Costing data for condominium sewers? - Question from Kenya

  • edna
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Costing data for condominium sewer

I'm hoping to understand the Bill of Quantity required to build a condominium sewer, focusing on quantities. That way, I can supplement this list of material requirements and associated volumes with local unit cost data, to get to a reliable cost estimate.

Kindly if you could share the information i will really appreciate.

Young water professional with developed interest on strategic sanitation planning and service provision and innovation systems in developing countries.
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  • muench
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Re: Costing data for condominium sewer?

Hi Edinah,

In order to help you better with your query, can you let us know what search methods you have used so far? Did a Google search bring up anything? I did a quick Google search and also searched in the SuSanA library ( www.susana.org/en/knowledge-hub/resource...publications/library ). Search for condomini as that would include the terms "condominium" and "condominial".
13 search results in the SuSanA library: www.susana.org/en/knowledge-hub/resource...title=&author=&year=

This document from 2005 has some costing data:
The Experience of Condominial Water and Sewerage Systems in Brazil - Case Studies from Brasilia, Salvador and Parauapebas
www.susana.org/en/knowledge-hub/resource.../library/details/441

You should also use the search terms "simplified" and also "non-conventional". (it's actually a hassle that we have so many terms for the same thing...)
There was this discussion forum thread:
forum.susana.org/conventional-sewers-sim...-simplified-sewerage

There was a document recommended from ps-eau from 2014:
Ily, J. et al. (2014). Non-conventional sewerage services - Methodological guide n° 7: When to choose this option, how to implement this solution. pS-Eau, France
www.susana.org/en/knowledge-hub/resource...library/details/2249

It also includes data on cost.

At the end of the day, you might have do the technical design for your particular situation (or get a civil engineer/consultant who can do it for you in case you haven't designed one before) to get the most accurate cost estimate.

Regards,
Elisabeth

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  • gracebeeler
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Re: Costing data for condominium sewer

Hi Edna,

Diagonal, a condominial company in Brazil has someone who speaks English. They should be able to help you with an estimate. www.diagonal.net
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  • edna
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Re: Costing data for condominium sewer

Thanks gracebeeler. I will surely delve into it

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  • edna
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Re: Costing data for condominium sewer?

Thanks Muench we really tried looking for online data however most of the available literature did not have the costing data. In addition we really wanted to understand the design and functionality of the system before we could come up with our own since this sanitation technology has been tried in 2 cities in Kenya but on a very micro level scale. Thanks for the response, it was worth for our study

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  • muench
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Re: Costing data for condominium sewer?

Hi Edinah,
Could you share with us some information about the two cities in Kenya that tried condominium sewers? Where was it and who funded the work? Any documents are photos that could be shared for the benefit of others?
Thanks,
Elisabeth

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  • kevintayler
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Re: Costing data for condominium sewer

Dear Edna

I have only just come across your post.

I think that you are actually asking two questions - one regarding quantities and the other regarding costs. Of course they are related but they are not exactly the same.

With regard to quantities, I would suggest developing a cost estimate for a typical standard length of branch sewer and then using this to calculate the cost of the total length of branch sewer. Collector sewers will have to be calculated separately but there are unlikely to be many for small and decentralised schemes.

The points to consider in the design include:

