11 MSS CAP Part 2_Appx H_FINAL

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GEOCIiEMICAL
EARTH - WATER - CHEMISTRY
Technical Memorandum
To Mark Filardi / HDR Engineering, Inc.
Name
From Gregory P. Miller
Date October 28, 2015
Subject Marshall Steam Station
Corrective Action Plan
Monitored Natural Attenuation — Tier I and II
This technical memorandum presents the Tier I and Tier II evaluation of the attenuation of
compounds dissolved in groundwater at the Marshall Steam Station (MSS), Gaston County,
North Carolina. The memorandum consists of three sections: Background on Monitored Natural
Attenuation (MNA) as a remedial alternative for coal combustion products; the Findings of the
Tier I MNA Demonstration activity, followed by the Findings of the Tier II Demonstration.
Investigative and data evaluation efforts are in progress as of the date of this memorandum.
The findings herein represent the understanding as of this date and are subject to revision as
new information becomes available.
BACKGROUND
Introduction to Monitored Natural Attenuation for Groundwater
MNA is a strategy and a set of procedures used to demonstrate that physiochemical and/or
biological processes in an aquifer will reduce concentrations of undesirable substances to levels
below regulatory concern. It has been broadly applied to releases of petroleum hydrocarbons in
many hydrogeological environments. There has been less application of MNA to the
remediation of inorganic or radiologic substances in groundwater than to organic compounds.
While MNA of organic contaminants is a readily accepted remedy at the State and Federal level,
inorganic attenuation is more complicated and there is limited implementation experience in
industry, science, and government.
Metals, radionuclides, and/or other inorganic compounds are found in all aquifers. The
mechanisms that regulate their release from solids and movement through aquifers are for the
most part the same processes that control movement of inorganics in aquifers impacted by Coal
Combustion Products (CCP) leachate. These processes attenuate the concentration of
inorganics in groundwater by depositing inorganics on aquifer solids. Unlike organic
compounds that break down from hydrolysis or bacterial action, a reduction in concentration of
dissolved inorganic compounds requires water to be removed from the aquifer, or the
compounds immobilized by conversion to, or adsorption onto, solids. When demonstrated that
the mechanism and permanence of natural processes will result in attenuation of undesirable
compounds to acceptable levels, then remediation can be conducted by verifying that the
remediation proceeds as predicted. MNA relies on natural processes to remove contaminants
of concern from groundwater resulting in lower cost, and less disturbance of ground and
infrastructure.
Active remediation of inorganic compounds in the subsurface may rely on processes that are
similar to or the same as natural attenuation mechanisms. Active remediation often seeks to
improve or hasten these natural processes through chemical or biological augmentation of the
aquifer. There are not clear distinctions between the late phases of conventional groundwater
Geochemical, LLC
PO Box 1468
Socorro, NM 87801 USA
[phone]
www.geochemical.com

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 2 of 27
remediation and MNA, but such distinctions may be unnecessary. Relying on limited or low -
energy active remediation as a preliminary step, then achieving final remedial goals through
MNA is sometimes called "enhanced MNA", or "enhanced attenuation." Active remediation
methods for petroleum products often leave residual dissolved contamination that is degraded
slowly, requiring monitoring under regulations allowing MNA. Enhanced MNA is a common
strategy in hydrocarbon remediation and the principle is adaptable to inorganic MNA.
Authorizing Statutes
MNA is a federally -recognized remedial technology that can meet Resource Conservation and
Recovery Act (RCRA) Corrective Action requirements and could be included when remedial
alternatives for legacy CCP management sites are evaluated. Implementation of MNA for
inorganics at RCRA facilities is clearly and favorably proposed by the United States
Environmental Protection Agency (EPA) in the 1999 Office of Solid Waste and Emergency
Response (OSWER) Directive 9200.4-7P. In that directive MNA is defined as:
"the reliance on natural attenuation processes (within the context of a carefully
controlled and monitored site cleanup approach) to achieve site -specific remediation
objectives within a time frame that is reasonable compared to that offered by other
more active methods. The `natural attenuation processes' that are at work in such a
remediation approach include a variety of physical, chemical, or biological processes
that, under favorable conditions, act without human intervention to reduce the mass,
toxicity, mobility, volume, or concentration of contaminants in soil or groundwater.
These in -situ processes include biodegradation; dispersion; dilution; sorption;
volatilization; radioactive decay; and chemical or biological stabilization,
transformation, or destruction of contaminants."
Site characterization and assessment of MNA is different for organic and inorganic strategies.
The focus in organic MNA is on a working understanding of the transformation rates and
daughter products when organic chemicals break down in aquifers. Complex organic
compounds are reduced to water, carbon dioxide, methane, and salts by biotic and abiotic
processes in organic MNA. The science and engineering looks to the dissolved phase
concentrations derived from groundwater samples. From those analytical results and aquifer
dimensions and flow rates, the mass and flux of organic contaminants is evaluated over time.
Meeting a single objective, mass reduction of organic compounds, is all that is needed to
validate the organic MNA remedial approach.
For inorganic contaminants, the scientific and engineering investigations must consider both the
dissolved and solid phase. This is because inorganic compounds are not destroyed (with the
exception of some radioactive decay chains), but become comingled with the aquifer solids.
Inorganic compounds that are removed from the dissolved phase are transferred to the aquifer
solids in inorganic MNA processes. The undesirable inorganic compound is not destroyed; its
location is changed, from dissolved and mobile to immobile via incorporation into/onto a solid.
Because inorganics are left in place, there is stakeholder concern about the stability and
longevity of the remedial action. It is partly this uncertainty regarding inorganic MNA that drives
the need for more in-depth study. While much of the chemistry is abiotic, biotic reactions can be
very important in some inorganic MNA pathways. Inorganic MNA has two focus points:
1. Demonstrate that the attenuation process is reducing contaminant mass in groundwater;
and,
2. Demonstrate that the remediation will meet long-term stability criteria without
intervention.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 3 of 27
Princiales of Inoraanic Attenuation
The 1999 OSWER Directive provides limited policy and implementation guidance for inorganic
MNA. EPA indicates that: the site -specific mechanisms of attenuation of inorganic contaminants
should be known; and, the stability of the remedial action should be evaluated under potential
changes in conditions. The OSWER Directive is fairly specific about the classes of attenuation
processes that may be proven effective, stating:
"MNA may, under certain conditions (e.g., through sorption or oxidation-reduction
reactions), effectively reduce the dissolved concentrations and/or toxic forms of
inorganic contaminants in groundwater and soil. Both metals and non-metals
(including radionuclides) may be attenuated by sorption reactions such as
precipitation, adsorption on the surfaces of soil minerals, absorption into the matrix of
soil minerals, or partitioning into organic matter."
"Oxidation-reduction (redox) reactions can transform the valence states of some
inorganic contaminants to less soluble and thus less mobile forms (e.g., hexavalent
uranium to tetravalent uranium) and/or to less toxic forms (e.g., hexavalent chromium
to trivalent chromium). Sorption and redox reactions are the dominant mechanisms
responsible for the reduction of mobility, toxicity, or bioavailability of inorganic
contaminants."
"It is necessary to know what specific mechanism (type of sorption or redox reaction)
is responsible for the attenuation of inorganics so that the stability of the mechanism
can be evaluated. For example, precipitation reactions and absorption into a soil's
solid structure (e.g., cesium into specific clay minerals) are generally stable, whereas
surface adsorption (e.g., uranium on iron -oxide minerals) and organic partitioning
(complexation reactions) are more reversible."
"Complexation of metals or radionuclides with carrier (chelating) agents (e.g.,
trivalent chromium with EDTA) may increase their concentrations in water and thus
enhance their mobility. Changes in a contaminant's concentration, pH, redox
potential, and chemical speciation may reduce a contaminant's stability at a site and
release it into the environment. Determining the existence, and demonstrating the
irreversibility, of these mechanisms is important to show that a MNA remedy is
sufficiently protective."
"Inorganic contaminants persist in the subsurface because, except for radioactive
decay, they are not degraded by the other natural attenuation processes. Often,
however, they may exist in forms that have low mobility, toxicity, or bioavailability
such that they pose a relatively low level of risk. Therefore, natural attenuation of
inorganic contaminants is most applicable to sites where immobilization or
radioactive decay is demonstrated to be in effect and the process/mechanism is
irreversible."
