Planning board hears engineers weigh monitored treatment plant against large subsurface septic fields for proposed development

Warren Longacre, an engineer with MJ Engineering, outlined a subsurface disposal option that would replace a centralized wastewater treatment plant with two 10,500‑gallon septic tanks, a dosing tank and a large absorption field sized according to soil percolation rates. Longacre said design uncertainty near the equestrian center led the team to use a conservative 11–15 minute perc rate rather than 1–5 minutes, which increases the field footprint; he estimated a design maximum day flow of about 18,600 gallons and calculated an absorption area need of roughly 23,500 square feet using a 0.8 gallons/day/square‑foot application rate.

Rodney Morrison, civil engineer for the applicant, described an alternative that pairs a packaged wastewater treatment plant with a constructed, vegetated corridor roughly 190–200 feet above the stream to slow, diffuse and increase infiltration of treated effluent before it reaches the watercourse. Morrison said the corridor is intended to improve outflow characteristics and is not being proposed to replace regulatory discharge requirements; he…