STORM SEWER & SANITARY SEWER

INTRODUCTION

Storm Sewer is the water gathered off of the streets and parking lots and even overflow from fields.  Sanitary Sewer is the water and solid matter that comes from toilets, sinks, showers, and washing machines.  So, storm water comes from the outdoors while sanitary sewer comes from indoors.  The two systems both operate in a similar way, just opposite of other utilities.  Instead of delivering a utility, they remove it.

Storm water is typically dumped directly in to the nearest river or lake, though often with small Water Quality Inlets (WQIs) in the drain inlets to clear a portion of the oils and other pollutants first.  Sanitary sewer is typically directed to a treatment plant first before being dumped in the river.

Combined Sewer was common in the 1800’s, but they were no longer allowed beginning in about the 1930’s.  Sanitary sewer has a standard peak flow each day, but storm sewer, of course, is unpredictable.  In the old combined systems, a massive rainfall produces overflow of both.  So, storm and sanitary overflow to the nearest river.

There are some small towns in America that still have Combined Sewers in place, though they are being replaced little by little.  But this is a much bigger problem for large cities, and even some of the biggest cities in America still operate this way.  New York City; Seattle, Washington; Portland, Oregon; and Washington D.C. all have Combined Sewers that dump storm and sanitary directly in to the oceans.

In New York City, 60% of the population is still on a Combined Sewer Overflow system, or CSO.  During any heavy rainfall the sanitary and storm overflow together.  The result is that every year, 20 billion gallons of feces-laden storm water is dumped directly in to the Hudson and East Rivers.

Sewers of either kind are predominantly gravity systems.  Everything flows downhill.  However, the landscape itself presents obstacles.  The local storm sewer does not need to all end up at the same place.  Water can be dumped into a river or a retention pond.

But sanitary sewer usually relies on a treatment plant at the end of the line, so there is a great deal more focus on funneling all of that sewage to a single point, and that requires lift stations, a place to pump the sewage upward, and then revert to a gravity system again.  In many cases, sanitary sewer is pressurized in pipes to allow a longer length of uphill transport.  This is known as pressurized sanitary.

The construction of sewer systems requires the most preliminary planning of any utility.  It is not just the common adage that “water flows downhill”, but that water must flow at a gradual slope over an extremely long distance.  That requires precise measurements on the depth of the beginning and end of every pipe in the system, a measurement that is taken on the bottom inside of each pipe (invert).

SANITARY SEWER

Also known as a Wastewater Collection System, sanitary systems gather water and solids from the buildings and keeps gathering into larger and larger pipes until it reaches the sewage treatment plant.

Being gravity fed, the pipes also get deeper and deeper as they accumulate, at least to some degree.  Even most small cities are too large to be able to lay their sanitary pipes in continually deeper and deeper trenches to keep the flow moving all the way from the farthest outskirts of town to the sewage treatment facility.  Once the pipes are down to a depth of about 20 to 25 feet, the pipe may then drain into a lift station which will pump the sewage up to a shallower depth pipe where it can start its downhill run again.

Sanitary sewer mains are typically in a very simple layout, usually manhole to manhole without any bends.  However, there are rare exceptions, but the big issue with sanitary is the laterals.  The lateral (service) pipes coming in from buildings only occasionally connect in to the main pipe at manholes.  The vast majority of laterals connect in to the main pipes at any given point along the main, often called Ghost Connections because they are not visible.

CLEAN-OUT

Clean-outs are an extension pipe which are built in to sanitary services.  They extend from the ground surface down to the service pipe at an angle, and are used for unclogging the service.  In residential areas they typically consist of nothing more than a PVC pipe sticking slightly up from the ground with a plastic screw-on cap.

In urban areas a clean-out is usually a metal-sleeved structure about 6 inches in diameter, sitting flush with the street or sidewalk.  They look a lot like water valves except that they will have “clean out” or “CO” on the metal lid.

There are also rare clean-outs on sanitary main lines.  If the main line has a point that is very prone to clogging, then they may place a clean-out in that area.  At first glance, these look like sanitary manholes, but once the lid is lifted, you can notice that there is a poly pipe extending downward, and then to an angle, just like any other clean-out.

