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# Modeling Drinking Water 

# Related Human Health Risks from Hydraulic Fracturing (HF) Additives Manu Sharma, M.S., P.E. Gradient, Cambridge, MA EPA HF Workshop March 29, 2011Copyright Gradient 2011 

# Analysis Objectives

• Understand potential drinking water related human health risks due to HF activities • Use simplified models and worst- case release scenarios consistent with a screening level analysis • Focus on New York State's Marcellus shale region • Evaluate drinking water risks due to:  Surface releases to groundwater and surface water 

##  Hypothetical migration from Marcellus to drinking water aquifers

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# Conceptual Site Model

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# Model HF Fluid

• Used model fluid composition presented in NYSDEC's SGEIS (NYSDEC, 2009) Purpose Compound HF Concentration (mg/L) Surfactant/Cross Linker/Scale Inhibitor Methanol 984 Biocide Glutaraldehyde 90 Corrosion Inhibitor Propargyl alcohol 1.5 Crosslinker Ethylene glycol 180 Breaker, Surfactant Propylene glycol 500 Breaker Diammonium peroxidisulphate 100 Crosslinker Monoethanolamine 18 Friction Reducer Acrylamide 10 Gelling Agent Naphtha (petroleum), hydrotreated heavy 275 Scale Inhibitor Formaldehyde 0.5 Solvent Xylene 3 Notes: 1) HF additive concentrations in model fluid, except naphtha, are less than their aqueous solubility limits.

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# Flowback Characterization Flowback data from samples collected from Marcellus shale in PA and WV (NYSDEC, 2009)

Notes: 1) Concentrations for all organics compounds in flowback listed above are less than their aqueous solubility limits. 2) A constituent, 4-nitroquinoline - 1 - oxide (4-NQO), was not evaluated since the reported concentrations appear to be anomalous. Parameter No. Samples No. Detected Units Maximum Median Inorganics Barium 34 34 mg/L 15700 661.5 Boron 26 9 mg/L 26.8 2.06 Bromide 6 6 mg/L 3070 616 Cadmium 29 5 mg/L 1.2 0.032 Cobalt 25 4 mg/L 0.58 0.3975 Copper 29 4 mg/L 0.157 0.035 Lithium 25 4 mg/L 161 55.75 Manganese 29 15 mg/L 14.5 2.18 Nickel 29 6 mg/l 0.137 0.0465 Strontium 30 27 mg/L 5841 821 Sulfate 58 45 mg/L 1270 3 Zinc 29 6 mg/l 0.09 0.048 Organics Benzene 29 14 ug/L 1950 479.5 Toluene 29 15 ug/L 3190 833 Ethyl Benzene 29 14 ug/L 164 53.6 Xylenes 22 14 ug/L 2670 487 Phenols 25 5 ug/L 440 191 5Copyright Gradient 2011 

# Surface Release Scenarios

• Two types of accidental releases simulated for HF additives and flowback
• Acute spill or release during down hole pumping  High release rate, short duration


# • Diffuse or chronic spill  Occasional drips and leaks during handling  Small volumes, but possibly over longer time periods

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# Diffuse Spill Release Scenario Diffuse Surface Release Scenario HF Fluid Used (gal/well) 4,030,000 Flowback Volume @ 20% (gal/well) 806,000 Number of Wells (per pad per year) 8 Total Flowback Volume (gal) 6,448,000 Spill Volume @ 1 % of Flowback Volume (gal) 64,480* Assumed spill area (acres) ~ 4 ** 

## (126m x 126m) 50% to Surface Water (gal) 32,240 50% to Soil/Groundwater Leaching (gal) 32,240 Notes: 1) * Represents 0.2% of HF used to frac 8 wells 2) ** Average pad size envisioned in New York (NYSDEC, 2009) 7Copyright Gradient 2011 

# Acute Spill Release Scenario Pipe/Pump Leak Scenario HF Injection Rate (gpm) 3,400 Rupture Duration (min) 5 HF Release (gal) 17,000 Assumed Spill Area (acres) 0.25 acre (33m x 33m) 50% to Surface Water (gal) 8,500 

## 50% to Soil/Groundwater Leaching (gal) 8,500
• Some spill data available in State databases • Data difficult to access and analyze • Largest reported spills – 8,000 to 13,000 gals 8Copyright Gradient 2011 

# Modeling Approach

• Groundwater release:  Partitioning in soil between aqueous and adsorbed phases (DAF pw

