Nebraska Administrative Code
Nebraska Department of Environment and Energy

Title 123 - Rules And Regulations For The Design, Operation And Maintenance Of Wastewater Works
Chapter 5 - Design Standards
Effective Date of Last Revision: September 4, 2019

The Department gives credit to the Recommended Standards for Wastewater Facilities, prepared by the Great Lakes-Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers as the primary source for the design standards included in Chapter 5.

001 General Design Criteria Requirements

001.01 Wastewater works will be designed in accordance with the design standards listed in this Title. Where specific standards are not included in this Title, the design engineer is to submit a proposed design to the Department for review and approval. The Department will consider approving designs that follow generally accepted engineering guidelines and standards published by national engineering societies, federal environmental agencies, public health boards, or in engineering textbooks used by accredited university engineering programs.

001.02 The hydraulic design of wastewater works will be based on historical flow records. In the absence of flow records, an average daily flow of at least 100 gallons per person per day from domestic sources is to be used. This includes a normal allowance for infiltration and inflow. Flow from commercial, institutional, and industrial sources is to be estimated from similar facilities that have historic flow records.

001.03 The organic loading rates used for designing wastewater treatment facilities is to be based on historical influent data, if at least one year of monthly sampling data exists. In the absence of such data, the design of wastewater treatment facilities are to use an organic loading rate of at least 0.17 pounds of five-day biochemical oxygen demand (BOD5) per person per day and a suspended solids loading rate of at least 0.20 pounds per person per day from domestic sources. The organic loading from commercial, institutional, and industrial sources is to be estimated from similar facilities that have loading records.

001.04 The design of discharging WWTF will be adequate to meet all NPDES permit limits. Flow measurement equipment and sampling locations will be included in the design as required to meet NPDES permit monitoring requirements.

001.05 The design of wastewater collection systems will not include overflow structures of any kind. The design of wastewater treatment facilities will not include passive or unvalved bypass structures that discharge to the ground surface or to waters of the state.

001.06 Wastewater works are to be designed to prevent untreated or partially treated wastewater from entering floodwaters of a 100-year flood and are to prevent floodwaters from entering the wastewater works. The deck of lift stations, the top of earthen dikes, and the top of all other
structures designed to store, convey, or treat wastewater or sludge will be at least one foot above the 100-year flood elevation.

001.07 All WWTF are to have an alternative source of power to provide pumping of wastewater through the treatment facility. The alternative source of power will be adequate to pump the peak day flow rate. This requirement is to be met by either an engine generator or by a second independent electrical supply source. Storage and subsequent treatment may also be used to meet this requirement.

001.08 All WWTF that have disinfection units are to have backup power provided for the disinfection process.

001.09 Each WWTF is to be enclosed with a fence, unless exempted by the Department. Fences shall be at least 42-inches high and adequate to keep out grazing animals, if located in rural areas, or pets and unauthorized persons if located in public areas. Suitable warning signs are to be posted.

001.10 All weather access roads will be provided to wastewater works, as necessary, to maintain normal operations of the wastewater works.

002 Gravity Sewers

002.01 Gravity sewers will be designed to achieve a minimum velocity of 2.0 feet per second when flowing full based on Manning’s Equation, using an “n” value of 0.013 (Refer to Chapter 6, 002 for approval of alternative designs).

002.02 The minimum diameter of public gravity sewer mains carrying raw domestic wastewater will be eight inches, except that six-inch sewers may be used if the distance between manholes is not greater than 400 feet, the total length of six-inch sewer is not greater than 800 feet, and the sewer is located where it will not need to be extended for future growth.

002.03 Gravity sewers will be designed with a uniform slope between manholes. This does not apply to inverted siphons.

002.04 Where velocities greater than 15 feet per second are attained, special provisions will be made to protect sewers from displacement by impact forces and erosion.

002.05 Sewers with slopes of 20% or greater will be reinforced with concrete anchors. Erosion collars will be provided around steep sewers where migrating storm water could cause erosion of pipe bedding.

002.06 Curvilinear sewers are restricted to simple curves. The radius of curvature will not be less than the pipe manufacturer’s recommendation or be less than 100 feet. Elbows or couplings with deflections greater than three degrees will not be used at pipe joints to create a curvilinear sewer. Curvilinear alignments are not to be achieved by bending the pipe barrel.

002.07 Inverted siphons will include at least two barrels, each not less than six-inches in diameter. Adequate head will be provided to assure velocities of at least 3.0 feet/second in all barrels when flowing at their maximum hydraulic capacity. Inlet and outlet control structures will be designed with adequate clearances for inspections and cleaning to occur. For two-barrel siphons, the inlet and outlet control structures will be designed so that flow can be diverted to either barrel to accommodate cleaning.

002.08 Sewers will be laid at least 10 feet horizontally from any existing or proposed water main. The distance will be measured from the outside edges of the two pipes. Where it is not practical to maintain the 10 foot horizontal separation, the sewer may be laid closer if the water main is in a separate trench or on an undisturbed earth shelf located on one side of the sewer, and the bottom of the water main is at least 18 inches above the top of the sewer. Where 10 feet of separation cannot be met, both the sewer and water main will be constructed of water main quality pipe and pressure tested to 150 pounds per square inch.

002.09 Sewers crossing water mains will be laid to provide 18 inches of vertical separation, measured from the outside edges of the two pipes. A full length of sewer pipe will be centered on the crossing so that its joints are as far as possible from the water main. When providing 18 inches of vertical separation is not achievable, one of the following two alternatives will be met to protect the water main: (a) either the sewer main will be constructed of water main quality pipe and pressure tested to 150 pounds per square inch, or (b) one of the mains will be encased in a watertight encasement pipe. Where the crossing is at a right angle, the protection will extend for 10 feet on each side of the crossing. Where the crossing is at an acute angle, the protection will extend to all points within 10 feet of the water main, measured perpendicular to the water main.

