Cahill Associates had been a pioneer and advocate of infiltration design systems for stormwater management for over twenty years, and continues to design innovative approaches that go well beyond the traditional detention basin solution. Based on the concept of sustaining the hydrologic cycle, CA has developed a number of methods and materials that infiltrate runoff, especially pervious pavements of asphalt concrete and Portland cement concrete that overlie stone storage beds. These systems convert a site design liability (impervious surfaces) into a "Better Management Practice" that sustains the natural soil infiltration and groundwater recharge of a given site. Designed to prevent any increase in runoff volume during the two-year frequency rainfall, they also mitigate the peak rate of runoff for more severe storms.
The soil mantle provides the best possible pollutant treatment system for NPS pollutants, and by slowly percolating through unsaturated upper horizons the groundwater is protected and pollutants transformed or removed from rainfall. Only Nitrate and other very soluble pollutants remain unchanged, and protection of aquifer systems requires that we reduce or eliminate the application of these pollutants of the land surface. The restoration of vegetation on the developed surface also contributes to sustaining the natural hydrologic balance, and so the integration of natural landscape design elements become an important part of our stormwater management systems. As in other site design considerations, CA uses the natural properties of the land to protect the water resources.
When the density of development prevents or severely limits the opportunity for infiltration, the only remaining options are to integrate rooftop stormwater management systems such as "Green Roofs", or capture and reuse the runoff from our built surfaces. CA has designed vegetated roof systems with US experts and developed several "storage and reuse" stormwater systems for both large industrial and commercial properties, especially parking garages. The integration of stormwater management "Green Roof" technologies with other environmental goals, such as alternative energy production by solar photovoltaic (PV) panels, in the Green Solar Canopy system, is an example of this "cross-fertilization" process that is reflected in all CA programs and designs.
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