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infiltration


We have a lot of conversations about the impact of people on the ecosystem, the cost to reuse wastewater, competing water demands, water limited areas etc.  All are valid issues to raise and since people control the outcomes in all of these situations, we need to be aware of consequences.  So while Florida is a leader is wastewater reuse for irrigation, it is kinda cool to see what happens when we think outside the box.  The Wakodahatchee wetland is a sewer treatment area created by Palm Beach County Utilities a number of years ago.  This is reclaimed quality water placed into an area specifically designed to allow for nutrient removal and aquifer recharge.  The County placed mosquitofish in the water to reduce mosquitos. Bluegills found there way.  So did the turtles and alligators.  But this is THE bird watching site in southern Palm Beach County.  And it is located between the wastewater plant and a neighborhood.  You can’t get parking easily.  This is an example where looking at the bigger picture seems to have a positive effect on the community and the ecosystem as well.  The birds don’t look unhappy.

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Happy 91st Pop! It’s been 2.5 years since you were last with us, but it’s funny how many things popped (no pun intended) up today that connect to you. Clearly you are still watching what goes on. We had a family summer cottage located 8 miles east of Grayling Michigan. So today I came across an old book entitled the Old AuSable written in 1963 by Hazen Miller, a U of M doctor (you were a U of M aerospace engineer) who wrote about the area back in the day (1870s to 1920s), just before your father purchased property along the AuSable River. It mentions the great grandfather of my dad’s summer playmates, one of whom just died last summer - his obit came up in my email today. Reminded me of many places I went as a kid. Funny it also reminded me of some of the old “names” that are now being lost to time, but created what exists today. It also helped with some perspective on a proposal I have been working on regarding water supplies and quality. The grayling fish disappeared by 1912 as a result of hanged on water quality (warming and silt), human impacts of logging on the fish and the introduction of other species. My proposal looks at impacts of human activity on SE Florida, especially as it relates to sea level rise and the need to capture additional soil storage capacity through infiltration trenches. The water cannot be discharged to tide due to Human-induced nutrient and roadway pollutants of the potential exists to impact fish populations. So we are looking at moving the infiltrated water to water plants in the future. We can treat the water there, cost effectively while solving another problem – diminishing water supplies for urban populations. This would diminish our need to deal with desalination and the disposal of concentrate, another proposal. Funny how sometimes it all comes together….Good times back then and up there. Making progress today. Thanks and keep on watching out for us!!


A recent Rolling Stone article outlines a potentially dismal future for south Florida.  I was quoted in the article and give the author a bunch of information.  It is hard to write articles that “pop” in the popular press while conveying facts and figures.  But I would suggest that the future is not quite as dismal as the article depicts.  The sea level rise has been ongoing for at least 140 years as indicated by the Key West tidal station, the longest running tidal gauge in the world, but the amount has been 9 inches since 1920.  True it appears that the sea level rise may be accelerating as a result of warming temperatures in the atmosphere that causes the oceans to expend, plus the loss of ice that runs off from glaciers, but 3 feet by 2100 seems the average or maybe the high average.  That is unlikely to inundate all of south Florida, but keeping the water table low will be a challenge.  I suggest that the challenge can be met and accomplish two goals.  In low lying areas the impact of sea level rise is really manifested as increasing groundwater tables.  An increased groundwater table means less soil storage capacity, which means smaller rainstorms will cause flooding.  The increased flooding is already creating a demand by residents for solutions from local public officials.  We have used exfiltration trenches (French drains) for many years, but increasing water tables will mean many of these systems will not function as they may be currently.  But what if we reverse the concept?  Instead of exfiltration, what if we allowed the water to infiltrate the pipe and go to a central wet well, and then pump the water out of the wet well?  I further suggest that the dumping large quantities of groundwater to the ocean or canals may not be permittable as a result of high nutrients, so what if this water is instead pumped to a water plant as a raw water supply?  Wouldn’t that solve two problems at once? Lots of excess fresh water supplies in an era where there are significant limitations in fresh water supplies?  Just thinking….. 

 

 


The concept of horizontal wells arises from riverbank filtration concepts.  Riverbank filtration has been practiced for nearly 200 year in Europe, where the concept was to remove debris form polluted waters by drawing through the banks of rivers.  Much of the concepts for groundwater flow are related to the filtration ability of water to move through a porous media.  The concept was to dig trenches along the river and draw water from the trenches as opposed to the polluted rivers.  The concept worked relatively well.  The result is an abundant, dependable supply of high-quality water with a constant temperature, low turbidity, and low levels of undesirable constituents such as viruses and bacteria. Riverbank filtration also provides an additional barrier to reduce precursors that might form disinfection byproducts during treatment.

