Combined sewer systems (CSSs) are sewers that carry domestic sewage, stormwater runoff, and industrial rainwater in the same pipe. Ideally, this water combination is taken to a wastewater treatment plant (WWTP), treated, and returned into a nearby waterbody. During dry weather, a combined sewer system will run accordingly, sending all water flow to the WWTP. However, severe or heavy wet weather can cause problems. A CSS manages excess runoff by overflowing it into a combined sewer outfall. These combined sewer outfalls lead to a nearby waterbody, thus causing pollution of the waterbody. This spillover is referred to as a combined sewer overflow (CSO). A depiction of a CSO can be found in the above image.
Some CSO contaminates include, but are not limited to: pathogens, oxygen-consuming pollutants, solids, nutrients, toxins, and floatable matter. These pollutants negatively affect our ecosystem by impacting the water quality thus harming the plant life, fish, and wildlife- ultimately harming humans. Beach closings and shellfish harvesting restrictions can also be attributed to CSOs.
Combined sewer systems were once a common engineering practice in urban areas. Smaller populations permitted CSSs to run as designed, only occasionally discharging untreated waste and toxic materials into the local waterbodies. Over the years, increasing populations and impervious areas have led to the CSO issues we have today. The EPA estimates CSOs are a priority water pollution concern for approximately 860 municipalities across the U.S. Many of these affected communities are located in the Northeast and Great Lakes regions. Some of these areas include Philadelphia, Chester, and Coatesville. Philadelphia and Chester both have combined sewer outfalls that let out into the Delaware River. The Coatesville combined sewer outfalls let out into Brandywine Creek. Philadelphia alone can be accredited for an annual 16 billion gallons of CSO discharge!
The EPA has a control policy for CSOs, published in 1994. This policy aids in guiding communities with CSSs to meet Clean Water Act goals through the National Pollutant Discharge Elimination System (NPDES) permitting program. The EPA has also developed a series of guidance documents that include long-term control measures. CSOs can also be mitigated through the use of Green Stormwater Infrastructure (GSI).
Some states, such as Washington, have greatly diminished their CSO discharge. They were able to reduce their CSO discharge average from 3.3 billion gallons (1988) to less than 1 billion gallons (2009). Hopefully with assistance through NPDES, GSIs, and the reduction of impervious space, the amount of CSOs can be greatly decreased.
You may already know about green roofs, but have you heard of blue roofs? Blue roofs are stormwater management systems located on the building roof that provides temporary storage and the slow release of stormwater. These systems have been found to be beneficial in urban areas, especially areas draining to combined sewer systems. They are usually designed for and installed on flat or mildly sloped roofs, where the systems temporarily detain water on the roof surface using two (2) main methods. The first method is roof check dam system and the second system is tray or rooftop water storage systems, which utilize flow restrictors.
Blue roofs have been found to be less expensive than green roofs and can significantly reduce the building’s cooling cost due to evaporation. In addition, the blue roofs increase the longevity of the roof by protecting them from ultraviolet radiation damage. Blue roofs may also be used as a free source of pressurized water for gardening, flushing toilets, as well as, washing cars. The blue roof technology has been found to be easily combined with green roofs, which adds to the aesthetics of the blue roofs. Finally, the blue technology does not require excavation, which minimizes the need to store excavated material or potential hauling costs.
One of the several potential limitations of the blue roof technology is the coordination of the design to avoid potential ponding around the building’s mechanical systems. Another second limitation is the coordination of the design to provide safe and effective access for maintenance purposes while limiting the ability to step or walk across the blue roof system, which would increase the potential for damage to the system and/or the rooftop. The blue roof system should also be located away from trees to avoid foliage from clogging the system. The potential clogging increased the need for regular inspections, therefore must be highly visible or have the availability to monitored by a permanent video and/or drone video. The additional inspections and maintenance could also increase the long-term costs to maintain the stormwater system. Another limitation is the potential cost of the removal and replacement if the roof is damaged and begins leaking. Some final limitations are the additional material costs and structural design costs to the rooftops due to the increase in loading associated with ponding on the rooftop.
