Groundwater risk assessment: human or animal burials

You need to follow this guidance if you are examining the potential or current effect of burials in a cemetery, or individually, as part of a risk assessment.

You may need to do a risk assessment, for example:

• as part of a planning application or condition
• when altering existing facilities
• following a pollution incident
• when ongoing environmental management of the site is needed, for example disposal of grey water

We have a tiered approach to risk assessment. Sites with the highest risk need a more detailed risk assessment than those with the lowest risk.

We will oppose any cemeteries where the risk assessment demonstrates that the risk to groundwater is high.

Source, pathway and receptor

You should use a source-pathway-receptor approach to follow this guide’s principles.

For groundwater risk assessments relating to burials, the:

• source is the buried human or animal remains
• pathway is the subsoil or other medium through which substances from the source permeate and travel
• receptor is the groundwater

Groundwater receptors can include:

• the groundwater itself
• any boreholes, wells and springs used for drinking water supplies
• groundwater-dependent ecosystems (such as wetland habitats) or other identified conservation sites that may be at risk (such as Sites of Special Scientific Interest)

To assess the risk at a site you will need a realistic estimate of the yearly maximum number of burials that take place or will take place, and whether these involve human or animal remains.

You must make sure any subsurface investigation of the soil and rock is at least 1 metre below the deepest grave.

You should use site specific hydrogeological data and, if necessary, seek specialist hydrogeological help to use this data in your risk assessment.

Tiered approach to risk assessment

You must not pollute groundwater. You need to carry out a risk assessment to show that:

• hazardous substances have been, or will be, prevented from entering groundwater
• any non-hazardous pollutants entering groundwater will be limited so you do not cause pollution
• microbiological contaminants will not endanger water resources or drinking water supplies

You should use a tiered approach for risk assessments. The cost, time and effort of doing an assessment is proportional to the effort or measures required to make the risks from the activity acceptable.

For all tiers you need to develop a conceptual model.

Tier 1 assessment: risk screening

For a tier 1 assessment, you need to do a desk study and a qualitative risk assessment. You can then assess the overall risk of the proposal as low, medium or high. For high and medium risks you need to do a more detailed tier 2 or 3 risk assessment. You will need to do a tier 3 risk assessment for the highest risk cemeteries.

Tier 2 and 3 assessments: detailed risk assessments

For tier 2 and 3 assessments you need to build on the information you gathered in your tier 1 assessment and refine your conceptual model.

If your risk assessment shows there will be pollution or even a risk of pollution, you need to work with your local council and us to address this.

Tier 2 and 3 minimum risk assessment requirements

For tier 2 and 3 assessments you need to supply the following minimum information.

Site description

Your risk assessment must show for:

• tier 2, a local survey to supplement Ordnance Survey maps
• tier 3, an accurate site survey based on location, area and topography – mark any landscaping included in the proposal

Number, type and sequence of burials

Your risk assessment must show for:

• tier 2, projections on which annual numbers are based – provide supporting data and explanations
• tier 3, the tier 2 projections and a plan of the proposed sequence of burial area use – indicate the expected progression over time

Meteorological factors

For tier 2, your risk assessment must show both the:

• long-term average data on local rainfall
• Met Office Rainfall and Evaporation Calculation System soil moisture data

For tier 3, your risk assessment must show an analysis of available data to find out all of the following:

• monthly mean, maximum and minimum effective rainfall
• soil moisture data for bare soil, short-rooted vegetation and deep-rooted vegetation

Soil and subsoil characteristics

Your risk assessment must show for:

• tier 2, soil survey maps and possible site investigation and percolation tests
• tier 3, site survey with augering and trial pits

Geology (including superficial) and hydrogeology

For tier 2, you must show geological and hydrogeological maps and histories. You may also need to include:

• limited site investigation (like trial pits and drilling)
• an evaluation of the groundwater vulnerability
• the presence of any source protection zones
• an assessment of the aquifer characteristics from published data

For tier 3, you need to provide the tier 2 information, plus:

• rock and soil characteristics
• presence of any potential shallow groundwater
• variations in water table recorded for at least 1 year of monthly measurements

Any boreholes you use must be appropriately designed to define the physical conditions of the surrounding groundwater. Gather data and carry out any suitable investigations (for example, to estimate permeability based on falling head test, bailing test, tracer tests).

You must have at least 3 investigation boreholes – 1 on the up-gradient side of the site and 2 close to the down-gradient boundary. You should be able to work out the groundwater flow direction from your investigation boreholes.

Monitoring

Your risk assessment must show:

• tier 2 groundwater monitoring data
• tier 3 groundwater monitoring data – off-site monitoring may be necessary

Proximity to water abstraction sources or resource

For tier 2, your risk assessment must show both:

• records of licensed abstractions within 1km  of the site
• local council records of private water supplies within 1km of the site (include surface and groundwater supplies)

Locating nearby private water supplies is important as not all of these supplies are licensed by us.