There have been numerous advances in the understanding of the environmental geochemistry
of inorganic compounds and metals since publication of the Directive in 1999. The inorganic
MNA topics discussed in the Directive are still valid, and form a first step to evaluate inorganic
MNA. Over the period of 2006-2010 EPA has released much more detailed guidance on
implementation of inorganic MNA and the Interstate Technical and Regulatory Council (ITRC)
has published on practical and regulatory aspects of implementing MNA inorganic at the State
regulatory level. These guidance documents are summarized in a following section.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 4 of 27
Governing Equations
The concentration of a dissolved compound in flowing groundwater changes over time due to
movement, mixing, and chemical reactions. The concentration of COls in MSS groundwater is
governed by these same processes. At MSS, groundwater movement and mixing probably
changes COI concentrations as much or more than chemical reactions do. Following source
control, COI concentrations in MSS groundwater will decrease due to the combination of these
processes, resulting in COI concentration attenuation.
The change in COI concentration with respect to time and place can be described by the
advection-dispersion equation (AIDE). The AIDE is used to determine the concentration of COI
in groundwater during remedial scenarios - including MNA. In differential form, including
reversible and irreversible sorption to solids, the AIDE is:
acazc _ac _Pb (5s _ ps_Pc
at aX ax e 9t
where:
C = concentration of solute in water
t = time
x = distance from source
D = Dispersivity
v = average groundwater velocity
Pb = solid bulk density
6 = solid porosity
S = concentration of solute on solid
N = rate of solute irreversible sorption
The first and second terms in the AIDE describe the change in COI concentration due to mixing
and diffusion in granular aquifers (D - Dispersivity), and the change in concentration from
groundwater flow moving the solute away from the point of interest (v - average groundwater
velocity), respectively.
The third term in the AIDE, related to concentration of solutes on solids and reversible sorption
processes, has alternate formulations that are very useful in solute fate and transport modeling.
The relationship between the concentrations of reversibly adsorbed solutes on solids and the
dissolved concentration in groundwater can be stated as a proportionality — Kd, where:
where:
Kd —
_ Scar
CcQi
SB is for the concentration of COI on solids, and
CB is for the concentration of COI in the water, when COI chemistry is at equilibrium.
Kd is a proportionality of concentration between the solids and the liquids in an aquifer. It
commonly has units of volume over mass. In order to use Kd in the AIDE formulation it is often
expressed as Retardation — R, where:
R = 1+PKd

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 5 of 27
In the Retardation equation we see the reappearance of bulk density and porosity from the AIDE
with the surface concentration term contained in the proportionality Kd. The effect of R and D on
solute transport time and concentration can be seen from the figure below for model transport of
retarded and non -retarded solutes with equal Dispersivity. Note that in the retarded case `a' that
velocity is divided by Retardation; an R value of 1 indicates no retardation. Retardation and
Dispersivity are conservative with respect to solute mass.
vt \ a b
O x, =
Cl+0 1)
[I
-D and R
D Only
Increasing Distance --)�
x,, = v t
If COI has a high Kd, it will have a high R. A high R puts higher contaminant mass on the solids
in proportion to the amount dissolved in water. When the water concentrations decrease to
background over time, the solids will release COls until that mass was exhausted to background
concentrations. If R is low, that return to background concentrations on solids will happen
relatively quickly. The final term in the AIDE is related to irreversible sorption processes.
To describe the attenuation of COI at MSS the inputs to the AIDE are satisfied as follows:
ADE
Variable
C
x
D
v
Pb
e
S
u
Data Source
Concentration measured from groundwater samples.
Time is determined by the nature of the problem to be investigated, e.g. the time
for COI in groundwater to fall below the 2L standard.
Distance is determined by the nature of the problem to be investigated.
Dispersivity is estimated from published values or determined from solute
concentrations over time using numerical models.
Average groundwater velocity varies in space and time and is supplied by a
calibrated groundwater flow model.
Bulk density measured from samples.
Porosity measured from samples.
Concentration measured from solid samples. Calculated Kd values from laboratory
batch and column testing.
Irreversible component of S. Not determined at this time.
Kd Calculations and Interpretation
There are many different mathematical models to describe sorption, Kd, Langmuir Isotherms,
and Freundlich Isotherms are common methods (USEPA, 1999). All of the models have
advantages and limitations. If you know the solution concentration, and can model or measure
the solid concentration, you can calculate Kd. If confidence in the model is high, the solution
concentration can be assumed and surface concentrations of COI calculated directly (Goldberg
et al., 2000; Dzomback and Morel, 1990).

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 6 of 27
One limitation to the Kd approach is that it does not describe the effect of variable pH conditions.
The question of pH is important on many levels. We know that COI will take on an electrical
charge based on pH, that the surfaces of minerals that adsorb COI are variably charged -again
dependent on pH, and that the propensity of COI to approach a surface depends on all of these
charges. To handle these complexities surface complexation theory was developed (Dzomback
and Morel, 1990).
Surface complexation theory states that we can describe these sorption reactions the same way
as we describe chemical reactions, as mass -action equations that have equilibrium constants.
K's are numerical constants for chemical mass -action equations. They express the equilibrium
relationships between chemicals. Setting an equilibrium chemical reaction with A and B as
reactants, C and D as products, where the variable is concentration:
A+B=C+D
the mass -action equation takes the form:
CD
K= .
AB
K is constant at constant temperature and pressure. Three constants are needed to model the
surface complexation approach, one for the COI adsorption to the surface and two to describe
the charging of the surface. The surface charging constants K_ and K+ are determined for pH -
dependent protonation-deprotonation reactions at the oxide surface. The protonation reactions
with the surface, SOH, are described by the two step reversible process below.
SOH + H+ <* SOH
K _ [SOHZ ] (FV1.)
p ex
S+ ISOH IH+] (RT
SO- + H+ <* SOH
K _[SO IH`] (-FVIY )
S- I SOH exp (RT
The mass -action relationship for COI (Kco,) can be expressed in a generic form as:
SOH+ H,COIy<* SHXCOIy- + H+
K=[SHXCOIy IH+ exp`—FVf,,
C01 [SOH HXCOI y (RT
where square brackets indicate concentrations (mol/L), F is the Faraday constant (C/mol), 4J is
the surface potential (V), R is the molar gas constant (J/mol K), T is the absolute temperature
(K), and the exponential terms represent solid -phase activity coefficients that correct for charges
on the surface complexes. Each Kco, mass -action expression must be constructed from a
balanced equation using the generic form above as an example. Mass -action constants can be
determined from adsorption experiments (Kd determinations) using the code FITEQL (Herbelin
and Westall, 1999) and several surface complexation sub -models are available in PHREEQC.
Irreversible Sorption of COls
Irreversible sorption of COls has been observed in/on a range of geomedia for over 100 years.
Here the irreversible sorption for COls is defined as: COls that are retained in the structure of

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 7 of 27
minerals and mineral -like inorganic and organic compounds on a time scale significantly longer
than reversible surface adsorption reactions. In most cases reversible surface sorption
reactions are instantaneous as compared to groundwater flow rates. Irreversible sorption
processes for COls are common in the natural environment. COls will be taken up to form part
of the mineral lattice of clay minerals, hydrous metal oxides, carbonates, and composted
organic material, as examples. Clay minerals and hydrous metal oxides are common at the
site. Release of COI from these materials is slow.
The chemical equilibrium between solutions and solids is a balance between the rate of forward
reactions and the rate of back reactions. Surface complexation adsorption processes are
reversible equilibrium reactions. Irreversible sorption is a process where the forward reaction is
so much faster than the back reaction that the reverse reaction is insignificant on the time scale
of interest. The remobilization mechanism is too slow to be significant. Irreversible sorption is a
COI sink; COI is removed from the flow system. First -order decay is one way to represent
irreversible sorption in a numerical model. First -order decay rates are also used to calculate the
half-life of a compound.
Inverse Modeling of Hydrologic Parameters
Determination of most of the physical properties that effect solute transport in granular aquifers
can be accomplished using laboratory or field tracer tests. Dispersivity, retardation, and
effective porosity can be quantified this way. These are important parameters for modeling of
solute transport in groundwater. Laboratory and field tracer tests are controlled experiments
often involving forward modeling of expected conditions to constrain the experimental design.
Determining the appropriate concentration of tracer to be used and how long to apply it to have
a successful experiment (source term) would be an example of forward modeling. Inverse
modeling is fitting of aquifer parameters to observed concentration/distance/time data.
Laboratory and field breakthrough curves (BTCs) generally trace smooth curves due to frequent
sampling and the ability to rerun experiments.
