NC0004961_Topographic Map/Discharge Assessment Plan_20160503

RECEIVED/ FN
MAY U 3 "1016
Water Quality
permitting Section

DUKE
ENERGY.
April 28, 2016
Jeffrey O. Poupart
Water Quality Permitting Section Chief
Division of Water Resources
Department of Environmental Quality
State of North Carolina
1617 Mail Service Center
Raleigh, NC 27699-1617
Harry K. Sidens
Senior Vice President
Environmental, Health & Safety
526 S Church Street
Mail Code EC3XP
Charlotte, NC 28202
[phone]
Subject: March 2, 2016 Insufficiency of Discharge Assessment Plans — Duke Energy Carolinas,
LLC and Duke Energy Progress, LLC
Dear Mr. Poupart:
This responds to your letter of March 2, 2016 to Duke Energy Carolinas, LLC and Duke Energy
Progress, LLC on March 2, 2016 regarding Duke Energy's proposed Discharge Assessment
Plans.
With regard to your letter describing changes in Section 3.2.2 Observation and Sampling:
• The discussion must include a statement noting that jurisdictional determinations regarding
the extent of waters of the United States and their relationship with identified seeps at the
subject facilities will be obtained from the United States Army Corps of Engineers (USA
COE).
Duke Energy does not yet have jurisdictional determinations from the US Army Corps of
Engineers for the relevant areas at all of the twelve sites mentioned in your letter. We submitted
applications for jurisdictional determinations in September, October, and November 2015 and
have since worked with the Corps of Engineers to schedule site visits and provide draft plats for
approval. Nonetheless, the timing of the approved jurisdictional determinations is up to the
Corps and outside of Duke's control. To date, out of these twelve sites, only Buck has an
approved jurisdictional determination, but we do not yet have the signed plats.
We will submit the maps you have requested for each site on a rolling basis, within a reasonable
period after the jurisdictional determinations are complete. In order to address the changes
described in your March 2, 2016 letter, we have added the following text at the start of Section
3.2.2.
Jurisdictional determinations regarding the extent of waters of the United States and
their relationship with identified seeps at the subject facilities will be obtained from the
United States Army Corps of Engineers (USA COE). Until jurisdictional determinations
are finalized by USA COE, preliminary information will be used to evaluate the seeps as
described in the section below.
RECEIVED/NCDEG/DWR
MAY 0 3 2016
Water Quality
Permitting Section

The second change in Section 3.2.2 described in your letter is as follows.
The schedule for water quality sampling of the seeps and related jurisdictional waters must
be more frequent than the semi-annual basis stated in the proposed DAPs. DWR
recommends a monthly monitoring schedule, consistent with the conditions described in the
DAPs' general assessment requirements, for all identified seeps that will continue for twelve
( 12) months. After that time, monitoring may be reduced to a semi-annual basis until such
monitoring becomes a requirement of the NPDES permit.
We do not believe sampling monthly as part of a revised Discharge Assessment Plan is
warranted. For the larger receiving waters, data is available from sampling associated with
NPDES permits that demonstrates the lack of impact on the larger surface waters of the state.
In addition, we are conducting weekly observations of all AOWs on a dam or dike slope,
sampling any new seeps, and providing the analytical results to DEQ. We recommend the
sampling frequency under the DAPs remain at twice/year with the weekly inspections of dam
slopes for any new seeps with data provided to DEQ. We recommend that we collectively focus
our resources on the completion of all of the NPDES Wastewater Permits for the Duke Energy
sites and implement appropriate sampling frequency for each of the permitted seeps in that
document .
However, in order to address the changes described in your March 2, 2016 letter, we have
added the following text in Section 3.2.2.
In addition to sampling conducted with the semi-annual assessments, additional seep
sampling will be conducted at locations and at a frequency as determined through
discussions with NC DEQ personnel.
We would like to work with DEQ to achieve alignment of the various (present and future)
documents involving required seep activities including:
• Discharge Assessment Plans
• Discharge Identification Plans
• NPDES Wastewater Permits
• EPA requirements
• Any future legal agreements with either DEQ or EPA
Duke Energy is committed to providing the Department with additional information to facilitate
the issuance of new NPDES Wastewater permits. The issues are complex and require special
consideration, as illustrated by the time elapsed since the permit applications were submitted.
We look forward to working with you further to resolve the issues identified here on a mutually
acceptable schedule.
Sincerely,
Harry Sideris
Senior Vice President
Environmental, Health and Safety

Riverbend Steam Station Ash Basin
Topographic Map and
Discharge Assessment Plan
NPDES Permit NC0004961
April 29, 2016

