SPECIAL REPORT 95-27

Silt Fence Testing for

Eagle River Flats Dredging

Karen S. Henry and Susan T. Hunnewell December 1995
Abstract

An estimated 1,000 to 2,000 waterfowl deaths have been noted annually

since 1980 in Eagle River Flats (ERF), Alaska, an artillery impact area

used by the Army. Waterfowl die because of the ingestion of unburned white

phosphorus (WP) particles deposited by incendiary. Remediation of the

site is currently being planned, and one of the techniques being considered

is the use of a remote-control dredge to excavate WP-contaminated sediment. Dredged material will be placed into a settling pond and allowed to

settle until a clear layer of water forms on the top of the sediments. The

water will then be released over a weir, across a concrete pad, through a

geotextile silt fence to a drain into the ERF. This report describes tests that

were conducted to evaluate how well candidate geotextiles for the silt fence

retained small particles (less than 0.1 mm in diameter) that were suspended in water being released back into the ERF. The soil used in the tests

was collected from ponds to be dredged. The testing program consisted of

two parts. Part I tests were standard engineering tests for silt fences, and

were used to select a product for further testing. Part II tests simulated field

conditions, and were conducted to determine whether the candidate geotextile

selected was likely to perform well. In the tests that simulated field conditions, the tests that used geotextiles achieved system filtering efficiencies of

99%, and the geotextile filter reduced the final total suspended solids contained in the water by a factor of 10. Negligible amounts of soil passed the

#200 sieve from water that flowed through the geotextile. However, it is

also noted that allowing the sediment to settle before decanting the water

resulted in system filtering efficiencies in excess of 90% when a silt fence

was not used in the test. Due to differences between lab and field use of this

product, several recommendations are made to help ensure the proper functioning of the geotextile when used in Eagle River Flats. These recommendations include monitoring the quantity of material with diameters larger

than 0.1 mm passing through the silt fence, careful and frequent visual

inspection of the silt fence to detect any signs of strength loss or damage,

having replacement geotextile available and properly stored at the site,

backflushing the silt fence with water or rubbing it with a squeegee regularly to help ensure proper flow rates across it, and not allowing the height

of soil retained on the upstream side of the fence to exceed one-half of the

height.

For conversion of SI units to non-SI units of measurement consult ASTM

Standard E380-93, Standard Practice for Use of the International System

of Units, published by the American Society for Testing and Materials,

1916 Race St., Philadelphia, Pa. 19103.

This report is printed on paper that contains a minimum of 50% recycled

material.
Special Report 95-27

Silt Fence Testing for

Eagle River Flats Dredging

Karen S. Henry and Susan T. Hunnewell December 1995

Prepared for

U.S. ARMY GARRISON, ALASKA

and

U.S. ARMY ENVIRONMENTAL CENTER

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Karen S. Henry, Research Civil Engineer, and Susan T.

Hunnewell, Civil Engineering Technician, Research and Engineering Directorate, U.S.

Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire.

Funding for this work was provided by the U.S. Army Garrison, Alaska, through the U.S.

Army Environmental Center, Aberdeen Proving Ground, Maryland, under MIPR no.

E87951037, Treatability Study–Continuation of Dredging Pilot Study.

The authors gratefully acknowledge the encouragement of and valuable discussions

with Michael Walsh, Mechanical Engineer, CRREL. The authors also thank Mr. Walsh and

Dr. Jean-Claude Tatinclaux of CRREL for their valuable critical review of this report.

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

Citation of brand names does not constitute an official endorsement or approval of the use

of such commercial products.

ii
CONTENTS

Page

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

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

Materials ............................................................................................................................. 2

Procedure ............................................................................................................................ 3

Part I ............................................................................................................................. 4

Part II ............................................................................................................................ 5

Results ................................................................................................................................ 5

Parts I and II ................................................................................................................ 5

Discussion ........................................................................................................................... 6

Overview of test results ............................................................................................. 6

Applying laboratory test results to the field use of the silt fence ........................ 7

Conclusion .......................................................................................................................... 7

Recommendations ............................................................................................................. 7

