2013_05_03 Buck Ash Basin - Proposed GW Assessment Work Plan

May 3, 2013 Via email: [e-mail]
Mr. Sean DeNeale
Duke Energy Carolinas, LLC
400 South Church Street
Charlotte, NC 28201-1006
Subject: Duke Energy Carolinas, LLC
Buck Steam Station Ash Basin - NPDES Permit NC0004774
Proposed Groundwater Assessment Work Plan

Dear Mr. DeNeale:
As requested by Mr. Ed Sullivan, P.E., of Duke Energy Carolinas, LLC (Duke Energy), HDR
Engineering, Inc. of the Carolinas (HDR) presents the proposed groundwater assessment work
plan. The proposed work plan presents the tasks for performing the assessment of the
exceedances of the North Carolina Administrative Code Title 15A Chapter 02L .0202 (g)
groundwater quality standards measured in groundwater monitoring wells at the Buck Steam
Station ash basin, located in Rowan County, North Carolina.
The tasks presented in the proposed groundwater assessment work plan were developed from
discussions and information provided by Duke Energy personnel and from a letter from Mr.
Andrew Pitner, P.G., North Carolina Department of Environment and Natural Resources
Division of Water Quality Aquifer Protection Section to Mr. Ed Sullivan and Mr. Allen Stowe,
both with Duke Energy, dated March 16, 2012.
HDR appreciates the opportunity to support Duke Energy with this project. Should you have any
questions regarding this submittal or need further information, please do not hesitate to contact
Bill Miller at [phone] or [e-mail].
Respectfully submitted,
HDR Engineering, Inc. of the Carolinas

William M. Miller, P.E.
Senior Engineer
Attachments: Duke Energy Carolinas, LLC, Buck Steam Station Ash Basin, NPDES Permit
NC0004774, Proposed Groundwater Assessment Work Plan

DUKE ENERGY CAROLINAS, LLC
BUCK STEAM STATION ASH BASIN
NPDES PERMIT NC0004774
PROPOSED GROUNDWATER ASSESSMENT
WORK PLAN

Prepared for:
DUKE ENERGY CAROLINAS, LLC
Charlotte, North Carolina

Prepared by:
HDR ENGINEERING, INC. OF THE CAROLINAS
Charlotte, North Carolina

May 3, 2013

BUCK STEAM STATION ASH BASIN
NPDES PERMIT NC0004774
PROPOSED GROUNDWATER ASSESSMENT WORK PLAN

TABLE OF CONTENTS

Section Title Page No.

1. INTRODUCTION ................................................................................................... 1 
2. SITE DESCRIPTION .............................................................................................. 2 
2.1 Plant Description ..........................................................................................................2 
2.2 Ash Basin Description ..................................................................................................2 
3. REGULATORY REQUIREMENTS ............................................................................ 4 
4. SITE HYDROGEOLOGY ........................................................................................ 5 
5. DESCRIPTION OF GROUNDWATER MONITORING SYSTEM .................................... 6 
6. GROUNDWATER MONITORING RESULTS ............................................................. 8 
7. GROUNDWATER ASSESSMENT WORK PLAN ........................................................ 9 
8. PROPOSED SCHEDULE FOR ASH BASIN GROUNDWATER ASSESSMENT REPORT 12 
9. REFERENCES ..................................................................................................... 13 

FIGURES
1 SITE LOCATION MAP
2 SITE LAYOUT MAP

iii
BUCK STEAM STATION ASH BASIN
NPDES PERMIT NC0004774
PROPOSED GROUNDWATER ASSESSMENT WORK PLAN

TABLE OF CONTENTS

TABLES
TABLE 1 – GROUNDWATER SAMPLING REQUIREMENTS 
TABLE 2 - EXCEEDANCES OF 2L STANDARDS 

APPENDIX
APPENDIX A - LETTER FROM ANDREW H. PITNER, P.G., REGIONAL AQUIFER
PROTECTION SUPERVISOR, NCDENR DIVISION OF WATER QUALITY,
TO ED SULLIVAN AND ALLEN STOWE, WATER MANAGEMENT,
DUKE ENERGY CORPORATION, DATED MARCH 16, 2012

1

Section 1
Introduction

Duke Energy Carolinas, LLC (Duke Energy), owns and operated the Buck Steam Station (Buck),
located on the Yadkin River in Rowan County, North Carolina (see Figure 1). The steam station
generated electricity by burning coal. Exceedances of the North Carolina Administrative Code
(NCAC) Title 15A Chapter 02L (g) groundwater quality standards (2L Standards) have been
measured in groundwater samples collected from groundwater monitoring wells at the Buck ash
basin. In a letter dated March 16, 2012, the North Carolina Department of Environment and
Natural Resources (NCDENR) Division of Water Quality (DWQ) Aquifer Protection Section
(APS) requested that Duke Energy begin additional assessment activities at stations where
measured and modeled concentrations of groundwater constituents exceed the 2L Standards at
the compliance boundary. This letter is included as Appendix A.

