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which could allow for a reduction in the number of raingardens if the designer was having difficulty incorporating the needed amount ofraingardens in those subwatcrsheds. Estimated Costs. Construction cost estimates were available (from the city's feasibility study) for Example 2. For the other projects, a construction cost estimate of $1 million per mile of road was used to estimate what percent of the total project cost the stormwater features represent. For the above examples, the estimated cost for implementation of the 0.8-inch event standard ranged between 7% and 14% of the total project cost. The range in percentages is mainly attributable to the type of BMPs incorporated, with the least expensive BMP being surface features. Therefore, Example 4 which solely relies on surface BMPs, is estimated at the low end ofthis range. CONCLUSION & RECOMMENDATION Capture of the runoff from the 0.8-inch event provides a good balance between water quality treatment and providing flexibility for road reconstruction projects. Where infiltration practices can be utilized, this standard approaches NURP standards for most soil types. W11ere infiltration cannot be met, capturing this event will reduce phosphorus levels by a significant amount. In addition, this event standard is clear, straightforward and should provide the clarity requested by city staff for road reconstruction projects. Therefore, it is recommended that the District consider adopting the 0.8-inch precipitation event as an option for road reconstruction projects. For clarification purposes the following table of standards for various types of roadway projects is suggested for incorporation into the District Rules. Type of Construction Proposed Stormwater Standards* I ~ New Road 2: 1.0 acre impervious . Rate control for the 1- and 1 OO-ycar events . Water quality treatment for the 2.5-inch event . Infiltration for the 0.34-inch event New Road < 1.0 acre impervious . Rate control for the 1- and 100-year events . Water quality/infiltration for the 0.8-inch event Expanded / Reconstructed Road . Rate control for the 1- and 1 OO-year events . Water quality/infiltration for the 0.8-inch event Rural to Urban Section Road . Rate control for the 1- and 1 OO-year events (addition of curb and gutter or . Water quality/infiltration for the 0.8-inch event storms ewer) I - Mill & Overlay of Road . Exempt Pervious Pavement or Pavers * [Exceptions to these standards include: 1) documented soil contaminants precluding the use of infiltration practices, 2) soil borings documenting high water table preventing adequate separation from water table and 3) road segments less than 100 LF. In these instances, use of structural devices such as swirl separators or catch basin sumps could be accepted.] Emmons & Olivier Resources, Inc. Page 7 of7