The amount of wastewater generated from unconventional oil and natural gas drilling in Pennsylvania has remained flat since 2011 as production has outpaced the drilling of new wells, according to an updated study by the Ben Franklin Shale Gas Innovation & Commercialization Center (SGICC).

SGICC commissioned the Pennsylvania-based consulting firm Wunz Associates LLC to update the study that was first released in 2012 using 2011 data. The SGICC is affiliated with the Pennsylvania Department of Community and Economic Development and was established to help foster the state’s technology companies working in the oil and gas industry.

In the updated study, released Wednesday, SGICC said operators produced about 1.8 billion gallons of oil and gas wastewater in 2014, or 42.9 million barrels. That’s mostly unchanged from what the study found in 2011. About 67% of the wastewater generated in 2014 was produced water, compared to 29% that was “frack” or flowback water generated during drilling and completion operations. That’s a reversal from 2011 when the majority of wastewater in the state was flowback water.

“This has occurred largely due to the slowdown in drilling and fracturing of wells by the industry and could reverse again in the future when natural gas and natural gas liquids (NGL) prices and drilling picks up again,” said SGICC Director William Hall. “Additionally, the amount of produced water is likely to decline over time since it is generated in proportion to the amount of gas or NGLs a well is producing, and that tends to drop off fairly rapidly after the initial years of production.”

The study also found that about 91% of wastewater is recycled or reused for new wells in the state. About 7.9% is transported for disposal in underground injection wells, which are almost all located in Ohio. Just 1.1% is treated and discharged to surface waters.

“In the future, as the number of producing wells increase without a matching proportional increase in frack water needs, recycling treated wastewater to the next frack job will become more difficult,” the study said. “Recycling requires the demand for water, but the ratio of water demand to water production will be static or will decrease when proportionately fewer wells are being fracked and more wells are in production.”

The study said alternatives to recycling, such as underground disposal, distillation, evaporation or treatment and surface water discharge would likely need to increase and be implemented. The study’s authors examined the Pennsylvania Department of Environmental Protection’s reporting records, which are self-reported by producers. It also interviewed several leading industry wastewater management companies in the state.