When horizontal directional drilling (HDD) emerged in the mid-1960s as a new way to install utility lines under immovable or unavoidable obstacles without significant surface disruptions, crossings spanned up to a few hundred feet guided by frequent potholing. That changed in 1971 when a 4-inch gas line was placed under a river in Watsonville, CA, USA, a location where potholing would not be possible.
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