TMDL Water Quality Pollutants

 Temperature • Bacteria • Mercury

The Upper Willamette Subbasin (see below) has stream segments that are listed under section 303(d) of the US Clean Water Act, that are exceeding water quality criteria for temperature, bacteria, dissolved oxygen, turbidity and toxics (mercury specifically in Benton County). County stormwater drains to these waterbodies as well as several wastewater and industrial users.

Source: Oregon DEQ (2008 [TMDL Process Visual] )

The following provides an overview of the TMDLs that Benton County is required to improve through the current Benton County Water Quality Implementation Plan and TMDL Water Quality Tracking Matrix (2008; with pending 5-year required update in 2013). The following provide causes and work that Benton County staff are completing to address water quality impairments:


Temperatures are documented by Oregon DEQ to be higher than historically, and is caused by a variety of human induced and environmental changes over time including: removal of shade producing vegetation along streams, discharging warmer water, reducing streamflows through pumping and drought and other factors. At times, the Willamette River and its tributaries are determined to be too warm to support healthy salmon and trout and other aquatice live. Elevated stream temperatures have contributed to the decline of threatened Coho, spring Chinook, and winter steelhead. Warmer water not only interferes with migration and spawning, but also makes the salmon and trout more susceptible to disease. Warm water also decreases chances of juvenile survival, affects egg and embryo development, alters juvenile fish growth rates and decreases their ability to compete for habitat and food with fish that are more tolerant of the temperature changes.

As documented in the table above, every stream with an established TMDL in Benton County is considered 'temperature limited'. The following actions have occurred to improve stream temperature including:

  • Temperature monitoring: summer monitoring (July-September) began in 2011 in partnership with OSU faculty. There is currently no required temperature monitoring, however a long term goal for county staff is to increase temperature monitoring in partnership with local cities and non-profits that are also collected water quality data (including temperature);
  • Outreach and Education: communities are informed about actions that they can take to protect water temperature such as protecting native riparian vegetation and not pumping seasonal streams during low flow seasons;
  • Stream setback requirements: Benton County requires all structures to be 25-50 linear feet from the top of the stream bank to support protection of property and stream channel movement/vegetation;
  • Riparian and Wetlands Project: Starting in 2009 Benton County Community Development was awarded a US EPA Wetlands Program Development grant funding to support an inventory to document current riparian resources and associated wetlands. The project consisted of over 16 community meetings, and extensive data collection on a range of scientific and social issues associated with long term riparian/wetland protection and enhancement Learn more about the current status of the project and stay up to date by joining the mailing list.

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In Benton County, bacteria (E. coli), among other pollutants, have been identified as a problem for water quality. The Water Quality Implementation Plan (WQIP) describes the actions Benton County will undertake to reduce pollution in order to restore and protect water quality in the Upper Willamette Subbasin. On-site sewage disposal systems, more commonly known as septic systems, serving rural properties can fail and contribute bacterial contamination to both ground water and surface water. Benton County maintains a staff of Registered Environmental Health Specialists that evaluate both residential and commercial properties and issue permits for new installations, repairs, and alterations. They issue Authorization Notices to place into service, reconnect to, change the use of, and increase the projected daily sewage flow into existing on-site systems and issue Existing System Evaluation Reports. They also respond to sewage complaints made by the public.

There are several problem areas in the county where older septic systems are suspected of contributing to groundwater pollution. These areas are identified in the Environmental Assessment Priority List (EAPL) maintained by Benton County. While the EAPL identifies multiple environmental health issues such as sewage, drinking water, hazardous waste, etc, the following table identifies areas potentially impacted by septic systems:

#1 South Third Street Corrected - Sewer
#2 Whitson Acres - No current action
#3 SW Corvallis Urban Growth Boundary - No current action
#4 North Albany - No current action
#5 Philomath Northern UGB - No current action
#6 Pioneer Village - No current action
#7 Fairplay Area - No current action
#8 Firview Subdivision - No current action
Note: Refer to Benton County Health Department, Environmental Assessment Priority List 2002, 2011 update for further details.

In addition, Benton County established an agreement with Oregon Department of Agriculture, Water Quality Division (ODA)that directs county staff to report agricultural related water quality issues (often associated with fecal coliform contamination from livestock) directly to ODA. Review the Agricultural Water Quality Complaint partnership.

Livestock and improperly functioning septic systems can increase various types of bacteria including fecal coliform in water quality limited streams.  Even kennel operators need to know how to manage their animal waste products to do their part.  A DEQ Fact Sheet on kennels is included in the documents below.  A factsheet on handling Mud and Manure is also included as well as a link to a Rural Living Handbook produced by the Benton County Soil and Water Conservation District.

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Mercury is a naturally occurring element in Benton County’s soils. Coal and other fossil fuels also contain mercury, which is released into the atmosphere when the fuels burn. The mercury in the air eventually falls to land, and is washed into streams along with the mercury naturally occurring in the soil. To reduce the amount of mercury found in Benton County’s waterways, soil erosion should be minimized and less fossil fuels should be burned. Currently, there are no known direct sources of mercury contamination within Benton County’s jurisdiction. The County recognizes that there are numerous potential direct and non-point sources of mercury but nearly all of the recognized sources fall under the authority of other jurisdictions and agencies. Benton County has developed an Erosion and Sediment Control program as part of the Benton County National Pollution Discharge Elimination System (NPDES) program, in addition to several other best management practices

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