Whenever the department is empowered under the terms of title 21 of this article to make a determination it may hear testimony and take proofs material for its information and may appoint a hearing officer by a written appointment, for that purpose. Every hearing officer so appointed shall be authorized to take such testimony and hear such proofs as may be material to the inquiry and report the proofs and testimony so taken, with his opinion as to the facts established thereby, to the department. The department may make such determination from the proofs and testimony taken before it or before such hearing officer or from any other data which shall be satisfactory to it, and the expenses of taking such testimony or proofs shall be deemed a part of the expense of the improvement to which it relates.