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Section 319
NONPOINT SOURCE PROGRAM SUCCESS STORY
AitMKJX,
Restoring Mining Sites, Riparian Areas and the Stream Channel Reduces
Turbidity in Slate Creek
Waterbody Improved
Hard rock mining activities (excavation of rock and ore) along
Alaska's Slate Creek resulted in reduced sinuosity (a measure of
the curve of a river; a river with higher sinuosity may support a greater diversity of aquatic species),
a nonfunctioning floodplain, open pits and loose-sediment mining waste piles that reduced riparian
function. Erosion of unstable areas created high levels of turbidity that violated water quality
standards, prompting the Alaska Department of Conservation (ADEC) to add a 2.5-mile segment
of Slate Creek to the Clean Water Act (CWA) section 303(d) list in 1994. In 1997-1998 and 2010, the
National Park Service (NFS) and other partners implemented projects to restore damaged portions
of Slate Creek by removing mining debris, removing tailings from the floodplain, and restructuring
and replanting the floodplain. Recent monitoring shows that the creek now meets the turbidity water
quality standard. As a result, ADEC has proposed to remove Slate Creek from the 2012 CWA section
303(d) list for its turbidity impairment; it will remain listed as impaired for metals.
Problem
Slate Creek (Figure 1), a tributary of Eldorado
Creek, is in Denali National Park and Preserve in
south central Alaska's Kantishna Hills. In the early
1900s, individual miners flocked to streams in the
Kantishna Mining District, including Slate Creek, to
seek their fortunes. The discovery of antimony (a
metal) deposits along Slate Creek led to hard rock
mining in the watershed, leaving behind open pits
and surface cuts. During the 1970s and 1980s, min-
ers used heavy equipment to excavate and trans-
port materials The companies left long rows of
eroding tailing piles (waste materials produced from
mining extraction processes) in the floodplain, as
well as eroding stream banks that remained devoid
of vegetation. All mining in Slate Creek ceased
in 1983 after the area became part of the Denali
National Park and Preserve, but the mined areas
remained damaged.
Eroding sediment from tailing piles and unvegetat-
ed areas generated high levels of turbidity in Slate
Creek. Alaska's water quality standard requires
that turbidity not exceed 5.0 nephelometric turbid-
ity units (NTU) above natural conditions when the
natural turbidity is 50 NTU or less. Data collected
downstream of the mined areas in 1983 and 1984
showed turbidity levels ranging as high as 39 NTU.
The natural background level of turbidity in Slate
Creek is between 1 NTU and 3 NTU. On the basis of
Figure 1. Slate Creek flows through Alaska's Denali National
Park and Preserve.
these data, combined with best professional judg-
ment concerning ongoing disturbances from past
mining, ADEC added a 2.5-mile segment of Slate
Creek to the 1994 Clean Water Act (CWA) section
303(d) list as impaired for turbidity.
	•	•	
SLATE CREEK
PROJECT AREA
Faiihankt
Miles

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Project Highlights
Slate Creek flows within the present-day boundaries
of Denali National Park and Preserve. Congress cre-
ated the park in 1917 as Mt McKinley National Park.
In 1980 Congress approved the Alaska National
interest Lands Conservation Act, which enlarged
the park to 6.1 million acres and renamed it Denal
National Park and Preserve. Because the Kantishna
Mining District was enveloped by the expansion
of the national park, mining slowed after 1980. A
court-ordered Kantishna Mining District-wide min-
ing injunction went into effect in 1985, pending an
environmental impact statement study. After that
study was completed in 1990, the NPS proceeded
to acquire many valid mining claims through a
federal takings process (reimbursing claim holders
for the mineral value of their claims). As the NPS
acquired the mined lands, the agency evaluated
each site for possible restoration activities.
The NPS developed a waterbody recovery plan for
Slate Creek in 1997 and began restoring four acres
of disturbed upland and stream channel areas near
an old antimony mine site. In 1997-1998 the NPS
used tailings to reconstruct a portion of the flood-
plain and created an anoxic drain with geotextiles
and 25,000 tons of limestone rock to intercept
groundwater flow and buffer acid drainage from
a small open mining pit. The NPS implemented
an extensive restoration project in the summer of
2010. The project included moving an erosion-prone
extended tailings pile away from the flood plain;
installing erosion control materials; removing old
mining and reclamation debris; re-contouring the
floodplain; breaking up the surface of an old road to
prevent motorized vehicle access; seeding, liming
and fertilizing remaining tailing piles to establish
vegetative cover and prevent erosion; and planting
willow cuttings. The NPS also relocated a portion of
the stream away from an area containing pit mines,
constructing a new 400-foot-long stream channel
using fabric-encapsulated stream bank treatments
(Figure 2). The Slate Creek restoration project was
completed in August 2010 (Figure 3).
Results
The restoration efforts have led to a decline in
erosion and in the turbidity levels in Slate Creek.
Substantial riparian revegetation has occurred
along many of the disturbed reaches, result-
ing in increased bank stability and a lower ero-
sion potential. Monitoring data collected by the
U.S. Geological Survey (USGS) in Slate Creek from
Figure 2. A new section of the
Slate Creek stream channel,
under construction.
2008 to 2011 show that
turbidity levels consis-
tently meet the standard
of less than 5 NTU above
background (Table 1). The
creek's turbidity levels are
now comparable to those
of other streams studied
by USGS in the Kantishna
area. On the basis of these
data, ADEC has proposed
to remove the 2.5-mile
segment of Slate Creek
from the state's 2012 list of
impaired waters for turbid-
ity impairment.
Figure 3. The new Slate Creek
stream channel, shortly after
project completion.
Table 1. Slate Creek
Turbidity Data
Summer 2008-2011)
Date
Turbidity NTU
7/13/2008
if .2
8/21/2008
< 2
9/11/2008
* 2
6/2/2009
14a
7/28/2009
2.1
8/11/2009
5.3
9/9/2009
< 2
6/1/2010
4.4
7/13/2010
4.1
9/7/2010
* 2
6/7/2011
if .2
7/21/2011
< 2
Single elevated turbidity reading
attributed to disturbance of stream
bottom while sampling.
Water quality monitoring
data collected in 2008-
2011	below the former anti-
mony mine site showed
that Slate Creek violates
water quality standards for
the metalloids arsenic and antimony, prompting the
ADEC to propose adding Slate Creek to the state's
2012	list of impaired waters for metals. The NPS and
its partners will continue working in the watershed
to address the arsenic and antimony impairments.
Partners and Funding
The NPS implemented restoration efforts, worked
with the USGS to track the progress of the water
quality recovery, and shared the data with ADEC
and the U.S. Environmental Protection Agency.
The NPS provided $2.5 million to Denali National
Park and Preserve in 2008-2010 for large-scale
restoration efforts in the Kantishna Mining District;
approximately $821,000 of that amount supported
the reclamation efforts in Slate Creek.
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U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-13-001N
April 2013
For additional information contact:
Chandra McGee, Alaska Department of
Environmental Conservation
907-451-2140 • chandra.mcgee@alaska.gov
Denny Capps, Denali National Park and Preserve
907-683-9598 • denny_capps@nps.gov

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