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i&i) NONPOINTSOIREESRCEESSSTORY

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Federal and State Efforts to Clean Up Historical Abandoned Mines in
Central Arizona Reduce Copper in Pinto Creek

... , | . .	. A 15-mile segment of Pinto Creek in Gila County, Arizona, was

Waterbody Improved designated as impaired for dissolved copper in 1998 on the Clean

Water Act (CWA) section 303(d) list of impaired waters. This segment of Pinto Creek flows through
Tonto National Forest. Between 2007 and 2022, the Arizona Department of Environmental Quality
(ADEQ) and the United States Forest Service (USFS) implemented remedial actions at six abandoned
mines that drain into this segment of Pinto Creek. The USFS remediated five abandoned mine sites,
and ADEQ remediated one site. Currently, surface water samples in Pinto Creek are meeting water
quality standards for dissolved copper.

Problem

Arizona has an estimated over 100,000 abandoned
mines across the state. These sites pose public safety
risks, and some discharge metals into nearby streams.
In 1998, a 15-mile segment of Pinto Creek was listed
as impaired for dissolved copper on the CWA section
303(d) list of impaired waters due to drainage from a
nearby abandoned mine. This segment of Pinto Creek
and the nearby Gibson Mine Tributary are primarily
located on the Tonto National Forest land (Figure 1).
The woodland and patchy shrubland is home to plants,
animals, and a handful of ranches. Undisturbed forest
areas provide critical habitat for the endangered
Mexican Spotted Owl and the endangered Arizona
hedgehog cactus.

Story Highlights

To tackle Arizona's widespread abandoned mine chal-
lenge, ADEQ partners with the USFS to collaborate
and combine resources. The USFS has remediated five
abandoned mine sites along Pinto Creek, including the
closure of 10 adits, 12 shafts, and five onsite consoli-
dation cells that hold a total of 8,000 cubic yards of
waste rock. The Gibson Mine, which is situated near
the Gibson Mine Tributary, was identified as the larg-
est copper source in Pinto Creek and was remediated
in phases byADEQ(Figure 2).

Figure 1. Aerial map of Pinto Creek and surrounding mine
sites cleaned up by ADEQ and USFS. Map courtesy of the
USFS, Tonto National Forest.

ADEQ's first remediation effort at Gibson Mine in 2007
removed 100,000 tons of mine-impacted soils from
the site. This reduced dissolved copper concentrations
by 50%, but surface water samples still did not meet
dissolved copper water quality standards.

The second remediation effort in 2016 included
implementing stormwater controls in which the site
was divided into undisturbed and disturbed land areas.

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Undisturbed land areas divert clean stormwater to
a bypass culvert and into the ephemeral tributary to
Pinto Creek. Disturbed land areas channel stormwater
to impoundments to be retained on site. These prac-
tices reduced dissolved copper concentrations by 75%,
but surface water samples still did not meet dissolved
copper water quality standards.

The final remediation effort began in October 2022
and consisted of the excavation and on-site consolida-
tion of "hot spot" areas. An x-ray fluorescence site
assessment identified eievated concentrations of
copper, allowing backfilling of hot spots with clean
cover and vegetation. Other efforts included improving
a bypass culvert headwall and installing a standpipe to
prevent clogging, improving a v-ditch to convey clean
stormwater, and Installing a turf-reinforced mat to
prevent erosion into the copper-rich bedrock.

Results

Surface water samples in Pinto Creek show that the
waterbody is meeting water quality standards for dis-
solved copper (Figure 3). ADEQ is working to remove
the Pinto Creek dissolved copper impairment from
the CVVA section 303(d) list of impaired waters. This

Figure 2. An aerial photo of the Gibson Mine site
during active remediation conducted by ADEQ in 2022.

Improvement In the water quality can only be attrib-
uted to the efforts of the USFS and ADEQ to identify,
prioritize, and remediate discharging abandoned mines
in the watershed.

Partners and Funding

Partners involved in Gibson mine remediation efforts
include the U.S. Environmental Protection Agency
(CWA section 319 nonpoint source funding), the USFS,
and private landowners.

1000

Figure 3. Dissolved copper concentrations in Pinto Creek (2000-2022).

^£D	U.S. Environmental Protection Agency

0** Office of Water
\ Washington, DC

I

, - -	EPA 841-F-24-001H

April 2024

For additional information contact:

Natalie Muilenberg

AZ Department of Environmental Quality
602-663-4519 » muilenberg.natalie@azdeq.gov

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