TRANSMITTAL LETTER FOR BOARD MEETING OF JULY 9, 2009
COMMITTEE ON ENGINEERING
Mr. Richard Lanyon, Executive Director
Title
Report on and request for policy guidance with respect to measures to reduce infiltration/inflow in local sanitary sewer systems
Body
Dear Sir:
This is pursuant to the Board of Commissioner’s request for a report on the status of the MWRD’s local sanitary sewer system rehabilitation program and new measures that may be considered to mitigate continuing impacts on the MWRD caused by local sewer system groundwater infiltration and stormwater inflow (referred to as I/I, or extraneous flow).
Background
The MWRD is the regional wastewater collection and treatment service provider for its 884 square mile service area. Local sewer systems (or “satellite sewer systems” as they are referred to by the United States Environmental Protection Agency (USEPA)) are directly connected to MWRD’s 554 miles of interceptor sewers at an estimated 5,000 points, and are owned, operated, and maintained by local municipalities, utility companies, townships, local sanitary districts, private entities, etc. There are roughly 10,000 miles of locally-owned public sewer mains and probably as many or more miles of privately owned building service lines tributary to MWRD’s interceptors and treatment plants.
The MWRD regulates construction and connection of local sewers to its wastewater collection and treatment system primarily through enforcement of its ordinances and the issuance of permits, which facilitate MWRD’s review of design and inspection of construction of such systems. However, many connections were made en masse without benefit of permit or MWRD inspection by virtue of previous annexations of entire municipalities to the MWRD’s corporate service area along with connection of their existing local sewer systems to the MWRD’s system.
There are two types of local sewer systems within the MWRD: combined sewer systems and separate sewer systems. Parts or all of 52 older municipalities have combined sewer systems where storm water is allowed to mix with sewage in a single pipe tributary to the MWRD treatment plant. With large storm events, combined sewer systems sometimes become overloaded and must be relieved by discharging overflow through sewer outfalls on area waterways in order to prevent basement sewer backup flooding. While combined sewer overflows (CSOs) are permitted by the IEPA, the 1994 CSO Policy, which was codified by Congress in 2000, along with the Illinois law and regulations, impose numerous regulatory requirements upon the CSOs, with the ultimate goal being either their elimination or reduction in quantity and volume to a level that will enable achievement of water quality standards. The MWRD has directly addressed the CSO issue with its Tunnel and Reservoir Plan project (TARP, or the Deep Tunnel) which intercepts combined sewer overflow and facilitates its treatment. Although combined sewers are designed to receive and convey stormwater, the underground piping and manholes of such systems must be constructed to be watertight in order to prevent infiltration of groundwater.
As for the other type of sewer system, approximately 125 municipalities, utility companies, townships, local sanitary districts, etc. comprising roughly 500 square miles, have separate sewer systems, which is the type of system that will be discussed henceforth in this report. With this more modern type of sewer system, one pipe system (sanitary sewer) serves to collect and convey sewage to a treatment plant, and another pipe or drainage system (storm sewer) exclusively handles stormwater and discharges it to a waterway.
Except for a very small amount of allowable, unavoidable groundwater which can seep through pipe joints, neither stormwater nor groundwater belongs in a separate sanitary sewer system. In a properly constructed and maintained sanitary sewer system, the sewer flow measured during dry weather should be the same as or just a small amount less than the flow measured during wet weather. But due to deterioration with age and inadequate or improper maintenance, and illegal/improper connections of stormwater and groundwater sources, sanitary sewers in both the public and private sector can become subject to entry of I/I which rob them of their hydraulic capacity to deliver sewage. This can lead to sanitary sewer overflows (SSOs) and basement sewer backup flooding. The Illinois Environmental Protection Agency (IEPA) and the USEPA consider SSOs to be illegal no matter what the cause. Additionally, the handling of I/I results in wasted resources and expense to treat clean water.
