NC0004979_Assessment Report_20100610

d1Duke CORPORATE EHS SERVICES
whEnergy@ Duke Energy Carolinas, LLC
Carolinas 526 SOUTH CHURCH STREET
CHARLOTTE, NC 28202
Mailing Address:
EC13K / P. 0. BOX 1006
CHARLOTTE, NC 28201-1006
June 10, 2010
Mr. Jay Sauber
Environmental Sciences Section
North Carolina Department of Environment
and Natural Resources
1621 Mail Service Center
Raleigh, NC 27699-1621
Subject: Allen Steam Station NPDES Permit No. NC0004979
Balanced and Indigenous Populations (BIP) Assessment Report
Supplemental Mayfly (Hexagenia spp.) and Sediment Sampling April 2010
Dear Mr. Sauber:
As a follow-up to the letter dated March 11, 2010 and our conference call on April 6, 2010 with
respect to the variability of the mean and total abundance of the burrowing mayfly Hexagenia
spp. near Allen Steam Station, additional sampling was conducted in April 2010. As
recommended, an additional monitoring location was added, as well as analysis of substrate
samples along with mayfly samples collected at four monitoring locations. Attached is a copy of
the results for your review. As suspected, mayfly presence or absence in the samples appears
related primarily to suitable substrate/habitat found at the Lake Wylie monitoring locations.
After your review, please advise if additional information will be needed to further address the
benthic macroinvertebrate community and Hexagenia populations in Lake Wylie near Allen
Steam Station. If you have any questions, please contact me at (980)-373-5710.
Sincerely,
9,6 -y -v L�'
Ron Lewis
Water Management
Attachment
xc w/att: Mr. Charles Weaver, NCDENR-DWQ, 1617 Mail Service Center, Raleigh, NC 27699-
1617
www.duke-energy.com

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SPRING SEDIMENT AND HEXAGENIA SAMPLING IN LAKE WYLIE
SEDIMENT ANALYSIS
Methods
Spring sampling was conducted on Lake Wylie on April 13, 2010 for the purpose of determining
the presence and abundance of Hexagenia in spring samples, as well as for sediment particle size
analyses. Samples were collected at four locations in the vicinity of the Allen Steam Station
(AS): Location A, well uplake of AS; Location B, at the mouth of the AS discharge; Location C,
at the confluence of the South Fork and Catawba River; and, Location D; a newly added location
in the South Fork upstream of the AS discharge, roughly between the Upper Armstrong bridge
and the AS discharge (Figure 1).
A petite ponar dredge (15.3cm X 15.3cm)- was used to collect five replicate samples for
sediments from each location at depths ranging from two — three meters below the surface of
Lake Wylie. The replicates were composited in labeled five -gallon buckets and returned to the
lab for processing and analysis of particle size. Samples were collected.
Each sediment composite was well mixed using a garden trawl and subsamples were removed
from each composite for individual analysis. Subsamples from each composite were placed in
Teflon -coated bake pans (5 cm in height, 20 cm in width, and 30 cm in length). Pans were filled
to the half -way mark with sediment, allowing for approximately 1,500 cm3 of sample. The
amount of .sediment from each five -grab composite was determined by filling the drying pans
with all of the material in each five -gallon bucket, counting the number of pans of material then
determining approximate volumes based on pan volumes. Pans comprising one subsample from
each composite were placed in a drying oven at 70 °C (158 °F) for at least 24.hours to insure the
samples were thoroughly dried. After drying, the material was removed from the pans, broken
up, and macerated to break up any agglomerates.
Fifteen sieves were selected to break down samples into component particle sizes. Sieve
numbers and sizes are presented in Table 1. Racks of five sieves each were placed in a
mechanical shaker (W. S. Tyler, Co., RO-TAP.) for 2.5 to 5.0 minutes. Fractions were removed
and placed in labeled sample containers. Each fraction was weighed on a one -,place, calibrated
scale (Scout -Pro, OHAUS®, max. wt. 2,000g). The composition of particle sizes was expressed
as a percentage of the total weight of the subsample analyzed.
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Results
Location A represented the largest volume of total sediment collected (-- 6,000 cm3), followed by
Locations B (-- 3,300 cm3), and D (-- 3,200 cm). Location C had the least amount of sediment
volume (-- 2,100 cm3). This indicated that while considerable viable substrate was available at
Location A, the viable sediment layer at Location C was comparatively thin and could have sat
atop underlying hardpan clay or bedrock.
At Location A, the largest percentage (<48%) of the sediment ranged in size from 125 — 250 µm,
representing mostly sand and fine sand particle sizes, with >35% of particles ranging from <53 —
125 µm, in the silt to very fine sand range (Table 1, Figure 2). The largest portion of the
substrate at Location B (>38%) was in the range of coarse sand to granular material (850 µm —
2.36 mm), with about one-third of the sediment in the sand to coarse sand range (250 — <850
gm). At Location C, over 26% of the substrate collected was greater than 4.75 mm. This large
material was composed primarily of Corbicula shells and shell fragments. Most of the remainder
of the sediment at this location (>48%) consisted of particles ranging from 125 — 850 µm, and
could be described as sand ranging from fine to coarse. Sediment at Location D was also
composed mainly of particles ranging from 125 — 850 µm in size, but this range represented a
much higher percentage of total sediment (<79%).
Clearly, Location A not only represented far more available substrate than at other sites, but
substrate particle sizes more suitable for certain macroinvertebrate species, including burrowing
mayflies. Location B substrate was considerably less suitable based on particle size, while
substrate at Location D was also unsuitable based on larger particle sizes. Location C appeared
to be less habitable than other locations based on much less available substrate and smaller
proportions of suitable particle sizes.
HEXAGENIA
Methods
Field sampling methods and laboratory methods for sorting macroinvertebrates were the same as
those presented in the five-year summary report of 2009, except that only Hexagenia were sorted
and identified from sample replicates.
N

