Infiltration Basin Typical Maintenance Requirements
Reporting Requirements
An initial installation certification (as-built) stamped by a Professional Engineer (P.E.) registered in the state of Wisconsin shall be submitted to the City Engineer upon completion of construction. The as-built shall be of sufficient detail to show the system was properly constructed and is functioning as designed. It shall include a statement by the certifying P.E. along with a marked-up drawing (as needed), infiltration observation, and photograph(s).
An annual report shall be submitted via email to City Stormwater Management staff. The report shall include records of all inspections and maintenance performed for the year. Inspections shall be done every calendar year, with reports being submitted by June 1 of the following year.
Maintenance Provisions
Owner shall maintain records of inspections, mowings, and survey data, all in accordance with Chapter 37 of the Madison General Ordinances. Infiltration Basin shall be designed, installed and maintained in accordance with WDNR Conservation Practice Standard #1003 Infiltration Basin.
At a minimum annually, visually inspect the basin, outfalls and outlet structure for deterioration or damage, erosion, obstructions, sediment build up, and general operation (including emergency drawdown & overflow devices if present). Check the condition at the receiving area/channels at the outlet and downstream from the release structures for stability and signs of erosion damage or sparse vegetation.
No structures of any kind are permitted within the infiltration basin area, without prior written approval of the City Engineer.
A topographic survey of the infiltration basin shall be taken once every three (3) years. The survey shall be of sufficient detail to ensure maintenance of basin and outlet structure design and integrity of outfall structures. Survey data shall be sealed by a registered land surveyor and submitted to City Engineer for review.
Siltation in the basin, as identified by the topographic survey, shall be dredged and disposed offsite in accordance with NR 347. Dredging shall be as required by the City Engineer.
Maintenance shall be required when system shows standing water beyond 72 hours of rain event. Visually inspect and record observation of system within 72 hours after a rain event greater than 0.5 inches. Include photos and copy of rain event data in report. If standing water is still present, maintenance is required. If the system fails visibly due to sustained sediment loading, the upper soil layer should be replaced and re-vegetated. Growing, native vegetation may be salvaged prior to replacing the upper soil layer.
Infiltration Observation After Rain Event
| Date of Rain Event | Rainfall Total (inches) | Date of Observation | Is Standing Water Present? | Observation Comments |
|---|---|---|---|---|
Vegetation Management
The infiltration basin shall be mowed to a minimum of twice per year. Mowing shall maintain a minimum grass height of 6 to 8 inches. All undesirable vegetation and volunteer tree growth shall be removed, including close proximity to any outfall and the outlet structure.
The Owner shall maintain vegetation by watering, weeding, hand pulling and/or herbicide applications, pruning and resetting plants to proper grades or vertical positions, as required to establish healthy, viable plantings. Herbicide treatments shall be performed by licensed applicators who are experienced with native and non-native plant identification. Herbicides will be used in full conformance with label requirements and application techniques will limit overspray and damage to off-target species.
The Owner is responsible for a spot selective invasive weed control treatment on the entire basin area once in the initial growing season, two times in the first full growing season after seeding, two times in the second full growing season after seeding, and three times in the third full growing season after seeding. This can include combinations of hand weed control and selective herbicide treatment. Herbicide treatment can be conducted with tools such as hand held or backpack sprayers. Examples of common invasive species to be controlled from spread are: Narrow-leaved cattail and reed canary grass in wetland areas; Canada thistle, Flowering spurge, Common teasel, Sweet clover, Red clover, Wild parsnip are examples of more upland type species to be controlled. Applications to perennial weeds need to occur prior to seed formation of such species. If such species do go to seed, contractor is responsible for cutting the seed heads, bagging them, and removing them from the project site. Herbicide applications that are necessary must be performed by qualified personnel trained in the identification of native species and also licensed appropriately for herbicide applications in the state or region in which they are applying.
Watering shall be provided every day for the first 10 days after installation, if rainfall is not sufficient. If vegetated in spring, water for 3 to 6 weeks after seed placement. If vegetated in the fall, water for 3 to 6 weeks in the spring if dry conditions exist until established. Apply water in a manner to preclude puddling, washing and erosion. The equivalent of one-half inch of rainfall per week shall be considered the minimum until germination.
All areas of the infiltration basin where the mulch has been displaced shall be re-mulched as needed. Additional mulch shall be applied annually.
Snow shall not be dumped directly onto the infiltration basin.
It is strongly recommended to avoid spreading salt on pavement that drains to the infiltration basin as salt can reduce the infiltration capacities of the soils and lead to a short basin life span. If it is known that the infiltration basin will be receiving chloride laden runoff, salt-tolerant plants shall be planted and the draw down device shall be opened for the snowy months and closed again in the spring.