APS calculation of PSI for underground

I am trying to get an encroachment easement from Arizona Public Services (APS) and need to provide them a engineered stamped report on PSI. My trenching project must go underground for a distance of 515 feet under a large transmission line. My electrical company is following a plan developed by the Wellton Mohawk Irrigation District and consistes of a single primary line 4 feet underground using 2 inch Schedule 40 PVC as conduit. The trench is being dug in a desert environment, soil is a small rock conglomerate, with some larger rocks thrown in. I will email drawings and requirements to interested parties.