HR: 1340h
AN: H23G-1731    [Abstracts]
TI: An Enhanced Method Using MODFLOW to simulate Groundwater Extraction/Injection through Wells Penetrating Multiple Aquifers
AU: * Teasdale, E
EM: eddy_teasdale@urscorp.com
AF: Eddy Teasdale, 1550 Humboldt Road, Suite 2, Chico, CA 95928, United States
AU: Zhang, J
EM: Jim_Zhang@urscorp.com
AF: Jim Zhang, 1333 Broadway, Suite 800, Oakland, CA 94612, United States
AU: Parrish, K
EM: kent_parrish@urscorp.com
AF: Kent Parrish, 2870 Gateway Oaks Drive, Suite 150, Sacramento, CA 95833, United States
AB: In a MODFLOW simulation of groundwater extraction and/or injection through a well penetrating multiple aquifers, the conventional method is to represent this type of well with a group of single-layer wells, each open to one of the model layers penetrated by the multi-layer wells Each of the single-layer wells have an individual rate specified for each stress period. Using this method, the total extraction and/or injection rate must be allocated among the individual layers. A common method of doing this is to divide the extraction and/or injection rates in proportion to the layer transmissivities. This partitioning has to be implemented by the user externally to MODFLOW for each multi-layer well and for each stress period in the MODFLOW well package. This approach fails to take into account the interconnection between various layers penetrated by the well, and is thus an incomplete solution to the problem. In both theory and practice, the extraction and/or injection rates through those well-penetrated aquifers also depend on the storativity and hydraulic head. Using transmissivity alone to partition the extraction and/or injection rates is only appropriate if both storativity and hydraulic head are very close for all well-penetrated aquifers. In cases where the top well-penetrated aquifer is unconfined, this method does not work because the storativity in an unconfined aquifer is often much higher than that of a confined aquifer. In addition, for transient flow simulations, the transmissivity of an unconfined aquifer changes with time due to the groundwater table variations resulting from extraction and/or injection (induced by constant or time-variable extraction/injection rates) or other time-variable boundary conditions such as seasonal groundwater recharge. This paper presents an enhanced method to resolve the above problem. With the new method, only the total extraction and/or injection rate of the well needs to be specified, and MODFLOW automatically allocates the extraction and/or injection rates for each well-penetrated layer during the simulation, based on the transimissivity, storativity, and hydraulic heads of each well-penetrated model layer. In addition, the interconnection between all well-penetrated layers is implemented. Test runs of example cases provide the comparison of flow and transport simulation results between using the conventional and the enhanced method, and simulation errors resulted from conventional methods are discussed.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting