All the comments are good. I ...

All the comments are good. I will venture that you will have some data needed which would be extremely difficult to collect. I live right in the center of a whole lake ecosystem with many wetlands and a rural town, two to sixty meters elevated above the wetlands and not on the same plane where rivers would flow. There are small streams which turn into torrents when big rains come but many times these are dry or has very limited travel. since there is no direct line of affluent/sewer matter flowing into the wetlands, we are unable to determine a case. The rural areas all have pit sewers and obviously affect the ground water. The point where your info starts getting diluted is the following. If you talk of a wetland as a reed base which filters the water, these are effective to clear polluted waste like liquid sewage. If your wetland consists of a peat layer which is between 500mm and 2000mm thick you have no idea how to formulate the content which moves in and out of that basin. If the town was elevated directly above and in line with the river system, the outcome would look very different. My local town has its own sewer works but it handles only the local hospital sewage. To determine exactly how much of the overflow in the pit system walks into the repository of clean water in undetected. Now, I have just indicated some aspects which would influence your data on an extreme level. At best you will come out with a guess and even that could be off target. I hope you get better advice than mine but keep it going folks, it is interesting to see the correlation in different aspects of the projects.