26. On the SFD GG, what value should I put into the three boxes at Step Two (which asks “What proportion of the contents of each type of on-site container are faecal sludge?”)?

In Step Two of the SFD Graphic Generator, users enter the proportion of the contents of each type of on-site container which are faecal sludge and which may be periodically emptied from tanks and pit latrines.  The remaining fraction is dealt with in different ways depending on the types of systems.  For guidance on what value to enter, users can refer to the detailed schematics of each system in the SFD Glossary. A general summary of recommended values is given below.  These values should be used in cases where there is no specific additional data on which more accurate estimates can be made:

Where tanks are connected to soak pits, use the default "100%" value. This will model the proportion of the contents which are emptied periodically (you will enter this value in the SFD matrix under F3) as 100% faecal sludge. The remaining not emptied fraction is made up of faecal sludge, which remains in the container, and infiltrate which soaks into the ground.  For systems in locations where risk of groundwater pollution is low, this fraction comprises variable F8. For systems in locations where risk of groundwater pollution is significant, this fraction comprises variable F15. (Refer to schematics L7 & S2)

Where tanks are connected to water bodies or to open ground use the default "100%" value. This will model the proportion of the contents that are emptied periodically (you will enter this value in the SFD matrix under F3) as 100% faecal sludge. The remaining not emptied fraction is made up of faecal sludge, which remains in the container and supernatant discharging to water bodies or open ground.  This fraction comprises variable F15. (Refer to schematic L9

Where fully lined tanks have no outlet or overflow, use the default "100%" value. This will model the contents as 100% faecal sludge and a proportion of this may be emptied periodically (you enter this value in the SFD matrix under F3). The remaining not emptied fraction is made up of faecal sludge and supernatant, which remain in the container. This fraction comprises variable F8. (Refer to schematic L10)

Where lined tanks with impermeable walls and open-bottoms and/or pits (all types) have no outlet or overflow (for example many “cubluks” in Indonesia), use the default "100%" value. This will model the contents as 100% faecal sludge and a proportion of this may be emptied periodically (you enter this value in the SFD matrix under F3). The remaining not emptied fraction is made up of faecal sludge, which remains in the container, and infiltrate which soaks into the ground. For systems in locations where risk of groundwater pollution is low this fraction comprises variable F8. For systems in locations where risk of groundwater pollution is significant this fraction comprises variable F15. (Refer to schematics L11 & S4)

Where septic tanks and fully lined tanks are connected to a sewer network, use a value of "50%". This will model half the contents as faecal sludge and a proportion of this may be emptied periodically (you enter this value in the SFD matrix under F3). The remaining not emptied fraction will comprise faecal sludge, which remains in the container, and is represented by variable F8. The other half of the contents is modelled as supernatant discharging into the sewer network, represented by variable S6. (Refer to schematic L6)

Where lined tanks with impermeable walls and open-bottoms are connected to a sewer network, use a value of "50%". This will model half the contents as faecal sludge and a proportion of this may be emptied periodically (you enter this value in the SFD matrix under F3). The remaining not emptied fraction will comprise faecal sludge, which remains in the container, and infiltrate which soaks into the ground. For systems in locations where risk of groundwater pollution is low this fraction comprises variable F8. For systems in locations where risk of groundwater pollution is significant this fraction comprises variable F15. The other half of the contents is modelled as supernatant discharging into the sewer network; where there is a low risk of groundwater pollution this is represented by variable S6, and where there is a significant risk of groundwater pollution this is represented by variable S7. (Refer to schematics L6 and S3)

Where tanks are connected to open drains, use a value of "50%". This will model half the contents as faecal sludge and a proportion of this may be emptied periodically (you enter this value in the SFD matrix under F3). The remaining not emptied fraction will comprise faecal sludge, which remains in the container and is represented by variable F15. The other half of the contents is modelled as supernatant discharging into the open drains, represented by variable S7. (Refer to schematic L8)

In situations where there is a mixture of sanitation system (for example, some septic tanks are connected to soak pits and some are connected to open drains) , the user can calculate the ratio of the systems to estimate the proportion of the content of the tanks which is faecal sludge.