The General Tab allows the setting of various simulation options relating to the multi-species water quality model.

FieldDescription
Pipe Surface Species Concentration Area Unit Area unit for Pipe Surface Concentration (ft^2, m^2, cm^2).
Reaction Rate Time UnitTime unit for reaction rate (Day, Hour, or Minute). 
Integration Method TypeNumerical method to solve reaction systems’ ordinary differential equations (ODE). Selections are the standard Euler integrator, the 5th Order Runge-Kutta integrator (RK5) and the 2nd Order Rosenbrock integrator (ROS2). 
Time Step (second)TIMESTEP is the water quality time step, in seconds.
Absolute Water Quality ToleranceAbsolute water quality tolerance is the value used to determine when two concentration levels of a species are the same. This setting applies to all species included in the model. Different values for individual species can be set in the Species section of the input (see below). 
Relative Water Quality ToleranceThe Relative water quality tolerance is the relative accuracy value used to adjust time steps in the RK5 and ROS2 integration method. It applies to all species included in the model. Different values for individual species can be set in the Species section of the input below. 
Coupling Integration with Algebraic SolverThe Coupling selection determines to what degree the solution of any algebraic equilibrium equations is coupled to the integration of the reaction rate equations. If coupling is not selected then the solution to the algebraic equations is only updated at the end of each integration time step. The algebraic variables maintain the values they had at the start of the time step while the ODEs are being numerically integrated. With coupling selected the updating is done whenever a new set of values for the rate-dependent variables in the reaction rate expressions is computed. This can occur at several intermediate times during the normal integration time step when using the RK5 and ROS2 integration methods. Thus the coupling selected option is more accurate, but can require significantly more computation time.