Editing Fairfax County, Virginia (section)

== Geology ==
The Piedmont hills in the central county are made up of ancient [[metamorphic rocks]] such as [[schist]], the roots of several ancestral ranges of the [[Appalachian Mountains]]. The western valley is floored with more recent [[shale]] and [[sandstone]]. This geology is similar to adjacent bands of rocks in [[Maryland]] and further south in [[Virginia]] along the eastern front of the Appalachian.

An area of {{convert|11|sqmi|km2|sigfig=1}} of the county is known to be underlain with natural [[asbestos]].<ref name="asbestos">{{cite web|url=http://www.fairfaxcounty.gov/hd/asb/|title=Naturally Occurring Asbestos in Fairfax County, Virginia|publisher=Fairfax County|access-date=September 5, 2016}}</ref> Much of the asbestos is known to emanate from fibrous [[tremolite]] or [[actinolite]]. The threat was discovered in 1987, prompting the county to establish laws to monitor air quality at construction sites, control soil taken from affected areas, and require freshly developed sites to lay {{convert|6|in|mm}} of clean, stable material over the ground.<ref>{{cite web |url=http://www.sciencenews.org/articles/20060708/bob9.asp |title=Dirty Little Secret |author=Janet Raloff |date=July 8, 2006 |work=Science News Online | archive-url =https://web.archive.org/web/20080116130144/http://www.sciencenews.org/articles/20060708/bob9.asp |archive-date=January 16, 2008|access-date=April 26, 2010}}</ref><ref>{{cite web |url=http://www.fairfaxcounty.gov/hd/hdpdf/tbrdpubfin.pdf |title=Control and Prevention of Asbestos Exposure from Construction in Naturally Occurring Asbestos |author=C. James Dusek and John M. Yetman| archive-url =https://web.archive.org/web/20060927184034/http://www.fairfaxcounty.gov/hd/hdpdf/tbrdpubfin.pdf |archive-date=September 27, 2006|access-date=July 12, 2013}}</ref>

During the construction of [[Centreville High School (Fairfax County, Virginia)|Centreville High School]], for instance, a large amount of asbestos-laden soil was removed and then trucked to [[Vienna, Virginia|Vienna]] for the construction of the [[Interstate 66|I-66]]/Nutley Street interchange. Fill dirt then had to be trucked in to make the site level.{{Citation needed|date=April 2010}} <!-- I know there is a reference for this, i saw it on a county website discussing the asbestos, but i can't find it now -->[[Marine clay]]s can be found in widespread areas of the county east of [[Interstate 95 in Virginia|Interstate 95]], mostly in the Franconia and Mount Vernon districts. These clays contribute to soil instability, leading to significant construction challenges for builders.<ref name="marine clays">{{cite web|url=http://www.fairfaxcounty.gov/dpwes/publications/marineclay.htm|title=Overcoming Problems with Marine Clays|publisher=Fairfax County|access-date=April 25, 2010|url-status=dead|archive-url=https://web.archive.org/web/20100407034317/http://www.fairfaxcounty.gov/dpwes/publications/marineclay.htm|archive-date=April 7, 2010}}</ref>