Continuous Water Quality Monitoring: An Approach to Verify and Address NPDES MS4 Requirements Associated with TMDLs

In 2013 the City of Columbia installed a continuous water quality monitoring network in the Gills Creek watershed. The network allows the City to evaluate baseline conditions, identify pollutant sources, and assess long term improvements in water quality. The watershed is impaired for dissolved oxygen (DO), and a Total Maximum Daily Load (TMDL) has been issued for this parameter. There are two state-run monitoring stations listed in the TMDL that collect runoff from within the Gills Creek watershed. The State collected a limited number of samples at these sites preceding the issuance of the TMDL. Recognizing that water pollutant concentrations are dynamic and depend upon recent meteorological conditions as well as seasonal cycles, the City has installed two of its three continuous monitoring stations at state-run sites as a means to better capture this variability and to accurately assess the City’s role in decreasing DO levels in Gills Creek.