Jordan Lake PH Turbidity Addendum TMDL

Addendum to B. Everett Jordan Reservoir TMDL
for High pH and Turbidity Impairments

March 6, 2014
EPA APPROVAL ON: April 3, 2014

[Waterbody IDs: High pH and Turbidity: 16-(37.3), 16-(37.5)a, 16-(37.5)b, 16-41-2-(9.5)
Turbidity: 16-41-1-(14)]

Cape Fear River Basin

Submitted by:
NC Department of Environment and Natural Resources
Division of Water Resources (DWR)
1611 Mail Service Center
Raleigh NC 27699-1611
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Introduction
The North Carolina Division of Water Quality (DWQ, now Division of Water Resources) developed a
Total Daily Maximum Load (TMDL) for the B. Everett Jordan Reservoir (Jordan Lake) to address
chlorophyll-a impairments. EPA Region 4 approved the TMDL on September 20, 2007 (DWQ, 2007).
Nutrient controls are the most common focus of management schemes for reducing excessive algal
growth and chlorophyll-a concentrations. Therefore, the Jordan Lake TMDL was written to address
total nitrogen (TN) and total phosphorus (TP) loads to the lake.

Jordan Lake is also listed for high pH and turbidity impairments in the 2002 303(d) list. This addendum
to the original TMDL addresses high pH and turbidity impairments within Jordan Lake. The impaired
waters and associated assessment units (AUs) are listed below:

Impairments Area AU
pH Haw River* 16-(37.3), 16-(37.5)a,
16-(37.5)b
Morgan Creek** 16-41-2-(9.5)
Turbidity Haw River* 16-(37.3), 16-(37.5)a,
16-(37.5)b
Morgan Creek** 16-41-2-(9.5)
New Hope Creek*** 16-41-1-(14)
*include Jordan Lake below normal pool elevation; **include Morgan Creek Arm of Jordan Lake;
***includes New Hope River Arm of Jordan Lake.

Impairment Description
Haw River arm and Morgan Creek arm of Jordan Lake are on the 2012 303(d) list for both high pH and
turbidity. The New Hope Creek Arm is listed for turbidity impairment. Figure 1 shows the locations of
the sampling stations and high pH and turbidity impairments.

The three parts of Jordan Lake that are listed in Category 5 - 303(d) list for high pH and turbidity
impairments are also impaired for chlorophyll-a but are in Category 4t due to the Jordan Lake TMDL
described above.

4

Figure 1. Locations of monitoring stations and impaired segments for high pH and turbidity in Jordan
Lake.

!.
!.
!.Cary
Chapel Hill
Apex
Apex
Durham
Pittsboro
US-64
NC-751
US-15,501
US-1
New Hope Creek
Haw River
Buckhorn Creek (Harris Lake)
Morgan Creek
Haw River
CPF086C
CPF055C
CPF081A1C
Lower New Hope
Haw River Arm
Upper New Hope
0 2 41 Km
±
Legend
!.Monitoring Stations
303(d) List for pH
303(d) List for turbidity
Primary Roads
Major Hydrography
Municipalities
Jordan Management Area
5

Water Quality Target

The North Carolina fresh water quality criteria for pH and turbidity in Class C waters state the
following:

pH: shall be normal for the waters in the area, which generally shall range between 6.0 and 9.0 except
that swamp waters may have a pH as low as 4.3 if it is the result of natural conditions;

