Title: Introduction Text: The Benthic Flux Sampling Device 2 (BFSD2) is a remotely operated instrument for in situ measurement of the exchange rate of contaminants and other biochemical compounds across the sediment-water interface. Information on flux rates is used in evaluating the risks posed by in-place sediment contamination. This Web Tool provides background information on the operation and capabilities of BFSD2 including a deployment video. Example results are also discussed from two Navy sites where BFSD2 has been employed to help to investigate the extent of metals and organic impact in coastal sediments.

Title: Background (1 of 2) Text: Contaminants, such as metals and organic compounds, enter shallow coastal waters from many sources including ships, shoreside facilities, municipal outfalls, spills, and nonpoint source runoff. Sediments typically are considered a primary sink for these contaminants. In addition to surface sources, contaminated groundwater may discharge through the sea floor potentially introducing contaminants into the sediments and discharging to the water column. To determine whether contaminants are moving into, out of, or remaining immobilized within the sediments, contaminant flux must be determined. Direct measurement of contaminant flux in coastal areas is often the best method to assess flux across the sediment/water interface because variations in chemical and physical properties make it impossible to rely on bulk sediment contaminant concentrations alone to predict flux, bioavailability, and thus, toxicity.

Title: Background (2 of 2) Text: The BFSD2 measures contaminant flux from sediments and is the only method currently available for in situ measurement. A prototype BFSD was developed by the U.S. Navy's SPAWAR Systems Center San Diego under its Environmental Sciences Program. The current version, BFSD2, was produced by Ocean Sensors, Inc. in San Diego using commercial off-the-shelf, replaceable, and repairable assemblies. The Navy holds a U.S. Patent (#543952) for the BFSD2. The BFSD2 is not commercially available; however, arrangements could be made for use of the existing unit or to have one built. Contacts for more information are provided at the end of this tool.

Title: Operation of BFSD2 Text: The BFSD2 is a remotely operated instrument for in situ measurement of contaminant flux rates from sediments. It measures the flux into or out of the sediment by isolating a known volume of water above a known surface area of sediment. The device then draws off samples from this volume of water over time. After the equipment is retrieved, the samples are sent to a laboratory for analysis. Increasing concentrations indicate that the contaminant is fluxing out of the sediment, and decreasing concentrations indicate that the contaminant is fluxing into the sediment.

Title: Equipment/Physical Characteristics Text: BFSD2 instrumentation consists of a pyramid-shaped tubular frame (tripod), an open-bottomed chamber, and associated sampling and control equipment. At the top of the tripod is an acoustically released buoy for instrumentation recovery. At the bottom of the tripod are the open-bottomed chamber and associated sampling gear, flow-through sensors, data acquisition and control unit, video camera system, power supply, and oxygen supply system. At the top of the frame is an acoustically released buoy for BFSD2 recovery. The BFSD2 is approximately 1.2 by 1.2 meters from leg to leg and weighs approximately 175 pounds. It is designed for use in coastal and inland waters to a maximum depth of 50 meters.

Title: Flow-Through Sensor System Text: Flow-Through Sensor System Sensors monitor conditions in the sampling chamber including conductivity, temperature, pressure, salinity, pH, and dissolved oxygen. Circulation in the flow-through sensor system is maintained using a constant flowrate pump adjusted to approximately 15 mL/sec.

Title: Flux Sampling Chamber Text: Flux Sampling Chamber The flux sampling chamber consists of a bottomless box, approximately 40 cm square by 18 cm tall, with a volume of approximately 30.0 L. The chamber is constructed of clear polycarbonate to avoid disrupting exchanges that may be biologically driven, and thus, light-sensitive. Triangular blocks of polycarbonate occupy the 90-degree angles to prevent corner stagnation. The top of the chamber is hinged at one edge so that it can be left open during deployment to minimize sediment disturbance. A computer control system closes the lid once the chamber is in place. A gasket ensures a positive seal. The lid is held in place by four permanent magnets on the chamber perimeter. The bottom of the chamber is a knife edge. A video camera and lights are used to verify that uniform minimum sediment penetration depth has been achieved and that there is good probability that a positive seal between the chamber and the sediment has been achieved.

