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Thurston County, Washington

The content on the Thurston County website is currently provided in English. We are providing the “Translation” for approximately 10 languages. The goal of the translation is to provide visitors with limited English proficiency to access information on the website in other languages. The translations do not translate all types of documents, and it may not give you an exact translation all the time. The translations are made through an automated process, which may not result in accurate or precise translations, particularly of technical and legal terminology.

Public Health and Social Services

Pollution Identification Correction (PIC)

Thurston County places a high level of importance on protecting and restoring water resources within its jurisdiction. The Pollution Identification, and Correction Program works throughout Thurston County to implement this goal. Through investigatory work, the PIC team works to eliminate or mitigate contamination to waters of the county.


  1. Identification of High-Risk Areas: Utilizing historical water quality data in combination with density and public use, the PIC Program concentrates on areas where substandard water quality is a high risk for Public Health.
  2. Investigatory Assessment: In high-risk areas, records research, site visits, sampling, and investigatory practices are performed to characterize and discover pollution sources.
  3. Remediation: Community engagement through partnership and education is the preferred method our PIC team employs. If needed, enforcement action will be taken to ensure degradation of the waters of our county is corrected.

Focus Areas

There are a multitude of possible pollution sources that can impact water quality. Below is a list of the main sources of concern for the PIC team – with fecal bacteria being our leading pollution source of concern, to ensure surface water and shellfish tissues are safe for human contact and consumption.

  • Nonpoint – Agriculture, Improperly Managed Animal Waste
  • Point Sources – Septic Systems, Illicit Discharges

Sanitary Surveys 

A community focused review of properties in our identified area of concern. Members of our team will walk with the homeowner over their parcel while providing education of required and best management practices in relation to our focus areas. For administrative purposes, historical record keeping, and grant funding, a survey form will be filled out by a member of our team, and other documentation or pictures may be taken during this walkthrough. Our team will direct you to the applicable subject matter expert and answer any questions you may have during this walkthrough.

Sanitary Surveys are performed to provide technical assistance, diagnose suspected issues, and be a proactive public health measure. We will start with your septic system, then move through the rest of our focus areas. It is important to note that sanitary surveys are not disciplinary focused but are intended to marshal action towards clean water in the county.  

Shoreline Surveys 

Fresh water discharges from sources such as streams, seeps, or bulkhead pipes entering Puget Sound are sampled to identify locations of human pollution. Multiple samples of potentially polluted water are taken to establish trends and verify results of these discharges – in both the wet, and dry season. As such, shoreline surveys are our baseline investigatory tool to reveal unidentified pollution sources.

  • Wet weather conditions: Water is flowing off parcels and stormwater is flowing in roadside ditches or storm systems and is representative of typical wet weather conditions.
  • Wet weather assessments can identify OSS failures caused by high seasonal groundwater and surface water drainage issues.
  • Dry weather conditions: A lack of the previously mentioned conditions, i.e., water is not flowing in roadside ditches or storm systems and is not comingled with precipitation.
  • Dry weather assessments can identify problems in areas where stormwater masks fecal pollution sources or where residences are only occupied in the summer.

It is important to note that shoreline surveys require coordination between property access, weather and flows, and laboratory capacity – this leads to a delayed, non-linear completion of shoreline portions. Identified pollution sources are thus corrected in combination with our progression through the shorelines of the county. Our goal is to sample the entirety of Thurston County shorelines every six years. You can find the historically performed and recent surveys detailed below:

  • 2022 – Totten Inlet – 19 hot spots 169 sample locations, 244 samples taken
  • 2022 – Eld Inlet – 41 hot spots, 252 sample locations, 424 samples taken

For a detailed explanation of our program – Thurston PIC Manual      


The Pollution Identification, and Correction (PIC) Program works with state and local agencies, non-governmental organizations, and private citizens throughout Thurston County to protect water resources. Below are a few of these entities.

  • Department of Ecology (DOE) – Washington’s environmental protection agency, that is committed to protecting, preserving, and enhancing Washington’s environment for current and future generations. Spills, shoreline management, and water quality are collaboration points between our entities.
  • Department Of Health (DOH) – Washington State’s overarching decentralized public health system. The Department of Health's mission is to protect and improve the health of people in Washington State They provide strategies and expertise to local health jurisdictions, while pursuing state focused excellence in health.
  • Lacey, Olympia Tumwater, and Thurston County Clean Water Alliance (LOTT) – LOTT provides wastewater management services for the urban area of north Thurston County, Washington. This includes wastewater treatment and production of Class A Reclaimed Water.
  • Thurston Conservation District (TCD) – A non-regulatory subdivision of state government, which matches local natural resource concerns and needs with applicable technical assistance and financial resources to solve on-the-ground conservation issues with proven effective conservation practices. They are our subject matter expert in regard to agricultural practices, stewardship, and shoreline management.
  • Stormwater Utility – Thurston County’s public work division that maintains and manages the public network of storm runoff systems.
  • Municipalities – Olympia, Lacey, Tumwater, Yelm, Rainer, Tenino, Bucoda.

