Orono Substation Expansion - Enviromental Assessment (1)

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I Mitigation Measures Avoidance of archaeological and historic architectural properties is the preferred Mitigation measure. The Project avoids historic architectural properties. Although the potential for the Project to impact undiscovered archaeological sites as low because of the Project's location within the existing Orono Substation site and along existing transportation corridors or in areas already disturbed by residential development,Xcel Energy will contract for archaeological surveys to be performed in two areas within the Project area,as identified by SHPO, to identify any previously unknown archaeological resources (Xcel Energy,2011a). In the event of an unanticipated discovery of cultural resources during Project construction,Xcel Energy will stop construction activities and consult with a professional archaeologist and the SHPO to determine the proper course of action. If a cultural resource or feature is determined to be potentially eligible for listing on the National Register of Historic Places,it will be avoided or mitigated before construction can resume (Xcel Energy,2011a). ' 5.18 Interference The Corona from transmission line conductors can generate electromagnetic noise at frequencies ' that may potentially impact electronic communication and similar devices,induding radios, televisions,microwave communications,and Global Positioning System (GPS)-based agricultural navigation systems. No impacts to electronic devices are anticipated as a result of the proposed project. Radio Interference ' Corona from transmission line conductors can generate electromagnetic "noise"in the radio frequency range.This noise may cause broadband interference at the same frequencies that many communication and media signals are transmitted.This noise can cause interference with the reception of these signals depending on the frequency and strength of the signal. Loose hardware on the transmission line may also cause interference. AM radio frequency interference typically occurs immediately under a transmission line and dissipates rapidly to either side. If radio interference from transmission line corona does occur, satisfactory reception from AM radio stations can be restored by appropriate modification of(or addition to) the receiving antenna system. FM radio receivers usually do not pick up interference from transmission lines because corona- generated radio frequency noise currents decrease in magnitude with increasing frequency and are quite small in the FM broadcast band(88-108 Mega Hertz);and the excellent interference rejection properties inherent in FM radio systems make them virtually immune to amplitude type disturbances. Television Both digital and satellite television are expected to have little interference from corona generated noise,but may experience other types of interference. Compared to analog broadcasts,digital television broadcast frequencies are high enough that any ' electromagnetic noise currents,if they were to exist at all,would be very small. Environmental Assessment PUC Docket E002/IL-11-223 Page 52 1