These are times of constant change and technology advancement. Improvements in computers, data communications and science and engineering affect every aspect of the way we live, work and survive. They have also influenced and changed the way many routine and specialty tasks are performed. However, until recently there has been one area in wastewater management that has seen very little change. This area is the way sewer systems are monitored and managed.
Potable water distribution systems have enjoyed SCADA-type automation over the last ten years. The same claim cannot be made for sewer systems. However, the same type of information is now needed for sewers, and system operators are beginning to ask the serious questions to get this information.
Reasons for Change
The basic reason for this information quest and general soul searching of collection system management techniques is associated with the modification of general maintenance activities. Most sewer systems are out of the way and out of sight. For this reason, they tend to get as little attention as possible. Therefore, reactive management and other complaint-driven techniques are generally the main forces used to keep them running.
Unfortunately, these are the same techniques used twenty or so years ago. During this earlier period, it was politically correct to direct any modernization or automation projects into more visible areas, like potable water. The only time a collection system came to the forefront was when a sewer overflowed into a politician's basement or an environmentalist's front lawn, or extensive damage was wreaked on general public property resulting in overbearing costs to the municipality. These disasters generally draw attention and action, but offer little practical information to support the solutions.
However, first and second line maintenance personnel who work the system daily can offer intuitive and field experience. The problem is that it was difficult then and still is today to get this information into a format for general use. Therefore, a war would break out between the engineers with theory, system operators with practical and intuitive experience and the political people who do not want the problem in the first place. It is the lack of hard data that has made these arguments difficult. With everyone's good intentions being brought to the table, deficiencies in the facts (data) cause the best intended programs to get scuttled. Therefore, funds over the years were directed to other projects and away from general sewer infrastructure improvements.
Another reason for this change is the relative cost to process sewage. Since 1990, there have been tremendous price increases in the aggregate cost to treat and dispose of wastewater and its by-products. In the case of inter-township connections, this cost can be a serious point of litigation especially where population-based or estimate flows are determined for billing. There appears to be no real short or long term solution without the proper data to support and justify the cost increases.
General contracting of services is another significant reason for evaluating the sewer infrastructure and implementing strategic management tools. The ability to determine baseline financial operating conditions is essential in bid evaluations or simply determining if the in-house operation is cost-effective. If a municipal or operating agency can initially lower its internal costs prior to contracting, it will ultimately lower the price of the general contract. This makes the service bids more competitive and provides more return for the ratepayers.
Therefore, the concept of Infrastructure Management Systems is rapidly being embraced as a way of providing a holistic approach to the care and planning of a sewer infrastructure system. It represents a way of modernizing maintenance, justifying programs, evaluating contract costs and providing facts for all parties involved. In order to understand the system and solution, one must understand the problems associated with the cause and effects a sewer infrastructure has on its attached and supported entities and have these facts backed up with hard data as proof.
Picture yourself at a position in an organization that is involved with the sewer infrastructure. You may be the manager, operator or engineer who is responsible for the continuance of a POTW. Everyone agrees that the actions of the sewers affect the actions within the plant. The municipal agencies or utility authority have invested heavily in modernizing the process operation with computers, PLCs, remote operators, smart transmitters and sensors, process software and training for the plant people. The plant personnel know exactly what is going on in the facility, or they can touch a button and find out. However, there are still questions they cannot answer.
- Why are there flow surges at the influent?
- Why can't the plant take storm flow at high tides during the spring and fall?
- Why do the plant flows drop when there is no rain for long periods?
- Why are there flooding complaints when pumps are slowed or gates are dipped to 50 percent during prolonged dry spells?
There are calls to the Sewer Maintenance personnel who can generally not provide the necessary answers to these events. Therefore, the occurrences remain unexplained. You know exactly the plant response for conditions, but you cannot predict when the condition will occur.
Did you forget something? No one forgot anything. The reality is that weather events are basically unpredictable, therefore you cannot know where the problem will occur. All of these issues are natural occurrences beyond which the Sewer Maintenance personnel can have answers for under the current constraints. Here, nature has full control of the event. These circumstances can only be monitored, and the reaction of the collector system can be followed based on the natural actions of the system response.
The Philadelphia Water Department Operations Engineering group realized some of these issues back in 1989, when they established and tested a Maintenance Dispatch System using sewer monitoring information. This successful project raised many potential uses for the information as it provided answers for the short term problems1. The success of using the data to investigate sewers provided the justification to get $3.5 million approved for expansion of the original monitoring network and a total of $7 million to interface all other components of the collector systems as well.
As Philadelphia forges ahead, many other utility operators are struggling to determine the best way to begin such a monitoring program. With very few case histories to learn from, it is difficult to form a basis to build like systems. Until electronic eyes are placed in the infrastructure, the response of the system will remain a mystery and the problems noted earlier will persist.
Are Sewers Really That Mysterious?