002.10 Sewers will not be laid closer than 50 feet horizontally from any water well.

002.11 Sewer pipe will be installed with proper bedding, haunching, and backfill material to adequately support the pipe and maintain its grade and alignment.

002.12 The following acceptance tests will be performed on newly constructed gravity sewers.

002.12A Alignment Test. For straight sections of sewer, an alignment test using either a lamp or a laser beam will be performed. The light or laser beam will be visible through the sewer between adjacent manholes.

002.12B Water Infiltration/Exfiltration Test. The measured leakage will not exceed 100 gallons per inch of pipe diameter per mile per day, with a minimum head pressure of two feet above the highest point of the sewer pipe. The Low-Pressure Air Test may substitute for this test.

002.12C Low-Pressure Air Test. The American Society for Testing and Materials (ASTM) test will be specified for the pipe material being tested. The Infiltration/Exfiltration test may substitute for this test.

002.12D Deflection Test. A 5% deflection test will be preformed on flexible sewer pipe. A rigid ball or mandrel, sized at 95% of the inside diameter of the pipe, will pass freely through the pipe without the aid of mechanical pulling devices. The test will be performed after the backfill has been in place at least 30 days.

002.13 Manholes will be provided at sewer main intersections, at changes of slope, pipe diameter, or alignment of straight sections, and at distances not greater than 400 feet. Where modern sewer cleaning equipment is available, manhole spacing up to 600 feet may be used. Manhole spacing beyond 600 feet will be considered for sewers 30 inches in diameter or greater. Cleanouts may be installed only at the end of six-inch or eight-inch sewer laterals that are less than 400 feet long if the minimum slope requirement is met.

002.14 Drop manholes will be provided wherever the invert of the entering sewer is 24 inches or more above the invert of the manhole. For new construction, the drop pipe will be outside of the manhole and encased in concrete to protect the manhole from unequal backfill pressures. Drop manholes will not necessarily be required for manholes installed on large diameter trunk or interceptor sewers where the invert of sewer laterals are set above the manhole invert to prevent standing water in the sewer laterals.

002.15 Manhole ring and cover assemblies exposed to street traffic will weigh at least 300 pounds. Manhole steps, if provided, will be made of corrosion resistant material.

002.16 The minimum diameter of manholes will be 48 inches. The minimum diameter of the access opening will be 22 inches.

002.17 The flow channels through manholes will be shaped to conform to the shape of the connecting sewer pipes. Concrete benches will be installed on each side of the flow channels and slope towards the channels with a minimum 1.0 % slope.

002.18 Sewers will be sized for the peak hourly flow, which is the average daily flow times a peak factor (F). Where historical flow records are not adequate to determine the peak factor in a service area, the peak factor will be calculated by the following formula, where P is the population equivalent of the service area in thousands.
002.19 Privately owned sanitary sewers for mobile home parks, recreational vehicle parks (RV parks) or campgrounds may be designed according to the following design standards as an alternative to the standards listed in 002.01-002.18 above.

002.19A Sanitary sewers within the park or campground will be at least six inches in diameter. The minimum slope for six-inch sewers will be 1.0%. Wyes and tee pipe connections are allowed at intersections in place of manholes.

002.19B Cleanouts will be installed at the upstream end of each sanitary sewer, at each change of direction, at each sewer intersection, at each change in pipe diameter, and installed at least every 150 feet of sewer length if one-way cleanouts are used or every 300 feet if two-way cleanouts are used.

002.19C Service lines will be at least four-inches in diameter. No more than two living units or campsites will connect to a four-inch service line. The minimum slope for four-inch service lines will be 2.0%.

002.19D Service lines for RV parks or campgrounds will include a trap below the frost line or be provided with removable gas-tight caps.

002.20 Small diameter gravity sewers will meet the following design standards:

002.20A Septic tanks or interceptor tanks, used to provide primary treatment, will have a tank capacity of at least 1000 gallons and meet all other design criteria of NDEQ Title 124, Rules and Regulations For the Design, Operation and Maintenance of On-Site Wastewater Treatment Systems.

002.20B Manholes will be installed at major impact points where flow measurement or sampling is necessary for regulatory or planning purposes.

002.20C Where manholes are not installed, cleanouts will be installed at the upstream end of each small diameter gravity sewer, at each change in pipe diameter, at significant changes of grade, at pipe intersections, and installed at least every 500 feet of sewer length if one-way cleanouts are used or every 1000 feet if two-way cleanouts are used.

002.20D Small diameter gravity sewers will have a minimum diameter of four inches.

002.20E Small diameter gravity sewers will be installed below the frost line.

002.20F Small diameter gravity sewers will pass the American Society for Testing and Materials (ASTM) low-pressure air test before being placed into service (See 002.12C).

002.21 Small diameter pressure sewers, using grinder pumps or septic tank effluent pumps, will meet the following design standards.

002.21A Cleanouts will be installed at the upstream end of each small diameter pressure sewer, at each change in pipe diameter, at pipe intersections, and installed at least every 500 feet of sewer length.

002.21B Isolation valves will be installed for each branch sewer line and not less than every 1000 feet of force main length.

002.21C Air release valves will be installed at local high points in the pressure sewer profile.

002.21D Small diameter pressure sewers will be installed below the frost line.

002.21E Each grinder pump or effluent pump will have an audio or visual high-water alarm provided.

002.21F Each service line will include an isolation valve and two check valves. A check valve included in the pump unit counts towards this requirement.

002.21G Standard dimension ratio (SDR) 26 polyvinyl chloride (PVC) pipe will not be used in diameters smaller than two inches.

003 Lift Stations

003.01 Lift stations will be protected from vandalism by fencing or lockable structures. Lift stations will be located so they are accessible to maintenance vehicles during all times of the year.