Title: Sampling Bottle Assembly Text: Sampling Bottle Assembly The sampling bottle assembly consists of 12 evacuated 250-mL Teflon collection bottles. The first sample is drawn through a 0.45-micron filter into the sample bottle upon closure of the lid at the start of autonomous operation. The remaining 11 samples are similarly collected at preprogrammed intervals throughout deployment.

Title: Oxygen Control Subsystem Text: Oxygen Control Subsystem Fluxes of many contaminants are sensitive to oxygen concentrations and oxygen levels can change quickly in water isolated in a chamber above sediment. Therefore, an oxygen supply system is used to maintain fairly constant oxygen levels. Ambient O2 is measured at the time of deployment, and maximum and minimum O2 concentrations are set at ambient +/- 1 mL/L. The system maintains O2 levels in the chamber within this range throughout deployment.

Title: Schematic of Deployment Text: The BFSD2 is deployed from a small surface craft using a light duty winch. It can be used in inland and coastal waters at depths up to 50 m and with bottom currents to 3 knots. The BFSD2 allows secure placement (bottom landing) with minimal disturbance of bottom sediments. Maximum deployment time is 4 days (96 hours). Deployment of the BFSD2 requires at least 3 people. One person is responsible for maneuvering, positioning, and securing the surface vessel. Two more people are needed for deploying and retrieving the BFSD2 itself.

Title: Video of BFSD2 Deployment Text: This video shows the BFSD2 as it is lowered into place and the lid of the sampling chamber is closed.

Title: Sample Collection Text: The BFSD2 is lowered into position with the lid open to minimize disturbance of the sediments. Once in place the lid is closed automatically. The system includes remote, real-time video imaging of the bottom site prior to sampling and video of the sample chamber documenting that the system was properly closed. The system allows programmable, microprocessor-controlled autonomous operation for up to 96 hours. The chamber isolates and maintains homogenous conditions in approximately 30 L of bottom water, including oxygen content within 1 mL/L of initial ambient conditions. During deployment, up to 12 250-mL in situ-filtered water samples are collected from the chamber at selected intervals.

Title: Blank Tests Text: Blank tests are performed to determine the background flux occurring in a particular water body that is not attributable to the sediment. A blank test is performed by sealing a polycarbonate panel across the bottom of the sampling chamber and lowering the BFSD2 to within several meters of the sediment surface. A standard operational procedure identical to the deployment is run for approximately 70 hours.

Title: Contaminants Assessed by BFSD2 Text: The BFSD2 can be used to determine the flux of trace metals, petroleum hydrocarbons, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). The California EPA has certified the BFSD2 as a Hazardous Waste Environmental Technology for quantifying the flux of metals in sediment. This certification indicates that the performance claims for the technology have been verified. Click here to view this certification. In addition, certification for use of the BFSD2 to quantify the flux of organics is in progress.

Title: Ancillary Data Collected by BFSD2 Text: Ancillary data collected by the BFSD2 include: Dissolved Oxygen Temperature Conductivity/Salinity pH Chamber Depth Video Imaging of Bottom

Title: Data Output from BFSD2 Text: Samples collected during deployment are sent to an analytical laboratory for chemical analysis. The results are then plotted in comparison to the blank test and the change in water concentrations over time can be determined. The results of the site deployment are shown in red and results of the blank test are shown in blue. With knowledge of the time intervals and the concentrations, a flux rate between the sediment and water in mass per surface area per unit time (µg/sq m/day) can be calculated.

