Methods for Collection, Storage and Manipulation of Sediments for Chemical and Toxicological Analyses: Technical Manual

LORAN LOng RAnge Navigation NAWQA National Water Quality Assessment Acronym List v Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses NDIR Non-Dispersive Infrared Detector NEP National Estuary Program NOAA National Oceanic and Atmospheric Administration NSI National Sediment Inventory NST National Status & Trends ORP Oxidation Reduction Potential OSHA Occupational Safety & Health Administration PCE Power Cost Efficiency POC Particulate Organic Carbon PSEP Puget Sound Estuary Program QA Quality Assurance QAPP Quality Assurance Project Plan QC Quality Control RADAR RAdio Detecting and Ranging ROV Remotely Operated Vehicle RPD Relative Percent Difference SATNAV SATellite NAVigation SCV Secondary Chronic Value SEM Simultaneously Extracted Metals SIM Selected Ion Monitoring SOC Suspended Organic Carbon SOD Sediment Oxygen Demand SOPs Standard Operating Procedures SPMD Semi-Permeable Membrane Device SRM Standard Reference Materials TIC Total Inorganic Carbon TMDLs Total Maximum Daily Loads TOC Total Organic Carbon TPH Total Petroleum Hydrocarbons TVS Total Volatile Solids vi US Environmental Protection Agency Technical Manual USEPA United States Environmental Protection Agency USGS United States Geologic Survey XRF X-Ray Fluorescence Acronym List vii Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses viii US Environmental Protection Agency Technical Manual Foreword Sediments provide essential habitat for many freshwater, estuarine, and marine organisms. In aquatic systems, most anthropogenic chemicals and waste materials, particularly persistent organic and inorganic chemicals, may accumulate in sediments. These sediments become repositories for many of the more toxic chemicals that are introduced into surface waters. United States Environmental Protection Agency’s National Sediment Inventory (NSI) (USEPA 1998), a biennial report to Congress on sediment quality in the United States, demonstrates that sediment contamination exists in every state of the country. Contaminated sediments represent a hazard to aquatic life through direct toxicity as well as to aquatic life, wildlife and human health through bioaccumulation in the food chain. Assessments of sediment quality commonly include analyses of anthropogenic contaminants, benthic community structure, physicochemical characteristics, and direct measures of whole sediment and pore water toxicity. Accurate assessment of environmental hazards posed by sediment contamination depends in large part on the accuracy and representativeness of these analyses. The methods described in this Manual are intended to provide the user with sediment collection, storage, and manipulation methods that are most likely to yield accurate, representative sediment quality data (e.g., toxicity, chemical) based on the experience of many monitoring programs and researchers. This Manual represents a compilation of information presented in many publications, including: • American Society for Testing and Materials (ASTM) 2000 document: Standard Guide for Storage, Characterization, and Manipulation of Sediments for Toxicological Testing, E- 1391-94. • Environment Canada 1994 manual: Guidance Document on Collection and Preparation of Sediments for Physicochemical Characterization and Biological Testing, EPS 1/RM/29. • U.S. Environmental Protection Agency. 2000 manual: Methods for Measuring the Toxicity and Bioaccumulation of Sediment-Associated Contaminants with Freshwater Invertebrates. Second Edition. EPA/600/R-99/064. • U.S. Environmental Protection Agency / Army Corps of Engineers. 1998. Inland Testing Manual: Evaluation of Dredged Material Proposed for Discharge in Waters of the U.S. - Testing Manual. EPA-823-B-98-004. • U.S. Environmental Protection Agency / Army Corps of Engineers. 1991. Ocean Testing Manual: Evaluation of Dredged Material Proposed for Ocean Disposal: Testing Manual. EPA-503/8-91/001. In addition to many recent peer-reviewed technical journal papers, other publications that were relied on extensively include: Foreword ix Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses • Puget Sound Estuary Program (PSEP) 1997 manual: Recommended Guidelines for Sampling Marine Sediment, Water Column, and Tissue in Puget Sound • Washington Department of Ecology 1995 Document: Guidance on the Development of Sediment Sampling and Analysis Plans Meeting the Requirements of the Sediment Management Standards • Great Lakes National Program Office (GLNPO) 1994 manual: Assessment and Remediation of Contaminated sediments (ARCS) Program - Assessment Guidance EPA-905-B94-002. • U.S. Environmental Protection Agency. 2000 document: Estuarine and Near Coastal Marine Waters: Bioassessment and Biocriteria Technical Guidance. EPA-822-B-00-004. This Manual addresses several needs identified in EPA’s Contaminated Sediment Strategy (USEPA 1998) including: (1) an organized discussion of activities involved in sediment sampling and sample processing; (2) important issues that need to be considered within each activity; and (3) recommendations on how to best address issues such as sampling design, proper sampling procedures, and sample manipulations. Throughout this Manual, different considerations pertaining to sampling and sample processing are presented depending on the program need (e.g., dredge remediation versus status and trends monitoring). EPA along with other agencies, assesses aquatic sediment quality under a variety of legislative requirements including: • National Environmental Policy Act (NEPA) • Clean Air Act; the Coastal Zone Management Act (CZMA) • Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) • Marine Protection, Research, and Sanctuaries Act (MPRSA) • Resource Conservation and Recovery Act (RCRA) • Toxic Substance Control Act (TSCA) • Clean Water Act (CWA) • Comprehensive, Environmental and Liability Act (CERCLA) • Great Lakes Critical Programs Act of 1990. In addition, many EPA offices coordinate sediment monitoring studies in specific geographic areas, such as through the Chesapeake Bay Program, the Great Lakes National Program, the Gulf of Mexico Program, the Washington State Sediment Management Standards Program, and in the States of Washington, Florida, California, New York, New Jersey, South Carolina, Texas, Massachusetts, and Wisconsin. To address its responsibilities within the above legislative acts, EPA has several ongoing programs that may involve sediment quality evaluation as summarized below. x US Environmental Protection Agency Technical Manual Dredged Material Management The U.S. Army Corps of Engineers (USACE), the Federal agency designated to maintain navigable waters, conducts a majority of the dredging projects and disposal under its Congressionally- authorized civil works program. The balance of dredging and disposal is conducted by a number of local public and private entities. In either case, the disposal is subjected to a regulatory program administered jointly by the USACE and EPA under Section 103 of the Marine Protection, Research, and Sanctuaries Act (MPRSA) for ocean disposal, and Section 404 of the Clean Water Act (CWA) for discharge at open water sites, confined disposal facilities with return flow to waters of the U.S., or for beneficial uses. EPA shares the responsibility of managing dredged material, principally in the development of the environmental criteria and guidelines by which proposed discharges are evaluated and disposal sites are selected, and in the exercise of its environmental oversight authority. Joint EPA/USACE guidance manuals detailing the testing and analysis protocols for dredged material disposal are well established. National Estuary Program EPA administers the National Estuary Program, established under the Clean Water Act to identify, restore, and protect nationally significant estuaries in the United States. Within the existing 28 programs, environmental monitoring is a key element of watershed protection strategies developed to maintain the chemical, physical, and biological properties of the estuarine ecosystems. The Puget Sound Estuary Program (PSEP), in particular, has been actively monitoring ecological health, including sediment quality, in Puget Sound, Washington for many years. PSEP, which includes EPA, the Puget Sound Water Quality Authority, and the Washington Department of Ecology, has developed sediment sampling and analysis procedures in collaboration with local governments and stakeholder groups (PSEP, 1997). The protocols are cited in and support the Washington Department of Ecology’s (WDE) sediment management standards regulation, and have served as the foundation for many other guidance documents such as those produced by Environment Canada (1994) and American Society of Testing Materials (ASTM, 2000). This manual frequently refers to PSEP and WDE guidance. Resource Conservation and Recovery Act (RCRA) Under RCRA, EPA assesses whether releases from a hazardous waste treatment, storage, or disposal facility have contaminated sediments and requires corrective action, including possible remediation, if contamination is discovered. In many cases, sediment sampling and analyses, as discussed in this manual, are needed in RCRA facility assessments and RCRA facility investigations. Office of Water The Office of Water has been expanding provisions for sediment monitoring under the Clean Water Act, in the national monitoring framework developed by the Intergovernmental Task Force on Monitoring Water Quality (ITFM, 1995). Through this framework, agreements have been reached with other Federal, State, and local agencies concerning incorporation of sediment monitoring protocols, sediment monitoring QA/QC procedures, and appropriate information system linkages into monitoring programs. The Office of Water and the Office of Information Resources Management are also ensuring that the capability to store and use sediment data is enhanced as part of the ongoing modernization of the Agency’s water quality data systems (STORET), and in coordination with the water quality data elements procedures being recommended by the National Methods and Data Comparability Board under the National Water Quality Monitoring Council. These data elements include information describing how samples were collected, stored, and processed prior to analysis. Foreword xi Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Regional Environmental Monitoring and Assessment Program (REMAP) REMAP, within the Office of Research and Development, gathers chemical and biological data describing sediment quality at many EMAP sampling stations. Data collected under REMAP are entered into the National Sediment Inventory (NSI). These data are used to