Blackland clay, wind and fine dust east of I-35
East of the interstate, the ground around Pflugerville is often dark clay soil from the blackland prairie. Dry, windy stretches loosen that soil, and open lots from continuing construction add to it. Homes with new landscaping have another source, since mulch, soil and freshly sodded yards stir up dust during mowing and edging.
Fine particles slip through weak filters and gather in return plenums. Lots in newer subdivisions also tend to be smaller, so houses sit close together with little shade, and attics bake in summer. High attic heat is hard on flexible duct, which can sag, split or loosen at joints over time.

