A storm drain receives runoff from a street 500 m long and 12 m wide and an adjacent pedestrian walkway that has a total are of 0.5 ha in size. Estimate the lead (Pb) concentration in the runoff. The design conditions are: (i) design storm intensity = 24.3 mm/hr, (ii) design storm duration = 30 min and (iii) design antecedent dry period = 3 days. Explain your calculations and state all assumptions made. (15 marks) 2. An assessment of P loading due to storm runoff is required for a small rural area. The land area for agriculture and residential use is estimated to be 40 ha and 20 ha, respectively. The design storm conditions are: (i) average dry period in between storm events = 2 days, (ii) design rainfall depth = 12.7mm, (iii) design rainfall duration = 60 min. (a.) estimate the initial P load (g) for the design dry period. (b.) the average P concentration in the runoff under design storm conditions. (c.) the mass of P (mg) washed off from the agriculture area after the first 10 minutes of runoff. [Hint: assume that the amount washed off from the agricultural area follows a first order reaction] Po – Pt = Po (1 – e-kRt) Explain your calculations and state all assumptions made. (15 marks) 3. A portion of the runoff volume time series, provided at 10 min intervals, for a storm event is shown in Table 1. The catchment area is 190 ha, the initial mass of solids on the surface is 20,000 kg and the surface is impervious. Assuming that the entire mass of solids is available for washoff, determine: (a.) The total solids, P (kg) remaining at each time interval. (b.) The total solids concentration C (mg/L) in the runoff, at each time interval. (c.) Plot Vol, rainfall intensity and C on the same plot for the time interval 0 – 100 min.