Publication Summary

The Washington State Department of Ecology conducted a total maximum daily load (TMDL) evaluation of the lower Nooksack River basin in 1997-1998. Because the lower river basin has a history of state bacteria standard violations, the TMDL focused on fecal coliform bacteria loading to the river from tributaries, sewage treatment plants, and other sources. Historical and TMDL data demonstrated the need for an aggressive approach to preventing fecal bacteria criteria violations.

The Washington State Department of Ecology conducted a total maximum daily load (TMDL) evaluation of the lower Nooksack River basin in 1997-1998. Because the lower river basin has a history of state bacteria standard violations, the TMDL focused on fecal coliform bacteria loading to the river from tributaries, sewage treatment plants, and other sources. Historical and TMDL data demonstrated the need for an aggressive approach to preventing fecal bacteria criteria violations.

The TMDL evaluation proposes fecal coliform bacteria targets more restrictive than the 100 cfu/100 mL geometric mean count criterion for Class A waters. A geometric mean of 39 cfu/100 mL is recommended for the lower Nooksack River. Compliance with this criterion should result in only 10% of the samples exceeding 200 cfu/100 mL, and a 48% reduction in annual bacteria loads. In addition, ten tributaries that are the major sources of bacteria loading to the river will require similarly stringent bacteria criteria to reduce their loads by 23% to 98%. A 4.5% reduction is recommended in upper watershed loads to meet the river TMDL target, and to ensure Class AA standards are met. Although a less significant source of bacteria loading, waste water treatment plants (WWTPs) will be required to undergo quality assurance testing on a quarterly basis, and they will need to meet a more stringent permit limit for bacteria. All dairies and animal feeding operations (AFOs) under permit have waste load allocations of zero.

Identifying and eliminating individual sources of contamination in Fishtrap and Bertrand creeks and other sub-basins that hold a high density of AFOs, dairies, and manured fields will be essential for the success of the TMDL. Also, a quick response to illegal discharges from manure lagoons, manure-spreading equipment, sewage pump stations, and WWTP outfalls will be required for the TMDL targets to be met. Limiting livestock access to waterbodies, correcting individual on-site systems, and controlling bacteria discharges to urban stormwater will also be necessary to achieve target compliance.

The recommended bacteria targets will bring Nooksack basin watercourses into compliance with Class A fecal coliform criteria, and will support recreational contact uses, as well as reduce the risk of drinking water contamination. Monte Carlo simulation results of a simple bacteria model for Portage Bay indicated that attaining the new bacteria target in the river would sufficiently protect water quality in the shellfish harvesting areas.

Link to EIM data for User Study ID NTMDL