003.02 Where ground water is encountered, lift stations will be designed to withstand buoyant forces.

003.03 Multiple pumps will be provided for all lift stations, except where four or fewer service connections are served and the total flow is less than 2000 gallons per day. Where two pumps are provided each will be capable of pumping the peak hourly flow. Where three or more pumps are provided, they will be sized to pump the peak hourly flow when the largest pump is out of service. The control system will have the ability to automatically alternate the pumps in operation.

003.04 Lift stations pumping raw wastewater will be designed to achieve a velocity of at least 2.0 feet per second in the force main.

003.05 Pumps handling raw wastewater will have suction and discharge openings at least four inches in diameter and be capable of pumping solid spheres at least three inches in diameter. This requirement does not apply to grinder pumps. Each pump will have an individual intake opening.

003.06 For custom built wet wells, the wet well floors will be sloped toward the pump inlets to minimize the accumulation of grit and wastewater solids.

003.07 Check valves and shutoff valves will be placed on the discharge pipe of each pump with the check valve located between the pump and the shutoff valve. Check valves will be located on horizontal pipe sections, except for ball check valves, which may be located on vertical sections. For satellite lift stations, the check valves and shut-off valves will be located in a separate chamber out of the wet well. Check valves that are an integral part of the pump may be used if the pump and valve can be removed from the wet well without maintenance personnel entering the wet well.

003.08 Where a valve pit is installed adjacent to a lift station it will include a drain line back to the lift station wet well. The drain line will include a flap valve to prevent gases from entering the valve pit.

003.09 Where a wet well/dry well type lift station is used, the dry well will be sealed off from the wet well so that wastewater and sewer gases cannot enter the dry well.

003.10 Where dry wells are located below the ground surface, permanent mechanical ventilation will be provided. Wet wells will be provided with permanent mechanical ventilation if valves, screens, or other equipment is located in the wet well that must be inspected and maintained by personnel entering the wet well.

003.11 When continuous mechanical ventilation is provided in wet wells, it will provide at least 12 complete air changes per hour. Continuous ventilation in dry wells will provide at least six complete air changes per hour. Intermittent mechanical ventilation, in either case, will provide at least 30 air changes per hour. The direction of forced air will be into the wet well or dry well.

003.12 Each satellite lift station will be equipped with an alarm system that is activated by power failure or a high water level. If the lift station serves at least 25 service connections and less than 24 hours of storage capacity exists at the lift station and in the collection system before a backup or sanitary sewer overflow occurs, the alarm will be telemetered to the responsible parties 24-hours a day. Where less than 25 service connections exist or where 24 hours of storage capacity is provided an audio and visual alarm will be provided.

003.13 Lift stations must be provided with emergency provisions to avoid backups into basements or sanitary sewer overflows. One of the following emergency provisions will be provided at each lift station:

003.13A The lift station will be connected to two independent electrical substations;

003.13B A storage capacity of 24 hours of flow is provided in the upstream sewer system or by storage structures, before a backup or sanitary sewer overflow occurs;

003.13C A permanent engine driven electrical generator is installed;

003.13D A portable electrical generator is kept available within one hour of travel time and two hours of storage capacity exists before a backup or sanitary sewer overflow occurs; or

003.13E A portable pump and adequate hose or piping is kept available within one hour of travel time and two hours of storage capacity exists before a backup or sanitary sewer overflow occurs.

003.13F Another method approved by the Department.

003.14 All satellite lift stations will be designed with a riser pipe on the downstream force main. The riser pipe will be fitted with quick connection couplings and shutoff valves, as necessary, to be used in emergencies with a portable pump.

004 Force Mains

004.01 Force mains will be sized so that a cleaning velocity of at least 2.0 feet per second is achieved at the minimum pumping rate of the lift station.

004.02 The minimum diameter of force mains transporting raw domestic wastewater will be four inches.

004.03 Force mains will be designed with air relief valves located at high points in the force main. Vacuum relief valves may be required where an evaluation of the design indicates they are needed.

004.04 Force mains discharging into manholes will enter the manhole no more than two feet above the gravity flow line.

004.05 Force mains and all installed valves and appurtenances will be designed to withstand the pumping shutoff head pressure. Force mains will be pressure tested equal to water mains.

004.06 Force mains will maintain the same separation distances to water mains and wells required for gravity sewers. See Chapter 5, 002.08 - 002.10.

004.07 Wastewater pumps will be selected that operate effectively over the range of head loss conditions that will exist over the life of the system. Piping system head capacity curves will be prepared for both the new pipe condition using the appropriate coefficient of roughness and for the aged pipe condition that will result after years of service. For the aged condition, a Hazen Williams “C” value not higher than 120 will be used for polyvinyl chloride (PVC), polyethylene or lined ductile iron, and for unlined iron or steel pipe a “C” value no higher than 100 will be used.

005 Wastewater Lagoons

005.01 The seepage rate of wastewater lagoons will not exceed one-eighth inch per day at the design maximum water depth. A lower seepage rate, or zero seepage, will be required if the Department determines that additional ground water protection is required. Ground water monitoring wells will be required where the Department determines that monitoring is necessary.

005.02 The liners of wastewater lagoons will be tested prior to the lagoon being placed into service. The test results will be submitted to the Department for review. Synthetic liners will be tested according to the manufacturer’s instructions or other tests required by the Department. Soil liners will have the seepage rate measured by one of the following tests:

005.02A An independent soils testing laboratory will determine the coefficient of permeability from undisturbed core samples taken from the liner. The seepage velocity will be calculated using Darcy’s Law at the design maximum water depth. Each permeability test will pass the seepage test. Areas that do not pass will be reworked and retested. The minimum number of core samples that will be tested is listed in the following table.
Permeability Testing
Number of Core Samples per Lagoon Cell
Water Surface Area of Lagoon Cell (Acres)
Permeability Tests Required from Cell Floor
Permeability Tests Required From Side Slopes
Greater than 24 acres
One per two acres
One per four acres

005.02B The seepage rate will be tested directly by filling the cell with water and measuring the change of water level over time. The test will run at least 21 days. A control device must be used to measure the effects of rainfall and evaporation during the test. If the water depth during the test is less than the design depth, the test result will be adjusted to calculate the seepage rate at the design water depth of the cell. This test will be conducted under the supervision of a professional engineer.

