(a) The engineering report must include a justification for the proposed sludge dewatering units, including design calculations, results from any pilot studies, all assumptions, and appropriate references.
(b) The design of a dewatering unit must be based on mass balance principles.
(c) General Requirements.
  (1) Centrate or Filtrate Recycle.
    (A) The drainage from beds and centrate or filtrate from dewatering units must be returned to the headworks of the wastewater treatment facility for treatment.
    (B) The design of a treatment unit downstream from a dewatering unit must be based on the organic load from the centrate or filtrate recycle.
  (2) Sludge with Industrial Waste Contributions. A dewatering system must prevent the release of any constituent (such as a free metal, an organic toxin, or a strong reducing or oxidizing compound) that adversely impacts human health, safety, or welfare, water quality, or compliance with the associated wastewater permit.
  (3) Redundancy.
    (A) A mechanical dewatering system must have at least two dewatering units, unless the engineering report justifies adequate storage or an alternative means of sludge handling.
    (B) Mechanical dewatering units must be able to dewater the average daily sludge flow with the largest dewatering unit out of service.
  (4) Storage Requirements.
    (A) A mechanical dewatering system must have separate storage if the equipment will not operate on a continuous basis and the wastewater treatment facility has no digesters with built-in short-term storage.
    (B) In-line storage of stabilized or unstabilized sludge must not interfere with any treatment unit.
    (C) The separate sludge storage from a primary digester must be aerated and mixed to prevent nuisance odor conditions.
  (5) Sampling Points. A dewatering system must have sampling stations before and after each dewatering unit and must allow periodic evaluation of the dewatering process.
  (6) Maintenance. Each dewatering system unit must have a bypass to allow for maintenance, repair, and replacement. The engineer must specify where the bypass flow will be routed in the engineering report.
(d) Sludge Conditioning.
  (1) The design and location of a chemical addition point must consider interactions of the chemical with other chemicals and processes used in the wastewater treatment facility.
  (2) A dewatering system must provide adequate mixing time for the reaction between an additive and the sludge. Any subsequent handling must eliminate floc shearing.
  (3) The engineering report must include a pilot plant or full-size performance data used to determine the characteristics and design dosage of any sludge additive.
  (4) The engineering report must justify the in-stream flocculation and coagulation system design by including comparable performance data or pilot plant data.
  (5) The engineering report must include whether the mixers require conditioning tanks.
  (6) The engineering report must include calculations for a range of detention times.
  (7) Solution storage capacity, at maximum chemical demand, must be based on:
    (A) the amount of chemical needed per shift for continuous processes; or
    (B) the amount of chemical needed for a full batch for intermittent and batch processes.
  (8) Solution storage capacity may be reduced if the specific chemical or additive selected is adversely affected by storage.
  (9) The engineering report must justify any storage volume reduction and any other method used to ensure a continuous supply of chemicals by accounting for chemical use through a full operating day or a full batch.
(e) Sludge Drying Beds.
  (1) The size of sludge drying beds must be based on data from a similar wastewater treatment facility in the same geographical area with the same influent sludge characteristics.
  (2) If the data required by paragraph (1) of this subsection is not available, or if the executive director determines that the data is not appropriate for a proposed wastewater treatment facility, the design of sludge drying beds must be based on the following:
    (A) Open Beds.
      (i) A sludge drying bed system must have at least two sludge drying beds.
      (ii) The engineering report must include the calculation of the minimum surface area for a sludge drying bed using the values in the following figure for an area of the state with less than 45 inches annual average rainfall or less than 50% annual average relative humidity, as determined by data from the nearest National Oceanic and Atmospheric Administration's weather station that has at least ten years of data. The entire period of record for the weather station must be used.
Attached Graphic
      (iii) Another method of sludge dewatering is required in lieu of a sludge drying bed in an area of the state that experiences either 45 or more inches of average annual rainfall or 50% or greater annual average relative humidity, as determined by data from the nearest National Oceanic and Atmospheric Administration's weather station that has at least ten years of data. The entire period of record for the weather station must be used.
      (iv) A sludge drying bed system must:
        (I) dewater sludge during normal operations;
        (II) provide accelerated sludge dewatering during abnormally wet conditions;
        (III) store accumulated sludge during periods of extended high humidity and rainfall;
        (IV) use an alternative dewatering method to dewater the sludge during periods of extended high humidity and rainfall; and
        (V) prevent the unauthorized discharge of solids from the sludge drying beds.
      (v) The engineering report must justify the use of innovative or non-conforming sludge drying beds in high rainfall, high relative humidity areas of the state, as described in clause (iii) of this subparagraph.
    (B) Gravel Media Beds. A gravel media bed must be laid in two or more layers. The gravel around the underdrains must be properly sized to allow drainage. The gravel around the underdrains must be at least 12 inches deep, extending at least 6.0 inches above the top of the underdrains. The top layer of a gravel media bed must be at least 3.0 inches thick and must consist of gravel 1/8 inch to 1/4 inch in size.
    (C) Sand Media Beds. A sand media bed must consist of at least 12 inches of sand with a uniformity coefficient of less than 4.0 and an effective grain size of at least 0.3 millimeters but not more than 75 millimeters above the top of the underdrain.
    (D) Underdrains.
      (i) The underdrains must be at least 4.0 inches in diameter and a slope of at least 1.0% to the drain.
      (ii) The underdrains must not be spaced more than 20 feet apart.
      (iii) The engineering report must specify where the flow from the underdrains will be routed.
    (E) Decanting. A sludge drying bed may have a method of decanting supernatant installed on the perimeter of the bed. The decanted liquid from a sludge drying bed must be returned to the headworks of the wastewater treatment facility or to the beginning of the secondary treatment process.
    (F) Walls.
      (i) The interior walls of a sludge drying bed must be watertight and extend 12 inches to 24 inches above and at least 6 inches below the bed surface.
      (ii) The exterior walls of a sludge drying bed must be watertight and extend 12 inches to 24 inches above the bed surface or ground elevation, whichever is higher.
    (G) Sludge Removal.
      (i) A sludge drying bed system must be arranged to facilitate sludge removal.
      (ii) The sludge drying beds must have concrete pads for vehicle support tracks on 20 foot centers for all percolation type sludge beds.
    (H) Sludge Influent.
      (i) A sludge pipe to the sludge drying beds must terminate at least 12 inches above the surface of the media and be arranged so that the pipe drains to a sump that pumps to the headworks of the wastewater treatment facility or the influent lift station.
      (ii) A sludge discharge point must have a concrete splash plate.
    (I) Drying Bed Bottom.
      (i) The bottom of a sludge drying bed must consist of a layer of clayey subsoil having a thickness of a least 1.0 foot and a permeability of less than 1 × 10-7 centimeters per second.
Cont'd...