CRREL REPORT 95-23

Persistence of

White Phosphorus Particles

in Sediment

Marianne E. Walsh, Charles M. Collins

and Charles Racine November 1995
For conversion of SI units to non-SI units of measurement consult Standard

Practice for Use of the International System of Units (SI), ASTM Standard E380-

93, published by the American Society for Testing and Materials, 1916 Race St.,

Philadelphia, Pa. 19103.

Abstract

Remediation of sediments at Eagle River Flats, a salt marsh contaminated with

particles of white phosphorus (P4), may require severe alterations of the wetland by dredging, draining or covering. However, some sediments may undergo

decontamination naturally in areas that are seasonally exposed to air. To predict

the persistence of white phosphorus particles in sediments, a literature review

was conducted for the physical and chemical properties of white phosphorus.

The persistence of millimeter-size white phosphorus particles was studied by

laboratory and field experiments. White phosphorus particles were found to be

persistent indefinitely in saturated sediments. In unsaturated sediments, loss

was rapid (within 24 hours) at 20°C and retarded by low temperatures.

Cover: Looking east along a transect across the main pond in Area C. Sediment

temperature and moisture were monitored at these study sites during the

summer of 1994.
CRREL Report 95-23

Persistence of

White Phosphorus Particles

in Sediment

Marianne E. Walsh, Charles M. Collins

and Charles Racine November 1995

Prepared for

U.S. ARMY ENVRIONMENTAL CENTER

Approved for public release; distribution is unlimited.

US Army Corps

of Engineers

Cold Regions Research &

Engineering Laboratory
PREFACE

This report was prepared by Marianne E. Walsh, Chemical Engineer, Applied Research

Division; Charles M. Collins, Research Physical Scientist; and Charles H. Racine, Research

Ecologist, Geological Sciences Division, Research and Engineering Directorate, U.S. Army

Cold Regions Research and Engineering Laboratory.

Funding for this work was provided by the U.S. Army Environmental Center, Aberdeen Proving Ground, Maryland, through U.S. Army Alaska, Ft. Richardson, William Gossweiler, Army Remedial Project Manager.

Technical review of the manuscript was provided by Dr. Thomas F. Jenkins and Brent

Koenen. The authors gratefully acknowledge support provided by Ronald Bailey, David

Dillingham, Timothy Hansen, Kurt Knuth, Dennis Lambert and Beth Nadeau, all of CRREL.

In addition, Laurie Angell, William Smith and Serge Breton of the Natural Resources Branch,

Directorate of Public Works, U.S. Army Alaska, Ft. Richardson, provided valuable assistance in the field. Alvin Converse, Thayer School of Engineering, Dartmouth College,

provided thoughtful suggestions.

ii
iii

CONTENTS

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

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

Chemical and physical properties of white phosphorus .................................................. 1

History ................................................................................................................................. 1

Properties of white phosphorus ...................................................................................... 2

Summary ............................................................................................................................. 8

Natural size reduction of white phosphorus particle in Eagle River Flats sediments . 8

Background ......................................................................................................................... 8

Incubation of P4 particles at constant temperature and moisture content ................ 8

Monitoring sediment moisture and temperature in Eagle River Flats ...................... 13

Resampling of field-contaminated sites ......................................................................... 30

Conclusions ............................................................................................................................. 35

Literature cited ........................................................................................................................ 35

Appendix A: Methods for laboratory study ....................................................................... 39

Appendix B: Methods for field investigations ................................................................... 43

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

ILLUSTRATIONS

Figure

1. Particles of white phosphorus isolated from Eagle River Flats sediment in 1994 . 1

2. Effect of temperature and air pressure on the oxidation of solid P4 ........................ 3

3. Oxidation pathway for white phosphorus in water................................................... 4

4. Pourbaix diagram for P4 in water ................................................................................. 5

5. Calculated dissolution of a 1-mm-diameter P4 particle in 25°C water .................... 6

6. Calculated sublimation pressure for P4 ........................................................................ 7

7. Intermittent ponded area of Eagle River Flats ............................................................ 9

8. Surface texture of P4 particles ........................................................................................ 11

9. Void in dry sediment formed as P4 particle sublimed ............................................... 11

10. Residual mass of white phosphorus particles found following incubation in

sediments ................................................................................................................. 12

11. Aerial view looking south across Eagle River Flats ................................................... 13

12. Eagle River Flats, showing the location of Area C, as well as the river, drainage

gullies and intermittent and permanent ponds ................................................. 14

13. Area C, showing bulrush marsh, permanent ponds, intermittent ponds, mudflats and levees ........................................................................................................ 14

14. Sampling locations in Area C and results of sediment analyses for white

phosphorus .............................................................................................................. 15

15. Aerial view of Area C ...................................................................................................... 16

16. Locations of study sites in Area C ................................................................................. 16

17. Study site in an intermittent pond area showing the datalogger ............................. 17

18. View looking west along transect across an intermittent pond area ....................... 17
iv

Figure

19. Permanently flooded site ............................................................................................... 18

20. Site in an intermittent pond in August ......................................................................... 18

21. Site on a mudflat vegetated with alkali grass and arrowgrass ................................. 19

22. Site on a river levee with a tall stand of beach rye ..................................................... 19

23. Moisture probe resistance and tensiometer readings obtained along the transect

in Area C .................................................................................................................. 20

24. Daily temperatures at 5, 10, 20 and 30 cm deep at each site ..................................... 20

25. Daily moisture probe resistance at 5, 10, 20 and 30 cm deep at each site................ 22

26. Hourly measurements of sediment temperature and moisture probe resistance

at 5 cm deep for sites 1–10 ..................................................................................... 26

27. Number of days that sediments at 5 cm deep were unsaturated vs. elevation...... 27

28. Moisture retention curve for a sediment sample collected 20 m south of the

transect between sites 3 and 4 in the intermittent pond ................................... 27

29. Water surface elevations measured in piezometers at sites 1–9 on May 24,

June 20 and August 19 ........................................................................................... 28

30. Average pond surface elevation at site 1...................................................................... 29

31. Residual P4 found in five replicate samples normalized to initial mass from

each site .................................................................................................................... 29

32. Frequency of flooding tides, 1989–1994 ....................................................................... 31

33. Site 883, in the intermittent pond of Area C, where high concentrations of white

phosphorus were detected in 1992 ....................................................................... 32

34. Pattern of WP contamination found during August 1992 and August 1994

around a site in an intermittently flooded pond in Area C .............................. 32

35. Number of samples in different concentration ranges in 1992 and 1994 ................ 33

36. Comparison of WP concentrations found in 1992 and 1994 around site 883, an

intermittent ponded site in Area C ...................................................................... 33

37. Detonation of a UXO, an 81-mm mortar round that contained white phosphorus, on May 20, 1992 ....................................................................................... 34

38. Crater, known as “Miller’s Hole,” produced by detonation of a UXO that

contained white phosphorus ................................................................................ 34

TABLE

1. Chemical and physical properties of white phosphorus ........................................... 2

2. Mass of P4 recovered as a vapor above soils containing 35 mg of P4 pellets .......... 8

3. Experimental parameters for the laboratory study .................................................... 9

4. Masses of eight replicate white phosphorus particles ............................................... 9

5. Mass of white phosphorus particles found following solvent extraction of

sediment ................................................................................................................... 10

6. Physical appearance of WP particles incubated at five moisture contents and

three temperatures .................................................................................................. 10

7. UTM coordinates and elevations of sites in Area C ................................................... 17

8. Water quality measurements and vegetation at sites in Area C ............................... 18

9. Measurements of moisture contents obtained in May, June and August 1994,

and measurements of dry bulk density obtained in August 1994 ................... 19

10. Maximum, average, median and minimum temperatures and periods below

saturation measured at 5, 10, 20 and 30 cm deep at each site between May

25 and 27 or August 27, 1994................................................................................. 23

11. Tensiometer measurements at 10 and 25 cm deep taken at the same time as

piezometer measurements of water surface ....................................................... 28

12. Results of Kruskal–Wallis test........................................................................................ 30

13. White phosphorus concentrations found at Miller’s Hole ........................................ 34
INTRODUCTION

Since 1990, CRREL researchers have been conducting field studies at Eagle River Flats, Alaska,

the impact area at Ft. Richardson (Racine et al.

1992a,b,c, 1993). Eagle River Flats was contaminated by the detonation of projectiles containing

white phosphorus, a smoke-producing munition.

Eagle River Flats is the first Army training area

identified with white phosphorus contamination.

Recent surveys at other army training areas have

revealed white phosphorus contamination (Simmers et al. 1994). Previous to our findings at Eagle

River Flats, white phosphorus was thought to be

nonpersistent in the environment.

The discovery of white phosphorus residues

from smoke rounds at Eagle River Flats has shown

that the current understanding of the environmental fate of white phosphorus is poor. Much of the

basic research on the chemistry of white phosphorus was conducted prior to 1950 and was not concerned with environmental fate. More recent work

on the environmental impact of training with

white phosphorus munitions concentrated on

downwind deposition of aerosols from the smoke

cloud (Marchetti 1979, Van Voris et al. 1987). These

studies examined white phosphorus particles

much smaller than the millimeter-size particles

(Fig. 1) found by examination of highly contaminated Eagle River Flats sediments. Lack of understanding of the environmental fate and transport

of white phosphorus residues precludes accurate

ecological assessments and efficient cleanup. This

report will review literature describing the chemical and physical properties of white phosphorus.

Then laboratory and field experiments will be described in which white phosphorus particles were

incubated in Eagle River Flats sediments at various temperatures and moisture contents.

Persistence of White Phosphorus Particles in Sediment

MARIANNE E. WALSH, CHARLES M. COLLINS AND CHARLES H. RACINE

CHEMICAL AND PHYSICAL PROPERTIES

OF WHITE PHOSPHORUS

History

As with many scientific discoveries, white

phosphorus was discovered by serendipity, in

1669 in Hamburg, when Hennig Brand distilled

urine with sand and coal while attempting to isolate metals for alchemy experiments (Mellor

Figure 1. Particles of white phosphorus (P4) isolated

from Eagle River Flats sediment in 1994. These particles were deposited from smoke munitions fired into Eagle

River Flats during army training. They were deposited

prior to February 1990 when artillery training was suspended at Eagle River Flats. Lead shot, shown for scale, is

2.7 mm in diameter.
Table 1. Chemical and physical properties of white

phosphorus.

Property Value Source*

Molecular structure P4 a

Molecular weight 124 amu a

Physical state at STP Solid a

Melting point 44°C a

Boiling point 280°C a

Appearance Waxy a

Transparent

Colorless (pure)

Mohs hardness 0.5 a

Density (20°C) 1.8 g/cm3 a

Vapor pressure (25°C) 0.043 torr a

Viscosity (50°C) 1.69 cP b

Solubility

in water (15°C) 2.4 mg/L c

3 mg/L d

in carbon disulfide (20°C) 13 × 106 mg/L a

in diethyl ether (20°C) 7,000 mg/L a

in benzene (20°C) 26,000 mg/L a

in mineral oil 12,000 mg/L d

Octanol–water partition coefficient 1200 c

Autoignition temperature 20–40°C e

Latent heat of fusion (44°C) 20 J/g a

Latent heat of sublimation (25°C) 455.2 J/g a

Latent heat of vaporization (287°C) 545 J/g a

Heat of combustion 24,000 J/g a

Critical point 675°C, 80 atm a

* a–Mellor (1928)

b–Kirk Othmer (1982)

c–Spanggord et al. (1985)

d–Stich (1953)

e–Dainton and Bevington (1946)

f–Van Wazer (1958)

2

1928). Phosphorus was subsequently named

from the Greek word for “light bearer” since it

glowed in the dark.

Properties of white phosphorus

Phosphorus occurs in both organic and inorganic forms in nature almost exclusively in oxidation state +5. Mean phosphorus concentrations in soil and crustal rocks are 430 and 1000

mg/kg, respectively (Sposito 1989), making it

the twelfth most abundant element in the lithosphere. Phosphorus plays vital roles in biological

systems in compounds such as ATP (adenosine

triphosphate), phospholipids, DNA (deoxyribonucleic acid) and phosphate buffers, and it is

found in the bones and teeth of vertebrates as

calcium phosphate.

Elemental phosphorus (oxidation state 0) does

not exist in nature; it is prepared commercially

by heating phosphate ores [Ca3(PO4)2] with sand

(SiO2) and coke in an electric furnace. White

phosphorus is a wax-like solid that ignites spontaneously in air between 30 and 40°C. Its molecular structure is that of a regular tetrahedron with

a phosphorus atom at each apex and a P–P distance of 0.22 nm. Since its molecular formula is

P4, its molecular weight is 124 amu. The high reactivity of white phosphorus is attributed to the

extreme bond strain involved in the bonding of

four phosphorus atoms in a tetrahedral configuration (Van Wazer 1958). Some chemical and

physical properties of white phosphorus are given in Table 1.

Elemental phosphorus exists in several allotropic forms: white, red and black. White phosphorus is sometimes referred to as yellow phosphorus since the commercially available grade

has a slight yellow color due to trace amounts of

red phosphorus as an impurity. Pure white phosphorus is colorless. The crystal structure is cubic;

a unit cell (a = 1.85 nm) contains 56 P4 tetrameric

molecules. The structure of red phosphorus is

variable. Several polymeric forms exist. Red

phosphorus, which is less reactive than white

phosphorus, is also used by the Army as a smoke

munition. Red phosphorus is nontoxic. Black

phosphorus is similar in structure to graphite. It

is the most stable form of elemental phosphorus;

it does not spontaneously ignite under normal

temperatures and humidities.

The oxidation of P4 has been studied extensively (Mellor 1928, Van Wazer 1958). The final

product of P4 oxidation is phosphorus pentoxide

(P4O10) via lower oxidation state oxides P4On,

where n = 1, 2,...9. Lesser amounts of phosphorus

trioxide (P4O6) and phosphorus tetraoxide

(P4O8) are products, depending on the availability of oxygen. Phosphorus trioxide is responsible

for the garlic-like smell immediately noticeable

when P4 is exposed to air. Phosphorus pentoxide

is one of the most hygroscopic substances

known. It will extract moisture from the atmosphere; the dense white cloud formed following

the bursting of a P4 projectile is actually moisture

condensing on oxidized white phosphorus.

