Exercise 1
You are thinking about purchasing a home in a rural area that has water supplied from a well that is screened over an interval 5 to 7 m below the water table. Upgradient from the property, there is a roadside motel/restaurant complex that is serviced by a septic system. You are concerned about potential for contamination of the well, so you have accessed the building permit records, and determined that the septic system drainfield is 30 m x 30 m in area with the downgradient edge located 300 m from the well. The drainfield is designed for wastewater loading of 1 cm/day (365 cm/yr). The site is underlain by a regional unconfined sand aquifer that has an average linear groundwater velocity of 100 m/yr. Precipitation, in this area, averages 90 cm/yr. Water balance calculations for a local river basin have established that evapotranspiration averages 60 cm/yr. Assuming that the aquifer has a saturated porosity of 0.3, and has sufficiently high transmissivity that pumping from the well does not materially alter flow paths, should I be concerned about the potential for contamination from the upgradient motel/ restaurant septic system?