Air Quality and Ecological Impacts

Our Approach to Air Quality and Ecological Impacts

At Milestone, we are committed to environmental stewardship and the preservation of natural resources. We continuously seek to identify improvement opportunities, utilizing industry best practices to reduce our operational footprint and minimize ecological impacts.

Air Quality

Milestone’s facilities are permitted through the TCEQ, the state level equivalent office of the U.S. Environmental Protection Agency (“EPA”). By nature of our operations, Milestone claims several permit-by-rule (“PBR”) authorities with the TCEQ. PBRs are allowable air permit authorizations that require facilities to meet certain general and specific requirements. There are over 100 PBRs that may be claimed or registered within the TCEQ’s air permitting program.

Milestone’s PBR claims are satisfied using EPA- and TCEQ-approved emissions estimation methods and published guidance. Based on the application of Milestone’s known inputs for these estimation methods, we satisfy all applicable PBR requirements per the TCEQ. To date, our operations have had zero incidents of non-compliance. In addition to trace amounts of traditional GHGs, Milestone’s air emissions include relatively small amounts of NMVOCs and other hazardous air pollutants (“HAPs”) emitted during the receipt, handling, temporary storage, processing, and disposal of waste at our slurry facilities and landfills. 

The table below shows air emissions by compound for the year ending December 31, 2020:

Air Emissions in Metric Tons  
Nitrogen oxide (“NOx”) (excluding N2O) not meaningful
Sulfur Oxides (“SOx”) not meaningful
Volatile organic compounds 19.35
Hazardous air pollutants 1.09

Ecological Impacts

At Milestone, sustainability is integrated into every element of our business. Our processes and facilities are designed to have minimal environmental impact and provide one-stop waste management solutions for our customers’ solid and liquid wastes. We build our slurry injection facilities and landfills close to our customers’ field operations to minimize transportation costs and transportation-related environmental impacts. Moreover, our proximity to customers’ operations reduces third-party transportation vehicle traffic and associated road safety risks. Milestone facilities are not situated within areas of dense population and are several kilometers from any nearby residential populations.


Our key performance indicators are an important tool to ensure we are managing the environmental impacts of our operations.

+ Volume of waste received

+ Load and truck washout count

+ Waste type

+ Wait time

+ Mass of carbon sequestered

+ Mass of fugitive GHG emissions avoided


Our sites receive non-hazardous E&P waste directly from customers’ field locations primarily via third-party transportation vehicles, including vacuum trucks, rear-end dumps, and liquid storage vehicles. We manage oilfield waste streams at two types of facilities: slurry injection facilities and landfills. At our slurry facilities, we separate non-injectable residual solids at the surface and send them to our “carbon sink” landfills. Meanwhile, drilling mud and other slurries are blended with produced saltwater and flowback water and injected into our Class II UIC wells. Our landfills are designed to manage both solid (e.g., drill cuttings) and liquid (e.g., drilling mud) waste streams.

Our integrated, multi-solution business model utilizes both slurry injection and landfill facilities to maximize resource efficiency, while simultaneously reducing the cost and environmental impact of each waste stream we handle. Most of the liquid waste received at our landfills is directed to our slurry injection facilities, allowing us to minimize the use of landfill airspace compared to landfill-only competitors through reduced use of added solidification material.

+ Land surface conservation: Our slurry injection facilities utilize a surface area that is approximately 1% of the surface area of a typical energy waste landfill.

+ Efficient use of landfill airspace: During 2020, Milestone injected approximately 2.9 million barrels of waste that would have otherwise been solidified and consumed landfill airspace.

Designed for the Environment

Milestone works to mitigate ecological impacts in all phases of activity, including pre-construction evaluations and ongoing operations. When selecting our slurry injection sites, we target receptive, permeable formations bounded by thousands of feet of stable confining layers. We also seek locations that minimize the total number of active and inactive wells permitted in the same target injection formation. If we are considering a site near an inactive or closed wellbore, we complete our due diligence to ensure that the wellbore has been correctly plugged and cemented. During our facility permit reviews with the various state agencies, we go through a rigorous process to demonstrate how our methods and technologies are proven to help to reduce overall environmental impact. Lastly, we seek to minimize our overall site footprint while maximizing our operational potential.

Every aspect of our engineering design has been considered to minimize Milestone’s environmental footprint. Our offloading bays and pits feature concrete floors and containment walls to prevent soil contamination, our overhead and underground piping are appropriately coated to minimize the potential for friction and breakage, and our fiberglass and steel storage tanks are coated with specially designed materials to reduce potential fugitive emissions sources. As we expand operations and evaluate new facilities, we integrate design improvement opportunities identified from existing operations.

We seek to be at the forefront of operations in the industry and we pride ourselves on minimizing our footprint and maintaining good housekeeping to guard against impacts to the surrounding environment. Our teams complete daily, weekly, and monthly housekeeping inspections of all facility operations, and immediately address identified issues to ensure we continue operating as top-tier facility. The North American Industrial Classification (“NAICS”) and the Standard Industrial Classification (“SIC”) identifies Milestone’s facilities for “Oil and Gas Field Services, not elsewhere classified” so they are not covered under the U.S. Environmental Protection Agency’s Toxic Release Inventory (“TRI”) regulations. However, we do maintain an active list of stored oil-containing materials, including those greater than 55-gallons, to ensure compliance with other federal and state programs.

A Different Kind of Landfill

For waste management companies, a core environmental consideration is designing landfills to contain and manage leachate, non-hazardous waste, and hazardous waste. Milestone’s two landfills are designed as “carbon sinks” with sophisticated liner systems to protect against leachate and monitor groundwater. The RCRA-exempt waste in these landfills include but are not limited to solid wastes generated within an oil and gas exploration lease, contaminated soil, drill cuttings, and other E&P-exempt slurry waste that is not suitable for injection via our slurry facilities. Any waste recovered in the leachate systems is either (i) returned to our slurry facilities through a sealed pipeline, where it is permanently sequestered via injection, or (ii) solidified with other forms of solid waste and sequestered in the landfill.

During 2020, Milestone had

ZERO incidents of non-compliance associated with environmental impacts and zero corrective actions implemented for landfill releases.

Infographic of a Milestone landfill

Sustainable Practices for Water Management

Water is an important component in Milestone’s operations. We make every effort to re-use water from appropriate sources while minimizing use of freshwater. Most of the water we utilize in our slurry injection operations is produced saltwater and flowback from our E&P customers. As an example, we use produced saltwater for our truck washout services, which greatly reduces freshwater use while simultaneously sequestering our customers’ produced saltwater in an environmentally sustainable manner. Saltwater assists our slurry filtration process to manage suspended solids prior to injection. In limited instances, when we do use freshwater, it is either delivered or extracted from non-potable groundwater sources. To avoid extracting more water than allowable under our agreements with local landowners, we have installed flow reducers and real-time meter systems on all freshwater well sources.

As a member of the energy ecosystem, Milestone shares our customers’ commitment of using resources responsibly and seeking ways to continually reduce the impact of our business.