By Elisabeth Law-wai
Thesis Advisors: Profs. Nickolas 1. Themelis and Tuncel Yegulalp
Field Work Advisors: Profs. Martin Stute and James Simpson
Department of Earth and Environmental Engineering
Fu Foundation School of Engineering & Applied Science
Groundwater contamination beneath the Winthrop landfill has shown concentrations of arsenic ranging from 19 to 308 parts per billion (ppb) while the Maximum Contaminant Level (MCL) is set at 50 ppb. Although a “pump and treat” system is continuously in operation for the purpose of arsenic decontamination., a plume of arsenic has been detected over a distance of about 200m (see Figure 2) from the landfill to the lake. The Winthrop Landfill, a Superfund site located in southwest Maine (latitude 44.275, longitude 69.988), is analysed by the Lamont-Doherty Earth Observatory (LDEO) as well as other agencies (including United Technologies Research Center and MacTec Corporation). For monitoring groundwater quality at this site, a number of multi-level wells were installed. This thesis is based on a research project led by Professors Martin Stute and James Simpson., amongst other scientists from Lamont-Doherty Earth Observatory (LDEO). In January 2001, sulfur hexafluoride (SF6) and bromide (NaBr) tracers were injected in the wells on the landfill in order to obtain a better understanding of the leachate and groundwater flows; the measurements of SF6 were performed by LDEO. Also, 300 samples were collected for the analysis of bromide and other anions. In the summer of 2001, the author, supervised by Prof Stute, carried out a series of experiments on the collected water samples. The experiment consisted of measuring the bromide (as the tracer), chloride, and sulfate concentrations of the 300 samples obtained from a number of wells and at different depths, by using the ion chromatograph technique.
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