Section NR 214.15 - Overland flow systems(1) SITE LOCATION CRITERIA. (a) An overland flow system shall be located at least 500 feet from the nearest inhabited dwelling, except that this distance may be reduced with the written consent of any affected owners and occupants. The department may require a greater distance depending on the type of system and potential for aesthetic and public health impacts.(b) An overland flow system shall be located at least 1,000 feet from a well serving a community public water supply system and at least 250 feet from other potable water supply wells.(c) The ground surface of the system shall have a minimum separation distance to bedrock and groundwater of at least 5 feet.(d) The system may not be located in the floodway as specified in ch. NR 116. Any system located in the floodplain shall conform to ch. NR 116 and may not be operated when the floodplain is flooded.(2) DESIGN AND CONSTRUCTION CRITERIA. (a) Overland flow systems shall be underlain by at least one foot of heavy textured soils such as clays or clay loams to retard leakage through the base.(b) The downslope flow distance shall be 100 feet or greater.(c) The downslope gradient for the overland flow fields shall be between 2% and 8%.(d) The system shall consist of at least 2 cells of approximately equal area which can be alternately loaded and rested. Where self-propelled equipment which operates on a continuous basis is installed and division into identifiable cells is impossible, its movement shall be regulated to provide alternate loading and resting of the soil. Note: It is recommended that an overland flow cell be rested for at least one third of the total time in the load/rest cycle.
(e) The overland flow treatment system design shall evaluate the interaction between the primary factors influencing system performance and efficiency, such as temperature, downslope flow distance, wastewater hydraulic application rate and the rest period, to optimize treatment on the site.(f) The overland flow system shall be arranged so that individual cells within the system can be taken out of service for resting without interrupting the discharge to the remaining cells.(g) The distribution equipment shall be arranged so that the wastewater will be evenly distributed over the entire area of an overland flow cell and the wastewater travels down the slope in non-channelized flow.(h) The wastewater distribution equipment shall be located at or near the ground level. Note: A pressurized distribution system is recommended for ease of operation.
(i) The wastewater distribution system shall be designed to allow easy cleaning of the distribution orifices. Flexibility to adjust the flow from individual orifices shall be provided to allow the system to be hydraulically balanced to minimize flow channeling.(j) An impermeable channel shall be provided for collecting runoff from the overland flow fields. The collection system shall be able to remove the effluent and the rain from a 10-year frequency, 24-hour duration rainfall event with only temporary backing up of water onto the fields.(k) The overland flow fields shall be vegetated with a water tolerant mixed perennial grass cover crop such as reed canary grass, tall fescue and orchard grass. A nurse crop shall be used to establish the perennial grass cover. The grass cover shall be maintained by frequent resting. (L) Erosion control measures shall be taken during construction to prevent erosion of soil into a surface water.(3) DISCHARGE LIMITATIONS. (a) The discharge to an overland flow system may not exceed the hydraulic, organic, nitrogen or other limitations specified in a WPDES permit or plans developed pursuant to a permit requirement. In determining discharge limitations, the department shall consider past operating performance, the ability of the system to treat the pollutants in the discharge, hydrogeologic characteristics of the site such as permeability and infiltration rates and other relevant information.(b) The flow rates in Table 2 shall be used as a guide to establish discharge limitations. The discharge flow rate is expressed as a flow per unit width of slope. Table 2
Design | Discharge Flow Rate |
Conservative | 0.16 gpm/ft |
Average | 0.33 gpm/ft |
Maximum | 0.60 gpm/ft |
(c) The concentration of any wastewater parameter that may impact groundwater quality shall be limited at the point of discharge to a value that will minimize the concentration of the substance in the groundwater to the extent technically and economically feasible and will prevent exceedence of the preventive action limit in the groundwater.(d) The discharge flow rate shall be limited to prevent erosion when the vegetative cover has not developed sufficiently to anchor the soil and create the filter mat necessary for effective wastewater treatment. This condition may occur during original or springtime system startup.(e) Winter operation may be allowed as long as the soil surface remains unfrozen. Since treatment efficiency decreases in the winter, the department may require storage or additional treatment of the runoff during cold weather.(4) DISCHARGE MONITORING REQUIREMENTS. (a) The overland flow system discharge shall be monitored for total daily flow.(b) The department may require in a WPDES permit that the discharge be monitored for BOD5, total suspended solids, forms of nitrogen, chloride, metals or any other pollutant that may be present. The department shall select the pollutants to be monitored and the required frequency of monitoring on a case-by-case basis by considering the potential public health impacts, probable environmental impact, soil and geologic conditions, past operating performance, concentrations and characteristics of pollutants in the discharge and other relevant information.(c) The department may require electronic or paper submittal of discharge monitoring reports and land application forms.(5) OPERATING REQUIREMENTS. (a) The discharge shall be alternately distributed to individual sections of the system in a regular load/rest cycle that allows sufficient resting to dry accumulated solids and maintain a complete grass cover.(b) The crop shall be cut and the cuttings removed at least twice per year, to stimulate grass growth and enhance nutrient removal from the system.(c) The department shall require each overland flow system owner or operator to submit a management plan for optimizing treatment system performance and demonstrating compliance with the requirements of this chapter. Following approval by the department, the treatment system shall be operated in conformance with the management plan. If the facility wishes to operate differently than specified in the approved plan, a written request shall be submitted to the department for approval to amend the management plan. The plan shall specify information on pretreatment processes, load and rest schedules, scheduled maintenance, vegetative cover management and removal, operational strategies for periods of adverse weather, monitoring procedures and any other pertinent information.(6) SOIL INVESTIGATION AND GROUNDWATER MONITORING REQUIREMENTS. The soil investigation and groundwater monitoring requirements for overland flow systems are specified in ss. NR 214.20 and 214.21.Wis. Admin. Code Department of Natural Resources NR 214.15
Cr. Register, June, 1990, No. 414, eff. 7-1-90; CR 09-123: cr. (4) (c) Register July 2010 No. 655, eff. 8-1-10.