Guidance For Sediment Quality Evaluations
November
1998
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2.0 Sampling Plan Design
2.1 Sediment Sampling
Plan
Generally, the goals of a sediment sampling
program include preliminary and definitive determination
of the nature and areal extent of contamination, and identification
of areas of highest contamination. Data may also be gathered
in support of ecological risk assessments, long-term monitoring,
or for sediment transport and deposition modeling. The sediment
sampling plan shall be a component of the Site Investigation
or Remedial Investigation Work Plan, and shall be prepared
pursuant to N.J.A.C. 7:26E and the NJDEP
Field Sampling Procedures Manual (FSPM, May 1992 or most recent version). Department approval may be required,
pursuant to the oversight document (for privately funded
projects) or contract in effect. Site-specific details regarding
the study objectives, data quality objectives, sampling
methodology, location, and depth of samples must be specified,
as well as field and laboratory quality control/quality
assurance procedures. Guidance and special considerations
for designing a sediment sampling scheme are provided herein
to supplement and highlight the regulatory requirements
and FSPM guidance; the reader is referred to these documents
for a comprehensive treatment of the subject.
- Number of Samples
The reader is referred to USEPA’s Sediment Sampling
Quality Assurance User’s Guide (USEPA, 1985) and the
NJDEP FSPM for guidance on statistically determining the
appropriate number of sediment samples.
- Location
In aquatic systems, the areas of greatest contamination
will generally occur in depositional areas, thus these
must be specifically targeted by the sampling plan.
Such depositional areas are generally characterized
by slow moving water where fine sediments tend to accumulate
(e.g., pool areas, river bends, etc.). Sediment samples
collected for chemical analysis, toxicity testing and
benthic community surveys must be spatially and temporally
co-located.
- Stream/River/Tidal Creeks Systems
An idealized approach to locating sediments samples
is as follows: The stream location adjacent to the
contaminated site most likely to receive contaminant
input via the chemical migration pathway is considered
the initial sample point. The study region is divided
into linear segments and sample transects located
systematically within each segment; the length of
the segments and distance between transects increases
with increasing distance downstream. This is depicted
in Figure 1, a diagram of a sampling plan indicating
15 sediment samples per segment region. In this
example, the first segment is from 0 to 1 km, the
second from 1 to 3 km, and third from 3 to 7 km.
The sampling transects are located at 1/4, 1/2,
and 3/4 the distance along each segment. Sample
points are located along the transects at 1/6, 1/3,
1/2, 2/3, and 5/6 the distance bank to bank (USEPA,
1985). In tidal creeks, the distance from bank to
bank is measured from the high water mark. Note
that upgradient sediment samples must be collected
(refer to Section 2.3),
thus similar sampling transects should be located
upstream of the initial sampling point.
The actual number and location of sample points
will be decided on a case-by-case basis, based on
the study objectives, water body dimensions, flow
conditions, substrate conditions, availability of
previous data, etc.
- Lakes/Lagoons/Pond Areas
Sediment samples must be biased toward inflow/outflow
areas and topographically low/deep areas where sediments
may be expected to accumulate. If there is no basis
for biasing, then random sampling of these areas
is required, pursuant to N.J.A.C. 7:26E-3.9(f).
- Sample Depth
Pursuant to N.J.A.C. 7:26E-4.1, surface and subsurface
sediment samples are required for contaminant delineation
and to assess the potential for resuspension of contaminated
sediments during flood/current-based scouring events,
dredging operations, or other disturbances. Surface sediment
samples must be taken at the 0-6" interval, generally
considered the biotic zone in sediments. Subsurface core
samples, 6-12" or deeper (actual depth based on site-specific
conditions), are appropriate in areas of known discharge
of contaminated groundwater to surface water (refer to
2.1.5. below) or where known historic discharges have
become overlain with newer sediment.
- Analytical Protocol and Additional Measurements
In addition to bulk chemistry analysis pursuant to N.J.A.C.
7:26E-2, a sediment quality evaluation may include
additional physical measurements, including but not limited
to river depth, flow rate, suspended solids, bed load,
pH, and temperature. Total organic carbon (TOC) and particle
grain size must be included as indicators of contaminant
bioavailability and the depositional nature of the sediments.
TOC is necessary for the determination of certain sample-specific
sediment quality guidelines ( refer to Section
3.0).
- Volatile Organic Contamination
The most prevalent scenario requiring the collection
of sediment samples when volatile organics are of potential
concern is when contaminated groundwater is known/suspected
to discharge to a surface water body. When this pathway
is being investigated, the sediment samples shall be collected
from the 6-12" interval. It should be noted that
non-aqueous samples to be analyzed for volatile organics
shall be sampled using a methanol extraction/preservation
method acceptable to the NJDEP pursuant to N.J.A.C. 7:26E-2.1
(a)4.
2.2 Special Consideration
for Sampling in Tidally-Influenced Areas
Salinity and tides can be strong factors
in the distribution of contaminants. The delineation of
the point at which these effects are most pronounced, and
the distribution of the highly contaminated sediments, might
be confounded by these factors. For example, as contaminated
water moves downstream, an abrupt increase in salinity can
cause a sudden change in contaminant solubility. When less
soluble, a contaminant may precipitate and appear in the
sediment at substantially higher concentrations than the
previous (i.e., upstream) location. These factors should
be taken into consideration and assessed when making decisions
regarding the selection of sample locations and relation
of contaminants to the site.