Turbidity: the turbidity in the receiving water shall not exceed 50 Nephelometric Turbidity Units (NTU)
in streams not designated as trout waters and 10 NTU in streams, lakes or reservoirs designated as
trout waters; for lakes and reservoirs not designated as trout waters, the turbidity shall not exceed 25
NTU; if turbidity exceeds these levels due to natural background conditions, the existing turbidity level
shall not be increased.
Monitoring Data
Jordan Lake has been monitored extensively since it was impounded in 1982. A detailed description of
data available is included in Tetra Tech (2001), which is available online. For this study, depth profiles
of pH and photic zone data of turbidity and chlorophyll a were obtained at the three stations shown in
Figure 1. The data used are from 1990 through August 2013, which covers the baseline period of 1997
to 2001 in the original Jordan Lake TMDL. Each station was generally sampled on the same day, Figure
2 shows the sampling frequency.
In Jordan Lake, pH and other physical parameters were measured at the surface (0.1 m below surface),
at every meter below the surface and near the bottom of each station. In order to investigate relationships
between pH and other water quality parameters (e.g. chlorophyll a) which were collected as photic-zone
composite samples, mean photic-zone pH values were calculated in this study as the average of
measurements between the surface and two times the Secchi depth.

Figure 2. Sampling date distribution.

Year
1990 1995 2000 2005 20100
50
100
150
200
250
300
350
6

pH – nutrient relationship
pH is a measure of the hydrogen ion activity in a solution. In natural water systems, pH tends to remain
within a narrow band of “neutral” conditions due to the buffering capabilities of inorganic carbon
species. The inorganic carbon buffering system is influenced greatly by a number of heterogeneous
reactions including atmospheric exchange of carbon dioxide, dissolution/precipitation of carbonate
minerals such as calcium carbonate, and photosynthesis / respiration (Chapra, 1997). pH values vary as a
result of all the above processes.
Depth profiles of pH are presented in Figures 3-5, together with water temperature (Temp) and dissolved
oxygen (DO) for different seasons. Results from station CPF081A1C are presented here as a reference
since New Hope Creek is not impaired for pH. Similar to Temp and DO, pH tends to be higher at the
surface and lower near the bottom of the water column. Vertical stratifications appear to be more
significant during summer for all the three variables. Figure 6 suggests that photic-zone pH normally
peaks during May to August at station CPF055C and during July to October at stations CPF081A1C and
CPF086C. Similar seasonal patterns were also observed for chlorophyll a concentrations.
Correlation coefficients between pH, temperature and DO are presented in Table 1. The restricted
maximum likelihood method in JMP was used to calculate the values. As temperature rises, pH and DO
normally decrease in pure water. These relationships often show up in Jordan Lake (indicated by the
negative correlations) during cold seasons when biological activities are low. However, biological
activities occurring in lake surface waters may drive such relationship into opposite direction. For
example, higher water temperature promotes algal growth, which produces more DO and consumes
carbon dioxide and in turn increases pH during the day. In addition, as temperature rises, the solubility
of carbon dioxide is reduced, likely leading to higher pH. When such processes dominate, positive
correlations show up between water temperature and pH and also between temperature and DO. The
stronger positive correlations between pH and temperature during warmer seasons indicate that highly
elevated pH is most likely resulted from biological activities such as excess algal growth.
Table 1. Correlations between pH, water temperature and DO.
pH vs. Temp pH vs. DO DO vs. Temp
CPF055C Spring 0.6010 0.3269 -0.0723
Summer 0.6518 0.7609 0.4870
Fall 0.1878 0.6184 -0.4242
Winter -0.0321 0.1370 -0.5798
CPF081A1C Spring 0.0389 0.4407 -0.4901
Summer 0.5096 0.4734 0.0640
Fall -0.0797 0.7169 -0.5237
Winter 0.0983 0.5810 -0.3241
CPF086C Spring -0.0056 0.5311 -0.3977
Summer 0.4914 0.5766 0.0891
Fall -0.1446 0.6544 -0.5875
Winter 0.1128 0.4538 -0.4092
7

Figure 3. Mean water temperature (Temp) (in °C), DO (in mg/l) and pH at different depth of the water
column at CPF055C. Error bars indicate one Standard Error from the mean.
8

Figure 4. Mean water temperature (Temp) (in °C), DO (in mg/l) and pH at different depth of the water
column at CPF081A1C. Error bars indicate one Standard Error from the mean.

