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Implementing Septic and Cesspool Upgrade Projects Reduces Total
Nitrogen Levels in Tonto Creek
Waterbodies Improved Two reac'nes °fT°nto Creek were listed on the state's 1996
Clean Water Act (CWA) section 303(d) list of impaired waters for
nutrients due to pollution from cesspools and leaking septic systems. Beginning in 2007, with the
help of CWA section 319 funding, Gila County worked with local landowners to upgrade or replace
failing septic systems that were contributing partially treated effluent to Tonto Creek. As a result,
nitrogen levels decreased enough to remove total nitrogen from the list of impairments for both
reaches of Tonto Creek in 2016.
Problem
Upper Tonto Creek is in the Tonto National Forest
in Gila County Arizona (Figure 1). Tonto Creek
flows approximately 73 miles before draining into
Theodore Roosevelt Lake. The Arizona Department
of Environmental Quality (ADEQ) added two reaches
(segments AZ15060105-013A_00 [8.1 miies long]
and AZ15060105-013B_00 [8.5 miles long]) of Tonto
Creek to the state's CWA section 303(d) list of impaired
waters in 1996 for nutrients (due to pollution from
cesspools and leaking septic systems). Escherichia coli
was added as a source of impairment in 1998.
Total maximum daily load (TMDL) reports were com-
pleted in 2004 for E. coli and in 2005 for total nitrogen.
The TMDL identified several nonpoint sources as
contributors to total nitrogen concentrations in Tonto
Creek including recreational uses and unincorporated
communities/summer home clusters.
The TMDL was written for the annual mean standard
for total nitrogen, which is 0.5 milligrams per liter
(mg/L) (the single sample maximum [SSM] is 2 mg/L).
The total nitrogen standard is not tied to a particular
designated use but is instead intended to protect
Theodore Roosevelt Lake from eutrophication. The
critical condition for total nitrogen in Tonto Creek
is the late spring to early fall recreation season. The
Arizona NEMO's 2008 Watershed-Based Plan: Salt
Watershed, researched and written by the University
of Arizona, gives an excellent overview of the water-
shed in which the Tonto Creek is located.
Dick Williams Creek
Horton
Creek
Tonton Creek
Fish Hatchery
Christopher Creek
Tonto Creek
Hunter Creek
Bear Flat
Development
Tonto Creek Haigler
Creek
Impaired Christopher Creek
Impaired Portion of Tonto Creek
Attaining Portion of Tonto Creek
Tributaries to Tonto & Christopher Creek
Tonto & Christopher Creek Wateshed
0 1.25 2.5
7.5
Figure 1. The Tonto Creek watershed is in central Arizona.
Story Highlights
ADEQ provided funding through three CWA section
319(h) grants for water quality improvement projects
in Tonto Creek (Figure 2). All three projects involved
upgrades to septic systems or on-site sewer projects.
The first grant funded a two-phase project by Gila
County Division of Health and Human Services in 2007.
in the first phase, numerous septic systems were
upgraded or replaced, including two cesspools close
to the Tonto Creek and four failing septic systems that
were discharging into Thompson Draw, a tributary
of Tonto Creek. The second phase of the Gila County
septic system upgrade project was completed 2 years
after the first phase. Phase two included upgrading

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AGFD Tonto Creek Fish Hatchery
Tonto Rim Christian Camp
Septic System Upgrades
I onto
Butter
Gila County Septic System Upgrades
Phase II
Gila County Septic System Upgrades
Phase I
R-Bar-C Boy Scout Camp ¦
Septic System Upgrades
Annual mean total nitrogen
(in mg/L)a
Tonto Creek reach #
AZ15060105-013A 00
0.499
0.405
AZ15060105-013B 00
0.406
0.308
Figure 2. Septic system upgrades were completed in
several watershed locations.
Table 1. Total nitrogen annual mean in Tonto Creek
stream reaches 13A and 13B.
0 Data from the U.S. Environmental Protection Agency's Grant
Reporting and Tracking System (GRTS) database.
Additionally, Arizona Game and Fish Department
made gradual upgrades to the Tonto Creek Fish
Hatchery outfall to reduce nutrient loading into Tonto
Creek. The upgrades included improving wetlands
at the outfall, reducing the number of large fish in
the "show pond," and improving the settling tanks.
These upgrades did not use ADEQ CWA section 319(h)
grant funds because they are related to meeting
Arizona Pollutant Discharge Elimination System permit
conditions.
Results
Effectiveness monitoring occurred from 2006 to
2014. After analyzing the 2013 and 2014 data, there is
evidence to support removing both reaches of Tonto
Creek (reaches 13A and 13B) from the impairment list
for total nitrogen. Data showed that total nitrogen
levels in both reaches were below the total nitrogen
standard of 0.5 mg/L as an annual mean in both
2103 and 2014 (Table 1). As a result, AZDEQ removed
nitrogen from the list of impairments for both reaches
of Tonto Creek in 2016. The reaches will remain listed
as impaired for phosphorus and E. coli.
Partners and Funding
Figure 3. I his home had a failing septic system that
was upgraded.
or replacing five septic systems on or near the creek
(Figure 3). The third, and most recent, project was the
Tonto Rim Christian Camp Water Quality Improvement
Project on Tonto Creek in 2010. The entire septic
system was replaced and upgraded.
Partners for these projects include Gila County Kohls
Ranch Homeowners Association, and Tonto Rim
Christian Camp. Gila County's Phase I project included
$168,311 in match (staff time and supplies). For
Phase II, Gila County provided $172,200 in match (staff
time and supplies). The Tonto Rim Christian Camp
matched their nonpoint source grant with $98,273
from various sources. The matching funds were tied to
a total of $740,000 in CWA section 319 funding.
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©
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-19-001L
March 2019
For additional information contact:
Jade Dickens
AZ Department of Environmental Quality
602-771-4115 • jdll@azdeq.gov

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