Phosphorus oxides hydrolyze in water to form

various oxyacids.

The reaction between P4 vapor and oxygen

has several anomalies that have intrigued scientists for over three hundred years (Semenov

1959). The reaction is characterized by a greenish

glow that occurs between two sharply defined

limits of oxygen pressure, which diverge as P4

pressure increases. Outside the limits, the rate is

so slow that it is undetectable. The lower limit is

affected by the size and surface condition of the

reaction vessel and the presence of other gases.
The lower limit is not a function of temperature,

while the upper limit decreases with increasing

temperature. These observations led to the theory

of branching-chain reactions. The reaction mechanism proposed by Dainton and Kimberley

(1950) is:

 (1) P4 + O2 → P4O + O initiation

 (2) P4 + O + M → P4O + M propagation

 (3) P4On + O2 → P4On+1 + O branching

 (n = 1, 2, ...9)

 (4) O + O2 + M → O3 + M termination

 (5) O + X → stable product termination

 (6) O + wall → adsorbed oxygen termination

where M is a third body and X is an inhibitor. The

rate equation given by Dainton and Kimberley

(1950) is:

 

dPO

d

P O

P M

OM X PM

4 10

4 2

4

2 4

[ ] = [ ][ ]

+ [ ][ ]

[ ][ ] + [ ] + − [ ][ ]













t

k

k

k k kk

1

2

4 5 62

1

10

8

(1)

where k1,2...6 are reaction constants for the six

equations for the reaction mechanism. The lower

limit of the glow reaction is due to “wall termination,” reaction (6). The constant for reaction (6) is

a function of the diffusivity of oxygen atoms in

the gas mixture, the diameter of the reaction vessel and the concentrations of P4, O2 and M. The

upper limit is due to homogeneous termination,

reactions (4) and (5). The constant for reaction (4)

is a function of a frequency factor for third-body

reactions, temperature, activation energy (4.3

3

kcal) and the concentrations of P4, O2 and M. The

reaction between P4 and O2 is rapid when the

denominator of the term in the parentheses approaches zero. Dainton and Kimberley (1950)

stated that within the limits of the glow reaction

the “rate appears only to be limited by the supply and interdiffusion of the reactants.”

Solid and liquid P4 may ignite spontaneously

in air. The autoignition temperature at atmospheric pressure for solid or supercooled liquid

P4 in dry air is 38°C (Dainton and Bevington

1946), and for a range of temperatures below

38°C (Fig. 2), P4 will slowly oxidize, producing a

greenish glow. Below 5°C, there is no reaction,

unless the pressure is reduced to less than atmospheric.

In 1681, Slare (Mellor 1928) made the following seemingly paradoxical observation:

It now being generally agreed that the fire

and flame of phosphorus have their pabulum

out of the air, I was willing to try this matter in

vacuo. To effect this I placed a considerable

lump of phosphorus under a glass, which I fixed

to an engine for exhausting the air: then presently working the engine, I found it to grow lighter

(i.e., the phosphorus to become more luminous), though a charcoal that was well kindled

would be quite extinguished at the first exhaustion; and upon the third or fourth draught,

which very well exhausted the glass, it much

increased in light, and continued to shine with

its increased light for a long time; on re-admitting the air, it returned again to its former dullness.

White phosphorus does not glow in oxygen at

1.5 atmospheres unless the temperature is raised

above the melting point (Mellor 1928). Several

researchers gathered evidence that the oxidation

of P4 occurs in the vapor phase. If a stream of air

is blown over the oxidizing P4, the glow appears

Figure 2. Effect of temperature and air pressure on the oxidation of

solid P4. (After Dainton and Bevington 1946).

150

100

50

0

– 60 – 40 – 20 0 20 40 60

Temperature (°C)

Air Pressure (kPa)

Slow Reaction Glow Region Flame Region
downstream (Van Wazer 1958). Rayleigh (Mellor

1928) observed that P4 is slightly volatile at room

temperature and that the increased luminosity

when the atmosphere is rarefied is due to the increased volatilization of the P4. Thorpe (Mellor

1928) concluded that P4 reacts with oxygen only

under conditions where the P4 volatilizes and

that

the glow itself is nothing but a slowly burning

flame, having an extremely low temperature,

caused by the chemical union of oxygen with

the vapours of phosphorus and phosphorus oxide. By suitable means this glow can be gradually augmented until it passes by regular gradation into the active vigorous combustion which

we ordinarily associate with flame.

The transition to burning with a bright yellow

flame occurs when the temperature is raised to

the ignition point or the pressure lowered below

a definite limit (Fig. 2). Autoignition may also

occur at room temperature if white phosphorus

is covered by cotton (Mellor 1928). Since the oxidation of P4 occurs by a reaction that occurs in

the vapor phase immediately adjacent to the solid phase, activities that result in higher concentrations of P4 vapor lead to autoignition. Dainton

and Bevington (1946) observed surface melting

as a solid piece of P4 underwent transition from

glow to flame. They speculated that not all the

heat of reaction is dissipated as light and that the

glow reaction is slightly exothermic. The heat

causing the melting came from the oxidation reaction in the spatially adjacent vapor phase,

which in turn raised the surface temperature of

the solid P4, leading to increased vapor pressure,

more heat and finally ignition.

Dainton and Bevington (1946) described the

greenish glow in terms of “width, intensity, and

distance from the phosphorus.” They concluded

that the rate of consumption of P4 vapor and oxygen was limited by the rate of diffusion of either

reactant into the reaction zone. The conclusion of

later work by Dainton and Kimberley (1950) was

that “the glow reaction is only limited in velocity

by the supply of phosphorus molecules to the reaction zone.” White phosphorus exposed to dry

air may form a layer of oxides that greatly reduces or stops the rate of oxidation (Russell 1903,

Dainton and Bevington 1946). White phosphorus

exposed to moist air forms a film of moisture that

may stop oxidation (Russell 1903). The development of the film is due to the formation of the

hygroscopic phosphorus pentoxide (P4O10).

White phosphorus will react with other oxidizing agents such as the halogens, sulfur and

4

(1) DISSOLUTION

Dissolved P

(up to 2.4 mg/L)

 Suspended P 4

(up to 100 mg/L)4

(2) OXIDATION OF P4

P + O 4 2

P + 3O 4 2

P O4 2

2P O2 3

(3) HYDROLYSIS TO OXYACIDS

P O + 6H O 42 2

2P O + 6H O 2 2 3

4H PO 3 2

4H PO 3 3

(4) OXIDATION TO ORTHOPHOSPHORIC ACID

H PO + O 3 2 2

2H PO + O 3 2 3 2H PO 3 4

H PO 3 4

Figure 3. Oxidation pathway for white phosphorus in

water. (After Sullivan et al. 1979.)

acids (e.g. nitric and sulfuric). The surface of solid P4 is oxidized by aqueous solutions of metal

salts such as copper sulfate, reducing salts of

copper to the metal via copper phosphide. In the

past, first aid for P4 burns included bathing the

P4 in aqueous copper sulfate (Konjoyan 1983),

which coated the P4 particles with black copper

phosphide (Mellor 1928) and prevented the P4

from reigniting. White phosphorus stored under

tap water will blacken due to reaction with copper cations dissolved in the water from copper

pipes (Rae 1916).

Studies of the oxidation of P4 in water are

summarized by Sullivan et al. (1979). Dissolved

P4 reacts with dissolved oxygen to form phosphinic (H3PO2) and phosphonic (H3PO3) acids,

which in turn oxidize to orthophosphoric acid

(H3PO4) (Fig. 3). Phosphine is also produced,

probably by hydrolysis (Spanggord et al. 1985).

When solid P4 is introduced into water containing dissolved oxygen, a film of oxidation product

forms on the surface. This film, the formation of

which is accompanied by hydrogen evolution,

was identified by Nikandrov and Smirnov (1983)

as (P4OH)2, an intermediate to the formation of

phosphorus pentoxide.

Factors that affect the environmental fate of

white phosphorus

At equilibrium, P4 does not exist in oxygenated aqueous or soil media. The thermodynamic

instability of P4 is illustrated in the potential-pH

equilibrium diagram for phosphorus in water at

25°C (Fig. 4). The domain of stability for P4 is
5

well below the domain of the stability of water

(Pourbaix 1966); that is, it can theoretically reduce water with the evolution of hydrogen.

However, this diagram is for the state of thermodynamic equilibrium and does not indicate the rate

at which equilibrium is achieved. Several factors

must be taken into account to assess the persistence of a chunk of solid P4 introduced into water

or saturated sediments.

Spanggord et al. (1983) reviewed the properties and processes associated with the environmental fate of P4. These included aqueous solubility, vapor pressure, sorption partition coefficient, octanol–water partition coefficient, leachability, Henry’s constant and rates of dissolution,

hydrolysis, oxidation, reduction and biotransformation.

Dissolution and aqueous solubility

White phosphorus is nonpolar, so it does not

dissolve readily in water. Spanggord et al. (1985)

measured the dissolution rate of a piece of P4 that

had a surface area of 1.25 cm2 exposed to 25°C

oxygen-saturated and nitrogen-purged water

flowing at 0.14–3.00 mL/min. Dissolution rates

ranged from 1.5 μg/hr for the slowest flow rate

to 6.7 μg/hr for the highest flow rate. There was

no difference in dissolution rate for white phosphorus exposed to oxygen-saturated or nitrogenpurged water.

Using these data and assuming that the rate of

dissolution per unit area is constant, we can calFigure 4. Pourbaix diagram for P4 in water showing that

P4 is not thermodynamically stable in water. The region

bordered by the heavy lines is the stability field of water. No

substance outside this field is stable in the presence of water

and atmospheric oxygen. (After Pourbaix 1966.)

culate the time for a spherical particle with an

initial diameter of 1 mm (surface area of 0.0314

cm2 and a mass of 953 μg) to dissolve from

 

d

d

g

cm hr

M

t = r ⋅ ×

1 5

1 25

4 2

2 .

. . μ π (2)

Since

 

dd d d M V r rr == = ρ ρ π ρπ

4

3

4 3 2 (3)

then dM in eq 2 may be replaced:

 

ρ π μ 4 π

1 5 4 2 2 rr rt d g

1.25 cm hr

d 2 = ⋅

. (4)

 

d = g

cm hr

d

0

2

0

r t

r=r

r=r

t

t t

∫ ∫ μ

⋅











( ) =

= 1 5

1 25

1 .

. /ρ (5)

 

d = g

cm hr

d

0

2

0

r t

r=r

r=r

t

t t

∫ ∫ μ

⋅











( ) =

= 1 5

1 25

1 .

. /ρ . (6)

Based on the amount of time for the radius to

go to zero, a P4 particle with an initial diameter of

1 mm would take about 8 years to dissolve at a

constant temperature of 25°C (Fig. 5) in slowly

flowing water.

Despite the slow dissolution rate, there is ample evidence that water becomes contaminated

by contact with P4. In industrial settings, P4 is freEH (mV)
0.2

0.4

0.6

0.8

1.0

0 2468

Mass (mg)

Time (years)

Figure 5. Calculated dissolution of a 1-mmdiameter P4 particle in 25°C water assuming the rate of dissolution per unit surface

area is constant [1.2 μg/(cm2 hr)]. The rate is

based on the data from Spanggord et al. (1985)

for the slowest flow rate tested.

quently held above its melting point so that it

may be poured and molded. Because the melting

point exceeds the autoignition temperature, large

quantities of water are used commercially either

for storage and handling of P4 or for washing

equipment that has been in contact with P4. This

“phossy water” contains suspended (colloidal)

and dissolved P4 (Dacre and Rosenblatt 1974).

Larger particles may also be suspended (Peer

1972). Release of phossy water has caused fish

kills in Canada (Idler 1969) and the United States

(Dacre and Rosenblatt 1974).

The aqueous solubility of P4, as measured by

Stich (1953), is 3 mg/L at 15°C, and this is the value reported in the Handbook of Chemistry and Physics. However, colloidal suspensions have concentrations up to 100 mg/L (Sullivan et al. 1979).

Spanggord et al. (1985) measured the aqueous

solubility of P4 by placing excess P4 in deoxygenated water, heating to 45°C, sonicating for 30 minutes, then stirring for 48 hours. Solutions were

then centrifuged at 7000 rpm for 60 minutes at

three temperatures. Measured P4 concentrations

were 2.4, 4.1 and 5.0 mg/L at 15, 25 and 35°C.

Because P4 is not an electrolyte, solubility in

saline solutions will decrease as salinity increases, a process known as “salting-out” (James 1986).

The effect is expressed mathematically by the Setschenow equation:

 

log s

s

s salt

M

M

K M

o

= (7)

where 

Mo

s is the solubility of the nonelectrolyte in

pure water and Ms is the solubility of the nonelectrolyte in the saline solution with a salt concentration of Msalt. Ks is a constant, known as the Setschenow or salting-out constant (James 1986). A

value for Ks has not been published.

Octanol–water partition coefficient

The octanol–water partition coefficient (Kow) is

the ratio of the concentration of a solute in the

organic phase (octanol) to the concentration of a

solute in water at equilibrium and is often used as

an indicator of the bioaccumulation potential of an

organic substance in fatty tissue of organisms and

of mobility and sorption in the environment. High

Kow values (>1000) mean a tendency for bioaccumulation, low mobility and sorption to organic

matter. Spanggord et al. (1985) measured Kow

using the method of Leo et al. (1971), where white

phosphorus concentrations were measured in both

the water and octanol phases. The mean of seven

determinations was 1200 ±100, indicating that P4 is

lipophilic and has the potential to bioaccumulate.

