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Bioretention Garden

City of Laconia, New Hampshire

Services: Civil Engineering, Stormwater
Client Served: City Laconia, Department of Public Works

The City of Laconia has taken strong efforts over the last 5 years to protect the water quality of the lakes that the community surrounds. The City recognizes that its aging stormwater infrastructure is no longer meeting the needs of the community due to climate change and land dramatic development over the last 10 years. Several areas are experiencing flooding due to undersized culverts and piping networks. Also, the older system was designed with one intent, to move stormwater off the roads and into the lake as fast as possible. Unfortunately, this design method also moves the pollution into the lake as well. The most recent project, funded through a NH DES grant secured by Lakes Region Planning Commission is a bioretention garden.

Engineered by Loureiro, the bioretention garden is designed using the powerful properties of compost and plants. Compost is very effective in removing stormwater pollutants such as petroleum hydrocarbons, bacteria, nutrients, and metals. The 850 square-foot bioretention garden on White Oaks Road will have the capability of treating and infiltrating the majority of rain storms that pass through this city of Laconia. As the rain enters the basin, it will infiltrate through the open rock surface and pass through a two and a half foot layer of compost. The compost will absorb the stormwater like a sponge and begin to remove the pollutants from the water. The treated stormwater will also slowly drain into the surrounding soils making its way into the groundwater, reducing the discharges to the lake. The discharge for this area is located on Paugus Bay and near the City drinking water intake, which makes this project even more important.

According to the EPA, bioretention gardens are capable of removing between 80% to 90% of petroleum hydrocarbons, sediment, and bacteria and 70% to 80% of nutrients like nitrogen and metals like copper and zinc which can affect the health of fish.


Loureiro designed a bioretention garden to remove stormwater pollutants;

  • The bioretention garden was designed using compost and plants
  • Compost is very effective in removing stormwater pollutants
  • The bioretention garden will treat and infiltrate the majority of rain storms that pass through this city of Laconia.
  • The treated stormwater will drain into the surrounding soils, reducing the discharges to the lake.