Data from groundwater monitoring programs can be used for determination of aquifer
parameters in the same manner as laboratory tests, if the data provide a fairly complete record
of changes in concentration of a dissolved solute. Ideally, monitoring would be frequent and the
rising limb and falling tail of the solute BTC would be captured with accuracy and precision.
Forward modeling of field conditions is possible if the source term is known or assumed.
BTC data from groundwater monitoring generally has an imperfect understanding of the
concentration (C) and duration (t) of the contaminant source over time — the source term. The
distance between the source (z) and the monitored well may also be hard to quantify.
A public -domain program for numerical evaluation of BTCs is available. CXTFIT, Version 2.1
(Toride et al., 1999), is useful for determining values for average linear velocity (v), dispersivity
(D), retardation (R), and decay (p), which is used to account for irreversible adsorption.
Independent data for v are available from the calibrated flow model, tests of hydraulic
conductivity, and measurement of gradients. Similarly, R has been determined independently
from laboratory measurements of bulk density (Pb), effective porosity (n), and partition
coefficients (Kd). Laboratory or field determined values for dispersivity (D) or decay (p) are not
available at this time.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 8 of 27
Coal Combustion Product Leachate Characteristics
Inorganic MNA relies on being able to observe, quantify, and in some cases modify subsurface
chemistry. There are major differences in the chemical characteristics of leachate across the
major groups of CCP (fly ash, bottom ash, pollution control residue), and complexities
introduced by co -disposal of different CCPs. The composition of leachate from CCP is highly
variable. Controls on leachate chemistry are numerous and are strongly influenced by site -
specific factors. Leachate chemistry is influenced to variable and unequal degrees by:
• The type of coal;
• The basin, sub basin, mine, or seam it is produced from;
• Variability of coal composition within the seam;
• Coal cleaning and pretreatment processes;
• Combustion conditions;
• Pollution control operations;
• CCP handling;
• CCP management strategies — impoundments, landfills or combined methods; and,
• Climate and environmental factors - such as hydrology, geology, and weather.
The preceding list of factors, that ultimately control the success of inorganic MNA, is imperfect
and not meant to be exhaustive. There is a large knowledge base on the geochemistry of CCP
and CCP leachate. That information is very helpful to constrain remedial strategies for legacy
CCP sites, but does not replace the detailed site -specific assessment of ash and aquifer
geochemistry required for inorganic MNA.
The Electric Power Research Institute (EPRI) has conducted extensive research on the
occurrence, concentration, and mobility of CCP leachate components. The selection criteria the
used to identify constituents of concern (COCs) included prevalence, mobility, and risk as
determined by comparison to water quality standards. EPRI's assessment identifies five
leachate constituents that are probably present in pore water at all legacy CCP management
sites; arsenic, boron, chromium, selenium, and sulfate. Each of these substances has triggered
at least one remedial action at a legacy CCP site. While these constituents are the primary
focus of concern due to their prevalence and mobility, several other inorganic constituents may
be of concern at legacy CCP management sites. From EPRI's 2006 effort the following
constituents are noted:
"The leachate data indicate that concentrations of antimony, arsenic, cadmium,
chromium, selenium, and thallium were higher than health -based MCLs in at least 10
percent of the samples. In addition, the 90th percentile concentrations of boron,
lithium, manganese, molybdenum, sodium, sulfate, and vanadium were higher than
alternative drinking water criteria. These constituents are more likely to trigger a
remedial action in the event of a leachate release than constituents that typically
have leachate concentrations lower than drinking water standards."
The EPRI listed constituents above are primary candidates for MNA because of their
occurrence, mobility and propensity to exceed drinking water standards at legacy CCP sites.
Not all of these constituents are amenable to remediation through MNA processes because of
their chemical properties. Table 1 compares the leachate chemistry as identified by the
previously listed EPA and EPRI sources, with the compounds suitable for inorganic MNA as
found in the EPA, EPRI, and ITRC guidance documents.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 9 of 27
The EPA sources cited identify the following thirteen COCs based on the potential for human
health and/or ecological impacts using a screening risk assessment: aluminum, arsenic,
antimony, barium, boron, cadmium, cobalt, chromium, lead, mercury, molybdenum, selenium,
and thallium. One of the findings of the 2009 EPA report was nine of the thirteen COCs listed
above were found in CCP leachate at levels of concern for groundwater protection, as indicated
in Table 1.
Published Guidance on Inorganic Monitored Natural Attenuation
United States Environmental Protection Agency Guidance
The EPA is the primary source of guidance on MNA. The EPA has published their inorganic
MNA guidance in three volumes. Volume 1 is a procedural and technical guide for implementing
MNA; Volume 2 is a detailed exploration of issues associated with inorganic MNA for nine
compounds; and Volume 3 contains discussion of MNA issues unique to radionuclides and a
detailed exploration of inorganic MNA for ten radionuclides. Volumes 1 and 2 were published in
2006 and Volume 3 in 2010. The EPA guidance documents cover inorganic MNA at a high level
of scientific detail. The EPA guidance, while not specific to CCP, is a technical resource on
evaluation of the feasibility of inorganic MNA for compounds as listed in Table 1.
Volume 1 introduces EPA's "Tiered Analysis Approach to Site Characterization"; the tiers being
four demonstrations or findings to be accomplished when implementing inorganic MNA.
Volume 1 provides specific technical guidance on implementing inorganic MNA using the four -
tiered approach. Volume 2 expands on the technical guidance to include specific strategies and
chemical mechanisms for arsenic, cadmium, chromium, copper, lead, nickel, nitrate,
perchlorate, and selenium inorganic MNA. Volume 3 presents the evaluation of MNA for
radionuclides.
Table 2 presents a simplification of the four tiered approach found in the EPA guidance. CCP
inorganic MNA is not considered by EPA to be a viable remedial alternative for groundwater
unless the leachate additions to groundwater have been controlled. Developing a site -specific
understanding of the mechanism by which inorganic MNA may attenuate (Tier II) and the
capacity of the aquifer to do so (Tier III) is a complex and iterative task. Volume 1 provides the
technical basis for inorganic MNA evaluations to accomplish Tier II and III goals. Monitoring of
inorganic MNA is necessarily more detailed than for many active remediation strategies and is
discussed in Volume 1.
Interstate Technology Research Council Guidance
In late 2010 ITRC published a decision framework for inorganic MNA. The document contains a
summary of the three -volume EPA guidance, expanded to decision framework for determining
MNA feasibility. Case studies are included and compared to the EPA four tiered approach. The
MNA implementation at the state level was surveyed and reported. The ITRC document
summarizes the topic of inorganic MNA, presents an introduction to the science, and presents a
strategy for training and implementation of inorganic MNA under state laws and regulations.
This guidance is not specific to CCP. As with the EPA guidance, it is a technical resource on
evaluation of the feasibility of inorganic MNA for compounds in Table 1.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 10 of 27
Table 1. Compounds in CCP leachate as compared to MNA guidance.
EPA CCP EPRI CCP EPA MNA ITRC MNA EPRI MNA
Aluminum (Al)
X
XX
Antimony Sb
XX
XX
Arsenic As
XXX
XXX
X
X
X
Barium (Ba)
XXX
X
Beryllium Be
X
X
Boron B
XX
XXX
X
Cadmium Cd
XX
XX
X
X
Calcium Ca
X
X
Chromium Cr
XXX
XXX
X
X
X
Cobalt (Co)
X
X
X
Copper (Cu)
X
X
X
Fluorine F
X
X
Iron Fe
X
X
Lithium Li
XX
Lead (Pb)
X
X
X
X
Magnesium M
X
Manganese Mn
X
XX
Mercury H
X
X
Molybdenum (Mo)
XX
XX
Nickel Ni
X
X
X
X
Potassium
X
X
Selenium Se
XXX
XXX
X
Silicon Si
X
Silver A
X
X
Sodium Na)
X
X
Strontium Sr
X
X
Thallium Th
XX
XX
Vanadium V
X
XX
Zinc (Zn)
X
X
X
H
X
X
Sulfate SO4
X
XXX
X
Dissolved Solids
X
XX
Radionuclides
X
X
EPA CCP: X=mentioned, XX= of concern, XXX=exceeds toxicity criteria
EPRI CCP: X= evaluated, XX= of concern, XXX=of concern and common
Table 2. Summary of US EPA four -tiered feasibility evaluation for inorganic MNA.
Tier I Source Control Is the contaminant mass in the plume decreasing?
Tier II Attenuation Mechanism Is the chemical mechanism well understood?
Tier III Attenuation Capacity Is the capacity and permanence of the mechanism
sufficient?
