In 1969, employees working at a dam in Oregon disposed of three old electrical capacitors by dumping them into a nearby river. Each capacitor contained 10 to 12 gal of oil heavily laden with polychlorinated biphenyls (PCBs). Over the years, the capacitors corroded and dispensed contaminated sediment over several acres in and along the river.
Intensive studies were performed by a remediation agency and their consultants. The studies' results revealed that the pollutants would be most efficiently removed by diver-assisted suction dredging and a $1.9-million budget.
Rain for Rent’s turnkey system was hoisted onto barges on the river.
The agency's proposition included:
- Divers with suction dredge pipe to remove PCB-tainted sediment;
- Sediment piped into treatment and filtration system staged on three barges tied side to side;
- Thirteen tanks to dewater the dredge stream;
- Decanted fluid pumped through sand filter and activated carbon vessel to remove PCBs prior to direct discharge back into the river; and
- Completion within 45 days to avoid interfering with upcoming salmon spawning season.
Rain for Rent responded to the agency's bid request with a site visit and performed an on-site sediment flocculation test to determine particulate size and loading, then reviewed the agency's available geological test and engineering data. Filtration specialists from Rain for Rent identified a series of technical concerns. They discovered that the initial dewatering plan would not accomplish the required effluent water quality within the allotted time frame. The time frame was not long enough for the solids and PCBs to settle in the tanks, which would prevent a continuous dredge operation.
Rain for Rent’s sound attenuated Power Prime pumps and sand media filters.
Rain for Rent offered a new set of technical specifications for a more efficient solution. The system design had to be approved by the project's consultants, the U.S. Army Corps of Engineers, several state and local water quality regulators, the U.S. Fish & Wildlife Service and local Native American associations.
With project approval obtained, Rain for Rent set up two DV-100 4-in. Power Prime pumps, one to pump silt at 400 gal per minute (gpm) into 13 dewatering boxes for primary sediment settling, and one to pump muddy water into three bi-level tanks. Due to the small particle size and the high solids concentration, a Chitosan flocculent injection system was used to accelerate settling.
The flow was pumped into three weir tanks for additional settling. A 6-in. DV-150 sound attenuated Power Prime pump, controlled by a radar gauge, was mounted to a weir tank and pumped the flow into a portable water quality monitoring system. This system was equipped with an AnDRU Box, which monitored the turbidity and recirculated the flow if the discharge was above the established 400 nephelometric turbidity units (NTU). The next step in the filtration process included one 48-4 sand filter, one BF-1000 with five micron bags, one PF-1000 with one micron cartridge and a 5,000-lb activated carbon vessel. The 500-gpm flow was again monitored for turbidity prior to final discharge, and showed a typical effluent of 0.15 NTUs—the river background was 3 NTU.
Rain for Rent safely completed the entire dredging and filtration project within the 45-day time limit. The salmon spawning season was uninterrupted and the Army Corps of Engineers was impressed with the creative solution.