Natural Attenuation for Groundwater Remediation

AbstractPreviously, the authors have developed the concept of in-situ reduction of hexavalent chromium in contaminated groundwater, using various forms of active reagent delivery, based on site geohydrological conditions. While these approaches are highly successful and cost effective, in some cases, such active approaches may not be appropriate. Rather, it may be appropriate to limit the spread of chromium contamination by formation of permeable reactive barriers or reactive zones through the borehole placement of aqueous reductants. A passive approach, utilizing bore-hole placed reactive barriers and Monitored Natural Attenuation (MNA), offers real advantages for groundwater remediation, especially in situations involving groundwater in fractured or cavernous bedrock, where the water table is at great depth, or where on-going activities in the source area limit access for more active approaches. A geochemical reactive barrier was used at a South Australian timber preservation facility sited over a cavernous limestone. After remedial activities within the plume achieved significant reduction of the mobile chromium mass, the applicable regulatory agency authorized MNA for control of residual contamination. A phased approach has been utilized at a Central Valley, California timber preservation site, to develop data on the radial spread of reductant injection through diffusion, and the longevity of the effect of such injection, and a full-scale remedial approach designed, recognizing limitations on injection imposed by limited access. The paper discusses the requirements to demonstrate the effectiveness of MNA. Case histories of successful application of the integrated approach of passive reduction and MNA are presented, as a cost-effective and environmentally-protective means of accomplishing remediation of hexavalent chromium in groundwater.

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1,2-DCA Natural Attenuation Evaluation in Groundwater: Insight by Dual Isotope 13C/37Cl and Molecular Analysis Approach

Water ◽

10.3390/w13050728 ◽

2021 ◽

Vol 13 (5) ◽

pp. 728

Author(s):

Giovanna Carpani ◽

Massimo Marchesi ◽

Ilaria Pietrini ◽

Luca Alberti ◽

Luciano Massimo Zaninetta ◽

...

Keyword(s):

Natural Attenuation ◽

Groundwater Remediation ◽

Source Area ◽

Enrichment Factors ◽

Contaminated Site ◽

Anaerobic Conditions ◽

Site Specific ◽

Main Site ◽

Dual Isotope ◽

Reductive Dehalogenase

Natural attenuation (NA) processes represent a valuable option in groundwater remediation. At a heavily 1,2-dichloroethane (1,2-DCA) contaminated site, Compound-Specific Isotope Analysis (CSIA) in combination with Biological Molecular Tools (BMTs) were implemented as a rigorous characterization approach to evaluate the occurrence of Natural Attenuation in the proximity of the source area. By the use of microcosm experiments, the potential for natural and enhanced biodegradation under anaerobic conditions was documented, following the dichloroelimination pathway. Enrichment factors of −9.1‰ and −11.3‰ were obtained for 13C while Geobacter spp. and reductive dehalogenase genes (rdhs) were identified as main site-specific biomarkers. At pilot scale, enrichments of 13.5‰ and 6.3‰ for δ13C and δ37Cl, respectively, high levels of reductive dehalogenase (rdh group VI) along with the dominance of Geobacter spp. indicated the occurrence of significant dichloroelimination processes in groundwater under anaerobic conditions. By using the site-specific enrichment factors, degradation extents over approximately 70–80% were estimated, highlighting the relevant potential of NA in 1,2-DCA degradation in the vicinity of the source area at the site. The proposed fine-tuned protocol, including CSIA and BMTs, is proven to be effective as a groundwater remediation strategy, properly assessing and monitoring NA at site scale.

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Natural Attenuation and Enhanced Bioremediation of Petroleum Hydrocarbons Geochemical Factors in Groundwater Remediation

Encyclopedia of Water ◽

10.1002/9781119300762.wsts0208 ◽

2019 ◽

pp. 1-5

Author(s):

James A. Jacobs ◽

David B. Vance

Keyword(s):

Natural Attenuation ◽

Petroleum Hydrocarbons ◽

Groundwater Remediation ◽

Geochemical Factors ◽

Enhanced Bioremediation

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