The Swamp School

Impacts to Wetlands

Impacts on wetlands from onshore development would be largely associated with the damage or loss of vegetation and habitat from seismic exploration, drilling, and construction activities. Because regulations prohibit direct impacts to wetlands from exploration and construction, only indirect impacts would be expected to occur. Activities that would impact wetlands would require permits from the Corps and/or state agencies.

The use of good engineering practices in the construction of well sites and facilities can greatly minimize impacts to wetlands.

For both onshore and offshore sites, impacts from normal operation could be associated with maintenance activities or decreases in air or water quality. Wetlands could be affected during any of the phases of developing an oil or gas site by the accidental spill or release of oil or gas during exploratory drilling, well completion, and production, as well as by accidental releases of drilling, production, and processing wastes.

In addition to wetlands, other special aquatic sites also occur in nearshore areas. These sites could also be affected by oil and gas development in a manner similar to that of wetlands.

Exploration. Wetlands occur in all areas of oil and gas potential. Although avoidance of wetlands during onshore exploration and drill site selection would generally be possible, direct impacts could potentially occur in some areas. Impacts to wetlands (crushing of vegetation or substrate compaction) may occur as a result of the exploration teams and equipment conducting the seismic evaluations entering wetland areas during exploration. Survival of many native plant species and seedling establishment may be adversely affected. Soil compacting may also convert some vegetated wetland areas to open water or submerged vegetation communities. Such impacts could potentially result in long-term
or major impacts on local wetlands, with effects in some cases lasting decades. Some wetland vegetation would also be disturbed or lost during installation of exploratory wells. It is very likely that invasive plant species would colonize areas of disturbance, resulting in probable long-term effects.

Construction. For onshore wells, construction of a permanent drilling pad and associated structures (pipelines, access roads, and utility corridors) near the coastline may result in both temporary and permanent impacts on wetlands. Construction impacts may include:

• Permanent loss of vegetation and associated habitat from clearing and grading
of the drill pad location;
• Permanent loss or disturbance of vegetation and habitat from clearing and
grading of any required access roads, pipeline routes, utility corridors, and any
associated construction support areas;
• Increased sedimentation in adjacent wetlands due to erosion and runoff from
construction areas;
• Disturbance of local wetland vegetation and biota due to changes to surface
and subsurface hydrology from altered surface runoff and infiltration patterns
and rates;
• Disturbance of local wetland vegetation due to changes in groundwater
hydrology from groundwater removal during drilling; and
• Habitat fragmentation due to siting of the drill pad, access roads, and pipeline
and utility corridors.
Onshore drill sites may range from up to 5 or more acres (2 ha) in size, and site development would require the removal of vegetation and disturbance of soil and/or sediments from the drill site. Should the drill pad location necessitate that any pipelines, access roads, and/or utility corridors cross streams or other aquatic habitats (such as wetlands), additional removal of wetland vegetation, soils, and sediments would also occur, resulting in further loss of wetland habitat. These wetland losses (potentially long-term in nature) could result in the localized reduction or loss of wetland functions, such as fish and wildlife habitat, attenuation of flooding and shoreline erosion, and removal of substances that reduce water quality.

Construction of drill sites, pipelines, roads, and utility corridors could also result in habitat fragmentation and separation of wetland areas, especially if construction took place in areas with existing roads and other facilities.

Indirect impacts on wetlands from the construction of onshore well sites may include altered hydrology from changes in surface drainage patterns or separation of surrounding wetland areas from adjacent water sources. Some wetlands, such as marshes and swamps are maintained in part by surface water flows, and the development of an oil or gas production site may result in both temporary and long-term changes to surface water inflow and/or outflow rates or patterns. Maintaining natural drainage patterns during site development can minimize such effects. Soil compaction resulting from construction adjacent to wetlands may reduce the infiltration rates of precipitation into the soil and underlying groundwater, thereby increasing surface water runoff rates as well as the sediment load carried by the runoff. Increased surface water runoff from the well site and any access road and pipeline corridors may also increase the fluctuation of water surface elevations in adjacent wetlands (especially during precipitation events), resulting in greater extremes of high and low water levels, including reductions of the base flows and increases in flood flows of adjacent streams.

Fens and bogs, which generally are not supported by surface flows, may be greatly affected by altered subsurface and surface hydrology. Water removal during drilling or the disposal of produced water may alter the subsurface hydrology on which the fens and bogs greatly depend. Hydrologic alteration of wetlands may result in an increase or decrease in the frequency, duration, depth, or extent of soil saturation or inundation, which is critical for many wetland plant species.

Fens may also experience a reduction in groundwater inflow if a high degree of development (with its introduction of impervious surfaces) occurs within the recharge area. The establishment of buffer zones around wetlands, areas in which soil disturbance and use of heavy equipment is avoided, can minimize many indirect impacts to wetland hydrology.

Changes in surface and subsurface hydrology may result in the replacement of one wetland community type for another, or they may promote wetland losses by conversion to upland communities or conversion of wetland vegetation communities to open water. Soil compaction may also result in the loss of species richness and diversity. Many native wetland species indicative of high-quality habitats are sensitive to disturbance and may be displaced by species more tolerant of disturbance or by invasive non-native species, thereby reducing biodiversity. Invasive plant species typically develop high population densities and thereby exclude most other plant species, reducing native species abundance and diversity. Diversity in invertebrate, fish, and wildlife communities utilizing that habitat may also subsequently be reduced.

Degradation of water quality as a result of increased sedimentation from construction areas and/or groundwater disposal of produced water may also affect wetlands. Without proper site preparation, erosion of disturbed soils or insufficiently stabilized soils and unstable slopes following site grading may result in sediment inputs and turbidity in wetlands that receive storm water runoff. Runoff from exposed soil surfaces, such as the drill site, access roads, or pipeline rights-of-way (ROWs), may create turbidity in wetlands, increased temperature, and lower dissolved oxygen. Runoff from washdown areas may contain cuttings when air drilling is used.

Erosion may occur at pipeline stream crossings. Sedimentation can alter plant communities, reducing plant density and biodiversity, decreasing sensitive species, and creating opportunities for invasive species establishment. The implementation of best management practices and good engineering practices, such as the use of silt fences for erosion and sedimentation control, would minimize such impacts to wetlands.

Operation

Access roads and utility corridor ROWs may allow for increased access and disturbance from recreational activities in previously undisturbed areas; the ROWs may also provide opportunities for invasive species to colonize these areas. Normal operations would include a variety of routine monitoring and maintenance activities that would not be expected to result in adverse environmental effects under normal circumstances. However, should concerns with a pipeline (e.g., unacceptable level of pipeline corrosion) or waste storage facilities (e.g., integrity concerns for on-site disposal pits for drilling muds) be identified during maintenance or monitoring, measures to address those concerns may include replacement or repair (such as the replacement of a section of buried pipeline), which could result in additional environmental impacts. In such an event, impacts would be similar in nature to those identified for construction, but would likely be of lesser magnitude because the resources would have
previously been disturbed during facility construction.

Air quality near operating facilities may be reduced during normal operations. Exhaust emissions from equipment, atmospheric releases from wells or processing facilities, or fugitive dust generated from exposed soils could have local adverse effects on wetland vegetation.

Storage or handling of waste products could introduce contaminants into wetlands, and contaminants could be present in storm water runoff that flows into wetlands. However, required pollution reduction measures would minimize air and water quality reductions near facilities, and these occurrences would generally be intermittent and infrequent. Subsequently, potential impacts to wetlands would be minimized.

Shallow groundwater may become degraded from disposal or injection of produced water and could potentially affect wetlands that receive groundwater discharge, such as fens, beyond the immediate facility location, vegetation and if biota are exposed to toxic contaminants. Subsequent effects may persist long-term. Injection is a widely accepted method for disposing of produced water. However, local and state regulations would likely direct operational requirements for the protection of groundwater, and collection, rather than discharge, of fluids may be required.

Accidental Spills and Releases. Spills of oil or drilling and processing waste materials may occur during each of the phases of oil and gas development, and these may affect wetland communities. With slant drilling, there is little potential for oil to migrate from the bottom hole (which would be located under the lake bottom) to overlying surface water, because the geologic units above the oil-bearing units will act to prevent such an upward movement of oil or gas. More likely is an accidental release at the
wellhead because of a blowout. However, the use of blowout preventers significantly reduces (but does not eliminate) the likelihood of such a release.

Uncontrolled onshore spills may cover vegetation and wetland soils and sediments and may result in the elimination of wetland biota in affected areas, including aquatic invertebrates and vegetation. The severity of the effect will depend on the chemical and toxicological nature of the released materials and the duration and frequency of the release. Spills of some petroleum products, such as diesel fuel, can result in higher mortality and poorer recovery of vegetation than would result from crude oil spills.

Exposure to spills may result in a decrease in the abundance of wetland plants and animals. Onshore spills that enter streams may impact delta, estuarine, and riverine wetlands. Spills that subsequently
enter lakes may also affect coastal lagoon, solution basin, and fringing wetlands along the coastline.

Spills may also result in the loss of sensitive wetland plant species, which often occur in high-quality undisturbed wetlands, and affected areas may become populated only by more tolerant species. Disturbance of wetland communities very often leads to colonization by invasive plant species, many of which are non-native. Therefore, spills may also promote the establishment of invasive plant species that may compete with and potentially displace native wetland vegetation. This would result in a decrease in the quality of the wetland and affect its role in providing wildlife habitat. Although spills from a variety of sources may affect wetlands, spills at onshore well sites are typically contained by barriers constructed around the well site.