In $1990,$ gasoline contamination is discovered during a routine site assessment at an urban siteIn $1990,$ gasoline contamination is discovered during a routine site assessment at an urban site

shown in the figure that follows. It is not known how long before $1990$ this contaminant reached

the site, assuming that it originated off$-$site. Based on the following data, make a justified

recommendation as to which gas station or stations are the likely culprits $($include all

assumptions$)$: Station A was established in $1978$; Station B in $1985$; station C$,$ in $1980.$ At the

site, hydraulic conductivity is $100f\frac{t}{d},$ porosity is $0\mathrm{.}3,$ gradient is $0\mathrm{.}00225,$ and transverse

dispersivity is $8ft.$

Hint:

$($i$)$ Consider advection and dispersion in a vertically well$-$mixed aquifer.

$($ii$)$ Transverse dispersivity is horizontal dispersivity in the direction perpendicular to

groundwater flow.

$($iii$)$ There is no water supply or other pumping well at the site.

$($iv$)$ You may neglect longitudinal dispersion $({}_L=0)$ or dispersion in the direction of

groundwater flow.

shown in the figure that follows. It is not known how long before $1990$ this contaminant reached

the site, assuming that it originated off$-$site. Based on the following data, make a justified

recommendation as to which gas station or stations are the likely culprits $($include all

assumptions$)$: Station A was established in $1978$; Station B in $1985$; station C$,$ in $1980.$ At the

site, hydraulic conductivity is $100f\frac{t}{d},$ porosity is $0\mathrm{.}3,$ gradient is $0\mathrm{.}00225,$ and transverse

dispersivity is $8ft.$

Hint:

$($i$)$ Consider advection and dispersion in a vertically well$-$mixed aquifer.

$($ii$)$ Transverse dispersivity is horizontal dispersivity in the direction perpendicular to

groundwater flow.

$($iii$)$ There is no water supply or other pumping well at the site.

$($iv$)$ You may neglect longitudinal dispersion $({}_L=0)$ or dispersion in the direction of

groundwater flow.