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Environ Stew C develop designsFebruary 3, 2004 Honorable Mayor Terry M. Duggan and City Council Members City Hall 50 W. 13th Street Dubuque IA 52001 Dear Mr. Mayor and Council Members: Over the past several months, the Environmental Stewardship Advisory Commission has been studying Low Impact Development as it relates to stormwater management. The Commission was part of the City's NPDES permit process last year in an oversight capacity and also by participating in various subcommittees. The Environmental Stewardship Advisory Commission recommends that Best Management Practices be implemented for new construction sites and construction renovations in order to: 1) improve water quality and, 2) confine stormwater runoff to the site on which it falls until peak flow has passed. The benefits of reduced stormwater runoff and improved water quality will improve Dubuque's economy and its citizens' health by: · Reducing physical damage from floods · Reducing costs of infrastructure for water treatment · Decreasing waterborne disease and costs related to its prevention and treatment. Attached are design criteda for new construction sites, which may be considered. The ESAC would recommend including these racommendations in various City ordinances that are already in place. For instance, ddveway curb cuts, street construction, and sidewalk construction already require permits from Yadous City departments. These, along with other construction that influences stormwater runoff, such as construction or replacement of patios and driveways, retaining walls, or various types of landscaping could also require a permit to insure that Best Management Practices are included. This recommendation reflects the City of Dubuque's commitment to the local economy, community activities and to the environment. The ESAC would recommend that City Council direct staff to consider the attached design criteria for new construction Sites and Best Management Practices in modifying existing ordinances. This would not only improve the stormwater runoff quality and reduce its amount, but also aid in the City's NPDES compliance requirements. If you have any questions, Commission members would be happy to address them. Environmental Stewardship Advisory Commission MB/cj CC: Environmental Stewardship Advisory Commission members Mary Rose Corrigan, RN, Public Health Specialist Michael C. Van Milligen, City Manager Gus Psihoyos, Assistant City Engineer Desi.qn criteria for new construction sites To meet the purposes above, we recommend that the following be required on all new construction sites. 1. Identification, delineation, and mitigation of all potential wetlands on a site. 2. Grading plans to conform to proposed and approved grading plans. Site to have topographic survey completed pdor to vegetation of the site to confirm conformance to grading plan. 3. Use of Revised Universal Soil Loss Equation (RUSLE) with a soil loss not to exceed 3 tons per acre. 4. Vegetation of the site within 30 days of excavation, with cover within 30 days of vegetation. New sites (subdivisions and sites over one acre) would be allowed to use a temporary cover crop. New home sites would be required to install turf. They would be allowed to keep a 15-ft. buffer from the foundation to allow construction activities to take place, providing erosion control methods (silt fencing or sediment logs) were installed to prevent soil from migration into turf areas. In the event vegetation could not be accomplished (e.g., winter months), erosion control mat or hydro mulch could be applied to the site to prevent erosion 5. Use of bio-retention in parking lots 6. Tree inventory of site to protect existing trees, if they have value, as either a landscape tree, lumber tree, or because of age and stature. 7. Planting of trees with a caliper (diameter 6" above ground) of not less than 2", or trees that will reach 2" caliper within the first year of planting. Design cdteda shall be to retain on the site 6.36" of rain in a 24-hour time span (100 year storm event). The contractor, or developer, may use any, or a combination of, BMPs to meet the design criteria. The following BMPs may be used to meet the above design criteria: 1. Low impact design 2. Permeable pavement 3. Rain Gardens 4. Use of some under ground vessel as storage for storm water run off. (This water can be used as for irrigation, car-washing etc. or plumbed to the home or business to be used in non-potable water applications.) Other Considerations 1. In the event that the cost of implementing BMPs is greater than the cost associated with normal development or construction cost, the stormwater utility could be used to cover the overage. 2. Pervious pavement could replace detention ponds and costs associated with their construction, maintenance, and loss of income from the lot(s) that they occupy. The streets, driveways, patios, landscape planting beds and underground vessels would become the detention area in the subdivision. 3. All the BMPs can be retrofitted in most sections of Dubuque. 4. Provides the City the opportunity to set the pace in Iowa for clean water and stormwater management. 5. Pervious pavement has the potential to reduce the cost associated with street maintenance as well as snow and ice control.