Risk assessment of water sources
Does anybody have any information on Risk assessment of boreholes, springs, wells and their catchment areas post-earthquake? Also any information on water safety plans would be good and training manuals on water quality monitoring and surveillance
3 Answers
One point that should be obvious with groundwater sources and an earthquake is that no reliance should be put on pre quake information because the tremors may well have disturbed the fissures in the aquifer that channel water and this can result in pollution finding a route to the groundwater. Also the headworks structures and linings if damaged may be permitting surface intrusion.
Regards
Steve Oxtoby
You can download the WHO Water Safety Plan Manual here: https://www.who.int/water_sanitation_health/publication_9789241562638/en/ Water safety plans are also covered in the Sphere Minimum Standards: https://www.spherehandbook.org/en/water-supply-standard-2-water-quality/
Water quality monitoring and surveillance is really dependent on the risks which in turn are dependent on both the source and the users of the water. Can you tell us more about the specific application?
General comments:
How the zones work? How do we define groundwater source protection zones?
The shape and size of a zone depends on the condition of the ground, how the groundwater is removed, and other environmental factors. When we define a zone we find out how the groundwater behaves in that area, what constructions there are to get the water out into the public water supply, and the process for doing this. From this we can develop a model of the groundwater environment on which to define the zones. We divide groundwater source catchments into four zones. The zones are divided as follows:
Zone 1 (Inner protection zone)
Any pollution that can travel to the borehole within 50 days from any point within the zone is classified as being inside zone 1. This applies at and below the water table. This zone also has a minimum 50 metre protection radius around the borehole. These criteria are designed to protect against the transmission of toxic chemicals and water-borne disease. Generally this means installing fences to prevent animal or unauthorised access, a concrete or impenetrable membrane immediately around the BH to prevent surface run off getting into the BH itself. Removal of upstream contamination sources, privies, etc from with the 50m radius.
Zone 2 (Outer protection zone)
The outer zone covers pollution that takes up to 400 days to travel to the borehole, or 25% of the total catchment area – whichever area is the biggest. This travel time is the minimum amount of time that we think pollutants need to be diluted, reduced in strength or delayed by the time they reach the borehole.
Zone 3 (Total catchment)
The total catchment is the total area needed to support removal of water from the borehole, and to support any discharge from the borehole.
Zone of special interest
Sometimes, we define a fourth zone. This is usually where local conditions mean that industrial sites and other polluters could affect the groundwater source even though they are outside the normal catchment area
Regards
Phil Bailey
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