Literature cited ................................................................................................................... 8

Appendix A: Step-by-step test procedures used in laboratory silt fence tests for

Eagle River Flats, Alaska .................................................................................... 9

Appendix B: Results of silt fence testing for Eagle River Flats, Alaska, July and

August 1994.......................................................................................................... 10

Abstract ............................................................................................................................... 12

ILLUSTRATIONS

Figure

1. Plan view and cross-section of the retention basin, with the inflow and

outflow structures ............................................................................................. 1

2. Plan view of weir–silt fence–outlet structure and cross-section of the silt

fence for the release of water from the settling pond for dredging

operations in Eagle River Flats, Alaska ......................................................... 2

3. Typical grain size distribution for soil collected from pond bottom in

Eagle River Flats, Alaska ................................................................................. 3

4. Diagram of flume used to conduct silt fence tests ............................................... 4

TABLES

Table

1. Properties of geotextiles tested ............................................................................. 3

2. Summary of Part I results...................................................................................... 6

3. Summary of Part II results .................................................................................... 6

iii
INTRODUCTION

Eagle River Flats (ERF) is an estuarine salt

marsh on the Cook Inlet that has been used by the

Army as an artillery impact area on Fort

Richardson in Anchorage, Alaska, since 1949. It is

also used by up to 5000 waterfowl per day during

annual migrations (Racine et al. 1992). An estimated 1000 to 2000 waterfowl deaths have been

noted annually in ERF since 1980. It was recently

determined that ingestion of unburned white

phosphorus (WP) particles deposited by smokeproducing incendiary is the primary cause of mortality (Racine et al. 1992). Waterfowl that circulate

bottom sediment through their bills and retain

food-sized particles for ingestion (e.g., dabbling

ducks and swans) are the most susceptible (Racine

et al. 1992). All firing of WP rounds into the ERF

ceased in 1990 and remediation of the site is currently being planned; however, this area will continue to be used for other types of artillery impact

during winter months when there is a solid ice

cover.

One of the remediation techniques being considered for the ERF is the use of a remotely-controlled dredge to excavate WP-contaminated sediment. Dredged spoils, containing various-sized

particles of WP, will be placed into a 90- by 90-m

settling pond (or retention basin) with 2-m-high

berms. There is a 7-m-wide × 1.2-m-high weir at

one corner of the settling pond for the purpose of

decanting water. The weir is fully adjustable in

height, in increments of 3.8 cm. Spoils will be

pumped into the basin, then allowed to settle until a clear layer of water forms on top of the sediments (a minimum of two hours). The water will

then be released over the weir, across a 2-m-wide

section of concrete pad, through a geotextile (referred to as a silt fence) and across the concrete

pad to a drain into the ERF (Fig. 1 and 2). The

Silt Fence Testing for Eagle River Flats Dredging

KAREN S. HENRY AND SUSAN T. HUNNEWELL

A'

A

90 m

90 m

0.6 m Ø

Outflow Pipe to ERF

Inflow

Structure

Inflow Pipe

(25.5 cm Ø) Chain Link

Cage

Adjustable

Weir

Silt

Fence Concrete

Wall

3:1

2:1

3:1

To

Dredge

127 m

1.2 m Ø Drop Inlet

w/0.6 m Ø Culvert

A-A'

Clear Water

Silt

Figure 1. Plan view and cross-section of the retention basin, with the inflow and

outflow structures.
water will flow over the weir with heads of 0.1 m

or less in order to avoid reaching a flow rate that

would significantly resuspend particles in the water being decanted. The silt fence is required as a

backup mechanism to retain particles that are 0.1

mm in diameter and larger because WP particles

of this size pose a significant threat to wildlife in

Eagle River Flats. (The primary means of removing WP particles of this size is allowing the spoils

to settle.) Once the dredged material is drained, it

will be treated to remove WP. At this time, the

specific remediation technique has not yet been

determined. It will most likely involve heating

and drying the sediment to volatilize the WP. Likewise, it is not yet known where the soil will be

placed after treatment.

