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COMPARISON OF MULTIPLE POINT AND COMPOSITE SAMPLING FOR THE PURPOSE OF MONITORING BATHING WATER QUALITY
Citation:
KINZELMAN, J. L., A. P. DUFOUR, L. J. WYMER, G. REES, K. R. POND, AND R. C. BAGLEY. COMPARISON OF MULTIPLE POINT AND COMPOSITE SAMPLING FOR THE PURPOSE OF MONITORING BATHING WATER QUALITY. LAKE AND RESERVOIR MANAGEMENT. North American Lake Management Society, Madison, WI, 22(2):95-102, (2006).
Impact/Purpose:
Develop new bathing beach monitoring protocols and new approaches for communicating risks associated with swimming and other recreational water activities.
Description:
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 Racine, WI beaches over a four month period (n = 68 days) in 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., Westbrook, ME). Results from this study indicate a reasonable expectation of a simple 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.