Evaluation of groundwater observation of landfills
About this good practice
control level for evaluation of groundwater pollution (gwp):
Test values of the Federal soil protection ordinance for the exposure pathway soil-groundwater.
Significant adverse environmental effect if the trigger level (tl) is exceeded (EU landfill directive, app. III, capital C).
Step 1: Determination of the value for the tl.
Method of Lower Saxonia and Bavaria:
tl = average value of gwp of inflow well + Double standard deviation σ + difference value
Difference values: conductivity +200 µS/cm, Ca +20, Mg +10, Na +20,K +10, NH4 +0.3, Cl- +30, SO4- +30, NO3- +10, DOC or TOC +4 all in mg/l, AOX + 20 µg/l
For the planning of the after care phase: estimate the time till the gwp undercuts the tl (criteria to end the after care).
The equation of RAMKE, EHRIG, KRÜMPELBECK is good approximation to the trend of gwp after the end of operational phase.
c (t) = c0 • e-k•t
c(t) – concentration at the moment t
c0 – concentration at the moment 0 (e.g. beginning of measurements)
k – reduction constant
t – time since 0 (e.g. since beginning of measurements)
If the trend is not clear (what mostly occur): using of linear regression
Inverse function of above equation by RAMKE, EHRIG, KRÜMPELBECK
ln c(t) = ln c0 + k . t
has the same structure like the regression equation
y = a + b . x
Computing the time till undercutting the tl with the help oft he regression equation (tl = y, converting the equation to t)
Financial or human resources are not necessary to set up and run these practice.
Evidence of success
By estimation of the trigger level users receive a realistic value taking into account the statistical fluctuations of the inflow values.
Users receive a forecast about the period in which the groundwater observation values fall below the trigger level. This can help to plan the after care phase. The undercutting of the trigger level can be a good criterion for the end of after care.
Using statistical methods consider that the course of groundwater pollution doesn’t give a clear Image.
Potential for learning or transfer
The most landfills in the EU member states are not equipped with a basic sealing system. The emissions from the waste in the cases of greater landfills or landfills with hazardous waste can pollute the ground water. Therefore a groundwater observation is necessary may be over a long time in the after care phase. For the landfill owner and the authorities it is important to plan the after care. An important role in this connection plays the trigger level.
The EU landfill directive requires a groundwater observation and set the frame. But it gives no help either for the determination of the trigger level or the evaluation of the groundwater observation results.
The practice can be used for the evaluation of the groundwater observation of landfills without a basic sealing system, which is remediated by applying a surface sealing system. In these cases a groundwater pollution is to await, which decreases over the time. But the groundwater values often are fluctuating.