Vulnerability and the unsaturated zone - the case for cemeteries

Abstract

Cemeteries are a special kind of land use with direct impact on the unsaturated zone. In a cemetery organic waste (the deceased incl. coffin) is deliberately interred at a depth usually corresponding with soil C horizons via a series of purposely cut pits (graves). Ultimately the designated area consists of a highly disturbed surface layer with a framework of in-situ soil walls and corridors, all 'sitting' on a continuous, yet most likely variable, sub-soil or weathered rock, irregular surface. The variability is due to natural processes, and the irregularity is due to differences in grave invert levels and altered topographic grades at the outset. The functional part of the cemetery as a whole, and anyone section within, is thus heterogeneous and anisotropic as a medium; this uppermost layer becoming a mixed Anthroposol and natural soil entity. The cemetery site experiences irregular infiltration and percolation effects, potentially very uneven distribution of infiltration processes or events, and ultimately of recharge to any local or regional groundwater system. A principal confounding concern is the local retention of water in the grave - the bucket effect. Ex-cemetery impacts are essentially of four kinds: (i) an excess of groundwater (from mounding, grave buckets, etc.); (ii) the discharge of a salty plume (small, but well documented); (iii) a nutrient plume - essentially inorganic forms of nitrogen; (iv) the potential for the spread of pathogenic bacteria and viruses. For properly sited and maintained cemeteries these impacts are likely to be non-existent or very minor. Impact type 'iv' represents the greatest potential threat, but is in the general context, relatively small. Historically, cemeteries have been poorly and/or thoughtlessly located e.g. on drainage lines, swampy soils, cliff edges, adjacent to drinking water wells and close to watertables; or have no buffer zones or suitable plantings to reduce off-site water migration. For new cemeteries and extensions to existent ones, an assessment of these impacts must be made in regard to aquifer vulnerability and recharge zones.