SANITARY SEWER EVALUATION OF INFLOW/INFILTRATION REDUCTION TECHNIQUES. Geoffrey Trent VanAllen. A Thesis Submitted to the Faculty of

Transcription

1 SANITARY SEWER EVALUATION OF INFLOW/INFILTRATION REDUCTION TECHNIQUES by Geoffrey Trent VanAllen A Thesis Submitted to the Faculty of The College of Engineering and Computer Science in Partial Fulfillment of the Requirements for the Degree of Master of Science Florida Atlantic University Boca Raton, Florida May 2015

2 Copyright by Geoffrey VanAllen 2015 ii

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4 ACKOWLEDGEMENTS I am using this opportunity to express my gratitude to everyone who supported me throughout the course of this project. I am thankful for their aspiring guidance, invaluably constructive criticism and friendly advice during the project work. I am sincerely grateful to them for sharing their truthful and illuminating views on a number of issues related to the project. iv

5 ABSTRACT Author: Title: Institution: Thesis Advisor: Degree: Trent VanAllen Sanitary Sewer Evaluation of Inflow/Infiltration Reduction Techniques Florida Atlantic University Dr. Frederick Bloetscher Masters of Science Year: 2015 Substantial savings in operations can be achieved by reducing the amount of wastewater that must be pumped and treated. Utilities have long dealt with the infiltration and inflow (I and I) issues in their system by televising their pipes and identifying leak points, but this primarily addresses only the infiltration part of I and I. Inflow, which creates hydraulic issues during rain events, leads to sanitary sewer overflows and can subject the utility to fines from regulatory agencies. As a result, dealing with the inflow portion of I and I is needed. The goal of this thesis is to differentiate inflow and infiltration from baseflow and to determine the effectiveness of different methods used to reduce inflow and infiltration in sanitary sewer lines. An analysis was conducted on the benefits and cost effectiveness of different inflow/infiltration approaches (slip-lining sewer lines, stormwater manhole inserts, replacing sewer lines, smoke testing, etc.) and cost savings municipalities can expect to receive from each. v

6 Unlike most other studies, which identify rainfall derived inflow and infiltration (RDII), the goal of this study was to develop a means to separate the flows into inflow, infiltration and baseflow. It was assumed that inflow into sanitary sewer lines is linearly related to rainfall and infiltration is linearly related to groundwater elevation. Based on these assumptions, inflow and infiltration could each be separated out from the wastewater flow, leaving only baseflow. Once the inflow and infiltration have been separated from the flows, pre and post flows could be compared to determine a percent reduction in both to develop a cost analysis. The conclusions developed from this project are directly related to the method for determining the inflow and infiltration reduction, which were related to rainfall and groundwater elevation, respectively. It was shown that inflow is directly related to rainfall, and infiltration (excluding inflow) is directly related to groundwater elevations. The results of the analysis showed that inflow and infiltration correction methods were effective in removing significant amounts of inflow and infiltration from the sanitary sewer system. However, when compared to the cost to complete the construction activities, it was evident that inflow reduction was much more cost effective. vi

7 SANITARY SEWER EVALUATION OF INFLOW/INFILTRATION REDUCTION TECHNIQUES TABLE OF TABLES... ix TABLE OF FIGURES... x 1.0 INTRODUCTION Early History Sewer Collection Systems Pressure Sewer Systems Understanding the Issues Terminology Inflow Infiltration Reduction Strategies Goals and Objectives METHODOLOGY RESULTS Bay Harbor Islands Dania Beach Cooper City Analysis Inflow Infiltration Water Wastewater Flow Analysis Cost Analysis vii

8 3.5.1 Dania Beach Cooper City Findings CONCLUSIONS APPENDICES REFERENCES viii

9 TABLE OF TABLES Table 3-1: Dania Beach Total Net Change Table 3-2: Cooper City Total Net Change Table 3-3: Percent Change in Inflow Table 3-4: Percent Change in Infiltration Table 3-5: Dania Beach Amount Saved Table 3-6: Cooper City Amount Saved ix

10 TABLE OF FIGURES Figure 1-1: Three Components of Wet-Weather Wastewater Flow (EPA, 2007)... 9 Figure 1-2: Installation Procedure (courtesy, USSI, Inc.) Figure 1-3: Inflow Defender Manhole Rain Dish showing installed dish, and both polycarbonate and polyethylene versions Figure 1-4: Smoke Test (courtesy, USSI) Figure 1-5: LDL Plug Design (courtesy, USSI, Inc.) Figure 1-6: Areas where further infiltration investigation via televising is needed only 15% of system Figure 3-1: Bay Harbor Islands Flow vs. Rainfall Figure 3-2: Flow vs. Rainfall From 2009 to Figure 3-3: Bay Harbor Islands Daily Flow vs. Rainfall for 2009 and Figure 3-4: Dania Beach Total Flow vs. Rainfall Figure 3-5: Dania Beach Flow vs. Rainfall for 2006 and Figure 3-6: Dania Beach Groundater Level Figure 3-7: Dania Beach Baseflow + Infiltration vs. Groundwater Elevations Figure 3-8: Dania Beach Baseflow + Infiltration vs. Groundwater Elevation and Rainfall Figure 3-9: Baseflow and Infiltration Vs. Groundwater Levels Figure 3-10: Baseflow and Infiltration vs. Groundwater Levels with Trendline x

