skip to main content

Public Health - Seattle & King County

Resident Self-Testing Protocol for testing soil

Some areas of King County, including Vashon-Maury Island and the adjacent King County mainland cities may have elevated levels of arsenic, lead and cadmium. This protocol has been developed to guide property owners and residents who would like to test their own soils.

Where to sample your soils

Levels of contamination will probably be different from one place to another on a property depending on the original amount of contamination, and subsequent soil disturbance. Because of that expected variation, four to six soil samples, spaced some distance apart, will provide better information about an individual property than a single sample.

Your choices about where to sample depend on the questions most important to you. For example:

  • If you want to know what the highest concentrations on your property are, sample in the areas where there has been the least animal, human or soil disturbance activity.

  • If you want to know what the concentrations are in areas used by children, pets, or others, sample those areas, knowing that the soil disturbance may mean you will get less information about the highest levels of contamination.

  • If these do not apply to your situation, you can sample from various well-spaced locations on your property.

Some areas should NOT be sampled because they may not give meaningful results. These would include:

  • Soils within six feet of a building. They are likely to be too disturbed to provide useful information.

  • Areas within 50 to100 feet of heavily traveled roads.

  • Areas where soil was recently brought in.
Materials you need
  • Make a simple drawing of where you are going to sample, and assign a unique code to each location to serve as an identifier. For example, you can devise your own code using letters, numbers, compass directions or any combination of these. Samples must be identified by this code. Distances can be estimated by pacing. Show relationships to buildings or other landmarks.

  • Collection containers - clean self-sealing type bags such as ZipLoc® bags or carefully washed glass jars with screw-type lids. Labs may provide sampling containers if asked. Use two self-sealing bags or one glass jar for each sample taken.

  • A clean spoon for each sample.

  • Writing paper that will show your name, address, date and code/identification number for each soil sample taken.
Sampling method
  • Remove surface vegetation from an area two to four inches in diameter.

  • Use a clean wooden, plastic or stainless steel spoon to take all the soil from the top two inches of the cleared area (use a separate spoon for each sample, or wash with soap and water between samples). Put four to eight ounces of soil in the sampling container chosen for the location. If using Zip-Loc® bags, double-bag by placing the filled bag into a second bag.

  • Place the sample identification paper (name, address, date and Code number) between the inner and outer Zip-Loc® bag, or if using jars or bottles, tape the identification information to the outside.

  • Carefully close sample containers and pack for shipping.
Laboratory analyses

If you are doing soil self-testing you will need to select an analytical laboratory to perform the chemical analyses. The Washington State Department of Ecology (Ecology) maintains a list of accredited laboratories. Information is available on these laboratories by calling (425) 649-7000.

Laboratory analyses will be out-of-pocket expenses to property owners. Costs charged by laboratories vary, however, and we cannot guarantee what the cost of the analysis will be. If you want expanded soil testing, it will be more expensive and is discussed below.

You can take samples to the lab directly or send them via UPS, Federal Express or other carrier service. Sample containers should be carefully closed and packed for shipping. Check with the lab you are using about the best method of delivery or carrier.

Attachment #A can be used as direction to the lab for sample processing and what analyses you are requesting. Detailed information on how the laboratory should proceed with the analyses is extremely important. You should also request a written report from the lab. These instructions ask for arsenic analyses only to help hold down costs and because arsenic is a general indicator of the concentration of other metals of concern.

What do the numbers mean?

Some useful ways to evaluate the soil sample test results you get back from the laboratory could include the following:

  • Comparison of results to uncontaminated regional background levels. See Ecology's lead and arsenic background levels document.

  • Comparison to regulatory cleanup standards for soil contamination such as the Ecology's Model Toxic Control Act (MTCA) or the U. S. Environmental Protection Agency Superfund Program. See Ecology's MTCA program.

  • Comparison to exposures from other non-soil pathways such as from food (diet), drinking water, and air; and

  • Comparison of results with other soil contamination levels reported in the region, such as the Tacoma-Ruston neighborhood or the City of Everett.
Expanded soil testing

You can get more complete and reliable information on contamination levels at a property with expanded soil testing at a greater cost. An expanded soil testing protocol could include some combination of collecting surface soils at more locations, collecting deeper soils in addition to surface soils, and analyzing for additional metals besides arsenic. For example:

  • More locations: More sampling locations can better characterize the variability and maximum concentrations of soil contamination in surface soils.

  • More depths: Deeper soil samples, especially in areas where soils have been disturbed or may be disturbed by future activities, will tell you possible variations in contaminant depth profiles, where surface soil samples alone might underestimate contaminant levels.

  • The detection limits for lead and cadmium should be no greater than 10 parts per million (ppm) and 1 ppm, respectively. Testing for additional metals will give you results for their soil concentrations that are more accurate than estimates that you will get by using arsenic as an indicator contaminant.