Even though arsenic is a naturally occurring substance, it is not one you want in your garden. Because arsenic was not always as controlled as it is today, your soil might contain high levels of arsenic and you don't even know it. Arsenic used to be a common ingredient in pesticides and fertilizers. Wood was also commonly treated with arsenic, which would then leak into the soil. If you suspect that your garden might contain arsenic, it is a good idea to get it tested.
Find a soil testing laboratory. Most University's Cooperative Extensions will be able to help you find one in your area.
Choose four to six spots in your garden to test. Locations should not be within 6 feet of a building or within 50 to 100 feet of heavily traveled roads. Avoid areas where soil was recently added from another location. Avoid the drip line of trees and areas near a rain spout or gutter. Each location should be about 5 to 10 feet away from each other.
Mark the areas you selected for testing on the map of your garden.
Remove any surface vegetation as well as the top 2 to 4 inches of soil. The area needs to be only about 2 to 4 inches wide.
Take all the soil from the top 2 inches in the first area you cleared, using your spoon (wooden, plastic or stainless steel).
Place the soil in your plastic bucket.
Repeat Steps 5 and 6 for each of the areas.
Mix the soil samples in the bucket thoroughly with a non-metal tool. Make sure the soil is uniformly combined.
Place about one cup of the soil mixture into the sample container.
Label the sample with your name, date, location, and the depth of sample on the label or container with a permanent marker.
Deliver the soil sample to the testing laboratory and wait for the results.