Correlated environmental impacts of wastewater management in a spatial context

• We model residential development in suburbia and exurbia in a monocentric then polycentric context.
• Suburbia and exurbia differ with respect to residential lot size and type of wastewater management infrastructure.
• We assess how wastewater management costs impact city width and residential pollution loads.
• In certain cases, regulating water quality through wastewater management costs induces increased land consumption.
• In the polycentric case, a unilateral modification of costs affects the entire metropolis.

In this paper we analyze how wastewater management affects water quality and urban spread, through agents' residential location choice between sewer-serviced suburbia, and septic dependent exurbia. We adopt an urban economics model of monocentric city, then a polycentric city, with two different residential areas: suburbia, where there is access to a sewer system and the residential lot size is small, and exurbia, where there is no access to sewerage and the residential lot size is larger to accommodate the sanitary arrangements to meet the regulation on individual septic systems. According to the abatement efficiency gap between wastewater treatment technologies, improving water quality may be achieved at the expense of higher or lower urban spread. We also conduct an analysis of a polycentric city to highlight how asymmetric decision making between primary and secondary cities may have beneficial consequences at the local level, but be detrimental to aggregate environmental performance of the polycentric city. Our conclusions illustrate the unexpected impacts, positive and negative, that managing an environmental issue can have on another issue on the same scale or the same issue on a larger scale.