Proposition 112 was included in the Colorado mid-term election ballot. The Proposition proposed to amend the Colorado statutes to require that new oil and natural gas development be located at least 2,500 feet from occupied structures, water sources, and areas designated as vulnerable. This was a significant proposed increase in setback, from the current 500 feet from a home or occupied building or 1,000 feet from high-occupancy buildings like schools or hospitals requirements. Colorado voters defeated this amendment to the Colorado statutes, though some are looking at the 2019 state legislature session to revisit setbacks.
The Niobrara-DJ Basin is a crude oil and liquids-rich gas play that is located in Northeast Colorado and Southeast Wyoming. This region of Colorado has undergone rapid growth in population over the past 10 years, such that exploration and production operations are in the vicinity of old and new neighborhoods and towns throughout the region.
This figure is from here: https://www.naturalgasintel.com/ext/resources/Basin-Pages/Niobrara/Niobrara_Counties.png