6. A mining process discharges a silty water into a clean brook at the rate of 5 cubic meters per minute. The silt content is 200 200 mg/L. What is the concentration in the brook during the rainy season (the brook flows at 50 cubic meters/min), and during a severe dry spell (the brook flows at 5 cubic meter/min)?

4) a) A wet sol in a barrel has mass of 100 kg. The barrel mass is 10 kg. Lab tests showed the water content of the soil is 5%. What is the dry mass of the soil? b) How many liters of water will be required to be added to increase the water content to 79% for optimum compaction? c) If the liquid imit is 60 and the plastic limit is 20; what will be the liquidity index if the moisture content is increased to 40%?

A lake has an inflow and outflow of 20x10^6 m^3/yr, a mean depth of 10 m and a surface area of 10x10^6 m^2. Waste is discharge to the surface layer at a rate of 10^5 gm/day. The upper 3 m of the lake form a well-mixed epilimnion while the remainder is mixed more slowly at a vertical dispersion rate of 1 m^2/day. What is the well-mixed concentration in the epilimnion and predict the concentration at the bottom of the lake as a function of time. How long can you use this model?

The base of a river in in contact with the top of an aquifer. A truck carrying bags of powdered cyanide is on a bridge crossing the river when a large bump causes one of the bags to fall into the river. The water in the river suddenly becomes polluted by the cyanide with a concentrations of 6.78 mg/L. The aquifer has an average linear ground water velocity of 0.256 m/day. Laboratory analyses data indicates that longitudinal dispersivity can be found through the equation: a = 0.86(log Ls)² where Ls is the length of the straight line path between two points along the path of transport. Find the longitudinal dispersion 108 m downstream from the bridge. Assume that the cyanide solute has a diffusion coefficient of 3.6 x 10 -5 m²/s and the aquifer has a coefficient related to tortuosity (o) equal to 0.8. Find the coefficient of hydrodynamic dispersion.