The UNH Stormwater Center field site.

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The University of New Hampshire Stormwater Center’s (UNHSC) field site sits adjacent to a nine-acre commuter parking lot in Durham, New Hampshire. The contributing drainage area—curbed and almost completely impervious—generates stormwater runoff typical of developed urban and suburban subcatchments. For nine months of the year, the parking lot is used near capacity by a combination of passenger vehicles and bus traffic. The pavement is frequently plowed, salted, and sanded during the winter.

The field site contains three classes of stormwater treatment systems: conventional, structural Best Management Practices (BMPs) such as swales and retention ponds; Low Impact Development (LID) stormwater designs such as tree filters, bioretention systems, and a gravel wetland; and manufactured BMPs such as hydrodynamic separators and subsurface infiltration/filtration systems.

The site is designed to test a range of stormwater treatment systems under the same conditions. The parallel but separate configuration of the systems installed at the site normalizes the variability typical in stormwater contaminant loading and regional rainfall characteristics. Each treatment is uniformly sized to address a Water Quality Volume (WQ_V) of one inch of rainfall from one acre of impervious surface.

The lot’s contaminant concentrations are above, or equal to, national norms for commercial parking lot runoff. Local climate is coastal, cool temperate forest. Average annual precipitation is 48 inches, with monthly averages of 4.1 (+/-0.5) inches. The mean annual temperature is 48°F, with an average of 15.8°F in January, and an average of 82°F in July. Depth of design for frost depth is 48 inches.