Groundwater infiltration can enter defective sewer systems through worn and cracked sewer pipes; defective or non-standard pipe joints; open joints caused by lateral offset or vertical differential displacement from improper or absent pipe bedding; leaky, ungasketed or unsealed connections to receiving pipes or manholes; cracks in manhole walls or bottoms; illegally connected gravity building foundation drains, and foundation drain sump pump discharge pipes; and illegally connected underdrain systems such as perforated pipe field or drain tiles. The source of the groundwater can be from a seasonal or permanent elevated water table which submerges the sanitary sewer, or a temporarily elevated water level in subsurface soils or crushed stone sewer pipe bedding and backfill from rainfall-induced infiltration. Another source of clear water which need not be treated, does not belong in a sewer system, may impact operation of a sewer system, and is often indistinguishable from groundwater in a sanitary sewer system is water from leaky watermains that finds its way underground into a sanitary sewer system. Exfiltrated stormwater from nearby, non-watertight storm sewers (which nearly all are in separate sewer areas), especially under surcharge from large rainfall events, is often another significant source of extraneous flow in a sanitary sewer system.
Stormwater inflow is rainwater or snowmelt that enters the sanitary sewer system through such defects as leaky manhole frames and covers (especially improper open pick-hole or open-grated covers; compounded where such covers are subject to inundation by a floodplain, drainage ditch or swale, or stormwater detention facility); illegally connected roof drains, yard drains, window-well drains and driveway drains; illegal cross-connections of storm/combined sewers with sanitary sewers; etc.
Keeping stormwater and groundwater separate from sewage in separate sewer areas is a central focus of the MWRD Sewer Permit Ordinance and its companion ordinance, the Manual of Procedures for the Administration of the Sewer Permit Ordinance (MOP). These ordinances regulate local public and private sewer construction to ensure proper routing and connection of sanitary sewage, stormwater, and groundwater to prevent waterway pollution and adverse public health, environmental, and economic impacts stemming from storm-sanitary cross-connections, SSOs and basement sewage backup flooding, and to protect the MWRD’s wastewater collection and treatment infrastructure and operations. Long-standing MWRD ordinance provisions requiring durable, watertight pipe materials and joints, and proper pipe bedding; overhead plumbing in buildings; proper routing of building foundation drains, roof drains, and floor drains; watertight manhole frames and covers, and adequately elevated building foundation openings for projects in floodplain; and stormwater detention to mitigate runoff generated by new development/redevelopment, are all based on the need to prevent entry of stormwater and groundwater into local sanitary sewer systems and thereby our interceptors and treatment plants.
Passage of MWRD Sewer Rehabilitation Ordinance Requirements
The 1971 Federal Clean Water Act (CWA) addressed water pollution and provided construction grant funding for pollution control projects which MWRD availed itself of in order to build the TARP Phase I tunnels and other capital projects. In 1973 the MWRD initiated Article 6.5 of the MOP, Correction of Existing Deficiencies in Separate Sewered Areas, pursuant to the CWA. Today it continues to enforce this provision specifically as a condition of its water reclamation plant NPDES permits issued by the IEPA as state administrator of the CWA for the USEPA.
The goals of Article 6.5, referred to as the MWRD sewer rehabilitation program, are removal of I/I from sanitary sewer systems to prevent water pollution, and elimination of basement sewage backups and other adverse sewer surcharging conditions that cause health hazards and financial losses.
Article 6.5 first called for all 125 local sanitary sewer system owners to measure flows in their sewer systems during dry and wet weather periods. Since many communities have multiple connections (as many as 41) to the MWRD’s interceptor, flowmetering data from sewer subsystems representing at least 85 percent of the total community population was allowed. For various reasons, including the costs associated with evaluating sewer systems and correcting defects, many local communities strongly opposed the MWRD’s sewer rehabilitation ordinance, and objected to MWRD involvement with existing locally-owned sanitary sewer systems, which the communities claimed were properly maintained.
