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Test Methods

Visible Crust Test Method:

Equipment:

Introduction:
The purpose of this test is to check whether a vacant lot is sufficiently crusted to prevent windblown dust. (Note: This test's primary function is to provide a simplified initial assessment of surface stability. However, if there is any doubt as to the lot's stability upon performing this test, the soil test method should be conducted to more thoroughly determine the surface's erodibility potential.)

Step 1:
Select a 1 by 1 foot Survey Area that is representative, or a typical example, of the crusted surface.

Step 2:
Hold the small steel ball one (1) foot off the ground directly above your survey area. Use a ruler or measuring tape to make sure that your hand is at the correct distance above the ground. Drop the ball within the survey area.

Step 3:
Pass/Fail Determination. Observe the ground around the ball closely before picking it up. Did the ball sink into the surface so that it is partially or fully surrounded by loose grains of dirt? Has it dropped out of view entirely? Then pick up the ball. Look closely where the ball fell. Are loose grains of dirt visible?

If you have answered "yes" to any of the previous questions, the surface has failed the first drop test. Note that if the ball causes a slight indentation on the surface but you do not see loose grains, the surface has passed the test.

Step 4:
Select two additional areas within the 1 by 1 foot survey area to drop the ball. Repeat Steps 2 and 3. If the surface passes two or all three of the drop tests, count your survey area as passing the test.

Step 5:
Select at least two other survey areas that are representative of the crusted surface. Pick the areas randomly and make sure they are spaced some distance apart. Drop the ball 3 times within each of these additional survey areas. Once again, if the surface passes the test twice or three times, count the survey area as passing the test.

Step 6:
Examine Results. If All of the survey areas have passed the test, the surface is stable, or sufficiently crusted. If one or more survey areas has failed the test, the surface is insufficiently crusted. Do another applicable test (see test method flowchart) If the surface fails the visible crust test, but there are minimal loose grains on the surface, EPA recommends that the soil test method be done. Where there is little loose material that can be collected, the surface is likely to pass the soil test method.

Question and Answer - Visible Crust Test Method

Question:
What if blowsand is on the crusted surface? (Blowsand is thin deposits of loose grains which have not originated from the surface you are testing, but have been blown there from some surrounding disturbed area. Blowsand tends to collect in certain areas rather than uniformly over the surface. If present, it will generally cover less than 50% of the entire vacant lot surface.)

Answer:
Clear the blowsand from the survey area surfaces on which you plan to drop the ball. Blowsand should not be a factor in your results.

Question:
What if material has been dumped or piled on the surface that is not blowsand, such as dirt or swimming pool waste?

Answer:
Do not do the visible crust test on those surfaces unless they have crusted over. Instead, do the Soil Test on any loose surface material.

Question:
What if two of the survey areas pass with flying colors and the third survey area fails miserably?

Answer:
Chances are that the third survey area is either part of an uncrusted portion of the lot or has a much lighter kind of crust or different soil type than that of the other two survey areas. This means that the third survey area represents a different kind of surface than the other survey areas. If this is the case, examine the disturbed surface areas on the lot carefully. Using measuring tape, segment off (literally or mentally) the portion(s) of the lot that the third survey area represents. Size it up in feet and select two additional 1 by 1 foot survey areas on which to do the visible crust test. Keep in mind that if all other areas on the lot have a stable crust except for the newly identified area, it would need to be at least ½ acre in size for disturbed surface RACM requirements to apply. RACM for motor vehicle disturbance (i.e. trespassing) would apply if tire tracks are present.

Question:
If a crust is present, but vegetation and/or rocks are also on the surface, which test should I do first?

Answer:
Always do the visible crust test first since it is the easiest, even if you see vegetation and/or rocks as well. Only if the visible crust test fails should you try another test. However, make sure that the surfaces you select for the visible crust test truly represent the entire disturbed area(s) on the lot. If you are uncertain whether a vegetated area has the same strength crust as an unvegetated area, do the visible crust test separately on each area.

