### Fate and Transport of Select Compounds of Interest in Fracing

Fluids Angus E. McGrath, Ph.D. March 28, 2011

## Overview

• Overview of Compounds of Interest (COIs) in Fracing Fluids • COIs

– Properties of Selected COIs

– Fate and Transport of COIs • Implications for Drinking Water QualityTaken From: Canadian Society of Unconventional Gas 

## Composition of Fracing Fluids

## COIs in Fracing Fluid Product Chemical Composition Linear gel delivery system Guar gum derivative

Diesel Water gelling agent Guar gum

Water Fumaric acid Linear gel polymer Fumaric acid

Adipic acid Linear gel polymer slurry Diesel oil #2 Cross - linker Boric acid

Ethylene Glycol Monoethanolamine Cross - linker Sodium tetraborate

decahydrate Product Chemical Composition Biocide 2,2 - dibromo- 3- nitrilopropionamide (DBNPA) Foaming agent Isopropanol

Salt of alkylamines Diethanolamine Foaming agent Ethanol

2 - Butoxyethanol Ester salt Polyglycol ether Water Acid treatment Hydrochloric acid Acid treatment Formic acid Breaker fluid Diammonium

peroxodisulfate

## Common COIs

• Muriatic acid or hydrochloric acid; • Guar gum; • Diesel (BTEX); • Ethanol and isopropanol ; • Sodium chloride; • Formic acid, Fumaric and adipic acids ; • Boric acid .

## Unconventional COIs

• Ethylene glycol (EG); • Diethanolamine (DEA); • 2,2 - Dibromo-3- nitrilo - propionamide (DBNPA); • 2 - Butoxy ethanol; and • Diammonium peroxosulfate (ammonium persulfate).

## Ethylene Glycol (EG)

• Liquid miscible in water • Low Kow and Henry’s constant • Common laboratory reagent – common contaminant in analyses – reason for elevated detection limits, 10 mg/L, detection limit actually ~0.2 mg/L or lower• Anaerobic biodegradation pathway (Dwyer, 1983, Huang, 2005): • Nitrate electron donor (Schramm and Schink , 1991). 

## Ethylene Glycol (EG)• Aerobic biodegradation pathway ( Gruden et al., 2001): EG  glycolic acid  oxalic acid  CO 2

• Persistence is moderate to low depending on microbial activity 

## Ethylene Glycol (EG)• Polar, colorless liquid, infinite solubility in water • Low Kow and Henry’s constant • DEA is considered mobile by EPA (2006) • EPA (2006) classified DEA as non persistent in soil and groundwater (half- life of days to weeks) 

## Diethanolamine (DEA)• In the presence of nitrite, DEA forms N nitrosodiethanolamine (NDELA): DEA + NO 2 -  NDELA

• EPA (2006) notes that NDELA persists in the environment but formation depends on NO 2 - concentration. 

## Diethanolamine (DEA)

## 2,2 - Dibromo - 3 - nitrilo- propionamide

• Solid – solubility 15 g/L at 25 o C • Low Kow and Henry’s constant • Nucleophilic substitution (with reducing agents, I - , HS - , HSO 3 - , S 2O 32 - , and SO 32 -) forms cyanoacetamide and bromide ( Exner et al., 1973) – short half- life (hours)

## 2,2 - Dibromo - 3 - nitrilo- propionamide

• DBNPA hydrolysis reaction has a half- life of 21 hr pH 7.4 and > 155 hr below pH 6, reaction as follows: DBNPA  dibromoacetonitrile + NH 3  dibromoacetoamide  dibromoacetic acid  glyoxylic acid + Br-  oxalic acid + CO 2  CO 2• Exner et al. (1973) reacted DBNPA with soil and soil extract (particle free) at pH 4.8 to 7.5 only ammonia and Br observed. • Reaction has a half- life of 4 to 25 hr. Fastest rate observed at highest pH. • Reaction attributed to microbial degradation. • Surface catalyzed hydrolysis also possible mechanism. 

## 2,2 - Dibromo - 3 - nitrilo- propionamide• DBNPA interacts with mineral surfaces retarding transport, but still a mobile compound • Not a persistent compound due to hydrolysis and microbial degradation 

## 2,2 - Dibromo - 3 - nitrilo- propionamide• Colorless liquid, miscible in water and most organic solvents, ether like odor • Low Kow and Henry’s constant • Considered mobile, but not persistent • Beihoffer and Ferguson (1994) observed that it has been detected in groundwater near US solid waste landfills (<0.4 to 84 ug/L) 

## 2- Butoxyethanol• Howard et al. (1991) estimated half- lives of 2 - butoxyethanol of 2–8 weeks in groundwater and 1 –4 weeks in soil, based on unacclimated aqueous aerobic biodegradation • IUCLID (2000) reports 95% biodegradation in 28 days • Hydrolysis unlikely in aqueous environment 

## 2- Butoxyethanol• Soluble, strong oxidant • Dissociates into ammonium and persulfate ions • Persulfate reacts readily with organic matter and reduced inorganic species • Activated to form persulfate radical by heat and ferrous iron 

## Ammonium Persulfate• Persulfate degrades to form sulfate ions • Half- life in the order of minutes to days depending on reaction conditions • Considered a mobile ion although will adsorb and react with both inorganic and organic surfaces • Short persistence decreases potential for mobility 

## Ammonium Persulfate

## Summary

• Ethylene glycol poses a potential risk for mobility and false positive detections but is not persistent • DEA mobility is retarded by mineral adsorption, but is not persistent • DBNPA mobility is retarded by mineral adsorption, but is not persistent • 2 - Butoxyethanol is mobile with limited retardation, but is not persistent• Ammonium persulfate is mobile but not persistent • Monitoring for any of these compounds may only be warranted if impacts from more concentrated reagents in fracing fluids are detected in wells • Other geochemical considerations...



## Summary

## Questions?