Enhanced In-Situ Bioremediation Process

Earth Tech, Inc. 

Project Description: The U.S. Environmental Protection

Agency (EPA) conducted an evaluation of the Enhanced In-Situ

Bioremediation Process, a biostimulation technology

developed by the U.S. Department of Energy (DOE) at the

Westinghouse Savannah River Plant site in Aiken, South

Carolina. DOE has licensed the process to Earth Tech, Inc.

(Earth Tech). The evaluation described in this bulletin was

carried out by the EPA Superfund Innovative Technology

Evaluation (SITE) Program. Earth Tech is utilizing the process

to deliver a mixture of air and gaseous phase nutrients, and/or

methane to contaminated groundwater in fractured bedrock at

a site in Roanoke, VA. These enhancements are delivered to

contaminated groundwater via an injection well and were

designed to stimulate and accelerate the growth of existing

microbial populations, especially methanotrophs. This type of

aerobic bacterium has the ability to metabolize methane and

produce enzymes capable of degrading chlorinated solvents

and their degradation products to non-hazardous constituents.

The primary components of Earth Tech’s treatment system

consist of an injection well, air injection equipment,

groundwater monitoring wells, and soil vapor monitoring points.

The injection well is designed to deliver air, nutrients, and

methane to groundwater in the bedrock 30 to 50 feet below

ground surface. For the system evaluated, the air was supplied

by a compressor that was capable of delivering 15-30 psi and

approximately 20 scfm to the injection well. The monitoring

wells and soil vapor monitoring points were installed

upgradient, down-gradient and cross-gradient relative to the

injection well location to delineate the zone of influence and to

monitor groundwater within and outside of the zone of

influence. The soil vapor monitoring points can be designed to

release or capture vapors that may build up in the overburden.

The monitoring wells were constructed in a manner to allow

them to be converted to either injection wells or soil vapor

extraction points. 

The typical injection system consists of air, nutrient, and

methane injection equipment; all can be housed in a temporary

building or shed. A compressor serves as the air source, and

includes a condensate tank ("trap") with a drain, an air line,

coalescing filters and pressure regulators and valves. The

methane and nitrous oxide provide the source of carbon and

nitrogen, respectively. Both are provided in standard gas

cylinders and are piped into the main air line using regulators

and flow meters. Triethyl phosphate (TEP), the phosphorous

source, is in liquid state and is stored in a pressure rated steel

tank. Air from the main line is diverted through the tank to

volatilize the TEP for subsurface delivery. The air, nitrous oxide,

and TEP are injected continuously while the methane is injected

on a pulsed schedule. The methane is closely monitored just

prior to injecting into subsurface wells to ensure that the

injection concentration does not exceed 4% by volume, thus

avoiding the methane lower explosive limit (LEL) of 5%.

Waste Applicability: The Enhanced In-Situ Bioremediation

process is applicable for treating volatile organic compounds

(VOCs) in groundwater that can be naturally biodegraded,

including some hard to degrade chlorinated VOCs. The mixture

of air and gaseous phase nutrients that is injected into the

subsurface provides an aerobic environment for contaminant

degradation. Toxic products resulting from anaerobic

degradation of chlorinated solvents (e.g., vinyl chloride) may be

broken down completely in this aerobic environment. The insitu process is especially applicable for hydrogeologically

complex sites where injected nutrient flow paths are uncertain

(i.e., in fractured bedrock gaseous phase nutrient injection is

more likely to affect a larger area than liquid nutrient injection).

The process is also applicable in situations where subsurface

utilities limit or preclude the use of technologies requiring

excavation.