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Rock Test Method:

Equipment:

Introduction:
This test method examines the wind-resistance effects of rocks and other non-erodible elements on disturbed surfaces. Non-erodible elements are objects larger than 1 centimeter (cm) in diameter that remain firmly in place even on windy days. Typically, this includes rocks, stones, glass fragments and hard-packed clumps of soil lying on or embedded in the surface. Vegetation does not count as a non-erodible element in this method. The purpose of this test is to estimate the percent cover of non-erodible elements on a given surface to see whether they take up enough space to offer protection against windblown dust. For simplification, the following test method refers to all non-erodible elements as "rocks".

Step 1:
Select a 1 by 1 meter Survey Area that represents the general rock distribution on the surface. (A 1 by 1 meter area is slightly greater than 3 ft. by 3 ft.) Mark off the survey area to distinguish it from the rest of the lot. This can be done using a pen to trace a straight, visible line in the dirt along the edge of the measuring tape or you can place short ropes, yard sticks, or other straight objects in a square around the survey area.

Step 2:
Examine the rocks or other elements in your survey area without moving any of them. Since you are only interested in rocks > 3/8 inch [1 centimeter (cm)] in diameter, measure the diameter of some of the smaller rocks to get a sense for which rocks you need to consider and which you should ignore.

Step 3:
Mentally group the rocks > 3/8 inch (1 cm) in diameter lying in the survey area into small, medium and large size categories. Or, if the rocks are all approximately the same size, simply select a rock of average size and typical shape. Without removing any rocks from the ground, count the number of rocks in the survey area in each size group and write down the resulting numbers. If there are numerous rocks to count in the survey area, EPA recommends that steps 4 through 8 be conducted for larger rocks first. Thus, if the results indicate cover of larger rocks is sufficiently stabilizing, it is unnecessary to count smaller size rocks.

Step 4:
Without removing rocks, select one or two average-size rocks in each group and measure their length and width. You may use either metric units or standard units. Using a calculator, multiply the length times the width of the rock(s) to get the average dimensions of the rocks in each group. Write down your results for each rock group.

Step 5:
For each rock group, multiply the average dimensions (length times width) by the number of rocks you counted in the group. Then, add up your results from each rock group to get the total rock area within your survey area.

Step 6:
Divide the total rock area you calculated in Step 5 by 2 (to get frontal area). Then divide the resulting number by the size of the survey area (make sure your units of measurement match), and multiply by 100 for percent rock cover. For example, if your total rock area is 1,400 square centimeters, divide this by 2 to get 700. Divide 700 by 10,000 (i.e. the survey area is 1 meter by 1 meter, which is 100 centimeters by 100 centimeters, or 10,000 centimeters) and multiply by 100. The result is 7% rock cover. If you do your rock measurements in inches, make sure you convert the survey area from meters to inches (1 inch = 2.54 centimeters).

Step 7:
Select and mark off two additional survey areas and repeat this test method. Make sure the additional survey areas also represent the general rock distribution on the disturbed surface. Average the percent cover results from all 3 survey areas to estimate the average percent of rock cover.

Step 8:
Examine Results. If the average rock cover is > 10%, the surface is STABLE. If the average rock cover is < 10%, continue on with Step 9.

Step 9:
If the average rock cover is < 10%, the surface may or may not be stable. You need to do the Soil Test Method to determine the soil's threshold friction velocity (TFV) and use the results from the rock test method as a correction (i.e. multiplication) factor. What this means is that if the rock cover is at least 1%, this helps to limit windblown dust. However, depending on the soil's ability to release fine dust particles into the air, the percent rock cover may or may not be sufficient enough to stabilize the surface. It is also possible that the soil itself has a high enough TFV to be stable without even accounting for rock cover.

Step 10:
Once you have conducted the Soil Test Method, use the table below to identify the appropriate correction factor to the TFV depending on the percent rock cover. Then multiply the correction factor by the TFV value for a final TFV estimate that is corrected for non-erodible elements.

Correction Factors for TFV

% Rock Cover Correction Factor
> 5% and < 10% 3
< 5% and > 1% 2
< 1% None

Question and Answer - Rock Test Method

Question:
Can I remove any of the rocks for measurement?

Answer:
You can remove small rocks that are not embedded in the soil for measurement. Do not remove rocks that are embedded or partially buried because your measurements should only reflect the part of the rock that is exposed on the surface.

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Soil Test Method:

Equipment:

Introduction: The purpose of this test method is to measure the threshold friction velocity, or TFV, of disturbed soil. TFV is the wind velocity necessary to initiate soil erosion. TFV can differ among disturbed vacant lots depending on the type of soil and to what extent it is disturbed. The lower the TFV, the greater the propensity for fine particles to be lifted at relatively low wind speeds. Since rocks and other non-erodible elements add protection against soil erosion, they raise TFV if present on the disturbed surface. A TFV of 100 cm/sec or greater is considered sufficiently protective.

Step 1:
Stack a set of sieves in order according to the size openings specified above, beginning with the largest size opening (4 mm) at the top. Place a collector pan underneath the bottom (0.25 mm) sieve.

Step 2:
Select a 1 foot by 1 foot survey area that is representative, or typical, of the disturbed surface. Mark this area using a cardboard frame. Check whether the surface is wet or damp. If so, return later to do this test method when the surface has dried.

Step 3:
Collect a sample of loose surface material to a depth of approximately 3/8 inch (1 cm) into a dustpan. This can best be done using a lightweight whisk broom/brush to carefully sweep the surface material within the marked survey area onto a spatula and lifting it into the dustpan. If you reach a hard, underlying subsurface that is < 3/8 inch in depth, do not continue collecting the sample by digging into the hard surface.

Step 4:
Check the dustpan for rocks or hard-packed clumps of soil collected in your sample. Measure their diameter and remove those larger than 3/8 inch (1 cm) in diameter from the sample.

Step 5:
Carefully pour the sample into the stack of sieves, minimizing release of dust particles by slowly brushing material into the stack with a whisk broom or paintbrush. (On windy days, use the trunk or door of a car as a wind barricade.) Cover the stack with a lid. Lift up the sieve stack and gently move it using broad, horizontal circular arm motions. Complete 10 clockwise and 10 counter-clockwise motions at a speed of approximately 1 second per motion. Be careful not to move the sieve too roughly in order to avoid breaking up any naturally clumped material.

Step 6:
Remove the lid from the stack and disassemble each sieve separately, beginning with the top sieve. As you remove each sieve, examine it to make sure that all of the material has been sifted to the finest sieve through which it can pass; e.g. material in each sieve (besides the top sieve that captures a range of larger elements) should look the same size. If this is not the case, re-stack the sieves and collector pan, cover the stack with the lid, and gently rotate it using the same circular arm motions as before an additional 10 times. (You only need to reassemble the sieve(s) that contain material which requires further sifting.)

Step 7:
Line up the sieves in a row as they are disassembled, with the 4 mm sieve at one end and the collector pan at the other. Slightly tilt and gently tap each sieve and the collector pan so that all material is collected on one side. The material in the sieves and collector pan should be on the same side relative to your position. Observe the relative amount of material in each sieve and the collector pan to determine which contains the greatest volume. If this is difficult to determine, use a graduated cylinder or a measuring cup to measure the relative volume.

Step 8:
Use the table below to estimate TFV for the sieve catch with the greatest volume estimated in Step 7. For example, if the sieve containing the greatest volume is the one with the 0.5 mm opening, TFV = 58 cm/second.

Sieve Size Opening (mm) TFV (cm/sec)
4 > 100
2 100
1 76
0.5 58
0.25 43
Collector Pan 30

* TFV values in this table take into account the aggregate size

distribution of particles between the different sieve size openings.

Step 9:
Repeat this procedure on at least two other representative areas on the disturbed surface. Average your TFV results from the three samples collected.

Step 10:
Examine Results. If the TFV you've calculated is greater than or equal to 100 cm/sec, the surface is STABLE.

If the TFV is < 100 cm/sec, do the Rock Test Method to see whether the TFV you calculated can be increased by a multiplication factor.

Question and Answer - Soil Test Method:

Question:
In the Soil Test Method, I'm supposed to remove rocks greater than 1 cm in diameter from the survey area. Should I use these in the Rock Test Method?