Contents
Duke Energy Carolinas, LLC I Discharge Assessment Plan I
Riverbend Steam Station Ash Basin J �� <
CONTENTS
Paqe
Contents......................................................................................................................................i
Figuresand Tables.....................................................................................................................ii
Section1 -
Introduction..............................................................................................................
1
Section 2 -
Site Background.......................................................................................................
3
2.1
Plant Description..................................................................................................3
2.2
Ash Basin Description..........................................................................................3
2.3
Site Geologic/Soil Framework..............................................................................4
2.4
Topographic Map and Identification of Discharges...............................................4
2.4.1 Engineered Drainage System for Earthen Dam........................................5
2.4.2 Non -Engineered Seep Identification.........................................................5
Section 3 -
Discharge Assessment Plan.....................................................................................
6
3.1
Purpose of Assessment.......................................................................................6
3.2
Assessment Procedure........................................................................................6
3.2.1 General Assessment Requirements.........................................................6
3.2.2 Observation and Sampling.......................................................................7
3.2.3 Evaluation................................................................................................9
3.2.4 Assessment Reporting.............................................................................9
Section4 -
References..............................................................................................................10

Duke Energy Carolinas, LLC ! Discharge Assessment Pian �J�
Riverbend Steam Station Ash Basin
FIGURES AND TABLES
Figures and Tables
Figure 1 — Site Location Map
Figure 2 — Topographic Map
Table 1 — Seep and Associated Discharge Locations and Descriptions
Table 2 — Laboratory Analytical Methods
Table 3 — Riverbend Steam Station — Example of Surface Water/Seep Monitoring Flow and
Analysis Results Table

Duke Energy Carolinas, LLC Discharge Assessment Plan �1J�
Riverbend Steam Station Ash Basin
SECTION 1 - INTRODUCTION
Section 1 - Introduction
The purpose of this document is to address the requirements of North Carolina General Statute
(GS)130A-309.210(a) topographic map and (b) Assessment of Discharges from Coal
Combustion Residuals Surface Impoundments to the Surface Waters of the State, as modified
by North Carolina Senate Bill 729, for the Riverbend Steam Station (RBSS) ash basin operated
under National Pollutant Discharge Elimination System (NPDES) Permit NC0004961.
The following requirements are contained in General Statute (GS) 130A -309.210(a):
(1) The owner of a coal combustion residuals surface impoundment shall identify all
discharges from the impoundment as provided in this subsection. The requirements for
identifying all discharges from an impoundment set out in this subsection are in addition
to any other requirements for identifying discharges applicable to the owners of coal
combustion residuals surface impoundments.
(2) No later than December 31, 2014, the owner of a coal combustion residuals surface
impoundment shall submit a topographic map that identifies the location of all (i)
outfalls from engineered channels designed or improved for the purpose of collecting
water from the toe of the impoundment and (ii) seeps and weeps discharging from the
impoundment that are not captured by engineered channels designed or improved for
the purpose of collecting water from the toe of the impoundment to the Department.
The topographic map shall comply with all of the following:
a. Be at a scale as required by the Department.
b. Specify the latitude and longitude of each toe drain outfall, seep, and weep.
c. Specify whether the discharge from each toe drain outfall, seep, and weep is
continuous or intermittent.
d. Provide an average flow measurement of the discharge from each toe drain outfall,
seep, and weep including a description of the method used to measure average flow.
e. Specify whether the discharge from each toe drain outfall, seep, and weep identified
reaches the surface waters of the State. If the discharge from a toe drain outfall,
seep, or weep reaches the surface waters of the State, the map shall specify the
latitude and longitude of where the discharge reaches the surface waters of the
State.
f. Include any other information related to the topographic map required by the
Department.
The following requirements are contained in General Statute (GS) 130A -309.210(b):
b) Assessment of Discharges from Coal Combustion Residuals Surface Impoundments to
the Surface Waters of the State. The owner of a coal combustion residuals surface
impoundment shall conduct an assessment of discharges from the coal combustion

Duke Energy Carolinas, LLC Discharge Assessment Plan �1J�
Riverbend Steam Station Ash Basin
SECTION 1 - INTRODUCTION
residuals surface impoundment to the surface waters of the State as provided in this
subsection. The requirements for assessment of discharges from the coal combustion
residuals surface impoundment to the surface waters of the State set out in this
subsection are in addition to any other requirements for the assessment of discharges
from coal combustion residuals surface impoundments to surface waters of the State
applicable to the owners of coal combustion residuals surface impoundments.
(1) No later than December 31, 2094, the owner of a coal combustion residuals surface
impoundment shall submit a proposed Discharge Assessment Plan to the
Department. The Discharge Assessment Plan shall include information sufficient to
allow the Department to determine whether any discharge, including a discharge
from a toe drain outfall, seep, or weep, has reached the surface waters of the State
and has caused a violation of surface water quality standards. The Discharge
Assessment Plan shall include, at a minimum, all of the following:
a. Upstream and downstream sampling locations within all channels that could
potentially carry a discharge.
b. A description of the surface water quality analyses that will be performed.
c. A sampling schedule, including frequency and duration of sampling activities.
d. Reporting requirements.
e. Any other information related to the identification of new discharges required by
the Department.
(2) The Department shall approve the Discharge Assessment Plan if it determines
that the Plan complies with the requirements of this subsection and will be sufficient
to protect public health, safety, and welfare; the environment; and natural resources.
(3) No later than 30 days from the approval of the Discharge Assessment Plan, the
owner shall begin implementation of the Plan in accordance with the Plan's
schedule.
The North Carolina Senate Bill 729 establishes the submittal date of this topographic map and
Discharge Assessment Plan no later than December 31, 2014.
The topographic map, developed to satisfy the requirements of GS1 30A-309.21 0(a), was
utilized as the basis for developing the assessment procedures presented in this plan, required
by GS 1 30A-309.21 0(b).

