Examples of these connections include sump pumps , drains, downspouts and streams. Often the entry points are improperly connected to a sanitary fixture such as a bathtub drain.
Joining a pipe or sump pump to an existing fixture may be illegal in some municipalities. Improperly or illegally connected lines can add as much as 7, gallons of water per day to a sewage system. With infiltration, groundwater enters the sewage system through cracks or leaks in the lines. Cracks in the system allow the entrance of groundwater whenever the soil becomes saturated, or the water table lies above the sanitary waste system. Infiltration occurs through age-related deterioration, poor design, improper installation or maintenance errors.
Damage to lines from external factors also allows for penetration into the system. Sewage line design allows for 20 to 50 years of use. If not regularly inspected or maintained, cracks can form undetected. The clear water distinction is merely a way of stating it does not have sewage in it.
The purpose of sanitary systems is to transport wastewater from showers, toilets, sinks and dishwashers. Water from these lines must be specially treated at wastewater facilities.
Groundwater should flow through stormwater lines. These lines do not necessarily require the same wastewater treatment before discharging their contents into the environment. When inflow and infiltration occur in the sewage system, the lines become overwhelmed by the additional clear water. It fills the sewer. Once at capacity, the sewer overflows — flooding basements, streets and sidewalks.
Communities downstream from the overflowing sewer system are often most affected. Due to their location, they must accommodate not only the flow from their sewage system but also the overflow from all communities upstream. Overflowing sewage systems are a public health risk, as not only does clear water, but also waste containing bacterial pathogens back up onto the street. The wastewater can also back up into creeks, rivers, lakes and streams, contaminating water supplies and endangering wildlife.
In addition to the potential health risks associated with infiltration, the additional water within the lines makes it more difficult for wastewater treatment plants to properly treat the volume that comes through the plant. As a result, poorly or untreated waste is ejected into the environment. Overflow due to infiltration and inflow is costly. Cities must pay to correct the problems. There are also costs associated with cleanup and potential lawsuits from affected homeowners.
There may also be fines related to damage caused by overflow if the issue is not corrected. Unfortunately, if cities do not regularly maintain and inspect their sewer systems, the signs of inflow and infiltration may not be evident until an overflow event occurs. Such an example would be the backup of pipes, flooding commercial and residential basements. Water flooding streets from manholes is another indicator.
Wastewater treatment plants may see an uptick in the amount of water passing through the system after a rain or snow event. Continually running or starting and stopping in a sump pump during one of these events or immediately following rain or snowmelt is another indicator. There are techniques cities can use to identify inflow and infiltration before it becomes a problem.
Periodic manhole inspections help to identify joint leaks or cracks from root infiltration. Cities should pay particularly close attention to manholes in lower-lying areas, such as ditches or wetlands, as these tend to get submerged in rain events. In residential areas, cities may use a technique known as smoke detection to locate cracks. During this test, cities pump a nontoxic smoke into the line, pressurizing it. The pressurized smoke follows the path of the pipes and highlights leaks in the sewage system.
Along with smoke testing, some areas use dye testing, often as a way to confirm smoke testing. Heavy rainfall - if there is heavy rainfall there is less chance of it being soaked up by the soil infiltration so it runs off into the river. The faster the water reaches the river, the more likely it will flood. Relief - a steep valley is more likely to flood than a flatter valley because the rainfall will run off into the river more quickly. Geology - permeable rocks allow water to pass through pores and cracks, whereas impermeable rocks do not.
If a valley is made up of impermeable rocks, there is a higher chance of flooding as there is an increase in surface run-off. Infiltration is affected by crop and land management practices that affect surface crusting, compaction, and soil organic matter.
Without the protective benefits of vegetative or residue cover, bare soil is subjected to the direct impact and erosive forces of raindrops that dislodge soil particles. Dislodged soil particles fill in and block surface pores, contributing to the development of surface crusts that restrict water movement into the soil. Soil organic matter affects infiltration through its positive affect on the development of stable soil aggregates, or crumbs. Highly aggregated soil has increased pore space and infiltration.
Soils high in organic matter also provide good habitat for soil biota, such as earthworms, that through their burrowing activities, increase pore space and create continuous pores linking surface to subsurface soil layers. When no more water will drain from the large soil pores, which occurs within one or two days after rainfall , the moisture level is described as being at field capacity.
Much of the moisture held in the soil at this level is available for uptake by growing plants. Soil moisture is considered low when it is present only in very small pores. Because water in small pores is held tightly, the energy available to roots for removing water is not sufficient to extract it at the rate that it is being transpired.
When this condition exists, the plant leaves wilt or curl, and this soil moisture level is called the wilting point.
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