Before and during dredging, in-stream water quality monitoring will be conducted to assess potential impacts from the dredging. The water quality monitoring will consist of real-time turbidity data and daily total suspended solids (TSS) sampling.
Turbidity is a measurement of water clarity, and is measured by quantifying the amount of light reflected by suspended and colloidal particles. TSS sampling measures the amount of particles which are suspended in the water column, suspended solids typically include silt and clay particles, plankton, algae, fine organic debris, or other particulate matter. Suspended solids are more likely to carry toxic chemicals, and can also negatively affect aquatic organisms, water temperature, and dissolved oxygen levels. TSS measurements will be correlated to turbidity data, such that dredging operator can adjust operations in real-time with turbidity levels.
Turbidity is a natural occurrence in all water bodies and, in addition to dredging, elevated readings can be caused by:
- Boat Traffic
- Storm Events
- Urban runoff
- Sewer Discharges
- Bottom feeders (such as carp) stirring up bottom sediments
- Excessive algal growth
The dredging contractor will measure turbidity both upstream and downstream of the dredging operation. The difference between these two points will be utilized to determine the impacts of the dredging operation on turbidity in an effort to discount natural (background) turbidity. If the difference between upstream and downstream readings is greater than 50 NTU, the dredging contractor is required to take immediate responses. These responses may include:
- Ensuring that all equipment is functioning properly
- Slowing dredging operations
- Pausing dredging until turbidity has been reduced
- Or installing turbidity curtains around the dredging area (required after three-consecutive days with impacts >50 NTU).