Tier IV Monitoring & Contingency How will monitoring be conducted? What actions will be
taken if monitorina indicates attenuation is lackina?

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 11 of 27
TIER I DEMONSTRATION FOR THE MARSHALL STEAM STATION
MNA is a candidate remedial technology for Constituents of Interest (COls) exceeding 2L
standards in groundwater at the MSS. Attenuation processes reduce the concentration or
toxicity of compounds in groundwater primarily by chemical interaction with aquifer solids.
When attenuation processes result in a reduction of contaminant concentrations in a
timeframe similar to other remedial technologies, attenuation can be an acceptable remedial
alternative (USEPA, 2007). This section documents that the first milestone in the Four -Tiered
MNA process has been achieved; attenuation of certain COls has been observed. This
successful Tier I demonstration is based on the methods contained in EPA guidance (USEPA,
2007). The MNA demonstration for certain COls will now be advanced to Tier II/III.
Data were collected on the distribution of COls in groundwater, porewater, and soil in three
dimensions to evaluate if attenuation was occurring. A strong positive correlation between COI
concentration in water and solid pairs indicates attenuation (USEPA, 2007) and is the first step
(Tier 1) in evaluation of MNA as a remedial technology.
EPA guidance defines Tier I (USEPA, 2007, page 6) as:
"Demonstration that the ground -water plume is not expanding and that sorption of the
contaminant onto aquifer solids is occurring where immobilization is the predominant
attenuation process."
Determination of plume stability or non -expansion generally follows source control. Quantitative
analysis of plume stability assuming source control was conducted as part of the numerical
modeling effort supporting the CAP. Fate and transport modeling used the site -specific
partitioning coefficients developed as part of a laboratory testing program to determine site -
specific attenuation capacities (Kd) for COls at MSS.
Tier I objectives were accomplished by chemical evaluation of collocated aquifer solids and
groundwater (i.e. solid/water pairs) as described in the EPA guidance (USEPA, 2007, page 6):
"Determination of contaminant sorption onto aquifer solids could be supported through
the collection of aquifer cores coincident with the locations of ground -water data
collection and analysis of contaminant concentrations on the retrieved aquifer solids."
MNA requires additional testing and data interpretation beyond Tier I to allow reasonable
comparison to other remedial alternatives with respect to efficacy, cost, stakeholder acceptance,
and time to meet remedial goals. This will be accomplished for COls by completing Tiers II and
III of MNA Demonstration.
The CSA found that groundwater COls at the site include antimony, arsenic, barium, beryllium,
boron, chloride, chromium, cobalt, iron, manganese, selenium, sulfate, thallium, TDS, and
vanadium. Antimony, chromium, cobalt, iron, manganese, and vanadium occur naturally in
regional groundwater; however, groundwater in proximity to ash units exceeds these
background values for chromium, cobalt, and manganese. Chloride, sulfate and TDS are
generally not attenuated by reactions with solids, but are reduced in concentration by diffusion,
mechanical mixing, or dilution. Here we consider water -solid pairs and site -specific Kd data as
evidence for attenuation for arsenic, barium, beryllium, boron, chromium, cobalt, manganese,
selenium, thallium, and vanadium.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 12 of 27
Water and solid chemistry data from the CSA were used to conduct the Tier I analysis. A single
extraction method was used on solids, USEPA SW-846 Method 3051A. When a water sample
could be matched with more than one solid sample in the screened section of the well, multiple
solid -water pairs were created. Non -detection (U values, below detection limit) were not used in
the comparison or were substitute values used. J values (presence indicated, below
quantification limit.) were used as reported. As reflected in Table 1 a total of 25 solid -water
pairs were used for the MSS Tier I Demonstration.
Tier I Analysis
Tier I analysis uses two lines of evidence for attenuation. Solid -water pair comparison of COI
concentrations are performed, a mutually rising relationship indicating attenuation (EPA 2007);
and, laboratory determination of the solid -water partitioning coefficient or Kd value (EPA 1999) is
used as measure of the propensity of COls to adsorb to site -specific solids and be attenuated.
If a solid -water pair comparison chart is not presented, there was insufficient data for Tier I
analysis for that element.
Laboratory determination of Kd was performed on 12 site -specific samples of soil, or partially
weathered rock (saprolite) from the transition zone (Table 4). Solid samples were batch
equilibrated to measure the adsorption of COls at varying concentrations. COls tested were
antimony (4 samples), arsenic, boron, cadmium, chromium, cobalt (4 samples), molybdenum,
selenium, thallium, and vanadium. Iron and manganese were not tested. Iron and manganese
Kd determinations were difficult due to the high concentrations of poorly crystalline iron and
manganese oxides and oxyhydroxides present in the Piedmont soils and saprolite. Tests are
conducted in duplicate to evaluate error. These multiple data points for each sample are
evaluated to determine if the observed data can be fit to an adsorption isotherm. If fitting is
supported, a Kd is calculated; blanks in Table 2 indicate that a reasonable isotherm was not
observed in that test. Isotherms were not obtained for antimony, boron, cobalt, molybdenum, or
selenium. Sample AB-12D 53.3-54 feet has been omitted because no isotherm fits were
obtained for this sample or its duplicate run for any COI reducing the sample set to 11. Table 4
also presents calculated median batch -test Kd values for each COI averaged across all tests,
the minimum and maximum values, and the ratio of the maximum to the minimum value as an
indication of the variance in the results.
Kd values vary from thousands of ml/g to single digits. The variation in the ratios of max/min Kd
is not correlated to the calculated medians of Kd. We can use the max/min ratio as a subjective
indicator of the potential for COI to have a Kd that is variable across geomedia. The relative
strength in binding based on the batch Kd data is: Thallium > Chromium > Arsenic > Vanadium >
Cadmium. The potential for a variable Kd across the site is in the order: Vanadium > Cadmium
> Arsenic > Thallium > Chromium.
Antimony
Antimony attenuation was not observed. A Kd value could not be determined from the
isotherms. Antimony should not be carried through to Tier II.
Arsenic
Arsenic attenuation using solid -water pairs was not observed (Figure 1). Kd determinations for
arsenic support the solid -water pair observation with a calculated median Kd of 336 ml/g.
Variability in observed Kd should be moderate with a Max/Min ration of 45.1. Laboratory
attenuation of arsenic has been observed, and the COI should be carried through to Tier II.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 13 of 27
Figure 1
8
7
R5
zs
�5
N 4
N
3
�2
L
1
LI
0 10 20 30 40 50
Arsenic (mglkg)
Barium
The soil -water pair concentrations of barium are plotted in Figure 2. The rising concentrations in
groundwater are somewhat matched by rising concentrations in solids, indicating that the solids
are attenuating barium concentrations in groundwater, but the trend line is driven by a single
high value. Kd determinations for barium were not made. Barium is rapidly attenuated in many
groundwater environments; however, the data and analysis do not support carrying barium
through to Tier II. Based on barium's textbook low mobility in groundwater environments and
weak solid -water pair relationship it is suggested that it be carried through to Tier II.
Figure 2
800
700
R 600
500
400
0
300
200
100
0
0 500 1000 1500 2000
Barium (mglkg)
Beryllium
Figure 3 depicts the solid -water pair analysis for boron. Attenuation is not observed in this plot.
Kd values for beryllium were not determined. Beryllium should not be carried through to Tier II.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 14 of 27
Figure 3
6000
ay 5000
m 4000
a
c
ran 3000
�a
3 2000
1000
m
0
0 10 20 30
Beryllium (mglkg)
Boron
Figure 4 depicts the solid -water pair analysis for boron. Attenuation is not observed in this plot.
Calculated site -specific boron Kd were not determined. Boron should not be carried through to
Tier II.
Figure 4
J 7
t3y
6
a5
G
�4
13
d3
C
02
m
1
n
0 2 4 6
Boron (mglkg)
Chromium
The solid -water pair concentrations of chromium are plotted in Figure 5. Attenuation is not
observed in this plot. Calculated site -specific chromium Kd values are high (median of 417
ml/g). It was difficult to fit isotherms for many samples (4 successful fits of 11 samples). The
attenuation of chromium at Marshall has been observed and chromium should be carried
through to a Tier 11 evaluation.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 15 of 27
Figure 5
18
16
14
12
rn 10
N_
13 8
6
0 4
L
U 2
IJ
0 200 400 600 800
Chromium (mglkg)
Cobalt
Cobalt attenuation was not observed in Figure 6. A Kd value could not be determined from the
isotherms. Cobalt should not be carried through to Tier II.
