HomeMy WebLinkAboutSec B Ch 9 03-08-38
Section B - Chapter 9
Sixmile Creek, Twelvemile Creek and Waxhaw Creek Catawba River Subbasin 03-08-38
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9.1 Subbasin Overview
This small subbasin includes portions of two ecoregions –
the Southern Outer Piedmont and the Carolina Slate Belt.
These tributaries to the Catawba River in South Carolina
have very low flows during the summer and may stop
flowing during drought periods. Much of the subbasin is
forested, but a greater percentage of the land is classified
as cultivated than in any other subbasin. This is changing
rapidly, however, as residential communities expand into
the area. Union County has the highest expected
population growth rate of any in the basin. The county
population is expected to increase by more than 40
percent in the next 20 years (Table A-6 and A-7).
No benthic macroinvertebrate community samples and
two fish community samples (Figure B-9 and Table B-18)
collected during this assessment period. Both sites were
sampled for the first time during this assessment period.
Refer to 2003 Catawba River Basinwide Assessment Report at
Subbasin 03-08-38 at a Glance
Land and Water Area
i2
Land area: 178mi2
Water area: 1mi2
Population Statistics
2000 Est. Pop.: 48,660 people
i2
Land Cover (percent)
Forest/Wetland: 61%
Surface Water: 1%
Urban: 4%
Counties
Municipalities
Charlotte, Indian Trail, Marvin,
Mineral Springs, Monroe, Stallings,
Waxhaw, Weddington and Wesley
Chapel
Agriculture: 35%
Mecklenburg and Union
Pop. Density: 277 persons/m
Total area: 179m
Major dischargers in this subbasin include the Union
County/Sixmile Creek (1.0 MGD) and Twelvemile Creek
WWTPs (2.5 MGD). There are two facilities in this
subbasin which are required to monitor effluent toxicity.
Since 1997, the Union County/Sixmile Creek WWTP
failed two tests and the Union County/Twelvemile Creek
WWTP failed three tests.
http://www.esb.enr.state.nc.us/bar.html
and Section A, Chapter 3 for more information on monitoring.
There is only one ambient monitoring site in this subbasin: Twelvemile Creek at NC 16. This
site has exhibited elevated conductivity since the early 1990s; other parameters have remained
stable since monitoring began in the early 1980s.
Nonpoint source runoff is a major source of water quality degradation in this subbasin.
However, acute and prolonged lack of flows during the summer intrinsically limits the diversity
of the aquatic life. No benthic macroinvertebrate samples have been collected from this subbasin
since 1992. Benthic macroinvertebrates have been collected only six times from three locations
since 1983. Four of the collections were made in the winter and early spring when flows were
the highest. Twelvemile and Waxhaw Creeks were last rated Good-Fair in the early 1990s. The
fish community in Twelvemile Creek declined from Good in 1997 to Good-Fair in 2002, while
Sixmile Creek maintained its Fair rating in 2002.
Section B: Chapter 9 - Catawba River Subbasin 03-08-38 183
Table B-18 DWQ Assessment and Use Support Ratings Summary for Monitored Waters in Subbasin 03-08-38
Biological Ambient Other 2004 1998
Sixmile Creek 11-138-3 C 8.8 mi.AL F-2 F--02 I -
Twelvemile Creek 11-138 C 3.0 mi.AL F-1 GF-02 C9819500 S -
Twelvemile Creek 11-138 C 3.0 mi.REC C9819500 NR -
Assessment Unit Number - Portion of DWQ Classified Index where monitoring is applied to assign a use support rating.
Use Categories:Monitoring data type: Use Support Ratings 2004:
AL - Aquatic Life F - Fish Community Survey E - Excellent S - Supporting, I - Impaired, NR - Not Rated
REC - Recreation G - Good
GF - Good-Fair
F - Fair
P - Poor
nce - no criteria exceeded
ce - criteria exceeded
Bioclassifcations:
Ambient Data
DWQ
Classification
Assessment Unit
NumberWaterbody Length / Area
Data Type with Map Number
and Data Results
Use Support Rating
Category
Section B: Chapter 9 - Catawba River Subbasin 03-08-38 185
Waters in Parts 9.3, 9.4 and 9.5 are identified by assessment unit number (AU#). This number is
used to track defined segments in the water quality assessment database, 303(d) Impaired waters
list, and the various tables in this basin plan. The assessment unit number is a subset of the
DWQ index number (classification identification number). A letter attached to the end of the
AU# indicates that the assessment is smaller than the DWQ index segment. No letter indicates
that the assessment unit and the DWQ index segment are the same.
Use support ratings are summarized in Part 9.2 below. Recommendations, current status and
future recommendations for waters that were Impaired in 1999 and newly Impaired waters are
discussed in Part 9.3 below. Supporting waters with noted water quality impacts are discussed in
Part 9.4 below. Other water quality issues are discussed in Part 9.5. Refer to Appendix III for
use support methods and more information on all monitored waters.
9.2 Use Support Assessment Summary
Use support ratings in subbasin 03-08-38 were assigned for aquatic life, fish consumption,
recreation and water supply. All waters in the subbasin are considered Impaired on an Evaluated
basis because of a fish consumption advice (Section A, Chapter 4, Part 4.10). All water supply
waters are Supporting on an Evaluated basis based on reports from DEH regional water
treatment plant consultants. Refer to Table B-19 for a summary of use support ratings by use
support category for waters in the subbasin.
