1. The study calculated greenhouse gas emissions from the production and distribution of silica sand proppants used in hydraulic fracturing. 2. It estimated total annual emissions of 4.5 million metric tons of CO2 equivalent from silica sand facilities in Wisconsin and transportation of sand to hydraulic fracturing sites across the country. 3. Accounting for proppant emissions would increase previous estimates of total hydraulic fracturing lifecycle emissions by 5-34%, highlighting the need to include this step in future assessments.

1. Results
Adams, T., Hart, M., & Schwartz, A. (2013). Transportation impacts of frac sand mining in the MAFC Region: Chippewa County case
study. National Center for Freight & Infrastructure Research & Education.
Chase, T. (2014, July 13). As rail moves frac sand across Wisconsin landscape, new conflicts emerge. WisconsinWatch.org.
EPA. (2004).Unit conversions, emissions factors, and other reference data. [Brochure]. http://www.epa.gov/cpd/pdf/brochure.pdf.
Griffin, M., Hendrickson, M., Jaramillo, P., & Venkatesh, A. (2011, August 5). Life cycle greenhouse gas emissions of Marcellus Shale
gas. Environmental Research Letters, 6. doi: 10.1088/1748-9326/6/3/034014.
MacKay, D.J.C., & Stone, T.J. (2013, September 9). Potential greenhouse gas emissions associated with shale gas extraction and use.
UK Dept. of Energy and Climate Change.
Northern Industrial Sands. (2012). Permit Application and Supplemental Document.
O’Sullivan, F., & Paltsev, S. (2012, November 26). Shale gas Production: Potential vs. actual greenhouse gas emissions. Environmental
Research Letters, 7, 1-5. DOI: 10.1088/1748-9326/7/4/044030.
U.S. Silica. (2013). U.S. Silica 2012 Sustainability Report. http://www.ussilicasustain.com/US_Silica_2012_Sustainability_Report.pdf
Wisconsin Department of Natural Resources. (2012,). Silica Sand Mining in Wisconsin.
Introduction / Background
Hydraulic fracturing is a method of oil and gas extraction that is rapidly emerging as one of
the largest sources of energy around the globe. It involves the use of a highly pressurized
Methods
The life-cycle of silica sand was divided into two
parts: Production (mining & processing) and Distribution (transportation from Wisconsin to
wells across the nation.) This research did not include any emissions that occur after the
delivery of silica sand to the well.
I. Production
The permits of the 143 active silica sand facilities in Wisconsin were searched for GHG data.
It was noted that the facilities that provided some emissions data only provided data from
two processes: sand blasting and sand drying. Since there are dozens of other processes
that occur on-site, the facility-reported emissions data was adjusted based on an extensive
document from Northern Industrial Sands (NIS) that provided hard data on the hours
of equipment used annually (bull-
dozers, backhoes, etc.) and the annual
mileage traveled (haul trucks, water
tanks, etc.) CO2e emissions per
year were calculated
(Equations 1 & 2). A percent increase between what NIS reported in their permit and what
was calculated from their separate raw data was applied to the other facilities’ data and
extrapolated statewide. Low and high estimations were used wherever possible.
II. Distribution
The CO2e emissions from distribution were calculated using
two widely cited values of silica sand output from Wisconsin:
26 million tons (Chase, 2014) and 40 million tons (Adams et
al., 2013). It was assumed that these silica sand tonnage
values were distributed equally to the top five silica sand
consuming states: Texas, Louisiana, states: Texas, Louisiana,
Colorado, Ohio, and North Dakota (National Center for Freight & Infrastructure, 2014). It
was assumed that transportation was carried out by rail (70%) and truck (30%) (U.S. Silica,
2013). Rail and truck specific CO2e rates with a fuel emissions factor of 0.011185 ton CO2 /
gal (EPA, 2004) were used to calculate total emissions from distribution (Equations 3 & 4).
Conclusions
The answers to the research questions are as follows:
1. Calculated GHG emissions from the proppant life-cycle totaled 4.5
million TPY, which is equivalent to the annual emissions of over
860,000 passenger vehicles.
Acknowledgements
References
I would like to profoundly thank University of California, Santa Barbara, for providing me
with the skills necessary to complete this project, as well as NASA for giving students the
exciting opportunity to present their research in a professional setting.
Climate Change and Hydraulic Fracturing Proppants:
Calculating the CO2e Emissions from Silica Sand Production in Wisconsin
Natalia Nelson
Research Questions
1. What numerical quantity of carbon dioxide equivalent (CO2e) emissions is released from
the production and distribution of silica sand proppant?