9

Figure 5. Mean water temperature (Temp) (in °C), DO (in mg/l) and pH at different depth of the water
column at CPF086C. Error bars indicate one Standard Error from the mean.

Fall Spring Summer Winter
Season
Depth (m)
0.0 1.0 2.0 3.0 4.0
5
10
15
20
25
0
2
4
6
8
10
12
6.6
7.0
7.4
7.8
8.2
8.6
0.0 1.0 2.0 3.0 4.0 0.0 1.0 2.0 3.0 4.0 0.0 1.0 2.0 3.0 4.0
10

Figure 6. Quantile plot of photic-zone pH, turbidity (NTU) and chlorophyll a concentrations (µg/l) at
different months.

CPF055C CPF081A1C CPF086C
Station
Month
0 2 4 6 8 10 12
pH
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
Tu
r
b
i
d
i
t
y
0
10
20
30
40
50
60
70
80
Ch
l
a
0
20
40
60
80
100
120
0 2 4 6 8 10 12 0 2 4 6 8 10 12
11

Figure 7. Scatter plots of pH vs. chlorophyll a concentrations and turbidity vs. chlorophyll a
concentrations at the three Jordan Lake stations.
Chlorophyll a has long been used as an index of the productivity and trophic condition of surface waters.
(Steele, 1962). High concentrations of chlorophyll a indicate algal blooms that respond to excessive
nutrient inputs. Algal blooms have dramatic effects on water chemistry, including pH. When algae
remove carbon dioxide during photosynthesis they raise the pH by increasing the level of hydroxide.
The opposite reaction occurs during respiration when carbon dioxide is produced, lowering hydroxide
and lowering the pH. Therefore, high pH is often associated with high chlorophyll a concentrations. This
can be seen in Figure 7.

y = 0.0281x + 7.1497
R² = 0.326
5
7
9
11
0 50 100
pH
Chlorophyll a (µg/l)
CPF055C 
y = ‐0.4237x + 27.051
R² = 0.2112
‐25
0
25
50
75
100
0 50 100
Tu
r
b
i
d
i
t
y
 (N
T
U
)
Chlorophyll a (µg/l)
CPF055C
y = 0.0105x + 7.4429
R² = 0.1165
5
7
9
11
0 50 100 150
pH
Chlorophyll a (µg/l)
CPF081A1C y = 0.1822x + 13.501
R² = 0.1583
0
25
50
75
0 50 100 150
Tu
r
b
i
d
i
t
y
 (N
T
U
)
Chlorophyll a (µg/l)
CPF081A1C
y = 0.0123x + 7.3432
R² = 0.1968
5
7
9
11
0 50 100 150
pH
Chlorophyll a (µg/l)
CPF086C y = 0.1968x + 10.058
R² = 0.3342
0
25
50
75
0 50 100 150
Tu
r
b
i
d
i
t
y
 (N
T
U
)
Chlorophyll a (µg/l)
CPF086C
12

Turbidity – nutrient relationship

Turbidity in water is a measure of how cloudy or murky the water is. It is normally caused by particles
suspended or dissolved in water that scatter light and hence make the water appear cloudy or murky.
Particulate matter can include sediment, fine organic and inorganic matter, soluble colored organic
compounds, algae, and other microscopic organisms. The sources of turbidity in lakes could be in-situ
production (e.g., algae or bank erosion) or runoff from the watershed.

Turbidity data at the three stations in Jordan Lake are available starting from June 2003. Seasonal
patterns of turbidity are not very clear (Figure 6); however, turbidity and chlorophyll a are linearly
correlated at stations CPF081A1C and CPF086C (Figure 7), suggesting algae contribution to turbidity at
the Morgan Creek and Upper New Hope arms of the lake. Such positive correlation does not exist at
station CPF055C. By contrast, at station CPF055C, turbidity appears to be driven by flow from its
drainage basin. In addition, at all the three stations, turbidity is closely correlated with total phosphorus
concentrations (Figure 8).

