Bioavailability Studies

As part of site characterization studies Benchmark scientists have conducted bioavailability studies to assess the availability of chemicals of concern and to evaluate potential bioaccumulation pathways.  The bioavailability of chemicals of concern is generally determined by the species of chemical found at the site, and the nature of the media containing the chemicals.  Many chemicals that can cause concern are not available to biota and may not represent an ecological threat.  A bioavailability study would evaluate all media (e.g., surface water, ground water, soil, sediment, vegetation, and prey organisms) that might contain the chemicals of concern and determine  exposure pathways for biota.  If an exposure pathway is identified, the study might also evaluate the potential exposure impact and the potential impact to lower trophic level organisms.

Chemical Evaluations

Site characterization also involves a chemical evaluation of site media to establish the nature and extent of potential contamination.  A thorough chemical evaluation would include collection and analysis of potentially impacted media from potentially impacted areas.  An initial sampling event might be used to pinpoint areas that need further study and to eliminate chemicals not found at the site from the analyte list.  A second sampling event could be required to focus on areas that are potentially impacted using a focused analyte list.  Benchmark scientists have conducted chemical evaluations at potentially contaminated industrial sites, at wastewater discharge sites, and sites where sediment removal is proposed.  Some of the methods used by Benchmark scientists for chemical evaluations are described on the following pages.

Remediation Monitoring

Benchmark scientists are experienced in developing and conducting monitoring programs for Remediation and Mitigation projects.  Monitoring programs are designed to monitor the progress of a project, evaluate the need for modification, and determine when the project has met remediation goals.  Benchmark scientists conduct vegetation cover surveys, erosion monitoring and control, invasive plant control, and water quality studies.  Benchmark scientists conduct vegetation cover studies using a variety of data sources and methods including line intercept, point intercept, aerial photographs, sample grids, and qualitative field observations.  Erosion monitoring and control is conducted during the monitoring phase of a project to ensure success of the project.  While a wetland project is developing, it is important to provide optimal conditions for growth and development of the desired plant species.  Benchmark staff control the invasion of undesirable plant species that may hinder or compete with desirable species.  Undesirable species are controlled through physical removal, herbicide application, controlled burning, or other methods.  Benchmark conducts surface water monitoring in the study area to assess the health of wetlands.  Remediation monitoring may also include a sampling program that provides a succession of samples of sediment, soil, water, or biota.  Changes in sample results can be used to evaluate the success of remediation efforts.

Sediment Sampling and Analysis

Benchmark scientists have collected and processed sediment samples from rivers, channels, marshes, lakes, bays, and beaches.  The chemical objectives and target depth of a sampling program will determine the methods used for sample collection and processing.

Surface Grabs - Surface sediment can be collected using a box core or ponar sampler.  These devices are used when shallow samples are desired and relatively large volumes may be needed (e.g., toxicity testing, sediment infauna assessment).

Sediment Coring - If deeper sediments are needed or a known depth stratum is desired, Benchmark scientists use a sediment core sampler.  Benchmark uses a lightweight piston corer for soft sediment less than 8 feet deep.  The piston corer is quickly deployed  and can be operated without heavy equipment.  A vibracorer is used when sediments are firm or more than 8 feet deep.  Sediment cores can be homogenized or sectioned by depth.

Sediment Profiling - When information about specific depths or specific sediment strata is needed, Benchmark scientists use a piston corer or a vibracorer.  Sediment cores are measured and extruded, or  the sampling tube is split to access sediment strata.  A sediment profile is produced when sub-samples are collected from successive sediment strata and analyzed for physical and/or chemical constituents.

Sediment Pore Water Analysis - Studies investigating dissolved or available chemicals might require pore water analysis.  Pore water samples are usually extracted using centrifugation or positive gas pressure, from core sections.  Pore water can be extracted under anaerobic conditions when target analytes might be lost through oxidation.

Surface Water Sampling and Analysis

Surface water samples are usually collected when  data about ambient conditions are needed.  Samples are collected using surface grabs or submersible pumps.  Samples can be used for chemical analysis or toxicity testing.  To obtain information about depth strata, or when contaminant concentrations are low and can be masked by sampling related contamination, other sampling techniques are used.

Ultra-clean Water Sampling - When contaminant concentrations are low and may be masked by sampling related contamination, Ultra-clean sampling techniques are used.  Ultra-clean sampling involves the use of peristaltic pumps and pre-cleaned Teflon® tubing.  Samples are collected from a continuous stream pumped from the target depth.  Special sample handling techniques are used to avoid sample contamination after collection.

Water Column Studies - Water column profiles can be developed by collecting discrete samples from specific depth strata using a sample bottle (i.e., Alpha or Beta Sampler), or pumping water from specific strata using a peristaltic pump.  Physical parameters (i.e., temperature, pH, conductivity, salinity) can also be collected at each sample point by attaching sensors to the sample bottle or pump intake.