The underground storage of a gas station has leaked gasoline into the ground. Among the constituents of gasoline are benzene, with a Kd value of 1.8 L/kg for the soil in that location, and toluene, with a Kd of 3.3 L/kg. The soil has a solids density of 2.6 kg/L and a hydraulic conductivity of 2.9 × 10^-5 m/s and is 37% pores (by volume). The site is to be remediated by pumping out and treating groundwater from a well 15 m downgradient from the site of the spill, where the water table is 0.4 m lower than at the leaking tank. How long will it take for:

a. benzene
b. toluene to reach the well?

Tom is having a problem with his washing machine. he notices that the machine vibrates violently at a frequency of 1500 rpm due to an unknown rotating unbalance. the machine is mounted on 4 springs each having a stiffness of 10 kn/m. tom wishes to add an undamped vibration absorber attached by a spring under the machine the machine working frequency ranges between 800 rpm to 2000 rpm and its total mass while loaded is assumed to be 80 kg a) what should be the mass of the absorber added to the machine so that the natural frequency falls outside the working range? b) after a first trial of an absorber using a mass of 35 kg, the amplitude of the oscillation was found to be 10 cm. what is the value of the rotating unbalance? c) using me-3.5 kg.m, find the optimal absorber (by minimizing its mass). what would be the amplitude of the oscillation of the absorber?