20151005 Duke Ash Basin SELC Draft HDR response final_20160418

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Memo
Date: October 7, 2015
Project: Duke Energy Groundwater Assessment Program
Comprehensive Site Assessment Reports
To: Ed Sullivan, Duke Energy
From: Rick Miller, Bill Miller, Malcolm Schaeffer, Scott Spinner, Chad Hearn, Tom
Yanoschack and Ty Ziegler, HDR
Subject: Southern Environmental Law Center Response Letter dated October 1, 2015
HDR Comments
On October 1, 2015, the Southern Environmental Law Center (SELC) provided comments
to the North Carolina Department of Environmental Quality (NCDEQ) (formerly the North
Carolina Department of Environment and Natural Resources [NCDENR]) describing what
the SELC considered to be critical flaws in Duke Energy's Comprehensive Site
Assessment (CSA) reports for Buck Steam Station (Buck), Allen Steam Station (Allen),
and Cliffside Steam Station (Cliffside). In particular, the SELC asserted that Duke Energy
(and by extension its consultant, HDR):
(1) offered conclusions to DEQ and the public unsupported by its currently
incomplete assessments,
(2) failed to evaluate the groundwater in the deep bedrock aquifer closest to the
neighboring drinking water wells,
(3) failed to drill monitoring wells that would tap into groundwater at the same depths
as neighboring drinking water supply wells,
(4) made assumptions that dramatically underestimate the speed at which
contaminated groundwater travels, and
(5) ignored or failed to collect critical data from neighboring drinking water wells
needed to accurately evaluate whether coal ash pollutants are contaminating
those wells.
HDR has considered these comments and offers the following responses.
hdrinc.com
440 S. Church Street, Suite 900; Charlotte, NC 28202
T 704.338.6700 F 704.338.6760

Ed Sullivan
October 7, 2015
SELC Assertion 1: Duke's Incomplete CSAs Do Not Support Its Public
Assertions
HDR Response: The CSA reports prepared by HDR provide substantive investigation
and sampling results that support the conclusions presented to NCDEQ and the public.
Based on the results of the site investigations, HDR identified supplemental investigation
needs and presented those needs as data gaps in each CSA report. The NCDEQ, Duke
Energy, and HDR understood and discussed the possibility of developing additional data
needs as a result of the site investigation process. Similar to HDR's experience in other
brownfield site assessments and remediation projects, our approach to the CSAs began
with an assessment of the overall groundwater contamination area. We then refined the
investigations to more fully examine site -specific and constituent -specific areas of
potential contamination, or to eliminate areas from potential risk associated with source -
related constituents. .
The purpose of the CSAs was to characterize the extent of contamination resulting from
historical production and storage of coal ash, evaluate the chemical and physical
characteristics of the contaminants, investigate the geology and hydrogeology of the site
including factors relating to contaminant transport, and examine risk to potential receptors
and exposure pathways. HDR is confident that the CSAs do, in fact, determine the
source -related constituents, provide substantive (but not conclusive) information regarding
the underlying geology and hydrogeology of the sites, and assess groundwater flow at the
sites and the potential risk to public and private drinking water wells and surface water
based upon the respective groundwater flow assessments. Where there were findings of
elevated concentrations of source -related constituents indicating potential contamination
in areas of incomplete groundwater data, HDR recommended, and is implementing in
collaboration with Duke Energy, a supplemental data collection and evaluation program to
refine the delineation of the horizontal and vertical extent of contamination and to identify
potential risk exposure to receptors.

Ed Sullivan
October 7, 2015
SELC Assertion 2: Duke Failed to Study the Bedrock Aquifer in the Area
Nearest to the Residential Drinking Water Wells
HDR Response: The intent of the CSAs was to investigate the geology and hydrogeology
of the sites (emphasis added) including factors relating to contaminant transport, and
examine exposure pathways and potential risks to receptors. The Groundwater
Assessment Work Plans (Work Plans) were submitted to NCDEQ for review and approval
prior to beginning field investigation activities. The Work Plans included what was believed
to be an adequate number of bedrock wells at locations and depths appropriate to
characterize the geology, the hydraulic properties, and the groundwater flow and direction
within the bedrock flow layer. Bedrock wells were established upgradient of the ash basins
to discern the background constituent concentrations within the upper layers of the
bedrock strata.