005.02C Wastewater lagoons with a water surface area less than one acre may use a two-barrel test. One barrel, without a bottom, will measure the seepage rate and the other barrel, with a solid bottom, will be used as a reference to account for rainfall and evaporation. A professional engineer will supervise this test and verify the results.

005.02D Another method approved by the Department.

005.03 The bottom elevation of soil liners for wastewater lagoons will be constructed at least four feet above the seasonal high ground water level, including the level of any perched ground water.

005.04 Wastewater lagoons will not be constructed within 100 feet from any water well or within 1000 feet from a community public water supply well.

005.05 Wastewater lagoons will not be constructed within 50 feet from a property line or within 200 feet from an existing dwelling, measured from the normal high water level of the lagoon.

005.06 Wastewater lagoons will be designed and constructed to prevent storm water runoff from flowing into the cells and to prevent storm water runoff or surface water flow from eroding the earthen dikes.

005.07 The top of wastewater lagoon dikes will be constructed at least one foot above the 100-year flood elevation at the site.

005.08 The top of wastewater lagoon dikes will have a minimum width of eight feet to accommodate maintenance vehicles.

005.09 Wastewater lagoons will be provided with influent flow measurement equipment capable of measuring the total influent flow. Elapsed time meters on lift station pump controls are acceptable to meet this requirement.

005.10 Discharging wastewater lagoons will be equipped with an effluent sampling location and a primary flow-measuring device to measure the discharge flow rate. Primary flow devices include parshall flumes, palmer-boelus flumes, V-notch weirs, rectangular weirs, trapezoidal weirs or similar devices. Level monitoring equipment or flow meters will be included with the primary flow-measuring device for continuous discharge lagoons, but is not required for controlled discharge lagoons.

005.11 All wastewater lagoons will be completely enclosed by a fence, unless exempted by the Department. The fencing will be at least 42 inches high and will include at least one lockable gate, a minimum of 10 feet wide.

005.12 A warning sign will be posted on each side of a wastewater lagoon system. Sides longer than 500 feet will have one sign for every 500 feet or fraction thereof. The signs will be at least 12 inches by 24 inches in size and clearly show the words “No Trespassing, Wastewater Lagoon” or similar language.

005.13 The organic loading rate of facultative lagoon systems will not exceed 30 pounds of five-day biochemical oxygen demand (BOD5) per acre per day for primary cells. The organic loading rate for the entire lagoon system will not exceed 25 pounds of BOD5 per acre per day.

005.14 Facultative lagoons will have a maximum water depth of six feet in primary cells and eight feet in secondary cells. Greater depths may be approved if mechanical aeration is provided.

005.15 Discharging wastewater lagoon systems will be designed with multiple cells that operate in series. Where two or more primary cells are provided, a control structure will be designed to split the flow proportionally or to divert the influent flow to either cell.

005.16 The finished floor elevation of wastewater lagoons will not vary more than three inches from the design elevation or grade.

005.17 After seepage testing is completed, newly constructed wastewater lagoons will be filled with two feet of water to protect the liner from damage and to reduce odors when the lagoons first receive wastewater. Lagoon cells that will not be placed into immediate service will follow the requirements of Chapter 11, 008.04.

005.18 Rapid Infiltration (RI) Cells will be designed according to the following design standards.

005.18A RI cells will have at least 10 feet from the bottom of the cell to the seasonal high ground water level.

005.18B RI cells will be designed to operate in a cycle consisting of a water application period followed by a drying period. The length of the drying period will be adequate to restore aerobic conditions to the soil and will not be shorter than the application period. The application period will include all time that any standing water is visible in the cell.

005.18C RI systems that discharge to ground water will be designed to achieve a total nitrogen concentration of 10 milligrams per liter (mg/l) or less entering ground water.

005.18D Ground water monitoring wells will be required at all rapid infiltration systems.

006 Mechanical Plants

006.01 Flow Measurement

006.01A Plants with an average daily design flow less than 50,000 gallons per day will have either influent or effluent flow measurement. Lift station elapsed time meters will satisfy this requirement.

006.01B Plants with an average daily design flow of 50,000 gallons per day or greater will have continuous flow measurement and totalizing equipment.

006.01C Flow measurement equipment will be sized to function accurately over the full range of flows received at the treatment plant. The flow measurement equipment will be protected from freezing.

006.02 Bar Screens & Comminutors

006.02A Every mechanical plant will have either screening devices or comminutors installed.

006.02B At least two flow channels will be provided for screens or comminutors. Each channel will be designed to handle the peak hourly flow.

006.02C Comminutors will be located after grit removal facilities. If grit removal is not provided, the flow channels upstream of comminutors will have a gravel trap installed to protect the comminutor from damage.

006.02D Where a comminutor is installed, a bypass bar screen will also be provided. Flows exceeding the operating capacity of the comminutor will automatically be diverted to the bar screen channel.

006.03 Grit Removal

006.03A Grit removal facilities, when provided, will be located after screening devices, but prior to comminutors or other treatment units.

006.03B Ventilation will be provided for grit removal facilities that are covered or housed in a building. Fresh air will be continuously forced into the facility at a minimum rate of 12 air changes per hour or intermittently at a minimum rate of 30 air changes per hour.

006.03C Grit removal facilities will be provided with drains to dewater the unit for maintenance and be equipped with a bypass line.

006.03D Grit removal facilities will be provided with means to dry and store grit prior to disposal. Grit removal and grit handling facilities will be protected from freezing.

006.04 Primary Clarifiers

006.04A Plants with an average daily design flow of 100,000 gallons per day or greater will have multiple primary clarifiers, if primary clarifiers are part of the facility. Each clarifier
will be capable of independent operation. When a single primary clarifier is provided, a bypass line to the secondary treatment unit will be provided.

