Why is Sediment Control and Dewatering Operations Regulated on Construction Sites?
Untreated water from construction dewatering operations may contain pollutants that, if discharged to a storm drainage system or natural water course, may exceed water quality standards of the receiving water. The intent of Provincial and Federal regulations is to prevent discharges from dewatering operations from contributing to the exceedance of water quality standards.
What are Considered Pollutants?
For our purposes, pollutants may be classified into three groups:
Sediment is the most common pollutant associated with dewatering operations on
construction sites. A visible pollutant, sediment concentration is typically monitored as turbidity,
total suspended solids, or suspended sediment concentration. Turbidity is a key parameter
monitored. Most dewatering operations require treatment to remove some amount of sediment.
pH is the other key parameter monitored. High pH readings are typically associated with shotcrete, concrete and grouting operations. Because such activities do not typically occur near dewatering operations, readings outside the pH limits (i.e., below a pH of 6.5 or above 8.5) are not typically expected. However, such readings may occur when grouting operations occur near a dewatering operation, where cooling water is used in concrete curing, or where concrete is being poured in an area that is being dewatered for the placement of a concrete pile or footing. Unlike sediment, pH is a non-visible pollutant.
This includes all other pollutants as defined in Federal and Provincial laws and regulations. These pollutants tend to be site-specific and are often associated with current or past use of the construction site or adjacent land. Commonly, “other pollutants” on construction sites include: nitrogen and phosphate from fertilizers (i.e., nutrients); organic materials from plant waste; metals such as arsenic, cadmium, copper, and lead; and constituents that affect pH or hardness.
Other pollutants may also include oil, grease, pesticides, solvents, fuels, trash, and bacteria from human/animal wastes. These pollutants may come from construction materials such as form release agents, concrete curing compound, concrete sealants, drilling compounds, welding waste, hydrating concrete, blasting grit, sawdust, and residues from pile driving hammers. We can provide detailed information about sediment removal methods and technologies that ensure compliance with all Federal and Provincial regulations.