– 4

10– 5

10– 6

10– 7

10– 8

w.c. = 46.4%

γ = 1.064 Mg/m3 d

10– 3

0 10 20 30 40

Effective Stress (kPa)

c. Below Optimum Water Content (– 9.4%)

10– 3

10– 4

10– 5

10– 6

10– 7

10– 8

w.c. = 28.8%

γ = 1.077 Mg/m3

d

Pad Perc Barrels

Pt. Crane

Area C

Basin

EOD Pad

Figure 13. Hydraulic conductivity barrel

test cells on the EOD pad.

a. Location of tests on the EOD pad.

17
Water

h

Gravel

Bentonite-sand

Grout

(typical)

Hgravel

Gravel

Water

h

Gravel

Sl d il

Hsludge

Hsilt

Water

h

Gravel

Hsludge

Gravel Gravel

b. Test site.

Figure 13 (cont‘d). Hydraulic conductivity barrel test cells on the EOD pad.

a. Water on gravel (unmodified pad). b. Sediment on gravel. c. Sludge on peaty silt.

Figure 14. Schematics of barrel tests on EOD pad.

native gravel and sand. To estimate the hydraulic

conductivity of the bare gravel pad without either

the sediment or the peaty silt liner, the barrel (Fig.

14a) was filled with water obtained from Eagle

River Flats (near the edge of the EOD pad) to a

depth of about 30 cm. This water was allowed to

soak into the pad to saturate the gravel beneath

the test barrel. Water was then added until the infiltration rate was about constant. The barrel was

then filled again with water to the 30-cm level and

the rate of infiltration into the test pad was measured. To estimate the hydraulic conductivity of

the ERF sediment on the gravel surface of the EOD

pad, water from the Flats was placed in the barrel

18
Figure 14 illustrates how hi and H for each of the

barrel tests were measured.

The EOD pad barrel percolation test results are

shown in Figures 15 and 16 and Table 8. Figure 15

shows that the estimated hydraulic conductivity

for the bare gravel pad was in the range of

1 × 10–2 to 1 × 10–3 cm/s, very high as we expected.

This result validated our assumption that the water pressure at the bottom of the barrels in the

gravel pad was roughly zero. One dose of sludge

(sediment–water mixture) reduced kest to less than

1 × 10–3 cm/s and a second dose further decreased

kest to about 1 × 10–4 cm/s, still short of reaching

the target level of 1 × 10–5 cm/s. Figure 16 shows

that a layer of compacted peaty silt will help

achieve that goal. In this case the sludge was

poured over the peaty silt in the bottom of the

barrel. The resulting estimated hydraulic conductivity was about 4 × 10–6 cm/s. This result validated the laboratory observations for the peaty silt.

To further substantiate these positive results,

barrel infiltration tests were also conducted directly on the compacted peaty silt liner in the retention basin. The locations of these tests are

shown in Figure 17. The peaty silt was compacted

with several passes of a smooth vibratory drum

roller on a loose lift about 25 cm thick. The water

contents and dry densities for each of the test locations are given in Table 9. The barrels were installed in the peaty silt liner as shown in Figure

18. We conducted one test with just Flats water in

the barrel and found the hydraulic conductivity

of the peaty silt to be just slightly greater than 1 ×

10–5 cm/s (Fig. 19, Table 10). At two other locations we used a sludge mixture as the permeant.

Figure 19 shows that with a sediment–water mixture similar to that expected from the dredging

operation, the hydraulic conductivity was reduced

to 1 × 10–5 cm/s. Furthermore, it continued to

decrease with time.

The hydraulic conductivities obtained from

field test results with the peaty silt are slightly

greater than the results obtained for low stress in

the laboratory. The reason for this is that the water content in the field was much higher than expected, about 60% rather than 38%. This can be

seen in Figure 20, where the hydraulic conductivities and dry densities are plotted versus the water

contents for both the laboratory and the field tests.

The higher-than-expected water content is probably due to the considerable rainfall that occurred

after the peaty silt was stockpiled in the basin area.

Nonetheless, the goal of achieving a hydraulic

to soak the gravel, and then a mixture of four parts

water to one part wet sediment was poured into

the barrel and allowed to settle overnight. The

barrel (Fig. 14b) was then filled to a depth of about

30 cm and water from the Flats was used to estimate the hydraulic conductivity of the sediment.

To determine the effectiveness of peaty silt in limiting the infiltration of water into the gravel pad,

a layer about 14 cm thick was compacted directly

on the gravel inside a test barrel (Fig. 14c). A water–sediment mixture was then poured into the

barrel over the peaty silt and allowed to settle. The

hydraulic conductivity was then estimated using

the same procedures as for the first two barrel

tests.

The infiltration rates in the EOD pad barrel tests

were used to estimate the hydraulic conductivity

of the gravel, the sediment, and the peaty silt. The

hydraulic conductivity (kest) was estimated using

Darcy’s equation for laminar flow:

q = ki (8)

where

q = the velocity of flow (cm/sec)

i = the hydraulic gradient (= h/H)

h = the pressure loss across the sample (cm)

H = the thickness of the sample (cm).

The infiltration tests on the EOD pad were conducted with a falling head, i.e., the elevation of

the water surface fell during each test. The resulting solution for the hydraulic conductivity for a

test with a falling head is

 

k H

t

h h

h h = −∆ − ln 1 0

2 0

 (cm/sec) (9)

where

∆t = time interval between making the h1

and h2 readings (sec)

h1 and h2 = water elevation heads at the start and

end of the test (cm)

h0 = water pressure head at the bottom of

the barrel (cm).

For the percolation tests in the barrel tests, the

k value determined is an estimated value because

the pressure head at the bottom of the barrel is

indeterminate. We assume that the water is freedraining at the bottom of the barrel (in the gravel)

and the water pressure is zero at the bottom of the

barrel, i.e., h0 = 0. Thus, eq 9 is reduced to

 

k H

t

h

h est = ln∆

1

2

(cm/sec). (10)

19
0 100 200 300 400

Time (min)

Hydraulic Conductivity (cm/s)

10– 1

10–2

10– 3

10– 4

10– 5

10– 6

Water

First

Sludge Dose

Target Maximum

Second

Sludge Dose

Figure 15. Results of barrel infiltration tests for unaltered and sedimented pad.

012

Time (min)

Hydraulic Conductivity (cm/s)

10–3

10–4

10– 5

10– 6

10– 7

10– 8

Target Maximum

3 x 103

Sludge on 14 cm 

peaty silt on gravel pad.

Figure 16. Results of barrel infiltration tests for sludge on peaty silt.

