O&R begins ramping up this week on the final phase of its project to clean up the coal tar residue at the former manufactured gas plant (MGP) site at 55 Gedney Street in the village of Nyack.
O&R already has successfully cleaned up the upland part of that lot.
In 2005 through 2006, O&R excavated and trucked out more than 20,000 tons of impacted soil and replaced it with clean fill on the western part of this site.
In 2006 and 2007, O&R solidified the coal tar residue located in soils along the river on the eastern part of the site and entombed these impacts in an underground cement monolith — a process known as in situ solidification.
When the work was complete, the site was covered with clean topsoil, 2-feet-deep, and restored to a park-like setting.
The in situ solidification process now will be repeated to address impacts remaining in soils along the shoreline.
A sheet-pile cofferdam will be installed along the shoreline to manage river water while the solidification process takes place.
Equipment for the solidification process includes large drill rigs with specialized augers and a batch plant to mix the cement slurry.
The top two feet of soil will be excavated and soils below will be mixed with the cement grout material to the depth of the coal tar residue and entombed.
Once the solidification process is completed, river sediments containing coal tar impacts will be dredged up and trucked to an approved off-site treatment/disposal facility.
Dredge work will extend approximately 150 feet into the river.
Before the sediments are trucked off site, they will be de-watered and amended to dry them out for transport.
The management of the sediments will take place under a large, tent-like, fabric structure equipped with an air-handling and carbon-filter air treatment system.
These air-handling devices will be shrouded with sound-dampening equipment.
The temporary structure will be approximately 68 feet wide, 82 feet long and 29 feet high.
Real-time air monitoring will be conducted on a 24-hour, seven-day per week basis at key perimeter points to ensure that air monitoring criteria are met so that odor mitigation steps can be taken if needed.
The excavated soil and sediments will be loaded into tractor-trailers, whose tires will be cleaned of any ground soil before leaving the site.
The trucks will proceed up Main Street, taking a right onto Polhemus Street, which leads directly to an entrance ramp to the NYS Thruway northbound.
This is the same route that was successfully used during the previous work at the site.
The excavated soil and sediments will be trucked for treatment and disposal to an approved, licensed facility in Keasbey, N.J.
The site will be restored to its current park-like setting with a stone-slope covering to protect the shoreline.
Currently, O&R estimates that approximately 19,500 tons of soil and sediment will be trucked out for disposal and about 6,850 cubic yards of soil will be solidified to entomb remaining coal tar residue.
The project is due to be completed by December 2014.
This phase of the project is expected to cost $9.8 million. To date, O&R has spent $14.9 million remediating the Nyack MGP site.
The construction work will be performed Monday through Friday 7 a.m. to 5 p.m.
Press Release, March 18, 2014