Point source pollution can be defined as pollution that enters a stream or river at a defined location. Several examples of point source pollution are defined in the following sections.
Combined Sewer Overflows
The combined sewer system was common prior to the mid-1950s and was a typical method used by many cities for removing unwanted surface water and wastewater. Combined sewers receive both storm and sanitary flow. Periodically combined sewers cannot handle the volume of water created from storm water runoff. When the combined sewers are overloaded, backups into basements and other low points can occur. To avoid this potential problem, overflows were designed into the combined sewer system to discharge excess flow. Prior to the 1950’s, little thought was given to the pollution problems associated with this type of system. Dilution was the solution to pollution. Typical CSO’s in Louisville consist of six parts storm water to one part sewage.
By the 1950’s, many cities were building wastewater treatment plants and separate sanitary sewer lines. Separating storm water from sanitary waste reduced the amount of water that had to be treated at the treatment plant and allowed storm water to go directly to the creeks and rivers. Rather than constructing completely new sanitary sewer lines, a series of larger pipes, "interceptors", were built. These lines "intercepted" most of the sanitary flow from the combined system, allowing the combined system to carry mostly storm water to the creeks. However, during heavy rains, the storm water mixes with the sanitary sewage, increasing the flow to the wastewater treatment plants. When the capacity of the interceptors has been exceeded, the excess storm water/sanitary mixture flows through the combined system and discharges into the creek or the Ohio River. This discharge event is called a Combined Sewer Overflow (CSO). CSOs were designed to relieve the overloaded combined sewers without flooding basements or damaging treatment plants.
MSD engineers and consultants have identified CSOs, and are currently evaluating ways to eliminate and/or reduce the impacts of the CSOs on streams. The Combined Sewer Overflow Plan (CSOP) identifies the method by which each CSO is to be addressed, both short-term and long-term. It will take decades to implement long-term control plans for Louisville’s CSOs. Since 1994, three CSOs have been eliminated. Several more are scheduled for elimination over the next few years. Many more are currently being modified to reduce further impacts.
Sanitary Sewer Overflows
The sanitary-only sewers are generally not as old or as large as the combined sewers. Sanitary sewers were never designed to carry storm water, and should only carry wastewater from homes, businesses and industries. Sanitary sewers transport flow directly to the wastewater treatment plant, where it is processed, and discharged to a river or creek.
As with the combined sewers, the sanitary sewers can become overloaded. Generally there are three common causes of overloaded sanitary sewers:
- the entry of ground water or surface water through broken pipes or old sewer joints;
- improper or illicit storm water connections. Examples are basement sump pumps, roof gutter drains, or surface water catch basins that have been connected to sanitary sewers rather than storm sewers; and
- too many sewer connections that exceed the capacity of a particular sewer, usually due to poor or unplanned development.
When sanitary sewers become overloaded, the excess volume is released at weak points in the system. Often these weak points are at manholes. These overflow events are called Sanitary Sewer Overflows (SSOs). SSOs can also occur at pump stations and treatment plants.
MSD has established a Sanitary Sewer Overflow Abatement and Elimination Plan (SSOAEP). This plan addresses the elimination of these discharges based upon their severity and frequency. Since 1994, one recurring wet weather SSO has been eliminated. There are currently 32 recurring wet weather SSOs within MSD’s jurisdiction. Two more will be eliminated by year 2000. Fourteen additional SSOs will be rehabilitated to reduce impacts from the frequency and/or volume of overflow by the end of 1999.
Another source of pollution in our streams is from package treatment plants. These are small wastewater treatment facilities, normally constructed and operated by owners other than MSD, with the purpose of providing service to suburban developments. These sewage treatment plants have proven to be mostly obsolete and unreliable. All too often, the privately owned package treatment plants operate beyond capacity, are operated poorly, and spill raw sewage directly into streams. MSD has taken an active role in purchasing and eliminating these sources of pollution. Package treatment plants acquired by MSD are typically operated at a higher standard than when operated by others, and stream pollution from these plants is reduced. These plants are taken offline and the sewage rerouted to larger, more effective treatment plants as soon as sewers can be constructed. Since the early 1970s, 175 of these treatment plants have been shut down.
