The City of Ithaca’s Stormwater Utility chapter describes the calculation of stormwater user fees charged for costs incurred by the City in providing stormwater services. This monthly fee is equal to the product of $4 and the number of Equivalent Residential Units (ERUs) of impervious surface area on the lot, less any credits for the lot approved by the Superintendent of Public Works. One ERU is equal to 2,300 square feet, the average amount of impervious surface area on a residential property as determined by the Common Council. The stormwater user fee may be reduced if the lot is eligible for credits. An engineered structure or practice for stormwater management that provides quality treatment and/or quantity attenuation shall be considered for credits by the Superintendent. Credits are calculated by the product of the lot’s stormwater user fee, the percentage of the total impervious surface area on a lot mitigated by the practice or structure, the practice or structure’s credit rate, and the practice or structure’s treatment efficiency. Practices or structures eligible for credits are enumerated in a list of “approved stormwater user fee credits” maintained and updated by the Superintendent and the Board.