SANITARY LATERALS – IN THE NEWS

Today sanitary laterals are being damaged on a regular basis across the country, usually by HDD drilling.  When a gas line is pushed through a sewer pipe it creates a volatile situation.  Natural gas is slightly lighter than air, and gas inside a sanitary lateral will naturally rise in to the house.  Once that gas comes in to contact with an ignition source, then the news media arrives to report on the tragedy.

Sanitary laterals have gone from being the least noticed utility, to one of the most talked about, talked about by the municipalities, the HDD crews, the home builders, and the Common Ground Alliance.  No one knows how this situation will eventually be resolved, but the desire to locate out plastic sanitary laterals has become a very common discussion in the utility industry.

Along with this issue is the fact that there is no clear line of ownership with sanitary laterals.  There are no meters or dividing lines on sanitary services like there are with every other utility.  Even if a sanitary lateral is hit, but without causing any other damage, there is still the question of who owns the damaged pipe – the homeowner or the municipality?

The obvious access to sanitary laterals are through those clean-outs.  The modern pipe cameras were specifically built to be pushed in to clean-outs to inspect for damage.  It may be tree roots, rotted pipes, and of course the possibility of damage from the new cable TV line that was bored in last week.  Pipe cameras are usually the “weapon of choice” for sanitary laterals, because they almost always have built in sondes which can be detected by a pipe and cable locator.

RECOGNIZING SANITARY MANHOLES

Storm and sanitary manholes are sometimes mislabeled.  Both are owned by the municipality, and when one cover is opened, it is not unusual for both to be opened, and they can be accidentally switched.

Of course, the smell of a sanitary manhole is usually quite distinctive, but that can be misleading.  Some sanitary manholes are being fed by far more showers, sinks, car washes, and washing machines than they are by toilets.

Also, storm drain systems are gathering water from the streets which is often coming from piles of decayed leaves, food scraps, dead rodents, the oil and grease residue on parking lots, and other nocuous items in the drain inlets, much of which has been lingering in there for years.

The most solid indicator of a sanitary manhole is not always smell, but a deep recessed tubular cut at the bottom of the manhole.  The outflow pipe of sanitary sewer must be at the very bottom of the manhole.  This helps ensure that the solid matter is going to be pushed along without getting caught up in the manhole.

Storm manholes will have an outflow pipe at the very bottom of the manhole, but not recessed below the manhole base.

PRESSURIZED SANITARY – FORCED MAIN SANITARY

Like any gravity system, sanitary pipes can only run downhill for a specified distance depending on the overall terrain.  Eventually the pipes reach a maximum vertical depth of roughly 25 to 30 feet.  At some point the sewage has to be raised.  It can be done with a lift station which pumps the sewage upward and in to a pipe to start the downhill flow again from manhole to manhole, or by not only pumping the sewage uphill, but also pumping the sewage in to a plastic pipe line

Pressurized sanitary pipe is usually restricted to using poly pipe.  The pipes do run manhole to manhole as standard sanitary does, but it will rarely run straight.  The pipes will sometimes have large shut-off valves in the manhole.

STORM SEWER

The basics of storm sewer are extremely simple: catch the water in the massive number of drain inlets along the street, the connecting pipes will keep the water flowing to larger and larger pipes, and eventually to an outflow at a river, lake or retention pond.  Not much to it.

However, there are a few issues here as well.  Since each town has its own unique layout and elevation changes, each storm system is unique in its layout as well.  Just like sanitary, most towns began their storm system in the 1800’s.  However, the storm systems have not just been added to, but continuously altered ever since.

Storm sewer is by its very nature the most continuously altered utility in any city or town.  Every time there is any increase in the amount of concrete or asphalt in town, then there will be an increase in the amount of rainfall dumping into the storm system.

If you own a house that does not have off-street parking, and you decide to have concrete poured for a driveway, now all that rainfall that would have gone in to the soil – is now pouring in to the gutter, and then to the nearest drain inlet, and then in to the storm pipes.

