A common issue designers and installers face while implementing an in-situ sediment remediation project using activated carbon is the need to apply material to inaccessible sediment.  Shallow waters, tidal fluctuation, trees, power lines, and steep slopes can prohibit the use of equipment such as telescoping conveyors, or even small pneumatic spreaders.

Jacobs Engineering, on behalf of Metro, faced all of these issues when tasked to apply SediMite to approximately 1.8 acres of contaminated sediment at the St. Johns Landfill in Portland, OR.  The site’s shallow, depositional characteristics created wide expanses of target sediment set between a relatively small navigable channel and steep, heavily vegetated banks.

To address these application challenges, a heavy-lift helicopter with a 4 cubic yard hopper/spreader was used to apply the SediMite pellets from above. The activated carbon dose requirement to remediate the organic contaminants in surficial sediment in-situ were achieved by predetermining the treatment area corresponding to the SediMite capacity of the hopper and marking these areas with sediment stakes.   The helicopter pilots used the markers to maneuver the aircraft and uniformly apply each hopper load. Two hoppers were used to minimize cycle time, with one hopper being filled while the other was being flown. The relatively high dose of activated carbon in SediMite and its relatively low bulk density allowed for minimal numbers of helicopter flights.

Sediment Solutions met client requests by providing pellets of carbon sourced from renewable feedstock, and in a specific formulation to withstand the forces of the mechanical spreader and minimize dust. Dust generation was limited and mitigated by rotor wash, and wet spray was not necessary. Verification sampling was conducted to document delivery of the intended dosing to the treatment areas.

With this application success, Jacobs Engineering demonstrated that SediMite pellets can be applied to logistically difficult sites and greatly increased the number of sites for which in-situ sediment remediation using activated carbon may be utilized.