A key requirement for an NPDES (Phase I) stormwater permit is developing and implementing a water quality monitoring program. The focus of the program, however, can vary depending on the goals of the permittee and other factors such as climate conditions and waterbody type.
A water quality monitoring program can also evolve as goals and conditions change over time. In the beginning, the City of Lincoln’s program consisted of discharge monitoring during storm events. The goal was to characterize urban stormwater runoff in the City of Lincoln.
Stormwater sample collected at a bioretention cell
The program then shifted its focus toward identifying sources of key pollutants – first nutrients (nitrogen and phosphorus), then E. coli bacteria. The results of these studies provided valuable insight and recommendations including installing stormwater Best Management Practices (BMPs) to capture and filter pollutants. Logically, the next step for the program should be to take a closer look at these installations. Therefore, the goal of the current program is to evaluate the effectiveness of stormwater BMPs found throughout the City of Lincoln.
There is a wide variety of stormwater BMPs scattered throughout the City of Lincoln. To meet permit requirements, five stormwater BMP sites were selected for the monitoring program. Site selection was based on availability, ease of access, and suitability for remote monitoring equipment installations. The sites are also diverse in stormwater BMP type and surrounding land use. Sites for the monitoring program include:
- Regional Bioretention (Residential Area)
- Permeable Pavers (Residential Area)
- Bioretention Cell (Mixed Commercial/Residential Area)
- Bioretention Cell (Commercial Area)
- Downspout Planters (Industrial Area)
How Are Stormwater BMPs Monitored?
The sites are equipped with remote monitoring equipment for “continuous” data collection. Available sensors include rainfall, water level, soil moisture, turbidity, and conductivity. However, sensors installed at each site vary depending on stormwater BMP type and configuration.
Example of graph showing rainfall and water level data at a regional bioretention area
In addition, water samples are collected during selected rain events. Samples are tested in the field for temperature, pH, turbidity, and conductivity. Some samples are sent to a lab for further analysis. They are tested for pollutants commonly found in stormwater runoff such as nutrients, metals, oil and grease, and e. coli bacteria.