Objectives of Sample Dredging & Testing:
a) To collect sediment samples which adequately characterize the project dredged materials for maintenance dredging project.
b) Analyzing the dredged material samples chemically and physically in order to provide information to determine if the sediments are contaminated
c) Documenting the field sampling and results of physical and chemical analyses and quality control measures
d) Collecting sufficient data to determine whether unacceptable adverse impacts would result from dredging and dredged material placement operations (upland placement or open water).
Dredge Sediment Sample Testing Approach
Site water and sediment samples are collected from the dredge site for the purpose of conducting testing to characterize the material that will be excavated during the dredging project. Sampling locations should be selected such that the sediment collection locations are evenly distributed over the dredge footprint, with bias towards areas of highest usage and activity.
Testing requirements will depend upon the history of the site, the surrounding area, past dredging information and the placement options desired by the dredging company. Data needed for the evaluation consists of chemical analyses of sediment, water, and elutriate samples. Collection of the physical parameters required includes grain-size analyses, percent solids, pH, temperature, and salinity. In limited instances, bioassays such as toxicity, survival and bioaccumulation would be needed to determine suitability of material prior to placement. Contacting the US Army Corps of Engineers to determine whether or not special requirements exist for the project area and if modifications to this testing protocol is required.
Bathymetric Surveys Volume Calculations
Hydrographic Survey and Volume Calculations
Hydrographic surveys are principle dredged contract management tool. Hydrographic surveys should be made prior to dredging to determine the existing depths within the project area and after dredging to determine the depths that were attained as a result of the dredging. Hydrographic surveys must be made in a timely manner immediately before initiation of dredging activities and immediately following completion of dredging. Quantity calculations must be made from survey data and based on precisely established horizontal and vertical controls.
Hydrographic Survey is typically conducted using:
• Single-Beam Surveying; and
• Multi-Beam Surveying
Once the hydrographic survey is completed, volume calculation is conducted by determining the volume of the prism formed between the sea floor surfaces prior and after dredging. The accuracy of the volume calculation depends upon the density of points surveyed. The advantage of multi beam over single beam is in the number of points it collects at any given time.
1) Physical Properties:
• Index Properties (ASTM D2487)
• Particle Size (ASTM D422)
• Moisture-Density Relationship (ASTM D1557)
• Bulk Density
• Organic Content (ASTM D2974)
2) Engineering Properties:
• Shear Strength (ASTM D-4767, 2850-87); Strength gain/loss overtime
• Compressibility (ASTM D-2435)
• Ambient Temperature effects on strength development
Meet Residential Soil Quality Criteria?
In general, an upland confined disposal facility (CDF) can accept contaminated dredged sediments once the operator demonstrates that placement of dredged material would not result in adverse impacts to the ecosystems and human health. The major potential adverse environmental impacts are surface and groundwater contamination. The discharge of contaminants from upland CDF to surface water must be minimized.
The magnitude of those impacts are dependent on the following:
A) Location of the facility and site specific conditions (including compatibility with adjacent and nearby land uses);
B) Characteristics of the dredged material proposed for placement at the facility (meets residential, non-residential, alternate soil clean-up criteria or else);
C) Design and construction of the facility (environmental controls such as leachate collection system or perimeter containment in place);
D) Operation of the facility; and
E) Final closure and use of the facility site (developed for industrial, residential, retail, recreational use).
Below Hazardous Waste Criteria
In accordance with EPA regulations, the following characteristics define whether or not a material is hazardous waste:
Polycyclic Aromatic Hydrocarbons (PAHs)
PAHs are a group of organic compounds that contain two or more fused aromatic rings. PAHs are formed and released into the environment as the result of combustion/pyrolysis. According to USEPA, exposure to PAHs can be from air contamination by smoke from fireplaces, wood stoves, furnaces burning coal or oil, and from smoked or charbroiled foods, smoking tobacco products, inhaling vehicle exhaust, and inhaling fumes from working exposure to coal tar and asphalt. PAHs also result from the production and processing of metals, coal, oil, and gas. PAHs tend to accumulate in soils by adhering to soil particles. The adhesion of PAHs in soil is dependent on the amount of organic matter present and the particle size of the soil. Adhesion of the PAHs in soil is greater with increased amounts of organic matter and with finer-grained sediments (silts and clays) as compared to coarser-grained sediments (sands).
These constituents are known by the USEPA as suspected of causing cancer in humans. PAHs are bioaccumulative and do not break down easily in the environment, thus they are subject to long-range air transport. These constituents are deposited as fine particulates over the landscape (i.e. paved areas, roof tops, undeveloped lands, and directly to surface waters). During precipitation events, PAHs are carried into storm water ditches, streams, and lakes in the form of runoff and are trapped in the environment by sediments. The watershed of the Lake is highly urbanized and the lake itself serves a storm water control function, therefore, the presence of these constituents in lake sediments does not indicate contaminants of an unknown origin. The
United States Geological Survey (USGS) has been investigating the presence of PAHs in urban lakes across the United States. Their investigations have identified coal-tar-based pavement sealcoat as a major source of elevated PAHs, especially in the central, southern, and eastern United States (Mahler and Van Metre, 2011). Coal-tar-based pavement sealcoat is often applied to driveways, playgrounds, and parking lots. In the USGS study, coal-tar-based sealcoat use was identified as the primary cause of upward trends in PAHs in urban lake sediment (Mahler and Van Metre, 2011).
Primary Sources for Dredged Sample Testing
a) USEPA and USACE (1998). Evaluation of Dredged Material Proposed for Discharge in Waters of the US – Testing Manual. Inland Testing Manual (“ITM”);
b) USACE (1995). QA/QC Guidance for Sampling and Analysis of Sediments, Water and Tissues for Dredged Material Evaluations(Chemical Evaluations). EPA-823-B-95-001;
c) USACE (2003). Evaluation of Dredged Material Proposed for Disposal at Island, Nearshore, or Upland Confined Disposal Facilities – Testing Manual;
d) US EPA and US Army Corps of Engineers (2003). Regional Implementation Agreement (RIA) for the Ocean Dredged Material Disposal Program.