ENTACT Environmental Remediation Services, Sediment Removal

Brook Sediment Removal and Bank Soil Remediation
Remedial activities performed by ENTACT included the removal of impacted sediments from within the stream bed and the adjacent bank, east and west of the stream bed to pre-determined elevation or as directed by post excavation confirmatory soil sampling. Stream bed sediments and bank soils were impacted with volatile organic compounds (VOCs) resulting from historical site operations.

After removal of impacted sediment, the stream bed was backfilled to original grade with compacted common fill placed to within 6 inches of final grade and a 6 inch layer of 6 mm gravel to final grade. Approximately 80 lineal feet of the stream bed subgrade was covered with a 40 mil HDPE geomembrane liner across the stream width to prevent re-contamination of remediated areas from groundwater influx. Riprap was manually installed in areas of the stream where the adjacent bank was disturbed as toe protection.

Disturbed stream bank areas were restored with common fill and topsoil. Common fill was placed in 6 inch compacted lifts from subgrade to within 6 inches of final grade with the final 6 inches backfilled with topsoil. The restored areas were disced and seeded with switchgrass, flat pea and red top seed mix. Seeded areas were mulched and natural fiber erosion control matting installed on seeded slopes. 12 inch diameter coir fiber logs were installed at the toe of the disturbed banks and secured in place with wooden stakes. Once in place, plant plugs were placed on the coir log spaced at 6 inch intervals. Plant plugs consisted of Swamp Milkweed, Sweet Flag, Sedges, Joe-Pie Weed, Blueflag Iris, Rushes, Cardinal Flower, Duck Potato and Bulrushes.

Tree and wetland shrub species located within the disturbed stream bank areas were replaced at a 1:1 and 1:1.25 ratio respectively. Tree species included Sweet Gum, Green Ash, Black Willow and Purpleosier Willow. Wetland shrubs included Red Osier Dogwood, Highbush Blueberry, Silky Dogwood and Smooth Adler. Two inches of mulch were placed around the perimeter of new plantings. Tree trunks were staked and wrapped with translucent plastic tubes for protection.

The stream bed is considered a State Open Waterway. The adjacent banks were delineated wetlands with intermediate wetlands value. Work within the stream bed and adjacent bank was performed under authority of the state environmental authority, Land Use Regulation Program, Statewide General Permit #4.