Introduction to AquaChem

AquaChem is a fully-integrated software package developed specifically for graphical and numerical analysis of geochemical data sets. AquaChem features a powerful database that can be customized and configured to include an unlimited number of attributes per sample and a built-in database of inorganic chemicals that are commonly-used for geochemical analyses, calculations and plotting.

AquaChem covers a wide range of calculations frequently used for the analysis, interpretation and comparison of aqueous geochemical data. The analysis tools range from simple unit transformations, mixing calculations, statistics and charge balances to more complex calculations involving correlation matrices and geothermometrics. These powerful analytical capabilities in AquaChem are complimented by a comprehensive selection of commonly-used graphical techniques to portray the chemical characteristics of geochemical and water quality data for single samples and groups of samples. The fully customizable graphical features in AquaChem facilitate the understanding and interpretation of the many complex interactions between the groundwater and aquifer materials. AquaChem's graphical plotting techniques include Piper, Stiff, Durov, Langelier-Ludwig, Schoeller and ternary diagrams, radial plots, scatter graphs, frequency histograms, pie charts, geothermometer plots and time series graphs.

In addition, AquaChem features a graphical interface to the popular geochemical modeling program PHREEQC for calculating equilibrium concentrations (or activities) of chemical species in solution and saturation indices of solid phases in equilibrium with a solution.

Once you start using AquaChem, you will see that it is truly one of the most powerful tools available for anyone dealing with the interpretation, analysis and modeling of simple or complex aqueous geochemical data sets.

AquaChem Main Features

• Automatic unit conversions (mg/l, mol/l, mmol/l, ppm, meq, SiO₂ in Si, H₂Si₃, etc.)
• Flexible data input methods (import from ASCII file or manual keyboard entry)
• Standard database functionality for performing queries and grouping data
• Built-in selection of common geochemical calculations and analysis methods
• Comprehensive selection of graphical techniques for representing and interpreting aqueous geochemical data
• Graphical interface to PHREEQC for geochemical modeling (PHREEQC executable included!)

AquaChem Database Features

Data Structure
AquaChem is built around a customizable database that can be configured to include an unlimited number of attributes per sample (e.g., chemical elements, gas concentration, isotopic composition, physical parameters, etc. Each sample in AquaChem can be characterized according to five basic parameter groups including: (1) Header Information (Sample ID, Location, Date, Geology, etc.), (2) Physical Data (Coordinates, sample depth, head, pH, Conductivity, etc.), (3) Cations (Ca, Mg, Na, K, etc.), (4) Anions (Cl, Br, SO4, NO3, etc.), and (5) Uncharged Compounds (Al, As, CO2, etc.).

Each of these parameter groups contains predefined parameters which can be used to create a data structure that is customized for your sampling and reporting requirements. The built-in database in AquaChem contains most major cations and anions and the chemical properties of each. Additional parameters that are not included can be easily added to the database together with guideline exceedence values for each parameter.

The AquaChem database offers standard database functionality for performing queries or adding and subtracting samples from the selected data set. A powerful search engine allows you to find and group data records according to virtually any search criterion associated with the data set. The selected samples can be easily saved in subgroups or temporarily isolated from the other records for further data processing and interpretation by AquaChem. 

Data Analysis
AquaChem uses the common measured values (cations and anions) for each sample to calculate additional geochemical parameters including water type, sum of anions, sum of cations, ion balance, TDS, hardness, alkalinity, common geochemical ratios, and dissolved minerals. In addition, AquaChem also performs more advanced calculations including:

• Basic statistical calculations such as average value, standard deviation and linear correlation matrices.
• Similarity analysis to calculate a linear regression between a single sample and all other samples of the record list.
• Mixing of two samples can be performed and the results written to the database and a new sample record.
• Chemical facies can be calculated based on the elements that are present by more than 20% of the total of all elements in equivalent concentration.
• Geothermometric calculations can be performed to estimate the original temperature at depth of sampled water.
• Upper and lower tolerance and guideline limit exceedences can be identified for every numeric parameter in the sample set.

AquaChem also produces printed reports for each record or for the entire database containing general sample information, isotope summaries, and a list of samples. All sample records can be exported to a tab-delimited ASCII file.

AquaChem Graphical Display Features

AquaChem's powerful graphical tools utilize 15 techniques commonly used by hydrogeologists and geochemists for analyzing and interpreting aqueous geochemical data sets for hundreds and even thousands of different samples. All text on each graphical display can be customized using a full selection of Windows true type fonts. The various graphical methods and the display options of AquaChem are discussed below.

Common Features for all Graphs
One of the most powerful features of AquaChem is the ability to simultaneously display and modify multiple plots, and to easily identify selected data points within each plot. This unique feature allows you to perform a comprehensive analysis of the data using several interpretation methods. Futhermore, each sample record in the database is directly linked to the graphs, so that any changes to the data are immediately updated on the graphs. This also allows you to easily identify specific sample records on each plot. Other common features include: fully customizable axes scale settings and unit selections for applicable graphs; complete selection of Windows True Type fonts for plot titles, legends, axis labels, and symbol labels; and proportional symbol sizes using concentration value for any measured or calculated parameter.