Now let’s look at this from another perspective, and we’ll pick on southeast Florida as is provides a great case study.  Sea level rise will inundate coastal property, both via coastal flooding and from a rise in groundwater. Since most stormwater drainage depends on gravity flow, drainage capacity will suffer as sea level rises reducing the head differential between interior surface waters and tide. Saltwater intrusion will be exacerbated. Furthermore, reduced soil storage capacity, groundwater flow and stormwater drainage capacity will contribute to increased flooding during heavy rain events in low-lying areas.  In low lying areas, current practices like exfiltration trenches will become impractical, as will dry retention will become wet retention.

Stormwater utilities will be faced with dramatic, currently unanticipated increases in capital expenditures and operating costs, and time will be needed for planning, design, securing permits and compliance. Additional local pumping stations on secondary canals will be needed to supplant the storm drainage system in order to prevent unacceptable ponding. Design capacities of these stations will depend on local rain patterns, drainage basin size and secondary canal system design.  Many will operate continuously, which means ongoing operations will increase substantially. Hundreds of pumping stations may be needed in some communities.

Permits will be a major challenge due to contaminants in the runoff as regulated by MS 4 Stormwater permits, and the inability to treat this water under the current structure. The cost and energy required for stormwater treatment would be a major concern going forward. But what if we sent this continuous flow to water plants as raw water?  All of a sudden we have a solution to two problems – stormwater and raw water supplies.  How often do you see a 2 for 1 solution?


Talk Radio discussion

Hi All.

This is a radio show I did this week.  One of 4 I have scheduled.  It talks about me and my company, outlook, thoughts.  Take a listen.  Let me know what you think!

Fred


In our prior blog discussions the theme has been leadership.  Vision is needed from leaders.  In the water industry that vision has to do with sustainability in light of competing interests for water supplies, completion for funds, maintaining infrastructure and communicating the importance of water to customers.  The need to fully to optimize management of water resources has been identified.  The argument goes like this.  Changes to the terrestrial surface decrease available recharge to groundwater and increase runoff.  Urbanization increases runoff due to imperviousness from buildings, parking lots, and roads and highways that replace forest or grassland cover, leading to runoff at a faster rate (flooding) and the inability to capture the water as easily.  In rural areas, increased evapotranspiration (ET) is observed in areas with large-scale irrigation, which lowers runoff and alters regional precipitation patterns. At the same time there are four competing sectors for water:  agriculture (40% in the US), power (39% in the US), urban uses (12.7%) and other.  Note the ecosystem is not considered.

New water supplies often have lesser quality than existing supplies, simply because users try to pick the best water that minimizes treatment requirements. But where water supplies and/or water quality is limited, energy demands rise, often to treat that water as well as serve new customers. For many non-industrial communities, the local water and wastewater treatment facilities are among the largest power users in a community.  Confounding the situation is trying to site communities where there is not water because the power industry needs water and the residents will need water.  It is a viscous cycle.  When you have limited water supplies, that means your development should be limited.  Your population and commercial growth cannot exceed the carrying capacity of the water supply, or eventually, you will run out.  Drawing water from more distant place can work for a time, but what is the long-term impact.  Remember the Colorado River no longer meets the ocean.  Likewise the Rio Grande is a trickle when it hits the Gulf of Mexico  As engineers, we can be pretty creative in coming up with ways to transfer water, but few ask if it is a good idea.

Likewise we can come up with solutions to treat water that otherwise could not be drunk, but, that may not always be the best of ideas. Adding to the challenge is that planning by drinking water, wastewater, and electric utilities occurs separately and is not integrated. Both sectors need to manage supplies for changes in demands throughout the year, but because they are planned for and managed separately, their production and use are often at the expense of the natural environment.  Conflicts will inevitably occur because separate planning occurs (for a multitude of reasons, including tradition, regulatory limitations, ease, location, limited organizational resources, governance structure, and mandated requirements). However, as demands for limited water resources continue to grow in places that are water limited, and as pressures on financial resources increase, there are benefits and synergies that can be realized from integrated planning for both water and electric utilities and for their respective stakeholders and communities. The link between energy and water is important – water efficiency can provide a large savings for consumers and the utility.   As a result, there is a need to move toward long-term, integrated processes, in which these resources are recognized as all being interconnected .  Only then can the challenges to fully to optimize management of water resources for all purposes be identified.

Anybody have any good examples out there?


