7. Monitoring

Monitoring data collected before, during, and after remediationThe act or process of abating, cleaning up, containing, or removing a substance (usually hazardous or infectious) from an environment. provide an objective basis for evaluating remedy performance and effectiveness. Monitoring data are used for gauging progress towards meeting the RAOs remedial action objectivesand determining whether further remediation or a change to the current remedy is required. The technologies addressed in this guidance document (MNR/EMNR, in situ treatment, cappingTechnology which covers contaminated sediment with material to isolate the contaminants from the surrounding environment., and removal) all require monitoring at various stages of implementation.

Monitoring is part of the planning process from the earliest phases of the project. Typically, a thorough site investigation (for example, an RIRemedial investigation) is performed as part of the process for developing a CSMconceptual site model, defining RAOs, and selecting a remedial action alternative. The RI is normally comprehensive; however, RI data may require supplementation to define the metrics that are used to assess the long-term effectiveness of the selected remedy. In most cases, multiple lines of evidencePieces of evidence are organized to show relationships among multiple hypotheses or complex interactions among agent, events, or processes. A weight of evidence approach includes the assignment of a numeric weight to each line of evidence. are used to determine the remedy success, regardless of whether the alternative includes dredging, capping, or MNR. Data from a variety of physical, chemical, and biological processes may be required to establish the metrics. Sediment deposition, resuspensionA renewed suspension of insoluble particles after they have been precipitated., and movement can complicate data interpretation, even for well-designed sediment monitoring programs. Adequate samples upgradient and downgradient of the area of interest aid in interpreting the monitoring data and understanding the processes that occur over the life of the monitoring program.

7.1 Types of Monitoring

Three basic types of monitoring related to sediment remediation are discussed in this chapter:

Baseline monitoring is performed prior to a remedial action to assess the conditions at the site prior to construction or prior to formal monitoring when demonstrating MNR. Baseline monitoring differs from site characterization in that not all measurements needed to characterize a site are carried forward in the monitoring program. The design for baseline monitoring is best completed after the characterization has determined the physical, chemical, or biological conditions to be measured later, the zones to be included in the monitoring design, and a consistent set of variables to be characterized throughout the monitoring program.

USEPA Monitoring

Monitoring should be conducted at most contaminated sediment sites for a variety of reasons, including: 1) to assess compliance with design and performance standards; 2) to assess short-term remedy performance and effectiveness in meeting sediment cleanup levels; and/or 3) to evaluate long-term remedy effectiveness in achieving RAOs and in reducing human health and/or environmental risk. In addition, monitoring data are usually needed to complete the five-year review process where such a review is necessary (USEPA 2005, Chapter 8).

Construction monitoring typically occurs during or immediately following implementation of the remedy and indicates whether the remedy has achieved design criteria (such as specifications for capA covering over material (contaminated sediment) used to isolate the contaminants from the surrounding environment. thickness, dredging depth, turbidity limits, sedimentation rates, water quality criteria, and perhaps resuspension levels). The construction monitoring plan must be strictly followed in order to evaluate compliance with design specifications. For example, improper placement of downstream particulate monitoring equipment during remedy construction could lead to erroneous conclusions regarding resuspension of sediments. Construction monitoring does not apply to sites where MNR has been selected as the remedy.

Post-remediation monitoring (sometimes referred to as long-term monitoring) takes place following implementation of the remedy and continues until the remedy has met the established goals. There are two types of post-remediation monitoring: performance monitoring and effectiveness monitoring. Performance monitoring indicates whether the remedy has met or is approaching the goals on a zone-by-zone basis (for example, to determine the physical integrity of a cap or sedimentation rates for MNR). Effectiveness monitoring focuses on whether the remedial action achieved the overall RAOs. Effectiveness monitoring is typically designed to determine whether the remedy has achieved the RAOs by analyzing fish tissue, benthic tissue, or other indicators of remedy success. Figure 7-1 describes sediment remediation monitoring programs.

Figure 7-1. Sediment remediation monitoring programs.

