Publication Summary

The Washington State Department of Ecology initiated a Total Maximum Daily Load for fecal coliform bacteria in North Creek, in south Snohomish County. Dry season concentrations higher than those in the wet season suggest that there is a continuous, steady component to the pollution loading. Since concentrations are relatively high during the wet season and flows are dramatically higher, there is also a storm-related component to the loading. Pollution sources in the basin are exclusively from diffuse sources (i.e., no municipal or industrial discharges). The predominant sources are agriculture, on-site disposal (septic) systems, and post-development activities attributable to urban development (e.g., domesticated animals).

The Washington State Department of Ecology initiated a Total Maximum Daily Load for fecal coliform bacteria in North Creek, in south Snohomish County. Dry season concentrations higher than those in the wet season suggest that there is a continuous, steady component to the pollution loading. Since concentrations are relatively high during the wet season and flows are dramatically higher, there is also a storm-related component to the loading. Pollution sources in the basin are exclusively from diffuse sources (i.e., no municipal or industrial discharges). The predominant sources are agriculture, on-site disposal (septic) systems, and post-development activities attributable to urban development (e.g., domesticated animals).

The best approach when developing control measures for these diffuse sources is to maintain or increase flow rates throughout the dry season while focusing on lowering concentrations in the water. Flow attenuation can be achieved in this watershed with detention ponds, establishing or restoring wetlands, and managing riparian corridors. A long-term monitoring strategy would be essential to track and evaluate the effectiveness of the source control measures.