Following the release of wastewater from a

white phosphorus production facility in Newfoundland, numerous studies were performed on

the bioaccumulation of P4 in marine animals

(Fletcher 1971, 1973, 1974). In animals exposed to

aqueous solutions of P4, white phosphorus was

found to concentrate in fatty tissues. However, if

the animals survived the exposure and were

placed in uncontaminated water, the P4 concentrations dropped below detectable levels. Similarly

Clarkson (1991) reported that white phosphorus

has been detected in the tissues of people who

died within a few days following ingestion of

white phosphorus but not in those that die after

longer periods. These results are similar to those

obtained in studies related to the P4 contamination

at Eagle River Flats. In carcasses of ducks from

Eagle River Flats, P4 concentrations were highest

in the fat and skin (Racine et al. 1992a,b,c, 1993,

Roebuck et al. 1994). Predators exposed to P4-contaminated meat initially accumulated P4 in fatty

tissues; when contaminated meat was replaced by

uncontaminated meat, P4 concentrations in tissues

6
7

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 8 16 24 32 40

Sublimation Pressure (torr)

Temperature (°C)

Figure 6. Calculated sublimation pressure for P4.

dropped below detectable levels (Nam et al.

1994). Thus, P4 is eliminated and does not

bioaccumulate in the same manner as other

lipophilic toxicants such as PCBs, which concentrate in upper trophic levels.

Vapor pressure

The vapor pressure of a liquid or solid is the

pressure of the gas phase in equilibrium with

the liquid or solid phase at a given temperature

and is used to assess the tendency of a substance to evaporate.

The vapor pressure of solid P4 has been

measured over the temperature range –23 to

41°C and ranged from 0.0004 to 0.13 torr (Dainton and Kimberley 1950, Nesmeyanov 1963). At

room temperature (20–25°C) the vapor pressure is 0.025–0.04 torr.

Van Wazer (1958) claimed that the following

equation for vapor pressure of solid P4 agrees

with experimental data:

log10P (torr) = 1.9198 – (3.084×10–3)T+

 2.7763 logT – (2.641×103)/T

 – (3.258×104)/T2 (8)

which yields a pressure of 0.04 torr at 25°C (Fig.

6).

At 25°C the vapor pressure of P4 is on the same

order of magnitude as many semi-volatiles such

as naphthalene. Thus, sublimation could be a significant process in the environment, depending

on temperature. In fact, sublimation of P4 from

soil was observed by Warnock (1972) when he investigated the potential use of white phosphorus

as a source of plant-available phosphoric acid.

During field studies, P4 was observed to escape

Table 2. Mass of P4 recovered as a vapor above soils containing 35 mg of P4 pellets. (After Warnock 1972.)

Soil

Soil Depth moisture Mass (μg) of P4 recovered

type (cm) (%) 1 2 3 5 6 7 days Total

Acid 2.5 8.6 6.4 2.5 0.5 * * * 9.4

Calcareous 2.5 9.3 3.1 4.9 1.6 * * * 9.6

Acid 10 8.6 1.1 0.2 0.2 * * * 1.5

Calcareous 10 9.3 1.8 1.6 1.1 * * * 4.6

Acid 5 4.3 2.3 1.0 0.5 2.2 1.2 0.3 7.5

Acid 5 11.2 2.2 0.6 5.0 0.3 1.7 0.9 10.7

Acid 5 18.1 1.3 2.8 0.5 0.5 0.7 0.2 5.8

Acid 5 31.9 1.8 0.8 0.3 0.6 1.1 0.3 4.7

* Not measured.

through the soil surface (concentrations higher

than 0.01 mg/m3, the threshold limit value, were

measured in a vapor cloud above soil containing

P4). In the laboratory, 35 mg of P4 as “pellets”

(size not reported) were placed at depths of 2.5

and 10 cm in pots containing 750 g of two types of

soil (acid and calcareous) of approximately 9%

moisture. The air above each pot of soil was monitored for P4 vapor for three days. The cumulative

mass of P4 in the air after three days was approximately 9.5 μg for the P4 at 2.5-cm depth and 1.5

and 4.6 μg for the acid and calcareous soils with

P4 at the 10-cm depth (Table 2). In a second experiment the effect of soil moisture on the amount of

P4 vapor escaping from soils containing 35 mg of

P4 pellets at 5-cm depth was monitored for seven

days. In all cases, P4 was detected in the air above

the soil (Table 2). There is no clear pattern as to

the effect of soil type, soil moisture or length of

time P4 was monitored. Unfortunately soil temperatures were only measured intermittently and
8

varied between 18 and 24°C. Given that the vapor

pressure would vary between 0.025 and 0.041 torr

over this temperature range, temperature effects

could dominate the effects of soil type, moisture

or time. In any case, the important observation is

that there is experimental evidence for P4 sublimation and escape from unsaturated soils.

Henry’s constant

The Henry’s Law constant is the ratio, at equilibrium, of the concentration (partial pressure) of

an analyte in the vapor phase to the concentration (mole/L) in aqueous solution. It may be

used to assess losses due to the transfer of P4

from water to the atmosphere. Spanggord et al.

(1985) measured the Henry’s Law constant for P4

as 2.1×10–3 atm-m3/mole, so the mass transfer of

P4 from water to the atmosphere could be significant. Spanggord et al. (1985) estimated the volatilization half-life of dissolved P4 in a turbulent

stream to be 0.8 hours, which is faster than the

oxidation half-life. This estimate is consistent

with the results of Xulong et al. (1987), who

found that agitation was the most significant factor contributing to the loss of P4 in a treatment

process for P4-contaminated water.

Summary

White phosphorus (P4) is thermodynamically

unstable in the presence of oxygen. In nature,

phosphorus is found in oxidation state +5 as orthophosphate ( 

PO4

–3 ). When white phosphorus

(oxidation state 0) is introduced into the environment, it will ultimately oxidize to orthophosphate, but the rate at which it oxidizes depends

on the availability of oxygen and the state in

which P4 is introduced (vapor, solid or aqueous

solution). Solid P4 introduced into anoxic, saline

aquatic environments is likely to persist indefinitely.

NATURAL SIZE REDUCTION OF

WHITE PHOSPHORUS PARTICLES

IN EAGLE RIVER FLATS SEDIMENTS

Background

Since 1990, when we identified white phosphorus as the cause of waterfowl deaths at Eagle

River Flats (Racine et al. 1992a,b,c), methods

have been discussed for decontaminating the

sediments. Remedial techniques currently under

investigation at Eagle River Flats (ERF) include

dredging, covering and pond draining. To preserve as much habitat as possible and make the

remedial process cost efficient, these techniques

will most likely be used only in those areas

where white phosphorus is persistent and will

continue to threaten waterfowl.

While white phosphorus is extremely toxic

(Clarkson 1991), it has the potential to form nontoxic phosphates. In the anoxic, saline sediments

of permanently ponded areas of ERF, phosphate

formation from solid, millimeter-size white

phosphorus particles (Fig. 1) will be extremely

slow. However, not all ponded areas of ERF are

permanently covered with water. During some

summers with extended periods between flooding high tides, the size of some ponds may be reduced significantly (Fig. 7). If exposed sediments

become unsaturated and the sediment temperature rises, some in-situ decontamination may be

occurring. Identification of these areas may reduce the total area that needs to be treated by

some other remediation strategy.

a. Pond with water. b. Same area with sediments exposed to air.

Figure 7. Intermittent ponded area of Eagle River Flats.
9

dissolved in 20 mL of isooctane by shaking for two

hours. For the P4 concentration in the extract to be

within the linear range of the GC detector, these

solutions had to be diluted by a factor of 5000.

Such a large dilution factor can contribute to a systematic error. The masses of the particles (Table 4),

as determined by GC, were in the range of 7.8–8.4

with a mean of 8.1 mg. The relative standard deviation (RSD) for these measurements was only

3.2%. Therefore, the measurements were very precise; however, the masses were higher than expected. For a 1.8-mm particle, the mass should be

approximately 6 mg. Our calibration standard was

checked against one prepared independently at

the Waterways Experiment Station and was found

to have the same GC response within experimental

error.

Recovery from sediment at various moisture contents. Triplicate sediment samples were prepared

at each of the five moisture contents used in this

experiment. One P4 particle was placed in each

sample, and then each sample was extracted with

isooctane. The P4 mass found in each sample was

determined by isooctane extraction and gas chromatography and compared with the mass found

in samples without sediment (Table 5). The average P4 mass found in the sediment samples was

7.99 mg, which yielded an average recovery of

97.8%, based on the samples without sediment

(8.17 mg).

Physical appearance of particles following incubation. Following incubation the physical appearance was noted of each particle that could be located (Table 6). Initially the particles were spherical

and had a smooth surface and a lustrous, translucent appearance. Following incubation the most

noticeable change in those particles where there

In this work, natural decontamination of ERF

sediments was investigated in three ways:

• A laboratory evaluation of the effect of sediment temperature and moisture on the persistence of P4 particles in ERF sediments;

• A field investigation to determine if sediment

moisture and temperature reach levels conducive to size reduction of P4 particles in Eagle

River Flats; and

• A field investigation of the pattern of P4 contamination around previously tested sites in

an intermittent ponded area to determine if

the level of P4 contamination had changed after exposure to air during the summer of 1993.

Incubation of P4 particles at constant

temperature and moisture content

Methods

To determine the effect of sediment temperature and moisture content on the persistence of P4

particles in ERF sediments, P4 particles of known

diameter (approximately 2 mm) were placed at a

depth of 3 cm in wet ERF sediment and the sediment was incubated in an environmental chamber

at a constant temperature. Table 3 gives the experimental variables. The temperatures were selected

to reflect sediment temperatures previously

measured in Eagle River Flats. The moisture

range was chosen to include unsaturated and saturated conditions. The sediment was contained in

8-×8-×6-cm plastic dishes, with one particle per

dish. At discrete time intervals, samples were taken to determine if the P4 particles had decreased in

size. Particle sizes were measured directly with a

micrometer, and gas chromatography (GC) was

used to determine particle masses as well as residual P4 that may be sorbed to the sediment or dissolved in the sediment moisture. Details of the

methods used are given in Appendix A.

Results

Precision and accuracy of the measurement of particle mass. Eight replicate particles produced in the

laboratory from molten white phosphorus were

Mass

7.97

8.33

7.77

8.35

8.39

8.18

7.77

7.97

mean = 8.09

max = 8.39

min = 7.77

std. dev. = 0.26

RSD (%) = 3.21

* Found following dissolution in isooctane, dilution

with isooctane and gas chromatographic analysis.

Mass

Table 4. Masses (mg) of

eight replicate white

phosphorus particles.*

Table 3. Experimental parameters for the

laboratory study on the effect of sediment

temperature and moisture on the persistence of white phosphorus particles.

Treatments

Temperatures: 4 , 15, 20°C

Approximate degree of saturation: 0.4, 0.6, 0.8, 1, >1
10

Table 6. Physical appearance of WP particles incubated at five moisture contents and three temperatures.

No. of No. of

Temp samples particles Surface appearance

(°C) examined found Spherical Smooth Pitted Lustrous White Orange Colorless Translucent Smoking

s = 0.45

4 14 14 10 7 13 10 6 0 11 14 0

15 13 11 9 1 9 3 8 0 2 11 0

20 6 0

s = 0.64

4 14 14 13 10 5 13 3 0 12 14 0

15 13 10 10 2 8 4 5 0 5 10 0

20 6 0

s = 0.82

4 12 12 12 12 1 12 1 0 12 12 0

15 15 6 4 3 2 6 0 1 3 6 0

20 10 6 5 5 1 5 0 0 4 6 4

s = 1

4 10 10 10 10 0 10 0 0 10 10 0

15 12 12 12 12 0 10 1 7 7 11 0

20 10 10 9 9 2 8 0 0 8 8 5

s >1

4 11 11 11 11 0 11 0 0 11 11 0

15 12 12 12 12 0 12 0 3 12 12 1

20 10 10 10 10 0 10 0 0 10 10 0

Table 5. Mass of white phosphorus

particles found following solvent

extraction of sediment at various

moisture contents s and gas chromatographic analysis.

WP mass Recovery

 s Rep. (mg) (%)

0.45 1 7.05 86.4

0.45 2 7.96 97.5

0.45 3 7.92 97.0

0.64 1 8.46 103.6

0.64 2 8.13 99.6

0.64 3 7.92 96.9

0.82 1 6.21 76.0

0.82 2 8.53 104.5

0.82 3 8.86 108.5

1 1 8.19 100.3

1 2 8.60 105.3

1 3 8.16 99.9

>1 1 8.27 101.3

>1 2 7.90 96.8

>1 3 7.66 93.8

no sediment 1 8.48

no sediment 2 7.85

mean = 8.01 97.8

std dev. = 0.57

%RSD= 7.16

high = 8.86 108.5

low = 6.21 76.0

range = 2.65 32.5

was change was a pitting or dimpling of the surface,

which gave the surface a whitish color (Fig. 8). This

dimpling may correspond to empty sediment pores

through which P4 vapor diffused. With time, particles

decreased in size and became irregular in shape. Several particles that had maximum linear diameters of approximately 1 mm appeared to have horn-like protrusions. Gross changes in surface texture and particle

Figure 8. Surface texture of P4 particles. The P4 particle on

the left is freshly made from molten P4. Three particles on the

right have been incubated in unsaturated sediment at 15°C for

three days. Voids are visible on the surface of each particle, giving a dimpled appearance. Graduations on the ruler are 0.5 mm.
11

FPO

size were only evident in those particles incubated at moisture contents below saturation. Almost all particles were translucent, and there

was no evidence of the oxidized coating that

forms when P4 is stored in water. Some particles

developed an orange tinge over part of the surface, similar to the color that develops when P4

is exposed to light. This color change may have

been an artifact from the microscope light used

to locate the particles.