At the Buck site, the upgradient background well (BG-1 BR located in the southwest corner
of the Duke Energy property boundary near Dukeville Road and Leonard Road) was
reported as dry due to insufficient water recharge to collect enough volume of water for
general chemistry samples. There was however sufficient volume of water at this well to
collect chemical speciation analysis samples. Results of speciation analysis were reported
in the CSA report (Table 10-7) and indicate constituent concentrations are similar to
background levels, with the exception of chromium. The CSA report data gap section
recommended that a replacement bedrock well for BG-1 BR be installed (labeled GAP
Well 6BR) if the well is unable to produce sufficient volume of water for future sampling
events.
Contrary to the SELC comment, HDR did install bedrock wells along the portion of the site
near the residential drinking water wells. HDR installed two bedrock wells east and
southeast of the Buck ash basins (GWA-2BR and GWA-3BR). Note that these wells
appear on Figure 1 of the SELC's October 1, 2015 response letter. Background bedrock
well BG-3BR is located approximately 1,300 feet topographically downgradient of private
drinking water supply wells at houses along Leonard Road. Analytical results from these
wells for U.S. Environmental Protection Agency (USEPA) detection monitoring
constituents boron, sulfate and Total Dissolved Solids (TDS) found either non -detectable
or low concentrations (CSA report Table 10-5), confirming no migration of source -related
constituents towards the private drinking water wells along Leonard Road.
Consideration could be given to installing one or two additional bedrock data gap wells to
further confirm the lack of source -related constituents adjacent to existing monitoring well
MW-8 S/D (shallow/deep) and the proposed data gap well GAP-4S/D.
SELC Assertion 3: None of Duke's Bedrock Monitoring Wells Serve as an
Apples -to -Apples Comparison with Off -Site Drinking Water Wells at Buck.
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Ed Sullivan
October 7, 2015
HDR Response: As noted in the response above, HDR did install bedrock wells along the
southern portion of the Buck site. The SELC states that the bedrock wells were improperly
constructed. All site wells were properly installed and constructed by certified well drillers,
in accordance with North Carolina well construction regulations, under the direction of a
Professional Geologist.
The well screen length was determined in consultation with NCDEQ and based on using a
discrete length to monitor the selected zone(s) in the bedrock. In bedrock wells, the
depths where the screens were installed were based on the Professional Geologist's
interpretation of the rock cores collected from the boring and on in -situ hydraulic
conductivity tests performed in the boring, and were placed in the predominant
groundwater flow zone.
In addition, it appears that the SELC is confused about what water levels in monitoring
wells (and drinking water wells) indicate. The S wells are screened across the water table
and provide water level data for inferring the general flow direction of the upper flow layer.
The D and BRU well screens are located in the upper portion of the bedrock, generally the
weathered/fractured bedrock of the transition zone, while the BR wells are screened in the
fractured, unweathered bedrock. The water levels in wells screened below the water table
are not static water levels; rather, they represent the potentiometric level of the water at
those depths. These wells provide data points used to produce the potentiometric contour
maps, which show the direction of groundwater flow in the transition zone and the bedrock
underlying the ash basin(s). Based on these three site -specific groundwater maps, any
source -related constituents in the groundwater flow downgradient in all three flow layers,
away from the residential wells.
SELC Assertion 4: Errors in Analysis and Faulty Assumptions Undermine
the Assurances Offered in Duke's Allen and Cliffside CSAs.
Allen Groundwater Assessment Discussion
SELC Comment: Duke used an incorrect method to compute hydraulic conductivity
values for all of the bedrock aquifer slug tests at Allen. As a result of these errors, the
Allen CSA underestimates the actual, measured bedrock permeability by a factor of 50 to
100.
HDR Response: Hydraulic conductivity for bedrock slug tests at Allen was calculated
using the fractured rock model developed by Barker and Black (1983). This method is
different than the method that was used to estimate hydraulic conductivity for the overlying
ash, fill, alluvium, and soil/saprolite. Use of the Barker and Black (1983) model was
deemed appropriate by HDR, as the method provides appropriate hydraulic conductivities

Ed Sullivan
October 7, 2015
for fractured bedrock and is consistent with recommendations of NCDEQ Division of
Water Quality (2007).'
