National Water-Quality Assessment (NAWQA) Program

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By Larry R. Shelton and Paul D. Capel

Open-File Report 94-458

Sacramento, California



Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

For printed copies of the published report contact:




Conversion Factors

Multiply                          By            To obtain
foot (ft)                       0.3048          meter
gallon (gal)                     3.785          liter
inch (in.)                       25.4           millimeter
square inch (lb/in2)             645.2          square millimeter
square mile (mi2)                2.590          square kilometer

Temperature is given in degrees Celsius ( C), which can be converted to 
degrees Fahrenheit ( F) by the following equation:

                            F=1.8( C)+32


cm, centimeter
g, gram
km2, square kilometer
L, liter
uL, microliter
um, micrometer
mL, milliliter
mm, millimeter

NAWQA, National Water Quality Assessment
NWQL, National Water Quality Laboratory
TOC, total organic carbon
USGS, U.S. Geological Survey


Basic Fixed Sites -- Sites on streams at which streamflow is measured and samples are collected for temperature, salinity, suspended sediment, major ions and metals, nutrients, and organic carbon to assess the broad-scale spatial and temporal character and transport of inorganic constituents of stream water in relation to hydrologic conditions and environmental settings.

Bed-Sediment and Tissue Studies -- Assessment of concentrations and distributions of trace elements and hydrophobic organic contaminants in stream bed sediment and tissues of aquatic organisms to identify potential sources and assess spatial distribution.

Ecological Studies -- Studies of biological communities habitat characteristics to evaluate the effects of physical and chemical characteristics of water and hydrologic conditions on aquatic biota and to determine how biological and habitat characteristics differ among environmental settings in Study Units.

Indicator Sites -- Stream sampling sites located at outlets of drainage basins with relatively homogeneous land use and physiographic conditions. Basins are as large and representative as possible, but still encompassing primarily one environmental setting (typically, 50 to 500 km2).

Integrator Site -- Stream sampling sites located downstream of drainage basins that are large and complex and often contain multiple environmental settings. Most Integrator Sites are on major streams with drainage basins that include a substantial portion of the Study Unit (typically, 10 to 100 percent).

Intensive Fixed Sites -- Basic Fixed Sites with increased sampling frequency during selected seasonal periods and analysis of dissolved pesticides for 1 year. One or two integrator Intensive Fixed Sites and one to four indicator Intensive Fixed Sites are present in most Study Units.

Occurrence and Distribution Assessment -- Assessment of the broad-scale geographic and seasonal distributions of water-quality conditions for surface and ground water of a Study Unit in relation to major contaminant sources and background conditions.

Occurrence Survey -- The first phase of study of trace elements and hydrophobic organic contaminants in stream bed sediment and tissues of aquatic organisms. The primary objective is to determine which target constituents are common and important to water-quality conditions in each Study Unit.

Spatial Distribution Survey -- Extension of the Occurrence Survey for bed sediments and tissues to improve geographic coverage, with particular emphasis on assessment of priority constituents identified in the Occurrence Survey.

Study Unit -- A major hydrologic system of the United States in which NAWQA studies are focused. NAWQA Study Units are geographically defined by a combination of ground- and surface-water features and usually encompass more than 10,000 km2 of land area. The NAWQA design is based on assessment of 60 Study Units, which collectively cover a large part of the Nation, encompass the majority of population and water use, and include diverse hydrologic systems that differ widely in natural and human factors that affect water quality.

Water-Column Studies -- Assessment of physical and chemical characteristics of stream water, including suspended sediment, dissolved solids, major ions and metals, nutrients, organic carbon, and dissolved pesticides, in relation to hydrologic conditions, sources, and transport.


By Larry R. Shelton and Paul D. Capel


A major component of the U.S. Geological Survey's National Water-Quality Assessment pro- gram is to characterize the geographic and seasonal distributions of water-quality conditions in relation to major contaminant sources. For streams, the assessment of trace elements and organic contaminants is accomplished through a two-phase assessment of stream bed sediments and tis- sues of aquatic organisms. The first phase of the strategy is to identify important constituents based on data collected from bed-sediment depositional zones. Fine-grained particles deposited in these zones are natural accumulators of trace elements and hydrophobic organic compounds. For the information to be comparable among studies in many different parts of the Nation, strate- gies for selecting stream sites and depositional zones are critical. Fine-grained surficial sediments are obtained from several depositional zones within a stream reach and composited to yield a sample representing average conditions. Sample collection and processing must be done consis- tently and by procedures specifically designed to separate the fine material into fractions that yield uncontaminated samples for trace-level analytes in the laboratory. Special coring samplers and other instruments made of Teflon are used for collection. Samples are processed through a 2.0-millimeter stainless-steel mesh sieve for organic contaminate analysis and a 63-micrometer nylon-cloth sieve for trace-element analysis. Quality assurance is maintained by strict collection and processing procedures, duplicate sampling, and a rigid cleaning procedure.


The National Water Quality Assessment (NAWQA) program of the U.S. Geological Survey (USGS) is designed to assess the status of and trends in the quality of the Nation's ground- and surface-water resources (Gilliom and others, 1994) and to develop an understanding of the major factors that affect water-quality conditions (Hirsch and others, 1988; Leahy and others, 1990). The design is based on bal- ancing the unique assessment requirements of individual hydrologic systems with a nationally consistent design structure that incorporates a multiscale, interdisciplinary approach. Investigations of water quality in 60 major hydrologic basins and aquifer systems, referred to as NAWQA Study Units, form the building blocks of the program.

The Occurrence and Distribution Assessment, described in Gilliom and others (1994), is the largest and most important component of the first intensive study phase in each Study Unit. The goal of the Occurrence and Distribution Assessment is to characterize, in a nationally consistent manner, the broad- scale geographic and seasonal distribution of water-quality conditions in relation to major contaminant sources and background conditions. The national study design for streams has three interrelated compo- nents. Water-Column Studies assess the occurrence and distribution of major ions, nutrients, and dissolved pesticides and their relation to hydrologic conditions, sources, and transport. Bed-Sediment and Tissue Studies assess the occurrence and spatial distribution of trace elements and hydrophobic organic contaminants. Ecological Studies evaluate the physical, chemical, and biological characteristics of streams relative to environmental settings. Sampling designs for these components coordinate sampling of varying intensity and scope throughout the study.

