Environmental Engineering Reference
In-Depth Information
4.2.1.4 GoreSampler
Another approach to passive-diffusion sampling involves the semiquantitative dosimeter introduced
by W.L. Gore Company. The Gore Module is a mix of proprietary adsorbents encased in Gore-Tex ® ,
a hydrophobic PTFE * membrane. The sorbents are shielded from microbes, sediment, and water so
that contaminants may partition into the enclosed air space according to their Henry's law
constants. Contaminants adsorb by diffusion, independent of concentrations or groundwater l ow
rates. For low concentrations of compounds with low Henry's law constants, such as 1,4-dioxane,
the Gore Modules must remain suspended in the monitoring well for a longer period of time than
for more volatile compounds. The device is 6 in. long and can be used to proi le vertical variation
of concentrations within a well screen. Adsorbed contaminants are then thermally desorbed and
analyzed by GC-MS (Anderson, 2005).
4.2.2 S AMPLING FOR 1,4-D IOXANE IN A IR AND L ANDFILL G AS
A variety of strategies are used to sample for gaseous air contaminants, including whole-air sam-
pling by i lling air-sampling vessels and in-i eld sample concentration by sorption of air contami-
nants to a variety of specialty sorbent tubes in the i eld. Air-sampling vessels include specialized
bags such as Tedlar ® bags or stainless steel canisters such as Summa canisters.
The objectives of air sampling vary widely. For worker health and safety, air sampling is per-
formed to monitor personal breathing zones in the workplace. Air quality studies monitor ambient
air quality, and soil vapor studies monitor for vapor intrusion into buildings from underlying
soil and groundwater contamination. Air-sampling equipment is also used to monitor for the
1,4-dioxane content of landi ll gas as a source of groundwater contamination at landi ll sites. Air
sampling for 1,4-dioxane may also be necessary for monitoring emissions from industrial facilities.
As discussed in Chapter 3, 1,4-dioxane is not likely to persist in the atmosphere owing to its rela-
tively short photodegradation half-life and low Henry's law constant. A detailed discussion of air
sampling is beyond the scope of this topic. This section provides a brief overview of available meth-
ods for sampling 1,4-dioxane in air.
The most common method for sampling 1,4-dioxane in air uses a stainless steel Summa canister
for analysis by EPA Method TO-15 (USEPA, 1999). The Summa canister is designed to be evacu-
ated to a near vacuum (0.05 mm Hg) and then opened to the i eld atmosphere to admit the sample at
a i xed rate controlled by a valve. The pressure differential draws the sample into the canister
through a l ow-restrictive inlet or mass-l ow controller. The canister is then sealed and delivered to
the laboratory for analysis by GC-MS.
Sampling gas trapped in soil is accomplished by applying a vacuum to a i ltered tube and
drawing the sample into a Summa canister, a Tedlar bag, a gas syringe, or a gas-tight glass bulb
(CalEPA, 2003). The choice of tubing and sample container may have a bearing on 1,4-dioxane
results. Some sample tubing has been shown to emit 1,4-dioxane to the sample, whereas other
tubing materials retain 1,4-dioxane, on the basis of a few tests with tubing (Hayes et al., 2006).
Tubing materials commonly used in soil sampling, and their potential to emit or retain 1,4-diox-
ane, are listed in Table 4.3 .
Similar testing on the contribution of 1,4-dioxane by Tedlar bags to air samples was con-
ducted in the Air Toxics Ltd study (Hayes et al., 2006). Tedlar bags were l ushed three times with
laboratory grade, humidii ed “zero-air” samples and then analyzed. 1,4-Dioxane was not found.
Testing with laboratory standards showed no difi culties recovering 1,4-dioxane from Tedlar
bags. The average recovery was 103%, with a relative standard deviation (RSD) of 5% (Hayes
et al., 2006).
* PTFE = polytetral uoroethylene. Gore-Tex is made from a polymer similar to Tel on.
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