What is the PENNVEST program and how does it work? PENNVEST is a low-interest loan program created by PHFA, the Department of Environmental Protection (DEP) and the PA Infrastructure Investment Authority to help Pennsylvania homeowners repair or replace their individual on-lot septic system or connect to a public septic system. Listen to find out all the ins and outs of this program from PHFA's Manager of Special Initiatives Roberta Schwalm.