NC0063096_Report_20031117

NPDES DOCUMENT SCANNINO COVER SHEET
NC0063096
Holly Springs WWTP
NPDES Permit:
Document Type:
Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Correspondence
Owner Name Change
(Deport
;.i'
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
November 17, 2003
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OF WATER
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�iri 1 Iris
Michael F. Easley, Governor
William G. Ross Jr., Secretary
North Carolina Department of Environment and Natural Resources
Alan W. Klimek, P. E. Director
Division of Water Quality
Colcen 1-1. Sullins, Deputy Director
Division of Water Quality
November 17, 2003
MEMORANDUM
To: Dave Goodrich
Through: Dianne Rei
From: Debra Owen '9'65--
^!.0VV
Enclosed is the final report on the Utley Creek Study conducted in July 2003. Three sites were sampled and data
collected indicates that the creek is nutrient enriched below the Holly Springs WWTP. In response to the availability
of these nutrients, Thomas Mill Pond is covered with thick mats of algae. Algal Growth Potential Test (AGPT) results
indicate that Thomas Mill Pond is nitrogen limited and the lower end of Utley Creek near Harris Lake is phosphorus
limited. The Control Mean Standing Crop at Thomas Mill Pond was 12.2 mg/L, indicating that nutrient
concentrations are more than sufficient to support nuisance algal blooms.
Previous studies of Utley Creek along with these AGPT results support the need for nutrient controls in the Utley
Creek watershed. Due to the size of Utley Creek and the location of the Holly Springs WWTP outfall, the plant's
discharge comprises more than 90% of the total stream flow, making it a significant source of nutrient input to Utley
Creek. While AGPT results indicate that nitrogen is the limiting nutrient below the WWTP at Thomas Mill Pond,
phosphorus is present in sufficient concentrations to continue to support nuisance algal blooms even with nitrogen
reductions in place.
Please let me know if you have any questions regarding the results of this study. I can be reached by telephone at
733-6510 ext. 210 or bye -mail at [e-mail].
Cc: Jimmie Overton
Ken Schuster
Darlene Kucken
Michelle Woolfolk
Attachments
N. C. Division of Water Quality 1621 Mail Service Center Raleigh, North Carolina 27699-1621
M
tdCCtEP;k
Customer Service
1-877-623-6748
Environmental Sciences Branch
Phone: [phone] FAX: [phone]

Utley Creek Nutrient Study
Wake County, North Carolina
Cape Fear River Subbasin 03-06-07
Purpose
The purpose of this study was to collect additional information, specifically Algal Growth Potential
Testing (AGPT) samples, to assist in determining the appropriate nutrient limits for the Holly Springs
WWTP. Algal Growth Potential Tests provide information on the capacity of a water body to support
nuisance algal populations and determine which nutrient may be responsible for limiting algal growth
(USEPA 1987). In order to perform this test, water is collected, autoclaved, and filtered. Samples are
then treated separately with additions of nitrogen and phosphorus. When the added nutrient results in
an increase in mean standing crop (MSC) over the control, that nutrient is said to be limiting to
phytoplankton growth, indicating that increases of the limiting nutrient to the water body could result in
nuisance algal populations.
The Town of Holly Springs permit for discharging to Utley Creek is up for renewal. Due to previous
studies, it has been determined that nutrient limits will be required. This study will help support
establishment of those limits.
Background
Utley Creek is a small steam in southwestern Wake County near the Town of Holly Springs. It has a
stream reach of approximately four miles and a 4.2 square mile watershed. The watershed consists of
forested land and rapidly growing residential areas. The Town of Holly Springs has a 1.5 MGD
wastewater treatment plant which discharges effluent into Utley Creek. Approximately one mile below
the WWTP outfall, Utley Creek enters Thomas Mill Pond, an estimated five -acre impoundment.
Thomas Mill Pond is owned and operated by Progress Energy (formerly Carolina Power and Light
Company). Approximately one mile below the dam on Thomas Mill Pond, Utley Creek enters another
Progress Energy owned and operated impoundment — Green Tree Reservoir. This reservoir has
historically been managed as a waterfowl sub -impoundment. Utilizing flashboard risers, the
impoundment is flooded during the winter months, then allowed to flow naturally during the summer.
Below the Green Tree Reservoir, Utley Creek flows for its final 0.8 miles before entering Harris Lake.
Harris Lake is a 1,680 hectare impoundment constructed by Progress Energy to provide cooling water
for the Shearon Harris Nuclear Plant. The lake, which includes a Wake County public park, is heavily
used for recreation.
In July 1996, a fish kill and severe algae bloom in Utley Creek prompted DWQ staff from the Raleigh
Regional Office and the Intensive Survey Unit to investigate and assess the cause. The staff
documented an extensive algae bloom in Thomas Mill Pond and Green Tree Reservoir. During this site
visit, chlorophyll a values in Thomas Mill Pond were 550 ug/L. Dissolved oxygen was 16.3 mg/L (193%
saturation), and pH was 10.3 standard units. Staff from ISU and the TMDUmodeling unit visited the
site again in July of 1997 and documented another algae bloom in Thomas Mill Pond and Green Tree
Reservoir. In July 1996 and 1997, during the fish kill/algal bloom investigations, the dominant algal
species in Thomas Mill Pond was Oscillatoria tenuis. This filamentous blue-green algae is widely
distributed in N.C. ponds and lakes and comprised 95% of the total algal biovolume at the time of the.
investigations.
Holly Springs increased its population by nearly 500% between 1990 and 2000 (US 2000 Census). It
was the largest increase among North Carolina's 537 cities, towns and villages. The Town was granted
an expansion in effluent flow to allow 1.5 MGD to be discharged into Utley Creek in June 2001. In
January, 2003, a permit to upgrade to 2.4 MGD, effective March 1, 2003, was issued to the Holly
Intensive Survey Unit 1 11/17/2003

