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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Vacant Lots and Selecting Representative Surfaces to Test

First estimate the overall size of the lot, then size up in square feet the total disturbed area(s):

Once you have determined that a lot is > 5,000 square feet, focus on determining whether the total amount of disturbed area adds up to ½ acre or more. Note that if there is evidence of motor vehicle trespass on a lot > 5,000 square feet, the lot owner/operator is required to prevent further trespass regardless of whether ½ acre has been disturbed.

If a vacant lot is crusted, regardless of other surface conditions (including vegetation), do the visible crust test method first:

The visible crust test is the simplest test. Only if a disturbed area fails the visible crust test should you try a different test. For example, if a crust covers the entire area that shows evidence of past disturbance and part of the crusted area is lightly vegetated, as long as the surface passes the visible crust test in both vegetated and unvegetated areas, no other test is necessary.

Your test(s) must accurately represent all disturbed areas:

Carefully examine the lot's disturbed surface(s). If there is more than one type of disturbance, soil, vegetation or other visibly distinguishing characteristics of the disturbed area, you need to test each representative surface separately for stability in random areas. See the document in this guidance titled "Vacant Lot Site Assessment Tips" to help you characterize surface disturbances.

Select random areas on which to conduct tests:

Where one representative, continuous disturbed surface area exists that is greater than 5,000 square feet, subdivide the surface into three contiguous areas of equal size. Exact measurements are not needed. Select a location approximately in the center of one subdivided area on which to conduct the test method. Repeat this procedure for the remaining two subdivided areas.

If there is more than one representative disturbed surface that requires testing, select 3 random locations on each representative disturbed surface and conduct the appropriate test method(s). The random locations selected should be reasonably distanced from each other with respect to the total size of the representative surface area or pockets that are being tested.

Confirm the appropriateness of any conclusions you reach about surface stability based on test method results:

Do not extrapolate test method results from one area to other disturbed areas unless they are representative. For example, if an uncrusted, vegetated surface adjoins a crusted surface, you cannot use results form the visible crust test on the crusted portion of the lot to represent the uncrusted, vegetated surface. Or, if one part of the lot has been weed abated and another disturbed by vehicles, test method results from each of these disturbances should be considered separately.

If you are not certain your test method results accurately represent the disturbanced portion or portions of the lot, randomly select more disturbed surface areas on which to do additional tests.

EPA recommends that photographs be taken which help confirm that surfaces on which tests have been done are representative of the disturbed surface area(s).

Once you've determined that a representative portion of a lot you've tested is stable, subtract its size in square feet from your initial assessment of disturbed area:

The purpose of having test methods is to check whether a surface that appears disturbed is stable or unstable. If it is stable, the dust-emitting effects of the disturbance have either been offset by natural processes or controlled by humans. Therefore, you do not need to consider a stabilized surface further unless it is re-disturbed.

Once you subtract the size area you've deemed stabilized, there may still be ½ acre or more of unstabilized surfaces on the lot that require control. Be sure to carefully and accurately assess the condition of all disturbed areas on the lot.

For more information:

Please contact Colleen McKaughan, Associate Director, air Division, U.S. EPA Region 9 at (520) 498-0118. Send questions and comments to r9.phoenixdust@epa.gov.
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