Loan Assistance

Below are a few entities that provide financial assistance to homeowners, communities, and business owners. Each has different qualification requirements for eligibility. Thurston County is not involved in these programs; direct all questions about the assistance programs to their representatives.

  • Craft3: Craft3 is a nonprofit lender – a community development financial institution (CDFI) – that uses capital to build resilience, lessen the racial wealth gap, and expand economic opportunity for all.
  • RCAC: RCAC provides training, technical and financial resources and advocacy so rural communities can achieve their goals and visions.
  • USDAThis program provides funding for clean and reliable drinking water systems, sanitary sewage disposal, sanitary solid waste disposal, and storm water drainage to households and businesses in eligible rural areas.


The Water Quality Program protects public health by monitoring surface and groundwaters of the county to identify trends and assess water quality, identify contaminants of concern (E. coli bacteria, nitrate-nitrogen, etc.), and advise the public of health risks. Preserving the quality of the waters of our county through correcting or mitigating pollution sources is our aim. There are many programs working to keep your water safe, learn about our work and how you can protect our water here.

Ambient Monitoring Program

The ambient water quality team monitors lakes and streams throughout Thurston County. Primarily tracking physical, chemical, and biological characteristics to create an overview of the trajectory and current health of our watersheds. All water quality data gathered is available to the public and shared interagency.

  • Monitor 12 stations on 9 lakes to determine long term (ambient) water quality.
  • Monitor 22 stations monthly and 11 quarterly on 33 streams determine long term (ambient) water quality.
  • Prepare reports that evaluate results and trends.
  • Monitor and respond to algae blooms on as many as eight different lakes each year.
Image of Budd Inlet at sundown

There are multiple indicators of water quality that our Ambient team samples for. Below you can find a brief synopsis for each indicator based on the type of water body sampled.


Water Quality Index 

The Water Quality Index (WQI) is designed to evaluate general water quality relative to expected standards. The WQI combines seven measures of water quality:

  • Four measure components are tied to the Water Quality Standards, including dissolved oxygen (DO), pH, temperature, and E. Coli (EC) bacteria).
  • Three measured components do not have numeric standards but relate to general ecosystem function. They are nitrogen, phosphorus, and turbidity.

The WQI summarizes data collected into scores from 1 to 100, with lower scores reflecting poor water quality and higher scores indicating cleaner water. Scores of 80 and above are sites considered the lowest concern for water quality impairment. Scores from 40 to 79 signify sites of moderate concern. Scores of 39 or less are sites where water quality did not meet expectations and are the highest concern for impairment. This key shows the values and coloration used for this report:

Water Quality Index Key

The concentration of Escherichia coli (EC) bacteria is used as an indicator of the presence of viruses and other pathogens in surface and ground water. The water quality standards for bacteria have two criteria: the geometric mean must not exceed 100 CFU/100mL and an upper limit value for no more than 10% of the samples to exceed 320. To calculate the central tendency of a sample distribution, the geometric mean is used because it tends to dampen the effect of very high or very low values.

While E. coli bacteria is the current primary contact indicator in the state Water Quality Standards, the Department of Ecology has not incorporated it into the current WQI metric. Therefore, some of our reports will provide a map of each watershed with individual sample sites colored according to the following key, to represent presence of E. Coli:

E.Coli Index Key


Dissolved Oxygen 
  • Dissolved oxygen (DO) is a major indicator of water quality. Aquatic life depends on an adequate level of oxygen dissolved in water to survive. Amount of available dissolved oxygen can depend on many factors including temperature, aquatic plants, and flow rate.
  • pH is a measure of the acid balance of a solution and is defined as the negative logarithm of hydrogen ion concentration. In unpolluted waters, pH is controlled by dissolved chemical compounds (mineral and organic materials) and biological processes (photosynthesis, respiration, and decomposition). Atmospheric deposition and pollution also affect pH. The pH of surface water affects the solubility and availability of some nutrients and toxic metals.
  • Water temperature affects many physical, chemical, and biological processes in aquatic systems. Warmer water holds less available dissolved oxygen necessary for aquatic life. Temperature is used as an indicating factor for stream health and ability to sustain different types and stages of life, especially for spawning salmonoids.
  • TCEH samples collected from lakes are analyzed for total phosphorus (TP) and total nitrogen (TN) as excess nutrients in surface waters can negatively affect public health and recreation.
  • Compared to the rich supply of other elements required for nutrition or structure, phosphorus is the least abundant and most commonly limits biological productivity. The State of Washington does not have established action levels for total phosphorus.
  • Nitrogen is also limiting to productivity, but supplies are more readily augmented by inputs from external sources. The State of Washington does not have established action levels for total nitrogen.
  • Suspended and dissolved materials in water cause light to be scattered rather than transmitted in straight lines. Turbidity measures the scattering of light and estimates the amount of suspended and dissolved materials such as silt, clay, finely divided organic and inorganic matter, chemicals, plankton, and other microscopic organisms. Excess suspended materials can prevent light penetration, interfere with fish activity, and once settled to the stream bottom, can smother eggs and invertebrate habitat. Turbidity standards are based on nephelometric turbidity units (NTU) over background. The Washington State standard is the same for the three aquatic life uses, both freshwater and marine, at Thurston County water quality sites. The maximum turbidity criteria shall not exceed:
    • 5 NTU over background, when the background is 50 NTU or less
    • An increase of 10% when the background is more than 50 NTU


Trophic State Indices (TSI)

The most used method to classify lakes is called the Carlson’s Trophic State Index (Carlson, 1977). Based on the productivity, this method uses three index variables: transparency (secchi disk depth), chlorophyll-a, and phosphorus concentrations. The values our team finds for these index variables are used to calculate index values for each trophic classification.

Trophic State Indices table


Color can reveal information about a lake’s nutrient load, algal growth, water quality and surrounding landscape. High concentrations of algae cause the watercolor to appear green, golden, or red. Weather, rocks and soil, land use practices, and types of trees and plants influence dissolved and suspended materials in the lake. Tannins and lignins, naturally occurring organic compounds from decomposition, can color the water yellow to brown.

TCEH observed the color of the water against the white background of the Secchi disk at one-meter depth and compared it to the Custer Color Strip (Figure 1).

Figure 1. TCEH compared the color of the water on the Secchi disk (1m) to the Custer Color Strip 

Custer Color Strip
  • Transparency of water to light has been used to approximate turbidity and phytoplankton populations. Secchi depth is closely correlated with the percentage of light transmission through water. The depth at which the Secchi disk is no longer visible approximates 10% of surface light; however, suspended particles in the water affect accuracy. TCEH recommends visibility of at least 1.2 meters, or four feet, at public swimming beaches.
  • TCEH samples collected from lakes are analyzed for total phosphorus (TP) and total nitrogen (TN) as excess nutrients in surface waters can negatively affect public health and recreation.
  • Compared to the rich supply of other elements required for nutrition or structure, phosphorus is the least abundant and most commonly limits biological productivity. Lakes in this region experience undesirable algae growth when the annual average surface phosphorus level reaches 30 µg/L (Gilliom, R.J. 1984). The action value is 20 µg/L (WAC 173-201A-230, 2021) at lower mesotrophic level of the lake.
  • Nitrogen is also limiting to lake productivity, but supplies are more readily augmented by inputs from external sources. The State of Washington does not have established action levels for surface total nitrogen.
  • Cyanobacteria, also known as blue-green algae, is a class of single celled organisms found in fresh and salt water. Warm temperatures, sunlight, and excess nutrients can cause blue-green algae to reproduce rapidly, creating blooms. These blooms may contain toxins, known as cyanotoxin, which can cause sickness in people and animals.
  • Washington State Department of Health sets recreational guidelines for freshwater cyanobacteria blooms when toxins are determined to be present (Table 2). TCEH samples local lakes in response to visible blooms in accordance with EPA standards. When these samples contain toxins above recreational guideline, warning signs are posted at local access points and public notices are published.


The figures below detail the locations sampled throughout Thurston County. It is important to clarify that sampling locations can and do change based upon water quality data, funding sources, resources and priorities of the County.

Map Of Stream Sampling Sites

Figure 1: Stream Sampling Locations

Map Of Lake Sampling Sites

Figure 2: Lake Sampling Locations

Contact us at 360-867-2685 or email us at if you have additional questions.

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