&ER&
United States
Environmental Protection
Agency
Sediment Issue
Use of Sediment Core Profiling in Assessing
Effectiveness of Monitored Natural Recovery
Introdution
Methods to Assess MNR Processes
Challenges Associated With Using
Core Methods
Case Studies
Wyckoff/Eagle Harbor
Superfund Site
Sangamo-Weston/
Twelvemile Creek/Lake Hartwell
Superfund Site
Conclusions
References
Purpose
The National Risk Management Research Lab-
oratory (NRMRL) of the U.S. Environmental
Protection Agency (U.S. EPA) is developing
effective, inexpensive remediation strategies for
contaminated sediments. Monitored Natural
Recovery (MNR) is included among such sedi-
ment management alternatives (1). Informa-
tion summarized in this Sediment Issue pertains
specifically to studies conducted by NRMRL
(2, 3) that evaluated the recovery of surface
sediments contaminated with polychlorinated
biphenyls (PCBs) and polycyclic aromatic
hydrocarbons (PAHs). This information is
intended to: a) be used as a reference for site
managers and U.S. EPA decision makers who
may be considering MNR as a contaminated
sediments management strategy, and b) provide
a better understanding of the mechanisms that
Sediment Core Sample Collection at Eagle Harbor
contribute to the natural recovery of contaminated sediments and
the tools used to assess the natural recovery processes.
The results of two NRMRL studies (2, 3) undertaken to evaluate
MNR processes and mechanisms are summarized below. These
two studies were conducted at a marine site (the Wyckoff/Eagle
Harbor Superfund Site off Bainbridge Island, WA) in cooperation
with U.S. EPA Region 10 and the U.S. Army Corps of Engineers,
and at a freshwater site (the Sangamo-Weston/Twelvemile Creek/
Lake Hartwell Superfund Site in Pickens County, SC) in coopera-
tion with U.S. EPA Region 4.
Introduction
MNR involves leaving contaminated sediments in place and
allowing ongoing physical, chemical, and biological processes to
contain, destroy, or otherwise reduce the bioavailability or toxicity
of contaminants in sediment (1), while implementing a monitoring
program to determine if attenuation of contaminants is occuring
(4, 5). Reduction of a contaminant's bioavailability and toxicity
occurs primarily at the sediment surface (typically defined as the
sediment-water interface). In net depositional environments, natu-
ral capping with relatively clean sediments is often the dominant
and more immediate recovery mechanism following source removal
and/or control (2). Natural sediment deposition may reduce
surface sediment contaminant concentrations over time, protect-
ing the water column and biota from diffusion and advection of
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contaminants from sediments (4). Additionally, deposition
will reduce both the risk of resuspension of contaminated
sediments during high-flow events and the potential for
contaminant transport into the food chain (4).
Similar to natural attenuation of terrestrial contaminants,
natural recovery of contaminated sediments relies on
careful assessment and long-term monitoring of sediment
recovery mechanisms, including sediment burial, con-
taminant weathering (e.g., dilution, volatilization, biodeg-
radation, and sequestration), degradation, and potential
transport.
Methods to Assess MNR Processes
For these two NRMRL studies (2, 3), assessment of MNR
processes began with the collection of sediment core
samples. Sediment cores can be used to establish vertical
contaminant concentration profiles, age date sediments,
and determine surface sedimentation and surface sediment
recovery rates. These approaches are summarized below.
Contaminant Profiling and Fingerprinting. The sedi-
ment core profile may provide a historical record of the
deposition on the bed surface; the sediment-water interface
represents the date of sample collection and increasingly
older sediments are found at increasing depths below the
surface (2). In a typical core profile, the deepest portion of
the core represents some time before contaminant-of-con-
cern (COC) release and, at a given depth, the maximum
COC concentration will reveal the time at which the sedi-
ments were impacted by the contaminant source. In net
depositional environments, core sediments above this area
of maximum concentration may show decreasing COC
concentrations as the source is contained or removed, and
relatively clean sediments have been deposited.
Chemical fingerprinting relies on analytical methods to
quantify unique chemical signatures or patterns in order
to identify or distinguish different chemical sources. For
example, PAHs often display unique compositions that
can be used to identify sources (6). PAHs are commonly
present in urban sedimentary environments due to long-
term accumulation from naturally occurring background
and urban run-off sources and as a result of releases from
industrial facilities. Conventional hydrocarbon finger-
printing and PAH homolog distributions can be used to
characterize contaminant sources and the extent of PAH
weathering (6).
Sediment Age Dating and PSD Analysis. Lead-210
(210Pb) or cesium-137 (137Cs) isotope analysis can be used
to enhance the core depositional profile by dating each
core segment, providing an age profile along the length
of the core. These two isotopes are relatively common in
sediments and can be used to determine the age of sedi-
ments over years or decades (7, 8). Age dating provides
information on the temporal variations of contaminant
release, sediment accumulation rates, and surface mixing
depths (7, 9-13). 137Cs is most useful in identifying strata
deposited in the early 1960s, a period of atmospheric
nuclear testing, while 210Pb is deposited continuously from
the atmosphere and can be used to estimate more recent
dates (4). These two isotopes partition to particle surfaces,
and their sorbed concentrations in sediment depend on the
sediment particle size distribution (PSD) (e.g., fine-grained
sediment generally contains higher activity than sandy sedi-
ment). Thus, the ability to accurately age date sediments
is influenced by the uniformity of the PSD through the
dated vertical profile and the historical consistency of the
sedimentation rate over the dated period. When these two
conditions are not met, the accuracy of the dating proce-
dure is compromised. Age dating results may be combined
with contaminant concentration profiles to estimate the
time required to meet surface sediment remediation or
recovery goals.
Surface Sedimentation and Surface Sediment Recovery
Rates. Using surface sedimentation requirements (i.e.,
target cleanup goals) and age dating results, the time for
surface sediment recovery can be predicted. Contami-
nant concentrations in sediment are plotted against depth
below the sediment-water interface, and best-fit logarith-
mic regressions are defined for the surface sediment data.
Best-fit logarithmic regressions are calculated to determine
95% prediction intervals for the dates when cleanup goals
would be met, assuming site and source conditions remain
constant.
Challenges Associated With Using
Core Methods
Several challenges may be associated with the use of sedi-
ment core techniques to assess MNR:
• Natural background and/or urban run-off may be an on-
going source of contamination to the sediments.
• Making future predictions based on extrapolation of past
data trends for sediment recovery rates may be difficult
because there is no guarantee that the fate processes caus-
ing the exponential decay of surface sediment
concentrations will continue at the same rate in the
future. Therefore, long-term monitoring must remain
an integral component of MNR so that the recovery of
surface sediments can be determined.
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Case Studies
Wyckoff/Eagle Harbor Superfund Site
Eagle Harbor, a shallow marine embayment of Bainbridge
Island, WA, was formerly the site of the Wyckoff wood-
treatment facility where large quantities of creosote were
used from the early 1900s to 1988. Historical creosote
seepage into the harbor resulted in substantial PAH
contamination in the harbor sediments over time (14).
Vertical contaminant profiling and age dating of sediment
cores were used to assess and document the history of
PAH accumulation, measure the extent of natural sedi-
ment capping, and document compositional changes and
sources over time and space around the Wyckoff Site and
within Eagle Harbor (2).
To control PAH migration into the water column and
surrounding sediments, the area with maximum PAH
concentrations was capped. Sediment cores were col-
lected from 10 locations in uncapped areas in Eagle
Harbor including six nearshore (near the Wyckoff facility)
and four toward the middle of the harbor, as shown in
Figure 1. These data (five segments per core) were used
to determine PAH sources, sediment deposition rate, and
PAH mass reduction due to weathering (e.g., dilution,
volatilization, biodegradation, and sequestration).
The results of total petroleum hydrocarbons (TPHs)
fingerprinting, analysis of 50 PAH compounds, and sedi-
ment age dating conducted on these core segment samples
facilitated the classification of the Eagle Harbor sediments
among three recognized primary PAH sources - namely,
natural background, urban run-off, and creosote (from
the former Wyckoff wood-processing facility).
The fingerprinting and source characterization
process is discussed in detail in a previous publica-
tion (6), but a brief description of how sources are
classified follows. Natural background fingerprints
exhibit odd-carbon dominated n-alkanes (C25— C
compounds), which are indicative of plant epi-
cuticular waxes from terrestrial plant debris. The
urban run-off fingerprint is dominated by discrete
peaks recognized as non-alkylated 3-, 4-, and 5-ring
PAHs such as phenanthrene, anthracene, fluoran-
thene, pyrene, chrysene, benzo(j,k)fluoranthene,
and indeno(l,2,3-cd)pyrene. Creosote fingerprints
are dominated by discrete peaks indentified as vari-
ous 2-ring PAHs (CQ - C4 naphthalenes) and 3- and
4-ring compounds such as phenanthrene, anthra-
cene, fluoranthene, and pyrene. Quantitative PAH
data are used to confirm the peak identification.
As creosote weathers, it becomes dominated by 4- to 6-ring
PAHs, increasingly resulting in PAH compounds resem-
bling those found in urban run-off. Comparing PAH re-
sults, as in Figure 2, with depth and age provides informa-
tion on the source. Total PAH (t-PAH) histograms were
constructed for each core, corresponding to the appropriate
sediment segment. From sediment cores collected nearest
the cap (near-shore) (Figure 2-b), it was determined that
surface sediment contamination was dominated by urban
run-off and weathered creosote, while deeper sediments
were heavily contaminated with relatively unweathered cre-
osote and some pure-phase creosote. Sediment character-
istics for five of the six near-shore samples did not permit
age dating; thus, estimated dates corresponding to depth
segments are not provided in Figure 2-b. Cores located
furthest from the cap in the center of the Harbor (Figure
2-c) were dominated by urban run-off with no signs of
creosote contamination. Sedimentation rates were similar
for the four cores located in the middle of the harbor and
one near-shore core, ranging from 0.54 to 1.10 gm/cm2-yr.
Sediment accumulation rates (cm/yr) are plotted against
core segment age in Figure 3, where sediment character-
istics permitted age dating. Cores having nonuniform
historical sediment deposition could not be dated using the
210Pb data. Only one core adjacent to the former Wyckoff
Facility (B01) and the mid-harbor cores (E01, E02, E03,
E04) could be dated; therefore, only sediment accumula-
tion rates for these cores are shown in Figure 3-
The results from this study (2) provided information on
the ability of Eagle Harbor sediments to recover under
natural conditions, identified the occurrence of creosote-
Explanation
O Coring Location
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Figure 1. Eagle Harbor Site Map Showing Coring Locations. Reprinted
with permission from (2). Copyright 2002, American Chemical Society.
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centrations and Contaminant Source Characteristics, (a) B03 core
located adjacent to the former Wyckoff Facility, (b) X03 core located
near shore, (c) E02 core located mid harbor. Reprinted with permission
from (2). Copyright 2002, American Chemical Society.
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Figure 3. Eagle Harbor Sediment Accumulation Rates for Selected
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EO cores located mid harbor). Reprinted with permission from (2).
Copyright 2002, American Chemical Society.
derived PAH weathering in off-cap surface sediments, and
distinguished between three distinct PAH sources in the
harbor (creosote, urban run-off, and natural background).
Recognition that urban run-off has contributed consistent-
ly to burial and served as an ongoing source of PAHs to the
harbor's sediments, albeit in comparatively low concentra-
tions, is a key piece of information. Such information may
influence future sediment management decisions for this
site with respect to long-term monitoring of surface sedi-
ments to assess cap performance.
Sangamo- Weston/Twelvemile Creek/Lake Hartwell
Superfund Site
At the Sangamo-Weston/Twelvemile Creek/Lake Hartwell
Superfund Site in South Carolina, the primary focus was
the recovery of PCB-contaminated surface sediments
resulting from natural sedimentation. As described in
U.S. EPA (14), Lake Hartwell was contaminated by PCBs
released from the Sangamo-Weston plant located upstream
of the study area. Capacitors were manufactured at this
plant from 1955 to 1978, and waste disposal practices
included land burial of off-specification capacitors and
wastewater treatment sludge on the plant site. An unspeci-
fied amount of PCBs were either buried or discharged with
effluent directly into the water (14). NRMRL conducted
a study in which core profiles were used to establish total
PCB (t-PCB) concentration profiles, age date sediments,
and determine surface sedimentation and surface sediment
recovery rates in 18 cores collected along 10 transects in
the lake, shown in Figure 4 (3).
Sediment
Impoundments
Figure 4. Lake Hartwell Transect Locations. Reprinted with
permission from (3). Copyright 2002, American Chemical Society.
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Vertical t-PCB concentration profiles were developed by
plotting concentration against core depth for both the
upgradient and downgradient transects. Figure 5 provides
an example of t-PCB concentration plotted against core
depth for two of the upgradient cores collected at Transects
T16 and Q. In both cores, the highest PCB concentra-
tions were associated with silt layers, which contained 57
± 6.9% silt and clay and 2.6 ± 0.86% total organic carbon
(TOC). The sand layers contained 96 ± 2.9% sand and
0.21 ± 0.08% TOC and had much lower PCB concentra-
tions. These vertical concentration profiles showed that
historical sediment releases resulted in substantial burial
of PCB-contaminated sediment by sand with low t-PCB
concentrations, so that each upgradient core contained
less than 1 mg/kg t-PCBs in the surface sand layers. This
concentration meets the cleanup goal of 1 mg/kg based
on the 1994 Record of Decision for Lake Hartwell (14).
Much higher PCB concentrations were present in buried
sediment with maximum t-PCB concentrations measured
at approximately 30 to 60 cm below the sediment-water
interface. These higher concentrations are associated with
the period of maximum PCB release into the watershed
circa 1960-1980.
To estimate the rate of surface sediment recovery, best-fit
logarithmic regressions were developed using surface sedi-
ment data by plotting sediment age against sediment con-
centration. As shown in Figure 6, sediment t-PCB con-
centrations are plotted against depth for six Lake Hartwell
cores; each figure also shows the cleanup goal of 1.0
mg/kg t-PCBs. Of these six cores, only cores from
Transects L (Figure 6-c) and T6 (Figure 6-f) fully penetrat-
ed the PCB-contaminated sediments to provide a complete
vertical profile of PCB contamination. For the Transect
L core, the vertical t-PCB concentration profile indicates
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interface, increasing in concentration with depth until the
maximum t-PCB concentration was measured at the 35 to
40 cm interval. The maximum t-PCB concentration was
followed by progressively decreasing concentrations with
depth until the t-PCB concentration approached the detec-
tion limit at ^85 cm below the sediment water interface,
where sediments were likely deposited at the onset of PCB
use at Sangamo-Weston. The sediments containing the
maximum PCB concentrations are associated with the
period of maximum PCB release into the watershed. For
the Transect T6 core, the maximum t-PCB concentration
occurred at the 15 to 20 cm depth interval; the shallower
depth may be explained by the observation that Transect
T6 had the lowest measured sedimentation rate. The be-
havior of the Transect J core profile (Figure 6-d) was incon-
sistent with the other cores collected in 2000 and cannot
readily be explained; the Transect J core was represented by
relatively low t-PCB concentrations (-1 to 1.5 mg/kg) over
the entire 30-cm profile.
Best-fit logarithmic regressions were calculated to develop
95% prediction intervals for the dates at which
cleanup goals would be met. Using these equations,
sedimentation requirements to achieve each of the surface
sediment cleanup goals were determined based on the
present t-PCB value. Estimated time to achieve the
1.0-mg/kg surface sediment recovery goal stipulated in the
Superfund Record of Decision (14) varied depending on
the location of the sample. Estimated surface recovery to
1 mg/kg was predicted to occur between 2000 and 2012
forTransect I cores, 1988 to 2011 forTransect L cores,
1995 to 2010 forTransect N cores, and 1992 to 2016 for
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Figure 6. Lake Hartwell Sediment t-PCB Concentrations (mg/kg) Plotted Against Depth Below Sediment-Water Interface for
Sediment Cores. Best-fit logarithmic curves are shown with corresponding equations and correlation coefficient to estimate surface
sediment recovery. Solid symbols (•) represent data used to generate the curves. Open symbols (o)represent remaining data for
depiction of vertical profile.Vertical dashed lines represent the 1-mg/kg t-PCB cleanup goal. Reprinted with permission from (3). Copyright
2002, American Chemical Society.
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Conclusions
The success of MNR as a risk reduction approach
typically is dependent on understanding the dynam-
ics of the contaminated environment and the fate and
mobility of the contaminant in that environment (1).
The natural recovery process evaluated at both study
sites summarized in this Sediment Issue relied on verti-
cal contaminant profiling and age dating of sediment
cores to assess the history of contaminant accumulation;
measure the extent of natural sediment capping; and
document contaminant accumulation, compositional
changes, and sources over time and space. For the Eagle
Harbor site, the investigation revealed that three dis-
tinct PAH sources (creosote, urban runoff, and natural
background) contributed to the sediment contamina-
tion, with urban runoff continuing as an on-going
source. In addition, no evidence was found to indicate
that the study area was being covered by natural depos-
its of clean, uncontaminated sediments; thus, MNR was
not employed as the final cleanup remedy.
Conversely, the cleanup plan for the Lake Hartwell site
relies on natural recovery, which involves natural cap-
ping by the deposition of clean sediment entering the
lake. The results of the investigation at this site were
used to determine surface sedimentation, surface sedi-
mentation rates, and predictions for the year cleanup
goals would be achieved in the surface sediment. Given
the inherent challenge of making future predictions
based on extrapolation of historical data, long-term
monitoring of the natural recovery remedy is needed at
this site to determine whether recovery of surface sedi-
ments continues to occur.
References
(1) United Stated Environmental Protection Agency. 2005.
Contaminated Sediment Remediation Guidance for
Hazardous Waste Sites, OSWER 9355.0-85, EPA540/
R05/012. December, http://www.epa.gov/superfund/
resources/sediment/pdfs/guidance/pdf.
(2) Brenner, R.C., V.S. Magar, J.A Ickes, J.E. Abbott, S.A
Stout, EA. Crecelius, and L.S. Bingler. 2002. Charac-
terization and Fate of PAH-Contaminated Sediments at
the Wyckoff/Eagle Harbor Superfund Site. Environ. Set.
TechnoL, 36(12): 2605-2613.
(3) Brenner, R.C., V.S. Magar, J.A. Ickes, EA. Foote, J.E.
Abbott, L. Bingler, and E.A. Crecelius. 2004. Long-
Term Recovery of PCB-Contaminated Surface Sediments
at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell
Superfund Site. Environ. Set. TechnoL, 38 (8): 2328-2337.
(4) Magar, V.S. 2001. Natural Recovery of Contaminated Sedi-
ments. /. Environ. Eng., 127(6): 473-474.
(5) National Research Council. 1997. Contaminated Sediments
in Ports and Waterways: Clean-up Strategies and Technologies:
National Academy Press; Washington, DC.
(6) Stout, S.A., V.S. Magar, R.M. Uhler, J. Ickes, J. Abbott, and
R. Brenner. 2001. Characterization of Naturally-occurring
and Anthropogenic PAHs in Urban Sediments — Wycoff/
Eagle Harbor Superfund Site. Environ. Forensics, 2: 287-300.
(7) Matisoff, G., E.G. Bonniwell, and P.J. Whiting. 2002a. Soil
Erosion and Sediment Sources in an Ohio Watershed using
Beryllium-7, Cesium-137, and Lead-210. /. Envrion. QuaL,
31: 54-61.
(8) Matisoff, G., E.G. Bonniwell, and P.J. Whiting. 2002b.
Radionuclides as Indicators of Sediment Transport in Agricul-
tural Watersheds that Drain to Lake Erie. /. Environ. Qual.,
31: 62-72.
(9) Koide, M., K.W. Burland, and E.D. Goldberg. 1973.
Th-228/Th-232 and Pb-210 Geochronologies in Marine
and Lake Sediments. Geochim. Et cosmochim, Acts.., 37:
1171-1187.
(10) Van Metre, PC. and E. Callender. 1997. Water-Quality
Trends in White Rock Creek Basin from 1912-94 Identified
Using Sediment Cored from White Rock Lake Reservoir,
Dallas, Texas. /. PaleolimnoL, 77:239-249.
(11) Van Metre, PC., J.T Wilson, E. Callender, and C.C. Fuller.
1998. "Similar Rates of Decrease of Persistent, Hydrophobic
and Particle-Reactive Contaminants in Riverine Systems."
Environ. Set. TechnoL, 32: 3312-3317.
(12) Van Metre, PC., B.J. Mahler, and E.T Furlong. 2000.
Urban Sprawl Leaves Its Signature. Environ. Sci. TechnoL, 34
(19): 4064-4070.
(13) Bloom, N.S. and E.A. Crecelius. 1987. Distribution of Sil-
ver, Mercury, Lead, Copper and Cadmium in Central Puget
Sound Sediments. Mar. Chem., 21: 377-390.
(14) United States Environmental Protection Agency. 1994. Su-
perfund Record of Decision: Sangamo-Weston/Twelvemile Creek/
Lake Hartwell Site, Pickens, GA: Operable Unit 2; EPA/ROD/
R04-94/178.
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