There’s also the pollution. “Every bit of dirt that we have to take off the site and throw away is expensive, because it’s contaminated with metals and other things,” says the environmental scientist Justin Reel of RK&K, who leads mitigation and hydrological planning for the project. “But for the low-level type of human interaction we’re proposing, with a fairly thin cover we can use it on the site effectively. If you don’t have frequent, regular, intended exposure, these contaminants aren’t super bad. Where we do anticipate frequent soil contact, like our upland islands, we are planning for a cover over top of any native soil.”[caption id="attachment_236" align="aligncenter" width="618"] South Wilmington Wetland Park Master Plan[/caption]
A single strategy
But resolving the polluted soil problem will be complex. “It’s one thing to clean up an area for humans. But if you’re bringing burrowing animals in, or shellfish,” a more stringent standard might be required, says Marian Young, the president of the remediation consultancy BrightFields. Scarfone quips, “For the amount of remediation we need, all the earthworms in the world aren’t going to be able to do.” Normally, he says, “for projects like this, you cap it. But here, we want to re-create a functioning system.”
This spring, the future park was cleared of dense Phragmites. The resulting open, savanna-like vista gave a delightful hint of how it might eventually look—or feel, anyway, because it has yet to be sculpted and engineered.[caption id="attachment_237" align="aligncenter" width="657"] Industrial detritus and invasive vegetation have occupied the site until now.[/caption]
Added water storage capacity and created habitats that can resist recruitment of invasives like Phragmites will both be achieved with a single strategy, lowering the site to alter the hydrology and establish “a different water regime than we have right now, which is very irregular and storm driven,” Reel says.
When there is a flush of stormwater from the residential neighborhood, it will collect in a forebay, to let sediment settle, and then will cross the site through a winding network of channels and ponds. These eventually converge on a short, straight connection from the park to the river that is partly open ditch and partly pipe.
At the river, the flow, as it is currently, will be controlled by a self-regulating tidegate. An open flow to the Christina and its tides was considered. That would promote the wetland’s naturalization and its connection to fisheries. But properties surrounding and contiguous to the park are low-lying.