The particles were difficult to locate. The moist

sediment surrounding the particles was not visibly changed. Some unsaturated samples (s = 0.64)

that were incubated at 20°C for 10 days were allowed to air-dry. Then a razor blade was used to

slice through the region where the particle was

planted. In each case, a small (1.8-mm), spherical

void with smooth sides was found. Sediment surrounding the void was slightly lighter in color

then the rest of the sediment. Previously we have

observed the formation of a dark, wet, phosphaterich halo around P4 particles in very dry sediments

(<10% moisture) (Racine et al. 1994) (Fig. 9). Sediments for this experiment were always moist;

therefore, water-soluble oxidation products could

freely diffuse away from the particle. Occasionally

a whiff of “smoke” was visible when the sediments were probed (Table 6). In almost all cases,

the sediment had to be sieved to find the P4 partiFigure 9. Void in dry sediment formed as P4

particle sublimed. Dark-colored hygroscopic

oxidation products are visible in the sediment

surrounding the void.

cle. In three instances, one at each temperature

tested, the particle was located without sieving,

and the sediment in direct contact with particle

was analyzed. P4 concentrations in this associated

sediment were 0.2 (4°C), 0.5 (15°C) and 6.6 μg/g

(20°C).

Residual mass of P4 particles. P4 particles were recovered from all samples incubated at 4°C. At this

low temperature, there were no significant reductions of the masses of P4 particles found, except

the particles isolated at the last sampling interval

(58 days) at the lowest moisture content (Fig. 10a),

where the mass for each particle was approximately half that of the original mass.

For samples incubated at 15°C (Fig. 10b), there

were no changes in particles incubated at saturation or above; however, there were significant reductions in particles incubated at the two lowest

moisture contents (s = 0.45 and 0.64) during 30

days of incubation. Following incubation for 57

days at 15°C, no P4 was detected in the samples at

the two lowest moisture contents. At s = 0.82, P4

loss was inconsistent. P4 was undetectable in

some samples after only one week of incubation

but was persistent in other samples for 38 days,

the last sample taken.

At 20°C (Fig. 10c) there were no changes in particles incubated at saturation or above; however,

there were significant reductions in particles incubated at the two lowest moisture contents (s =

0.45 and 0.64) after only one day of incubation.

Again at s = 0.82, P4 loss was inconsistent. P4 was

undetectable in some samples after only 10 days

of incubation but was persistent in other samples

for over 20 days (the last sampling interval).

Based on the data obtained in the laboratory,

persistence for 2-mm-diameter particles can be

estimated. In a previous study, most particles isolated from Eagle River Flats sediments were

smaller than 2 mm (Racine et al. 1993). For moist

sediments that were well below saturation (s <

0.6) at 20°C, 99.9% of the mass was lost in one day

and 99.999% was lost by 10 days. At 15°C, 99.9%

was lost by 30 days and >99.999% was lost by 60

days. Only a 50% loss was observed at 4°C at the

lowest moisture content after 56 days; thus, at this

low temperature, particles can persist for several

months or longer in unsaturated sediments. Since

no loss of mass was observed in saturated sediments at any temperatures, P4 particles can be

assumed to persist indefinitely in saturated sediments. For sediments that have moisture contents

slightly less than saturation, loss of P4 mass can

occur but at an unpredictable rate.
12

a. 4°C

b. 15°C

c. 20°C

10 –6

10 –5

10 –4

10 –3

10 –2

10 –1

10 0

10 1

0 10 20 30 40 50 60

s = 0.45

s = 0.64

s = 0.82

s = 1.00

s > 1.00

M/Mo

Time (days)

10 –6

10 –5

10 –4

10 –3

10 –2

10 –1

10 0

10 1

0 10 20 30 40 50 70

s = 0.45

s = 0.64

s = 0.82

s = 1.00

s > 1.00

M/Mo

Time (days)

60

10 –6

10 –5

10 –4

10 –3

10 –2

10 –1

10 0

10 1

0 10 20 30 40 50 60

s = 0.45

s = 0.64

s = 0.82

s = 1.00

s > 1.00

M/Mo

Time (days)

Figure 10. Residual mass (M) of white phosphorus particles found

following incubation in sediments at various moisture contents

and temperatures normalized to the average initial mass (Mo) of

white phosphorus.
The difference in length of persistence at 20°C

and 15°C in unsaturated sediments may be due to

oxidation. As discussed earlier, P4O10 is formed

by a branching-chain reaction (Dainton and Bevington 1946, Dainton and Kimberley 1950). The

reaction is slow unless the partial pressures of

oxygen and P4 vapor are within certain limits.

Since the lower limit is inversely proportional to

the pressure of P4, the vapor pressure at 15°C may

be below the critical pressure for a fast reaction. A

value for the critical pressure is difficult to predict

since it also depends on the diameter of the reaction vessel, in this case, the pore diameter. The

“wall” of the vessel terminates the reaction by

scavenging the oxygen atoms, which are the

chain centers. The vapor pressure at 20°C may be

high enough for a fast reaction. Since the oxidation of intermediate products (P4On, n = 2...9) to

P4O10 is highly exothermic, the temperature surrounding the particle will rise. Any rise in temperature near the surface of the P4 particle would

be accompanied by an increase in vapor pressure,

and therefore greater production of P4O10 and

more heat, until the supply of P4 falls below the

critical pressure as the particle diminishes in size.

Oxygen is not required for the loss of P4 in unsaturated conditions. The vapor pressure is high

enough that loss will occur as long as there is free

pore space and hence gas exchange between sediment air and the atmosphere. For example, when

field-contaminated sediments were dried at room

temperature under nitrogen and under air, the

loss was the same after 60 days (Walsh et al. 1993).

The formation of oxidation products in the pore

spaces surrounding P4 particles may actually

slow loss by forming a diffusion barrier.

In our laboratory experiment, sediment moisture was the more important of the two factors

tested in terms of persistence of P4 in ERF sediments. As a solid particle in saturated sediment, P4 is persistent. However, in sediment with free pore space, P4 can change to

the vapor phase and diffuse away or be oxi13

dized. Factors that slow the change of P4 from a

solid to a vapor are the same as those that limit

diffusion. Diffusion continues as long as there is

free pore space (Baver 1956). Free pore space,

however, is reduced by compaction or increased

wetness.

Monitoring sediment moisture and

temperature in Eagle River Flats

Methods

Eagle River Flats (ERF) is an 865-ha estuarine

salt marsh at the mouth of the Eagle River on Knik

Arm in upper Cook Inlet (Fig. 11). As described by

Racine et al. (1993), the main channel of the Eagle

River meanders generally through the middle of

ERF. On either side of the river, levees, mudflats,

marshes, meadows and intermittent and permanent ponds occur in zones determined by elevation, which in turn affects salinity, frequency of

tidal inundation and sedimentation rate. Permanent ponds along the edge of ERF are also influenced by freshwater influx.

The field experiment to monitor sediment temperature and moisture was conducted in a part of

ERF known as “Area C” (Fig. 12). Located on the

east side of the Eagle River, Area C includes a single large pond and several interconnected smaller

ponds and inlets (Fig. 13). The main pond (10 ha)

is bordered by bulrush and sedge marsh to the

east and south, mudflats to the west and deeper

small pools with bulrush marsh to the north.

Fresh water enters from the east edge, and three

distributary channels drain the area to the west.

Distributary channels also allow tidal inflow into

the pond during flooding high tides. The frequency of flooding during the summer depends on the

maximum height of the monthly series of peak

high tides. Monthly peak high tides above about

31 ft at Anchorage (or about 4.79 m mean sea

Figure 11. Aerial view looking south across Eagle River Flats.
14

level) will fill the pond basin. During the summer of 1994, flooding high tides occurred on May

24–27, June 23–25 and September 6–9.

Area C contains several targets and impact

craters and has been a focus of study for waterfowl mortality and sediment sampling (Racine et

al. 1992a,b,c, 1993). Most of the white phosphorus contamination was detected in the permanently flooded sections (Fig. 14).

Figure 12. Eagle River Flats, showing the location of Area C, as well

as the river, drainage gullies and intermittent and permanent ponds.

Figure 13. Area C, showing bulrush marsh, permanent ponds, intermittent ponds, mudflats and levees.

The gradual change in elevation along the

east–west transect from the main pond in Area C

to the levee next to the Eagle River results in a

gradient in the duration of exposure of the sediments to air (i.e. lower elevations are covered

with standing water for a longer time than higher elevations). Exposed sediments have the potential to become unsaturated during periods

without standing water. In this study, sediment

       



     

     











































  







 

 

 





















































 









 

























































































N

Permanent Ponds

Intermittent Ponds 

Drainage Gullies

 

0 500 1000 m

Upland

Upland

Knik Arm

Area C
15

Upland

0 200 m Eagle

River

Not Detected

< 0.001 mg/kg

0.001-0.099

0.1-9.99

> 10

Permanent Ponds

Intermittent Ponds

Drainage Gullies

N

Figure 14. Sampling locations in Area C and results of sediment analyses for white phosphorus.

moisture and temperature at ten sites along the

east–west transect (Fig. 15, 16 and 17) were monitored to see if conditions are conducive to natural

attenuation of P4 during some part of the summer.

Universal Transverse Mercator coordinates and

elevations for the ten study sites in Area C are given in Table 7. The overall length of the transect

was 636 m, with a total elevation change of 0.52 m

(Fig. 16). Water quality measurements were made

in May when the ponds were full (Fig. 18), and

vegetation was recorded in August (Fig. 18).

In addition, P4 particles, produced in the laboratory as described above, were planted at each

site and recovered at the end of the summer to see

if the mass of the P4 particles decreased. Details of

the procedures used are given in Appendix B.

Results

Site characteristics. The conductivity of the water in the ponded sites increased towards the

west (towards the river) (Table 8). The water at

each site was slightly alkaline, and reducing conditions (i.e. low redox potentials) were found in

the sediments at each site.

Vegetation varied significantly between sites

(Table 8). The permanently flooded site (site 1)

had a dense stand of mare’s tail (Hippurus tetragona) (Fig. 19). The intermittent pond sites (sites

2–5) were mostly bare, with a few arrowgrass

seedlings and glasswort (Fig. 20). Mudflat sites

(6 and 7) were sparsely vegetated with alkali

grass and arrowgrass (Fig. 21). The density of

vegetation was higher at the mudflat site closest
16

a. In May 1992, when ponds were full.

Figure 15. Aerial view of Area C.

0 200 m

N

Upland

Permanent Ponds

Intermittent Ponds

Eagle River

Drainage Gullies

10

9 8 7 6 5 4 3 2 1

883

Miller's

Hole

b. In August 1994, when ponds were low. The transect is

visible as a thin line running east–west from a permanently

flooded zone to the east through the intermittent ponded area,

across the mudflat zone to the levee adjacent to the Eagle River.

Figure 16. Locations of study sites in Area C. Sediment temperature and

moisture were monitored and white phosphorus particles incubated between May and August at sites numbered 1 to 10. Sites 883 and Miller’s

Hole are field-contaminated sites which were sampled to determine P4 concentrations.
17

Table 7. UTM coordinates and elevations of sites in Area C where sediment

temperatures and moisture levels were monitored and white phosphorus

particles incubated, May–August, 1994.

Distance Elev. change

UTM coordinates between Elev. between

Field site Easting Northing sites (m) (m) sites (m) Site descriptor

1 355,171.6 6,801,180.4 4.70 Permanently saturated

2 355,105.8 6,801,192.5 66.9 4.74 0.04 Intermittent pond area

3 355,013.4 6,801,197.7 92.5 4.78 0.04 Intermittent pond area

4 354,917.7 6,801,208.1 96.3 4.80 0.02 Intermittent pond area

5 354,893.5 6,801,212.1 24.5 4.85 0.05 Intermittent pond area

6 354,836.9 6,801,216.9 56.8 4.87 0.02 Mudflat

7 354,713.4 6,801,230.2 124.2 4.92 0.05 Mudflat

8 354,593.0 6,801,243.0 121.1 4.99 0.07 Mudflat

9 354,553.3 6,801,247.3 39.9 5.06 0.07 River levee

10 354,539.1 6,801,248.7 14.3 5.22 0.16 River levee

a. May. b. August.

Figure 18. View looking west along transect across an intermittent pond area.

Figure 17. Study site in an intermittent pond area showing the datalogger with a solar panel mounted on a tripod. Data for sediment moisture and temperature were recorded every 10 minutes and averaged hourly from May 25

to August 26. Lath surrounds area where P4 particles were

planted. Tensiometers and the piezometer are also visible.
Table 8. Water quality measurements and vegetation at sites in Area C where

sediment temperatures and moisture levels were monitored and white phosphorus particles incubated, May–August, 1994.

Water quality (May 1994)

Depth Cond. Redox

Site (cm) (mmho/cm) (mvolts) pH Vegetation (August 1994)

1 12 17.1 –177 7.7 Mare’s tail (Hippurus tetraphylla)

2 8 17.6 –169 8.3 Unvegetated

3 4.5 18.6 –182 8.5 1% arrowgrass (Triglochin maritima) seedlings

4 2 24 –111 8.6 1% glasswort (Salicornia europea)

5 1 24 –55 8.7 1% glasswort, arrowgrass seedlings

6 0 Alkali grass (Puccinelia hultenii), arrowgrass

7 0 Alkali grass, arrowgrass, 40% bare ground

8 0 Goose tongue (Plantago maritima), alkali grass,

arrowgrass, kenipod (Atriplex gmelini),

cinquefoil (Potentilla egedii), 20% bare ground

9 0 Beach rye (Elymus arenarius), cinquefoil

10 0 Goose tongue, beach rye (40%), cinquefoil

18

Figure 19. Permanently flooded site (site 1)

with a dense stand of Hippurus tetragona.

Figure 20. Site in an intermittent pond in August.

The surface is cracked and covered with precipitated salt.

A few glasswort and arrowgrass seedlings punctuate the

mostly bare sediment.

to the river levee (site 8) with the addition of

goose tongue, kenipod and cinquefoil to the

stand of alkali grass and arrowgrass. The two

river levee sites were densely vegetated with a

tall stand of beach rye (Fig. 22).

Gravimetric moisture content measurements

were obtained in May (Table 9) while sediments

were saturated at the pond and mudflat sites.