For tier 3, you risk assessment must show the tier 2 information, plus any additional water features within 1km of the site including all:

• groundwater
• drainage
• flood risk
• surface water features (read more about water features surveys)

Data assessment

Your risk assessment must show for:

• tier 2, simple pollutant flux and water balance calculations, such as dilution at the water table
• tier 3, possible use of more sophisticated models to assess attenuation (reduce the effect of)

Proximity to housing or other developments

Tier 2 and 3 risk assessments must check local, regional or national planning authority for potential:

• residential, educational, commercial or industrial developments
• roads, rail and mineral extractions

Monitoring groundwater

You do not need to monitor the groundwater at your site if the risk assessment shows that the risk to groundwater is low enough to make monitoring unnecessary. If you do need to monitor groundwater, the frequency and extent of monitoring will depend on the degree of risk.

Follow the groundwater monitoring principles and the technical guidance for monitoring groundwater.

You need to carry out monitoring to:

• define the baseline water quality and physical conditions in surrounding groundwater and surface waters before development
• identify all vulnerable receptors and help identify potential pathways
• provide an early warning of adverse environmental impacts

If your monitoring identifies pollution, you must stop further burials, investigate, and stop the pollution before you can start burials again. You must tell us.

Minimum monitoring requirements

You may need to consider what parameters you are monitoring on a site-specific basis. For example, you may need to include formaldehyde, organics, hazardous substances and bacterial indicators. You should get suitably qualified professional advice when considering any groundwater monitoring requirements.

Where you need to monitor groundwater, you must meet the following minimum requirements for pre-development and ongoing burials.

Minimum number of boreholes

You must have at least 3 investigation boreholes – 1 on the up-gradient side of the site and 2 close to the down-gradient boundary. You should be able to work out the groundwater flow direction from your monitoring boreholes.

Minimum borehole monitoring period

You should monitor:

• for 1 year before the site is developed
• for a period of 3 years after the first burial

For the highest risk sites, we may require you to increase the frequency or extent of monitoring, both before development and in the longer term. Any monitoring requirements for such sites will be set out in your environmental permit. This will depend on the sensitivity of the site – the results can be reviewed accordingly.

Surface water monitoring points

For surface waters that are at risk you should have 1 monitoring point upstream and 1 downstream. You should make sure you monitor them on a monthly basis.

Baseline conditions

The minimum frequency for monitoring baseline conditions and the monitoring suite (the determinands) before development is either quarterly or 6 monthly.

Quarterly you should monitor for water level, pH, temperature, electrical conductivity,

dissolved oxygen, ammonium, total oxidised nitrogen (nitrate and nitrite), chlorine

Every 6 months you should monitor for sulphate, total organic carbon, biological oxygen demand, chemical oxygen demand, alkalinity, sodium, potassium, calcium, magnesium, iron, manganese, cadmium, chromium, copper, nickel, lead, zinc, phosphorus, formaldehyde (if allowed at the burial location), mercury.

Long-term monitoring

Once the site is in use every 6 months you should monitor the following: water level, pH, temperature, electrical conductivity, dissolved oxygen, total oxidised nitrogen (nitrate and nitrite), total organic carbon, biological oxygen demand, chemical oxygen demand, ammonium, sulphate, chlorine, sodium, potassium, calcium, magnesium, iron, phosphorus, formaldehyde (if allowed at the burial location), mercury

You may also need to increase the frequency of monitoring for higher risk sites or decrease it to annual monitoring if monitoring shows stable conditions.

Pollutant release from body decay

You can use the following information to calculate the potential release of pollutants from the decomposition of a typical human body.

Composition of the human body by percentage of its weight is:

• water 64% 
• protein 20% 
• carbohydrate 1% 
• mineral salts 5% 
• fat 10% 

The elemental composition of a human body based on a 70 kilogram body is:

• Oxygen 43,000 grams
• Carbon 16,000 grams
• Hydrogen 7,000 grams
• Nitrogen 1,800 grams
• Calcium 1,100 grams
• Phosphorus 500 grams
• Sulphur 140 grams
• Potassium 140 grams
• Sodium 100 grams
• Chlorine 95 grams
• Magnesium 18 grams
• Iron 4.2 grams
• Copper 0.07 grams
• Lead 0.12 grams
• Cadmium 0.05 grams
• Nickel 0.01 grams
• Uranium 0.00009 grams

Factors affecting the rate of decomposition

Decomposition relies on the rate of activity of degrading organisms and on the rate of the biochemical reactions involved. Factors which could influence the degradation rate include:

• age at death
• body mass index
• cause of death
• integrity of the corpse
• burial depth
• preservatives

Site related factors include:

• geological and hydrogeological characteristics of the soil, including soil type, permeability and porosity
• microbiological characteristics of the soil
• mechanical, structural and resistance parameters of the soil
• coffin or other container construction
• land cover – land cover and topography will affect infiltration and water logging which will delay decomposition
• climate
• depth of unsaturated zone

How these factors interact can be complex. In 80% of cemetery burials, complete skeletonisation of the body would be within:

• 10 years for soil burial
• 30 years for entombment

Decay and dissolution

Bone dissolution is a slow process and will depend on the acidity of the surroundings. Skeletal materials may be expected to show faster dissolution in acid soils than more neutral soils.