This report describes tests that were conducted

to evaluate how well candidate geotextiles for the

silt fence retained small particles that were suspended in water being released back into the ERF.

Filtering efficiency, defined as the percentage

of soil particles removed from sediment-laden

water by a geotextile over a period of 25 minutes,

was the main criterion evaluated (ASTM D 5141

1992). Some tests also included a measure of per-

* Apparent opening size: A property that indicates the

approximate largest particle diameter that would effectively pass through the geotextile.

cent of soil retained (by weight) on the #200 sieve

(mesh size of 0.075 mm) still contained in water

filtered by the geotextile. The retention of particles of 0.1 mm and larger is the most important

function of the geotextile in this application; therefore, selection of products for testing was limited

to geotextiles with available apparent opening

sizes* (AOS) of approximately 0.1 mm.

MATERIALS

The soil used in the laboratory test was collected from ponds to be dredged in Eagle River

Flats, Alaska. It is primarily glacially derived

silt; a typical grain size distribution of the soil

to be dredged is shown in Figure 3 (Lawson

and Brockett 1993). Table 1 lists the geotextiles

tested along with properties of interest as provided by the manufacturers.

Figure 2. Plan view of weir–silt fence–outlet structure and cross section of the silt fence for the

release of water from the settling pond for dredging operations in Eagle River Flats, Alaska.

9.8 m

1.2 m

(typ.)

2.4 m

(typ.)

1.3 m

(typ.)

1.2 m Ø

Inlet

2.1 m

1.6 cm

Rebar Cross-brace

5 cm 

Galv. Pipe

25.4

cm

4.8 m

3.3 m

Fabric Clamp Strip

(9.8 x 0.05 x 0.03 m)

Weir Boards

(0.05 x 0.15 x 2.4 m)

34.3 cm

25.4 cm

Reinf. Conc.

Holding Pond

Steel

W-beams

Weir

Silt

Fence

of Berm

Top

1.4 m

Geotextile

Fabric

57.2 cm

54.6 cm

127

cm

11.4 cm

45.7 cm 

Reinf. Conc. Pad

Fabric

Chain-link

Fence

Silt Fence Cross-section

2-m-high

Berm

Silt Fence Cross Section

2
PROCEDURE

The testing for this project consisted of two

parts. Part I tests were conducted according to

ASTM D 5141, Standard Test Method for Determining Filtering Efficiency and Flow Rate of a Geotextile

for Silt Fence Application Using Site-Specific Soil

(ASTM 1992). Thus, an accepted engineering standard was used to compare candidate geotextiles.

Part II tests simulated field conditions, and were

conducted to determine whether the candidate

geotextile selected from the Part I tests was likely

to perform well. Procedures followed in both experiments are included in Appendix A. Figure 4 is

a diagram of the flume used for the tests, including a gate that was added for Part II tests.

1000 100 10 1 0.1 0.01 0.001

Cobbles Silt or Clay

Gravel Sand

Coarse Fine C'rse Medium Fine

3 3/

4 4 10 20 40 140 200

U.S. Std. Sieve Size and No. Hydrometer

100

80

60

40

20

0

Percent Finer by Weight

Percent Coarser by Weight

0

20

40

60

80

100

Grain Size (mm) Figure 3. Typical grain size distribution for

soil collected from pond bottom in Eagle River

Flats, Alaska (from Lawson and Brockett 1993).

Several means of sampling soil-laden water for

total suspended solids (TSS) were tested before

the start of the experimental program by mixing

150 g of dry soil with 500 mL of water in a laboratory blender before adding it to 49.5 L of water.

(These are the amounts of soil and water recommended by ASTM D 5141.) The soil–water mixture was placed in a 0.5-m-diameter × 0.75-mhigh plastic container, and vigorously stirred with

a 0.25-m-wide paint stirrer attached to an electric

drill. Samples were collected with a commercially

available 250-mL-capacity water sampler while

the water was still being agitated. This resulted in

TSS determinations within 2% of the known TSS

from the quantity of oven-dry soil added to the

water. The PVC Coliwasa water sampler used is

Table 1. Properties of geotextiles tested.

