Is a septic tank connected to a soak pit an appropriate onsite sanitation system for households in hill cities ?
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I want to know more about the feasibility of having a septic in a vicinity of a water source and high water table, whether it is safe as per the concern linked to ground water contamination.
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For the construction of septic tanks followed by soak pits, the CPHEEO recommends adherence to BIS Code 2470 Part I and Part II. These codes take into account site-specific factors such as topography—including slope, drainage, gravity-based flow—and the required distance from water bodies. It is also advised to conduct a percolation test to assess soil stability and permeability.
However, in hilly and rocky terrains, alternate disposal methods are recommended when soak pits do not function effectively.
The land subsidence incident in Joshimath, Uttarakhand, in 2023 serves as a cautionary example. It highlighted how the widespread use of unlined soak pits and greywater discharge contributed to slope instability. According to the National Disaster Management Authority (NDMA), and as reported by Down to Earth, over 90% of households in Joshimath discharged greywater and effluent through soak pits. This practice exacerbated subsurface erosion in a town already situated on unstable morainic debris from historical landslides.
In such geologically sensitive areas, it is safer to adopt treatment systems followed by alternative disposal methods. Context-appropriate solutions—such as bio-digesters, compact DEWATS units, or reinvented toilets—should be considered based on site feasibility. These approaches also align with established guidelines such as the CPHEEO Manual – Part C (2013).
