WQ0009267_Modification_20230508

o Dewberry Engineers Inc. 919.881.9939
Dewberry 2610 Wycliff Road, Suite 410 919.881.9923 fax
Raleigh, NC 27607-3073 www.dewberry.com
May 8, 2023
Division of Water Resources
Non-Discharge Branch
Attn: Nathanial Thornburg, Environmental Program Supervisor II
1617 Mail Service Center
Raleigh, NC 27699-1617
RE: Ponderosa Land Application System Permit Renewal Application and Authorization to Construct
Dear Mr. Thornburg,
Dewberry is pleased to submit the enclosed permit renewal application package on behalf of Wake
County for the Non-Discharge permit WQ0001203. Wake County is also requesting authorization to
construct modifications to the chlorine disinfection system and storage building.
Enclosed for your consideration are the process and electrical drawings for the chlorine disinfection
system and storage building. Specifications for process equipment have been included. A final design
package with structural, architectural, and mechanical design will be submitted to Wake County for
appropriate building permitting. Additionally, potable water will be supplied by Aqua America, Inc to the
new building for an eyewash, safety shower, hose bib, and hand washing sink. Potable water service line
details, including final locations of the above equipment, will be provided in the building permit application
to Wake County.
The modifications to the Ponderosa land application system chlorine disinfection system are considered a
minor modification. The following changes are proposed:
• Replacing the gaseous chlorine system with liquid sodium hypochlorite for disinfection. The same
carrier water system will be utilized with yard piping changes to bring the carrier water to the new
building. Calculations for sizing the sodium hypochlorite storage tote and chlorine metering pump
are included in this submittal.
• Control measures for duckweed on the surface of the lagoon are being investigated, with a
floating cover as the preferred alternative.
• Continuous effluent residual chlorine and pH measurements will be taken with an in-line analyzer.
This is an improvement on current operations which rely on manual periodic readings with field
kits. The operator will record effluent residual chlorine and pH from the new analyzer.
• A recirculation line will be added to the chlorine contact chamber for the operator to direct flow
from the chlorine contact chamber effluent pump back into the lagoon until a satisfactory chlorine
residual is reached in the effluent. When the effluent residual chlorine is satisfactory, a manual
valve will be used to direct the effluent to land application. This is an improvement from current
operations where the initial discharge from the chlorine contact chamber has likely not undergone
sufficient disinfection.
• Currently the lower liquid level of the lagoon is limited by the depth of the influent pipe to the
chlorine contact chamber. Wake County desires the flexibility to lower the lagoon further in
preparation for severe wet weather events. A second influent pipe will be added which allows the
operator to lower the lagoon an additional 12 inches. The second influent pipe will have the same
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Mr.Thornburg
Ponderosa Land Application System
May 5,2023
self-cleaning intake screen as the existing.
• The existing effluent flow meter will be moved above grade for easier access for maintenance
and replacement for calibration. It will be located in a heated HotBox, per Wake County design
guidelines.
• An additional sump pump will be added to the influent flow meter sump to provide additional
protection to the influent flow meter.
• Remote monitoring for the influent flow meter, effluent flow meter, and the chlorine and pH
analyzer will be available in the new building.
• A new 16' x 24' concrete block building will house the chlorine storage and dosing equipment,
miscellaneous storage, desk, emergency eyewash and safety shower, hand washing sink and
electrical equipment. Placement of the building will require relocating part of the lagoon perimeter
fence. The new building will be provided with ventilation and heat to prevent freezing. The
existing garden shed used for storage will be demolished after the new building has been
constructed.
• The sequence of construction will ensure that a discharge does not occur without chlorine
disinfection. Cut over to the new sodium hypochlorite system can occur during a period of no
discharge and the gaseous chlorine system will not be demolished until the sodium hypochlorite
system is operational.
This submission includes:
• Form WWIS-R-01-21.
• Attachment A Certification issued January 24, 2023.
• Chlorine dosage calculations.
• Process and electrical drawings for the chlorine disinfection system and storage building.
• Technical specifications for process equipment.
Please feel free to contact me at 919-424-3764 with any questions regarding this application package.
Sincerely,
Leigh Dudley, PE
Associate, Senior Project Manager
CC: Jeffrey Merritt, PE, Wake County
Kevin Witchger, PE, Wake County
Abigail Brinkman, El, Dewberry Dewberry
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