1. Sewer material - different countries use different materials - plastic, concrete, clay etc. Most probably plastic in Kenya.
2. Sewer diameter - Condominial and 'simplified' sewerage theory assumes a minimum 100mm diameter. This is OK up to a point (the assumptions on peak flow factors are questionable) but is likely to give inadequate capacity if storm flows get into the sewer - which is some situations is difficult to avoid. Conventional standards often specify a minimum 150mm diameter, more in some countries. This is theoretically less hydraulically efficient at low flows but I suspect that other factors are more important in the real world - not least siltation.
3. Sewer depth - this has to be sufficient to provide a fall on connections and to ensure that there is no structural damage from traffic. Condominial sewers are laid at shallow depths and I have designed and built concrete sewers in Pakistan with as little as 250mm cover. Sewer depth is also affected by slope, particularly where the topography is flat.
4. Access - in theory, condominial can use rodding eyes rather than manholes and chambers but I think that most systems in Brazil actually use small chambers. The advantage of a shallow sewer is that you don't need a large manhole - only a smaller chamber that allows access for rodding or other maintenance tasks from the surface. I would say that something of the order of 450mm x 450mm can work for very shallow sewers. The Orangi Pilot Project uses circular chambers with a diameter of about 900mm, perhaps less.
5. Chamber spacing - this depends to some extent on the equipment that is available for clearing blockages - I have seen sewers rodded with crude bamboo rods wired together for distances up to about 25 metres but more is possible with proper sewer rods with screwed ends.
6. Provision for any bedding that may be required and perhaps for concrete protection under heavily trafficked roads.
7. House connections - some or all of which may be paid by the householder.

Once you have decided on parameters and have an outline design, with typical manhole/chamber spacing determined, it should not be too difficult to work out the quantities. (Excavation and backfilling should not be very much). The issue then is how to obtain unit costs to put into the outline bill of quantities. One point to note here is that material costs will vary considerably from country to country. Do not assume that you can use costs from Brazil for Kenya.

Another point is that costs depend on the specification used. Figures given in the literature for the cost of Brazilian condominial sewers suggest that they may be up to 10 times more costly than similar sewers built using the Orangi Pilot Project approach. This is presumably partly explained by the differences in material costs but also reflects the much higher design standards used in Brazil - to give one example, OPP chamber covers do not have any sort of frame, which makes them cheap but also means that they break very easily- which is the last thing that you want from a manhole/chamber cover since it allows extraneous material to enter and block the sewer.

One last point is that local standards are often very conservative and may not allow some of the standards used in Brazil.

I hope that this is helpful. I could expand on specific points if required

Best of luck with your endeavours

Kevin

Kevin Tayler
Independent water and sanitation consultant
Horsham
UK
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  • edna
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Re: Costing data for condominium sewer?

Hi Elisabeth,

Sorry for responding late. We encountered two versions of condominium sewer in Kisumu and Malindi. The Kisumu one was built by Pamoja trust(NGO) in 2016. Its designed in manner than the pipes from the households drain into one big manhole which then drains into the main sewer line that is managed by the utility. Its pretty small and might have like 33 maholes in total. The second version is in Malindi town and it was built in 1996 by Malindi municipality. It is designed in a manner that several households connect to a small manhole which then drains to a big holding tank which is then connected with 3 soak pits. This means 15-20 households are served by one big holding tank. This system has never been emptied since it was built and it was only built in areas that had municipal houses. Apparently i would say its still micro as its not functional in all the areas it was built.

Thanks, i hope it will be helpful, but should someone need more information i can elaborate.

Young water professional with developed interest on strategic sanitation planning and service provision and innovation systems in developing countries.
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  • edna
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Re: Costing data for condominium sewer

Hi Kevin,

This is really helpful, you actually nailed on what we were looking out for. We already developed the design and BOQ of course considering the Kenyan context but it also varies from one city to another. Should anything arise up i will surely keep in touch with you.


Thanks,
Edinah

Young water professional with developed interest on strategic sanitation planning and service provision and innovation systems in developing countries.
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  • kevintayler
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Re: Costing data for condominium sewer

HI Edna

Good to know that my comments were useful. I did not mention treatment. It is interesting that both the examples that you give, from Kisumu and Malindi, have connections from several households to a shared chamber and that, in the Malindi case, discharge is to a tank that is basically a septic tank followed by a soakaway. It is also interesting that it has never been desludged - which is something that seems to be quite common.

One thing that I would stress is the importance of ensuring that the sewer acts as a closed conduit with no unwanted solids getting into it. From that point of view, the manhole/chamber cover design is really important. The other point is that it is important to provide traps on connections. Otherwise, there may be problems with rats and other pests.

I am attaching a couple of notes that I produced many years ago, which might be useful.

Best regards

Kevin
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Kevin Tayler
Independent water and sanitation consultant
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