006.04B The minimum sidewall depth of primary clarifiers will be 10 feet.

006.04C The horizontal distance from the inlet to outlet will be at least 10 feet, unless the design includes a method to prevent short-circuiting.

006.04D The surface overflow rate will not exceed 1000 gallons per day per square foot at the average daily flow or 3000 gallons per day per square foot at the peak hourly flow. Returned flows from later treatment units will be included in the flow used to calculate the surface overflow rate.

006.05 Activated Sludge Basins

006.05A The dimensions of each aeration tank will be such that it maintains effective mixing and utilization of air. Vertically mixed tanks will have a liquid depth of not less than 10 feet or greater than 30 feet. Horizontally mixed tanks will have a minimum liquid depth of 5.5 feet.

006.05B All aeration tanks will have a freeboard of not less than 18 inches. Aeration tanks using mechanical surface aerators will have at least three feet of freeboard.

006.05C Inlets and outlets for each aeration basin will be suitably equipped with valves, gates, stop plates, weirs, and other devices to permit controlling the flow to any unit and maintain reasonably constant liquid levels. Where multiple aeration basins are provided, the hydraulic properties of the inlets and outlets will be sized to carry the design peak instantaneous flow with any single aeration tank out of service.

006.05D Channels and pipes that carry solids in suspension will be designed to maintain a self-cleansing velocity at all rates of flow within the design limits. Open channels will be designed to prevent splashing out of the channel.

006.05E The shape of aeration tanks, the location of influent and return sludge pipes, and the aeration equipment will be designed to prevent short-circuiting through the tanks.

006.05F The rate of sludge return will be controlled by means of variable speed motors, drives, valves, or timers to pump sludge at the required rates. If motor driven return sludge pumps are used, a minimum of two pumps is required. The pumps will be sized to meet the required pumping rates with the largest pump out of service. Pumps will have at least a 3-inch
suction and discharge opening. No standby unit is required for air lift pumps, provided the design facilitates rapid and easy cleaning. Airlift pumps will be at least 3 inches in diameter. Airlift
pumps used to waste or return sludge will be designed so their operation is unaffected by changes of air demand of other treatment units.

006.05G Return sludge piping will be at least four inches in diameter and designed to maintain a velocity of not less than two feet per second when return facilities are operating at normal return rates. Suitable devices will be provided for measuring and controlling the return rate. The flow will be returned near the inlet or head end of the aeration tank, so that it rapidly mixes with the influent. Return sludge piping will be designed to provide the operator easy access for collection of return sludge samples.

006.05H Sludge wasting facilities will be provided for all activated sludge facilities. Sludge wasting facilities include units such as sludge thickening tanks, sludge digestion facilities, sludge storage tanks, dewatering facilities or any practical combination of these units. A means of measuring, controlling, and sampling of waste activated sludge must be provided.

006.05I Aeration equipment will be capable of maintaining a minimum dissolved oxygen concentration of 2.0 milligrams per liter in the mixed liquor at all times and provide thorough mixing of the mixed liquor. For all activated sludge processes, except extended aeration, the minimum oxygen requirements will be 1.1 pounds of oxygen per pound of the design peak hourly five-day biochemical oxygen demand (BOD5) applied to the aeration tank. For the extended aeration process the minimum oxygen requirement will be 1.5 pounds of oxygen per pound of the design peak hourly BOD5 applied to the aeration tank.

Where nitrification is required, the oxygen requirement for oxidizing ammonia must be added to the above requirement for oxidation of five-day biochemical oxygen demand. The minimum nitrogenous oxygen requirement will be 4.6 pounds of oxygen per pound of the design peak hourly total Kjeldahl nitrogen applied to the aeration tank.

006.05J The design of the diffused air system will be based on either standard engineering equations that calculate the transfer efficiency using such factors as tank depth, alpha and beta factors, device transfer efficiencies, wastewater temperature and altitude of the plant or empirically determined air requirements. Designs based on standard engineering equations will include the transfer efficiency in the specifications.

Empirical air requirements for all activated sludge processes, except extended aeration, will be a minimum of 1500 cubic feet of air (at standard conditions of pressure, temperature, and humidity) per pound of five-day biochemical oxygen demand (BOD5) applied to the aeration tank. For the extended aeration process the air requirements will be 2050 cubic feet of air per pound of BOD5 applied to the aeration tank.

006.05K The specified capacity of blowers or air compressors will take into account the range of ambient air conditions that may occur at the site.

006.05L A minimum of two blowers will be provided for any activated sludge facility. The capacities of blowers or air compressors will be able to meet the air demand of the system with the largest unit out of service.

006.05M Plants with less than four independent aeration tanks will be designed to allow removal of the diffusers for service or replacement without dewatering the tank.

006.05N In the absence of specific design information, the oxygen requirements will be calculated using a transfer rate not to exceed two pounds of oxygen per horsepower per hour. The design requirements of a mechanical aeration system will maintain a dissolved oxygen concentration of two milligrams per liter in the mixed liquor at all times throughout the tank, maintain solids in suspension, and meet the oxygen demand requirements with the largest unit out of service.

006.06 Trickling Filters

006.06A Trickling filters will be preceded by primary sedimentation to remove scum, grease, and floatable debris or by other suitable treatment facilities.

006.06B The volume of trickling filter media will be based upon pilot testing with the particular wastewater or by using design equations. The volume of media will be calculated on the design maximum day organic loading. The design volume will also include treatment of the organic loading of recycle flows from other treatment units such as, digester supernatant, mechanical dewatering supernatant, or others.

006.06C Media will have a minimum depth of six feet above the underdrains. Rock or slag media will not exceed 10 feet in depth. Manufactured media will not exceed the depth recommended by the manufacturer.

006.06D Rock media will not contain more than five percent by weight of pieces whose longest dimension is three times the least dimension. It will be free of thin, elongated and flat pieces, dust, clay, sand, or fine material and will conform to the following size and grading.

