Chemical Suppressants

We are evaluating the longevity of various types of chemical and biological dust suppressants which are being used to control dust erosion from barren, disturbed sandy loam soils. During June 1999, chemical and biological dusts suppressants were applied to barren, sandy loam, roto-tilled agricultural type land. The types and characteristics for each of these suppressants are given in our 2000 A&WMA annual meeting paper. Twenty-one 5,000 square foot plots were prepared on fallow agricultural land. Each test plot is 50 by 100 feet with 25-feet separation of undisturbed land between each plot. The plots are oriented north-to-south (the 100 feet distance from west to east) since the prevailing wind is from the southwest. The access road is to the east of the row of test plots. The upwind fetch is stable so that blow sand and other saltating particles impacting these suppressant surfaces are minimal. Vehicular and even foot traffic are prohibited on these suppressant plots. Generally, the vendor of each product applied the suppressant according to standard commercial protocol under our supervision. In addition, we flooded one plot and placed a two-inch layer of wood chips on another plot.

Annually, and ideally in the fall, when the ambient winds are lightest and the soils the direst, Midwest Research Institute has evaluated these plots for 5 years using a variety of techniques. Table 6 summarizes the field visits of MRI through November 2003. The 2003 field tests constitute the final evaluation for these suppressant plots. During these evaluations, MRI has continually enhanced their ability to quantify wind-generated emissions of PM using a combination of their unique portable wind tunnel and their recently developed semi-quantitative methods.

After 2-3 years, most of the chemical dust suppressants show no discernable stabilization effect beyond the effect of natural crusting. The natural crusting of these sandy loam soils results in a 75% control efficiency. Only the wood chips showed high dust control effectiveness throughout the period. These wood chips showed only a small degradation in surface coverage over time. In particular, the wood chips resist the decay that occurs with most chemical suppressants, resulting from abundant solar insolation and freeze/thaw/ cycles.

There was substantial yearly variability in the surface dust re-suspension potential for these test plots. Year 3 (2001) showed an order of magnitude higher potential than year 2 (February) 2001. Year 4 (November 2002) was similar to year 3 and Year 5 (November 2003) was much lower than Years 2 and 4. The results are believed to vary with moisture content of the soil (effects of precipitation and upwind prescribed flooding) and with the occurrence of high wind events that leave deposited dusts on the soil surface. For example, the high surface dust quantities in Year 3 may have resulted from tilling of fields immediately upwind of the test plots. The low surface dust quantities in Year 5 may have resulted from ongoing flooding of areas surrounding the test plots by the Bureau of Sanitation for secondary effluent.