Public Works Dispatch

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Drinking Water Monitoring Program

In compliance with the Federal Safe Drinking Water Act, the City of Salem routinely collects and tests water quality samples for possible contaminants. Sampling and monitoring procedures occur within the distribution system (in town), at the Geren Island Water Treatment Facility, and at several locations in the North Santiam River watershed. 

Watershed monitoring in normal conditions

In-Town (distribution system) monitoring

The City of Salem collects water quality samples from 48 different locations across the water distribution system. These sample locations were chosen with the assistance of the Oregon Health Authority Drinking Water Program, and are strategically located to provide monitoring in all areas of the distribution system. A bacteriological sample is collected at each site approximately once a week. Temperature, pH, turbidity, chlorine residuals, and additional water quality parameters are also collected.   A summary of the water quality data collected each year is compiled in Salem's Annual Water Quality Report and published online.


Watershed (algae) monitoring


The City also monitors conditions in the North Santiam River and Detroit Reservoir. Algae and cyanotoxins, in addition to other water quality parameters, are monitored in the watershed.  Data collected from the watershed can be used to adjust drinking water treatment processes at Geren Island, if needed. This allows us to provide high quality water to our residents and customers.

Monitoring in the watershed typically begins in April or May and ends in September or October (algae season), depending on the weather conditions and Detroit Reservoir water levels.

Preparation for algae season

Algal blooms, a common occurrence in surface water, have been visible in Detroit Reservoir, from spring through fall for the last few years. Some algal blooms are known to produce harmful cyanotoxins, but others do not.  In May 2018, water quality samples revealed that cyanotoxins were detected in Salem's drinking water distribution system above a Health Advisory Level (HAL) for the first time.  In response, a drinking water advisory was issued, based upon the level of cyanotoxins detected, to vulnerable populations in Salem.

To ensure safe drinking water for Salem residents and address new drinking water regulations from the Oregon Health Authority, the City of Salem follows a robust water quality sampling and testing process.  

During algae season, we are required to sample drinking water for cyanotoxins in two locations: (1) before treatment, from the intake to the water filtration plant prior to any treatment (source water); and (2) after treatment, the point at which the treated water enters the distribution system (treated water) if there is a detection above 0.3 parts per billion (ppb) in the untreated source water.

We are following the required sampling protocol and taking additional samples in the watershed, at different steps in the treatment process and in the water distribution system. This way, we can be sure whether the treatment is working. And, these additional tests allow our staff to better assess changing conditions in the treated water and add more treatment steps if needed to provide safe water. 

When algae is present in Detroit Reservoir

As soon as algal blooms are seen at the Log Boom in Detroit Lake, the sampling frequency increases to five days per week at the Intake.  This water quality data will be posted to our website.

When cyanotoxins are present in Detroit Reservoir

If cyanotoxins from the algal blooms are also detected in Detroit Reservoir, additional drinking water treatment processes will be triggered at the Geren Island Water Treatment Facility.

If cyanotoxins are detected at the Intake, the sampling frequency immediately increases to seven days per week and drinking water treatment processes are modified to include increased chlorine dosage and/or powdered activated carbon.  Additional sampling locations, (including Aldersgate - entrance to Salem's drinking water distribution system), are also activated to provide additional water quality data.


Some Terms Explained

Log Boom

The Log Boom is just above the spillway at Detroit Reservoir.  When algal blooms are detected here water quality sampling at the Middle Intake increases to five days per week.


This is where North Santiam River water enters Salem's drinking water treatment facility (Geren Island Water Treatment Facility).



This is where water that has been treated at the Geren Island Treatment Facility (finished water) enters Salem's drinking water distribution system.

Health Advisory Level (HAL)

As defined by OAR 333-061-0520(8), health advisory level is a concentration of a cyanotoxin determined by the US Environmental Protection Agency, as specified in OAR 333-061-0530(1), at or below which adverse health effects are not expected to occur if consuming water containing cyanotoxins at this concentration for up to 10-days.