- Departments H-Z
- Planning & Public Works
- Stormwater & Flooding
- Our Projects
- Plans and Studies
- Clarks Creek (TMDL) Project
Clarks Creek (TMDL) Project
Clarks Creek is a very important water resource. It provides habitat for five species of salmonids and is home to Tribal and state fish hatcheries. Currently, the creek does not meet standards for dissolved oxygen and fine sediment. To help address this concern, the Washington State Department of Ecology worked with the Puyallup Tribe of Indians, Environmental Protection Agency, and local stakeholders to develop a total maximum daily load, or TMDL, for the creek.
You can view the TMDL on Ecology's website. The TMDL identifies the maximum amount of pollution the creek can accept while still meeting regulatory standards. It then assigned specific targets to help reduce pollution and restore water quality.
The Clarks Creek Restoration Plan outlines the County’s strategy to comply with the TMDL and restore water quality to the creek. The Plan identifies capital projects and programmatic actions to treat stormwater flow and reduce sediment loads into Clarks Creek. It will be funded through a combination of local investments and state and federal grants.
The Plan also recommends a comprehensive reassessment of water quality after five years of implementation efforts. The Reassessment is now underway, and results will help the County to adaptively manage future water quality improvement efforts. You can view related documents to the right under our "Document Library".
Frequently Asked Questions
- What is a TMDL?
- What’s the difference between a TMDL and other types of water quality improvement plans?
- Is Clarks Creek the only TMDL in Pierce County?
- What are the main water quality problems in Clarks Creek?
- Would dredging fix the problem of excess sediment in Clarks Creek?
- How do the agencies charged with improving Clarks Creek know they are targeting the correct sources?
- What strategies are being used to address the impairments in Clarks Creek?
- Could excess iron cause the types of impairments found in Clarks Creek?
- Are nutrients from groundwater causing the impairments in Clarks Creek?
A TMDL, or total maximum daily load, is a regulatory term from the 1972 Clean Water Act. A TMDL is a type of study that determines how much of a pollutant a waterbody can receive and still meet water quality standards. If pollutant levels are higher than a waterbody can digest, then limits are imposed on how much of the pollutant can be discharged by stakeholders in the watershed. You can think of TMDLs as a pollution “diet” developed to guide a watershed back to health. If the TMDL is calculated correctly and the numeric targets are achieved for each pollution source, the water body should return to a healthy condition over time.
In Washington state, TMDLs are developed and administered by the Department of Ecology. The Environmental Protection Agency (EPA) then reviews and certifies the TMDL, or else develops and issues their own revised version. TMDLs may include any number of water bodies and pollution types. For instance, the Clarks Creek Dissolved Oxygen and Sediment TMDL addresses two separate water quality parameters in Clarks Creek and its four main tributaries (Rody, Woodland, Diru and Meeker Creeks).
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.
- How do the agencies charged with improving Clarks Creek know they are targeting the correct sources?
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.
- 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.