Every single plot of open soil or grass that is being covered by a driveway, a parking lot, a convenience store, a house, or an office building is increasing the water flow in to the storm pipes.  And the addition of a large shopping area will undoubtedly push the storm system far beyond its capability.  During any road work project, an update to the storm system is almost automatic.

Another issue is the language.  The nomenclature for storm systems is almost certainly the most diverse of any utility.  There are a wide variety of names used for almost any storm water feature.  There are differences across the country, and an even larger variety in other countries.  However, some of this variety is from private property use.  Those who provide products and services for homeowners to control storm water have their own nomenclature, and often it is the same wording as municipal storm, but with different meanings.

On this site, all terminology is meant in reference to municipal storm systems only.  This terminology is not universal in any way, but is hopefully the most commonly used. 

Storm sewer systems also have the widest use of materials for pipes.  Just about every type of pipe that has ever been produced has been used in storm sewers at one time or another: iron, corrugated metal, RCP, clay pipe, PVC, bituminized fiber, and several others.

DRAIN INLETS AND CATCH BASINS

Inlets are any structure which allow water in to the storm system.  They can be grated inlets or slotted inlets, and in a wide variety of shapes and sizes.  The shape and size of an inlet opening is usually determined by the specific terrain where it is placed.

Grated inlets are the most common inlet with a metal grate on top.  These can be square, rectangular, or even round. These are the common curb inlets.

Some inlets have a domed top to better restrict incoming debris.  These drains are usually in private property and will usually have only small poly pipes that drain to the nearest municipal drain inlet.

Slotted inlets have thin long aluminum covers, and meant for collecting a massive amount of rainwater along a curb or airport runway in a shorter period of time.

There are also very heavy-duty inlets which are made of thick iron, rectangular in shape, and have only a few top holes for inflow.  These are used in areas with a good deal of semitruck traffic.  Their purpose is to serve somewhat as storm manholes but still allowing some water in.

The term Catch Basin is often used interchangeably with Drain Inlet, but to be more specific, a Catch Basin is a type of Drain Inlet, one that has an outflow pipe that is well above the bottom of the basin.  This prevents leaves and other debris from clogging up the pipes farther downstream.

WATER QUALITY INLET – WQI

We don’t often see the real amount of oil and transmission fluid that is winding up in the streets and parking lots because the next rain will wash much of it in to the storm system – and then to the rivers.

Some people call them separators or inserts.  They are also more specifically called grease separators or oil separators.   However, the U.S.D.O.T. refers to them as WQI’s for Water Quality Inlets.  All of these are meant to be used in Catch Basins, as opposed to regular Drain Inlets.

The purpose of WQI’s is to comply with EPA requirements and catch most of those hydrocarbons before they enter the main storm system.

There are several different companies which have been producing WQI’s, and these designs can be drastically different from each other.  Most of them are patented designs, so each manufacturer has had to create a WQI which is very different from previous designs.  Another has small metal boxed areas within the drain, and a metal lid.  Another looks more like someone dropped a small beer keg inside of the drain, and the outgoing pipe is constructed below this barrel structure, dropping vertical out of the drain, and only then takes a 90-degree bend towards the main system.

One design is not an addition to the catch basin, but a specially designed catch basin.  This is really nothing more than an elbowed pipe coming in to the catch basin, and extending down below the water line.  These are called Dry Sump Catch Basins.

Once installed, WQIs are rarely cleaned out, so quite often, about a year after any WQI is installed they no longer serve any purpose.  A 1993 study by the Metropolitan Washington Council of Governments showed that although regular maintenance is the key to WQI’s, that maintenance is not necessarily being followed.  A personal inspection of WQI’s will undoubtedly show that these are almost never maintained.  Many cities installed WQI’s, and then seemed to forget about them.  This can create a new problem because as a residue collector, they may well be filling up with “….many priority pollutants, including polyaromatic hydrocarbons, trace metals, phthalates, phenol, toluene, and possibly methylene chloride.” 

All WQI’s should be treated the same as sanitary manholes.  The water coming in is storm water, but it has been collecting oil, grease, transmission fluid, detergents, and any other number of chemicals from the street, the parking lot, the car wash, and the factory.

