148
and metering line. In this case, most of the pad can be allowed to return to a climax
ecology. However, if an operator intends to re-frack the wells at some future date,
access to the entire pad would be needed to accommodate the large amount of
equipment and materials. The costs of having to re-clear brush and trees from an
overgrown five acre pad for a re-frack might be considerably higher than the routine
cost of just maintaining it during periodic visits until a re-frack can be accomplished. In this case, ecological succession will be put on hold until there is no
longer a need for the large pad.
The techniques applied to the management of these large, cleared drill pad areas
over time on different shale plays in different parts of the country can have an impact
on the local ecology. How ecological succession proceeds under different approaches
could provide valuable insights for ecologists monitoring this process around construction sites, abandoned buildings, and other infrastructure.
8.3 Aquatic and Marine Ecosystems
Along with degradation of aquatic ecosystems from surface spills of frack chemicals or produced fluids, the main impact shale gas development has on streams is to
affect runoff from the increase in impervious surface area in small watersheds. A
study done in Maryland a number of years ago found that once about 10% of the
surface area in a watershed becomes impervious (i.e., roads, rooftops, driveways,
parking lots, etc.), the stream biota undergo shifts in population, reductions in diversity, and reduced population density. The 10% threshold seems to be the point at
which storm water runoff events become too intense for normal aquatic ecosystems,
and declines in population are observed (Barnes et al. 2002).
A runoff modeling study at the DOE National Energy Technology Laboratory
(NETL) assumed that a single drill pad and associated access roads add about 3.25
hectares (8 acres) of impervious surface area to a watershed (Soeder 2017). The
model outputs showed that impacts to a stream varied with catchment area and land
use type. The least impaired land use type is forest, and the threshold for stream
impact from a single drill pad in a forested watershed occurs when the catchment
area is 5 square km (2 square miles) or less. Other land use types already have some
degree of hydrologic impairment, so the threshold for stream impacts from a single
drill pad on these lands will affect a larger catchment area. Stream impact thresholds
for drill pads on agricultural land were found to affect catchment areas of 6.5 square
km (2.5 square miles), and streams were impacted when a drill pad was placed on
urbanized land within a catchment area of 13 square km (5 square miles).
With a few notable exceptions like the Barnett Shale development in the urbanized Dallas-Ft. Worth area, most shale gas well pads are located in rural areas that
are forested or agricultural. The impact to watersheds of placing drill pads and associated infrastructure on these lands are not completely understood. Certainly, replacing eight acres of water-absorbing forest with eight acres of impervious surface will
probably degrade nearby water resources. However, placing a drill pad on
8 Impacts to Human Health and Ecosystems
and metering line. In this case, most of the pad can be allowed to return to a climax
ecology. However, if an operator intends to re-frack the wells at some future date,
access to the entire pad would be needed to accommodate the large amount of
equipment and materials. The costs of having to re-clear brush and trees from an
overgrown five acre pad for a re-frack might be considerably higher than the routine
cost of just maintaining it during periodic visits until a re-frack can be accomplished. In this case, ecological succession will be put on hold until there is no
longer a need for the large pad.
The techniques applied to the management of these large, cleared drill pad areas
over time on different shale plays in different parts of the country can have an impact
on the local ecology. How ecological succession proceeds under different approaches
could provide valuable insights for ecologists monitoring this process around construction sites, abandoned buildings, and other infrastructure.
8.3 Aquatic and Marine Ecosystems
Along with degradation of aquatic ecosystems from surface spills of frack chemicals or produced fluids, the main impact shale gas development has on streams is to
affect runoff from the increase in impervious surface area in small watersheds. A
study done in Maryland a number of years ago found that once about 10% of the
surface area in a watershed becomes impervious (i.e., roads, rooftops, driveways,
parking lots, etc.), the stream biota undergo shifts in population, reductions in diversity, and reduced population density. The 10% threshold seems to be the point at
which storm water runoff events become too intense for normal aquatic ecosystems,
and declines in population are observed (Barnes et al. 2002).
A runoff modeling study at the DOE National Energy Technology Laboratory
(NETL) assumed that a single drill pad and associated access roads add about 3.25
hectares (8 acres) of impervious surface area to a watershed (Soeder 2017). The
model outputs showed that impacts to a stream varied with catchment area and land
use type. The least impaired land use type is forest, and the threshold for stream
impact from a single drill pad in a forested watershed occurs when the catchment
area is 5 square km (2 square miles) or less. Other land use types already have some
degree of hydrologic impairment, so the threshold for stream impacts from a single
drill pad on these lands will affect a larger catchment area. Stream impact thresholds
for drill pads on agricultural land were found to affect catchment areas of 6.5 square
km (2.5 square miles), and streams were impacted when a drill pad was placed on
urbanized land within a catchment area of 13 square km (5 square miles).
With a few notable exceptions like the Barnett Shale development in the urbanized Dallas-Ft. Worth area, most shale gas well pads are located in rural areas that
are forested or agricultural. The impact to watersheds of placing drill pads and associated infrastructure on these lands are not completely understood. Certainly, replacing eight acres of water-absorbing forest with eight acres of impervious surface will
probably degrade nearby water resources. However, placing a drill pad on
8 Impacts to Human Health and Ecosystems