Evaluating System for Ground‐Water Contamination Hazards Due to Gas‐Well Drilling on the Glaciated Appalachian Plateau

Abstract

Recent drilling for natural gas in the Glaciated Appalachian Plateau area of northwestern Pennsylvania has caused limited, but increasing ground‐water contamination. By evaluating hydrogeologic parameters at a proposed gas well site, such as the ground‐water flow system, permeability of surficial sediments, and the presence of fracture zones, the contamination hazard of the site can be assessed. Three case studies document that the most hazardous sites are generally located on or near valley walls of major drainageways. The relatively steep hydraulic gradient, the frequent presence of highly permeable surficial sediments, and the low to moderate dilution of contaminants along the intermediate‐length flow paths at these sites all contribute to a relatively high pollution hazard. In addition to locating gas wells in high‐hazard hydrogeologic zones, allowing the annulus of gas wells to become pressurized is the other major factor contributing to aquifer contamination.

Well water contamination in a rural community in southwestern Pennsylvania near unconventional shale gas extraction

“…In addition, hydraulic fracturing can increase the permeability of the targeted deep formations by creating new fractures or propagating existing fractures thereby creating flow pathways for the upward migration of gases and fluids. [11,14,17,18] Establishing a definitive link between hydraulic fracturing itself and groundwater contamination has been challenging. The Energy Policy Act of 2005, Section 322 Hydraulic Fracturing amends the Safe Drinking Water Act to exclude "(i) the underground injection of natural gas for purposes of storage and (ii) the underground injection of fluids or propping agents (other than diesel fuels) pursuant to hydraulic fracturing operations related to oil, gas, or geothermal production activities."…”

“…[5][6][7][8][9][10] Freshwater aquifers may be contaminated by brines or hydrocarbons from underlying formations, chemicals used in the drilling or fracturing processes, waste water, and the natural gas itself through a number of pathways. [11][12][13][14][15][16][17][18] These include but are not limited to surface contamination from leaky impoundments and spills, poor well construction resulting in failed cement and improper casing, a pressurized annulus, as well as pre-existing faults and legacy issues from previous mining and drilling operations. [11,12,19] Well construction issues involving casing and cementing failures of the gas wells account for most contamination incidents.…”

“…[11][12][13][14][15][16][17][18] These include but are not limited to surface contamination from leaky impoundments and spills, poor well construction resulting in failed cement and improper casing, a pressurized annulus, as well as pre-existing faults and legacy issues from previous mining and drilling operations. [11,12,19] Well construction issues involving casing and cementing failures of the gas wells account for most contamination incidents. [19] They result in the creation of vertical migration pathways for fluids to migrate from the surface downward or from deep formations under extreme pressure upwards.…”

Current perspectives on unconventional shale gas extraction in the Appalachian Basin

“…[97][98][99][100] In what now seems prescient, a hydrogeologist from Allegheny College, Samuel S. Harrison published two papers in the mid 1980s that discussed the groundwater contamination potential of hydraulic fracturing in the Appalachian Basin. [101,102] Among the routes of contamination considered were leaking slush pits (impoundments), surface discharge during fracturing or servicing, and road application of brine; from the subsurface through pre-existing natural fractures, a faulty bottom seal above the production zone as well as brine and gas from strata above the production zone; leaking from a pressurized annulus; and from casing of insufficient depth or improper construction. [101,102] Flow of fluids towards the surface through advective transport and natural fractures may be accelerated by the hydraulic fracturing process.…”

“…[101,102] Among the routes of contamination considered were leaking slush pits (impoundments), surface discharge during fracturing or servicing, and road application of brine; from the subsurface through pre-existing natural fractures, a faulty bottom seal above the production zone as well as brine and gas from strata above the production zone; leaking from a pressurized annulus; and from casing of insufficient depth or improper construction. [101,102] Flow of fluids towards the surface through advective transport and natural fractures may be accelerated by the hydraulic fracturing process. [97] A recent study bears out the concern for proper casing as they documented that over the past thirteen years, unconventional wells had a sixfold higher number of casing and/or cement issues reported.…”