Hazardous Substance Research Centers/South & Southwest

Sediment Monitoring Programs

Although research shows caps contain pollutants under ideal conditions, concerns remain about failures caused by uncontrollable outside effects, such as burrowing bioturbators, isolated scouring, or accidental penetrations by anchors ortrawling nets. Some natural processes also contribute to the release of pollutants from sediments.

An effective monitoring program consists of the following five steps defined by capping specialists in the U.S. Army Corps of Engineers:

Step 1:
Choose Meaningful and Attainable Monitoring Objectives

The objectives for an effective monitoring program include:

Defining the extent and thickness of the cap;
Measuring whether the desired capping thickness is maintained;
Determining if the contaminated sediments remain isolated.

Step 2:
Develop a Monitoring Plan

To determine how successful you are in reaching these or other objectives, you must choose appropriate techniques to monitor physical, chemical, and biological processes:

Physical processes
Key processes include:

The extent and thickness of the capping layer;
The potential for erosion due to currents and wave action;
Consolidation of deposits and underlying sediment layers.

These processes are measured by using periodic precision bathymetry, sediment profiling camera surveys, settlement plates, and other instrumentation.

Chemical processes
A key chemical process to monitor is the potential mixing of clean capping material and contaminated sediments during and after placement. These processes are measured by:

Analyzing sediment or interstitial water to define the chemical profiles of contaminated and capping layers;
Sampling cores over time to assess upward contaminant migration

Biological processes
Key biological processes to monitor are the toxicity and bioaccumulation that occur when contaminants migrate or the cap is breached. These processes are measured by sampling and analysis to determine if bioturbating organisms have invaded the capped site.

Step 3:
Develop Hypotheses to Test Capping Intervention

Make hypotheses of the result accomplished by capping and design measurements of physical, chemical, and biological processes. If these measurements contradict established hypotheses, monitor the capped area more intensively or develop an environmental control action.

Step 4:
Designate Sampling Design and Method

Select techniques and equipment that best fit the capping site. Remember that, depending on the soil type, collection of samples may leave holes that can threaten the integrity of the cap and may need to be refilled. Some of the most important techniques and equipment include:

Navigation and positioning equipment to accurately locate the site;

Precision bathymetric instrumentation to survey the location, size,and thickness of the cap;

A sediment profiling camera that sensitively detects thin layers within sediment profiles;

Grab samplers or coring devices to extract samples;

Still and video photography of capping sites;

Instruments to sample bioturbating organisms.

Step 5:
Designate Management Options

Design management actions to take if measurements of physical, chemical, and biological processes contradict expected results. These actions may range from unintrusive site monitoring to the introduction of new capping material.

You have completed the In-Situ Capping Primer. For more information on this topic, select the link to "Technical Notes" in the navigation bar to the left.