Measurement of Natural Losses of LNAPL Using CO₂ Traps

Abstract

Efflux of CO2 above releases of petroleum light nonaqueous phase liquids (LNAPLs) has emerged as a critical parameter for resolving natural losses of LNAPLs and managing LNAPL sites. Current approaches for resolving CO2 efflux include gradient, flux chamber, and mass balance methods. Herein a new method for measuring CO2 efflux above LNAPL bodies, referred to as CO2 traps, is introduced. CO2 traps involve an upper and a lower solid phase sorbent elements that convert CO2 gas into solid phase carbonates. The sorbent is placed in an open vertical section of 10 cm ID polyvinyl chloride (PVC) pipe located at grade. The lower sorbent element captures CO2 released from the subsurface via diffusion and advection. The upper sorbent element prevents atmospheric CO2 from reaching the lower sorbent element. CO2 traps provide integral measurement of CO2 efflux based over the period of deployment, typically 2 to 4 weeks. Favorable attributes of CO2 traps include simplicity, generation of integral (time averaged) measurement, and a simple means of capturing CO2 for carbon isotope analysis. Results from open and closed laboratory experiments indicate that CO2 traps quantitatively capture CO2 . Results from the deployment of 23 CO2 traps at a former refinery indicate natural loss rates of LNAPL (measured in the fall, likely concurrent with high soil temperatures and consequently high degradation rates) ranging from 13,400 to 130,000 liters per hectare per year (L/Ha/year). A set of field triplicates indicates a coefficient of variation of 18% (resulting from local spatial variations and issues with measurement accuracy).

Comparison of bacterial and archaeal communities in depth-resolved zones in an LNAPL body

“…The presence of distinct microbial phylotypes in the contaminated core as compared to the clean core, coupled with recently published data indicating that hydrocarbon degradation is actively occurring at the site studied herein (McCoy et al 2014). provides evidence linking observed microbial phylotypes with hydrocarbon degradation processes within the LNAPL body.…”

“…Toluene was not detected in any of the soil or water samples (305 samples assayed). The relatively low levels of GRO and absence of toluene, combined with recently published data showing higher CO 2 fluxes at grade compared to nearby uncontaminated locations (McCoy et al 2014). indicated ongoing microbial degradation.…”

“…The refinery was active from 1923 to 1982, and thus, subsurface microbial communities have been influenced by LNAPL for nearly a century. Additionally, evidence of active biodegradation has recently been reported for this site (McCoy et al 2014). indicating that microorganisms capable of degrading hydrocarbons in LNAPL zones are present.…”

Digital Innovation: The Next Disruptive but Transformative Remediation Frontier

“…NSZD describes the natural loss of LNAPL due to dissolution, volatilization, and most importantly, biodegradation (ITRC ). Over the last several years, studies have shown that NSZD rates are on the order of 100s to 1000s of gallons per acre per year (Sihota et al ; McCoy et al , Palaia, 2016; Garg et al ).…”

Measuring Carbon-based Contaminant Mineralization Using Combined CO₂ Flux and Radiocarbon Analyses

“…Closed-system flux chambers and gas flux models have been used to determine net respiration in contaminated soils 12,13,[15][16][17] . In these studies, spatial measurements directly associated with a contaminant plume and with background areas showed enhanced biodegradation of organic contaminants.…”