Title: Factors Influencing Performance of BFSD2 Text: Factors influencing performance of the BFSD2 include: 1. Sediment Physical Conditions. The sampling chamber must seal with the sediment to function properly. The primary cause for lack or loss of seal is porosity of the sediment because of large grain size. Evaluation of performance indicators immediately after retrieval can detect loss of seal and prevent unnecessary analytical costs. 2. Sediment Contaminant Levels. The lower limit for resolving significant flux levels is based on blank test results. Sites having sample levels lower than blank results cannot be resolved with high confidence. These results are reported as statistical probabilities with confidence limits. 3. Site Marine Conditions. BFSD2 must maintain a good chamber lid seal. Surface vessel turbulence and/or prop wash, tidal and/or local currents, or even large fish distributions can jar the magnetically held lid. Momentary loss of the lid seal can allow ambient seawater to enter the chamber and refresh the sequestered sample water. Although this can be detected by performance indicators, some or all of the deployment can be negated by loss of lid seal. 4. Target Analytes. The BFSD2 initially was designed for evaluating trace metal flux. Materials in contact with sample water, minimum sample volume, filtering, holding time, sample preservation and handling, cleaning and decontamination, and other facets were designed specifically for trace metal application. Methods for evaluating organic contaminant flux are being developed. Organics analysis is influenced by small sample size and in situ filtering. Laboratory detection limits for extraction type organic analyses may be too high for practicable use.

Title: Cost of Using BFSD2 (1 of 5) Text: Cost information presented here is taken from SPAWAR's Technical Report No. 1826 (SPAWAR, 2000) based on field demonstrations in San Diego Bay and Pearl Harbor. Expected cost for a deployment assessing trace metals and having two sites (12 samples per site) and a blank test would be approximately $165,000. The time frame for completing a BFSD2 project is approximately 10 months from pre-operational through post-operational phases. The operational costs for the BFSD2 are largely driven by analytical laboratory costs. The low detection limits required to achieve meaningful flux measurements require specialized equipment and highly skilled technicians. Other BFSD2 operational costs are driven primarily by labor, supplies, and transportation costs. Cost breakdown for the pre-operational, operational, and post-operational phases of deployment are shown in the following pages.

Title: Pre-operational Phase Costs (2 of 5) Text: Pre-operational costs are those incurred prior to field operations. These costs include expenses involved with site research and applicability, logistics planning and scheduling, equipment maintenance and repair, and pre-deployment readiness preparations (supplies, packing, checkout). The pre-operational phase typically requires approximately 11 weeks.

Title: Operational Phase Costs (3 of 5) Text: Costs incurred during field operations include expenses involved with equipment transportation, personnel travel and per diem; field facilities (shoreside work area; surface vessel, handling equipment); and deployment, recovery, and turnaround on a 5-day cycle. Analytical costs include analysis of one blank test and the required number of sites (usually 12 samples per site) for trace metals. The operational phase costs for one site, including transportation, setup and a blank test, are approximately $48,640, of which 49% is for analysis of samples. Each additional site adds $21,700 to the total, of which 55% is for sample analysis. These costs assume 60-day laboratory analysis time, which can be reduced to 30 days or less at additional cost. The standard 5-day operations period for a 72-hr BFSD2 deployment fits conveniently in a standard work week schedule. The operational phase typically requires approximately 16 weeks assuming one blank test and two sites. This is largely driven by the 60-day laboratory analysis time.

Title: Post-operational Costs (4 of 5) Text: Post-operational costs are those incurred following completion of site operations. These costs include equipment packing and transportation; personnel travel; data processing, analysis, and interpretation; and report preparation. Post-operational costs are largely labor costs to process, analyze, interpret and report the results. Costs are approximately the same regardless of the number of deployments, assuming the sites have the same general geophysical and geochemical characteristics. The post-operational phase typically requires approximately four months to complete.

