Construction & Development (BMP)
Construction sites can generate a variety of pollutants that may be discharged (via storm water) and adversely affect beneficial uses of receiving water bodies. Of particular concern are the impacts of sediment. Sediment can be detrimental to aquatic life (primary producers, benthic invertebrates, and fish) by interfering with:
- Oxygen exchange in water bodies
In addition to impacts directly associated with sediment, various pollutants can also be transported along with sediment particles leaving construction sites. Such pollutants include metals, nutrients, pesticides and pathogens. Other pollutants of concern from construction sites are:
- Construction debris
- Concrete washout residue
- Construction chemicals
- Oil and grease
In order to control erosion and discharge of other pollutants on receiving waters, the State Water Resources Control Board (SWRCB) developed Waste Discharge Requirements for Discharges of Storm Water Runoff Associated with Construction Activity and issued a statewide general National Pollutant Discharge Elimination System (NPDES) permit (Construction General Permit). The primary objective of the Construction General Permit is to reduce erosion and minimize or eliminate sediment and non-storm water discharges from construction sites by implementing appropriate measures to reduce potential impacts on water bodies. Individuals or entities that own land where one acre or greater of soil is planned to be disturbed must seek coverage under the Construction General Permit.
New Development & Redevelopment
New development and significant redevelopment projects can adversely affect receiving water bodies for decades if post-construction storm water management elements are not implemented and maintained over the life span of the project. These impacts can generally occur in two ways. First, new and redevelopment can cause an increase in the type and quantity (e.g., concentration and/or volume) of pollutants in storm water runoff. As runoff flows over areas altered by development, it picks up harmful sediment and chemicals such as oil and grease, pesticides, heavy metals, and nutrients (e.g., nitrogen and phosphorus). These pollutants often become suspended in runoff, where they can adversely affect aquatic organisms (i.e., toxicity), and are eventually carried to receiving waters, such as lakes, ponds, and streams. When deposited in water bodies, pollutants can enter the food chain through small aquatic life, eventually entering the tissues of fish and humans and cause harmful effects.
The second kind of post-construction runoff impact occurs by changing the natural hydrology of a land area through the creation of new impervious surfaces during development. Increased impervious surfaces interrupts the natural cycle of gradual percolation of water through vegetation and soil by altering the timing and quantity of peak flows. Instead, water is collected from surfaces such as asphalt and concrete and routed to drainage systems where large volumes of runoff quickly flow to the nearest receiving water. The effects of this process include stream bank scouring, bank erosion and downstream flooding, which often lead to a loss of aquatic life and damage to property.
Several studies have shown that controlling pollutants once they have entered into the storm drain system is more difficult and expensive than preventing or reducing the pollutants at the source. If areas proposed for new development or redevelopment are planned, designed, and constructed in a manner that considers storm water runoff issues, then future pollutant loading from these areas will be reduced.