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Better Site Design Bannerman (1992) documented the significance of parking lot runoff. His study showed that for commercial and particularly industrial land uses, parking lots are a critical source of stormwater pollution (Figure 10.1). In fact, parking lot runoff accounted for approximately one-fourth to two-thirds of the suspended solids, total phosphorus, total copper, and total zinc loads in the commercial and industrial areas studied. Although parking lots are a significant source of stormwater pollution, many communities do not require developers to provide stormwater quality controL. In addition, opportunities to minimize the amount of stormwater runoff generated or to manage runoff are often overlooked. RECOMMENDED PfftAaTI([E There are several techniques that communities can use to reduce the volume of stormwater generated at parking lots. These include: Q reducing minimum parking requirements to allow smaller lots to be built (see Principle No.6); o allowing developers to use pervious materials for spillover parking (see Principle No.8); and o promoting the use of parking garages which expose less impervious cover to rainfall (see Principle No.9). Another option is to require onsite stormwater management. Existing landscape areas in parking lots can be used to provide some stormwater management. Many communities already require developers to landscape parking lot islands. Typically, the landscaping is used to enhance the appearance of a parking lot or to visually separate land uses or development. These areas often account for 10 - 15% of the total parking lot surface area (see Table 10.1). Table 10.1: l?arrki;1g Loti: LalTio1scape ReqlUlili'iEmel111~ foli' ViIi"iO!.ll$ (ommmoitiiEs Jurisdiction { ... Portland, Oregon St. Tammany Parish, Louisiana James City County, Virginia CoUeton County, South Carolina Requirrements o Landscaping requi.red in building and street setbacks (typically 5 - 10 feet in width) o Landscaping primarily consists of ground cover plants and a mixture of trees, high shrubs, and low shrubs o Two trees must be provided for every eight (8) parking spaces (excluding commercial parking garages and multi-level parking) o Landscaping required for off-street parking areas containing ten or more parking spaces. o Existing trees must be preserved (as feasible) G Landscaped areas must account forr at least 10% of the parking lot surface area e At least one tree and two shrubs must be provided for every five parking spaces o Landscaping required for lots containing 20 or more parking spaces o Ten percent ohhe tot must be landscaped o Natural vegetation must be presei'Ved --./. - 84- '.- -