With the varying cost benefits and cost limitations, it is extremely important to perform proper due diligence in determining if this technology would be an overall cost benefit for your project’s proposed use.
Strap on your boots and batten down the hatches – we’ve got another major hurricane on the way. The latest tempest comes in the form of Irma, which has the potential to be one of the most powerful hurricanes ever recorded in the Atlantic. After it has already inundated several Caribbean islands, leaving streets flooded and a wake of destruction, Irma is setting her sights on the contiguous United States – first stop, Florida.
A state of emergency has already been declared in the sunshine state as this category 5 hurricane carries its 175+ mph winds and incalculable amounts of rain toward southern Florida. But predicting exactly where and how strong the hammer will fall is not quite crystal clear. Meteorologists run several models, such as the NAM, European, and GFS, to map the likely path of weather events but they often disagree. Running multiple models is helpful in providing a range of possible outcomes but they can only go so far, as the data used for the modeling is constantly changing. In the case of hurricanes, this makes it tough to figure out how your house will be affected and whether or not it will look like a newly discovered Atlantis. Despite the uncertainty, it is always a good idea to be on the safe side and prepare for the worst. The best way to do this is to incorporate effective stormwater management into the house/building design, but this takes weeks and months and is done during the planning and construction phase of a project. This proactive approach is good in theory but does little for people who rent or had no input into the design of their house. In these cases, measures should be taken to prevent and limit the amount of water that finds its way inside. This is typically achieved with sandbags at doors and other possible ingresses but those are usually in high demand. Even now parts of Florida are so strapped for sandbags that they are only giving out 10 per household. But there are other, more Macgyver-like measures to keep the inside of your house dry (see below).
- Plastic trash bags 1/3 filled with water make good substitutes for sandbags at doorways
- Paint cans or 5-gallon buckets can support and elevate your furniture if you are going to get water in your house
- Use duct tape to seal your garage door to the floor to prevent water intrusion
These options are good preventative measures but you should always heed the warnings and recommendations of local officials when dealing with the potential catastrophe of hurricanes. We all saw what happened with Harvey and no one wants a repeat with Irma. Stay safe and stay dry.
I wanna know…have you ever seen (9 trillion gallons of) the rain?
I felt like titling this blog post “Houston, we have a problem” was insensitive. But now that I’ve brought it up…yeah, Houston, we have a problem (or two). The problems began long before Harvey. Did you know Houston was the 4th largest city in America with about 2.3 million people? And it’s not just large in population – urban sprawl has caused low-density development over a large footprint, so the population isn’t concentrated, it’s a lot of impervious surface over a large area (600 mi2). Houston is also notorious for being laissez-faire about zoning regulations. This, coupled with the fact that the city is flat and the downtown is only 50 feet above sea-level, means the water has nowhere to go but up. So, I guess that’s one positive! Only can go up from here!
Photo Above: We’ve seen terrifying images of inundated roadways, but the Stormwater management system of Houston was allegedly designed to allow freeways to transform into rivers during flooding. The idea being that these makeshift bayous would move water away from local areas.
While some experts argue that the solution to preventing this type of catastrophe is reducing impervious coverage, others believe that approach is a band-aid on a heart attack. Improving water conveyance, decreasing water velocity, adding vegetation, and reclaiming Stormwater are some other design considerations being encouraged in urban areas. A more dogmatic opinion is that areas such as Houston and New Orleans should never have been so heavily developed, to begin with, and that catastrophe was imminent. Although up for debate, climate change produces stronger and unpredictable storms. No matter how proactive we believe we’re being during design, mother nature has a mind of her own.
Hurricane Harvey reminds us of the importance of Stormwater management. It may appear to be an unwarranted cost, but that’s only because it is usually silent. We don’t see it working, so we have trouble understanding its importance. However, with a disaster like this, we’re forced to acknowledge how essential Stormwater management controls are in protecting the rest of our infrastructure. We can’t design our water infrastructure for a 1-million-year storm, and we shouldn’t. But as a community, we can cooperate with the regulations set in place to mitigate the effects of potential natural disasters.
