Progress in Remediation of Groundwater at Petroleum Sites in California

McHugh, Thomas E.; Kulkarni, Poonam R.; Newell, Charles J.; Connor, John A.; Garg, Sanjay

doi:10.1111/gwat.12136

Cited by 27 publications

(44 citation statements)

References 8 publications

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“…Using the Ng model as a foundation, a planning‐level NSZD model can be used to address questions about how long NSZD will take to remove a certain fraction of the LNAPL that was released, and how long it will take to remove a particular constituent down to a particular target level. The inputs to the model would be: (1) current NSZD rate; (2) type of hydrocarbon that was released and the current mass fraction of the various constituent buckets; (3) degradation rates for the lower solubility buckets, as a starting point, can be obtained from Ng et al (), and for soluble components from site‐specific source‐zone groundwater concentration vs. time data (e.g., k source for each BTEX compound [McHugh et al ]); and (4) percentage removal of the bulk LNAPL or of a constituent bucket that would be needed to achieve specific remediation targets (such as a groundwater concentration goal or a LNAPL saturation reduction goal). More work is needed to better understand how to measure and process the proper input data for use in this planning‐level LNAPL remediation timeframe model.…”

Section: Key Learningsmentioning

confidence: 99%

Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change

Garg¹,

Newell²,

Kulkarni³

et al. 2017

Groundwater Monitoring Rem

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Natural source zone depletion (NSZD) has emerged as a practical alternative for restoration of light non‐aqueous phase liquid (LNAPL) sites that are in the later stages of their remediation lifecycle. Due to significant research, the NSZD conceptual model has evolved dramatically in recent years, and methanogenesis is now accepted as a dominant attenuation process (e.g., Lundegard and Johnson ; Ng et al. ). Most of the methane is generated within the pore space adjacent to LNAPL (Ng et al. ) from where it migrates through the unsaturated zone (e.g., Amos and Mayer ), where it is oxidized. While great progress has been made, there are still some important gaps in our understanding of NSZD. NSZD measurements provide little insight on which constituents are actually degrading; it is unclear which rate‐limiting factors that can be manipulated to increase NSZD rates; and how longevity of the bulk LNAPL and its key constituents can be predicted. Various threads of literature were pursued to shed light on some of the questions listed above. Several processes that may influence NSZD or its measurement were identified: temperature, inhibition from acetate buildup, protozoa predation, presence of electron acceptors, inhibition from volatile hydrocarbons, alkalinity/pH, and the availability of nutrients can all affect methanogenesis rates, while factors such as moisture content and soil type can influence its measurement. The methanogenic process appears to have a sequenced utilization of the constituents or chemical classes present in the LNAPL due to varying thermodynamic feasibility, biodegradability, and effects of inhibition, but the bulk NSZD rate appears to remain quasi‐zero order. A simplified version of the reactive transport model presented by Ng et al. has the potential to be a useful tool for predicting the longevity of key LNAPL constituents or chemical fractions, and of bulk LNAPL, but more work is needed to obtain key input parameters such as chemical classes and their biodegradation rates and any potential inhibitions.

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Section: Key Learningsmentioning

confidence: 99%

Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change

Garg¹,

Newell²,

Kulkarni³

et al. 2017

Groundwater Monitoring Rem

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“…Individual studies on plume lengths include 22 to 289 sites per study. Studies on plume stability conditions include 34 to 271 sites per study, with one study addressing the overall plume concentration trends observed at over 4000 UST sites in California (McHugh et al ). Duration of Groundwater Monitoring History . A number of the studies selected sites with longer‐term monitoring periods so as establish plume trends with less uncertainty associated with seasonal fluctuations, sampling variability, and attenuation rates for compounds, such as MTBE, which have been observed to require longer acclimation periods for biodegradation.…”

Section: Compilation Of Data From Published Studiesmentioning

confidence: 99%

Review of Quantitative Surveys of the Length and Stability of MTBE, TBA, and Benzene Plumes in Groundwater at UST Sites

