[[File:Susana logo.png|right|90px|alt=Susana logo.png]]This article is based on a [http://www.susana.org/en/resources/library/details/1229 98 factsheet] that deals with the planning of sustainable sanitation for urban and peri-urban areas of developing countries and its importance for achieving comprehensive and inclusive sanitation coverage in cities.
=== 1. Summary ===
Groundwater quality and sanitation are often linked as pollution of groundwater from unsafe household sanitation systems through nutrients, pathogens and organic micropollutants (including emerging contaminants) can occur.
=== 2. Why care about groundwater ===
[[File:Well, Lusaka.jpg|thumb|right|200px|Figure 1: Unprotected well at close distance of a pit latrine in Well, Lusaka, Zambia (source: K. Mayumbelo, 2006).jpg]]Compared to surface water bodies, groundwater resources are better protected against pollution and evaporation during dry seasons, therefore they represent a more important and efficient form of water storage. Furthermore, the development costs are usually comparatively low; as groundwater is a local resource which normally needs only simple water treatment and for small systems requires only very simple distribution systems. Natural groundwater, unaffected by human activities, is free of pathogens and in many areas free of undesirable chemical substances.
In arid and semi-arid countries groundwater is very often the sole resource for agricultural irrigation. All these facts turn groundwater in most areas of the world into an affordable, reliable and an inevitable key element of sustainable human development.
=== 3. Introduction to groundwater pollution ===
Historically it was widely believed that groundwater is generally pure and safe for drinking purposes even without treatment. However, in the past few decades, cases of disease outbreaks due to the consumption of untreated, contaminated groundwater have increasingly been reported.
=== 4. Pathogenic pollution ===
Pathogens cause diseases such as cholera, hepatitis A and diarrhoea. In those countries where groundwater is the sole source of drinking water, prevention of faecal-oral transmission should be a highly prioritised public health outcome. Once pathogens have infiltrated into the groundwater it takes different amounts of time for different types of pathogens to die off. During this time, groundwater travels a certain distance depending on the permeability of the aquifer (i.e. the groundwater body). In addition to natural die-off, pathogen removal is also a result of adsorption and filtration through the soil and sub-surface media.
It must be noted that it requires professional experience and knowledge of the subsurface conditions to estimate the minimum distance in the soil aquifer system, which results in a travel time of 50 days. If there is doubt, always use a conservative estimate and account for larger distances.
===5. Chemical pollution === [[File:Cl DOC.jpg|thumb|right|200px|Figure 2: Range of increased chloride and Dissolved Organic Carbon (Cl DOC) concentrations in groundwater from wastewater infiltration research areas (Foster and Chilton, 2004).jpg]]Beside pathogens, human excreta contain organic matter, nitrogen and phosphorus. Urban wastewater has a high organic content (Figure 2), which is relatively easily oxidised under aerobic conditions. Where the water table is deep, oxygen and micro-organisms in the unsaturated zone of the aquifer may remove (degrade) much of the organic matter.
The more and more anaerobic (i.e. lacking oxygen) the groundwater environment becomes the more microorganisms are forced to utilise other substances, other than oxygen, for degradation of organic matter and thereby release their metabolism products into the groundwater. This results in a fundamental change in the groundwater chemistry, including increases of dissolved ammonia, manganese, iron, hydrogen sulfide, methane and possibly also metalloid substances such as arsenic.
==== a) Pollution due to nitrogen compounds ====
The nitrogen (N) cycle is complex; the predominant wastewater and animal manure related nitrogen form entering the (un)saturated zone from untreated sewage is ammonium while from treated sewage and from chemical fertilisers it is nitrate. The main mechanism for the transformation of N from wastewater that has infiltrated in the soil is denitrification, whereby first ammonium (NH4+) from wastewater is oxidised into nitrate (NO3-, called nitrification). Then, further in the aquifer, provided that anaerobic conditions prevail, nitrate is reduced into nitrogen gas (N2, called denitrification), which is stable and ultimately may escape to the atmosphere.
==== b) Pollution due to phosphorus ====
The main source of phosphorus in wastewater is inorganic orthophosphate and organic phosphorus. Due to anaerobic digestion, the latter is usually transformed into orthophosphate. Phosphorus transport in groundwater exists, however health threats occur only indirectly. Phosphate in aquifers is usually bound to iron-oxides (Dzombak, Morel, 1990) or precipitates as phosphate minerals, like hydroxy-apatite, vivianite, variscite or strengite.
==== c) Pollution due to other anthropogenic induced pollutants ====
In some settings, due to the infiltration of wastewater, toxic compounds like arsenic are released. Of the various routes of exposure to arsenic, drinking water probably poses the greatest threat to human health. The International Agency for Research on Cancer (IARC) has classified arsenic as a Group 1 human carcinogen.<br/>Serious and long lasting groundwater contamination is known to result from chemical substances like chlorinated, hydrocarbons, BTEX, polycyclic aromated hydrocarbons (PAH), which are often introduced via leakages or spillage events. Where such industry chemicals are discharged into the wastewater, the drainage system is providing an additional entrance pathway to groundwater.
