Discussion by Ben Sosewitz
General Superintendent
The Metropolitan Sanitary District of Greater Chicago; Chicago, Illinois
Comments Pertaining to Paper entitled Discharges from Urban Storm Water Runoff Mixed Storm
Overflow and Treated Sewage
1. Characteristics of Storm Water Runoff: in Relation to Treated Effluent The Metropolitan
Sanitary District of Greater Chicago has only some limited data pertaining to storm runoff, which is
summarized in Table 1. These data show suspended solids ranging from 4 to 99 mg/1, BOD values from
1 to 13 mg/1 and ammonia nitrogen levels from 0.2 to 4.5 mg/1. The suspended solids are low
compared to other reported values, which may be due to the limited drainage area from which the
storm water was collected and the fact that areas involved are frequently swept and otherwise very
well maintained. In addition, the storm events being reviewed were of low intensity.
The effluents from three major treatment plants of Sanitary District, on an annual average (1970)
showed the following ranges: Suspended Solids mg/114 to 23, BOD mg/1 14 to 17, Ammonia Nitrogen
6.1 to 14.2.
A study carried out in Tulsa, Oklahoma (S. Cleveland, R, Ramsey, P. Walters, "Storm Water
Pollution from Urban Land Activity", presented at Storm and Combined Sewer Seminar, FWQA
Chicago, Illinois June 22-23, 1970), shows relatively similar ranges for BOD, 8 to 18 mg/1. However,
the suspended solids were considerably higher, average values ranged from 84 to 2052 mg/1 which are
comparable to the concentrations plotted in the author's figure 6.
The wide variations in the suspended solids were attributed to the topography and type of area.
The low value was for runoff coming from well-kept drainage ditches along an airport runway. The
highest value was found from an area in which a housing complex was under construction. These levels
are reported to be 10 to 20 times higher than concentrations for the city of Tulsa's sewage treatment
plants.
These results would support Soderlund's findings that BOD and nitrogen levels are less than in
treated sewage as stated on page 4.
However, during a given period of storm runoff, as the author has pointed out, the total pounds of
any one pollutant discharged would also depend upon the relative volumes of storm runoff as
compared to treated effluent.
In a study completed during 1970 of the quality of stormwater from urban land area in Durban,
North Carolina - Dr. Edward H. Bryan, Manager Environmental Projects, Ecology Division, Rex
Chainbelt, Inc. Milwaukee, Wisconsin, concluded that the annual contribution of BOD from urban
stormwater was approximately equal to that discharged from the secondary sewage treatment serving
the same drainage basin. This was in the order of 1.5 population equivalents per acre per day on a
drainage basin with a population density of nine persons per acre. The contribution of total organic
matter as measured by both the Chemical Oxygen Demand and Volatile Total Solids Determination
was larger than that which would be contributed to the receiving stream (and projected impoundment)
by raw, sanitary sewage from a strictly residential urban area. A summary of the data from this study
is contained in Table 2.
2. Estimation of amount of combined sewer overflow: G. Söderland has used for his estimated that
1 percent of the total amount of domestic sewage in a year is overflow. (Page 5).
It has been estimated that for the Chicago Metropolitan Area that approximately 3 percent of the
annual sewage volume is discharged to the waterways during storm as combined sewer overflows.
Similarly, a United States Public Health Service study titled "Pollution Effects of Stormwater and
Overflows from Combined Sewer System," dated November 1964, found that an average of 3 to 5
percent of all raw wastewater is annually discharged by overflow from combined sewers to
watercourses.
3. Characteristics of stormwater run-off in relation to combined sewer overflow:
G. Söderland states that the stormwater run-off contains a considerably greater quantity of
suspended solids, about the same amount of BOD and nitrogen, and 10 percent of the amount of
phosphorus than the storm overflow.
Based upon the assumption that 1 percent of the total amount of domestic sewage in a year is
overflow, the author calculates that urban stormwater contains considerably greater quantities of
suspended solids (about 18 to 20 times) about the same amount of BOD and nitrogen, and 10 percent
of the phosphorus as combined storm overflows (shown in author's Table 4).
However, in addition to the greater percentage of combined sewer overflows and subsequently
larger volumes as previously noted, the actual combined sewer overflows may have greater
concentrations of contaminants than storm runoff.