Storms highlight the need to reduce infiltration and inflow into the collection system so as not to overwhelm the piping system causing plant damage or sewage overflows into streets, so much of the focus has been on dealing with removal of infiltration and inflow through televising the sewer system and sealing or lining sections where leaks are noted.  However, many miles of videotape show virtually nothing, so significant money is spent to find “nothing.”  Part of this is because “infiltration” and “inflow” are not the same, and storm events do not highlight infiltration nearly as much inflow.

The manholes and clean-outs are required for access and removal of material that may build up in the piping system and for changes in direction of the pipe.  Manholes are traditionally pre-cast concrete or brick, with brick being the method of choice until the 1960s.  Brick manholes suffer from the same problems as vitrified clay sewer lines – the grout is not waterproof so the grout can leak significant amounts of groundwater.  The manhole cover may not seal perfectly, becoming another source of infiltration.  Pre-cast concrete manholes resolve part this problem, but concrete is not impervious either.  While elastomeric or bituminous seals are placed between successive manhole rings, the concrete is still exposed.  Many utilities will require the exterior of the manholes to have a coal-tar or epoxy covering the exterior which helps to keep water out.

Inflow results form a direct connection between the sewer system and the surface.  The removal or accidental breaking of a cleanout, unsealed manhole covers, laterals on private property, connected gutters or storm ponds, damaged chimneys from paving roads, or cracking of the pipe may be a significant source of inflow to the system.  All are potential sources of inflow which can be identified easily during storm events.  The peaking that correlates with the rainfall is inflow, not infiltration since infiltration is part of the base flow that creeps upward with time.  When operators see peaks, this is not indicative of infiltration which is groundwater.  Think inflow.   Inflow causes peaks in run time on lift station pumps, and create potential overflows at the plant.  The good news is that simple, low tech methods can be used to detect inflow, which should be the precursor to any infiltration investigation.

The following outlines a basic program for inflow detection and correction for any utility system.  The order is important, and pursuing all steps will resolve the majority of issues.  The first step is inspection of all sanitary sewer manholes for damage, leakage or other problems, which while seeming obvious, usually surprises.  The manhole inspection should include documentation of condition, GPS location, and some form of numbering if not currently available.  Most manholes have limited condition issues, but where the bench or walls are in poor conditions, that should be repaired with an impregnating resin.

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 traffic.  The crack between the ring and cover can leak a lot of water.  The intent of the chimney seal is to prevent inflow from the area beneath the rim of the manhole, but above the cone.

The next step is to put dishes into the manholes.  One might think that only manholes in low lying areas get water into them, but surprisingly every manhole dish that is properly installed has water in it.  Hence assume that all manholes leak water between the rim and cover.  Most collection system workers are familiar with dishes at the bottom of the manhole where they are of limited use.  This is because the dish deforms when filled with water or is knocked in when the cover is flipped.  The solution is a deeper dish with reinforcing ribs.  No ribs, don’t use it.  A gasket is required.

Once the manholes are sealed, smoke testing can identify obvious surface connections.  The normal notifications, inspection and documentation will identify broken or missing cleanout caps, surface breaks on public and private property, connection of gutters to the sewer system, and stormwater connections.  All should be documented via photograph, by associated address and public or private location. The public openings at cleanouts can be corrected immediately.  However, if the cleanout is broken, it may indicate mower or vehicle damage, that can occur again.  If missing, the resident may be using the cleanout to drain the yard.  In either case the collection system needs to be protected.  USSI (http://www.elastaseal.com/about_us.html), located in Venice, FL developed a solution, called the LDL plug to correct those commonly broken or commonly opened cleanouts to reduce inflow.

Notices should then be sent to property owners with documentation of the inflow connections to their property.  This is sometimes the most difficult part of the program due to political will, but it is necessary.  This finishes the inflow correction portion of the project, but one more step will help focus efforts for the second “i”.

The final step is a low flow investigation, which is intended to focus on 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:

  • 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 where flow is derived from.  Generally a 2 inch wide bead of water is a limit of “significant” infiltration.

Documentation of all problems and corrections in a report to utility that identifies problem, location and recommended repair.  Identification of sewer system leaks, including those on private property (via location of smoke on private property).

The example in Dania Beach, FL was that the last step indicated that only 15% of the sewer system needed to be televised.  This saved the City almost $1.2 million.  Their total costs is under $1.4 million for all parts of the project, spread over several years and contracts.  Overall the hope is that the inflow and infiltration programs together will save $400,000/yr, a five year payback.  But the key is to insure you get the inflow as well as the infiltration… Otherwise storms will continue to overwhelm plants, creating public health concerns and ruining your reuse program.

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