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Infiltration and inflow (I&I) caused many systems over the winter and through the spring runoff to experience extreme peaks in sewer flows to wastewater reclamation facilities and disposal fields. Rainfall and snow melt can enter wastewater collection systems as inflow, meaning that it comes in through service laterals from items such as sump pumps, downspouts and yard drains or flows in through manhole covers or catch basins. Infiltration, on the other hand, is caused by the increased precipitation and runoff causing a rise in groundwater level and then the groundwater leaking into the collection system through defective pipes, pipe joints, connections and other subsurface infrastructure such as manholes, wet wells, treatment vaults and equalization basins. Infiltration can occur not just from a rise in groundwater level, but also by way of rainfall entering the collection system via rapid percolation of the soils and shallow infiltration around manholes.
Although modern construction, inspection and testing of collection system infrastructure significantly reduces I&I in new systems, operators and utilities have to recognize that I&I can be present in any system. Typical wastewater collection system with modern construction materials averages infiltration through gasketed joints of 25 Gal/Day/Inch Diameter/Mile (Uni-Bell Handbook of PVC Pipe). For 8” sewer pipe, that is 38 gallons per day (GPD)/1,000 feet of pipe and for 10” sewer, 47 GPD/1,000 feet of pipe. Older infrastructure with sewer collection systems in disrepair can experience infiltration on the order of five to ten times or more greater than this average.
Inflow is usually reduced through modern construction practices. Through building permit reviews and homeowner education, major reductions in the number of connections from rainfall areas to the collection system can be seen. For inflow through public infrastructure, the major sources are not present in modern sewer collection system design, such as storm sewer catch basins connected to sewer manholes. Also, when manholes are placed in potentially flooded areas, there is an abundance of gasketed manhole cover products on the market to keep that rainwater out.
What to do next? For systems throughout our region which saw major I&I issues throughout the winter and spring, it is best to start addressing the problem with some common sense approaches. Completing visual inspections of the collection system and addressing any known I&I problems first, is the best place to start. Operators often know the unique items in their system which may be the biggest concern for I&I. Next, depending on the size of the system, working with homeowners to educate them on the problems the wastewater system faces with I&I and empower them to work to independently eliminate sources of inflow on their properties.
With the easy problems tackled, wastewater utilities and operators should then look to implement regular inspections of the subsurface infrastructure throughout the system. Today this is accomplished by use of closed circuit television (CCTV) inspection of gravity lines. Video inspection can identify major failures in pipe connections, pipe collapse, poor lateral connections and areas of excessive groundwater entering the system. Utilities should have regular video inspection completed of the entire collection system and these types of inspections are typically required by State discharge permits. Additional emerging technologies for pipe inspection include pipe penetrating radar, light detection and ranging (LIDAR) scanning and sonar. These emerging technologies provide detailed profiles and imagery of pipe condition; they do not have the ability to stop and observe the flows in the pipe as available with video, however multiple images are blended to show flow moving while the sensors travel through the pipe. LIDAR types of pipe scans do provide more details of the pipe, such as roundness and other slight pipe deflections that are sometimes difficult to see with CCTV.
After inspections are completed of the system, utilities and operators must begin the difficult task of allocating resources to address deficiencies. Since these types of repairs are typically shouldered by existing rate payers, finding resources can difficult. System operators must be diligent in bringing these issues to their customers and managing bodies because leaving the problem go for too long can result in fines and orders from the State to address the problems; which is the last place any utility wants to find itself.
Some rainwater gets to the treatment plant … who cares? Modern wastewater reclamation facilities are extremely sensitive biological habitats for good bugs that love to digest our wastewater and turn it into methane gas that can be exhausted and sludge that we can dry and haul to landfills. When excessive amounts of rainwater is sent to our treatment plants, all of these good bugs lose their carbon (food) source and get washed away. When the bugs get washed away, the plant cannot properly treat the regular wastewater flows that come back in high concentration following the storm event or temporary groundwater rise. A wastewater reclamation facility which experiences events like this may be required to divert large flows to emergency holding ponds (if available) or risk violating discharge permit limitations which can result in fines and orders from the State.
