This is an appeal from a judgment of the circuit court for Waukesha County, Robert T. McGraw, Circuit Judge. The judgment estopped the Milwaukee Metropolitan Sewerage District (MMSD) from changing its method of charging the plaintiff municipalities for the recovery of the capital costs of MMSDs sewerage processing and water pollution abatement facilities. It further adJudged, in accordance with the special verdict of the jury, the reasonable value of the capital costs of sewerage service MMSD provided to the plaintiff municipalities. The City of Brookfield, Village of Butler, Village of Menomonee Falls, City of Mequon, City of New Berlin, Village of Elm Grove, City of Muskego, Village of Germantown, and the Village of Thiensville are the plaintiff municipalities. They receive sewerage services from MMSD, but they are located outside MMSDs statutory boundaries. MMSD originally calculated the capital cost charges to the plaintiff municipalities through a usage based formula. Subsequently, MMSD attempted to change to a property value based formula.