Cost-benefit considerations for bioretention

Plot of total cost of construction and maintenance per water quality volume for wet basins. The dashed line represents average cost and the two solids lines represent the range of costs. Source: Mn/DOT, 2005

Construction and Maintenance Costs

General cost etimation methods can be used by site planners to compare the relative construction and maintenance costs for structural BMPs. However, it is recommended that construction and maintenance budgets should be based on site specific information. Once the construction plans are created, designers could use the table below and the cost estimation worksheet. The table below lists the site components that are specific to bioretention practices. Not included in this table are those cost items that are common to all construction projects, such as mobilization, traffic control, erosion and sediment control, permitting, etc.

Recommended maintenance activities for bioretention areas.
Link to this table

Activity	Schedule
Prune and weed to maintain appearance. Mulch replacement when erosion is evident. Remove trash and debris. Mow filter strip	As needed
Inspect inflow points for clogging (off-line systems). Remove any sediment. Inspect filter strip/grass channel for erosion or gullying. Re-seed or sod as necessary. Trees and shrubs should be inspected to evaluate their health and remove any dead or severely diseased vegetation.	Semi-annually
Inspect and remove any sediment and debris build-up in pre-treatment areas. Inspect inflow points and bioretention surface for build up of road sand associated with spring melt period. Remove as necessary and replant areas that have been impacted by sand/salt build up.	Annually
Replace mulch over the entire area. Replace pea gravel diaphragm or filter fabric if warranted. The planting soils should be tested for pH to establish acidic levels. If the pH is below 5.2, limestone should be applied. If the pH is above 7.0 to 8.0, then iron sulfate plus sulfur can be added to reduce the pH.	2 to 3 years