CATCH BASIN – MANHOLE

As the storm water nears the river where it will dump, it is common to place a large manhole, not a typical catch basin, and not a typical WQI.  Instead, this will be large manhole with 3 separate chambers.  They tend to resemble a combination of three manhole structures in one.  Each section serves a different purpose in separating the water from the oil and other contaminants.  Water pours from one chamber to the next, and reduces the pollutants with each chamber.  These are usually about twenty feet from end to end with 3 manhole lids, one for each section of the inlet.

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STORM AND SANITARY TERMINOLOGY

APRON:

A flared extension to pipes to allow a wider flow of water in or out.  These are usually restricted for use on culvert storm pipes.  The apron will usually be the same material as the pipe, so, an RCP culvert will have an RCP apron; a CMP pipe will have a CMP apron.

AVERAGE FLOWS:

Average flows are typically dry weather sewer flows over a specific period of time and expressed in gallons per day.  Since any sewer system needs to be designed for maximum capacity, average flows are not used as the basis for designing a sewer piping system.

BOX CULVERT:

A squared or rectangular culvert, almost always made of reinforced concrete, and usually at least 6 feet across, but can be 20 feet across or more.  Larger box culverts may be referred to as an aqueduct.

CATCH BASIN:

A type of drain inlet, but one that specifically has an outflow pipe well above the bottom of the basin.  This prevents leaves and other debris from flowing downstream, and clogging the system.  Catch Basins must be cleaned out on a regular schedule or they become useless.

CLEAN OUT:

A pipe rising from a sanitary lateral to the ground surface.  Used to access the lateral to free blockages.  Clean Outs are usually located inside the property line on sanitary laterals, but there are rare Clean Outs on sanitary main lines.  In residential areas Clean Outs are typically plastic with a plastic screw-on top.  In commercial areas they are typically completely flush with the ground and have a metal top.

COMBINATION INLET:

A drainage inlet that is usually composed of a curb-opening inlet and a grated inlet, but may include a grate inlet and a slotted drain inlet.

COMBINED SEWER OVERFLOW – CSO

A system that combines the storm sewer with the sanitary sewer.  Common in the 1800’s.  No city is allowed to install a system like this today, but there are still cities that have CSOs in place such as New York City, Seattle and Washington D.C.

CULVERT: 

Any storm pipe that extends only from one side of a road or railway to the other side.  If the culvert water flows in to the storm system, then the culvert is technically a part of the storm system.  However, there are numerous other small culvert pipes used under driveways that cross irrigation ditches.

CURB-OPENING INLET:

A drainage inlet that is placed in to the roadway curb allowing water to flow in straight from the gutter.

DESIGN FLOWS:

Design flows are peak flows, the maximum amount of water projected to enter the system.  Design flows are used to design or upgrade a sewer system.

DETENTION POND/RETENTION POND:

A large open artificially constructed pond for collecting large amounts of water during heavy rainfall.  Looking much like a very small and dry lake, they may have any number of incoming pipes.  They only time they contain water is right after a heavy rainfall, then the water naturally percolates down into the ground.

A detention pond has an outflow pipe which allows a small amount of water to gradually flow to the storm system, while a retention pond is made for water removal by evaporation and ground seepage alone and does not have an outflow pipe.  Therefore, the only difference between them is that a detention pond has an outflow pipe, while a retention pond does not.

DRAIN INLET

Any of the boxed structures with grated lids which are placed in the roadway or at the roadside in a low point or swale to collect rainwater.

Today these are almost always made of reinforced concrete.  They may be only 3 or 4 feet in depth, though they can be much deeper.  These are the most common feature in any storm water system.

DROP DOWN MANHOLE:

A sanitary manhole with two openings from the same incoming pipe.  Meant for preventing backup in the sanitary system.  These are noticeable in the manhole because of having two incoming pipes, one directly above the other, and both of them the same size and material.

Since these are a more modern feature, the pipe material is usually poly.

DRY SUMP CATCH BASIN:

A Catch Basin with an outflow pipe that extends in to the basin, and then bends down in to the basin.  A type of WQI.

