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Mercury Variability in domestic wells

Project Title:Mercury Variability in domestic wells
Project Number: LJ00D2Y
Project Chief:
Project Start Date: 01-JUL-2007
Project End Date: 30-SEP-2010

Project Objectives

The first objective is to design a sampling protocol that produces water samples that best represent the water user’s actual exposure to Hg in domestic-well water by evaluating the variation in Hg concentration with time during well purging. The second objective is to better understand the forms of Hg present and the chemical environment in which they exist. The third objective is to determine whether Hg concentrations vary with rate of pumping—in other words, determining whether low-flow pumping at observation wells underestimates the amount of Hg that would be yielded by a domestic well, with higher pumping rate, in the same location.

Statement of Problem

Since 1982, mercury (Hg) concentrations that exceed the State and USEPA maximum contaminant level (MCL) of 2 g/L have been reported for water withdrawn from more than 600 domestic wells finished in the unconfined Kirkwood-Cohansey aquifer system in southern New Jersey. Actions have been taken to protect well owners from further exposure by providing treatment systems or hookups to public-water supplies, and the sources of, and process affecting, the Hg contamination have been investigated. Several outstanding questions that remain impinge upon human health. The first issue is the representative nature of the samples collected from domestic wells—that is, do existing sampling protocols provide “representative” samples, and do these samples contain Hg at levels that represent the greatest risk to the users of water from a given well? Do certain conditions associated with pumping result in “spikes” in Hg concentration? The second issue is the forms of Hg present in the well water—that is, does the water consumed from domestic wells contain primarily inorganic Hg, or are there significant concentrations of methyl mercury (the most toxic form), or other organic forms of Hg? Other than health issues, the forms of Hg present in well water likely affect how Hg moves through the aquifer—information that is important in predicting how the contamination may spread from one location to another. This proposal addresses aspects of these two major questions.

Strategy and Approach

Three separate sampling phases are proposed, each building on results from the previous phase or phases. A subset of the water samples collected would be analyzed for several Hg species, total and dissolved iron, also total (TOC) and dissolved (DOC) organic carbon and ultraviolet absorbing organic constituents (which indicate the aromaticity of organic carbon (OC)). The phases are designed so as to answer the maximum number of relevant questions with a minimum of field efforts. If chloride complexes, Hg0 and MeHg do not appear to constitute most of the total Hg present, additional funding can be sought and a sampling plan can be formulated with an entity that can analyze additional organic (ethylated) forms of Hg.

Phase 1. Hg variation at the tap with time of system purging;

Phase 2. Hg variation with locale (pressure tank and/or treatment tank, kitchen tap, outside tap) of sampling;

Phase 3. Effect of pump rate on Hg concentrations.

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