This report describes methods for collecting and processing bed-sediment samples from streams for analysis of trace elements and hydrophobic organic contaminants as part of the Occurrence and Distri- bution Assessment component of the NAWQA program. Complimentary methods and procedures for col- lecting and processing biological tissues are described in Crawford and Luoma (1993). Although the methods and techniques described in this report are intended to meet the goals of the NAWQA program, they can be adapted for use in other programs of the USGS Water Resources Division, as well as by other Federal and State agencies. These methods will evolve as additional experience is gained and as measurement and analysis techniques improve. The glossary in this report includes brief definitions of study components, indicated throughout the report with capital first letters, and related key terms.


Determination of constituent concentrations in bed sediments is a widely used approach to monitor and assess contaminant distributions in streams (Feltz, 1980; De Groot and others, 1982; Ackermann and others, 1983; Smith and others, 1988; Horowitz, 1990). There are several reasons for analyzing bed sediment for trace elements and hydrophobic organic contaminants. First, fine-grained particles and organic matter are natural accumulators of trace elements and hydrophobic organic contaminants in streams, the majority of which are highly sorptive and associated with particulate matter in almost all natural surface- water regimes. A large fraction of the total mass of these chemical constituents is usually associated with fine-grained sediments, including clay and silt particles and particulate organic carbon. Consequently, even though the water may contain only small quantities of these constituents, suspended sediment and bed sediment may contain relatively large concentrations. Second, nonpoint-source contributions of many of these contaminants may be intermittent or storm related; as a result, the contaminants may not be detected in single or periodic water samples. Bed sediments in depositional environments of streams provide a time- integrated sample of particulate matter transported by a stream. Third, when combined with biological tissue analysis, bed-sediment concentrations provide a useful measure of the potential bioaccumulation of trace elements and hydrophobic organic contaminants at a particular site.

The concentration of trace elements on stream bed materials is strongly affected by the particle-size distribution of the sample (Rickert and others, 1977; Wilber and Hunter, 1979). Generally, the con- centration of trace elements on stream bed materials increases as particle size decreases. However, the concentration of organic contaminants attached to bed sediments is not significantly affected by particle- size distribution and is probably more a function of the concentration of organic matter in the sample (Goerlitz and Law, 1974). To increase the probability of detecting trace elements and to enhance the comparability of data among sites, bed-sediment samples should be sieved and the fine-grained fraction analyzed for the contaminants of interest. For trace elements, the silt-clay fraction smaller than 63 m should be saved for analysis. For pesticides and other organic contaminants, sand and silt-clay fraction smaller than 2.0 mm should be saved for analysis.

The appropriate season and hydrologic conditions for sampling stream bed sediment are determined by current and antecedent discharge conditions. Access to the sampling site can be limited during seasonal high-flow conditions. Unusually high flows can wash out, redistribute, or bury substantial parts of semi- meant deposits; therefore, sampling should be delayed following major discharge to allow fresh sediment to deposit. The amount of time to reestablish sediment deposits depends on the amount of sediment in transport and on the streamflow. Independent judgement is needed in making these decisions. When sampling for bed sediment and tissues during summer or autumn, low-flow conditions are recommended to provide maximum direct access to the stream bed and to minimize seasonal streamflow variability.

Bed-Sediment and Tissue Studies are done in two phases to assess trace elements and hydrophobic organic contaminants, as described by Gilliom and others (1994). The Occurrence Survey is designed to provide an initial identification of important constituents in the Study Unit based on data from relatively few sites. The analytical constituents for bed sediments in the Occurrence Survey is summarized in table 1. The Occurrence Survey is the first phase of distribution assessment and its results guide the design of the more extensive Spatial Distribution Survey. Data from both phases are combined for assessing contaminant distribution.

The primary objective of the Occurrence Survey is to determine the target constituents and their importance to water-quality conditions in the Study Unit. Relative importance is determined by the magnitude of constituent levels and the extent of their occurrence. Highest importance is assigned to constituents at elevated levels over a wide geographic area or within many small areas over a substantial part of the Study Unit. Site selection and sampling strategy are designed to maximize the probability of detecting important constituents in the Study Unit.

The site-selection strategy for the 15 to 20 sites sampled for the Occurrence Survey builds on the selection of fixed sites for water-column and ecological sampling. Sampling designs for Bed-Sediment and Tissue Studies, Water-Column Studies, and Ecological Studies rely on coordinated sampling of varying intensity and scope at two general types of sites, Integrator Sites and Indicator Sites. Integrator Sites are chosen to represent water-quality conditions of streams and rivers in large basins that are often affected by complex combinations of land-use settings, point sources, and natural influences. Indicator Sites, in contrast, are chosen to represent water-quality conditions of streams in relatively homogeneous and usually smaller basins associated with specific individual environmental settings (for example, a particular combination of land-use and geologic setting). Most NAWQA Study Units have three to five Integrator Sites and four to eight Indicator Sites. The choice of additional Indicator Sites for the Occurrence Survey is a balance between locating sites where contamination is known to be probable and dispersing sites so that streams draining each major environmental setting in the Study Unit are sampled. Additional Integrator Sites for the Occurrence Survey are chosen on large streams to provide a coarse downstream network of sites where large-scale problems not detected in smaller basins have a reasonable chance of being detected. Usually one or two Indicator Sites are selected to represent the broadest possible range of background trace-element levels expected in the Study Unit. These reference Indicator Sites also serve to assess background occurrence of synthetic organic chemicals.

The Spatial Distribution Survey adds improved geographic coverage, with particular emphasis on assessment of priority constituents identified in the Occurrence Survey. Occurrence Survey results affect the analytical strategy and the geographic distribution of sampling sites. The combined data from the two phases of sampling provide a basic description of spatial distribution for the Study Unit, with emphasis on priority constituents, and support initial evaluation of sources and biological availability for priority constituents.

