NC0028916_Pretreatment_HWA_Review_20190424

ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
LINDA CULPEPPER,
Director
NORTH CAROLINA
Errlr M"fl1#1tt&� Quarrry
April 24, 2019
(sent via email: [e-mail])
Brian Bowles, ORC
Town of Troy
315 N. Main Street
Troy, NC 27371
Subject: Pretreatment Review of Headworks Analysis - Approved
Town of Troy (NPDES Permit No. NC0028916)
Montgomery County
Dear Mr. Bowles:
The Pretreatment, Emergency Response, and Collection Systems (PERCS) Unit of the Division of Water
Resources has reviewed the Headworks Analysis (HWA) for the Town of Troy. The HWA was received by
the Division on February 12, 2019.
The Division concurs with the HWA calculations for all Pollutants of Concerns, with the corrections
outlined below. These approved Maximum Allowable Headworks Loadings (MAHLs), Maximum
Allowable Industrial Loadings (MAILS), and the basis for these values are found on the last page of the
enclosed HWA spreadsheet, which has the corrections marked. The results of the HWA are also listed in
the bottom section of the enclosed Allocation Table.
The following observations were noted during the review of the HWA:
1. Changes to the HWA Approved Today: Please feel free to contact PERCS if you have any questions
about the changes outlined below, or would like to discuss possible alternatives. All corrected
spreadsheets are attached, and electronic versions were emailed to you for your files.
a. POTW Uncontrollable Flow: POTW average uncontrollable flow in cell C9 was corrected to
0.536 MGD, as uncontrollable flow is the difference between WWTP average flow minus the
sum of SIU flow (see Uncontrollable Mass Balance spreadsheet).
b. Minimum Pass -through Loading for Ammonia: PERCS chose to use design criteria loading for
ammonia (cell J19) based on influent design criteria of 40 mg/I, as it appears that design
loading is more conservative than NPDES loading based on permit limit and removal rate.
c. Copper, Silver, and Zinc Water Quality Action Levels: PERCS chose not to use water quality
action levels for copper, silver, and zinc as water quality standards. Use of action levels are
North Carolina Department of Environmental Quality I Division of Water Resources
512 North Salisbury Street 11617 Mail Service Center I Raleigh, North Carolina 27699-1617
919.707.9000

not normally required criteria for HWA if the WWTP is consistently passing its Whole Effluent
Toxicity Test (WET).
d. Inhibition Loading Calculations table: PERCS updated literature inhibition criteria for
chromium, copper, lead, and nickel, based on more conservative nitrification values, since the
WWTP has ammonia limits.
e. SIU Uncontrollable Mass Balance spreadsheet:
i. Average Influent Loadings: WWTP average influent loadings for several the
parameterswere updated, perthe provided removal rate spreadsheet (see attached).
ii. Uncontrollable Concentrations to be used in HWA: Uncontrollable concentrations to
be used in HWA for several parameters were updated and carried over to the HWA
spreadsheet based on more conservative and representative values.
2. HWA Due Date: The HWA approved today is based on DMR and STMP data for the period of
January 2018 through December 2018. Unless conditions at the POTW change significantly and
thus warrant an earlier submittal (see Comprehensive Guide, Section B), the POTW must submit
the followings:
a. Updated STMP due by December 1, 2019. It appears that your NPDES permit expires June
30, 2019. Please ensure to update current approved STMP with any changes from the
upcoming permit renewal. Also, please review the State recommended lower PQLs for
several parameters, specially silver, recommended PQL is lug/I, and compare with the current
approved STMP DLs, and update as necessary. Please contact PERCS if you have any question.
b. Updated HWA/AT due by January 31, 2024.
c. Per permit condition Part IV, Section D and 40 CFR 122.44, POTWs must submit an updated
HWA within 180 days of the receipt of NPDES permit. Please note that, per EPA, POTWS who
receive NPDES permit after April 2016, must evaluate water quality standards based on site -
specific dissolved metals criteria, 7Q10, stream flow and hardness. If there are no site specific
effluent and upstream harness, you should be able to use default hardness of 25 mg/I. Please
refer to PERCS website to download Calculator spreadsheet to calculate water quality
standards (Total Metals allocated), and update stream standards column within HWA
spreadsheet.
Thank you for your continued cooperation with the Pretreatment Program. If you have any questions or
comments, please contact Monti Hassan at [phone] or email at [e-mail].
Sincerely,
�y:
Hasa;. H-
66374CA 137482.
ontl assan
Division of Water Resources
M H/Troy. H WA.04
Enclosure: HWA AT, Removal Rate, SIU Mass Balance spreadsheets
CC: PERCs Unit (ecopy)
Central Files (LF)
FRO