Wet Weather or In-Stream Stormwater Monitoring

In-stream monitoring provides data to calculate pollutant load estimates based on the percentage of each land use and the corresponding pollutant concentration for the entire City. 
The six monitoring sites are strategically located within the City's major drainage basins to characterize the quality of receiving streams during rainfall events. Samples are collected during certain rain events on a quarterly basis to determine the effects of urban storm water run-off on Greensboro's receiving stream water quality.

North Buffalo and South Buffalo Creeks drain the majority (two-thirds) of area located within Greensboro’s City limits. Two sites were selected on each stream, one in each of the upper basins, to characterize the headwaters of the streams and one in each of the lower basins to characterize the pollutants from the entire City. One site was selected on the lower portion of Horsepen Creek, which is a major tributary to Lake Brandt, and one site was selected on Reedy Fork Creek, which is the other major tributary to the drinking water supply reservoirs. These two sites were selected to estimate pollutant loading to the City’s drinking water supply.

Each site is sampled once per quarter (3 month period) using automatic sampling equipment to collect the water samples. The samplers are programmed to start when the water in the creek rises to a certain level, usually six inches above the normal flow level. Once started, the sampler fills eight bottles with 1000-ml of stormwater each for a total eight liters of first flush or “grab” sample.

After the grab sample is collected the sampling equipment continues to collect stormwater every 20 minutes for three hours. This sample water is combined based on the measured flow to make a flow-weighted “composite” sample that represents the first three hours of the storm when pollutant concentrations are expected to be representative. The grab and composite samples are then placed in their corresponding laboratory bottles and shipped to a private laboratory for analysis.