Originally, the MWRD mandated an average daily wet weather flow rate limit of 100 gallons per capita per day (gpcpd). If sewer flow in response to a rainfall of at least 1-inch or more in 24-hours did not exceed 100 gpcpd, the sewer would be deemed compliant; otherwise, the local sanitary sewer system owner would need to undertake a sewer rehabilitation program including a sewer system evaluation survey (SSES) with systematic I/I source identification and subsequent correction of I/I defects and post-rehabilitation flow monitoring under an MWRD-approved funding plan and schedule not exceeding three years.
The 100 gpcpd standard was subsequently found by the MWRD as being unrealistic and virtually unachievable especially with older sewer systems, and the ordinance was amended to allow an average daily wet weather flow rate limit of 150 gallons per day, which is approximately the design capacity of MWRD’s receiving interceptor sewers.
Even with the new, less-restrictive standard, the level of rehabilitation program effort among the communities continued to vary widely. Aside from the usual low priority, out-of-sight-out-of mind mentality which sewers generally suffer under until major problems arise, and aside from lack of funding for many of the communities, one of the underlying reasons for non-compliance was lack of incentive. Communities not markedly suffering from I/I related sewer problems such as overflows or basement sewer backup flooding were reluctant to spend money on I/I reduction programs. Also, most communities wanted to avoid dealing with sewers and internal plumbing on private property, even though it is widely recognized that the I/I from private property defects can represent from 60 to 80 percent of the total I/I in a sanitary sewer system, and compliance could not be achieved without addressing private sector I/I sources.
Some communities became frustrated with having expended large efforts and sums of money on I/I corrective work, and finding through post-rehabilitation flow monitoring that there was little or no reduction in I/I (in some subsystems post-rehab monitoring actually showed there was even more I/I after sewer rehabilitation). Assuming proper flow monitoring technique and interpretation of results, and aside from the quality of sewer rehabilitation work performed or there being additional defects developing and/or illegal connections being made in the interim time between pre-rehab and post-rehab flow measurements, there were several possible explanations for this, including the phenomenon known as “I/I migration” or “leak chasing.” (Defective sewer systems were so porous that they in effect were acting as underdrain systems, allowing entry of groundwater and lowering the local permanent or seasonal groundwater table via the sewer pipes and their surrounding crushed stone bedding and backfill). Lining and making point repairs to public sewers and repairing manhole leaks at lower elevations of the sewer system resulted in the water table rising with water finding its way into sewer system defects at higher elevations in the systems, such as cracks and leaky joints in private sector building service sewers not previously addressed.
Regional municipal association officials were petitioned by their member communities to appeal to the MWRD Board to make the MWRD sewer rehabilitation requirements less restrictive. IEPA and USEPA became a party to the discussions and negotiations between the municipal conferences and the MWRD. The eventual outcome was the Sewer Summit Agreement (November 1985) approved by IEPA, USEPA, MWRD and municipal conferences.
The Sewer Summit Agreement introduced the I/I Corrective Action Program (ICAP) compliance option which bases the amount of required I/I removal on the results of a cost-effectiveness analysis that compares the cost for correcting an I/I defect with the cost to let it remain in the system and continue to convey and treat the I/I it generates. Communities were allowed to choose either the ICAP option or the existing 150 gpcpd compliance option.
There are several less than desirable features associated with the ICAP option methodology. Illegal connections were allowed to be considered in the analyses whereas some MWRD staff believed that an illegal connection is exactly that and not a sewer deterioration defect, and therefore should be removed from the system without analysis (otherwise, illegal connections made subsequently could also theoretically be justified to remain in place on the basis of cost-effectiveness analysis). Also, the ICAP option requirements do not prescribe that the cost-effectiveness analysis account for the cost of basement flooding and SSO damages (including penalties), inclusion of which would drive the need for more I/I removal.
Status of Sewer Rehabilitation Programs
The status of the overall MWRD sewer rehabilitation program is reported annually to the IEPA via the MWRD’s report entitled Excessive Infiltration/Inflow Elimination Programs (latest edition October 2008), found on the MWRD’s website, www.mwrd.org <http://www.mwrd.org>. A copy of this report is also transmitted to the MWRD Commissioners and to all MWRD communities and agencies which own separate sanitary sewer systems.
