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Successful application of GCW technology requires that its zone of influence (ZOI) be known and predicted prior to installation. For each GCW System, a unique, site-specific hydraulic zone of influence will be established.
Dr. Herrling (1992) and Dr. Stamm (1997) of the Institute of Hydraulics, University of Karlsruhe, Germany developed for IEGa program which rely on the input of accurate geologic and hydrogeologic data. Throughout the years, this program has been continually modified based on the results of literally hundreds of full-scale field installations, such that it oftenprovides the most accurate prediction of GCW flow dynamics. Â
The following estimations, assumptions and simplifications are often used for die purpose of modelling the hydraulic zone of influence for a site-specific GCW configuration:Â
Aquifer Parameters
The site-specific aquifer parameters clearly exert the greatest influence on GCW Operation and efficiency. The following are typical of those factors considered important in the proper selection and design of a GCW System:
- Organic and/or inorganic constituents of interest (COI) type and concentration;
- COI plume dimensions
- Vertical saturated thickness of the aquifer containing COI;
- Depth to groundwater;
- Seasonal fluctuation in depth;
- Groundwater flow direction;
- Remedial objectives;
- Average expected COI load;
- Aquifer type (confined, unconfined);
- Horizontal hydraulic conductivity (Kh);
- Vertical hydraulic conductivity (Kv);
- Hydraulic gradient;
- Groundwater flow velocity;
- Aquifer porosity;
- Geology (boring logs, presence of confining layers); and lower permeable zones;
- Inorganic elements (Ca, Mg, Fe, Mn);
Engineering and Design Parameters
The hydraulic influence of a GCW System also depends on a number of engineering and design parameters specific to a given application. Specifically,
- Internal groundwater pumping rate Q;
- Length of screen sections;
- Distance between screen sections;
- Well diameter;
MODELLING THEÂ ZONE OF INFLUENCE (ZOI) OF A GCW
Based on the information provided the following parameter of the ZOI of a Groundwater Circulation Well (GCW) will be calculated with the Herrling / Stamm Model:
- The upstream and downstream Stagnation points (S);
- The bottom width of capture zone (Bb);
- The top width of capture zone (Bt)
- The cross section of the capture zone (A)
- Ratio of upstream influx to well dischargeÂ
- The well distance D (maximum spacing between two GCW Systems);
- Circulation time (that required for a unit volume of water to move from the outflow zone of the well through the zone of influence of the GCW System, and back into the inflow zone of the well).
Modeling Results
Input parameters (see below) of Herrling`s modeling for the following site conditions are calculated below:
| Input parameters |
Data |
| Thickness of aquifer (m) |
7,00 |
| Well discharge through GCW; Q (m³/h); Estimated base on site hydrogeology |
4,00 |
| Effective Porosity, % |
0,20 |
| Screen length of GCW - m - |
2,00 |
| Horizontal hydraulic conductivity –Kh (m/sec) |
5,5E-5 |
| Vertical hydraulic conductivity Kv (m/sec), Assumed Kh/Kv = 10 |
5,5E-6 |
| Groundwater velocity – Va( m/d) |
0,08316 |
 
1)Â The upstream and downstream stagnation point (S) = 26m
2)Â The bottom width of capture zone (Bb) = 75m
3)Â The top width of capture zone (Bt) = 28m
4)Â The distance D (maximum space between GCW systems) = 57m
5) Circulation time (that required for a unit volume of water to move from the outflow zone of the well through the zone of influence of the GCW system, and back into the inflow zone of the well)
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