7.2 Developing a Monitoring Plan

Several guidance documents are available to help project managers develop monitoring plans for sediment remediation efforts. In particular, Chapter 8 of USEPA's guidance (2005a) applies to monitoring plans at sediment sites. USEPA (2005a) addresses remedial action and long-term monitoring and describes a six-step process for developing and implementing a monitoring plan. For sites that require a sediment cap, USEPA’s Great Lakes National Program Office capping guidance (Palermo 1998) presents extensive guidance on monitoring. The Great Lakes guide presents a five-step process that is similar to the USEPA 2005 process. Another guide, Implementation Guide for Assessing and Managing Contaminated Sediment at Navy Facilities (NAVFAC 2003b) contains information on design and implementation of monitoring plans for contaminated sediment management programs. Monitoring considerations discussed include: (a) spatial trends in dynamic systems; (b) co-occurrence between sediment contaminant concentrations, toxicity, and bioaccumulationThe accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost. Thus, the longer the biological half-life of the substance the greater the risk of chronic poisoning, even if environmental levels of the toxin are not very high.; and (c) geochemical normalizers in data interpretation. The Navy has also issued a guide entitled Long-Term Monitoring Strategies for Contaminated Sediment Management (SPAWAR 2010), which emphasizes the need to define an exit strategy as part of the monitoring plan. The Navy also developed the Technical Guidance on Monitored Natural Recovery at Contaminated Sediment Sites (NAVFAC 2009) and U.S. Navy-SPAWAR (ESTCP Project ER-0622), which provide information on the design of monitoring programs. Another useful guide, Monitored Natural Recovery at Contaminated Sediment Sites (Magar et al. 2009), was developed under the auspices of the Environmental Security Technology Certification Program (ESTCP). This document discusses the lines of evidence used for assessing MNR and the baseline and long-term monitoring approaches to be used in the evaluation process.

Planning for Monitoring Programs

  • Establish monitoring objectives.
  • Determine measures needed to satisfy monitoring objectives.
  • Define sampling units and monitoring boundaries.
  • Specify how data will be used to satisfy the objectives.
  • Consider uncertainty.
  • Design the monitoring program.

The following section describes a process to develop an effective monitoring plan that incorporates USEPA’s systematic planning process, known as the Data Quality Objectives Process. This guidance emphasizes the development of a complete set of specifications for the design of a monitoring program to maximize the probability that data collected is adequate to draw conclusions regarding whether remedy performance and effectiveness criteria are being met. This process results in a desired degree of confidence and requires that the statistical analysis parameters are identified early in the planning process. Monitoring program considerations specific to remediation of contaminated sediment sites include:

7.3 Planning Monitoring Programs

When planning a sediment remediation monitoring program, the CSM should be periodically revisited and updated. Previous contaminant source, pathway, and receptorA plant, animal, or human that is typically the focus of a risk assessment following the direct or indirect exposure to a potentially toxic substance. elements may change upon implementation of the remedy if differing site conditions are encountered during construction. The monitoring plan should include contingencies and be flexible enough to adapt to changing circumstances. The monitoring program should be designed using results from site characterization and pre-design studies to address site-specific considerations.

7.3.1 Establish Monitoring Program Objectives, Questions, Decision Points, and Time Frames

Monitoring program objectives, questions, decision points, and time frames should be established prior to any detailed consideration of what to measure, how often or where to measure, or how long to measure a particular parameter. When defining objectives, avoid open-ended statements (such as "to determine whether the remedy is working") and instead describe measurable objectives, questions, and decision points. Consider SMARTspecific, measurable, attainable, relevant, and time bound (specific, measurable, attainable, relevant, and time bound) criteria when formulating objectives. Sediment remediation monitoring program objectives should address the three main types of monitoring shown in Figure 7-1.

