United States
Environmental Protection
Agency
Office Of Water
(WH-553)
EPA841-F-33-003
November 1992
Number 3
&EPA TMDL Case Study
West Fork of Clear Creek
Key Feature:
Project Name:
Location:
Scope/Size:
Land Type:
Type of Activity:
Pollutant(s):
Program Integration:
TMDL Development:
Data Sources:
Data Mechanisms:
Monitoring Plan:
Control Measures:
A seasonal TMDL using narrative
standards for certain parameters
West Clear Creek
EPA Region Yin/Clear Creek
County, Colorado/Woods Creek and
the West Fork of Clear Creek
Subwatershed area 19.8 mi2
High mountains
Mine dewatering/metals mining,
molybdenum
Toxics, metals
Regional/State/local
PS, NFS
State and local
Mass balance equation
Yes
BMPs
TMDL site
FIGURE 1. Location of the West Fork Watershed
Summary: The West Fork of Clear Creek (West Fork), impaired by trace metals from mining activities, is listed under
Clean Water Act section 304(1) (USEPA, 1988). There are two mining sites along Woods Creek, which is in the West
Fork drainage. The Urad mine is an inactive site, and the Henderson mine is an active site. Discharges from both mines
are controlled through NPDES permits. Although the State of Colorado defined waste load allocations (WLAs) for the
Urad mine and mill in 1989 (Colorado Department of Health, 1989a) and the Henderson mine and mill in 1990 (Colorado
Department of Health, 1990), monitoring data collected by the mines to fulfill their permit requirements led EPA to
conclude that implementation of the WLAs alone would not attain all applicable water quality standards (WQSs) for
Woods Creek and the West Fork. EPA also believed that, while the State had established these WLAs, total maximum
daily loads (TMDLs) had not been established. EPA fulfilled its responsibility under section 303(d) by establishing the
necessary TMDLs itself. The TMDLs were calculated using a simple mass balance equation based on the effluent and
stream flows and pollutant concentrations hi the monitoring data. Ambient monitoring indicates that the most critical point
for the metals contamination from the sites occurs close to the point of discharge. The metals concentrations tend to
attenuate downstream from the source. Under these conditions the use of a mass balance equation is acceptable. The
TMDLs were developed on a seasonal basis by using flows and concentrations specific to each season. This was done for
economic reasons to minimize the treatment and control measures necessary to meet the specified WLAs. A combination
of nonpoint and point source controls will be used to comply with permitted loads hi order to meet instream water quality
standards. The best management practices (BMPs) include plugging an inactive mine portal, installation of toe
(groundwater) drains in the tailing piles, and construction of channels to divert runoff around the tailing piles. At the
Urad site, active treatment of discharge combined with the BMPs will be the most likely means of achieving water quality
standards. The Henderson site already employs active treatment, including chemical addition and settling. All water that
is collected by these BMPs is treated before it is discharged to the creek. Waste loads have been allocated between the
two facilities on an equal concentration basis with three seasonal allocation periods. Additional data gathering is required
of the discharger to collect fate/transport data and to develop site-specific criteria for metals.
Contact: Bruce Zander* U.S. EPA Region VIII, Water Division^ 999 18th SL> 5te. 500t Denver, CO 80202-2406*
* t>hone (303)2934580
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BACKGROUND
Programmatic Issues
The State of Colorado defined waste load allocations
(WLAs) of the pollutants listed in Table 1 for the Urad
mine and mill in 1989 (Colorado Department of Health,
1989a) and the Henderson mine and mill in 1990
(Colorado Department of Health, 1990). Both of these
facilities discharge tailings and water into Woods Creek,
which flows into the West Fork as shown in Figure 2.
Basinwide monitoring data collected by both of the
mines to fulfill their permit requirements led EPA to
conclude that implementation of the WLAs alone would
not attain all applicable water quality standards (WQSs)
foe Woods Creek and the West Fork. EPA also believed
that, while the State had established these WLAs for
each discharger, total maximum daily loads (TMDLs)
had not been established for either water body.
It is EPA's responsibility under section 303(d) of the
dean Water Act (CWA) to review and approve the
TMDLs developed by a State to ensure that applicable
WQSs will be met when the controls advocated by the
TMDLs are implemented (USEPA, 1991a). Section
303(d) requires EPA to establish a TMDL when, after
careful review, it disapproves of a TMDL that has been
developed by a State. It is also appropriate for EPA to
establish TMDLs where a State fails to do so in a timely
fashion (see Scott vs. City of Hammond, 741 F.2d 992
(7th cir. 1984), cert.den.10S S.CL979). Since no
approved State-developed TMDL existed for these
sections of Woods Creek or the West Fork, EPA fulfilled
its responsibility under section 303(d) by establishing the
necessary TMDLs itself.