AOS1 Permittivity2

Geotextile Product Construction (mm) (sec–1)

A Texel F-300 NW PET 0.04–0.05 0.31

B Texel Geo 9 NW PET, 0.06–0.125 1.72

reinforced

C Amoco L17811 NW PP 0.075 not available

D Amoco 4551 NW PP 0.150 1.9

1 Apparent opening size: A property that indicates the approximate largest

particle diameter that would effectively pass through the geotextile.

2 Permittivity of geotextiles refers to the volumetric flow rate of water per

unit cross-sectional area per unit head under laminar flow conditions, in the

normal direction.

Notes: NW = nonwoven, PET = polyester, PP = polypropylene

3
Figure 4. Diagram of flume used to conduct silt fence tests.

available from Forestry Suppliers, Inc., Jackson,

Mississippi.

Part I

Twelve tests were conducted in Part I; there

were three replications for each of four geotextiles,

tested in random order. The initial TSS of the sediment-laden water released to the flume was either 2830 mg/L or 2880 mg/L, depending on how

much rinse water was used after the mixture was

released. The procedure described in ASTM D 5141

(1992) was followed, with three minor adjustments, listed below:

1) In order to break apart aggregated soil particles, the soil was mixed in a blender with

500 mL of water before being added to the

rest of the water.

2) The soil–water mixture was released into

the flume immediately after one minute of

agitation (i.e., agitation was not continued

during the release).

3) Rather than taking one depth-integrated

sample, three samples of soil-laden water

using a PVC Coliwasa water sampler were

taken and analyzed independently for TSS.

Each sample was approximately 50 mL.

In test 2, the back of the geotextile was scraped

with a spoon about 15 minutes after the test was

begun and a significant increase in the instantaneous flow rate of water through the geotextile

was noted. This procedure probably resulted in

an increased amount of sediment passing through

the geotextile and is discussed further in a later

section.

Aluminum Gutter

75-L Plastic

or Nonmetallic

Container

75-L Plastic

or Nonmetallic

Container

Wooden Block

75-L Plastic

or Nonmetallic

Container

Steel Plate (with

countersink screws)

75-L Plastic

or Nonmetallic

Container

Stirrer

Geotextile

Drill

8% Grade

Front View Side View

Top View

10 cm

30 cm

42.5 cm

85 cm

125 cm

40 cm

23.5 cm

13 cm

Gate for

Part II 

Tests

95 cm

4
Part II

Part II test conditions simulated field use of the

silt fence. The soil–water mixture had a TSS value

equal to the expected maximum TSS of the

dredged material. The mixture was made with

brackish water, then allowed to settle before releasing the top layer of relatively clear water. Six

tests were conducted: three without a geotextile

and three using geotextile B.

Following is a list of the changes made to the

ASTM procedure for Part II tests:

1) The TSS of the soil–water mixture was 2.0 ×

105 mg/L (67 times that prescribed by ASTM

D 5141 1992) and the salinity of the water

used was 4.5 ppt (vs. fresh water).

2) A 28-cm-high impermeable gate was installed 23.5 cm from the back of the flume to

allow the soil to settle out of the mixture.

The top 13 cm of the gate was removable to

allow decantation in a manner similar to the

lowering of the weir on the settling pond.

These changes were implemented as follows:

For the first test, the soil–water mixture

was released from the top container into the

back of the flume. It consisted of 46.6 L of

water, 233 g of sea salt, and 9248 g of ovendry soil. This mixture settled until there was

a clear water/sediment interface located 5

cm below the removable portion of the gate

(approximately two hours). The test was conducted by quickly lifting the top portion of

the gate and releasing the upper layer of

water all at once.

Due to lack of soil and time, it was not

desirable to remake the entire 50 L of soil–

water mixture for the second, third, and

fourth tests. Therefore, the amount of soil

and water lost in the first test was determined* (222.0 g and 24.0 L, respectively, with

a salt content of 111.7 g), then added to the

soil and water that had remained behind the

gate. The entire soil–water mixture was

stirred vigorously by hand for one minute.