assess status and trends on a regional scale, particularly for aquatic systems that may have water quality and/or sediment quality impairment. Comprehensive, Environmental and Liability Act (CERCLA) Under CERCLA, EPA carries out a detailed analysis at a site, evaluating the risks posed by contaminants to human health and the environment, and the feasibility of various response action alternatives to reduce risk. The Risk Assessment Guidance for Superfund (USEPA, 1997) provides a framework for the assessment of human health and environmental impacts. The CERCLA Program is using the EPA-wide sediment testing methods of the Tiered Testing Framework in the Remedial Investigation/Feasibility Study (CRI/FS) stage of analysis to help determine options for remedial actions. Much of the guidance presented in this manual supports the Tiered Testing Framework applicable to CERCLA sites. Great Lakes Critical Programs Act of 1990 Annex 14 of the Great Lakes Water Quality Agreement between the United States and Canada (as amended by the 1987 Protocol) stipulates that the cooperating parties will identify the nature and extent of sediment contamination in the Great Lakes, develop methods to assess impacts, and evaluate the technological capability of programs to remedy such contamination. The 1987 amendments to the Clean Water Act authorized the Great Lakes National Program Office (GLNPO) to coordinate and conduct studies and demonstration projects relating to the appropriate treatment of toxic contaminants in bottom sediments. To fulfill the requirements of the Act, GLNPO initiated the Assessment and Remediation of Contaminated Sediments (ARCS) Program to help address contaminated sediment concerns in the development of Remedial Action Plans (RAPs) for all 43 Great Lakes Areas of Concern (AOCs, as identified by the United States and Canadian governments), as well as similar concerns in the development of Lakewide Management Plans. This manual frequently relies on information documented by the GLNPO and the ARCS program. xii US Environmental Protection Agency Technical Manual TABLE OF CONTENTS Page Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Acronym List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii List of Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix Technical and Grammatical Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi Using the Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiv 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.2 Significance and Use of this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.3 Applicability and Scope of this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 2. SEDIMENT MONITORING AND ASSESSMENT STUDY PLANS . . . . . . . . . . . . . 2-1 2.1 Data Quality Objectives Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 2.2 Study Plan Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5 2.2.1 Definition of the Study Area and Study Site . . . . . . . . . . . . . . . . . . . . . . . 2-5 2.2.2 Controlling Sources of Variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5 2.2.3 Sampling Using an Index Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6 2.3 Sampling Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7 2.3.1 Probabilistic and Random Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7 2.3.2 Targeted Sampling Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10 2.4 Measurement Quality Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11 2.4.1 Sample Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12 2.4.2 Number of Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15 2.4.3 Replicate and Composite Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15 2.5 Site-Specific Selection Considerations for Selecting Sediment Sampling Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17 2.5.1 Review Available Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19 2.5.2 Site Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19 2.5.3 Identify Sediment Deposition and Erosional Zones . . . . . . . . . . . . . . . . . 2-19 2.6 Positioning Methods for Locating Sampling Stations . . . . . . . . . . . . . . . . . . . . . 2-20 2.7 Preparations for Field Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21 2.8 Health and Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23 3. COLLECTION OF WHOLE SEDIMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3.2 Types of Sediment Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5 3.2.1 Grab Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5 3.2.2 Core Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9 3.3 Sample Acceptability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13 3.4 Equipment Decontamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14 3.5 Field Measurements and Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15 3.6 Documentation of Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17 Table of Contents xiii Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses TABLE OF CONTENTS (CONTINUED) Page 4. FIELD SAMPLE PROCESSING, TRANSPORT, AND STORAGE OF SEDIMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1 Sample Containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1.1 Container Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 4.1.2 Container Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 4.2 Subsampling and Compositing Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 4.2.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 4.2.2 Grab Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6 4.2.3 Core Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 4.3 Homogenization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11 4.3.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11 4.4 Sample Transport and Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13 4.4.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13 4.5 Sample Holding Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15 5. SEDIMENT MANIPULATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.1 Sieving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.1.1 Sieving Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 5.1.2 Alternatives to Sieving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 5.2 Formulated Sediment and Organic Carbon Modification . . . . . . . . . . . . . . . . . . . 5-6 5.2.1 General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5.2.2 Sediment Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 5.2.3 Organic Carbon Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 5.3 Spiking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 5.3.1 Preparation for Spiking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9 5.3.2 Methods for Spiking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10 5.3.3 Equilibration Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 5.3.4 Use of Organic Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 5.4 Preparation of Sediment Dilutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 5.5 Preparation of Sediment Elutriates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14 6. COLLECTION OF INTERSTITIAL WATER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.2 In-situ Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 6.2.1 Peeper Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 6.2.2 Suction Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7 6.2.3 Processing of Field-Collected Interstitial Water Sample . . . . . . . . . . . . . 6-8 6.3 Ex-situ Extraction of Interstitial Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8 6.3.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8 6.3.2 Centrifugation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10 6.3.3 Sediment Squeezing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12 6.3.4 Pressurized and Vacuum Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12 xiv US Environmental Protection Agency Technical Manual TABLE OF CONTENTS (CONTINUED) Page 7. QUALITY ASSURANCE AND QUALITY CONTROL . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.1 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.2 QA/QC Procedures for Sediment Collection and Manipulation . . . . . . . . . . . . . . . 7-2 7.3 The Quality Assurance Project Plan (QAPP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2 7.4 Standard Operating Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3 7.5 Sediment Sample Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3 7.6 Sample Tracking Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4 7.7 Record Keeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5 7.8 QA Audits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5 7.9 Corrective Action (Management of Non-conformance Events) . . . . . . . . . . . . . . . 7-5 7.10 Data Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6 8. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 APPENDICES A EXAMPLES OF SEDIMENT QUALITY SAMPLING DESIGNS USING THE DATA QUALITY OBJECTIVES (DQO) PROCESS B EXAMPLES OF MEASUREMENT QUALITY OBJECTIVES USED IN SEDIMENT QUALITY MONITORING STUDIES C STATISTICAL CONSIDERATIONS IN DETERMINING THE APPROPRIATE NUMBER OF REPLICATE SAMPLES NEEDED AT EACH SAMPLING STATION D ADVANTAGES AND DISADVANTAGES OF DIFFERENT STATION POSITIONING TECHNIQUES E ADVANTAGES, DISADVANTAGES AND ILLUSTRATIONS OF GRAB AND CORE SAMPLING DEVICES USED IN SEDIMENT MONITORING STUDIES F EXAMPLES OF FIELD FORMS USED TO DOCUMENT STATION AND SAMPLE CHARACTERISTICS AND SAMPLE TRACKING G PHYSICO-CHEMICAL SEDIMENT CHARACTERIZATION Table of Contents xv Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses xvi US Environmental Protection Agency Technical Manual LIST OF TABLES Table Page 2-1 Suggestions for selecting an appropriate sampling design (from USEPA 2000b) . . . . . . . . 2-9 2-2 Conventional sediment variables and their use in sediment investigations (Adapted from WDE, 1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13 2-3 Typical sediment volume requirements for various analyses per sample . . . . . . . . . . . . . 2-14 2-4 Practical considerations for site-specific selection of sampling stations in developing a sampling plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-18 4-1 Recommended sampling containers, holding times, and storage conditions for common types of sediment analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 6-1 In Situ interstitial water collection methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 LIST OF FIGURES Figure Page 1-1 Flow chart summarizing activities for collection, storage, and manipulation of sediments and interstitial water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 2-1 Flow chart summarizing the process that should be implemented in designing and performing a monitoring study (modified from MacDonald et al. (1991) . . . . . . . . . . 