What do YOU think Houston (and other flood prone regions) should do to mitigate widespread catastrophe in the future? Visit the D.L.Howell Facebook page and leave us your comments!
Water is pretty amazing. It is in everything we do from basic cooking and cleaning to generating hydroelectric power. However, this natural resource can be destructive. Excessive amounts of water at one time can cause significant problems to the surrounding areas if not properly managed in the form of erosion. Erosion is a naturally occurring event where water gradually removes soil and rock from one area and carries it downstream to another where it settles. This is the same process which carved out the Grand Canyon millions of years ago.
This process has been accelerated by the development of the land to accommodate new roads, bridges, buildings, and farmland for our ever expanding population. This increased rate of erosion causes problems both at the area where the erosion is taking place and the areas downstream where the soil is being deposited. To help mitigate this problem, sites are developed to control the amount of water is running off of the property. Typically, the idea is to reduce the amount of runoff generated by the new building or parking lot, to what it was before it was developed or some fraction of the predeveloped rate. This is done in an effort to reduce the impact of the new development. Typically the installation of a subsurface infiltration bed or an above ground basin accomplishes this. To prevent soil from leaving the site during construction activities, a combination of silt fencing, socks, sediment traps and other control devices are implemented around the site to control the sediment leaving the site before the ground can be destabilized. These control measures help to prevent sediment from ending up in streets, the neighboring properties, and existing stormwater management systems.
The Oroville Dam and its spillways are examples of the effect that water can have on the surrounding land in large quantities. During January and February, Northern California experienced a record amount of rainfall, the most in 100 years which resulted in a massive amount of water to flow into the Feather River and required the spillway to be opened to release some of the water to bring the dam down to safe levels. Quickly after the initial storm, a second heavy storm event occurred causing, even more, water to be released through the spillway and eventually the emergency spillway. This massive increase in flow eventually started to cause damage with the water quickly eroding the soil underneath and causing chunks of the spillway to be taken downstream and damage Fish Hatcheries, and eventually, lead to the low lying areas downstream of the dam to be evacuated due to concern of the possible failure and collapse of the emergency spillway. Eventually, the water levels were able to be lowered enough that the spillways were able to be closed, with construction workers immediately working around the clock to remove and replace the spillways, filling in the areas eroded away by the high flows, before the arrival of the next winter.
For as long as I can remember, there have always been those in favor of development and those against it. My opinion, although a little biased, is that building is not only necessary but benefits the economy for millions of families. For those who oppose it, it seems like the common argument is that they don’t want anyone “moving into their back yard” or “taking away their great views”. My response to this is, “Unless you live in a teepee, you also moved into someone’s back yard and/or stole their beautiful views when your house was built.” Another less opinionated view to this debate is to consider the economic benefits that building has on our society.
Construction and infrastructure have always been considered the backbone of the US economy. In 2016, the top five US builders closed on more than 117,000 dwelling units and had combined revenues of over 40 billion. The top 200 US builders closed on a combined total of almost 310,000 dwelling units for a whopping 112 billion in revenues. That equates to approximately 100,000 more homes than are in all of Chester County. Keep in mind that this is just the construction of new homes; not commercial or institutional projects or infrastructures like roads or bridges nor does it include all of the remodeling projects that happen annually in this country. This is only the top 200 builders, all of which had revenues exceeding 50 million dollars annually. There are probably hundreds or even thousands of smaller builders that didn’t make it on the list but still, collectively, construct thousands of new homes each year.
When looking at this in terms of how many people this puts to work or how many families it feeds, it’s an even easier argument to sell. The 2015 US census for per capita income was just shy of $30,000/year, and the median family income was just over $68,000/year. This means that the top 200 builders, last year alone, generated enough revenue to employ 3.7 million people and/or 1.65 million families. Building homes also generate billions of dollars each year in property taxes to pay for our teachers, police officers, firefighters and municipal workers, and funds the maintenance of millions of miles of local roads. So, before you think of opposing the next planned community, you may want to stop for a minute and think about how you or your family might benefit from all the jobs, taxes and income it will create for your local community.