Results
Temperatures and dissolved oxygen concentrations were recorded from sampling depths at each
location on April 13 (Table 2). Temperatures ranged from 16.1 °C at Location D, the newly
added location upstream of the AS discharge to 23.1 °C at Location B, at the mouth of the
discharge. Dissolved oxygen concentrations ranged from 7.63 mg/L at Location C to 9.16 mg/L
at Location D.
The highest numbers of Hexagenia were observed in replicates from Location A, while
Hexagenia were absent from all replicates collected from Locations C and D (Table 2). Several
Hexagenia were collected from Location B replicates. Compared to summer populations, the
mean density of Hexagenia from Location A was substantially higher than summer densities
observed at this location during 1994 — 2008 (Figure 3).
The absence of Hexagenia from Location C may have been due, in part, to the limited amount
and overall unsuitability of the substrate from that location. As to the absence of these insects
from Location D, substrate deficiencies may have also played a role since substrate type was
mostly sand and coarse sand (Table 1, Figure 2).
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Table 1. Sediment sample weights, weights of particle fractions, and percent composition of
each fraction from samples collected on Lake Wylie, NC on April 13, 2010.
Sieve.
Number
Size
Location A
Location B
Location C
Location D
Wt.
%
Wt.
%
Wt.
%
Wt.
%
4
4.75 mm
49.9
2.79
19.7
1.11
368.9
26.09
26.3
1.33
6
3.35 mm
11.4
0.64
'17.5
0.98
7.1
0.50
15.3
0.77
8
2.36 mm
10.1
0.57
21.2
1.19
13.0
1 0.92
41.6
2.1
12
1.70 mm
10.0
0.56
172.3
9.68
27.9
1.97
25.9
1.31
16
1.18 mm
10.7
0.60
266.6
14.94
52.0
3.68
66.9
3.38
20
850 µm
11.3
0.63
251.0
14.1
47.2
3.34
41.3
2.09
30
600 µm
12.6
0.70
189.8
10.66
46.1
1 3.26
38.9
1.96
40
425 µm
55.4
3.1
190.8
10.72
59.7
4.22
70.9
3.58
60
250 µm
129.9
7.26
212.7
11.95
168.7
11.93
767.1
38.74
80
180 µm
157.9
8.82
81.5
4.58
176.5
12.48
515.0
26.01
100
150 µm
43.3
2.42
35.9
2.02
79.5
5.62
114.2
5.77
120
125 µm
652.4
36.46
50.6
2.84
155.6
1 11.01
55.9
2.82
140
106 µm
40.3
2.25
41.5
2.33
41.9
2.96
31.5
1.59
200
75 µm
384.7
21.5
89.8
5.04
112.2
7.94
52.0
2.63
270
53 µm
50.3
2.81
37.6
2.11
29.5
2.09
45.8
2.31
<53 µm
159.3
8.90
102.4
1 5.75
28.1
11.99
71.7
3.62
Total
1,789.4
1,780.3
1,413.9
1
1,980.3
Table 2. Raw counts of Hexagenia observed in samples collected on April 13, 2010, and
temperatures and dissolved oxygen values recorded at the time of sampling.
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Figure 1. Macroinvertebrate and sediment monitoring locations in the vicinity of Allen Steam
Station on Lake Wylie, NC sampled on April 13, 2010.

Figure 2. Sediment particle size composition at locations sampled in Lake Wylie, NC on April
13, 2010.
Figure 3. Mean densities (no ./M2) of Hexagenia collected annually at all locations from 1994 — 2008
and densities recorded from three locations in the spring of 2010. No Hexagenia were
collected at newly added Location D.
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