Demonstration Results: A pilot-scale technology

demonstration of the Enhanced In-Situ Bioremediation process

was conducted from March 1998 to July 1999 at the ITT

Industries Night Vision (ITTNV) Division plant in Roanoke,

Virginia. The ITTNV facility is an active manufacturing plant that

produces night vision devices and related night vision products

for both government and commercial customers. Groundwater

contamination at the facility has resulted from tank leaks of both

chlorinated and non-chlorinated compounds, which were used

as manufacturing cleaning solvents. Remediation is being

conducted at the facility as a RCRA Interim Measure (IM), and

is complicated by target VOCs occurring in fractured bedrock
below the surface. This logistical complexity presented by the

area geology was a key factor for selecting the Enhanced InSitu Bioremediation process.

The demonstration study area was located adjacent to ITTNV’s

commercial operations building (Building 3), and was

immediately downgradient of a contamination source that had

resulted from a leak of an underground waste solvent tank. The

study area is the only location at the facility where the source

release has contaminated the groundwater with both

chlorinated and non-chlorinated groups of VOCs. Several VOC

compounds have been detected in the groundwater at this

location above their respective Federal Maximum Contaminant

Level (MCL). These compounds include actual solvents, such

as trichloroethene (TCE) and 1,1,1-trichloroethane (TCA), as

well as several of their breakdown products. Prior to the start of

the demonstration methane was present and TCE was absent

from some of the wells. These observations strongly suggest

that anaerobic degradation of TCE was naturally occurring.

The Earth Tech system installed at the study area consisted of

eleven monitoring points. These included an injection well, four

monitoring wells located within the radius of influence, two

monitoring wells located outside of the radius of influence (i.e.,

one upgradient and one downgradient), and four soil vapor

monitoring points. Selection of the specific contaminants and

wells to evaluate was based on review of historical site data,

results from a pre-demonstration sampling event, and on a

statistical analysis. Emphasis was placed on sampling the four

monitoring wells located within the radius of influence, which

were designated as "critical wells." Four specific contaminants

were associated with these wells that exhibited acceptable

temporal and spatial variability for evaluating the technology.

These "critical analytes" included chloroethane (CA), 1,1-

Dichloroethane (1,1-DCA), cis-1,2-Dichloroethene (cis-1,2-

DCE), and Vinyl Chloride (VC). TCE was not selected because

it did not exhibit acceptable temporal and spatial variability. 

The primary objective of the demonstration was to evaluate

Earth Tech’s claim that there would be a minimum of 75%

reduction (with a 0.1 level of significance) in the groundwater

concentration of each of the four critical analytes within the zone

of influence, following six months of treatment. However,

process optimization and modifications resulted in extending

the evaluation period to sixteen months. Based on the abovementioned claim and pre-demonstration data, an experimental

design was developed to guide the evaluation. During the

baseline and final sampling events, one groundwater sample

from each of the four critical wells was collected for VOC

analysis daily for seven consecutive days (for a total of 28

samples per event).

Results from the Earth Tech In-Situ Bioremediation Technology

demonstration are presented in Table 1 and are based on the

28 baseline and 28 final samples for the four critical analytes.

VOC concentrations were determined by EPA SW-846 Method

8260. The results indicate that the targeted 75 percent reduction

was achieved or exceeded for two of the four critical

compounds, from baseline to final events. 

Table 1. Groundwater Results.

Target

Compound

 Contaminant

Concentration 

(μg/L)1

Average

Percent

Reduction

Statistically

Significant

Percent

Reduction2

Baselin

e

Final

CA 330 210 36 4

1,1-DCA 960 190 80 71

cis-1,2-DCE 3,100 90 97 95

VC 1,100 45 96 92

1 Values are the average of 28 results from four wells, and rounded to

two significant digits.

2 Percent reductions shown represent the Lower Confidence Limit

(LCL) for the Average Percent Reductions, with a 0.1 level of

significance.

An Innovative Technology Evaluation Report (ITER) describing

the complete demonstration will be available in the near future.

For further information please contact the following:

 

EPA Project Manager

Vince Gallardo

U.S. EPA

National Risk Management Research Laboratory (NRMRL)

26 West Martin Luther King Jr. Drive

Cincinnati, OH 45268

(513) 569-7176

E-mail: gallardo.vincente@epa.gov