11 Figure 3-11: Dania Beach Baseflow + Infiltration vs. Groundwater Levels for 2009, 2012 and Figure 3-12: Total Flows with Time in Cooper City Figure 3-13: Cooper City Flow vs. Rainfall for 2011 and Figure 3-14: Cooper City Groundwater Elevations Figure 3-15: Cooper City Baseflow + Infiltration vs. Groundwater Elevations Figure 3-16: Cooper City Baseflow + Infiltration vs. Groundwater Levels for 2011 to Figure 3-17: Baseflow and Infiltration vs. Groundwater Levels with Trendline Figure 3-18: Cooper City Baseflow + Infiltration vs. Groundwater Levels Figure 3-19: Dania Beach Water Flow Per Day Figure 3-20: Cooper City Water Flow Per Day Figure 3-21: Dania Beach Water Flow Per Month Figure 3-22: Cooper City Water Flow Per Month xi

12 1.0 INTRODUCTION As outlined by Bryan Fagan (2012) in Elixir, civilizations expanded as far as water supplies would allow. But as civilizations expanded, the potential for disease incidence increased. The Romans understood the need to move wastes away from drinking water, using channels to move wastes to rivers that would further move the material from humans. Historically civilizations developed near rivers and lakes that would remove the waters with little thought as to the consequences. In 1849, John Snow demonstrated that cholera in London was related to a specific well on Broad Street, which precipitated the development of sewers in London. Since that time, sewer systems have developed in response to development, facilitating the further development of nations. The access to safe water is correlated with advancements of civilization. Sanitary sewer lines serve a vital role in the health and safety of the public. Beneath our streets exists a network of sanitary sewer lines that are essential in the efficient conveyance of wastewater. These systems are designed to convey the wastewater from the source to wastewater treatment plants. Typical sources of wastewater include toilets, sinks and showers, as well as industrial and commercial wastes. One thing that these sources have in common is that they are all fundamental parts of our everyday lives. Without the existence of these sewage collection systems, many of the water quality standards we take for granted would not be possible. This would lead to a significant increase in both ecological and psychological damage due to the significant increase in pollution, much as was seen up until The Cuyahoga 1

13 River, which burned on the surface periodically for almost 100 years, last in 1969, catalyzed a movement to restore degraded rivers and was essential in helping pass the Federal Clean Water Act of 1972 (Zeitler 2001). At the same time, most people take the existence of sewer collection systems for granted because they are out of sight. They assume that when the water leaves the toilet, shower or sink, the waste just disappears, but this is far from the truth. Sanitary sewer collection systems include a variety of infrastructure: gravity pipelines, force main pipes, pump stations, manholes, lift stations and other devices used to collect and transport wastewater from residential and commercial properties. Most of the over 16,000 sewer collection systems within the United States are owned and operated by local municipalities (Sterling et al 2010). With an ever increasing population, the existing municipal collection systems are being pushed to their limits because of the increasing amount of wastewater they are required to transport. A 1999 study conducted on 42 wastewater utilities, which served approximately 26 million individuals, throughout the United States revealed that sewer lines ranged from 117 years old to new (Black & Veatch, 1999). Additionally, the study found that 18% of the sewer lines were installed in the last 10 years, 41% in the last 20 years, 82% in the last 50 years and 98% in the 100 years (Black & Veatch, 1999). Much of the older sewer systems were built well before increasing legislation led to more stringent design regulations regarding sanitary sewer collection systems. Older gravity sanitary sewer lines were constructed mainly of vitrified clay, brick and concrete, while modern sewers were constructed primarily of clay, but also of plastic, ductile iron, steel and reinforced concrete (Lai 2008). Most force mains were constructed of ferrous materials (such as welded steel, ductile iron, or cast iron) or if newer, plastic 2

14 (polyvinyl chloride (PVC) or high density polyethylene (HDPE)), while large-diameter force mains have also been constructed of pre-stressed and reinforced concrete (Tucicillo et al 2010). Service laterals are typically constructed of clay, steel or PVC pipe. A 1998 study conducted for EPA, which included 13 wastewater utilities found that gravity sewer systems consisted of 61% vitrified clay, 20% plastics, 7% reinforced concrete, 7% unreinforced concrete, and 5% other, which matches findings found in south Florida (see later discussion). The same study found that over 50% of force mains were constructed using ductile iron pipe (Arbour and Kerri, 1998). Based on the 1998 study a significant portion of our nations gravity sewers lines are still using vitrified clay pipes. The problem is that the older vitrified clay pipes crumble as they age creating potential areas for groundwater to enter the system Early History With the discovery of waterborne bacteria in the mid 1800 s it was recognized that contaminated water must not be allowed to enter the drinking water supply, and was the main reason for the construction of sanitary sewers in Europe and later in the United States (Sikora 2004). By the 1880 s s vitrified clay pipe was the material of choice for a lot of the sewers up to 30 inches internal diameter (Schladweiler 2002). Prior to 1950, the vitrified clay pipes did not have a joint furnished by the pipe manufacturer. The joints were made in the field using cement mortar. The cement mortar joints may have been initially water-tight and root-resistant, but tended to deteriorate over time because of their rigidity, roots which seek out wet surfaces and the potential corrosive conditions associated with hydrogen sulfide (Lai 2008). Additionally, pipe lengths were much smaller requiring many more joint connections. The length of the pipes increased 3

