Assume a factory releases a continuous flow of wastewater into a local stream, resulting in an in-stream carcinogen concentration of 0.72 mg/L just below the outfall. Suppose this carcinogen has an oral potency factor of 0.45 (mg/kg-day)-1 and that it is degradable with a reaction rate coefficient k of 0.23/day. To keep the problem simple, assume that the stream is uniform in cross section, flowing at the rate of 2 mph, and that there is no other sources or sinks for this carcinogen. At a distance of 150 miles downstream, a town uses this stream as is only source of water. Estimate the individual residential lifetime cancer risk caused by drinking this water.

Ashielded metal arc-welding operation is accomplished in a work cell by a fitter and a welder. the fitter takes 5.5 min to load components into the welding fixture at the beginning of the work cycle, and 1.5 min to unload the completed weldment at the end of the cycle. the total ength of the weld seams 1200 mm, and the travel speed used by the welder averages 300 mm/min. every 600 mm of seam length, the welding stick must be changed, which takes 0.8 min. while the fitter is working, the welder is idle (resting): and while the welder is working the fitter is idle. (a) determine the average arc-on time as a fraction of the work cycle time. (b) how much improvement in arc-on time would result if the welder used flux-cored arc welding (manually operated), given that the spool of weld wire must be changed every 10 weldments, and it takes the welder 5.0 min to accomplish the change? (c) what are the production rates for these two cases (weldments completed per hour)? attach your work and solutions.