Figure 8. Turbidity vs. flow and total phosphorus (TP) in Jordan Lake.

Jordan Lake TMDL and Nutrient Management Strategy

The Jordan Lake TMDL assigned separate loading reduction targets to the major arms of the reservoir
for both total nitrogen and total phosphorus. Nutrient load reductions targets from 1997-2001 baseline
loading are shown in Figure 9 for each arm.

y = 0.0076x + 6.7528
R² = 0.6081
0
25
50
75
100
0 5000 10000 15000
Tu
r
b
i
d
i
t
y
 (N
T
U
)
Flow (cfs)
CPF055C
y = 345.11x ‐15.843
R² = 0.5833
0
25
50
75
100
0 0.05 0.1 0.15 0.2 0.25
Tu
r
b
i
d
i
t
y
 (N
T
U
)
TP (mg/l)
CPF055C
y = 264.46x ‐5.5037
R² = 0.5633
0
25
50
75
0 0.05 0.1 0.15 0.2
Tu
r
b
i
d
i
t
y
 (N
T
U
)
TP (mg/l)
CPF081A1C
y = 213.13x ‐0.3327
R² = 0.5868
0
25
50
75
0 0.05 0.1 0.15 0.2
Tu
r
b
i
d
i
t
y
 (N
T
U
)
TP (mg/l)
CPF086C
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In addition to the TMDL, North Carolina adopted mandatory Jordan Lake Rules in 2009 to reduce the
amount of nutrient pollution entering Jordan Lake. Full text of the rules can be found at
www.jordanlake.org. The rules require:
 Stormwater management programs for new and existing development.
 Protection of existing vegetated riparian buffers.
 Reductions of nutrient loading from point source discharges.
 Reductions of nutrient runoff from agriculture.
 Sound fertilizer management.

The required watershed reductions specified in the Jordan Lake TMDL are expected to reduce nutrient
loading as well as sediment runoff to the lake. As a result, the chlorophyll a standard in the lake is
expected to be met after full implementation. Due to close relationships between pH and chlorophyll a at
all three stations in Jordan Lake, the pH standard is expected to be met as well. High turbidity in the
Morgan Creek and Upper New Hope arms of the lake is at least partially caused by in-situ algal growth.
High turbidity in the lower portion of Jordan Lake below the conjunction of Haw River is closely
associated with runoff and phosphorus. As sediment and phosphorus runoff, and in-situ algal growth are
reduced, the turbidity standard in Jordan Lake is expected to be met.

Regular monitoring will continue throughout implementation to ensure that standards are attained.
DWR may reevaluate the need for individual TMDLs for pH and/or turbidity in Jordan Lake if the
required reductions are determined to be insufficient.

14

Figure 9. Nutrient load percent reduction targets from 1997-2001 baseline. Note that there is no loading
reduction target for the Lower New Hope Arm; the TMDL provides a loading cap equal to 1997-2001
baseline nutrient loads. There is no 303(d) listing for high pH and turbidity for the Lower New Hope
Arm.

Public Participation
DWQ staff, the Triangle J Council of Governments, and the Piedmont Triad Council of Governments
initialized an extensive stakeholder process in 2003 to receive stakeholder input on the Jordan Lake
nutrient reduction strategy. A total of 21 stakeholder meetings were held between May 2003 and
December 2004 to discuss TMDL development, modeling issues, target setting, and nutrient
management strategy development.

The Jordan Lake TMDL was public noticed in the relevant counties on April 1, 2007 in four local
newspapers (the Durham Herald-Sun, the Winston-Salem Journal, the Greensboro News & Record, and
the Raleigh News & Observer). The TMDL was also public noticed through the North Carolina Water
Resources Research Institute email list serve. Finally, the TMDL was available on DWQ’s website
during the comment period.

