The recent issue of Damage Prevention Professional Magazine shows photos which point out the need to watch out for buried utility lines hear the surface. While damages which occur in such instances are often blamed on construction contractors who are digging, there's much to suggest that when such damages take place, utility companies and the firms they contract to install underground lines may bear some of the blame.
While all but three states require marks to be within 18 to 24 inches of the actual underground location of buried lines and pipes, not every state's laws speak to the matter of depth of lines. However, a number of states do provide guidance on the matter, as does a federal study, suggesting that it's recognized that lines should be buried deep enough to ensure that light digging or scraping doesn't hit them.
I've seen many cases where utilities did not bury lines anywhere near the depth required for placement in SCDOT right-of-ways. While the worst outcome was service interruptions and nasty letters from utility companies, the reality is that worse things can happen to a contractor's employees who are working at or near the site of excavation. Many of the incidents I have investigated have been lines placed less than twelve inches from the surface.
In South Carolina, Section 110 of state's new laws (for which I was one of the lead negotiators) does allow some exemptions for work that will not go deeper than twelve inches for homeowners, farmers and public road maintenance agencies (but there is talk that superseding federal laws may eventually eliminate these exemption categories), based on the notion that lines are generally buried far deeper.
Also, in South Carolina, Section 18.104.22.168 of the Utilities Accommodation Manual of the South Carolina Department of Transportation requires that “the minimum depth of bury shall be forty-two (42) below the lowest point of the roadway cross section” for any utility placement. This is a practice which has been applied in other states as well.
A quick search turned up three examples: Arkansas - 48", Iowa - 30 to 48", Minnesota - 36", as well as a federal study which recommended 40 inches. There are many other examples of local, county and state highway agencies who have adopted standards dictating depths of three or four feet.
While caution when digging is a must, safety and underground utilities is a two-way street. Blaming contractors isn't going to fix this problem (even though it can help). Utilities who want to avoid these outcomes need to step up to the plate and do a better job of the safe placement of underground utilities. Hopefully future changes in laws at the state level will provide needed clarity on these issues and make it clear that safety with underground utilities are a SHARED responsibility.