After stirring, the soil–water mixture was

allowed to settle until the soil/water interface reached a level of 5 cm below the removable portion of the gate. Then the next

test was conducted.

3) The flume was set at a 1% (vs. 8%) grade to

simulate the slope of the dredged material

being deposited from a 1-m-high dredge outlet pipe located 125 m from the weir.

4) At about eight minutes and 16 minutes after

the water mixture was released, the downstream side of the geotextile was scraped

with a spatula to increase the water flow

through the geotextile. A practice like this

will be performed in the field in order to

maintain water flow through the silt fence

as long as possible. The silt fence will either

be backflushed with water or scraped with a

long-handled squeegee.

5) After the TSS samples were collected, the

remaining soil–water mixture was poured

through a #200 sieve (0.075-diameter opening size) so that the effectiveness of the

geotextile in retaining particles of 0.1 mm

and larger could be estimated.

RESULTS

A complete list of results from Parts I and II is

included in Appendix B. The filtering efficiency is

defined as the percentage of soil particles retained

by the silt fence. The “system filtering efficiency”

in Part II tests was determined analogously by

comparing the final TSS of the sediment-laden

water (whether or not a geotextile was present) to

the original TSS of the water allowed to settle in

the back of the flume.

Parts I and II

Table 2 is a summary of Part I results. Christopher and Holtz (1985) recommend a minimum

filtering efficiency of 75% and flow rate of 0.012

m3 m–2 min–1. Geotextiles A and B performed relatively well, and geotextiles C and D performed

poorly. However, only geotextile B was selected

for further study, because it had the desirable characteristic of being reinforced and because the time

required to perform the Part II tests was limited.

Table 3 summarizes the results from Part II.

The tests that used geotextiles achieved system

filtering efficiencies of 99%, and the geotextile filter reduced the final TSS values by a factor of 10.

The “average effective filtering efficiency” for the

geotextile, determined by comparing the final TSS

values for the geotextile tests to those from the

tests without geotextiles, was 89%.

Comparing the final TSS measurements of tests

3 and 7 with test 1 in Table 3 suggests that the

* This was calculated by averaging the total suspended

solids found in the three samples and multiplying by

the volume of water lost.

5
Table 2. Summary of Part I results.

Standard Standard

Flow rate Average deviation Average FE deviation

Test no. Material (m3m–2 min–1) flow rate flow rate FE (%) FE (%) FE

1 A 0.026 71.40

5 A 0.026 0.026 3.9E–6 66.69 69.6 2.5

9 A 0.026 70.56

6 B 0.026 76.11

11 B 0.026 0.026 2.8E–4 73.38 72.8 3.7

12 B 0.026 68.82

4 C 0.026 54.38

7 C 0.026 0.026 8.0E–5 61.08 58.7 3.7

8 C 0.026 60.52

2 D 0.026 39.19

3 D 0.026 0.026 2.9E–5 48.33 45.5 5.5

10 D 0.026 48.89

Note: FE = filtering efficiency

Table 3. Summary of Part II results.

Flow rate Final TSS FE of system Percent retained

Test no. Geotextile? (m3m–2 min–1) (mg/L) (%) on #200 sieve

1 No 9249 95.3 did not measure

3 No 6360 96.8 1

7 No 14466 92.7 3

2 Yes 0.063 654 99.7 < 0.1

4 Yes 0.024 1185 99.4 < 0.1

6 Yes 0.120 1465 99.3 did not measure

* J. LaFleur, Professor of Civil Engineering, École

Polytechnique, Montreal, Quebec, Canada.

the instantaneous flow rate of water through the

geotextile—thought to be due to the destruction

of the filter cake—was noted. The lower filtering

efficiency of this test compared to the other tests

with the same geotextile suggests that scraping

the downstream side of the geotextile during the

test increased the amount of soil that passed

through it. The Part II test procedure incorporated

scraping the downstream side of the geotextile

because similar techniques will be used in the field

to promote increased water flow rate across it.

