Learn how to install a stormwater BMP, from site checks on soils, slope and groundwater to sizing, permits, utility locates, construction steps and catch basin insert installation.
BMP installation starts before excavation. Confirm drainage area, soils, slope, water table depth and available space, size the unit to the design storm your jurisdiction sets, and locate utilities. Then build in sequence (excavate, place structure or media, connect, stabilize) while construction controls protect the unit. A catch basin insert is the exception, because it drops into an existing inlet without excavation.
What is a stormwater BMP, and which structural types get installed?
Structural BMPs are, in the Iowa DNR's description, "engineered and constructed systems that are used to treat the stormwater at either the point of generation or the point of discharge." Detention ponds and constructed wetlands are the examples it gives. Non-structural BMPs cover prevention, education and management practices.
The structural families you will meet on sites are basins and ponds, wetlands, filtration systems such as biofiltration, permeable pavement and tree trenches, swales, underground vaults and inlet inserts. The same manual notes that no single BMP can address all stormwater problems. Each has limits based on drainage area, available land, cost and pollutant type, so the first job is sorting formats by site constraint.
A working rule: if you have open ground and soils that drain, an infiltration or filtration basin is available. If soils are tight or the water table is shallow, you need a lined or underdrained filter or a wet system. If you have a built-out site with existing inlets and no room, retrofit the inlet.
Which site conditions do you assess first?
Drainage area, slope, soil group, depth to groundwater and buffers decide feasibility. EPA's BMP Siting Tool screens locations against criteria such as drainage area, slope, hydrological soil group, groundwater table depth, and road, stream and building buffers.
The Connecticut Stormwater Quality Manual lists the same physical factors: contributing drainage area, site slope, soil infiltration capacity and depth to seasonal high groundwater and bedrock. EPA's basin design guide adds head and highly impervious urban sites to its six primary feasibility factors. Record each one before you pick a format, and confirm physical conditions with the testing your local manual requires.
How do soils and groundwater change the design?
Soil survey maps are a first screen only. The Auburn LID Handbook advises using the USDA Web Soil Survey for initial interpretation, then having a professional soil scientist or classifier evaluate the proposed site, because map units contain inclusions of other soils.
Infiltration needs permeable ground. EPA's TMDL implementation manual says recharge BMPs depend mainly on soil hydraulic conductivity and groundwater elevation, and that a conductivity of 0.5 inches per hour or greater is generally desired.
Where soils are slow, filter instead of infiltrate. The Minnesota Stormwater Manual says media has a high infiltration rate but underlying C or D soils typically do not, so an underdrain goes into the design. It also says biofiltration media should be 3 feet or more thick. Wet swales suit sites where the water table sits very close to the surface or water does not drain out of the swale.
How do the prerequisites compare by BMP type?
Each type carries its own drainage area, footprint and soil limits. The table uses limits stated in the Minnesota manual.
How is a BMP sized?
Capacity follows the water quality volume or design storm in your local manual, so pull those criteria from your jurisdiction before drawing anything. The Connecticut and New Hampshire manuals above show that each state sets its own selection and sizing rules.
Type-specific limits then apply on top. A biofiltration basin must meet the 48 hour drawdown time and be sized so crews can maintain it, per the Minnesota manual. Permeable pavement is limited by the ratio of contributing area to pavement area. Your engineer works from the local storm depth, the drainage area and its impervious cover, then checks the result against these limits.
What utility locating and permits come before digging?
Call for utility locates, confirm permit coverage and have the SWPPP in place before you disturb ground. Utility locating is standard practice; make the call through your state one-call service and mark all lines before excavation.
Permit timing depends on your state. The operator must develop the SWPPP before submitting the Notice of Intent and before any construction activity, and submit the NOI electronically through myDEQ. The SWPPP must also name the person responsible for on-site implementation.
What are the installation steps for a basin, swale or filter?
Install erosion controls first, then excavate without compacting the subgrade, place geotextile, underdrain and media, connect inlet and outlet, and stabilize.
- Install perimeter sediment controls and mark the BMP footprint, keeping equipment off the infiltration area.
- Excavate to design grade with light equipment, leaving the subgrade uncompacted.
- Place geotextile, stone and underdrain where the design calls for them.
- Place media to the specified depth in lifts.
- Build the inlet, outlet, overflow and any pretreatment.
- Grade, seed or plant, and stabilize side slopes.
What construction-phase protections keep the BMP working?
Keep construction sediment out of the unit until the drainage area is stabilized. Divert runoff around the BMP, or leave final media and surfaces for last, because fines clog filter media and infiltration surfaces quickly. Restrict heavy equipment on infiltration areas to avoid compaction, and inspect controls after storms. Commission the BMP only once the contributing area is vegetated or paved.
How is a catch basin insert installed in an existing inlet?
Measure the basin, select or fabricate an insert to fit, set it under the grate and confirm crews can reach it for maintenance. Inserts need no excavation, so the site-condition screening above matters far less than basin geometry and access.
Our Ultra Urban® Filter is custom-fabricated to each basin's shape and size and installs as a drop-in insert without excavation, pumps or power. A site assessment, which reviews contaminants, flows, available space, effluent targets and maintenance access, is the way to start; begin from this page.