Permanent stormwater practices (e.g. Wet Pond, Bioretention Device, Infiltration Basin) installed as part of a stormwater management permit are required to be maintained by the property owner. Maintenance is critical for the practices to operate as designed and to effectively treat runoff from the site. The pollutant removal, channel protection, and flood control capabilities of all practices will decrease if regular inspection and necessary maintenance is not performed.

The cost, level of effort and expertise required to maintain stormwater practices varies, depending on the type, size and complexity of the practice. Routine maintenance, such as mowing and removing debris or trash, is needed multiple times each year and can easily be performed by most landowners. More significant maintenance, such as removing accumulated sediment is needed less frequently, but requires more skilled labor and special equipment. Inspection and repair of critical structural features, such as embankments and outlet structures, needs to be performed by a qualified professional that has experience in the construction, inspection, and repair of these features. The financial cost of maintaining stormwater practices should be understood at the time of permitting and planned for after construction is complete.

A signed and notarized stormwater maintenance agreement, with $30 recording fee (made out to “Register of Deeds”), is required before a stormwater permit can be issued. The agreement binds maintenance to the current property owner and details specific maintenance tasks for practices located on the site.

All stormwater practices constructed as part of this project are permanent and must be maintained in a functional state. Land use, impervious areas and stormwater practices shall not be significantly altered without written permission from the County’s Water Resources Engineering Division. Owner shall maintain records of inspections and maintenance as described below, in accordance with Dane County Ordinance, Chapter 14.

• At a minimum, all components of the wet pond, including inlets, outlets, riprap, and safety shelf, and sediment depth, shall be inspected annually. [Identify how to reach any forebay, safety shelf, inlet and outlet structures].
• Embankments shall be kept clear of woody vegetation.
• To maximize filtration, mowing in buffer areas around stormwater ponds should be minimized. If occasional mowing is necessary, the mowing height is recommended to be no shorter than 6 inches. Applications of fertilizer, herbicide, pesticide or other chemicals are discouraged unless an approved chemical application plan is on file with the County’s Water Resources Engineering Division.
• Sediment removal shall be required once the average depth of the permanent pool is 3.5 ft. At a minimum, [include minimum frequency of accumulated sediment removal, and disposal locations for accumulated sediment] (NR 500, Wis. Adm. Code).
• [Address weed or algae growth and removal, insect and wildlife control and any landscaping practices. WDNR . 10/07 6 ]
• [If a liner is used, show how the liner will be protected from damage during sediment removal or when the liner is undergoing repair.]
• Excavation is prohibited below the original design depth unless geotechnical analysis is completed in accordance with DNR’s guidance document “Wet Detention Pond (1001).”
• Repairs must restore the component to the specifications of the approved plan.

• Trash and other debris should be removed regularly to prevent clogging
• Dry ponds should be inspected at least twice a year to ensure they are operating properly and to check for any potential problems, such as: sediment accumulation, subsidence, erosion, damage to the emergency spillway, and woody vegetation.
• Accumulated sediment should be removed from the pond as necessary. Sediment removal will be more frequent than in a wet pond due to the smaller storage volume.

• 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.
• Native Vegetation - Mowing (cutting) or burning shall be used to maintain the vegetation.
  • Establishment - The first mowing of newly planted seed shall occur once it reaches a height of 10 to 12 inches.
  • Mowing
    • Mowing shall reduce the height of plants to 5 to 6 inches.
    • After establishment, if burning cannot be accommodated, mowing shall occur once in the spring (prior to April 15) or in the fall (after November 1). The area shall be mowed to a height of 5 to 6 inches.
  • Burning
    • 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)
    • Burning shall be done two consecutive years and then up to three years can pass before the next burning.
    • Under no circumstances shall burning occur every other year.
• 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.
• Trash shall be removed as quickly as possible once observed.
• 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.
• Repairs must restore the component to the specifications of the approved plan.

• The Owner is responsible for carrying out typical maintenance activities for bioretention areas and shall include details on these activities that are consistent with the following standards:
• Inspect soil and repair eroded areas on a monthly basis;
• Remove litter and debris on a monthly basis;
• Add additional mulch, if present in the approved plan, on an annual basis;
• Water plants as needed during first growing season and during dry periods after first growing season;
• Re-mulch void areas as needed;
• Treat diseased trees and shrubs as needed.
• 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, if present in the approved plan, can be discontinued at maturity provided that a dense vegetation layer is formed.
• If not listed above, all components of the bioretention basin shall be inspected on an annual basis at a minimum.
• Repairs must restore the component to the specifications of the approved plan.
• If ponded water remains after 24 hours, the basin is considered failed and requires restoration to the approved plan.

