Microsoft's plans to expand its huge datacenter in Quincy will undergo a public hearing, giving people a chance to weigh in on the addition of 13 diesel backup generators planned for the complex.

The center already has 24 generators that can produce 60 megawatts of backup power. The expansion would add the capacity for an additional 32 megawatts, according to a release from the state Department of Ecology.

A higher level of environment review is being done with the expansion because of new state rules that took effect in 2008 and because the state's looking at the effect of the cluster of datacenter that developed in Quincy.

From the release:

Considered by itself, the Microsoft expansion would not necessitate the third-tier review. But due to the interest expressed by other data companies to expand or build in the Quincy area, Ecology was concerned that the cumulative effect of diesel engine emissions should be assessed. This approach elevated Ecology's review of Microsoft's permit request to the director's level.

They're located in Quincy because of cheap hydropower generated by dams on the Columbia River, but the backup generators emit diesel engine exhaust particulate (DEEP), a toxic air pollutant. That triggered a review of the project's health impact.

In applying for the expansion, Microsoft offered to take steps to cut emissions from its current generators by up to 49 percent. It began running the Quincy center in 2008.

That led to the agency to decide "that the cumulative health risks from DEEP exposure as a result of Microsoft's proposed expansion project are acceptable, and the proposed maximum annual facility-wide fuel usage reduction would result in a greater environmental benefit to the state of Washington."

The company plans to install the 13 Caterpillar 3516C diesel engines in phases (shown in this image from the Ecology Department), starting with five in 2010, four in 2011 and the remaining four in 2011 or 2012.

Microsoft expects to burn up to 139,493 gallons per year in the new engines during testing, storms and outages. Maximum fuel use at the overall site is expected to decline from 890,021 gallons per year to 439,493 after the project's done and changes are made.

At this point, the state is inviting public comment on a permit for Microsoft. The permit was proposed Aug. 20.

The hearing is scheduled for Sept. 28 at Quincy City Hall. It begins with presentations at 5:30 p.m. and the actualy hearing at 7. Written comments will be accepted until Oct. 4.