Of 125 communities with separate sanitary sewer systems subject to the MWRD sewer rehabilitation requirements, a total of 103 communities chose the ICAP compliance option, and the remaining 22 elected the 150 gpcpd compliance option.
Eight communities are still not in compliance with the MWRD sewer rehabilitation requirements, although they adopted the less-restrictive, ICAP compliance option. All eight were under court-ordered consent decrees. During administration of MWRD’s overall program, a total of 56 communities were under such consent decrees.
Approved ICAP option sewer system wet weather flow values range from 122 to 2,378 gpcpd. Eight communities have approved flow rates of more than 1,000 gpcpd.
The average (weighted) wet weather flow rate of all ICAP community sanitary sewer systems based on the figures in the MWRD’s annual I/I report is 475 gpcpd (residual I/I of 325 gpcpd), which is an amount that exceeds the typical design capacity of a local sanitary sewer system and MWRD interceptors.
Approved 150 gpcpd compliance option sewer system values range from 25 gpcpd (a sewer system for a community college) to 179 gpcpd (which is larger than 150 because MWRD allows up to a 20 percent compliance latitude).
Attached Exhibit A, which is based on Table 6 from the aforementioned MWRD annual report on local I/I programs, shows the local sewer systems compliance status, selected compliance option, population equivalent, and post rehabilitation sewer system wet weather flow rate. Local agencies that are marked with a dash (“-“) have not yet completed their rehabilitation programs.
Several points should be made in regard to the data shown in the table.
First, the “Post-Rehab Flow” rate values for the 117 communities in compliance represent the wet weather flow rate measurements the communities submitted that indicated I/I removal program completion and compliance. In the case of ICAP option communities, the required target rates are not shown, and the post-rehab rates may be as much as 20 percent higher than the target rates due to the compliance value tolerance allowed by the MWRD.
Second “Residual Excessive I/I” values shown in the table are simply the post-rehabilitation flow rate values minus 150 gpcpd, since MWRD considers anything over 150 gpcpd as excessive even though it may be “compliant’ with regard to the ICAP option under the Sewer Summit Agreement.
Lastly, and perhaps most importantly, the Post-Rehab Flow rate values have not changed since they were entered into the report. Dates of compliance are not shown in the table and vary widely; some of the flow figures in the report may be 25 years old or older. By and large no recent sewer rehabilitation flow monitoring has been performed, so the current condition of individual local sewer systems with respect to I/I is unknown at this time.
All communities that completed their programs have been required to submit annual reports to the MWRD on their Long Term Maintenance and Operation Programs (LTMOPs) to help ensure continuous sanitary sewer system maintenance in order to keep I/I at or below the approved levels. The quality of local sewer management as indicated by the submitted reports is highly variable among communities. Where maintenance is indicated to be less than adequate, the MWRD issues advisory letters urging that maintenance be stepped up. In general, periodic flow metering to monitor current wet weather flow levels in sanitary sewer systems/subsystems is encouraged by the MWRD but is not mandatory.
Difficulties in Conducting Flow Monitoring and Sewer Evaluation and Correction
Problems with wet weather flow measurement, I/I quantity determination, and I/I removal program effectiveness determination are:
• No two storms are alike as to rainfall duration, intensity, distribution of rainfall across a sewershed, and antecedent conditions (e.g. how dry or wet soils are from recent rainfalls). This is one reason why in some instances communities performed sewer rehabilitation work and yet their post-rehabilitation flow monitoring showed no or little I/I reduction and sometimes even an increase in I/I levels as compared with the results of pre-rehab flow monitoring. It should be noted that MWRD purchased a number of flow meters, had its inspectors trained to use them, and conducted its own confirmation flow monitoring whenever a community submitted its own flow monitoring data that indicated successful completion of an I/I removal program and compliance with its target flow rate. Often our monitoring, performed with a subsequent rainfall, indicated inadequate I/I reduction and, therefore, non-compliance. Disputes arose, the MWRD was challenged as to the flow monitoring expertise of its staff, and the MWRD eventually dropped such confirmation flow monitoring.