20
Table 8. Field percolation tests.

Height of Flow Hydraulic

Time water rate conductivity

(min) (in.) (cm3/s) (cm/s)

Perk tests with water on gravel

0 6.00

10 3.00 15.46 3.18E-03

0 6.00

10 3.50 12.88 2.51E-03

0 6.00

10 3.88 10.95 2.05E-03

0 6.00

10 3.88 10.95 2.05E-03

0 6.00

10 3.88 10.95 2.05E-03

0 6.00

10 3.75 11.60 2.20E-03

20 2.25 7.73 2.38E-03

30 1.13 5.80 3.18E-03

38 0.00 7.25 1.19E-02

Water on first sludge dose on gravel

0 7.00

20 6.00 2.58 3.66E-04

40 5.00 2.58 4.33E-04

60 4.13 2.25 4.57E-04

80 3.41 1.85 4.55E-04

100 2.63 2.01 6.17E-04

120 1.78 2.17 9.12E-04

Water on second sludge dose on gravel

0 8.25

10 7.75 2.58 2.98E-04

20 7.50 1.29 1.56E-04

50 7.00 0.86 1.09E-04

100 6.25 0.77 1.08E-04

150 5.88 0.39 5.89E-05

200 5.28 0.61 1.01E-04

250 4.81 0.48 8.85E-05

300 4.38 0.45 9.07E-05

350 3.91 0.48 1.08E-04

Water on first sludge dose on peaty silt

1 15.88

1023 15.63 0.013 3.62E-06

2418 15.25 0.014 4.05E-06

East Site

Center Site

NW Site

Berm BM

Pt. Crane

Figure 17. Retention basin barrel infiltration and permeability test locations.

Table 9. Field compaction test results for peaty

silt.

Water Dry

Sample content density

number (%) (g/cm3)

PL-1 58.3 0.915

PL-2 60.8 0.891

PL-3 55.2 0.917

21
Water

Sludge

Silt

Gravel

Figure 18. Barrel infiltration test cell in retention basin.

a. Schematic of cell.

b. Test site.

22
0 5 10 15 25

Time (days)

Hydraulic Conductivity (cm/s)

10– 3

10–4

10– 5

10– 6

10– 7

10– 8

Target Maximum

20

Water on 13 cm

Peaty Silt

Sludge on 16 cm

Peaty Silt

Water on 20 cm

Peaty Silt

Table 10. Field infiltration tests in basin liner.

Height of Hydraulic

Time water conductivity

(min) (cm) (cm/s)

Water on 13 cm peaty silt on gravel in basin

0 15.75

1118 14.63 1.40E-05

2496 13.50 1.23E-05

6961 9.50 1.67E-05

Sludge on 16 cm peaty silt on gravel in basin

0 10.50

1117 10.00 1.20E-05

2495 9.50 1.02E-05

6960 8.63 5.95E-06

Water on 20 cm peaty silt on gravel in basin

0 15.00

4460 13.25 9.42E-06

17765 11.00 4.74E-06

20269 10.80 2.48E-06

23515 10.40 3.94E-06

26005 10.25 1.98E-06

27750 10.10 2.86E-06

30510 9.90 2.45E-06

Figure 19. Results of barrel

infiltration tests for

sediment on peaty silt liner.

0.6

10– 3

10– 4

10– 5

10– 6

10– 7

10– 8

b.

20 40 50 60 70

Compaction Water Content (%)

Hydraulic Conductivity (cm/s)

30

b. Hydraulic conductivity vs. water content.

Figure 20. Composite of lab and field permeability test

results for peaty silt.

a. Dry density vs. water content.

a.

1.4

1.2

1.0

0.8

0.6

Dry Density (g/cm )3

S = 100%

Lab Tests

Field Tests

23
conductivity of 1 × 10–5 cm/s or less in the basin

area with the peaty silt as a liner is achievable. Figure 20b shows that as long as the water content is

in the range of about 38–60%, the peaty silt will

provide the desired protection against infiltration.

At water contents below 38% the hydraulic conductivity of the peaty silt increases significantly,

much as would be expected.

Model calculation

A model was then constructed and data from

the preceding tests input to determine feasibility

of the design (Appendix B). One important factor

in the determination of the adequacy of the design is the additional water that will be percolating

through the pad because of the retention basin. In

Anchorage, average yearly precipitation is equivalent to 38.7 cm of water. Table 11 shows the results

of the model for dredging a 0.8-ha site over an

eight-day period. As is indicated, the amount of

water that will pass through the basin into the EOD

pad is about one quarter what would normally

pass through the pad through natural precipitation. This model, as well as the results of the tests

done on the physical characteristics of the EOD

pad and retention basin materials, indicated that

the basin as designed would satisfy the requirements of the RPMs as well as be feasible for the

pilot dredge program. The RPMs thus approved

the use of the EOD pad for the dredge spoils retention basin.

SITE PREPARATION

Prior to deployment of the dredge, much site

preparation and construction work needed to be

carried out. Among the major projects were construction of the retention basin and its associated

structures, the drop inlet structure and inflow

pads; a road from the EOD pad to Clunie Creek,

where the dredge was to be deployed into the

Table 11. Retention basin model results

summary.

Drainage

System characteristic Pad Weir

Cumulative totals in cubic meters 969 17,684

Equivalence in cm of water/year 12 218.5

Figure 21. Retention basin berms.

24
Flats; a pad at Clunie Creek where deployment

would be based; and setting up the cable traverse

system for guiding the dredge during dredging

operations. Assistance from several entities, including the DPW, Roads and Grounds at Fort

Richardson, and several military functions, was

critical in the completion of these tasks.

The largest project was the construction of the

retention basin, where spoils from the dredging

operation are pumped for decantation and treatment. The retention basin is a 0.78-ha earthen structure constructed of compacted gravel and lined

on the bottom and inner sides with a 15- to 20-cmthick compacted layer of peaty silt. The berms encircling the basin are 2 m high with 2:1 interior

and 3:1 exterior slopes. The tops of the berms are

approximately 2.5 m wide (Fig. 21). The interior

face of the berms are lined with two layers of peaty

silt sandwiching an erosion control geotextile fabric. Two 8-m-square concrete pads for spoils outflow are located 3 m off the northwest berm near

the north and west corners of the basin. Jersey barriers are placed in a staggered chevron pattern to

break the flow of the spoils into the basin. The pads

are surrounded by chain-link fence on three sides

to contain any passed-through ordnance and to

restrict access to the pads (Fig. 22).

A drop inlet structure located at the south corner of the basin is used for decanting the supernatant back to the Flats after settling (Fig. 4). The

structure consists of an adjustable weir, a filtering

fence 2 m behind the weir, and a 1.2-m ø drop inlet 1.4 m behind the fence. The drop inlet connects

to a 0.6-m ø corrugated culvert that empties out in

a highly vegetated section of Area C in the Flats.

Construction of the basin was initiated in July

of 1994. Due to the hazardous conditions, the work

was performed by the Roads and Grounds section of the DPW with help from other support

functions at Fort Richardson. Originally, the existing berms on the EOD pad were to be utilized

as part of the retention basin, but these were found

to be unsatisfactory by the site engineer. As work

progressed and equipment operators became more

familiar with the site and its associated hazards,

additional changes were made in the basin design

and construction. The northeastern section of the

basin area was heavily used for ordnance disposal

and detonation in the 1950s. When the operators

tried to level the area using cut and fill (the corner

Figure 22. Spoils line outlet pads.