Since ample monitoring data were available for Woods
Creek and the West Fork, and the data seemed sufficient
to support determination of a TMDL that would meet
water quality standards, a one-time calculation of the
TMDL was planned and executed. Had there been
serious doubt that the TMDL would result in the
attainment of water quality standards, due to insufficient
data about the resource or other reasons, a phased
approach to TMDL development would have been
chosen. The following sections describe the study area
and the development of TMDLs by EPA.
The Resource
The Town of Empire, Colorado, is approximately 8 miles
below the confluence of Woods Creek and the West Fork
of Clear Creek in the southern Rocky Mountains (see
Figure 2), an area characterized by high mountains and
tablelands with high relief and boralf soils. Clear Creek
eventually discharges into the South Platte River,
downstream of Denver, Colorado. Pine, spruce, fir,
bcntgrass, sedge, fescue, and bluegrass are the dominant
vegetation (Omemik, 1987). The land is kept primarily
as forest and woodland, although there is some grazing.
TABLE 1. Colorado Numeric Water Quality
Standards for Woods Creek and the West
Fork of Clear Creek1
PARAMETER"
Classification
Nuneric Standards
Dissolved Oxygen:
Normal
Spawning
PH
Fecal Coliform
Ammonia
TRC
Cyanide (free)
SasHjS
Nitrite
Arsenic
Copper
Lead
Mercury
Nickel
Selenium
Silver
Zinc
Iron
Cadmium
Chromium (tri)
Chromium (tot)
Manganese (tot)
Boron
Temporary
Modifications
Cadmium
Manganese
Zinc
Other Criteria
Aluminum -chronic
Uranium-chronic
Radium 226/228
WOODS
CREEK
Segment 7
Aquatic Life
(cold)/2
Recreation/2
6.0
7.0
6.5 - 9.0
2000/100 mL
0.02 on-ionized
0.003
0.005
0.002 (undis)
0.05
0.05
0.023
0.025
0.00005
0.1
0.05
0.0001
0.1
1.0
0.002
0.1
0.025
1.1
0.014
9.4
0.74
0.150
1.50
5.0 (pCi/L)
WEST FORK
Segment 5
(below Woods
Creek)
Aquatic Life
(coldyi
Recreation/2
Agriculture
6.0
7.0
6.5 - 9.0
2000/100 mL
0.02 nn-ionized
0.003
0.005
0.002 (undis)
0.05
0.05
0.023
0.025
0.00005
0.1
0.02
0.0001
0.1
1.0
0.003
0.1
0.025
1.1
0.75
0.150
1.50
5.0
* Standards in effect when TMDL was established.
k Units in ing/L unless otherwise noted.
Average annual rainfall is approximately 30 inches, and
average annual runoff approaches 20 inches (USGS,
1985).
The topography, land use, soil types, and relatively high
rainfall and runoff combine to create a moderate to high
erosion potential. While background contributions to
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s Monitoring Stations
P Pipe Outfall
I Water intake
•+• Henderson Mine
| Urad Mine
Vest Fork of Clear Creek
N
Town of
Empire
FIGURE 2. Hie West Fork of Clear Creek
instream pollution are small, flow conditions in the
watershed significantly contribute to transport of
pollutants within the watershed. Periods of high runoff
can transport larger quantities of pollutants more quickly,
while periods of low flow offer less instream dilution.
This increases the potential impact of discharge from the
mining operations.
Woods Creek is approximately 4.5 miles long, with a
drainage of about 9.6 square miles. The West Fork of
Clear Creek, above its confluence with Woods Creek, is
approximately 4.25 miles long. Its drainage is about
10.2 square miles, and average annual discharge is
approximately 1.3 cubic feet per second (cfe). West
Fork flow ranges from 0.8 cfe in the winter to 4.0 cfe in
the summer. Average annual flow in Woods Creek is
slightly higher, averaging 2.06 cfs above the mine
tailings discharges and 3.38 cfs at the mouth. Seasonal
flow variations are similar for both.
Water in the upper reaches of Clear Creek is used
primarily for cropland irrigation and municipal supply.
