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===Municipal Sanitary Infrastructure - Sanitary sewer inflow and infiltration (I&I)=== | ===Municipal Sanitary Infrastructure - Sanitary sewer inflow and infiltration (I&I)=== | ||
+ | [[File:I&I.png|300px|thumb|alt=image showing how to estimate I&I|<font size=3>Example of how to estimate inputs from infiltration and inflow ([https://www3.epa.gov/region1/sso/pdfs/Guide4EstimatingInfiltrationInflow.pdf]).</font size>]] | ||
+ | |||
+ | Groundwater infiltration and rainfall derived inflow and infiltration, commonly referred to as inflow, are components of most sanitary sewer systems. These inputs, called I&I, should be a minor component of the sanitary sewer flow. However, infiltration and inflow may | ||
+ | be considered excessive when it is the cause of overflows (SSO) or bypasses in the sanitary sewer system. In addition, I&I is treated at wastewater treatment plants even though it is relatively clean water, resulting in extra cost. | ||
+ | |||
+ | EPA provides guidance for estimating the input and importance of I&I in a sanitary sewer system. To assess extraneous water entering your system at least a year of influent flow data to the treatment facility should be examined. For infiltration analysis, flow data collected during the high groundwater periods is used. For inflow analysis, the Average Wet Weather (AWW) flow can be estimated from flow data for a | ||
+ | one week period when there has been significant rain. If a single storm event is used to analyze wet weather inflow, it should be an event large enough to cause surface ponding and runoff. Other techniques can be used to determine the presence of I&I, including manhole testing and maintenance, dye tracing, smoke testing, use of cameras, and private property inspection for improper connections. Examples of improper connections include downspouts, groundwater sump pumps, foundation drains, drains from window wells and outdoor basement stairwells and drains from driveways. | ||
+ | |||
+ | Proper evaluation of I&I sources is necessary to manage them. Once detected, they can be eliminated or minimized. Several cities, for example, have programs and ordinances prohibiting illicit connections on private property. | ||
+ | |||
+ | For more information, see [https://www3.epa.gov/region1/sso/pdfs/Guide4EstimatingInfiltrationInflow.pdf], [http://www.globalw.com/support/inflow.html], [http://www.sehinc.com/news/how-identify-and-reduce-inflow-and-infiltration-ii-collection-system#:~:text=Inflow%20happens%20when%20groundwater%20and,defects%20within%20the%20collection%20system.&text=Infiltration%20is%20when%20groundwater%20enters,that%20let%20the%20water%20in], [http://www.msdlouky.org/programs/ii.htm] | ||
===Municipal Sanitary Infrastructure - Illicit sanitary connections to MS4s=== | ===Municipal Sanitary Infrastructure - Illicit sanitary connections to MS4s=== |
The MPCA, working with stakeholders, developed a checklist for conducting an inventory of bacteria sources. The checklist is not a permit requirement but may be used to meet permit requirements. This page provides guidance and supporting information for the checklist.
Link to the checklist: File:Checklist for bacteria source inventory.xlsx
The checklist contains four worhsheets.
These are discussed below.
This sheet provides basic general information about the checklist.
This is the sheet where users enter information. Column A contains different categories of bacteria sources and specific sources within each category. The categories include the following.
Columns B through G are where users input information.
This section provides some basic information about each of the potential sources included in the checklist. Where appropriate we include links where additional information can be found.
Combined sewer systems (CSS) are sewers that are designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. During wet weather conditions, the volume of stormwater runoff can exceed the capacity of the CSS infrastructure, including both the piping system and/or the treatment plant. This is common where where older CSS infrastructure is in place, combining sanitary and storm drain flows. When the capacity of the CSS is exceeded, excess water can bypass treatment and bypassed flow will be mixed with the treated water prior to disinfection and just prior to discharge to the receiving water. While both stormwater runoff and sanitary sewer discharges contain bacteria, concentrations are much higher in untreated sewage. Thus, CSOs can lead to very high concentrations of bacteria in water delivered to receiving waters. For more information, see [3], [4], [5], [6], [7].
Sanitary sewer systems collect and transport domestic, commercial, and industrial wastewater. Some sanitary sewer systems may contain limited amounts of stormwater and infiltrated ground water to treatment facilities, but they are designed to carry just sewage and industrial wastewater. Occasionally, sanitary sewers will release raw sewage. These types of releases are called sanitary sewer overflows (SSOs). Possible causes of SSOs include blockages, line breaks, sewer defects that allow stormwater and groundwater to overload the system, power failures, improper sewer design, and vandalism. The adjacent image indicates line blockages appear to be an important cause of SSOs. An EPA survey indicated SSOs are most common during wet weather flows.
SSOs that discharge to surface waters are considered point source discharges and are thus prohibited unless authorized by a NPDES permit. SSOs may be indicative of improper operation and maintenance of the sewer systems, and may violate NPDES permit conditions. Effective illicit discharge and elimination practices and programs minimize the occurrence and impacts from SSOs. Other management strategies include the following.
For more information, see [8], [9], [10], [11]
Groundwater infiltration and rainfall derived inflow and infiltration, commonly referred to as inflow, are components of most sanitary sewer systems. These inputs, called I&I, should be a minor component of the sanitary sewer flow. However, infiltration and inflow may be considered excessive when it is the cause of overflows (SSO) or bypasses in the sanitary sewer system. In addition, I&I is treated at wastewater treatment plants even though it is relatively clean water, resulting in extra cost.
EPA provides guidance for estimating the input and importance of I&I in a sanitary sewer system. To assess extraneous water entering your system at least a year of influent flow data to the treatment facility should be examined. For infiltration analysis, flow data collected during the high groundwater periods is used. For inflow analysis, the Average Wet Weather (AWW) flow can be estimated from flow data for a one week period when there has been significant rain. If a single storm event is used to analyze wet weather inflow, it should be an event large enough to cause surface ponding and runoff. Other techniques can be used to determine the presence of I&I, including manhole testing and maintenance, dye tracing, smoke testing, use of cameras, and private property inspection for improper connections. Examples of improper connections include downspouts, groundwater sump pumps, foundation drains, drains from window wells and outdoor basement stairwells and drains from driveways.
Proper evaluation of I&I sources is necessary to manage them. Once detected, they can be eliminated or minimized. Several cities, for example, have programs and ordinances prohibiting illicit connections on private property.
For more information, see [12], [13], [14], [15]