25
was ≈ 3 m higher than the opposite corner), some

small-caliber ordnance detonated and operations

were halted. Leveling recommenced under a new

strategy: filling the low end of the basin floor with

trucked-in material. Throughout the construction

process, changes to the system were necessary due

to additional requirements pertaining to the RCRA

status of the site. By September, the final design

was approved and construction wrapped up in

time for the initiation of dredging.

In addition to the construction of the basin

structure, the Roads and Grounds office was

tasked with the construction of a road through the

wooded area between the EOD pad and Clunie

Point, on the southern side of Clunie Creek where

it meets the Flats. A cul-de-sac large enough to turn

a full-size tractor-trailer was required at the end

of the road. A gravel ramp to Clunie Creek, the

deepest water easily accessible to vehicle traffic,

was installed to facilitate placement of the dredge

in the Flats. These areas are referred to in this report as Clunie Pad. Geotextile was laid over the

area used for the pad prior to graveling due to the

wet, spongy nature of the ground in this area. Prior

to deployment, EOD personnel swept the area for

UXOs to reduce the ubiquitous hazards posed by

munitions.

 With construction of the shore-based structures

drawing to a close, the tasks associated with the

actual operation of the dredge system were begun.

Primary among these tasks were the construction

and deployment of concrete piers or deadweights

for the dredge traverse system (Fig. 23). Guidance

on weight and configuration of these items was

difficult to obtain. In most cases, lateral cable systems are braced to trees along the shoreline. This

was not possible at the Flats. A decision was made

to use cubic meter concrete deadweights with provisions for lifting and attaching lateral cable components on the top of each block. (Each weighs

approximately two tons.)

The layout for the blocks was determined from

previous sampling of the area and reports of waterfowl mortality during feeding. Locations for the

placement of the deadweights were surveyed in

from a temporary benchmark located on the northeast corner of Clunie Pad using a total station and

marked with stakes and flagging. UH-60 helicopters were used to place the deadweights at their

designated points. A UH-1 helicopter was then

used to assist in retrieving the sling gear. Initial

tightening of the lateral winch cables indicated that

a single block was not sufficient in the Flats due

to the lubricity of the mud and vegetation as well

as the unstable footing, so the blocks were doubled

up and cinched together.

With the deadweights in place, the remainder

of the support equipment was assembled. The lateral winch and cable system was installed at the

first location off the mouth of Clunie Creek. The

spoils line, consisting of 12-m sections of PE pipe,

was run from the edge of Clunie Creek, up the

road towards the basin, through the woods, and

up over the berm to the northern outflow pad.

Equipment and spare parts were assembled on

Clunie Pad.

Concrete Pier

Area to be Dredged

Floating Dredge Unit

Traversing Cable

Tension Triangle

Lateral Positioning 

Winch

Control Cabinet

To Retention 

Basin

Genset/

Cable Reel

Floating Discharge Line

Comer Sheave

Figure 23. Dredge traverse system.

26
After much work on the equipment, all systems

were integrated and operational. A last-minute

requirement that a box be placed between the

dredgehead and pump delayed initiation of dredging for about a week. The device, called a “boom

box” (Fig. 24), reduces the velocity of the flow over

a length of about 1.2 m up to a factor of seven. The

theory is that heavier objects, such as mortar

rounds, will drop out before reaching the pump.

A self-dumping feature was built in to allow disposal of any collected debris.

INSTRUMENTATION AND SAMPLING

Several parameters related to the dredging process need to be monitored to ensure that the process is effective and that there is no collateral contamination occurring due to dredging activities.

Process efficacy can be determined by sampling

of the spoils and the retention basin sediments.

Pond recontamination due to dredging is a more

difficult parameter to measure because of the extremely hazardous nature of the operation. The

most obvious area that may become contaminated

is near the dredge during dredging operations.

Unfortunately, the area around the dredge must

be evacuated while actively dredging. Post-dredging sampling is the only current method of measuring dredge area contamination. This is being

done by other researchers (Lawson and Brockett

1993) and thus will not be discussed here. However, at the outflow from the basin, effluent can be

sampled and contaminant levels measured.

The best method of determining whether the

dredge is removing WP from the Flats is to analyze material that is being pumped to the retention basin. Due to safety considerations, material

within the basin cannot be sampled during active

dredging and no sampling can easily occur on the

dredge, so a tap was put into the spoils line just

below the top of the berm (Fig. 25). This tap consisted of a pitless adapter, a ball valve, and a 1-m

length of 1/2-in. (1.27 cm) Tygon tubing. A 5-gal.

PE bucket was used to collect spoils for integrated

samples, which were collected hourly. Storage of

samples was simplified due to the low ambient

temperature: it did not get above 7°C during

dredging operations. Samples were shipped overnight to CRREL upon cessation of operations for

analysis there. A standard operation procedure for

sample collection and storage is included in Appendix C.

To measure the basin parameters that will afFigure 24. Ordnance retention receptacle.

27
Figure 26. Retention basin instrumentation station.

Figure 25. Dredge spoils sampling station.

28
fect the natural remediation of the WP, four solarpowered instrumentation stations were erected

(Fig. 26). Each station contains a rechargeable 12-

V power supply, a Campbell CR-10 datalogger, an

SM-716 storage module, a four-sensor thermistor

string, and a four-sensor moisture block string.

Temperature and moisture content are two factors

that greatly influence the sublimation process of

white phosphorus and thus must be monitored to

evaluate remediation efficiency.* In addition to the

standard sensor suite, one instrumentation station,

located in the center of the basin, has an ultrasonic

water level gauge and an air temperature sensor.

The water level sensor is a Campbell Model

UDG01 Ultrasonic Depth Gauge, which incorporates a Polaroid ultrasonic transducer and model

6500 sonar ranging module. It is mounted on an

arm located about 2.5 m above the original basin

bottom. The air temperature sensor is a Campbell

Model 701 thermistor sensor mounted in a gilled

enclosure. Air temperature and spoils level are

monitored as part of the remediation process

within the basin.

Outflow of the supernatant is monitored to ensure that the Flats are not being recontaminated

by the dredging process. After passing over the

weir and through the filtering fence, the supernatant is sampled for later analysis for WP contamination. During the 1994 field season, the amount

of spoils pumped into the retention basin was insufficient to accumulate sufficient supernatant to

pass through the drop inlet structure, and thus no

samples were taken. The standard operation procedure for this sampling is described in Appendix D for further reference for the 1995 field season. The possible availability of a mobile field lab

and the use of fiber-optic headspace analysis will

make sample storage and processing much simpler and more reliable.