As the weather gets warmer, and we slowly forget about the issues that plagued our wastewater systems with high I&I over the winter and spring, be diligent and start addressing the problems now. Just because I&I may not be a problem today, we know it can take just one wet season to turn our collection system world upside down.
No one appreciates precipitation, especially in the form of snow, more than Nevadans. We love to ski on it, swim in it, boat on it, fish in it and water our yards with it. Most importantly, we understand, more than most, that is a precious commodity. This year the snow gods have blessed us with a tremendous bounty! 706 inches have fallen to date at our own Mt. Rose Ski Resort extending our season until Memorial Day – giving us the unique opportunity to both ski and boat in the same weekend. Historically, 1938 brought us our biggest snowfall at 819 inches recorded at Donner Pass by the Central Pacific Railroad. We most likely won’t catch up to that, but it is snowing as I write this.
Lake Tahoe’s water level sits at 6,226.81 feet, which is almost five feet above where it sat the last two years on this date. The LA Times reported that just under one foot or 33.6 billion gallons of water was added to the lake in the first week of January alone this year. An additional five feet then would equal approximately 135 billion gallons more water stored in the lake than in 2015 and 2016 – not accounting for the water being let out into the Truckee River.
Mountain snowpack is Mother Nature’s reservoir system. On average across the Sierra Nevada range, there is 164% of the April 1st average water content in the current snowpack. So far, Mother Nature has been doing an amazing job of completely eliminating the drought without a whole lot of damage – snow, then a little rain, warming up to just flood a little bit, more snow, a little more rain, warming, cooling. If this pattern continues, not only will the man-made reservoirs be full, but the aquifers in California may completely bounce back creating a healthy snowpack to surface water to ground water ratio. If not, and it gets too warm too fast, our precious snowpack reserve could be wasted. Either way, whether we get lucky or not, just a heads up to the State planners out there…make sure our water infrastructure is up to the task. Catch it when we have it; so we can save it when we don’t.
Since the passing of our founder, George Shaw and the creation of the scholarship in his name, we feel honored to announce that, to date, the George ShawScholarship has been awarded to five University of Nevada, Reno engineering students.
Congratulations to Francisco and Aaron
We congratulate the two most recent recipients; Francisco Ramirez and Aaron Smith and thank them for their kind notes of appreciation. Francisco is a graduate of Sparks High School and is majoring in civil engineering and minoring in renewable energy. Aaron is a graduate of Douglas HighSchool in Minden, Nevada and is majoring in environmental engineering.
Our scholarship was established as an endowment and exists in perpetuity. It is available each academic year for a student who is a Nevada resident enrolled at the University of Nevada, Reno in the field of civil or environmental engineering.
The Partners at Shaw Engineering, like George, are UNR Engineering School graduates, born and raised in Nevada. We feel privileged to have the ability and opportunity as individuals and a firm to support the growth and future of the young engineers in our State.
Sliplining Sewers With Cured in Place Pipes: A Cost-Effective Method of Trenchless Rehabilitation for Existing Pipelines
Perhaps the oldest of all trenchless techniques, sliplining involves inserting a new pipe into an existing pipe to repair leaks or restore structural stability. This technique is still used today, however, advanced technologies have enabled companies to use an even more efficient and versatile method.
Cured in place pipe (CIPP) is a resin-saturated, felt tubing that is coated with a permanently bonded layer of polypropylene.
The installation process involves pulling the tubing into the existing pipe and circulating hot water or steam throughout it. This process inflates the tube so that it fits against the existing pipe walls and cures the resin, creating a tight-fitting, corrosion-resistant pipe within a pipe.
Once the pipe is installed, service laterals are restored with a robotic cutting device and a camera inspection is conducted to ensure the new pipe has adhered to the existing pipe correctly.
