1.   Purpose and objectives

     Calculation of pathlines and travel times in ground water systems, both due to pumpage from a number of wells and under natural (initial) flow conditions, expressed in terms of the relevant flux components.

2.   Description

     The flow is described by Darcy's law and the mass continuity equation. Existing analytical solutions are used to calculate the pathlines and  travel times in either the backward mode (tracing starts at well screens) or forward mode (tracing starts at arbitrary points in space).

     Steady-state, sequence of steady-states, and transient systems can be modelled, including forward and backward particle tracking. The well rates can vary either step-wise or piece-wise linearly in time. The horizontal components of the natural flow in aquifers (preceding the well pumpage) can be specified by means of a 2nd order polynomial.

     The system can handle the following cases:

     - Multi-layered aquifer-aquitard system, assuming horizontal flow in 
       aquifers and vertical flow over separating and/or overlying 
       aquitards with up to 10 aquifers. The wells fully penetrate the 
       relevant aquifers. The layers are laterally homogeneous and 
       isotropic. This includes the classical Hantush (single aquifer-
       aquitard) and Theis (single confined aquifer) systems. The vertical 
       velocity component in the aquifers is approximated by mass 
       continuity considerations.

     - Fully three-dimensional flow in a single aquifer overlain by an 
       aquitard. The wells may partially penetrate the aquifer. The 
       aquifer and aquitard are laterally homogeneous. The aquifer can be 
       anisotropic in depth.  The vertical velocity component in the 
       aquifer is exactly calculated and follows from the governing 
       equation.

       In both cases, a laterally infinite system is assumed and storage in aquitards is neglected which implies that the vertical velocity is constant over the whole aquitard thickness.

3.   Input

     Well data (location and abstraction rate), natural flow data and hydrogeologic parameters pertaining to aquifers (transmissivity, hydraulic conductivity, storage coefficient, thickness and porosity) and aquitards (hydraulic resistance, thickness and porosity).

4.   Output

     - Plot of pathlines and travel times in horizontal 2-D (x/y);

     - Plot of pathlines and travel times in vertical 2-D (x/z or y/z);

     - Plot of travel time contours at a given depth level in the system.

5.   Operational requirements and restrictions

     The AQ-software packages run on Personal Computers under DOS, OS2 and WINDOWS95 operating systems. A pen plotter is required, unless other plot viewing systems are used. Two types of plotters are supported: HP7475A (or HP-compatible) and Calcomp MODEL84/81.

     AQ-AS consists of a number of computer programs communicating through data files. The programs are controlled interactively through screen menus in English, and feature a unit versatility and full error checking procedures.

     The model can be handled by persons familiar with general hydrogeological principles and groundwater modelling concepts. A basic knowledge of statistics is required.

     Easy installation following the manual. The model package takes a short time to acquire proficiency in handling. As the source code is not supplied, no FORTRAN compiler is needed.

6.   Form of presentation

     Run version of the computer program package on a number of diskettes. A comprehensive users' manual in English.

7.   Operational experience

     The model has been widely used in, primarily, The Netherlands since 1987, especially in the operationally orientated areas of groundwater investigations, e.g. by water supply companies and consulting engineers.

8.   Originator and technical support

     The program is developed at IWACO B.V., Consultants for Water and Environment, Rotterdam, The Netherlands. Technical support will be provided by IWACO B.V.

9.   Availability

     From the HOMS National Reference Centre for The Netherlands.

10.  Conditions on use

     A charge will be made for supplying the model. Updates of the new run versions will be forwarded to users automatically during a certain period of time.