Managing stormwater in Oregon - graph

LimnoTech evaluated the effect of sampling frequency and number of sampling locations on uncertainty in pollutant concentrations, identifying the most efficient strategy to meet project goals.

Managing stormwater in Oregon

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Success Story

Helping Oregon Utility Comply with New Type of Watershed-Based Permit

Clean Water Services (CWS) is the sanitary sewer and surface water management utility for more than 473,000 customers in urban Washington County, OR and adjoining areas. CWS was issued a watershed-based, integrated, municipal NPDES Permit that covers its responsibilities in the Tualatin Basin—the first permit of its kind in the nation. LimnoTech assisted CWS in efficiently complying with permit requirements.


The watershed-based permit included a number of requirements, including revision of the management plan and development of a monitoring plan for stormwater. The permit also required evaluation of stormwater discharges to determine whether they were contributing to impairment.


LimnoTech worked closely with CWS to define specific goals for the monitoring plan and develop a strategy to efficiently meet those goals. The monitoring plan was targeted to determine compliance with the municipal separate storm sewer system permit, refine the selection and implementation of stormwater best management practices, and support an adaptive management approach to address water quality issues and a TMDL for the basin. LimnoTech also conducted statistical analyses regarding the reasonable potential that stormwater discharges were contributing to water quality impairment.


The stormwater monitoring plan was integrated into CWS’s comprehensive monitoring program, meeting both stormwater and other programmatic needs in a cost-effective way. The monitoring plan was designed to support an adaptive management approach to achieving the TMDL. LimnoTech’s assessment of the stormwater discharges is expected to allow CWS to avoid unnecessary future permit requirements.