PUBLIC NOTICE
The N.C. Department of Environmental Quality Stormwater Program is seeking public comments on an update to “Chapter 10: Wet Detention Basins” of the state’s Stormwater BMP Manual. The update will change the TN removal credit assigned to wet detention basins from 25 to 30 percent. Public comments on this change will be accepted for the next 30 calendar days (until May 19, 2016). Comments should be emailed to: stormwater@ncdenr.gov. Please include “BMP” in the subject line.
In the interim, applicants who wish to take advantage of this additional TN removal credit may do so immediately.
This change to the Stormwater BMP Manual is supported by data provided by the NCSU Stormwater Engineering group. Based on six research studies, NCSU engineers observed a 29 percent reduction between median concentrations of TN in the influent versus the effluent of wet ponds. The NCSU engineers estimate that a modest amount of evaporation would be expected between storm events (approximately 10 percent of annual inflow volume) and that this would “bump up” the load of nutrients reduced by 10 percent (see table below).
Mean and Median Site Pollutant Reductions
|
Pollutant |
Median Reduction in Concentration |
Median Reduction in Load |
|
TN |
29% |
32% |
|
TP |
26% |
29% |