• Sewer clogging by fats, oils and greases (FOG), root intrusion, and sediment deposition are the primary causes of local system SSOs and backups. Such clogging interferes with sewer condition evaluation and related wet weather flow rate measurement. If wet weather flow monitoring is performed before complete sewer system cleaning and root removal in at least the public sector sewer system (it would be very difficult to accomplish completely in all the private sewer lines), wet weather flow rates and I/I levels will be significantly underestimated due to flow rate restriction caused by the clogging.
• Sewer surcharging that occurs during a rain event due to I/I may cause flow reversal (backup), which makes it difficult to interpret and accurately quantify flow metering results due to the measured negative flow direction.
• If flow monitoring is conducted when seasonal groundwater table is low and therefore the sewer system is not submerged, the flow monitoring data will not reflect the full extent of sewer system infiltration or rainfall-induced inflow I/I defects.
Problems in identifying sources of I/I include:
• Access for personnel to inspect private sector exterior sewers and interior plumbing may be denied by residents.
• Smoke testing for illegally connected downspouts, yard drains, window wells, driveway drains may be precluded due to existence of sewer or plumbing check-valves or odor-control sewer traps (water-filled elbows in a sewer system to prevent odors).
• Although many communities have earnestly addressed identification and removal of external and internal I/I sources and illegal connections on private property, many postpone doing so for a variety of reasons. Often, if the I/I in a local sewer system is not overly high and it can largely be attributed to identified public sector sewer system defects, the system owner will perform the public sector I/I removal work and perhaps exterior private sector work such as downspout removal. If post-rehabilitation flow monitoring shows that sewer system I/I reduction achieved by the public sector sewer work is insufficient, only then will the community address private sector I/I sources.
• In at least one case, a municipality inspected all its buildings and paid the whole bill for correction of all illegal sump pump connections (over 300 homes). In some cases, municipalities have paid partially. On occasion, MWRD has been approached by municipalities inquiring as to whether it would help co-pay for illegal connection removal, and the MWRD has declined.
• Depending on the nature of the illegal connection, the footprint of the building, and the extent of the work, the cost to correct illegal connections on property can range from tens of dollars (to disconnect a downspout by cutting, capping, and redirect a downspout to discharge to grade); hundreds of dollars (to re-pipe and eliminate diverter valves, for example); to $3,000 and up to $10,000 or more for correction of illegal sump pumps and gravity footing drains connected to the sanitary sewer system.
With respect to bullet number one above, the courts have acknowledged that local municipalities have a powerful tool at their disposal to conduct inspections on private property. In Magnuson v. City of Hickory Hills, 933 F.2d 562 (1991), the Seventh Circuit Court of Appeals held that Hickory Hills had the right to terminate water service to a homeowner if the homeowner refused to allow the City access to the home to inspect for illegal sewer connections.
Basement Flooding and Factors Contributing to Illegal Connection
There are three major kinds of basement flooding, only one of which is caused or exacerbated by I/I in a sanitary sewer system:
• Basement flooding caused by local waterway overbank flooding as with construction in floodplain; or from intentional installation of vortex restrictors in the outflow pipes of storm sewer catch-basins to prevent sewer system overloading and sewage back flooding; or from inadequate/undersigned stormwater drainage facilities or accidental blockage of storm sewers, street inlets, and open-grates on storm manholes as by fallen tree leaves, either of which under heavy rainfall may result in street and yard surface ponding with floodwater entering basement foundation openings and window-wells.
• Basement seepage flooding from groundwater or rainfall-induced groundwater infiltration entering basements through cracks in basement walls or floors, or basement sumps where discharge sump pumps cannot handle the incoming rate of flow.
• Sanitary (or combined) sewer backup flooding, where basements are flooded by sewage backing from overloaded and/or clogged building service sewer lines or sewer mains. This type of basement flooding can be caused by I/I, especially by groundwater/stormwater sump pumps and downspouts connected to the sanitary building service sewer. Generally, overhead plumbing, which the MWRD requires for all new building construction, prevents this type of basement flooding.
