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Probability Monitoring Design and Implementation in South Carolina

David Chestnut

South Carolina Department of Health and Environmental Control, Bureau of Water, Columbia , South Carolina

The South Carolina Department of Health and Environmental Control employs a variety of tactics in its water quality monitoring design to address the wide-ranging data requirements of its regulatory and management activities including: permanent fixed-site locations, an annual basin-specific focus, a statewide probability-based design with new sites selected each year, and the capability for supplementary sites to satisfy special issue needs.

Monitoring sites are generally sampled as point locations in or on a waterbody. Historically site locations were selected to track specific activities: point source discharges, land use activities, etc. Each site can be evaluated individually to determine classified use attainment and the need for inclusion on the §303(d) list of impaired waters.

Because §305(b) requires reporting the sizes of different waterbody types by classified use attainment condition and the size impacted by various causes, it necessitates assigning a distance or area “represented” by each monitoring site. This is generally a subjective process conducted with each state using a different approach. Since monitoring site selection typically favors locations with suspected problems this can result in a skewed picture of overall conditions.

Statewide probability-based monitoring for streams, lakes, and estuaries is one of SCDHEC’s newest tactics. The main intent is to make statements about statewide resource conditions, with confidence estimates, to satisfy §305(b) reporting requirements. Multiple site visits also provide sufficient data to support our assessment methodology and allow §303(d) listing of impaired waters.

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