Post Construction Stormwater Technical Standards
Note: The technical design guidelines in Part 2 have been replaced by the storm water Post-construction Technical Standards for meeting regulatory requirements in Wisconsin.
Bioretention for Infiltration
Operation and Maintenance
- An operation and maintenance plan shall be developed that is consistent with the purposes of this infiltration device, its intended life, safety requirements and the criteria for its design. The plan shall be developed for inspection, operation and maintenance of the device. The plan shall assign responsibility for activities and the qualifications of the personnel performing the work.
- At a minimum, the plan shall address operation and maintenance of all vegetative and non-vegetative components identified in this standard.
- At a minimum, the plan shall also include details on the following: frequency of inspections; inspecting for sediment buildup and clogging, erosion, trash and debris build-up and plant health; frequency of sediment removal; disposal locations for sediment; pH testing of the soil; frequency of soil, mulch, and plant replacement; inlet and outlet maintenance, and providing access to perform the operation and maintenance activities. The maintenance activities in the plan shall be consistent with Table 6.
Table 6. Typical Maintenance Activities for Bioretention Areas
As necessary during first growing season
Water as necessary during dry periods
As needed after first growing season
Re-mulch void areas
Treat diseased trees and shrubs
inspect soil and repair eroded areas
Remove liter and debris
Add additional mulch
Once per year
- Snow shall not be dumped directly onto the conditioned planting bed.
- If the bioretention device receives runoff only from residential land uses other than streets, the mulch layer can be discontinued at maturity provided that a dense vegetation layer is formed.
Operations and Maintenance
An operation and maintenance plan shall be developed that is consistent with the purposes of this practice, intended life of the components, safety requirements, and the criteria for the design. There may be state and local laws that require adequate O&M of public and private facilities and the identification of responsible parties. At a minimum, the plan shall include:
A. Inspection Intervals – At minimum, quarterly inspections shall occur. Inspection shall include spreader and overflow spillway for indication of failure. Note the condition of vegetation as part of inspection. If standing water is observed over 50% of the basin floor 3 days after rainfall, the basin is clogged and measures should be undertaken to unclog it. (See section VIII.C).
B. Native Vegetation - Maintenance of Native Vegetation – Mowing (cutting) or burning shall be used to maintain the vegetation.
1. Establishment - The first mowing of newly planted seed shall occur once it reaches a height of 10 to 12 inches.
a. Mowing shall reduce the height of plants to 5 to 6 inches.
b. After establishment, if burning cannot be accommodated, mowing shall occur once in the fall (after November 1). The area shall be mowed to a height of 5 to 6 inches.
a. Routine Maintenance - Beginning the second year, burning shall occur in the early spring (prior to May 1st) or in the late fall (after November 1st)
b. Burning shall be done two consecutive years and then up to three years can pass before the next burning.
c. Under no circumstances shall burning occur every other year.
C. Restoration Procedures – these include removing the top 2 to 3 inches, chisel plowing and adding topsoil and compost. If deep tilling is used, the basin shall be drained and the soils dried to a depth of 8 inches. If the basin was planted in turf grass and clogging again occurs after these restoration procedures have been used, the owner /operator shall replant with prairie style vegetation using the soil preparation method recommended by the native nursery in the area.
D. Trash shall be removed as quickly as possible once observed.
E. Pretreatment – If wet detention is used, see WDNR Conservation Practice Technical Standard Wet Detention Basin (1001) for operations and maintenance requirements.
F. Winter Maintenance – All draw down devices in the pond shall be opened during winter months to discourage infiltration of runoff water containing high levels of chlorides. If this practice is an enclosed basin, the use of chloride deicers shall be limited in the area draining to the basin to reduce the chance of exceeding the limits in ch. NR 140
Operation and Maintenance
Operation and Maintenance (O&M) plans for infiltration trenches shall at a minimum include the maintenance events and frequencies as outlined in the Inspection Checklists in App. A. Perform monthly physical inspections from April through October during the first year of operation. Also, O&M plans shall address the following:
A. Accumulated material or debris on the surface of the infiltration trench shall be removed immediately when discovered.
