Hiding in plain sight - compatible noise levels for sparsely populated areas

In 1974, the EPA "Levels Document" proclaimed 55 LDN to be the universally acceptable community noise level for any and all locations, or so you might be led to believe. To this day, a 48.6 dBA continuous sound level is a ubiquitous criterion for power plants, gas compressor stations, and other industrial infrastructure located in sparsely populated areas, regardless of the prevailing ambient levels and/or perceptual characteristics of the intruding noise. However, the 55 LDN universal dictum generalizes a special case, that of transportation noise in urban environments, for which this simple method is indeed a valid proxy. Roughly seventy years of research has yielded a sturdy consensus regarding other factors that also strongly influence the compatibility of industrial noise with residential living. A more comprehensive approach to compatible levels is summarized in the Levels Document as well as in present-day engineering and national standards. This paper presents an overview of references and methods for determining compatible levels, along with some examples of clearly incompatible noise observed in rural environments with weak or no regulation.