The last monitoring instrument directly related

to the dredging operation is a Hydrolab station

located at Canoe Point. The Hydrolab is connected

to an instrumentation station similar to those located in the basin. The addition of the Hydrolab

enables the measurement of water quality parameters such as dissolved oxygen, pH, conductivity,

salinity, temperature and depth. This station will

give a good indication of the dredge’s effect on

the surrounding pond. Although this station was

installed and operating during the dredging operation, time limitations and equipment problems

prevented dredging in the area adjacent to the

Hydrolab, so it was not directly affected. However,

the data collected can be utilized as baseline data

for comparative purposes for next year’s work.

In addition to these sensors and the related sampling and analysis, several other studies interleaved with the dredging project to determine

impact and the efficacy of this remediation strategy. Invertebrate sampling in the area to be

dredged was conducted by Carl Bouwkamp of

AEHA, and a vegetation survey was conducted

in this area by Charles Racine of CRREL. Marianne

Walsh, also of CRREL, obtained and analyzed surface sediment samples to indicate the degree of

contamination of the area to be dredged (Racine

et al. 1993). Work by Dan Lawson in relation to

physical systems processes will indicate

redeposition of sediments caused by dredging and

natural processes.

A study planned for this season to determine

the effectiveness of the remediation strategy for

the retention basin was not conducted due to the

small volume of spoils generated during this

year’s abbreviated dredging season. This study

will be conducted next year in association with

Marianne Walsh’s remediation work.

DREDGING ACTIVITY

Prior to commencing active dredging activities,

a series of pumping tests was conducted to qualitatively determine the operating parameters of the

dredging system. In these tests, we pumped clear

water through the spoils line to the retention basin. Due to changes in basin design to address concerns of the RPMs, the vertical head of the system

is about 3 m greater than the dredge specifications

indicated. This greatly affects dredge performance

and thus tests were conducted to ensure the system would perform adequately for our needs. The

pump tests also were used to check the spoils line

for weak points and to indicate the effect the boom

box would have on dredge operation. Line pressures and system performance can be indicated

only from pumping water, because when spoils

are pumped, the density of the material increases,

thus decreasing flow rate while increasing line

pressure. Fundamental fluid dynamics relationships for dredging illustrate this (Huston 1970):

SG = ρ/1000 (kg/m3) (11)

*M.E. Walsh, Applied Research Division, U.S. Army

Cold Regions Research and Engineering Laboratory,

Hanover, New Hampshire.

29
Qs = 36.8 (Ph)/SG (∑hi) (m3/hour) (12)

ph = (∑hi) (SG) (9.806) (Pa) (13)

where

SG = specific gravity

ρ = fluid density (kg/m3)

Qs = flow rate

Ph = power (kW)

hi = head components (kg)

ph = line pressure.

Even these relationships give only an indication

of the system performance due to the vagaries of

actual production, such as variable spoils ratio,

fluctuating line velocities, and variable friction

head losses.

Active dredging commenced on 15 October following completion of pumping tests. Dredging

was restricted to the mouth of Clunie Creek adjacent to the ramp leading into the creek and out

towards the point diagonally across the inlet.

Dredged depth was 70–100 cm from the water

surface, with dredged width of 2.5 m. The dredge

removed material from a traverse approximately

35 m long. Dredging occurred over a period of two

days, with a total of about three hours of actual

material removal occurring. Problems with flexible hose connections and the loss of suction due

to dredge modifications (boom box) limited dredging activities, and the onset of winter on the 16th

terminated operations (Fig. 27).

During the active dredging, two samples were

obtained from the spoils line tap for future

analysis. One sample was taken during each day’s

pumping. Spoils outflow was also monitored from

behind the berm. A camera onboard the dredge

also recorded the process at the dredgehead. Some

suspended sediment in the vicinity of the

dredgehead was evident when pumping problems

occurred, but the water quickly cleared when

pumping resumed. Observations at the spoils line

outflow pad indicate that a large amount of

bottom vegetation was present in the area

dredged. Production rates were not measured and

cannot be estimated, as personnel had to be

below the top of the berm. The ratio of solids to supernatant in the samples taken from the spoils line

was our only indication of production rate. The

ratio in these samples was ≈ 10:1 water to soil.

Figure 27. Cessation of dredging activities.

30
RESULTS

Analysis of spoils samples

Two 500-mL samples from the spoils line were

obtained, one from each of the two days on which

dredging took place. These samples were analyzed

at CRREL using an SRI gas chromatograph. Analyses were performed by Marianne Walsh. The first

sample, taken on the 15th of October, indicated

no white phosphorus present. The second sample

was highly contaminated, with a concentration of

2.7 μg/g, or 5843 μg/L. This sample had to be diluted 500:1 to read on scale on the instrument. For

comparison, the WP calibration standard concentration is 73 μg/L. This indicates that a highly contaminated area in Clunie Inlet was dredged. A

comparison of chromatograms is shown in

Figure 28.

There was no outflow of supernatant through

the weir due to dredging activity, so no samples

were taken for analysis. On the 19th, some flow

through the filter fabric on the weir as well as

through the filter fence due to snowmelt did occur, but no sampling was conducted as sampling

equipment and containers had been put into storage for the next season.

0 5

Blank

Time (min)

Calibration Standard

(73 μg/L)

02468 2.74

P4

Dredge Spoils:

Clunie Cr. Inlet

(16 Oct ‘94)

02468 2.75

Figure 28. Comparative chromatograms for spoils analysis.

Data from stations

Data from the four basin stations and the

Hydrolab were collected over the period 5–19

October and 8–19 October, respectively. These data

are not important to this year’s work due to

the limited amount of dredging that occurred.

In addition, a 20-cm snowstorm on the 16th biased the Hydrolab data as well as the basin level

readings. The most interesting data are temperature data, as they indicate the conditions under

which dredging was conducted. Figure 29 is a

graphical representation of pertinent data from

these stations.

Estimated dredged material quantity

An estimation of the material dredged is problematic due to the constraints imposed by the

Safety Plan. However, we can get a rough estimate

from the approximate area dredged. Using the

numbers stated above, a total of about 52 m3 of

material was removed from Clunie Inlet. An estimate of the mass of white phosphorus cannot be

made from the limited amount of data obtained.

With the resumption of dredging activity next

spring, a larger database may allow a calculation

of mass flow or quantity of WP removed.

31
DISCUSSION

The area dredged during the 1994 field season

was much smaller than originally planned. Delays

in procurement and setup as well as safety concerns pushed the initiation of dredging back to

mid-October. Most of the problems were surmounted over the brief season at the end of the

fall, but each problem required time, which was

not available. The primary goal for this season was

to deploy a dredge and remove contaminated sediments from the Flats, depositing them in the retention basin for further treatment, and this we

did accomplish (Fig. 30).