Duke Energy Carolinas, LLC i Discharge Assessment Plan 1
Riverbend Steam Station Ash Basin < ��
SECTION 2 - SITE BACKGROUND
Section 2 - Site Background
2.1 Plant Description
RBSS is a former coal-fired electricity generating facility which had a capacity of 454 megawatts
located in Gaston County, North Carolina, near the town of Mt. Holly (Figure 1). As of April 1,
2013, all of the coal-fired units have been retired. The seven -unit station began commercial
operation in 1929 with two units and then expanded to seven by 1954. During its final years of
operation, RBSS was considered a cycling station and was brought online to supplement
energy supply when electricity demand was at its highest.
2.2 Ash Basin Description
The ash basin system consists of a Primary Cell and a Secondary Cell, separated by an
intermediate dike. The ash basin at RBSS originally consisted of a single -cell basin
commissioned in 1957 and was expanded in 1979. The single basin was divided by constructing
a divider dike to form two separate cells in 1986.
The ash basin is located approximately 2,400 feet to the northeast of the power plant, adjacent
to Mountain Island Lake, as shown on Figure 2. The Primary Cell is impounded by an earthen
embankment dike, referred to as Dam #1 (Primary), located on the west side of the Primary
Cell. The Secondary Cell is impounded by an earthen embankment dike, referred to as Dam #2
(Secondary), located along the northeast side of the Secondary Cell. The toe areas for both
dikes are in close proximity to Mountain Island Lake.
The surface area of the Primary Cell is approximately 41 acres with an approximate maximum
pond elevation of 724 feet. The surface area of the Secondary Cell is approximately 28 acres
with an approximate maximum pond elevation of 714 feet. The full pond elevation of Mountain
Island Lake is approximately 646.8 feet.
The ash basin system was an integral part of the station's wastewater treatment system which
predominantly received inflows from the ash removal system, station yard drain sump, and
stormwater flows. During station operations, inflows to the ash basin were highly variable due to
the cyclical nature of station operations. The inflows from the ash removal system and the
station yard drain sump are discharged through sluice lines into the Primary Cell. The discharge
from the Primary Cell to the Secondary Cell is through a concrete discharge tower located near
the divider dike.
Although the station is retired, wastewater effluent from other non -ash -related station
discharges to the ash basin is discharged from the Secondary Cell, through a concrete
discharge tower, to Mountain Island Lake. The concrete discharge tower drains through a 30 -
inch -diameter corrugated metal pipe (CMP) into a concrete -lined channel that discharges to
Mountain Island Lake. The ash basin pond elevation is controlled by the use of concrete
stoplogs.
3

Duke Energy Carolinas, LLC I Discharge Assessment Plan �1J�
Riverbend Steam Station Ash Basin
SECTION 2 - SITE BACKGROUND
2.3 Site Geologic/Soil Framework
RBSS is located in the Charlotte terrane within the Piedmont province. The Piedmont province
is bounded to the east and southeast by the Atlantic Coastal Plain and to the west by the
escarpment of the Blue Ridge Mountains, covering a distance of 150 to 225 miles (LeGrand,
2004). Piedmont bedrock primarily consists of igneous and metamorphic bedrock. The fractured
bedrock is overlain by a mantle of unconsolidated material known as regolith. The regolith
includes, where present, the soil zone, a zone of weathered, decomposed bedrock known as
saprolite, and where present, alluvium. Saprolite, the product of chemical and mechanical
weathering of the underlying bedrock, is typically composed of clay and coarser granular
material up to boulder size and may reflect the texture of the rock from which it was formed. The
weathering product of granitic rocks may be quartz -rich and sandy -textured, whereas rocks poor
in quartz and rich in feldspar and other soluble minerals form a more clayey saprolite. The
regolith serves as the principal storage reservoir for the underlying bedrock (LeGrand, 2004).
A transition zone may occur at the base of the regolith between the soil-saprolite and the
unweathered bedrock. This transition zone of partially weathered rock is a zone of relatively
high permeability compared to the overlying soil-saprolite and the underlying bedrock (LeGrand,
2004).
RBSS is located in the Charlotte terrane of the Carolina Zone (Pippin et al., 2008), or in the
older belt terminology, the Charlotte Belt of the Piedmont physiographic province (Piedmont).
The Charlotte terrane is characterized by mostly felsic to mafic plutonic rocks which intrude a
suite of mainly metaigneous rocks and minor metasedimentary rocks (Pippin et al., 2008).
Groundwater flow paths in the Piedmont are almost invariably restricted to the zone underlying
the topographic slope extending from a topographic divide to an adjacent stream. LeGrand
describes this as the local slope aquifer system. Under natural conditions, the general direction
of groundwater flow can be approximated from the surface topography (LeGrand 2004).
Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation.
Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater
discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains
(LeGrand 2004).
The RBSS ash basin is generally bounded to the north by the earthen dike and a natural ridge
located between the south bank of the Catawba River on Mountain Island Lake and the north
side of Horseshoe Bend Beach Road. Horseshoe Bend Beach Road runs generally west to east
and is located along a local topographic divide. The geology/groundwater conditions at the site
are expected to be generally consistent with the characteristics of the conceptual groundwater
model developed by LeGrand for the Piedmont region.
2.4 Topographic Map and Identification of Discharges
A topographic map is presented in Figure 2 to meet the requirements of GS 130A -309.210(a) in
the identification of outfalls from engineered channels, as well as seeps and weeps.
4

