Design and Implementation of an Integrated Biosparging and In-Situ Air

Stripping Remedial Strategy Authors: Omer J. Uppal, Elisa Buckley, Matthew J. Ambrusch, Nadira Najib, Robert Koto, Stewart H. Abrams

Langan Engineering & Environmental Services, Inc., 619 River Drive Center 1, Elmwood Park, NJ 07407

ABSTRACT

Background: This presentation provides a case study of the design and construction of a full-scale

biosparging and in-situ air stripping remediation system that was implemented to remediate the

volatile organic compound (VOC) impacts in groundwater at a site in northern New Jersey. The

subject site was originated in 1929 as a manufacturing facility and was operated by multiple

owners and tenants until 2000. Although, the site has a number of areas of concern, the

remediation system was designed and installed to primarily target a shallow groundwater plume

containing elevated concentrations of benzene, toluene, ethylbenzene, xylenes (BTEX) and

trichloroethene.

Activities: The remediation system consists of nine biosparge wells; seven wells completed to

approximately 36 feet below ground surface (bgs) and one nested well consisting of a shallow and

a deep screen completed to approximately 26 and 36 feet bgs, respectively. Trenches were

excavated to install the below grade system manifold connecting the injection points to the

process equipment. The process equipment consists of a 10 horse-power (hp) air compressor

capable of providing an air flow rate of approximately 50 standard cubic feet per minute (scfm) at

a pressure of 70 pounds per square inch (psi). The system was innovatively designed with

flexibility to be able to operate in an air sparging/stripping mode, in the event more aggressive

mass removal is needed to treat the high contaminant concentrations in an expedited manner. The

installation of the system was further complicated by the rehabilitation of a large overhead

superhighway, requiring additional coordination with the highway construction activities.

Results: Groundwater data collected before the system was activated in June 2012 indicated a

slight decreasing trend in BTEX compound concentrations. The presence of petroleum degrading

heterotrophs in the saturated soils suggested aerobic degradation was likely responsible for the

observed decreasing concentration trends. Benzene levels near where the highest concentration

of BTEX degrading microbes was observed, decreased from approximately 70 milligrams per liter

(mg/L) to 45 mg/L between June and December 2011. Dissolved oxygen (DO) concentrations were

detected as low as 0.26 mg/L. The operation of the remediation system resulted in a substantial

increase in DO concentrations within the target plume area, increased concentrations of aerobic

bacteria, and substantially improved BTEX degradation rates. The results of the recent

groundwater sampling events, operational data of the remediation system, and the overall BTEX

concentration trends are presented in this case study.

SITE LAYOUT MAP

OPERATION, MAINTENANCE, & MONITORING

EFFECTIVENESS

INSTALLATION AND CONSTRUCTION

TARGET GROUNDWATER IMPACTS

AOC-17 Groundwater

• BTEX , TCE , various metals above NJDEP GWQS in MW-3, MW-4, MW-15, and MW-18 thru MW-21

• Presence of petroleum degrading heterotrophs

• Classification Exception Area (CEA) – metals remaining in groundwater

• Biosparge System – Enhance VOC degradation

• Installed April - June 2012

• 9 sparge points

• BSP-1 thru BSP-7 screened from 34 to 36 feet below grade

• BSP-8 screened from 24 to 26 and 34 to 36 feet below grade

• Process equipment has capacity to be an air sparge system

• 35 SCFM at 175 PSI

• Modifications to well point configuration due to major utility obstructions and bridge

construction

• System has been operating since July 2012

• Annual groundwater sampling event in surrounding monitoring wells

• Monthly site visits to ensure system is operating as designed

• Compressor - 20-25 SCFM at approximately 5 PSI

• Biosparge Points – 2-3 SCFM at approximately 5 PSI

• Adjust/Optimize, as required

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m&p-Xylenes

o-Xylene

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Xylenes (Total)

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Xylenes (Total)

Lithology

• Fill (i.e., sand, silt, gravel) to 4-8 ft bgs

• Glacial Till (i.e., sand, silt, clay, cobbles) to approximately 45 ft bgs (bedrock)

• Slight to moderate increase in dissolved oxygen (DO)

observed in most MW’s in the injection area

• MW-18 - .66 mg/L to 3.95 mg/L

• MW-16 - .40 mg/L to .79 mg/L

• Biosparge systems take time to have a significant

remedial effect

• Effective DO distribution

• Microbial growth

• System innovatively designed such that it can be

converted to an air sparge system, if required

• Expedited mass removal

• Stripping in addition to biological degradation

• Site is segmented into three parcels, Parcel A, Parcel B, and Parcel C

• Parcel A has 17 areas of concern (AOC), alone

• In-situ air stripping of dissolved VOCs in groundwater:

• Henry’s Law Constant

• Vapor Pressure

Air Sparging

• Contaminant’s Henry’s Law Constant Required

for Effective Stripping > 1x 10-5 atm.m3/mol

• Benzene = 5.50 X 10-3 atm.m3/mol

• PCE = 1.84 X 10-2 atm.m3/mol

• TCE = 1.03 X 10-2 atm.m3/mol

• Toluene = 6.64 x 10-3 atm.m3/mol

• The effectiveness/efficiency of air sparging

depends on:

• Achievable air flow rate

• Contaminants of Concern

• Lithology

• Effective ROI