Cities that installed their sewage collection systems before the 1930s typically used single piping systems to transport both urban runoff and sewage. This type of collection system is referred to as a combined sewer system (CSS). The cities' rationale when combined sewers were built was that it would be cheaper to build just a single system. Burrian, Steven J., et al. (1999)."The Historical Development of Wet-Weather Flow Management." EPA, National Risk Management Research Laboratory, Cincinnati, OH. Document No. EPA/600/JA-99/275. In these systems a sudden large rainfall that exceeds sewage treatment capacity is allowed to overflow directly from storm drains into receiving waters via structures called combined sewer overflows.EPA. "Combined Sewer Overflow (CSO) Control Policy." Federal Register, 59 FR 18688. April 19, 1994. Storm drains are typically  at shallower depths than combined sewers ; because , while storm drains are designed to accept surface runoff from streets, combined sewers were designed to also accept sewage flows from buildings with basements  .
Cities that installed their sewage collection systems before the 1930s typically used single piping systems to transport both urban runoff and sewage. This type of collection system is referred to as a combined sewer system (CSS). The cities' rationale when combined sewers were built was that it would be cheaper to build just a single system. In these systems a sudden large rainfall that exceeds sewage treatment capacity is allowed to overflow directly from storm drains into receiving waters via structures called combined sewer overflows.EPA. "Combined Sewer Overflow (CSO) Control Policy." Federal Register, 59 FR 18688. April 19, 1994. Storm drains are typically installed at shallower depths than combined sewers . This is because combined sewers were designed to accept sewage flows from buildings with basements , in addition to receiving surface runoff from streets .
D
Burrian, Steven J., et al. (1999)."The Historical Development of Wet-Weather Flow Management." EPA, National Risk Management Research Laboratory, Cincinnati, OH. Document No. EPA/600/JA-99/275.
A
installed
R
; because , while storm drains are designed to accept surface runoff from streets,
. This is because
D
also
A
, in addition to receiving surface runoff from streets