Illegal dumping of chemicals, household products, garbage, septic waste, commercial waste, industrial waste, and yard waste can create impacts in streams. Illegally dumped or discharged waste can frequently produce impacts to plants and animals. Organic waste and yard waste can also stimulate bacteria and algae, causing rapid growth in populations, and resulting in reduced oxygen levels in the water. Dumped materials may draw undesirable animals, create foul odors, and present physical dangers to wildlife and people.
Illegal dumping of material can also restrict the stream and force water to back-up behind debris. This can cause the water to overflow the stream banks and flood upstream areas.
Hundreds of chemical spills occur annually in the Louisville metropolitan area. However, with 24-hour response and required spill control plans, environmental impacts are greatly reduced.
Non-Point Source Pollution
Non-point source pollution occurs when rainfall runs over land or through the ground, picks up pollutants and deposits them in streams, rivers and lakes. Per the Environmental Protection Agency (EPA), non-point source pollution remains the Nation’s largest source of water quality problems. It is now the primary reason most rivers, streams and lakes do not meet "fishable/swimmable" criteria. Non-point source pollution is widespread because it can occur any time there are activities which disturb the land or water. Agriculture, forestry, grazing, physical changes to stream channels, construction, and habitat degradation are potential sources of non-point source pollution. Agriculture is the leading contributor of water quality impairments in rivers, lakes, and non-urban streams in Kentucky. Urban runoff from streets, parking lots and roofs, is often the largest source of pollution for streams and other urban water bodies. Several examples of non-point source pollution are defined in the following sections.
Storm Water Runoff
As Jefferson County developed, much of the land that was once covered with vegetation was paved to form roads/streets, parking lots, neighborhoods and shopping centers. When rain falls on these impervious surfaces the water does not soak into the ground. Instead, the water that hits paved surfaces, runs off these surfaces and into drainage ditches and storm sewers (that may act as a point source), eventually entering streams. This storm water has two major impacts on the streams - delivery of pollutants and increased or decreased flow, which causes sediment transport and scouring.
Nutrients necessary for plant growth like nitrogen and phosphorous can cause serious problems in streams when their concentrations get too high. When property owners over-fertilize their lawns or use garden chemicals incorrectly, the excess chemicals are washed into the stream during a rainfall. Excessive nitrogen in streams will encourage rampant growth of algae. When these large "blooms" of algae die, or get so large and thick that the bottom layers die, bacterial decomposition starts and this process uses the oxygen available in the water. Oxygen levels may dip dangerously low, "suffocating" fish and other aquatic organisms. Excessive nutrients also encourage undesirable algae species to grow in streams. Unfortunately, these species make poor quality food for the insects, fish, and other organisms. These undesirable species outcompete those species that are better quality food sources. This results in fewer viable sources of food for the fish and insects.
Property owners should seek alternatives to lawn chemicals or at the least, use fertilizers sparingly and apply them at the appropriate time of the year.
Septic Tank Systems
In a septic tank system, wastewater is routed to a large underground tank where the waste decomposes and settles to the bottom. The water at the top then goes to a series of pipes with holes that allow the water to soak into the ground. The system can work relatively well if the tank is cleaned regularly and if the soil characteristics are such that the ground will absorb the water slowly.
In many areas of Jefferson County the soil is primarily clay and poorly drained, and the water table high. During periods of rain, the ground becomes saturated and the ground water table rises above the level of the septic tank system. Raw sewage stands in yards and drainage ditches and eventually makes its way to the streams.
Septic tanks were originally designed and used as temporary sanitary sewer treatment systems. The intent was to replace these temporary systems with sanitary sewers when they became available. Development in Jefferson County has exceeded MSD’s ability to keep up with the demand for sanitary sewers. The result is many areas of the county must rely on temporary septic tanks until the time sewers are constructed.