Stormwater Management Standards Manual - Toledo Metropolitan ...

1.4 Impacts of Development on Water Quality
As urban and rural land is developed, changes in land use contribute new or additional stormwater
runoff pollutants. In addition, the increased impervious surfaces quickly drain these pollutants into
receiving waterways. Vehicles and deteriorating urban structures deposit trace metals, oil, and grease
onto streets and parking lots. Leaves, litter, animal droppings, soil from construction sites, fertilizers, and
pesticides are all carried over the land. These and other toxic substances are then carried by stormwater
and conveyed through creeks, ditches and storm drains into our rivers and lakes (Figure 1-2).
CATEGORIES OF PRIMARY STORMWATER CONTAMINANTS
Category
Metals
Organic Chemicals
Pathogens
Nutrients
Biochemical Oxygen Demand (BOD)
Sediment
EXAMPLES
zinc, cadmium, copper, chromium, arsenic, lead
pesticides, oil, gasoline, grease
bacteria, viruses, protozoa
phosphorous, nitrogen
grass clippings, hydrocarbons, animal waste, fallen leaves
topsoil, sand, silt , clay
Salts
sodium chloride, calcium chloride
Figure 1- 2 Categories of Primary Stormwater Contaminants
Source: Bannerman, R.T., D.W. Owens, R.B. Dodds, and N.J. Hornewer, Sources of Pollution in Wisconsin Stormwater, Water,
Science and Technology vol. 28, no. 3-5, 1993.
In short, the ecology of both urban and rural streams may be completely reshaped by the extreme
shifts in hydrology, morphology and water quality that accompany the development process. The
stresses that these changes place on the aquatic community, although gradual and often not
immediately visible, are profound. To mitigate these impacts, it is necessary to reevaluate the way
that land is developed and stormwater is managed. The following discussion provides a framework
for this reevaluation, which must encompass the entire development process from land use
planning and zoning to site design and construction.
1.5 Framework for Design of Stormwater Management Systems
Thoughtful site planning can reduce the negative impacts associated with land development.
Towards this end, communities, regulatory agencies, and designers must begin to evaluate the
impact of each individual development project over the long term, and at a watershed scale. Such
an approach requires the use of a system of stormwater controls or Best Management Practices
(BMPs) to ensure that the volume, rate, timing and pollutant load of runoff remains similar to that
which occurred prior to development. This system may include both nonstructural and structural
methods and should be designed to provide both source controls and site controls. These are
techniques which, respectively, reduce the amount of stormwater generated by development
activities and those which transport, pre-treat or treat the remaining stormwater generated in a
manner conducive to greater infiltration, lower maintenance or improved efficiency (Figure 1-3).
Third Edition Stormwater Standards Manual September 2008 Page 23