Figure 6
25
III
0 10 20 30 40
Cobalt (mg/kg)
Manganese
Manganese attenuation was not observed in the plot of solid -water pairs in Figure 7. A Kd value
was not tested. Manganese should not be carried through to Tier II.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 16 of 27
Figure 7
8000
J 7000
6000
c 5000
H
4000
w 3000
2000
1000
A
0 200 400 600 800
Manganese (mglkg)
Selenium
Selenium attenuation using solid -water pairs was not observed. There were less than three
data pairs, preventing analysis. The calculations of a Kd for selenium was unsuccessful.
Selenium should not be carried through to Tier 11.
Thallium
Thallium attenuation using solid -water pairs was not observed. There were less than three data
pairs, preventing analysis. The calculations of a Kd of 556 ml/g for thallium (batch) indicated
that it should be moderately attenuated at the site. The Max/Min ratio of 24.6 suggests that little
variation in Kd across the site is to be expected. Natural attenuation of thallium should be
observed and the COI should be carried through to Tier 11 on the basis of the moderate -high Kd
observations in batch tests.
Vanadium
Vanadium attenuation using solid -water pairs was not observed in Figure 8. The calculations of
a Kd of 221 ml/g for vanadium (batch) indicated that it should be moderately to strongly
attenuated at the site. The Max/Min ratio of 247 suggests that major variation in Kd across the
site is to be expected. Natural attenuation of vanadium should be observed and the COI should
be carried through to Tier II on the basis of the strong Kd observations in batch tests.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 17 of 27
Figure 8
25
20
If]
0 10 20 30
Vanadium (mglkg)
Tier I Findings
The groundwater COI's for MSS are antimony, arsenic, barium, beryllium, boron, chloride,
chromium, cobalt, iron, manganese, selenium, sulfate, thallium, TDS, and vanadium. Tier I
analysis of solid water pairs and Kd values for antimony, arsenic, barium, beryllium, boron,
chromium, cobalt, manganese, selenium, thallium, and vanadium was conducted. The Tier
analysis indicates that arsenic, barium, chromium, thallium, and vanadium should be carried
through to Tier II determinations of mechanism.
TIER II DEMONSTRATION FOR THE MARSHALL STEAM STATION
MNA is a candidate remedial technology for the groundwater COls originating on MSS property.
A strong positive correlation between COI concentrations in solid -water pairs indicates
attenuation. Correlation was demonstrated as documented in the Tier I demonstration. This
section covers Tier II demonstration of mechanism and rate for COI attenuation.
Attenuation processes reduce the concentration or toxicity of compounds in groundwater
primarily by advection, dispersion, and chemical interaction with aquifer solids. When
attenuation processes result in a reduction of contaminant concentrations in a timeframe similar
to other remedial technologies, attenuation can be an acceptable remedial alternative (USEPA,
2007). In completion, the Tier I, II, and III MNA demonstrations indicate that MNA is operable
on a timescale comparable to active remedial technologies (e.g. pump and treat) that have been
screened for the MSS groundwater portion of the CAP. MNA is being considered in the CAP for
MSS groundwater as a remedial technology. Data were collected on the distribution of COI in
groundwater and geomedia in three dimensions to evaluate if attenuation was occurring. The
first use of the data was to evaluate the premise of COI attenuation (Tier 1) using a subset of
results from the approved data collection program.
The groundwater COls for MSS are antimony, arsenic, boron, chromium, cobalt, iron, lead,
manganese, sulfate, thallium, vanadium and TDS. Tier I analysis indicates that arsenic, barium
chromium, and thallium should be carried through to Tier 11 determinations of mechanism.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 18 of 27
The process was intended to be flexible based on findings (the observational approach) or in
response to agency comments or new scientific opportunities that may arise. EPA guidance
defines Tier II (USEPA, 2007, page 6) as;
"Determination of the mechanism and rate of the attenuation process."
and, continues on page 7 with further clarification on rate:
"The objective under Tier 11 analysis would be to eliminate sites where further
analysis shows that attenuation rates are insufficient for attaining cleanup
objectives established for the site within a timeframe that is reasonable
compared to other remedial alternatives."
MNA tasks require an observational approach and the reliance on predictive models increases
over the duration of the project (Tier I to III). The MNA demonstration process results in
increasing levels of confidence in the reliability of MNA as a remedial solution. There are two
technical paths that contribute to the same site conceptual model. There is a technical path
primarily related to calculations and modeling of groundwater flow, contaminant transport, and
how fate and transport of the COls is affected by remedial alternatives, attenuation, or no action.
Supporting those calculations are geochemical activities primarily related to technical evaluation
of COI attenuation capacity, permanence, and remedial effectiveness over time. The technical
activities proposed for the CSA relied on our pre -Tier I best understanding of COI attenuation
processes in MSS groundwater and were subject to change based on observation, study
objectives, or Tier goal attainment by alternate methods.
Site Conceptual Model for Attenuation
Lithologic Controls on Water Quality
The USGS and NCDENER recently completed regional studies (USGS 2009, USGS 2013) of
the groundwater chemical quality in the Blue Ridge and Piedmont Provinces. MSS is located in
the Milton Geozone of USGS 2009, a minor province occupying about 3.4 % of the surface area
of the Blue Ridge and Piedmont Provinces in NC. The lithologies at the site are comprised of
two tectono-stratigraphic packages of rocks. The upper package of Ordovician age rocks
consists of metavolcanic rocks of amphibolite grade metamorphism. The older package consists
of clastic metasedimentary rocks of Neoproterozic to Lower Palezoic age also metamorphosed
to amphibolite grade. Bedrock groundwater in the Milton Geozone is variable but the basic ionic
compositions of most waters are either calcium -sodium bicarbonate or a calcium -magnesium
bicarbonate type. A notable consideration from the two recent USGS papers is that is it
possible to roughly rank the potential for natural background occurrence of heavy metals (Sb,
As, Ba, Co, Cr, V and Zn as examples) by rock type as Mafic Crystalline > Felsic Crystalline >
Siliciclastic > Carbonate > Recent Alluvium. Mafic material (igneous -origin rock that contains
larger percentages of Fe and Mn silicates than quartz or feldspars) has a link to background
levels of heavy metals at Marshall. Mafic minerals have the same connection. The Marshall
surface geologic mapping indicates metavolcanic rocks varying from intermediate compositions
(10-30% mafic minerals) to felsic (5-15 % mafic minerals) are present. Surface geologic
mapping indicates the near proximity of granite rock types (High Shoals Granite) that are also
could influence subsurface trace metal occurrence.
Mineralogical Controls on Attenuation
COls are adsorbed to organic matter, oxide minerals, and clay minerals. These are the
predominant sources and sinks for COls in groundwater, soil, or sediment. All of these solids
are present in subsurface materials at MSS. COls adsorbed on these solids equilibrates with

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 19 of 27
solution COI concentrations. Some COls adsorbed to clays migrates from clay edges to clay
inter -layer spaces.
The strength of partitioning of COls from groundwater to solids ranges from loosely bound by
ion exchange reactions, to irreversibly bound in clay structures or chemical precipitates. By
example, through the method of selective or partial extractions (Tessier et al., 1979) mineral
phases and sediment fractions associated with higher concentrations of COls through
attenuation can be identified. By mineral or size separation and chemical extraction the solids
that contribute to attenuation can be classified and segregated for degree of effect. The degree
of COI partitioning (Kd and p) over a range of concentrations can be determined by testing co -
located solids and groundwater, or the examination of COI concentration over time in
groundwater at a fixed location for the purpose of solving the ADE. This and other information is
used to calculate the amount of COI removal, and time to achievement of remedial objectives
using a MNA remedial approach.
Role of Site Lithology
Typically geologic materials are sampled off site and away from potential contamination to
establish baseline values for comparison to those analyzed from study sites. In lieu of detailed
offsite sampling, published values for average crustal abundances can be utilized to evaluate
whether indigenous materials contribute to COI concentrations in an area. For this report,
crustal abundance values from Wedepohl (1978) are used for comparison to samples analyzed
at the Marshall site. Table 5 presents average crustal abundances for comparison.
Site Geologic Formation Influence on COI Occurrence
Tonalite — Tonalite (mqd of Goldmith, et al., 1988) crops out in the southeast portion of the
MSS in the area of the active ash basin and FGD residue landfill. Tonalites (metadiorites) are a
relatively common basement rock in many Proterozoic and accretionary terrains with a
composition of approximate equal amounts of quartz, plagioclase feldspar, biotite, hornblende,
and epidote with subordinate sphene, potassium feldspar and magnetite. No whole rock
petrology for rocks specifically at the site is available at this time. The average crustal
abundances as proxy for uncontaminated tonalite near the Marshall site are presented in Table
5 for the COI inventory.
