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Laboratory and field procedures are outlined for accurate and precise measurements
Despite the fact that existing 40 Code of Federal Regulations (CFR) methods are inadequate for measuring metal concentrations approaching freshwater background levels, regulatory limits on trace metals have increased, sometimes several orders of magnitude. To ensure compliance with such limits, wastewater treatment facilities need a practical collection and analysis method for freshwater and wastewater samples.
The Virginia Department of Environmental Quality (VADEQ) and the Virginia Division of Consolidated Laboratory Services, following a 1S month pilot project, have developed such a method. The project team based its procedures on improvements to U.S. Geological Survey (USGS), U.S. Environmental Protection Agency (EPA), and other procedures. The team's approach to compliancebased clean metals monitoring explains how metals laboratories can be converted to trace metals laboratories, sample equipment can be modified and cleaned, and protocols can ensure effective measurement where toxicity is significant.
VADEQ and the laboratory services group designed their pilot project to determine if current technology can be used to accurately measure dissolved metal concentrations less than 1.0 ug/L using clean techniques. The project also was designed to develop protocols for wastewater treatment plant effluent collection and analysis that could be incorporated into guidance and freshwater protocols for an ambient water quality-monitoring program.
System Design
The project team first had to select an analytical system capable of measuring trace metals in the range of the lowest expected concentration. It compared Virginia Water Quality Standards to the accepted test procedures in 40 CFR 136 (see Table 1, p. 66).
Mass spectrometry methods were chosen because they offered the largest range of analytes, the best possible detection limits, and the least amount of interference. The atomic emis sion method was selected for screening samples (to adjust the dilution range for the more sensitive mass spectrometry technique) and for use on high concentration samples. Using a target method detection limit (MDL) of one-tenth the water quality standard, the team decided the mass spectrometer technique would be most suitable for producing acceptable accuracy at the lowest concentration range.
The next significant consideration was how to control contamination in the laboratory and the field. When measuring at trace concentrations, small amounts of background contamination and interference can be significant. The most...