Regional Pond, Brownfield Cap, and Stormwater Strategy
A 9-acre former rail yard is being redeveloped with 280 apartments, 15,000 square feet of retail, and a new street. The site is 78% impervious after build-out. The team proposes green roofs, permeable pavement in surface parking, and discharge to a regional detention pond built in 1990. The pond is outside the project boundary, is already at its permitted capacity during the design storm, and is owned by the county. The team wants to count the pond as the project's stormwater management strategy and use the green roofs to claim heat island reduction. The site is contaminated with petroleum hydrocarbons at two to six feet below grade; the remediation plan requires a cap and restricts infiltration. The project is pursuing the brownfield remediation credit in Smart Location and Linkage and wants to avoid duplicating documentation.
1. Can the regional pond be counted? What must the team demonstrate for the stormwater credit?
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The county pond cannot be counted merely because stormwater flows there. It is outside the boundary and already at permitted capacity during the design storm, so the project would be relying on capacity that is not attributable to it. A reviewer would ask for legal control, dedicated additional storage, and a hydrologic calculation showing that the project's runoff volume and water-quality treatment are actually managed. If the team cannot secure dedicated capacity, it should manage stormwater on site: green roofs and permeable pavement reduce runoff, but on a 78% impervious site they are unlikely to be sufficient alone. Because contamination restricts infiltration, the design should use lined biofiltration, storage with underdrains, or reuse, and should model performance for the applicable storm. The pond could still be part of a combined strategy only if the project creates and controls new capacity.
2. How should the team coordinate stormwater, heat island, and brownfield remediation?
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Treat the three issues as one site-planning problem. The remediation cap limits infiltration, so do not design infiltration basins that puncture the cap; place green infrastructure above the cap with an underdrain and a liner, and route flows to storage or treatment. Green roofs reduce both runoff and heat island, and high-SRI or shaded pavement can address the parking areas; trees and shade structures can improve pedestrian comfort. For the brownfield credit, document the remediation plan, cap, and long-term monitoring separately, but cross-reference the stormwater design so the reviewer can see that the cap and the green infrastructure are compatible. Do not double-count the same green roof area as both infiltration and heat-island strategy without showing the calculation.
3. What documentation package would a reviewer expect for these claims?
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Submit a hydrologic and hydraulic model, soil and groundwater data, the remediation cap design, and as-built drawings for green roofs, permeable pavement, and underdrains. Include the pond capacity letter or easement if any off-site capacity is claimed, a maintenance plan with inspection frequencies, and the heat-island calculation with material specifications and shade areas. A reviewer will look for consistency between the site plan, the stormwater narrative, and the brownfield remediation documents.