Duke Energy Carolinas, LLC I Crscnarge Assessment P;ar FN
Steam Station Ash Bas;n
SECTION 2 - SITE BACKGROUND
Seepage is the movement of wastewater from the ash basin through the ash basin
embankment, the embankment foundation, the embankment abutments, basin rim, through
residual material in areas adjacent to the ash basin. A seep is defined in this document as an
expression of seepage at the ground surface. A weep is understood to have the same meaning
as a seep.
Indicators of seepage include areas where water is observed on the ground surface and/or
where vegetation suggests the presence of seepage. Seepage can emerge anywhere on the
downstream face, beyond the toe, or on the downstream abutments at elevations below normal
pool. Seepage may vary in appearance from a "soft," wet area to a flowing "spring." Seepage
may show up first as only an area where the vegetation is lusher and darker green than
surrounding vegetation. Cattails, reeds, mosses, and other marsh vegetation often become
established in a seepage area. However, in many instances, indicators of seeps do not
necessarily indicate the presence of seeps. Areas of apparent iron staining and/or excess iron
bacteria may also indicate the presence of a seep.
Locations of seepage at the ground surface adjacent to the ash basin have been identified and
are shown in Figure 2. These areas include the earthen embankments which impound the ash
basin as well as adjacent areas where water from the ash basin may have infiltrated into the
underlying residual materials and expressed as seepage.
2.4.1 Engineered Drainage System for Earthen Dam
Earth dams are subject to seepage through the embankment, foundation, and abutments.
Seepage control is necessary to prevent excessive uplift pressures, instability of the
downstream slope, piping through the embankment and/or foundation, and erosion of material
by migration into open joints in the foundation and abutments. The control of seepage is
performed by the use of engineered drains such as blanket drains, trench drains, and/or toe
drains. In certain cases, horizontal pipes may be installed into the embankment to collect and
control seepage. It is standard engineering practice to collect the seepage and convey seepage
away from the dam.
The RBSS ash basin dam was constructed with a drainage system, which is monitored by Duke
Energy. The drainage features, or outfalls, associated with the ash basin dam are shown as
required by GS 130A-309.210(a)(2)(i) on Figure 2.
2.4.2 Non -Engineered Seep Identification
Topographic maps of the site were reviewed to identify regions of the site where there was a
potential for ash -basin -related seepage to be present. These regions were determined by
comparing ash basin full pond elevations to adjacent topography with ground surface elevations
lower than the ash basin full pond elevation. HDR staff performed site observations within these
identified areas as part of NPDES inspections during the reapplication process during multiple
site visits from November 2013 through April 2014 and documented locations where seepage
was apparent at the time of the site visit. These seeps are identified as required by GS 130A-
309.210(a)(2)(ii) on Figure 2.
I

Duke Energy Carolinas, LLC 1 Discharge Assessment P!an FN
Steam Station Ash Basin
SECTION 3 - DISCHARGE ASSESSMENT PLAN
Section 3 - Discharge Assessment Plan
3.1 Purpose of Assessment
The purpose of the assessment is to determine whether existing, known discharges from toe
drain outfalls, seeps, and weeps associated with the coal combustion residuals surface
impoundment (ash basin) have reached the surface waters of the State and have caused a
violation of surface water quality standards as required by North Carolina General Statute 130A -
309.210(b).
Figure 2 and Table 1 present the background and downstream sampling locations to be
considered as part of this Discharge Assessment Plan (DAP). These locations may be
assessed by comparing surface water sampling analytical results of the associated background
location with the corresponding downstream location. For discharges located at the toe of a
dam, an upstream location within the channel may not have been possible to isolate for
comparison given the proximity to the ash basin, which would have the same chemical
composition as the discharge itself. As such, the upstream location was established upstream
of the ash basin and is considered "background." For discharges located a distance from the
ash basin, an identified upstream or "background" location for sampling may be compared to the
downstream portion of the discharge channel. The background and downstream sampling
locations are shown on Figure 2 with "B" and "D" identifiers, respectively, and the corresponding
seep locations associated with the sampling locations are indicated on Table 1.
3.2 Assessment Procedure
The assessment procedure associated with the Riverbend ash basin is provided within this
section. In addition to the specific requirements for the assessment, Section 3.2 also provides
the general requirements, the frequency of assessment, documentation requirements, and a
description of the surface water quality analyses that will be performed.
3.2.1 General Assessment Requirements
Assessments are to be performed in three phases as follows:
Observation and Sampling (assessment site visit)
Evaluation
• Assessment Reporting
The assessment site visit shall be performed when the background and downstream locations
are accessible and not influenced by weather events. Locations on or adjacent to the ash basin
embankments should be performed within two months after mowing, if possible. In addition, the
assessment site visit should not be performed if the following precipitation amounts have
occurred in the respective time period preceding the planned assessment site visit:
Precipitation of 0.1 inches or greater within 72 hours or
Precipitation of 0.5 inches or greater within 96 hours
The assessments shall be performed under the direction of a qualified Professional Engineer or
Professional Geologist on a semi-annual basis during two nonadjacent quarters. The date of the

Duke Energy Carolinas, LLC Discharge Assessment Plan I
Riverbend Steam Station Ash Basin J ��
SECTION 3 - DISCHARGE ASSESSMENT PLAN
initial assessment site visit shall be selected no later than 30 days from the approval of the
Discharge Assessment Plan and should fall within one of the semi-annual timeframes.
Additional seep locations that may have been identified and documented in an Identification of
New Discharge report(s) shall be reviewed prior to performing an assessment site visit, if
available.
3.2.2 Observation and Sampling
Jurisdictional determinations regarding the extent of waters of the United States and their
relationship with identified seeps at the subject facilities will be obtained from the United States
Army Corps of Engineers (USACE). Until jurisdictional determinations are finalized by USACE,
preliminary information will be used to evaluate the seeps as described in the section below.
The initial assessment site visit should be performed to document baseline conditions of the
discharge channel, including location, extent (i.e., dimensions of affected area), and flow of
each discharge. Discharge channel background and downstream locations should be verified
using a Global Positioning System (GPS) device. Photographs should be taken from vantage
points that can be replicated during subsequent semi-annual assessments.
Initial and subsequent assessment site visits shall document a minimum of the following to
respond to the requirements in 130A -309.210.1(b):
Record the most recent ash basin water surface elevation and compare to the seep and
outfall and associated discharge location surface water elevations.
For each discharge channel, the observer shall note the following as applicable on the
day of the assessment site visit:
o Is the discharge channel flowing at the time of the assessment site visit?
o Does the discharge channel visibly flow into a Water of the U.S. at the time of the
assessment site visit?
o How far away is the nearest Water of the U.S.?
o Document evidence that flow has or could reach a Water of the U.S. (e.g.,
description of flow, including extent and/or direction) and describe the observed
condition. Evidence that flow could or has reached a Water of the U.S. may be
indicated by an inspection of the adjacent and downstream topographic drainage
features.
o Observe and document the condition of the discharge channel and outfall of the
engineered channel or seep location with photographs. Photographs are to be
taken from similar direction and scale as photographs taken during the initial
assessment site visit.
Record flow rate within the discharge channel, if measureable, using the following
methods:

Duke Energy Carolinas, LLC Discharge Assessment Plan �J1�
Riverbend Steam Station Ash Basin
SECTION 3 - DISCHARGE ASSESSMENT PLAN
Timed -volumetric method: Collect a volume of water from the discharge of the PVC
pipe directly into an appropriately sized container. Measure volumes (in mL) in the
field utilizing a graduated container. Record the amount of time (in seconds)
needed to collect the volume of water and calculate the flows (in MGD) for the
timed volume.
o A V -notch weir apparatus will be installed, if necessary, during the initial
assessment site visit to impound seepage at locations with a defined channel.
Once the impounded seep reaches equilibrium discharge, flows will be measured
using the timed -volumetric method described above.
o Area -velocity method: Measure point velocities and water depth at a minimum of
20 stations along a transect setup perpendicular to the direction of flow using a
Swoffer® 3000 flow meter mounted to a standard United States Geologic Survey
(USGS) top -set wading rod. Utilize the average velocity and cross-sectional area
of the wetted channel to calculate flows in MGD.
Collect water quality samples using the following methods::
o Collect background and downstream samples during a period with minimal
preceding rainfall to minimize potential effects of stormwater runoff. Sampling
procedures should prevent the entrainment of soils and sediment in water samples
that can result in analytical results not being representative of the flow. Because
Areas of Wetness (AOWs)/seeps often have poorly defined flow channels and
minimal channel depth, conventional grab samples collected directly into laboratory
containers or intermediate vessels is not possible without disturbance and
entrainment of soils and sediments. Further, many AOWs are contiguous with low-
lying areas subject to surface water runoff and resulting heavy sediment loading
during storm events or are near surface waters subject to flooding such that
representative samples of the AOW cannot be obtained. If the facility is unable to
obtain an AOW sample due to the dry, low flow or high flow conditions preventing
the facility from obtaining a representative sample, a "no flow" result or "excessive
flow" will be recorded.
After collection, samples will be preserved and stored according to parameter -
specific methods and delivered to the laboratory under proper Chain -of -Custody
(COC) procedures.
o Analytical parameters for analysis include: Fluoride, Arsenic, Cadmium, Copper,
Chromium, Nickel, Lead, Selenium, and Mercury. This list includes all parameters
previously identified for seep sampling at Duke Energy power plants for which
relevant stream water quality standards are in place. (This list is responsive to the
statutory requirement for the discharge assessment to allow determination whether
discharges from toe drain outfalls, seeps, or weeps have reached surface waters
and caused a violation of surface water quality standards.) Analyses shall be
conducted by Duke Energy's Huntersville analytical laboratory (NC Wastewater
Certification #248) and Pace Analytical Laboratories (NC Wastewater Certification

Duke Energy Carolinas.. LLC I Discharge Assessment Plan �1J�
Riverbend Steam Station Ash Basin
SECTION 3 - DISCHARGE ASSESSMENT PLAN
# 12). Laboratory analytical methods used for each constituent are provided in
Table 2.
o Seep in-situ measurements: In-situ field parameters (temperature and pH) shall be
measured utilizing calibrated field meters either at the discharge of the seep
directly, at the discharge of the flow measurement devices, or in the water pool
created behind the device, if sufficient water depth did not exist at the device
discharge.
Mountain Island Lake and Ash Basin Sample Collection Method: Water quality
samples and in-situ measurements from the Catawba River shall be collected at a
location upstream and downstream of the ash basin. Additionally, water samples
and in-situ measurements shall be collected from an in -process ash basin location.
The grab samples shall be collected from the river and basin's surface (0.3 m)
directly into appropriate sample bottles.
In addition to sampling conducted with the semi-annual assessments, additional seep
sampling will be conducted at locations and at a frequency as determined through
discussions with NC DEQ personnel.
3.2.3 Evaluation
Evaluation of the data from the initial assessment site visit will establish baseline conditions and
will serve as the basis for comparison for subsequent assessment site visit results. Evaluation of
observations and sampling results shall include location, extent (i.e., dimensions of affected
area), and flow of each discharge. The analytical results of the upstream and downstream
locations shall be compared to the 15A NCAC 2B standards for surface water quality upon
receipt to identify potential exceedances.
3.2.4 Assessment Reporting
Each assessment site visit shall be documented by the individual performing the assessment as
described in Section 3.2.2 to meet the requirements in 130A -309.210.1(b). The report should
contain site background, observation and sampling methodology, and a summary of the
observations and descriptions of the discharge channels observed, changes in observations
compared to previous assessment events, estimates of flows quantities, and photographs of
discharges and outfalls of engineered channels designed or improved for collecting water from
the impoundment. Photographs are to be numbered and captioned. The flow and analytical
results shall be recorded and presented in tables similar to the examples provided as Tables 1
and 3. The analytical results shall be compared to the 15A NCAC 2B standards for surface
water quality and exceedances highlighted. This information shall be compiled, reviewed, and
submitted to NC DEQ within 90 days from the Observation and Sampling event.

Duke Energy Carolinas, LLC Discharge Assessment Plan �1J�
Riverbend Steam Station Ash Basin
SECTION 4 - REFERENCES
Section 4 - References
LeGrand, Harry, Sr. 2004. A Master Conceptual Model for Hydrogeological Site
Characterization in the Piedmont and Mountain Region of North Carolina, North Carolina
Department of Environment and Natural Resources.
North Carolina Department of Environment and Natural Resources. 2007. Dam Operation,
Maintenance, and Inspection Manual, North Carolina Department of Environment and
Natural Resources, Division of Land Resources, Land Quality Division, 1985 (Revised
2007).
Pippin, C.G., Chapman, M.J., Huffman, B.A., Heller, M.J., and Schelgel, M.E. 2008.
Hydrogeologic setting, ground -water flow, and ground -water quality at the Langtree
Peninsula research station, Iredell County, North Carolina, 2000-2005: U.S. Geological
Survey Scientific Investigations Report 2008-5055, 89 p. (available online at
hftp://pubs.water.usgs.gov/sir2008-5055).
,3

