E4252 - Environmental Engineering
Software:
QUAL2K
Proposed effluent discharge into an urbanized river
The quality of water is an often discussed issue in environmental engineering. One of the points is to predict the impact of wastewater discharges in a river. The Housatonic River in western Connecticut receives wastewater effluent from a number of industrial and municipal point dischargers. Constituents in the wastewater can exert a considerable biochemical oxygen demand, leading to depleted dissolved oxygen concentrations in the river. Conversely, dissolved oxygen concentrations in the river can be replenished by the overlying atmosphere via natural reaeration processes. Typically, dissolved oxygen concentrations in the river are subject to regulatory criteria (i.e. minimum values), which must be collectively satisfied by all existing and proposed dischargers to the river.
In this exercise, the town of Gaylordsville, CT, proposes to build a new municipal wastewater treatment facility, and discharge the treated water into the Housatonic River. The main objective is to determine the design capacity of the treatment facility by predicting the amount of wastewater that can be discharged without exceeding applicable water quality criteria in the river. Existing point discharges located downstream in New Milford, CT, must be accounted for. To accomplish this, a water quality model for the Housatonic River has to be developped. A typical model testing, calibration and prediction approach follows.
Although the Housatonic River can be characterized as a one-dimensional riverine system, factors of heterogeneities prohibit the use of simple analytical models. Therefore, a numerical model must be employed, which separates the system into a series of homogeneous segments; a material balance is performed for each segment, incorporating inflows from the adjacent upstream segment and any point source discharges, and computing the outflow to the adjacent downstream segment. This modeling exercise should be completed using QUAL2K, a 1-D numerical water quality model distributed by EPA. Although this model allows more complexity, in this exercise, only the primary processes that affect dissolved oxygen in response to pointdischarges, BOD and atmospheric reaeration are considered.
The exercise is essentially a computer-based laboratory session, designed to be completed in a single class. All modeling software and inputs are fully developed and tested before the laboratory session. Detailed and illustrated instructions for running the relevant aspects of the model are provided, so students focus on the simulation exercise rather than the mechanics of running the model. The objective is to use the modeling platform as a tool to better understand groundwater flow concepts, not to provide training on how to expertly run the software.
This exercise is intended to reinforce the material that is covered in CIEE E4252 Environmental Engineering. Furthermore, the exercise demonstrates the ability of numerical methods to solve more complex and realistic problems than what can typically be done using analytical methods.
[EPA's QUAL2K model description]
