Sediment Issue 

Use of Sediment Core Profiling in Assessing 

Effectiveness of Monitored Natural Recovery
 

Purpose 

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 Laboratory (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 sediment management alternatives (1). Information 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 cooperation 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, natural 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, protecting the water column and biota from diffusion and advection of 
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, contaminant weathering (e.g., dilution, volatilization, biodegradation, 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 sediment 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-concern (COC) release and, at a given depth, the maximum 

COC concentration will reveal the time at which the sediments 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 longterm accumulation from naturally occurring background 

and urban run-off sources and as a result of releases from 

industrial facilities. Conventional hydrocarbon fingerprinting 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 sediments 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 sediment). 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 procedure 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. Contaminant concentrations in sediment are plotted against depth 

below the sediment-water interface, and best-fit logarithmic 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 sediment core techniques to assess MNR: 

• Natural background and/or urban run-off may be an ongoing 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 causing 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. 

2 
 

Case Studies 

Wyckoff/Eagle Harbor Superfund Site 

Eagle Harbor, a shallow marine embayment of Bainbridge 

Island, WA, was formerly the site of the Wyckoff woodtreatment 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 sediment 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 collected 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 sediment 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 publication (6), but a brief description of how sources are 

classified follows. Natural background fingerprints 

exhibit odd-carbon dominated n-alkanes (C25– C31 

compounds), which are indicative of plant epicuticular 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, fluoranthene, pyrene, chrysene, benzo(j,k)fluoranthene, 

and indeno(1,2,3-cd)pyrene. Creosote fingerprints 

are dominated by discrete peaks indentified as various 2-ring PAHs (C0

 – C4 naphthalenes) and 3- and 

4-ring compounds such as phenanthrene, anthracene, 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 resembling those found in urban run-off. Comparing PAH results, as in Figure 2, with depth and age provides information 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 creosote and some pure-phase creosote. Sediment characteristics 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 characteristics 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 accumulation 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 creosoteFigure 1. Eagle Harbor Site Map Showing Coring Locations. Reprinted 

with permission from (2). Copyright 2002, American Chemical Society. 

3 
 

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 consistently to burial and served as an ongoing source of PAHs to the 

harbor’s sediments, albeit in comparatively low concentrations, 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 sediments 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 unspecified 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). 

Figure 2. Eagle Harbor PAH Histograms Showing t-PAH Concentrations 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. 

Figure 3. Eagle Harbor Sediment Accumulation Rates for Selected 

Harbor Cores (B01 core adjacent to the former Wyckoff Facility; 

EO cores located mid harbor). Reprinted with permission from (2). 

Copyright 2002, American Chemical Society. 

Figure 4. Lake Hartwell Transect Locations. Reprinted with 

permission from (3). Copyright 2002, American Chemical Society. 

4 
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 concentrations 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 concentrations. 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 sediment data by plotting sediment age against sediment concentration. As shown in Figure 6, sediment t-PCB concentrations 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 penetrated 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 

relatively low t-PCB concentrations at the sediment-water 

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 detection 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 behavior of the Transect J core profile (Figure 6-d) was inconsistent 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 

for Transect I cores, 1988 to 2011 for Transect L cores, 

1995 to 2010 for Transect N cores, and 1992 to 2016 for 

Transect O cores. 

Figure 5. Vertical t-PCB Concentration Profiles for Cores Collected from Upgradient 

Transects T16(a) and Q(b). Silt/sand layers are shown on the right-hand side of each 

figure. Vertical axes are not to scale. Reprinted with permission from (3). Copyright 2004, 

American Chemical Society. 

5 
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 (○)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. 

6 
Conclusions 

The success of MNR as a risk reduction approach 

typically is dependent on understanding the dynamics 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 vertical 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 distinct PAH sources (creosote, urban runoff, and natural 

background) contributed to the sediment contamination, 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 deposits 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 capping by the deposition of clean sediment entering the 

lake. The results of the investigation at this site were 

used to determine surface sedimentation, surface sedimentation 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 sediments 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, E.A. Crecelius, and L.S. Bingler. 2002. Characterization and Fate of PAH-Contaminated Sediments at 

the Wyckoff/Eagle Harbor Superfund Site. Environ. Sci. 

Technol., 36 (12): 2605-2613. 

(3)	 Brenner, R.C., V.S. Magar, J.A. Ickes, E.A. Foote, J.E. 

Abbott, L. Bingler, and E.A. Crecelius. 2004. LongTerm Recovery of PCB-Contaminated Surface Sediments 

at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell 

Superfund Site. Environ. Sci. Technol., 38 (8): 2328-2337. 

(4)	 Magar, V.S. 2001. Natural Recovery of Contaminated Sediments. J. 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.C. Bonniwell, and P.J. Whiting. 2002a. Soil 

Erosion and Sediment Sources in an Ohio Watershed using 

Beryllium-7, Cesium-137, and Lead-210. J. Envrion. Qual., 

31: 54-61. 

(8)	 Matisoff, G., E.C. Bonniwell, and P.J. Whiting. 2002b. 

Radionuclides as Indicators of Sediment Transport in Agricultural Watersheds that Drain to Lake Erie. J. 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, Acta., 37: 

1171-1187. 

(10) Van Metre, P.C. 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. J. Paleolimnol., 17: 239-249. 

(11) Van Metre, P.C., 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. Sci. Technol., 32: 3312-3317. 

(12) Van Metre, P.C., 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 Silver, Mercury, Lead, Copper and Cadmium in Central Puget 

Sound Sediments. Mar. Chem., 21: 377-390. 

(14) United States Environmental Protection Agency. 1994. Superfund Record of Decision: Sangamo-Weston/Twelvemile Creek/ 

Lake Hartwell Site, Pickens, GA: Operable Unit 2; EPA/ROD/ 

R04-94/178. 

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