2-2 2-2 Flow chart summarizing the Data Quality Objectives Process (after USEPA 2000a) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 2-3 Description of various sampling methods (adapted from USEPA 2000c) . . . . . . . . . . . . . . 2-8 3-1 General types of considerations or objectives that are appropriate for grab or core sampling devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3-2 Flowchart for selecting appropriate grab samplers based on site-specific or design factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3-3 Flowchart for selecting appropriate core samplers based on site-specific factors . . . . . . . . 3-3 3-4 Illustrations of acceptable and unacceptable grab samples . . . . . . . . . . . . . . . . . . . . . . . . 3-15 4-1 Flowchart of suggested sediment processing procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4-2 Alternatives for subsampling and compositing sediment grab samples . . . . . . . . . . . . . . . . 4-8 4-3 Alternatives for subsampling and compositing sediment core samples . . . . . . . . . . . . . . . . 4-9 Table of Contents xvii Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses LIST OF FIGURES (CONTINUED) Figure Page 5-1 Flowchart depicting relationships between common sediment manipulations including important considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 6-1 Considerations for selecting the appropriate type of interstitial water sampling method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 6-2 Front view and components of peeper sampling devices (top: plate device; bottom: cylindrical probe) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6 6-3 Summary of recommended procedures and considerations for laboratory isolation of interstitial water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9 xviii US Environmental Protection Agency Technical Manual LIST OF RECOMMENDATION BOXES Chapter 2 Page Box #1 What type of sampling strategy should be used . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10 Box #2 How many samples and how much sample volume should be collected . . . . . . . 2-14 Box #3 How should station positioning be performed . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20 Box #4 What health and safety precautions should be followed . . . . . . . . . . . . . . . . . . . . 2-24 Chapter 3 Box #1 What are appropriate sampling devices given different study objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9 Box #2 How should sampling devices be used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13 Box #3 What information should be documented for each sample collected . . . . . . . . . . 3-16 Chapter 4 Box #1 Sample containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 Box #2 How should sediment samples be subsampled and composited . . . . . . . . . . . . . . . 4-5 Box #3 How should samples be homogenized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11 Box #4 Sample transport and storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14 Box #5 How long should samples be stored before analysis . . . . . . . . . . . . . . . . . . . . . . . 4-15 Chapter 5 Box #1 Should sediment be sieved prior to analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 Box #2 What type of sieve should be used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 Box #3 How should sediments be spiked with a chemical or other test material . . . . . . . . 5-9 Box #4 How should sediment elutriates be performed . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15 Chapter 6 Box #1 In-situ interstitial water collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 Box #2 Extraction of interstitial water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10 Table of Contents xix Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses xx US Environmental Protection Agency Technical Manual Technical Terms The following definitions were derived primarily from ASTM, USEPA, ACOE, and Environment Canada sources. Acid Volatile Sulfide. The sulfides removed from sediment by cold acid extraction, consisting mainly of iron sulfide. AVS is the principal binding phase in sediment for divalent metals. Artifact. An undesirable, detectable feature (e.g., chemical or physical change) in a sample, that has resulted from sampling, sample handling or storage, or from manipulations of the sample. Benthic. Associated with the bottom of a waterbody. Bioaccumulation. The net accumulation of a substance by an organism as a result of uptake from all environmental sources. Bioavailability. The degree to which a chemical is taken up by aquatic organisms. Chain-of-custody. The documentation that establishes the control of a sample between the time it is collected and the time it is analyzed. It usually applies to legal samples to demonstrate that there was no tampering with, or contamination of, the sample during this time. Clean. Denotes a sediment or water test sample determined to not contain concentrations of contaminants which cause apparent and unacceptable harm (or effects) to the test organisms. Composite sample. A sample that is formed by combining material from more than one sample or subsample. Concentration. The ratio of weight or volume of test material(s) to the weight or volume of sediment or water. Contaminated sediment. Sediment containing chemical substances at concentrations that pose a known or suspected threat to environmental or human health. Control sediment. A sediment that is essentially free of contaminants and is used routinely to assess the acceptability of a test. Any contaminants in control sediment may originate from the global spread of pollutants and do not reflect any substantial input from local or non-point sources. Comparing test sediments to control sediments is a measure of the toxicity of a test sediment beyond inevitable background contamination. Core sample. A sediment sample collected to obtain a vertical profile using a variety of instruments. Data Quality Objectives (DQOs). Qualitative and quantitative statements that clarify the purpose of the monitoring study, define the most appropriate type of data to collect, and determine the most appropriate methods and conditions under which to collect them. Decontamination. A process of washing or rinsing that removes chemicals adhering to equipment and supplies. Terms xxi Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Ecotox Thresholds (ET). Benchmark values in ecological risk assessments defined as media- specific contaminant concentrations above which there is sufficient concern regarding adverse ecological effects to warrant further site investigation. Elutriate. An aqueous solution obtained after adding water to a solid substance or loose material (e.g., sediment, tailings, drilling mud, dredge spoil), shaking the mixture, then centrifuging or filtering it or decanting the supernatant. Equilibration. The condition in which a material or contaminant is at steady state between the solid or particulate sediment and the interstitial water. Formulated Sediment. Mixtures of materials used to mimic a natural sediment. Global Positioning system (GPS). A navigation system that relies on satellite information. It can give continuous position reports(i.e., latitude and longitude) that vary in accuracy depending on the sophistication of the receiving unit. Grab. Any device designed to “bite” or “scoop” into the bottom sediment of a lake, stream, estuary, ocean, and similar habitats to sample the benthos. Grabs are samplers with jaws that are forced shut by weights, lever arms, springs or cables. Scoops are grab samplers that scoop sediment with a rotating container. Head Space. The space in the storage container between the top of the sample and the lid of the container. Holding time. The period of time during which a sediment or water sample can be stored after collection, and before analysis or use in a biological test. Changes that occur in sediments or water should be minimal during this period and the integrity of the sample should not be compromised to any substantial degree with respect to its physical, chemical, or biological characteristics. Homogenization. The complete mixing of sediment, either by hand or mechanical means, until physical, chemical, and /or biological homogeneity of the sample is achieved. Index Period. Specific time period in which sampling or in-situ analyses are conducted. Generally pertains to an ecologically important season and/or desired environmental conditions under which sampling is performed. In Situ. Refers to the original (field) location from which test samples are collected, or at which organisms are exposed to undisturbed water or sediments for extended periods. Interferences. Characteristics of sediments or sediment test systems that can potentially affect analytical results or test organism response aside from responses related to sediment contamination. Types of interferences include: non-contaminant characteristics (e.g., sediment texture or grain size, lighting); changes in chemical bioavailability due to sample handling or storage (e.g., ammonia generation); and the presence of indigenous organisms. Also referred to as confounding factors. Interstitial water. Water occupying space between sediment or soil particles. Measurement Quality Objectives (MQOs). Statements that describe the amount, type, and quality of data needed to address the overall project objectives. xxii US Environmental Protection Agency Technical Manual Overlying water. The water placed over sediment in a test chamber during a test. Peepers. Devices that collect interstitial water by diffusion through membranes attached to collection chambers. The chambers are typically placed in the sediment for extended periods of time to allow for equilibration between the internal water environment of the peeper and the surrounding ambient sediment/interstitial water matrix. Pore water. See interstitial water. Quality Assurance Project Plan. Project-specific document that specifies the data quality and quantity requirements needed for the study as well as all procedures that will be used to collect, analyze, and report those data. Reference sediment. A whole sediment, collected near an area of concern, that is used as a point of comparison to assess sediment conditions exclusive of the material(s) or activities of interest. The reference sediment may be used as an indicator of localized sediment conditions exclusive of the specific pollutant input of concern. Such sediment would be collected near the site of concern and would represent the background conditions resulting from any localized pollutant inputs as well as global pollutant input. Program-specific guidance documents should be consulted, as some EPA