Groundwater is a fundamental part of the hydrological cycle, whose development, efficient management and good understanding, guarantee the permanence of the water resource over time.

Today, industrial, agricultural and poor environmental practice have caused that many aquifers and aquitards are being impacted anthropically by organic and inorganic compounds whose immediate result, leads to a progressive degradation of groundwater and environment.

Characterization and management of groundwater resources, involves a comprehensive set of tools analysis to determine the characteristics of an aquifer (type and geometry, piezometry, quantification of hydraulic parameters and transport, water balance, degree of quality and exploitation, etc.). In the last decade, an essential part of all hydro geological study, must be supported by a numerical modeling of flow of underground water and transport of pollutants, whose applications are manifold, but to name but a few, a model serves to:

A model is defined as the total or partial representation of a natural system. There are different types of models; specifically the numeric are those, where the representation of an aquifer (or part of it), is carried out via differential equations (general equation of flow, general transport and Darcy law equation), which are solved by numerical methods (approximation) for each element of the domain.

CAM uses a method of solution called finite difference, through which the domain is divided into rectangles (model in 2-D), or parallelepipeds (3-D model), and aims to solve the differential equations, obtaining hydraulic loading ("h" in feet or meters above sea level) and the final concentration (Cf in mg/L) to the center of each cell of the mesh, depending on the time.

Therefore applies the Visual MODFLOW software, developed by Waterloo Hydro geologic Inc. (WHI), which is widely accepted by national agencies (CNA, IMTA) and international (USGS, EPA).

GI-GO (Garbage In-Garbage Out) principle.
The main limitation in a numerical model is that requires a large number of data, so it is necessary to have an extensive knowledge of the site. Therefore, it is necessary to develop a conceptual model prior, consistent with the reality, which is supported with data from piezometric levels, concentrations of the solute, determinations of hydraulic parameters by means of trials slug and/or pumping, physical parameters and mechanics of soil, hydro-geochemistry, chemical soil parameters and water balance. It is very important to stress that a numerical model is not a panacea and if you don't have a degree of important knowledge of the site, can fall into the trap set up by the GI-GO principle: Garbage In - Garbage Out, i.e. introduction of inconsistent data, return results inconsistent.

Modeling of LNAPL's
While the MODFLOW code is a software with multiple applications, it has some limitations, it can not simulate all aspects of an aquifer system and its use (of advanced character) narrows on the basis of the scope of each project in particular. Porous aquifers have been impacted by oil spills less dense than water, is very common aquifer see contaminated by a boom in free phase, known as LNAPL.

Less dense than water compounds, not miscible in it (LNAPL's for its acronym in English Light Non-Aqueous Phase Liquids), tend to form a layer that sits at the top of the phreatic surface, flowing at one speed lower than the actual speed of flow. The LNAPL's mean a great challenge in the environmental field, because they represent the fraction of the increased risk in a polluted aquifer

For evaluating and managing sites contaminated by LNAPL's, CAM applies a model developed by the American Petroleum Institute (API) based on the equations of Van Genuchten, Richards and Bill Darcy, called LNAPL's Calculation Tools, which complemented the characterization of free stages, determining the actual speed of the LNAPL, volume and degree of saturation of the hydrocarbon in soil final concentration at distances and specific receptors of the dissolved phase, the change in the composition of the source vs time zone as well as, the recovery rate of the hydrocarbons taking into account in various account technical remediation, mainly by trenches, wells with skimmers and Dual Phase Extraction systems.

Application of EPA models
Depending on the scope and complexity of the type of project, CAM evaluates the implementation of various models that do not require an advanced modeling detail, however, required the simulation of the toxic compound to determine arrival times and rallies expected for external potential receptors at different intervals of time. This CAM applies two models produced by the Environmental Protection Agency (EPA) with different applications: