Diesel back-up generators generate electricity in an inefficient, pollution-intensive way. VA DEQ should be helping to meet the goals of the VA Clean Economy Act (VCEA).  Allowing back-up generators to serve peak loads runs directly counter to the goals of that act, which aim to reduce carbon intensity of our generation mix by phasing out fossil generation and ramping up renewable sources.

Diesel generators are also key sources of particulate matter and other criteria air pollutants.  Given that many data centers are immediately adjacent to residential areas, the human health risks of allowing significantly longer running times for diesel generators (with concomitant higher emissions) are quite high, and unnecessary. 

Moreover, most of the data centers are in Northern Virginia, which is a non-attainment area for PM2.5 and ozone.  Given that the extended diesel usage would be occurring during power brown-outs or outages (generally occurring during hot air temperatures and high cooling loads), and this tends to coincide with meteorological conditions associated with worst air quality, the proposed relaxation of diesel operating guidelines would be likely to exacerbate air quality problems just when they are already most critical.  This could cost the region tens or hundreds of millions of dollars in compliance costs for other sources.  

The generators are loud and cause serious noise issues as well.

In a Clean Air Act context, there's no way that diesel generators are best available control technology.  If data centers really need to run on back-up power for long periods of time, they should use a combination of renewable energy generation (on-site or through power purchase agreements) and battery energy storage systems (BESS).  This would be a carbon-free, pollution-free, noise-free solution.  It would also be consistent with many of the data centers' corporate commitments for carbon neutrality.  And it would support attainment of the VCEA, rather than conflicting with it.

In short, rather than weakening standards for back-up generation, I urge you to tighten the standards.

Thanks for your consideration.