15 over this time period from 2 feet to 3 feet, and then to 4 feet; today s vitrified clay pipes are typically 10 feet long but can have a much larger diameter than the early vitrified clay pipes. The short lengths of the pipes create numerous connections that fail, and combine to create the potential for significant leakage from the pipe. Additionally, vitrified clay pipes are known for brittleness (USACE 1984), which can cause the pipes to crack, break or collapse in sections of piping where the soil has been disturbed. In areas where cracking has occurred, roots will enter and over time the roots will damage or block the line (Schladweiler 2002) Sewer Collection Systems Gravity lines use slope to convey flow via gravitational forces (Feeney et al 2009). Gravity collection systems include manholes, service laterals, and cleanouts. Manholes are vertical openings in the pipe providing connection between pipe segments and provide an access point for maintenance on the sewer line. Service laterals are the gravity lines that convey wastewater from a building s foundation to the sanitary line, or main, in the street (Feeney et al 2009). Older manholes were constructed of bricks, however today s manholes are typically constructed of precast concrete. Both have a cast iron manhole cover. Because sewer lines exist under ground, only the manhole cover is visible to the public. Since gravity systems are unpressurized they are much more susceptible to blockages from grease or substances commonly dumped down drains that should not be. The manhole provides an access point to view the flow of the pipe and to remove any material blocking the flow of the wastewater. Much like the older vitrified clay pipes, older manholes that were created from bricks typically have greater potential 4

16 for leaks than newer manholes created from precast concrete because the mortar used in the brick manholes was not water proof (Schladweiler 2002) Pressure Sewer Systems Force mains, unlike gravity sewer lines, are pressurized lines used to convey pumped sewage (Feeney et al 2009). Force main systems are needed in areas where it is difficult to use gravity systems because of the terrain. Low lying areas, for example, might use force mains because the flat ground makes it harder to use gravity systems. Because the systems are pressurized, force mains don t have manholes or cleanouts. One advantage of force mains is that they are less susceptible to blockage from grease. In order to pressurize the system the force mains are connected to pump stations. Pump stations are added to create the pressure in the system to keep the sewage moving. Additionally pump stations are needed where force mains connect to gravity pipes Understanding the Issues Infiltration is the water entering a sewer system and service connections from groundwater leaking through defective pipes, pipe joints, damaged house lateral connections, or manhole walls (Feeney et al 2009). Infiltration most often is related to a high groundwater table that is observed during a wet season or in response to a severe storm. Damaged lateral connections are thought to be a major contributing factor to infiltration in sanitary sewers (Swaner and Thompson 1994). In areas where the pipes lie in the groundwater, water moves thru the cracks or joints in the piping system and enter the sewer collection system. In areas like South Florida where large amount of pipes lie below the water table, cracks in the pipes provide a constant source of infiltration. 5

17 Inflow is stormwater that enters a sanitary sewer system through catch basins, roof leaders, cleanouts, foundation drains, sump pumps, open manholes, and cellar, yard, and area drains (Merrill et al 2004). This can include inflow from depressed manhole lids and frames, downspouts, and cross-connections with storm sewers (Vallabhaneni et al 2007). Direct inflow sources such downspouts and sump pumps are no longer acceptable, however they still exist and contribute to the total inflow. These direct connections are typically improperly or illegally connected to the sewer collection system. Excessive inflow leads directly to surcharges sewer lines and is a major cause of SSOs. Literature review to support the assumptions that inflow is related to rainfall events and infiltration is related to groundwater elevation includes: inflow is that portion of a sewer flow hydrograph above the normal dry weather flow pattern that is the sewer flow response to rainfall or snowmelt in a sewershed (Bennett et al 1999); and infiltration most often is related to a high groundwater table that is observed during the wet season or in response to a severe storm (Lai 2008). Ultimately this information could be used by municipalities for future planning purposes as they continue to look for the most cost effective means to remove inflow and infiltration and comply with current and future regulations on sanitary sewer overflows. Both force mains and gravity sewers have a maximum capacity for which they can transport the wastewater; this capacity is based on criteria such as the diameter of the pipe and the capacity of the downstream pump station. When the sewer line reaches its capacity the pipe becomes surcharged possibly causing a sanitary sewer overflow. The most significant concern about sanitary sewer collection systems reaching their capacity and becoming surcharged is the possibility of sanitary sewer overflows created by 6

18 excessive inflow during storm events Sanitary sewer overflows, is the discharge of untreated sewage from a separate sanitary sewer system, including overflows and basement backups (Black and Veatch 2000). A sewer system is considered surcharged when it is overloaded and the pipe is completely full, possibly leading to the release of some amount of sewage. This discharge of untreated wastewater is considered a sanitary sewer overflow and is prohibited under the Clean Water Act requirements for National Pollutant Discharge Elimination System (NPDES) permits. This discharge of untreated wastewater is hazardous to the environment and the well-being of the public. Sanitary sewer overflows have effects that are wide reaching and include the contamination of drinking water, the closure of community beaches, and other environmental and public health distresses. Overflows typically occur for one of the following reasons: rain events, construction damage, blockages, structural failures, mechanical failures, collapsed sewer pipes, broken sewer pipes, insufficient capacity or vandalism. One of the major contributing factors to why sewer collection systems have insufficient capacity is the existence of inflow and infiltration in the systems. Inflow and infiltration represent a significant portion of the total amount of wastewater that is delivered to the wastewater treatment. Every day billions of gallons of water that entered the sewage collection system as either inflow or infiltration are treated by wastewater treatment plants, which waste both capital and operational dollars. The Miami-Dade Department of Regulatory and Economic Resources, formerly referred to as Department of Environmental Resources Management, Water and Sewer Section reports that Miami-Dade County treats in excess of 100 million gallons per day of water that enters the collection system as inflow and infiltration which has led to two billion dollar consent orders for the utility. So limiting infiltration and inflow saves the utilities 7

