The Consent Order resolving Oneida County's sewage dispute with the State has been posted at the Oneida County website. It reveals some interesting details on how the situation leading to the State's action unfolded, and what the solution will involve. Some of the words may be confusing. I will try to sort out the Consent Order's terminology over a few posts and provide a bit of background to make its meaning more clear. "Plumbing" is today's subject.
CSOs, SSOs, POTWs, and Inflow and Infiltration . . .
People living in isolated areas usually get their water from wells and dispose of their waste through septic fields. This works as long as enough space is maintained to keep the waste from contaminating the well.
As settlements become more densely populated, interference between one person's septic field and another's water well can become a health problem. Urbanization also causes runoff from roofs and paving, which can cause flooding. The solution for both problems is for residents to pool their resources and build facilities to take the storm and waste water away.
When our older urban areas were constructed (e.g. Utica and nearby villages), the practice was for storm water, industrial and and sanitary waste to be combined and collected by the same system (i.e., a Combined Sewer) and discharged to the nearest stream. This was "state of the art" and made sense at that time. It was believed that "The Solution to Pollution is Dilution" -- that is, if wastewater was combined with enough clean water, pollutants would become too diluted to cause harm. This worked when the amount of waste was small in comparison with the flow in the receiving stream. Of course, as communities grew, the waste component grew as well, sufficient dilution did not take place, and epidemics resulted.
Communities later developed Publicly Owned Treatment Works (POTWs) to take the combined flows and treat them to make them harmless before releasing them to streams. However, because storm water was included, collection systems and POTWs had to be designed to accommodate variable amounts of water. Since communities could not afford to build systems large enough to collect and treat every drop of the largest flows (which occurred only during storms or snow melt), overflows of untreated waste mixed with storm water (Combined Sewer Overflows or CSOs) were allowed. Had these overflows not been allowed, the flows would back up into people's basements and elsewhere. The impact of the waste water, however, would be reduced by dilution since the overflows would usually happen only during periods of heavy rain or snow melt.
As time went on and people became more knowledgeable about how to handle waste, it seemed more cost effective to separate the waste water from the storm water and just treat the waste water. Newer developments are now required to build separate Sanitary Sewers, which send waste water directly to the POTW, and Storm Water Sewers, which usually discharge directly to streams without treatment. Long existing communities such as Greater Utica have both combined and separate systems in place.
In theory, Sanitary Sewers should be sized to never overflow, however overflow points to streams (Sanitary Sewer Overflows or SSOs) sometimes develop in those situations when the sewer's capacity is exceeded, e.g. when sewage backs up into people's homes. SSOs are unintentional. Overflows of sanitary sewers can occur when storm water somehow finds its way into the Sanitary Sewer -- for example, when people hook downspouts or floor drains into the sewer (inflow), or as the sewer pipes age and crack, allowing seepage to go in (infiltration). SSOs can also occur when something gets into the system that blocks the flow.
Treatment at the POTW - Primary, Secondary, Tertiary...
Primary, secondary, and tertiary treatments represent a progression in technology, going from the simple to the complex.
Primary treatment is essentially mechanical, removing pollutants that can be easily separated from the waste stream. The waste stream can be passed through screens to remove larger objects. It can then be directed into tanks where the flow is stilled. In the tanks, dense materials will settle to the bottom, and light materials will float to the top, allowing the materials to be separated from the liquid.
Secondary treatment involves biological processes and filtration. Bacteria can be used to break down pollutants such as fats and grease in the waste stream. Liquid pollutants can be used to grow biomass, which then can be removed from the waste stream by filters.
Tertiary treatment is the last before the waste water is discharged into the receiving body of water. The emphasis here is disinfection (e.g., by chlorination, ultraviolet light, or ozone). It can also involve more complex biological processes and filtering.
For a more detailed explanation of sewage treatment, see Wikipedia.
That's the plumbing.
A Consent Order Primer, Part 2 will address how laws are used to protect streams.
[Note: Articles in this series may be revised from time to time to provide additional detail and explanation as time allows, and as current events warrant.]