Twenty to 30 sites are typically sampled for the Spatial Distribution Survey, including a resampling of selected sites sampled during the Occurrence Survey. The general goals in site selection for the Spatial Distribution Survey are to attain (1) improved representation of the most important environmental settings in the Study Unit by increasing the number of Indicator Sites and (2) adequate spatial resolution in priority mainstem channels and major tributaries by increasing the number of Integrator Sites. Large areas with low contaminant levels and low variance require relatively few sites. However, parts of a Study Unit may require a significant increase in site density compared to the Occurrence Survey to assess priority constituents. The sampling strategy for bed sediment in the Spatial Distribution Survey is similar to the Occurrence Survey except that the scope is reduced, as appropriate, based on results of the Occurrence Survey.

Table 1. Analytical constituents for bed-sediment Occurrence Survey

[Tissue samples analysed only for constituents indicated by *]

                      Trace elements and major metals
Aluminum*	Cerium		Lead		Potassium	Titanium
Antimony	Chromium*	Lithium		Scendium	Total carbon  
  (Stibium)	Cobalt		Magnesium	Selenium*	Uranium
Arsenic*	Copper*		Manganese*	Silver*		Vanadium*
Barium*		Europium	Mercury*	Sodium		Yttrium
Beryllium*	Gallium		Molybdenum	Strontium	Ytterbium
Bismuth		Gold		Neodymium	Sulfur		Zinc
Boron		Iron*		Nickel*		Tantalum	
Cadmium*	Holmium		Niobium		Thorium		
Calcium		Lanthanum	Phosphorus	Tin		
                           Organic contaminants
Organochlorine insecticides and polychlorinated biphenyls
Aldrin*			Endosulfan I		Mirex*
cis-chlordane*		Endrin*			cis-Nonachlor*
trans-chlordane*	Heptachlor*		trans-Nonachlor*
Chloroneb		Heptachlor epoxide*	Oxychlordane*
Dacthal*		alpha-HCH*		Polychlorinated
o,p'-DDD*		beta-HCH*		  biphenyls
p,p'-DDD*		gamma-HCH		  (PCBs-total)*
o,p'-DDE*		  (Lindane)*		cis-Permethrin
p,p'-DDE*		Isodrin			trans-Permethrin 
o,p'-DDT*		Methoxychlor, o,p'*	Pentachloroanisole*
p,p'-DDT*		Methoxychlor, p,p'*	Toxaphene*
Other semivolatile organic contaminants
Acenaphthene*				Di-n-butyl Phthalate
Acenaphthylene*				2,4-Dinitrophenol
Acridine				2,4-Dinitrotoluene
C8-Alkylphenols				2,6-Dinitrotoluene
Anthracene*				Di-n-octyl Phthalate
Anthraquinone				bis(2-Ethylhexyl) Phthalate
Azobenzene				2-Ethylnaphthalene
Benzo(a)anthracene*			Fluoranthene
Benzo(b)fluoranthene* 			9H-Fluorene
Benzo(k)fluoranthene*			Hexachlorobenzene*
Benzo(g,h,i)perylene*			Hexachloroethane
Benzo(a)pyrene*				Indeno(1,2,3-cd) pyrene*
Benzo(c)quinoline			Isophorone
2,2'-Biquinoline			Isoquinoline
4-Bromophenylphenylether		2-Methylanthracene
Butylbenzyl Phthalate			2-Methyl-4,6-Dinitrophenol
9H-Carbazole				4,5-Methylenephenanthrene
bis(2-Chloroethoxy) methane		1-Methyl-9H-Fluorene
bis(2-Chloroethyl) ether		1-Methylphenanthrene
bis(2-Chloroisopropyl) ether		1-Methylpyrene
4-Chloro-3-methylphenol			Naphthalene*
2-Chlorophenol				Nitrobenzene
2-Chloronaphthalene			2-Nitrophenol
4-Chlorophenylphenylether		4-Nitrophenol
p-Cresol				N-Nitroso-Diphenylamine
Chrysene*				N-Nitroso-Di-n-Propyl Amine
Dibenzo(a,h)anthracene			Phenanthrene*
Dibenzothiophene			Pyrene*
1,2-Dichlorobenzene			Pentachloronitrobenzene
1,3-Dichlorobenzene			Pentachlorophenol
1,4-Dichlorobenzene			Phenanthridine
2,4-Dichlorophenol			Phenol
Diethyl Phthalate			Quinoline
3,5-Dimethylphenol			2,3,5,6-Tetramethylphenol
1,2-Dimethylnaphthalene			1,2,4-Trichlorobenzene*
1,6-Dimethylnaphthalene			2,4,6-Trichlorophenol 
2,6-Dimethylnaphthalene			2,4,6-Trimethylphenol
Dimethyl Phthalate			2,3,6-Trimethylnaphthalene
Carbonate                  Total organic carbon


The sample-collection strategy for bed sediment focuses on obtaining samples of fine-grained surficial sediments from natural depositional zones during low-flow conditions and on compositing samples from several depositional zones within a stream reach. This strategy is designed to yield a representative sample of fine-grained surficial bed sediments. The procedures are suitable for sampling most stream sites, and every effort is made to follow this approach to ensure national consistency among Study Units. The exact approach described may not be attainable for some stream systems or sites, and local conditions may require some adaptation. However, the basic philosophy and conceptual approach outlined in these guidelines should be maintained.


The term "site" generally refers to a reach of the stream approximately 100 m in length upstream from a water-column sampling or streamflow measurement site. However, this definition is flexible and varies somewhat with local conditions. Actual reach length is defined at each site by a combination of factors, including stream geomorphology and meander wavelength (Meador and others, 1993). Locations in streams where the energy regime is low and fine-grained particles accumulate in the stream bed are termed "depositional zones." Depositional zones can cover large areas at some sites and small pockets at other sites. The stream velocities at these zones have decreased and the fine-grained particles have deposited in the stream bed. Depositional zones include areas on the inside bend of a stream or areas downstream from obstacles such as boulders, islands, sand bars, or simply shallow waters near the shore. Wadeable depositional zones are preferred because they are easy to identify and to sample.

