Land surface disturbance activities, such as construction and agriculture, create an environment for erosion of fine soil material that causes turbidity. There are of course well-established erosion and sedimentation control practices that constitute approved BMPs referred to in the turbidity standard. When these practices are properly designed, installed, and maintained, they can be quite effective in the prevention of sediment movement to natural waters. However under certain conditions, it is recognized that these practices fail to prevent the fine soil particles causing turbidity from reaching surface waters. That results in the loophole in the standard.
Standard setting involves a balancing of costs and benefits.
If the levels of turbidity in the standard are often violated downstream of land disturbance activities that are served by approved but ineffective BMPs, then the implication is that the additional erosion control costs to meet the numeric NTU levels are not justified by the expected benefits. Yet, in other situations, such as NTU violations due to non-construction urban runoff, the implication of the standard is that the turbidity control costs are justified. This apparent inconsistency needs to be re-examined. Certainly, the total cost and distribution of costs of pollutant control can vary by source type and result in regulations that accommodate these variations. However, the acknowledged shortcomings of approved practices to adequately reduce turbidity strongly suggest that the Sedimentation Control Commission and the Environmental Management Commission should revisit the way this standard is written.