HDR Engineering, Inc. of the Carolinas (HDR) has prepared this proposed groundwater
assessment work plan for the Buck ash basin on behalf of Duke Energy. This document presents
a proposed work plan for performing the groundwater assessment at the monitoring wells with
measured exceedances of the 2L Standards.

2
Section 2
Site Description

2.1 Plant Description
Buck is a six unit coal-fired electricity generating facility with a capacity of 256 megawatts
located on the Yadkin River in Rowan County, North Carolina. Buck began commercial
operations in 1926. As of April 1, 2013, all of the coal fired units have been retired. Three
simple cycle combustion turbine units were in operation at the Buck site until their retirement in
October 2012. The site also contains the new Buck Combustion Turbine Combined Cycle Plant,
a 620-megawatt natural gas powered electricity generating station. The site is approximately 640
acres in area.
2.2 Ash Basin Description
The ash basin system at the plant was used to retain and settle ash generated from coal
combustion at the Buck plant. The discharge from the ash basin is permitted by the NCDENR
DWQ under the National Pollution Discharge Elimination System (NPDES) Permit NC0004774.
The ash basin system consists of three cells, the associated earthen dikes, discharge structures,
and two canals (see Figure 2). The ash generated from the combustion process was sluiced to the
Primary Cell through ash discharge lines. Flow from the Primary Cell entered the Old Primary
Cell via the Primary Cell Discharge Tower. Flow from the Old Primary Cell entered the
Secondary Cell via the Old Primary Cell Discharge Structure. Flow from the Secondary Cell
was then discharged to the Yadkin River through the Secondary Cell Discharge Tower.
The waste boundary for the Primary Cell encompasses approximately 90.0 acres. For purposes of
delineating the waste boundary, the Old Primary Cell and the Secondary Cell are considered a
single unit, encompassing approximately 80.7 acres. The Secondary Cell was developed by
increasing the elevation of the earthen dike along the Yadkin River and constructing an
intermediate dike across the ash placed in the Old Primary Cell.
The approximate pond elevations for the cells are: Primary Cell – pond elevation 705 feet; Old
Primary Cell – pond elevation 682 feet; Secondary Cell – pond elevation 674 feet. The elevation
of the Yadkin River near the site is approximately 624 feet.
Section 2 Site Description

3
The ash basin system was operated as an integral part of the station’s wastewater treatment
system. During operation of the coal-fired units, the ash basin received inflows from the
following:
 Ash removal system
 Station yard drain sump
 Stormwater flows
 Station wastewater
 Combined cycle wastewater

4
Section 3
Regulatory Requirements

The NPDES program regulates wastewater discharges to surface waters to ensure that surface
water quality standards are maintained. Buck operates under NPDES Permit NC0004774, which
authorizes discharge of the ash basin in accordance with effluent limitations, monitoring
requirements, and other conditions set forth in the permit. The NPDES permitting program
requires that permits be renewed every five years. The most recent NPDES permit renewal at
Buck became effective on January 1, 2012 and expires August 31, 2016.
In addition to surface water monitoring, the NPDES permit requires groundwater monitoring to
be conducted. Permit Condition A (11) Attachment XX, Version 1.1, dated June 15, 2011, lists
the groundwater monitoring wells to be sampled, the parameters to be analyzed, and the
requirements for sampling frequency and reporting the results. These groundwater monitoring
requirements are provided in Table 1.
The groundwater monitoring wells required by the NPDES permit, except for MW-6S and MW-
6D, were installed by Duke Energy in November and December 2010. Groundwater monitoring
wells MW-6S and MW-6D were installed in June 2006. The locations for the monitoring wells
were approved by the NCDENR DWQ APS. These monitoring wells are sampled three times
per year and the results are submitted to the NCDENR DWQ.