Separate objectives must be developed for each type or phase of monitoring. An effective way to clearly convey the objectives of the monitoring program is to identify and state the specific questions that must be answered in order to achieve the objectives. If subordinate questions are tied to specific measurements needed to address the higher level questions, consider organizing these questions in a logical hierarchy so that the relationship between questions is clear. The results of monitoring answer the questions that may be used to support a decision about what course of action to take (for example, to change remedial technologies or move from MNR to an active remediation alternative). A decision statement should be developed to explain clearly what finding will lead to the action. A flowchart constructed to diagram the sequencing and to depict alternative pathways leading to all possible outcomes can be helpful. Examples of these time lines to depict monitoring phase sequencing are shown in Figures 3.1, Figure 3.2, and Figure 3.3 in SPAWAR (2010).

The objective of baseline characterization is to determine the conditions such as average concentration and distribution of contaminants and other parameters of interest in each zone prior to remedy implementation. If the environmental problem reflects seasonally dynamic variations (such as methyl mercury production or sedimentation rates), then baseline characterization must represent the seasonal variations. For example, avoid comparing winter results to summer summer results, or high precipitation1) The formation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid; or 2) rain, sleet, hail, snow and other forms of water falling from the sky. seasons compared to dry seasons. These comparisons can result in incorrect conclusions that reflect seasonal effects rather than remedy effectiveness.

Ideally, long-term monitoring is considered during site characterization. Data representative of baseline (pre-remedy) conditions and background (data from upgradient, upstream, or reference locations) should be collected as part of the RI or similar site characterization efforts. For some sites, however, additional baseline considerations are required to obtain measurements of variables that were not previously collected or to provide spatial or temporal coverage. For example, at large complex sites, it may be necessary to assess different zones (Section 2.9) to ensure that baseline conditions are established for each zone. Each zone would then be monitored to evaluate the implementation and post-remedy conditions within that zone, with RAOs established for that zone.

The objective of monitoring during remedy implementation is to determine whether the established design criteria are being met. For example, for hydraulic dredgingDredging by use of a large suction pipe mounted on a hull and supported and moved about by a boom, a mechanical agitator, or cutter head which churns up earth in front of the pipe, and centrifugal pumps mounted on a dredge which suck up water and loose solids., the relevant questions may be:

If capping is the primary remedy, the relevant questions may be:

Corrective measures, if necessary, can then be implemented. Similarly, for MNR a relevant question could be:

The time frame for monitoring must be established. For example, sampling may be required during, and a few days following, capping to determine whether resuspended sediment and water quality stabilizes. Physical changes can be measured immediately following the remedy (for example, did dredging remove the planned depth, or was a cap of a specified thickness emplaced?). Biological measures, however, may require a longer time frame before meaningful changes can be observed.

Objectives related to post-remediation monitoring are established to determine whether the remedy is achieving the RAOs. Often, short- and long-term objectives relate to the measurable performance of the remedy on a zone-by-zone basis, and the effectiveness of the remedy for the site in general over time. For example:

Monitoring must be tailored to the specifics of the site. Several examples of short- and long-term questions are shown below:

For each question a specific, testable hypothesis can be stated. For example, a short-term hypothesis (post-remediation) may be: 

Stating the null hypothesis as having achieved the goal is appropriate, since that is expected to be true after remediation. This approach leads to a statistical test that requires the data to demonstrate that the site continues to be "dirty" (to reject the null as stated above, that the site is now "clean"). Similar testable hypotheses should be developed for each secondary question and the design of the monitoring program should ensure adequate data to test each stated hypothesis.

7.3.2 Determine Measures Needed to Satisfy Monitoring Program Objectives

With established monitoring objectives, the next step is to determine what measurements or other information is needed. The goal is to derive the most cost-effective design that will meet the objectives.

Depending on the objectives, monitoring may include:

The source of data is important. For existing information locate QA/QCquality assurance/quality control and other metadata, including location, depth and date of samples, sample collection method, and sample analysis methods. This supporting information establishes the reliability of the data and may indicate any limitations associated with its use.

For new data, establish the methods available for obtaining the information, including the sample collection method and analytical methods. When chemical measurements are required, the target analytes or COCs must be included. For each analyte, the concentration level at which it is important to obtain quantitative measurements should be stipulated. This information can then be used to determine whether analytical methods are available that can provide measurements at or below the required levels and can be used to evaluate the suitability of existing data sources.

