Flow Nets

$131$

PROBLEM $17$

FLOW NETS IN HETEROGENEOUS AQUIFERS REFRACTION OF STREAMLINES, FLOW VELOCITY

Estimate the path of groundwater contamination that would develop from the spill site shown in Figure $17\mathrm{.}1$ if no remedial action was taken. Three monitoring wells, MW$1,$ MW$2$ and MW$3,$ were drilled around the spill to determine the immediate direction of groundwater flow. Water table elevations recorded in the unconfined silty sand aquifer were $467\mathrm{.}98,467\mathrm{.}82,$ and $467\mathrm{.}53$ meters above sea level respectively. The hydraulic conductivity of the porous medium was estimated to be $4\mathrm{.}3{10}^{-6}\frac{m}{s}$ based on laboratory analyses of core samples. Two short pumping tests were performed in the nearby domestic wells DW$1$ and DW$2$ and yielded hydraulic conductivity of $1\mathrm{.}45{10}^{-5}\frac{m}{s}$ and $6\mathrm{.}11{10}^{-6}\frac{m}{s}$ respectively. The water table elevations recorded in DW$1$ and DW$2$ before the test were $467\mathrm{.}32$ and $467\mathrm{.}23$ meters. The hydraulic conductivity of the main sandy gravel aquifer in the area, that has been alternately and discontinuously pumped by two municipal wells, is $2\mathrm{.}81{10}^{-5}\frac{m}{s}.$ The water table recorded in W$1$ during a long pumping break was $466\mathrm{.}91$ meters.

If it is shown that the main aquifer is threatened by the spill, estimate the time needed for the pollution to reach the aquifer assuming that there is no reaction between the pollutant and the porous media$/$groundwater$.$