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The top diameter of the Single VIP should be between 1 to 1.5mand be dug at least 3mdeep, although the deeper the better. Deep pits can last up to 15, 20, 30 or more years. As the effluent leaches from the Single VIP and migrates through unsaturated soils, faecal organisms are removed. The degree of faecal organism removal varies with soil type, distance traveled, moisture and other environmental factors and thus, it is difficult to estimate the necessary distance between a pit and a water source. A minimum distance of 30m between the pit and a water source is recommended to limit exposure to chemical and biological contamination.
{{procontable | pro=
- Sludge requires secondary treatment and/or appropriate discharge. <br> - Costs to empty may be significant compared to capital costs. <br> - Low reduction in BOD and pathogens.
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==Adequacy==
To keep the Single VIP free of flies and odours, regular cleaning and maintenance is required. Dead flies, spider webs, dust and other debris should be removed from the ventilation screen to ensure a good flow of air.
==Acknowledgements==
{{:Acknowledgements Sanitation}}
==Referencesand external links==* Elizabeth Tilley et.al (2008). [http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_sesp/downloads_sesp/compendium_high.pdf Compendium of Sanitation Systems and Technologies] ([http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_sesp/downloads_sesp/compendium_low.pdf low res version]). Department of Water and Sanitation in Development Countries ([http://www.sandec.ch/ Sandec]) at the Swiss Federal Institute of Aquatic Science and Technology (Eawag). (Provides a full overview of sanitation systems.)
* Mara, DD. (1996). Low-Cost Urban Sanitation. Wiley, Chichester, UK. (Provides detailed design information.)