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