Answer:
No. It is best to do these two methods on separate surface areas to avoid confusion. The survey area for the Rock Test Method is larger than the survey area for the Soil Test Method. Plus, since rocks are removed from the surface in the Soil Test Method, you could potentially overestimate their frontal area in the Rock Test Method.

Question:
If there are hard-packed clumps of dirt on the surface, do I sieve these clumps along with the rest of the soil sample?

Answer:
If the hard-packed clumps are 1 cm or greater in size, extract them from the sample. After you complete the Soil Test Method, you should do the Rock Test Method in a larger survey area, treating the hard-packed clumps the same as you would rocks. (This is because they qualify as non-erodible elements.) Then use results from the Rock Test Method to adjust your TFV to account for the hard-packed clumps.

Question:
Can I combine all three collected soil samples into the sieve stack at once to save time?

Answer:
You may try combining the three samples after removing rocks or other non-erodible elements greater than 1 cm in diameter from each sample only if the mass of the three samples is approximately the same. However, combined samples may be more difficult to sieve and require reassembling and re-shaking of the sieves more than once. Also, it may be difficult to visibly compare the volume of material caught in the sieves after they have been disassembled. Therefore, combining samples is not recommended.

Question:
If I see dust particles escaping when I collect a sample and transfer it to the sieves, should I start over?

Answer:
Not necessarily. A small amount of dust particles can escape without influencing the TFV results. In fact, it is very difficult to avoid having some dust escape. However, if you rush when collecting and/or transferring a sample to the sieves, you may cause too much dust to escape thus potentially causing error in your results. Or, on a relatively windy day you may lose too much dust unless you set up a wind barricade. Avoid doing this test at all on very windy days.

Question:
If you're not sure which sieve contains the greatest amount of material, can you weigh the sieves for comparison?

Answer:
While, typically, more volume corresponds to greater weight, this is not always the case. Use a measuring cup or graduated cylinder if necessary.

Question:
When determining TFV in step 8, can I combine material in the largest 2 sieves to estimate volume?

Answer:
No. This may fundamentally alter the premises upon which the method is bused and lead to an incorrect determination of stability.

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Flat Vegetation Test Method:

Equipment:

Introduction:
This test method examines the protection of flat vegetation against wind erosion on disturbed surfaces. Flat vegetation includes rooted vegetation or unattached vegetative debris lying horizontally on a surface. It can be alive or dead, but wind must not be able to move it or blow it away. Examples include flat, low-lying plants, horizontally flattened grass, or clumps of hay that are bunched. The purpose of this test is to estimate the percent cover of flat vegetation on a disturbed surface to see whether it sufficiently protects against windblown dust.

Step 1:
Select an area preferably 100 ft. by 100 ft. that represents the typical distribution of flat vegetation on the disturbed surface. Stretch the measuring tape low and taut across the area to its full length and firmly anchor both ends of the tape with screwdrivers. If regular rows of vegetation exist, place the tape diagonally across (approx. 45 degrees) so that it is neither parallel nor perpendicular to the vegetated rows.

Step 2:
Stand directly above the 1-foot mark on the measuring tape. Use a 3/32 inch diameter brazing rod (or other object of the same size) to usually pinpoint the area centered just above the 1-foot mark of the tape.

Step 3:
Observe the ground (from a 90 degree angle) that lies directly underneath the rod. Count the surface as vegetated if you see vegetation underneath. Do not count the underlying surface as vegetated if you see bare soil, even if the bare soil you observe is open space between the appendages of a plant. Do not count the surface as vegetated if the vegetation fills in only a portion of the area directly beneath the rod. If you see a rock or stone greater than 1 cm in diameter under the rod, count the surface as "vegetated", since rocks and other non-erodible elements provide equivalent protection.

Step 4:
Move along the entire length of the measuring tape and repeat your observation at each 1 foot interval along one edge of the tape. Be as consistent as possible in counting the presence of vegetation underneath the area you pinpoint with the brazing rod. Record the number of positive vegetation counts as you go along. In total, you should make 100 observations just above each one foot mark along one side of the tape unless the disturbed surface area you are testing is less than 100 feet across in the direction you have placed the tape. If this is the case, divide the number of positive vegetation counts you recorded by the total number of observations made and multiply by 100 to obtain the percent vegetation cover.

