EE was working on top of a primary sump with an EE wrapping a vertical 18"" cpvc pipe with a sealing tape. As EE handed the wrap to EE, EE went to reposition self to receive the wrap and EE's foot slipped thru an opening on the pipe support and fell to EE's left, landing on EE's left forearm. Both EE's were wearing fall protection at time of the incident.