Sampling in Large Rivers

Large river exhibits a high degree of heterogeneity in composition and characteristics in space and time, which makes it challenging to collect representative samples.  Sampling strategies for large rivers are often based on convenience, experience, expert intuition and other subjective judgments.  Sampling locations, sampling frequency, and the number of sampling sites selected can affect the quality and applicability of the resulting water quality data and thus influence decision making in the Section 303(d) list.

This project considers several sampling projects undertaken in a single river-the Monongahela River-over a three years period. These sampling projects each had different goals and therefore different sampling protocols for selection of sites and sampling frequency. One project focused on drinking water source quality and thus sampled only at drinking water plant intakes. Another project focused on characterization of the river at well-mixed locations downstream of navigational control structures. The final project included sampling at both drinking water intakes and well-mixed river sites; however, samples were taken only in response to reports of elevated conductivity, resulting in sampling predominately during low flow conditions.

These distinct sampling protocols provide key comparative data to determine the relative representativeness of different collection protocols to answer questions related to in-stream criteria for protection of potable water supplies.