Dredging in an active impact area presents

many unique problems that can be addressed only

-15

-10

-5

0

5

10

15

20

-15

-10

-5

0

5

10

15

20

5 Oct 8 Oct 11 Oct 14 Oct 17 Oct 20 Oct 1994

Air Temperature

Thermistor No. 1: 4 cm

Thermistor No. 4: 80 cm

Accumulation (cm)

Temperature (°C)

Accumulation (cm)

Snow

Dredging

0

2

4

6

8

10

12

14

-200

-150

-100

-50

0

50

100

150

200

10 Oct 12 Oct 14 Oct 16 Oct 18 Oct 1994

Water Depth (mm)

Water Temperature (°C)

Conductivity (mS/cm)

pH

Water 

Depth

Snow

Dredging

Salinity °/

°°° ( )

a. Temperature profiles and level data from basin stations.

b. Canoe Point Hydrolab data.

Figure 29. Data from instrumentation stations.

32
in a deliberate, cautious manner. Experience

gained over the course of time will result in increased efficiencies and a loosening of restrictions

of personnel activities. Some problems still remain,

including developing a Safety Plan acceptable to

all parties. The “boom box” between the

dredgehead and pump is a major design problem

that needs to be addressed before dredging can

resume next season. Other problems may arise

with further experience with the system.

At this juncture, it is not possible to determine

if dredging is a cost-effective method of

remediation. It has been shown that dredging will

remove WP from the Flats, but no data are available for attenuation in the basin or contamination

of the supernatant or the area adjacent to the

dredged area. Effects of contaminated supernatant

on invertebrate fauna in the undredged areas adjacent to the dredge and downstream of the basin

outflow pipe have yet to be conclusively determined. Further work will be necessary to get a

more definitive picture.

Due to the late start of the active dredging operations, most of the actual dredging goals were

not fully met. Primarily, we were not able to dredge

a sufficient amount of material to conclusively

determine the feasibility of dredging or obtain an

indication of costs involved. We were also not able

to conduct any of the post-dredging treatment

studies that are important in proving the feasibility of using the retention basin as a basis for largescale natural attenuation of contaminated sediments through land farming. These shortcomings

can be addressed with resumption of dredging

activities next field season. Attenuation studies

will be conducted with Marianne Walsh as an

extension of her previous natural attenuation

work.

One issue not addressed in the 1994 field scope

of work is the eventual disposition of the treated

sediments. To make the dredging option more economical, the retention basin will need to be reused.

That will require the excavation of the dried and

consolidated sediments. Placing these treated sediments back in the Flats has been determined to be

impractical from a regulatory point of view, although technologically it is feasible. The option

currently being considered is spreading the treated

spoils on the EOD pad adjacent to the basin, using them as a capping or sub-capping material.

Characteristics of the pad and the pad capped by

a thin layer of spoils have been determined from

1994 field work and can be used by the RPMs in

determining the acceptability of this option.

Figure 30. Pumping contaminated spoils from the Flats.

33
LITERATURE CITED

ASTM Standard D 698 (1992) Standard test

method for laboratory compaction characteristics

of soil using standard effort. American Society for

Testing and Materials, Annual Book of ASTM Standards, Sect. 4, 4.08: 166–173.

ASTM Standard D 5084 (1992) Standard test

method for measurement of hydraulic conductivity of saturated and porous materials using a flexible wall perimeter. American Society for Testing

and Materials, Annual Book of ASTM Standards,

Sect. 4, 4.08: 1161–1171.

Henry, K.S. and S.T. Hunnewell (1995) Silt fence

testing for Eagle River Flats dredging. USA Cold

Regions Research and Engineering Laboratory,

Special Report 95-27.

Henry, K.S., M.R. Walsh and S.T. Hunnewell

(1996) Testing and performance of silt fence for

dredging operations. In Proceedings, Geofilters 96,

J. Lefleur and A.L. Rollins (Ed.). École Polytechnique, Montréal, Québec, Canada.

Hicks, T.G. (Ed.) (1972) Standard Handbook of Engineering Calculations. St. Louis, Missouri: McGraw-Hill.

Huston, J. (1970) Hydraulic Dredging: Theoretical and

Applied. Cambridge, Maryland: Cornell Maritime

Press.

Lambe, T.W. and R.V. Whitman (1969) Soil Mechanics. New York: John Wiley and Sons, Inc.

Lawson, D.E. and B.E. Brockett (1993) Preliminary

assessment of sedimentation and erosion in Eagle

River Flats, south-central Alaska. USA Cold Regions Research and Engineering Laboratory,

CRREL Report 93-23.

Montgomery, R.L. (1978) Methodology for design

of fine-grained dredged material containment areas for solids retention. U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi. Technical Report D-78-56.

Palermo, M.R. (1984) Design of confined disposal

areas for retention of contaminants. In Dredging

and Dredged Material Disposal, Proceedings of the

Conference Dredging ‘84, Vol. 2, R.L. Montgomery

and J.W. Leach (Ed.). New York City, New York:

American Society of Civil Engineers.

Palermo, M.R., R.L. Montgomery and M.E.

Poindexter (1978) Guidelines for designing, operating, and managing dredged material disposal

areas. Defense Technical Information Center, Alexandria, Virginia. Technical Report DS-78-10.

Poindexter, M.E. (1984) Long-term management

of confined disposal areas. In Dredging and Dredged

Material Disposal, Proceedings of the Conference

Dredging ‘84, Vol. 2, R.L. Montgomery and J.W.

Leach (Eds.). New York City, New York: American Society of Civil Engineers.

Praudic, V. (1970) Surface charge characteristics

of sea sediments in estuaries. The Geological Society of America, Memoir 133, p. 91–120.

Racine, C.H., M.E. Walsh, C.M. Collins, D.E.

Lawson, K.S. Henry, L. Reitsma, B. Steele, R. Harris and T.S. Bird (1993) White phosphorus contamination of salt marsh sediments at Eagle River

Flats, Alaska: FY 92 Final Report. U.S. Army Environmental Center, Aberdeen Proving Ground,

Maryland. Report No. ENAEC-IR-CR-93063.

Sherman, L.E. (1984) Low turbidity dredging:

Technique in lake restoration. In Dredging and

Dredged Material Disposal, Proceedings of the Conference Dredging ‘84, Vol. 2, R.L. Montgomery and

J.W. Leach (Ed.). New York City, New York: American Society of Civil Engineers.

Thackson, E.L., R.L. Montgomery and M.R.

Palermo (1984) Settling of dredged material slurries. In Dredging and Dredged Material Disposal, Proceedings of the Conference Dredging ‘84, Vol. 2,

R.L. Montgomery and J.W. Leach (Ed.). New York

City, New York: American Society of Civil Engineers.

U.S. Army (1981) FM 9-13: Ammunition Handbook.

Walsh, M.R. and D.A. L’Heureux (1995) ERF Cab

Blast Test. USA Cold Regions Research and Engineering Laboratory, Videotape #T95006.

34
*From FM 9-13, Ammunition Handbook (U.S. Army 1981). All rounds high explosive (HE).