Title: Factors Influencing Costs for Using BFSD2 (5 of 5) Text: The factors influencing cost include, in order of importance: 1. Analytical Laboratory Costs. Analysis of samples by specialized analytical labs accounts for approximately 50% of total BFSD2 project costs. 2. Blank Tests. The larger the number of sites within a common bay, harbor, or other defined location, the smaller the proportional cost per site for blank tests. 3. Remote Location. Acquisition of local resources such as a surface vessel configured with a davit or A-frame and equipment shipping costs influence total project costs the most. Other costs such as transportation, per diem, materials, supplies and labor costs have less influence on total project costs. 4. Work Schedule. Limited site access or availability can influence cost because of the need to adjust work hours.

Title: Advantages of BFSD2 Text: Advantages of the BFSD2 include the following: It is easily implemented in the field. It is readily deployed from a small boat or vessel with a winch. Sampling, data logging, and control functions are performed automatically based on pre-programmed parameters. Samples are collected without diver assistance, minimizing cost, sampling time, and safety issues. Equipment/materials are suitable for prolonged use in a marine environment. The data provide source quantification for comparison to other sources and input to models. Presently, there is no other viable method for direct quantification of sediments as sources. BFSD2 data can be used to assess bioavailability, because many studies indicate that resolubilized contaminants are more readily available for uptake. Data analysis can help determine the cleansing rate of contaminated sediments due to natural biogeochemical cycling of the in-place contaminants, assuming that there is no on-going source of contamination. BFSD2 is a nonintrusive monitoring tool for sites that have been capped. BFSD2 provides information for validation of hypotheses and for use in models to predict the response of marine sediments to various contaminants. Cleanup costs potentially can be reduced for sites where it can be demonstrated that flux of contaminants is limited. Estimated disposal costs for dredged contaminated sediment range from $100 to $1,000 per cubic yard.

Title: Limitations of BFSD2 Text: Limitations on use of the BFSD2 include the following: Multiple deployments may be needed to characterize temporal (seasonal) and spatial variations. Currently, BFSD2 is only certified for metals-contaminated sediments. There is a lower limit on the flux rates that can be calculated from data collected by BFSD2. BFSD2 cannot be used below 50 meters or in currents above 3 knots. Deployment is limited to four days based on available battery capacity.

Title: Case Studies Text: Studies using the BFSD2 were performed at San Diego Bay and Pearl Harbor. The purpose of these studies was to: Evaluate whether a statistically significant flux was occurring at the test locations, Evaluate the BFSD2 performance for repeatability, and Evaluate the range of conditions in which the BFSD2 can be operated. Results from these case studies were used as preliminary data for more extensive studies. Although decisions are still being made for these sites, the BFSD2 data on contaminant fluxes may be useful in determining whether the contaminants are bioavailable to organisms and whether removal or treatment of the sediment is necessary.

Title: San Diego Bay Case Study (1 of 6) Text: The BFSD2 was deployed at the San Diego Bay, Paleta Creek site in 1998 to measure flux of metals. Two deployments were performed at the same site two weeks apart to evaluate repeatability of results. In 2001, one deployment was made at this site to demonstrate measurement of organics (PAHs and PCBs).

Title: Deployment at Paleta Creek Site (2 of 6) Text: This photo shows the BFSD2 being deployed at the Paleta Creek site in San Diego Bay, CA.

Title: Results from Paleta Creek 1st Demo (3 of 6) Text: Results from the first demonstration at Paleta Creek indicated that cadmium, lead, nickel and zinc had fluxes out of the sediment that were highly significant compared to the blank chamber results. Manganese also had a positive outward flux but the statistical confidence was lower. Copper had a negative flux (sediment uptake) although statistical confidence was low. The site sample concentrations are plotted in red and the blank test concentrations are plotted in blue.

Title: Results from Paleta Creek 2nd Demo (4 of 6) Text: Results from the second demonstration at Paleta Creek were similar to the first demonstration results with the exception of lead. Cadmium, nickel and zinc all had fluxes out of the sediment that were highly significant compared to blank results. The magnitude of the flux was similar but slightly lower than the first demonstration. Manganese again had a positive outward flux but low statistical significance. Copper flux was negative (sediment uptake), but had very low statistical confidence.

