McAllister Wellfield Project
City of Olympia Public Works Department - November 2007

Background
Currently, The City of Olympia's primary source of water is McAllister Springs. The Springs are located at the headwaters of McAllister Creek in northeastern Thurston County. McAllister Springs has served the City effectively since the 1940s. Water emerging from the Springs is very high quality. However, the Springs location is vulnerable to potential contamination from:

• A spill at the Burlington Northern rail line, which is immediately above the Springs; and
• The surface water pond adjacent to the Springs. During the summer, when water usage increases, it is possible that the Springsí pumps might draw from the pond.

The Washington State Department of Health (DOH) has encouraged the City to develop an alternate source that is more protected from these potential water quality problems. The City views this as a high priority for protection of public health.

There are two additional concerns regarding the Springs:

• During the dry summer months, the City is sometimes unable to use its full water right. This is made worse by a slow but steady decline in water output over time.
• Due to vulnerability to contamination, federal regulations require additional treatment at the Springs by 2012. This treatment, known as ultraviolet disinfection, is expected to cost approximately 8 million dollars to construct and $85,000 annually for operation and maintenance.

Decision to move to McAllister Wellfield
The City reviewed numerous solutions to address the issues at McAllister Springs. After analysis, the City determined that the best solution was to move the water production site from McAllister Springs to groundwater wells at a more protected location, known as the McAllister Wellfield.

The City purchased the wellfield site as well as 100 acres of development rights adjacent to the site. Consultants then conducted pumping tests which verified that this location is capable of producing the needed quantity of water supply.

Groundwater Model
The move from the Springs to the Wellfield requires a water right transfer approved by the Washington State Department of Ecology (Ecology).

As part of any water rights transfer process, Ecology requires utilities to offset or "mitigate" unacceptable impacts on their proposed water use on surrounding water bodies

In order to understand what these impacts might be, the City spent nearly eight years, and close to $1 million to develop a sophisticated groundwater model. The model simulated the groundwater dynamics of the area, including interactions with nearby surface waters.

The model provides a conservative prediction of the potential effects of moving to the McAllister Wellfield.

Predicted Impacts from Pumping
The mosts current model results show that by reducing or eliminating pumping at McAllister Springs, the wellfield will result in significantly higher flows in McAllister Creek.

At the same time, groundwater pumping at the wellfield is predicted to cause relatively small depletions of flow in other nearby surface water bodies.

Water bodies that are predicted to be impacted by pumping at the Wellfield include:

• Nisqually River
• Deschutes River
• Lake St. Clair
• Woodland Creek, and
• The Tri-Lakes (Long, Patterson, and Hicks).

Mitigation of Predicted Impacts
The City of Olympia is committed to sustainability and resource stewardship. The City is using its conservation ethic to guide the development of a mitigation plan for the McAllister Wellfield

As an example, the City is pursuing the purchase of water rights in the area of Lake St. Clair to address any impacts associated with the new wellfield.

The City of Olympia is also partnering with the Cities of Yelm and Lacey to develop regional mitigation strategies for other water bodies that may be impacted. Possible mitigation actions include habitat restoration, recharging groundwater with reclaimed water, and acquiring water rights.

The three cities are consulting with the Nisqually and Squaxin Indian Tribes on the development of these mitigation strategies.

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