Step 5:
Examine results. Add together the number of times you counted the surface as vegetated. This is the percent cover of flat vegetation. For example, if you counted the surface as vegetated 60 times, flat vegetation cover is 60%.

Step 6:
Remove the measuring tape and repeat this test method on two different areas that represent the typical distribution of flat vegetation on the disturbed surface. Average your results for a final estimate of flat vegetation cover. If the average flat vegetation cover is >50%, the surface is STABLE.

Graphic Presentation of a measuring tape and 3/32 inch diameter rod being used to determine whether or not to count a piece of flat vegetation or vegetative debris

Question and Answer - Flat Vegetation Test Method:

Question:
Should I kneel or squat when making observations at one-foot intervals to view the surface more closely?

Answer:
No. This may make it difficult to observe the surface at a 90 degree angle. You will, however, need to bend at the waist to look directly down at the brazing rod as you hold it along the side of the tape to view the surface below. Also, a standing position facilitates easier movement between one-foot intervals.

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Standing Vegetation Test Method:

Equipment:

Introduction:
This test method examines the protection against wind erosion offered by standing (e.g. upright) vegetation on disturbed surfaces. Standing vegetation includes plants, grasses, shrubs, etc. that are rooted and vertically oriented. In other words, if the vegetation is not lying flat on the surface, it counts as standing, including shrubs that are only 1 inch in height. Standing vegetation includes dead vegetation as long as it is firmly rooted. The purpose of this test is to estimate the percent (frontal area) cover of standing vegetation on a disturbed surface to see whether individual vegetative units sufficiently protect against windblown dust. For simplicity, individual vegetative units are referred to below as "plants".

Step 1:
Check whether there is one or more than one species of vegetation. If there is more than one species, observe whether the different species intermix over the same disturbed area or whether they are isolated from each other. For disturbed areas where the vegetation is mixed and/or not uniformly distributed, do a simple sketch of the vegetative layout within the disturbed area. DO THE FOLLOWING TEST METHOD SEPARATELY FOR EACH DIFFERENT SPECIES, IF PRESENT. (Note: results from this test method cannot be extrapolated to pockets of disturbed area that do not have any vegetation.)

Step 2:
Select a survey area that represents the typical distribution of the vegetation. If the vegetation consists of large individual units such as sagebrush or cacti, estimate their average height and multiply by 10 for the square footage of the area you should survey. For example, if the average height of the large vegetation is 3 feet, the survey area should be 30 ft. by 30 ft. For smaller vegetation, select a 3 ft. by 3 ft. survey area. Smaller vegetation inlcudes weeds, plants, grass or other vegetation. If you are not sure how to classify the vegetation, check whether an individual structure can be easily uprooted. If so, it should be classified as small for the purpose of selection a survey area, even if it is greater than 1 foot in height. Mark off the survey area so you can tell which vegetation is in or out of the survey area.

Step 3:
Observe whether the vegetation is all approximately the same in height and width or whether it varies in size. If it is approximately the same in size, count and record the number of individual plants within the survey area. If the vegetation differs in size, mentally separate the plants into groups with similar dimensions, such as small, medium and large. Then count the number of plants within each group and record the total number for each group separately. (If the vegetation grows in clumps, count each clump as a single unit.)

Step 4:
Select an individual plant that represents the average height and width of the vegetation (for each group, if applicable). GO TO THE VEGETATIVE DENSITY PROCEDURE BELOW TO SEE WHETHER IT APPLIES. Once you do the vegetative density procedure, you may assume the same vegetative density for plants of the same species but with different sizes. If you do not need to do the vegetative density procedure, multiply the plant's height times width to calculate its Frontal Area. (For survey areas larger than 9 square feet, estimate the average height and width of the vegetation to calculate Frontal Area.) For plants in different size groups, calculate the Frontal Area for a representative plant from each group.

Step 5:
Use the following equations to calculate percent cover of standing vegetation.

