increase in wastewater flowrates. Possible sources are roof leaders. vard and areaway drains, access port covers. cross connections from storm drains and catch basins. and combined systems Total inflow. The sum of the direct inflow at any point in the system plus any flow discharged from the system upstream through overflows, pumping station bypasses, and the like Delayed inflow. Stormwater that may require several days or more to drain through the collection system Delayed inflow can include the discharge of sump pumps from cellar drainage as well as the slowed entry of surface water through access ports(manholes) in ponded areas The initial impetus in the United States for defining and identifying infiltration/inflow was the Federal Water Pollution Control Act Amendments of 1972. By correcting infiltration/inflow problems and fits to the commu and overflows in the collection system. (2) increasing the efficiency of operation of wastewater-treatmen facilities, and(3) improving the utilization of collection system hydraulic capacity for wastewater Infiltration into Collection Systems. One portion of the rainfall in a given area runs quickly into the stormwater systems or other drainage channels, another portion evaporates or is absorbed by vegetation; and the remainder percolates into the ground, becoming groundwater. The proportion of the rainfall that percolates into the ground depends on the character of the surface and soil formation and on the rate and r frost, decreases the opportunity for precipitation to become groundwater and increases the surface runoff correspondingly. The amount of ground water flowing from a given area may vary from a negligible amount for a highly impervious district or a district with a dense subsoil to 25 or 30 percent of the rainfall for a semi-pervious district with a sandy subsoil permitting rapid passage of water. The percolation of water through the ground from rivers or other bodies of water sometimes has considerable effect on the groundwater table, which rises and falls continually The presence of high groundwater resul ts in leakage into the collection systems and in an increase in the quantity of wastewater and the expense of disposing of it. The amount of flow that can enter a collection system from groundwater, or infiltration, may range from 0.01 to 1.0 m/d. mm-km or more. Infiltration may also be estimated based on the area served by the collection sy stem and may range from 0. 2 to 28 m /ha.d. The variation in the amount of infiltration encompasses a wide range because the lot sizes may vary in area, which in turn affects the length and extent of the collection system network. During heavy ains, when there may be leakage through access port covers or inflow as well as infiltration, the rate may exceed500m3/ha·d Infiltration/inflow is a variable part of the wastewater, depending on the quality of the material and workmanship in constructing the collection systems and building connections, the character of the maintenance,and the elevation of the groundwater compared with that of the collection system. The rate and quantity of infiltration depend on the length of the collection system. the area served. the soil and topographic condi nd. to a certain extent the population density( which affects the number and total length of house connections). Although the elevation of the water table varies with the quantity of rain and melting snow percolating into the ground, the leakage through defective joints, porous concrete, and cracks has been large enough, in some cases, to lower the ground water table to the level of the collection stem Most of the piping systems built during the first half of the 20th century were laid with cement mortar joints or hot poured bituminous compound ioints. Access ports were almost always constructed of brick masonry. Deterioration of pipe joints, pipe-to-access port joints, and the waterproofing of brickwork has resulted in a high potential for infiltration into these old sewers. The use of high quality pipe with dense walls, pre-cast access port sections, and joints sealed with rubber or synthetic gaskets is standard practice in modern collection-sYstem design. The use of these improved materials has greatly reduced infiltration into and exfiltration from newly constructed collection systems, and infiltration rates with time are expected to be much slower than with older sewers. Inflow into Collection Systems. The direct inflow can cause an almost immediate increase in flowrates In sanitary systems Exfiltration from Collection Systems Collection systems that have high infiltration rates and are in need of rehabilitation also may exhibit his exfiltration. When exfiltration occurs, untreated wastewater leaks out of pipe joints and service connections. If the piping and ioints are in poor condition significant quantities of wastewater may see into the ground travel through the gravel bedding of the piping system, or even surface in extreme cases. Seepage of untreated wastewater into the ground near shallow wells can result in pollution of the water supply. Well contamination has occurred in urban areas such as Los Angeles, California, where collection3-4 increase in wastewater flowrates. Possible sources are roof leaders, yard and areaway drains, access port covers, cross connections from