Passing 4 ½ inch screen - 100%
Retained on 3 inch screen – 95-100% by weight
Passing 2 inch screen – 0 – 2% by weight
Passing 1 inch screen – 0-1% by weight

006.06E Manufactured media will be resistant to ultraviolet degradation, disintegration, erosion, aging, all common acids and alkalis, organic compounds, and fungus or biological attack. Media will be structurally capable of supporting the weight of a person or a suitable access walkway will be provided for maintenance of the distributor. Manufactured media for carbonaceous treatment will not have a specific area greater than 30 square feet per cubic foot. Manufactured media for second stage ammonia treatment will not have a specific area greater than 45 square feet per cubic foot.

006.06F The piping system, including dosing and distributor equipment, will be designed to provide capacity for the design peak hourly flow including the recirculation rate. The design recirculation ratio (ratio of recirculation flow to design average flow) will be based on the amount of variation in plant flow between design minimum daily flow and design peak hourly flow.

006.06G he piping system will be designed for recirculation as required to achieve the design wetting rate, or design dosing rate, and to achieve the design treatment efficiencies. The design of recirculation facilities will provide for continuity of service, variable recirculation rates, measurement of the recirculation rate, and subject to control by the plant operator. A minimum of two recirculation pumps must be provided.

006.06H The wastewater will be distributed by rotary, fixed nozzle, or other suitable distributor that ensures uniform distribution over the entire surface area. The distribution equipment will be able to apply wastewater at the design hydraulic loading rate (gallons per minute per square foot) or dosing rate (inches per revolution). At design average flow, the deviation from a calculated uniformly distributed volume per square foot of the filter surface will not exceed plus or minus 10 percent at any point.

006.06I There will be a minimum of 12 inches of clearance between the media and the distribution arms.

006.06J A freeboard of four feet or more will be provided for tall manufactured uncovered trickling filters to contain windblown spray.

006.06K Appropriate valves, sluice gates, or other structures will be provided to enable flooding of the filter. Access will be provided around the periphery of the underdrain system to allow flushing of the underdrains.

006.06L The underdrain system will cover the entire floor of the filter. Inlet openings into the underdrains will have an unsubmerged combined area equal to at least 15 percent of the surface area of the filter. The underdrains will have a minimum slope of one percent. Effluent channels will be designed to produce a minimum velocity of two feet per second at design average daily flow rates including recirculated flows.

006.06M The underdrain system and effluent channels will be designed to permit free passage of air. The size of the drains and channels will be designed such that no more than 50 percent of their cross-sectional area will be submerged under design peak flow conditions. Forced ventilation will be provided for covered trickling filters to insure adequate oxygen for process requirements. The design of ventilation equipment will provide for operator control of air-flow in accordance with outdoor seasonal temperatures.

006.06N All distribution devices, underdrains, channels, and pipes will be installed so that they allow for proper maintenance.

006.07 Intermediate and Final Clarifiers

006.07A Facilities with an average daily design flow of 100,000 gallons per day or greater will have multiple final clarifiers. Effective flow splitting devices and control appurtenances will be provided to permit proper proportioning of flows and solids to each unit, throughout the expected range of flows.

006.07B The minimum distance between inlet and outlet will be 10 feet, unless the design includes a method of preventing short-circuiting. The minimum side water depth will be 12 feet. Walls of settling tanks will extend at least six inches above the surrounding ground surface and will have a minimum of 12 inches of freeboard.

006.07C Surface overflow rates will be calculated based on design average and design peak hourly influent flow conditions. The solids loading rate will be calculated based on the design average daily flow or design maximum day flow plus the design maximum return sludge rate plus the design mixed liquor suspended solids (MLSS).

006.07D Influent pipes and center columns of circular clarifiers will have a maximum velocity of 2.0 feet per second. Inlet structures will be designed to dissipate the inlet velocity, to distribute the flow equally both horizontally and vertically and to prevent short-circuiting. Corner pockets and dead ends will be eliminated and corners fillets or channeling will be used where necessary. Provisions will be made to eliminate or remove floating materials from inlet structures.

006.07E Overflow weirs will be adjustable to correct for differential settlement. Weirs will be located to optimize hydraulic detention time and minimize short-circuiting. The loading rate at design peak hourly flow will not exceed 20,000 gallons per day per lineal foot of weir for plants with a design flow less than one million gallons per day (MGD) or 30,000 gallons per day per lineal foot of weir for plants with a design flow greater than one million gallons per day. Weir troughs will be designed to prevent submergence at design peak hourly flow and maintain a velocity of 1.0 foot per second at one-half the design average flow.

006.07F Provisions for scum collection and removal will be provided for all clarifiers. Scum will be discharged to a sludge treatment unit or scum storage unit that prevents recycling of the scum through the secondary treatment units. Scum will not be discharged to the head of the plant, unless it can be permanently removed from the system in a primary clarifier or similar treatment unit.

006.07G All final and intermediate clarifiers will have a mechanical sludge scraper or collection system. Suction withdrawal will be provided for activated sludge final clarifiers with a diameter greater than 60 feet. Each settling tank will have its own sludge withdrawal lines to insure adequate control of sludge wasting from each tank.

006.07H All settling tanks will be equipped with appropriate equipment such as machinery covers, walkways, handrails, area lighting, and slip resistance surfaces that enhance the safety of the operator. The design will provide for convenient and safe access to routinely checked items such as gear-boxes, scum removal mechanisms, baffles, weirs, inlet areas, and effluent channels.

006.08 Sludge Treatment, Storage, and Disposal

006.08A Facilities for the treatment and storage of sludge will be provided at all mechanical wastewater treatment plants, unless arrangements are made for processing sludge at another treatment facility. Where sludge is hauled off site for treatment and disposal, an all-weather access road to the treatment plant will be provided.

