For each siren, the area around the siren is divided into Polar coordinates of 24 150 segments and the radial distance (r) from the siren. For each segment an acoustic ray is projected based on the rated sound pressure level output, as described in Section 14. The acoustic ray sound pressure level is reduced by each of the applicable attenuation factors and site specific terrain factors described above. For each sound ray, the distance from the source corresponding to C-weighted 70 dBC and 60 dBC is determined as a point (X, Y) coordinate
for a Cartesian coordinate grid system. The ontours are scaled and overlaid on US Geological Survey topographical maps. This entire process is then repeated for each and every set of source-receiver pairs and used to develop a matrix of values from which the sound contours can be extrapolated for the entire EPZ.