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HomeMy WebLinkAbout; Public Works Service Plan Sanitation; Public Works Service Plan Sanitation 2003/2004; 2004-07-26Sanitation Operations Division Service Plan Proposal Activity Description Sanitation Operations maintains 18 pump stations that pump wastewater uphill from one location of the gravity system to another. The gravity system is the portion of the sewer system where the wastewater flows without assistance. Each station has a wet well that the wastewater flows into prior to being pumped out of the station. The wet wells keep a supply of water in the system so that the pumps don't go dry, which would burn out the pumps. These wet wells need to be cleaned periodically, because the grease, debris and sand from the wastewater can settle at the bottoms. If there is too much buildup, the material can get into the pumps, clog them and cause them to fail. Too much grease can also block the incoming line, causing the wastewater to back up into the system and possibly creating sewage spills. Grease can also create unpleasant odors, which affect the public. The current process for cleaning the wet wells is to stop the wastewater from flowing in, shut down the pumps, and then use the vactor to pump out the water so that the wells can be cleaned. Once the water is out, the method for cleaning varies depending on the size of the wet well and the design. Some of the wet wells can be vacuumed and power washed. Others require a confined entry, which involves 3-6 people. Someone has to suit up and enter the wet well to sweep the debris out to where it can be vacuumed, and there is a safety procedure that the crew has to follow. Since Sanitation Operations only has four maintenance workers, cleaning wet wells requires that they borrow maintenance workers from other crews when a confined entry is required. When the opening to the wet well is closed, the wastewater builds up into the sewer system. The wastewater can only be allowed to build up in the system for a certain amount of time (varies by station depending on the flow) before it will start coming out in other places. Therefore, the amount of time available for cleaning depends on how fast the wastewater can be vacuumed out. The wet wells should be cleaned between one and four times a year, depending on the station. Problem Description Sanitation Operations is not able to clean the wet wells during the day at two of the largest pump stations - Home Plant and Fox's, and is predicting that they wilt soon have a problem cleaning the Poinsettia wet well during the day as more units are added in that area and the flow to the station increases (right now they can clean during the day during periods of low flow). The reason for the difficulty is that the vactor can only pump about 80-100 gallons per minute, so during the day when the flow is higher, they can't pump the water out fast enough to allow them to clean the wet wells before they have to let the flow back in. Additionally, at the Foxes station, the opening at the top of the Page 1 of 4 Updated 7/26/04 station is not over the opening at the bottom where they access the wet well for cleaning. The vactor hose is too rigid to bend between the two openings, even when flexible tubing is used, so it can't be used alone to pump the water out. Because the wet well is so deep (about 29'), it is difficult to find a pump that has effective suction at that depth. A submersible pump is needed to pump the water up to the vactor. We don't currently have one that can do that and would need to rent one. The wet wells at Home Plant and Fox's can be cleaned between 1am and Sam when the flow is lower, but it requires 6 people for each location because of the confined entry procedures and this is extremely difficult to schedule. It is also hard on the employees. Additionally, even at periods of low flow, it still takes 30-35 minutes to pump out the wet wells, which does not leave much time for a thorough cleaning. Because of the difficulties involved in cleaning these wet wells, the crew ends up skimming the debris off of the top or sweeping it around inside the wet well to break it up and prevent if from damaging the pumps, instead of being able to perform the necessary cleaning. At the Poinsettia Station, as the flow increases, there will not be enough time to empty the water out and clean the wet well during the day. Again, this is because of the rate at which the vactor can pump. Another problem Sanitation Operations has identified with the larger stations is that in the event that there is an emergency and the pumps fail, the division does not have the equipment necessary to bypass the station and keep the wastewater flowing. Fox's, Batiquitos and Poinsettia have an emergency bypass, which would allow them to hook up a portable pump. This would allow the wastewater to keep pumping and "bypass" the station. The Home Plant station does not have bypass capabilities, but a portable pump could be used to pump the water out of the wet well and up to the next part of the gravity system. There has only been one emergency in the past decade that required that a large pump be rented, but Sanitation Operations has concern about what would happen if a disaster would strike as it can be difficult to quickly rent pumps this large. Ideally, Sanitation Operations would like to be able to clean all the wet wells during the day, and eliminate the need for confined entry if possible. This would require a pump that could pump at least 650-800 gallons per minute (GPM), at 30' of suction. The crew could then pump out all of the wastewater and debris, and power wash the inside without having to enter the bottom part of the wet well. They would also like to be better prepared in case of emergency and have the capability to bypass a station and keep the wastewater flowing. This would require a large pump that can pump 1000-1500 (GPM) and can pump that much water uphill 190 feet (the longest distance between a pump station and the next location of the gravity line (this is called the "lift")). Page 2 of 4 Updated 7/26/04 Idea/Recommendation Sanitation Operations' original idea was to purchase a portable diesel pump that can pump 1000-1500GPM at 190 feet of lift. They could attach the portable pump to the force main at Fox's and Poinsettia and use it to bypass the pump station. This would allow the wastewaterto keep flowing and not have to back up into the system during the cleaning. This would remove the time constraint on cleaning that is imposed by the amount of time the wastewater can be allowed to back up into the system and give Sanitation Operations the time needed to vacuum out the wet well and scrape the grease from the walls. At Home Plant, they could use the pump to quickly pump out the water, increasing the time they have to clean the wet well. Both of these could be accomplished during the day, even during periods of high flow. These pumps might also be able to pump out debris as well as water, allowing the crew to clean the wet well by power washing and eliminating the need for a confined entry. The pump could be used for other things too. It could be used for emergency bypasses in our system in case of a pump failure. This would result in a quicker response time than if a pump was rented and less sewage would therefore be spilled. Since sewage spills have an impact on the health and safety of the public and the environment, minimizing sewage spills is important. The pump could also be used to train the crew in emergency preparedness. However, once the analysis was done, it was apparent that Sanitation Operations did not have enough data to justify the purchase of a new pump at this time. The cost of a pump big enough to be used for bypass purposes is $64,000, and more research needs to be done to determine whether purchasing a pump is the best option, and what size/type of pump would be needed. Sanitation Operations has revised their idea and is now proposing to do a pilot program to determine the best way to clean the three wet wells mentioned above, and also to evaluate what the best option is for being prepared for an emergency. Pilot Program The pilot program for wet well cleaning would be set up to evaluate the possible ways to clean the wet wells at Fox's, Home Plant and Poinsettia pump stations as well as to look at emergency needs and solutions. This would include looking at contracting, renting vs. purchasing, and different types of equipment. The group has identified three areas that need to be evaluated: 1. Contracting vs. In-house. Research will be done to identify possible contractors and get a courtesy quote. Preliminary research was done during the FY 03-04 Service Plan and it proved difficult to find a company that had the capability to clean the three wet wells because of their depth. A wider search needs to be Page 3 of 4 Updated 7/26/04 done, and the Division is planning to contact some other agencies to find out how they maintain their wet wells. Costs for both contracting and performing the work in house need to be gathered and compared. Impacts on the Maintenance Management program would also need to be evaluated. 2. Equipment. One of the difficulties in trying to justify purchasing a pump was that the group was unclear on what size and type of pump would be best suited for their needs, particularly because each wet well is different and has different requirements for how the cleaning can be done. Also, cleaning during the day when the flow is higher presents different challenges than cleaning at night when the flow is lower. The crew is proposing to schedule wet well cleaning twice during FY 04-05. They are planning to attempt the cleaning during the day, and will rent different equipment each time. The current plan is to rent a smaller, submersible pump for one cleaning, and then rent a larger, truck mounted portable pump (that can be used to bypass the station) for the second cleaning. This should allow the crew to determine which size and type of pump best meets their needs. They will also compare the costs of renting the pumps to purchasing them and decide which would be a better option given the amount of time they would expect to use them. 3. Emergencies. One of the concerns Sanitation Operations has is that if there is a disaster and one of the larger pump stations becomes unavailable, they don't have a pump large enough to use to bypass the station. Currently, it is assumed that if there is an emergency, a pump could be rented until the pump station is operational again. That is probably a reasonable assumption for the pump stations that have lower flow and a shorter distance/incline to pump the wastewater. Smaller pumps are easier to find and can be rented and picked up with short notice. However, the larger pump stations handle more wastewater and pump it farther (Batiquitos has approximately 150' of lift, and Poinsettia has approximately 190') and the pumps that are large enough are more difficult to find and typically have to be scheduled in advance so they may not be readily available if disaster strikes. Sanitation Operations needs to determine what would be needed in an emergency and what the options are for meeting this need. Conclusion During the FY 03-04 Service Plan, Sanitation Operations identified some problems with wet well cleaning and with their ability to respond to emergencies if a pump station goes down. They identified some possible alternatives and did some research into their options, including contracting and different types of equipment, and concluded that they need more information to make a recommendation as to the best way to solve the problems. Therefore, they will be conducting a pilot program in FY 04-05 to try to gather the information needed to make a decision. Page 4 of 4 Updated 7/26/04