Granite (High Shoals Granite) — Granite (IPhs of Goldmith, et al., 1988) is present on the
northwest portion of the site and underlies the industrial landfill. Granites are a relatively
common basement rock in many Proterozoic and accretionary terrains with a composition of
approximate equal amounts of quartz, potassium feldspar, plagioclase with subordinate
muscovite, biotite, amphibole, and magnetite. The High Shoals Granite has been
metamorphosed. No whole rock petrology for rocks specifically at the site is available at this
time. The average crustal abundances as proxy for uncontaminated granite near the Marshall
site are presented in Table 5 for the COI inventory.
Quartz-Sericite Schist — Quartz-sericite schist (Unit Zbs of Goldsmith et al., 1988) is present
through the center of the property, along a NE -SW trend. The schist underlies the ash landfill.
The mineralogical composition of typical quartz-sericite schist is quartz and muscovite with
accessory chloritoid, biotite, pyrite, hematite, andalusite, kyanite, sillimanite, chlorite, tourmaline,
zircon, graphite and potassium feldspar. The average crustal abundances as proxy for
uncontaminated quartz-sericite schist at Marshall are presented in Table 5 for the COI
inventory.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 20 of 27
Biotite Gneiss (metagranodiorite) — Biotite gneiss is present on the eastern margin of the site
and underlies a small portion of the active ash basin. The biotite gneiss rocks at the MSS are
essentially dacites that have undergone amphibolite grade metamorphism. These rocks tend to
form schists and gneisses consisting of amphibole, biotite, plagioclase, quartz with subordinated
amounts of potassium feldspar and chlorite. The average crustal abundances as proxy for
uncontaminated biotite gneiss at Marshall are presented in Table M-1 for the COI inventory.
Summary of Whole Rock Influence on COI Occurrence
All whole rock analyses show significant values over average crustal abundance for arsenic and
cobalt. In addition, antimony is elevated in all whole rock borings and significantly in AB-9D.
Chrome and vanadium are also elevated in most borings. The magnitudes of these values are
significantly above the reported average crustal abundances and suggest contamination from
the overlying ash.
Soil Development Influence on COI Occurrence
Soil formation typically results in the loss of common soluble cations and the accumulation of
quartz and clay. Feldspars are hydrolyzed to clays. The natural concentration of COCs by
weathering and soil development on the lithologies noted above is significant (Table 5). Could
observed COI elevation be from natural processes? All COI values are significantly elevated
above average crustal abundance in almost all soil borings (MSS CSA Report, Table 6-3) for As
and Co. Antimony and selenium are significantly elevated in boring AB-15D. The increasing
abundance of clay during the natural weathering process can conceivably result in an increase
in COI content with time. However, the values derived during the CSA report suggest the
concentrations are being introduced from the ash, especially borings AB-15D (As, Sb, and Se)
and to a lesser extent in AB-8D and AB-6Br (As). Reported values for borings into the transition
zone (MSS CSA Report, Table 6-5) are also elevated for As and Co. These reported values are
well over average crustal abundances suggesting transport of these COI in to the transition
zone from the overlying ash. Other COI do not appear elevated in the transition zone over
average crustal abundance except vanadium which is slightly elevated. Natural processes do
not explain the observed COI distribution at MSS, although natural processes can concentrate
COls to levels above regulatory concern.
Mechanisms for Natural Attenuation at MSS
Active precipitation of COI secondary minerals at the site appears unlikely, with exception of
iron and manganese oxides and oxyhydroxides. The very low abundances of the other elements
suggest saturation of these elements and precipitation as secondary oxides, arsenates, or
carbonates is not attained.
The attenuation of chemical contamination by reaction with existing natural materials may play a
significant role at the site. The abundant clay content of the soils and host rock lithologies
suggests much of the COI concentrations in the ash basin and ash storage may be attenuated
by these materials. Harder (1970) and Perry (1972) showed in pioneering studies that boron is
adsorbed and incorporated into illite and chloritic clays respectively. The low content of boron in
most rivers is attributed to the same processes. Thallium is also documented to be adsorbed to
clays, especially potassium and rubidium types, as well as to iron and manganese oxides.
Vanadium is also adsorbed and incorporated into clay structures and oxide coatings (Butler,
1953). Krauskopf (1956) suggests vanadium displays a preference for adsorption in decreasing
order from Fe oxides > Mn oxides > montmorillonite > organic matter. In addition to the reported
abundance of clays at the site, there is significant potential for more clay to be present as an
alteration product on the surfaces of the abundant feldspars reported in the soils and rocks.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 21 of 27
Adsorption to iron oxides and hydroxides has long been demonstrated for As, B, Ba, Cd, Co, Cr,
Co, Fe(II), Hg, Mn, Ni, Pb, Sb, Se, SO4-2, V and Zn (Dzomback and Morel, 1990). Soil
chemistry results show abundant Fe203 and MnO values in soils from the site (Table 6-2, MSS
CSA Report) and a strong potential for adsorption. High A1203 (aluminum hydroxide) content is
an indicator of clay minerals and also can indicate the presence common soil -forming aluminum
oxyhydroxides gibbsite, boehmite and diaspore. Adsorption to most -common gibbsite has been
demonstrated for As, B, Cd, Co, Cr, Co, Fe(II), Hg, Mn, Ni, Pb, Se, SO4 2, and Zn (Karamalidis
and Dzomback, 2010) . No amorphous phase content is currently reported from the CSA
mineralogical studies; however, high iron, manganese and aluminum content in Method 3051A
extractions presage quantification in reporting to follow. When quantified, amorphous Fe-Mn-AI
oxide -hydroxides or on amorphous organic materials provide significant potential for natural
attenuation of the COI. Amorphous phase content will be determined on soil samples in order
to consider adsorption potential.
Tier II Discussion & Conclusions
Following successful completion of a Tier I demonstration that arsenic, barium, beryllium, boron,
chromium, cobalt, lead, thallium and vanadium are attenuating in groundwater at MSS, a
conceptual model for COI attenuation involving reversible and irreversible interaction with clay
minerals, metal oxides, and organic matter is proposed. A Tier II demonstration based on that
conceptual model was partially executed. The findings follow:
1. The sampling obtained geomedia representative of the material that the COI plume will
traverse.
2. Clay minerals and Fe-Mn-AI oxides were found in all samples. Organic matter is
probably not a significant sink for COI at MSS.
3. Chemical extractions identified that COls were concentrated in samples exposed to
groundwater containing higher concentrations of COls, validating the attenuation
conceptual model.
4. Chemical extractions were used to determine a probable range of Kd values that
suggest attenuation is taking place for arsenic, barium chromium, and thallium.
5. Additional data collection is necessary to complete the Tier II assessment with respect to
specific attenuation mechanisms for each COI, and quantification of the magnitude of
that attenuation by specific geomedia to support numerical modeling.
Data Gaps and Recommendations
Tier II demonstrations address the mechanism and rate of attenuation. The mineralogical and
physical characterization of solids with respect to type and adsorbed COI concentrations leads
to predictions of COI attenuation expected in the future. Selective extraction (wet chemical
analysis of solids), hydrostratigraphy, and broad water quality data collection provide part of the
information needed to compare MNA to other remedial alternatives in the Tier II evaluation.
The data collected to date has provided critical information on using MNA at MSS and supports
Tier II evaluations. To continue to Tier II and advance to Tier III additional data collection is
necessary. The data evaluation and analysis process for MNA is complex and iterative. The
following table proposes some specific geochemical analysis approaches to completing Tier II
evaluation of mechanism and support Tier III determinations of attenuation capacity of COls.
Quantification of the crystalline and amorphous hydrous metal oxides of aluminum, iron and
manganese (HAO, HFO, and HMO respectively) by partial extraction is proceeding with the
UNCC effort on Kd quantification and will be very useful when available. Many of the other

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 22 of 27
methods can be performed on archived materials. It was noted in the Tier I evaluation that
additional solid -water pair data is needed from areas of higher concentration to improve the fit to
these field adsorption isotherms (Field Kd). This will provide opportunity for additional data
collection on samples that may be unavailable in archive. Field testing to determine dispersivity
would also require redeployment to the site for testing activities.
Analysis
Action
Method
Purpose
Group
Wet
Partial
Chemical extractions
Chemical analysis of extracts provides
Chemical
Extractions of
with differing degrees
information on what solid materials the
Analysis
Sediments
of action.