The ideal site-planning procedure is to identify 5 to 10 wadeable depositional zones containing fine-grained particulate matter at each site and to estimate the areal extent of each zone. The goal is to select depositional zones that represent upstream influences and various flow regimes; that is, left bank, right bank, center channel, and different depths of water. This will ensure that the sediment sample represents depositional patterns from various flow regimes and sources within the reach. Each depositional zone at a sampling site will be subsampled several times, and the subsamples will be composited with samples from other depositional zones sampled at the same site (fig. 1). The number of samples from each zone will be based on the areal size of each zone (that is, the larger the areal size of the zone, the greater the number of subsamples collected). Compositing will smooth the local scale variability and represent the average contaminant levels present at the site.

Figure 1. A typical depositional zone site. A - Water-column sampling site. B - One-hundred-meter stream reach. C - Depositional zones. D - Bed sediment sampling locations.


Moving variable distances upstream or downstream from the water-column sampling or streamflow measurement site to find suitable depositional zones may be necessary because of the diverse nature of different streams and site locations, some of which are selected primarily for purposes other than bed-sediment sampling. The ideal sampling reach can be expanded when needed to encompass suitable depositional zones (Klusman, 1980). The preferred approach is to extend the reach by selecting inundated depositional zones in the stream channel, but continuing to include only basin conditions representative for the chosen site. However, side channels and bodies of water disconnected seasonally can contain viable depositional zones if they are part of the active stream for most of the year.

The comparability of sediments exposed directly to the atmosphere to those continually covered with water is unknown, especially for organic contaminants. Therefore, all sampled zones should be underwater from the time of deposit until collection. If all the depositional zones within a reasonable distance of a site have dried, a bed-sediment sample should be collected from a partially wetted zone. This partially wetted zone would include low-wetland areas near, but not attached to, the actual stream channel. Partially wetted zones should only be sampled when no other sites are available, and sampling conditions should be documented in the field notes and data records as a potential outlier. An advisable alternative would be to revisit the site when additional depositional zones are available.


Equipment and supplies for collecting and processing stream bed-sediment samples for analyses of trace elements and organic contaminants are listed in table 2. The use of each is explained in the following discussions of samplers and sieving equipment, preparation for sampling, sampling procedures, and sample processing.

Table 2. Equipment and supplies for collecting and processing samples.

[gal, gallon; g/L, gram per liter; in. inch; L, liter; mL, milliliter; mm, millimeter]

Sampling and Processing



The following list of suppliers produce the above equipment to the recommended specifications. Listing a specific company is not intended as an endorsement.

    * QW Service Unit            ** Gilson Co Inc 
      4500 SW 40th Ave              P.O. Box 677
      Ocala, FL 34474               Worthing, OH 43085
      352 237-5514                  800 444-1508

    # Cole-Parmer Inst.          ## Geotech
      7425 N Oak Park Ave           1441 W. 46th Ave
      Chicago, IL 60648             Denver, CO 80211
      800 323-4340                  303 433-7101


Given the multiple objectives of the Occurrence and Distribution Assessment phase of the NAWQA program and the simultaneous sampling for trace elements and organic contaminants, the choice of stream bed-sediment sampler(s) is particularly important. The attributes of the sampler must include (1) the ability to sample surficial sediments without loss of the fine material in the sediment/water interface and (2) the ability to sample sediment without contaminating the trace elements or organic compounds. These attri- butes exclude most of the traditional bed-sediment samplers and sampling techniques.

Three types of samplers meet the above attributes. One is a suspended-coring sampler (box core, dredge, or gravity core) for use in nonwadeable, low-velocity areas of the streams. The second is a hand- coring sampler like the Guillotine, a Teflon sampler specifically designed to sample shallow depositional zones. The third is simply a scoop or Teflon spoon that can remove the fine surficial material deposited between rocks and debris in wadeable areas. These three types of samplers should be suitable for most environments encountered in the Occurrence and Distribution Assessment phase of the NAWQA program. The use of these samplers is described in the section "Sample Collection."

The suspended-coring samplers should be made of stainless steel. These samplers are best suited for sampling soft sediments during low-flow conditions. One possible suspended-coring sampler is the Ekman dredge, with spring-loaded jaws that close on the bottom and flaps that close on the top to completely enclose a 9-in2 parcel of sediment and overlying water. The dredge or box core can be inserted into the bed with a long handle or lowered from a boat on a cable through the water. A gravity-core sampler is a weighted tube that is dropped from a boat into the stream bed, and the resulting core is held in place by vacuum inside the tube when top flaps are closed. With care these samplers can collect a core without disturbing the fine surficial materials.

The Guillotine sampler (fig. 2) is a hand-held core sampler designed to sample fine-grained materials in the depositional zones without disturbing or contaminating the sediments. The parts of the Guillotine in contact with the final core (the fraction for analyses) are made exclusively of Teflon. The Guillotine is inserted by hand into the depositional zone in the stream bed. A bottom plug and a top blade confine the core and overlying water, which allows a 1.5-inch-diameter core to be removed from the stream without disturbing the sediment, fine surficial particles, or trapped native water. The overlying native water is removed, and the sediment core is positioned to separate the upper layer of fine-sediment fraction for sieving (fig. 3). The clear Teflon tube allows inspection of the upper fraction of the core for the selection that best fits the study criteria for sampling only fine-grained depositional layers.

At many sampling sites, application of the suspended-coring or Guillotine samplers do not produce enough useable sample of the fine-bed material. A Teflon spoon, scoop, or spatula also can produce the desired sample. The spatula can remove thin layers of surficial sediments, and the scoop or spoon can remove the bed material from between rocks and debris. Care must be taken to prevent the fine sediments from being washed away by the stream when bringing the sample to the surface.

Some sampling situations can require alternative equipment and methods. Alternatives should be utilized only when the recommended approach is not possible. Quality-assurance requirements for trace-level analyses should be followed, and undisturbed, near-surface bed sediments should be sampled in a manner that yields samples comparable to the recommended methods. Alternative equipment and methods need to be fully documented.

