542F04009
\ Radial Plume Mapping of Gaseous
SET
Scanning Open-Path FTIR
Through the Measurement and Monitoring Technologies for the 21 st Century (21 M2) initiative,
EPA's Office of Solid Waste and Emergency Response (OSWER) is identifying and supporting
deployment of promising measurement and monitoring technologies by matching existing and
emerging technologies with OSWER program and client needs in the fields of waste management
and site cleanup. OSWER has identified a number of "needs areas" as the focus of 21 M2. These
needs reflect evolving requirements across all waste programs. A recent list and description of
needs is available at the 21 M2 Internet site at http://www.cluin.org/Drograms/21m2/needs_cftn
Background
This fact sheet summarizes the results of an air
emissions evaluation using a scanning open-path
Fourier transform infrared (OP-FUR) spectro-
meter and an Optical Remote Sensing—Radial
Plume Mapping (ORS-RPM) method at a closed
municipal landfill. The city of Somersworth, NH,
operated the landfill from the mid-1930s to 1981.
Unknown quantities of sludge, solvent, acid, dye,
metal, and laboratory or pharmaceutical waste
were disposed of at this site which was placed on
the Superfund National Priorities List on
September 8, 1983. The city installed a permeable
soil cover in 2001 as part of the remedial action
and is considering soccer fields and other open-air
recreational reuse options for the site. However,
the potential flux of gaseous emissions, such as
methane and air toxics, from the degradation of
the landfilled waste could present a hazard to
individuals using the fields. Region 1, in
cooperation with the 21 M2 program, proposed an
OP-FTIR/RPM survey to measure the extent of
any gases escaping from the landfill.
How OP-FTIR and RPM Work
The deployment used at the Somersworth landfill
involved transmitting a collimated infrared light
beam, modulated by a Michelson interferometer,
from the OP-FTIR instrument through the target
area to a retroreflector (mirror) target. The light
beam was then reflected back through the target
area to a detector inside the OP-FTIR instrument.
The data were collected as an interferogram,
which was mathematically manipulated to
produce an infrared spectra that can be used to
identify and quantify several organic chemicals at
parts per billion per volume levels.
Since the system measures average concentration
over the path length, several retroreflectors were
used in each scanned beam configuration to
provide more spatial detail on the location of
potential hotspots or areas of locally high concen-
trations. The site was divided into five areas that
were gridded so that a retroreflector could be
placed in each grid to create a series of radial
paths for each area. To determine total flux for the
landfill, a series of retroreflectors was placed
down wind. Retroreflectors were placed on the
landfill surface at ground level and at several
heights using a scissor jack to measure the vertical
change in average concentration (Figure 1).
Project Objectives
The principal objectives of the project were to
demonstrate the operation and function of OP-
FTIR technology to:
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Office of Superfund Remediation
and Technology Innovation
EPA/542/F-04/009
Determine the average surface concentration
distribution of contaminants across the site.
Identify major emissions hotspots.
Estimate the total and hotspot flux of
detectable compounds from the landfill.
Wind Direction
Figure 1. Schematic of OP-FTIR Configuration for
Measuring Vertical Flux
Project Results
Average Concentrations
Methane was detected at the site with average
concentrations ranging from background to 6.5
ppm (Figure 2). The global methane background
value of 1.75 ppm was subtracted from all
methane concentrations measured. No volatile
organic compounds (VOCs) were detected above
the detection limits of the OP-FTIR instruments.
The detection limits for the majority of the VOCs
were generally less than 30 ppb.
Figure 2. Contour Map of Measured Surface Methane
Concentrations at the Site
The emission concentrations were calculated
using data averaged from several different
consecutive cycles. A cycle consists of a complete
set of measurements for all retroreflector positions
in a designated area with each individual
measurement taking approximately 30 seconds.
The results were plotted on a 2-dimensional
isopleth map.
Identification of Hotspots
Three hotspots were detected at the site. To
further investigate the most intense hotspot (6.5
ppm above background), investigators redeployed
the retroreflectors close to the grid square where
the hotspot had been detected. This redeployment
survey indicated that the source of the highest
emissions was on the south slope of the valley
adjacent to a ball field. That area had a hole that
may have been dug for a utility pole that was
never installed.
Estimate of Emission Fluxes
The emissions flux through a 200-meter by 23-
meter vertical plane was determined by multiply-
ing the area integrated concentration by the
component of the wind speed normal to the plane.
This resulted in a flux value of 5.8 g/s, which is
the estimated emission rate for the entire landfill.
The methane hotspot near the ball field accounted
for 57 percent of the site's methane flux.
Project Information
For more information on this study, contact Roger
Duwart, U.S. EPA Region 1, 617-918-1259,
duwart.roperfa).epa.gov or
Susan Thorneloe, U.S. EPA Research Triangle
Park, 919-541-2709, thomeloe.susanfatepa.gov
Additional Information
More information also can be found at the
following locations:
• 21M2 program.
http://cluin.ore/Droprams/21m2/QT
• Dan Powell, U.S. EPA, 703-603-7196,
powell.danfg).epa.gov
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