Gowanus Canal CAG Meeting
Tuesday, June 26, 2018
Mary Star of the Sea Senior Apartments, 41 1st Street
Announcements:
Doug Sarno opened the meeting at 6:35.
The May meeting summary was approved with no revisions.
Project Updates
Christos Tsiamis, Remedial Project Manager for EPA, presented the updates.
The Fourth Street Basin pilot study at the top of the canal is being conducted under order with National Grid for dredging of sediments and reconstruction of the cut-off wall in the study area. Approximately 12 feet of sediment was removed at an efficient pace. Some additional areas still need to be addressed, which have enough tar with potential to move upward and overwhelm the cap to be placed there. We studied this aspect at the 7th Street Basin pilot three years ago, and because this is also a pilot study, we did not feel like it makes sense to bring back the equipment and go after these materials at this time. We will do that when we begin the actual cleanup project. Surprisingly, the native sediment is very compact. We cannot use the buckets that dig up the soft-sediment to remove this native sediment, so as a result the process is going slower. This lesson informs us how to approach the middle/main part of the canal. Because of the compacting, the way we’re approaching it with sand now, the process is going slower but moving nevertheless.
The engineers used new techniques to estimate contamination in the native sediment with a potential to migrate. From what we can see visually of the material, the conclusions from indirect measures proves to be that we are correct. We are learning a lot of lessons, and the pace changes according to difficulties we encounter. EPA has done a couple of excavations, and once we’re done with that we will begin the cap, targeting the end of summer now, not June, because of the need to excavate different material. One thing we will be trying there is two ways of laying the cap – a mixture of sand and clay, then sand and activated carbon and then sand.
We will also explore how to install the cap, what is the proper technique, so this process will take time. There are two methods, 1) hydraulic, placing material out of a pipe like a sprinkler that moves back and forth, and 2) mechanical capping, using a barge and bucket (like ones used during dredging) and placeing deposits of cap material into the water
We will try both methods side by side to decide which one to use during the full installation. This is the work remaining on the pilot; there are still lots of problems to be solved, but we’re engineers and we like problems.
The EPA has been in discussion with the PRP engineers and have recommended a different approach to meet the timeline for a February 2019 design completion date. They are allowed to submit designs a little later in April 2019, but they must hire a construction engineer up front instead of waiting until the end of the design and going to bids. So this new option means having a construction group onboard, accepted, and ready to go as soon as the design is complete, and will bring results in how quickly we can begin construction. We should start in early 2020 rather than later in the year. Dredging at the top of canal should start by 2020.