Section Env-Wq 716.14 - Sludge Drying Beds(a) Sludge drying beds shall be sized based on 2.0 square feet per capita when the drying bed is the primary method of dewatering and 1.0 square feet per capita when the drying bed is to be used as a backup dewatering unit.(b) Sludge drying beds shall include an impervious membrane under the underdrain system.(c) The lower course of gravel around the underdrains shall be graded and a total of 12 inches in depth, extending 6 inches above the top of the underdrains. A 3-inch layer of gravel 1/8-inch to 1/4-inch in size shall be placed above the gravel bedding.(d) The top layer of the bed shall consist of a level-graded 9 to 12 inches of clean sand with an effective grain size of 0.3 to 0.6 mm or a comparably graded artificial media.(e) Subnatant collected from the underdrains shall be returned to the treatment process prior to the biological treatment unit.(f) Drying beds shall be covered to protect from precipitation.(g) Bed underdrains shall be ductile iron, HDPE, PVC, or concrete pipe no less than 4 inches in diameter and spaced not more than 10 feet between centers.(h) Paved surface beds shall be prohibited.(i) Bed walls shall be watertight and extend 15 to 18 inches above the top layer or surrounding topography, whichever is higher, and 6 inches below the invert of the underdrain. Outer walls shall be curbed to prevent soil from washing on to the beds.(j) Not fewer than 2 beds shall be provided.(k) Sludge drying beds shall be permitted in accordance with Env-Or 700.(l) Alternative dewatering methods or sludge storage shall be provided during cold weather months when sludge drying beds are not effective.N.H. Code Admin. R. Env-Wq 716.14
Adopted byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.