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Ground Water Sampling at ISCO Sites - Residual Oxidant Impact on Sample Quality and Sample Preservation Guideline
Citation:
Ko, S. AND S. Huling. Ground Water Sampling at ISCO Sites - Residual Oxidant Impact on Sample Quality and Sample Preservation Guideline. Presented at 18th National Conference on Advanced Oxidation Technologies for Treatment of Water, Air, and Soil, November 12 - 15, 2012.
Impact/Purpose:
Poster presentation at the 18th National Conference on Advanced Oxidation Technologies for Treatment of Water, Air, and Soil, Crowne Plaza Riverfront, Jacksonville, FL, Nov 12-15, 2012.
Description:
In-situ chemical oxidation (ISCO) involves the delivery of a chemical oxidant into the subsurface where oxidative reactions transform ground water contaminants into less toxic or harmless byproducts. Due to oxidant persistence, ground water samples collected at hazardous waste sites may contain both the contaminant(s) and the oxidant in a “binary mixture”. The commingling of organic contaminants and oxidant residuals in ground water samples is mainly the result of heterogeneities in aquifer materials, and consequently, the heterogeneous distribution of oxidants and contaminants. Ground water solutes can enter a monitoring well screen from different lithologic zones, containing different concentrations of oxidants and contaminants. The effects of binary mixtures also extend to bench-scale studies where residual oxidants occur in laboratory reactors and aqueous samples are collected and analyzed for VOCs. Assuming an oxidant is present in either ground water or bench-scale aqueous samples, and the binary sample is not appropriately detected and preserved, the quality of the sample is likely to be compromised. Binary mixtures comprised of sodium persulfate (0.1– 2.5 g L-1) and volatile organic compounds (VOCs) (benzene, toluene, m-xylene, perchloroethylene, trichloroethylene) were analyzed using gas chromatography (GC) purge and trap, GC mass spectroscopy headspace. A significant decline (42–100%) in VOC was measured in binary mixtures. However, VOCs in binary mixture preserved through the addition of ascorbic acid were recovered in the range of 99-100%. High concentrations of ascorbic acid (42 – 420 mM) did not interfere in the measurement of the VOCs, and did not negatively impact the analytical instruments. A binary mixture of permanganate (MnO4-) and VOCs was required stoichiometric quantities of the preservative to fully neutralize the oxidant. The mechanism of preservation using ascorbic acid is via direct reaction with MnO4-, rat