Statistical Analysis of Secondary Water Quality Impacts from Enhanced Reductive Bioremediation

• Published in: Ground water monitoring & remediation Vol. 35; no. 4; pp. 67 - 77
• Main Authors: Tillotson, J. M., Borden, R. C.
• Format: Journal Article
• Language: English
• Published: Malden, USA Wiley Periodicals, Inc 01.11.2015; Wiley Subscription Services, Inc
• Subjects: Bioremediation; Contaminants; Groundwater; Iron; Monitoring; Plumes; Water quality; Water treatment
• ISSN: 1069-3629; 1745-6592
• DOI: 10.1111/gwmr.12132

Enhanced reductive bioremediation (ERB) is effective for treating a broad range of groundwater contaminants, but does result in secondary water quality impacts (SWQIs). Monitoring data from 47 ERB projects were analyzed to gain a better understanding of the formation and extent of SWQIs. The database analysis revealed that SWQIs occur at virtually every site, including reduced levels of background aqueous electron acceptors (O₂, NO₃ ⁻, and SO₄ ² ⁻), increases in dissolved‐phase metals (Fe and Mn), and the production of CH₄. However, the SWQI “plume” that is produced is usually confined within the original contaminant plume. As a result, SWQIs from ERB are unlikely to adversely impact potable water supplies. SWQIs do attenuate with distance downgradient, with concentrations often returning to near background levels. The results of the database analysis were combined with previous research to develop a general conceptual model (CM) of SWQI production, mobilization, and attenuation. This CM can assist in identifying conditions where SWQIs may pose a concern. These can include sites with low iron/high sulfate (H₂S mobilization), high groundwater velocity (SWQIs at distances far downgradient), and sites with low CH₄ anaerobic oxidation rates (CH₄ migration).