In our new research, Pits versus Tanks: Risks and Mitigation Options for On-site Storage of Wastewater from Shale Gas and Tight Oil Development, we worked with our RFF coauthors Skyler Roeshot, Nathan Richardson, and Jan Mares to examine the environmental risks associated with the storage of wastewater from shale gas and tight oil operations and evaluated regulations and technologies that might help reduce those risks. Based on this work, we make six recommendations for regulators who are working to reduce the risks to human and ecological health from the use of pits and tanks for storing shale gas and tight oil wastewater:
- Prioritize the development of policies, practices, and technologies that address pit overflows, tank overfills, and liner malfunctions.
Our analysis of state spill databases indicates that pit overflows, tank overfills, and liner malfunctions are the most common causes for the release of oil and gas wastewater into the environment. This pattern in the data suggests that regulations and industry practices that target these three types of incidents would be effective in reducing the frequency of spills and, as a result, the risk of human and ecosystem exposure to toxic substances in flowback and produced water.
- Avoid outright bans of either pits or tanks.
Although tanks seem to offer more environmental protection than pits, there are some situations in which pits are superior. For example, pits are less susceptible to spills in the face of vandalism and lightning strikes, and pits typically involve fewer pipes and valves that can fail or be left open due to human error. On strict economic grounds, tanks are not always more expensive than pits, hence their growing popularity.
- Instead, integrate specifications regarding fluid storage in pits with specifications regarding fluid storage in tanks so that operators have the flexibility to choose the least-cost storage solution that meets given performance standards.
Our analysis suggests that smaller and less frequent spills occur with tanks than with pits (see our infographic). However, tanks are not a magic bullet, and because of a lack of information on the overall number of pits and tanks, it is not possible to ascertain whether tanks lead to fewer and smaller spills because they are actually safer or because a smaller number of them are currently being used.
- Promote uniform reporting and disclosure standards across states.
Our survey of state regulations of on-site shale gas and tight oil wastewater storage revealed significant heterogeneity across states in the number and stringency of regulated elements. This heterogeneity is not necessarily a negative; differences in regulations between one state and another may be justified by differences in the underlying geology, for example. However, the heterogeneity does provide an opportunity for states to learn from each other’s experiences; states may benefit by adopting a regulation that has worked well in another state or by eliminating a regulation that has been ineffective elsewhere.
- Furthermore, make these uniform state reports available on a searchable and sortable database.
An easily searchable and sortable state database of spills is an invaluable tool that can improve our understanding of the risks associated with pits and tanks used in oil and gas production. The ability to search for specific incidents and sort them according to their parameters can also help regulators and decisionmakers in the oil and gas industry adopt policies, practices, and technologies that target the most frequent and severe spill types. The New Mexico Oil Conservation Division’s database can serve as a model for this kind of useful resource, although the utility of the system could be significantly improved by incorporating an inventory of existing pits and tanks so that the number of reported spills can be put into perspective. Ideally, states should adopt a uniform reporting standard that will allow for a comparison of the outcomes of different approaches to risk mitigation.
- Promote further research to better understand the risks.
We identified several knowledge gaps that prevent us from gaining a comprehensive understanding of the risks that shale gas and tight oil wastewater storage in pits and tanks poses to human and ecological health. Specifically, future research would ideally seek new evidence regarding (a) the degree of exposure to substances in shale gas and tight oil wastewater through surface spills and leaching into groundwater; (b) the suitability of existing liner technology when it is specifically applied to pits storing flowback and produced water from hydraulic fracturing; and (c) the risks for ecological systems posed by shale gas and tight oil wastewater stored in pits and tanks.
