Tillamook’s Storm Water Management Challenge
The city is currently engaged in a major construction project to build a new wastewater treatment plant. But even as that is under way, another major project must soon be addressed: our aging storm water system.
In 2004, the City of Tillamook undertook a study of the storm water sewer system that carries away storm runoff. The study was done because of increasing requirements under the Federal Clean Water Act, which is overseen through the Authority of the Oregon Department of Environmental Quality (DEQ). Under these regulations, cities must prevent polluted storm water from being discharged into local rivers and streams. And this year, DEQ has ordered the city to take steps to put a plan into action.
Tillamook is at the confluence of several rivers and streams. The city, which has grown up over more than 100 years, has a collection of storm sewers that were installed at various times – many without the planning needed to ensure proper operation. The 2004 study was designed to develop a master plan to correct the city’s storm water system deficiencies. Its primary purpose was to describe existing water quality problems in Tillamook Bay, identify the source points for these problems in Tillamook City’s storm water discharges and propose solutions.
As part of the study, engineers mapped the existing system and recorded the size and condition of underground storm water pipes, as well as junctions where multiple pipelines converge. Then the study team looked at seasonal storm water loads, factored in variations over years and periodic flood data. They used all of this information to map out a general plan for improving the system and correcting problem areas.
Study Findings
Among the findings of the study were the following:
- Most of the City’s runoff is generated at point sources. That is, it is deposited into rivers and streams from specific “outfall” pipe points. There are not large amounts of water that run off into streams from random surface sources.
- Suspended sediments in most City runoff are at very minor concentrations and have little impact compared with stream sediments generated during flooding events. The City only contributes about 1-2% of the total suspended sediments to the Trask River and Hoquarten Slough.
- E. coli bacteria in runoff from some of the City’s outfalls appear to exceed DEQ’s regulatory limit for the Trask River.
- Some spots were identified in which the storm sewer and the sanitary sewer are cross-connected, allowing biological contaminants to enter the storm water discharge and allowing high volumes of storm water to enter the sanitary sewer, causing water flow surges at the treatment plant during storms.
- The City’s storm runoff accounts for from 30% to 40% of the total bacteria loadings in the Trask River.
- It is estimated that between 10% and 15% of the total bacteria loading in Tillamook Bay arises from the City’s storm runoff.
Recommendations
The study made general recommendations for $1.42 million in high-priority improvements to the storm sewer network and another $1.82 million for improvements to improve water flow, as well as just under $900,000 in other lower-priority projects – all in 2004 dollars.
Funding Challenges
The 2004 study also acknowledged that the City had no funding mechanism in place to make the needed improvements. However, DEQ is now asking the city to address the system deficiencies and find a way to pay for improvements. These discussions have begun.
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