006.08B Treatment plants using suspended growth processes (activated sludge variations) will, at a minimum, be provided with on-site sludge storage facilities to allow for proper sludge wasting and operational control of the treatment process.

006.08.C Sludge withdrawal piping will have a minimum diameter of eight-inches for gravity withdrawal, and six-inches for pump suction and discharge lines. There will be a minimum of four feet of head above the discharge pipe where withdrawal is by gravity. Provisions for draining and flushing discharge lines will be provided for all gravity sludge piping. The minimum slope for gravity piping will be three percent. A minimum positive head of 24 inches will be provided at the suction side of centrifugal pumps. Suction heads for positive displacement pumps will not exceed 10 feet.

006.08D Anaerobic Sludge Digestion

006.08D1 Digester tanks will be covered with either a fixed or floating cover. Covers will be sealed to protect against gas leaks. The top of the tank will have at least two manholes,
not less than 30 inches in diameter, in addition to the gas dome.

006.08D2 The tank bottom will slope towards the withdrawal pipe. A minimum bottom slope of 1:12 is required for tanks equipped with a suction mechanism for sludge withdrawal. A minimum slope of 1:4 is required where sludge is to be removed by gravity.

006.08D3 Where mixing equipment is not provided within the digester, multiple sludge inlets, outlets, and other suction or discharge points will be used to achieve mixing and allow for flexibility of operation. One inlet will discharge above the liquid level near the tank center to facilitate the breakup of scum. Raw sludge inlets will be designed to avoid short-circuiting.

006.08D4 An unvalved, vented overflow will be included to prevent damage to the digester in case of accidental overfilling. The overflow will return the sludge to a treatment unit.

006.08D5 Where rational calculations are not submitted to justify the required tank capacity for heated, anaerobic digestion of domestic wastewater sludge, the minimum volume for completely mixed systems will be 1000 cubic feet of active digester volume for each 80 pounds of volatile solids per day. Where partial mixing is provided, the minimum volume will be 1000 cubic feet of active digester volume for each 40 pounds of volatile solids per day.

006.08D6 In two stage systems, where the secondary digesters are utilized for thickening and storage, the volume of the secondary digesters will not be used to meet the volume requirement for sludge digestion.

006.08D7 The digester gas system will be designed so that gas is under positive pressure during all normal operations, including during sludge removal from the digester. All enclosed building areas where gas leaks could occur will be provided with ventilation systems.

006.08D8 Supernatant piping will not be less than six-inches in diameter.

006.08E Aerobic Digestion

006.08E1 Where aerobic digesters are used, multiple units will be provided where the design average wastewater flow is at least 100,000 gallons per day.

006.08E2 Volatile suspended solids loading will not exceed 300 pounds per 1,000 cubic feet of volume per day in the digestion units.

006.08E3 A minimum of 15 days of solids retention time will be provided for waste activated sludge and 20 days for a combination of primary and waste activated sludge, or for primary sludge alone. In order to qualify as a Process to Significantly Reduce Pathogens (See Title 119 – Rules and Regulations Pertaining to the Issuance of Permits Under the National Pollutant Discharge Elimination System, Chapter 12, 004), aerobic digestion processes will have a minimum mean cell residence time of 40 days at 20° Celsius and 60 days at 15° Celsius. If supernatant separation is performed in the digestion tank, additional volume is required to allow for decanting. This added volume will not be included in the determination of mean cell residence or solids retention time.

006.08E4 Sufficient air will be provided to keep solids in suspension and maintain a dissolved oxygen concentration of 1.0 milligram per liter. The minimum amount of air supply will be 30 cubic feet per minute per 1000 cubic feet of tank volume with the largest blower out of service. The minimum requirement for mechanical aerators will be 1.0 horsepower per 1000 cubic feet of digester volume.

006.08E5 Facilities will be provided for the separation and decanting of supernatant. The supernatant draw off unit will be designed to prevent recycling of scum and grease back to the wastewater treatment processes. A method for the collection and disposal of scum and grease will be provided.

006.08E6 An unvalved high-level overflow will be provided to return digester overflow back to the head of the plant or to a secondary treatment unit to protect against accidental overfilling.

006.09 Disinfection

006.09A Chlorine Disinfection

006.09A1 The chlorination system and equipment will be sized to produce an effluent meeting applicable bacterial limits at design peak flow conditions.

006.09A2 Where 100 or 150 pound chlorine gas cylinders are used, the cylinders will be stored in an upright position with adequate support brackets and chains at the two-thirds cylinder height for each cylinder. Storage containers for hypo-chlorite solutions will be of sturdy, non-metallic lined construction and will be provided with secure tank tops and pressure relief and overflowing piping. Storage tanks will be vented outside. Tanks will be located where leakage will not cause corrosion or damage to other equipment. A means of secondary containment to control spills and facilitate cleanup will be provided.

006.09A3 Scales for weighing cylinders and containers will be provided at all plants using chlorine gas.

006.09 A4 The disinfectant will be mixed as rapidly as possible. A minimum contact time of 15 minutes at design peak hourly flow or maximum pumping rate will be provided after thorough mixing. The chlorine contact tank will be constructed to reduce short-circuiting.

006.09A5 Piping systems will be as simple as possible and selected and manufactured to be suitable for chlorine service. Piping will be well supported and protected against temperature extremes. The chlorine piping will be color-coded and labeled to distinguish it from other plant piping. Piping and fittings for chlorine and sulfur dioxide will be designed so that interconnection between the two systems cannot occur.

006.09A6 If gas chlorination equipment or chlorine cylinders are to be in a building used for other purposes, a gas-tight room will separate this equipment from other portions of the building. Floor drains from the chlorine room will not be connected to floor drains from other rooms. Doors to this room will open to the outside, and will be equipped with panic hardware. Rooms will be at ground level and should permit easy access to all equipment. Storage areas for one-ton cylinders will be separated from the feed area. A clear glass, gas-tight window will be installed in an exterior door or interior wall of the chlorinator room to permit the units to be viewed without entering the room.