B. Snow shall not be placed in the effective infiltration area. It may be placed on the pretreatment area.
C. Any outlet structure, pipe or swale shall be cleaned of accumulated material or debris immediately when discovered, or at least twice each year.
D. Water depth in the observation pipe shall be measured and recorded twice per year at 72 to 80 hours after a rainfall event of 0.5 inches or more during a 24-hour period. Water depth in the observation pipe existing 72 hours after any storm event indicates additional monitoring may be needed to determine if maintenance or corrective action is necessary. The infiltration trench will be considered to be failing if observation of water depth shows that less than 90% of the trench’s storage volume is available 72 hours after the last storm event.
Operations and Maintenance
A. An operation and maintenance plan shall be written for the intended life of the permeable pavement system. The plan shall include an inspection checklist and schedule.
B. The following activities shall be prohibited from occurring on the permeable pavement surface:
1. Temporary or permanent stockpiling of soil or other material that can potentially cause or contribute to clogging.
2. Application of pavement seal-coating.
3. Application of sand for deicing.
C. Inspection of the permeable pavement system shall be conducted at least once per year to evaluate the following:
1. Pavement Condition – Inspect permeable pavement surfaces for settlement, deformation or cracking.
2. Surface Infiltration – Inspect permeable pavement surfaces for sedimentation or evidence of ponding.
3. Drainage – Inspect observation wells 72 hours after a rain event of 0.5 inches or greater to verify that the aggregate storage reservoir is draining down effectively.
4. Outfalls - Inspect underdrain outfall locations for obstructions and erosion.
5. Run-on Areas – Inspect run-on areas for adequate cover and stability.
D. Maintenance of the permeable pavement system shall be conducted as follows:
1. Clean the pavement surface using industry recommended methods, such as regenerative air or vacuum sweeping, at least twice per year in accordance with Section V.G.
2. If water ponding persists on the pavement surface after a storm event, clean the pavement surface to mitigate clogging.
3. Repair any settlement, deformations or cracking that are significant enough to adversely impact the water quality function of the system.
4. Repair blocked, restricted or eroding underdrain outfalls.
5. Repair and/or replant eroding run-on areas.
6. For permeable pavers/blocks with joints that are filled with aggregate:
a. Replenish the joint aggregate in accordance with industry recommendations.
b. If necessary, remediate the system by extracting accumulated debris and aggregate from the joints using a vacuum and re-filling the joints with new aggregate.
7. For porous asphalt and pervious concrete, repairs may be done with conventional impervious materials if the total impervious repair areas do not exceed 10% of the original permeable surface area and runoff from the repair areas will run on to adjacent permeable areas. The 10% threshold may only be exceeded if design calculations confirm that the system is still able to accept the full loading for which it was originally designed.
E. If the pavement surface infiltration rate is questionable at any time during the effective life of the pavement, the administering authority may require infiltration rate testing to verify that the surface infiltration rate is no lower than 10 in/hr. If the surface infiltration rate is lower than 10 in/hr, appropriate action shall be taken to restore the infiltration rate to an acceptable level based on the remaining effective life of the pavement.
F. If verification of in place pavement surface infiltration rates is necessary, conduct pavement surface infiltration rate testing per ASTM C1701 Standard Test Method for Infiltration Rate of In Place Pervious Concrete for pervious concrete and porous asphalt, ASTM C1781 Standard Test Method of Surface Infiltration Rate of Permeable Unit Pavement Systems for permeable pavers/blocks or other methods approved by the administering authority.
G. Qualified personnel, as determined by the administering authority, shall perform inspection, infiltration testing and maintenance work.
H. All inspection, infiltration testing and maintenance activities shall be documented in written reports. All written reports shall be made available on request by the administering authority.
