Sampling and Laboratory Analysis for Solvent Stabilizers - Environmental Investigation and Remediation - page 195

analytical error (O'Neill, 2006). Another comparison involved 10 wells completed at different
depths in a saprolite aquifer formation in the South Carolina Piedmont. RPP samplers are advanta-
geous in this setting because monitoring wells recharge very slowly when pumped or bailed for
conventional sampling. A best-i t line to a scatter plot of RPP results versus conventional sampling
results falls close to the 1:1 line, with a regression error ( R 2 ) of 0.92 (O'Neill, 2006). A third com-
parison found that RPP was less reliable for 1,4-dioxane sampling than the Snap Sampler but was
comparable to low-l ow purge methods (Parsons, 2005).
4.2.1.3 Snap Sampler
The Snap Sampler is a whole-water grab sampler that equilibrates with ambient natural groundwa-
ter l owing through the well screen (Britt, 2004). The Snap Sampler is used to retrieve a sample of
uni ltered water in 40 mL VOA vials or 125 or 350 mL polypropylene bottles from a discrete depth
(S. Britt, personal communication, 2007). The sampler is a double-ended, spring-loaded VOA vial
or polypropylene bottle that seals beneath the water surface. Figure 4.2 shows a Snap Sampler. The
sample does not come into contact with the atmosphere prior to injection into a gas chromatograph.
In i eld comparison tests, the Snap Sampler has consistently collected higher concentrations of
VOCs in samples than are typically found in samples retrieved by using other passive sampling
devices, bailers, or sampling pumps (Britt, 2004). Conventional sampling introduces air into the
sample by purging monitoring wells before retrieving a sample and by decanting the sample through
the air into a laboratory VOA vial.
In a i eld comparison conducted at a site in Los Angeles, 1,4-dioxane results in samples collected
by using the Snap Sampler were about 80% higher than results from purging three well casing
volumes (2330 ppb Snap Sampler versus 1310 ppb conventional sampling) (S. Britt, personal
FIGURE 4.2 The Snap Sampler. (From Britt, S., 2004, The Snap Sampler. Paper presented to the Interstate
Technology Regulatory Council Diffusion Sampler Team, Albuquerque, NM, October 28, 2004. With
permission.)