City of Salem Watershed Monitoring Program

Algal blooms are a natural process. In the past few years, algae is usually seen in Detroit Reservoir, Salem’s drinking water source, from April or May through September or October. That was different in late May 2018—and what caused the City to issue a drinking water advisory​. We saw cyanotoxins in our water distribution system for the first time.

The City will continue to collect water quality samples to ensure safe drinking water for Salem. If the levels reach the Environmental Protection Agency (EPA) Health Advisory notification threshold, the City will issue an advisory. The City will continue to provide water quality updates to the community, as they come in.

Normal watershed monitoring operations

Monitoring typically begins in April or May of each year, depending on the weather conditions and Detroit Reservoir water levels. Our monitoring season typically ends in September or October.

Steps of a normal monitoring cycle

  • Weekly samples are collected from eight primary locations at Detroit Reservoir
    • Blowout Creek
    • Heater Creek
    • Breitenbush
    • Log Boom
    • Log Boom at shallow spillway
    • Log boom at Penstock depth
    • Hoover Arm
    • Packsaddle Park
  • Weekly samples are collected at two sites within the Geren Island Water Treatment Facility
    • Middle Intake
    • Slow Sand Filters
  • Samples collected provide the following indicators
    • Algae type
    • Algae enumeration (count)
    • Nutrients
  • Other factors monitored
    • Wind speed
    • Temperature
    • Water quality data using YSI datasonde equipment

Water quality samples are routinely collected from these locations throughout the watershed: Packsaddle Park, Heater Creek, Log Boom, Breitenbush Arm, Hoover Arm, Blowout Creek

​Indicators of an algae bloom

  • Visible scum on the surface of the water

  • Visible particulate matter present free floating within the water column

  • Decrease of depth visibility within water column using Secchi Disk

  • A combination of water quality parameter readings from the YSI datasonde indicating dissolved oxygen has increased, pH increased (becoming basic), temperature of water has increased, and the blue green algae sensor detects an increase in color.

​Steps followed in a monitoring cycle when an algae bloom is present

Staff increase the volume of the sampling sites and the frequency of the sampling. The number of sampling locations and the frequency of our sampling depend on the severity and location of the bloom at Detroit Reservoir.

Typical sample sites include:

  • Blowout Creek
  • Heater Creek
  • Log Boom
  • Log Boom at shallow spillway
  • Packsaddle Park
  • Intake to the Geren Island Water Treatment Facility—called Middle Intake
  • Combined Filter Effluent (CFE)
  • Aldersgate

The sampling process is similar to normal watershed operations in that staff sample for algae (type), algae enumerations (count), and toxins, and recording field observation data (wind, temperatures, etc.) as well as retrieving water quality data from an YSI datasonde.

Other strategies used to keep our drinking water safe during an algae bloom

In late May 2018, during the time of Salem’s drinking water advisory, we adjusted the chlorine and pH levels, flushed water lines, and added water from underground supplemental water systems to dilute the toxin, since it was first detected in the samples.

When an algae bloom is present, our first step is to modify the treatment of our drinking water through a combination of the following options:

  • Shutting down the intake at Geren Island for short durations to allow water to pass by plant
  • Utilizing a “roughing filter” to filter water before pumping water to finished water filter
  • Blending raw river water to the subsurface groundwater
  • Increasing the chlorine residual
  • Decreasing the pH
  • Flushing the distribution system 

​The City will continue to work on new approaches to Salem’s water infrastructure to ensure safe drinking water. We are evaluating our infrastructure and looking to see where we can make improvements to ensure safe drinking water for our community and our water customers.

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