19 millions of dollars and allows them to instead use the money on other needed maintenance projects. The most common consequence of inflow and infiltration are overflows during rainfall from manholes, controlled overflow points, pump stations and treatment plants (Haarhoff 2011) Terminology Figure 1-1 is a modification of the figure presented in the EPA document titled Computer Tools for Sanitary Sewer System Capacity Analysis and Planning, released October The figure depicts the three major components of wet-weather wastewater flow: base water flow (BWF), ground water infiltration (GWI), and inflow. The figure is meant to show a typical distribution of the three components during a rain event. The rain event is represented as the blue bar graph at the top of the figure. The question is what the quantities of each are in relation to potable water and one another. 8

20 Figure 1-1: Three Components of Wet-Weather Wastewater Flow (EPA, 2007) Base water flow (BWF) is considered the untreated wastewater discharged from residential, commercial and industrial facilities that enter the sanitary sewer collection system to be transported to a wastewater treatment plant. The BWF only includes wastewater discharged from sources and does not include wastewater from inflow or infiltration. The BWF will fluctuate throughout the day depending on the amount of wastewater created. Typically the lowest BWF occurs from 1 AM to 5 AM when people are sleeping and not using water. Conversely the BWF is the highest in the morning and evening before and after people go to work. Figure 1.1 shows how the base water flow fluctuates in comparison to time. 9

21 Because much of the sewage collection systems in South Florida exist under the water table there is a constant stream of ground water infiltration into system. There is not much daily fluctuation in the ground water infiltration as is shown in Figure 1-1. Ground water infiltration flows do not fluctuate greatly in sanitary sewer lines during wet-weather conditions. However there are seasonal variations due to changes in the water table. Typically the highest levels of ground water infiltration in South Florida occur in summer when the water table is at its highest (E Sciences 2013); this is different from most other parts of the country when the water table is at its highest in late winter and spring. Dry weather flow (DWF) includes both the base water flow and ground water infiltration. It is the flow in a sanitary sewer collection system during periods of dry weather in which the sanitary sewer is under minimum influence from inflow. Unlike groundwater infiltration that enters the collection system without much fluctuation, inflow has significant fluctuations that relate to the size of the rain event. In Figure 1-1 it can be seen that the greatest inflow occurs at the peak of the rain event; this is because inflow is dependent on the occurrence of a rain event. From the figure it can also been seen that before the rain event occurred the inflow was zero. Inflow contributes to greater than designed for flows in sewer systems and is a major component of peak wastewater flows. From Figure 1-1 it is seen that during the peak of the rain event the inflow greatly increases the total flow in the system, it is during this time that the system has its greatest potential in becoming surcharged and overflowing. Because inflow adds such a significant amount of flows during a rain event it is typically responsible for capacity related sanitary sewer overflows. 10

22 Collection and treatment systems are exceeding design capacities well ahead of their original design life as a result of infiltration and inflow (Merrill et al 2004). Non base-flows result in surcharging, backups, bypasses, and reduced treatment efficiency (Merrill et al 2004). Consequently, the ability of the utilities to effectively limit and remove inflow in the sanitary sewer collection systems is becoming more important as the systems begin to reach or exceed their design capacity. 1.2 Inflow Infiltration Reduction Strategies Municipalities can implement several different strategies to collect information on the structural integrity and capacity issues relating to the maintenance of the sanitary sewer collections systems that may impair the system to properly convey wastewater. Primarily these strategies are evaluated on their ability to reduce inflow and infiltration from entering the sewer collection system. These evaluations must also take into the financial aspects that are induced from these different strategies. Therefore, inflow and infiltration reduction strategies must be evaluated before work is commenced on their effectiveness in comparison to the cost inducted from the work. Ideally municipalities would have the economic freedom to replace their entire aging infrastructure; however the reality is that due to limited budgets, cost restraints most be implemented to ensure that the most cost effective strategy is conducted. Therefore, before construction is completed pre-construction assessment of the present condition of the sanitary sewer collection should be completed to accurately determine the most effective strategy to properly remediate the collection system. The most common activities conducted to assess the systems prior to initiating rehabilitation activities include: smoke testing, dye testing, manhole inspections, sewer 11

