VII. Should Underground Lines be
Considered for Additional Mitigation?
In some instances, a new transmission line may be constructed underground rather than overhead. 280 Citizens recommends that although a transmission line may be placed underground, this should not prohibit consideration of additional mitigation measures for an underground line. Sierra and PacifiCorp argue that the cost of underground construction and the resulting reduction in EMF are sufficient to meet the Commission's Prudent Avoidance Policy. Thus, Sierra and PacifiCorp recommend against any additional EMF mitigation spending for underground lines. PG&E, quoting D.04-08-046, recommends that underground lines not receive any low-cost mitigation funds except for "typical trenching and duct bank construction costs that may be incurred because the route may not be as direct as otherwise possible if strategic placement were not undertaken"20
As noted in the utility design guidelines,21 underground transmission lines typically reduce magnetic fields in comparison to overhead line construction. We also note that underground lines are usually more costly than overhead line construction. Nevertheless, there may be instances in which additional mitigation may be appropriate for an underground transmission line. In D.04-08-046 we noted the intense public concern regarding the particular circumstances in locating a portion of the Jefferson-Martin transmission line in a residential area, and thus we required PG&E to lower the trench depth of this underground transmission line by an additional five feet in all residential areas where this would lower magnetic fields by at least 15%.22 This additional depth was required as well as strategic line placement that already mitigated EMF exposure.
Although we expect that placing a transmission line underground should normally provide sufficient mitigation, we will not adopt a policy that totally excludes additional mitigation for underground lines should special circumstances warrant some additional cost in order to achieve significant further EMF mitigation.
20 D.04-08-046, mimeo., pp. 105-106.
21 See, for example, SDG&E EMF Design Guidelines For Transmission, Distribution and Substation Facilities, May 23, 1994 , p. 28.
22 D.04-08-046, mimeo., p. 107.