DRY WELL:

A concrete manhole with a slotted lid so water can easily pour in.  However, Dry Wells are not constructed with a solid wall all the way down.  Instead, they may have an open area at the bottom filled with gravel, or at least a number of regularly spaced holes along the side of the manhole.  This allows the storm water to drain out into the surrounding earth, but well below the surface, and lessens the amount of water dumping into the municipal system.

Dry Wells are typically found in large grass areas, either in municipally owned park areas, or on business property with large landscaped areas.

FRENCH DRAIN:

Used to drain water away from a building.  They consist of a hard cloth tube, laid underground around the building, and connected to a plastic pipe.  The rain from the roof is usually channeled to certain points through the rain gutter, then down to the yard.  The heaviest concentration of rainfall on any given lot will be in a narrow corridor around the building.  For any building that has a basement area, or lower level, French drains are a permanent way to keep that lower area from flooding.  The hard cloth material in a French drain will help to soak up the water.  A connecting small pipe, usually PVC, will be placed underground and positioned to dump the water into the gutter.  Once the instillation is completed, the only visible portion of a French Drain will be the outlet pipe to the gutter, the scupper, and usually cemented right in to the gutter.

GRATE INLET – see DRAIN INLET

GREASE TRAP:

Grease traps are not a storm or sanitary feature.  They have been included here only for convenience.  They are used to collect grease from restaurants and fast- food joints.

A boxed manhole commonly found in the parking lots or back door areas of restaurants and food processing plants.  Instead of dumping all of the used grease into the sanitary system, the grease has a special dump pipe which runs out to the grease trap.  You can find two or more of these on the backside of most restaurants.

They have no outflow.  It requires a vacuum truck to suck the grease out when they get close to full capacity.

GUTTER:

The portion of the roadway adjacent to the curb which is utilized to convey storm water to the inlets.

INFILTRATION:

Infiltration is groundwater that enters the sewer pipes through cracks, pipe joints and other system leaks.  Infiltration is therefore any incoming water to a sewer system that is unintentional.

INFLOW:

Inflow is all of the intentional flow of water coming in to any sewer system.

INVERT:

A measurement from a specific point at the ground surface down to the inside bottom of a pipe.

LIFT STATION:

A structure, usually found only in sanitary systems, for pumping deep sewage up to a higher elevation pipe.  Lift stations usually consist of two structures next to each other: a manhole that contains the pump, and a fenced area with the mechanical features.

PERFORATED DRAIN:

Pipe placed in a “T” shape at the side of a highway or airport runway, used to drain the water out away from the road.  This is a PVC pipe with regularly spaced holes for collecting water runoff.  A connecting pipe then extends out towards a ditch, creek, or manhole.

The outflow of perforated drains often have a metal screen cover to keep rodents out, but these can be easily removed by simply sliding them up and off.

PRESSURIZED SANITARY – FORCED MAIN SANITARY

A portion of a sanitary system with the sewage pumped through pressurized pipe, usually poly pipe.  The manholes will usually have shut-off valves.

SCUPPER:

A vertical hole through a bridge deck for the purpose of deck drainage.  This can also be a horizontal hole in the curb with a pipe coming from a roof drain or French drain.

SLIP-LINED PIPE

A newer process of restoring old sewage pipes, usually sanitary pipes, by inserting a poly lining which is then heated by pumped air, and hardens in to a new pipe lining.  This can restore old pipe that is close to crumbling without the need for excavation.  This is sometimes called CIPP for Cured In Place Pipe.

SLOTTED DRAINS:

These come in different sizes, but they are all long thin metal structures with a slotted top.  They will have a connecting pipe, usually a 4-inch PVC that connects with a standard drain inlet.  In this way they can pull a great deal of water off of a roadway in a very short time.  Slotted drains are very common along airport runways for obvious reasons.  They can also be found on some street curb in areas which may be prone to huge cloud bursts.

A very antiquated slot drain on a brick road.

TREATMENT PLANT:

Small towns may dump their sewage directly in to a fenced leech field, but cities usually require treatment plants to treat the sanitary sewage.

VEG DITCH:

A vegetation ditch is any open earth ditch.  If the ditch drains into the storm system then it is technically part of the storm system.