Operation and maintenance of bioretention

Operation and Maintenance

Overview

The most frequently cited maintenance concern for bioretention is surface and under-drain clogging caused by organic matter, fine silts, hydrocarbons, and algal matter. Common operational problems include:

• Standing water
• Clogged filter surface
• Inlet, outlet or under-drains clogged

Recommendations described in this chapter are aimed at preventing these common problems.

Design Phase Maintenance Considerations

Implicit in the design guidance in the previous sections is the fact that many design elements of bioretention systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include: limiting drainage area, providing easy site access (REQUIRED), providing pre-treatment (REQUIRED), and utilizing native plantings.

Construction Phase Maintenance

Proper construction methods and sequencing play a significant role in reducing problems with operation and maintenance (O&M). In particular, with construction of bioretention practices, the most important action for preventing operation and maintenance difficulties is to ensure that the contributing drainage area has been fully stabilized prior to bringing the practice on line.

Warning: It is required that the contributing drainage area has been fully stabilized prior to bringing the practice on line

Inspections during construction are needed to ensure that the bioretention practice is built in accordance with the approved design and standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided here.

BIORETENTION - Construction inspection checklist

Post-construction Operation and Maintenance

Warning: A maintenance plan clarifying maintenance responsibility is REQUIRED.

Effective long-term operation of bioretention practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected life span of the facility, but will also improve aesthetics and property value. Some important post-construction considerations are provided below along with RECOMMENDED maintenance standards.

• A site specific O&M plan that includes the following considerations should be prepared by the designer prior to putting the stormwater filtration practice into operation:
  • Operating instructions for outlet component
  • Vegetation maintenance schedule
  • Inspection checklists
  • Routine maintenance checklists
• A legally binding and enforceable maintenance agreement should be executed between the practice owner and the local review authority.
• Adequate access must be provided for all bioretention facilities for inspection, maintenance, and landscaping upkeep, including appropriate equipment and vehicles.
• The surface of the ponding area may become clogged with fine sediment over time. Core aeration or cultivating of non-vegetated areas may be required to ensure adequate filtration.
• Bioretention areas should not be used as dedicated snow storage areas:
  • Areas designed for infiltration should be protected from excessive snow storage where sand and salt is applied
  • Specific soil storage areas should be assigned that will provide some filtration before the stormwater reaches the infiltration areas.
  • When used for snow storage, or if used to treat parking lot runoff, the bioretention area should be planted with salt tolerant, and non-woody plant species
• Bioretention areas should always be inspected for sand build-up on the surface following the spring melt event.
• General maintenance activities and schedule are provided in the table below.

Recommended minimum setback requirements. This represents the minimum distance from the infiltration practice to the structure of concern. If the structure is aboveground, the distance is measured from the edge of the permeable pavement to the structure. If the structure is underground, the setback distance represents the distance from the point of infiltration through the bottom of the permeable pavement system to the structure.
Link to this table

Setback from	Minimum Distance [feet]
Property Line	10
Building Foundation*	10
Private Well	50
Septic System Tank/Leach Field	35
* Minimum with slopes directed away from the building.