programs have specific definitions and requirements for reference sediment. Sampling Platform A working space, such as the deck of a boat, from which all sample collection activities are conducted. Sediment. Particulate material that usually lies below water, or formulated particulate material that is intended to lie below water in a test. Sediment Quality Triad. A weight-of-evidence sediment quality assessment approach which integrates data from sediment toxicity tests, chemical analyses, and benthic community assessments. Sieving. Selectively removing certain size fractions of the sediment sample by processing sediment through selected mesh sizes. Site. A study area that can be comprised of multiple sampling stations. Spiking. Addition of a known amount of test material to a sediment often used as a quality control check for bias due to interference or matrix effects. Station. A sampling location within a study area or site, where physical, chemical, or biological sampling and/or testing occurs. Supernatant. The water separated from a sediment/water mixture following centrifugation or other separation techniques. Toxicity. The property of a chemical, or combination of chemicals, to adversely affect organisms, tissues or cells. Whole sediment. Sediment and associated interstitial water which have had minimal manipulation. Also referred to as bulk sediment. Terms xxiii Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Grammatical Terms Consistent with guidance formulated by the American Society for Testing and Materials (ASTM), the following grammatical phrases, used in this manual, are defined as follows: The words “must”, “should”, “may”, “can”, and “might” have specific meanings in this manual. “Must” is used to express an absolute requirement, that is, to produce accurate results, a sample ought to be handled or manipulated in a specified manner, unless the purpose of the study requires a different procedure. “Should” is used to state that the specified condition or procedure is recommended and ought to be met if possible. Although violation of one “should” is rarely a serious matter, violations of several will often render the results questionable. “Desirable” is used in connection with less important factors. “May” is used to mean “is allowed to.” “Can” is used to mean “is able to.” “Might” is used to mean “could possibly.” Thus, the classic distinction between “may” and “can” is preserved, and “might” is not used as a synonym for either “may” or “can.” Using the Manual Throughout this Manual, there are three categories of information that are organized into text boxes as part of the effort to make this methods document more useful and accessible to users. Each box always appears with the same icon throughout the Manual: Recommendations for procedures and equipment. Consideration, or issues, that should be addressed Checklists of information The full list of Recommendation Boxes are identified on page xix as part of the Table of Contents. xxiv US Environmental Protection Agency Technical Manual Introduction CHAPTER 1 1.1 Background Protecting sediment quality is an important part of restoring and maintaining the biological integrity of our Nation’s waters as well as protecting aquatic life, wildlife and human health. Sediment is an integral component of aquatic ecosystems, providing habitat, feeding, spawning, and rearing areas for many aquatic organisms. Sediment also serves as a reservoir for pollutants and therefore a potential source of pollutants to the water column, organisms, and ultimately human consumers of those organisms. These pollutants can arise from a number of sources, including municipal and industrial discharges, urban and agricultural runoff, atmospheric deposition, and port operations. Contaminated sediment can cause lethal and sublethal effects in benthic (sediment-dwelling) and other sediment-associated organisms. In addition, natural and human disturbances can release pollutants to the overlying water, where pelagic (water column) organisms can be exposed. Sediment pollutants can reduce or eliminate species of recreational, commercial, or ecological importance, either through direct effects or by affecting the food supply that sustainable populations require. Furthermore, some sediment pollutants can bioaccumulate through the food chain and pose health risks to wildlife and human consumers even when sediment-dwelling organisms are not themselves impacted. The extent and severity of sediment contamination in the U.S. has been documented in the National Sediment Inventory (NSI)1 and through other historical information. The NSI screening evaluation of sediment contamination data indicates that associated adverse effects are probable in thousands of locations throughout the country. The results emphasize the widespread need to address sediment contamination in the U.S. 1.2 Significance and Use of this Manual Sediment quality assessment is an important component of water quality protection programs. Sediment assessments commonly include physicochemical characterization, toxicity tests, and/or bioaccumulation tests, as well as benthic community analyses. USEPA’s NSI, for example, collates this information to develop a biennial report to Congress on sediment quality in the United States, required under the Water Resources Development Act of 1992. The use of consistent sediment collection, manipulation, and storage methods will help provide high quality samples with which accurate data can be obtained for the national inventory and for other programs to prevent, remediate, and manage contaminated sediment. It is now widely known that the methods used in sample collection, transport, handling, storage, and manipulation of sediments and interstitial waters can influence the physicochemical properties and 1The National Sediment Inventory, or NSI, is the database of sediment quality information used to develop EPA’s 1997 Report to Congress, The Incidence and Severity of Sediment Contamination in Surface Waters of the United States, Volume 1: National Sediment Quality Survey (U.S. EPA, 1997a). The database is updated periodically with new available information on sediment quality at sites throughout the U.S. http://www.epa.gov/OST/cs/report.html Chapter 1: Introduction 1-1 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses the results of chemical, toxicity, and bioaccumulation analyses. Addressing these variables in an appropriate and systematic manner will help assure more accurate sediment quality data and facilitate comparisons among sediment studies. This Technical Manual provides current information and recommendations for collecting and handling sediments for physicochemical characterization and biological testing, using procedures that are most likely to maintain in situ conditions, most accurately represent the sediment in question, or satisfy particular program needs, to help ensure consistent, high quality data collection. 1.3 Applicability and Scope of this Manual This manual is intended to provide technical support to those who design or perform sediment quality studies under a variety of regulatory and non-regulatory programs. Information is provided concerning general sampling design considerations, field and laboratory facilities needed, safety, sampling equipment, sample storage and transport procedures, and sample manipulation issues common to chemical or toxicological analyses. Information contained in this manual reflects the knowledge and experience of several internationally-known sources including American Society for Testing and Materials (ASTM), Puget Sound Estuary Program (PSEP), Washington State Department of Ecology (WDE), United States Environmental Protection Agency (USEPA), US Army Corps of Engineers (ACOE), National Oceanic and Atmospheric Administration (NOAA), and Environment Canada. This manual attempts to present a coherent set of recommendations on field sampling techniques and sediment/interstitial water sample processing based on the above sources, as well as extensive information in the current peer-reviewed literature. As the scope of this manual is broad, it is impossible to adequately present detailed information on every aspect of sediment sampling and processing for all situations or all programs. Nor is such detailed guidance warranted because much of this information (e.g., how to operate a particular sampling device or how to use a Geographical Positioning System (GPS) device) already exists in other published materials referenced in this manual. Furthermore, many programs have specific sampling and sample processing procedures. While an attempt is made to give examples from different programs, the manual repeatedly instructs the reader to check their own specific program requirements. Given the above constraints, this manual: (1) presents an organized discussion of activities involved in sediment sampling and sample processing; (2) alerts the user to important issues that need to be considered within each activity; and (3) gives recommendations on how to best address the issues raised such that appropriate samples are collected and analyzed. An attempt is made to alert the user to different considerations pertaining to sampling and sample processing depending on the program need (e.g., dredge remediation versus status and trends monitoring). Figure 1-1 presents a flow chart of the general activities discussed in this manual. The organization of these activities reflects the desire to give field personnel and managers a useful tool for choosing appropriate sampling locations, characterize those locations, collect and store samples, and manipulate those samples for analyses. Chapters are written so that the reader could obtain information on only one activity or set of activities (e.g., subsampling or sample processing), if desired, without necessarily reading the entire manual. Many sections are cross-referenced so that the reader is alerted to relevant issues that might be covered elsewhere in the manual. This is particularly important for certain chemical or toxicological applications in which appropriate sample processing or laboratory procedures are associated with specific field sampling procedures. 