Site Map Diagrams
Detailed site maps can be imported from DXF files and overlaid with sample point locations. This provides a familiar point of reference when you are analyzing sample data by simultaneously displaying several plot types on the same screen. The symbols representing the sample locations can be customized according to shape and color. In addition, the map plot can be used to display the location of different water facies or the symbols can be scaled according to the concentration of a selected measured element. The highlighted sample points indicate samples that are selected in the database and are also highlighted on all other open graphical displays.

Stiff Diagrams
The Stiff diagrams in AquaChem are plotted for individual samples as a method of graphically comparing the concentration of selected anions and cations for several individual samples. The shape formed by the Stiff diagrams will quickly identify samples that have similar compositions and are particularly useful when used as map symbols to show the geographic location of different water facies.

Radial Diagrams
The radial diagrams in AquaChem are plotted for individual samples as a method of graphically comparing the concentrations of measured parameters for several individual samples. The shape formed by the radial diagrams will quickly identify samples that have similar compositions and are particularly useful when used as map symbols to show the geographic location of different water facies.

Pie Charts
The pie charts in AquaChem are used to plot the concentrations ratio of the major ions (or any combination of parameters) for individual samples. As with the Stiff and radial diagrams, the pie chart is used to graphically compare the concentration ratios of several measured parameters for several different samples. The color and patterns used to identify each parameter are customizable.

Piper Diagrams
The Piper diagram in AquaChem plots the major ions as percentages of milli-equivalents in two base triangles. The total cations and the total anions are set equal to 100% and the data points in the two triangles are projected onto an adjacent grid. This plot reveals useful properties and relationships for large sample groups. The main purpose of the Piper diagram is to show clustering of data points to indicate samples that have similar compositions.

The Piper diagram in AquaChem can be used to plot all samples in the open database or selected sample groups. In addition, the symbols representing the sample values can be customized according to shape and color. The highlighted sample points indicate samples that are selected in the database and are also highlighted on all other open graphical displays.

Durov Diagrams
The Durov diagram in AquaChem is an alternative to the Piper diagram. The Durov diagram plots the major ions as percentages of milli-equivalents in two base triangles. The total cations and the total anions are set equal to 100% and the data points in the two triangles are projected onto a square grid that lies perpendicular to the third axis in each triangle. This plot reveals useful properties and relationships for large sample groups. The main purpose of the Durov diagram is to show clustering of data points to indicate samples that have similar compositions.

The Durov diagram can be used to plot all samples in the open database or selected sample groups. In addition, the symbols representing the sample values can be customized according to shape and color. Other options include individual multiplication factors for each selected ion to prevent data point accumulation along a base line. The highlighted sample points indicate samples that are selected in the database and are also highlighted on all other open graphical displays.

Ternary Diagrams
A ternary diagram in AquaChem is also used to identify trends and relationships between groups of samples. However, it is generally easier to understand than Piper or Durov diagrams since it involves fewer parameters and does not involve projections of data points onto a grid. Like the Piper diagram, the ternary diagram plots the ions as percentages of their concentration values. The ternary diagram is not limited to using only meq units.

The ternary diagram can be used to plot all samples in the open database or selected sample groups. In addition, the symbols representing the sample values can be customized according to shape and color. Other options include individual multiplication factors for each selected ion to prevent data point accumulation along a base line. The highlighted sample points indicate samples that are selected in the database and are also highlighted on all other open graphical displays.

Langelier-Ludwig Diagram
The Langelier-Ludwig square diagram in AquaChem is similar to the projection areas of the Piper and Durov diagrams. Suitable groupings of cations and anions are selected and plotted as percentages of milli-equivalents. By convention, the sums of the selected cations are plotted on the y-axis, and the sum of the selected anions are plotted on the x-axis. Each axis ranges from 0 to 50 meq%.

All major elements can be displayed in one plot with the Langelier-Ludwig diagram. However, like the Piper and Durov diagrams, it displays relative ratios rather than absolute concentrations.

The Langelier-Ludwig diagram can be used to plot all samples in the open database or selected sample groups. In addition, the symbols representing the sample values can be customized according to shape and color. The highlighted sample points indicate samples that are selected in the database and are also highlighted on all other open graphical displays.

Schoeller Diagrams
These semi-logarithmic diagrams were developed to represent major ion analyses in meq/l and to demonstrate different hydrochemical water types on the same diagram. This type of graphical representation has the advantage that unlike the trilinear diagrams, actual sample concentrations are displayed and compared.

The Schoeller diagram in AquaChem can be used to plot all samples in the open database or selected sample groups only. Up to 10 different parameters can be included along the x-axis and the symbols representing the sample points can be customized according to shape and color. The highlighted lines indicate specific samples that are selected in the database and are also highlighted on all other open graphical displays.

Scatter Plots
The X-Y scatter plots are the most simple initial approach to the interpretation of geochemical data. Single plots of ion relationship and parameters that show significant data can be easily created and patterns are quickly identified and easily understood. Both normal scale and log scales are supported for the x and y axes and multiplication factors can be applied to either the x or y element. Element ratios and sums may also be included for either axes.