Table B-19 Summary of Use Support Ratings by Use Support Category in Subbasin 03-08-38
Use Support
Rating
Aquatic
Life
Fish
Consumption Recreation Water
Supply
Monitored Waters
mi 0 0 0
Impaired 8.8 mi 0 0 0
Not Rated 13.6 mi 0 3.0 mi 0
Total 25.4 mi 0 3.0 mi 0
Unmonitored Waters
Supporting 0 0 0 0
Impaired 0 166.4 mi 0 0
Not Rated 74.0 mi 0 0
No Data 67.0 mi 0 163.4 mi 0
Total 141.0 mi 166.4 mi 163.4 mi 0
Totals
All Waters 166.4 mi 166.4 mi 166.4 mi 0
Supporting 3.0
Note: All waters include monitored, evaluated and waters that were not assessed.
Section B: Chapter 9 - Catawba River Subbasin 03-08-38 186
9.3 Status and Recommendations of Previously and Newly Impaired
Waters
The following waters were identified in the 1999 basin plan as Impaired or are newly Impaired
based on recent data. The current status and recommendations for addressing these waters are
presented below. These waters are identified by assessment unit number (AU#). Refer to the
overview above for more information on AUs.
9.3.1 Sixmile Creek [AU# 11-138-3]
Sixmile Creek flows along the border between Mecklenburg and Union counties and drains the
southeast and southwest portions of each county, respectively. The 8.8-mile segment from its
source to the NC/SC border is Impaired for aquatic life because of a Fair bioclassification at site
F-2. The South Carolina portion is Impaired because of elevated fecal coliform levels.
1999 Recommendations
DWQ recommended that the two remaining dischargers not connected to Charlotte Mecklenburg
Utilities sewer lines perform an Engineering Alternative Analysis (EAA). DWQ stated that the
stream was too small to rate and would not be sampled during the next assessment period.
Current Status and 2004 Recommendations
Since the 1999 plan, all NPDES point sources have been removed from Sixmile Creek.
Charlotte-Mecklenburg Utilities Department constructed the collection system in the watershed
and purchased the private wastewater collection systems. Therefore, EAAs are no longer
applicable. DWQ biologists also determined that while the creek was too small in late summer
to rate using benthic methodologies, a fish community analyses performed in the wetter spring
season is appropriate. DWQ, therefore, again sampled this creek in 2002.
Despite the removal of all NPDES discharges, Sixmile Creek received the highest conductivity
rating of any stream in the basin during the 2002 sampling effort. It was also noted that cattle
had access to the stream. These two points and the natural low flow state of this stream indicate
its sensitivity to nonpoint source runoff. DWQ encourages Union County to develop
management strategies that address runoff in this developing watershed. Please refer to Section
A, Chapter 4, Part 4.11 for more suggestions on land use planning. DWQ will work with local
resource agencies to implement agricultural BMPs for cattle exclusion.
9.4 Status and Recommendations for Waters with Noted Impacts
The surface waters discussed in this section are not Impaired. However, notable water quality
problems and concerns have been documented for some waters based on this assessment. While
these waters are not Impaired, attention and resources should be focused on these waters to
prevent additional degradation or facilitate water quality improvement. Waters in the following
section are identified by assessment unit number (AU#). See overview for more information on
AUs.
Section B: Chapter 9 - Catawba River Subbasin 03-08-38 187
9.4.1 Twelvemile Creek [AU# 11-138]
Current Status and 2004 Recommendations
The watershed of Twelvemile Creek abuts the Crooked Creek watershed in the Yadkin-Pee Dee
River basin. There are no NPDES facilities within the watershed. The South Carolina portion of
the stream is Impaired because of copper, turbidity and fecal coliform concentrations.
From 1997 to 2002, the bioclassification at site F-1 declined from Good to Good-Fair, and no
pollution intolerant species were found. Additionally, suspended sediment from the West Fork
Twelvemile Creek colored the entire Twelvemile Creek channel. A study should be conducted
to compare fish populations and habitat in the East and West Forks of Twelvemile Creek to the
mainstem in hopes of determining the primary stressors in this watershed. In the meantime,
DWQ encourages Union County to develop management strategies that address runoff in this
developing watershed. Please refer to Section A, Chapter 4, Part 4.11 for more suggestions on
land use planning.
9.5 Additional Water Quality Issues within Subbasin 03-08-38
9.5.1 Waxhaw Creek [AU# 11-139]
Current Status and 2004 Recommendations
The Catawba Lands Conservancy (CLC) identified Waxhaw Creek in Southwest Union County
as a priority for land protection efforts because it is the only stream in the Catawba River basin
that supports populations of the federally endangered Carolina heelsplitter mussel. A total of
only six populations of this mussel occur in the entire world, including one other North Carolina
population in Goose Creek, in the Yadkin-Pee Dee River basin. Perhaps the single most
important factor in the conservation of the Carolina heelsplitter is protecting the water quality of
their creek habitats, including the use of forested buffers and prevention of siltation and other
sources of pollution.
Funded by a grant from the NC Clean Water Management Trust Fund and the Conservation
Trust for North Carolina, the Conservancy conducted a study of the integrity of the stream
corridor and identified areas most important for conservation and restoration activities. DWQ
supports the work being conducted by CLC and will assist in any way possible to protect this
unique resource. DWQ also encourages Union County to develop management strategies that
address runoff in this developing watershed. Please refer to Section A, Chapter 4, Part 4.11 for
more suggestions on land use planning.
The downstream portion of Waxhaw Creek in South Carolina is Impaired because of elevated
copper and fecal coliform concentrations. Consequently, in the future, North Carolina will be
subject to an interstate TMDL. DWQ will work cooperatively with South Carolina as they
develop a TMDL for Waxhaw Creek.
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