River levee sediments did not appear to be saturated when sampled. Samples were taken again

in June just prior to a flooding high tide, then

again in August. At the two later sampling times,

the moisture contents were less than in May at all

sites except the permanently flooded site. The dry

bulk density generally increased with depth,

mostly likely due to consolidation from freeze–

thaw cycles, earthquakes, wet–dry cycles etc. Tensiometer and moisture probe resistance measurements were plotted vs. moisture content for

depths of 10 and 25 cm (Fig. 23) to determine the

moisture contents for saturation for undisturbed

sediments under field conditions. Both measurements indicate saturation for sediments with

moisture contents above 40% (dry weight basis) at

10 cm and above 35% at 25 cm. These moisture

contents are lower than that determined for the

homogenized sediment in the laboratory, most

likely due to consolidation in the field.

The highest temperatures were measured at a

depth of 5 cm, and temperatures at 10 cm were

only slightly less than at 5 cm (Fig. 24). The average temperatures at 5 cm deep were between 16

FPO
19

and 17°C for the ponded and mudflat sites and

15°C on the river levee. The date of the maximum

average hourly temperature at 5 cm occurred in

June in the ponded sites and in June or July in the

mudflat sites (Table 10). Each of these days had

over 10 hours of sunshine (NOAA 1994). The average temperatures were lowest at 30 cm deep (15°C

for ponded and mudflat sites and 13°C for levee

sites), and the date of maximum temperature occurred later than at shallower depths.

The time periods when sediments were unsaturated are indicated by an increase in the moisture probe resistances (Fig. 25 and 26). The length

of time the top 5 cm of sediment was unsaturated

increased with increasing elevation (Fig. 27).

Over the time period monitored, site 1, with the

lowest elevation, was always saturated, while site

10, the highest elevation, was always unsaturated

(Table 10). Unsaturated sediments were detected

at 5 cm deep at the two intermittent ponded site

Figure 21. Site on a mudflat vegetated with alkali

grass and arrowgrass.

Figure 22. Site on a river levee with a tall stand of

beach rye.

* Site 3 on Aug. 20, Sites 7, 8, 9 and 10 on Aug. 22, Sites 2, 4 and 5 on Aug. 23, Site 1 on Aug. 24.

Dry bulk

Depth Moisture content (% dry weight basis) density*

Site (cm) May 14 May 19 June 21 August* (g/cm3)

Permanently flooded

1 5 124 119 107 0.72

1 10 61 88 0.87

1 20 59 44 34 35 1.41

1 30 39 39 33 33 1.53

Intermittent pond

2 5 56 78 64 46 1.18

2 10 61 48 39 1.27

2 20 42 47 39 33 1.32

2 30 36 36 30 31 1.38

3 5 45 63 48 42 1.21

3 10 49 48 38 1.25

3 20 44 46 40 36 1.27

3 30 35 41 30 30 1.40

4 5 63 62 42 37 1.27

4 10 48 50 38 37 1.24

4 20 42 46 37 34 1.28

4 30 42 41 34 29 1.39

5 5 54 62 43 37 1.28

5 10 49 48 43 35 1.25

5 20 42 39 37 34 1.32

5 30 44 38 34 31 1.41

Mudflat

6 5 50 44 40 35 1.34

6 10 42 41 35 35 1.36

6 20 42 41 36 33 1.38

6 30 39 38 36 34 1.31

7 5 48 49 38 40 1.26

7 10 46 41 39 35 1.32

7 20 39 38 33 33 1.40

7 30 42 37 34 34 1.31

8 5 45 48 36 37 1.19

8 10 41 41 34 30 1.25

8 20 38 39 32 29 1.38

8 30 38 37 32 31 1.38

River levee

9 5 35 35 30 31 1.19

9 10 31 36 30 29 1.11

9 20 31 36 30 27 1.16

9 30 31 33 30 29 1.39

10 5 36 36 31 30 1.30

10 10 35 35 29 25 1.26

10 20 32 32 27 26 1.21

10 30 31 32 28 29 1.35

Dry bulk

Depth Moisture content (% dry weight basis) density*

Site (cm) May 14 May 19 June 21 August* (g/cm3)

Table 9. Measurements of moisture contents obtained in May, June and August 1994, and measurements

of dry bulk density obtained in August 1994.
0

10

20

30

40

0.25 0.30 0.35 0.40 0.45 0.50

10 cm Depth Resistance

Tension

Moisture Probe Resistance (kohms)

Moisture Content (dry weight basis)

0

0.2

0.4

0.6

0.8

1.0

Figure 23. Moisture probe resistance and tensiometer readings obtained along the transect in Area C.

5

10

15

20

25

5 cm

10 cm

20 cm

30 cm

Temperature (°C)

25

May Jun Jul Aug

10 20 10 20 10 20

5

10

15

20

25Temperature (°C)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

0

5

10

15

20

25

30

35

0.25 0.30 0.35 0.40 0.45 0.50

25 cm Average Depth

Tension (cbars)

Moisture Content (dry weight basis)

Resistance

Tension

a. Site 1—Permanently flooded. b. Site 2—Intermittent pond.

5

10

15

20

25Temperature (°C)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

5

10

15

20

25Temperature (°C)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

c. Site 3—Intermittent pond. d. Site 4—Intermittent pond.

Figure 24. Daily (24-hour average) temperatures at 5, 10, 20 and 30 cm deep at each site.

20
21

5

10

15

20

25

Temperature (°C)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

5

10

15

20

25Temperature (°C)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

e. Site 5—Intermittent pond. f. Site 6—Mudflat.

5 cm

10 cm

20 cm

30 cm

5

10

15

20

25Temperature (°C)

25

May Jun Jul Aug

10 20 10 20 10 20

g. Site 7—Mudflat.

5

10

15

20

25

Temperature (°C)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

h. Site 8—Mudflat.

Figure 24 (cont’d).

closest to site 1 (sites 2 and 3) starting August 12

and July 31, respectively. The remaining mudflat

and intermittent ponded sites became unsaturated at 5 cm deep in June but were rewetted by the

flooding high tides of June 23–25. Because of this

rewetting, most of these sites were saturated

during the part of the summer when the potential solar radiation is at its maximum. Unsaturated conditions were detected again in July and

persisted over the period monitored. Unsaturated conditions were detected later with increasing depth. Unsaturated conditions were detected

down to 30 cm deep at sites with elevations of

≥4.8 m (sites 4–10) (Fig. 25, Table 10).

Air-entry pressure. Based on the moisture characteristic curve for a sample collected from the

intermittent pond area (Fig. 28), the air-entry

pressure was approximately 5 cbars for this finegrained sediment. In the field a pressure of this

magnitude can occur by a drop in water table

such that the equivalent head pressure between

the surface of the sediment and the surface of the

water table is 5 cbars. By expressing pressure in

units of “cm of water” (10.2 cm of water = 1 cbar),

we can estimate that a drop in the water table of

51 cm would result in air entry or desaturation of
22

5

10

15

20

25

Temperature (°C)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

5

10

15

20

25

Temperature (°C)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

i. Site 9—River levee. j. Site 10—River levee.

Figure 24 (cont’d). Daily (24-hour average) temperatures at 5, 10, 20 and 30 cm deep at each site.

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20 25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

a. Site 1—Permanently flooded. b. Site 2—Intermittent pond.

Figure 25. Daily (24-hour average) moisture probe resistance at 5, 10, 20 and 30 cm deep at each site.
23

Table 10. Maximum, average, median and minimum temperatures and periods below saturation

measured at 5, 10, 20 and 30 cm deep at each site between May 25 and August 26 or 27, 1994.

Date of

Maximum maximum Average Minimum Hours > 20°C

temperature temperature temperature temperature Hours Dates below and

Site (°C) (°C) (°C) (°C) > 20°C saturation unsaturated

5 cm deep

1 23 June 15 20:00 17 11 191 none 0

2 24 June 14 20:00 17 8.9 357 Aug. 12–end* 44

3 26 June 30 18:00 16 6.8 392 July 31–end 88

4 26 June 30 18:00 16 6.6 381 June 18, July 20–21, July 28–end 150

5 27 June 30 17:00 16 8.1 412 June 18, July 20–end 169

6 26 July 29 18:00 17 7.2 491 June 18–20, July 20 – end 258

7 26 June 14 18:00 16 7.3 354 June 18–21, July 15–end 217

8 24 June 14 18:00 16 6.7 239 June 12–24, July 9–end 209

9 21 July 29 18:00 15 5.5 39 May 31–June 24, June 27–end 39

10 20 Aug. 3 17:00 15 6.3 30 May 31–end 0

10 cm deep

1 21 June 15 23:00 16 10 47 none 0

2 22 June 14 22:00 17 10 193 Aug. 18–end† 0

3 22 June 30 21:00 16 10 175 Aug. 16–end 23

4 23 June 30 20:00 16 9.5 194 July 29–end 88

5 23 June 30 20:00 16 9.8 194 July 29–end 103

6 23 June 15 20:00 16 8.6 283 June 18–20, July 20 – end 186

7 23 June 15 19:00 16 9.0 232 June 18–21, July 15–end 159

8 21 June 15 20:00 16 9.0 49 June 12–24, July 9–end 49

9 18 Aug. 3 20:00 14 7.5 0 May 31–June 24, June 27–end 0

10 19 July 30 20:00 14 7.6 0 May 31–end 0

20 cm deep`

1 19 June 16 02:00 16 9.0 0 none

2 19 July 16 24:00 16 9.4 0 none 0

3 19 July 1 23:00 16 9.2 0 none 0

4 19 July 1 24:00 16 9.1 0 Aug. 8–end† 0

5 20 July 1 24:00 16 9.2 10 Aug. 1–end 0

6 20 Aug. 10 22:00 16 9.2 3 July 30 – end 3

7 19 Aug. 10 22:00 16 9.2 0 June 20–21, July 16–end 0

8 19 June 15 23:00 16 8.7 0 June 12–24, July 9–end 0

9 17 Aug. 10 22:00 14 7.3 0 May 31–June 24, June 27–end 0

10 17 Aug. 10 23:00 14 7.0 0 May 31–end 0

30 cm deep

1 17 July 2 07:00 15 8.1 0 none 0

2 18 July 16 04:00 15 8.8 0 none 0

3 18 Aug. 19 02:00 15 8.5 0 none 0

4 18 Aug. 11 03:00 15 8.3 0 Aug. 13–end 0

5 18 Aug. 11 02:00 15 8.4 0 Aug. 4–end 0

6 18 Aug. 19 02:00 15 8.8 0 Aug. 5–end 0

7 18 Aug. 11 03:00 15 8.9 0 July 17–end 0

8 18 Aug. 11 02:00 15 9.0 0 June 15–24, July 11–end 0

9 16 Aug. 11 04:00 13 7.1 0 May 31–June 24, June 29–end 0

10 16 Aug. 11 04:00 13 6.7 0 May 31–end 0

* End of time period in which data were recorded (Aug. 26 for Sites 4-10, and Aug. 27 for Sites 1–3). Flooding tide

occurred on Sept. 6.
24

25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

c. Site 3—Intermittent pond. d. Site 4—Intermittent pond.

e. Site 5—Intermittent pond. f. Site 6—Mudflat.

Figure 25 (cont’d). Daily (24-hour average) moisture probe resistance at 5, 10, 20 and 30 cm deep at each site.
25

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

25

May Jun Jul Aug

10 20 10 20 10 20

0

0.2

0.4

0.6

0.8

1.0

Resistance (kohms)

5 cm

10 cm

20 cm

30 cm

Figure 25 (cont’d).

g. Site 7—Mudflat.

h. Site 8—Mudflat.

i. Site 9—River levee. j. Site 10—River levee.
26

30

20

10

0

25 

1.0

0.8

0.6

0.4

0.2

Temperature (°C)

Resistance (kohms)

Temperature

Resistance

0

May Jun Jul Aug 10 20 10 20 10 20

30

20

10

0

25 10 20

1.0

0.8

0.6

0.4

0.2

Temperature (°C)

Resistance (kohms)

Temperature

Resistance

0

May Jun Jul Aug

10 20 10 20

a. Site 1—Permanently flooded.

30

20

10

0

25 

1.0

0.8

0.6

0.4

0.2

Temperature (°C)

Resistance (kohms)

Temperature

Resistance

0

May Jun Jul Aug

10 20 10 20 10 20

c. Site 3—Intermittent pond.

30

20

10

0

25 

1.0

0.8

0.6

0.4

0.2

Temperature (°C)

Resistance (kohms)

Temperature

Resistance

0

May Jun Jul Aug 10 20 10 20 10 20

30

20

10

0

25 

1.0

0.8

0.6

0.4

0.2

Temperature (°C)

Resistance (kohms)

Temperature

Resistance

0

May Jun Jul Aug 10 20 10 20 10 20

e. Site 5—Intermittent pond.

30

20

10

0

25 

1.0

0.8

0.6

0.4

0.2

Temperature (°C)

Resistance (kohms)

Temperature

Resistance

0

May Jun Jul Aug

10 20 10 20 10 20

30

20

10

0

25 

1.0

0.8

0.6

0.4

0.2

Temperature (°C)

Resistance (kohms)

Temperature

Resistance

0

May Jun Jul Aug

10 20 10 20 10 20

g. Site 7—Mudflat.

30

20

10

0

25 

1.0

0.8

0.6

0.4

0.2

Temperature (°C)

Resistance (kohms)

Temperature

Resistance

0

May Jun Jul Aug 10 20 10 20 10 20

Figure 26. Hourly measurements of sediment temperature (°C) and moisture probe resistance (kohms) at 5 cm

deep for sites 1–10.

h. Site 8—Mudflat.

f. Site 6—Mudflat.

d. Site 4—Intermittent pond.

b. Site 2—Intermittent pond.
27

Temperature (°C) 30

20

10

0

25

May Jun Jul Aug

1.0

0.8

0.6

0.4

0.2

0

Temperature

Resistance

Resistance (kohms)

10 20 10 20 10 20

30

20

10

0

25

May Jun Jul Aug

1.0

0.8

0.6

0.4

0.2

0

Temperature

Resistance

Temperature (°C)

Resistance (kohms)

10 20 10 20 10 20

the surface sediments. The actual air-entry value

in the field will vary with the heterogeneity of

the sizes of sediment pores. Sediment with

cracks and channels (macropores) would have a

lower value (Hemond and Chen 1990).

