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Private Landowners Partner with the State to Clean Up Abandoned
Mine Area Affecting the Hassayampa River
Waterbody Improved An abandoned mine si,e was releasi"e pollution into the upper
Hassayampa River in central Arizona. As a result, the Arizona
Department of Environmental Quality (ADEQ) added the river (from its headwaters to its confluence
with Copper Creek) to the 1992 Clean Water Act section 303(d) list of impaired waters for zinc,
cadmium, and copper. ADEQ and local landowners worked to remediate multiple sources of mine
waste in 2021-2022, and the levels of in-stream cadmium, copper, and zinc have dropped.
Problem
The headwaters of the Hassayampa River are south
of Prescott, Arizona, in the Bradshaw Mountains, The
river is approximately 11.2 miles long and lies above
5,000 feet of elevation. The Hassayampa River basin
is part of the Middle Gila watershed and is contained
within the Prescott National Forest. Recreational
and agricultural usages predominate. The river runs
through the small mountain community of Potato
Patch, with a population of about 700.
Elevated levels of metals from an abandoned mine site
prompted ADEQ to add a segment of the Hassayampa
River—from its headwaters to its confluence with
Copper Creek (IHUC# 15070103-007A)-to its 1992
list of impaired waters for zinc, cadmium, and copper.
The upper portions of the reach are on private land,
and the water flows through sections of the Prescott
National Forest. Designated uses for this segment of
the Hassayampa River are aquatic and wildlife cold
water, full body contact, fish consumption, agricul-
tural irrigation, and agricultural livestock watering. In
2002, ADEQ.completed a total maximum daily load
(TMDL) for the river, which identified the McKinley Mill
abandoned mine site (Figure 1) as a source of metals
contamination (Table 1). In 2006, ADEQ also listed the
reach as impaired for pH.
Spring snowmelt and monsoon and fall rains drive the
high flows in the Hassayampa River. During low-flow
episodes, groundwater is the primary source of the
Hassayampa River. On the McKinley Mill site, a waste
pile covering approximately a half-acre was deposited
at a steep grade, situated above the stream channel
and wetland area (Figure 2).
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Table 1. Metal loads at the McKinley Mill site, per the 2002 Hassayampa TMDL
Q (CFS)
Hardness
(mg/L)
Dissolved
metais
Natural background
Downstream of wetlands
Measured load
(kg/day)
Load (kg/day)
Cone. (jtig/'L)
Load (kg/day)
Cone. (jug/L)
0.15
108
Cadmium
2.5
0.001
3
0.001
0
0.15
108
Copper
7.5
0.003
35
0.013
0.01
0.15
108
Zinc
20
0.007
130
0.046
0.039
3.97
28
Cadmium
2.5
0.024
2.5
0.024
0
3.97
28
Copper
7.5
0.073
38
0.369
0.296
3.97
28
Zinc
20
0.194
40
0.388
0.194
Notes: Q. = Peak rate of runoff; mg/L = milligrams per liter; kg = kilogram; |ag/L = micrograms per liter
Story Highlights
In 2021, In cooperation with conscientious private
landowners and contractors, ADEQ removed the old mill's
hopper structure from the property. Between October
and December 2022, the waste pile was regraded, and
it was capped to prevent water from infiltrating. At the
same time, a gabion wall was constructed along the toe of
the waste pile (Figure 4). Consistent communication with
stakeholders in this small, tight-knit community was criti-
cal to the success of this project. Neighboring property
owners also contributed by sharing their local knowledge
and insights from living in and visiting Potato Patch.
Results
The remediation of the McKinley Mill site is expected
to improve surface water quality in this section of the
Hassayampa River. Data collected for effectiveness after
construction is ongoing. The initial sampling efforts
show a decreasing impact from the mine area over time
for dissolved cadmium, copper, and zinc. Efforts will
continue to identify and resolve other contamination
sources in this watershed with the goal of removing
this river segment from the impaired waters list.
Partners and Funding
The primary partners on this project were the private
landowners who formed Mountain Girl, LLC. They
purchased the property and used Arizona's Prospective
Purchaser's Agreement program to limit liability associ-
ated with acquiring the abandoned mine, and they
allowed ADEQ.site access to perform the remediation.
Tetra Tech, Inc., and their subcontractor, Environmental
Response, inc., were valuable partners in the remedia-
tion. Overall, the project cost close to $500,000 and
was supported by CWA section 319 funds.
Figure 2. McKinley Mill mining waste pile.
Figure 3. Mine waste in the stream channel.
Figure 4. Regraded and capped waste pile with new
gabion wall at the toe.
^£D U.S. Environmental Protection Agency
0** Office of Water
\ Washington, DC
I
EPA 841-F-24-001B
PROt^° February 2024
For additional information contact:
Natalie Muilenberg
Arizona Department of Environmental Quality
602-771-6403 • muilenberg.natalie@azdeq,gov
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