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Kinzelman, J., A. Dufour, L. Wymer, G. Rees,
K. Pond, and R. Bagley. Comparison of Multiple and Composite Sampling for
Monitoring Bathing Water Quality. The USEPA Beaches Environmental Assessment and Coastal Health Act
(BEACH Act) requires states to develop monitoring and notification programs
for recreational waters using approved bacterial indicators. Implementation of an
appropriate monitoring program can, under some circumstances, be expensive. This study
explored the use of composite sampling at two order to determine whether compositing can provide a valid,
unbiased, and cost-effective measure of water quality. Multiple point sampling occurred
throughout the bathing season with water samples collected daily from three or four fixed
locations along each beach. From each individual sample, well-mixed aliquots were
combined to form a composite sample. Individual and composite samples were assayed
identically for Escherichia coli using
Colilert-18 and Quanti-Tray 2000 (IDEXX Laboratories, Inc., 1:1 ratio between the composite samples and the arithmetic mean of
the individual samples. Additionally, log variance of the composite sample
results did not differ significantly from that of the single sample averages (p >
0.2). Empirical values for log standard deviations varied by no more than 7% between the
composite sample and individually assayed samples. Thus compositing, as performed in
this study, appears to introduce neither bias nor additional variability into the
monitoring results and stands as a reasonable alternative to data sets derived from single-sample
methods. Regulatory programs adopting this approach could maintain sample integrity
while reducing the costs associated with recreational water quality assessment. Julie Kinzelman, Ph.D., MT (ASCP) Microbiologist City of Racine Health Department PH 262-636-9501 FX 262-636-9576 julie.kinzelman@cityofracine.org |