Groundwater Protection

City staff testing groundwater well

Groundwater equals drinking water

One hundred percent of Olympia's drinking water comes from groundwater. Activities on the surface of the land have the potential to contaminate and deplete our groundwater.

Drinking Water Protection Areas (DWPAs)

DWPAs are large areas (of several square-miles) surrounding each of our water supply wells that mark their primary recharge areas. Federal, State, and county regulations, as well as Olympia's municipal code, are in place in these areas to protect our community's drinking water supply.

McAllister Wellfield

The McAllister Wellfield DWPA is located in north Thurston County about nine miles east of Olympia. The Wellfield supplies the City's entire water service area year-round, typically providing about 85 percent of the City's drinking water. The Utility developed the McAllister Wellfield in 2014 to replace the more vulnerable McAllister Springs source.

East Olympia

Three DWPAs in southeast Olympia protect three wells: Shana Park Well, Indian Summer Well, and Hoffman Well. Shana Park Well and Indian Summer Well are both treated and available for year-round use, although they are sometimes not used in the winter months. Hoffman Well is an untreated source, occasionally used on a seasonal basis. Together these wells provide up to about six percent of the City's water supply when they are operating.

Briggs Well

In East Olympia, a DWPA has been delineated for the planned Briggs Well, which is currently scheduled for completion in 2019. The well is planned to be located in the Briggs Village development near Ward Lake.

West Olympia

Two DWPAs in West Olympia protect three wells. Two wells in the Allison Springs DWPA provide about ten percent of the City's total supply, primarily between May and October. Kaiser Well is on standby only as an emergency supply.

DWPA Lookup Map


Using this map

Zoom in on an area or type an address in the search box to find out whether a property is with a Drinking Water Protection Area (DWPA) or to see how close a property is to a groundwater capture zone.

  • Areas in BLUE indicate a Drinking Water Protection Area (DWPA)
  • Areas in GRAY indicate parcels inside a Drinking Water Protection Area (DWPA)

How you can help protect our groundwater

Report hazardous spills immediately

Call the City's Spills Hotline at 360.753.8333 anytime (24/7) you witness a spill or suspect hazardous material has been discharged onto the ground or to Olympia’s streets or water bodies. Check out our Reporting Spills webpage for things to watch for and notes to take that will help with the follow-up investigation.

In the event of a large spill (such as from vehicle accidents or heating oil tanks) call 9-1-1

For spills that occur outside the City limits, please call Thurston County at 360.867.2099.

Septic systems

Most of the wastewater generated within the City of Olympia is conveyed to regional collection and treatment facilities via a sanitary sewer system. However, many privately owned and maintained septic systems are also used to treat and dispose of wastewater. And unfortunately, when a septic system is improperly maintained, it can be a source of contamination to groundwater.

A septic system treats and disposes of liquid wastewater from single- and multi-family homes, businesses, schools and other dwellings. The wastewater does not go to a regional collection and treatment facility (such as those owned by LOTT Cleanwater Alliance). Instead, the wastewater enters a septic tank and drain field for initial treatment, and then seeps into the ground where it is further treated by organisms and soil particles. If the septic system isn’t functioning or maintained properly, the wastewater can seep untreated into our regional groundwater resources. 

There are about 4,150 privately owned and maintained septic systems in use within Olympia’s city limits and urban growth area. Many thousands more are in use outside these City boundaries.

To see where your wastewater goes and specifically to see if you use a septic system, enter your address in our Sewer Lookup Map.  If you live within a City drinking water (wellhead) protection area - which is described under the next question - and use a septic system to dispose of your wastewater, it is especially important to properly maintain your septic system. 

Throughout Thurston County, groundwater is our main source of drinking water.  This is true whether we receive water from a city water system, a private water system, or a privately owned well. So it benefits everyone if we’re all careful to take steps to protect our groundwater, including properly maintaining septic systems. 

Properly functioning and maintained septic systems can help protect Olympia’s and all of Thurston County’s regional groundwater and drinking water supplies. Conversely, poorly maintained septic systems can seep untreated wastewater into soil, resulting in contaminated groundwater. And contamination can come from many household, yard-care and personal care and health products we all typically use, such as cleaners, paints, fertilizers, pesticides, and medicines. 

Olympia’s water supply comes from nine groundwater wells located within seven drinking water protection areas (DWPA).  These large areas – each several square miles in size – surround the City’s wells to mark their primary groundwater recharge areas.  Rainfall, snowmelt, storm water runoff, and seepage from septic systems within these recharge areas replenishes our groundwater supply.  A map of Olympia’s drinking water protection areas shows they extend both inside and outside the City’s limits and urban growth area.  Check to see if you live within one of our drinking water protection areas:

Safely maintaining a septic system can be simple:
• Don’t put strong household chemicals, paint, pesticides, fertilizers, and similar hazardous products down sinks or toilets. Keep grease and coffee grounds out of the system.
• Don’t flush diapers, cigarette butts, tampons or condoms down the toilet.
• Don’t use septic system additives or drain cleaners.
• Don’t park on or build patios or carports over your drain field.  (Doing so may break pipes and compact the soil.) 
• Use less water. (Too much water can shorten the time wastewater spends in the system.)
• Inspect your system once a year; most need to be pumped every 3-5 years.  An inspection may show you need to pump more or less often and can help find problems while they are still easy to fix.