Water surface elevations. Water surface elevations were recorded three times using piezometers. The first measurement was seven hours after a flooding high tide on May 24. The second

measurement was on June 20, three and one-half

weeks after a flooding tide and three days prior

to the next series of flooding tides. The last measurement was on August 19, seven and one-half

weeks after a flooding tide and two and one-half

weeks before the next series of flooding high

tides.

In May, water was present in all piezometers

(Fig. 29). The water surface elevation was above

or within 1 cm of the surface of the sediments at

sites 1–7. At site 8, the mudflat site near the river

levee, water was 20 cm below the sediment surface, and at site 9, on the river levee, it was 33 cm

below the sediment surface. Between the May

and June measurements, the water surface elevations dropped significantly at all sites except the

permanently flooded site (site 1). On June 20, piFigure 26 (cont’d).

0

20

40

60

80

100

4.6 4.8 5.0 5.2

y = –799.47 + 172.53x R = 0.96438 

Number of Days

Elevation (m)

Figure 27. Number of days that sediments at 5 cm

deep were unsaturated vs. elevation.

46

50

54

58

62

0 20 40 60 80 100

Moisture Content (%)

Pressure (cbars)

Figure 28. Moisture retention curve for a sediment

sample collected 20 m south of the transect between

sites 3 and 4 in the intermittent pond.

i. Site 9—River levee. j. Site 10—River levee.
28

4

5

6

3.546 3.548 3.550 3.552 x 105

Elevation (m)

UTM Easting (m)

May 24

June 

20

Aug 

19 

Piezometer 

Sediment 

Surface 

Permanent Pond

97 5 8 43 1 6 2

Site Number

Mudflat Intermittent Pond

River 

Levee

Figure 29. Water surface elevations (dashed lines)

measured in piezometers at sites 1–9 on May 24, June

20 and August 19.

ezometers at sites 5–9 were dry, indicating that the

water surface elevation was greater than 75 cm

below the sediment surface at each of the mudflat

and river levee sites, and greater than 68 cm below

for site 5 at the edge of the intermittent pond. East

along the transect across the intermittent ponded

area, water surface elevations were 46, 21 and 4

cm below the sediment surface at sites 4, 3 and 2,

respectively. At the permanently flooded site, the

water surface elevation in the piezometer was 14

cm above the sediment surface and 4 cm higher

than the pond surface elevation. At the time of the

last measurement on August 19, piezometers at

sites 5–9 were dry, and the water surface elevations were lower at the remaining sites. The depth

to water was 75, 68 and 52 cm at sites 4, 3 and 2,

respectively.* Based on the moisture retention

curve, the water surface elevation at each of these

sites is sufficiently below the sediment surface to

desaturate the surface sediments. At site 1 the water surface elevation inside the piezometer was

again 4 cm higher than the pond surface.

Tensiometer measurements were taken at six

sites at the same time as piezometer measureTable 11. Tensiometer measurements at 10 and 25

cm deep taken at the same time as piezometer

measurements of water surface.

Depth* (cm) to

water surface Tension (cbars)

Site Date in piezometer 10 cm deep* 25 cm deep*

Intermittent Pond

3 June 20 21 4 4

3 Aug. 19 68 10 10

4 June 20 46 4 4

4 Aug. 19 75 30 20

5 June 20 >68 5 4

5 Aug. 19 >68 28 16

Mudflat

6 June 20 >77 9 4

6 Aug. 19 >77 27 21

7 June 20 >76 10 8

7 Aug. 19 >76 25 23

River Levee

9 June 20 >88 23 20

9 Aug. 20 >88 38 34

*Depth from sediment surface.

ments. The tension exceeded 5 cbar, the estimated

air-entry value, at each site in August when the

depth to water surface was over 50 cm, indicating

that the surface sediments were below saturation

(Table 11).

These data give some insight into the relationship between surface water and ground water

along the transect and their influence on moisture

levels in the surface sediments. At site 1, the permanently flooded site, upwelling of ground water

appears to be high enough to prevent drying by

evaporation. At the remaining sites, saturation of

the surface sediments appears to be primarily the

result of flooding high tides. Following a flood

event, a combination of downward seepage and

evaporation loss dewaters the surface sediments.

Measurement of water level at permanently flooded

site. The elevation of the pond surface at site 1 was

monitored hourly from June 15 to August 27 using

an Ultrasonic Depth Gage interfaced with a datalogger. Given that the elevation of site 1 is 4.7 m,

the sensor indicates that the 24-hour average water depth at this site was 7.9 cm on June 15 and

declined by approximately 0.5 cm per day until

June 21(Fig. 30). Then the series of flooding tides

on June 23–25 deepened the pond to 25 cm. A full

month passed before water levels returned to preflood levels. The first week after the last flood

event (June 25–July 2), the drop averaged 1.5 cm

per day. Once the pond surface elevation reached

4.85 m, which is the elevation of site 5 at the edge

of the pond, the drop slowed to 0.5 cm per day until the water depth was 6 cm on July 21. The pond

* Data obtained from Beth Nadeau indicated that water surface elevation continued to drop after our August measurements. On September 3, piezometers were dry at a depth of

80 cm in the intermittent pond near site 3.
level then fluctuated over the remaining time

monitored, with the lowest water depth (3 cm) recorded on August 18.

Residual white phosphorus. On August 22–23, five

samples were removed from each site to examine

the physical appearance of P4 particles. When particles were found, they appeared to be unchanged

(i.e. they were lustrous in appearance). In the intermittent ponded sites, significant surface cracking of the drying sediment was observed. For all

samples that were located within or adjacent to

cracks, the P4 particle was not found. In one sample, a spherical void space with a diameter of 1.8

mm (the original diameter of the P4 particle) was

observed.

The mass of P4 in each of the five replicate samples remaining at each site on August 30 was normalized to the initial mass and plotted vs. site (Fig.

31). There was no change in the mass of P4 particles removed from the permanently flooded site

(site 1). The results for the intermittent ponded

sites and mudflat sites were similar to those observed in the laboratory for the samples incubated

at degree of saturation of 0.82 at 15 or 20°C. The

mass of P4 for at least one replicate was reduced by

several orders of magnitude. According to a

Kruskal–Wallis test (a nonparametric equivalent of

one-way ANOVA), the length of time in which unsaturated conditions existed had a significant effect on the residual mass of white phosphorus

found at each site (p = 0.0027) (Table 12). For those

sites where unsaturated conditions were detected

(sites 2–10), the length of time sediments were unsaturated and sediment temperatures were greater

than or equal to 20°C at 5 cm deep also had a significant effect but less so (p = 0.0234) (Table 12).

Resampling of field-contaminated sites

Method

In August 1992 we examined the variability in

P4 contamination around a highly contaminated

site in the intermittent pond of Area C (Racine et

29

Figure 31. Residual P4 found in five replicate samples normalized to initial mass from each site.

Site 1 is permanently flooded, sites 2–5 are intermittently flooded, sites 6–8 are on the mudflat,

and sites 9–10 are on the river levee.

101

100

10– 1

10– 2

10– 3

10– 4

10– 5

Site 1 2 3 4 5 6 7 8 9 10

M/Mo

Figure 30. Average (24-hour) pond surface elevation at site 1.

4.7

4.8

4.9

5.0

Water Surface Elevation (m)

20 30 10 20 30 10 20 30

June July August
Table 12. Results of Kruskal–Wallis test to determine if a) the

length of time sediments were unsaturated at 5 cm deep or b) the

length of time unsaturated and temperature greater than or

equal to 20°C had an effect on residual WP found at each site.

Number of days

unsaturated Site Mean rank

0 1 44.8

16 2 35.8

28 3 28.6

34 4 20

40 5 26.4

42 6 21.5

48 7 32.4

63 8 24.4

87 9 6

89 10 15.1

H = 25.2; p = 0.0027.

Number of days

unsaturated and

T>20°C Site Mean rank

0 10 21.5

39 9 1

44 2 6

88 3 34.2

150 4 27.8

169 5 20

209 8 26.4

217 7 23.6

258 6 32.4

H = 17.7; p = 0.0234.

al. 1993). Samples were taken at 1-m intervals out

to 5 m along eight axes around the center point

(Site 883) (Fig. 16). P4 particles were isolated and

measured from the sample collected at the center

point (Racine et al. 1993). During 1993, Anchorage experienced an unusually warm and dry

summer, and this area was above the water level

through June and July 1993. We revisited this site

on August 19,1994, and repeated the close-interval sampling to determine if the pattern and level

of contamination had changed.

In addition, samples were collected from the

crater (Miller’s Hole) (Fig. 16) produced by the

detonation of an 81-mm P4 smoke round in May

1992. Samples were taken from the rim and center of the crater. Details of the procedures used to

collect the samples are given in Appendix B.

Results

Sampling for white phosphorus contamination by various agencies continued at Eagle River

Flats in 1994 (Racine and Cate 1995). Any white

phosphorus detected by these field sampling efforts has persisted in ERF since at least February

1990, when training with white phosphorus munitions was suspended at Eagle River Flats.

White phosphorus continues to be detected at

high concentrations in the permanent ponds of

Area C. In contrast, intermittent ponded areas

and mudflats tend to have low concentrations or

undetectable levels of white phosphorus. For example, the transect described above passed

through a heavily cratered area (10–25% crater

cover), yet no white phosphorus was detected in

the mudflat and river levee samples, and trace

amounts (near or below the certified reporting

limit) were found in the intermittent ponded

area. This pattern of contamination indicates that

white phosphorus may be persistent only in the

permanently flooded areas. However, one site in

the intermittent pond of Area C (Site 883) was

found in 1992 to have very high concentrations of

white phosphorus (>200 μg/g) (Fig. 16). From

tide table data for 1990 to 1994 (Fig. 32) and the

assumption that the flats flooded every time the

predicted high tide for Anchorage was greater

than 31 ft, this site was mostly likely exposed to

air each summer except for 1991 when the flats

flooded each month. The longest period of exposure was in 1993, when Anchorage also experienced an unusually warm, dry summer. Given

an elevation of 4.77 m and the drying data obtained along the transect described above, the

moisture content of the surface sediments probably decreased below saturation during the summer of 1993. The water depth was approximately

8 cm when the site was sampled in August 1992,

and the site was subaerially exposed when sampled in August 1994 (Fig. 33).

When sampled in 1992 and 1994, sediment

was taken at 1-m intervals in a radial pattern

(Fig. 34). Samples taken in 1994 showed that the

moisture content ranged from 40 to 46% on a dry

weight basis. The patterns of contamination for

August 1992 and August 1994 (Fig. 34) show that

there is a reduction in the number of samples in

the highest-concentration group (>10 μg/g),

from four to one (Fig. 35). There is also an increase in the number of samples in the lowestconcentration group (<0.001 μg/g), from 15 to 25.

The results were compared using a sign test for

paired observations. If the differences between

30
31

31

32

33

34

High Tide (ft)

10 Weeks

May Jun Jul Aug

10 20 10 20 10 20

Sept Oct

10 20 10 20 10 20

8 Weeks

31

32

33

34

High Tide (ft)

May Jun Jul Aug

10 20 10 20 10 20

Sept Oct

10 20 10 20 10 20

a. 1989. b. 1990.

31

32

33

34

High Tide (ft)

May Jun Jul Aug

10 20 10 20 10 20

Sept Oct

10 20 10 20 10 20

May Jun Jul Aug

10 20 10 20 10 20

Sept Oct

10 20 10 20 10 20

31

32

33

34

High Tide (ft)

9 Weeks

c. 1991. d. 1992.

May Jun Jul Aug

10 20 10 20 10 20

Sept Oct

10 20 10 20 10 20

11 Weeks

31

32

33

34

High Tide (ft)

e. 1993.

Figure 32. Frequency of flooding tides, 1989–1994,

assuming that the flats flooded each time Anchorage

tide tables predicted a high tide of 31 ft or greater.

Sources of uncertainty about this field-contaminated site include the date it was contaminated, the

type of round that produced the contamination

(mortar or howitzer), where the round exploded,

the type of fuse (point detonating or other) and the

initial white phosphorus concentration. However,

we do have this information for another site in the

intermittent pond of Area C, a site where unexploded ordnance (UXO), an 81-mm mortar round

the concentrations found in 1992 and 1994 were

due solely to random error, the observation of an

increase in concentration would be just as likely

as an observation of a decrease. Of the 41 pairs

compared, 22 showed a decrease, 7 showed an increase, and 12 were below the detection limit (Fig.

36). The number of samples showing a decrease

between 1992 and 1994 is significant at the 0.05

significance level.
32

6801190

6801188

6801186

6801184

6801182

6801180

6801178

354976 354978 354980 354982 354984 354986 354988

East (m)

North (m)

WP Concentration

(μg/g)

> 10

0.1-9.9

0.001-0.099

< 0.001

a. 1992

6801190

6801188

6801186

6801184

6801182

6801180

6801178

354976 354978 354980 354982 354984 354986 354988

East (m)

North (m)

WP Concentration

(μg/g)

> 10

0.1-9.9

0.001-0.099

< 0.001

b. 1994

b. 1994.

a. 1992.

Figure 34. Pattern of WP contamination

found during August 1992 and August

1994 around a site in an intermittently

flooded pond in Area C.

Figure 33. Site 883, in the intermittent pond of Area

C, where high concentrations of white phosphorus

were detected in 1992.
33

Site Number

883

0.0001

22 Decrease

12 Below Detection Limit

7 Increase

WP Concentration (μg/g)

972

977

982

974

998

997

1001

1005

1002

1006

975

984

988

990

995

1007

976

980

1003

978

0.001 0.01 0.1 1.0 10 100 1000

1992

1994

that contained white phosphorus, was exploded

on 20 May 1992. The UXO was exploded for the

safety of researchers. Since the shell of this UXO

was extremely corroded, the filler material was

not identified as white phosphorus until a dense

white cloud formed when the round detonated

(Fig. 37). The crater produced by this explosion

has been called “Miller’s Hole” (Fig. 38) for the

EOD team member who detonated the round.