15

A draft of this addendum to the Jordan Lake TMDL was publicly noticed through various means, including
electronic notification of the draft addendum to known interested parties. The addendum to the Jordan Lake
TMDL was available on the DWR’s website at http://portal.ncdenr.org/web/wq/ps/mtu/tmdl/tmdls during the
comment period. The public comment period lasted from January 16 through February 17, 2014. Copies of
the public notices are included in Appendix A.

DWR received three sets of public comments on the addendum to the Jordan Lake TMDL. Summaries of the
comments and DWR responses are included in Appendix B.

Reference

Chapra, S.C., 1997, Surface Water Quality Modeling, McGraw-Hill Companies Inc., 844p.

Steele, J.H., 1962, Environmental control of photosynthesis in the sea. Limnol. Oceanog., 7: 137-150.

Tetra Tech, 2001, Jordan Lake Nutrient Response Modeling Project: Existing Data Memorandum
http://portal.ncdenr.org/c/document_library/get_file?uuid=1130e42e-b843-4455-bf96-
4acf79153420&groupId=38364

DWQ, 2007, B. Everett Jordan Reservoir, North Carolina Phase I Total Maximum Daily Load, NC
Department of Environment and Natural Resources, Division of Water Quality
http://portal.ncdenr.org/c/document_library/get_file?uuid=bc043b19-0787-466f-aa7b-
779717e55201&groupId=38364

16

Appendix A. Public Notice of Addendum to Jordan TMDL to Address High pH and Turbidity

The TMDL public comment period was announced on both the NC DWR Modeling and Assessment
Branch’s website and the Water Resources Research Institute of the University of North Carolina (WRRI)
email listserv on January 16, 2014.

 Notice on the Modeling and Assessment Branch’s Website: http://portal.ncdenr.org/web/wq/ps/mtu

1/16/14 The Draft Addendum to the Jordan Lake TMDL for High pH and Turbidity Impairment is available for public 
comment. Comment submittal instructions are available with the above link.  

 WRRI listserv email received regarding public comment period:

From: Lin, Jing  
Sent: Thursday, January 16, 2014 12:12 PM 
To: 'wrri‐[e-mail]' 
Subject: DRAFT Addendum to B. Everett Jordan Reservoir TMDL to Address High pH and Turbidity Impairments Now 
Available for Public Comment 

North Carolina Department of Environment and Natural Resources 
Division of Water Resources 

January 16, 2014 

Now Available for Public Comment 

DRAFT Addendum to B. Everett Jordan Reservoir TMDL to Address High pH and Turbidity Impairments 

The Addendum proposes that pH and turbidity standards are expected to be met within Jordan Lake as a result of full 
implementation of the existing required nutrient load reductions specified in the original Jordan Lake TMDL.  No additional 
load reductions or other requirements are proposed. 

The Addendum document can be found at http://portal.ncdenr.org/c/document_library/get_file?uuid=b3089f81‐40a2‐
4031‐b7e4‐0fbef93f8406&groupId=38364. The draft Addendum was developed to meet requirements of Section 303(d) of 
the Federal Water Pollution Control Act. It is subject to approval by EPA.  

Interested parties are invited to comment on the draft Addendum by February 17th, 2014. Comments should be directed to 
Jing Lin at [e-mail]. 

The document may be modified based on the comments received. Comments and responses on the Addendum will be 
included in the TMDL package to be submitted to EPA.   

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ 
Jing Lin 
Modeling and Assessment Branch 
NC DWR‐Water Planning 
Email: [e-mail] 
Phone: 919‐807‐6410 

17

Appendix B. Public Comments Responsiveness Summary

The public comment period extended from January 16 through February 17, 2014. Comments were
received from six organizations jointly (American Rivers, Cape Fear River Watch, Haw River
Assembly, NC Conservation Network, Southern Environmental Law Center, WakeUp Wake County),
NC Department of Transportation, and the City of Durham. These comments with the NC Division of
Water Resources’ responses are provided below.

