Older warehouses are said to be producing the runoff.
By: Paul Koepp
Runoff from warehouses built during the 1980s and 1990s is to blame for flooding in Pigeon Swamp State Park, according to a recently completed stormwater impact study of the Davidsons Mill Road area near the N.J. Turnpike.
The runoff that has flowed west under the Turnpike and into the park in recent years has been coming from the sites of several nearby warehouses constructed since 1989. However, all of the companies in question followed the stormwater management rules that were in place at the time, said officials from the Cranford-based PMK Group, which did the study.
PMK presented its findings Sept. 5 to the Davidsons Mill Road Area Committee, which was set up by the Township Council in March 2006 to investigate flooding in the area. The two groups will formally report their findings and recommendations to the council in October.
The study, which cost the township about $123,000, was paid for in part by developer Trammell Crow, which gave the township $100,000 for the study after the Planning Board rejected its plan to build three warehouses at the intersection of Route 535 and Davidsons Mill Road. Unchanged plans were approved one month later.
Jean Dvorak, a Deans Rhode Hall Road resident who is a member of the Davidsons Mill Road Area Committee, had previously questioned whether PMK could be objective in determining whether the widening of the Turnpike in the late 1980s had caused the flooding. The company has had contracts to work for the N.J. Turnpike Authority.
PMK officials said at the Sept. 5 meeting that a project to widen the N.J. Turnpike from Exit 9 to Exit 8A had an insignificant impact on flooding in the park. They said the construction of warehouses by Wakefern in 1989, by Circuit City in 1997, and by Opus in 1999 had caused most of the problem, because their detention basins merely shifted runoff downstream instead of returning it to the ground. Still, the companies had actually exceeded state Department of Environmental Protection stormwater regulations at that time.
"We were looking for a smoking gun, asking if somebody didn’t build something right. We couldn’t find it," said Joseph Skupien, PMK’s runoff expert. "Everyone followed the rules they were supposed to follow."
At the time the Wakefern, Circuit City and Opus warehouses were built, DEP rules only required the rate of runoff to be reduced, meaning that the same volume of water could run off the properties over a longer period of time. The rules are more strict now, requiring volume reductions.
The runoff from the warehouse sites flows through two culverts under the N.J. Turnpike, across a farm field, and into a utility right-of-way in the Pigeon Swamp State Park.
"The warehouses met the old rules, but they screwed up the system. They proved that the old regulations stunk," said Dan Van Abs, chair of the Davidsons Mill Road Area Committee.
The PMK study found that those three warehouse complexes increased the area’s impervious surface coverage from 5 percent to 30 percent. As a result, the volume of water flowing into the park and the duration of standing water after a heavy rain both increased by up to 150 percent, Mr. Skupien said.
The Trammell Crow warehouses, along with warehouses built recently by CNJ and IDI, would bring the impervious coverage up to 50 percent. But newly designed infiltration basins could return water to the ground much more efficiently, possibly bringing runoff levels down to where they were before the area was developed, Mr. Skupien said. He said the area’s soil is very favorable to infiltration, but the basins must be actively maintained to make sure they drain properly.
Mr. Skupien praised the township’s new stormwater regulations, which were adopted in March 2007, saying they are "ahead of the state rules." The township now requires that annual groundwater recharge volumes be maintained through runoff infiltration, and 40 percent of non-building impervious surfaces, like parking lots, must be permeable. He said that if the rules are strictly enforced, there should be less flooding in Pigeon Swamp.
The 1,078-acre park is not open to the public. However, Ms. Dvorak said its water should be protected from contaminated runoff from the N.J. Turnpike, which she said could threaten the breeding areas of numerous amphibian species and turtles.
"The park is an environmentally fragile ecosystem," she said. "Some of the interior lands have been untouched since prehistoric times."
The PMK study did not address water quality.
Ms. Dvorak also said she would like the township to make its stormwater rules even tougher and to consider making the older warehouses replace their detention basins with the more effective infiltration basins if the flooding continues.
Mr. Van Abs said the township should use the N.J. Turnpike Authority’s plans to widen the Turnpike again as leverage by asking the DEP to condition its approval on improving of the Turnpike’s stormwater management facilities near the park.