1-2 US Environmental Protection Agency Technical Manual Figure 1-1. Flow chart summarizing activities for collection, storage, and manipulation of sediments and interstitial water. Chapter 1: Introduction 1-3 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses The methods contained in this manual are widely applicable to any entity wishing to collect consistent, high quality sediment data. This manual does not provide guidance on how to implement any specific regulatory requirement, or design a particular sediment quality assessment, but rather it is a compilation of technical methods on how to best collect environmental samples that most appropriately address common sampling objectives. Although the data from these samples might be used in environmental decision-making at a variety of levels, this manual does not address how data are to be used. The Foreword section summarizes a variety of EPA programs that assess sediment quality and may benefit from the methods described in this manual. Other Agencies and programs are also encouraged to consider these methods in order to generate consistent and high quality sediment data. The information presented in this manual should not be viewed as the final statement on all the recommended procedures. Some of the areas covered in this document (e.g., sediment holding time, formulated sediment composition, interstitial water collection and processing) are being actively researched and debated. As data from sediment monitoring and research becomes more available in the future, EPA may update this manual as necessary. 1-4 US Environmental Protection Agency CHAPTER 2 Technical Manual Sediment Monitoring and Assessment Study Plans Every study site and project are unique; therefore, sediment monitoring and assessment study plans should be carefully prepared to best meet the project objectives (MacDonald et al., 1991; see Figure 2-1). Considerations The initial issues that need to be considered prior to preparing study plans are... ! define the potential problem or general project objective ! determine what resources (e.g., time, money, personnel) are available for the project ! review existing information and identify specific objectives of the study ! determine what data are likely to be needed to answer project objectives, including the role of site-specific conditions and/or issues that might influence the process of data collection and analyses Before collecting any environmental data, it is important to determine the type, quantity, and quality of data needed to meet the project objectives (e.g., specific parameters to be measured) and support a decision based on the results of data collection and observation. Not doing so creates the risk of expending too much effort on data collection (i.e., more data are collected than necessary), not expending enough effort on data collection (i.e., more data are necessary than were collected), or expending the wrong effort (i.e., the wrong data are collected). 2.1 Data Quality Objectives Process The Data Quality Objectives (DQO) Process developed by EPA (GLNPO, 1994; USEPA, 2000a) is a flexible planning tool that systematically addresses the above issues in a coherent manner. The purpose of this process is to improve the effectiveness, efficiency, and defensibility of decisions made based on the data collected, and to do so in an effective manner (USEPA, 2000a). The information compiled in the DQO process is used to develop a project-specific Quality Assurance Project Plan (QAPP) (see Chapter 7 and USEPA, 2000a) which should be used to plan the majority of sediment quality monitoring or assessment studies. In some instances, a programmatic QAPP may be prepared, as necessary, on a project-by-project basis. The Data Quality Objectives (DQO) process addresses the uses of the data (most importantly, the decision(s) to be made) and other factors that will influence the type and amount of data to be collected (e.g., the problem being addressed, existing information, information needed before a decision can be made, and available resources). From these factors the qualitative and quantitative data needs are determined (see Figure 2-2). DQOs are qualitative and quantitative statements that clarify the purpose of the monitoring study, define the most appropriate type of data to collect, and determine the most appropriate methods and conditions under which to collect them. The products of the DQO process are criteria for data quality and a data collection design that ensures that data will meet the criteria. Chapter 2: Sediment Monitoring and Assessment Study Plans 2-1 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Figure 2-1. Flow chart summarizing the process that should be implemented in designing and performing a monitoring study (modified from MacDonald et al. (1991)). 2-2 US Environmental Protection Agency Technical Manual Figure 2-2. Flow chart summarizing the Data Quality Objectives Process (after USEPA, 2000a). Chapter 2: Sediment Monitoring and Assessment Study Plans 2-3 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Checklist In the DQO process, the following steps should be addressed: � Clearly state the problem: purpose and objectives, available resources, members of the project team: e.g., The purpose might be to evaluate current sediment quality conditions, historical conditions, evaluate remediation effects, or validate a sediment model. It is important to review and evaluate available historical data relevant to the study at this point in the process. � Identify the decision; the questions(s) the study attempts to address: e.g., Is site A more toxic than site B?; Are sediments in Lake Y less toxic now than they used to be?; Does the sediment at site D need to be remediated? What point or nonpoint sources are contributing to sediment contamination? � Identify inputs to the decision: information and measurements that need to be obtained; e.g., analyses of specific contaminants, toxicity test results, biological assessments, bioaccumulation data, habitat assessments, hydrology, and water quality characterization. � Define the study boundaries (spatial and temporal). Identify potential sources of contamination; determine the location of sediment deposition zones; determine the frequency of sampling and need for a seasonal sampling and/or sampling during a specific index period; consider areas of previous dredged or fill material discharges/disposal. Consideration of hydraulic patterns, flow event frequency, and/or sedimentation rates could be critical for determining sampling frequency and locations. � Develop a decision rule: define parameters of interest and determine the value of a parameter that would cause follow-up action of some kind; e.g., exceedance of Sediment Quality Guideline value, NOAA Effect Range Median (ERM) value, or toxicity effect (e.g., 50% mortality), results in some action (Long et al., 1995). For example, in the Great Lakes Assessment and Remediation of Contaminated Sediments (ARCS) Program, one decision rule was: if total PCB concentration exceeds a particular action level, then the sediments will be classified as toxic and considered for remediation (GLNPO, 1994). Specifying decision rules or criteria is especially critical in sediment remediation programs and any study in which the results could be subject to legal scrutiny (e.g., superfund). � Specify limits on decision errors: establish the measurement quality objectives (MQOs) which include determining the level of confidence required from the data; precision, bids, representativeness, and completeness of data; the sample size (weight or volume) required to satisfy the analytical methods and QA/QC program for all analytical tests; the number of samples required, to be within limits on decision errors, and compositing needed, if any. � Optimize the design: choose appropriate sampling and processing methods; select appropriate method for determining the location of sampling stations; select an appropriate positioning method for the site and study. Consult historical data and a statistician before the study begins regarding the sampling design (i.e., the frequency, number, and location of field-collected samples) that will best satisfy study objectives. 2-4 US Environmental Protection Agency Technical Manual For most programs, a Sampling and Analysis Plan (SAP) is developed prior to sampling which should describe the study objectives, sampling design and procedures, and other aspects of the DQO process outlined above (see Appendix B for an example of SAP requirements recommended by Washington State Department of Ecology). The following sections provide guidance on many of the primary issues that should be addressed in the study plan. 2.2 Study Plan Considerations Monitoring and assessment studies are performed for a variety of reasons (ITFM, 1995) and sediment assessment studies can serve many different purposes. Developing an appropriate sampling plan is one of the most critical steps in monitoring and assessment studies. The sampling plan, including definition of the site and sampling design, will be a product of the general study objectives (Figure 2-1). Station location, selection, and sampling methods will necessarily follow from the study design. Ultimately, the study plan should control extraneous sources of variability or error to the extent possible so that data are appropriately representative of the sediment and fulfill the study objectives. 2.2.1 Definition of the Study Area and Study Site The study area refers to the body of water that contains the study site(s) to be monitored and/or assessed, as well as adjacent areas (land or water) that might affect or influence the conditions of the study site. The study site refers to the body of water and associated sediments to be monitored and/or assessed. EMAP, for example, often defines a site as an area of concern (AOC) which might extend several miles in length, or may encompass large geographical or coastal areas. CERCLA defines a site in terms of a specific source of contamination such as a waste disposal area. The size of the study area will greatly influence the type of sampling design (see Section 2.3) and site positioning methods that are appropriate (see Section 2.6). The boundaries of the study area need to be clearly defined at the outset and should be outlined on a hydrographic chart or topographic map. 2.2.2 Controlling Sources of Variability Common purposes of sediment quality studies: • Status and trends • Evaluating program or BMP (best management practice) effectiveness • Validating sediment quality models • Designing regulatory programs • Identifying whether significant contamination exists and extent of contamination • Identifying sources of contamination • Ranking existing and identifying emerging problems • Establishing goals for sediment remediation • Evaluating dredged or fill material discharges/disposal A key factor in effectively designing a sediment quality study is controlling those sources of variability in which one is not interested (USEPA 2000a,b). There are two major sources of variability that, with proper planning, can be minimized, or at least accounted for, in the design process, thereby ensuring a successful study. In statistical terms, the two sources of variability are sampling error and measurement error (USEPA 2000b; Solomon et al., 1997). Sampling error is the error attributable to selecting a certain sampling station that might not be representative of the site or population of sample units (e.g., an estuary or a CERCLA site). Sampling error is controlled by either: (1) using unbiased methods to select stations if one is performing general monitoring of a given site (USEPA, 2000b); or (2) several stations along a spatial gradient if a specific location is being targeted (see Section 2.3). Chapter 2: Sediment Monitoring and Assessment Study Plans 2-5 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Measurement error is the degree to which the investigator accurately characterizes the sampling unit or station. Thus, measurement error includes components of natural spatial and temporal variability within the sample unit as well as actual errors of omission or commission by the investigator. Measurement error is controlled by using standardized and comparable methods: standardized methods include proper training of personnel and quality assurance procedures. To help minimize measurement error, each station should be sampled in the same way, within a site or study, using a standardized set of procedures and in the same time frame to minimize confounding sources of variability (see Section 2.2.3). In analytical laboratory or toxicity procedures, measurement error is estimated by duplicate determinations on some subset of samples (but not necessarily all). Similarly, in field investigations, some subset of sample units (e.g., 10% of the sites) should be measured more than once to estimate measurement error (see Replicate and Composite Samples, Section 2.4.3). Measurement error can be reduced by analyzing multiple observations at each station (e.g., multiple grab samples at each sampling station, multiple observations during a season), or by collecting depth-integrated, or spatially integrated (composite) samples (see Section 2.4.3). Optimizing sampling design requires consideration of tradeoffs among the measures used, the effect that is considered meaningful, desired power, desired confidence, and resources available for the sampling program. Statistical power is the ability of a given sampling design to detect an effect that Checklist To minimize measurement error: � Sample all stations similarly within a study � Use standardized procedures � Sample during the same time period � Collect and analyze multiple samples at a station � Collect and analyze composited samples actually exists, and will be a product of the collection methods, analytical procedures, and quality control processes used. Power is typically expressed as the probability of correctly finding a difference among sites or between reference and test sites (e.g., toxicity or biological impairment) when one exists. For a fixed confidence level (e.g., 90%), power can be increased by increasing the sample size or the number of replicates (see Section 2.4.3 for more information). Most programs do not estimate power of their sampling design because this generally requires prior information such as pilot sampling, which entails further resources. One study (Gilfillan et al., 1995) reported power estimates for a shoreline monitoring program following the Valdez oil spill in Prince William Sound, Alaska. However, these estimates were computed after the sampling took place. It is desirable to estimate power before sampling is performed to ensure credibility of non-significant results (see Appendix C). 2.2.3 Sampling Using an Index Period Most monitoring programs do not have the resources to characterize variability or to assess sediment quality for all seasons. Sampling can be restricted to an index period when biological and/or toxicological measures are expected to show the greatest response to pollution stress and within- season variability is small (Holland, 1985; Barbour et al., 1999). This type of sampling might be especially advantageous for characterizing sediment toxicity, sediment chemistry, and benthic macroinvertebrate and other biological assemblages (USEPA, 2000c). In addition, this approach is useful if sediment contamination is related to, or being separated from, high flow events. By sampling overlying waters during both low and high flow conditions, the relative contribution of 2-6 US Environmental Protection Agency Technical Manual each to pollutant loads or sediment contamination can be better assessed, thereby better directing remedial activities, or other watershed improvements. Those programs that sample the same site over multiple years (e.g., many EMAP and superfund studies), are interested in obtaining comparable data with which they can assess changes over time, or following remediation (GLNPO, 1994). In these cases, index period sampling is especially useful because hydrological regime (and therefore biological processes) is likely to be more similar between similar seasons than among different seasons. 2.3 Sampling Designs As mentioned in earlier sections of this chapter, the type of sampling design used is a function of the study Data Quality Objectives and more specifically, the types of questions to be answered by the study. A summary of various sampling designs is presented in Figure 2-3 along with recommendations concerning the conditions under which a given design is appropriate. Generally, sampling designs fall into two major categories: random or probabilistic, and targeted (USEPA, 2000b). USEPA (2000b;c) present a thorough discussion of sampling design issues and detailed information on different sampling designs. Some program- specific guidance documents (e.g., USEPA/ACOE 1991, 1998 for dredged material disposal issues) also discuss relevant sampling designs. Table 2-1 presents suggested sampling designs given different Sampling Design refers to the array, or network, of sampling sites selected for a monitoring program; usually taking one of two forms: • Probabilistic Design — Network that includes sampling sites selected randomly in order to provide an unbiased assessment of the condition of the waterbody at a scale above the individual site or stream; can address questions at multiple scales. • Targeted Design — Network that includes sampling sites selected based on known existing problems, knowledge of upcoming events in the watershed, or a surrounding area that will adversely affect the waterbody such as development or deforestation; or installation of BMPs or habitat restoration that are intended to improve waterbody quality; provides assessments of individual sites or reaches. overall objectives and constraints. Appendix A presents hypothetical examples of sediment quality monitoring designs given different objectives or regulatory applications. 2.3.1 Probabilistic and Random Sampling Probability-based or random sampling designs avoid bias in the results of sampling by randomly assigning and selecting sampling locations. A probability design requires that all sampling units have a known probability of being selected. Both EPA’s Environmental Monitoring Assessment Program and NOAA’s National Status and Trends Program use a probabilistic sampling design to infer regional and national patterns with respect to contamination or biological effects. Sites can be selected on the basis of a truly random scheme or in a systematic way (e.g., sample every 10 meters along a randomly chosen transect). In simple random sampling, all sampling units have an equal probability of selection. This design is appropriate for estimating means and totals of environmental variables if the population is homogeneous. To apply simple random sampling, it is necessary to identify all potential sampling times or locations, then randomly select individual times or locations for sampling. Chapter 2: Sediment Monitoring and Assessment Study Plans 2-7 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses In grid or systematic sampling, the first sampling location is chosen randomly and all subsequent stations are placed at regular intervals (e.g. 50m apart) throughout the study area. Clearly, the number of sampling locations could be large if the study area is large and one desires “fine-grained” contaminant or toxicological information. Thus, depending on the types of analyses desired, such sampling might become expensive unless the study area is relatively small and/or the density of stations (that is how closely spaced are the stations) is relatively low. Grid sampling might be effective for detecting previously unknown “hot spots” in a limited study area. Figure 2-3. Description of various sampling methods. Adapted from USEPA, 2000c. In stratified designs, the selection probabilities might differ among strata. Stratified random sampling consists of dividing the target population into non-overlapping parts or subregions (e.g., ecoregions, watersheds, or specific dredging or remediation sites) termed strata to obtain a better estimate of the mean or total for the entire population. The information required to delineate the strata and estimate sampling frequency must either be known prior to sampling using historic data, available information and knowledge of ecological function, or obtained in a pilot study. Sampling locations are randomly selected from within each of the strata. Stratified random sampling is often used in sediment quality monitoring because certain environmental variables can vary by time of day, season, hydrodynamics, or other factors. Major environmental monitoring programs that incorporate a stratified random design include EPA’s Mid-Atlantic Integrated Assessment (MAIA). One disadvantage of using random designs is the possibility of encountering unsampleable sites that were randomly selected by the computer. Such problems result in the need to reposition the vessel to an alternate location. Furthermore, if one is sampling to determine the percent spatial extent of 2-8 US Environmental Protection Agency Technical Manual degradation, it might be important to sample beyond the boundaries of the study area to better evaluate the limits of the impacted area. A related design is multistage sampling in which large subareas within the study area are first selected (usually on the basis of professional knowledge or previously collected information). Stations are then randomly located within each subarea to yield average or pooled estimates of the variables of interest (e.g., concentration of a particular contaminant or acute toxicity to Hyalella) for each subarea. This type of sampling is especially useful for statistically comparing variables among specific parts of a study area. Table 2-1. Suggestions for selecting an appropriate sampling design (from USEPA 2000b). If you are... and you have... consider using... in order to... performing a