Evaluación numérica de un sistema de remediación de aguas subterráneas ante el derrame de hidrocarburos en la zona no saturada de un acuífero aluvial costero

Abstract

In the construction and operation project of the Puerto Nuevo seaport located in the municipality of Ciénaga Magdalena, there is a contingency due to the rupture of a pipe located at one (1) meter depth that generates in 2018 the spill of approximately 25,000 gallons of biodiesel for 30 days in a coastal alluvial aquifer. In this context, a conceptual hydrogeological model-MHC and numerical flow and transport-MNFT model is developed from secondary information. The latter, in its transitory stage, develops a remediation technique by extraction of groundwater and product in the free phase that acts as a physical measure of confinement or containment.

Thus, in this research the main equations of flow and transport of the unsaturated zone-NSZ and saturated are developed, and the concepts associated with saline intrusion are explained. The definition of the transport parameters as a relation of the dispersivities is carried out from a regression analysis of the current line of the aquifer where the contingency occurs, while, for those associated with the ZNS, the pedotransference functions are used. from the texture and density of the dry soil (Gupta and Larson (1979), in the absence of laboratory analysis where the moisture retention curves are determined for the analysis of the hydraulic conductivity of the ZNS (Gupta and Larson 1979) In this sense, and considering that the objective of this research is to evaluate a groundwater extraction remediation technique, groundwater extraction is described in a general way, which must be accompanied by another remediation technique focused on the ZNS that complies with the reference limit for the comparison of sites impacted by hydrocarbons of the Ministry of Environment and Sustainable Development-MADS , (2008).

This work is developed in 3 phases, which are divided into describing and compiling information from the case study with the objective of building the MHC and MNFT in the second phase, including the analysis of the remediation technique. In this way, the third phase consists of analyzing the results of the numerical model of flow and transport under conservative conditions, this means that the solute in the alluvial aquifer does not present delay, and the ZNS is not considered. Thus, it is important to highlight that in the second phase the MHC is adjusted where the flow boundaries are defined, the geology is refined, the potential recharge is characterized and calculated, and the dynamics of the Toribio River as the main tributary of the river's domain is analyzed. model. Regarding the hydrodynamic parameters, the RETC software is used to calculate the parameters of the ZNS from pedotransference functions, and those of the saturated zone from pumping tests and bibliographic information according to the type of hydrogeological unit. Following the above, the MHC is finished with the calculation of the parameters of the adsorption isotherm using the Freundlich model, from laboratory tests on soils with similar granulometry as that of the study area. Once the MHC is built, a numerical model is structured in the FEFLOW program which is calibrated using the trial and error method and the PEST algorithm included in the program. With the numerical model of flow in transitory state, it is determined that the variable corresponding to the Freundlich isotherm is fundamental to define the behavior of the solute, concluding that the values ​​proposed by Seferou, (2013) are adequate for the pollution plume to have a propagation similar to that defined in the dispersivities relationship and that does not reach the monitoring wells PZ-05 and PZ-06 one month after the contingency event ends.

Finally, it is concluded that the remediation technique by groundwater extraction manages to reduce the concentration of biodiesel in the alluvial aquifer to less than 0.29 mg / l MADS (2008) and that the numerical evaluation of pollutant dispersion should consider the ZNS and the time delay. This is due to the fact that the results with a non-conservative solute show a decrease in the contamination plume of 63% in distance and 90% in concentration compared to the results of the conservative numerical model.