The compliance boundary for groundwater quality at the Buck ash basin is defined in accordance
with T15 A NCAC 02L .0107(a) as being established at either 500 feet from the waste or at the
property boundary, whichever is closer to the waste. The location of the monitoring wells, the
waste boundary, and the compliance boundary are shown on Figure 2.

5
Section 4
Site Hydrogeology
Buck and its associated ash basin system are located in the Charlotte Belt of the Piedmont
physiographic province (Piedmont). The predominant rocks of the Charlotte belt are schists and
gneisses of the amphibolite metamorphic facies, intruded by a complex sequence of plutonic
rocks. The soils that overlie the bedrock in the area have generally formed from the in-place
weathering of the parent bedrock. These soils are termed residuum (residual soils) and saprolite.
The residuum is typically finer-grained, and has a higher clay content than the underlying
saprolite. The highly weathered saprolite generally retains the overall structure and appearance
of the underlying bedrock. The saprolite grades into partially weathered rock and finally into
bedrock.
Groundwater generally occurs within the residuum and saprolite under unconfined conditions.
Often, the heterogeneous nature of the soil results in variable porosities and permeabilities both
laterally and vertically. However, low permeability units that would result in confining
conditions between the overlying soils and bedrock are generally absent. In the underlying
bedrock, groundwater occurs predominately in fractures and joints, and flow may occur under
either unconfined or confined conditions.
The Primary Cell and the Old Primary Cell ash basins are generally bounded to the southeast by
a surface water divide running approximately along Leonard Road. An un-named tributary to
the Yadkin River is located to the west of the Primary Cell, to the west of Dukeville Road. The
Yadkin River is located to the north and northeast of the ash basins. 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.

6
Section 5
Description of Groundwater Monitoring System

As discussed in Section 3, groundwater monitoring is performed in accordance with the
requirements of the NPDES permit. The groundwater monitoring for the ash basin consists of
the following monitoring wells: MW-6S, MW-6D, MW-7S, MW-7D, MW-8S, MW-8D, MW-
9S, MW-9D, MW-10D, MW-11S, MW-11D, MW-12S, MW-12D, and MW-13D. These wells
are sampled in March, July, and November of each year.
The locations for the monitoring wells were selected in consultation with the NCDENR DWQ
APS.
Monitoring wells MW-6S, MW-7S, MW-8S, MW-9S, MW-11S, and MW-12S were installed by
rotary drilling methods using hollow stem augers, with the well screen installed above auger
refusal to monitor the shallow aquifer within the saprolite layer. The screen lengths for these
wells range from 10 feet to 15 feet. The screens were installed with screen intervals ranging
from 3.8 feet to 13.8 feet below ground surface (bgs) at MW-9S to 6 feet to 21 feet bgs at MW-
8S.
Monitoring wells MW-6D, MW-7D, MW-8D, MW-9D, MW-10D, MW-11D, MW-12D, and
MW-13D were installed by rotary drilling methods using hollow stem augers and by rock coring
techniques (HQ or NQ diameter barrel) with the well screen installed in the uppermost region of
the fractured rock transition zone. These wells were constructed with screen lengths ranging
from 5 feet to 15 feet. The screens were installed with screen intervals ranging from 24.2 feet to
29.2 feet bgs at MW-9D to 103.5 feet to 108.5 feet bgs at MW-6D.
Monitoring wells MW-6S and MW-6D are located to the south of the Primary Cell at the
compliance boundary and are considered by Duke Energy to represent background water quality
conditions. The other ash basin monitoring wells were also installed at or near the compliance
boundary.
The monitoring wells at Buck are equipped with dedicated bladder-type pumps.
Monitoring wells MW-1S, MW-1D, MW-2S, MW-2D, MW-3S, MW-3D, MW-4S, MW-4D,
MW-5S, MW-5D, MW-6S and MW-6D were installed by Duke Energy in 2006 as part of a
voluntary monitoring system. When the compliance groundwater monitoring program began,
Section 5 Description of Groundwater Monitoring System

7
MW-6S and MW-6D were incorporated into the compliance monitoring well system. The wells
installed as part of the voluntary monitoring system are not shown on Figure 2. No samples are
currently being collected from the voluntary wells.

8
Section 6
Groundwater Monitoring Results

Through April 2013, the monitoring wells at Buck have been sampled a total of seven times.
These monitoring wells were sampled in:
 March 2011
 July 2011
 November 2011
 March 2012
 July 2012
 November 2012
 March 2013
With the exception of boron, chromium, iron, manganese, sulfate, total dissolved solids (TDS),
and pH, the results for all monitored parameters less than the 2L Standards.
Table 2 lists the monitoring wells and the range of analytical results for the wells with
exceedances of the 2L Standards.

