Geothermal Energy: Resource Exploration and Drilling Impacts
Potential environmental impacts from exploration and drilling activities are generally temporary and of relatively small magnitude.
Activities during the resource exploration and drilling phase are temporary and are conducted at a smaller scale than those during the construction, operations and maintenance, and decommissioning and site reclamation phases. The impacts described for each resource would occur from typical exploration and drilling activities, such as localized ground clearing, vehicular traffic, seismic testing, positioning of equipment, and drilling. Most impacts during the resource exploration and drilling phase would be associated with the development (improving or constructing) of access roads and exploratory and flow testing wells. Many of these impacts would be reduced by implementing good industry practices and restoring disturbed areas once drilling activities have been completed. Potential impacts from these activities are presented below, by the type of affected resource.
Primary sources of noise associated with exploration include earth-moving equipment (related to road, well pad, and sump pit construction), vehicle traffic, seismic surveys, blasting, and drill rig operations. Well drilling and testing activities are estimated to produce noise levels ranging from about 80 to 115 decibels at the site boundary.
Emissions generated during the exploration and drilling phase include exhaust from vehicular traffic and drill rigs, fugitive dust from traffic on paved and unpaved roads, and the release of geothermal fluid vapors (especially hydrogen sulfide, carbon dioxide, mercury, arsenic, and boron, if present in the reservoir). Initial exploration activities such as surveying and sampling would have minimal air quality impacts. Activities such as site clearing and grading, road construction, well pad development, sump pit construction, and the drilling of production and injection wells would have more intense exhaust-related emissions over a period of 1 to 5 years. Impacts would depend upon the amount, duration, location, and characteristics of the emissions and the meteorological conditions (e.g., wind speed and direction, precipitation, and relative humidity). Emissions during this phase would not have a measurable impact on climate change. State and local regulators may require permits and air monitoring programs.
Cultural resources could be impacted if additional roads or routes are developed across or within the historic landscape of a cultural resource. Additional roads could lead to increased surface and subsurface disturbance that could increase illegal collection and vandalism. The magnitude and extent of impacts would depend on the current state of the resources and their eligibility for the National Register of Historic Places. Drilling activities could result in long-term impacts on archeological artifacts and historic buildings or structures, if present.
Surveys conducted during this phase to evaluate the presence and/or significance of cultural resources in the area would assist developers in locating sensitive resources and siting project facilities in order to avoid or minimize impacts to these resources.
Most impacts to ecological resources (vegetation, wildlife, aquatic biota, special status species, and their habitats) would be low to moderate and localized during exploration and drilling (although impacts due to noise could be high). Activities such as site clearing and grading, road construction, well drilling, ancillary facility construction, and vehicle traffic have the potential to affect ecological resources by disturbing habitat, increasing erosion and runoff, and creating noise at the project site. Impacts to vegetation include loss of native species and species diversity; increased risk of invasive species; increased risk of topsoil erosion and seed bank depletion; increased risk of fire; and alteration of water and seed dispersal.
Exploration and drilling activities have the potential to destroy or injure wildlife (especially species with limited mobility); disrupt the breeding, migration, and foraging behavior of wildlife; reduce habitat quality and species diversity; disturb habitat (e.g., causing loss of cover or food source); reduce the reproductive success of some species (e.g., amphibians). Accidental spills could be toxic to fish and wildlife. The noise from seismic surveys and drilling has a high potential to disturb wildlife and affect breeding, foraging, and migrating behavior. If not fenced or covered in netting, sump pits containing high concentrations of minerals and chemicals from drilling fluids could adversely impact animals (e.g., birds, wild horses and burros, and grazing livestock).
Surveys conducted during this phase to evaluate the presence and/or significance of ecological resources in the area would assist developers in locating sensitive resources and siting project facilities in order to avoid or minimize impacts to these resources.
Exploration activities are limited and would not result in significant long-term impacts in any resource area; therefore, environmental justice is not expected to be an issue during this phase.
Hazardous Materials and Waste Management
Seismic and exploratory well crews may generate waste (plastic, paper, containers, fuel leaks/spills, food, and human waste). Wastes produced by drilling would include drilling fluid and muds, geothermal fluids (and remaining sludge in sump pits after evaporation), used oil and filters, spilled fuel, drill cuttings, spent and unused solvents, scrap metal, solid waste, and garbage.
Drilling wastes include hydraulic fluids, pipe dope, used oils and oil filters, rigwash, spilled fuel, drill cuttings, drums and containers, spent and unused solvents, paint and paint washes, sandblast media, scrap metal, solid waste, and garbage. Wastes associated with drilling fluids include oil derivatives (e.g., such as polycyclic aromatic hydrocarbons [PAHs], spilled chemicals, suspended and dissolved solids, phenols, cadmium, chromium, copper, lead, mercury, nickel, and drilling mud additives, including potentially harmful contaminants such as chromate and barite). Adverse impacts could result if hazardous wastes are not properly handled and are released to the environment.
Produced geothermal fluids would be routed to sumps or pits and left to evaporate. Remaining sludge then would be removed and transported to licensed off-site locations for disposal.
Health and Safety
Potential human health and safety impacts during the exploration and drilling phase would include exposures to drilling muds, geothermal fluids or steam, and hazardous materials such as petroleum, oils, and lubricants; and the increased risk of serious injury or accidents (especially to the drilling crew). Adverse health impacts could also occur from dust generation and emissions. The potential for these impacts to occur is low if appropriate safety procedures are implemented.
Temporary and localized impacts to land use would result from exploration and drilling activities. These activities could create a temporary disturbance in the immediate vicinity of a surveying or drilling site (e.g., to recreational activities or livestock grazing). The magnitude and extent of impacts from constructing additional roads would depend on the current land use in the area; however, long-term impacts on land use would be minimized by reclaiming all roads and routes that are not needed once exploration and drilling activities are completed. All other land uses on land under well pads would be precluded as long as they are in operation. Exploration activities are unlikely to affect mining and energy development activities, military operations, livestock grazing, or aviation on surrounding lands. Activities affecting resources and values identified for protection areas would likely be prohibited.
Paleontological resources are nonrenewable resources. Disturbance to such resources, whether through mechanical surface disturbance, erosion, or paleontological excavation, irrevocably alters or destroys them. The potential for impacts on paleontological resources is high where grading for access roads and drilling sites intercept geologic units with important fossil resources. Seismic surveys, ground clearing, and vehicular traffic have the potential to impact the fossil resources at the surface. The disturbance caused by all these activities could increase illegal collection and vandalism.
Surveys conducted during this phase to evaluate the presence and/or significance of paleontological resources in the area would assist developers in locating significant resources so they can be studied and collected or so that project facilities can be sited in other areas.
As the activities conducted during the exploration and drilling phase are temporary and limited in scope, they would not result in significant socioeconomic impacts on employment, local services, or property values.
Soils and Geologic Resources
Impacts to soils and geologic resources would be proportional to the amount of disturbance. The amount of surface disturbance and use of geologic materials during exploration would be minimal. Surface effects from vehicular traffic could occur in areas that contain special soils. The loss of biological or desert crusts can substantially increase water and wind erosion. Also, soil compaction due to development activities at the exploratory well pads and along access roads would reduce aeration, permeability, and water-holding capacity of the soils and cause an increase in surface runoff, potentially causing increased sheet, rill, and gully erosion. The excavation and reapplication of surface soils could cause the mixing of shallow soil horizons, resulting in a blending of soil characteristics and types. This blending would modify the physical characteristics of the soils, including structure, texture, and rock content, that could lead to reduced permeability and increased runoff from these areas. Soil compaction and blending could also impact the viability of future vegetation. Any geologic resources within the areas of disturbance would not be accessible during the life of the development. Possible geological hazards (earthquakes, landslides, and subsidence) could be activated by drilling and blasting. Altering drainage patterns could also accelerate erosion and create slope instability.
TransportationNo impacts on transportation are anticipated during the exploration and drilling phase. Transportation activities would be temporary and intermittent and limited to low volumes of light utility trucks and personal vehicles.
Impacts to visual resources would be considered adverse if the landscape were substantially degraded or modified. Exploration and drilling activities would have only temporary and minor visual effects, resulting from the presence of drill rigs, workers, vehicles, and other equipment (including lighting for safety); and from vegetation damage, scarring of the terrain, and altering landforms or contours. Reclamation following exploration and drilling to restore visual resources to pre-disturbance conditions would lessen these impacts.
Water Resources (Surface Water and Groundwater)
Impacts to water resources during the exploration and drilling phase would range from low to high. Survey activities would have little or no impact on surface water or groundwater. Exploration drilling would involve some ground-disturbing activities that could lead to increased erosion and surface runoff. Drilling into the reservoir can create pathways for geothermal fluids (which are under high pressure) to rise and mix with shallower groundwater. Impacts of these pathways may include the alteration of natural circulation of geothermal fluids and the usefulness of the resource. Geothermal fluids may also degrade the quality of shallow aquifers. Best management practices based on stormwater pollution prevention requirements and other industry guidelines would ensure that soil erosion and surface runoff is controlled. Proper drilling practices and closure and capping of wells can reduce the potential for drilling-related impacts.
Temporary impacts to surface water may also occur as a result of the release of geothermal fluids during well testing, if they are not contained. Geothermal fluids are hot and highly mineralized and, if released to surface water, could cause thermal changes and changes in water quality. Accidental spills of geothermal fluids could occur due to well blowouts during drilling, leaks in piping or well heads, or overflow from sump pits. Proper well casing and drilling techniques would minimize these risks.
Extracting geothermal fluids could also cause drawdowns in connected shallower aquifers, potentially affecting connected springs or streams. The potential for these types of adverse effects is moderate to high; but may be reduced through extensive aquifer testing and selection combined with compliance with the state and federal regulations that protect water quality and the limitations of water rights as issued.
During the exploration and drilling phase, water would be required for dust control, making concrete, consumptive use by the construction crew, and in drilling of wells. Depending on availability, it may be trucked in from off-site or obtained from local groundwater wells or nearby municipal supplies.