Encompassing the longest free-flowing river in the eastern United States, the Delaware River Basin also happens to sit partially on top of the Marcellus Shale, the second largest gas field in the world. To date, a moratorium put in place by the Delaware River Basin Commission has kept gas companies out of the Delaware River Basin — but environmental groups worry that without a permanent ban, the basin could be opened to fracking at a moment’s notice.

Now, a new study seeks, for the first time, to quantify the environmental impact of opening the Delaware River Basin to fracking — and what natural gas extraction could mean for the communities that call the region home.

The Delaware River, which begins its flow from springs tucked away in New York’s Catskill Mountains, winds for nearly 400 miles before emptying into the Delaware Bay and, eventually, the Atlantic Ocean. Along the way, its watershed drains an area of 12,800 square miles, and supplies drinking water for nearly 20 million people — more than 5 percent of the country — along the East Coast.

The Delaware River Basin — which encompasses parts of Pennsylvania, Delaware, New Jersey, and New York — also happens to contain part of the Marcellus Formation, a rock formation that extends 95,000 square miles from West Virginia to New York. The Marcellus Formation is made up of shale, and inside of that shale sits vast reserves of natural gas — untapped for centuries, until a technology known as hydraulic fracturing, or fracking, made extracting the natural gas possible.

Until now, the portion of the Marcellus shale that is contained within the Delaware River Basin has been off limits to fracking, stalled by a moratorium put in place by the Delaware River Basin Commission (DRBC). But that moratorium is only temporary — and with natural gas companies eying potential reserves beneath the basin, the Delaware Riverkeeper Network, an advocacy group aimed at preserving the health of the Delaware River, commissioned CNA, an independent, non-partisan, non-profit research firm to take a look at what could happen to the region if the Delaware River Basin is opened up to fracking.

“We are perpetually on the precipice of drilling and fracking coming to our watershed,” Delaware Riverkeeper Maya van Rossum told ThinkProgress. “There’s constant pressure. We have never felt confident that we could just sit idly by and count on this moratorium holding.”

Looking at a scenario where both the Delaware River Basin moratorium and the New York State fracking ban are reversed, CNA used statistical analysis to understand where fracking wells would likely go within the basin. Using statistical tools, researchers analyzed the locations of current wells within the interior of the Marcellus Shale. They looked at site-specific qualities, like slope, distance from roads, distance from pipelines, and how far the shale is from the surface, to paint a picture of where wells are currently located. They then used mapping layers to look for areas in the Delaware River Basin that matched those conditions. From their analysis, they determined that up to 4,000 new fracking wells could be created in the Delaware River Basin if the moratorium were to be lifted.

The group then looked at the environmental impacts that these wells could have on the region, breaking those impacts into the categories of land, water, and air. In terms of land, the largest impact of fracking in the Delaware River Basin, CNA found, would be changes in land use — specifically, the conversion of forested ecosystems into roads, wells, and pipelines for extracting and exporting the gas. For each well, CNA found that an average of 17 to 23 acres of direct land cover changes would occur — and 75 percent of all land changes would be due to pipeline building. For the complete Delaware River Basin, under the scenario put forth by CNA, a total of 18 to 26 square miles of land would be converted to serve the fracking wells — the equivalent of building as many as 840 Walmart Supercenters in the area.

The loss of land would degrade forest ecosystems, CNA found, causing forest cores — the areas inside of the forests that typically house the highest density and diversity of species and store the most carbon — to become fragmented and turn into more vulnerable forest edges. Overall, a scenario where 4,000 new fracking wells are constructed within the Delaware River Basin would lead to a 5 to 10 percent decrease in forest cores, along with a 2 to 8 percent gain in forest edges.

The study also looked at how fracking would impact local watersheds and streams within the Delaware River Basin (though it did not consider the larger downstream implications on the Delaware River itself).

“Water is central to the process of hydraulic fracking, for chemical mixing, for fracking itself, and then a significant amount of that water can come back as produced water,” Paul Faeth, Director of Energy, Water and Climate research at CNA, told reporters on a press call, adding that each fracking well uses around 4.5 million gallons of water for its extraction operations. CNA found that the impact on the region’s water resources — of water pulled from streams to serve the needs of fracking companies — varies greatly based on each stream’s flow, and is much lower in years with a great deal of precipitation than in drought years. At most, however, CNA found that fracking could reduce stream flows by up to 70 percent, while potentially raising the amount of dangerous contaminants, like barium, 500 percent compared to background levels.

Additionally, the study found that the construction of fracking wells — and subsequent extraction of natural gas — could have significant health impacts for the communities directly neighboring the wells. Researchers looked at one county in particular — Wayne County, which would likely see the most well development — and found that up to 30,000 residents could be impacted by emissions of nitrous oxide, mostly from compressors gathering gas and taking it to market. If the whole basin is taken into account, another 15,000 residents in other counties could also face air quality issues.

“To see that in one county, 60 percent of the population have their health impacted by drilling and fracking in their communities, that is really alarming,” van Rossum said. But she also said that the study’s findings didn’t surprise her.

“What the study confirms is what we have always said, which is that the harm that is inflicted by shale gas extraction is far reaching, wide ranging, short term and long term,” she said. “It doesn’t matter if you reduce, to a certain extent, one harm or another. You cannot make shale gas extraction safe for the environment and communities.”

Anthony Ingraffea, professor emeritus of civil and environmental engineering at Cornell University who was not involved with the CNA study, called the study “timely and exhaustive.”

“The epoch of anecdotes is over,” he told reporters on a press call. “We now have hard scientific evidence of the harmful impacts of fracking development.”

The study adds to a growing body of scientific literature looking at the potential impacts of fracking, on both a regional and national scale. According to Ingraffea, 580 different scientific studies have looked into fracking, with 80 percent of those published since January 1 of 2013. Earlier this year, the EPA released its long-awaited draft assessment on the impact fracking has on water pollution, concluding that while the process has several key vulnerabilities, there is no evidence of widespread, of systematic impacts on the United States’ drinking water.