In carrying out the purposes of this chapter or chapter
90.56 RCW the department shall, in conjunction with either the adoption of rules, consideration of an application for a waste discharge permit or the termination or modification of such permit, or proceedings in adjudicative hearings, have the authority to issue process and subpoena witnesses effective throughout the state on its own behalf or that of an interested party, compel their attendance, administer oaths, take the testimony of any person under oath and, in connection therewith require the production for examination of any books or papers relating to the matter under consideration by the department. In case of disobedience on the part of any person to comply with any subpoena issued by the department, or on the refusal of any witness to testify to any matters regarding which he or she may be lawfully interrogated, it shall be the duty of the superior court of any county, or of the judge thereof, on application of the department, to compel obedience by proceedings for contempt, as in the case of disobedience of the requirements of a subpoena issued from such court or a refusal to testify therein. In connection with the authority granted under this section no witness or other person shall be required to divulge trade secrets or secret processes. Persons responding to a subpoena as provided herein shall be entitled to fees as are witnesses in superior court.