Figure 2. Guillotine, a hand-held core sampler. Collection (1.5 x 8 in) and final (1.5 x 2in) tubes are FEP Teflon, union block (2.5 in sq) and blade are PFT Teflon, and extruder (12 in) and plug are PVC.

Figure 3. Schematic of the Guillotine sampler in operation. A - Open blade and insert into depositional zone. B - Clear bed material. C - Insert plug and close blade. D - Move from stream, remove blade, and decant water. E - Extrude core to desired position. F - Insert the blade to guillotine the core. G - Discard lower core and save the upper core.


Two different sieves are required to process a sample for trace elements and organic contaminants. A 63- m mesh nylon-sieve cloth held in a plastic frame is used for sieving sediment samples for trace-element analyses, and a 2.0-mm stainless-steel sieve is used for processing samples for organic-contaminants analyses. Procedures for sieving these samples are described later in the section "Sample Processing."


All equipment should be cleaned prior to field activities and between sites. Cleaning procedures are designed to control contamination by removing paper, glue, plasticizers, oils, and metals from the sampling and processing equipment. The equipment should be stored in a plastic food-storage container after cleaning. An overview of the proper cleaning procedures is given in table 3.

Prepare a large tub or sink with a 0.2-percent phosphate-free detergent. Wash and soak for 30 minutes all equipment the Guillotine, spatula, spoon, scoop, Ekman dredge, glass bowl, policeman, stainless-steel sieve, plastic sieve frame, nylon-mesh sieve material, plastic funnel, and the Teflon and plastic wash bottles. Rinse with copious amounts of tap water and then with deionized water as the final rinse. Three sequential 1-L rinses are more efficient then one 3-L rinse.

Fill the Teflon wash bottle with methanol for further cleaning of the equipment used for processing the samples for organic contaminant analyses. Fill the 500-mL plastic wash bottle with a 5 percent (by volume) solution of hydrochloric acid (HCL). Rinse all the equipment used for trace element collecting and processing with a minimum amount of acid.

Trace-Element Equipment Rinse equipment used in collecting and processing samples for trace-element Vanalyses (plastic-sieve frame, mesh nylon-sieve material, plastic funnel, Teflon policeman, and plastic wash bottles) with a 5-percent, high-purity, nitric-acid solution. Follow the acid rinse with multiple rinses of deionized water. Store in sealable plastic containers.

Organic-Contaminants Equipment Rinse equipment used in collecting and processing samples for organic-contaminant analysis (stainless-steel sieve and a separate Teflon policeman) with residue-grade methanol. Air dry equipment and wrap in aluminum foil and place in sealable plastic containers.

Table 3. Reference guide for collecting and processing stream bed-sediment samples.

[min, minute; cm, centimeter; L, liter; m, micrometer; mL, milliliter; g, gram]

EQUIPMENT CLEANING (prior to sampling)

Trace-element processing equipment
Organic-contaminant processing equipment
COLLECTING PROCEDURE Wadeable zone (Guillotine sampler) Wadeable zone (spoon, scoop, or spatula sampler) Nonwadeable zone (Ekman dredge) SAMPLE PROCESSING Trace elements - Sieve-frame method Trace elements - Bag method Office or local lab processing Organic contaminants Particle size FIELD DOCUMENTATION FINAL CLEANING


The surficial 2 to 3 cm of bed sediment within each depositional zone at a sampling site is subsampled several times, and the subsamples are composited with samples from other depositional zones sampled at the same site (fig. 1). The number of samples from each zone should be proportional to the relative size of each zone (for example, the larger the areal size of the depositional zone, the larger the number of subsamples collected). Compositing subsamples from different depositional zones will smooth the local scale variability and provide samples that are more representative of the average or mean contaminant concentrations. Confidence in the estimate of the mean concentration of contaminants in a composite sample increases as the number of subsamples in the composite increases.

In situations where the guidelines for sample collection are feasible with reasonable modifications, but the Study Unit team members determine that an alternative type of sample is required to assess site conditions adequately, both types of samples should be collected for analysis. In situations where the guidelines for sample collection cannot be met, independent judgement of the Study Unit team members is important. For example, at stream sites where the amount of available fine-grained material is insufficient for trace-element analysis, an alternative particle-size fraction is necessary. Similarly, in situations where large amounts of organic matter in bed sediments make field sieving impossible, an alternative procedure may be necessary. Whenever sample collection or processing methods deviate significantly from these guidelines, the specific procedures used need to be documented.

Prior to sampling depositional zones at each site, prepare an area on shore near the zones to accumulate the sample and for later processing. On a clean plastic tarpaulin, using latex gloves, unwrap the precleaned equipment and rinse with native water. For an overview of sampling procedures, see table 3.

Consider other activities simultaneously occurring at the site when planning the sample collection. Plan carefully the location of each activity in the stream reach and the sequence of events to avoid the possibility of contaminating the results. For example, the sampling of organisms for tissue analysis may be done during the same site visit as stream bed-sediment sampling, but the depositional zones for stream bed-sediment sampling should not be disturbed during biological sampling. Therefore, bed-sediment sampling should be prior to or upstream from biological sampling and other activities.

Avoid collecting a stream bed-sediment sample near or downstream of a bridge, bridge pier, or debris. The potential for sediment contamination is high in these areas.


Approach the identified depositional zone by moving upstream to avoid disturbing the area to be sampled. Place an electronic thermistor into the stream bed and record the temperature.


Assemble the Guillotine sampler: collection tube, union block, and final tube (fig. 3). Mark graduations (in centimeters) on the inside top portion of the union block to assist in determining the extruded core depth.

Insert the Guillotine into the stream bed at least 2 cm. Avoid inserting any deeper than necessary and, if possible, stay within the layers of fine-grained material. The extraction process is easier if the coarse- grained sediments are avoided.

Clear the bed material from the exterior of the core (by hand) from the downstream side. Carefully slide the plug under the Guillotine and insert it into the bottom of the collection tube. Slide the blade into the union block (closing the Guillotine) to prevent disturbance of the water/bed interface. Sometimes the coring tube can be inserted into the depositional zone deep enough to seal the bottom in a tight clay lens. The plug will not be needed if this can be achieved.

