Compute the answer of the given problem

Problem- a spill of hazardous chemical has occurred on a road parallel to a river. Two rows of wells were installed parallel to the road/river. The hydraulic head of all wells in row 1 is 200m and in row 2 is 150m. The contaminated water is flowing from the spill site toward the river. The wells of row 2 are planned to be used to pump the contaminated water away so that it does not reach the river. The pump rate must be at least as high as the rate of groundwater flow toward the river. The road is 2000m from the wells in row 2.

Part 1- How much time will pass after the spill until the contaminated water will reach the wells in row 2? The porosity is 30%

I want assistance to find the right solution of the above problem.