The crater produced has provided an opportunity for monitoring the persistence of white phosphorus in an intermittent pond. The elevation of

the rim of the crater is 4.77 m, while the center is

only 4.45 m. Because of this elevation difference,

the rim is subaerially exposed for longer periods of

time than the center. The initial white phosphorus

concentrations in the center were over 2000 μg/g

(Table 13). Over the summer of 1992, the concentration in the center appears to have decreased by

one order of magnitude (approximately 90%). An30

20

10

0

> 10 0.1-9.9 0.001-0.099 < 0.001

White Phosphorus Concentration (μg/g)

Number of Samples

1992

1994

Figure 35. Number of samples in different concentration ranges in 1992 and 1994.

Figure 36. Comparison of WP concentrations found in 1992

and 1994 around site 883, an intermittent ponded site in

Area C.
34

Figure 37. Detonation of a UXO, an 81-mm mortar

round that contained white phosphorus, on May

20, 1992.

Figure 38. Crater, known as “Miller’s Hole,” produced by detonation of a UXO that contained

white phosphorus. White phosphorus concentrations in sediment from the rim and bottom of the crater have been measured each spring and fall since the

explosion.

other order-of-magnitude change (approximately

99% decrease) has taken two years. Even with the

uncertainty associated with subsampling error,

the general trend has been a decrease in P4 concentration in the crater center since June 1992,

with the majority of the change taking place over

the summer. The white phosphorus concentration in the crater rim has changed in a different

pattern. The initial white phosphorus concentrations were very high (980 μg/g). After 29 days the

decrease was greater than 99.9% and after 93 days

was greater than 99.999%. When sampled in June

1993 and May 1994 there has been an apparent increase in concentration from the previous August. Most likely some mixing of sediment may

occur when the crater is underwater or by slight

shifting of the ice at this site. When last sampled

in August 1994, the surface sediment was exposed and cracked. White phosphorus was not

detectable in the rim of the crater, showing that

white phosphorus did not persist during subaerial exposure during the summer.

CONCLUSIONS

In laboratory experiments where P4 particles

were incubated under constant moisture contents (degree of saturation = 0.45, 0.64, 0.82, 1 or

>1) and temperatures (4, 15 or 20°C), P4 particles

were persistent at moisture contents at or above

saturation. P4 particles incubated well below saturation (s = 0.45 or 0.64) were lost within 24

hours at 20°C and within 30 days at 15°C, but

they persisted over the time interval tested (approximately 60 days) at 4°C. For samples incubated slightly below saturation (s = 0.82), the reTable 13. White phosphorus concentrations

found at Miller’s Hole, a crater produced by

the detonation of a UXO (81-mm mortar

smoke round) in the intermittent pond of

Area C.

Date Days since Concentration (μg/g)

sampled explosion Center Rim

May 20, 92 0 2400 980 (silt), 34,500

(orange residue)

June 18, 92 29 5600 0.237

Aug. 21, 92 93 184 0.00427

June 23, 93 399 187 0.0175

Aug. 27, 93 464 81.5 0.00177

May 16, 94 726 49.5 34.1*

Aug. 30, 94 832 9.5 <0.00088

* Crater under water. Sediment very fluid.
sults were variable, with significant loss in some

samples and no change in other samples.

In field experiments where P4 particles were

incubated at a depth of 5 cm in salt marsh sediments, P4 was persistent in the permanently

flooded area, but there was loss of P4 in areas

with unsaturated sediments. Unsaturated conditions were detected down to 30 cm at monitoring

sites on the river levee and mudflat and two intermittent pond sites, indicating that loss of P4 is

possible at depth. However, at depth, loss is likely to be slower due to consolidation, lower temperatures and longer periods of saturation.

Resampling of field-contaminated sites in an

intermittent pond also showed loss of P4 after

the area was subaerially exposed. Continued

monitoring of white phosphorus concentrations

in field-contaminated sites will eliminate some

of the uncertainty associated with the persistence of P4 in near-saturated conditions and provide additional information about the rate of

natural attenuation in intermittent pond areas.

This understanding will enhance the ability to

predict the fate of P4 and its associated ecological

risk within an estuarine salt marsh.

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39

PRODUCTION OF PARTICLES

White phosphorus was obtained as sticks (16.1

mm in diameter), stored in water, from Aldrich

Chemical Co. (Milwaukee, Wisconsin). One stick

of P4 was placed in an 18.3-cm-diameter glass

dish under 3 cm of reagent water, and a razor

blade was used to obtain a 2-mm slice. The edges

of the slice were cut away so that only P4 from the

interior of the stick was used. The mass of each

slice was approximately 700 mg. The piece of P4

was transferred under water to a test tube

(13×100 mm), and the test tube was then placed

in a 1-L beaker containing reagent-grade water.

Additional test tubes containing reagent-grade

water were placed in the 1-L beaker. These test

tubes served to isolate the particles of P4 once

they are produced.

The 1-L beaker containing the test tubes and P4

were placed on a Corning hotplate and the water

heated to 54°C (10°C higher then the melting

point of P4). The beaker was removed from the

hotplate; then 3-μL droplets obtained from the

molten P4 using a Gilson Microman Positive Displacement Pipet (size M25) equipped with disposable capillaries and pistons. Droplets of this

size maintain a spherical shape. Each droplet was

transferred under water to individual test tubes

(only one droplet was placed in each test tube

since molten P4 droplets merge to form a larger

droplet). The test tubes containing the P4 droplets

were cooled in a refrigerator (4°C). P4 can supercool (i.e. remain liquid below the melting point);

thus the water had to be cooled well below 44°C

to ensure solidification of the P4.

To measure the diameter of each particle, each

particle was transferred to a glass petri dish containing reagent-grade water, and the diameter

was obtained using an SPI (Swiss Precision Instruments) 6-in. caliper with 0.1-mm gradations.

Previously we have measured diameters of 127 P4

particles produced in this laboratory by the method described above. The mean (± standard deviaAPPENDIX A: METHODS FOR LABORATORY STUDY

Incubation of P4 Particles at Constant Temperature and Moisture Content

tion) diameter was 1.79 ± 0.06 (3.2% relative standard deviation). After the diameter was measured, each particle was transferred with a forceps from the petri dish to an amber vial containing cold reagent-grade water. Particles were

placed in sediment samples within a few hours of

production.

PREPARATION OF SEDIMENT SAMPLES

Sediments

Uncontaminated sediment from Eagle River

Flats was air-dried and homogenized. A set of

samples at one test temperature required approximately 40 kg of air-dried sediment. The sediment

was air-dried in a fume hood at room temperature (22°C) for two weeks. Since ERF sediments

are silt and clay size, the sediments hardened as

they dried. During drying, the hardening sediment was broken apart with a large stainless steel

spoon and mixed thoroughly. A mortar and pestle was used to break apart the hard clumps. To

thoroughly homogenize the sediment, the sediment was processed in 1-L batches in a Cuisinart

(Model DLC-X) processor. The moisture content

of the air-dried, homogenized sediment was determined gravimetrically (difference in weight

before and after heating at 105°C for 24 hours).

The ERF sediment air-dried in our laboratory was

approximately 2% moisture (on a dry weight basis).

Determination of moisture contents to be tested

The moisture content levels were chosen to reflect those that may be expected in exposed Eagle

River Flats sediments. Following the thawing

each spring of the ice covering Eagle River Flats,

most of the flats is covered by water, and sediments throughout the flats are saturated. Following drainage through gullies and evapotranspiration, the area covered by water gradually shrinks

in size until the flats is periodically reflooded by

high tides exceeding 31 ft. Thus the area exposed
to air shrinks and grows in a cyclic pattern

throughout the summer. If the sediments are exposed for a sufficient length of time, their moisture content may fall below saturation. While unconsolidated pond bottom sediments in permanently flooded areas have moisture contents up

to 200% on a dry weight basis, sediments in intermittent ponds have much lower moisture contents. For example, in the top 10 cm of exposed

pond sediments in early July 1993, sediment

moisture levels were between 30 and 35% (on a

dry weight basis). Moisture levels between 35

and 40% were measured down to 30 cm deep.

Since these moisture levels represent conditions

that exist for extended periods between high

tides, moisture levels in this range were chosen

for this experiment.

The moisture content at saturation was estimated by a variety of techniques. One way was

by making assumptions based on the properties

of clay-size sediments. This approach is shown

below:

Assume 100 g of oven-dried clay, with 60%

porosity and a density of 2.65 g/cm3

Then:

Volume of solids = 100 g ÷ 2.65 g/cm3 = 37.7

cm3 = (1 – 0.60) × Total Volume

Total Volume = 37.7 cm3 ÷ (1 – 0.60) = 94.3

cm3

Volume of voids = 94.3 cm3 – 37.7 cm3 = 56.6

cm3.

If all voids are filled with water, then:

% moisture = (56.6 cm3 ÷ 1 g/cm3) ÷ 100 g =

56.6%.

A tensiometer was also used to estimate the

moisture content at saturation. Pore water tension, expressed as negative millibars, is zero at or

above saturation and increases (actually becomes

negative) below saturation. In the laboratory at

CRREL, sediment samples from ERF were wetted

to obtain moisture contents over the range of 35–

60% moisture (using the procedure given below),

and a tensiometer from Soil Measurements Systems was used to measure the pore water tension.

Based on these measurements, the saturation was

between 50 and 55% moisture (on a dry weight

basis).

Another experimental approach was to gradually add water to a known amount of sediment

until no further water was absorbed. In the lab at

CRREL, 300 g of oven-dried ERF sediment absorbed 160 g of water, indicating that the saturation was 53%.

Based on these three estimates, the moisture

level at saturation is in the range of 50–55% for

the homogenized sediment in the lab. To simulate

moisture levels that may be expected in air-exposed ERF sediments, the following levels were

tested: 25% (s = 0.45), 35% (s = 0.64) (measured in

field in July 1993), 45% (s = 0.82), 55% (s = 1), 65%

(s >1), where s is the degree of saturation.

Labeling

At each temperature, sediments were moistened to one of five moisture contents (Table 3). At

each moisture content, there were 25 replicates

prepared. Therefore, each test at a given temperature required 125 sediment samples in individual

plastic containers. Plastic (high-density polyethylene) containers (8 × 8 × 6 cm) were labeled with

the incubation temperature, the desired moisture

content and a number between 1 and 25 (for example: 20°C—55%—12).

Pretreatment of sediments

The equivalent of 300 g of oven-dried sediment was placed in each of 125 containers for

each test temperature. The actual amount of sediment added depended on the moisture content of

the air-dried sediment. For example, if the moisture content of the air-dried sediment was determined to be 1.75% (on a dry weight basis), then

each dish was filled with 305 g of air-dried sediment (300 + 0.0175 × 300 = 305). Then reagentgrade water (MilliQ, Millipore Corporation) was

added to the obtain the desired moisture content.

For example, a sediment sample containing the

equivalent of 300 g of oven-dried sediment wetted to 55% moisture (on a dry weight basis) required 165 g water (0.55 × 300 = 165). Since airdried sediment had 5.25 g of water associated

with it, only 160 g of water had to be added to

obtain a sample at 55% moisture. Samples were

wetted at least three days prior to placement of

the white phosphorus particles. Samples were

equilibrated at the appropriate temperature and

rewetted daily to replace water lost by evaporation. Prewetting of the sediment served to compact the sediment to more closely approximate

field conditions.

Placement of P4 particles

At the two lowest moisture contents, a 3-cmlong core was removed from the center of each

40
sediment sample using an 18.9-mm-diameter

polypropylene corer (produced by cutting off the

tapered end of a 20-cm3 syringe). One P4 particle

was quickly transferred into the center of the hole

in the sediment sample, and the core was quickly

replaced. The sediment surrounding the core was

gently compacted to fill in the voids around the

core. An additional 5 g of water was added so that

the wet sediment was sufficiently fluid to flow

into the voids surrounding the core; this additional water increased the initial moisture content by

1.7%.

At the three higher moisture contents, a 2-mmdiameter hole was made using a wooden dowel,

and the particle was pushed down to a depth of 3

cm. Then the sides of the sample were gently

squeezed to seal the hole.

INCUBATION OF SEDIMENT SAMPLES

Samples incubated at 15 and 20°C were placed

in a Labline Biotronette plant growth chamber.

Since only one growth chamber was available, one

experimental treatment was completed before the

next one was initiated. Samples incubated at 4°C

were placed in a coldroom at CRREL. Samples at

each temperature were placed in random order

and were rearranged on each working day. To

maintain the moisture content, samples were

weighed, and any water lost by evaporation was

replaced with reagent-grade water. To prevent excessive loss of moisture overnight and over weekends, sample containers were placed in larger

plastic containers (66 × 46 × 15 cm) and loosely

covered with a plastic lid. This procedure maintained the relative humidity close to 100% and

slowed evaporative losses.

RECOVERY OF PARTICLES

The residual P4 was measured periodically during incubation. At each sampling interval, two

samples were taken for microscopic examination.

The sediment sample was placed on the stage of a

Cambridge Instruments dissecting scope, and at a

magnification of 10×, the sediment overlying the

residual particle was gently removed and placed

on a 30-mesh sieve. The material on the mesh was

rinsed with distilled water to remove fine-grained

sediment. Sediment was removed in 1-mm depth

increments down to a depth of 4 cm or until the P4

particle was found. If the particle was found, its

diameter was measured using a micrometer, the

appearance of the particle and the surrounding

sediment was noted, and the particle and sediment were shaken separately in isooctane prior to

gas chromatographic analysis.

If P4 particles were not located by examining

the samples, three additional samples were analyzed by solvent extraction followed by gas chromatography (Walsh and Taylor 1993). The sediment surrounding the residual particle was obtained using a 26.5-mm-diameter polypropylene

corer (produced by cutting off the tapered end of

a 50-cm3 syringe). The corer was centered over

the area where the P4 particle was placed and

pushed to the bottom of the container. The sediment was transferred to a 120-mL glass jar

equipped with a Teflon-lined cap, and the P4 was

extracted with isooctane and analyzed by gas

chromatography using the procedure outlined in

the analytical method. Fifteen additional samples

were prepared (three replicates at each moisture

content) and extracted immediately to establish

the day 0 mass of P4.

