Chapter NR 110

NR 110.15(5)(q)1. 1. Sewage treatment facilities shall be enclosed with a fence to discourage entry of animals or unauthorized persons.

NR 110.15(5)(q)2. 2. Hand rails shall be installed around all treatment tanks and in other areas of the facility where the potential of falling exists.

NR 110.15(5)(q)3. 3. The department recommends the following safety measure be considered in the design of wastewater treatment facilities:

NR 110.15(5)(q)3.a. a. Provision of first aid equipment;

NR 110.15(5)(q)3.b. b. Posting of “No Smoking” signs in hazardous areas;

NR 110.15(5)(q)3.c. c. Provision of protective clothing and equipment such as gas masks, goggles, gloves, hard hats, and safety harness;

NR 110.15(5)(q)3.d. d. Portable blower and hose;

NR 110.15(5)(q)3.e. e. Portable lighting equipment; and

NR 110.15(5)(q)3.f. f. Nonpotable water supply bibs which are labeled.

NR 110.15(5)(q)4. 4. The safety and health rules set forth in ch. SPS 332, and appropriate federal and local safety codes shall be adhered to in the operation of wastewater treatment plants.

NR 110.15(5)(q)5. 5. Specific safety requirements for hazardous chemical handling are found in s. NR 110.22 (4).

NR 110.15(5)(q)6. 6. Specific safety requirements for chlorination facilities are found in s. NR 110.23 (2) (g).

NR 110.15(6) (6) Water supply.

NR 110.15(6)(a) (a) Potable supply. Any sewage treatment facility which has a laboratory shall be provided with a potable water supply.

NR 110.15(6)(b) (b) Plumbing. Sewage treatment facility plumbing systems shall be designed in accordance with ch. SPS 382.

NR 110.15(6)(c) (c) Connection to public water systems. Connection of a sewage treatment facility plumbing system to a public water system shall comply with the requirements of s. NR 811.25 and ch. SPS 382.

NR 110.15(6)(d) (d) On-site wells. Construction of wells for supplying water to a sewage treatment facility shall comply with the requirements of the approval obtained under s. NR 812.09 (4) (b).

NR 110.15 History History: Cr. Register, November, 1974, No. 227, eff. 12-1-74; r. and recr. (1) (c), Register, March, 1978, No. 267, eff. 4-1-78; r. and recr. Register, February, 1983, No. 326, eff. 3-1-83, cr. (4) (d), Register, November, 1990, No. 419, eff. 12-1-90; corrections in (5) and (6) made under s. 13.93 (2m) (b) 7., Stats., Register, September, 1995, No. 477; corrections in (5) (q) 4., (6) (b), and (c) were made under s. 13.93 (2m) (b) 7., Stats., Register, May, 2001, No. 545; CR 09-123: am. (2) (a) and (4) (c), cr. (3) (e) Register July 2010 No. 655, eff. 8-1-10; corrections in (5) (q) 4., (6) (b) and (c) made under s. 13.92 (4) (b) 7., Stats., Register January 2012 No. 673; CR 12-027: r. (2) (c) to (e), r. and recr. (5) (d), am. (5) (g), r. and recr. (5) (h) Register July 2013 No. 691, eff. 8-1-13; CR 18-095: am. (6) (d) Register June 2020 No. 774, eff. 7-1-20; correction in (6) (b) made under s. 35.17, Stats., Register June 2020 No. 774.

NR 110.16 NR 110.16 Screening devices.

NR 110.16(1) (1) General design considerations.

NR 110.16(1)(a) (a) Applicability. All wastewater treatment plants shall be provided with protection for pumps and other equipment by installing coarse screens, bar racks, mechanically cleaned bar racks or comminutors.

NR 110.16(1)(b) (b) Location.

NR 110.16(1)(b)1. 1. Screening devices installed in a building where other equipment or offices are located shall be separated from the rest of the building and provided with separate outside entrances.

NR 110.16(1)(b)2. 2. Screening devices shall be provided with convenient access.

NR 110.16(1)(b)3. 3. Screening devices may not be located such that changes in backwater elevations will interfere with the accuracy of upstream flow measuring equipment.

NR 110.16(1)(c) (c) Ventilation. Screening areas shall be ventilated.