1•
.r
Springs WWTP. Contingent to this upgrade, a monthly average limit of 6.0 mg/L for total nitrogen and
0.5 mg/L for total phosphorus would be required.
Prior to that in 2000, a study to document and assess the causes of nutrient enrichment in Utley Creek
was conducted by the Intensive Survey Unit. The study consisted of six site visits from May 5 to August
31, 2000. The nutrient load in Utley Creek was determined to be originating from the Town of Holly
Springs WWTP. Under normal summer low -flow conditions, the WWTP effluent provided approximately
91 % of the total stream flow for Utley Creek. On average (based on grab samples), during the six
sampling events, the WWTP discharged 65 pounds per day of total nitrogen, 26 pounds per day of total
phosphorus, and 0.8 pounds per day of ammonia. It was determined to be the main nutrient source in
Utley Creek.
Study Results
Four sampling sites were chosen for data collection: upstream of the Holly Springs WWTP (UC1),
Thomas Mill Pond (UC2), Green Tree Reservoir (UC3), and the mouth of Utley Creek in Harris Lake
(UC4). Figure 1 shows the location of these sites in relation to Holly Springs WWTP and Harris Lake.
Figure 1. Utley Creek showing locations of sampling sites.
Two teams were responsible for data collection with both teams sampling the same day, one team
upstream of the WWTP (UC1) and at Thomas Mill Pond (UC2) and the other near Harris Lake at Utley
Creek (UC4). Due to the ongoing construction of a residential development, which borders Utley
Intensive Survey Unit 2
11/17/2003

Creek, access to Green Tree Reservoir (UC3) was not possible. Therefore, no data were collected
from this site. Physical and chemical data was collected at each site. AGPT samples were collected at
Thomas Mill Pond and upstream of Harris Lake. Table 1 shows the data collected.
Table 1. Sampling Parameters for Utley Creek Nutrient Study.
Sampling Parameters
Upstream of WWTP
UC1
Thomas Mill Pond
UC2
Upstream of Harris Lake
UC4
Physical Data
Dissolved Oxygen (mg/L)
•
.
•
Water Temperature (°C)
•
•
•
Conductivity (umhos/cm)
•
•
•
pH (s.u.)
•
•
•
Secchi Depth (m)
•
Chemistry Data*
Total Solids (mg/L)
•
•
•
Suspended Solids (mg/L)
•
•
•
Turbidity (NTU)
•
•
•
Chlorophyll a (ug/L)
•
•
•
Ammonia (mg/L)
•
•
•
TKN (mg/L)
•
•
•
NO2 plus NO3 (mg/L)
•
•
•
Total Phosphorus (mg/L)
•
•
•
AGPT
•
* Grab samples
Site Descriptions
Utley Creek Upstream of WWTP (UC1)
Utley Creek in the vicinity of the WWTP outfall is approximately three to four feet wide. At the time of
this study, drought conditions had reduced the depth of the water to approximately six inches. The
water was flowing and was clear. There were no visible signs of algal mats, clumps or flecks in the
water.
Utley Creek at Thomas Mill Pond (UC2)
Figures 2 and 3 show Thomas Mill Pond. Mats of fibrous algae are located throughout the pond,
especially at the lower end near the dam (Figure 3).
Intensive Survey Unit 3 11/17/2003

Figure 2. Thomas Mill Pond (UC2)
Figure 3. Closer view of the floating algae mats located at the lower end of Thomas Mill Pond.
Intensive Survey Unit
4 11 / 17/2003