APPENDIX A: DREDGING SURVEY INFORMATION PACKAGE

The following are excerpts from the ERF information package that was assembled

and distributed to several dredge manufacturers visited in January and February

of 1994. The objective of this information was to give the manufacturers sufficient

information to determine the feasibility of dredging in the Flats.

Information Package for Dredge Manufacturers

LOCATION: Eagle River Flats, Fort Richardson, Alaska.

AREA TO BE DREDGED: Ponds in Area C. Area C is approximately 45 acres total,

consisting of a large 25-acre pond connected to several smaller ponds.

WATER DEPTH: Varies between < 1” to 15”.

TIDES: Pond areas will flood only during extreme high tides occurring in combination with high river discharge.

DREDGING DEPTH: 24” to 30” maximum.

MAXIMUM DISTANCE FROM DREDGE TO SPOIL AREA: ≈ 2500’ maximum.

PUMPING ELEVATION: Approximately 8’ to 10’ maximum.

MATERIAL TO BE DREDGED: Silt or clay, mostly silt.

RECORDED ORDNANCE FIRED INTO ERF: ≈ 100,000 (× 10% = 10K UXOs).

ORDNANCE SPECIFICATIONS

Mortar Rounds*

• 60 mm Weight: ≈ 4 pounds

Diameter: 2 3/8”ø

Length: 9.6–14.7” (Total)

2.75–5” (Fin assembly)

• 81 mm Weight: ≈ 10 pounds

Diameter: 3 3/16”ø

Length: 13–24” (Total)

3.5–7.8” (Fin assembly)

• 107 mm Weight: ≈ 26 pounds

Diameter: 4.2” ø

Length: 20–26” (Total)

(No fin assembly)

Howitzer Rounds*

• 105 mm Weight: ≈ 40 pounds

Diameter: 4.13” ø

Length: 16.9” (Total)

Unexploded ordnance

It has been estimated that 100,000 artillery rounds have been fired into ERF. The

standard stated dud rate for artillery rounds is on the order of 10% (4%–20%). This

gives us a maximum of 10,000 rounds of unexploded ordnance (UXOs). There is no

way of telling how many of these still exist and are dangerous. If one assumes that

most UXOs were fired into heavily utilized areas or ranges, then a significant portion of these duds may have been detonated or destroyed by subsequent incoming

rounds. Very few UXOs have been observed at or near the surface of the Flats,

although this is not necessarily an indication that there are very few UXOs. Mortar

35
tail fin assemblies, on the other hand, are much more ubiquitous, as there is an

assembly somewhere on the Flats for every 60- and 81-mm round lobbed.

Our current understanding is that UXOs are to be handled only by the Explosive Ordnance Disposal (EOD) team at the base. There are two options for dredging around the UXOs: suction (non-contact) dredging of silt around the UXO, allowing it to fall away from or be bypassed by the dredge, or dredging with a mechanical auger as a dredgehead, which will chew up the smaller and more oxidized

UXOs, hopefully without detonating the rounds. More intact rounds may be driven

into the mud or be ridden over. An explosion cannot be ruled out. Problems may

arise with the compromising of a white phosphorus (WP) round. Pump cavitation

or discharge exposure may spontaneously ignite the WP.

36
APPENDIX B: RETENTION BASIN MODEL

The following model of the retention basin to be constructed on the EOD pad

was developed by M.R. Walsh and E.J. Chamberlain of CRREL. The model assumes

input from the dredge at 382 m3/hour, with a 4:1 water-to-saturated-soil ratio. The

following are the parameters on which this model is based:

• Hydraulic conductivity of sludge = 15 × 10–4 mm/sec.

• Hydraulic conductivity of the 152-mm compacted liner = 58 × 10–6 mm/sec (Corrected for 15° C).

• No compaction of sludge layer (and associated decrease in hydraulic conductivity) assumed.

• Three-hour settling time between pumping and decanting over weir.

• Remove 7.6 cm/hour from height of weir for each of first four hours (Hours 12–

15). Fifth hour (Hour 16) is a decanting drain.

• Ref.: Annual precipitation in Anchorage area ≈ 38.9 cm (15.3”)/yr.

• 7.3-m- (24’) long weir.

• k = 1.5 × 10–4 cm/sec.

The following are conditions set on the model:

Site size: 9680 m2 (≈ 2.5 acres)

Water in per eight-hour day @ 382 m3/hour: 2850 m3

Saturated sludge pumped per day: 610 m3

Sludge depth per day, 0.8-ha site: 0.075 m (75.4 mm)

Water depth per day, 0.8-ha site: 302.4 mm

Water depth per hour, 0.8-ha site: 37.9 mm

Equations used throughout this model and given following the model.

37
Drain Excess water Additional Thickness Height of Q water Q water Drainage Decant

time (dt) quantity: thickness of of sludge water column pad weir thru pad over weir Error

Day Hour (hours) Q in (m3) sludge (mm) (mm) (mm) (m3) (m3) (m3) (m3) (m3)

1 1 15.5 306 9.4 9.40 37.6 2.0 0

2 14.5 306 9.4 18.80 75.2 2.6 0

3 13.5 306 9.4 28.20 112.7 3.2 0

4 12.5 306 9.4 37.60 150.1 3.8 0

5 11.5 306 9.4 47.00 187.5 4.4 0

6 10.5 306 9.4 56.40 224.7 5.0 0

7 9.5 306 9.4 65.80 262.0 5.5 0

8 8.5 306 9.4 75.20 299.1 6.1 0

9 7.5 0 0.0 75.20 298.3 6.7 0

10 6.5 0 0.0 75.20 297.5 6.7 0

11 5.5 0 0.0 75.20 296.6 6.7 0

12 4.5 0 0.0 75.20 242.7 6.7 429

13 3.5 0 0.0 75.20 170.0 6.0 582

14 2.5 0 0.0 75.20 113.4 5.1 453

15 1.5 0 0.0 75.20 43.2 4.3 563

16 0.5 0 0.0 75.20 16.2 3.4 216 78 2243 –4.3

2 1 15.5 306 9.4 84.60 37.4 3.1 0

2 14.5 306 9.4 94.00 74.9 3.5 0

3 13.5 306 9.4 103.40 112.3 4.1 0

4 12.5 306 9.4 112.80 149.6 4.6 0

5 11.5 306 9.4 122.20 186.9 5.2 0

6 10.5 306 9.4 131.60 224.1 5.8 0

7 9.5 306 9.4 141.00 261.2 6.4 0

8 8.5 306 9.4 150.40 298.2 6.9 0

9 7.5 0 0.0 150.40 297.3 7.5 0

10 6.5 0 0.0 150.40 296.4 7.5 0

11 5.5 0 0.0 150.40 295.5 7.5 0

12 4.5 0 0.0 150.40 241.5 7.5 429

13 3.5 0 0.0 150.40 169.1 6.8 578

14 2.5 0 0.0 150.40 112.5 5.9 452

15 1.5 0 0.0 150.40 42.7 5.2 560

16 0.5 0 0.0 150.40 15.9 4.3 212 92 2232 –4.3

Table B1. Retention basin drainage and infiltration model.