storm drains and catch basins, and combined systems. Total inflow. The sum of the direct inflow at any point in the system plus any flow discharged from the system upstream through overflows, pumping station bypasses, and the like. Delayed inflow. Stormwater that may require several days or more to drain through the collection system. Delayed inflow can include the discharge of sump pumps from cellar drainage as well as the slowed entry of surface water through access ports (manholes) in ponded areas. The initial impetus in the United States for defining and identifying infiltration/inflow was the Federal Water Pollution Control Act Amendments of 1972. By correcting infiltration/inflow problems and "tightening" the collection system, benefits to the community include (1) reducing wastewater backups and overflows in the collection system, (2) increasing the efficiency of operation of wastewater-treatment facilities, and (3) improving the utilization of collection system hydraulic capacity for wastewater requiring treatment instead of for infiltration/inflow. Infiltration into Collection Systems. One portion of the rainfall in a given area runs quickly into the stormwater systems or other drainage channels; another portion evaporates or is absorbed by vegetation; and the remainder percolates into the ground, becoming groundwater. The proportion of the rainfall that percolates into the ground depends on the character of the surface and soil formation and on the rate and distribution of the precipitation. Any reduction in permeability, such as that due to buildings, pavements, or frost, decreases the opportunity for precipitation to become groundwater and increases the surface runoff correspondingly, The amount of ground water flowing from a given area may vary from a negligible amount for a highly impervious district or a district with a dense subsoil to 25 or 30 percent of the rainfall for a semi-pervious district with a sandy subsoil permitting rapid passage of water. The percolation of water through the ground from rivers or other bodies of water sometimes has considerable effect on the groundwater table, which rises and falls continually. The presence of high groundwater results in leakage into the collection systems and in an increase in the quantity of wastewater and the expense of disposing of it. The amount of flow that can enter a collection system from groundwater, or infiltration, may range from 0.01 to 1.0 m3 /d·mm-km or more. Infiltration may also be estimated based on the area served by the collection system and may range from 0.2 to 28 m3 /ha·d. The variation in the amount of infiltration encompasses a wide range because the lot sizes may vary in area, which in turn affects the length and extent of the collection system network. During heavy rains, when there may be leakage through access port covers or inflow as well as infiltration, the rate may exceed 500 m3 /ha·d. Infiltration/inflow is a variable part of the wastewater, depending on the quality of the material and workmanship in constructing the collection systems and building connections, the character of the maintenance, and the elevation of the groundwater compared with that of the collection system. The rate and quantity of infiltration depend on the length of the collection system, the area served, the soil and topographic conditions, and, to a certain extent, the population density (which affects the number and total length of house connections). Although the elevation of the water table varies with the quantity of rain and melting snow percolating into the ground, the leakage through defective joints, porous concrete, and cracks has been large enough, in some cases, to lower the ground water table to the level of the collection system. Most of the piping systems built during the first half of the 20th century were laid with cement mortar joints or hot poured bituminous compound joints. Access ports were almost always constructed of brick masonry. Deterioration of pipe joints, pipe-to-access port joints, and the waterproofing of brickwork has resulted in a high potential for infiltration into these old sewers. The use of high quality pipe with dense walls, pre-cast access port sections, and joints sealed with rubber or synthetic gaskets is standard practice in modern collection-system design. The use of these improved materials has greatly reduced infiltration into and exfiltration from newly constructed collection systems, and infiltration rates with time are expected to be much slower than with older sewers. Inflow into Collection Systems. The direct inflow can cause an almost immediate increase in flowrates in sanitary systems. Exfiltration from Collection Systems Collection systems that have high infiltration rates and are in need of rehabilitation also may exhibit high exfiltration. When exfiltration occurs, untreated wastewater leaks out of pipe joints and service connections. If the piping and joints are in poor condition, significant quantities of wastewater may seep into the ground, travel through the gravel bedding of the piping system, or even surface in extreme cases. Seepage of untreated wastewater into the ground near shallow wells can result in pollution of the water supply. Well contamination has occurred in urban areas such as Los Angeles, California, where collection