Tag Archives: rain

Sewage: rain to the river, poop to the fields, nothing to your basement

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I’ve written a fair amount about sewage over the years, including the benefits of small dams, and problems of combined sewers, but I thought I’d write here about something really fundamental: sewage has two components, poop and rain, and they should be kept separate. The poop and related liquids are known as sanitary sewage. Ideally it is the treated, saved and used as fertilizer. Rain, known as storm sewage, needs to go to the rivers at a controlled speed, unmixed with sanitary sewage. Sorry to say, in many counties, mine included, the two are mixed following every rain, costing us unnecessary money, and making swimming unsafe, and boating (sometimes) unpleasant.

Our system is not quite mixed, but is semi-separate. It only mixes in a “big” rain, more than 1/2″, something that happens once per month, on average. The Pipes are semi-connected as shown below.

Combined sewer system, like in our county, Oakland MI. We use little dams in the pipe system to semi-separate the flows. Here, showing a rain-induced overflow of combined sewage, a CSO.

The pipes of a sanitary sewage system can be relatively small in diameter as this flow is continuous, but never that large. The cost of treatment is high, per gallon though. Some of this cost can be recovered in fertilizer value.

Stormwater flow, by contrast, requires big pipes because the flow, while episodic and be 10,000 more than the sanitary flow. A city can go for weeks without storm flow as there’re is no rain. A storm will then drop more water in an hour than all the sanitary sewage of the last few weeks. You need large diameter stormwater pipes, and you typically want retention basins so that even these pipes are not overwhelmed, and to provide a little settling. The pipes should direct storm water to the nearest river. In our county we mixed the two for historical reasons. This adds tremendously to the cost of sewage treatment, and we find we regularly overwhelm the treatment facility. When this happens, as shown above, sanitary sewage is flushed into the riveras I described ten years ago in a post focussed on pollution from combined sewers. If the rains are really heavy, they back up “sanitary” sewage into basements as well. More commonly, once or twice a month where I live, we just pollute the river. Several cities with combined sewers have separated them recently. Paris, for example, ahead of the 2024 Summer Olympics.

To get an idea of the relative size of the flows in our county, note that Oakland county is a square 30 miles by 30 miles. That’s 900 square miles, or 25.1 billion square feet. In th4e event of a, not uncommon, 2″ rain on this area, we must deal with 4.2 billion cubic feet of water or 33 billion gallons. Some of this absorbs into the ground, but much of it runs goes to pipes heading to the rivers. Ideally we retain some of it above ground for an hour or more because the pipes can’t handle this flow. Even with retention, our rivers rise some 10 feet typically and begin to flow at many miles per hour after a storm. They can be seen carrying trees along, and massively eroding the soil, even in areas that were prepared appropriately.

A home based approach to sewage. Many homes near me have this setup — with internal plumbing and a septic field for sewage treatment. Often, these homes are near a stream that flows at least temporarily.

Sanitary sewage flows are far less voluminous. Our county has roughly 1 million people who flush about 100 million gallons per day, generally sending this to our sanitary sewage treatment plants. That averages a mere 4 million gallons per hour, or 500,000 cubic feet. That’s roughly 8000 times less flow than the storm flow. If any significant fraction of the rainwater goes into our sanitary system, it will quickly overwhelm it and back up into our basements.

Many people try to get out of paying the high price for municipal sewage treatment by making their own small system with a septic tank an a septic field. I think this is a great idea, a benefit for them and the county. I will be happy to direct them to appropriate educational materials so that home waste flows to the septic tank where anaerobic bacteria break things down, it should then flow to a septic field that filters the nutrients and allows aerobic bacteria to break things down further. Nutrients in the sewage helps whatever you plant and, as we say, “the grass is always greenest over the septic tank.” As for the county on the whole, I wish we got real value from the fertilizer, as Milwaukee does, and wish we’d separate the sewers.

Robert Buxbaum, February 23, 2025

How to avoid wet basements

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My house is surrounded my mulch — it absorbs enough rainwater that I rarely have to water.

Generally speaking water gets to your basement from rain, and the basic way you avoid wet basements is by providing some more attractive spot for the rainwater to go to. There are two main options here: divert the water to a lake or mulch-filled spot at least 8 feet away from your home, or divert it to a well-operated street or storm drain. My personal preference is a combination of both.

At right I show a picture of my home taken on a particularly nice day in the spring. Out front is a mulch-filled garden and some grass. On the side, not shown is a driveway. Most of the rain that hits our lawn and gardens is retained in 4 inches of mulch, and waters the plants. Four inches of mulch-covered ground will hold at least four inches of rainwater. Most of the rain that hits the house is diverted to downspouts and flows down the driveway to the street. Keeping some rainwater in the mulch means you don’t have to pay so much to water the trees and shrubs. The tree at the center here is an apple tree. I like fruit trees like this, they really suck up water, and I like the apples. We also have blueberries and roses, and a decorative pear (I like pears too, but they are messy).

In my opinion, you want some slope even in the lawn area, so excess rainwater will run to the sewers and not form a yard-lake, but that’s a professional preferences; it’s not always practical and some prefer a brief (vernal ) lake. A vernal lake is one that forms only in the spring. If you’ve got one, you may want to fill it with mulch or add trees that are more water tolerant than the apple, e.g. swamp oak or red cedar. Trees remove excess water via transpiration (enhanced evaporation). Red Cedars grow “knees” allowing them to survive with their roots completely submerged.

For many homes, the trick to avoiding a flooded basement is to get the water away from your home and to the street or a retention area.

