Study design and analytical results used to evaluate a surface-water point sampler for volatile organic compounds

Abstract

The most common technique used to sample streams for volatile organic compounds (VOCs) is dipping volatile organic analysis (VOA) vials by hand midstream. This technique does not assure that samples are collected in a consistent manner. A point sampler was designed to collect samples for the U.S. Geological Survey National WaterQuality Assessment (NAWQA) Program in surface water in a uniform and consistent manner nationwide. This report documents the study design used to evaluate the VOC point sampler, as well as comparative data from glass-siphoning and hand-dipping methods used in the laboratory and field, respectively. Quality-control data collected during the evaluation, specifically source-solution blanks, canister blanks, equipment blanks, and field blanks, also are presented. The study indicates that the VOC point sampler collects samples in a representative manner, as compared to the glass-siphoning and handdipping methods. The relative standard deviation for replicate samples collected by the VOC point sampler was less than 10 percent for 57 of 73 VOCs calculated, indicating a high degree of sample reproducibility. Analyte loss was found to be negligible based, in part, on a comparison of laboratory data to expected recovered concentrations. Furthermore, the cleaning protocol was found to be effective in eliminating any contamination of water samples from the point sampler. INTRODUCTION Ground water has been sampled for the analysis of volatile organic compounds (VOCs) by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program since 1993. To understand the occurrence of VOCs in other components of the hydrologic cycle, the NAWQA Program began sampling small urban streams for VOCs in 1996. Prior to NAWQA's national emphasis on VOCs, little work had been done within the USGS on VOC field methods or sampling equipment for collecting VOCs from surface water. The most common technique used to sample streams for VOCs is dipping volatile organic analysis (VOA) vials by hand midstream. Consequently, the USGS did not have specific guidelines or a proven sampler to collect VOC samples from surface water. To collect VOC samples from surface water in a uniform and consistent manner nationwide, a surfacewater VOC point sampler was designed by the USGS and Wildlife Supply Company (Wildco) located in Saginaw, Michigan. The sampler (fig. 1) is manufactured by Wildco and is constructed of stainless steel and refrigeration-grade copper. The sampler was designed to collect a sample intended for VOC analysis at a single point in shallow urban streams. The VOC point sampler currently (1998) is being used by NAWQA's study units to collect samples from about 10 urban streams (Lopes and Price, 1997). Guidance on the proper use of the sampler in the field has been developed and documented by Shelton (1997). The purposes of this report are to: (1) document the study design used to evaluate the surface-water VOC point sampler and (2) report the analytical results. This report documents the analytical data