# )  Downward migration through vadose zone (DAF L

# )  Mixing into groundwater flowing to a well (DAF gw

# )


# • Surface water release:  Mass- balance mixing

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# Groundwater Pathway

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# HF Concentration in Drinking Water Well

Cwell 

# = Concentration at well (μg/L) C HF 

# = Concentration of HF additive released to the surface (μg/L) DAF pw 

# = Dilution factor for initial pore water concentration (unitless) DAF L 

# = Dilution factor from pore water to leachate at the water table (unitless) DAF gw 

# = Dilution factor of leachate into groundwater (unitless)
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# Surface Spill to Surface Water

• Mass- balance mixing of spill directly into stream flow: C sw 

## = HF concentration in surface water (μg/L) Q HF 

## = Discharge of HF or flowback fluid Q sw 

## = Stream flow
• Lowest annual mean daily discharge (LAMDD) at 10 th 

### percentile stream in the region of New York overlying the Marcellus (8.1 cfs) • Based on data from 147 USGS stations overlying Southern New York State 12Copyright Gradient 2011 

# Model Input Parameters Parameter Value Source Net infiltration (cm/yr) 36 . 8 (cm/yr) USGS ( 1998 ) Water content ( ) 0 . 3 cm 3

### /cm 3 

### US EPA, 1996 Porosity ( ) 0 . 43 cm 3

### /cm 3 

### US EPA, 1996 Bulk density ( ) 1 . 5 g/cm 3 

### US EPA, 1996 Organic carbon (f oc 

### ) 0 . 006 g- oc/g-soil US EPA, 1996 Chemical OC partition coefficient (Koc 

### ) Chemical -specific (L/kg) Compound -specific Dispersivity 0.25, 0.5, 2.5 cm Typical range of values Initial soil contamination depth (xo 

### ) 2 cm, 7 cm Calculated based on spill characteristics
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# Model Input Parameters Parameter Diffuse Spill Acute Spill Spill Area (A) ~ 4 acres 0.25 acres Spill Width (W) 126 m 33 m Depth water table 5 m, 10 m 5 m, 10 m Total Percolation (q = I × A) 5,613 m 3

### /yr 395 m 3

### /yr Groundwater Specific Discharge** (QD 

### ) 10 -4 

### cm 3

### /cm 2

### -sec 31.5 m 3

### /m 2

### -yr 10 -4 

### cm 3

### /cm 2

### -sec 31.5 m 3

### /m 2

### -yr Groundwater Flow Volume (Q) Well Depth (20 m) 77,900 (m 3

### /yr) 20,655 (m 3

### /yr) Well Depth (50 m) 194,743 (m 3

### /yr) 51,637 (m 3

### /yr) Notes: 1) ** Assumed K = 10 -2 cm/sec and a horizontal gradient of 1% - typical values for glacial outwash (sand) deposits 14Copyright Gradient 2011 

# Summary of DAFs Diffuse Spill Acute Spill DAF pw Compound – specific Compound - specific 

## DAF L Vadose Zone Depth 5 m 57, 78, 164 18, 25, 52 10 m 78, 108, 222 25, 35, 73 

## DAF gw Well Depth 20 m 15 53 50 m 36 132 US EPA (1996) 90th Percentile DAF ~ 15 ~ 600 

## Combined DAF (DAF L 

## x DAF gw

## ) ** 1,170 – 3,888 1,325 – 4,620 

## Surface Water DAF * 59,000 n/a 15 *10th percentile LAMDD ** Median DAF L used in combined DAF calculationCopyright Gradient 2011 

# Risks from Diffuse HF Fluid Spills Hazard Quotient Parameter Groundwater

Upperbound (ug/l) Surface Water 10th

Percentile LAMDD (ug/l) Drinking Water RBC

(ug/L) RBC Basis Groundwater Upperbound Surface Water

10th Percentile LAMDD Methanol 811.2 17 18,000 EPA RSL n 0.05 0.00093 Glutaraldehyde 57.9 1.53 5,600 OPP RED RfD 0.01 0.00027 Propargyl alcohol 1.2 0.03 73 EPA RSL n 0.02 0.00035 Ethylene glycol 152.8 3.06 73,000 EPA RSL n 0.002 0.00004 Propylene glycol 422.4 8.49 730,000 EPA RSL n 0.001 0.00001 Diammonium peroxidisulphate 85.5 1.70 479.5 Derived** 0.18 0.00354 Monoethanolamine 15.1 0.31 1,400 Derived** 0.01 0.0022 Acrylamide* NA NA 0.015 EPA RSL c <1 <1 Naphtha 9.4 4.67 1,300 TPHCWG, 1997 0.007 0.00359 Formaldehyde 0.3 0.01 7,300 EPA RSL n 0.00005 0.000001 Xylenes 0.2 0.05 10,000 Drinking water MCL 0.00002 0.00001 16 * Given its extremely short half- life, estimated to be less than 36 hours in soil, and less than 12 days in water (US EPA, 1994), acrylamide is expected to biodegrade rapidly to levels below the RBC. ** Derived using reported no observable adverse effects level and an uncertainty factor.Copyright Gradient 2011 

