NC0047384_Application (ATC) Cover Ltr_20200108

hazenandsawyer.com

January 3, 2020
Attn: Min Xiao
Complex Permitting Unit
Division of Water Resources – Water Quality Permitting Section
1617 Mail Service Center
Raleigh, NC 27699-1617
Re: Modification to Authorization to Construct No. 047384A07
Dear Ms. Xiao:
On behalf of the City of Greensboro, Hazen and Sawyer is submitting the enclosed modification to the
existing Authorization to Construct No. 047384A07 for the T.Z. Osborne Water Reclamation Facility
(WRF) BNR Upgrade Project - Package 4.
The project and authorization to construct originally included: the conversion of the existing aeration
basins 1 through 12 to a 5-stage biological nutrient removal (BNR) process, new mixers in post-anoxic
cells, fine bubble diffuser modifications, construction of nitrified recycle (NRCY) pumping systems, air
piping modifications, six new aeration basins, new aeration basin influent channel mixers, odor control
improvements consisting of three new carbon scrubbers, and two new electrical facilities. The anticipated
project final completion is March 23, 2021.
A 2016 Preliminary Engineering Report titled “Package 4: Biological Nutrient Removal” evaluated the
biological nutrient removal upgrades required for TZO to treat additional influent loads (i.e. cBOD5 and
ammonia) while complying with the Jordan Lake Rules. The report recommended the replacement of the
existing multi-stage blowers with larger blowers be included in the COG’s Capital Improvements Plan
(CIP) to supply maximum day air demand at the increased influent cBOD5 loads in the near future. The
report identified that there would be a deficiency of approximately 28,950 icfm in the blower system
capacity when the plant reached its buildout flow of 56 mgd.
Following the start of construction for the project in January 2018, additional cBOD5 data was collected
from the plant and the data showed that while influent nutrient loads remained similar to design
conditions, the primary effluent cBOD5 average concentration from October 2017 to February 2018 were
approximately 20% higher than design concentrations. This increase in cBOD5 concentration means the
additional blower capacity will be required earlier than originally anticipated.
The City has decided to increase the plant's blower capacity as part of the ongoing Package 4 project by
replacing one of the existing multi-stage blowers with a larger (37,075 icfm) single-stage blower.