Water impact in shale hydraulic fracturing is an issue that just won’t go away. A high level of concern by homeowners, communities, political leaders, and regulators threatens the industry’s social license to operate in some areas. Many jurisdictions prohibit or restrict shale extraction.

In many cases, their concerns focus on water impacts – water sourcing, transportation, and storage of fresh and produced water – in addition to concerns about impacts to groundwater and surface water.

This is particularly crucial for operating in the Marcellus and Utica formations of the northeastern US. Many oil and gas executives that may be based in the dryer, flatter areas of Texas and Oklahoma experience a new reality when they come to Pennsylvania.

They find that hilly terrain often causes a need for cut-and-fill operations to build water impoundments. Frequent rainfall and soft soils result in slope stability, maintenance, and erosion control issues. In many cases, the drillsites are remote, and the hills block cellular communication, making emergency response difficult.

This means managing water is one of the key success factors for shale oil and gas extraction. Companies that develop water management skills and a reputation for managing water effectively stand a better chance of faster regulatory approvals as well as fewer reputation-and environment-damaging unplanned releases.

Geosynthetic liners

Part of the answer to the need to store the required large volumes of fresh water and produced water as well as for stormwater control basins may come from another industry with a pressing need to manage water impacts – the solid waste sector.

One of the potential impacts of landfill operations comes from precipitation that falls on the site’s surface and percolates through the landfill, potentially picking up contaminants that might include heavy metals and petroleum byproducts. The resulting liquid or “leachate” is potentially impacted and must be prevented from migrating into groundwater or surface water.

For more than 50 years landfill operators have managed this risk by lining the bottom of a future landfill with impervious materials that prevent leachate from migrating so it can be captured and managed appropriately.

The geosynthetic materials commonly used as barriers include geomembranes and geosynthetic clay liners. Geomembranes vary with the type of resin used (LLDPE, HDPE, PVC, and others) as well as the additives, texture, and thickness. Material type selection often depends on the nature of the contaminants to be managed.

Geosynthetic clay liners often are more expensive than most geomembranes but may be the most cost-effective solution in the long run, depending on factors such as the potential impact of a leak or spill.

Solutions that work in landfills can be adapted for use in hydraulic fracturing. The oil and gas industry can take comfort in the fact that these materials have been tried and tested in long-term applications, there is extensive literature supporting their reliability, and environmental regulators understand the materials and

their application. Also, there is an extensive industry manufacturing these geosynthetics at cost-effective prices and an expansive contractor base familiar with installing them.

Geomembranes and other geosynthetic liners

There are many variables that affect the success of using geosynthetic liners in water impoundments, so making an informed choice is crucial. It is important to have access to the expertise of professionals who understand the characteristics of the site, the purpose of the impoundment, the relative merits of the different materials and impoundment designs, and the realities of constructing these structures.

Freshwater impoundments. In freshwater impoundments, for example, it is imperative to include an under-drain system to prevent gas “whales” – pockets of gas trapped below the geomembrane liner with no means of escape. Underdrain systems can include sand bedding layers, thick needle-punched nonwoven geotextiles, drainage geocomposites, and geotextiles fitted with small perforated pipes within their cross sections.

Many of the impoundments in the Marcellus and Utica formations are constructed using traditional cut-and-fill earthwork techniques, but some freshwater impoundments may need to be mobile due to a high water table or permitting issues. Mobile impoundments may be created using steel trusses overlain by geomembrane. While often more costly to build than in-ground impoundments, steel-truss construction has the advantage of flexibility – often needing only reasonably flat, competent ground. Also, because they can be taken down and rebuilt elsewhere, these impoundments may be the best solution for short-term service needs.

Flowback water and waste impoundments. Produced water that contains drill cuttings, proppant, and frac fluids as well as natural contaminants may require a more robust solution. This might include a primary and secondary liner with a collection system between them and a detection system beyond the secondary liner. This type of system is common in landfills where leachate will be generated over hundreds of years, so the technology is well understood by regulatory authorities, manufacturers, and contractors.

Success factors in designing and building impoundments. Following are some points to consider based on experience in this field:

  • Due to the potential impacts of the unplanned release of water, particularly flowback water, it is important for members of the oil and gas sector to work with partners that have experience designing such structures;
  • It may be best to work with engineering firms and constructors who have local experience given the wide range of regulations pertaining to such projects on a local or state level. Partners with experience designing and building containment structures for landfills may offer the greatest efficacy. In addition, these organizations are likely to have familiarity with the local geology and hydrology; and
  • Quality control is vital during the liner installation. A fusion weld or extrusion weld is used to seam LLDPE or HDPE geomembranes. Field crews must have proper qualifications, training, and experience to complete these exacting tasks. The geosynthetic contractor will usually be required to carry out nondestructive field testing of every seam and weld. Destructive tests are often specified to be completed at intervals with a third-party construction quality-assurance consultant present at all times. A leak-detection survey, carried out before the pit is put into service, can help ensure the safe and problem-free operation of the impoundment.
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