For the Part II tests, the TSS values from tests

without geotextiles were used to estimate the TSS

content of water that reached the geotextile. This

TSS value was approximately 3.5 times that of the

TSS of the water used in the Part I tests (10,025

mg/L vs. 2880 mg/L). However, the flow rates of

the Part I and Part II tests with geotextiles were

similar. This most likely resulted from the practice of scraping the geotextile in Part II.

Part II test results clearly show the importance

practice of not mixing the soil and water in a

blender for each test in Part II did not significantly influence the TSS measurements of the soil–

water mixture.

DISCUSSION

Overview of test results

In all tests using geotextiles, the water flow

rate through the material slowed with time. This

probably happened because the sediment-laden

water flowing through the geotextile formed a

filter cake of soil particles on the upstream side

(LaFleur 1994, personal communication*). In test

2 of Part I, the downstream side of the geotextile

was scraped with a spoon about 15 minutes after

the test was begun and a significant increase in

6
of allowing the dredged sediment to settle before

decanting water. This alone resulted in system

filtering efficiencies in excess of 90%.

In tests 2 and 4 of Part II, a small fraction of soil

was retained on the #200 sieve from the water

that flowed through the geotextile. Since the

geotextile also had the effect of reducing the final

amount of TSS in the water by a factor of 10, the

percentage of soil with a minimum diameter of

0.1 mm was clearly negligible when the geotextile

filtered the suspension. The Part II results also

clearly demonstrate the importance of allowing

the spoils to settle before decanting the water. This

practice resulted in system filtering efficiencies in

excess of 90%.

Applying laboratory test results

to the field use of the silt fence

The estimated velocity of flow over a weir is

 

V gh = 2 (1)

where V is the velocity of the water flow, g is the

acceleration of gravity, and h is the head of the

water on the weir (Roberson and Crowe 1975).

Because the head of water on the weir was the

same in the laboratory as expected in the field, the

initial flow rates over the weir in the field and the

gate in the laboratory are approximately equal. In

the field, the velocity of water flow through the

silt fence might be somewhat less due to effects of

end contractions on the weir, turbulence created

when water falls onto the concrete pad, and friction drag from the concrete pad as the water flows

over it. However, the length of time that the water

is flowing at relatively high velocities will probably be longer than that experienced in the laboratory test. Thus, there are unquantified differences in water flow rates and time of water flow

between the laboratory and the field that could

have opposite effects on the long-term filtering

efficiency of the silt fence. Therefore, the quantity

of material with diameters larger than 0.1 mm

passing through the silt fence should be monitored in the field to ensure that the silt fence is

performing as intended.

Geosynthetics are known to experience strength

degradation when exposed to ultraviolet light for

more than a few days. When left exposed for periods of about a year, material loss has also been

observed. Koerner (1990) noted that standard

specifications for geotextile silt fences require that

a minimum of 70% of the original tensile strength

remain after exposure to ultraviolet radiation according to ASTM D 4355 (1992). Although most

geotextiles have some ultraviolet stabilizing additives incorporated during manufacture, the results of ASTM D 4355 (1992) are not available for

geotextile B. Furthermore, geotextile B is usually

used for some combination of reinforcement, separation, and stabilization, i.e., in situations where

it is exposed to sunlight for only a short time

during construction (Geotechnical Fabrics Report

1993). Thus, the silt fence should be carefully monitored during use, and replacement material should

be readily available and properly stored at the

site in the event that unacceptable strength degradation of the material occurs.

CONCLUSION

Among the four geotextiles tested, geotextile B

is the best geosynthetic candidate available to perform the filtering of WP particles in ERF. It effectively retained particles of 0.075 mm and larger.

RECOMMENDATIONS

The following recommendations are made to

help ensure the proper functioning of geotextile B

as a silt fence in Eagle River Flats:

1. The quantity of material with diameters

larger than 0.1 mm passing through the silt

fence should be monitored during field operation.

2. The silt fence should be carefully visually

inspected frequently to detect any signs of

strength loss due to ultraviolet degradation

or other damage.

3. Replacement geotextile should be readily

available and properly stored at the site.

Proper storage includes wrapping in black

plastic and storing in a dry area indoors

where it is not exposed to freezing temperatures.