FIGURES
AND
TABLES

CO
„ MOUNTAIN 1 SLANA �+ /
,LAKE,
�. Pce-
J% -�--
NECK
it
ASH BASIN
V
Po«er Nlant
a/
Substa.•Water Tank
Duke, Power V Wage
RIVERBEND STEAM STATION l�
c 16
/ Bridged 48
NOTES. 6 - `�
I. SOLRCES. USGS TOPr_.CRAPFiC NAP - NT. ISLAND LAKE. -11r
TREATED 1993. USGS TOPOCRAPF+C NAP - LeKE NORMAN ,�
SOLTF.:;RE4?EC 1993 \ _ N.-.
SCALE iFEET) i - s
1
1000 0 1000 2000
SITE LOCATION MAP
RIVERBEND STEAM STATION
DUKE ENERGY CAROLINAS, LLC
GASTON COUNTY, NORTH CAROLINA
DATE
SEPTEMBER 30. 2014
FIGURE
1

DER STORAGE
J i, olk
0!"
RIVERBEND W 1 PTpo
STEAM STATION
' NPCI—S,
' 41
UR
NOTES:
1. PARCEL DATA FOR THE SITE WAS OBTAINED FROM DUKE ENERGY REAL ESTATE AND IS APPROXIMATE. SCALE (FEET
2- TOPOGRAPHY DATA PROVIDED BY DUKE ENERGY.
3. WASTE BOUNDARY IS APPROXIMATE. -300, a jcc 600
4. GROUNDWATER MONITORING WELL LOCATIONS PROVIDED BY DUKE ENERGY.
S. SEEP SAMPLING LOCATIONS WERE OBTAINED BY HDR USING A TRIMBLE HANDHELD GPS UNIT ON APRIL 29, 2014. r - 600'
6. WATER QUALITY AND NPDES SAMPLE LOCATIONS WERE PROVIDED BY DUKE ENERGY AND ARE APPROXIMATE.
7. NPDES OUTFALL LOCATIONS WERE PROVIDED BY DUKE ENERGY AND ARE APPROXIMATE-
S. S-10 NOT SAMPLED DUE TO INSUFFICIENT FLOW.
9. * INDICATES SEEP SAMPLING LOCATIONS WERE NOT RECORDED WITH GPS UNIT AND ARE APPROXIMATE.
ASH BASIN
SECONDARY CEL
H)�
LEGEND:
DUKE ENERGY PROPERTY BOUNDARY
WASTE BOUNDARY
MOUNTAIN ISLAND LAKE BOUNDARY
TOPOGRAPHIC CONTOUR
S 41 SEEP SAMPLE LOCATION
WATER QUALITY SAMPLE LOCATION
00"1 A NPDES OUTFALL LOCATION
COMPLIANCE GROUNDWATER MONITORING WELL
le VOLUNTARY GROUNDWATER MONITORING WELL
DISCHARGE SAMPLING LOCATIONS
BACKGROUND SAMPLING LOCATIONS
A
TOPOGRAPHIC MAP WITH IDENTIFIED DATE
SEEPS AND OUTFALLS DECEMBER, 2014
DUKE ENERGY CAROLINAS, LLC
RIVERBEND STEAM STATION ASH BASIN FIGURE
NPDES PERMIT #NC0004961 1 2
GASTON COUNTY, NORTH CAROLINA
an
J *7
s.
4D wn
Id
....
... .....
LEGEND:
DUKE ENERGY PROPERTY BOUNDARY
WASTE BOUNDARY
MOUNTAIN ISLAND LAKE BOUNDARY
TOPOGRAPHIC CONTOUR
S 41 SEEP SAMPLE LOCATION
WATER QUALITY SAMPLE LOCATION
00"1 A NPDES OUTFALL LOCATION
COMPLIANCE GROUNDWATER MONITORING WELL
le VOLUNTARY GROUNDWATER MONITORING WELL
DISCHARGE SAMPLING LOCATIONS
BACKGROUND SAMPLING LOCATIONS
A
TOPOGRAPHIC MAP WITH IDENTIFIED DATE
SEEPS AND OUTFALLS DECEMBER, 2014
DUKE ENERGY CAROLINAS, LLC
RIVERBEND STEAM STATION ASH BASIN FIGURE
NPDES PERMIT #NC0004961 1 2
GASTON COUNTY, NORTH CAROLINA