The primary designated uses of the affected reaches are
(1) cold water aquatic habitat and (2) recreation, although
downstream uses include municipal water supply and
irrigation. Most greatly threatened by metal-containing
runoff from tailing piles along Woods Creek is the
waterbody's use as a habitat for aquatic life.
ASSESSING AND CHARACTERIZING
THE PROBLEM
Targeting and Prioritizing
Because the Urad mine and mill and the Henderson mine
and mill are both located along Woods Creek, authorities
suspected that priority pollutants might be present in the
water column and in tbe bottom sediments, as wen.
Monitoring supported this speculation, indicating that
designated uses along the upper reaches of dear Creek,
which includes the West Fork, were impaired by
concentrations of trace metals originating from the
mines' tailing piles. The presence of these pollutants in
the West Fork caused it to be placed on the State's
304(1) list of impaired waters. Since it was on the 304(1)
list and there was also a need to reissue NPDES permits
for Henderson and Urad, West Fork became a high
priority for TMDL development.
Monitoring and Data Bases
A number of organizations conduct monitoring along the
West Fork and Woods Creek. Both the Urad mine and
the Henderson mine voluntarily monitor water quality at
their discharges to facilitate reissuance of their NPDES
permits. The U.S. Forest Service, the U.S. Geological
Survey, and the Colorado Departments of Health and
Natural Resources also monitor water quality at stations
along the affected reaches.
A good data base is one that has a long period of record,
broad spatial coverage, and consistency in sampling and
analytical methods (USEPA, 1991b). The West Fork
data base is considered to have a fair period of record,
broad spatial coverage within the subwatershed, and
relatively good consistency in sampling and analytical
methods since most of the data used to develop the
TMDLs were collected by the dischargers.
The past monitoring programs for this area were not
specifically designed to support development of a
watershed TMDL. Nevertheless, they have proven very
useful. The data were and are used to determine whether
water quality standards are being met, to indicate water
quality trends, to increase the accuracy of modeling, and
to provide better information to revise established
TMDLs, if necessary.
TMDL DEVELOPMENT
Determining the Load/Waste Load Allocation
Scheme
The objective of a TMDL is to allocate loads among all
of the pollutant sources throughout a watershed so that
appropriate control measures can be implemented and
water quality standards achieved. The numeric water
quality criteria used to develop TMDLs for Woods Creek
and the West Fork of Clear Creek were presented in
Table 1. In addition to current Colorado Standards,
numeric criteria for aluminum (Al), radium (Rd), and
uranium (U) were included in the table. Since there
were no numeric standards for Al, Rd, or U in effect for
Woods Creek or the West Fork, criteria from the State's
Basic Standards and Methodologies for Surface Water
3,1,0 (5 CCR 102-8) (Colorado Department of Health,
1989b) were used.
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Ooce the physical and chemical attributes of the West
Fork and Woods Creek were examined and the targeted
pollutants determined, the assimilative capacity of the
water bodies was estimated. The load of pollutants that
may enter these or any other water bodies without
violating water quality standards depends on the physical
attributes of the water body, such as flow and
temperature, and its chemical characteristics, such as
instream concentrations of metals and hardness.
Critical, or design, flows were chosen to ensure that
water quality excursions would not exceed an acceptable
frequency. The 30E3 flow (30-day, 3-year, biologically-
based tow flow) was chosen for Woods Creek.
BiologicaEy-based flows arc preferable to hydrologically-
bascd flows, when available. The 7Q10 flow (7-day, 10-
year, hydrologically-based low flow) was chosen for the
West Fork, because the 30E3 flow was not available.
Upstream, or background, loadings were determined next,
and all sources contributing to the load were identified.
The Urad and Henderson mines are the primary sources
of pollution in the area. Since there is little human
activity upstream, it was not surprising to find that
background concentrations of metals in Woods Creek and
the West Fork are low when compared with the loadings
attributed to the two mines. Efforts to control pollutant
loadings, therefore, focused on the mines.
A series of data pertaining to critical stream flows,
effluent discharge, and pollutant concentrations was used
by EPA to define the TMDLs. EPA relied, for the most
part, on data reported in the draft Henderson permit
(Colorado Department of Health, 1990) and a simple
mass balance equation that is used by the State of
Colorado to define water quality-based effluent limits. A
margin of safety (MDS), which is required within each
TMDL, was incorporated through conservative
assumptions. If these assumptions had been deemed
insufficient, an additional MOS could have been added
as a separate component of the TMDL. Figure 3
illustrates the design flows that were used and the
location of the various discharges.