Visually inspect the core for adequate fine material. An appropriate core will have layers of fine- to coarse-grained material with the finer material near the sediment/water interface. Discard the entire core if it does not contain the desired fine material or if the core is disturbed in any way. Keep the sampler upright and carefully move the assembly (with stream bed core) from the stream to the processing area. Avoid disturbing the sediment/water interface. Decide how much of the core to save. Select the top portion of the core that best represents the fine depositional material, but no deeper than approximately 2.0 cm.

Remove the blade and decant the liquid from the top of the core with a syringe and tubing. Do not disturb the particulate matter. Discard the liquid. With the extruder, push the core (and plug) through the collection tube and union block and into the final tube to the depth previously selected.

Slice the core by reinserting the blade through the union block. Remove the collection tube containing the lower portion of the core and discard the unwanted bed material. Invert the remaining assembly (union block, blade, and final tube) into the glass bowl for compositing. Remove the blade and assist the core removal by tapping the tube against the bowl. Rinse the Guillotine in the stream before reusing.

Repeat the sampling process by collecting core samples from 5 to 10 locations in each depositional zone. If possible, use a total of 5 to 10 different depositional zones at each sampling site to ensure representative sampling. Approximately 1.5 L of wet sediment (about 50 cores 1 cm deep or 25 cores 2 cm deep) will be needed in the composite sample. Obtain more than enough composite sample for the sieving and splitting steps as adding additional sample to the composite without bias once the processing begins is difficult.


A Teflon spoon, scoop, or spatula can be used to remove thin layers of sediment from the bottom of stream beds when the water is shallow (less than a foot) and there is little or no flow. Carefully remove the top layer of surficial fine material from the stream bed (approximately 1 to 2 cm). Avoid removing more material than necessary. Sieving is easier if the sandy material is avoided. Use the Teflon scoop or spatula for removing large smooth deposits and the Teflon spoon for removing the fine material in tight areas between rocks and debris. Each scoop or spoon should represent approximately 2 in2 of bottom area 1 to 2 cm deep.

Extra care is necessary to protect the fine sediments from being washed away by the stream. Bring the sample to the stream surface in such a way as to avoid losing the fine material. Inspect the sample for adequate fine material and then deposit the sample in the glass bowl for compositing.

The depositional zone should be subsampled 5 to 10 times. Vary the number of subsamples in each zone when the scoop or spoon yields different volumes. Sample a total of 5 to 10 different depositional zones per site to complete the areal coverage and produce the necessary volume of material, approximately 1.5 L of wet sediment (about 50 scoops 1 cm deep or 25 scoops 2 cm deep). Obtain more than enough composite sample for the sieving and splitting steps as adding additional sample to the composite without bias once the processing begins is difficult.


If there are no wadeable depositional zones, a 9-in2 stainless-steel Ekman dredge or similar coring device can be used as an alternate collection method. The dredge is either suspended from a cable on a reel or hand operated at the end of a long rigid handle. The dredge can remotely collect a bottom core of fine-grained material without seriously disturbing the sediment/water interface.

Open and lock the jaws of the dredge and then lower it into a known depositional zone. Allow the open box to settle into the sediment to a depth dependent on the porosity and composition of the sediment and the mass of weights attached to the sampler. The dredge should penetrate the depositional zone at least 6 cm to avoid disturbing the particulate matter when the jaws close. Additional weights on the dredge may be required for deeper streams. Deploy the messenger to close the jaws and then carefully bring the dredge (and stream bed-sediment sample) to the surface.

Open the doors on the top of the dredge. Remove 4 to 12 subcores from the dredge with the Guillotine sampler, spoon, or scoop. Avoid extracting the subcores near the metal edges of the dredge. It may be easier to decant the overlying water from the dredge before subcoring. Continue to process the subcores following the procedures described in the "Wadeable Zone" section. The final coring and compositing methods should be identical, no matter what initial procedure is used for sampling.

NOTE: Independent field judgements are important in this procedure. The intent of the guidelines is to provide a consistent national framework for making good and reasonable decisions that best achieve study goals. Specific numbers of zones and cores are included only to give a sense of the general level of intensity and detail required.


Sediment samples for several types of analyses can be processed from the composite depositional sample. This guide describes the processing for three sample types. One sample will be sieved to less than 63 m and analyzed for trace elements, major ions, and organic and inorganic carbon. A second sample will be sieved to less than 2.0 mm and analyzed for organic contaminants, total-organic carbon (TOC), total-inorganic carbon, and percent moisture. The third sample also will be sieved to less than 2.0 mm and analyzed for percent particle-size distribution less then 63 m (sand/silt). An overview of the proper sampling procedures is given in table 2.


Wear latex gloves and thoroughly mix (homogenize) the composite sample in the glass bowl using the Teflon spatula.


Sieve-Frame Method

Stretch the 63- m mesh nylon-sieve cloth over the plastic-sieve frame and attach retaining ring. Assemble in series the 63- m mesh nylon cloth sieve and the plastic funnel over a 500-mL plastic receiving bottle.

Place a small amount of composite sample onto the 63- m mesh nylon sieve with the spatula. Pressure sieve the sample using native water that has been collected directly from the stream into the 500-mL plastic-wash bottle. The fine sediments pass through the sieve with a stream of water (pressure sieved) delivered by a wash bottle.

Work small amounts of bed material through the sieve at a time, discarding the material remaining on the sieve. It is not necessary to sieve all the material that is less than 63 m in each aliquot.

NOTE: Shaking the sieve aggressively will help separate the fines.

If additional wash water is needed, allow the sieved sediment/native water to settle several minutes and decant only the native water back into the wash bottle for reuse. Continue to reuse the native water until the necessary sample is obtained (a depth of approximately 1 cm in the receiving bottle). The analyses of inorganic constituents will require 10 g (dry weight) of sieved sediment.

