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Title: Silt fence testing for Eagle River Flats dredging
Authors: U.S. Army Environmental Center.
U.S. Army Garrison (Alaska)
Henry, Karen S.
Hunnewell, Susan T.
Keywords: Dredging
Silt fence
Filtering efficiency
White phosphorus
Eagle River Flats, Alaska
Fort Richardson, Alaska
Publisher: Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Special report (Cold Regions Research and Engineering Laboratory (U.S.)) ; 95-27.
Description: Special Report
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.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Special Report

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