Formatted Title

Field Pilot to Evaluate Feasibility of Enhanced LNAPL Depletion with Gypsum Land Application

Background/Objectives

Delivery of sulfate to the subsurface at petroleum hydrocarbon (PHC) impacted sites has been demonstrated as a viable remedial technology to enhance biodegradation of benzene, toluene, ethylbenzene and xylenes (BTEX) in groundwater. Under different site conditions, sulfate delivery with gypsum land application (Kolhatkar & Schnobrich, 2017; Wei et al., 2018; and Sra et al., 2022) or installation of permeable filled borings with gypsum (Buscheck et al., 2019) has successfully enhanced rate of attenuation of benzene concentration in groundwater (Sra et al., 2023). It is anticipated that PHC source zones depletion rates can also be enhanced by availability of electron acceptors like sulfate in the source zone. Baedecker et al. (2018) reported significant differences in the extent of depletion of various hydrocarbon constituents between two light non-aqueous phase liquid (LNAPL) bodies associated with a 30-year-old crude oil release in a shallow aquifer. Their data suggested that these differences were related to the depth of LNAPL and presence of permeable soils above LNAPL, local topography and amount of recharge reaching the LNAPL all of which controlled the availability of nutrients and electron acceptors (e.g., sulfate and nitrate) necessary for biodegradation of hydrocarbons.

We initiated a field pilot to evaluate if sulfate-mediated biodegradation of LNAPL could significantly enhance LNAPL depletion. If feasible, this approach has the potential to be a cost-effective remedial alternative for LNAPL management.

Approach/Activities

At a refinery site, gypsum land application (GLA) was conducted at the accessible portions within the footprint of a former LNAPL release.   Three monitoring wells, located within the LNAPL footprint and with measurable LNAPL were considered for this study.  Two monitoring wells are located within the GLA footprint, and the third monitoring well is located at an upgradient location affected by the same LNAPL release but outside the area of GLA.  The upgradient monitoring well was used as a ‘natural biodegradation control’ location to evaluate changes under natural conditions. LNAPL and groundwater samples in contact with LNAPL from these three monitoring wells were periodically analyzed for 1) detailed LNAPL composition and 2) groundwater concentrations of dissolved BTEX, nitrate, sulfate, sulfide, Fe(II), methane, dissolved inorganic carbon (DIC), δ¹³C-benzene, δ²H-benzene, δ³⁴S-sulfate and δ¹³C-DIC. Multiple lines of evidence from these groundwater analyses were used to document biodegradation stimulated by sulfate delivery with GLA. LNAPL depletion estimates from the two wells influenced by sulfate delivery and the control well were evaluated as described in Devaull et al., 2020.

Results/Lessons Learned

Results

Approximately 300 days after GLA, the LNAPL composition data indicate qualitative differences in LNAPL depletion between the natural biodegradation control and the two monitoring wells influenced by sulfate delivery. Groundwater analyses indicate active biodegradation at all three monitoring wells with significant enrichment of δ³⁴S-sulfate observed for wells within the footprint of GLA indicating sulfate mediated biodegradation of PHCs.

References

1. Kolhatkar, R., and M. Schnobrich. 2017. Land Application of Sulfate Salts for Enhanced Natural Attenuation of Benzene in Groundwater: A Case Study, Groundwater Monitoring & Remediation, 37 no. 2: 43-57 (Open Access). https://doi.org/10.1111/gwmr.12209
2. Wei, Y., N.R. Thomson, R. Aravena, M. Marchesi, J.F. Barker, E.L. Madsen, R. Kolhatkar, T. Buscheck, D. Hunkeler, and C.M. DeRito. 2018. Infiltration of Sulfate to Enhance Sulfate-Reducing Biodegradation of Petroleum Hydrocarbons. Groundwater Monitoring & Remediation 38 no. 4: 73-87. (Open Access). https://ngwa.onlinelibrary.wiley.com/doi/pdfdirect/10.1111/gwmr.12298
3. Sra, K.S., Ponsin, V., Kolhatkar, R., Hunkeler, D., Thomson, N.R., Madsen, E.L. and Buscheck, T. 2022. Sulfate Land Application Enhances Biodegradation in a Petroleum Hydrocarbon Smear Zone, Groundwater Monitoring & Remediation, 43, no. 1: 44-59 (Open Access). https://doi.org/10.1111/gwmr.12547
4. Buscheck, T., Mackay, D., Paradis, C., Schmidt, R. and de Sieyes, N., 2019. Enhancing microbial sulfate reduction of hydrocarbons in groundwater using permeable filled borings, Groundwater Monitoring & Remediation, 39 no. 3: 48-60 (Open Access). https://doi.org/10.1111/gwmr.12346
5. Sra, K., Kolhatkar, R., Segal, D., and Wilson, J., 2023. Sulfate Delivery Methods to Accelerate BTEX Biodegradation and Expedite Site Closure, LUSTLine Bulletin 93, 15-21. LUST-line-Issue-93-Final.pdf (neiwpcc.org)
6. Baedecker, M.J., Eganhouse, R.P., Qi, H., Cozzarelli, I.M., Trost, J.J. and Bekins, B.A., 2018. Weathering of Oil in a Surficial Aquifer. Groundwater, 56: 797-809. (Open Access). https://doi.org/10.1111/gwat.12619
7. DeVaull, G.E., Rhodes, I.A.L., Hinojosa, E. and Bruce, C.L. (2020), Petroleum NAPL Depletion Estimates and Selection of Marker Constituents from Compositional Analysis. Groundwater Monitoring & Remediation, 40: 44-53. (Open Access). https://ngwa.onlinelibrary.wiley.com/doi/epdf/10.1111/gwmr.12410