23 line and lateral inspections by video means. Each approach is effective at predicting different aspects of the inflow/infiltration into the system and the results from their findings can used to determine whether system itself is dealing with an inflow or infiltration problem, because ultimately the strategies to repair systems dealing with inflow or infiltration issues are different. According to Bloetscher et al (2014) resolving the inflow problems is straightforward. He notes that inflow should be the first priority, followed by traditional televising and lining projects (Bloetscher 2014). Utilities see that reducing the potential regulatory actions from overflows is an important risk issue to address. Bloetscher et al (2014) note that the order of inflow implementation is important, and pursuing all steps in order will resolve the majority of inflow. Removing inflow also minimizes unneeded videotaping of the collection system which permits more dollars to go toward fixing problems. The first inflow correction step is inspection of all sanitary sewer manholes for damage, leakage or other problems. Most manholes have limited condition issues, but where the bench or walls are in poor conditions, that should be repaired with an impregnating resin. Deterioration may be an indication of wastewater quality concerns requiring the addition of chemicals to reduce the impact of hydrogen sulfide. Next is repair/sealing of chimneys in all manholes to reduce inflow from the street during flooding events. The chimney includes the ring, cement extensions, lift rings, brick or cement used to raise the manhole ring. Manhole covers are often disturbed during paving or as a result of vibration from traffic and temperature differential which breaks the seal between the steel ring and concrete. The crack between the ring and cover can leak a lot of water as demonstrated by a Miami-Dade County test conducted in 12

24 2010. To properly seal the system, a flexible polymer based coating, installed in accordance with the following procedure should be used (see Figure 1-2). Figure 1-2: Installation Procedure (courtesy, USSI, Inc.) The next step is to put dishes into the manholes. Surprisingly every manhole dish that is properly installed has water in it. Most collection system workers are familiar with dishes at the bottom of the manhole where they are of limited use. This is because those dishes deform when filled with water or constructed in such a manner that allows them to 13

25 be knocked in when the cover is flipped (Bloetscher et al 2014). Figure 1-3 shows two examples (note the person standing in the upside-down dish). The key is the appropriate reinforcing to prevent dishes from dropping into the manhole. The gasket seal should be made of a closed cell neoprene material with pressure sensitive adhesive on one side for adhering to dish body. Figure 1-3: Inflow Defender Manhole Rain Dish showing installed dish, and both polycarbonate and polyethylene versions. *Note the ribs and depth of dish that improves long-term strength. Note polycarbonate is required for newer, 30 or 48 inch manhole Once the manholes are sealed, smoke testing can identify obvious surface connections (see Figure 1-4). The normal protocol for smoke testing will identify broken or missing cleanout caps, surface breaks on public and private property, connection of gutters to the sewer system, and stormwater connections. The openings at cleanouts in 14

26 the right-of-way can be corrected immediately using utility funds. Figure 1-5 shows the LDL plug which is used to seal the cleanout. Figure 1-4: Smoke Test (courtesy, USSI) 15

27 Figure 1-5: LDL Plug Design (courtesy, USSI, Inc.) The final step is a low flow investigation, which is intended to target the infiltration piece of the problem. Such an event will take several days and must be planned to determine priority manhole to start with and sequencing. Based on a projected plan and route, the following is the protocol based on identifying where there is and is not flow (Bloetscher et al 2014): Open the manholes Inspecting them for flow Determining if flow is significant. If investigation of basin will end and new basin will be started. If flow exists, open consecutive manholes upstream to determine 16

28 where flow is derived from. Generally a 2-inch wide bead of water is a limit of significant infiltration. Figure 1-6 is an example from Dania Beach. What they found was that after 20 years of no work, only 15% of the pipe segments indicated infiltration leakage. This reduced the televising and lining portion off their lining program by over $1.2 million, which more than paid for the inflow reduction project (Bloetscher et al 2014). 17

29 Figure 1-6: Areas where further infiltration investigation via televising is needed only 15% of system 18

30 Infiltration is best handled with an internal sanitary sewer system inspection, which includes manhole inspection and sewer line and lateral inspection via camera. Such an inspection assists utilities in determining the structural condition, the presence of roots, condition of joints, depth of debris in the line, and depth of flow (USEPA 2005). Closed-circuit television (CCTV) is the most common assessment tool conducted by municipalities to gauge the current condition of their collection system. A 2004 research project, which surveyed large wastewater utility districts, found that 100% of the 31 survey respondents relied almost exclusively on CCTV as the primary means to inspect pipes (Thomson 2004). One of the key downsides of the CCTV approach is that it requires equipment, time and manpower, which greatly increases the cost associated with its completion. In addition, miles of pipe may have no defects, which means money is spent on non-productive activities. Internal pipe inspection does nothing to address inflow but it can identify sources of inflow. Testing which includes dye testing can be used to identify leaks which allow unwanted inflow into the sewer system and determine the location of illicit connections (USEPA 2005). The results from the condition assessment form the basis for characterizing the defects, identifying deficiencies, and prioritizing the system rehabilitation needs (ASCE 2004). There are many rehabilitation methods, the choice of methods will depend on pipe size, type, location, dimensional changes, sewer flow, material deposition, surface conditions, severity of inflow/infiltration and other physical factors (NEIWPCC 2003). Typically structural repair of the sewer lines involve either removing and replacing existing sewer lines or lining existing sewer lines. Lining of existing sewer lines involves using trenchless pipe rehabilitation techniques, which include slip lining and cured-inplace-pipe. Rehabilitation of sewer pipes is increasingly being accomplished with 19