When you model the decay and dissolution of a human corpse, you should consider the following:

• skeletonisation of a buried corpse may take 10 years to complete
• embalming with formaldehyde may delay decay but quantifiable effects data are not available – assume the same rates of decay for embalmed and unembalmed bodies
• assume the same decay rates for ‘green’ and conventional burial sites
• initial in-grave decomposition conditions are usually aerobic but the body rapidly reaches an anaerobic state

You also should assume a constant linear rate for degradation of the body, with delays for components known to be resistant or shielded in some way. For example:

• not all components will be readily degraded or solubilised during the skeletonisation process – phosphorus and calcium are mainly present in bone – estimate bone dissolution to take around 10 years after burial
• tissue degradation by aerobic processes will be limited by oxygen availability – expect it to occur at a constant rate in relation to depth, partial pressure or recharge rate, once the initial oxygen in the grave has gone
• degradation by anaerobic processes will be limited by availability of electron acceptors and controlled via recharge – expect it to occur at a constant rate
• tissue degradation by fermentation will be limited by microbial access to tissue surfaces – expect a linear degradation rate

The time it takes for a body to completely disappear, including the skeleton, is unclear and variable. A typical time period for ‘time to dust or removal’ is often modelled as 100 years.

Contaminant decay rates and timings

Contaminant: Calcium

• Mass per burial: 1,100 grams
• Available mass for release: 1,100 grams
• Release start year: 10
• Release end year: 100
• Kinetic release model: Zero-order
• Release rate per burial: 12.22 grams per year

Contaminant: Carbon (body + coffin contribution)

• Mass per burial: 16,000 grams plus 10,000 grams (Assumes a coffin mass of 15,000 grams)
• Available mass for release: 14,800 grams plus 10,000 grams (Assumes a coffin mass of 15,000 grams. Assumes that 1,200 grams are collagen found in bone and similar tissues. This collagen is degraded after skeletonisation and is therefore lost over 10 years )
• Release start year: 0
• Release end year: 10
• Kinetic release model: Zero-order
• Release rate per burial: 2,480 grams per year

Contaminant: Carbon (collagen fraction)

• Mass per burial: 1,200 grams
• Available mass for release: 1,200 grams (Assumes that in a 16,000-gram body, 1,200 grams are collagen found in bone and similar tissues. This collagen is degraded after skeletonisation and is therefore lost over 10 years)
• Release start year: 10
• Release end year: 20
• Kinetic release model: Zero-order
• Release rate per burial: 120 grams per year

Contaminant: Nitrogen (body + coffin contribution)

• Mass per burial: 1,800 grams plus 500 grams (Assumes a coffin mass of 15,000 grams and relies on catalytic hydrolysis of resin occurring in situ)
• Available mass for release: 1,400 grams plus 500 grams (Assumes that 400 grams are collagen found in bone and similar tissues. This collagen is degraded after skeletonisation and is therefore lost over 10 years. Also relies on catalytic hydrolysis of resin occurring in situ))
• Release start year: 0
• Release end year: 10
• Kinetic release model: Zero-order
• Release rate per burial: 190 grams per year

Contaminant: Nitrogen

• Mass per burial: 400 grams
• Available mass for release: 400 grams
• Release start year: 10
• Release end year: 20
• Kinetic release model: Zero-order
• Release rate per burial: 40 grams per year

Contaminant: Mercury

• Mass per burial: 3 grams
• Available mass for release: 3 grams
• Release start year: 0
• Release end year: 2,600
• Kinetic release model: Zero-order
• Release rate per burial: 1.12 times 10 to the minus 3 grams per year

Contaminant: Phosphorus

• Mass per burial: 500 grams
• Available mass for release: 500 grams
• Release start year: 10
• Release end year: 100
• Kinetic release model: Zero-order
• Release rate per burial: 5.55 grams per year

Contaminant: Formaldehyde

• Mass per burial: 180 grams
• Available mass for release: 180 grams
• Release start year: 0
• Release end year: 0.25 years
• Kinetic release model: Single-event release
• Release rate per burial: Not applicable

Contaminant: Formaldehyde

• Mass per burial: 500 grams (Relies on catalytic hydrolysis of resin occurring in situ)
• Available mass for release: 500 grams (Relies on catalytic hydrolysis of resin occurring in situ)
• Release start year: 0
• Release end year: 10
• Kinetic release model: Zero-order (Relies on catalytic hydrolysis of resin occurring in situ)
• Release rate per burial: 50 grams per year

Typical infiltration rates

The numbers and proximity of the buried in a cemetery or natural burial ground will vary.