Connor¹,

Kamath

Walker

et al. 2014

Groundwater

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Quantitative information regarding the length and stability condition of groundwater plumes of benzene, methyl tert-butyl ether (MTBE), and tert-butyl alcohol (TBA) has been compiled from thousands of underground storage tank (UST) sites in the United States where gasoline fuel releases have occurred. This paper presents a review and summary of 13 published scientific surveys, of which 10 address benzene and/or MTBE plumes only, and 3 address benzene, MTBE, and TBA plumes. These data show the observed lengths of benzene and MTBE plumes to be relatively consistent among various regions and hydrogeologic settings, with median lengths at a delineation limit of 10 μg/L falling into relatively narrow ranges from 101 to 185 feet for benzene and 110 to 178 feet for MTBE. The observed statistical distributions of MTBE and benzene plumes show the two plume types to be of comparable lengths, with 90th percentile MTBE plume lengths moderately exceeding benzene plume lengths by 16% at a 10-μg/L delineation limit (400 feet vs. 345 feet) and 25% at a 5-μg/L delineation limit (530 feet vs. 425 feet). Stability analyses for benzene and MTBE plumes found 94 and 93% of these plumes, respectively, to be in a nonexpanding condition, and over 91% of individual monitoring wells to exhibit nonincreasing concentration trends. Three published studies addressing TBA found TBA plumes to be of comparable length to MTBE and benzene plumes, with 86% of wells in one study showing nonincreasing concentration trends.

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“…This approach has proven successful for evaluating long-term monitoring data from multiple sites to provide a more informed basis for understanding typical contaminant trends over time. 25,26 In this study, this type of evaluation was used to quantify attenuation rates and identify factors that influence observed attenuation patterns to better understand how these conditions will dictate the appropriate management strategies.…”

Section: ■ Introductionmentioning

confidence: 99%

Evidence of 1,4-Dioxane Attenuation at Groundwater Sites Contaminated with Chlorinated Solvents and 1,4-Dioxane

Adamson

Anderson

Mahendra

et al. 2015

Environ. Sci. Technol.

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103

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There is a critical need to develop appropriate management strategies for 1,4-dioxane (dioxane) due to its widespread occurrence and perceived recalcitrance at groundwater sites where chlorinated solvents are present. A comprehensive evaluation of California state (GeoTracker) and Air Force monitoring records was used to provide significant evidence of dioxane attenuation at field sites. Temporal changes in the site-wide maximum concentrations were used to estimate source attenuation rates at the GeoTracker sites (median length of monitoring period = 6.8 years). While attenuation could not be established at all sites, statistically significant positive attenuation rates were confirmed at 22 sites. At sites where dioxane and chlorinated solvents were present, the median value of all statistically significant dioxane source attenuation rates (equivalent half-life = 31 months; n = 34) was lower than 1,1,1-trichloroethane (TCA) but similar to 1,1-dichloroethene (1,1-DCE) and trichloroethene (TCE). Dioxane attenuation rates were positively correlated with rates for 1,1-DCE and TCE but not TCA. At this set of sites, there was little evidence that chlorinated solvent remedial efforts (e.g., chemical oxidation, enhanced bioremediation) impacted dioxane attenuation. Attenuation rates based on well-specific records from the Air Force data set confirmed significant dioxane attenuation (131 out of 441 wells) at a similar frequency and extent (median equivalent half-life = 48 months) as observed at the California sites. Linear discriminant analysis established a positive correlation between dioxane attenuation and increasing concentrations of dissolved oxygen, while the same analysis found a negative correlation with metals and CVOC concentrations. The magnitude and prevalence of dioxane attenuation documented here suggest that natural attenuation may be used to manage some but not necessarily all dioxane-impacted sites.

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Progress in Remediation of Groundwater at Petroleum Sites in California

Cited by 27 publications

References 8 publications

Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change

Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change

Review of Quantitative Surveys of the Length and Stability of MTBE, TBA, and Benzene Plumes in Groundwater at UST Sites

Evidence of 1,4-Dioxane Attenuation at Groundwater Sites Contaminated with Chlorinated Solvents and 1,4-Dioxane

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