31 trenchless methods because generally it is more cost-effective than open cut, avoids many surface constraints, lessens disruption of other services, minimizes surface reinstatement needs, reduces surface disruption including traffic disruption, reduces surface settlement and environmental disturbance, and allows installation of services at greater depths than would normally be considered cost effective for trenching (ASCE 2004). Another rehabilitation technique is the repair of broken or cracked manholes. Typical repairs made to manholes are to cracked bases, tie-ins to an existing manhole, coating the inside, or resealing or replacing a ring and cover (NEIWPCC 2003). 1.3 Goals and Objectives Substantial savings in operations can be achieved by reducing the amount of wastewater that must be pumped and treated. Utilities have long dealt with the infiltration and inflow (I and I) issues in their system by televising their pipes and identifying leak points, but this primarily addresses only the infiltration part of I and I. Inflow, which creates hydraulic issues during rain events, leads to sanitary sewer overflows and can subject the utility to fines from regulatory agencies. As a result, dealing with the inflow portion of I and I is needed. The goal of this thesis is to differentiate inflow and infiltration from baseflow and to determine the effectiveness of different methods used to reduce inflow and infiltration in sanitary sewer lines. To accomplish this a relationship was drawn between the benefits and cost effectiveness of different inflow/infiltration approaches (slip-lining sewer lines, stormwater manhole dishes, manhole seals, smoke testing, etc.) and cost savings municipalities can expect to receive from each method. Cost effectiveness, as presented in this study, is meant to 20

32 mean the reduction in inflow and/or infiltration and cost to complete the construction activity. 21

33 2.0 METHODOLOGY Sewer inflow is a result of rainfall discharged into sewer systems during storm events. Consequently, during times of no rainfall there is no inflow. During large storm events municipalities experience a large increase in sewer flow as a result of inflow; inflow is the most common cause of sanitary sewer overflows. Infiltration does not cause overflows, and infiltration into pipes stops when the pipes are surcharged. Some of the most common calculators of RDII include: constant unit rate methods; percentage of rainfall volume (R-value) methods, percentage of streamflow methods, synthetic unit hydrograph methods, probabilistic methods, predictive equation based on synthetic rainfall/flow regression methods, predictive equation based on synthetic streamflow and basin characteristics methods, and RDII as a component of hydraulic software methods (Merrill et al 2003). These methods would not be appropriate for the purposes of this study due to the desire to separate inflow and infiltration. Unlike most other studies, which identify rainfall derived inflow and infiltration (RDII), the goal of this study was to develop a means to separate the flows into inflow, infiltration and baseflow. Consequently, a new approach would need to be developed which would allow for inflow calculations based on the size of rainfall events. This approach would be based on the assumption that there is a linear relationship between rainfall and inflow. It was hypothesized that as the size of the storm event increased the amount of inflow would also increase. 22

34 There is a need to separate inflow and infiltration because inflow and infiltration are different, the methods to correct deficiencies in both are different, and the benefits may vary. The reasoning for this approach was to use these values to develop a cost analysis of the effectiveness for inflow and infiltration construction techniques, since the techniques used to alleviate them are different. Additionally, this approach would allow us to predict future flows based on the construction activity completed at a site. So if a relationship can be drawn between size of rainfall event and amount of inflow, and the groundwater elevation and amount of infiltration; then the cost effectiveness can be determined based on the reduction of inflow and infiltration from construction activities and future flows averted can be calculated which can provide an additional monetary cost savings. Three south Florida sewer systems were chosen for analysis. All three were relatively small and served clear areas. The utilities were chosen because they had readily available information on daily flows and pump station records, and two participated with inflow and infiltration removal programs. Data for Dania Beach was gathered from 2005 to The original sewer pipes were installed in the 1960s. Cooper City data was available from 2011 to Their pipelines were installed in the late 1970s. Bay Harbor Islands has data from 2011 to 2013; their infrastructure is from the 1960s. All three recognized issues with excess flows in the utility system. All three were interested in resolving issues with inflow and infiltration at reasonable cost. All three realized significant flows during rain events although none reported SSOs. Daily flows were generated. Rainfall records for the closest rain station were acquired from DBHydro from the South Florida Water Management District. 23

35 It was hypothesized that inflow into sanitary sewer lines is linearly related to rainfall and infiltration is linearly related to groundwater elevation. Based on these assumptions inflow and infiltration could each be separated out from the wastewater flow, leaving only baseflow. Once the inflow and infiltration have been separated from the flows, pre and post flows could be compared to determine a percent reduction in both to develop a cost analysis. The inflow is the easiest to remove and was extracted first. Rainfall and inflow should be related (Merrill 2004). The means to address the inflow and rainfall is to correlate these factors to determine flow volumes based on rainfall events. Inflow is expected to increase with time so to address this issue, rain events from different years to indicate how the inflow increases annually. Rainfall and inflow relationships can then be developed and utilized to extract the inflow component from the total sewer flow. The infiltration amount was postulated to be related to the groundwater level. For the south Florida case studies, groundwater is shallow for most of the year, most of the pipe was assumed to be below the water table. Consideration was made about the changes in flows due to population fluctuations. All users of the systems were assumed to use wells for irrigation. The expectation was that the water discharged to the sewer system is a relatively constant percentage of the total potable water pumped. Baseflow would not be of significance in this study, and it was assumed that any increases or decreases of baseflow over the study time period were negligible. Basic statistical means were used to develop correlations and extract the three components. It was assumed that rainfall and inflow were linearly related; a linear regression analysis was completed to extrapolate inflow values based on assumed rainfall 24

