This appeal presents three issues:
(1) Was the department’s 1967 hearing res judicata, thereby foreclosing it from conducting additional hearings;
(2) Did the department act arbitrarily and capriciously in denying the appellant’s request for a declaratory ruling; and
(3) Did an additional hearing by the department constitute an unconstitutional usurpation of the judiciary’s authority?
Applicability of the doctrine of res judicata.
It has long been established in this jurisdiction that the doctrine of res judicata has no application to the proceeding of an administrative agency such as the department. In Duel v. State Farm Mut. Automobile Ins. Co. (1942), 240 Wis. 161, 1 N. W. 2d 887, 2 N. W. 2d 871, an insurance commissioner refused to grant a license to a foreign corporation despite the fact that his predecessor had previously granted the license. In response to the company’s assertion that the commission’s previous determination was res judicata, this court stated at page 181:
“The extent of the power of an administrative body or agency to reconsider its own findings or orders has nothing to do with res adjudicata; the latter doctrine *626applies solely to courts. See Lange Canning Co. v. Industrial Comm. 183 Wis. 583, 197 N. W. 722; Hinrichs v. Industrial Comm. 225 Wis. 195, 273 N. W. 545; Maryland Casualty Co. v. Industrial Comm. 230 Wis. 363, 284 N. W. 36. . . .”
The appellant’s reliance upon Buhler v. Department of Agriculture (1938), 229 Wis. 133, 280 N. W. 367, is misplaced. After citing Buhler for the proposition that one is entitled to a fair hearing before an agency, no showing of unfairness has been presented. Any expense or inconvenience which will be incurred by the appellant as a result of further hearing is justified by subsequent changes in such factors as population, water consumption and sewage volume.
Arbitrary and capricious action of the department.
The appellant contends that the department’s refusal to issue a declaratory ruling authorized by sec. 227.06,2 *627Stats., was arbitrary and capricious. This contention is predicated upon the assumption that all necessary information was acquired at the 1967 hearing and upon the fact that another hearing will result in additional expense to the city.
In Jabs v. State Board of Personnel (1967), 34 Wis. 2d 245, 251, 148 N. W. 2d 853, this court described an arbitrary or capricious decision as “ *. . . one which is either so unreasonable as to be without a rational basis or the result of an unconsidered, wilful and irrational choice of conduct/ . . .” See also: Robertson Transportation Co. v. Public Service Comm. (1968), 39 Wis. 2d 653, 661, 159 N. W. 2d 636.
In the instant case the department did exactly as required by sec. 227.06, Stats. It denied the petition in writing, promptly notified the appellant of its decision and briefly stated its reasons for denial. One such reason was the change in circumstances since the 1967 hearing.
Prior to the commencement of the 1967 hearing it was specifically noted that such hearing was for informational purposes only and that additional hearings might be necessary before the issuance of mandatory orders. Clearly, the department’s refusal to grant a declaratory ruling that it had no authority to conduct another hearing was consistent with its initial pronouncement and not “an unconsidered, wilful and irrational choice of *628conduct.” The problem of pollution in the Fond du Lac area, has existed for many years and grows worse each day. The department has been vested with the responsibility of abating pollution and should be allowed to exercise its discretion in the discharge of this responsibility.
Usurpation of judicial functions.
Citing In re City of Fond du Lac, supra, the appellant argues that the county court has determined the facts of the case and that any further hearings by the department would constitute usurpation of the judiciary’s power to make factual determinations.
In re City of Fond du Lac, supra, simply declared the statutory procedure 3 for the formation of metropolitan sewerage systems unconstitutional in that they unlawfully granted courts authority to decide questions which were “political” rather than “factual” in nature.
In determining that the county court could not, as a matter of law, decide what was the “best” solution to the pollution problem, this court did not intend that the county court’s “factual” determination should foreclose the department from conducting additional hearings. To have so held would have been in direct conflict with the legislature’s express intention to vest pollution abatement authority in the department.
We conclude that the department’s 1967 hearing was not res judicata, that the department did not act arbitrarily and capriciously in denying the appellant’s request for a declaratory ruling, and that any additional hearing would not constitute an unconstitutional usurpation of the judiciary’s authority.
By the Court. — Judgment affirmed.