Table 3 gives a summary of some samplings which were conducted at various combined storm
319
General Superintendent
The Metropolitan Sanitary District of Greater Chicago; Chicago, Illinois
Comments Pertaining to Paper entitled Discharges from Urban Storm Water Runoff Mixed Storm
Overflow and Treated Sewage
1. Characteristics of Storm Water Runoff: in Relation to Treated Effluent The Metropolitan
Sanitary District of Greater Chicago has only some limited data pertaining to storm runoff, which is
summarized in Table 1. These data show suspended solids ranging from 4 to 99 mg/1, BOD values from
1 to 13 mg/1 and ammonia nitrogen levels from 0.2 to 4.5 mg/1. The suspended solids are low
compared to other reported values, which may be due to the limited drainage area from which the
storm water was collected and the fact that areas involved are frequently swept and otherwise very
well maintained. In addition, the storm events being reviewed were of low intensity.
The effluents from three major treatment plants of Sanitary District, on an annual average (1970)
showed the following ranges: Suspended Solids mg/114 to 23, BOD mg/1 14 to 17, Ammonia Nitrogen
6.1 to 14.2.
A study carried out in Tulsa, Oklahoma (S. Cleveland, R, Ramsey, P. Walters, "Storm Water
Pollution from Urban Land Activity", presented at Storm and Combined Sewer Seminar, FWQA
Chicago, Illinois June 22-23, 1970), shows relatively similar ranges for BOD, 8 to 18 mg/1. However,
the suspended solids were considerably higher, average values ranged from 84 to 2052 mg/1 which are
comparable to the concentrations plotted in the author's figure 6.
The wide variations in the suspended solids were attributed to the topography and type of area.
The low value was for runoff coming from well-kept drainage ditches along an airport runway. The
highest value was found from an area in which a housing complex was under construction. These levels
are reported to be 10 to 20 times higher than concentrations for the city of Tulsa's sewage treatment
plants.
These results would support Soderlund's findings that BOD and nitrogen levels are less than in
treated sewage as stated on page 4.
However, during a given period of storm runoff, as the author has pointed out, the total pounds of
any one pollutant discharged would also depend upon the relative volumes of storm runoff as
compared to treated effluent.
In a study completed during 1970 of the quality of stormwater from urban land area in Durban,
North Carolina - Dr. Edward H. Bryan, Manager Environmental Projects, Ecology Division, Rex
Chainbelt, Inc. Milwaukee, Wisconsin, concluded that the annual contribution of BOD from urban
stormwater was approximately equal to that discharged from the secondary sewage treatment serving
the same drainage basin. This was in the order of 1.5 population equivalents per acre per day on a
drainage basin with a population density of nine persons per acre. The contribution of total organic
matter as measured by both the Chemical Oxygen Demand and Volatile Total Solids Determination
was larger than that which would be contributed to the receiving stream (and projected impoundment)
by raw, sanitary sewage from a strictly residential urban area. A summary of the data from this study
is contained in Table 2.
2. Estimation of amount of combined sewer overflow: G. Söderland has used for his estimated that
1 percent of the total amount of domestic sewage in a year is overflow. (Page 5).
It has been estimated that for the Chicago Metropolitan Area that approximately 3 percent of the
annual sewage volume is discharged to the waterways during storm as combined sewer overflows.
Similarly, a United States Public Health Service study titled "Pollution Effects of Stormwater and
Overflows from Combined Sewer System," dated November 1964, found that an average of 3 to 5
percent of all raw wastewater is annually discharged by overflow from combined sewers to
watercourses.
3. Characteristics of stormwater run-off in relation to combined sewer overflow:
G. Söderland states that the stormwater run-off contains a considerably greater quantity of
suspended solids, about the same amount of BOD and nitrogen, and 10 percent of the amount of
phosphorus than the storm overflow.
Based upon the assumption that 1 percent of the total amount of domestic sewage in a year is
overflow, the author calculates that urban stormwater contains considerably greater quantities of
suspended solids (about 18 to 20 times) about the same amount of BOD and nitrogen, and 10 percent
of the phosphorus as combined storm overflows (shown in author's Table 4).
However, in addition to the greater percentage of combined sewer overflows and subsequently
larger volumes as previously noted, the actual combined sewer overflows may have greater
concentrations of contaminants than storm runoff.
Table 3 gives a summary of some samplings which were conducted at various combined storm
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