A study from the University of Colorado shows older vertical oil and gas wells have a higher probability of causing groundwater contamination, than newer horizontal wells. The study looked at the frequency of well integrity issues in the Wattenberg Field in central Colorado. Results showed the majority of new horizontal oil and gas wells in the area have been built with surface casing extending deeper than state regulations require, reducing the likelihood of groundwater contamination. Vertical wells that were studied had shorter surface casing, increasing the possibility of ground water contamination. The view an abstract of the report, click here.