4. The silt fence should be backflushed with

water or rubbed with a squeegee regularly

to help ensure proper flow rates across it.

5. According to Christopher and Holtz (1985),

soil retained on the upstream side of the silt

fence should never exceed one-half the

height of the fence (0.6 m) due to the potential danger of water overtopping the fence.

Thus, if soil buildup behind the fence

reaches this height, it should be removed.

7
LITERATURE CITED

ASTM D 4355 (1992) Standard test methods for

deterioration of geotextiles from exposure to ultraviolet light and water (xenon arc-type apparatus). ASTM 1992 Annual Book of ASTM Standards:

Soil and Rock; Dimension Stone; Geosynthetics, vol.

4.08, p. 704–706.

ASTM D 5141 (1992) Standard test method for

determining filtering efficiency and flow rate of a

geotextile for silt fence application using site-specific soil. ASTM 1992 Annual Book of ASTM Standards: Soil and Rock; Dimension Stone; Geosynthetics,

vol. 4.08, p. 1214–1217.

Christopher, B.R. and R.D. Holtz (1985) Geotextile

Engineering Manual. FHWA-TS-86-203. Washington, D.C.: Federal Highways Administration.

Geotechnical Fabrics Report (1993) 1994 Specifiers Guide. St. Paul, Minnesota: Industrial Fabrics

Association, International.

Koerner, R.M. (1990) Designing With Geosynthetics,

Second Edition. Englewood Cliffs, New Jersey:

Prentice Hall.

Lawson, D.E. and B.E. Brockett (1993) Preliminary assessment of sedimentation and erosion in

Eagle River Flats, south-central Alaska. USA Cold

Regions Research and Engineering Laboratory,

CRREL Report 93-23.

Racine, C.H., M.E. Walsh, B.D. Roebuck, C.M.

Collins, D. Calkins, L. Reitsma, P. Buchli, and G.

Goldfarb (1992) White phosphorus poisoning of

waterfowl in an Alaskan salt marsh. Journal of Wildlife Diseases, 28(4): 669–673.

Roberson, J.A. and C.T. Crowe (1975) Engineering

Fluid Mechanics. Boston, Massachusetts: Houghton

Mifflin Company.

8
APPENDIX A: STEP-BY-STEP TEST PROCEDURES USED IN

LABORATORY SILT FENCE TESTS FOR EAGLE RIVER FLATS, ALASKA

13. Repeat steps 11 and 12 until three samples

have been obtained.

14. Determine the TSS of the three samples according to ASTM D 5141.

Silt fence tests for

site-specific conditions

1. Set flume at a 1% grade, and ensure that the

top of the vertical barrier, located 23.5 cm

from the back of the flume, is fastened in

place.

2. Mix 9248 g of dry soil collected from ERF

ponds in 46.6 L of water. The water should

have a salinity of 4.5 ppt, and the soil should

be mixed in a blender with the water. The

entire mixture should be stirred for one

minute and released to the flume. (Note that

this is a mixture of 16.7% by volume of soil

in water.)

3. Let the mixture stand in the back of the flume

until a clear layer of water, 13 cm high, forms.

This will take about two hours.

4. Remove (all at once) the top portion of the

vertical barrier in the flume.

5. Catch all of the water and sediment in a large

container. At about eight minutes and 16

minutes after release of the water, scrape the

downstream side of the geotextile with a

spoon to induce water flow through it. After

25 minutes, stir the water and material in

the container for one minute and take three

depth-integrated samples. Note that the gutter may have to be cleaned out first.

6. Determine TSS on the three samples according to ASTM D 5141.

Silt fence test procedure

(from ASTM standard D 5141)

1. Set flume at an 8% grade.

2. Fasten geotextile across flume opening. Be

sure there are no wrinkles or loose sections.

3. Wet the geotextile with 50 L of tap water.

4. Determine the water content of the soil, and

weigh out 150 grams of dry soil. Record

weight of the soil.

5. Mix the soil in the blender with 500 mL of

water: 10 seconds on low, 10 seconds on high.