SELC Comment: These errors led Duke to offer unsupported hydrogeologic
interpretations and conclusions in the Allen CSA with regard to groundwater flow and
chemical transport rates and directions (horizontal and vertical).
HDR Response: Chemical transport rates were not discussed in the CSA report. HDR
specified in the first paragraph of Section 13 of the report that contaminant fate and
transport would be a component of the groundwater modeling to be included in the
Corrective Action Plan (CAP). Additionally, hydraulic conductivity has no effect on the
direction of groundwater flow, only the rate. The horizontal and vertical gradients affect
overall groundwater flow direction.
SELC Comment: Because the permeability of the weathered bedrock is similar to the
overlying soils, the CSA interpretation that the bedrock acts as a lower confining layer for
groundwater flow and chemical transport is incorrect.
HDR Response: Nowhere in the Allen CSA report is there an "interpretation that the
bedrock acts as a lower confining layer for groundwater flow and chemical transport".
Also, the CSA report does not state that constituents of interest (COls) cannot migrate into
the bedrock. The CSA states that the groundwater system at Allen is an interconnected,
unconfined aquifer system.
SELC Comment: Therefore, the CSA conclusions that (1) all site groundwater discharges
into the Catawba River (Lake Wylie) and (2) groundwater and dissolved coal -ash
constituents are restricted from migrating to the west toward the residential and water
supply wells are not supported by the data. The significant hydraulic conductivity of the
bedrock formation is further demonstrated by the large measured downward hydraulic
gradient (i.e., downward flow component) from overburden to bedrock at many well
clusters across the site.
HDR Response: The first sentence of SELC's comment appears to be based completely
on the assertion that the hydraulic conductivity of the bedrock has been underestimated
and that lower hydraulic conductivity has an effect on groundwater flow direction. The
Groundwater Flow and Potentiometric Surface Maps (CSA report Figures 6-5, 6-6, and 6-
7), prepared based upon investigation data, clearly show eastward groundwater flow
toward Lake Wylie. This flow pattern is consistent with the LeGrand conceptual model for
hydrogeological site characterization of Piedmont sites in North Carolina where
groundwater flows from regions of higher potential discharging into streams and rivers.
NCDNER DWQ. 2007. Performance and Analysis of Aquifer Slug Tests and Pumping Tests
Policy: Memorandum dated May 31, 2007.
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Ed Sullivan
October 7, 2015
The Shallow Water Table Surface - Shallow Wells (S) and Potentiometric Surface - Deep
Wells (D) maps (CSA report Figures 6-5 and 6-6) have a northern flow component toward
the Allen discharge canal as would be expected.
Regarding the second sentence of SELC's comment, hydraulic gradients and hydraulic
conductivity are not interrelated; rather, they are independent of each other. Hydraulic
conductivity is a material property, whereas hydraulic gradient is a geometric property.
Therefore, a large measured downward hydraulic gradient is unrelated to the hydraulic
conductivity of the material. These two independent parameters along with the effective
porosity of the material are used to estimate seepage (groundwater) velocities.
SELC Comment: Of particular importance is the strong downward groundwater flow
component along most of the eastern site boundary next to the Catawba River. Based on
the hydraulic data presented in the CSA, at most only a portion of the site groundwater is
discharging into the river. Much more hydrogeologic data (e.g., vertical hydraulic;
gradients beneath the river and in the riverbed, riverbed permeability, soil permeability
beneath the river bed, etc.) are needed to address this major data gap.
HDR Response: Three well pairs located along the eastern property boundary next to the
Catawba River indicate upward hydraulic gradients (upward flow, not downward flow as
stated by SELC). The gradients are shown in Table 11-14 in the Allen CSA report. This
upward flow indicates groundwater discharge towards the Catawba River. HDR does not
believe that there are data gaps concerning this matter. As described above, this flow
pattern is consistent with the LeGrand hydrogeological conceptual model for sites in the
Piedmont region.
SELC Comment: In a related error, Duke Energy's mistaken interpretations of bedrock
permeability led Duke to prematurely dismiss the potential for westward and downward
groundwater flow and contaminant transport to impact the many private and public water
supply wells located very close to the compliance boundary. No off -site bedrock
monitoring wells were installed and hydraulic analyses were not performed to evaluate the
effects of groundwater extraction from these wells on three-dimensional site groundwater
flow. These CSA data gaps are even more important in light of Duke's errors in measuring
bedrock permeability.