1) One comment expressed support for this Addendum to address pH and turbidity impairment in
Jordan Lake.

Response: DWR appreciates the stated support.

2) One comment expressed concern about using total nitrogen and total phosphorus as surrogates
for pH and turbidity impairments in Jordan Lake.

Response: Although the Jordan Lake TMDL and Rules were not designed to achieve pH or
turbidity compliance in the Lake, the required watershed reductions specified in the Jordan Lake
TMDL are expected to reduce nutrient loading as well as sediment runoff to the lake. As a result,
the chlorophyll a standard in the lake is expected to be met after full implementation. Due to
close relationships between pH and chlorophyll a at all three stations in Jordan Lake, the pH
standard is expected to be met as well. High turbidity in the Morgan Creek and Upper New Hope
arms of the lake is at least partially caused by in-situ algal growth. High turbidity in the lower
portion of Jordan Lake below the conjunction of Haw River is closely associated with runoff and
phosphorus. As sediment and phosphorus runoff, and in-situ algal growth are reduced, the
turbidity standard in Jordan Lake is expected to be met.

3) One comment mentioned that some AUs covered in this Addendum are not listed under Category
5 in the draft 2014 NC Water Quality Assessment suggesting improving water quality and that
pH and turbidity are parameters which are not well suited for direct load calculations, and thus
the TMDL management approach. Has the Division considered a Category 4b approach for
these two parameters?

Response: The draft 2014 NC 303(d) list is subject to EPA approval. TMDLs are developed for
waters on the most current approved 303(d) list, i.e., 2012. Category 4b would be more
appropriate for waters without an existing approved TMDL.

4) Two comments asked for more information about the data used for the analysis.

Response: Figure 2 and additional text were added to the Addendum to explain the time period
and frequency of data collection that was used in the analysis (p.5, under section Monitoring
Data). Some text was also reorganized to avoid confusion about the calculation of photic-zone
pH.

18

5) One comment asked to include a significance test for Figures 6 and 7 and a regression equation
added to the turbidity vs. chlorophyll a graph for station CPF055C in Figure 6.

Response: The intent of this analysis was to explore the relationships between the variables and
was not designed to conduct statistical significance test. However, we conducted Analysis of
Variance in response to the comment and found that all linear relations presented in Figures 6
and 7 are strongly statistically significant. In addition, a regression equation was added to the
graph as recommended by the comment.

6) One comment recommended that “the amended TMDL must explicitly acknowledge the point
source character of MS4 stormwater.”

Response: As stated in the original Jordan Lake TMDL, “No attempt was made to separate
permitted (WLA-SW) and nonpermitted (LA) loading associated with nonpoint sources. EPA
requires that loads allocated to NPDES permitted stormwater be placed in the wasteload
allocation, which had previously been reserved for continuous point source loads (EPA 2002).
Since the WLA allocation associated with NPDES permitted stormwater was not separated in a
formal manner, the percent reduction associated with the management area (i.e. Upper New
Hope Arm, Lower New Hope Arm, and Haw River Arm) will apply. According to the Phase II
rules, MS4 permittees are responsible for reducing the loads associated with stormwater outfalls
for which it owns or otherwise has responsible control.” (p.49). The point source nature of MS4
stormwater was recognized in the original TMDL, although formal separation (from non-
permitted stormwater) in loading was not quantified.

7) One comment recommended that “the addendum must acknowledge the need to implement load
reductions upstream” and that “in light of the state’s failure to curb the ongoing growth of
loading into the lake, and the prospect of substantive revisions during the process of rules
readoption, the Jordan rules cannot be said by themselves to provide reasonable assurance that
TMDL reductions will be achieved. The addendum should assert that the load reductions
required by the TMDL will at a minimum be realized for point sources through their NPDES
permits.”