Add the mixture to tap water to make 50 L

of soil and water in the top container.

6. Agitate the mixture with the stirrer (paint

stirrer on drill) for one minute.

7. Immediately after stirring, release the mixture. Release should take less than 10 seconds. Start timer at release!

8. Rinse the mixing container with 2–3 L of

water. Record the total amount of water

used. Calculate initial TSS based on the 150

g of soil and the total volume of water.

9. Time the flow of water through the geotextile

until no water remains behind the geotextile

or 25 minutes have elapsed. If 25 minutes

elapse, measure the distance from the geotextile to the edge of the water behind the

geotextile. Record the time of flow and the

distance, if appropriate.

10. Collect all of the mixture in a container.

11. Agitate the mixture with the stirrer for one

minute.

12. After one minute of stirring, obtain a depthintegrated sample while continuing to stir

the mixture. Record the volume of the sample

taken.

9
Note that for the Part II tests containing geotextiles, the flow rates were determined by calculating the volume of water and soil left behind the

fence at 25 minutes, then subtracting that from

APPENDIX B: RESULTS OF SILT FENCE TESTING FOR

EAGLE RIVER FLATS, ALASKA, JULY AND AUGUST 1994

0.05 m3 (50 L), the initial volume of water and soil.

The parameters and equation used to determine

the volume of soil and water left at the end of 25

minutes are defined in the figure below:

a b

1%

l

Volume ≈ (a · l · w) – (1/2 · l · (a–b) · w)

Figure B-1. Sketch of flume, defining the variables used

to estimate the volume of water in the flume remaining

after 25 minutes. Variables a and b were both measured.

10
11
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December 1995

Silt Fence Testing for Eagle River Flats Dredging

MIPR no. E87951037

Karen S. Henry and Susan T. Hunnewell

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 95-27

Hanover, New Hampshire 03755-1290

U.S. Army Garrison, Alaska

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland 21010-5401

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

15

Dredging Geotextile Silt fence

Filtering efficiency Remediation White phosphorus

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

An estimated 1,000 to 2,000 waterfowl deaths have been noted annually since 1980 in Eagle River Flats (ERF),

Alaska, an artillery impact area used by the Army. Waterfowl die because of the ingestion of unburned white

phosphorus (WP) particles deposited by incendiary. Remediation of the site is currently being planned, and

one of the techniques being considered is the use of a remote-control dredge to excavate WP-contaminated

sediment. Dredged material will be placed into a settling pond and allowed to settle until a clear layer of water

forms on the top of the sediments. The water will then be released over a weir, across a concrete pad, through

a geotextile silt fence to a drain into the ERF. This report describes tests that were conducted to evaluate how

well candidate geotextiles for the silt fence retained small particles (less than 0.1 mm in diameter) that were

suspended in water being released back into the ERF. The soil used in the tests was collected from ponds to be

dredged. The testing program consisted of two parts. Part I tests were standard engineering tests for silt

fences, and were used to select a product for further testing. Part II tests simulated field conditions, and were

conducted to determine whether the candidate geotextile selected was likely to perform well. In the tests that

simulated field conditions, the tests that used geotextiles achieved system filtering efficiencies of 99%, and the

geotextile filter reduced the final total suspended solids contained in the water by a factor of 10. Negligible

amounts of soil passed the #200 sieve from water that flowed through the geotextile. However, it is also noted
13. ABSTRACT (cont’d.)

that allowing the sediment to settle before decanting the water resulted in system filtering efficiencies in excess

of 90% when a silt fence was not used in the test. Due to differences between lab and field use of this product,

several recommendations are made to help ensure the proper functioning of the geotextile when used in Eagle

River Flats. These recommendations include monitoring the quantity of material with diameters larger than 0.1

mm passing through the silt fence, careful and frequent visual inspection of the silt fence to detect any signs of

strength loss or damage, having replacement geotextile available and properly stored at the site, backflushing

the silt fence with water or rubbing it with a squeegee regularly to help ensure proper flow rates across it, and

not allowing the height of soil retained on the upstream side of the fence to exceed one-half of the height.

14