A hydrochemical evaluation is required to analyze the state of water quality on a certain study zone as well as the impact of industrial/mining/agricultural activities.
This article shows a proposed methodology to carry out a hydrochemical evaluation at a basin scale.
Objectives of hydrochemical evaluations
While planning the hydrochemical evaluation, it is necessary to consider some tasks to obtain the necessary amount of data which will help us to understand the physical-chemical characteristics of the main springs, wetlands and superficial water bodies located in the area.
The hydrochemical evaluation will also have as objectives:
- Understand the status of water quality and its interaction with the ecosystem.
- Understand the interaction between water chemistry and groundwater flow.
- Evaluate the impact of filtrations in some components.
- Determine the origin of certain contaminants in superficial water and groundwater.
Here we present and orgaziation propopsal of ahydrochemical evaluation that fills the proposed objectives.
1. Revision of relevant information
These documents can be elaborated by different institutions for different purposes. Some of the documents that should be checked are:
- Detailed and Semi-detailed Environmental Impact Assessments.
- Hydrological and Hydrogeological Assesments.
- Water quality monitoring reports, among others.
Each monitoring point has to be registered, including its coordinates, date, field parameters and the components to be used in the hydrochemical evaluation.
In this phase, the spatial and temporal distribution of points are analyzed in order to identify areas with less density of points and the ones that show incongruence with the reported data.
2. Field monitoring
Based on the analysis of zones with less density of data (Section 1), a field monitoring is organized. The parameters to monitor depend on the necessity to complete data. These can be fields parameters, major ions, nutrients or even coliforms.
Take into account not only the time to measure the data, but also the time to analyze the data in the laboratory, since the next step depends on this factor
3. Data compilation
In first place, a table with the following data is needed:
Name /East coordinate / North coordinate / Date / Source
The table must indicate the reference system of the coordinates. The source of data can be from previous reports or field data.
4. FIeld data analysis
FIeld data is evaluated as a first analysis to understand the water quality.
In this phase a table with the following data has to be generated:
Name / East coordinate / North coordinate / Date / Source / pH / Temp (°C) / CE (uS/cm) / eH (mV)
The coordinate system must be indicated.
On this phase, a thematic map for the parameters (pH, Temp (°C), CE (uS/cm), eH (mV)) is generated. It is recommended to use colorscale and/or normalization of the size of the icons by concentration or magnitude of the parameter.
This phase includess a discussion of tendencies observed and correlation between a field parameter with the rest.
Depending on the amount of data, it is possible to elaborate tables of behavior of a field parameter over time.
5. Laboratory data analysis
Laboratory data will be evaluated on a second phase. Here, a table with the following data is organized:
Name / East coordinate / North coordinate / Date / Source / Concentrations (mg/l)
The concentrations can be from anions, metals, nutrients or other components like pesticides, detergents, oils, etc.
On this phase a thematic map per component of interest has to be made. Depending on the magnitudes and tendencies, up to 5 "interest" components can be represented.
Here, the following diagrams are also made:
- Piper Diagram
- Collins Diagram
- Stiff Diagram
- Schoeller Diagram
- Hydrochemical sections
Depending on the amount of data, it is possible to elaborate tables to represent the behavior of a component over time.
Based on the maps and diagrams on this section, it is possible to discuss the principal characteristics of the distribution of the component in the study zone. The location of points in the diagrams reveal certain characteristics of water regarding the quality and flow regime, which will be reported on this section.
With the data analysis made on Sections 4 and 5, conclusions about the following items will be made:
- Flow regime, water cycle and relation with the status of water quality.
- Spatial distribution of field parameters and components, and its comparison with the current normative.
- Considerations about the original state of water quality
- Considerations about the factors that influence water quality and its evidence in observed data.
- Origin of water from springs based on its chemistry, among others.