Geology
An area of 11 square miles (30 km2) of the county is known to be underlain with natural asbestos. Much of the asbestos is known to emanate from fibrous tremolite or actinolite. Approximately 20 years ago, when the threat was discovered, the county established laws to monitor air quality at construction sites, control soil taken from affected areas, and require freshly developed sites to lay 6 inches (150 mm) of clean, stable material over the ground.
For instance, during the construction of Centreville High School a large amount of asbestos-laden soil was removed and then trucked to Vienna for the construction of the I-66/Nutley Street interchange. Fill dirt then had to be trucked in to make the site level. Marine clays can be found in widespread areas of the county east of Interstate 95, mostly in the Lee and Mount Vernon districts. These clays contribute to soil instability, leading to significant construction challenges for builders.
Read more about this topic: Fairfax County, Virginia