Methods of Groundwater Vulnerability and Protectability Assessment - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 8

quartzite, massive igneous and metamorphic rock); 20 (claystone, silt-
stone, shale, marlstone);
F is the jointing and karstification indicator with values: 0.3 (strongly
jointed, fractured, or karstic), 0.5 (moderately karstic), 1(moderately
jointed, slightly karstic; or no data), 4 (slightly jointed), and 25
(nonjointed).

4. Unsaturated zone thickness T (sum of layer thicknesses T n ).

The resulting groundwater protectability index P T is calculated as

PPPQHP

T =+++

,

1 2

where

PSW

1 =⋅

is the protective effectiveness of the soil;

( )

PWRT RT = + ++  R nn

2 1 1 2 2

is the total protective effectiveness of the unsaturated zone layers, accounting for
lithology and rock disturbance (fracturing, karst); and Q = 500 and HP =1500 are
scores added a perched aquifer and a confined aquifer, respectively, if present.
Using the P T index, the groundwater protectability categories are determined as
follows: very low ( P T < 500), low (500-1000), average (1000-2000), high (2000-
3000), and very high (3000-4000).
The most problematic procedure of the method is the selection and substan-
tiation of the separate indicator scores for a given area.
The method was used in Germany [ Von Hoyer and Söfner , 1998] and other
countries [ Margane et al ., 1999]. It became the base for the PI method described
below.
The PI method of regional assessment of intrinsic groundwater vulnerability
was developed by Goldscheider [2005] especially for karst areas, but it can be used
for any other hydrogeological conditions. Although based on the German method
described above, in contrast, it specifically takes into account the zones of fast infiltra-
tion related with the accumulation of surface runoff in depressions and direct influx
of water into the upper aquifer through the open karst forms (caves, holes, etc.).
The resulting index of groundwater vulnerability is assessed as a product of
two indicators:
1.

Protective capacity of soil and unsaturated zone, P , with scores 1 (very low),
2 (low), 3 (average), 4 (high), and 5 (very high). Increasing scores by one point
corresponds to a tenfold increase of protective capacity.

2. Infiltration conditions, I , is an indicator of the influence of fast infiltration

zones, with scores 0-0.2 (maximum), 0.2-0.4 (high), 0.4-0.6 (average),
0.6-0.8 (low), and 0.8-1 (very low).