Utley Creek Upstream of Harris Lake (UC4)
A view of the mouth of Utley Creek at Harris Lake is shown in Figure 4. A thick growth of aquatic plants
occurs from bank to bank, making access up into the creek from the lake by boat very difficult. To
collect water samples at this end of the creek for this study, a canoe was used. The aquatic plant
community in this area is diverse and includes lotus (Nelumbo lutea), water lily (Nymphaea odorata),
pondweeds (Potamogeton sp.), naiads (Najas sp.) and water primrose (Ludwigia sp.) (Figures 5 and 6).
Figure 4. Looking upstream into the mouth of Utley Creek from Harris Lake. Note thick growth of
aquatic vegetation.
Intensive Survey Unit 5 11/17/2003

Figure 5. Lotus in lower end of Utley Creek.
Figure 6. Water primrose in lower end of Utley Creek
Intensive Survey Unit
6 11/17/2003

Chemical and Physical Data
Chemical and physical data collected at the three sites sampled on July 28, 2003 are presented in
Table 2. Nutrient concentrations were greatest at Thomas Mill Pond (UC2) as compared with those at
UC1 (above the WWTP) and UC4 (at Harris Lake). Percent dissolved oxygen saturation (182.7%) and
chlorophyll a concentrations (94 ug/L) were greater than the applicable state water quality standards for
these parameters, 110% and 40 ug/L respectively. It should be noted that even in the presences of an
extensive algal bloom, nutrient concentrations at UC2 were above those at UC1, as were the physical
data, total suspended solids and turbidity.
Table 2. Phvsical and nutrient data
PHYSICAL DATA
Water
CHEMISTRY DATA
Solids
Solids
LakeName
Smiling
Depth
DO Ternp
pH
Cond.
Percent
TP TKN NH3 NOx TN TON TIN Chla Total Suspendetl Turbidty
Station
m
mil_ C
s.u.
pmhos/cm
SAT
m9fL mg4. rngfL mpg_ m9t mglL ng+L pgt mall..
mg&
NTU
Utley Creek ups WWTP
UC1
G15
8.0 22.0
7.2
68
91.5%
0.02 <0.20 <0.02 0.18 0.19 0.09 0.19 <1 69
<2.5
3.5
Utley Creek at Thomas Mill Pond •
UC2
0.15
14.4 27.6
9.0
365
182.7%
G49 1.50 <0.02 0.08 1.58 1.49 0.09 94 270
13.0
11.0
Utley Creek 0.25 mi ups from
mouth at Harris Lake •
UC4
0.15
1.5 24.6
5.4
63
18.0%
0.03 0.61 <0.02 <0.02 0.62 0.60 0.02 10 96
7.0
5.2
• AGPT sample taken
Nutrient uptake by algae in Thomas Mill Pond may account for the decrease in nutrient concentrations
further downstream at Harris Lake (UC4).
AGPT Data
Algal Growth Potential Test results from UC2 and UC4 are presented in Table 3. A MSC of 5 mg/I or
less generally is a level that will not promote excessive algal growths. Mean Standing Crops exceeding
10 mg/L are associated with highly productive waters, which may be subject to frequent nuisance algal
blooms and fish kills. At UC2, the Control MSC of 12.2 mg/L indicates that nutrient concentrations are
currently more than sufficient to support nuisance blooms. Field data and visuals support this finding
(Figures 2 and 3). The results from the addition of nitrogen or phosphorus indicate that nitrogen is the
limiting nutrient (three -fold increase in the MSC over the control) at Thomas Mill Pond (UC2). However,
the phosphorus -spiked sample still had an AGPT of 10.4 mg/L indicating that a reduction in nitrogen
without concurrent reductions in phosphorus would not sufficiently control nuisance blooms and aquatic
vegetation.
Table 3. Algal Growth Potential Test Results
AGPT MSC*
Station
Mean
Control
(mg/L)
Mean
Control + N
(mg/L)
Mean
Control + P
(mg/L)
Limiting
Nutrient
UC2 (Utley Creek at Thomas Mill Pond)
12.2
33.2
10.4
Nitrogen
UC4 (Utley Creek 0.25 mi ups Harris Lake)
0.6
0.4
3.5
Phosphorus
* MSC = Mean Standing Crop
The AGPT results at Harris Lake (UC4) seem to indicate that current in -stream concentrations are not
sufficient to result in nuisance algal blooms.
Intensive Survey Unit 7
11/17/2003

Conclusion
Previous studies and these AGPT results support the need for nutrient controls in the Utley Creek
watershed. Due to the location of the Holly Springs WWTP and the size of Utley Creek, the plant's
discharge comprises greater than 90% of the total stream flow making it a significant source of nutrients
to Utley Creek. Algal Growth Potential Testing indicates that while nitrogen is the limiting nutrient below
the WWTP at Thomas Mill Pond, phosphorus is in sufficient concentrations to continue to support
nuisance algal blooms even with nitrogen reductions.
Intensive Survey Unit 8 11/17/2003