Our project uses an innovative green roof design to eliminate water pollution, increase infiltration, eliminate source contaminates, and treat the building\'s stormwater. In our efforts to treat as much roof runoff for quality as possible, we have redirected the runoff from the impervious roof area towards the pervious (green roof) area allowing the runoff to infiltrate, collect into under-drain pipes, and eventually become overflow collected within the area drains. This will reduce or eliminate pollutant loadings by allowing the stormwater runoff to first filter into the soil and vegetation. This stormwater design is a non-structural, alternative surface with innovative methods in a densely populated downtown area. We have disconnected the impervious rooftop areas (a strategy recognized by the state of Maryland) to infiltrate its runoff and treat for TSS. This design will greatly reduce the release of TSS into the municipal water system. The green roof covers more than half of the roof surface and treats 100% of the stormwater that falls on this portion of the roof. The entire roof area is 25,525 SF, of which the cooling tower area is 1,200 SF, and the green roof area is 13,046 SF. The cooling tower drainage area will be the only remaining impervious area that has not been directed towards a green roof area - this constitutes less than 5% of the entire roof. In view of the fact that 90% of the annual rainfall volume will be 100% TSS treated, we would like to submit a credit interpretation request to consider the impervious rooftop runoff that drains towards the green roof area, as "green roof runoff." We feel that the disconnection strategy used for the impervious rooftop areas makes it appropriate to calculate the redirected impervious area as pervious.
The project team has requested that runoff from an impervious roof area, that drains to a green roof area, be considered as an impervious area for the sake of calculations. The intent of SSc6.2 is to remove pollutants from stormwater runoff by increasing on-site infiltration and/or eliminating sources of contaminants. BMPs specified in the stormwater management plan are expected to remove 80% of average annual post development TSS and are considered to meet these criteria if they are designed in accordance with state or local programs which have adopted these standards. This CIR discusses a stormwater management plan that reduces impervious cover, promotes infiltration, and captures and treats the stormwater runoff from over 90% of the average annual rainfall using acceptable best management practices (BMPs). In this case, over 95% of rainfall on the rooftop either falls directly on or is guided to the green roof for treatment. The green roof is expected to treat (remove rainborne and rooftop collected TSS) from 100% of the runoff falling on and directed to it. Because greater than 95% of the roof is treated by the green roof vegetation (to a level of 100% TSS removal), the goal of removing 80% of the average annual TSS should be achieved. The described approach appears to meet the intent of CS v2.0 SSc6.2 for this project. Applicable Internationally.