Response: TP limits added to the large dischargers’ permits went into effect in 2010. At least
eight out of fourteen large dischargers (>0.1 MGD, collectively accounting for 99.4% of the
total permitted flow) in Jordan watershed have either upgraded or plan to upgrade their
treatment systems. We anticipate that the wasteload reductions required by the TMDL will be
realized for point sources through their NPDES permits.

8) One comment suggested to “include a statement describing the impaired uses that have resulted
in a Category 5 listings for pH and turbidity.”

Response: As stated in the original Jordan Lake TMDL (p.7) “Surface water classifications are
designations applied to surface water bodies that define the best uses to be protected within
these waters (e.g., swimming, fishing, and drinking water supply) and carry with them an
associated set of water quality standards to protect those uses. The New Hope Creek Arm of
Jordan Reservoir is classified as a WS-IV B NSW CA. The Haw River Arm of Jordan Reservoir is
19

classified as WS-IV NSW CA. Combined, the waters of the reservoir are protected for water
supply, primary and secondary recreation, fishing, wildlife, fish and aquatic life propagation and
survival, agriculture and other uses suitable for Class C. Jordan Reservoir was designated as a
Nutrient Sensitive Water (NSW) in 1983.” The best uses for Jordan Lake were not repeated in
this Addendum. The corresponding water quality criteria for pH and turbidity were included in
this Addendum in page 5.

9) One comment suggested that New Hope Creek is not impaired for pH and analyses using
CPF081A1C should be removed from the section titled “pH – nutrient relationship”.

Response: A statement was added to the Addendum (p.5) that results from station CPF081A1C
was presented as a reference since New Hope Creek is not impaired for pH.

10) One comment suggested that the “turbidity – nutrient relationship” sections should be revisited
to include quantitative support of the relationship and discussion on sediment sources of
turbidity.

Response: The multiple sources of turbidity were discussed in the 1st paragraph under Section
Turbidity – Nutrient Relationship. Sediment as a source of turbidity was acknowledged.
However, this Addendum is not intended to forecast turbidity as a function of algae and/or
sediment, rather to show that the original Jordan TMDL and the associated management
strategy, which will reduce algae production in the lake and sediment loading to the lake, would
also reduce turbidity and result in turbidity meeting criteria in the lake. The Addendum also
states that “Regular monitoring will continue throughout implementation to ensure that
standards are attained. DWR may reevaluate the need for individual TMDLs for pH and/or
turbidity in Jordan Lake if the required reductions are determined to be insufficient.”

11) One comment recommended to include a discussion of other turbidity impairments upstream of
the lake segments. It states: “Third Fork Creek and Northeast Creek are currently in the 303(d)
List for turbidity; a TMDL exists for Third Fork Creek. These creeks are major tributaries to the
Upper New Hope Arm of Jordan Lake. The City of Durham has recently completed extensive
work on a Northeast Creek water quality model, which indicated that in-stream erosion was a
significant contributor to sediment and turbidity in Northeast Creek. It is unclear how
management of sediment and turbidity in Northeast Creek is related to this TMDL for Jordan
Lake.”

Response: The Addendum is not intended to address impairment in tributaries. We appreciate
the work that Durham has done to provide more information on turbidity in Northeast Creek.

12) One comment suggested that the turbidity-chlorophyll a relationship be evaluated by season. The
comment questioned the increase of turbidity in the winter.

Response: High turbidity in winter months was noted at station CPF055C, as suggested by the
comment that “it is related to in-stream erosion related to higher seasonal stream flow.” This
relationship was recognized in the Addendum (e.g. Figure 8 turbidity vs. flow at CPF055C). In
20

addition, turbidity data were available only after June 2003 (p. 12). Separating the analysis into
four seasons would much reduce the sample size and affect the quality of the analysis.

13) One comment suggested that the Jordan Lake TMDL and Nutrient Management Strategy section
should accurately reflect the implementation of the strategy. The third sentence in the first
paragraph states that the same percent reduction was applied to “all sources” throughout the
watershed, which is incorrect.

Response: The statement was removed from the Addendum.