20 Mesocosms at the Puyallup LID research center mimic bioretention on a smaller scale. The mesocosms are plastic tanks approximately 2 meters in diameter and 1.25 meters tall.

Published in 2016, this research paper focused on the use of the mesocosms to investigate various soil mixes dosed with stormwater containing known concentrations of pollutants.

The facility collects stormwater from roads and rooftops in a large cistern (approx. 11,356 liters, or 3000 gallons) allowing for the application of stormwater at various hydraulic and pollutant loads.

During targeted rain events, stormwater is distributed by gravity from the cistern through weirs at known volumes to the mesocosms. Each mesocosm has an under-drain and a two-stage control structure to control hydraulic residence time, saturated zone, and ponding depth.

Between storms, dead storage in the tank can be used to mix synthetic stormwater mixtures and dose the mesocosms with desired volumes and pollutant concentrations. The flexibility of the collection and delivery system allows for the application of various pollutants of concern as scientists and agencies in the region determine research needs.