General information about septic systems can be found on Thurston County’s Septic System website or by calling the County’s Septic Help Line at 360.867.2669.  The City’s Wastewater Utility has information about our Septic to Sewer Program, Septic Tank Effluent Pump (STEP) systems, and where to dispose of RV waste.

Your landscape matters

Using low-maintenance, native and drought-tolerant plants in your landscape is a sustainable way to help protect our groundwater. These easy-to-care-for garden plants require less water and typically need very little (if any fertilizer) - and even rarely are pesticides needed. Download our Landscape Plans Packet for a variety of easily adaptable, pre-made landscape plans and helpful plant lists. And visit our Storm and Surface Water Utility webpage to learn more about low impact development rain gardens, vegetated rooftops, rain barrels and other pollution prevention actions.

Fertilize wisely

Nitrates from lawn fertilizers pose a major threat to our drinking water. If you want to fertilize your lawn or garden, it's important to pick the right time and to use the right type and amount of fertilizer for long-lasting results that also protect our water resources.

  1. Pick the right time
    For a spring application, wait until mid-May or early June when heavy rains have passed so that less fertilizer will be wasted by seeping unused into the ground. Fertilizing at this time also helps avoid a growth surge when the lawn is already vigorously growing so you won't have to mow as often. In the fall, September or early October is also a good time to fertilize, before the heavy rains start.
  2. Pick the right product
    Fertilizer nutrients in "slow-release" forms are available to plants over a longer period of time, meaning fewer nutrients are wasted or lost as pollutants. Look for products that are organic or polymer-coated or are made from sulfur, isobutylidene diurea (IBDU), methylene urea, and "ureaform" and have at least 50% water-insoluble nitrogen.
  3. Choose the best N-P-K ratio
    Numbers like 8-3-1 or 32-3-3 are typically provided somewhere on the back of the bag. The first number tells you the percentage of Nitrogen (N) in the product. Look for a product that has a balance close to a proportion of 3-1-2.
  4. Use the right amount
    Compare your lawn's actual square footage with the treatable square footage on the fertilizer bag. Often times you will not need to use an entire bag.
  5. Only use about 1 pound of nitrogen each time you fertilize
    To figure out how to get 1 pound of Nitrogen on your lawn, do the following calculation. Look at the first number in the N-P-K ratio on your bag. Divide 100 by this number. This number will tell you how much of the fertilizer needs to be applied to 1,000 square feet to supply 1 pound of actual Nitrogen. For most solid fertilizers, 1 pound equals about 4 cups of product.

    And get this! If you mulch-mow, grass clippings add about 1 pound of Nitrogen, so subtract an application or use 3/4 of a pound of Nitrogen each time.

Rules for new developments

All non-exempt new developments within a Drinking Water Protection Area are required to meet certain standards to help prevent groundwater contamination.

For complete details or more information about any of the following requirements see OMC 18.32.200-18.32.240

Minimum mitigation standards

  1. A hazardous materials management (spill) plan is required if the project will be using, storing, handling or disposing of hazardous materials. The minimum quantity thresholds for this requirement and detailed elements of the spill plan are provided under OMC 18.32.235.
  2. Landscaping and irrigation standards of OMC 18.32.225 include the following:

    a. Restrictions on the use of highly water-soluble fertilizers.

    b. Limitations on total turf area and requirements for the use of native and drought-tolerant plants. See our Landscape Plans Packet for plant options.

    c. Irrigation systems designed and managed to maximize efficient use of water, with an irrigation consultation required when the system is installed.
  3. A report that inventories existing wells on the property and decommissioning procedures if needed.
  4. Granting City access to the property to provide outreach and informational materials, and to ensure compliance with these requirements.

Dedicated groundwater monitoring well
A groundwater monitoring well may be required where storm water is infiltrated, or where other groundwater contamination risks or monitoring needs are identified. View details in the Engineering Design and Development Standards (EDDS)

Hydrogeological reports
When the City determines that risks from a project or activity are not well known, a hydrogeological report may be required. This report provides City staff with information about site geology, groundwater quality and flow, surface water, and possible effects from the proposed project.

Outside City limits?

Land within our Drinking Water Protection Areas that falls outside of the Olympia City limits and urban growth area are governed by either Thurston County, the City of Lacey or the City of Tumwater Codes.


Contact Susan Clark at 360.753.8321 or

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