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Stormwater Monitoring Helps Maintain Water Quality

Clean water is important to healthy communities. Taking samples of the water flowing in the streams and through stormwater pipes during storms helps the City better understand the effects that stormwater runoff has on Salem’s streams.

About Stormwater

Stormwater is generated from rain that falls in an urban setting and lands on hardened surfaces such as streets, parking areas, and residential rooftops. Stormwater does not soak into the ground. It runs off hardened surfaces. Pollutants on these surfaces can be carried away by stormwater runoff as the runoff is transported to the nearest stream by the stormwater system that includes catch basins, ditches, and pipes. In most situations, stormwater receives little or no treatment to remove the pollution it carries.

In-Pipe and Instream Stormwater Sampling

The City operates under a federal stormwater permit that includes a requirement to sample stormwater for pollutants in local streams and in stormwater pipes.

Types of In-Pipe Sampling

In-pipe sampling helps identify the type and concentration of pollutants flowing through the storm pipes and into the nearest stream. Under the current stormwater permit, the City conducts the following sampling activities from the piped storm system:

  • Automated sampling
    An automated sampler collects stormwater from the piped storm system for the duration of a selected rain event. These samples are analyzed for sediment, nutrients, and metals.
  • Grab sampling
    Bacteria, pH, temperature, specific conductivity, turbidity, and dissolved oxygen samples are also collected from the pipe during the selected storm.
  • Pesticide sampling
    Samples are collected directly from the piped storm system during selected rain events and sent to a lab to be analyzed for a suite of insecticides, herbicides, and fungicides.
  • Mercury sampling
    Samples are collected directly from the piped storm system during selected rain events and sent to a lab to be analyzed for low-level total and dissolved mercury and low-level total and dissolved methyl mercury.

Types of Instream Monitoring and Sampling

Samples are also collected directly from streams during storms as well as during non-rain events. Under the current stormwater permit, the City conducts the following monitoring and sampling of streams:

  • Continuous water quality monitoring
    The City maintains a network of 10 water quality monitoring stations on five different streams within Salem. The stations are placed where a stream enters the City and where it exits the City or joins another stream. Monitoring stations report basic water quality parameters (pH, temperature, specific conductivity, turbidity, dissolved oxygen, and stream height) every 15 minutes, 24 hours a day, 7 days a week. The stations are also programmed to check the data and send out an alarm if a drastic change in any of the water quality parameters is detected. These alarms are received by the City’s 24-hour dispatch center, which sends staff out to investigate if warranted.
  • Monthly instream sampling
    Samples are collected once a month from 11 of the streams within City limits and from the Willamette River for a total of 24 sites. Samples are analyzed for pH, temperature, specific conductivity, turbidity, dissolved oxygen, nutrients, and bacteria. This sampling has been done since July 2001, and is the City’s longest set of water quality data.
  • Biological sampling
    A thorough stream assessment of different stream reaches is conducted periodically to gather information on aquatic insects, fish, and habitat within the stream.

Documents and Annual Reports

Information about the federal stormwater permit is available on the Municipal Separate Storm Sewer System (MS4) Discharge Permits and Annual Reports page.

Documents and and annual reports related to stormwater monitoring can be downloaded from the list below.