COI is associated with and the COI
concentration on those materials.
Total Analysis
Complete digestion
HNO3 + HF digestion provides a total
of sediment. Method
COI analysis of solid matrix to compare
3052.
with partial extractions. More sensitive
for trace metals than oxide analysis.
Physical
Field
Field logging and
Record used for field selection of
Analysis
Sedimentology
classification by
samples for preservation and analysis,
geologist.
selection of screen elevations for well
installation, and correlation of
stratigraphy between borings.
Office
Mineralogy by visual
Knowledge of the aquifer mineralogy and
Petrography
examination by
relative percentages of minerals is
geologist. Bulk
needed to evaluate observed
samples and thin
groundwater chemistry and potential for
section. Optical and
COI attenuation by reaction with aquifer
electron microscopy.
solids.
XRD
Mineral identification
Used to identify clay minerals and
Reitveld
by X-Ray Diffraction.
confirm/ support visual determinations of
mineralogy.
EDS
Energy Dispersive
Provides information on the location and
Spectroscopy
relative concentration of trace elements
on mineral surfaces and polished
sections.
Hydrologic
Tracer tests and
Site specific determinations of
Parameters
break -through curve
dispersivity are needed
analysis.
Surface
Surface area of
Determination of reactive area of the
Chemistry
sediments.
aquifer material. Needed to scale the
results of chemical determination.

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October 28, 2015
Page 23 of 27
REFERENCES AND CITATIONS
Butler, J.R., 1953, The geochemistry and mineralogy of rock weathering. I. The Lizard area:
Geochimica et Cosmochimica Acta, v. 4, p. 157.
Dzomback and Morel, 1990. Dzomback, D.A., Morel, F.M.M., 1990. Surface Complexation
Modeling: Hydrous Ferric Oxide. John Wylie and Sons, New York.
EPRI, 2005. Chemical Constituents in Coal Combustion Product Leachate: Boron, EPRI, Palo
Alto, CA. 2005. 1005258.
EPRI, 2006. Groundwater Remediation of Inorganic Constituents at Coal Combustion Product
Management Sites: Overview of Technologies, Focusing on Permeable Reactive Barriers.
EPRI, Palo Alto, CA: 2006. 1012584.
Goldberg et al., 2000. Goldberg, S., Lesch, S. M., and D. L. Suarez. Predicting Boron
Adsorption by Soils Using Soil Chemical Parameters in the Constant Capacitance Model.
Soil Sci. Soc. Am. J., 64(5): 1356-1363, 2000.
Goldsmith, R., Milton, D.J., and Horton, J.W. Jr., 1988, Geologic map of the Charlotte 1 ° x 2°
Quadrangle, North Carolina and South Carolina, 6 p.
Harder, H., 1970, Boron content of sediments as a tool in facies analysis: Sedimentary Geology,
v. 4, p. 153.
Herbelin and Westall, 1999. A. L. Herbelin and J. C. Westall. FITEQL - A Computer Program
for Determination of Chemical Equilibrium Constants from Experimental Data. Report 99-01,
Department of Chemistry, Oregon State University, Corvallis, OR 97331. 1999.
ITRC, 2010. A Decision Framework for Applying Monitored Natural Attenuation Processes to
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Regulatory Council
Karamalidis and Dzomback, 2010. Karamalidis, A. K., Dzomback, D.A., 2010. Surface
Complexation Modeling: Gibbsite. John Wylie and Sons, New York.
Krauskopf, K., 1955, Sedimentary deposits of rare metals: Economic Geology, v. 50, p. 411.
Perry, E.A. Jr., 1972, Diagenesis and the validity of the boron paleosalinity technique: American
Journal of Science, v. 272, p. 150.
Tessier 1979. Tessier, A., Campbell, P. G. C., and M. Bisson. Sequential Extraction Procedure
for the Speciation of Particulate Trace Metals. Analytical Chem., 51(7)844-850.
Thayer et al., 1970. Thayer, P.A., Kirstein, D.S., and Ingram, R.L., 1970, Stratigraphy,
sedimentology, and economic geology of Marshall Basin, North Carolina: Carolina
Geological Society Guidebook, 29p.

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October 28, 2015
Page 24 of 27
Toride, et al., 1999. Toride, N., F.J. Leij, and M.Th. van Genuchten, The CXTFIT Code for
Estimating Transport Parameters from Laboratory or Field Tracer Experiments: Version 2.1.
US Department of Agriculture, Agricultural Research Service, US Salinity Laboratory, April,
1999. Research Report No. 137
USEPA, 1999. Understanding Variation in Partition Coefficient, Kd, Values. Volume I: The Kd
Model Of Measurement, And Application Of Chemical Reaction Codes. EPA 402-R-99-
004A. United States Environmental Protection Agency, Office of Air and Radiation, August
1999.
USEPA, 2007. Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Vol. 1:
Technical Basis for Assessment. 2007. US EPA, EPA/600/R-07/139.
USGS, 2009. Harden, S L., M J. Chapman, and D A. Harned. Characterization of Groundwater
Quality Based on Regional Geologic Setting in the Piedmont and Blue Ridge Physiographic
Provinces, North Carolina. U.S. Geological Survey Scientific Investigations Report 2009-
5149.
USGS, 2013. Chapman, M.J., C. A. Cravotta III, Z. Szabo, and B.D. Lindsey. Naturally
Occurring Contaminants in the Piedmont and Blue Ridge Crystalline -Rock Aquifers and
Piedmont Early Mesozoic Basin Siliciclastic-Rock Aquifers, Eastern United States. 1994-
2008. U.S. Geological Survey Scientific Investigations Report 2013-5072.

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 25 of 27
Table 3. Solid -water hairs used for Tier I demonstration - MSS
GW Soil Analytel aluminum I aluminum I Antimony I Antimony I Arsenic I Arsenic I Barium I Barium I Boron I Boron I Beryllium I Beryllium I Cadmium I Cadmium I Chromium I Chromium I Cobalt I Cobalt I Copper I Copper I Won I Iron I Lead I Lead Wngan-jWnganesel Mercury I Mercury I Molymdenu I Molybdenu I Nickel I Nickel I Selenium I Selenium I Strontium I Strontium I Thallium I Thallium I Vanadium I Vanadium I Zmc I Zim I
25 mdkq uq/L ma/kq uq/L mduq/ kq L mq/kq uq/L mq/ka ug1L ma/kq uq/L mq/kq uq/L mq/kq uglL mq/ka uq/L ma/ka PAIPAI L malka L malka un/L makq PAIL mdkq PAILLm mdkq uq/mdkq uq/L mdkq uq/L mo/kq uq/L m./k. Pq/L mdkq uq/L mq/kq uq/L