9
Section 7
Groundwater Assessment Work Plan

Exceedances of the 2L Standards for boron, chromium, iron, manganese, sulfate, TDS, and pH
have been measured at the groundwater monitoring wells listed in Table 2.
The proposed groundwater assessment work plan will evaluate the exceedances of the 2L
Standards to determine if the exceedances are naturally occurring, if they are caused by
particulate matter which is preserved in the sample as a result of well construction and/or
sampling procedures, or if the exceedances can be attributed to impacts from the ash basin
The groundwater assessment will include the following tasks:
Task 1 Develop a Site Hydrogeologic Conceptual Model - Available reports and data on
site geotechnical, geologic, and hydrologic conditions will be reviewed and used to
develop a site hydrogeologic conceptual model. The NCDENR document,
Hydrogeologic Investigation and Reporting Policy Memorandum, dated May 31,
2007, will be used as general guidance.
Task 2 Discuss Site History and Land Uses – A discussion of the site history and land uses
will be developed.
Task 3 Review Ash Basin Water Quality Data - Data on ash basin water quality will be
reviewed to determine if a suitable “fingerprint” of ash basin water quality can be
determined. If a suitable “fingerprint” of ash basin water quality can be determined,
the parameters and constituents associated with the “fingerprint” will be used with the
analytical results from the monitoring wells to determine if the exceedances in the
monitoring wells can be attributed to impacts from the ash basin. This data will be
provided by Duke Energy and will include NPDES-related monitoring data and
additional data collected by Duke Energy from the ash basin during the upcoming
July 2013 sampling event.
The ash basin data will be reviewed relative to groundwater sampling results for
constituents included in the ash basin groundwater monitoring program and for major
Section 7 Groundwater Assessment Work Plan

10
anion and cation data also collected during the July 2013 groundwater sampling
event. The groundwater monitoring results at the monitoring wells with exceedances
will be compared to the ash basin water quality data by utilizing water quality plots
(i.e., Piper diagrams, Stiff diagrams, or others) to understand the possible influence of
the ash basin on the groundwater quality at the monitoring wells with exceedances.
Task 4 Review Ash Leaching Data – Existing results for leaching tests on ash will be
reviewed to determine if the existing data can be used as input to the assessment or if
additional leaching tests need to be performed. Additional leaching tests will be
performed if needed and the results will be included in the assessment.
Task 5 Evaluate Well Construction Information – Well installation records will be
reviewed to determine if well construction methods are contributing to the
exceedances.
Task 6 Evaluate Exceedances Against Background Well Results – The analytical results
from the wells with exceedances will be evaluated against results from the site
background well to determine if the exceedances can be attributed to background
water quality conditions.
Task 7 Evaluate Exceedances Against Turbidity Values – Exceedances will be evaluated
against turbidity values measured during sampling to determine if the exceedances
are a result of sediment or particulate matter which is preserved in the sample as a
result of well construction or sampling methods.
Task 8 Evaluate Sampling Flow Rates – Sample collection flow rates will be evaluated to
determine if the flow rates are affecting results. The use of low flow sampling
techniques will be evaluated for selected wells.
Task 9 Collect and Analyze Filtered and Unfiltered Samples – Groundwater samples
collected for compliance monitoring are not filtered in the field. In order to provide
additional information for the assessment of exceedances, both unfiltered and filtered
samples will be collected and analyzed for all parameters listed in Table 1 except
Section 7 Groundwater Assessment Work Plan

11
chloride, nitrate, sulfate, pH, and TDS. The field filtration will be performed with an
in-line, sealed, 0.45 micron filter.
Task 10 Collect Reduction/Oxidation Field Parameters – Reduction/oxidation (redox)
processes can alternately mobilize or immobilize metals associated with naturally
occurring aquifer materials. Iron and manganese are commonly associated with
Piedmont soils. The redox conditions may be a factor in the concentrations of iron
and manganese observed at selected monitoring well locations. Additional field
parameters (i.e., dissolved oxygen and redox potential) will be collected at selected
wells to characterize the redox conditions at these locations. A discussion of the
redox conditions at the wells will be provided in the report.
Task 11 Perform Statistical Analyses of the Sampling Results – Statistical analyses of
groundwater monitoring results will be performed to determine if the exceedances
can be attributed to the ash basin water quality or if the exceedances can be attributed
to naturally occurring background concentrations. The NCDENR document,
Evaluating Metals in Groundwater at DWQ Permitted Facilities: A Technical
Assistance Document for DWQ Staff, dated July 2012, will be used as general
guidance.