The scatter plot in AquaChem can be used to plot all samples in the open database or selected sample groups. The symbols representing the sample points can be customized according to shape and color. The highlighted data points indicate specific samples that are selected in the database and are also highlighted on all other open graphical displays.

Frequency Histograms
Frequency histograms are most commonly used to check the number of populations within a given range of measured values. This allows you to view a large number of samples without the diagram becoming too cluttered with data points. The frequency of samples within the given ranges can be plotted according to percentages or numbers of samples.

The frequency histogram can be used to plot all samples in the open database or selected sample groups. The range of values can be customized up to 10 or more groups and the individual samples can be identified at the associated value along the x-axis. The highlighted data points indicate specific samples that are selected in the database and are also highlighted on all other open graphical displays.

Time Series Graphs
The evolution of physical and chemical parameters for a given sampling location is a standard technique for interpreting hydrochemical and hydrogeological processes in natural waters. AquaChem allows you to plot time-series graphs for any numeric parameter in your database, and axes are customizable to suit your display requirements.

The time series graph plot can be used to plot all samples in the open database or selected sample groups. The symbols representing the sample points can be customized according to shape and color. The highlighted data points indicate specific samples that are selected in the database and are also highlighted on all other open graphical displays.

Geothermometer Plots
Geothermometer plots can be used to test the quality of geothermometer estimates for a given geological and hydrogeological condition.

The Giggenbach Triangle
The Giggenbach triangle is composed of three zones; (1) immature waters along the base; (2) partially equilibrated waters in the middle; and (3) fully equilibrated waters along the upper curve. Depending on where the composition of a given sample lies within this triangle, you can estimate the extent of rock-water equilibrium based on the concentrations of K, Mg and Na.

Log (K)-1000/T Plots
The linear log (K)-1000/T plots can be used for samples from boreholes where you know the insitu temperature of the formation. It can be used to: (i) check the usability of thermometers on a set of samples; (ii) plot the chemistry versus formation temperature; (iii) search for the geothermometer with the best fit; and (iv) develop new chemical geothermometers for parameters which show linear behavior.

Printing Results
AquaChem prints all reports and graphical displays to any printer or plotter supported by Windows 95/NT. The printing utility allows you to size and arrange the location of an unlimited number of open graphical displays on the page. This is particularly useful for comparing Stiff and radial diagrams from multiple samples or for using several different graphical displays to interpret groups of samples in each plot. Two lines of titles can be added at the top of the page while a single line of footer information can be added at the bottom of the page.

The PHREEQC Interface

PHREEQC is a program for performing aqueous geochemical calculations and modeling including:

• Speciation and saturation-index calculations;
• Reaction-path and advective-transport calculations involving specified irreversible reactions, mixing of solutions, mineral and gas equilibria, surface complexation reactions, and ion-exchange reactions; and
• Inverse modeling to find sets of mineral and gas mole transfers that account for composition differences between waters, within specified compositional uncertainties.

As the name might suggest, PHREEQC is written in the C programming language and is derived from the Fortran program PHREEQE (Parkhurst et al., 1980). PHREEQC is essentially an upgrade from the previous versions of PHREEQE since it retains all of the functionality and incorporates many improvements and new features.

Creating PHREEQC Input Files
AquaChem provides a direct interface to PHREEQC for creating the input files and running the simulations (WATEQ data files can also be read by PHREEQC). A full working version of PHREEQC is included with AquaChem and can be executed directly from the interface. In order to run a geochemical simulation using PHREEQC, you must specify at least one solution to use in the simulation. The main advantage of the AquaChem interface is that it provides a direct link between PHREEQC input and output files and the AquaChem database files. This database link allows for instantaneous preparation of hundreds of solutions using samples from the database. Alternatively, you can also use the interface to load modeled solutions from previous simulations or to manually prepare solutions. These features will save you an incredible amount of time and hassle when you are dealing with a large number of samples (e.g., simultaneous speciation of many samples).

The AquaChem PHREEQC interface also provides a link between the specified solutions and other PHREEQC operations including adding reactions to the solutions; defining mineral phases for equilibration with the solutions; mixing solutions; adding gas phases to the solutions; specifying ion exchanges; performing 1-D transport simulations, and inverse modeling.

Once the properties of the solutions have been defined, you simply execute the PHREEQC program directly from the AquaChem interface and the simulation calculations will take place. If additional modifications are required, AquaChem allows you to edit the PHREEQC input text file directly from the interface.

Importing PHREEQC Results
AquaChem allows you to import the PHREEQC modeling output file (.pun file) into your database for creating graphs and tables for reports and for statistically analyzing the results. When the appropriate PHREEQC simulation output file is selected and imported, the results will be displayed in a spreadsheet. These results can be copied and pasted to other Windows applications or imported into your AquaChem database.

AquaChem Documentation
AquaChem is accompanied by a comprehensive user's manual containing easy-to-follow instructions and a step-by-step tutorial. Free technical support is provided by phone, fax and e-mail.

AquaChem Requirements: PC Pentium with 8 MB RAM, 10 MB free disk space and Windows 95/98/2000/NT.