Proprietary Storm Water Sedimentation Devices
Device Installation and Maintenance Requirements
Proprietary sedimentation devices shall be installed and maintained in a manner consistent with laboratory testing and modeling assumptions used to predict effectiveness. This includes the following requirements:
1. The device shall be installed in accordance with manufacturer recommendations.
2. The installed device shall be equipped with an internal or external bypass to divert flows in excess of the design treatment flow rate. a. For the Theoretical Sedimentation Modeling Method, the design treatment flow rate shall not exceed .08 cfs/ft2, where ft2 is the cross sectional area of the primary sedimentation chamber. Note: See Considerations VI.D. for the derivation of this factor. b. For the Laboratory Data-Based Sedimentation Modeling Method, the design treatment flow rate shall be determined through the scour verification testing conducted under Appendix B, Part 4.0.
3. Accumulated pollutants shall be removed from the device as recommended by the manufacturer. This includes periodic removal of sediment to maintain device efficiency and reduce scour. Sediment shall not be allowed to accumulate to a depth greater than the maximum recommended sediment storage depth.
4. If the device is modeled using the Theoretical Sedimentation Modeling Method, the device shall be equipped with either a permanent pool having a depth at least three (3) feet above the maximum sediment storage depth to reduce scour, or shall be equipped with internal flow control structures to reduce scour velocities. Note: See Consideration VI.E for a discussion of scour.
Operation and Maintenance
Prepare a site-specific annual inspection and maintenance plan for the swales that addresses the following:
A. Identify the responsible party.
B. Limit off-street parking or other activities that may cause rutting or soil compaction in swales and repair as needed.
C. Inspect swales annually to detect and remedy nuisance conditions such as standing water, weeds, woody growth, and trash dumping. Limit the use of pesticides and fertilizer if swale is used for water quality control.
D. State the proper vegetation type and design height for dense vegetation in the maintenance plan, and maintain the specified height when mowing or cutting.
E. Remove sediment when infiltration rates are impeded, sediment accumulation is visible, or if standing water exists for 48 hours after a rainfall/runoff event. Avoid compaction of the soil in the swale during the sediment removal process. After sediment removal, repair any damaged or eroded areas by filling with topsoil that meets appropriate infiltration requirements. If compaction occurs, restore the swale infiltration capacity by mitigating for compaction as described in V.G.6.b. Mitigation practices can include subsoiling or chisel plowing as described in V.G.6.b. Reseed as needed to reestablish vegetation.
F. Implement erosion control measures if erosion during construction or maintenance becomes severe enough to prevent establishment of vegetation. Refer to WDNR Conservation Practice Standards “Channel Erosion Mat” (1053), “Mulching for Construction Sites” (1058), and “Seeding for Construction Site Erosion Control” (1059) for further guidance.
Wet Detention Pond
Operation and Maintenance
Develop an operation and maintenance plan that is consistent with the purposes of this practice, the wet detention pond’s intended life, safety requirements and the criteria for its design. The operation and maintenance plan will:
A. Identify the responsible party for operation, maintenance and documentation of the plan.
B. Require sediment removal once the average depth of the permanent pool is 3.5 ft. At a minimum, include details in the plan on inspecting sediment depths, frequency of accumulated sediment removal, and disposal locations for accumulated sediment (NR 500, Wis. Adm. Code).
C. Include inlet and outlet maintenance, keeping embankments clear of woody vegetation, and providing access to perform the operation and maintenance activities.
D. Identify how to reach any forebay, safety shelf, inlet and outlet structures.
E. Address weed or algae growth and removal, insect and wildlife control and any landscaping practices.
F. If a liner is used, show how the liner will be protected from damage during sediment removal or when the liner is undergoing repair.
G. Prohibit excavation below the original design depth unless geotechnical analysis is completed in accordance with V.A.1.b & c.
EPA State Listing: