Our Negative Carbon Footprint

Milestone’s Negative Carbon Footprint

Slurry injection is the core component of our business. Our slurry facilities utilize a closed-loop disposal well system to inject liquid E&P waste streams into highly permeable geological strata thousands of feet below usable groundwater. This system prevents the hydrocarbons contained in our customers’ waste from volatilizing or otherwise degrading into fugitive emissions, and instead permanently sequesters them beneath the earth’s surface. Such fugitive emissions would otherwise occur naturally over time through reactions between the hydrocarbons and other physical, physio-chemical, and/or biological elements at the surface (i.e., weathering) if they had been disposed of through common practices such as land application. With the largest slurry injection installed capacity base in the U.S., we sequester far more emissions than we directly and indirectly generate through our operations. Milestone, therefore, has a materially negative carbon footprint.

Leachate recovered is being blended into other solid waste and reinterred in our landfill.

Leachate recovered is being blended into other solid waste and reinterred in our landfill.

Direct Emissions

“Scope 1” emissions are defined as direct GHG emissions from sources that are owned or controlled by a company. We present our emission values for traditional GHG (CO2 and methane) as well as additional disclosure of the “carbon dioxide potential” from non-methane volatile organic compounds (“NMVOCs”) emissions from potential atmospheric oxidation after the initial fugitive release. Limited guidance exists for the accounting treatment of potential atmospheric oxidation of fugitive NMVOCs. We believe this increased transparency enhances the comparability of our operations with traditional land application disposal methods in terms of total carbon impact. 

Milestone’s gross Scope 1 emissions, which exclude any sequestration impact from slurry injection, come from three primary sources. First, at our slurry facilities, the waste we receive contains a small portion of non-injectable solids. We separate these solids at the surface and send them to a nearby Milestone or third-party landfill for disposal. The remaining slurry waste is blended with produced saltwater, injected underground, and permanently sequestered. During this process, minor fugitive emissions of GHG and other NMVOCs occur during receipt, handling, and temporary storage of waste prior to injection. We account for the GHG and NMVOC emissions from our slurry injection facilities by using known customer-speciated waste inputs and federal and state approved guidance and methods in accordance with our facility air permits from the Texas Commission on Environmental Quality (“TCEQ”). During 2020, these GHG emissions amounted to 15 MT CO2e (129 MT of total “carbon dioxide potential” when accounting for potential atmospheric oxidation of NMVOC emissions).

Second, our landfills can generate gross Scope 1 emissions that are fugitive in nature. In addition to combustion and fugitive emissions of GHGs, aerobic volatilization and degradation of NMVOCs occurs when landfill waste is received, handled, and temporarily stored before internment in the landfill cell. Once inside the cell, anaerobic degradation of remaining hydrocarbons takes place over time through a reduction process, i.e., interaction of carbon molecules with hydrogen and other organic matter in the landfill cell. Compared to municipal solid waste (“MSW”) landfills, the organic matter in oilfield waste landfills such as ours is considerably more homogeneous in chemical composition. Heterogeneity of organic matter in MSW landfill waste causes much faster anaerobic degradation of matter into GHGs, primarily methane. Thus, on a volumetric basis, an oilfield waste landfill generates substantially less (if any) landfill gas per time interval than a similarly sized MSW landfill. We account for the GHG and NMVOC emissions of our landfills in accordance with our facility air permits from the TCEQ, using known customer-speciated waste inputs as well as federal and state approved guidance and methods. Based on this methodology, our fugitive emissions of GHG are de minimis, and the entirety of landfill fugitive emissions consists of NMVOCs.8 During 2020, the total “carbon dioxide potential” of these NMVOC emissions was 66 MT CO2e. 

Lastly, while we do not have the vehicle fleet commonly associated with many waste management competitors, our field personnel routinely utilize approximately 12 diesel-fueled pickup trucks and other off-road equipment. We include emissions from these vehicles and equipment, amounting to 1,332 MT CO2e, in our total gross Scope 1 emissions calculations.

A graphic image of a leaf with "Net Negative" written across it.

Indirect Emissions

Indirect GHG emissions are emissions that are a consequence of the operations of a company but occur at sources owned or controlled by another company. Indirect emissions are referred to as either “Scope 2” or “Scope 3”. Our Scope 2 emissions are generated by the utility companies that provide the electricity we use in our operations. During 2020, all electricity consumed in our operations originated from the Electric Reliability Council of Texas (“ERCOT”) grid. 

Scope 3 emissions represent all indirect GHG emissions, not included in Scope 2, that occur in our value chain, including both upstream and downstream emissions. Given the nature of our business, vehicle fuel consumed by our contracted transportation comprises essentially all of our material Scope 3 emissions. The table below shows our gross and net emissions for the year ended December 31, 2020.

Global Greenhouse Gas Emissions in Metric Tons of CO2e  
Scope 1 emissions avoided through carbon sequestration9 (231,764)
Scope 1 direct emissions from operations 1,347
Scope 2 indirect emissions from electricity consumed 3,741
Scope 3 other indirect emissions10 464
Net 2020 emissions (226,212)

Helping Our Customers Achieve Net Zero

Milestone’s slurry injection process can play an impactful role in reducing the carbon footprint of our E&P customers’ operations. We estimate that using slurry injection, rather than land application, can reduce (i) the carbon impact of an E&P company’s operations by approximately 0.4 kg CO2e per barrel of oil equivalent (“BOE”) and (ii) its gross direct emissions by approximately 600,000 MT CO2e over a 10-year period (see the accompanying case study). This is the equivalent annual emissions of over 13,000 passenger vehicles.14



Reduced Carbon Footprint

Switching from land application to slurry injection


Case Study

An E&P customer with gross production of 400,000 BOE per day during 2020 is targeting a 25% reduction in its gross GHG emissions intensity over 10 years versus a baseline of 15 kg CO2e/BOE. Assuming the customer employs a maintenance capital allocation strategy, i.e., no production growth, holding production constant would require approximately 200 new wells placed on production each year.15 This customer would achieve approximately 11% of its emissions intensity target reduction simply by partnering with Milestone to inject the drilling mud and slurry waste from each new well rather than settling for land application. Milestone would permanently sequester cumulative emissions of 600,000 MT CO2e over the 10-year period.16


11% emissions
intensity target reduction simply by partnering with Milestone

Milestone’s Net Negative Carbon Emissions

In 2020, Milestone conducted a sequestration analysis of samples collected from our slurry injection stream to determine the average total petroleum hydrocarbon (“TPH”) content. The analysis examined the carbon sequestration effect of Milestone’s slurry injection disposal practices in comparison to the traditional practice of land application disposal. Through collaboration with SCS Engineers (“SCS”), an environmental consulting firm based in California, we developed a methodology for estimating the carbon sequestration impact from our slurry injection process compared to land application.

Based on SCS’s analysis of the waste samples, the average barrel of slurry waste (i.e., excluding produced saltwater and flowback water) injected by Milestone contains approximately 95 kilograms of CO2e per barrel (“kg CO2e/bbl”).11 One hundred percent of the TPH contained in our injection stream is permanently sequestered in deep, geologically secure formations. During 2020 and 2019, Milestone sequestered approximately 279,000 and 464,000 MT CO2e via our slurry injection operations, respectively.12 If our customers had used traditional land application disposal for their slurry waste instead of Milestone’s closed-loop injection system, we estimate their collective gross emissions would have been greater by 232,000 and 385,000 MT CO2e during 2020 and 2019, respectively.13

See our Measuring Milestone's Carbon Footprint section for an executive summary of the study we conducted with SCS, which outlines our measurement methodology for the emissions and sequestration impacts of our slurry injection process.

Sequestered metric tons carbon dioxide equivalent (“MT CO2e”) compared to CO2e emissions from passenger vehicles per year equivalent*


8 Our landfill emissions were calculated by a third-party engineering firm registered within the State of Texas. These volumes were calculated using equations and programs approved by the U.S. Environmental Protection Agency (“EPA”) and TCEQ to support Milestone’s air permit applications. The submittal and approval of such applications are required by the TCEQ and TXRRC prior to commencing operations of the landfill. By their nature, landfills utilize a natural attenuation process comprised of both aerobic and anaerobic degradation of organic content. As organic matter degrades, the complex molecular chains are broken down (with the support of microscopic bacteria within the various waste streams) and chemically produce various compounds that contribute the total emissions from the landfill operations. Based on the nature of their operations and the sheer number of locations, the EPA has developed extensive studies and literature on these effects in MSW landfills. These MSW landfills are permitted and approved by the EPA and other state enforcement agencies to primarily serve public community operations and contain a variety of organic and inorganic non-hazardous products. In contrast, Milestone’s landfill operations are permitted by the TXRRC, with air permitting oversight from TCEQ, and serve the oil and gas industry. Milestone has identified the lack of supporting literature on E&P waste and the landfill degradation effects as a data gap. We plan to further study the emissions generated within their E&P waste landfills with the intent to provide the industry with supporting empirical data. As a leader in the oilfield waste disposal industry, Milestone prides itself on being a good steward of their environmental processes and lead the industry to a more sustainable future.

9See “Milestone’s Net Negative Carbon Emissions.”

10Milestone’s emissions for 3rd party trucking consist of two components: (1) ton-miles traveled and (2) engine idle time. Each round trip will have elements of both depending on the Milestone facility location and trucks destinations.

11Per our historical volume data, an estimated 5% of slurry receipt volume consists of non-injectable solids (e.g., cuttings) that are removed via surface equipment and sent offsite for disposal.

12Net emissions (sequestration) figure reflects gross CO2e emitted less gross CO2e sequestered.

13Based on a 75 kg increase in gross emissions per barrel of slurry waste generated if disposed of via land application, or approximately 79% of the TPH content per barrel.

*Emissions from one passenger vehicle in one year = 4.6 MT CO2e. as per U.S. Environmental Protection Agency Greenhouse Gas Equivalencies Calculator

14The EPA calculates that gasoline powered passenger vehicles emit the equivalent of 4.60 MT CO2e per vehicle per year

15Assumes a 22% base production decline and 50 new wells placed on production per quarter; new wells assumed to have 10,000-foot productive lateral lengths, 1,200 BOE/day initial quarterly production, and a 75% first-year effective decline rate.

16Assumes full emissions/sequestration impact per new well occurs in the year new wells are placed on production.