Just across the county border, a few miles from Tracy and a stone’s throw from Mountain House, two energy companies are looking to plop down power plants. But these two projects are not created equal.

On one hand, there is a project by Mariposa Energy LLC, an outfit owned by Mitsubishi.

Its 10-acre footprint will be 2½ miles west of Mountain House’s edge and the San Joaquin County line, but renderings provided by Mariposa show that the four 80-foot cooling towers shouldn’t impact the quality of the westward view any more than the area’s many existing power lines and the windmills that dot the Altamont Hills behind.

Its impacts on air quality seem to be similarly small. Despite being permitted to run 4,000 hours a year, Mariposa execs don’t foresee running the 200 megawatt facility — a peaker plant designed to go on- and off-line quickly to meet changing demand — more than 600 hours per annum. And pollution tests projected for the maximum 4,000-hours-a-year level indicate that the risk to the nearby downwind communities — namely Mountain House and Tracy — is virtually nil.

This is no off-the-cuff decision for the company, either. The site was chosen, Mariposa officials say, over some 50 others because of nearby infrastructure — the next-door Byron Bethany Irrigation District will provide water, Pacific Gas and Electric Co. can provide natural gas to fire the plant via nearby pipelines, and its electricity can be plugged into the grid through the substations and transmission lines that cross the area.

Plus, the company already has an energy purchase agreement with PG&E that will cover the first 10 years of the plant’s expected 40-year lifespan. The plant should also create eight full-time jobs once it opens in 2012.

For these reasons, the Mariposa project strikes us as a good fit, even though power plants typically don’t make the best neighbors.

The flip side

On the other hand, however, is the East Altamont Energy Center, a Calpine project. This proposal makes Mariposa’s truly look like a welcome addition to the neighborhood.

First on our list of concerns is the project’s size. Calpine would build a 1,100-megawatt facility that could run as many as 8,000 hours each year, and it would likely run far closer to full-time than Mariposa’s proposed peaker plant.

Second on our list is its proximity to Mountain House. East Altamont is nearly twice as close to the town as the Mariposa project — less than 3,000 feet from the fence of Mountain House.

Third, the East Altamont permit process began in 2001 and was approved by the California Energy Commission in 2003. As construction on Mountain House only began in 2001, it’s unlikely that present and future residents — those who will consider the plant a neighbor — had a say in its construction.

Though it has state approval, the East Altamont project is on hold for now — Calpine has until August 2011 to get a power purchase agreement together and begin construction.

And that’s fine with us. Because while we realize the need for increased energy production in California, this project doesn’t seem to fit its location.

The main worry

But really, our biggest concern applies to both energy projects. Namely, that Alameda County seems more than willing to place its less-than-ideal industries in someone else’s backyard.

Alameda County, which includes Oakland, Berkeley and Pleasanton, is mostly on the west side of the Altamont Hills. Only a tiny corner of it touches the flatlands of the Central Valley — the very corner where the Mariposa and East Altamont projects are slated for. That is no coincidence.

Nor is it a coincidence that Alameda County was ready to host a 1,120-megawatt plant off Patterson Pass Road, also on this side of the Altamont Hills. (At least, as of last week, that project is dead in the water.)

It appears Alameda County would like to reap the benefits of having a new energy plant or three within its borders, while exporting the negatives — both real and perceived — to its over-the-hill neighbors.

San Joaquin County residents, not those in Alameda, look as if they will deal with the shadow of these projects. And whether those impacts are small or large, nonexistent or life-changing, is entirely beside the point.

The Mariposa project, on its own merits, makes sense to us, and we’re ready to see that plant spring to life. But it is a disturbing development when seen as part of a larger trend in which Alameda County approves heavy industry for San Joaquin County’s side of the hills.

By the numbers:

• 194: Megawatts that will be produced by the proposed Mariposa Energy Project.

• 4: Number of turbines, powered by burning natural gas, at the Mariposa plant.

• 80: Feet, in height, of the four cooling stacks that will accompany the turbines.

• 2½: Miles that will be between the Mariposa plant and the edge of Mountain House.

• 1.8: Miles of water pipeline that will be built for the plant.

• 0.1: Miles of natural gas pipeline that will be built for the plant.

• 10: Length, in years, of the plant’s power purchase agreement with Pacific Gas and Electric Co.

• 40: Number of years the Mariposa plant is designed to run, according to company executives.