2. How do these emissions compare to life-cycle CO2e emissions of hydraulic fracturing?
3. Should proppant production be included in future CO2e life-cycle assessments of
hydraulic fracturing?
mixture of water, proppants, and chemicals to fracture deep
underground rock formations and release oil or natural gas.
Each well requires thousands of tons of proppants, most
commonly silica sand, to “prop” open the induced fractures.
In the past decade, the production of silica sand has grown
into a massive industry, with Wisconsin leading the production
boom due to its ancient quartz geological formations. Silica
sand is mined, processed, and distributed from Wisconsin to hydraulic fracturing wells
across the nation. Numerous life-cycle assessments have been conducted on hydraulic
fracturing greenhouse gas (GHG) emissions, but life-cycle emissions from proppant
production are absent from scholarship. This research aims to fill this unstudied gap in the
relationship between hydraulic fracturing and climate change, as GHG emissions from
energy-intensive processes must be drastically reduced in order to sustain a healthy planet.
Mining Processing Transportation
Equation 1: NIS Hourly Data CO2e Emissions
ℎ𝑜𝑢𝑟𝑠 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑢𝑠𝑒
𝑦𝑒𝑎𝑟
𝑥
𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑔𝑟𝑎𝑚𝑠 𝐶𝑂2 𝑒
ℎ𝑜𝑢𝑟
𝑥
𝑡𝑜𝑛
𝑔𝑟𝑎𝑚
=
𝑡𝑜𝑛 𝐶𝑂2 𝑒
𝑦𝑒𝑎𝑟
Equation 2: NIS Mileage Data CO2e Emissions
𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑡𝑟𝑖𝑝𝑠
𝑦𝑒𝑎𝑟
𝑥
𝑓𝑒𝑒𝑡
𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑡𝑟𝑖𝑝𝑠
𝑥
𝑚𝑖𝑙𝑒
𝑓𝑒𝑒𝑡
𝑥
𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑓𝑢𝑒𝑙 𝑢𝑠𝑒𝑑
𝑚𝑖𝑙𝑒
𝑥
𝑡𝑜𝑛 𝐶𝑂2 𝑒
𝑔𝑎𝑙𝑙𝑜𝑛 𝑓𝑢𝑒𝑙 𝑢𝑠𝑒𝑑
=
𝑡𝑜𝑛 𝐶𝑂2 𝑒
𝑦𝑒𝑎𝑟
CO2e Emissions from Silica
Sand Production &
Transportation in Wisconsin
(1) Production
Facility Reported
Emissions
NIS Case Study
Calculated
Emissions
Hourly
Data
Percent Increase
in Emissions
Adjusted Facility
Emissions
Total CO2e Emissions
Traffic
Data
(2) Distribution
Rail
Combined Rail &
Truck Distribution
Emissions
Truck
Methods Continued
Equation 3: Rail Transportation CO2e Emissions
𝑚𝑖𝑙𝑒𝑠 𝑡𝑜 𝑑𝑒𝑠𝑡𝑖𝑛𝑎𝑡𝑖𝑜𝑛 𝑥
𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑑𝑖𝑒𝑠𝑒𝑙 𝑓𝑢𝑒𝑙 𝑢𝑠𝑒𝑑
𝑚𝑖𝑙𝑒
𝑥 𝑡𝑜𝑛 𝐶𝑂2 𝑒 = 𝑡𝑜𝑛 𝐶𝑂2 𝑒
Equation 4: Truck Transportation CO2e Emissions
The flowchart at
right is a graphic
summary of the
steps used to
calculate total CO2e
emissions from the
production and
distribution of silica
sand proppant in
Wisconsin.
III. Total
Calculated GHG emissions from
production and distribution were added together. The total tonnage was
converted to emissions per ton of silica sand produced. This value was
compared to three previously conducted life-cycle assessments of
hydraulic fracturing GHG emissions: Griffin et al. (2011), MacKay & Stone
(2013), and O’Sullivan & Paltsev (2011). Assuming the average well
requires 2,500 tons of proppant (U.S. Silica, 2013; Wisconsin Dept. of
Natural Resources, 2012), the calculated life-cycle CO2e emissions per ton
of silica sand produced was compared to the three studies to estimate the
percent increase that would occur if proppant production was included in
future hydraulic fracturing life-cycle assessments.
I. Production
Out of the 143 active silica sand facilities in Wisconsin, only 28 (20%)
provided CO2e emissions data in their permits (Graph 1), which illustrated
the lack of facility GHG data publicly available. It was calculated that
facilities’ emissions data were
approximately 5 – 11% higher than reported (Table 1), as NIS reported a
value of 27,460 ton CO2e emissions per year (TPY) in their permit but low
and high values of 28,880 TPY and 30,465 TPY were calculated based on the
data they provided in their document. This corresponded to adjusted
facility average emissions value of 33,410 TPY -35,318 TPY. Statewide, it was
found that the silica sand industry in Wisconsin emits approximately 3.3
million TPY.
II. Distribution
It was calculated that distribution of silica sand from Wisconsin to hydraulic
fracturing wells across the nation emitted 936,356 TPY – 1,440,349 TPY. It
was found that rail transportation is 3 times more efficient.
Results Continued
III. Total
It was calculated the CO2e emissions
from Production (75% of total) and
Distribution (25% of total) statewide
totaled ~4.5 million TPY (Table 2), which corresponded to a value of 0.10-
0.19 tons CO2e released in the life-cycle of one ton of silica sand
proppant. When compared
to the three previously
conducted assessments
of the hydraulic fracturing
life-cycle, it was found that
proppant CO2e emissions
compose 5-34% of total
hydraulic fracturing CO2e emissions (Table 3).
Table 2: Summary of Silica Sand Proppant Production
and Distribution CO2e Emissions in Wisconsin (TPY)
Lower Estimate Upper Estimate
Production 3,247,452 3,432,910
Transportation 936,356 1,440,349
Total 4,183,808 4,873,259
𝑡𝑜𝑛𝑠 𝑠𝑎𝑛𝑑 ℎ𝑎𝑢𝑙𝑒𝑑 𝑥 𝑚𝑖𝑙𝑒𝑠 𝑡𝑜 𝑑𝑒𝑠𝑡𝑖𝑛𝑎𝑡𝑖𝑜𝑛 𝑥
𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑑𝑖𝑒𝑠𝑒𝑙 𝑓𝑢𝑒𝑙 𝑢𝑠𝑒𝑑
𝑡𝑜𝑛 𝑚𝑖𝑙𝑒𝑠
𝑥
𝑡𝑜𝑛 𝐶𝑂2 𝑒
𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑑𝑖𝑒𝑠𝑒𝑙 𝑓𝑢𝑒𝑙 𝑢𝑠𝑒𝑑
= 𝑡𝑜𝑛 𝐶𝑂2 𝑒
Table 1: Summary of Calculated CO2 Emissions Data and NIS
Provided Data (TPY)
Facility-Reported Data Calculated Estimate
Blasting 149
Sand Dryer 27,311
Total 27,460
Calculated Emissions Data Lower Estimate Upper Estimate
Calculated Hourly Data Totals 345 494
Calculated Traffic Data Totals 1074 2510
Total Additional Emissions 1419 3004
Total Estimated Emissions
(Facility-Reported + Calculated)
28,880 30,465
Percent of Total Emissions Added 5% 11%
Table 3: Summary of Percent Increase in Overall Hydraulic
Fracturing Emissions due to Silica Sand Production
Authors Scope Finding (t
CO2e per
well)
Percent Increase in Emissions
of Silica Sand Production
(Lower and Upper Estimates)
O’Sullivan &
Paltsev (2011)
Least extensive 1,378 19% 34%
Griffith et al.
(2011)
Extensive 5,500 15% 27%
MacKay &
Stone (2013)
Most extensive 4,887 5% 10%
27
53
108
28
Graph 1: 143 Facilities' GHG
Data from Permits
Unidentified by Air
Permit Search Tool
Identified; No records
Identified; Records; No
CO2e Emissions Data
Identified; Records;
CO2e Emissions Data
2. If proppant CO2e emissions were included in life-cycle analyses of total
hydraulic fracturing emissions, findings would increase by 5-34%.
3. GHG emissions from proppant production should absolutely be
included in future life-cycle assessments of hydraulic fracturing. A 5-
34% increase is extremely significant for scientists, policy-makers, and
the public to make crucial decisions about energy production.
Suggestions for emissions reduction include: decrease
the distance between the mining and processing sites,
upgrade equipment efficiency, switch transportation
from truck to, and research the feasibility of recycling
proppants after well injection. Additionally, there is a
lack of data surrounding proppants and GHG emissions and it is
recommended that long-term CO2e monitoring systems be set in place
in order for scientists to have access to quantitative data. Climate
change is one of the greatest challenges faced by the human race, and
with carbon-intensive hydraulic fracturing and subsequent proppant
production rapidly expanding, this research is only one of many future
studies that should be conducted to fully quantify and ultimately reduce
the GHG emissions for the benefit of the planet and its inhabitants.