Wastewater memo

4742 North 24th Street Suite 270 
Phoenix, Arizona 85016 
Main: 877 627 3772 
 
 
 
Sewer Memorandum 
To: 
Town of Wickenburg 
From: 
Casey Whiteman, PE 
Date: 
December 10, 2025 
Subject: 
Preliminary Sewer Memo 
Project No.: 
2026.02 
 
 
Terrible’s (the Project) is a gas station facility being developed north and east of SR-93, and 
east of Scenic Loop Road in Wickenburg, Arizona. The Project consists of approximately 5.75 acres in 
a portion of Section 21 in Township 1 South, Range 7 East of the Gila and Salt River Meridian. The 
Project will consist of a new convenience store, gas pumps, parking, and space for a future car wash. 
The Project is within the City of Wickenburg (City) in Yavapai County.  However, the Project lies outside 
of any designated wastewater service provider’s service area. All onsite wastewater infrastructure 
required for serving the Project will be privately owned and operated by Terrible’s.  
 
The proposed wastewater system infrastructure for the Project was evaluated consistent with 
the design criteria provided in the Design Standards for Water and Wastewater Systems (City of 
Phoenix, 2021) and the 2017 Arizona Administrative Code (AAC, 2017). More specifically, the septic 
design follows guidelines set forth in the Arizona Administrative Code Title 18, Chapter 9 Department 
of Environmental Quality – Water Pollution Control (AAC Title 18-9). Anticipated wastewater demands 
for the Project are shown below in Table 1. More detailed calculations have been provided as an 
attachment.  
Table 1: Wastewater Demands 
Land Use 
Average Day Demand 
(gpm) 
(gpd) 
Commercial 
0.3 
375 
Car Wash 
TBD 
TBD 
TOTAL: 
0.3 
375 
 
The convenience store and site amenities will be constructed prior to the car wash facility to 
reduce initial sewer demands.  
 
There is no existing City sewer infrastructure near the Project vicinity. Therefore, the Project 
will be serviced by a private onsite wastewater treatment system. The onsite wastewater treatment 
system will be located at the southwest corner of the Site and will consist of a precast concrete septic

Project No. 2026.02 
December 10, 2025 
Page 2 | 2 
 
tank designed per section R18-9-A314A of the ACC. The effluent from the septic tank will flow to a 
distribution box and be evenly distributed to the disposal field. The final system sizing will be 
determined using data obtained in the field for the soil absorption rate (SAR). Detailed calculations for 
the sizing and disposal fields will be provided in the final wastewater report for the Project.  
 
Once City sewer is available adjacent to the Project site, the Project will connect to the City’s 
sewer system and will decommission the septic field. Sewer stubs are provided to the ROW to allow 
for future connection to the city-maintained sewer system.  
HC

Sewer Flow Calculations - Preliminary
Terrible's
Wickenburg, AZ
December-25
SF
(gpd)
(gpm)
Building 1
5,000.0
375
0.3
GRAND TOTAL
5,000
375
0.3
Notes:
Flow Factors:
Average Day Flow for commerical buildings
75 gal/1000 SF
Area
Average Daily Flow