FACT SHEET FOR NPDES PERMIT DEVELOPMENT
NPDES No. NC0088307
Applicant/Facility Name: New Hanover County Water and Sewer District WTP
Applicant Address: 230 Market Place Drive, Wilmington, NC 28403
Facility Address: NC 28411, Wilmington, NC
Permitted Flow 1.38 MGD / 2.0 MGD
Type of Waste: WTP concentrate and filter backwash
Facility/Permit Status: New
County: New Hanover
Atlantic Intercoastal Regional Office: WiRO
Stream Classification: SA – ORW State Grid / USGS Quad: Scotts Hill
303(d) Listed? Yes Permit Writer: Teresa Rodriguez
Subbasin: 03-06-24 Date: 1/16/07
Stream index: 18-87-(11.5)
Drainage Area (mi2): Tidal
s7Q10 (cfs) N/A
Average Flow (cfs):
Lat. 34 16’ 28” N Long. 77 45’ 37” W
New Hanover County is proposing to build a Water Treatment Plant located northwest of US17 in
Wilmington, near Old Oak Road and the proposed Military Cutoff Extension Corridor. The plant will
have a design potable water capacity of 6.0 MGD with a planed expansion to 9.0 MGD. The source
water will be groundwater from the Pee Dee and Castle Hayne aquifers. Two separate treatment trains
are proposed. Groundwater from the Pee Dee aquifer will be treated by cartridge filtration and
nanofiltration. The groundwater from the Castle Hayne aquifer will be treated by oxidation with
potassium permanganate, tray aeration, greensand filtration, cartridge filtration and nanofiltration.
The proposed WTP includes treatment for the filters backwash. Approximately 0.1 MGD will be
generated from backwashing the greensand filters. The water will be conveyed to a storage tank for
clarification. Clarified water will be decanted and conveyed to the membrane concentrate discharge line.
The nanofiltration units are expected to generate approximately 1.38 MGD in backwash water and
membrane concentrate. When the plant is expanded to 9 MGD the expected discharge flow is 2 MGD.
Wastewater will be discharged to the Atlantic Intercoastal Waterway (AIWW). A 5.1 mile, 16” force
main will transport the wastewater from the WTP to the AIWW near the bridge to Figure 8 Island on
Bridge Road. A diffuser with four 8” ports will be installed at the discharge location at a depth of
approximately 12 feet. The ports will be distributed over a 12-foot square base.
A Finding of No Significant Impact was issued for the project by the State Clearinghouse on September
22, 2005. The FONSI includes the discharge of 2.0 MGD to the AIWW.
The County submitted an Engineering Alternative Analysis for the proposed effluent discharge. They
evaluated non-discharge alternatives, reuse, connection to a POTW, and direct discharge. Land
application in this area is severely restricted by the high concentration of dissolved solids and sodium in
the discharge. Discharge to the Wilmington WWTP was evaluated. The estimate to connect to
Wilmington is approximately $5 million for a pump station and 8 miles of force main. The direct
discharge was the most economical environmentally feasible alternative.
A diffuser will be installed near the bridge to Figure 8 Island on Bridge Road. A two dimensional
hydrodynamic and dispersion model was completed to evaluate the effect of the discharge on the AIWW.
The model predicts salinity concentrations in the intermediate and far field regions surrounding the
diffuser. The mean concentration of salinity in the AIWW is 35 ppt. Predicted effluent salinity
concentration is 0.5 ppt. The model predicted that the salinity should be at background concentrations
within 500 feet of the diffuser.
The receiving stream is impaired for shellfish harvesting. The segment is not impaired for recreation.
The Intracoastal Waterway in subbasin 03-06-24 is listed as impaired in the draft 2006 303(d) list for
shellfish harvesting, the parameter of concern is Fecal Coliform, the sources are unknown.
Permit limits were developed according to the Division’s Water Treatment Plant permitting strategy for
membrane treatment systems and requirements for SA and ORW waters. According to 15A NCAC 02B
.0225 a public hearing is mandatory for ORW waters.
Proposed limits and monitoring requirements:
Parameter Permit requirement
Flow Limits of 1.38 MGD and 2 MGD (upon expansion)
Temperature Effluent, upstream, and downstream monitoring
Dissolved Oxygen Effluent, upstream, and downstream monitoring
Salinity Effluent, upstream, and downstream monitoring
Conductivity Effluent, upstream, and downstream monitoring
pH Limit of 6.8 to 8.5 SI
Total Dissolved Solids Effluent Monitoring
Total Residual Chlorine Effluent Monitoring
Turbidity Turbidity of receiving water shall not exceed 25 NTU, if turbidity exceeds this level due to
natural background conditions, the existing turbidity level shall not be increased
Total Cyanide Effluent Monitoring
Total Copper Effluent Monitoring
Total Iron Effluent Monitoring
Total Lead Effluent Monitoring
Total Chloride Effluent Monitoring
Total Zinc Effluent Monitoring
Total Fluoride Effluent Monitoring
NH3-N Effluent Monitoring
Total Nitrogen Effluent Monitoring
Total Phosphorus Effluent Monitoring
Acute Toxicity3 Quarterly Monitoring
Upstream and downstream samples are proposed at three locations, one as a background check, at 1000
feet upstream of the discharge, one at 500 feet upstream of the discharge and one at 500 feet downstream
of the discharge.
PROPOSED SCHEDULE FOR PERMIT ISSUANCE
Draft Permit to Public Notice: January 17, 2007
Public Hearing: February 21, 2007
NPDES DIVISION CONTACT
If you have questions regarding any of the above information or on the attached permit, please contact
Teresa Rodriguez at (919) 733-5083 ext. 553.
NAME: ____ DATE:
REGIONAL OFFICE COMMENTS
SUPERVISOR: ____ DATE: