Risks posed are :
• Geotechnical or engineering , related to the mechanical properties of the ground ; and / or
• Environmental or sanitary , implying all hydrological and health risks ;
• Social or cultural , related to innate belief and the right to burial .
Currently , best practice is very generic and based on aspects related to the depth of investigation and the distance from surface water , drinking water , and the groundwater table ( Fig . 2 ; Croucamp & Richards 2002 ; Dent & Knight 1998 ; Dippenaar 2014 ; DWA n . d .; EA 2004 ; Engelbrecht 2000 ; Fisher 1992 ; Fisher & Croucamp 1993 ; Hall & Hanbury 1990 ; NIEA 2012 ; WHO 1996 ; Young et al . 2002 ). Additional generic specifications include :
• Deep water table ;
• Absence of perched water tables ;
• Soil hydraulic conductivity 1x10-7 to 5x10-5cm / s ;
• Thick excavatable soils ;
• No proximate water supply or drainage features ;
• Stability of sidewalls ;
• Surface gradient 2 – 6 ° ( 9 ° in exceptional cases ); and
• Space for adequate future expansion .
Geotechnical risks are mostly based on the appropriateness of the site in terms of the depth of excavation by affordable means , the stability of the excavation ( whether due to volume change or subsidence in soils , or the stability of the grave following excavation until closure ), and the suitability of the excavated materials to be used as backfill .
Sanitary risks entail groundwater , surface water , drinking water , and any other health or environmental matters potentially influenced by the development as a cemetery . Here the depth to the water table ( or the thickness of the vadose or unsaturated zone ) and permeability of the site materials are the most important aspects .
Impacts of cemeteries
Cemetery development entails anthropogenic changes to the receiving environment and the environment inevitably affects the suitability of a site as a cemetery ( A-F ).
Poorly backfilled graves can result in a preferential infiltration zone , rapidly flooding the coffin . Mounded backfill , on the other hand , can divert water to preferentially infiltrate adjacent to graves , resulting in surface runoff and erosion . When coffins eventually collapse , the
A
B
C
D
Drinking water source > 250 – 500m River , well , spring > 30 – 100m
Depth of investigation > 1.8 – 2.8m
Vadose zone > 2.5m
Backfill > 1.0m
Subsoil > 1.0m Groundwater > 4.0m
E
ENGINEERING GEOLOGICAL / GEOTECHNICAL
Excavatability ease to 1.80m
Stability sidewalls stable for prolonged periods
Workability material to be used as compacted backfill
SANITARY / ENVIRONMENTAL / HYDROGEOLOGICAL
Water table thickness of protective vadose zone
Subsoil permeability preventing ponding and rapid infiltration
Backfill permeability preventing ponding and rapid infiltration
Figure 2 : Generic international and South African minimum requirements for siting of cemeteries ( top ) and the approach to cemetery site suitability ranking proposed by Hall and Hanbury ( 1990 ) ( bottom ).
F
A-F : Some geotechnical and environmental risks posed by cemeteries : [ A ] orange staining indicating periodical wet conditions in Cenozoic Sands ( Western Cape ); [ B ] standing water in a grave near a wetland ( Gauteng ); [ C ] sinkhole due to irrigation ( Gauteng ); [ D ] unstable excavation in weak soil ( Western Cape ); [ E ] difficult excavation ( Northern Cape ); and [ F ] difficult backfill and proximate receptors ( Northern Cape ).
18 Water Sewage & Effluent November / December 2017