It is the City’s intent to encourage sound technical design practices that reduce the negative impact of development on the storm water drainage system through a credit system. Properties whose impact on the drainage system is significantly limited or has been effectively reduced through specific controls shall be entitled to a credit adjustment that may be applied to its storm water service charge. A credit adjustment application must be filed in writing with the City Administrator. The application shall include all necessary information from a registered Iowa Land Surveyor or Professional Engineer to clearly demonstrate the credits sought, pertinent maps and design calculations, e.g. pre-development and post-development runoff rates, storage volumes, etc., and the proposed and/or resulting hydrologic response of the property to rainfall events. Using the information provided by the applicant, the City Administrator shall conduct a technical review of the conditions on the property and respond to the application in writing within 30 days. Billing adjustments required to implement credits shall be applied retroactively to the date the customer submitted a complete application. Adjustments shall be made by crediting the customer’s storm water service charge until any overpayment has been fully repaid. A pending application for credit shall not constitute a valid reason for nonpayment of the current storm water service charges. Credit adjustments shall be applied as follows:
1. Quantity Reduction (40% maximum).
A. Rate Reduction Credit – 25 percent credit. Storm water facilities that control the post-development peak rate of storm water runoff at the pre-development rate of the two-year design storm.
B. Additional Rate Reduction Credit – 10 percent credit. Storm water facilities that qualify for a rate reduction credit can also qualify for the additional rate reduction credit if they reduce the post-development peak rate for the two-year design storm by at least 20 percent of the pre-development flow rate.
C. Additional Volume Credit – 5 percent credit. Storm water facilities that qualify for a rate reduction credit can also qualify for an additional volume credit if they provide 20 percent more storage volume than required for the 100-year design storm. This does not include required freeboard above an emergency spillway.
2. Quality Credit (10 percent maximum).
A. Implement Best Management Practices (BMP) – 5 percent credit per approved best management practice (BMP). Quality credits will be available to properties where structural or non-structural storm water BMPs are located and which are used to treat storm water runoff, specifically total suspended solid (TSS) loads. Professional techniques such as those published in the Iowa Stormwater Management Manual, or by the U.S. EPA, National Resource Conservation Service, American Society of Civil Engineers, and other professional organizations will be considered. A quality credit can also be applied in addition to any approved quantity reduction credits, such as a wet detention pond that is designed to remove at least 80 percent total suspended solids (TSS).
B. Applicants for non-structural storm water BMPs including filter strips and natural preservation areas may be eligible for credit provided the owner’s engineer can provide calculations showing removal of 80 percent TSS.
The owner shall supply maintenance information along with their application. Any association agreements or contracts for inspection and/or maintenance are required to be disclosed as part of the application. Indicate the schedule for major maintenance that will be performed and how many times per year basic maintenance (such as erosion control and/or mowing) activities are performed. Inspection reports shall be filed with the City every third year, as calculated from the original application date, in order to maintain any level of credit. If a property owner fails to file required inspection reports or if a random City inspection results in failure, the City will send a letter informing the property owner of the required action to avoid revocation of the credits. If the property owner fails to take the required action, the credits will be revoked until the situation is corrected. No retroactive credits will be given during said lapse period. Credits will be restored on the effective date of the submittal of the property owner’s acceptable response.