=== 6. Pollution due to organic micro pollutants ===
Organic micropollutants or so called “emerging contaminants” are now frequently being detected in wastewater and the environment in concentrations up to several μg/L, although they might have been present already for decades (Ternes, 2009). Prominent examples of emerging contaminants are pharmaceuticals, estrogens, ingredients of personal care products, biocides, flame retardants, benzothiazoles, benzotriazoles or perfluorinated compounds (PFC). Organic micropollutants are usually quite small (molecular weight predominantly varies between 50 and 1000 Da), therefore regular municipal WWTPs or on-site sanitation systems do not remove these polar persistent organic pollutants.
=== 7. Protecting groundwater from pollution ===
[[File:Protection areas.jpg|thumb|right|200px|Figure 3: Protection areas in a catchment where the well is in Zone 1 on the left side (source: © Bayerisches Landesamt für Umwelt (LfU)).jpg]]<span style="line-height: 20.7999992370605px"></span>The difference between groundwater resources as a whole and the source of groundwater for use can be explained through its management: When groundwater is well managed, the resource as a whole is protected for current and future uses; while we protect a currently used groundwater source in a defined area with specific and often very specific measures regarding land use.
==== a) Source protection ====
The best way to protect groundwater is to prevent contaminants from entering the aquifer which pose a threat to water quality and are hazardous to human health. One practical way to achieve this is land-use planning. In order to prevent groundwater contamination, drinking water protection areas are delineated around production wells or springs (see Figure 3).
==== b) Resource protection====
An empirical model to map aquifer vulnerability has been developed by the USA National Water Well Association and the Environment Protection Agency. The DRASTIC approach refers to hydrogeological units incorporating major factors which affect and control groundwater movement (Depth to groundwater table, net Recharge, Aquifer media, Soil media, Topography, vadose zone media Impact and hydraulic Conductivity of the aquifer). These factors form the acronym DRASTIC and give their rated and weighted input to the numerical DRASTIC index (USEPA, 1987). This index, in combination with the mappable hydrogeological settings, creates a groundwater vulnerability map. The approach helps to prioritise monitoring and protection measures.
==== c) How to protect the groundwater resource ====
An integrated water resources management (IWRM) approach is needed in the urban context as it explicitly recognises the complex sets of interdependent relationships which exist within and between human and environmental systems. One guideline of an IWRM approach is that water decisions should be made at the lowest appropriate scale.
=== 8. Productive land use and groundwater protection ===
[[File:Water flux catchment zone.jpg|thumb|right|200px|Figure 4: Catchment with its water fluxes (ET = Evapotranspiration, discharge = surface and subsurface outflow) (source: Falkenmark, 2004)Water flux catchment zone.jpg]]If a given area for agricultural production is to be used most efficiently, crop harvests need to be increased by fertiliser application. Local conditions limit the maximum amount of fertiliser that can be applied. This is determined by plant uptake depending on the crop specimen and by effective field capacity depending on the soil type. Fertiliser application exceeding this amount will cause a leaching to the groundwater. Poor timing and inappropriate dosing of fertiliser or application on sandy soil may cause leaching of nitrates into the groundwater.
Most synthetic fertilisers consist of a combination of phosphorus (P), nitrogen (N) and potassium (K). While phosphorus and potassium are prone to sorption processes in the soil, nitrogen reaches the groundwater at the same time as the percolating water. Therefore, in order to prevent high nitrate concentrations in groundwater over the longer term and eutrophication of surface waters, regulations on fertiliser application should be developed and enforced. Organic fertiliser, which produces less leakage of nitrate into the groundwater (UBA, 2002) is preferred over synthetic fertiliser, and soil should be managed in a sustainable way. Erosion, leakages of nutrients and loss of humus should be avoided.
=== 9. Policy recommendations ===
[[File:Open drain,senegal.jpg|thumb|right|200px|Figure 5: In densely populated areas infiltration of wastewater threatens groundwater resources in Senegal. Note also the water pipe in the Open drain which is a common but unsafe practice (source: BGR, 2005)senegal.jpg]]The following recommendations were developed by the participants of the international symposium “Coupling groundwater protection and sustainable sanitation” which took place in Hannover, Germany in 2008 (BGR, 2008).
*Both, groundwater protection and sustainable sanitation represent basic tasks for all development planning. Every new settlement should take groundwater resources into account and the protection of aquifers should have a high priority. Land-use planning, based on a holistic approach and therefore economically, socially and ecologically sound, is required to protect precious resources like groundwater.
*To fulfil the five sustainability criteria, a sanitation system has to be not only economically viable, socially acceptable, and technically and institutionally appropriate, it should also protect the environment and the natural resources. Geoscientific aspects have to be considered during sanitation planning, including climate, hydrogeology, soil characteristics and geo-morphology.
=== 10. Acknowledgements ===
SuSanA factsheet: Sustainable sanitation and groundwater protection. April 2012. [http://susana.org susana.org]
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