DWQ-2025-003479

TECHNICAL MEMORANDUM

TO: Danielle Lenze, UPDES Individual Permits Section Manager
FROM: Eric Sahm, Project Manager
DATE: April 15, 2025
SUBJECT: Grantsville, Utah WWTP – WLA Request for Permit Modification
CC: Markus Seat, Christy Monteith; Grantsville City
PROJECT NO.: 002362.C
This document serves as a request for a Wasteload Analysis (WLA) as required by the State as
part of the process to modify the City’s current discharge permit. AQUA Engineering is assisting
the City with design of a new wastewater treatment plant (WWTP) to address recent additions
and changes to their discharge permit (including new nutrient limits) as well as increase treatment
capacity to accommodate anticipated growth in the service area. The following information is
provided as requested by the State to initiate the WLA and permit modifications.
1. Owner/Responsible Agent: Grantsville City, Utah
Contact: Markus Seat – Deputy Public Works Director
429 E Main Street, Grantsville, UT 84029
435-884-3411
[e-mail]

2. Type of Business: Municipal Cooperation

3. Project Description:

The proposed WWTP includes a new activated sludge process incorporating new
headworks facilities, biological nutrient removal, aeration basins, clarifiers, and
disinfection to meet new permit limits and increase treatment capacity. The project
includes new solids handling, storage, and dewatering facilities. The design is in
accordance with design criteria and recommendations identified in the 2022 Sewage
Master Plan.

4. Treatment Process Summary:

The proposed treatment process is designed to handle average daily flows (ADF) of up to
3 MGD and peak hour flows up to 8 MGD equivalent. The current lagoon system has a
listed design capacity of 1.5 MGD. The new WWTP is proposed to provide nutrient
(specifically phosphorus) removal in response to new limits added in the revised discharge
permit. (UPDES Permit UT 0021130). The WWTP includes the following major
processes:

Headworks Screens: ¼” perforated band screens
Headworks Grit Removal: Two (duty/standby) vortex grit removal chambers and
associated grit pump/washer.

Grantsville, Utah WWTP – WLA Request for Permit Modification
April 15, 2025
Page 2

Innovative Engineering Solutions
Biological Nutrient Removal & Aeration Basins: Three (3) parallel anaerobic chambers to
facilitate biological phosphorous removal. Screened wastewater from the headworks is
mixed with Return Activated Sludge (RAS) in the anaerobic chambers. Effluent from the
anaerobic chambers flows into three (3) parallel anoxic chambers where internal recycle
from the aeration basins is mixed in. The anoxic chambers provide an oxygen poor
environment for denitrification. Flow from the anoxic basins passes into the aeration
basins, where fine bubble diffusers provide oxygen for nitrification, BOD removal, and
phosphorus uptake. Internal recycle is pumped from the effluent end of all three aeration
basins back to the head of the anoxic basins.

Secondary Clarifiers: Effluent from the aeration basins flows to two (2) 80-foot diameter
secondary clarifiers. Clarifiers separate solids from the wastewater, allowing clear water
to continue to disinfection. Sludge settles to the bottom of the clarifiers and is pumped
back to the anaerobic basin as RAS. A portion of the sludge is wasted as waste activated
sludge or WAS. Progressive cavity pumps direct WAS to the solids holding tank and/or
direction to dewatering fan presses.

UV Disinfection: Clarified water passes through open-channel UV banks to eliminate
pathogens. The project includes two parallel UV channels, each equipped with 2 UV
banks. Disinfected flow is then directed to the existing outfall of the WWTP.

Solids Handling: Solids handling includes an aerated solids holding tank, polymer system,
and fan press dewatering skids. WAS can be pumped to the holding tank, direct to
dewatering, or to both at various rates as directed by operators. The dewatering system
includes polymer dosing skids (duty/standby) and duty/standby dewatering skids.
Dewatered sludge is conveyed to a dumpster for off-site disposal.

5. Receiving Water: The receiving water for the new plant will stay at the current location,
located at latitude 40°37’15” and longitude 112°26’50”.

6. Quantity and Quality of Water Entering the Treatment System:
a. Design Flow: 3 MGD (Average Daily Flow). Peak Hour Flow: 8 MGD equivalent
b. Effluent Data: Design effluent quality based on other similar facilities:
BOD: < 25 mg/L (< 625 #/day)
TSS: < 25 mg/L (< 625 #/day)
Total Nitrogen: < 10 mg/L (< 250 #/day) Not a current permit requirement but
anticipated based on the proposed process.
Total Phosphorus: < 1 mg/L ( < 25 #/day)
E. Coli: < 126 MPN/100 mL
c. The City and current WWTP have an existing permit. We assume that the State has
stream data from the previous WLA. A copy of a previous WLA Level I Review is
attached for reference.

7. Payment: See attached letter from Grantsville regarding payment. .