MEMO: Rutland Power Plant

August 26, 1999      Ref 1812
To: Annette Smith
From: Peter Guldberg
Re: Rutland Power Plant

Air Quality

Thank you for all of the maps you e-mailed.The topographical features of the site will present the developer with a challenge in terms of meeting the air quality regulatory limits because terrain above stack top (assuming 200' stacks) exists only 1.2 km to the west, and the plumes from the plant will impact the slopes of Bald Mountain to the east in Rutland and Mendon,and Boardman Hill to the west in Clarendon.Demonstrating that the plant will meet the available Prevention of Significant Deterioration (PSD) increments for Particulate Matter in this high terrain will be the principal challenge in obtaining an air quality permit for the plant.

Noise

The greatest potential impacts from a 1080 MW plant on this site involve noise and visible plumes.A single 250 MW combustion turbine with no noise control will produce a sound power level at stack top of about 134 dBA (A-weighted decibels).Four 250 MW units have the potential to produce a stack top sound power level of 140 dBA. Calculating the attenuation of sound with distance, the sound pressure level for a 1080 MW plant without noise controls at a distance of 25 miles could be 40 dBA. Given that rural, nighttime background sound pressure levels are 30 dBA or lower, this means the plant might be audible as far as 25 miles away, producing a sounds twice as loud as the nighttime background sound level.(Every 10 dBA increase in sound pressure level is perceived as a doubling of "loudness". Every 10 dBA increase represents a ten-fold increase in sound pressure.) Given the low ambient sound levels in rural Vermont, this suggests that a Best Available Noise Control Technology (BANCT) analysis should be required for the plant.

Other equipment at a power plant besides the stacks generate sounds of course, and an accurate evaluation of the Rutland plant's impacts requires first that we have some specific information on the design.

Visible Plume

The water vapor condensate plume from a combustion turbine stack will sometimes exceed 500 feet in length under winter conditions of low temperature and high humidity.Power plant plumes also typically rise vertically in the air 2 to 5 times the physical stack height, making condensate plumes very visible from a distance.The proposed site in Rutland will produce greater visual impacts than most sites because of the local meteorology, i.e. the predominance of weather conditions in the winter that favor the creation of long, visible plumes, and the high terrain east and west of the site that looks down on the site. Any specific conclusions about visual impacts, of course, require data on the plant design.

If water cooling is proposed for the plant, then a second visible plume from the wet cooling towers will be added to the landscape, and this low level plume has the potential to cause extensive fogging and icing impacts on nearby roadways and rail lines.