• Permeable pavement systems shall be inspected at least twice per year. Inspections are recommended to be made during and after heavy rainfalls (eg: 2.9” or more over the area of the permeable pavement system within a 24 hour period). An alternative to inspecting during heavy rainfalls would be to apply sufficient water onto the permeable pavement system to simulate a heavy rainfall. Inspection of the permeable pavement system shall be conducted to evaluate the following:
  • Pavement Condition – Inspect permeable pavement surfaces for settlement, deformation or cracking.
  • Surface Infiltration – Inspect permeable pavement surfaces for sedimentation or evidence of ponding.
  • 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.
  • Outfalls - Inspect underdrain outfall locations for obstructions and erosion.
  • Run-on Areas – Inspect run-on areas for adequate cover and stability.
• Clean the permeable pavement at least twice per year (once in early spring and once in late fall) using industry recommended methods, such as regenerative air or vacuum sweeping. After vacuuming, the permeable pavement system shall be tested and inspected again for ponding. If ponding still occurs, the owner shall coordinate the necessary repairs and/or replacement as approved by the County’s Water Resources Engineering Division.
• To prevent surface clogging, clean the permeable pavement when the following conditions are observed:
  • Excessive surface ponding after a storm event.
  • Surface overflows during routine storm events.
  • Substantial areas with visible accumulation of sediment or debris.
• Clean conventional pavements in run-on areas prior to spring storm events. For run-on ratios greater than 3:1, clean conventional pavements at least once in the early spring and at least once in the late fall.
• Repair any settlement, deformations or cracking that are significant enough to adversely impact the water quality function of the system.
• Repair blocked, restricted or eroding underdrain outfalls.
• Repair and/or replant eroding run-on areas.
• For permeable pavers/blocks with joints that are filled with aggregate:
  • Replenish the joint aggregate in accordance with industry recommendations.
  • 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.
• For permeable asphalt and 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.
• The following activities shall be prohibited from occurring on the permeable pavement surface: temporary or permanent stockpiling of soil, snow or other material that can potentially cause or contribute to clogging; application of pavement seal-coating; application of sand for deicing.
• 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.
• If verification of in place pavement surface infiltration rates is necessary, conduct pavement surface infiltration rate testing per ASTM C1701, ASTM C1781, or other methods approved by the County.
• Repairs must restore the component to the specifications of the approved plan.

• The Owner shall install and maintain a [insert oil control device called for per design], or equal, to mitigate sediment and/or oil and grease in stormwater runoff.
• Inlet filters shall be maintained per manufacturer guidelines.
• Inlet filters shall be inspected quarterly. Repair work needs to be done whenever the performance of a stormwater structure is compromised.
• Inlet filters shall be replaced once a year, or more frequently, if the filter is damaged.
• Owner shall maintain records of inspections, cleaning and replacement of the device or components of the device.

• Visual inspection of components shall be performed and debris removed from inlets and storm sewer manholes.
• Repair inlet/outlet areas that are damaged or show signs or erosion.
• Rip-rap shall be replaced as necessary.
• Repairs must restore the component to the specifications of the approved plan.

• Inspect swales annually to detect and remedy nuisance conditions such as standing water or trash dumping. The swale shall be [specify design vegetation type]. Annual inspection should determine if vegetation is per plans (i.e., appropriate vegetation present, lack of weeds and woody growth), and if not, measures should be taken to establish appropriate vegetation.
• Areas of swale showing signs of soil erosion should be repaired.
• Areas of swale with no vegetation shall be restored to good vegetated catch.
• Limit off-street parking or other activities that may cause rutting or soil compaction in swales and repair as needed.
• Limit the use of pesticides and fertilizer if swale is used for water quality control.
• Maintain a height of [specify design height for vegetation] when mowing or cutting.
• 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. [Remove compaction language, if swale does not provide infiltration]. Reseed as needed to reestablish vegetation.
• Repairs must restore the component to the specifications of the approved plan.

• Perform monthly physical inspections during the first year of operation, then annually.
• Accumulated material or debris on the surface of the infiltration trench shall be removed immediately when discovered.
• Snow shall not be placed in the effective infiltration area. It may be placed on the pretreatment area, if present.
• Any outlet structure, pipe or swale shall be cleaned of accumulated material or debris immediately when discovered, or at least twice each year.
• Water depth in the observation pipe shall be measured and recorded twice per year at 72 hours after a rainfall event of 0.5 inches or more during a 24-hour period. The infiltration trench will be considered failing if water is present 72 hours after the last storm event.
• Repairs must restore the component to the specifications of the approved plan.

• Perform monthly physical inspections during the first year of operation, then annually.
• Water depth in the chamber shall be measured and recorded twice per year 72 hours after a rainfall event of 0.5 inches or more during a 24-hour period. The infiltration trench will be considered failing if water is present 72 hours after the last storm event.
• Repairs must restore the component to the specifications of the approved plan.

• Proprietary filtration 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:
  • The device shall be installed in accordance with manufacturer recommendations.
  • the installed device shall be equipped with an internal or external bypass to divert flows in excess of the design treatment flow rate.
• Filtration devices shall be inspected semi-annually in early spring and early fall. Cleaning of TSS and other debris shall be performed anytime the sediment in the unit reaches 8 inches in depth or the volume exceeds 15% of the total storage volume.