Although I/I can cause or worsen SSOs and basement sewer backup flooding, such sanitary sewer problems can and do occur during dry weather with little or no I/I in the system under the following circumstances:
• sewer clogging or blockage due to fats, oil, grease buildup (FOG), which is the most common cause of SSOs;
• clogging from deposition of silt or sediment, debris, or vandalism;
• root intrusion; and sewer collapses, offsets, or differential settling (although all these lead to entry of I/I if the sewer is submerged within the perennial or seasonal water table); and
• improper design of sewers: undersizing of sewers or overloading (e.g. underestimation of sewage flow loading when the sewers were designed, or added flows from outside the original service area); pipes constructed with inadequate slopes which result in solids deposition related flow restriction; etc.
A common motivation for homeowners to illegally connect building foundation sump pumps to sanitary sewer systems is absence of an effective stormwater drainage system serving their property. For example, homeowners with poor backyard drainage may have their outlet pipes from their foundation drain sump pumps discharge to the backyard, which worsens on-site flooding problems. Usually with the aid of a plumber and without knowledge of the local municipality, their groundwater/storm-water piping system is re-plumbed to connect to their building sanitary sewer service line. Similarly, to help prevent basement seepage and reduce energy costs for continuously running sump pumps, homeowners may have yard or area drains installed and connected to the sanitary sewer system as an outlet for their stormwater.
Impacts of Local Sewer System Excessive I/I on the MWRD
Impacts of excessive I/I in local sewer systems on MWRD infrastructure and operations include:
• Occurrences of interceptor SSOs during larger rainfall events due to I/I-related overloading. Sometimes the SSOs are caused or exacerbated by unlawful simultaneous pumping at local community sanitary sewer pump stations which discharge flows at nearly twice the allowable sewage flow rate. Excessive I/I in sewer flows from a community decreases MWRD interceptor capacity provided for sewer flows from other communities.
• Occurrences of inadequate sewage treatment at MWRD treatment plants during extreme rainfall events resulting in bypasses of inadequately treated sewage.
• Increase in MWRD pumping and sewage treatment and disposal costs borne by taxpayers for wasteful, needless treatment of clear water. Flows during wet weather received at MWRD treatment plants exclusively serving communities with separate sewer systems have experienced flow rates on the order of ten times dry weather flow.
• Deposition of sediments from silt-laden, rainfall-induced stormwater and groundwater from local sewer systems in MWRD interceptors which reduces their capacity and results in the need for more frequent interceptor cleaning and sediment removal.
• IEPA/USEPA claims against the MWRD arising from SSOs, CSOs and treatment plant bypasses.
• Negative press reports which MWRD must respond to and correct when local communities experiencing basement flooding attempt to shift blame to the MWRD by unjustifiably claiming inadequate interceptor capacity or incorrectly referring to MWRD interceptors as storm sewer or stormwater drainage facilities.
Recommendations
The problem of I/I and extraneous flows in local separate sanitary sewer systems is serious and growing, and implementation of corrective measures need to be considered.
The following local sewer system I/I control measures are recommended for consideration whether or not a new broad-based I/I elimination program initiative is called for.
• Require that communities provide evidence of formal training of their sewer and plumbing inspection staff to help ensure proper connection and routing of sewage, stormwater and groundwater at the outset of building construction and occupancy and in follow-up inspections.
• Require all communities to enforce replacement or relining of existing building sanitary sewer service lines in the case of building teardowns or major renovations, unless televising definitively proves that a sewer line is in good condition.
• Require that existing building sewer service lines be relined (or at a community’s option, replaced) where I/I levels remain high after other sources of I/I have been addressed.
• Require or make clear through education efforts that all abandoned sanitary sewer lines must be removed or properly sealed off to prevent I/I. Also, new drain tile/perforated pipe connections to sanitary and combined sewers are prohibited, and existing ones must be disconnected or sealed off from these types of sewers, except in the case of foundation drains in combined sewer areas which serve to protect structures.