12
Section 8
Proposed Schedule for Groundwater Assessment
Report

The groundwater assessment report will present the results of the work proposed in Section 7.
The next sampling event for the groundwater monitoring wells at the Buck ash basin will occur
in July 2013.
The proposed submittal schedule for the Buck ash basin groundwater assessment report is
approximately 120 days after the next scheduled groundwater sampling event at Buck or 150
days after the next scheduled groundwater sampling event if redevelopment of one or more of
the monitoring wells is required. The approximate submittal date for the Buck ash basin
groundwater assessment report based on a 120-day schedule is October 31, 2013. This proposed
schedule is contingent on approval of this proposed work plan prior to the July 2013 sampling
event.

13
Section 9
References

Harry E. LeGrand, 2004, A Master Conceptual Model for Hydrogeological Site Characterization
in the Piedmont and Mountain Region of North Carolina, A Guidance Manual, North
Carolina Department of Environment and Natural Resources Division of Water Quality,
Groundwater Section.

FIGURES

High Rock Lake
Yad
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R
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Ash BasinAsh BasinAsh Basin
Buck Steam Station
700700650
700650
650 65065
0
650
6506507007006
5
0 650650
650
70070070065
0 650650
650
650
6
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650700
700 700
7007
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L o n g F e r r y R d
Long
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RdLeonardR dLeonar
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Leonard RdLeonard RdDukeville RdDukevill
eRd
1,000 0 1,000 2,000
Notes:
1. Sources: US Topo; 2011, USGS National Map
Aerial Imagery; 2010 North Carolina
Statewide Orthoimagery, NC Geospatial &
Technology Management Office
SCALE (FEET)
HDR Engineering, Inc.of the Carolinas
License Number: F-0116
440 South Church Street, Charlotte, NC 28202
SITE LOCATION MAPBUCK STEAM STATIONDUKE ENERGY CAROLINAS, LLCROWAN COUNTY, NORTH CAROLINA
DATE
FIGURE
May 3, 20131