006.09A7 Forced, mechanical ventilation will be installed that provides one complete air exchange per minute when the room is occupied. The entrance to the air exhaust duct from the room will be near the floor. The point of discharge will be located so as not to contaminate the air inlet of another building. Air inlets will be located to provide cross ventilation with air at such a temperature that will not adversely affect the chlorination equipment. The outside air inlet will be at least three feet above grade. The vent hose from the chlorinator will discharge to the outside atmosphere above grade.

006.09A8 Switches for fans and lights will be located outside the room at the entrance. If the fan can be controlled from more than one point, a labeled signal light indicating fan operation should be provided at each entrance.

006.09A9 Respiratory protection equipment, meeting the requirements of National Institute for Occupational Safety and Health (NIOSH) will be available where chlorine gas is handled, and will be stored at a convenient location, but not inside any room where chorine is used or stored.

006.09B Dechlorination

006.09B1 The dechlorination chemical will be introduced at a point in the process where the hydraulic turbulence is adequate to assure complete and thorough mixing. If no point exists, mechanical mixing will be provided. A minimum of 30 seconds for mixing and contact time will be provided at the design peak hourly flow or maximum rate of pumping.

006.09C Ultraviolet (UV) Radiation Disinfection

006.09C1 For facilities with a design average day flow of 100,000 gallons or more, a UV disinfection system will consist of multiple banks of lamp modules in series that are capable of continuously disinfecting the effluent with one bank out of service.

006.09C2 Provisions will be made for easy removal and inspection of the UV lamps without draining the disinfection chamber.

006.09C3 The contact chamber will be designed so that the UV lamps remain submerged at all times during operation and to maintain a near constant water level at all design flow conditions.

007 Truck Wash Wastewater Treatment Facilities

007.01 Livestock Truck Washes

007.01A Livestock truck washes will either connect to a public sanitary sewer system or to a wastewater works designed and constructed according to the following standards.

007.01B Livestock truck washes will include wash pads that capture all wash water from the washing operation and convey it to the wastewater works. Wash pads will be constructed of concrete or another impermeable material.

007.01C One of the following wastewater systems will be used for livestock truck washes.

1) A complete retention facultative lagoon system.
2) A wastewater storage pond and land application system.
3) A solids separation system, wastewater storage pond and land application system.
4) Another system proposed by the owner and approved by the Department.

007.01D Lagoons and storage ponds used for truck washes will meet the design standards and testing requirements in Chapter 5, 005.

007.01E Wastewater facilities designed to separate solids from the wash water for separate handling and disposal will include a settling pit and a solids storage unit as specified below.

007.01E1 Solids settling pits will be constructed of concrete and will be watertight. Pits will have at least 24-hour detention time and be designed to contain both floatable and settleable solids. The design will include a method to remove solids from the pit.

007.01E2 Solids storage units will be watertight structures designed to dry and store solids removed from solids settling pits. A drain system will return surplus water back to the solids settling pit or to the lagoon. At least 120 days of solids storage will be provided with controls to prevent storm water runoff.

007.01F The hydraulic design of the WWTF will be based on historic flow records from other facilities using similar washing equipment. Where verifiable flow records do not exist, a flow not less than1500 gallons per truck washed will be used for design.

007.01G The solids handling capacity will be based on data from similar facilities or on specific data from the owner’s operation, such as the size of animals, the length of trips, the type of bedding material, and manure production rates. In the absence of specific data, the design will assume ten cubic feet of solids (bedding and manure) generated from each truck washed.

007.01H Livestock truck washes will receive written approval, including site approval, from the Department prior to land applying wastewater or wastewater solids.

007.01I Irrigation piping networks used to apply lagoon water will be equipped with check valves, vacuum relief valves, and low pressure drains, as necessary, to protect ground water wells or other sources or irrigation water from contamination from the back flow of lagoon water.

007.01J Livestock truck wash projects that are submitted for approval must include a written management plan adequate to prevent chemical tank trucks, garbage trucks, septage haulers, or other vehicles that could contain hazardous, toxic, or pathogenic wastes from using the livestock truck wash. Any security devices or structures described in the management plan to regulate usage must be shown on the plans submitted for approval.

007.01K A livestock truck wash that was reviewed and approved by the Department as part of an animal feeding operation (AFO) that has received approval for the livestock waste control facility under Title 130, Livestock Waste Control Regulations, is exempt from the construction permit requirements of this Title.

008 Constructed Wetlands

008.01 Primary treatment will be provided for constructed wetlands. Lagoons will not be used to provide primary treatment for vegetated submerged bed constructed wetlands unless a reliable means to remove algae is provided.

008.02 Multiple constructed wetland cells will be provided if the design flow is 5000 gallons per day or greater. Bypass structures will be included to allow each cell to be isolated.

008.03 Constructed wetland systems will be designed to prevent storm water runoff from entering any part of the wastewater works, unless specifically designed to treat runoff.

008.04 Constructed wetland cells that treat domestic strength wastewater will have seepage rates no greater than one-eighth inch per day. Liners for constructed wetlands cells that treat higher strength wastewater will meet the seepage rate specified by the Department for the specific waste.

008.05 The bottom of the soil liner will be at least four feet above the seasonal high ground water level.

008.06 Effluent structures will be equipped with water level control devices capable of controlling the water depth in the wetland cell anywhere from the maximum design level to the bottom of the cell.

008.07 The gravel media installed in vegetated submerged bed constructed wetlands will be graded gravel, sized not less than three-eighths inch or larger than one-inch in diameter. Except that:

008.07A Up to six inches of washed pea gravel may be laid above the media to aid in plant rooting, and

008.07B One-inch to three-inch cobbles may be installed at the influent and effluent ends to assist in flow distribution and collection.

Enabling Legislation: Neb. Rev. Stat. §81-1504(10)

Legal Citation: Title 123, Ch. 5, Nebraska Department of Environment and Energy