Sediment sampling must be conducted during
consistent tidal conditions. Either an ebb tide or flood
tide interval is appropriate and shall be decided on a case-by-case
basis. The tidal stage must be recorded. Samples must be
collected from depositional areas (e.g., intertidal areas
along the shoreline, which are often marked by emergent
vegetation and muddy or organic bottoms, as well as mudflats,
etc.).
2.3 Chemical Characterization
of Upgradient and/or Offsite Reference Conditions
When investigating sediment contamination
in order to determine if it is linked to site operations,
it is important to establish the chemical composition of
upgradient sediments. These data also aid in the assessment
of the site’s contamination relative to the regional quality
of the water body being investigated and in the development
of remedial goals. The SRP recognizes that many of the State’s
water bodies, especially in urban/industrial settings, have
become contaminated by historic point and non-point discharges,
resulting in the diffuse, anthropogenic contamination of
sediments at concentrations greater than natural background.
Additionally, upgradient sediments can be contaminated by
the site because of tidal influences. While it is difficult
to distinguish between site and non site-related contamination
at these settings, it is the policy of NJDEP as well as
USEPA Region II to make a reasonable attempt to do so. If
potential sources of contamination are present upstream
of the site, and it is believed that these sources have
contributed to the contamination detected on-site, these
upgradient areas should be sampled, and professional judgment
should dictate how these data are to be interpreted/utilized
(refer to Section 3.0). Note
that these results will not be considered representative
of true reference (i.e., natural background) conditions.
Certain site-specific conditions or study
objectives may warrant the sampling of an offsite local
reference location. The need for such data shall be determined
on a case-by-case basis in consultation with BEERA/ETRA.
For upgradient and offsite reference locations,
SRP recommends the collection of a minimum of three (3)
to five (5) samples to establish a range of reference location
contaminant concentrations (the larger number of samples
is recommended due to sediment heterogeneity). Samples shall
be collected from areas outside the site’s potential influence.
The samples must not be collected from locations directly
influenced by or in close proximity to other obvious sources
of contamination (i.e., other hazardous waste sites, sewer/storm
water outfalls, tributaries, other point and non-point source
discharges, etc.). If a local reference site is included
in the sampling plan, it must be of comparable habitat to
the study area. Upstream areas influenced by tides shall
be sampled at locations determined to be within the mixing
zone to delineate upstream migration of contaminants as
well as upstream of any mixing zone in order to assess local
ambient conditions. At a minimum, upgradient and local reference
samples shall receive the same chemical analyses as site-related
samples. Additional determinations, such as benthic community
structure, may be required on a case-by-case basis.
2.4 Surface Water Quality Investigations and Criteria
Pursuant to N.J.A.C. 7:26E-3.8 and 4.5,
a surface water investigation is required when there is
evidence that surface water may have been impacted by site-related
contamination. Additionally, since the release of contaminants
from sediments may play a substantial role in surface water
contamination, especially in quiescent aquatic systems such
as lakes, wetlands, ponds and intermittent or slow moving
streams, it is appropriate to include surface water samples
in the overall assessment of sediment quality. Surface water
quality data also serve as a tool for the interpretation
of related biological test data.
Details for surface water sampling plan
design, field sampling methodology, and analytical requirements
are found in N.J.A.C. 7:26E and the NJDEP FSPM.
As a general guide, surface water samples should be collected
near banks/depositional areas where water current is slower
and there is greater retention time for the surface water
to accumulate contaminants from sediment. Since contaminated
groundwater and surface water can serve as sources of sediment
contamination, obvious surface-runoff channels, leachate
seeps, groundwater discharge areas, etc., should be targeted.
Determination of the number and location of samples should
be made after all surface water migration pathways and discharge
points have been identified; the potential for upstream
contaminant migration in tidal water bodies must be addressed.
Surface water samples must be collocated
spatially and temporally with sediment samples. In addition
to bulk chemical analysis, measurements for salinity (in
estuarine systems), pH, dissolved oxygen, and total hardness
(as mg/1 CaCO3) are required.
Surface water risks to aquatic receptors are evaluated based on comparison of measured concentrations with acute and chronic Surface Water Quality Standards (N.J.A.C. 7:9B) and surface water screening criteria where Surface Water Quality Standards (SWQS) do not exist. The SWQS and surface water screening criteria can be viewed at http://www.nj.gov/dep/srp/guidance/ecoscreening/. The most recent version of the list entitled Surface Water Quality Criteria Applicable to New Jersey can be obtained from the Standards Assessment and Modeling Unit, Office of Environmental Planning, at 609-633-7020. Those criteria that require a hardness value to derive the applicable criterion must employ a station-specific hardness value, not an average value.
For inorganic contaminants, it is recommended
by the USEPA Region II Biological Technical Assistance Group
(BTAG) and the SRP that both dissolved and total recoverable
metals be measured. Most aquatic water quality criteria
are based on the dissolved (filtered) form of the metal;
however, the total recoverable (unfiltered) inorganic value
is more indicative of total contaminant exposure and should
be used for risk-management decision-making. Additionally,
USEPA Office of Water recommends that Superfund ecological
risk assessments consider inorganics on a total recoverable
basis to conservatively avoid underestimation of bioavailable
metals. (USEPA, 1993). Together, the two sets of measurements
are used to judge regulatory compliance as well as potential
adverse ecological impact.
References
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