Using this method can eliminate the need for a complete pipeline bypass and lessen the interruption of traffic in the vicinity. Sliplining an existing sewer pipeline with CIPP technology will also increase flow capacity because the wastewater will move smoothly through the new pipe.
When compared to other methods, sliplining is an efficient, cost-effective solution to sewer pipe rehabilitation. Shaw Engineering has designed and managed CIPP projects. We continue to seek out more cost-saving solutions for our clients every day.
Significant progress was made on the construction of a new lift station in Fallon, when four pieces of heavy concrete were set in place to make what will eventually become the wet well. The wet well will receive all process wastewater from a new dry milk plant.
The wet well is made up of five pieces – four barrel sections and a lid. These four pieces of pre-cast concrete weigh an average of 33 thousand pounds and require a crane to lift and move them into place. In addition to managing the weight of these heavy sections, the construction of this wet well was done below the ground surface making this step in the process difficult to complete.
“One of the most challenging parts of the construction is the underground work, so getting the wet well set was a big step,” said Steve Brigman, P.E. “We have a really high ground water situation at the site, which complicates the construction and makes it difficult to predict conditions at the bottom of the excavation.”
Despite the troubles mother nature presented, the contractor, Resource Development Company in Sparks, Nevada, was able to complete the setting of the wet well on schedule and without any complications.
Once completed, the new triplex pumping station will house three submersible pumps to move the industrial wastewater into the existing sewage treatment plant nearby. The pumps will work to lift the wastewater approximately 40 feet from the lift station to the plant headwork, increasing the average daily amount of wastewater intake from 1 million gallons to 1.4 million gallons.
In addition to the lift station there is also a composite sampler station and a Parshall flume vault under construction. The composite sampler will take hourly samples of the wastewater, monitoring the PH and temperature. The Parshall flume vault is an hourglass-shaped open channel system that will work to measure the volume of wastewater that flows into the lift station.
Data monitoring and wastewater sampling will help ensure compliance of the new dry milk plant to strict, regulated standards.
Construction of the Fallon lift station is expected to be completed December, 2013.
Did you know that over ten years ago Shaw Engineering was drawing up the plans to make your kids, and possibly even your summer, the greatest time you’ve ever had? That’s right, the power behind the pumps and the brains behind the waves for your slippery, watery, wet and wild time at Wild Island Family Adventure Park were the intelligent, innovative engineers at our firm. Now before you jump, or slide, to conclusions let me tell you a little bit about what we did to make this park so fun.
Have you ever wondered how all that water gets to the top of the slides after you came rushing down to the bottom with it? Have you ever wondered how the lazy river gets it’s power so you can, in fact, be lazy?
There is more to it than what the eye can see. There is more than just the fun colors and cool slide design. It involves calculations, inspections and safety regulations. It involves pumps and filters and drains that all work together to create the ten-second water slide that cools you down in the mid summer months.
The entire park is set up on a water sharing system. The main water source for all of the slides is the lazy river. There is a pump system underneath the concrete that sucks the water into pipes to be transported to each slide. Hydraulic pumps then move the water up to the top of the slide to be used for everyone’s entertainment. Once the water reaches the bottom of the slide, it is then pulled into a filtration system to be cleaned and decontaminated. When this process is over, water is moved back into the lazy river to start the cycle again. But that isn’t all that is going on; there are things happening behind the scenes as well.
In the midst of all these pumps, pipes and slides are drains to help control the flow of water. These drains are built and installed in accordance to safety regulations to ensure the safety of everyone who enters the park. This part of the system is on the inside of the pools and is visible to the public.
You see, the intelligent minds here at Shaw Engineering didn’t design the most exciting part of the water park but they do design the parts that make it all work. Without water, you just couldn’t have a water park.
Now, I will leave you with an interesting and fun fact that can serve as an example of the power behind the pumps Shaw Engineering designs. The pools, rivers and slides in the park can use as much as 2000 gallons of water per minute. It’s a good thing our engineers designed a water system to recycle and reuse the resources!