Groundwater Management action Plan stage 3. Characterising and prioritising groundwater pollution threats. Decision Support System Tool - example from Narayanganj - lessons learnt.
For stage 1 an example is given of using the Excel version of the Decision Support System Tool to assess urban activities and liquid waste disposal methods for Narajanganj, Bangladesh.
For stage 2 the pollution threat is assessed using simple approximations of groundwater setting.
Two scenarios were assessed, because there are two hydrogeological settings with distinctly different hazard susceptibility in Narayanganj. The cover of clayey superficial deposits (soil and Recent alluvium) is variable, resulting in near-unconfined conditions in the west and south of the project area and probable semi-confined condition in central districts north of the city. Also, a number of deep brick pits are present especially on the west side of the project area. These not only remove clayey brickearth down to the shallow aquifer surface, sometimes to depth of more than 15m, but also provide large excavations up to several tens of hectares in size some of which are being used for domestic and industrial solid waste disposal. These brick pits significantly reduce the hydraulic inaccessibility of the shallow aquifer.
Scenario A assessed the less vulnerable semi-confined setting while Scenario B assessed the effect where a semi-confining layer is either thin, absent or has been removed.