Some shallow water boreholes penetrated in clean sands that are close to a dumpsite were observed to have some black precipitous sediments.
the water samples collected from borehole adjacent to dumpsite are best for water sample collection. The leachate should be tested for nutrients, trace metals, trace organics, pharmaceuticals beside others.
The first step would be to either look at relatively long term groundwater quality monitoring data covering upstream and downstream of the dump-site to get a sense of the influence of the leachate infiltration to subsurface and groundwater. The upstreamm or background water quality data would be important for comparison. If this type of data is not available (usually the case if it is just a dumpsite and nt a sanitary landfill with monitoring network) you may want to perform a preliminary sampling looking for relevant quality constituents. In case of MSW land disposal, you can look for BOD, COD, TOC and particularly chloride would be a good indicator since it is conservative and you might expect a few thousands of ppm chloride in leachate. You will also have to look at the leachate quality as well. Heavy metals typically have very low concentration in MSW leachate, not quite a concern and often not a good indicator of MSW leachate infiltration.
Secondly, if you have basic information on the properties of subsurface soil and depth of groundwater and alike, you can perform a simple mathematical modeling or stochastic modeling using approaches developed by US EPA in EPACMTP model. You can have a look at it and see if you can employ that kind of modeling.
I agree with my peers about this problem. Gaining an understanding of the groundwater flow and basic aquifer hydrogeology is very important. Assuming you have enough observation wells to determine the groundwater flow direction, then you can determine which wells are actually upgradient and which ones are downgradient. Then you look for key tracers like chloride and perhaps boron in observation wells. I would also be concerned about organic contaminants at the site if it was an uncontrolled dump site. In many similar sites in the USA, TCE or other similar organic chemicals (many solvents) may have been dumped. These organic chemicals may not all behave like chloride or boron. They have specific gravities greater than 1.0 which means they can travel on their own density currents and generally follow the slope of the underlying confining unit. Therefore, while the predominant groundwater flow may be in one direction, dense chemicals (also called DNAPL for dense non-aqeous phase liquids) may move in the opposite direction if the geology is right.
Tank you all for your comments. The dump site is not a landfill but an open waste dumpsite that have been in use for some time. Edwin , pls what is the full meaning of MSW? Christopher, can I get a more detailed information on the USEPA model you mentioned. Once more thank you for your insightful comments!
I agree with the others, first establish groundwater depth and flow direction, and of course the local geology! Google earth may help for liniaments and a topographical profile (if it is a high resolution area). Than try to map the plume with geophysics. In most cases there will be a good contrast in resistivity. If you cannot establish the groundwater flow direction, 360 degree around the side should be examined.
Groundwater flow direction, can be meassured with at least 3 piezometers (assuming more or less homogenious aquifer) and a waterlevel instrument. May be there are some wells close to the area.
Even when it is not a homogenious aquifer, start with frequency domain methods to test if you can detect the plume, depending the depth of the groundwater and aquifer characterisitics. More simple methods like wenner profiling will do the Job also. it is important to use the right electrode configuration and distance.
Combine this with 2D DC resisisitivty (preferable CVES/RET) to get an 3 dimensional picture.
On this information install piezometers with "minifilters" to get chemical samples and for future monitoring. Plastic filters of at least 2 inch can be very usefull for borelogging (gamma and conductivity) to combine the resistivity information and water quality.
I hope this will help.
When it is open dump different steps should be considered:
1- identify the up and down sream for water drainage.
2- counter the open dump by making its limits.
3- at the down part, make a dig of 1-2 m of large in order to collect the landfill leachate.
4- transfert the leachate to a treatment plant if it is possible and /or treated it insitu.
I agree to look for BOD, COD, TOC, and trace metals, moreover, the chloride, Sodium would be a good indicator since it is conservative and you might expect a few thousands of ppm chloride and sodium in leachate (look to soil as background). You will also have to look at the leachate quality as well. Heavy metals typically have very low concentration in leachate, but not quite a concern and often not a good indicator of MSW leachate infiltration.
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