screening phase of an investigation and with an understanding of a relatively small-scale problem a limited budget and/or a limited schedule judgmental or targeted sampling assess whether further investigation is warranted that should include a statistical probabilistic sampling design. developing an understanding of when contamination is present adequate budget for the number of samples needed systematic sampling have coverage of the time periods of interest. developing an understanding of where contamination is present adequate budget for the number of samples needed grid sampling have coverage of the area of concern and have a given level of confidence that you would have detected a hot spot of a given size. estimating a population mean adequate budget budget constraints and analytical costs that are high compared to sampling costs budget constraints and professional knowledge or inexpensive screening measurement that can assess the relative amounts of the contaminant at specific field sample locations systematic or grid sampling compositing ranked set sampling also produce information on spatial or temporal patterns. produce an equally precise or a more precise estimate of the mean with fewer analyses and lower cost. reduce the number of analyses needed for a given level of precision. estimating a population mean or proportion spatial or temporal information on contaminant patterns stratified sampling increase the precision of the estimate with the same number of samples, or achieve the same precision with fewer samples and lower cost. delineating the boundaries of an area of contamination a field screening method stratified sampling simultaneously uses all observations in estimating the mean. estimating the prevalence of a rare trait analytical costs that are high compared to sampling costs random and composite sampling produce an equally precise or more precise estimate of the prevalence with fewer analyses and lower cost. assessing whether a population contains a rare trait the ability to physically mix aliquots from the samples and then retest additional aliquots composite sampling and retesting classify all samples at reduced cost by not analyzing every sample. Chapter 2: Sediment Monitoring and Assessment Study Plans 2-9 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Recommendation Box #1 What type of sampling strategy should be used? � Historical data, if available, should be considered when selecting sampling stations. � Location of sediment depositional zones can be important in defining subareas for sampling or for stratifying sampling in some programs. � If the objective of the survey is to identify areas of toxic and/or contaminated sediments on a quantitative spatial and/or temporal basis (e.g., superfund site), a systematic or regular grid-sampling strategy might be most appropriate (USEPA, 2000b). � If the monitoring objective is to determine sediment contamination originating from a specific source or tributary, a targeted site location design might be most appropriate. Factors affecting dispersion of substances or materials from the point source (e.g., currents) should be considered. � Stratified random sampling should be used where historical, sediment-mapping data are available and there are well-defined zones of different sediment types or adjacent land uses (Burton, 1991). This design is commonly used in NOAA National Status and Trends (NS&T) monitoring of sediment quality to ensure that the data can be attributed to the strata in which they were collected (Long et al., 1996). � For dredge management programs, multi-stage, stratified-random, or even targeted sampling is often appropriate, since the need is to represent specific areas to be dredged and disposed. � For watershed or regional assessment programs, a probabilistic sampling design might be most appropriate. � Small-scale, targeted study designs might require many samples within a small area if fine spatial resolution is needed (e.g., Superfund). Use of random sampling designs might also miss relationships among variables, especially if there is a relationship between an explanatory and a response variable. As an example, estimation of benthic response or contaminant concentration, in relation to a discharge or landfill leachate stream, requires sampling targeted around the potential contaminant source, including stations presumably unaffected by the source (e.g., Warwick and Clarke, 1991). A simple random selection of stations is not likely to capture the entire range needed because most stations would likely be relatively removed from the location of interest. 2.3.2 Targeted Sampling Designs In targeted (also referred to as judgmental, or model-based) designs, stations are selected based on prior knowledge of other factors, such as contaminant loading, depth, salinity, and substrate type. The sediment studies conducted in the Clark Fork River (Pascoe and DalSoglio, 1994; Brumbaugh et al., 1994), in which contaminated areas were a focus, used a targeted sampling design. Targeted designs are useful if the objective of the investigation is to screen an area(s) for the presence or absence of contamination at levels of concern, such as risk-based screening levels or toxicity, or to compare specific sediments against reference conditions or biological guidelines. In general, targeted sampling is appropriate for situations in which any of the following apply (USEPA, 2000b): 2-10 US Environmental Protection Agency Technical Manual • The site boundaries are well defined or the site physically distinct (e.g., superfund or CERCLA site, proposed dredging unit). • Small numbers of samples will be selected for analysis/characterization. • Information is desired for a particular condition (e.g., “worst case”) or location. • There is reliable historical and physical knowledge about the feature or condition under investigation. • The objective of the investigation is to screen an area(s) for the presence or absence of contamination at levels of concern, such as risk-based screening levels. (Note that if such contamination is found, follow-up sampling is likely to involve one or more statistical designs to compare specific sediments against reference conditions, chemical or biological guidelines, or applicable sediment quality values). • Schedule or budget limitations preclude the possibility of implementing a statistical design. • Experimental testing of a known pollution gradient to develop or verify testing methods or models (i.e., as in evaluations of toxicity tests, Long et al., 1990). Because targeted sampling designs often can be quickly implemented at a relatively low cost, this type of sampling can often meet schedule and budgetary constraints that cannot be met by implementing a statistical design. In many situations, targeted sampling offers an additional important benefit of providing an appropriate level-of-effort for meeting investigation objectives without excessive consumption of project resources. Targeted sampling, however, limits the inferences made to the stations actually sampled and analyzed. Extrapolation from those stations to the overall population from which the stations were sampled is subject to unknown selection bias. This bias might be unimportant for those regulatory programs in which information is needed for a particular condition or location (e.g., Dredged Management Materials Program or Superfund). 2.4 Measurement Quality Objectives As noted in Section 2.1, a key aspect of the DQO process is specifying measurement quality objectives (MQOs): statements that describe the amount, type, and quality of data needed to address the overall project objectives. Appendix B presents examples of MQOs and sampling designs that have been used in several different programs. Also included in Appendix B is excerpted information from Washington Department of Ecology’s Sampling and Analysis Plan Guidance (WDE, 1995). Similar to Quality Assurance Project Plans (QAPP) mentioned earlier in Section 2.1, a Sampling and Analysis Plan includes, among other things, many of the elements of the Data Quality Objectives Process, including MQOs. A key factor determining the types of MQOs needed in a given project or study is the types of analyses required because these will determine the amount of sample required (see Section 2.4.1) and how samples are processed (see Chapter 4). The case examples presented in Appendix B illustrate a variety of chemical, biological, and toxicological analyses that are often included in sediment quality monitoring projects. Metals, organic chemicals (including pesticides, PAHs, and PCBs), whole Chapter 2: Sediment Monitoring and Assessment Study Plans 2-11 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses sediment toxicity, and organism bioaccumulation of specific target chemicals, are frequently analyzed in many sediment monitoring programs. A number of other, more “conventional” parameters, are also often analyzed as well to help interpret chemical, biological, and toxicological data collected in a project. Table 2-2 summarizes many of the commonly measured conventional parameters and their uses in sediment quality studies (WDE, 1995). It is important that conventional parameters receive as much careful attention, in terms of sampling and sample processing procedures, as do the contaminants or parameters of direct interest. The guidance presented in Chapters 3 and 4 provides information on proper sampling and sample processing procedures, respectively, to ensure that one has appropriate samples for these analyses. This section concentrates on three aspects of MQO development that are generally applicable to all sediment quality studies, regardless of the particular program or objectives: sample volume, number of samples, and replication vs. composite sampling. Checklist MQOs are defined in terms of the following attributes: � Detection Limit – The lowest concentration of an analyte that a specified analytical procedure can reliably detect. � Bias – The difference between an observed value and the “true” value (or known concentration) of the parameter being measured; bias is the first component of accuracy, which is the ability to obtain precisely a nonbiased (true) value. � Precision – The level of agreement among multiple measurements of the same characteristic; precision is the second component of accuracy. � Representativeness – The degree to which the data collected accurately represent the population of interest (e.g., contaminant concentrations). � Comparability – The similarity of data from different sources included within individual or multiple data sets; the similarity of analytical methods and data from related projects across areas of concern. � Completeness – The quantity of data that is successfully collected with respect to the amount intended in the experimental design. 2.4.1 Sample Volume Before commencing a sampling program, the type and number of analyses and tests should be determined, and the required volume of sediment per sample calculated. Each physicochemical and biological test requires a specific amount of sediment which, for chemical analyses, depends on the detection limits attainable and extraction efficiency by the procedure and, for biological testing, depends on the test organisms and test method. Typical sediment volume requirements for each end use are summarized in Table 2-3. Specific program guidance should be consulted regarding sample volumes that might be required. 2-12 US Environmental Protection Agency Technical Manual Table 2-2. Conventional sediment variables and their use in sediment investigations (Adapted from WDE, 1995). Conventional Sediment Variable Use Total organic carbon (TOC) • Normalization of the concentrations of nonionizable organic compounds • Identification of appropriate reference sediments for biological tests Acid Volatile Sulfide (AVS) • Normalization of the concentrations of divalent metals in anoxic sediments Sediment grain size • Identification of appropriate reference sediments for biological tests • Interpretation of sediment toxicity test data and benthic macroinvertebrate abundance data • Evaluation of sediment transport and deposition • Evaluation of remedial alternatives Total solids • Expression of chemical concentrations on a dry- weight basis Ammonia • Interpretation of sediment toxicity test data Total sulfides • Interpretation of sediment toxicity test data When determining the sample volumes necessary, one must know what is required for all of the sample analyses (considering adequate replication) and it is also helpful to know the general characteristics of the sediments being sampled. For example, if interstitial water analyses or elutriate tests are to be conducted, the percent water (or percent dry weight) of the sediment will greatly affect the amount of water extracted. Many non-compacted, depositional sediments have interstitial water contents ranging from 30 to 70%. However, interstitial waters are very difficult to remove from sandy or gravel-rich sediments. For benthic macroinvertebrate bioassessment analyses, sampling a prescribed area of benthic substrate is at least as important as sampling a given volume of sediment. In many programs, macroinvertebrates are sampled using multiple grab samples within a given station location, typically to a standard sediment depth (e.g., per 10-20 cm of sediment; Klemm et al., 1990; GLNPO, 1994; Long et al., 1996; USEPA 2000c ). More than 6 liters of sediment from each station might be necessary in order to have adequate numbers of organisms for analyses, especially in many lakes, estuaries, and large rivers (Barbour et al., 1999). However, this is very site specific and should be determined by the field sampling crew. This only applies to whole sediment sampling methods and not to surficial stream methods using methods such as kick-nets and Surber samplers. If the sediment quality triad approach is used (i.e., biological, toxicological, and physicochemical analyses performed on samples from the same sites), more than 10 liters of sediment from each site might be required depending on the specific analyses conducted. NOAA routinely collects 7-8 liters of sediment at each station for multiple toxicity tests and chemical analyses (Long et al., 1996). Chapter 2: Sediment Monitoring and Assessment Study Plans 2-13 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Table 2-3. Typical sediment volume requirements for various analyses per sample Sediment Analysis Minimum Sample Volume Inorganic chemicals 90 mL Non-petroleum organic chemicals 230 mL Other chemical parameters (e.g., total organic carbon, moisture content) 300 mL Particle size 230 mL Petroleum hydrocarbons 1 250-1000 mL Acute and chronic whole sediment toxicity tests 2 1-2 L Bioaccumulation tests 3 15 L Benthic macroinvertebrate assessments 8-16 L Pore water extraction 2 L Elutriate preparation 1 L 1 The maximum volume (1000 mL) is required only for oil and grease analysis; otherwise, 250 mL is sufficient. 2 Amount needed per whole sediment test (i.e., one species) assuming 8 replicates per sample and test volumes specified in USEPA, 2000d 3 Based on an average of 3 L of sediment per test chamber and 5 replicates (USEPA, 2000d). Recommendation Box #2 How many samples and how much sample volume should be collected? � The testing laboratory should be consulted to confirm the amount of sediment required for all desired analyses. � The amount of sediment needed from a given site will depend on the number and types of analyses to be performed. If biological, toxicological, and chemical analyses are required (sediment triad approach), then at least 10 liters of sediment might be required from each station. � Since sampling events might be expensive and/or difficult to replicate, it is useful to collect extra samples if possible, in the event of problems encountered by the analytical laboratories, failure of performance criteria in assays, or need to verify/validate results. � Consider compositing samples from a given station or across similar station types to reduce the number of samples needed. 2-14 US Environmental Protection Agency Technical Manual 2.4.2 Number of Samples The number of samples collected directly affects the representativeness and completeness of the data for purposes of addressing project goals. As a general rule, a greater number of samples will yield better definition of the areal extent of contamination or toxicity. Many programs specify a certain number of samples per location (e.g., CERCLA site or dredging unit). Accordingly, sample requirements should be determined on a case-by-case basis. The number of samples to be collected will ultimately be an outcome of the questions asked. For example, if one is interested in characterizing effects of a point source or a gradient (e.g., effects of certain tributaries or land uses on a lake or estuary), then many samples in a relatively small area might need to be collected and analyzed. If, however, Considerations The appropriate number of samples is usually determined by... ! size of the study site ! type and distribution of the contaminants being measured ! characteristics and homogeneity of the sediment ! concentrations of contaminants likely to be found in the sediments ! sample volume requirements ! desired level of statistical resolution or precision one is interested in screening “hot spots” or locations of high contamination within a watershed or water body, relatively few samples at regularly-spaced locations might be appropriate. In most monitoring and assessment studies, the number of samples to be collected usually results from a compromise between the ideal and the practical. The major practical constraints are the costs of analyses and logistics of sample collection. The major costs associated with the collection of sediment samples are those for travel to the site and for sample analysis. The costs of actual on-site sampling are minimal by comparison. Consequently, it is good practice to collect an excess number of samples, and a subset equal to the minimum number required is selected for analysis. The archived replicate samples can be used to replace lost samples, for data verification, to rerun analyses yielding questionable results, or for the independent testing of a posteriori hypotheses that might arise from screening the initial data. However, storage of sediments might result in changes in bioavailability of chemical contaminants (see Section 4.5). Therefore, follow-up testing of archived samples should be done cautiously. 2.4.3 Replicate and Composite Samples Replicate Samples As mentioned in the previous section, the number of samples collected and analyzed will always be a compromise between the desire of obtaining high quality data that fully addresses the overall project objectives (MQOs) and the constraints imposed by analytical costs, sampling effort, and study logistics. Therefore, every sampling program needs to find a balance between obtaining information to satisfy the stated DQOs or study goals in a cost-effective manner, and yet have enough confidence in the data to make appropriate decisions (e.g., remediation, dredging; Step 3 in the DQO process, Figure 2-2). Two different concepts are used to satisfy this challenge: replication and sample compositing. Replication is used to assess precision of a particular measure and can take many forms depending on the type of precision desired. For most programs, analytical replicates are the most frequently used form of replication because most MQOs are concerned with analytical data quality (see examples in Chapter 2: Sediment Monitoring and Assessment Study Plans 2-15 Methods for Collection, Storage, and Manipulation of Sediments for Chemical and Toxicological Analyses Appendix B). The extent of analytical replication (duplicates) varies with the program or study DQOs. Performing duplicate analyses on at least 10% of the samples collected is considered satisfactory for most programs (GLNPO, 1994; USEPA/ACOE, 1991; PSEP, 1997a; USEPA/ACOE, 1998). An MQO of � 20 - 30% relative percent difference (RPD) is commonly used for analytical replicates depending on the analyte. Field replicates can provide useful information on the spatial distribution of contaminants at a station and the heterogeneity of sediment quality within a site. Furthermore, field replicates provide true replication at a station (analytical replicates and split samples at a station provide a measure of precision for a given sample, not the station) and therefore can be used to statistically compare analyses (e.g., toxicity, tissue concentration, whole sediment concentration) across stations. Results of field replicate analysis yield the overall variability or precision of both the field and laboratory operations (as well as the variability between the replicate samples themselves, apart from any procedural error). Because field replicate analyses integrate a number of different sources of variability, they might be difficult to interpret. As a result, failure to meet a precision MQO Checklist Replication can take several forms and satisfy different purposes: � Collect field replicate samples at a station if there is a need to statistically compare results among stations within a site. � Analytical replicates: separate laboratory analyses on subsamples from the same field sample. � Field replicates: separate samples collected at a station each of which is analyzed individually. � Field-split replicates: a single field sample is split into subsamples, ea