Clarks Creek (TMDL) Project

The Department of Ecology began the process of developing the Clarks Creek TMDL in 2010. TMDLs can be very expensive and difficult to develop, so Pierce County proposed an alternative approach called a Straight to Implementation strategy. Ecology declined the County’s offer, embarking on the multi-year process to develop a formal TMDL. During that time, EPA was developing policy guidance to allow for alternative water pollution control strategies. EPA issued a policy memorandum in 2013, outlining the importance of alternative plans and encouraging states to begin using them by 2018. An Alternative Plan often allows implementing agencies greater (local governments) flexibility to enact pollution control measures more quickly, saving significant time and resources. Determining what type of alternative plan is appropriate is a case-specific decision made by the State and the implementing jurisdiction. Alternative plans include Section 319 nonpoint control plans, Category 5r restoration plans, Straight to Implementation plans, Source Water Protection plans and Category 4b plans. 

EPA and Ecology now support the development of Alternative Plans to encourage the most effective means for enhancing water quality protection. Ecology recognizes there are other approaches that are more sensitive to resource constraints and local needs. Ecology supports the development of Alternative Plans if they are suitably designed to treat the impaired waterbody, and include specific implementation actions to expedite restoration. Under a TMDL alternative program, the water body would remain on the 303(d) impaired waters list until the water quality standards were re-attained. During that time, the TMDL development is deferred as long as satisfactory progress is maintained.

For example, an Alternative Plan may be the more effective approach for improving water quality when the causes of the impairment are easily identified. Often, the proposed solutions are based on well-established best practices that have broad stakeholder support. The County is now in the process of developing a Category 5r restoration plan for Clover Creek. This will include enhanced monitoring and analysis to determine pollutant sources and develop clean water targets. It will also emphasize proven and effective strategies known for improving water quality. 5r plans, like all Alternative Plans, must provide Ecology, EPA, and local stakeholders reasonable assurance that the Plan will be successful once implemented. 

In the case of Clarks Creek, Ecology did not believe a TMDL Alternative Plan would be sufficient. Alternative TMDL strategies were just emerging as a new approach in Washington State at that time. The formal TMDL development for Clarks Creek was well underway when EPA issued their 2013 policy memorandum. That being the case, EPA certified the Clarks Creek TMDL in 2014, Pierce County submitted its TMDL implementation Plan in 2017, and Ecology approved it in 2019.

No. Clarks Creek is one of several existing TMDLs in Pierce County. Others include:

• Inner Commencement Bay Dioxin TMDL – 1992
• Wapato Lake Total Phosphorus TMDL – 1993 
• Puyallup River BOD and Ammonia-N TMDL – 1994 
• Clarks and Meeker Creek Fecal Coliform TMDL – 2004
• Nisqually River Bacteria and Dissolved Oxygen TMDL – 2005 
• Upper White River Sediment and Temperature TMDL – 2006
• South Prairie Creek Fecal Coliform TMDL – 2006
• Puyallup Watershed Fecal Coliform TMDL – 2011
• Clover Creek DO, Fecal Coliform, and Temperature TMDL Alternative – Under Development
• Lower White River pH TMDL – Under Development

According to Department of Ecology there are 135 TMDLs approved or in development statewide.

Clarks Creek is impaired for two pollutants, sediment and dissolved oxygen. These impairments are based on criteria developed by the State to protect salmon, primary contact recreation (swimming), and domestic water supply. Numerical water quality standards do not yet exist for fine sediment, but Ecology determined there is excessive fine sediment in Clarks Creek compared to other reference streams. Measurements also show that dissolved oxygen occasionally falls below standards during both summer and winter.

It is possible that dredging Clarks Creek could improve water quality by removing the deep, fine sediment deposits that exist throughout the mainstem. However, dredging does not address the sources of sediment, so the creek would likely fill with sediment again over time. Typically, dredging projects are considered to be a complex and expensive project to permit and implement, and may require periodic maintenance dredging. In addition, dredging is often an extreme option with serious impacts to water quality, channel stability and fish habitat. Therefore, dredging Clarks Creek has not been the preferred approach.  

The City of Puyallup is currently conducting a dredging feasibility study with Northwest Hydraulic Consultants. This report will provide additional information to help evaluate whether dredging may be a cost-effective and sustainable strategy for Clarks Creek in the future.

Between 2010 and 2013, Ecology reviewed existing data, conducted water quality monitoring, and employed water quality computer models called HSPF and QUAL2Kw to evaluate the sediment and dissolved oxygen impairments in Clarks Creek. They also compared Clarks Creek to reference streams in other Puget Sound lowland areas that supported healthy fish habitat. They issued their findings in a 2014 TMDL study report. The study showed that reducing the volume of untreated stormwater runoff, reducing sediment loads, increasing riparian shade, and removing elodea would ultimately result in Clarks Creek re-attaining water quality standards. 

The Clarks Creek Restoration Plan, which outlines how the County will achieve the pollutant targets established in the TMDL report, also includes a 5-Year Reassessment Study. The Reassessment involves a comprehensive monitoring program to address key data gaps and support more robust modeling using a combination of QUAL2Kw, HSPF, and HEC-RAS. The monitoring and modeling results will improve our understanding of the watershed. 

At the end of 2020, Pierce County completed the monitoring program required by the 5-Year Reassessment Study. Data analysis and modeling will be completed by the end of 2021. Once completed, the 5-Year Reassessment Study will help us assess whether the actions and targets in the TMDL report will achieve water quality standards, or whether refinement of those actions and targets are necessary restore water quality in Clarks Creek.

Several strategies have been employed to address impairments in Clarks Creek. 

These include:

• Installing new stormwater facilities to capture and treat runoff,
• Retrofitting older stormwater facilities to improve capacity and treatment level,
• Improved facility maintenance to ensure optimal performance,
• Constructing in-stream structures to stop erosion and capture fine sediments (visit the Rody Creek, Diru Creek, and Clarks Creek bank stabilization project websites for more information),
• Using regenerative-air street sweepers to prevent fine sediment from entering the creek,
• Manual removal of invasive elodea from the streambed,
• Identifying areas for improved riparian shade coverage,
• Education and outreach to reduce nonpoint pollution sources,
• Testing in-stream fine sediment removal technologies,
• Comprehensive monitoring and analysis to identify water quality stressors.

This issue was not specifically evaluated in the TMDL study, and currently there are no available data to support the idea that iron levels are a key driver for water quality impairments in Clarks Creek. High concentrations of both iron and manganese are quite common in glacial aquifers like those found in our region.

In 2020, nutrient levels measured in groundwater springs flowing into Clarks Creek were not high enough to think they are causing the impairments in Clarks Creek. It is true that excess nutrients in the creek likely encourage elodea growth and other factors that can reduce dissolved oxygen levels. However, the level of nutrients measured in groundwater samples from Maplewood Spring is low. Pierce County monitoring data show that nutrient loads from surface runoff and nonpoint sources (such as pet waste, fertilizer and fine sediment) are often much higher than levels seen in groundwater. That is why the TMDL study included targets for capturing and treating stormwater and improving riparian buffers.