NC0039331_Response to NOV-2021-LV-0005_20210122

TETRA TECH
January 20, 2021
Ms. Vanessa Manuel
Assistant Regional Supervisor
Water Quality Regional Operations Section
Raleigh Regional Office
Division of Water Resources
North Carolina Department of Environmental Quality
3800 Barrett Dr.
Raleigh, NC 27609
Subject: Response to NOV-2021-LV-0005 for Bonlee School wastewater system
Dear Ms. Manuel:
In response to the above referenced NOV for BOD exceedances in October 2020, we refer you to the
attached response to a similar NOV for BOD exceedances at this facility in September 2020. Specifically,
during a routine inspection of the system in late October, we discovered that the recirculation ratio for
the recirculating sand filters was not set properly. This observation, exacerbated by the return of students
for in -person learning in September, appears to be the cause of BOD exceedances observed in September
and October. The recirculation ratio was set in November and the BOD measurements for November
were below detection limits.
We respectively request that the penalty for the referenced BOD violations be waived as Chatham County
Schools works to improve the treatment performance of the wastewater system serving Bonlee School.
Please contact me if you have any questions and thank you for your consideration.
Sincerely,
Tetra Tech Engineering, P.C.
I AvtAtto
Victor D'Amato, PE
Associate Director
cc: Randy Drumheller (CCS), Bernadette Lilly (CCS), Mario Tobar (CCS), John Poteat (ORC), Adam Pickett (ORC)
Enclosed: December 3, 2020 NOV response
Tetra Tech Engineering, P.C.
One Park Drive, Suite 200, P.O. Box 14409, Research Triangle Park, NC 27709
Tel [phone] Fax [phone]

TETRA TECH
December 3, 2020
Ms. Vanessa Manuel
Assistant Regional Supervisor
Water Quality Regional Operations Section
Raleigh Regional Office
Division of Water Resources
North Carolina Department of Environmental Quality
3800 Barrett Dr.
Raleigh, NC 27609
Subject: Response to NOV-2020-LV-0829 for Bonlee School wastewater system
Dear Ms. Manuel:
During a proactive inspection of the Bonlee School wastewater treatment system in late October of 2020,
it was discovered that the distribution box for setting the recirculation rate for the recirculating sand filter
was not effectively splitting flow. The current box has only two outlet pipes: one for forward flow to the
effluent discharge tank and one for recirculating flow back to the sand filter. The pipes are both fitted
with speed levelers to attempt to adjust the recirculation ratio, but it does not appear that this has been
effective and we estimate that the recirculation ratio is closer to 1:1 than the 3:1 or 4:1 recommended for
recirculating sand filters. We believe that this insufficient recirculation rate is negatively impacting
treatment and are actively working to adjust the settings in the existing box while working on a plan to
replace the distribution box with a more effective flow splitting device.
We respectively request that the penalty for the referenced BOD violations be waived as Chatham County
Schools works to improve the treatment performance of the wastewater system serving Bonlee School.
Please contact me if you have any questions and thank you for your consideration.
Sincerely,
Tetra Tech Engineering, P.C.
(\l'A1/2,-to
Victor D'Amato, PE
Associate Director
cc: Randy Drumheller (CCS), Bernadette Lilly (CCS), Mario Tobar (CCS), John Poteat (ORC), Adam Pickett (ORC)
Tetra Tech Engineering, P.C.
One Park Drive, Suite 200, P.O. Box 14409, Research Triangle Park, NC 27709
Tel [phone] Fax [phone]