First I'll start with a history lesson. Let's say about 100 years ago Town X was growing to the point where dumping sewage from homes straight into the local ditch became a health hazard (some small communities and individual rural houses today still do this). To get rid of the health hazard they decided to install a pipe to carry the sewage from the homes to the nearest river. Someone came up with the great idea to also use it as a storm sewer to carry away stormwater to solve their drainage problems - why put in two separate pipes when one can do both jobs? This was great for a while until the Town population grew to the point where there was so much sewage going to the river it started showing negative impacts. So then it was finally decided to build a treatment plant to treat the sewage (this started occurring about the 1930's or 1940's). To get the sewage to the treatment plant, an "interceptor sewer" was installed parallel to the river and "intercepted" all the sewer pipes which dumped directly into the river. Generally a manhole was placed where the interceptor sewer crossed the older sewers, but the remaining segment of the old pipe going to the river was left as an "overflow" pipe - a dam was installed in the manhole to direct dry-weather flows (just sewage, no rainwater) to the treatment plant, but in higher flows when it rained the level in the sewer exceeded the height of the dam and some of the "diluted" combined flow (sewage combined with stormwater) was discharged to the river. The mentality at that time was that the diluted sewage was harmless to the river (dilution is the solution to pollution!). Wastewater treatment plants have a limited hydraulic capacity, and if too much flow is pushed through a plant it can wash out the good bugs which treat the sewage, leaving a facility which cannot provide adequate treatment and will take weeks or even months to recover - so it was better to overflow the high wet-weather flows back in the sewer system than to send it all to the plant. So that is how "combined sewer overflows" (CSO's) came about, and exist today in many communities. I think combined sewers were being installed as late as the 1960's. As growth occurred and it became apparent that combined sewers were no longer the answer, separate sanitary sewers were then installed (carrying only sanitary sewage). But since this growth occurs on the outer fringes of a community, the separate sanitary sewers still have to discharge to the older parts of the sewer system (which are still combined sewers) in order to flow to the treatment plant.
The best thing that happened to our waters was the Clean Water Act of 1970 (or was it 1971?). That law basically required a much higher degree of treatment be provided by treatment plants, thereby requiring communities with sewers and plants to expand and upgrade - inadequate treatment was the primary problem at this time. But to go along with this, the EPA started a grants program to help fund this nation-wide mandate - they provided 75% of the money with grants (Free Money!), and the state chipped in 10% - so the city/town only paid 15% of the cost. A LOT was accomplished under this program. But that program and money dried out by the late 1980's. Once the upgrade of the plants were done and that problem addressed, the focus then shifted in the early 1990's to combined sewer overflows being the next biggest problem for our nations waters. So things have been progressing (although very slowly) since then to address CSO's. But now there is no free money to go along with it, because it is not a nation-wide problem and only affects about 13 or so states (with Indiana having the most or second-most CSO communities) - therefore the federal government has no real incentive to come up with another grants program to help fund this work. So it is left to the states and individual communities - the state has been and is still developing rules/regulations that the cities/towns will have to meet. But the cities/towns are in no hurry to do anything because there is no free money available, which means they will have to pay for it themselves by raising sewer rates - and it will cost A LOT of money to correct.
CSO communities had to submit Long-Term CSO Control Plans to IDEM over the past few years - these plans basically include several projects to be done over 5-20 years (depending on the financial impact on the community) to get down to 4-6 overflows per year. An example of one community we work for, a city of about 6,000, it will take about $8,000,000 to do - and that is back in 2002 dollars (we submitted the Plan in April 2002 and it has still not been reviewed by IDEM - a shortage of manpower at IDEM is a major issue). This will raise their sewer rates from about $25/month to about $60/month - and herein lies the problem why communities have not done anything - the local politicians obviously don't want to raise sewer rates and be held accountable by the citizens, so they sit back and wait until they HAVE to do it (to meet new IDEM mandates or permit requirements, which are still being developed) so they have someone to blame it on and take the heat off themselves. They would rather have sewage flowing into the rivers than to raise sewer rates.
But the state/IDEM is not free of blame - they have been toying around with this whole CSO issue for over ten years, and still do not have things figured out. They are essentially trying to do the bare minimum they can do to get EPA's blessing but still minimize the financial blow to the Indiana communities. Things are progressing, but this problem didn't happen overnight and won't be resolved overnight.
Now that is pretty much what you usually hear as far as Combined Sewer Overflows. Cities and Towns which have sewer systems which are separate sanitary sewers (generally installed after the 1960's) can have Sanitary Sewer Overflows (SSO's). While CSO discharges are permitted, SSO's are not - communities with separate sanitary sewers are not allowed to have any overflows - but a lot do. Mainly due to leaky sewers and manholes (usually due to the old clay pipe which had poor joints) which allow in a lot of groundwater, and due to illegal street inlet connections and downspout and sump pump connections from homes, clear water gets into these systems and overloads the pipe which were not sized to handle the higher flows - the result is sewage overflowing out manhole lids. This problem is just as widespread as the CSO problem, but a lot of these SSO's go unreported and IDEM is not aware of them. We had a client that had 100 SSO's in 2000 - that's like 1 in every 4 days they had an overflow. With a new larger interceptor sewer to get the flows to the plant and new treatment plant to handle and treat the higher flows, at a cost of $7,500,000, they have had zero overflows since November 2003 - so it can be fixed, it just takes time and money - it raised their sewer rates from $35/month to $60/month. But here again we have had a lot of clients with Town Council members who know they have overflows, but won't fix them because they don't want to spend the money- period.
Its pretty frustrating for me personally - as a fisherman I want clean water, but I have to work for some communities who know they have sewage going into rivers but won't do anything about it because it will cost a lot of money and they don't want to upset the ratepayers, which apparently is more important to them than clean water.
While sewage discharged into our waters is nothing to smile about, I personally think sedimentation of our waters is a more important issue with regards to sustaining or improving gamefish populations, but that's a whole nother topic and I have to get back to work!