Design tool for estimation of buffer requirement for enhanced reductive dechlorination of chlorinated solvents in groundwater

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Courtesy of RNAS Remediation Products

Abstract

To assist in the design of enhanced reductive dechlorination systems for in situ remediation of chlorinated solvent source zones, the software BUCHLORAC (Buffering Of Dechlorination Acidity) was developed to pr edict the amount of buffer required to maintain the groundwater pH in a DNAPL treatment zone within the optimal range for dechlorinating bacteria. Reductive dechlorination is an acid-forming process with hydrochloric acid and organic acids typically building up in the treatment zone. Remediation of source zones is associated with such extensive localized dechlorination that it may be common for the soils’ natural buffering capacity to be exceeded. As groundwater acidification may inhibit the activity of dechlorina ting microorganisms and thus slow or stall the remediation process, sufficient alkalinity must be present to maintain a near-neutral pH. BUCHLORAC is a Windows Graphical Inte rface based on an abiotic geochemical model that is implemented through the pr ogram PHREEQC. BUCHLORAC allows users to estimate the buffer requirements for their specific operating and design conditions including, for example, site water chemistry, mi neralogy, amount of chlorinated solvent to be degraded, type of organi c substrate and buffering additive and design inhibition pH. Keywords: alkalinity, bicarbonate, dechlorination, dehalogenation, PHREEQC, BUCHLORAC, TCE, PCE, contaminated aquifer, remediation, DNAPL.

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