Sewer Systems 6

[dik]

I'm a bit out of my league, here.

Is it true that many cities have both a stormwater system as well as a sanitary system? It is my understanding that these are often combined into one sanitary system.

Is it common for cities to take run-off from roads and divert them directly to 'retention ponds'? I had thought that road run-off went to the storm sewer system via catchbasins to 'trap' sediment.

Can someone enlighten me?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[fel3]

Combined sewers are a big problem, so current practice is to provide completely separate storm drainage and sanitary sewer systems. That being said, many older cities in the United States still have combined sewer systems or partially combined sewer systems and they are (or should be) working to completely separate the two.

For more info, look here:

https://en.wikipedia.org/wiki/Combined_sewer

https://www.epa.gov/npdes/combined-sewer-overflows-csos

I'm in Fresno, California (population about 500,000) and have only encountered one combined sewer system and that was back in the early 2000s. And, it happened to be in my own city: about 100 acres (IIRC) in downtown had decades-old storm drains that discharged into the sewer system. I have worked on projects across the state, but this is the only combined sewer I have seen around here.

In the San Joaquin Valley, which is relatively flat, most storm drainage systems I know of discharge to ponds. Here in Fresno, the Fresno Metropolitan Flood Control District and the Fresno Irrigation District are interconnected and share some facilities, which permits converting runoff into irrigation water. I have designed pumping stations for moving that water. In some places, storm drainage systems will ultimately discharge into lakes, rivers, or the ocean. In these cases, water quality becomes an issue and now we see a lot of storm drainage treatment systems at the points of discharge.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[dik]

Thanks

With the retention ponds, I'm referring to taking all the surface water, including roads to the pond, not just surface run-off. This includes whatever tire abrasion products and whatever vehicle oil products. I've used retention ponds for site stormwater management.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

dik....different jurisdictions have different rules for handling runoff for pollution abatement, for storage and for allowable offsite discharge. It is common for sites having a lot of pavement to take the first inch of runoff and retain that on site for pollution abatement and the next runoff amount to be detained with enough storage to mitigate the downstream from being overloaded. The detention system works like a surge suppressor.

 

[dik]

Thanks Ron, how is detained to keep pollutants out of the groundwater? A large 'grease trap'?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[robyengIT]

in Italy, for handling runoff for pollution abatement as said by Ron, we consider a volume equivalent to the first five minutes of rain of the interested area. After that the further storm water in diverted to a separate drainage system. Storm water and sanitary system are separate because sanitary system is calculated for its best performance : a lot of water (storm) is very negative

 

[bimr]

dik,

Review this course as it may answer your questions:

stormwater management

 

[dik]

How is the timing volume achieved.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Is that other drainage system on site pondage?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Thanks, guys... I'll take a look at the info, bimr.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[bimr]

A dry detention basin is the most common method to satisfy both stormwater detention and stormwater quality requirements. Typically the first 0.5 inches of stormwater runoff, over the entire contributing drainage area, is defined as the first flush volume. That volume is used to size the dry retention basin.

 

[dik]

Thanks bimr, and the dry detention basin has an overflow that allows the balance to move onwards?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[cvg]

note that first flush capture / treatment is common in the US and required as part of NPDES permit requirements which vary by state and region.

https://www.epa.gov/npdes

not sure what is required in Canada or other countries

 

[dik]

Thanks, cvg. What happens to the effluent trapped in the 'first flush' basin?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[fel3]

Ultimately, your SS and SD designs must conform to local requirements and such state and federal regulations that apply. Local requirements vary quite a bit. For example, most agencies around here do not take percolation into account for sizing basins. This is because over time the bottom and sides of the basin may clog without regular maintenance....and maintenance is often far from regular. But, a few agencies around here do take percolation into account.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[dik]

thanks... so the road 'crud' is just allowed to remain in the initial pondage... no attempt to remove it from the system, maybe other than dredging or something.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[bimr]

Dik,

You need to clarify whether your project involves public stormwater or private development stormwater. You also need to research the regulations where your project is located as the requirements may vary with location. Some states like Washington are ahead of the curve as far as developing the regulations. That is the reason for the confusion, some locations have implemented stormwater regulations and others have not implemented stormwater regulations. There is also a lack of funding for monitoring stormwater from MS4s.

Here is a link to the Washington regulations fort he planning and design of stormwater management facilities for existing and new Washington State highways, rest areas, park-and-ride lots, ferry terminals, and highway maintenance facilities throughout the state. The HRM establishes minimum requirements and provides uniform technical guidance.

Washington

The MS4s are responsible for monitoring stormwater. Polluted stormwater runoff is commonly transported through municipal separate storm sewer systems (MS4s), and then often discharged, untreated, into local water bodies.

An MS4 is a conveyance or system of conveyances that is:
1. owned by a state, city, town, village, or other public entity that discharges to waters of the U.S.,
2. designed or used to collect or convey stormwater (e.g., storm drains, pipes, ditches),
3. not a combined sewer, and
4. not part of a sewage treatment plant, or publicly owned treatment works (POTW).

MS4s in U.S. Census Bureau defined urbanized areas, as well as MS4s designated by the permitting authority, are required to obtain NPDES permit coverage for their stormwater discharges.

When the MS4 has a discharge permit, the MS4 (owned by a state, city, town, village, or other public entity) is then responsible for monitoring the stormwater from private development that discharges into the MS4. Since the MS4 has the permit, the MS4 will go back to the various private stormwater sources and mandate improvements in stormwater discharged from private sources.

 

[cvg]

depending on the location, treatment may be active or passive. watercourses discharging directly into rivers, lakes and the ocean may be more suitable for active treatment.

active would be treatment in a device such as a stormceptor. due to the volume of runoff, it would be difficult and prohibitively expensive to try and actively filter and treat all storm runoff, so most is passively treated.

passive would be evaporation/percolation of the water and settlement of the sediment in the bottom of the basin.

 

[dik]

Thanks bimr and cvg...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[fel3]

dik...

Some agencies dredge their ponds on a regular basis (e.g., our local Fresno Metropolitan Flood Control District) and some don't.

Some agencies capture as much "junk" as they can upstream of the pond. The first flush storm event each season is the biggie.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill