DDW-2025-009011

195 North 1950 West • Salt Lake City, UT
Mailing Address: P.O. Box 144830 • Salt Lake City, UT 84114-4830
Telephone [phone] • Fax [phone] • T.D.D. [phone]
www.deq.utah.gov
Printed on 100% rec cled a e
State of Utah

Department of
Environmental Quality

Kimberly D. Shelley
Executive Director

DIVISION OF DRINKING WATER
Tim Davis
Director

SPENCER J. COX
Governor

DEIDRE HENDERSON
Lieutenant Governor

July 11, 2022

Matthew Mackay
Zion Canyon Water System
NPS Zion National Park
State Route 9
Springdale, Utah 84767

Subject: System-Specific Minimum Sizing Standards
Zion Canyon Water System, System #27051, File #11522

Dear Matthew Mackay:

Based on the water use data submitted to the Division of Water Rights (DWRi), the following
system-specific minimum sizing standards have been set for Zion Canyon Water System:

Peak Day Source Demand (gal/day/ERC) – 2,149 gal/day/ERC
Average Annual Demand (gal/yr/ERC) – 980,727 gal/yr/ERC
Equalization Storage (gal/ERC) – 2,687 gal/ERC
Fire Storage (gal) – 120,000 gal

These standards are effective as of the date of this letter. A summary of the water use data and
calculations used to set the minimum sizing standards is attached for your reference. The Division
plans to evaluate these standards every 3 years, or upon request.

Water System Background

The Zion Canyon Water System is located Washington County and serves large amounts of
visitors and staff who maintain that portion of Zion National Park. The system utilizes four
springs and multiple storage tanks to provide safe drinking water to visitors and staff.
Matthew Mackay
Page 2 of 3
July 11, 2022

Minimum Sizing Standard Background

Per Utah Code 19-4-114, the information needed for the Division of Drinking Water (the
Division) to set system-specific minimum sizing standards may be based on water use data
submitted to the DWRi, or alternatively, a community water system can submit an engineering
study to the Division if the water system’s water use data is not representative of future use or the
water system does not yet have actual water use data.

Actual water use data was available through DWRi and an engineering study was not submitted to
the Division for review. Therefore, the Division analyzed the submitted DWRi water use data and
sent a draft summary of the resulting system-specific minimum sizing standards to your office on
May 23, 2022. The Division allowed for 30 days for your water system to review the draft system-
specific minimum sizing. The division has not received any comments up to the time of the
writing of this letter. Therefore, the Division is setting system-specific minimum sizing standard
for Zion Canyon Water System.

Water Use Data Definitions

Peak Day Source Demand is the total flow into a public water system to meet the demand of the
water system on the day of highest water consumption in a calendar year.

Average Annual Demand is the total quantity of drinking water flowing into a public water system
within a calendar year.

Total Equivalent Residential Connections (ERCs) term represents the number of residential service
connections and the number of equivalent residential connections for non-residential connections
(commercial, industrial, institutional connections).

Minimum Equalization Storage requirement is a volume that is equivalent to the amount of water needed to
meet the average day culinary demand for public water systems. Equalized storage per ERC is calculated
by dividing the Average Annual Demand per ERC data by the number of operational days in a year.

Fire Storage was set based on the International Fire Code (IFC) for 1000 gpm for two hours for a total of
120,000 gallons as a default in the absence of confirmation from the local fire authority. Your system’s
fire suppression storage requirement may be different.

Storage Capacity

Based on your systems storage facilities and the storage minimum sizing requirement established in this
letter, your system is compliant with the minimum storage capacity requirements.

Source Capacity

The Division has documentation of established safe yields for all your system sources. Using total
system wide safe yields and the source minimum sizing requirement established in this letter
Matthew Mackay
Page 3 of 3
July 11, 2022

indicates your water system is deficient with minimum source capacity requirements. Work with
the Division to correct the lack of minimum source capacity.

If you have any questions regarding this letter, please contact Cameron Draney, P.E. of this office,
at [phone], or Michael Newberry, Engineering Manager, at [phone]. 

Sincerely,

Michael Newberry, P.E.
Engineering Manager

CLD/mrn/mdb

Enclosures
1. Utah Department of Environmental Quality Division of Drinking Water Minimum Sizing Standards
Summary Report

cc: Jeremy Roberts, Southwest Utah Health Department, [e-mail]
Paul Wright, P.E., District Engineer, [e-mail]
Matthew Mackay, Zion Canyon Water System, [e-mail]
Cameron Draney, P.E., Division of Drinking Water, [e-mail]
Ted Black, Office of the State Fire Marshal, [e-mail]

DDW-2022-029548
Utah Department of Environmental Quality
Division of Drinking Water
Minimum Sizing Standards

Date Standard Effective: Wed Jun 29 16:24:16 MDT 2022
Peak Day Source Demand per ERC (gal/day): 2,149
Average Annual Demand per ERC (gal/day): 980,727
Equalization Storage per ERC (gal/day): 2,687
ZION CANYON WATER SYSTEM PWS ID: UTAH27051
Admin Name: MATTHEW LEE MACKAY
Address:
City, State, Zip: ,
Phone: [phone]
Email: [e-mail]
System Type: Community
Population: 3,380
MINIMUM SIZING STANDARD
MINIMUM SIZING STANDARD CALCULATIONS VARIABILITY
Data from these reporting years: 2019, 2020, 2021
Max Peak Day Source Demand per ERC (gal/day): 1,797
Max Average Annual Demand per ERC (gal/day): 817,954
Max Equalization Storage per ERC (gal/day): 2,241
x
x
x
(1 + 0.196)
(1 + 0.199)
(1 + 0.199)
=
=
=
2,149
980,726
2,686
DWRi WATER USE DATA REPORTED
Equalization per ERC (gal): 2,687
Existing Storage (gal): 1,550,000
ERCs: 180
Required Storage w/o Fire Flow: 403,380
Required Fire Storage (gal): 120,000
Required Storage w/Fire (gal): 523,380
Storage Deficiency: 0
Storage Deficiency (%): 0.0
No Storage Deficiency
Peak Day Source Demand per ERC (gpm): 1.49
Existing Source Capacity (gpm): 186
ERCs: 180
Required Resource Capacity (gpm): 268
Source Deficiency: 84
Source Deficiency (%): 31.34
Source Deficient
Year Peak
Day
Source
Demand
(gal/day)
Average
Annual
Demand
(gallons)
ERCs Peak
Demand
per ERC
(gal/day)
Avg
Annual
Demand
per ERC
(gal/day)
Equaliza
tion
Storage
per ERC
(gal/day)
OP
Days
2020 296,524 126,097,819.98 165 1,797 764,230 2,088 366
2021 224,837 118,603,246.98 145 1,551 817,954 2,241 365
2019 270,456 122,770,881.27 180 1,503 682,061 1,869 365
Variability:0.241 0.196 0.199 0.199
Year Peak Month Average
(gal/day)
Peak Month Average
per ERD (gal/day)
Ratio of PD/ERC to
Peak Month Avg/ERC
2020 471,615 2,858 0.63
2021 379,458 2,617 0.59
2019 297,284 1,652 0.91
CAPACITY CALCULATIONS FOR STORAGE
CAPACITY CALCULATIONS FOR SOURCES
SYSTEM STORAGE AND SOURCE INVENTORY
Storage ID Storage Name Effective Volume (GAL)
ST004 OAK CREEK 50K 50,000
ST001 BIRCH RESERVOIR 1,000,000
ST002 GROTTO RESERVOIR 300,000
ST005 OAK CREEK 200K 200,000
Storage Totals: 1,550,000 GAL
Source ID Source Name Flow Rate (GPM)
WS001 BIRCH SPRINGS 92.6
WS002 WATERCRESS SPRING 33.5
WS003 LOWER GROTTO SPRING 6.9
WS004 UPPER GROTTO SPRING 53.6
Source Totals: 186 GPM