Title: Paleta Creek Sediment Flux of Metals (5 of 6) Text: Comparing the estimated overlying water concentrations to the measured concentrations indicates that contribution caused by sediment fluxes ranges from a high of 4.5% for cadmium to a low of 0.2% for manganese. These estimates could be used to evaluate the potential benefit of a sediment removal or capping action compared to a no-action or natural recovery scenario.

Title: Results from Paleta Creek Organics Demo (6 of 6) Text: The BFSD2 was deployed in March 2001 to evaluate the ability to measure flux rates for organics. Three replicate equipment blank tests were performed to establish statistical baseline performance. Graphs for several of the PAHs and PCBs measured at the Paleta Creek site are shown here.

Title: Pearl Harbor Case Study (1 of 6) Text: Deployments were performed at two geographically different sites (Middle Loch and Bishop Point) in Pearl Harbor to test the ability of the BFSD2 to demonstrate characteristically different data for the two sites and to showcase the analysis and interpretation of results.

Title: Shipping the BFSD2 to Pearl Harbor (2 of 6) Text: The BFSD2 was shipped to Hawaii for the Pearl Harbor demonstration. The reusable shipping container was designed for compatibility with commercial air cargo carriers and includes compartments, shelves and storage bays sufficient for the BFSD2 and all materials and supplies needed for extended field operations. Shipping weight was approximately 1,450 lbs.

Title: Deployment and Retrieval at Middle Loch (3 of 6) Text: These photos show the deployment and retrieval of the BFSD2 at the Middle Loch site in Pearl Harbor, Hawaii.

Title: Results from Middle Loch (4 of 6) Text: Copper, cadmium, and nickel had fluxes out of the sediment that were highly significant when compared to the blank chamber results. Zinc also had an outward flux but a lower statistical confidence. Lead had a negative flux (sediment uptake), but with lower statistical confidence. Flux of manganese was negative when calculated for all samples, but positive when only the first five samples were used. The drop may be due to oxidation and subsequent precipitation or flocculation when the chamber reached a high concentration. Silica flux was out of the sediment and highly significant.

Title: Deployment and Retrieval at Bishop Point (5 of 6) Text: These photos show the deployment and retrieval at the Bishop Point site in Pearl Harbor, Hawaii.

Title: Results from Bishop Point (6 of 6) Text: Results from the Bishop Point Demonstration were significantly different than the Middle Loch results, with the exception of the cadmium flux estimate, which was nearly identical. Copper, cadmium, manganese, and zinc had highly significant fluxes out of the sediment when compared to blank chamber results. The magnitude of copper and zinc fluxes were markedly higher than for Middle Loch. Nickel flux was lower with reduced confidence. Manganese flux was nonlinear and concentrations leveled off after three samples. Silica flux was highly significant and was higher than at Middle Loch. Bishop Point fluxes were higher than Middle Loch with the exception of nickel which was slightly lower. These results can be used in assessing biological exposure to metals. For example, while copper is present at similar concentrations in the bulk sediment at both sites, the flux rates were significantly higher at the Bishop Point site indicating that copper may be more available for uptake by biological receptors at this site.

Title: Technology Certification Text: The California EPA has certified the BFSD2 as a Hazardous Waste Environmental Technology for quantifying the flux of metals in sediment. This certification indicates that the performance claims for the technology have been verified. This certification can be found at the following Web site: http://www.calepa.ca.gov/calcert/CertifiedTech/BenthFlu.htm In addition, certification for use of the BFSD2 to quantify the flux of organics is in progress.

Title: References Text: The following report is available on BFSD2: SPAWAR. 2000. Quantifying In Situ Metal Contaminant Mobility in Marine Sediments

Title: Contact Information Text: For more information about the BFSD2, please contact: SPAWAR POC (619) 553-2804 or (619) 553-5333 or NFESC POC (805) 982-1656 PRTH_NFESCT2@navy.mil