Topic Area: 9b. Natural Source Zone Depletion

Formatted Title:

Modeling Residual LNAPL and Impacts to Groundwater Using a Kinetic Approach

Background/Objectives:

Modeling LNAPL recovery endpoints and definitions of residual LNAPL have been hotly debated and investigated for decades. In general, what is left after all recoverable LNAPL has been removed is residual LNAPL. Residual NAPL becomes exceedingly important when the LNAPL contains high concentrations of toxins such as benzene that impact groundwater.

The site is an active pipeline and bulk storage facility in the Gulf Coast Region. Crude oil was released in 2011. Two LNAPL plumes encompassing 8,800 m² persisted after emergency recovery efforts, limited excavation, and operation of a dual-phase mechanical system for just under three years. RPI’s BOS 200+ activated carbon technology was injected in 2017.

Approach/Activities:

When it comes to activated carbon-based technologies, the industry has focused on the adsorption properties as a basis for treatment design. Developmental work at RPI using activated carbon pre-loaded with petroleum hydrocarbon demonstrated that rates of degradation appear to follow a zero order kinetic model. This is vastly different from first order kinetic models that are normally observed and supports the idea that the rate of degradation is coupled to the surface area of the activated carbon. Development of this model is discussed.

Over 1,100 soil samples were collected from 128 borings along with over 200 samples of groundwater to obtain a fresh conceptual model of the distribution of contaminant mass. A kinetic model for mass removal over time was prepared based on these data. The projected timeline for elimination of LNAPL was 18 to 24 months.

The crude oil contained a high percentage of light aromatic constituents in the C₆ to C₁₂ range which accounted for 80% to 90% of the total TPH in groundwater. A secondary model was developed using dissolved benzene concentrations to predict the presence of LNAPL in contact with groundwater. Based on historical analytical and gauging data, the model suggested any location with dissolved benzene above 50 ppb had a high probability of exhibiting PSH. This model was used concurrently with the kinetic design to track mass removal over time. In addition, evidence of biological activity was also tracked through analysis of anions, ammonia, low molecular weight gases, carbon dioxide, and generation of alcohols.

Beaux Jennings

Affiliation

Track

Refine Results

(Group 1, Poster Board #38) Modeling Residual LNAPL and Impacts to Groundwater using a Kinetic Approach