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Lake Agawam in Southampton Village this past August. Lake Agawam in Southampton Village
Dredging Southampton Village’s Lake Agawam will be a costly and lengthy project, ranging from $16.5 million and three years to dredge just the north end of the ailing water body, to tens of millions of dollars and potentially decades to dredge the entire lake.
Chic Voorhis, an environmental consultant with engineering firm Nelson, Pope & Voorhis, presented his dredging assessment report to the Village Board on November 23. Voorhis has been a consultant to the village for many years, but for this particular project he noted that he is working with funding provided by the State Department of Environmental Conservation.
Driving up the cost of any proposed dredging project is the expense of shipping the dredge spoils off Long Island and paying disposal fees. Before the material can be loaded into trucks, it must be dewatered, which could involve filling Geotubes with dredge spoils and letting them sit at the south end of the lake for two to three months.
Alternatively, the village is eying a belt press technology for dewatering that would take up less space but require much more time.
Lead and arsenic levels in the lake sediment exceed the DEC’s protection of groundwater guidance values, Voorhis noted. A pesticide was also found to be present in excess of acceptable levels. “Most if not all material would likely need to be transported off Long Island because of those protection of groundwater standards,” he said.
The dredging project would use a hydraulic dredge, which Voorhis explained involves creating a slurry of sediment that is then pumped to an area where it can be dewatered. “You need space, and in the case of Lake Agawam — just because of the surrounding land use and areas — there are no real good options,” he said.
Voorhis said a 2019 report suggested using the Southampton Town Trustees-owned parking lot at the south end of the lake and part of Gin Lane as dewatering sites. That would involve closing a portion of Gin Lane seasonally.
The materials would sit in geotextile dewatering bags for two to three months. The capacity of the area is only 27,000 cubic yards, he noted. If the village chose to only dredge the 65,000 cubic yards of material on the north side of the lake, it would take three seasons to complete the project, at a cost of $5.5 million per season, based on 2019 estimates.
Dredging the entire lake of 336,425 cubic yards of material and dewatering in Geotubes would take 12 to 13 years and $72.7 million, according to Voorhis’s report. Payloaders or excavators would then be needed to load the material for transport for disposal. He said trucking through the village would obviously cause disruption: He estimated 30 trucks running per day for 30 days each spring.
The water will be tested before it returns to the lake. “The hope is that it would not require any special handling,” Voorhis said.
To reduce how much material must be hauled away, the DEC pitched “in-lake soil retention” as an option, Voorhis said. Materials would be capped in the lake and used to create marsh.
“If we just created an island or a peninsula, they said that would be considered fill in a freshwater wetlands, and it would not be permitted — but if it’s created as marsh, that potentially could reduce the amount of material that’s removed,” Voorhis said.
Another option that the village has is to use a belt press. Less material would be removed from the lake annually, but there would be less disruption, according to Voorhis. The press would dry out the material more thoroughly, which would reduce disposal costs.
Voorhis noted that the belt press technology is only offered by one company, Z-Filter. Peter Campbell, a village resident, is the U.S. representative of the international company.
“If we were to use this type of technology, it would be a much longer-term project — and when I say longer, it could go over the course of decades,” Voorhis said.
“What happens if we don’t do anything?” Village Board member Roy Stevenson asked. “And conversely, if we do, do something, how do we stop the lake from getting polluted again from all the same stuff coming into the lake over the next 20 or 30 or 40 years and creating the same problem?”
Voorhis said there is an influx of nitrogen and phosphorus into the lake from cesspools, sanity systems, stormwater, waterfowl, atmospheric deposition and other sources. “Reducing stormwater inputs into the lake is a huge benefit,” he said.
He pointed out that the Lake Agawam management plan prepared by his company from 2007-2009 showed the watershed goes all the way up to County Road 39, and since then, there has been a huge effort to reduce the raw stormwater that enters the lake.
A number of storm drains have been installed in the village to capture runoff so the water can recharge in the groundwater table before entering the lake.
New innovative/alternative sanitary systems and plans to add sewers to the village’s downtown will also help, according to Voorhis, as well as reducing landscaping and fertilization near the lake.
“Many small incremental improvements are needed to improve the water quality of the lake,” he said. “So dredging the sediments is one of them — it is considered to be a major one — but other remedies do need to be implemented and are being implemented that we hope would reduce sediment input as well as pollutant input.”
