The air has been contaminated by the smoke from the ______ f

SAT语法题
Some beaches are frequently contaminated by untreated sewage that flows into the ocean,which can last for several days.
请问代词是不是一定指代离自己最近的名词? 这里的which是不是指ocean?

英语翻译
The most effective approach for cleaning up contaminated surface water is to prevent further discharges from contaminated sources and enable natural biological,chemical,and physical processes to break down the existing contamination.In some surface water bodies where natural processes are not enough to break down the contaminants,other cleanup approaches such as mixing and aeration may be required to further promote natural cleanup.A significant source of surface water contamination may be contaminated sediments.Contaminated sediments generally contain persistent contaminants and are difficult to clean up.Three main approaches to cleaning up contaminated sediments are:1) remove them by dredging; 2) place a cover over them to prevent contact with the surface water; or 3) allow natural processes to cover them or break them down over time.For contamination that does not mix with surface water and floats on the surface,such as that encountered during an oil spill,contamination can be removed by skimming it from the surface using a "boom."

英语翻译
conversion of sulfur contaminated heavy oils to light crude by means of hydro cracking

可否说river was contaminated by the paper mill.
是by paper mill还是by dirty water?

英语翻译
urface water can become contaminated in many ways.Surface water can be contaminated when hazardous substances are discharged directly from an outfall pipe or channel or when they receive contaminated storm water runoff.Direct discharges can come from industrial sources or from certain older sewer systems that overflow during wet weather.Storm water runoff becomes contaminated when rain water comes into contact with contaminated soil and either dissolves the contamination or carries contaminated soil particles.Surface water can also be contaminated when contaminated groundwater reaches the surface through a spring,or when contaminants in the air are deposited on the surface waterSurface water can also be contaminated when contaminated groundwater reaches the surface through a spring,or when contaminants in the air are deposited on the surface water.Contaminated soil particles carried by storm water runoff or contaminants from the air can sink to the bottom of a surface water body,mix with the sediment,and remain.
第一个是Surface water，掉了一个S。