Selection of silt fence filter to retain suspended toxic particles

Abstract

A silt fence filter was required to retain potentially toxic particles of 0.1 mm-diameter and larger that could become suspended in water decanted from contaminated dredge spoils. An experimental study was performed to select it. The experiments consisted of two parts, Part 1 tests were conducted according to an accepted engineering standard to compare four candidate geotextiles. Part 2 tests simulated expected field conditions, and were conducted to determine whether one geotextile selected from the Part 1 tests was likely to perform well. The geotextile selected for Part 2 tests retained particles of 0.1 mm and larger, and was installed as a silt fence filter in the field. The silt fence filter was removed shortly after dredging began because it clogged, primarily due to unexpected, high amounts of suspended sediment in the supernatant. The design of the support structure for the silt fence did not permit maintenance of the filter, which may have prevented its failure. The failure may also have been prevented if salt or other materials used to promote flocculation of the dredged spoils were readily available and used on the spoils. The selection procedure described may be helpful because the conditions tested for in the laboratory are likely to occur or could be induced.