The TMDLs for Woods Creek and the West Fork were
developed on a seasonal basis by using flows and
concentrations specific to each season within the mass
balance equation. The most stringent discharge limits
apply only when the receiving waters are least able to
safely accommodate pollutant loadings (e.g., during
critical low flows). This was done for economic reasons
to minimize the treatment and control measures
necessary for the mines to meet their specified waste
load allocations. In addition, the CWA calls for the
consideration of seasonality when establishing TMDLs
(see section 303(d) of the CWA). Though seasonal
allocations were more cost-effective for the mine
Urad
Mine
Portal
Cplugged)
Henderson
Mine
Woods Greek
Upper Urad Lower Urad Lower Urad
Tailings Tailings Reservoir
West Fork
Woods Creek
Woods creek £3)
Henderson. Discharge
Urad Discharge £5 *
Sri
O
m
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the complexity of determining a seasonal
control program increased difficulties with program
administration and tracking of permit compliance.
Seasonal fluctuations in the assimilative capacity of a
water body vary greatly under different conditions and
need to be carefully examined when developing a
seasonal TMDL. Three seasonal divisions were chosen
for the West Fork. Calculations were then made for each
of the parameters listed in Table 1. Figure 3 shows the
relation of stream flow, in this case the critical flow, to
mine discharge for the winter, summer, and fall.
Discharges were based on the mean flow values reported
in the State's permit rationales (Colorado Department of
Health, 1989a and 1990), except for the Urad winter low
flow. The winter flow was based on observed flows
coming from the underdrains, as well as unaccounted
inflows around the tailings, when stream flow was at its
lowest (December through February). EPA allocated
waste loads for cadmium, manganese, and zinc at the
Urad and Henderson mines from TMDLs that were based
on WQSs for the West Fork. Waste loads for the other
parameters were allocated from TMDLs based on the
WQSs specifically set for Woods Creek. EPA proposed
that the facility discharges be allocated equivalent
discharge concentrations, even though the volume of
discharge differs.
Calculations were performed for each parameter to
determine the effluent limits that would meet water
quality standards. The most stringent limits are in place
during October through May, when stream flows are
lowest. From June to July stream flow for this area
tends to be highest and the assimilative capacity of the
stream is also increased; therefore, a larger waste load
was allocated. Table 2 presents the seasonal TMDL for
zinc in order to demonstrate how the total load was
divided both seasonally and between the dischargers.
The zinc TMDL for the West Fork was used to
determine the permitted zinc WLAs for the two facilities.
IMPLEMENTATION OF POLLUTION
CONTROLS
A combination of best management practices (BMPs)
and point source controls was used to implement the
TMDLs for Woods Creek and the West Fork. The ia-
place and proposed BMPs that constitute the current plan
include the plugging of the inactive Urad mine portal,
isolation of the tailings from runoff, and installation of
toe (groundwater) drains in the tailing piles (Zander,
telephone contact, May 20, 1992). Plugging the mine
portal stopped flow from the mine to Woods Creek,
effectively ending pollution loadings from this source.
As water levels in the mine rise, the flow will redirect to
the Henderson mine area, where it will receive treatment.
Collection channels are some of the BMPs designed to
divert runoff away from the tailing piles in order to
reduce flow through them. Toe drains collect water that
does pass through the tailing piles so that it can be
treated to acceptable levels before it is discharged to
Woods Creek. The Henderson site currently treats
discharged water by chemical addition and settling.
Active treatment is also being considered for the Urad
site.
Ongoing studies are evaluating the most effective
combination of point source and nonpoint source
controls, and the current plan may be reevaluated based
on the results of these studies. Initial costs for
implementation of the currently proposed BMPs and
point source controls, for both sites, have been estimated
at less than $2 million. Cost estimates for other plans
under consideration are not currently available.
FOLLOW-UP
Monitoring
Follow-up monitoring is necessary to indicate whether a
TMDL adequately protects water quality and the aquatic
community and to better quantify loads, verify models,
and evaluate the effectiveness of controls. Point source
dischargers are required to provide periodic reports
regarding NPDES permit compliance. The permittee is
responsible for implementing the monitoring plan and
ensuring that water quality, hydrologic, and biological
information is obtained. Monitoring requirements can be
put into a permit as long as the data are gathered for the
purpose of writing the permit limit Although the Urad
and Henderson permits do not contain specific TMDL
monitoring requirements, the monitoring that is
TABLE 2. Total Maximum Daily Load for Zinc to Achieve Instream Water Quality Standards' (after USEPA,1991c)
Oct-May
Inn-July
Ang-Sep
TMDL at Month of
Woods Creek
Z53
8.14
4.91
LA Background in
Woods Creek
0.06 (10.0)
0.50 (10.0)
0.16 (10.0)
WLAfor
Urad
0.40 (147)
Z13 (411)
1.27(246)
WLAfor
Henderson
2.07 (147)
5.51 (411)
3.49 (246)
West Fork TMDL
below Woods Creek
2.68 (100)
8.79 (100)
5.65 (100)
West Fork LA Background
Above Woods Creek •
0.15 (34.0)
0.64 (34.0)
0.73 (34.0)
* All values given in pounds per day with g/L in parenthesis.