36 values. A regression analysis was used because it focuses on dependent variables, and can provide understanding of how the dependent variable (inflow) changes when independent variable (rainfall) is varied. The regression analysis could also be used to predict future inflow values based on rainfall. Once the linear relationship between rainfall and inflow was determined, any rainfall could be entered into the regression analysis to determine the associated inflow value. Once the inflow values were separated, the relationship between groundwater elevation values and flows were developed using the Pearson product-moment correlation coefficient. This time the dependent value was the baseflow+infiltration and independent variable was the groundwater elevation. Since it was assumed that fluctuations in baseflow were negligible, any changes between baseflow+infiltration were assumed to be a result of fluctuations in infiltration. Analysis of water use by day of the week and by month was considered. These analyses were completed to draw comparison between wastewater flow and water flow in order to be able to predict wastewater flow when only water flow data was available. Also included in this analysis was a comparison of wastewater flow as a percentage of water flow. 25

37 Jan-09 Mar-09 May-09 Jul-09 Sep-09 Nov-09 Jan-10 Mar-10 May-10 Jul-10 Sep-10 Nov-10 Jan-11 Mar-11 May-11 Jul-11 Sep-11 Nov-11 Jan-12 Mar-12 May-12 Jul-12 Sep-12 Nov-12 Flow Rainfall (in) 3.0 RESULTS 3.1 Bay Harbor Islands Figure 3-1 is a comparison of the 2011 daily flows vs. rainfall in Bay Harbor Islands. Figure 3-1 demonstrates that when rainfall increases the daily flows within the municipality also increase. This increase in flow during wet weather flows is directly related to inflow being discharged into the sewer collection system during rainfall events. 4,000,000 Flow vs. Rainfall ,500, ,000, ,500,000 2,000,000 1,500,000 Flow (Gallons) Rainfall ,000, , Figure 3-1: Bay Harbor Islands Flow vs. Rainfall Daily flow and rainfall values were graphed to see if there was correlation between rainfall and an increase in flows. In Figure 3-2 it can be seen that there was a clear increase in flow as the storm event increased. This confirms that storm events and an increase in flow are related. 26

38 Flow (Gallons) Flow vs. Rainfall Values From 2009 to ,000,000 1,800,000 1,600,000 1,400,000 1,200,000 1,000, , , , , Rainfall Figure 3-2: Flow vs. Rainfall From 2009 to 2012 A more simplistic approach than was described in previous studies reviewed was developed which would demonstrate a linear relationship between rainfall and inflow (Merrill, et al 2004). Figure 3-3, which is a graph of the daily flows in gallons vs. rainfall in Bay Harbor Islands from 2009 and 2012 provides this approach. From the graph it can be seen that a 2.0 inch rainfall event created a greater flow in 2012 than in 2009, which is directly related to an increase in inflow as the sewer collection system became more susceptible to inflow between 2009 to Comparing the slope of the lines a percent increase in inflow can be determined from the two years, which can be used later in the cost analysis. Bay Harbor Islands information is presented in this section of the report because no inflow construction activities were completed during the study years. Consequently, the flow information from this municipality will be used to calculate a baseline for an inflow increase per year that can be expected. Based on the information provided in Figure 3-3 the inflow increased by 42% from 2009 to 2012 in 27

39 Flow (Gallons) Bay Harbor Islands, which would be an approximate increase in inflow of 14% per year. This number will be used in future calculations to help approximate amount of cost savings municipalities can expect from inflow corrective activities. It should be noted that any comparison to previous years inflow should not only take into account the amount of decrease from the previous year, but also the amount of potential increase in inflow if no inflow reduction activities were conducted. Flow vs. Rainfall for 2009 and ,000,000 1,800,000 y = x y = x ,600,000 1,400,000 1,200,000 1,000, , , , , Rainfall Figure 3-3: Bay Harbor Islands Daily Flow vs. Rainfall for 2009 and 2012 No information pertaining to groundwater elevations within Bay Harbor Islands was available because there were no monitoring wells measuring groundwater on the island. Consequently, due to the limited information available no attempt was made to calculate infiltration within Bay Harbor Islands. 28

40 Jan-06 May-06 Sep-06 Jan-07 May-07 Sep-07 Jan-08 May-08 Sep-08 Jan-09 May-09 Sep-09 Jan-10 May-10 Sep-10 Jan-11 May-11 Sep-11 Jan-12 May-12 Sep-12 Jan-13 May-13 Sep-13 Flow (MGD) Rainfall (in) 3.2 Dania Beach Initial remediation activities of the wastewater collection system in Dania Beach was initiated in 2008 and progressed through Initial activities included smoke testing, sealing manhole covers and adding dishes to existing manholes. These initial activities were completed to reduce inflow into the system. A comparison of the pre-inflow reduction activities and post-inflow reduction activities flow vs. rainfall values are presented in Figure flow values, which were the earliest flow values available, were selected as the pre-inflow reduction values, and 2009 flow values, which were collected following inflow reduction activities, were selected as the post-inflow reduction values. 10 Flow vs. Rainfall Flow (MGD) Rainfall (in) Figure 3-4: Dania Beach Total Flow vs. Rainfall 29