NR 110.16(1)(d) (d) Channels.

NR 110.16(1)(d)1. 1. The channel preceding and following the screen shall be shaped to minimize settling of solids. Fillets shall be installed as necessary.

NR 110.16(1)(d)2. 2. The screen channel invert must be at least 8 centimeters (3 inches) below the invert of the incoming sewer.

NR 110.16(1)(d)3. 3. Where multiple screening units are installed the channels shall be equipped with the necessary gates to direct flow from any one screening unit. Methods for dewatering each channel shall be provided.

NR 110.16(1)(d)4. 4. Entrance channels shall be designed to distribute flow uniformly to the screening units.

NR 110.16(1)(e) (e) Handling screenings. Adequate facilities must be provided for removal, handling and storage of screenings in a sanitary manner. Hand-cleaned screening facilities must include an accessible platform from which the operator may rake screenings. Suitable drainage facilities must be provided for both the platform and the storage areas.

NR 110.16(2) (2) Design requirements for screening devices.

NR 110.16(2)(a) (a) Bar screens.

NR 110.16(2)(a)1. 1. Clear spacing between bars may not be less than 2.5 centimeters (1 inch), nor more than 5 centimeters (2 inches).

NR 110.16(2)(a)2. 2. Bar screens must be placed on a slope of 30 to 45 degrees with the horizontal with the exception of those installed for emergency use.

NR 110.16(2)(a)3. 3. Approach velocities may be no less than 38 centimeters per second (1.25 feet per second) at design average flow conditions to prevent settling, and no greater than 91 centimeters per second (3 feet per second) at maximum design daily flow to prevent forcing material through the openings.

NR 110.16(2)(b) (b) Mechanical screens.

NR 110.16(2)(b)1. 1. Maximum clean spacing between bars may not exceed 5 centimeters (2 inches).

NR 110.16(2)(b)2. 2. Approach velocities may be no less than 38 centimeters per second (1.25 feet per second) at average design flow conditions to prevent settling, and no greater than 91 centimeters per second (3 feet per second) at maximum daily flow to prevent forcing material through the openings.

NR 110.16(2)(b)3. 3. All mechanical units which are operated by timing devices shall be provided with auxiliary controls which will set the cleaning mechanism in operation at a preset high water elevation.

NR 110.16(2)(b)4. 4. Automatic controls shall be supplemented by a manual override. Manual overrides shall be located in view of the equipment.

NR 110.16(2)(b)5. 5. Electrical fixtures and controls in screening areas where hazardous gases may accumulate shall meet the requirements of the national electrical code for class 1, group D, division 1 locations.

NR 110.16(2)(c) (c) Comminutors.

NR 110.16(2)(c)1. 1. Comminutors shall be designed to comminute the maximum design flow rate.

NR 110.16(2)(c)2. 2. Comminutor channels shall be designed to contain the upstream water depth associated with the head loss which occurs at maximum design flow without surcharging the incoming sewer or other treatment processes. The expected head loss shall take into account the effects of clogging during operation.

NR 110.16(2)(c)3. 3. Comminutor channels shall be equipped with drains.

NR 110.16(2)(c)4. 4. A screened bypass channel shall be provided so that the comminutor may be removed from service for maintenance.

NR 110.16(2)(c)5. 5. Bypass channels will not be required where 2 comminutors are installed. Each comminutor shall be capable of comminuting the maximum design flow.

NR 110.16(2)(c)6. 6. Control switches or a disconnecting device for the comminutor shall be located in view of the comminutor.

NR 110.16(2)(c)7. 7. Electrical fixtures and controls in comminutors areas where hazardous gases may accumulate shall meet the requirements of the national electrical code for class 1, group D, division 1 locations.

NR 110.16 History History: Cr. Register, November, 1974, No. 227, eff. 12-1-74; r. and recr. Register, February, 1983, No. 326, eff. 3-1-83.

NR 110.17 NR 110.17 Grit removal facilities.

NR 110.17(1) (1) Applicability. Grit removal facilities are recommended for all sewage plants and are required for plants receiving sewage from combined sewers or from sewer systems receiving substantial amounts of grit.

NR 110.17(2) (2) Design considerations.

NR 110.17(2)(a) (a) Location. Where practical, grit chambers should precede influent pumps. When installed, grit chambers shall precede all major treatment units.

