Two complementary executable water-quality modeling tools (CausticTitration_PO4mg.exe, CausticTitration_PO4moles.exe) simulate equilibrium processes that may attenuate dissolved concentrations of phosphate (PO4) plus associated concentrations of iron (Fe), aluminum (Al), manganese (Mn), calcium (Ca), and sulfate (SO4) as pH and other solution characteristics change during titration with a caustic agent (e.g. NaOH).
The executable binary code and required input data files for local application are available for download at https://code.usgs.gov/water/phreeq-n-titration-po4-adsorption/-/archive…. Instructions for installing and running the executable files are provided in the document, Instructions_PHREEQ-N-Titration-PO4-AdsorptionModels.docx, which is included in folder, "PHREEQ-N-Titration-PO4-Adsorption_v1.0.0" along with the two executable files (CausticTitration_PO4mg.exe, CausticTitration_PO4moles.exe) and the three required data files (water_quality_defaults_PO4mg.xml, water_quality_defaults_PO4moles.xml, and wateq4fREYsKinetics.dat), plus example case study xml data files. A current version of IPhreeqcCOM for Windows, described below, is required for execution. Upon execution, the user interface (UI) displays and facilitates adjustment to water-quality variables, such as the initial solute concentrations, and important system variables, such as sorbent properties and/or potential for mineral precipitation to occur, without changing the underlying coding. Output from each executable model is available in graphical and tabular format. A screen capture showing an example UI (figure PQ-1) and summaries of the relevant thermodynamic data (tables PQ-1 to PQ-4) are included as worksheets in the Excel file, PHREEQ-N-Titration-PO4-Adsorption_SupplementalInformation.xlsx, included with this software release.