Based on 20% solids and 5 ppt salinity, lined basin.

38
Drain Excess water Additional Thickness Height of Q water Q water Drainage Decant

time (dt) quantity: thickness of of sludge water column pad weir thru pad over weir Error

Day Hour (hours) Q in (m3) sludge (mm) (mm) (mm) (m3) (m3) (m3) (m3) (m3)

3 1 15.5 306 9.4 159.80 37.3 4.0 0

2 14.5 306 9.4 169.20 74.7 4.3 0

3 13.5 306 9.4 178.60 112.0 4.9 0

4 12.5 306 9.4 188.00 149.2 5.5 0

5 11.5 306 9.4 197.40 186.4 6.0 0

6 10.5 306 9.4 206.80 223.5 6.6 0

7 9.5 306 9.4 216.20 260.5 7.1 0

8 8.5 306 9.4 225.60 297.4 7.7 0

9 7.5 0 0.0 225.60 296.4 8.2 0

10 6.5 0 0.0 225.60 295.4 8.2 0

11 5.5 0 0.0 225.60 294.4 8.2 0

12 4.5 0 0.0 225.60 240.3 8.2 429

13 3.5 0 0.0 225.60 167.9 7.5 578

14 2.5 0 0.0 225.60 111.2 6.7 452

15 1.5 0 0.0 225.60 41.3 6.0 559

16 0.5 0 0.0 225.60 15.5 5.1 204 104 2222 –4.3

4 1 15.5 306 9.4 235.00 37.2 4.8 0

2 14.5 306 9.4 244.40 74.5 5.2 0

3 13.5 306 9.4 253.80 111.7 5.7 0

4 12.5 306 9.4 263.20 148.8 6.3 0

5 11.5 306 9.4 272.60 185.9 6.8 0

6 10.5 306 9.4 282.00 222.9 7.4 0

7 9.5 306 9.4 291.40 259.8 7.9 0

8 8.5 306 9.4 300.80 296.6 8.4 0

9 7.5 0 0.0 300.80 295.5 9.0 0

10 6.5 0 0.0 300.80 294.4 8.9 0

11 5.5 0 0.0 300.80 293.3 8.9 0

12 4.5 0 0.0 300.80 239.2 8.9 429

13 3.5 0 0.0 300.80 166.8 8.3 577

14 2.5 0 0.0 300.80 110.0 7.4 452

15 1.5 0 0.0 300.80 40.1 6.7 559

16 0.5 0 0.0 300.80 15.1 5.9 196 117 2214 –4.3

Table B1 (cont‘d).

39
Drain Excess water Additional Thickness Height of Q water Q water Drainage Decant

time (dt) quantity: thickness of of sludge water column pad weir thru pad over weir Error

Day Hour (hours) Q in (m3) sludge (mm) (mm) (mm) (m3) (m3) (m3) (m3) (m3)

5 1 15.5 306 9.4 310.20 37.1 5.6 0

2 14.5 306 9.4 319.60 74.3 6.0 0

3 13.5 306 9.4 329.00 111.4 6.5 0

4 12.5 306 9.4 338.40 148.4 7.0 0

5 11.5 306 9.4 347.80 185.4 7.6 0

6 10.5 306 9.4 357.20 222.3 8.1 0

7 9.5 306 9.4 366.60 259.1 8.6 0

8 8.5 306 9.4 376.00 295.9 9.1 0

9 7.5 0 0.0 376.00 294.7 9.7 0

10 6.5 0 0.0 376.00 293.5 9.6 0

11 5.5 0 0.0 376.00 292.3 9.6 0

12 4.5 0 0.0 376.00 238.1 9.6 429

13 3.5 0 0.0 376.00 165.7 9.0 576

14 2.5 0 0.0 376.00 108.8 8.1 452

15 1.5 0 0.0 376.00 38.9 7.5 558

16 0.5 0 0.0 376.00 14.7 6.6 189 128 2205 –4.3

6 1 15.5 306 9.4 385.40 37.0 6.4 0

2 14.5 306 9.4 394.80 74.1 6.7 0

3 13.5 306 9.4 404.20 111.1 7.2 0

4 12.5 306 9.4 413.60 148.1 7.8 0

5 11.5 306 9.4 423.00 184.9 8.3 0

6 10.5 306 9.4 432.40 221.7 8.8 0

7 9.5 306 9.4 441.80 258.5 9.3 0

8 8.5 306 9.4 451.20 295.2 9.8 0

9 7.5 0 0.0 451.20 293.9 10.3 0

10 6.5 0 0.0 451.20 292.6 10.3 0

11 5.5 0 0.0 451.20 291.4 10.3 0

12 4.5 0 0.0 451.20 237.0 10.3 429

13 3.5 0 0.0 451.20 164.6 9.6 576

14 2.5 0 0.0 451.20 107.7 8.8 452

15 1.5 0 0.0 451.20 37.7 8.2 558

16 0.5 0 0.0 451.20 14.3 7.4 182 139 2197 –4.3

Table B1. Retention basin drainage and infiltration model (cont‘d).

40
Drain Excess water Additional Thickness Height of Q water Q water Drainage Decant

time (dt) quantity: thickness of of sludge water column pad weir thru pad over weir Error

Day Hour (hours) Q in (m3) sludge (mm) (mm) (mm) (m3) (m3) (m3) (m3) (m3)

7 1 15.5 306 9.4 460.60 36.9 7.1 0

2 14.5 306 9.4 470.00 73.9 7.4 0

3 13.5 306 9.4 479.40 110.8 8.0 0

4 12.5 306 9.4 488.80 147.7 8.5 0

5 11.5 306 9.4 498.20 184.5 9.0 0

6 10.5 306 9.4 507.60 221.2 9.5 0

7 9.5 306 9.4 517.00 257.9 10.0 0

8 8.5 306 9.4 526.40 294.5 10.5 0

9 7.5 0 0.0 526.40 293.1 11.0 0

10 6.5 0 0.0 526.40 291.8 10.9 0

11 5.5 0 0.0 526.40 290.4 10.9 0

12 4.5 0 0.0 526.40 236.0 10.9 429

13 3.5 0 0.0 526.40 163.6 10.3 575

14 2.5 0 0.0 526.40 106.6 9.5 452

15 1.5 0 0.0 526.40 36.6 8.8 557

16 0.5 0 0.0 526.40 14.0 8.1 175 150 2189 –4.3

8 1 15.5 306 9.4 535.80 36.9 7.8 0

2 14.5 306 9.4 545.20 73.8 8.1 0

3 13.5 306 9.4 554.60 110.6 8.6 0

4 12.5 306 9.4 564.00 147.4 9.1 0

5 11.5 306 9.4 573.40 184.1 9.6 0

6 10.5 306 9.4 582.80 220.7 10.1 0

7 9.5 306 9.4 592.20 257.3 10.6 0

8 8.5 306 9.4 601.60 293.8 11.1 0

9 7.5 0 0.0 601.60 292.4 11.6 0

10 6.5 0 0.0 601.60 291.0 11.6 0

11 5.5 0 0.0 601.60 289.5 11.5 0

12 4.5 0 0.0 601.60 235.1 11.5 429

13 3.5 0 0.0 601.60 162.7 10.9 575

14 2.5 0 0.0 601.60 105.6 10.1 452

15 1.5 0 0.0 601.60 35.6 9.5 557

16 0.5 0 0.0 601.60 13.6 8.7 169 161 2182 –4.3

Table B1 (cont‘d).