DETERMINATION OF

SAMPLING INTERVALS

A rigid sampling interval was not set initially.

Because the vapor pressure of P4 is an exponential function of temperature, the rate of loss of P4

was expected to be significantly higher at 20°C

then at 4°C, so the sampling intervals were shorter for the higher temperatures. In addition, sublimation of P4 depends on the diffusion coefficient

of P4 vapor. The diffusion coefficient of P4 in sediment is unknown but can be assumed to be less

than in air. In sediment the effective diffusion coefficient decreases as moisture content increases.

Thus the sampling interval for the high-moisturecontent samples was longer than the lower-moisture-content samples.

Based on a previous experiment in which ERF

sediments were air-dried at 20°C, samples below

saturation at or above 20°C were sampled intensively within the first two weeks of incubation.

ANALYSIS OF DATA

Moisture content was expressed as degree of

saturation. Residual particle masses were normalized to the day 0 mass (M/Mo) and plotted

vs. time. Regression analyses were performed if

appropriate to see if significant changes in mass

occurred as a function of time.

41
APPENDIX B: METHODS FOR FIELD INVESTIGATIONS

Monitoring Sediment Moisture and Temperature in Eagle River Flats and

Resampling of Field-Contaminated Sites

FIELD STUDY TO MONITOR SEDIMENT

MOISTURE AND TEMPERATURE

Selection of sites

Sites were selected along an east–west transect

through Area C, extending from a permanently

flooded zone to the east through the intermittent

ponded area to the west, across the mudflat zone to

the levee adjacent to the Eagle River (Fig. 15). Sites

were selected based on elevation. The elevation

change along this transect was on the order of 50

cm, and sites were chosen to represent this gradient. Sites were not be located in gullies. First, a survey of the elevation change between the permanently flooded site and the river levee was conducted by measuring the elevation at 16 points

along the transect. Then study sites were selected

such that one site (site 1) was permanently flooded,

four sites (sites 2–5) were in the intermittent pond,

three sites were on mudflat (sites 6–8), and two

sites were on the river levee (sites 9–10) (Fig. 16).

Surveying was performed using a Leitz SET4C

electronic total station and a triple reflective prism

mounted on a 1.45-m-tall prism rod. One person

ran the total station, while two people occupied

each site to be surveyed with the prism rod.

A control point located on the platform of an

observation tower in Area C pond was surveyed in

from “BM Crane,” one of the four permanent survey benchmarks with known coordinates and elevations located on high points around the perimeter of ERF. The surveyed-in control point on the

tower platform was then used as a temporary

benchmark (TBM). Universal Transverse Mercator

(UTM) coordinates and the elevation were calculated for the TBM. This TBM was then used to provide horizontal and elevation control for the survey of the transect through Area C.

The electronic total station was set up on the

tower platform, over the control point, and the instrument was back-sighted to a reference azimuth

mark. The two-person party moved to each location to be surveyed, and the triple prism on the

prism rod was placed on the ground at each site. To

achieve uniformity in surveying elevations, the tip

of the prism rod was placed inside a bucket, which

was in a tub placed on the ground surface. This

provided a uniform bearing surface for the rod tip,

keeping it from sinking down into the soft mud.

The horizontal angle and vertical distance from the

total station to the prism were then measured and

recorded. Based on the horizontal angle and vertical distance from the control point, the height of

the total station above the control point, and the

height of the prism above the survey point, a set of

UTM coordinates and an elevation for the survey

point were calculated.

Only uncontaminated sites were selected. The

sediment at each site was tested for the presence of

P4 particles using a field screening procedure

(Walsh et al., in prep). This method involves

spreading a thin layer of sediment across the bottom of an 8-in.-diameter aluminum pie pan and

heating the pan on a propane camp stove. The

presence of P4 particles is detected by localized areas of intense flame, which leaves a bright orange

residue. To confirm that sites were free of contamination, samples of the surface sediment were analyzed using the laboratory method.

Conditions at each site, such as water depth,

vegetation, water conductivity, pH and redox potential, were recorded. Water depth was measured

using a tape measure, vegetation was identified by

Dr. Charles Racine, and water conductivity, pH

and redox potential were measured with a YSI

Model 3500 water quality meter.

Measurement of sediment temperature

and moisture

Sediment temperature and moisture were measured every 10 minutes and averaged hourly from

May 25 to August 26 using sensors interfaced with

43
Campbell Scientific (Logan, Utah) CR10 dataloggers. The average hourly measurements were

stored on Campbell Scientific SM716 storage

modules. Each datalogger was installed on an instrument tripod with a 3-m center mast to keep

the datalogger above flooding tide levels (Fig.

17). These tripods were self supporting and did

not require any stakes to be driven into the

ground for anchoring. The dataloggers were

powered with 12-V rechargeable batteries, which

were trickle charged with a MSX5 5-W solar panel attached to the top of the center mast.

Soil temperatures were monitored using Model 107B soil–water temperature probes, which utilized the Fenwal Electronics UUT51J1 thermistor

probe, which has an accuracy of ±0.4°C over the

range –33°C to +48°C. Probes were placed 5, 10,

20 and 30 cm deep at each site.

Sediment moisture was monitored at 5, 10, 20

and 30 cm deep at each site using Model 257 (Watermark 200) soil moisture sensors, which estimate the soil water potential in the range of 0–2

bar. The output from the sensors is the ratio of excitation voltage to signal voltage, from which resistance is calculated. Resistance is functionally

related to soil water potential. A sensor in saturated sediment will give a resistance near zero; as

sediment dries, resistance increases. These sensors have internal gypsum tablets, which reduce

the error associated with changing salinity.

Periodically samples were collected for determination of the gravimetric moisture content.

Samples were collected down to 30 cm using an

Oakfield Model B 2-cm-diameter soil sampling

tube. Recovered soil cores were split into subsamples, placed into plastic bags, labeled with site

number, depth and date, and returned to the field

laboratory for determination of gravimetric water content.

The gravimetric water content θg of a sample

of moist soil was measured by weighing the

moist soil sample, drying it at 105°C for 24 hours

to remove the water, and reweighing it.

θg = (mass wet soil – massdry soil)/mass dry soil.

Bulk density measurements

Sediment samples were collected from each

site to determine the bulk density. A 35-cm-deep

pit was dug at each site; then brass cylinders (i.d.

= 5.39 cm, length = 3.0 cm ) were pressed into the

undisturbed sediment of the side wall of the pit at

5, 10, 20 and 30 cm deep. The sediment was dug

out around the outside of each cylinder, and the

cylinders were capped and returned to the lab.

The total volume of sediment was weighed, dried

for 24 hours at 105°C and reweighed, and the dry

bulk density of the sediment ρb was estimated:

ρb = massdry soil/volumecylinder .

This method slightly underestimated the bulk

density since the cores shrank slightly upon drying.

Tensiometers

A series of SoilMoisture (SoilMoisture Equipment Corp., Santa Barbara, California) Series

2725 tensiometers were installed at six sites to

provide another measure of near-surface sediment moisture. Tensiometers provide a direct analog readout of soil suction in centibars. The tensiometers consist of a sealed hollow plastic tube

filled with water with a porous ceramic tip at the

bottom. As the sediment surrounding the buried

ceramic tip dries out, water is drawn out through

the ceramic tip, creating a suction within the hollow tube. The resulting suction is read by an attached dial gauge, which is graduated from 0 to

100 centibars (kPa) of soil suction. The tensiometers were installed at 25 and 10 cm deep (the minimum depth for the model of tensiometer) at

three sites within the intermittent ponded area,

two sites on the mudflat and one site on the river

levee.

Air-entry value

Using a standard Tempe pressure cell (SoilMoisture Equipment Corp., Santa Barbara, California), a moisture retention curve (Hillel 1982)

was determined for a sediment sample collected

south of the transect between sites 3 and 4 (Fig.

16) in the intermittent ponded area (at site 883

discussed in the next section). This curve was

used to estimate the air-entry value, which gives

an indication of how far the water table must

drop before surface sediments become unsaturated. It also gives an estimate of the tensiometer

reading corresponding to the onset of unsaturated conditions as sediments dry. To generate the

curve, air pressure was applied to a core of saturated sediment placed on a porous ceramic plate

in the Tempe pressure cell. Air pressure was incrementally increased, and the amount of water

forced out of the sediment was recorded. The airentry value corresponds to the pressure at which

capillary forces are overcome and air begins to

penetrate the sediment matrix.

44
45

Placement of P4 particles

In mid-May, before the series of flooding tides

beginning May 23, P4 particles were planted at

each site. Ten >5-cm-deep cores were obtained at

each site using an Oakfield Model B 2-cm-diameter soil sampling tube. Cores were obtained within

a 0.25-m2 area and were approximately 20 cm

apart. Within the 0.25-m2 area, cores were obtained from areas with similar conditions (i.e. similar water depth, vegetation cover). A P4 particle

produced in the laboratory was placed at a depth

of 3–5 cm within each core, and each core was

placed within a nylon mesh bag. The bag was tied

off, and survey tape and string were attached.

Each site was surrounded by survey lath, and

strings from the nylon bags were tied around the

lath. The cores were left undisturbed until August.

Retrieval of P4 particles

In August the nylon bags containing the cores

were retrieved. On August 22–23 five cores were

recovered for visual examination. These cores

were placed in plastic bags in a cooler, returned to

our field lab, and, on the same day as collection

from the field, examined. If a P4 particle was

found, its diameter was measured using a micrometer, and the appearance of the particle and

the surrounding sediment was noted.

The rest of the cores were recovered on August

30 and prepared for analysis of P4 residues by gas

chromatography. The cores were removed from

the nylon bags and placed in preweighed jars containing 10 mL of reagent-grade water. These samples were cooled to 4°C and returned to CRREL,

where isooctane was added and the samples were

shaken overnight. The residual P4 in the isooctane

extracts was determined by gas chromatography.

Analysis of data

The mass of P4 remaining for each of five replicate particles at each location was determined following solvent extraction using the standard laboratory method for P4 residue in sediment. Residual

particle masses were normalized to the Day 0 mass

(M/Mo) and plotted vs. location.

RESAMPLING OF PREVIOUSLY

CHARACTERIZED CONTAMINATED SITE

Collection of samples

Site 883 was relocated based on UTM coordinates and the presence of the stubs of some lath

that had been used to mark the site in 1992. The

Water surface elevations

Piezometers were used to measure the water

surface elevation along the transect. Each piezometer was constructed from 1.9-cm-i.d. CPVC

pipe. Slots were cut at one end of the tube to allow

water to enter. Slots (1 mm wide) were spaced at

1-cm intervals on either side of the first 10 cm of

each 1.52-m-long pipe. A nylon mesh was pulled

over the slotted end and secured with duct tape.

On May 20, piezometers were inserted to a depth

of approximately 80 cm at sites 1–9. A 2-cm-diameter placement tool was gently inserted into the

ground to form a pilot hole slightly smaller than

the o.d. of the CPVC pipe. The piezometer pipe

was then inserted into the hole. The turf at site 10

(river levee) was too thick to allow gentle insertion of the placement tool, so no piezometer was

placed at this site. The water level inside each

pipe was read on a periodic basis using a thin

wooden dowel. Water levels were measured on

May 24, June 20 and August 19.

Water level measurements at the

permanently flooded site

Pond water levels were monitored at the permanently flooded site (site 1) using a Campbell

Scientific UDG01 ultrasonic depth gauge. The

depth gauge was attached to the end of a bracket

arm, which was in turn attached to the center

mast of the tripod. The sensor was suspended on

the bracket arm approximately 2.5 m above the

water surface. The primary components of the

depth gauge sensor are the Polaroid ultrasonic

transducer and the Polaroid 6500 sonar ranging

module (CSI 1993). The sensor measures the distance from the bottom of the sensor to a surface

by bouncing an ultrasonic pulse off of the surface

and listening for the return echo. The distance to

the surface is determined from the elapsed time.

The speed of sound in air depends on the air temperature, so that is also measured by the datalogger at the same time. The signal from the depth

gauge sensor is processed by the datalogger, corrected for the air temperature, and stored. Readings were taken by the datalogger every ten minutes and averaged every hour. The accuracy of

the depth gauge sensor for the setup we used is

±1 cm. The elevation for the bottom of the depth

gauge sensor was established by surveying from

a known control point. Water surface elevations

were determined from the difference between the

water surface and the elevation of the bottom of

the sensor.
UTM coordinates for site 883, the center point of

the close-interval sampling, are 354,981.6E,

6,801,183.8N. The site was located 160 m west of

the observation tower in Area C and was marked

with survey lath. Surface samples were collected

at the center point and at 1-m intervals from the

center point out to 5 m, for a total of 41 samples.

Eight duplicates were taken also. Samples were

shipped to Waterways Experiment Station

(Vicksburg, Mississippi) for analysis of P4 using

46

the gas chromatographic procedure developed at

CRREL. Samples taken from the smoke round crater were shipped to CRREL for analysis of P4.

Analysis of data

Nonparametric statistics (sign test for paired

observations) (Natrella 1963) were used to compare the concentrations found in 1992 and 1994

around site 883. Nonparametric statistics were

used since the data are not normally distributed.
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November 1995

Persistence of White Phosphorus Particles in Sediment

Marianne E. Walsh, Charles M. Collins and Charles H. Racine

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road CRREL Report 95-23

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161.

Remediation of sediments at Eagle River Flats, a salt marsh contaminated with particles of white phosphorus (P4), may require severe alterations of the wetland by dredging, draining or covering. However, some

sediments may undergo decontamination naturally in areas that are seasonally exposed to air. To predict the

persistence of white phosphorus particles in sediments, a literature review was conducted for the physical

and chemical properties of white phosphorus. The persistence of millimeter-size white phosphorus particles

was studied by laboratory and field experiments. White phosphorus particles were found to be persistent indefinitely in saturated sediments. In unsaturated sediments, loss was rapid (within 24 hours) at 20°C and retarded by low temperatures.

Contamination Sediment

Eagle River Flats White phosphorus

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

52