The Columbia South Shore Well Field

The Portland Water Bureau’s Columbia South Shore Well Field (CSSWF) is the second largest water supply in Oregon. (The largest is Portland’s Bull Run watershed surface water supply.) The well field is the largest groundwater supply in Oregon.

The CSSWF:

• is a source of high quality drinking water
• can provide 82-102 million gallons a day of water depending on the length of the pumping duration
• consists of about 27 groundwater wells that pump water from three aquifers located in a five square mile area on the south shore of the Columbia River
• is an ideal location to serve as the secondary source of Portland’s drinking water. It is close to the metropolitan area and is not affected by potential turbidity, forest fires, and landslides in the same way that a surface water system like Bull Run could be
• Development of the well field started in 1975

• The wells began serving drinking water customers for the first time in the summer of 1985

As a summer supply augmentation:

• Groundwater wells augment drinking water supply in summer and early fall as needed depending on weather (This is when people use the most water and there is typically little rainfall.)
• During this same time, the operation of the Bull Run supply system results in lower river flows, warmer water temperatures and altered habitat for fish in the Bull Run River .
• During drier than normal summers, the CSSWF helps ensure that we have enough water for customers and also enough to release cold water into the river for fish when they are spawning.
• Each year, the Portland Water Bureau prepares the seasonal water supply augmentation and contingency plan, commonly referred to as the summer supply plan. This plan outlines a comprehensive strategy for augmenting the baseline water resources if needed during the peak demand season – when weather is hottest and driest.

As an emergency back up supply:

• The CSSWF is an emergency backup supply when the Bull Run water becomes unavailable. For example, seven large storms in the last 23 years have resulted in increased turbidity (suspended sediment) levels in the Bull Run reservoirs.  At these times, the well field supplied all the drinking water to Portland customers for short periods.

Groundwater water quality

• Samples from CSSWF groundwater wells are collected at least twice a year, even when groundwater is not being used for drinking water supply
• When groundwater is being used for drinking water supply, many more samples are collected and tested These analyses ensure that the Portland Water Bureau is serving high quality water and meeting all federal and state drinking water regulations.
• The most recent water quality results, are reported in the Triannual Water Quality Report. Groundwater water quality data are included in this report when groundwater has been used as part of the drinking water supply in the period of time that the report covers.  

Protecting Portland’s groundwater