Dane County Stormwater Manual

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====== Stormwater Maintenance ======

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.

For practice specific flyers, see the [[Stormwater Resources]] page. 

=====Maintenance Agreement=====
A signed and notarized {{:stormwater_maintenance_agreement.pdf |Stormwater Maintenance Agreement}} ( {{ :maintenance_agreement.doc| }}), with $30 recording fee (made out to "Register of Deeds") must be provided before a stormwater permit can be issued. Once recorded, this document binds maintenance requirements to the property owner. The agreement must have an Exhibit A that provides the legal description of the property and details specific maintenance tasks for practices located on the site. {{ :wiki:images:maintenance_exhibit_b.pdf |Exhibit B}} shows a simplified site plan and clearly identifies the location of all stormwater practices.

{{ :wiki:images:maintenance_map.png?600 |}}

====General Maintenance Requirements====

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.

====Specific Maintenance Requirements====

===Wet Pond===

  * Annually inspect all components of the wet pond, including inlets, outlets, riprap, and safety shelf, and sediment depth.
  * Keep embankments clear of woody vegetation.
  * Mowing in buffer areas around stormwater ponds should be minimized. If occasional mowing is necessary, mow no shorter than 6 inches.
  * Application of fertilizer, herbicide, pesticide or other chemicals is discouraged.
  * Remove sediment from permanent pool once average depth is 3.5 feet or less. Protect liner from damage during sediment removal, if present.
  * Excavation is prohibited below the original design depth unless approved by Dane County Water Resources Engineering Department.
  * Repairs must restore the practice to the approved plan design.

===Dry Pond===

  * Remove trash and other debris regularly to prevent clogging of outlet structure.
  * Inspect twice a year to ensure proper operation and check for any potential problems, such as: sediment accumulation, subsidence, erosion, damage to the emergency spillway, and woody vegetation.
  * Removed accumulated sediment from the pond as necessary. Sediment removal will be more frequent than in a wet pond due to the smaller storage volume.
  * Repairs must restore the practice to the approved plan design.

===Infiltration Basin===

  * Inspect quarterly to ensure proper function and check for any potential problems. Inspect overflow spillway for indication of failure and make note of vegetation condition. If standing water is observed over 50% of the basin floor 3 days after rainfall, the basin is clogged and must be restored.
  * Remove trash and other debris regularly.
  * Mowing or burning shall be used to maintain the vegetation.
    * Mow newly planted seed once it reaches a height of 10 to 12 inches down to a height of 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) to a height of 5 to 6 inches. 
    * Burning may begin the second year, in the early spring (prior to May 1st) or in the late fall (after November 1st). Burning shall be done two consecutive years, then up to three years passing before the next burning. Under no circumstances shall burning occur every other year.
  * Restoration includes removing the top 2 to 3 inches, chisel plowing, then adding topsoil and compost before seeding. 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. 
  * During winter months, all draw down devices in the pond shall be opened to discourage infiltration of runoff water containing high levels of chlorides.
  * Repairs must restore the practice to the approved plan design.

===Bioretention Device===

  * Inspect quarterly to ensure proper function and check for any potential problems. If standing water is observed 24 hours after rainfall, the basin is failed and must be restored according to the approved plan design.
  * Maintain vegetation type specified in approved plan. Remove all other vegetation from device as needed.
  * Repair eroded areas as needed.
  * Remove litter and debris regularly.
  * Re-mulch voids areas as needed.
  * Water plants as needed during first growing season and during dry periods after first growing season.
  * Treat diseased trees and shrubs as needed.
  * Do not dump snow into device.
  * Once a dense vegetation layer is formed, additional mulch does not need to be added.
  * Repairs must restore the practice to the approved plan design.

===Permeable Pavement===

  * Inspect permeable pavement sections at least twice per year.  Inspections are recommended after heavy rainfalls. 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 – Repair any settlement, deformations or cracking that are significant enough to adversely impact the water quality function of the system.
    * 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 - Repair blocked, restricted or eroding underdrain outfalls.
    * Run-on Areas – Repair eroding areas.
  * 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, test the system and inspect for ponding. If ponding still occurs, the owner shall coordinate the necessary repairs and/or replacement as approved by the Dane County Water Resources Engineering Division.
  * Clean the permeable pavement when the following conditions are observed: 
    * Excessive surface ponding after a storm event.
    * Surface overflows during routine storm events. 
    * Substantial run-on areas with visible accumulation of sediment or debris are observed.
  * 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.
  * 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.
  * 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 practice to the approved plan design.

===Sorbent Inlet Filters===

  * Maintain [insert oil control device called for per design], or equal, according to the manufacturer's guidelines.
  * Inspect inlet filters quarterly. Repair when the performance of a filter is compromised.
  * Replace inlet filters once a year and if the filter is damaged.

===Storm Sewer===

  * Inspect storm sewer after rainfall and remove debris from inlets and outfalls
  * Repair inlets and outfalls that are damaged or show signs of erosion.
  * Replace rip-rap as necessary.
  * Repairs must restore the system to the approved plan design.

===Vegetated Swale===

  * Inspect swales annually to detect and remedy nuisance conditions such as standing water or trash dumping.
  * Maintain vegetation type and height specified in approved plan.
  * Repair areas of swale showing signs of erosion. 
  * Limit off-street parking or other activities that may cause rutting or soil compaction in swales.
  * Limit the use of pesticides and fertilizer.
  * Remove sediment when visible or if standing water exists for 24 hours after a rainfall/runoff event. After sediment removal, repair any damaged or eroded areas by filling with topsoil, reseeding and matting to reestablish vegetation. 
  * Repairs must restore the practice to the approved plan design.

===Infiltration Trench===

  * Inspect monthly during the first year of operation, then twice per year. The infiltration trench is considered failed if water is present in the observation well 72 hours after the last storm event and must be restored according to the approved plan design.
  * Remove accumulated material or debris on the surface of the trench and outlet regularly.
  * Do not be dump snow into trench.
  * Repairs must restore the practice to the approved plan design.

===Underground Infiltration Chamber===

  * Inspect monthly during the first year of operation, then twice per year, in early spring and early fall. The infiltration chamber is considered failed if water is present 72 hours after the last storm event and must be restored according to the approved plan design.
  * Repairs must restore the practice to the approved plan design.


===Filtration Device===

  * Maintain [insert device name] according to the manufacturer's guidelines.
  * Inspect filtration devices twice per year, in early spring and early fall.  Removal of sediment and debris shall be performed once 8 inches in depth or the volume exceeds 15% of the total storage volume.

====Additional Forms====
{{ ::release_of_restriction.pdf |Release of Deed Restriction}}