NC0085812_Correspondence_20240214

Hazen
Grassy Branch WRF Expansion
Authorization to Construct Permit — Review Comment Responses
ATC Application
1. Page 5: Peak Hourly Flow is missing.
The historical data indicates that the peak hourly flow matches the peak day flow. Refer to
Attachment 1. The application has been updated to reflect this.
2. Page 5: Residual Management Plan — How will the additional sludge be disposed? Provide
confirmation that the hauler can handle the increased hauling and the land application/landfill will
accept the additional sludge.
The Residual Management Plan is unchanged. The proposed sludge holding tank will allow for
the storage of an additional 10,000 gallons of waste activated sludge (WAS). WAS will be
decanted from the sludge holding tank when needed and transferred to Crooked Creek Water
Reclamation Facility (WRF), which is another Union County Water (UCW) managed facility.
Refer to Attachment 3 for confirmation from UCW's land application contractor.
3. Page 6: Annual influent ammonia concentration is higher than the design influent.
Design criteria were adjusted to accommodate an ammonia influent concentration of 33 mg/l.
Refer to updated ATC Application file.
4. Page 8: Aerobic tank type is missing.
The aerobic tanks will be extended aeration single stage nitrification process, the ATC
Application file has been updated to reflect this.
Page 10: Three blowers are listed for the entire plant, please specify which units will be used.
Looking at drawing M-163, the EQ basin blowers seem separate, are those new blowers?
Previous ATC Application only accounts for new blowers at the Package Treatment Plant. Each
aeration tank will be supplied process air by one blower, while the third blower will act as a
swing.
The equalization tank will utilize the four (4) existing blowers on -site. Refer to updated ATC
Application file and the following language within the previously provided cover letter:
The following existing facilities at the Grassy Branch WWTP provide sufficient capacity to support the
proposed expansion to 0.12 mgd with no modifications:
• Blowers: The four (4) existing blowers are sized sufficiently to provide process air for
Equalization Basins.
Hazen and Sawyer • 9101 Southern Pine Blvd, Suite 250 • Charlotte, NC 28273 • 704.357.3150

Hazen
ATC Package
1. The facility will be constructed prior to the construction of the EQ basin, at what flow and
peaking factor will the facility operate without the EQ basins? How will it affect the hydraulic
profile?
The EQ basin is an existing structure that is being repurposed into equalization storage. Refer to
Specification 01 14 00, Coordination with Owner's Operations.
2. The influent pump capacity at peak flow assumes how many pumps are in service?
Two duty pumps and one stand-by pump. See Specification 43 25 13, Submersible Solids -
Handling Pumps.
What is the expected BOD5 removal? Did not see the calculations and did not see the design
effluent concentration.
The secondary process (aeration tanks and secondary clarifiers) will provide a minimum of 85%
five-day biochemical oxygen demand (BOD5) removal efficiency as shown in Attachment 2. The
design effluent concentrations have been updated on page 6 of the ATC Application. The BOD5
final effluent permit concentrations will be 5 mg/1 in summer and 10 mg/l in winter.
4. For the clarifiers, how was the maximum design influent TSS concentration assumed? Did not
see TSS removal rate in other treatment units that would lower the influent concentration of 232
mg/l in earlier calculations.
Refer to provided design criteria within the previously submitted ATC Package. Refer to
Attachment 2 for totals suspended solids TSS removal in secondary clarifiers.
The maximum design influent TSS to the clarifiers is the mixed liquor suspended solids (MLSS)
concentration from the aeration tanks. The package treatment plant is designed to treat the design
criteria conditions stated at a minimum week temperature of 12°C with a MLSS concentration of
3,000 mg/L and aerobic solids retention time of 16 days.
TSS performance requirements for cloth disk filtration are also provided in Specification 46 61
41, Disk Filtration System.
Grassy Branch WRF Expansion Page 2 of 2
Authorization to Construct Permit — Review Comment Responses