• Require that all sewer system-connected residential and non-residential buildings be routinely inspected for illegal connections by local municipalities on a 5-year or more frequent cycle.
• Consider whether the MWRD should require that, as with storm sewers in combined sewer areas tributary to our treatment plants, separate storm sewers be designed and constructed to be watertight with respect to pipe exfiltration. Exfiltration from leaky storm sewers, especially storm sewers during rain events in relative close proximity to sanitary sewers can contribute significantly to I/I in the sanitary sewer system. Other advantages for requiring storm sewer watertightness is prevention of subsurface soil washout and void creation which can lead to sinkholes/ground subsidence, pavement cracking and potholes, and building collapse; deposition of soil material in downstream sewers and interceptors which can restrict flow capacity and lead to backups and overflows; and deposition of soil sediment in, and discharge of high suspended solids laden stormwater flow to, waterways, lakes and wetlands.
In view of increasing I/I flows to MWRD treatment plants and I/I-induced SSOs from MWRD interceptors, the following local sanitary sewer system I/I removal program initiatives are presented for possible consideration:
Alternative 1 Require each community known to be causing SSOs in either MWRD’s system or their own to perform an I/I removal program sufficient to eliminate the SSOs. In the case of multiple communities tributary to the MWRD system SSO point, flow monitoring must be undertaken by all the tributary communities (or the MWRD) to determine the extent of the I/I contribution to the SSO problem.
Alternative 2 For communities in MWRD water reclamation plant Facilities Planning Areas (FPAs) where wet weather flows are recognized to be exceedingly high and problematic for MWRD (e.g. the Hanover Park Basin), require monitoring of wet weather flows and implementation of I/I removal programs accordingly to reach a level of 150 gpcpd. (This may be complicated by combined sewer system flow contribution. Only three of MWRD’s eight FPA service basins are exclusively served by separate sanitary sewer systems). Require that the rehabilitation program include the identification and elimination of all exterior and interior private sector illegal connections.
Alternative 3 Universally require all communities to monitor flows whether or not I/I-related problems are indicated, and perform I/I source identification and rehabilitation to reduce flows to 150 gpcpd. Require that the rehabilitation program include the identification and elimination of all exterior and interior private sector illegal connections. If a local system is causing MWRD SSOs, require corrective action measures prescribed in Alternative 1 above.
Alternative 4 Consider assessing MWRD user charge fees for excess I/I based on appropriate MWRD sewage conveyance and treatment O&M costs. The definition of excess I/I would need to be established. Continual flow monitoring to determine actual annual fees could be problematic. A set rate based on one-time monitoring unless and until significant I/I removal is demonstrated and post-rehab flow monitoring to justify a reduction in annual user fee could be employed.
Alternative 5 Require all communities to conduct flow monitoring to verify their sewer systems are at their approved ICAP or their 150 gpcpd compliance option flow rates. Those communities that exceed their target rate must perform additional I/I identification or removal so as not to exceed it. Consider requiring additional I/I removal where basement flooding occurs to a level where no basement flooding occurs under an established “design” rainfall event. Require the removal of all illegal connections from the system.
Alternative 6 Implement the currently proposed Federal Capacity, Management, Operation, and Maintenance (CMOM) program requirements that will apply to all satellite sewer system owners as well as regional interceptor and treatment owners such as the MWRD, and develop I/I removal requirements as needed accordingly. Authorization of CMOM requirements was put on hold by the previous Federal administration, and it is unknown if and when the CMOM requirements will finally be authorized by the current Federal administration and whether they will be modified before authorization.
A combination of elements from several or all of the alternatives above, or others which may subsequently arise may eventually be considered.
It is recommended that any alternatives MWRD selects for further consideration or implementation be discussed with the IEPA and the USEPA to ensure acceptability by both agencies.
It is requested that the Board of Commissioners provide policy guidance on and authorize the Engineering Department to evaluate and consider the above measures to stem the impacts of excessive I/I in local sanitary sewer systems.
Respectfully Submitted, Joseph P. Sobanski, Director of Engineering, NV:JRR
Attachment