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conducted by the facilities to fulfill requirements for
permit compliance also provides information that is
useful for evaluating the effectiveness of the TMDL.
The data will also enable EPA to determine what
changes occur in the stream as a result of BMP
installation and how long it takes the stream to react
Specifically, changes in stream flow, effluent discharge,
and water quality due to plugging of the mine portal will
be monitored, and new discharges, such as those from
the toe drains, will be monitored to determine discharge
characteristics. Since the TMDL process is iterative and
monitoring data are crucial to updating and, if necessary,
revising TMDLs, future planning activities will benefit
from these data.
Monitoring on West Fork, immediately below Woods
Creek, has already shown that plugging the Urad mine
portal has resulted in improved stream biology. A
dramatic increase in the density and variety of
macroinvertcbrate populations and sharp growth in the
trout population are a strong indication that the BMP is
helping to achieve water quality objectives.
Considerations
A TMDL is based on a specific set of water quality and
flow data and on State water quality standards. When
water quality standards are modified or additional data
become available, it may be necessary to revise the
TMDL to reflect these changes. When there is more
information on the upper West Fork drainage, more
sophisticated modeling that can account for metals
speciation and partitioning, the role of the lower Urad
Reservoir, and variations in loading over time is planned.
Recently gathered data have already indicated that the
seasonal delineation should be modified, changing the
grouping of months to more closely reflect the
hydrologic cycle of the Woods Creek basin. The State
recently developed updated TMDLs for metals in the
West Fork based on revised water quality standards and
re-evaluated design flows. The level of point source
treatment that is called for in the updated TMDLs is
particularly intense because of more stringent standards
for the receiving water due to limited dilution at low
flow. The seasonal delineation has not been redefined by
the State's TMDLs. These TMDLs were incorporated
Into an updated permit for the Urad site that became
effective June 1,1992 (Colorado Department of Health,
1992). A petition may be submitted to open the
Henderson permit for re-evaluation based on the more
recent water quality criteria.
REFERENCES
Colorado Department of Health. 1989a. NPDES Permit
Number CO-0041467. Water Quality Control Division,
Colorado.
Colorado Department of Health. 1989b. Basic
Standards and Methodologies for Surface Water 3.1.0
(5 CCR 1002-8). Water Quality Control Division,
Colorado.
Colorado Department of Health. 1990. Draft NPDES
Permit Number CO-0000230, Public Notice. Water
Quality Control Division, Colorado.
Colorado Department of Health. 1992. NPDES Permit
Number CO-0041467 (Amended). Water Quality
Control Division, Colorado.
Omernik, J.M. 1987. Ecoregions of the conterminous
United States. Annals of the Association of American
Geographers 77(1):118-125.
USEPA, 1988. Final guidance for implementation of
requirements under section 304(1) of the Clean Water Act
as Amended. U.S. Environmental Protection Agency,
Office of Water Regulations and Standards and Office of
Water Enforcement and Policy. Washington, DC.
USEPA. 1991a. Guidance for water quality-based
decisions: The TMDL process. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
USEPA. 1991b. Workshop on the water quality-based
approach for point and nonpoint source controls.
Meeting summary. U.S. Environmental Protection
Agency, Office of Water, Washington, D.C.
USEPA. 1991c. NPDES and statement of basis for
permit number CO-0041467 for Climax Molybdenum
Company - Urad Mine and Mill. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
USGS. 1985. National water summary for 1985. U.S.
Geological Survey. Water-Supply Paper 2300.
Has case study was prepared by Tetea Tech, fnc,» Fairfax^
VA, ifi ettftjnncdott vrfih fcPA Offcse d. Wetfands, Oceans
ami Watersheds, Wateished Managowatt SectfoB, TO
obtain copies, contact your EPA Regional
Coordinator,
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