**6. Conclusions**

 The use of large-volume, horizontal hydraulic fracturing has expanded across the U.S. and inspired talk of American energy independence and a renaissance of manufacturing. At the same time hydraulic fracturing has also become a lightning rod in public debates that pitches neighbors against each other and prompted calls for moratoria and greater scientific scrutiny from environmental groups and community health advocates. This chapter is an attempt to summarize the main sources of environmental pollution and health risks that arise during the lifespan of a hydraulically fractured well. It is a reminder that the reader that unconventional oil and gas production is an industrial activity that is noisy, dirty, and that generates substantial amounts of waste. Some of these side effects occur primarily on the well pad and in its immediate vicinity, where they pose risks to workers and residents. Others manifest themselves regionally and even globally and thus add to the pollution burden of people and communities who are far away from oil and gas production. The regulatory environment in which oil and gas development takes place usually creates obstacles for people to receive information and seek redress for pollution and health effects they might experience. Indeed, the burden of proof of causality between unconventional oil and gas operations as the source of the impacts is often on the individual or community and requires a level of scientific knowledge and information that is beyond their capacity. This is where regulators, public health officials, and the scientific community need to focus and together with the oil and gas industry develop mechanisms for greater transparency, meaningful data collection, and targeted epidemiological and toxicological studies. Unconventional oil and gas development is projected to continue its growth path and will remain a part of life in many rural and also urban communities across the U.S. In order to facilitate a co-existence that is based on trust, prioritizes safety over profits, and invests in local communities, the discussed health risks need to be addressed comprehensively and form the evidentiary basis for regulatory action.
