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    What are Combined Sewers?

    seperatesewer.jpgcombined.jpgGrand Rapids has been a leader in the State of Michigan in eliminating combined sewer overflow (CSO). Combined Sewers were a common construction practice until the 1920s. In the late 1980s the City of Grand Rapids embarked on a comprehensive program to eliminate all combined sewer overflows (CSO) in the City. Believe it or not, installing the CSOs was a significant step in improving water quality. The result of these efforts has been a 99.8% + reduction in CSOs to date with less combined sewer overflow every year. Only the last drop remains of the CSO Program. There were 59 CSO locations prior to corrective work started in the early 1990s. Today, only 4  need to be completed.

    Grand Rapids Combined Sewer Overflow History (Billion Gallons)

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    How much CSO was discharged in Grand Rapids in 2011?
    In 2011 the City of Grand Rapids discharged 49.266 million gallons of combined sewage. This represents .26% of the State total which was 18.7 billion gallons.
     
    What needs to be done yet?
    The City of Grand Rapids was issued a long term combined sewer overflow control program by the State of Michigan in 1988. This program defines the requirements and dates when the City must eliminate combined sewer overflows. The City is required by this program to eliminate all combined sewer overflows by December 31, 2019.
     
    How much will this cost? 
    From 1991 to 1999 the City’s west side subsystem combined sewer system (3.1 square miles) was separated at a cost of $160M. Currently sewer separation in the City’s east side subsystem combined sewer system (3.4 square miles) is underway with expenditures of just over $100M to date with $20M in construction costs remaining. These costs are reflected in Grand Rapids’ sewer rates which our residents have invested for the benefit of the entire Watershed. As of January 2011 greater than 99% of the entire City’s combined sewer overflow volume has been eliminated at a cost of $360M. The area reconstructed is equivalent to rebuilding the entire infrastructure of a City the size of Grand Haven.

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    ConstructionTimeline:    

           F-10     Complete
           F-01     2013
           W-21   2013
           F-03     2016
           F-04     2016

     

     

     

     

     

     

     

     

     

      In the late 1980's the City of Grand Rapids embarked on a comprehensive program to eliminate all combined sewer overflows (CSO) in the City. The result of these efforts has been a 99.7% + reduction in CSO to date with less combined sewer overflow every year. You can find out more about what the City has done below.

    There are two (2) types of overflows reported as part of the State of Michigan CSO reporting requirements.

    1. In-System Overflows - These occur when a sanitary sewer becomes overloaded due to Stormwater.  The sanitary sewer overflows to a nearby storm sewer and the untreated mixture of Stormwater and sanitary sewage flows to the Grand River.
    2. Market Avenue Retention Basin (MARB) - When the wastewater plant reaches its treatment capacity of 90 million gallons per day excess flow is diverted to MARB.  This flow is a mixture of Stormwater and sanitary sewage.  MARB can store 30 million gallons and for most wet weather events that is sufficient.  When volumes exceed 30 million gallons MARB provides settling, floatable removal, disinfection using Sodium Hypochrite and dechlorination utilizing Sulfur Bisulfate.  The overflow to the river is designated as "partially treated" and is typically comparable to the wastewater plant effluent quality.  The disinfection process typically results in fecal coliform (E. coli is a subset of fecal coliform) counts of less than 200 colonies per 100 milliliters.

    The City has gone from 59 in system overflow points in 1991 to 5 remaining.

    April 2011 Market Avenue Retention Basin Overflow Data as compared to the Wastewater Treatment Plant Discharge Permit.

     

    Overflow (MG)

    BOD (mg/l)

    Ammonia (mg/l)

    Solids (TSS mg/l)

    Phosphorus (mg/l)

    Fecal Coliform (c/100ml)

    4/27/2011

    10.22

    29

    2.70

    34

    0.89

    18

    4/28/2011

    37.74

    28

    3.60

    26

    0.90

    13

    4/29/2011

    1.33

    23

    2.70

    13

    0.80

    200

    WWTP Permit

    N/A

    38 (7Day)

    18

    44 (7DAY)

    1.0

    400 (7DAY)

     

    The Grand River was monitored for E. coli during and after the event. (All results are colonies/100ml). 

    Sample Date

    Grand River Park

    Riverside Park

    4/28/2011

    387

    261

    4/30/2011

    196

    166

    5/02/2011

    74

    54

    Geometric Mean

    178

    133

     

    E. coli Total Body Contact Standards for Beaches. 

     Sample results are compared to the Total Body Contact Standards contained in Part 125 of the Michigan Public Health Code which are as follows:

    •  300 E. coli colonies per 100 milliliters, as a geometric mean of all samples collected at a beach during one sample event;
    • 130 E. coli colonies per 100 milliliters, as a geometric mean of all samples collected over a 30-day period.

    If either of the above standards is exceeded at a bathing beach, the owner/operator is contacted and instructed to close the beach.

    State of Michigan CSO Information

    EPA CSO Information