TABLES

TABLE 1 – GROUNDWATER SAMPLING REQUIREMENTS

Well Nomenclature Parameter Description Frequency
Monitoring Wells:
MW-6S, MW-6D,
MW-7S, MW-7D,
MW-8S, MW-8D,
MW-9S, MW-9D,
MW-10D, MW-11S,
MW-11D, MW-12S,
MW-12D, MW-13D
Antimony Chromium Nickel Thallium
March, July,
November
Arsenic Copper Nitrate Water Level
Barium Iron pH Zinc
Boron Lead Selenium
Cadmium Manganese Sulfate
Chloride Mercury TDS
TABLE 2 - EXCEEDANCES OF 2L STANDARDS   Boron Chromium Iron Manganese Sulfate TDS pH 2L Standard 700 µg/L 10 µg/L 300 µg/L 50 µg/L 250 mg/L 500 mg/L 6.5 - 8.5 SU Well ID Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances µg/L µg/L µg/L µg/L mg/L mg/L SU Comments Concerning Exceedances MW-6S No Exceedances No Exceedances 323 59 – 114 No Exceedances No Exceedances 4.5 – 5.5 The only iron concentration exceedance occurred during first sampling event. The last 6 sampling events iron has been <2L Standard. Results for manganese and pH have generally been consistent over the period of monitoring. MW-6D No Exceedances No Exceedances No Exceedances No Exceedances No Exceedances No Exceedances 5.8 The only pH exceedance occurred in July 2012. MW-7S No Exceedances No Exceedances No Exceedances 57 - 71 No Exceedances No Exceedances 5.8 – 6.2 Three of the monitoring events have had manganese concentrations >2L Standard, and four events have been <2L Standard. pH has generally been consistent over the period of monitoring. MW-7D No Exceedances No Exceedances 334 – 453 87 – 129 No Exceedances No Exceedances 6.4 Three of the monitoring events have had iron concentrations >2L Standard, and four events have been <2L Standard. Manganese concentrations have been <2L Standard during 4 of the 7 monitoring events including the last 3 events. November 2012 and March 2013 sampling events are the lowest manganese concentrations measured during the monitoring period (19 µg/L). pH has been decreasing over the period of monitoring. March 2013 sampling event is the first pH exceedance. MW-8S No Exceedances No Exceedances 559 – 2,000 62 – 360 No Exceedances No Exceedances 6.0 – 6.3 Iron concentrations may be affected by turbidity which has ranged from 2 to 70 NTUs. When turbidity has been <10 NTUs the measured iron concentrations have been <2L Standard (the case in 3 of the 7 sample events. Manganese (Mn) concentrations may also be affected by turbidity. One Mn exceedance occurred when turbidity was <10 NTUs, but concentrations were < 2L Standard during the other 2 low turbidity (<10 NTUs) events. Well may be a candidate for low flow sampling. pH has generally been consistent over the period of monitoring. MW-8D No Exceedances No Exceedances 353 No Exceedances No Exceedances No Exceedances 6.2 – 6.4 Only iron exceedance occurred during the first monitoring event; last 6 events iron has been below 2L Standard. pH has generally been consistent over the period of monitoring. MW-9S No Exceedances No Exceedances 366 – 584 55 – 88 No Exceedances No Exceedances 5.3 – 6.5 Iron exceedances of 2L Standard were during first 2 sampling events. Manganese concentration was >2L Standard during first 3 of the 7 monitoring events, but has been <2L Standard during the last 4 sampling events and the concentrations overall appear to be generally decreasing. pH has generally been consistent over the period of monitoring. MW-9D No Exceedances No Exceedances 370 No Exceedances No Exceedances No Exceedances 5.2 – 6.5 Only iron exceedance occurred during first monitoring event (turbidity = 15 NTU). pH has generally been consistent over the period of monitoring.
TABLE 2 - EXCEEDANCES OF 2L STANDARDS   Boron Chromium Iron Manganese Sulfate TDS pH 2L Standard 700 µg/L 10 µg/L 300 µg/L 50 µg/L 250 mg/L 500 mg/L 6.5 - 8.5 SU Well ID Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances Range of Exceedances µg/L µg/L µg/L µg/L mg/L mg/L SU Comments Concerning Exceedances MW-10D No Exceedances No Exceedances 335 310 – 1,130 320 – 350 561 – 630 5.5 – 6.3 Only iron exceedance occurred during first monitoring event. Manganese concentrations and pH appear to be generally decreasing over the monitoring period. Sulfate and TDS have generally been consistent over the period of monitoring. MW-11S No Exceedances No Exceedances 570 – 870 106 – 242 No Exceedances No Exceedances 5.9 – 6.3 Iron concentrations have been <2L Standard during 5 of the 7 monitoring events. Manganese concentrations appear to be generally decreasing over the monitoring period. pH has generally been consistent over the period of monitoring. MW-11D 1,130 – 1,290 No Exceedances 318 – 3,230 56 – 122 No Exceedances No Exceedances 5.7 – 6.0 Boron concentrations and pH have generally been consistent over the period of monitoring. Iron and manganese concentrations have been generally increasing over the period of monitoring. Turbidity has also generally been increasing from an initial reading of 13 NTU to 277 NTU during the March 2013 monitoring event. Well may need redevelopment. MW-12S No Exceedances 11 – 28 478 52 – 444 No Exceedances No Exceedances 5.9 – 6.3 Chromium exceedances occurred only during the first 3 monitoring events. Chromium has been less than the method reporting limit (MRL) during the last 4 monitoring events. Only iron concentration exceedance occurred during the first monitoring event. Manganese concentrations have been generally decreasing over the period of monitoring with the lowest concentration measured during the March 2013 monitoring event (52 µg/L). pH has generally been consistent over the period of monitoring. MW-12D No Exceedances No Exceedances 530 – 1,070 No Exceedances No Exceedances No Exceedances 5.9 – 6.4 Iron concentration has been generally decreasing over the monitoring period, along with turbidity. Iron concentrations have been <2L Standard the last 3 monitoring events. pH has generally been consistent over the period of monitoring. MW-13D No Exceedances No Exceedances No Exceedances No Exceedances No Exceedances No Exceedances 6.1 – 6.4 pH readings have generally been consistent over the period of monitoring.

APPENDIX A
LETTER FROM ANDREW H. PITNER, P.G., REGIONAL AQUIFER
PROTECTION SUPERVISOR, NCDENR DIVISION OF WATER QUALITY,
TO ED SULLIVAN AND ALLEN STOWE, WATER MANAGEMENT, DUKE
ENERGY CORPORATION, DATED MARCH 16, 2012