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Methods and instrumentation for quanitfying contaminant loads from large watersheds, 1994

By: Sweat, M.J.


Little is known of sources and relative amounts of heavy metal and organic contaminants being discharged by major tributaries to the Great Lakes. In order to identify sources and quantify discharges of contaminants, streamflowgaging stations were constructed as near as practicable to the mouths of 11 Lake Michigan tributaries. Realtime turbidity, temperature, and stage are measured, and daily suspended sediment samples are collected. At seven sites, acousticvelocity meters were installed, allowing for real-time quantification of discharge under seiche conditions. Equal-width interval, depth-integrated, composite samples for organic and heavy metal contaminants are collected. Ultraclean techniques are used to collect water samples for analysis of low concentrations of metals. Numbers of water samples were determined by the responsiveness of streams to meteorological events; numbers range from 16 per water year on nonresponsive streams to 46 on the most responsive streams. Sample frequency is designed to represent different parts of the hydrograph for as many meteorological events as possible. From 25 to 60 percent of water samples have been collected and analyzed. A relation is hypothesized between turbidity, suspendedsolids concentration, and instantaneous discharge, to permit development of a predictive model for relating contaminant loads to instantaneous discharge.

Additionally, little is known about contaminant discharges from combinedsewer overflows. Four combinedsewer overflows to the Detroit River are being monitored as mentioned above. At three sites, water samples are collected directly from an enclosed sewer; bottommounted magnetic and doppler flow loggers quantify discharge and trigger sampling. At the fourth site, instrumentation is similar to that used at the Lake Michigan tributaries. Samples are collected at discrete intervals that represent different parts of the hydrograph. A relation between combined sewer discharges and contaminant load is less certain for combinedsewer overflows than it is for tributary discharge because of expected large variation associated with the duration of combined sewer overflows, time between events, and drainagebasin characteristics.

Sweat, M.J., 1994, Methods and instrumentation for quanitfying contaminant loads from large watersheds: American Geophysical Union, 1994 Fall Meeting, Final Program

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