When it comes to rain that falls on your hose, one option is to send it to a vernal lake, the other option is to sent it to the street. If neither is working, and you find water in your basement, your first step is to try to figure out where your rainwater goes and how it got there. Follow the water when it’s raining or right after and see where it goes. Very often, you’ll discover that your downspouts or your driveway drain into unfortunate spots: spots that drain to your basement. To the extent possible, don’t let downspout water congregate in a porous spot near your house. One simple correction is to add extenders on the downspouts so that the water goes further away, and not right next to your wall. At left, I show a simple, cheap extender. It’s for sale in most hardware stores. Plastic or concrete downspout pans work too, and provide a good, first line of defense agains a flood basement. I use several to get water draining down my driveway and away from the house.

Sometimes, despite your best efforts, your driveway or patio slopes to your house. If this is the case, and if you are not quite ready to replace your driveway or patio, you might want to calk around your house where it meets the driveway or patio. If the slope isn’t too great, this will keep rainwater out for a while — perhaps long enough for it to dry off, or for most of the rainwater to go elsewhere. When my driveway was put in, I made sure that it sloped away from the house, but then the ground settled, and now it doesn’t quite. I’ve put in caulk and a dirt-dam at the edge of the house. It keeps the water out long enough that it (mostly) drains to the street or evaporates.

A drain valve. Use this to keep other people’s sewer water out of your basement.

There is one more source of wet basement water, one that hits the houses in my area once a year or so. In our area of Oakland county, Michigan, we have combined storm and sanitary sewers. Every so often, after a big rain, other people’s rainwater and sanitary sewage will come up through the basement drains. This is really a 3rd world sewer system, but we have it this way because when it was put in, in the 1900s, it was first world. One option if you have this is to put in a one-way drain valve. There are various options, and I suggest a relatively cheap one. The one shown at right costs about $15 at Ace hardware. It will keep out enough water, long enough to protect the important things in your home. The other option, cheaper and far more hill-billy, is to stuff rags over your basement drains, and put a brick over the rags. I’ll let you guess what I have in my basement.

Robert Buxbaum, June 13, 2019

A plague of combined sewers

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The major typhoid and cholera epidemics of the US, and the plague of the Al Qaeda camps, 2009 are understood to have been caused by bad sewage, in particular by the practice of combining sanitary + storm sewage. Medieval plagues too may have been caused by combined sewers.

Combined sewer system showing an rain-induced overflow, a CSO.

A combined sewer system showing an rain-induced overflow, a CSO.

A combined system is shows at right. Part of the problem is that the outfall is hard to contain, so they tend to spew sewage into the lakes and drinking water as shown. They are also more prone to back up during rain storms; separated systems can back up too, but far less often. When combined sewers back up, turds and other infected material flows into home basements. In a previous post, “follow the feces,” I showed the path that Oakland county’s combined sewers outfalls take when they drain (every other week) into Lake St. Clair just upstream of the water intake, and I detailed why, every few years we back up sewage into basements. I’d like to now talk a bit more about financial cost and what I’d like to do.

The combined sewer system shown above includes a small weir dam. During dry periods and small rain events, the dam keeps the sewage from the lake by redirecting it to the treatment plant. This protects the lakes so that sometimes the beaches are open, but there’s an operation cost: we end up treating a lot of rain water as if it were sewage. During larger rains, the dam overflows. This protects our basements (usually) but it does so at the expense of the drinking water, and of the water in Lake St. Clair and Lake Erie.

As a way to protect our lakes somewhat Oakland county has added a retention facility, the George W. Kuhn. This facility includes the weir shown above and a huge tank for sewage overflows. During dry periods, the weir holds back the flow of toilet and sink water so that it will flow down the pipe (collector) to the treatment plant in Detroit, and so it does not flow into the lake. Treatment in Detroit is expensive, but nonpolluting. During somewhat bigger rains the weir overflows to the holding tank. It is only during yet-bigger rains (currently every other week) that the mixture of rain and toilet sewage overwhelms the tank and is sent to the river and lake. The mess this makes of the lake is shown in the video following. During really big rains, like those of August 2014, the mixed sewage backs up in the pipes, and flows back into our basements. With either discharge, we run the risk of plague: Typhoid, Cholera, Legionnaires…

Some water-borne plagues are worse than others. With some plagues, you can have a carrier, a person who can infect many others without becoming deathly sick him or herself. Typhoid Mary was a famous carrier of the 1920s. She infected (and killed) hundreds in New York without herself becoming sick. A more recent drinking water plague, showed up in Milwaukee 25 years ago. Some 400,000 people were infected, and 70 or so died. Milwaukee disinfected its drinking water with chlorine and a bacteria that entered the system was chlorine tolerant. Milwaukee switched to ozone disinfection but Detroit still uses chlorine.

Combined sewers require much larger sewage treatment plants than you’d need for just sanitary sewage. Detroit’s plant is huge and its size will need to be doubled to meet new, stricter standards unless we bite the bullet and separate our sewage. Our current system doesn’t usually meet even the current, lower standards. The plant overflows and operation cost are high since you have to treat lots of rainwater. These operation costs will keep getter higher as pollution laws get tougher.

In Oakland county, MI we’ve started to build more and more big tanks to hold back and redirect the water so it doesn’t overwhelm the sewage plants. The GWK tank occupies 1 1/2 miles by about 100 feet beneath a golf course. It’s overwhelmed every other week. Just think of the tank you’d need to hold the water from 4″ of rain on 900 square mile area (Oakland county is 900 square miles). Oakland’s politicians seem happy to spend money on these tanks because it creates jobs and graft and because it suggests that something is being done. They blame politics when rain overwhelms the tank. I say it’s time to end the farce and separate our sewers. My preference is to separate the sewers through the use of French drains or bio-swales, and through the use of weir dams. I’m running for drain commissioner. Here’s something I’ve written on the chemistry of sewage, and on the joy of dams.

Dr. Robert E. Buxbaum, July 1-Sept 16, 2016.