BG-IS
10400
3.4
86.7
22
0.52
48.1
3.3
13
0.66
82.7
0.43
20400
60
3.3
279
140
1.2
30.2
2.4
0.5U
77.5
200
0.019
54.1
1.5
42.5
BG-3D
29900
0.45
1670
690
0.32
42
625
2.7
31.9
1.9
23.2
1.1
31500
298
21
1.1
380
7.3
0.5 U
128
160
76.9
21.6
66.4
5.1
AB-1S
12900
1200
4.5
109
97
0.98
1.4
5200
0.2
6.5
0.83
22.8
19.4
1
35400
1800
24
0.35
138
7600
0.015
2.6
5.2
5.4
800
0.27
62.7
40.3
22
AB-2S
12000
140
86.8
78
0.56
40
4.9
7.4
4.2
16100
36
13
408
420
0.011
0.2
1.7
2.6
89
28.7
52.5
9.7
AB-9S
24200
52
4.8
0.86
426
22
0.2 U
0.89
405
12
24.5
1.8
42.2
3.8
26200
49
7.9
0.43
460
110
0.0079
0.34
169
1.7
0.3
165
44
0.062
75.7
0.32
65.3
4.5
AL -IS
17900
1200
0.26
3.9
7.2
288
220
8.4
1.5
4200
0.62
1.3
13.8
10.2
9
1.5
22100
71
6.7
352
3500
0.033
0.32
1.3
9.7
10.5
71
2900
0.16
41.8
84.6
25
AL -IS
21000
1200
0.26
4.3
7.2
402
220
8.4
3
4200
0.62
1.9
13.8
7.4
10.2
5
1.5
27100
71
9.2
576
3500
0.32
1.9
9.7
10.5
119
2900
0.16
52.3
91.6
25
GWA-2S
21700
246
93
0.074
1.1
0.028
14.6
2.2
18.7
2.1
2
9.5
36700
8.2
0.97
633
84
12.6
1.2
4.4
0.24
5.1
25
0.14
118
60.6
8.1
GWA-3S
10500
140
34
0.56
0.033
4.7
0.67
6.3
0.54
8.2
1.9
16300
10.5
0.12
641
90
0.34
1.1
0.8
7.6
47
29
0.37
62.3
15
GWA-4S
1 13200
87.4
38
1.4
0.12
4.7
0.43
6.1
3.5
30.7
4.9
13100
5.2
0.46
568
1400
0.0061
0.2
1.1
1.8
1.2
1
7.9
1 51
44.2
14.9
GWA-4S
9220
134
38
0.5
0.12
7.5
0.43
7.1
3.5
82.8
4.9
18200
0.46
426
1400
0.2
1.1
3.3
1.2
8.8
51
44.1
27
GWA-5S
23000
0.14
490
26
2.6
36
3.1
0.32
8.3
0.94
7.3
1.5
31500
9.3
0.077
509
130
0.71
4.5
5.9
60.7
81
67.7
0.3
101
18
GWA-6S
2350
0.52
38
67
0.096
0.38
0.42
0.62
0.57
3400
4.2
78.1
82
0.28
0.84
3.2
68
5.9 U
10.3
31
GWA-7S
15000
0.28
138
230
1
37
0.027
176
0.55
13.4
3.8
23.2
6.5
21100
190
10.7
0.82
103
310
1.7
62.7
5
38.8
220
0.1
83.1
0.96
39.6
6.5
GWA-7S
7070
7.8
0.28
160
230
0.34 U
37
0.027
31.6
0.55
13.4
3.8
15.8
6.5
43600
190
0.82
679
310
0.0072
1.7
34.8
5
8.9
220
0.1
23.7
0.96
10
6.5
GWA-SS
15500
0.14
198
17
0.91
26
17.3
1.3
10.2
0.27
12.7
0.88
27800
5.5
0.094
348
31
0.18
8.1
0.93
38.9
160
66.9
2.5
84.4
5.7
GWA-8S
17200
0.14
194
17
0.68
26
19
1.3
10.2
0.27
5.3
0.88
28600
5.6
0.094
442
31
0.18
8.3
0.93
34.8
160
70.4
2.5
90.7
5.7
OB-1 WLO
4800
1
3.2
75.6
47
1 1.3
25
1
2.3
0.43
0.98
0.47
8910
15.1
0.14
164
25
1.5
0.8
28.4
26
0.062
12.1
38.3
8.3
MW-14S
1 21900
130
0.26
497
23
4.8
0.56
1.5
2500
0.13
39.5
0.64
14.8
8.5
84.6
9
57800
12
0.06
218
50
12.9
1 0.41 1
23.5
43.5
5.5
65.5
1800
0.066
145
1
68.5
10
MW-14S
1 20000
130
0.26
401
23
3.5
0.56
2.3
25M
0.13
41.7
0.64
20.8
8.5
86.8
9
51200
14.2
0.06
399
50
10.8
0.41
14.6
43.5
5.5
31.8
1800
0.066
231
63.7
10
AB-5BR
5110
0.17
1.5
97.9
280
0.19
11.6
0.55
5
8.2
7
3.7
16WO
660
0.44
163
610
1.8
7.4
9.2
0.44
22.2
1600
0.021
1 22
1 0.44
32.8
70
AB-9BR
1 10000
0.38
5.9
1
568
90
0.42
13.7
2.7
6.3
1.2
15600
3.7
0.17
366
5
10.6
15
0.66
0.49
43.5
240
0.039
33.8
2.4
54
7
AB-15BR
6910
0.26
0.4
334
120
20.7
0.54
5.5
4.8
0.37
10800
12.
214
280
1.2
15.7
0.36
21.7
1100
27.2
43.7
11
AL-2BR
15400
0.27
3.5
0.46
685
140
0.14
2000
0.029
21.8
16
8.4
35.9
1.5
29600
0.1
293
0.31
38.3
i
12.4
0.94
23.4
51
1700
0..
73.5
4
67.7
BG-2BR
1 8970
39.9
161
280
0.2
6.6
9.6
24.2
19700
6.6
312
30
0.32
3.8
40.1
38.5
260
69.6
49.8
10

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 26 of 27
Table 4. Kd data used for Tier I evaluation - MSS
Marshall
AB-15
AB-15
AB - 1 BR
AB - 1 BR
AB - 6BR
AB - 6BR
AS - 1 D
AS - 1 D
AB - 4D
AB - 4D
AB - 8D
AB - 8D
AB - 11 D
AB - 11 D
AB - 16D
AB - 16D
AB - 2S
AB - 2S
GWA - 2
GWA - 2
GWA - 1
GWA - 1
Metals
20 - 25 FT
20 - 25 FT
33 - 33.5 133
- 33.5 157.5
- 59 157.5
- 59 146
FT
46 FT
63.3 - 70.
63.3 - 70.
30 - 32.5 F
30 - 32.5 112.5
- 15 112.5
- 15 113
- 15 FT
13 - 15 Fr
31 - 32 Fr
31 - 32 FT
83.5 - 84.
83.5 - 84.
50 - 52 FT
50 - 52 FT
Antimony
Arsenic
469.3
459.9
32.8
36.6
52.1
48.2
11
11.6
343.2
336.6
340
356.4
399.5
401.6
495.8
496.5
36.6
34
316.5
336.4
Boron
Cadmium
893.7
870.7
21.3
20.4
149.2
149.5
52.2
48.7
108.1
76.5
429.1
429
296.7
330.5
1210.2
1080.9
62
62.8
170.6
172.7
196.6
194
Chromium
467.2
387
447.5
351.4
Cobalt
Molybdenum
Selenium
Thallium
192.5
223.7
107.7
103.1
610.6
677.9
521.8
479.5
121
86.2
565.4
546.3
1845.3
1624.1
803.8
795.1
75.1
76
678.4
673.2
730.9
695.4
Vanadium
228.1
237.8
6.5
5.7
1265
1405.1
525.3
547.21
190.8
194.3
23.8
22.7
Median Kd
Max/Min
Thallium
555.85
Vanadium
247
Chromium
417.25
Cadmium
59.3
Arsenic
336.5
Arsenic
45.1
Vanadium
211.2
Thallium
24.6
Cadmium
171.65
Chromium
1.3
Antimony
Antimony
Boron
Boron
Cobalt
Cobalt
Molybdenum
Molybdenum
Selenium
Selenium

M. Filardi
MSS MNA Tier I & II
October 28, 2015
Page 27 of 27
Table 5. Average trace metal composition for tonalite at the Marshall Steam Station.
(ppm) B V Cr Co As
Se
Sb
TI
Tonalite (mqd)
14
99
18
7
1.4
0.1
0.2
0.7
Granite (IPhs)
7
72
4
4
1
0.1
0.3
1.4
Quartz-sericite schist (Zbs)
55
108
109
9
0.5
0.1
0.3
0.7
Biotite gneiss (bgf)
5
56
56
13
2
0.1
1
0.3
Soil (MSS CSA max)
500
900
42
48
7
4
Transistion Zone (MSS CSA max)
500
200
42
8
1
1
Whole Rock (MSS CSA max)
400
500
54
11
1
5

Summary of Statistically Derived Kd Values - Marshall Steam Station
Variable
Num Obs
# Missing
Minimum
Maximum
Mean
SD
SEM
MAD/0.675
Skewness
Kurtosis
CV
Arsenic
42
30
10.4
767.3
198.8
198
30.55
138.5
1.082
0.895
0.996
Boron
10
55
1.1
2.6
1.9
0.499
0.158
0.741
-0.181
-1.153
0.263
Cadmium
28
44
48.1
3399
452
811.7
153.4
152.2
3.245
9.915
1.796
Manganese
8
58
8.4
124.4
37.45
39.99
14.14
24.02
1.686
3.135
1.068
Molybdenum
14
55
5.1
39.1
19.78
10.56
2.823
8.747
0.575
-0.224
0.534
Selenium
14
55
2.3
95.4
58.12
30.39
8.122
34.1
-0.685
-0.307
0.523
Thallium
28
38
15.3
902.7
392.8
275.4
52.04
403
0.159
-1.273
0.701
Vanadium
26
46
2.7
13700
1126
3356
658.2
68.2
3.416
10.72
2.981
Note: Prepared by Geochemical, LLC based on UNCC laboratory results.
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