When you do a risk assessment for green burials you must consider:

• lower burial densities
• whether trees or shrubs are planted on the grave – this will alter the biological and recharge conditions through the grave

The time it takes for pollutants to flush from a buried body relates to effective rainfall and the infiltration rate through the soil and grave. When you do your risk assessment you will need to consider infiltration rates and adjust your calculations accordingly.

Estimate the possible average composition of effluent reaching the water table beneath the burial ground by dividing the pollutant release by the total annual infiltration.

Below you will find estimates of water infiltration (litres per year) through a typical grave plot. It’s based on an average annual rainfall of 650mm and typical evapotranspiration losses. Each grave and surrounding area is considered to be centred on:

• 5.06 square metres for a typical municipal cemetery with 1,976 graves per hectare
• 6.32 square metres for green burial sites with 1,580 graves per hectare

For a grave cover of chippings the total annual infiltration is 1250 litres split between surface infiltration of 750 litres per year and infiltration from gras surrounds of 500 litres per year.

For a grave cover of grass the total annual infiltration is 1000 litres split between surface infiltration of 500 litres per year and infiltration from gras surrounds of 500 litres per year.

For a green burial the total annual infiltration is 1010 litres split between surface infiltration of 250 litres per year and infiltration from gras surrounds of 760 litres per year.

Potential groundwater pollutants from human burials

The end products of body degradation will occur as:

• volatile gaseous products such as carbon dioxide, methane and ammonia – these will migrate up to the surface by diffusion and advection
• soluble and suspended components such as ammonium and micro-organisms – these will migrate down through the subsurface with recharge

The soluble and suspended components risk polluting groundwater. They include:

• ammoniacal nitrogen
• total oxidised nitrogen (nitrate and nitrite)
• formaldehyde (used in embalming fluid and coffin manufacture)
• mercury (as amalgam in dental fillings)
• other metals (mostly of medical or jewellery origin)
• pathogens (including bacteria and viruses)
• phosphorus and calcium (from bone)

Attenuation (reduce the effect) of pollutants from burial sites

Pollutants from burial sites may migrate into the:

• soil zone surrounding the burial
• unsaturated zone of the underlying aquifer
• saturated zone of the aquifer

Different degradation processes will occur in each zone. The depth of grave and depth of soil underneath a grave will affect how pollutants transform and degrade.

For example, in shallow soil zones or deep graves, the attenuation of pollutants from a burial will rely more on the processes in the unsaturated zone and saturated zone. Soil zone processes will be less important.

After a burial the main processes of attenuation are in the:

• soil zone – intense chemical and biochemical degradation, filtration and sorption (there is usually enough air for rapid oxidation of pollutants unless the soil is waterlogged)
• unsaturated zone – sorption and filtration but reduced chemical and biochemical degradation
• saturated zone – dilution and dispersion (the extent of filtration depends on the nature of the aquifer; chemical reactions depend on the groundwater chemistry)

There is less chemical and biological activity below the soil, in the unsaturated zone. Oxygen diffusion from the surface is low and low oxygen (anoxic) conditions may develop. This may affect the production of some pollutants (for example nitrate). However, chemical and biochemical reactions may continue to attenuate (reduce the effect of) pollutants. Filtration and sorption may continue to de-mobilise particulates and some dissolved pollutants.

Micro-organisms and pathogens

Potential micro-organisms and pathogens from decomposing bodies could include:

• unicellular organisms and their resting stages such as giardia and cryptosporidium
• bacteria, fungi and their spores
• viruses

Only bacteria present a realistic threat of increasing after burial. Viruses, such as coronavirus, cannot replicate without a living host cell and so are not a concern after burial.

The transport of micro-organisms and pathogens in groundwater depends on their size, shape and how they travel through the aquifer – for example through the subsurface pores of aquifer systems as opposed to fractures.

The potential for the aquifer matrix to remove micro-organisms and pathogens by filtration depends on its nature. Where the major route for groundwater flow is through a porous intergranular matrix, like sandstone aquifers, there is a high filtration potential.

Aquifers where fractures are the main flow route, like chalk aquifers, have limited potential for filtration.

Water abstracted from a shallow depth has a shorter travel time within the aquifer. Therefore, it is more likely to be at risk of transporting micro-organisms and pathogens than water abstracted from a greater depth, which has a longer residence time.

Because of the short travel time, many springs and shallow wells are more vulnerable to microbial pollution problems than deep wells or boreholes.