A survey sampling approach is presented for estimating upper centiles of aggregate distributions of surface water pesticide concentrations obtained from water monitoring programs with large sample sizes but variable sampling frequency. It is applied to three atrazine monitoring programs of Community Water Systems (CWS) that used surface water as their drinking water source: 1. The nationwide Safe Drinking Water Act (SDWA) data, 2. The Syngenta Voluntary Monitoring Program (VMP), and 3. The Atrazine Monitoring Program (AMP). Requisite sample sizes are determined using statistical tolerance limits, relative standard error, and the Woodruff interval sample size criterion. These analyses provide 99.9% confidence that the existing data include the 99.9th centile atrazine concentration for CWS raw and finished drinking water in the Midwest atrazine use areas and in the nationwide SDWA dataset, assuming no bias due to nonrandom selection of CWS and monitored days during these years. The general validity of these approaches is established by a simulation that shows estimates to be close to target quantities for weights based on sampling probabilities or time intervals between samples.

Survey sampling approach for estimating upper centile pesticide concentrations from surface water monitoring

244th National Meeting (2012)

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