Computation of lot area. In computing the area of any lot, no part of a public or private way and no part of a pond or river shall be included. At least 80,000 contiguous square feet or 100% of the required lot area, whichever is less, of every lot laid out for residential use shall be land exclusive of area subject to protection under the Wetlands Protection Act, MGL c. 131, § 40. Each lot shall be capable of containing a one-hundred-fifty-foot-diameter circle within which there is no area subject to protection under the Wetlands Protection Act, MGL c. 131, § 40, and within which any principal building shall be located. All easements, except easements specifically serving the individual dwelling, shall not intersect with the one-hundred-fifty-foot-diameter circle.