NR 110.17(2)(b) (b) Protection. All grit chambers shall be preceded by a bar rack, coarse screen or comminutor.

NR 110.17(2)(c) (c) Housed facilities.

NR 110.17(2)(c)1. 1. Enclosed grit removal areas shall be ventilated. Fresh air shall be introduced continuously at a rate of 12 air changes per hour, or intermittently at a rate of 30 air changes per hour.

NR 110.17(2)(c)2. 2. All electrical work in enclosed grit removal areas where hazardous gases may accumulate shall meet the requirements of the national electrical code for class 1, group D, division 1 locations.

NR 110.17(2)(d) (d) Number of units. Grit removal facilities shall have at least 2 hand-cleaned units, or a mechanically cleaned unit with a bypass.

NR 110.17(2)(e) (e) Grit handling.

NR 110.17(2)(e)1. 1. All facilities not provided with positive velocity control shall include means for grit washing to further separate organic and inorganic materials.

NR 110.17(2)(e)2. 2. Grit removal facilities located in deep pits shall be provided with mechanical equipment for hoisting or transporting grit to ground level. Impervious, nonslip, working surfaces with adequate drainage shall be provided for grit handling areas. Storage areas for wasted grit shall be provided.

NR 110.17(2)(f) (f) Basis of design. Design of grit chambers shall be based on the size and specific gravity of the grit particle to be removed. If this information is not obtained from actual field measurements, then the design shall assume removal of all particles retained on a 65 mesh (0.21 mm) sieve and having a minimum specific gravity of 2.65. The design requirements of sub. (3) are based on these assumptions.

NR 110.17(3) (3) Design requirements.

NR 110.17(3)(a) (a) General requirements.

NR 110.17(3)(a)1. 1. Inlet turbulence into grit chambers shall be minimized.

NR 110.17(3)(a)2. 2. Drains or other means for dewatering each grit unit must be provided.

NR 110.17(3)(a)3. 3. An adequate supply of water under pressure shall be provided for cleaning grit equipment.

NR 110.17(3)(b) (b) Velocity controlled grit chambers. Positive hydraulic control shall be provided to maintain a channel velocity of 30 centimeters per second (one foot per second) through the expected flow range. Positive hydraulic control shall be provided by one of the following:

NR 110.17(3)(b)1. 1. A flow channel with a parabolic cross-section;

NR 110.17(3)(b)2. 2. A proportionate weir; or

NR 110.17(3)(b)3. 3. A Parshall flume.

NR 110.17(3)(c) (c) Aerated grit chambers.

NR 110.17(3)(c)1. 1. Air rates should be in the range of 4.6 to 12.4 liters per second per meter (3 to 8 cubic feet per minute per foot) of tank length.

NR 110.17(3)(c)2. 2. The detention time at the maximum design flow rate should not exceed 3 minutes.

NR 110.17(3)(c)3. 3. Inlets and outlets shall be designed to prevent short circuiting.

NR 110.17(3)(c)4. 4. The design of the grit chamber shall be such to avoid producing dead spaces.

NR 110.17(3)(d) (d) Short-term sedimentation tanks.

NR 110.17(3)(d)1. 1. Inlets shall be designed to distribute flow evenly across the tank.

NR 110.17(3)(d)2. 2. Tanks shall be deep enough to prevent turbulent flow.

NR 110.17(3)(d)3. 3. An additional depth of 15 to 25 centimeters (6 to 10 inches) shall be provided for raking mechanisms.

NR 110.17(3)(d)4. 4. Surface area of the sedimentation tank shall be designed not to exceed a surface settling rate of 1,900 cubic meters per day per square meter (46,000 gallons per day per square foot).

NR 110.17 History History: Cr. Register, November, 1974, No. 227, eff. 12-1-74; r. and recr. Register, February, 1983, No. 326, eff. 3-1-83.

NR 110.18 NR 110.18 Settling tanks.

NR 110.18(1) (1) Design considerations.

NR 110.18(1)(a) (a) Multiple settling tanks.

NR 110.18(1)(a)1. 1. Multiple settling tanks shall be provided at all sewage treatment plants with an average design flow which exceeds 1,890 cubic meters per day (0.5 million gallons per day).