Bag Method

This method can be used in place of the pressure-sieving procedure. The plastic sieve frame is not used for this method; instead, place an aliquot (2 to 3 tablespoons) of the composite sample directly on the mesh nylon-sieve cloth and draw up each corner of the cloth to form a bag with the sample inside. Aggressively dip the bag in a beaker filled with 450 mL of native water. Continual dipping and squeezing will help separate the fines. Care should be taken to ensure that the nylon mesh is not stretched or damaged. Use additional aliquots until the proper volume of fine material is sieved, and then transfer the sample to a 500-mL plastic bottle.


Pack the sediment/native-water samples on ice (do not freeze) for transport to the local office/ laboratory for further processing as follows: store the sample in a refrigerator and allow the sediments to settle until water is clear. This process could take 2 to 3 days, but no longer than 1 week. Decant the liquid to approximately 1 cm of the sediment/water interface with a syringe. Discard the decanted liquid. Centrifuging the sample might be necessary if the fine sediment has not settled within a week. Follow the cleanup procedure for preparing the centrifuge tubes.


Place the 2.0-mm stainless-steel sieve over a 1,000-mL glass jar. Gently work an aliquot of the sample through the sieve with a Teflon policeman or spatula. Do not use water. Collect the sample in a 1,000-mL wide-mouth glass jar. The bottom of the sieve may require periodic removal of the material that adheres to it. Fill the jar approximately half full; 500 mL of wet sediment is needed for analyses of organic contaminants, TOC, and percent moisture.


Using the same 2.0-mm sieve described above, continue to sieve until approximately 2 cm of wet sediment accumulates into a 1,000-mL plastic jar. For particle-size analyses, 50 g dry weight of material is needed.


Study Units that have coastal drainage systems or wetland areas may have difficulty collecting traditional depositional zone bed samples. Wetland areas typically do not have erosion which transports and deposits silt and clay. However, vegetation and algae moving through the system dies, settles to the bottom, decays, and becomes a mat of organic muck. This organic material can be used for the Occurrence and Distribution Assessment phase of the National Water Quality Assessment Program as an indicator of contaminates transported and present in the drainage system. When collecting bed samples that are predominately organic material, the above processing guidelines must be modified. Bed samples rich in organic material will not pass through a 63 micron sieve, therefore a 2 millimeter sieved fraction will be used for trace element analyses. This procedure requires the results be stored under a different set of parameter codes. Also, larger amounts of sieved material are required for analyses because organic material has less weight per volume then silt and clay. For National Synthesis, the interpretation of the analytical results of the organic deposit can be normalized to the results of the silt and clay analyses by comparing total organic carbon (TOC) values.


For this procedure, subsample at least 25 times to a depth of 10 to 15 centimeters using a slotted Teflon spoon, scoop, or spatula. Carefully remove the organic material from the stream bed, discarding the excess liquid, without losing the fines. Composite 2 to 3 liters of organic material into a large glass bowl.


Attach the 63 micron mesh sieve cloth to the plastic frame and assemble over the funnel and 500mL plastic jar as usual. Place the additional 2.0 mm nylon mesh sieve material over the 63 micron cloth sieve frame. Place an aliquot of the composite sample on the 2.0 mm sieve. Carefully work the sample through the two sieves with a Teflon policeman, and by shake aggressively. Process several aliquots of the sample then inspect the liquid that has been collected in the jar. If the liquid is very cloudy it may be possible to achieve a traditional bed sediment sample of silt and clay. Analyzing only the <63 micron fraction for trace elements is the preferred procedure when enough silt and clay can be found in the stream bed. So, if possible process the sample following the procedures listed in the 'Sample Processing' section. However, if the liquid in the jar is clear or contains minimal fine sediments, continue with this modified procedure. Accurate field judgement is required to determine which procedure will produce the best results to achieve the project criteria. Continuity within a basin or Study Unit might also be important. If it is important to know the ratio of silt and clay to organic material request the laboratory to do a percent ash analyses.

TRACE ELEMENTS (Less then 2mm Fraction)

If it is determined that the trace element sample will be the <2.0 mm fraction, continue to process the sample through only the 2.0 mm sieve and collect all of this fraction in a 500mL wide mouth plastic jar. The desired sample can probably be achieved by aggressively shaking the sieve. Discard any material not passing through the 2 mm sieve. For the trace element analyses 10 grams of dry material is required. That will require filling the 500mL jar about one fourth (120 mLs) full of wet organic material. Allow the fine sediments to settle for several days then decant the liquid leaving only wet sediments. Label the sample so that the Central Laboratory will realize that this is a <2.0 mm fraction for trace element analyses.


The samples for organic contaminates and particle size analyses will be processed through a 2.0 mm stainless steel sieve as originally described. However, with 25 grams of dry material required for each analyses the glass 500 mL jar should be about two thirds full (300 mL) of the wet organic material for the organic contaminate analyses and fill the plastic 500 mL jar with 300 mL for the particle size determination. Sieving this large amount of material may generate more liquid then is desirable, if so, allow the fines to settle then decant the excess liquid.


Trace-Element Samples Pack without ice and ship to the National Water Quality Laboratory (NWQL) for distribution to the appropriate laboratories for analyses.

Organic-Contaminant Samples Place in a protective sleeve, pack in ice (do not freeze), and ship by overnight carrier to the NWQL within 3 days of collection.

Particle-Size Samples Ship in plastic container to the local sediment laboratory for a percent sand/silt analyses.


Use the standard U.S. Geological Survey surface-water-quality field notes. Complete pages 1, 2, and 3, expanding on the section describing the "bottom." Include standard field measurements of water temperature, stream bed-sediment temperature, specific conductance, pH, dissolved oxygen, and alkalinity, as described in Shelton (1994). Record a rated or measured stream discharge. Draw an areal sketch of the stream reach identifying the depositional zones. Note and describe the nature and extent of zones selected for sampling and the approximate locations within each zone where cores were extracted. Note the time and location of other activities at the site such as fish shocking, discharge measurements, and dredging. Identify the following: map scale, compass direction, bridges, bridge piers, trees, and so forth. Document derivation from the sampling protocol that may introduce anomalies or bias to the results.