HDR Response: SELC is correct in saying there were no bedrock wells installed off -site
to the west of the ash basin. However, off -site bedrock wells were not included in the
NCDEQ-approved Work Plan. NCDEQ stated in their November 5, 2014 comment letter
that, "Specifically, continuous core shall be collected from land surface to a depth of at
least 50 feet into fresh, competent bedrock at a sufficient number of locations inside and
outside of ash basin to understand the flow system in areas proposed for modeling and
(or) areas of contaminant concern." Proposed bedrock well locations were presented to
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Ed Sullivan
October 7, 2015
NCDEQ in the December 30, 2014 Work Plan and additional bedrock well locations were
added per the NCDEQ-issued Conditional Approval letter dated February 24, 2015.
There were two shallow and deep well pairs installed off -site to confirm hydraulic
gradients and groundwater flow direction to the west of the northwest extent of the ash
basin (inactive ash basin). Groundwater elevations confirmed groundwater flow direction
is consistent with the slope -aquifer system and is from west to east toward the ash basin.
Additional wells west of the ash basin have been proposed as part of the data gap work to
better understand what localized effect the numerous private drinking water supply wells
have on groundwater in the residential area adjacent to the Allen site.
Cliffside Groundwater Assessment Discussion
Based on groundwater flow directions determined for the shallow and deep monitoring
well network installed at the Cliffside site, groundwater flow is predominantly to the north
toward the Broad River with Suck Creek, having a localized effect on groundwater flow
direction toward the creek in the central portion of the Cliffside site. No groundwater
elevation information gathered during the CSA investigation or the ground surface
topography suggests that groundwater flow direction at the site is to the east (toward
residential properties) or south (toward off -site water supply wells). Pumping influence
was not taken into consideration due to the lack of information regarding private water
supply well construction and pumping rates. HDR is not aware of any identified data gaps
suggesting that additional wells be installed to further delineate the horizontal extent of
contamination in the area of private drinking water wells.
A separate water supply well evaluation is being conducted for select water samples
collected by NCDEQ from drinking water wells surrounding the Cliffside site. This
evaluation will take into consideration water results collected by NCDEQ in the offsite
drinking water wells and will provide a comparison to background monitoring well
concentrations reported at the Cliffside site, regional naturally occurring concentrations,
and source area porewater concentrations reported for the Cliffside site. Results of this
evaluation will address the SELC's concern regarding whether the drinking water wells are
being affected by the ash storage areas at Cliffside, which was not a specific objective
outlined in the NCDEQ approved Work Plan.
SELC Assertion 5: Duke Disregarded Groundwater Analytical Data for
Sampled Off -Site Drinking Water Wells near Buck, Allen, and Cliffside.
HDR Response: The screening -level human health risk assessment provided in the CSA
reports incorporated results from site sampling activities, including those that indicated
potential impacts from the ash basins. The risk assessment was performed using on -site
constituent concentrations from impacted areas; therefore, the results are conservative as
no attenuation was assumed in the initial assessment. Additionally, there was no
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Ed Sullivan
October 7, 2015
consideration of background levels of metals in the screening -level risk assessment at this
stage of the evaluation.
The CSA does not incorporate (it was not the purpose of the CSA) the off -site
groundwater data generated from the NCDEQ Drinking Water Well Water Testing
Program sampling and analysis. Furthermore, the specific well depths, screening levels,
construction methods, and pumping rates and frequency are unknown, as NCDEQ did not
provide this information. Thus, a detailed analysis of the drinking water wells' impact to
groundwater was not able to be performed. Based on consultation with Duke Energy and
NCDEQ, a summary of the NCDEQ-reported data was included in the CSA report.
HDR is preparing an evaluation of analytical results collected from the NCDEQ Drinking
Water Well Sampling Program for each of the Duke Energy fossil stations located in North
Carolina. This evaluation will consider the NCDEQ's analytical results and information
collected for the CSA, regional background water quality data, and analytical results from
a Duke Energy employee drinking water well sampling program for wells located in the
same region as the particular plant. The evaluation will determine if groundwater
exceedances in the NCDEQ sampled wells can be attributed to the ash basins.
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