Stormwater and Stream Monitoring
- Staff collecting water samples from a stormwater wetland.
- Staff collecting water samples from a stormwater outfall.
The Stormwater Management Division operates three primary programs to monitor stormwater pollution and ambient stream conditions throughout Raleigh. Below is a summary of each program.
NPDES Monitoring Program
Ambient water quality conditions are monitored at 18 locations throughout Raleigh as part of the City's National Pollution Discharge Elimination System (NPDES) General Stormwater Permit. Water quality samples are collected every three months from within major tributaries of the Neuse River.
Field measurements for dissolved oxygen, pH, conductivity, and temperature are taken at each major tributary using two water quality meters: a YSI 550a and a Fischer Scientific AP85. Grab samples of water are collected from each stream and then taken to a private laboratory for analysis. Parameters for the NPDES Monitoring Program include total suspended solids, turbidity, total hardness, E. coli bacteria, various forms of nutrients such as nitrogen and phosphorus, and metals such as copper and zinc.
This data is used to establish a baseline for water quality in Raleigh's streams and to enable staff to evaluate long term trends in surface water quality.
Benthic Macroinvertebrate Monitoring Program
Benthic macroinvertebrates, or benthos, are aquatic invertebrates (bugs) that live in stream beds. The phrase benthic macroinvertebrate comes from three terms put together (benthic = stream bed, macro = large, invertebrate = animal without a backbone). Benthos surveys are performed at 22 stream locations throughout Raleigh every July and August. Kick nets, sweep nets, and other tools are used to collect macroinvertebrates for later identification.
The number and diversity of these organisms is a good indicator of water quality. For example, a healthy stream will support a large number of macroinvertebrates as well as a diverse population of macroinvertebrate types. An unhealthy stream may only support a small number of macroinvertebrates and not a very diverse population.
Conducting these benthic macroinvertebrate surveys helps examine water quality impacts on stream biology.
BMP Monitoring Program
Best Management Practices (BMPs) can be seen in a variety of applications including bioretention areas (also known as rain gardens), wetlands, wet ponds, stream buffers, sand filters, and others devices. BMPs are engineered to remove pollutants from stormwater runoff thereby allowing the filtered runoff to flow to a nearby stream.
As the City completes construction on various BMPs, some of these are monitored to measure the pollutant removal efficiency, or how well the BMP is working to remove pollutants from the stormwater pollution cycle.
Stormwater Management staff currently monitor four BMP locations: two bioretention areas, one wetland, and one lake which is planned for a future BMP project. Water quality samples are collected as runoff flows into each BMP when it rains and then water samples are collected as the water flows out of the BMP. The inflow and outflow samples allow staff to compare the water quality of the water flowing into the BMP against the quality of the water flowing out of the BMP. The ultimate goal is to have the water leaving the BMP cleaner than the water flowing into the BMP.
Field measurements for pH and temperature are recorded and grab samples of the stormwater are analyzed for oil and grease, biological and chemical oxygen demand, total suspended solids, turbidity, E. coli bacteria, various forms of nutrients such as nitrogen and phosphorus, and metals including copper, chromium, cadmium, lead, and zinc.