For the last three years, Marcellus Shale development has had no impact on the water quality of streams, rivers and watersheds in northern Pennsylvania and the southern tier of New York, according to a report by the Susquehanna River Basin Commission (SRBC).

In its third report on water quality in the basin, the SRBC said data from 2010-2013 at 58 of its 59 continuous monitoring stations — officially, the Remote Water Quality Monitoring Network (RWQMN) — showed there were no changes in water quality, and with few exceptions water chemistry also indicated good water quality.

The commission also found that aquatic insect monitoring was not adversely impacted by the density of oil and gas development in the region.

“[The] impacts of unconventional gas drilling and related infrastructural activities on stream biota are a significant concern for many people,” the SRBC said in the report’s 36-page executive summary. “One of the priorities of SRBC is to remain vigilant in monitoring for impacts as the industry progresses.”

The SRBC said that within the RWQMN region, gas well density ranges from 0 to 3.7 wells per square mile. But the commission said that for the three-year period, there was “not a strong visual pattern” between gas well density and the Index of Biotic Integrity (IBI) score SRBC uses to indicate the health of macroinvertebrates.

The commission said that since unconventional drilling allows for multiple wells on a pad, well pad density was calculated for each of the 58 watersheds tested; it found that they ranged from 0 to 1.3 pads per square mile.

“A similar visual pattern between gas pad density and IBI score was evident,” the SRBC said. “Neither well density nor well pad density appear strongly related to [the] macroinvertebrate IBI score. Indeed, using a linear regression model, neither factor explained greater than 1% of the variability in IBI scores for any given year.”

Elsewhere, the commission added that “macroinvertebrate IBI scores do not show a correlation to drilled wells or well pad densities, but rather to in-stream habitat; and well distance from the monitoring station was also not a good predictor of IBI score.”

The SRBC said that in watersheds with no unconventional gas drilling located upstream from a RWQMN monitoring station, IBI scores ranged from 29-100. According to the commission, the scores represent the lowest and highest IBI scores recorded during the three-year sample period.

“As a result of the small sample size…even a small change at either of the sites can cause a large shift in the box plot so those results should be regarded in that light,” the SRBC said, adding that there was no unconventional gas drilling in more than 30% of the watersheds where macroinvertebrate samples were collected through 2013.

The SRBC added that the “number of unconventional gas wells near the sampling site was not a good predictor of IBI score, as it accounted for no more than 1% of the variability in IBI score for any year or proximate distance.”

Previous reports on water quality in the basin were released by the commission in 2012 and 2013 (see Shale Daily, July 8, 2013; April 16, 2012). RWQMN was launched in 2010.

Although the report appears to exonerate shale gas development, the SRBC conceded that “a few incidents have occurred as a result of drilling activities upstream of select monitoring stations. In those cases, Pennsylvania agencies have used the continuous water chemistry data to track the events and determine if any water quality impacts occurred.”

SRBC is a compact established by the federal government in 1971 and based in Harrisburg that manages the water resources of the Susquehanna River Basin. The commission regulates some development within the Marcellus Shale in parts of New York, Pennsylvania and Maryland. The Susquehanna River starts in Cooperstown, NY, and flows 444 miles to Havre de Grace, MD, where the river meets the Chesapeake Bay. Representatives from Pennsylvania, New York, Maryland and the Army Corps of Engineers serve as commissioners.