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Enbridge Energy, LP Hoover& Keith, Inc. Waterloo Pump Station—Noise Impact Analysis RN 3083/JN 4796 APPENDIX B— Estimated Contribution of Station (10/10/14) ANALYSIS METHODOLOGY AND SOURCE OF SOUND DATA In general, the predicted sound level contributed by the pumping station equipment was calculated as a function of frequency from estimated unweighted octave-band ("O.B.") sound power levels ("PWLs")for each significant sound source. The following summarizes the acoustical analysis procedure for the Station: ➢ Initially, unweighted O.B. PWL values of the significant noise sources were determined from equipment manufacturer's sound data and/or actual sound level measurements performed by H&K at similar type of equipment/components expected for this facility. ➢ Then, expected noise reduction (NR) or attenuation in dB per O.B. frequency due to any noise control measures, hemispherical sound propagation (discussed in more detail below*) and atmospheric sound absorption (discussed in more detail below**)were subtracted from the unweighted O.B. PWLs to obtain the unweighted O.B. SPLs of each noise source. The sound attenuation effect due to shielding by buildings and/or enclosures has been conservatively ignored. The sound attenuation effect due to foliage or land contour was not considered in the analysis since there is probably minimum attenuation due to foliage. ➢ Finally, the resulting estimated unweighted O.B. SPLs for all noise sources associated with the Station (with noise control and other sound attenuation effects)were logarithmically summed, and the total O.B. SPLs for all noise sources were corrected for A-weighting to provide the estimated overall A-wt. sound level contributed by the Station at the Property Line. *Attenuation due to hemispherical sound propagation: Sound propagates outwards in all directions (i.e., length, width, height)from a point source, and the sound energy of a noise source decreases with increasing distance from the source. In the case of hemispherical sound propagation, the source is located on a flat continuous plane/surface(e.g., ground), and the sound radiates hemispherically(i.e., outward, over and above the surface)from the sound source. The following equation is the theoretical decrease of sound energy when determining the resulting SPL values of a noise source at a specific distance("r") of a receiver from the estimated PWL values: Decrease in SPL("hemispherical propagation")from a noise source= 20*log(r)—2.3 dB where"r" is distance of the receiver from the noise source. **Attenuation due to air absorption:Air absorbs sound energy, and the amount of absorption ("attenuation") is dependent on the temperature and relative humidity(R.H.)of air and frequency of sound. For example, the attenuation due to air absorption for 1000 Hz O.B. SPL is approximately 1.5 dB per 1,000 feet for standard day conditions(i.e., no wind, 60 deg. F. and 70%or 50% R.H.). The estimated unweighted O.B. PWLs of the motor-driven pumps, piping, substation equipment and any other site equipment were estimated from field sound measurements by H&K on similar equipment and/or from sound data provided by the equipment manufacturer. B-3