The evolutionary process is now catching up to the sewer infrastructure. The best run wastewater treatment facility falls short when it does not understand the system response of the sewer system that conveys the wastewater to it. The best planned, best maintained facility cannot possibly know what is going on outside the plant gates and within the sewer system by intuition or desktop modeling. There are simply too many variables that are caused by external events2. These variables are the mystery of the sewer system. They are solved by providing the POTWs with good, reliable information through a total infrastructure management system in a format easily understood by anyone.
Proactive agencies have determined that there must be relatively easy ways for information to be brought from the sewers to an administrator's desk without an extensive time loss or degradation of the data. The ability to produce timely information about actions and reactions within the sewer system for evaluation and presentation is in its infancy. In 1988, the Philadelphia Water Department discovered that there were no large scale infrastructure management systems available after installation of 54 sewer level meters. Therefore, in 1989 they developed their own system as a prototype. This system became a great operational success and led to the general expansion of the program. Other cities have attempted the same endeavor with mixed results. This was due to the lack of products on the market capable of providing this service. Therefore, infrastructure management systems need to be custom made. The general dilemmas that exist for low bid contracts and "or equal" products make custom fabrication of these systems a nightmare even for seasoned professionals.
However, the age of PC-based systems and commitments from various manufacturers can ease this frustration. Specifications can now be written around certain products, or entire systems can be procured and implemented from one source. Inexpensive and less complex PC networking can also provide this information across the enterprise with little difficulty.
The Small System
The author makes an arbitrary split between communities less than and greater than 100,000 people. An arbitrary split is also made at the 36-inch pipe diameter level. If your community falls below these two criteria, this discussion classifies it as a small community. These systems have good choices at very reasonable costs with the proliferation of PC-based systems. Basic monitoring programs can be set up with relatively inexpensive dataloggers, level sensors, waterproof enclosures and the software as provided by the datalogger manufacturer. Most manufacturers of dataloggers provide an interrogation package that will provide reasonable results. If flow is desired as a parameter, the meter manufacturers generally have off-the-shelf software to perform this purpose. These packages generally have scheduling functions that will call the sites automatically and poll for the data. Some packages even have basic alarming functions that can be implemented for determining problems as they happen.
If a more sophisticated system is desired, the basic datalogging package probably will not be the answer. Process software manufacturers have seen this opportunity and are providing drivers for the datalogging products in order to present a greater functionality to the basic system.
There also is the option of finding a full service provider for a turn key solution. There are several small, reputable providers of these services available along with the large providers. The choice is based strictly on the confines and needs of the community.
All of this requires a complete understanding of the sewer infrastructure system by the purchaser of these products. Any approach or provider will fail (or appear to fail) unless there is a full commitment by the infrastructure management team to fully support the program and understand its goals.
The Large System
Like anything large, these infrastructure systems are logistical nightmares unless properly managed and documented. Just as with the small systems, targets and goals need to be laid out. However, large systems generally have more lofty goals that sometimes are unrealistic. They also tend to be completely custom based on the design, size, complexity and physical age of the sewer infrastructure. Fortunately, there are several options for large scale systems that are at least approximately 70 percent configured. It would certainly behoove system operators not to allow a general contractor or local integrators make the final determination for internal equipment compatibility. Let this responsibility reside with the equipment manufacturer for maximum success.
Large scale systems also may have the problem of large pipes. Flows, conditions and installation problems make these types of systems formidable to install, but not impossible. Here, knowledge of your system is crucial for knowing what equipment is applicable and which equipment is not. Know your system as well as you can and the good and applicable equipment will be apparent.
The investment in these systems requires a return on the investment. If properly installed and used, the benefits listed in Table 1 can be obtained. There are many other specific uses for monitored information. Those shown in the table represent only a few of the many potential uses of the derived information. As more systems are installed, the application of the information will expand to fill the agency's need.
- Day, T., The Use of Sewer Monitoring Information for Operations and Maintenance, EPA Conference on Sanitary Sewer Overflows, April 1995.
- A. R. Drinkwater, et. al., A Guide to Short Term Flow Surveys of Sewer System, WRc Engineering, 1987 p. 7-9.
About the Author:
Thomas J. Day is an electrical engineering specialist with the Treatment Headquarters Division of the Philadelphia Water Department.
Table 1: Sewer Infrastructure Benefits
- Overall sewer system response to any event or lack of events
- Specific responses to particular events or other occurrences of interest.
- Hydraulic effects from pump stations and POTW influent stations.
- Hydraulic response information for the POTW to assist in tuning the process.
- Instant or near real-time information concerning custody transfer or other revenue-generation stations.
- Verification of localized flooding based on citizen complaints.
- Calibration information for computerized hydraulic models.
- Legal information in a suitable format for litigation or other courtroom analysis.
- Maintenance information for more effective deployment of street forces.
- Engineering information for short and long term planning or zoning requirement.
- Compliance information for regulatory agencies and other enforcement bodies.