Steady-state design of vertical wells for liquids addition at bioreactor landfills

The rate at which liquids can be added to a vertical well, the lateral zone of impact of the well, and the liquids volume needed to wet the waste within the zone of impact of the well are the key inputs needed to design a vertical well system. This paper presents design charts that can be used to estimate these inputs as a function of municipal solid waste properties (porosity, hydraulic conductivity, and anisotropy ratio), well dimensions (radius and screen length), and injection pressure. SEEP/W modeling was conducted to estimate the key design inputs for a range of conditions practically encountered for a vertical well installed in landfilled waste. The flow rate, lateral zone of impact of a well, liquids volume added, and injection pressure were normalized with the waste properties and well dimensions to formulate dimensionless variables. A series of design charts were created to present dimensionless steady-state flow rate, lateral zone of impact, and the dimensionless liquid volume needed to reach a steady-state condition, as a function of dimensionless input variables. By using dimensionless variables formulated for this work, these charts permit the user to estimate the steady-state design variables described above for a wide range of configurations and conditions beyond those simulated without the need for further modeling. The results of the study suggest that the lateral extent of the well can be estimated using Darcy’s equation and assuming saturated unit-gradient vertical flow regime below the well bottom. An example problem is presented to illustrate the use of the design charts. The scenario described in the example problem was also modeled with SEEP/W, and the results were compared with those obtained from the design charts to demonstrate the validity of design charts for scenarios other than those used for the development of the design charts. The methodology presented in this paper should be thought of as a means to provide a set of bounds that an engineer can use along with their judgment in the design of a system for a specific site.