Inspect and thoroughly wash all equipment with deionized water after each use. All traces of sediment should be removed prior to storage or reuse. Equipment that cannot be cleaned (for example, the 63-m mesh nylon-sieve cloth) should be discarded. Refer to "Equipment Cleaning" section for the proper procedure to use prior to sampling at the next site. Store the equipment used exclusively for trace-element processing in sealable plastic containers and plastic food-storage containers. Wrap the equipment used exclusively for organic-contaminant processing in aluminum foil and store in plastic food-storage containers. Equipment common to both processes should be protected from contamination and stored in a sealed container.


Quality data are assured through a sampling and analytical approach designed to minimize or compensate for potential sources of contamination and variability. Quality assurance is verified through independent sampling and analyses.


The awareness and avoidance of chemical contamination are necessary in each step of sample collection and processing: sampling, subsampling, field processing, shipping, and laboratory processing. Because sediments are natural accumulators of the target analytes, there is less concern of gross-sample contamination than in the water column. Nevertheless, extreme care must be taken to avoid contamination. The simultaneous sampling and field processing of stream bed sediment for trace elements and organic contaminants make the avoidance of contamination a unique challenge. The optimum materials for contacting samples collected for organic-contaminant analyses include glass, stainless steel, and Teflon. The optimum materials for trace-element analyses include plastics, glass, and Teflon (avoid contact with the stainless-steel coring samplers). The materials common to both lists, glass and Teflon, are the materials of choice to contact the bed sediments when analyzing for both trace elements and organic contaminants.

The cleaning procedures are designed to control contamination by removing paper, glue, plasticizer, oils, and metals from the sampling and processing equipment. This removal of contaminants is accomplished by a thorough soap and water cleaning and rinsing followed by solvent rinses for the organic-contaminant processing equipment and acid rinses for the trace-element processing equipment.


The primary potential sources of variability in stream bed-sediment composition at a site are temporal variability, areal variability among depositional zones, areal variability within depositional zones, and depth variability. Temporal variability is managed by collecting all samples during low-flow conditions when changes with time are expected to be minimal. Areal variability is minimized by compositing samples within and among zones to yield an average for the reach. Variability in depth is managed through a consistent sampling approach of surficial sediment, visual inspection, and sampling-depth management.


The quality-assurance steps designed into the sampling strategy and methods will be verified during the first phase of sampling by a comparative study of duplicate sample collection and analyses that aggregates all potential sources of variability. If the verification indicates quality-control problems, more specific tests will be designed as required. Specific types of quality-assurance samples should be outlined for specific projects within the division. A set of guidelines in the NAWQA program assist the Study Unit team members in the collection of quality-assurance samples (Quality-Control Objectives and Procedures for NAWQA Surface-Water Sites, written communications, U.S. Geological Survey Memorandum dated May, 1996). Laboratory precision is monitored and verified by routinely analyzing spit or blank samples with every set of 20 samples analyzed.

References Cited

Ackermann, F., Bergmann, H., and Schleichert, V., 1983, Monitoring of heavy metals in coastal and estuarine sediments--a question of grain size: 20 m versus <60 m: Environmental Technology Letters, v. 4, p. 317-328.

Crawford, J.K., and Luoma, S.N., 1993, Guidelines for studies of contaminants in biological tissues for the National Water-Quality Assessment program: U.S. Geological Survey Open-File Report 92-494, 69 p.

De Groot, A., Zshuppe, K., and Salomans, W., 1982, Standardization of methods of analysis for heavy metals in sediments: Hydrobiologia, v. 92, p. 689-695.

Feltz, H.R., 1980, Significance of bottom material data in evaluating water quality, in Baker, R., ed., Contaminants and Sediments, v. 1: Ann Arbor Michigan, Ann Arbor Science Publishers, Inc., p. 271-287.

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1994, Design of the National Water-Quality Assessment program: Occurrence and distribution assessment: U.S. Geological Survey Open-File Report 94-314, 50 p.

Goerlitz, D.F., and Law, L.M., 1974, Distribution of chlorinated hydrocarbons in stream-bottom material: U.S. Geological Survey, Journal of Research, v. 21, no. 5, p. 443-541.

Hirsch, R.M., Alley, W.M., and Wilber, W.G., 1988, Concepts for a National Water-Quality Assessment program: U.S. Geological Survey Circular 1021, 42 p.

Horowitz, A.J., 1990, The role of sediment-trace element chemistry in water-quality monitoring and the need for standard analytical methods, in Hall, J., and Glysson, D., eds., Monitoring water in the 1990's: Meeting new challenges: Philadelphia, American Society for Testing and Materials STP 1102.

Klusman, R.W., 1980, Sampling designs for biochemical baseline studies in the Colorado oil shale region: A manual for practical application: U.S. Department of Energy Report DOE/EV/10298-2, 180 p.

Leahy, P.P., Rosenshein, J.S., and Knopman, D.S., 1990, Implementation plan for the National Water-Quality Assessment program: U.S. Geological Survey Open-File Report 90-174, 10 p.

Meador, M.R., Hupp, C.R., Cuffney, T.F., and Gurtz, M.E., 1993, Methods for characterizing stream habitat as part of the National Water-Quality Assessment program: U.S. Geological Survey Open-File Report 93-408, 48 p.

Rickert, D.A., Kennedy, V.C., McKenzie, S.W., and Hines, W.G., 1977, A synoptic survey of trace metals in bottom sediments of the Willamette River, Oregon: U.S. Geological Survey Circular 715-F, 27 p.

Shelton, L.R., 1994, Field guide for collecting and processing stream-water samples for the National Water-Quality Assessment program: U.S. Geological Survey Open-File Report 94-455, 44 p.

Smith, J.A., Witkowski, P.J., and Fusillo, T.V., 1988, Manmade organic compounds in the surface waters of the United States: A review of current understanding: U.S. Geological Survey Circular 1007, p. 2.

Wilber, W.G., and Hunter, J.V., 1979, The impact of urbanization on the distribution of heavy metals in bottom sediments of the Saddle River: Water Resources Bulletin, v. 15, no. 3, p. 790-800.

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