IN-SITU AIR STRIPPING BENCH-SCALE TESTING FOR TREATMENT OF 1,4-DIOXANE IN GROUNDWATER Omer Uppal1, Kawalpreet Kaur1, Nadira Najib, Stewart H. Abrams1, Michael C. Marley2

1Langan Engineering & Environmental Services, Inc., Elmwood Park, New Jersey, USA 2 XDD, LLC, Stratham, New Hampshire, USA

• 1,4-Dioxane (C4H8O2) is a cyclic ether • Widely used as a solvent stabilizer in manufacturing sector,

particularly with 1,1,1-trichloroethane (TCA) • Found at many sites already enacting remedies for

chlorinated solvents o In 1990, the total U.S. production volume of 1,4-

dioxane was between 10,500,000 and 18,300,000 pounds (U.S. EPA 1995a).

o In 1992, a total 1.13 million pounds of 1,4-dioxane released into the U.S. environment (TRI92 1994).

• EPA has listed the compound as a Group B2 probable human carcinogen

• Cleanup criteria vary by state, ranging from 3 to 85 ug/L • Several states do not have enforceable clean up criteria. • U.S. EPA Regions 3, 6, and 9 Screening Criteria = 6.1 ug/L

(Preliminary Remediation Goal)

• Air Stripping o Low volatility of 1,4-dioxane prevents transfer to air

• Granular Activated Carbon o Low Koc - Does not adsorb to organic material

• Microbial Degradation o Not viable under ambient conditions, possible under

enhanced conditions • Advanced Oxidation Processes

o Hydrogen Peroxide o Ultraviolet Light (UV) o Ozone o Alkaline Activated Persulfate

TREATMENT TECHNOLOGIES

1,4 DIOXANE

INTRODUCTION

1,4-dioxane is an emerging groundwater contaminant that has challenged remedial project managers and water utility operators to redesign treatment systems to cost effectively treat this contaminant. 1,4-dioxane does not respond adequately to the conventional air stripping, granular activated carbon treatment, or biodegradation processes, due to its low volatility from water and unique physical and chemical properties. 1,4-dioxane’s high solubility, low affinity for organic matter in soil, moderate vapor pressure (38.09 mm Hg at 25º C), and low Henry’s Law Constant (4.80 x 10-6 atm m3/mol at 25º C) lead to low volatilization of this compound from aqueous phase.

The results of the 1,4-dioxane air stripping analysis performed using well established Henry’s Law Constant and mass transfer coefficient (aqueous to gaseous mass transfer) relationships indicate that in-situ air stripping using two or multiple air sparge curtains (rows of sparge wells) is capable of reducing low levels of 1,4-dioxane in groundwater with a removal efficiency of approximately 70% or more (Uppal et al.,2012).

Supplemental modeling and analysis was performed to investigate the sensitivity of 1,4-dioxane’s stripping ability for varying air injection flow rate, groundwater velocity, ratio of volumetric air flow to volumetric water flow (air to water [A:W] ratio), mass transfer coefficient, treatment residence time, number of air sparge curtains, and subsurface temperature.

MODELING RESULTS

WORK IN PROGRESS • In-situ air stripping model calibration utilizing:

o Commercial air stripper models o Actual air stripper influent/effluent concentration data base o Groundwater air sparging sites data base

• Bench Testing • Field Pilot Testing

• 1,4-dioxane removal efficiency of 70% or higher can be achieved via two or multiple sparge curtains

• Cost effective and sustainable in-situ air stripping approach for 1,4-dioxane treatment

• Highly viable for sites with low level widespread occurrence of 1,4-dioxane in groundwater

PARAMETERS AFFECTING STRIPPING

• Air injection flow rate • Groundwater velocity • Ratio of volumetric air flow to volumetric water flow (air to water ratio) • Treatment residence time • Number of sparge curtains (rows of sparge wells)

Volumetric Airflow

Rate to Water Flow

Rate

%Removal of 1,4 Dioxane

via Air stripping

4800 50%

9600 66%

14400 74%

19200 79%

28800 85%

38400 88%

48000 91%

In-SITU STRIPPING ABILITY ANALYSIS

• Aqueous to Gaseous Mass Transfer Analysis Approach: o The following mass balance equation was used to analyze the in-situ stripping

ability of 1,4-dioxane:

Sparging Trench Dimensions

5 to 10 ft

Where:

C L,e = COC concentration in reactor/trench effluent (ug/L), 20 ft

C L,i = COC concentration in reactor/trench influent (ug/L),

Qg = Gas or air flow rate (ft3/day),

QL = Liquid or groundwater flow rate per unit length (ft3/day),

Hc = Henry’s law constant (unitless), and Groundwater Flow

φ = Saturation parameter

Where:

K(La)COC = Mass transfer coefficient for COCs (1/day), and

V = Volume of reactor per unit length/porosity (ft3).

Contaminant ‘s Henry’s Law Constant Required for Effective Stripping > 1x 10-5 atm.m3/mol • The mass transfer coefficient (KLa) for 1,4-dioxane was derived from various air

stripping models provided by vendors (KLa)1,4-dioxane = 46

• Applicable to existing and proposed installations • Conventional or defensive sparging trench systems • Accurate prediction of mass transfer & 1,4-dioxane removal

CONCLUSIONS