Agua Subterranea

Universidad de Guanajuato
Departamento de Ingeniería Química
Ciencia y Tecnología Ambiental
Octubre 2010

GROUNDWATER EXERCISES

(1) The hydraulic conductivity of an aquifer is 5 X 10-3cm/sec, the hydraulic gradient is 0.02, and the porosity is 0.2.
(a) What is the specific discharge, qa, in this aquifer?
(b) Calculate the maximum velocity at which dissolved salt could move throughthis aquifer.
(c) Assume the aquifer is 5 m thick. What is its transmissivity? What is the discharge per unit of distance perpendicular to the water flow (bqa)?.

(2) A well of 0.1 m radius isinstalled in the aquifer of question (1) above and is pumped at a rate averaging 80 l/min.
(a) Estimate drawdown in this well if the radius of influence is 100 ft.
(b) Estimate the hydraulic gradientin the aquifer at distances of 20 and 75 ft., both directly upstream and downstream of the well.

(3) In a sand having 1-mm median grain size and porosity of 0.25, how high must specific dischargebe to make the mechanical dispersion coefficient equal to the effective molecular diffusion coefficient?

(4) A domestic well is located 30 m upstream from a neighbor’s septic system. If domesticuse of water is 1000 l/day, what is the minimum regional flow (bqa) that will just suffice to keep septic effluent from entering the well (easiest to do analytically)?

(5) A municipal well pumping1200 m3/day is located 100 m from a major river. Aquifer transmissivity is 800 m3/day, aquifer thickness is 30 m, and the background hydraulic gradient (i.e., in the absence of the well) toward theriver is 0.002.
(a) Discuss the calculation of drawdown if the well is 2 m in diameter.
(b) A large spill releases carbon tetrachloride (CCI4) into the river upstream, resulting in the river waternow containing 50 ppm dissolved CCI4. What maximum concentration do you expect to see in the well if no corrective action is taken? What do you recommend the municipal well operator do to prevent...