Standard methods that provide measurements of an analyte class may be appropriate. If these standard methods are incapable of achieving the required detection limits, or existing data sets have detection limits above levels of interest, an alternate method of monitoring the system may be appropriate. When multiple methods with adequate detection limits are available, compare the analytical performance of each method such as PARCCSprecision, accuracy, representativeness, comparability, completeness and sensitivity (precision, accuracy, representativeness, comparability, completeness and sensitivity), cost, availability, and turnaround time.

To establish the relevance of each measurement to the objective, assemble the monitoring parameters, performance expectations, and analytical methods in a matrix. Then, list the study questions as a series of columns and each of the individual inputs as a series of rows. The level of detail may vary from associating study questions with broad categories of information (such as concentrations of semi-volatile constituents in sediment) using a simple check mark, to a more detailed analysis such as denoting individual constituents and completing the cells in the matrix with the thresholds for each constituent that the measurement methods must be able to detect. If it is not clear what question a measurement will be used to answer, then consider deleting the measurement. While measurements may not necessarily add to the cost of sampling and analysis, they may add to the cost of data validation, maintenance of the database, and data interpretation and analysis.

For many sediment sites, numerical criteria (such as cleanup levels) may be established. Alternatively, monitoring data may be compared to other measurements obtained for the project (for instance, comparing information for one area or point in time to that for another area or point in time). For projects involving characterization of on-site conditions and comparison to upgradient or background conditions, discrete data sets may be required to clarify conditions in upgradient or background populations.

Technology-specific monitoring parameters and approaches for baseline, construction, and post-remediation monitoring are discussed in each technology overview.

Note that measurements that are used to establish remedy performance and effectiveness should be clearly defined and characterized prior to remedy implementation. These measurements establish a before-and-after comparison to evaluate remedial action effectiveness in achieving RAOs.

7.3.3 Define Sampling Units and Monitoring Boundaries

The boundaries for the monitoring program must be documented. Clearly define where, when, and what monitoring measurements must be obtained. Maps, pictures, or descriptions should clearly depict what portion of the environment or what set of conditions the monitoring effort is intended to represent, and identify the time frame necessary. Within zones (Section 2.5), a map should illustrate site conditions that influence the selection of remedial technologies (such as horizontal and lateral COC distribution, bathymetryThe measurement of or the information from water depth at various places in a body of water., sediment stability, sediment deposition rates, hydrodynamicsThe branch of science that deals with the dynamics of fluids, especially that are incompressible, in motion., and others; see Table 2-2). For many sediment monitoring programs, data or information will be needed to understand conditions in three dimensions. In these cases, specify the boundaries for each. For example, if data will be needed to represent different layers of sediment or water, specify boundaries for each of those dimensions. By displaying these boundaries on maps, it is possible to show how data points represent the areas of interest. The map, picture, or description establishes boundaries on a large scale, while the sampling plans focus on the number and allocation of samples within these boundaries that are necessary to adequately represent the conditions in the area.

Sampling units can be defined as the portion of the physical environment from which one or more samples may be taken to obtain measurements appropriate for the intended use. For samples of water, sediment, fish, or other organisms, these units can be defined to be as small as the dimensions of an individual sample, or can be defined to represent larger areas that encompass multiple samples including composites. Sampling units can be intervals of time (such as weekly average surface water concentrations). Multiple considerations based on sampling theory can be used to establish the actual dimensions of a sampling unit and, when appropriate, these considerations can be addressed during the design of the study. For existing data sets, unless metadata are available that discuss the dimensions of sampling units, it may be necessary to assume the sampling unit is simply the dimensions of the sample itself. If a list of sampling units can be identified, then it should be included and the basis for the list provided.

If the monitoring project is expected to support decisions at a scale smaller than the overall study boundaries (sometimes referred to as the scale of inference), the boundaries for these decision units should be specified. For example, if a study is designed to represent the entire site but decision makers want to be able to generate estimates for, and make separate decisions about (or compare) each zone within the site, it must be clearly stated. It may be important to define zones based on characteristics such as grain size or depositional environment to avoid comparisons of concentrations between fine grain clays and silts and coarse sands. Defining multiple decision units can affect the design and may influence the adequacy of existing data sets. A study design adequate to answer questions about the entire site with an acceptable degree of certainty may not be adequate to answer questions on individual portions of that area or individual time periods.

During remedy construction monitoring, it is important to specify what the samples are intended to represent so as to avoid improper placement of monitoring equipment (such as down stream particulate monitoring stations). If incorrect boundaries are selected, then samples taken to represent the areas of interest may lead to incorrect conclusions about the effects of placing the cap or performing dredging.

For many projects, it is equally important to establish and document temporal boundaries that specify the particular time frame the project is intended to represent. For dynamic media such as outfalls, streams, or rivers, temporal boundaries may stipulate specific conditions or periods of time that measurements must represent. For example, a monitoring program designed to sample after a specified event such as a flood, storm, or river level may suggest a potential effect on the integrity of a cap. For remedial alternatives that may result in a temporary increase in available contaminants (such as through resuspension), the length of time that will be necessary for meaningful results (such as decreases in tissue concentration) may require that temporal boundaries be incorporated into the design of the monitoring effort.

7.3.4 Specify How Measurements Will be Used to Satisfy the Objectives

To ensure that an efficient and effective monitoring program is established, take the time to document how each measurement will be used to answer one or more of the subordinate or primary questions. Be as specific as possible—indicate whether data will be used to estimate a mean value for a zone or time period, or some other measurement parameter. For results used to decide upon a course of action, a simple if-then decision rule can be formulated, with the "if" part being the conditions represented by monitoring (such as the mean concentrations, or the estimated rate of reduction of the mean concentration over some time-frame) and the "then" part representing the course of action to be taken.

For measurements that are not readily linked to a question, if it is possible to explain how they may be useful (such as in data interpretation or trend analysis), a determination can be made as to whether to include them in the design or not.

7.3.5 Specify Desired Level of Certainty

For monitoring programs, it is important to state the level of confidence required to discern changes of a specified magnitude (based on the expected behavior of the remedy). Together with an estimate of the expected variability in the data results, this level of confidence directly influences the number of samples that will be needed. The confidence level is one key to understanding the variability associated with the rate of change for a particular process, such as a decline in tissue concentrations that occurs after the remedy is implemented. Whether the remedy includes dredging, capping, MNR, or a combination of these remedies, the variability in the system determines the level of confidence that the remedy will meet the RAOs. Projecting the remedy success and potential need for future remedial measures depends upon a reliable baseline that describes the nature of site variability. USEPA’s DQO guidance (2006b) discusses the process of setting performance criteria and recognizes that establishing performance criteria can be done in a number of ways. While it is desirable to identify quantitative limits on uncertainty, a graded approach to this quantification can focus specifications on the most critical metrics, while leaving the other metrics more qualitative.

7.3.6 Design the Monitoring Program

When practical, a statistical design should be used to support the selection of the most efficient monitoring program for assessing whether the objectives are being met. Baseline data can be used to estimate the variability of the various metrics of interest. An estimate of the variance, along with the specifications for uncertainty and magnitude of change that is important to detect, can be used to generate a sample size for the monitoring program. Working with a project team (including a design statistician for more complex programs), the sample size (frequency and number of samples per sampling event) can be selected. A design team can evaluate the use of compositing and other efficient sampling methods in order to arrive at design alternatives that generate data of adequate quality to discern changes over time. The data quality and statistical aspects of monitoring design are beyond the scope of this guidance; however, the methods used must be defensible and the analysis presented clearly.

7.4 Additional Resources

Several existing guidance documents provide discussions of monitoring concepts and program design considerations for contaminated sediment sites:

Publication Date: August 2014

Permission is granted to refer to or quote from this publication with the customary acknowledgment of the source (see suggested citation and disclaimer).


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