Table 1 - Riverbend Steam Station Ash Basin - Seep and Associated Discharge Locations and Descriptions
Notes:
1. Flow description for each Seep sample location is based on multiple site visits performed by HDR from November 2013 until April 2014
2. Flow measurements and analytical samples were collected (except for S-10) on April 29, 2014
Discharge Location
Seep
Location Coordinates
(NAD ea)
Flow
Flow Measurement
Background
Discharge Location and Discharge Sampling
Coordinates
(NAD 81)
Discharge
Description
(MGD) and Method
Locations
Location
ID
Latitude
Longitude
Latitude
Longitude
0.163
West of Primary Cell; north of Cinder Storage Area
S-1
35.365
-80.967
Continuous
timed -volumetric
1-D
35.366
-80.967
0.00056
West of Primary Cell dike
S-2
35.365
-80.966
Continuous
timed -volumetric
1-D
of Secondary Cell downgradient from the toe
S-3
35.369
-80.965
Continuous
0.West
of the Secondary Cell
35.369
-80.966
timed -volumetric
2-D
0.00562
North of Secondary Cell downgradient from the toe
S-435.371
-80.963
Continuous
of the Secondary Cell
timed -volumetric
3-D
35.371
-80.963
0.01754
North of the Secondary Cell along the toe slope of
S5
35.370
-80.963
Continuous
the northern Secondary Cell abutment
timed -volumetric
3-D
East and downgradient of the ash basin; flowing
S-6
35.367
-60.958
Continuous
0.00287
downgradient
timed -volumetric
1-8
4-D
East and downgradient of the ash basin; flowing
S-7
35.367
-80.957
Continuous
0.02085
downgradient
35.366
80.956
timed -volumetric
4-D
0.0332
East of the ash basin and Secondary Cell dike
SB
35.365
-80.956
Continuous
timed -volumetric
4-D
00245
North of the Secondary Cell north abutment near
S-9
35.371
-80.963
Continuous
.
timed .volumetric
the toe
35.371
80.963
3-D
0.01206
East of the Secondary Cell dike downstream at the
5-10
35.369
-80.960
Intermittent
toe of the dike
timed -volumetric
4-D
0.00835
East of the Secondary Cell dike downstream at the
5-11
35.369
-80.960
Continuous
timed -volumetric
toe of the dike
35.366
80.956
4-D
0.00566
At the end of a concrete channel downstream of
S-12
35.368
-80.959
Continuous
the Secondary Cell dike
timed -volumetric
4-D
Notes:
1. Flow description for each Seep sample location is based on multiple site visits performed by HDR from November 2013 until April 2014
2. Flow measurements and analytical samples were collected (except for S-10) on April 29, 2014

Table 2 — Laboratory Analytical Methods
Parameter
Method
ReportingLimit
Units
Laboratory
Fluoride (F)
EPA 300.0
1
mg/I
Duke Energy
Mercury (Hg)
EPA 245.1
0.05
Pg/1
Duke Energy
Arsenic (As)
EPA 200.8
1
Pg/I
Duke Energy
Cadmium (Cd)
EPA 200.8
1
Ng/l
Duke Energy
Chromium (Cr)
EPA 200.8
1
Pg/I
Duke Energy
Copper (Cu)
EPA 200.8
1
Ng/I
Duke Energy
Lead (Pb)
EPA 200.8
1
Ng/I
Duke Energy
Nickel (Ni)
EPA 200.8
1
Ng/I
Duke Energy
Selenium (Se)
EPA 200.8
1
Ng/I
Duke Energy

Table 3 - Riverbend Steam Station - Example of Surface Water/Seep Monitoring Flow and Analysis Results Table
Parameter
Units
S-1
S-2
S-3
S-4
S-5
S-6
S-7
S-8
S-9
S-11
S-12
Mountain
Island -
U stream
Mountain
Island -
Downstream
Fluoride
mg/I
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
< 1
Hg - Mercury (71900)
Ng/l
<
0.05
<
0.05
<
0.05
<
0.05
<
0.05
<
0.05
<
0.05
<
0.05
<
0.05
<
0.05
<
0.05
<
0.05
< 0.05
As - Arsenic (01002)
Ng/I
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
< 1
Cd - Cadmium (01027)
Ng/I
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
< 1
Cr -Chromium (01034)
Ng/I
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
< 1
Cu - Copper (01042)
Ng/I
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
1.58
1.63
1.68
Pb - Lead (01051)
Ng/I
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
<
1
< 1
Ni - Nickel (01067)
Ng/I
<
1
<
1
<
8.77
<
1
2.47
<
1
2.07
<
1
1.48
1.1
6.33
<
1
< 1
Se - Selenium (01147)
Ng/I
<
1
<
1
<
1
<
1
<
1
<
1
<
1
3.58
7
<
1
<
1
<
1
< 1
pH
s.u.
5.9
6.76
5.57
7.98
6.29
7.62
6.62
6.76
6.38
5.9
6.02
7.19
7.21
Temperature°C
15.81
16.8
16.75
15.84
16.49
16.59
15.71
17.23
16.01
15.56
17.53
17.96
17.99
Flow
MGD
0.00056
0.0044
0.00562
0.01754
0.00287
0.02085
0.0332
0.0245
0.01206
0.00835
0.00568
N/A
N/A
Notes:
1. Flow measurements and analytical samples were collected on April 29, 2014
2. N/A indicates not applicable
3. Flow was not exhibited at S-10 during the time of seep sampling