41 Flow (MGD) Based on a comparison of sewer flows for similar rainstorm events, it can be seen in Figure 3-5, that there was a clear reduction in inflow between 2006 and In total there was a 54.8% reduction in inflow from 2006 to 2009, which represents a significant decrease of inflow into the system during rain events. 7 Flow vs. Rainfall for 2006 and 2009 Change per year = 18.3% y = x y = x Rainfall (in) Figure 3-5: Dania Beach Flow vs. Rainfall for 2006 and 2009 An increase in infiltration can also result from large storm event that increases the groundwater table, which results in an increase in infiltration from damaged sewer lines residing below the water table. It was assumed that as the groundwater elevation became closer to the surface, it would cause an increase in infiltration. Based on the previous calculation for inflow, which was subtracted from the daily flow for each day, baseflow+infiltration was determined for each day. This value was then compared to groundwater depth and rainfall. If the earlier assumption was correct then all three should have similar peaks and valleys. 30

42 Jan-06 May-06 Sep-06 Jan-07 May-07 Sep-07 Jan-08 May-08 Sep-08 Jan-09 May-09 Sep-09 Jan-10 May-10 Sep-10 Jan-11 May-11 Sep-11 Jan-12 May-12 Sep-12 Jan-13 May-13 Sep-13 GW Elevation (ft) Figure 3-6 provides the groundwater elevation for the Dania Beach, which were gathered from the South Florida Water Management District DBHydro Browser. 7 6 Groundwater Level GW Elevation Figure 3-6: Dania Beach Groundwater Level Figure 3-7 provides a graphical representation of this comparison between baseflow and infiltration and groundwater elevations. Figure 3-8 provides a comparison of the baseflow+infiltration values, groundwater elevations, and rainfall. Infiltration amounts were calculated based on the assumption, which was graphically demonstrated in Figure 3-8, that infiltration into sanitary sewer lines fluctuates based on groundwater depth, which can vary based on rainfall events. 31

43 Jan-06 May-06 Sep-06 Jan-07 May-07 Sep-07 Jan-08 May-08 Sep-08 Jan-09 May-09 Sep-09 Jan-10 May-10 Sep-10 Jan-11 May-11 Sep-11 Jan-12 May-12 Sep-12 Jan-13 May-13 Flow (MGD) GW Elevation Rainfall (in) Jan-06 May-06 Sep-06 Jan-07 May-07 Sep-07 Jan-08 May-08 Sep-08 Jan-09 May-09 Sep-09 Jan-10 May-10 Sep-10 Jan-11 May-11 Sep-11 Jan-12 May-12 Sep-12 Jan-13 May-13 Flow (MGD) GW Elevation (ft) Baseflow and Infiltration vs. GW Elevation Baseflow and Infiltration Groundwater Level Figure 3-7: Dania Beach Baseflow + Infiltration vs. Groundwater Elevations Baseflow and Infiltration vs. GW Elevation and Rainfall Baseflow and Infiltration Groundwater Level Rainfall Figure 3-8: Dania Beach Baseflow + Infiltration vs. Groundwater Elevation and Rainfall 32

44 A statistical analysis was completed to compare the baseflow + infiltration, groundwater level and rainfall values to determine the correlation between the values in order to mathematically determine whether the values are related. In order to complete the statistical analysis, the Pearson product-moment correlation was selected, because it would provide a measure of the degree of linear dependence between the variables. Pearson values range between +1 and -1, where +1 and -1 are defined as having a total correlation and 0 is defined as having no correlation. The Pearson product-moment correlation coefficient is a measure of the strength of a linear association between two variables and is denoted by the letter r. However, programs are available that allow users to calculate the coefficient using multiple variables by using the MCORREL function in EXCEL. The Pearson product-moment correlation coefficient was calculated for the baseflow+infiltration, groundwater level and rainfall values and was determined to be 0.7. According to Dancey and Reidy (2014) a value between 0.7 and 0.9 represents a strong correlation. Consequently, it was determined that there was a strong relationship between rainfall, groundwater elevations, and baseflow+infiltration. The period shown in Figure 3-7 is relevant because inflow correction was undertaken between the years 2006 and 2009, but infiltration correction work was not. This provides a baseline approximation of the yearly increase in infiltration that can be expected. The infiltration calculation conducted in this study is based on the assumption that the increase in baseflow between the two years is negligible, which leaves any increase or decrease between the baseflow + infiltration values between the two years to be a direct result of infiltration. Based on this assumption, the percent decrease or increase in the infiltration was calculated as the percent difference between the two slopes of the lines. Consequently, it was calculated that the percent increase in 33

45 Baseflow and Infiltration (MGD) infiltration from 2006 to 2009 in Dania Beach was 27.7%, which results in a percent increase of 9.2% per year. This yearly percent increase will be used in the cost analysis, which is presented later in this paper, and will be used to approximate the cost savings accumulated by each construction technique. Following initial activities, infiltration reduction activities were completed, which included CCTV analysis of the system and lining pipes in areas where broken or cracked pipes were observed. Figure 3-9 provides a graphical representation between the groundwater levels and baseflow and infiltration values. Figure 3-10 provides a trendline to values which were provided in Figure 3-9. From the figure it can be seen that as groundwater gets closer to the surface the baseflow+infiltration values increase, which was to be expected Baseflow and Infiltration (MGD) vs. Groundwater Levels (ft) Groundwater Levels (ft) Figure 3-9: Baseflow and Infiltration vs. Groundwater Levels 34