41
Flow Summary

System Characteristic Q Pad Q Weir Error

Cumulative totals (Cubic meters) 969 17,684 –34

Error (%) 0.18

Equivalence in mm of water/year 120 2,185 –4

Notes: Hydraulic conductivity of sludge = 15 • 10–4 mm/sec.

Hydraulic conductivity of the 152-mm compacted liner = 58 • 10–6 mm/sec

(corrected for 15° C).

No compaction of sludge layer (and associated decrease in hydraulic conductivity)

assumed.

Three-hour settling time between pumping and decanting over weir.

Remove 76.2 mm/hr from weir for first four hours (Hours 12–15). Fifth hour (Hour

16) is a decanting drain.

Ref: Annual precipitation in Anchorage area ≈ 390 mm/yr.

7.3-m-long weir.

Key to Calculations

Equations used (See Day 8, Hour 3: Row 145).

Note: Column H corresponds to Q water (Pad), F to Thickness of Sludge, and G to

Height of Water Column

G144 + 37.8 – (H145 • 1000/8090) (Height of Water Column)

8090 • 3600 • [(68 • 10–6)/1000] • (152 + F144 + G144)/{152 + [F144 • (68 • 10–6)/(15 •

10–4)]}

(Q water: Pad)

Equations used (See Day 8, Hour 13: Row 133).

Note: Column H corresponds to Q water (Pad), F to Thickness of Sludge, and G to

Height of Water Column

G149 – (H150 + I150) • 1000/8090 (Height of Water Column)

8090 • 3600 • [(68 • 10–6)/1000] • (152 + F149 + G149)/{152 + [F149 • (68 • 10–6)/(15

• 10–4)]}

(Q water: Pad)

8.09 • [152 – (G148 – G149) – 12 • 25.4 • {1/[1.63 + 1/SQRT({6 – [(G148 – G149)/

25.4]}/12)]}2]

(Q water: Weir)

8090 2-acre site size in square meters

2850 Water in per 8-hr day @382 m3/hr.

610 Sludge in per day (m3)

0.075 Sludge depth (m) per day, 2-acre site.

75.4 Sludge depth (mm) per day, 2-acre site.

302.4 Water depth (mm) per day, 2-acre site.

37.8 Water depth (mm) per hour, 2-acre site.

k = 15E(–4) mm/sec

42
APPENDIX C: SPOILS SAMPLE COLLECTION, STORAGE,

AND SHIPMENT SOP

Sample collection

Collection point: Spoils line, approximately 12 m upstream from crest of retention

pond berm.

Sampling access: 13-mm pitless adapter on side of spoils line. Ball valve shutoff.

Sample strategy: Composite sample method. Samples are taken at 15-minute intervals by directing a stream of spoils from the spoils line through the

pitless adapter, valve and 1 m of Tygon tubing into a 19-L PE bucket.

After four samples have been taken, the volume is stirred and a

500-ml composite sample taken using a PE ladle. The sample container is a clear, wide-mouth 500-ml glass sample jar, level 2A clean

(Eagle-Pitcher P/N 232-16C). Time, date and approximate dredge

location are noted. The bucket is then emptied and rinsed twice

with distilled water for reuse.

Sample storage

Temperature: Temperature is not to exceed 15° C.

Location: Samples are not to be stored in direct sunlight. Whenever possible,

they will be stored in a cooler.

Documentation: All samples are to be labeled. Documentation will reside with

samples whenever practicable. A duplicate set of documentation

will be retained by the P.I. or sampler.

Sample shipment

Samples are to be shipped overnight or second-day air, whichever

method is most practicable. Samples are to be shipped to ensure

temperature does not exceed 15° C. Adequate packing to ensure

sample integrity will be used. Containers are to be sealed with a

chain of custody document attached.

43
44

APPENDIX D: DECANTED SUPERNATANT SAMPLE COLLECTION,

STORAGE, AND SHIPMENT SOP

Sample collection

Collection point: Drop inlet structure outlet pipe egress point.

Sampling access: Open area accessible at all times.

Sample strategy: Grab sample taken once or twice a day during decanting process.

Samples taken by placing the mouth of a 1-L amber glass sample

bottle, level 2A clean (Eagle-Pitcher P/N 223-32A), in the path of

the outflow from the outlet pipe. Time and date are noted.

Sample storage

Temperature: Temperature is not to exceed 15° C.

Location: Samples are not to be stored in direct sunlight. Whenever possible,

they will be stored in a cooler.

Documentation: All samples are to be labeled. Documentation will reside with

samples whenever practicable. A duplicate set of documentation

will be retained by the P.I. or sampler.

Sample shipment

Samples are to be shipped overnight or second-day air, whichever

method is most practicable. Samples are to be shipped to ensure

temperature does not exceed 15° C. Adequate packing to ensure

sample integrity will be used. Containers are to be sealed with a

chain of custody document attached.
1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

6. AUTHORS

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

 REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING

 AGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

14. SUBJECT TERMS 15. NUMBER OF PAGES

16. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

 OF REPORT OF THIS PAGE OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and

maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,

including suggestion for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington,

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

September 1996

Dredging in an Active Artillery Impact Area

Eagle River Flats, Alaska

Michael R. Walsh, Edwin J. Chamberlain, Karen S. Henry,

Donald E. Garfield and Ed Sorenson

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road

Hanover, New Hampshire 03755-1290

Special Report 96-22

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

Remediation of sediments in permanently ponded areas at Eagle River Flats, a salt marsh contaminated with white

phosphorus (WP), may require dredging. Because the Flats were used as a firing range impact area for over 40

years by the U.S. military, there is much unexploded ordnance, which will require that any dredging equipment be

remotely controlled. To treat the sediment pumped from dredged areas, a spoils retention basin was designed,

constructed, and tested. This basin contains several innovations, including a natural peaty-silt liner and a geofabric

barrier to inhibit reintroduction of WP into the environment, and is designed for the natural remediation of the WP.

The dredging system was deployed in October of 1994, with sampling indicating that WP-contaminated areas

were removed from the dredged area. An early snowfall curtailed operations shortly after initiation.

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland 21010-5401

52

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

Dredging Natural remediation White phosphorus

Eagle River Flats Remote control (WP or P4)

Geofabrics Spoils retention basin