# Risks from Diffuse Flowback Spills Hazard Quotient Parameter Groundwater

Upperbound (ug/l) Surface Water 10th Percentile LAMDD (ug/l) Drinking Water

RBC (ug/L) RBC Basis Leaching to Groundwater Upperbound Surface Water

10th Percentile LAMDD Barium 65 267 2,000 Drinking water MCL 0.03 0.13 Boron 1 0.46 7,300 EPA RSL n 0.0002 0.0001 Bromide 2,624 52 6,000 WHO 0.4 0.01 Cadmium 0.0027 0.02 5 Drinking water MCL 0.0005 0.004 Cobalt 0.0022 0.01 11 EPA RSL n 0.0002 0.0009 Copper 0.0008 0.003 1,300 Drinking water MCL 0.0000006 0.000002 Iron 5.5 14 26,000 EPA RSL n 0.0002 0.0005 Lithium 0.09 3 70 Derived (see Section 5) 0.001 0.04 Manganese 0.04 0.25 880 EPA RSL n 0.00004 0.0003 Nickel 0.0004 0.002 730 EPA RSL n 0.0000005 0.000003 Strontium 28 99 22,000 EPA RSL n 0.001 0.005 Sulfate 1,085 22 500,000 EPA Health - based level/MCL Canada (sulfate) 0.002 0.00004 Zinc 0.0002 0.002 11,000 EPA RSL n 0.00000002 0.0000001 Organics Benzene 1 0.03 5 Drinking water MCL 0.1 0.007 Ethyl Benzene 0.01 0.003 700 Drinking water MCL 0.00001 0.000004 Toluene 0.30 0.054 1,000 Drinking water MCL 0.0003 0.0001 Xylenes 0.14 0.045 10,000 Drinking water MCL 0.00001 0.000005 Phenols 0.11 0.007 11,000 EPA RSL n (phenol) 0.00001 0.000001 17Copyright Gradient 2011 

# Assumptions/Limitations

• Surface release on unconsolidated deposits
• Mixing in drinking water aquifer assumes porous media system
• Complete mixing at a drinking water well – a reasonable assumption


# • Releases of dissolved organics (except naphtha) – consistent with injected fluids
• Potential releases from impoundments not simulated
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# Surface Release Findings
• Human health risks via drinking water affected by model HF fluid/flowback surface spills are expected to be insignificant
• Number of conservative assumptions used

– Release scenarios

– Limited attenuation mechanisms

– Expected to result in overestimated exposure concentrations


# • EPA case studies would be useful for validating that modeled DAFs are conservative
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# Marcellus Migration

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# Transport via Fractures
• Highly unlikely in Marcellus shale
• Aquifers separated by thousands of feet of low conductivity rock

– Multiple rock units

– Isolate high TDS water from drinking water aquifers

– Have resulted in trapped methane for geologic time scales


# • HF induced fractures are expected to be constrained

– Short duration of HF treatment (1 to 2 days)

– Layered rock system • Many stress contrasts limit fracture growth • Embedded concretions stop hydraulic fractures



## – Field data show that actual fracture growth is limited and remains thousands of feet below drinking water aquifers (Fisher, 2010) 21Copyright Gradient 2011 22

Source: Fisher (2010)Copyright Gradient 2011 23 Source: Fisher (2010)Copyright Gradient 2011 24 

# Marcellus Cross - Section

Source: USGS, 2005Copyright Gradient 2011 

# Transport via Pore Spaces

• Migration during HF process infeasible

– HF takes 1 to 2 days

– ICF (2009) concluded that HF pressure would have to remain applied for years to thousands of years for transport to drinking water aquifers


# • Migration of “trapped fluids” post- HF also not expected

– Low hydraulic conductivity of shale and overlying rocks

– Multiple phases (water, oil, and gas) further reduce ability to transmit water

– High capillary pressures

– Unclear if there is a driving head, especially considering brine density

– Extreme - case migration analysis undertaken 25Copyright Gradient 2011 

# Extreme - Case Migration Analysis
• Darcy’s law based analysis with simplifying assumptions

– Ignore brine density and multi - phase effects

– Ignore retardation and biodegradation


# • Only considers mixing with porewater in bedrock 

# and in drinking water aquifer

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# Predicted Dilution -Attenuation Factors for Upward Migration

Surface Aquifer Thickness DAFBR



## (Mixing within Bedrock ) * 

## DAFaq



## (Mixing in Shallow Aquifer Flow) Combined DAF

DAFBR 

## × DAFaq 

## 100 ft >300 5,500 >1.65 x 10 6 

## 1,000 ft >300 29,000 >8.7 x 10 6

Note: DAF

aq based on migration from 4,500- foot length fracture zone upward to aquifer of specified thicknesses. * From ICF (2009). 

## Extreme - case analysis indicate that additive concentrations would be significantly attenuated if they were to reach drinking water aquifers

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# Conclusions
• Generalized scenarios provide a framework to understand potential human health risks to drinking water from HF activities

– Upward migration from Shale implausible exposure pathway

– Risks from surface spills and vertical migration from Marcellus Shale expected to be insignificant for model HF fluid and flowback

– Additional model sensitivity analyses being undertaken to define effect of input parameter variability and uncertainty


# • EPA case studies and other data could help validate modeling results 28Copyright Gradient 2011 

# Equations and References

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# Porewater DAF

or
Where: DAF pw 

## = Pore Water DAF

C pw 

## = Concentration in pore water = Soil water content (cm 3 

## – water/cm 3 

## – soil) Kd 

## = Soil water partition coefficient (L/Kg); and S = Soil dry bulk density (g/cm 3

## ) 30Copyright Gradient 2011 

# Leaching DAF
• Downward transport through the vadose zone (Enfield et al

.,1982)
Where: C o 

## = Initial concentration in leachate

Zo 

## = Initial contaminant depth D = Dispersion coefficient C L 

## = Leachate concentration at water table v = Percolation rate 

# • DAF L 

# = 1/(C L



# /C o

# ) – averaged over the time period that leachate enters the water table 31Copyright Gradient 2011 

# Groundwater DAF

• Transport of chemicals to a drinking water well:

 C gw 

# = Concentration at a well  QI 

# = Volumetric rate of downward seepage  Q gw 

# = Groundwater flow rate through aquifer cross section to drinking water well screen bottom 32Copyright Gradient 2011 

# References

33 Enfield, CG; Carsel, RF; Cohen, SZ; Phan, T; Walters, DM. 1982. "Approximating pollutant transport to ground

water." Ground Water 20(6):711 -722. Fisher, K. 2010. "Data Confirm Safety of Well Fracturing." The American Oil & Gas Reporter, July. Gradient. 2009. "Human Health Risk Evaluation For Hydraulic Fracturing Fluid Additives Marcellus Shale Formation, New York.” 127p ., December 31. ICF International. 2009. "Technical assistance for the draft supplemental generic EIS: oil, gas and solution mining regulatory program

— Well permit issuance for horizontal drilling and high-volume hydraulic fracturing to develop the Marcellus shale and other low-permeability gas reservoirs." August 7. New York State Dept. of Environmental Conservation (NYSDEC). 2009. "Supplemental Generic Environmental Impact Statement on the Oil, Gas and Solution Mining Regulatory Program: Well Permit Issuance for Horizontal Drilling and High-Volume Hydraulic Fracturing to Develop the Marcellus Shale and other Low Permeability Gas Reservoirs (Draft)." Division of Mineral Resources, Bureau of Oil & Gas Regulation, 804p., September. US EPA. 1996. "Soil Screening Guidance: Technical Background Document." Office of Solid Waste and Emergency Response. NTIS PB96-963502; EPA- 540/R-95/128; OSWER Publication 9355.4- 17A. Accessed on January 29, 2001 at www.epa.gov/oerrpage/superfund/resources/soil/toc.htm, May. United States Geological Survey (USGS). 1998. "Water Resources of the Batavia Kill Basin at Windham, Greene County, New York." USGS Water-Resources Investigations Report 98 -4036. 105p. United States Geological Survey (USGS). 2005. “Assessment of Undiscovered Natural Gas Resources in Devonian Black Shales, Appalachian Basin, Eastern U.S.A.” U.S. Geological Survey Open File Report 2005 - 1268.