GROUP 1 (Frontal Area X Number of plants counted) + GROUP 2 (Frontal Area X Number of plants counted)...etc... = Total Frontal Area

(Total Frontal Area / Survey Area) X 100 = Percent Cover of Standing Vegetation

*(Ensure consistent units of measurement. For example, if your Total Frontal Area is 500 square inches and your survey area is 9 square ft., divide 500 by 1296 square inches rather than by 9 square feet.)

Step 6:
Repeat this method on two additional distinct survey areas and average together your percent cover standing vegetation results.

Note: IF you do this method for more than one species of vegetation and the different species are intermixed and uniformly distributed, you may add together the percent cover results associated with both species.

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Vegetative Density Procedure:

Observe the density of a typical individual plant.
You do not need to do this procedure if:

Cut a typical plant in the disturbed area to within 1 centimeter (i.e. as close to the surface as you can). If cutting the piece of vegetation may result in structural detachment, uproot it instead. However, do not factor any portion of the subsurface material into the density results.

  Create a grid with 1 inch or ½ inch square boxes. The easiest way to do this is using a ruler, pen and paper. However, if you anticipate regular use of the grid at several sites, use transparency (overhead projection) sheets over white paper and erasable markers. For plants that exceed the size of standard paper, use oversized paper or invisible tape to attach several sheets together. If the plant is small, use ½ inch squares.

Lay the plant flat on top of the grid (but do not apply pressure to flatten it). Trace its shape along the outer edge according to the most appropriate Figure on the next page. Note: the main difference between Figures 2 and 3 is that in Figure 2, the plant's width is narrow at its base and broadens to its tallest height. In Figure 3, the plant's width narrows to its tallest height.

Remove the plant from the grid. Count and record the total number of gridline intersections within the outlined area, not counting the intersections that connect with the outlined shape you have drawn. You should have counted at least 10 intersections and preferably more than 20. (If you counted less than 10, redo the grid with smaller size boxes.) Using a pencil or pen, fill in small circles (no more than 1/10 of an inch in diameter) at each gridline intersection you counted.

Replace the plant back on the grid within its outlined shape. Observe the grid from a distance of 2 feet directly above it (use a ruler to measure the distance). Count and record the total number of circled gridline intersections you fully observe. (The ones you don't count will be either completely or partially hidden by a piece of vegetation.) Use the equations below to calculate percent vegetative density.

Eq.   [(Number of circled gridlines counted / Total number of gridline intersections counted within the outlined area) X 100] = Percent Open Space.

Eq.   100 - Percent Open Space = Percent Vegetative Density

Calculating Frontal Area:

If Percent Vegetative Density is < 30%:

- use the following equations to calculate Frontal Area.

Eq.   Percent Vegetative Density/100 = Vegetative Density

Eq.   [Maximum Plant Height X Maximum Plant Width] X [Vegetative Density/0.4]0.5 = Frontal Area

If Percent Vegetative Density is > 30%:

- use the equations below to trace the shape of the plant on your grid to calculate Frontal Area.

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Obtaining Equipment for Vacant Lot Test Methods:

Visible Crust Test Method:

This test method requires a small steel ball that is 5/8 inches in diameter with a mass of 16.33 grams. It may commonly be referred to as a "ballbearing". Ballbearings are available at full service hardware stores.

Rock Test Method:

The equipment is commonly available at office supply or hardware stores.

Soil Test Method:

A set of sieves with the following openings: 4 millimeters (mm), 2mm, 1 mm, 0.5 mm and 0.25 mm, a lid and collector pan can be purchased at a laboratory supply store. Such stores may be listed in telephone directories under "Laboratory Equipment & Supplies" or you may conduct an internet search using the key words "test sieve". When ordering sieves, specify the following:

Tyler sieve numbers 5, 10, 18, 35 and 60, respectively.
8 inch diameter sieves as opposed to 12 inch diameter. (The 8 inch diameter sieves are easier to handle due to less weight and bulk.)
Full height (as opposed to half height) individual sieves.
While optional, special certification of the mesh sizes on each sieve is not necessary.

The remaining equipment needed for the Soil Test Method is commonly available at hardware stores, grocery stores, or office supply stores.

Flat Vegetation Test Method:

The equipment is commonly available at office supply or hardware stores.

Standing Vegetation Test Method:

The equipment is commonly available at office supply or hardware stores.

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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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