Methods

Water Column Monitoring: 18 stations were selected for monitoring sites in the Elizabeth River and Hampton Roads.  Environmental water samples are collected by FIMS personnel bimonthly at 18 Elizabeth River station locations selected by the VADEQ.  Sample custody issues are eliminated by utilizing the same  analyze water samples. Once collected, all environmental samples are maintained in locked storage prior to analysis. All vessels used for collecting samples are free of TBT containing antifoulants and water samples are collected in sample storage containers to avoid cross contamination of samples via sampling gear. Samples are collected as near to high slack water as possible and the sampling information recorded on each container and in a field notebook. Water is collected from the top meter of the water column with care to exclude the surface microlayer. Sample bottles are rinsed twice with ambient water prior to collection of the sample. Field blanks were carried on each sampling trip and the samples are kept in the dark on ice in the field for transport back to the laboratory. To document sampling variability, duplicate 2 liter samples are collected at four stations during each sampling trip (>20% replication). Once returned to the laboratory the samples are preserved with HCL to below pH 2 and kept at 4^oC in the dark in a locked cold room prior to analysis.

Tributyltin analysis: Water samples are analyzed for butylins by an adaption of the methodology published earlier (Unger et. al. 1986) which has been described in detail in a manual prepared for the Virginia DEQ (Unger, 1996).  This is the same analytical method used in all previous TBT monitoring and assures comparability with historical data. Analysis of extraction blanks (>10%), sample duplicates (>10%), matrix spikes and matrix spike duplicates document the accuracy and precision of these analyses to assure project data objectives are met. The method detection limit is 1 ng/L and has been determined using the procedures recommended by the DEQ and described in detail in the report “Elizabeth River TBT Monitoring Report on TBT Methodology Detection Limit, Precision and Linearity” (Figure).