Work is underway near the playground at Tisbury School to install a new type of leaching system for treated wastewater. Its main purpose is to help reduce nitrogen-loading in Lake Tashmoo and Lagoon Pond.
The system utilizes two vertical “wicks,” which consist of holes two feet in diameter, about the size of a manhole, and about 100 feet deep, according to Tisbury department of public works director Fred LaPiana. They are about 100 feet apart and 10 feet away from the road on West William Street, on the far side of the school playground, within the town road layout.
The Wright-Pierce engineering firm custom-designed the wicks. Layne Inc. is installing them and hopes to get the drilling done and the equipment moved before school starts, Mr. LaPiana told The Times in a phone conversation Monday. The wicks will be capped with a heavy steel cover and separated from the playground area with a split rail fence.
“The key with this system is that to reintroduce treated water back into the environment in the conventional sense would require clear-cutting acres of land to install a leaching field – this just involves two-foot diameter holes,” Mr. LaPiana said. “With trees and land being so precious in this town, this is an ideal solution.”
Treated water from Tisbury’s central wastewater collection plant will be pumped to the wicks via a pipe already in service to the leaching field behind the new emergency services facility. The water will flow down the wicks through small stones about 60 feet deep to be discharged away from the path of the groundwater that runs into the ponds.
“Even though the nitrogen levels are low in the treated water that leaves our plant, given the great volumes of water that are released, over time even a small amount tends to build up in the ponds,” Mr. LaPiana said. “We want to make sure the treated water doesn’t go into the ponds, but eventually finds it way back to the harbor, where it has less impact. That’s why this location was chosen.”
Once the leaching system project and wastewater plant upgrade are complete, Mr. LaPiana said the town will invite businesses in the B-2 district that would like to hook up to the wastewater plant to do so. They will be responsible for installing a pipe to hook up their buildings to the sewer system. “This project provides them an opportunity to dispose of their wastewater so that it doesn’t impact Tashmoo Pond,” Mr. LaPiana said.
The cost of the leaching system project, including the engineering work, is about $500,000, Mr. LaPiana said. At town meeting last April Tisbury voters approved borrowing $990,000 to add the leaching field and make upgrades to increase capacity at the wastewater treatment plant. Mr. LaPiana said the projects would be funded from revenues from current customers in the town’s sewer enterprise fund. He also has applied for a grant through the U.S. Department of Agriculture to offset some of the costs.