MATERIALS - SR95

Silt Fence Testing for Eagle River Flats Dredging

PROCEDURE - SR95_270008

SR95_27
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2

Holding Pond

(0.05 x 0.15 x 2.4 m)

Weir

(9.8 x 0.05 x 0.03 m)

Silt

Fence

2-m-high

Berm

Siilltt Fence Crross-secttiion

S Fence C oss S ec on

4.8 m

Figure 2. Plan view of weirsilt fenceoutlet 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.

water will flow over the weir with heads of 0.1 m

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

or less in order to avoid reaching a flow rate that

(mesh size of 0.075 mm) still contained in water

would significantly resuspend particles in the wa-

filtered by the geotextile. The retention of par-

ter being decanted. The silt fence is required as a

ticles of 0.1 mm and larger is the most important

backup mechanism to retain particles that are 0.1

function of the geotextile in this application; there-

mm in diameter and larger because WP particles

fore, selection of products for testing was limited

of this size pose a significant threat to wildlife in

to geotextiles with available apparent opening

Eagle River Flats. (The primary means of remov-

sizes* (AOS) of approximately 0.1 mm.

ing WP particles of this size is allowing the spoils

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

MATERIALS

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

specific remediation technique has not yet been

The soil used in the laboratory test was col-

determined. It will most likely involve heating

lected from ponds to be dredged in Eagle River

and drying the sediment to volatilize the WP. Like-

Flats, Alaska. It is primarily glacially derived

wise, it is not yet known where the soil will be

silt; a typical grain size distribution of the soil

placed after treatment.

to be dredged is shown in Figure 3 (Lawson

This report describes tests that were conducted

and Brockett 1993). Table 1 lists the geotextiles

to evaluate how well candidate geotextiles for the

tested along with properties of interest as pro-

silt fence retained small particles that were sus-

vided by the manufacturers.

pended 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,

* Apparent opening size: A property that indicates the

was the main criterion evaluated (ASTM D 5141

approximate largest particle diameter that would ef-

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

fectively pass through the geotextile.

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