Methods of Groundwater Vulnerability and Protectability Assessment - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 12

Table 1.1 Scores for groundwater table depth H.

Depth range H ≤ 10 m 10 m < H ≤ 20 m 20 m < H ≤ 30 m 30 m < H ≤ 40 m H > 40 m

Score 1 2 3 4 5

Table 1.2 Scores for low-permeable deposit thickness and lithology.

Lithology Group of Deposits/(Hydraulic Conductivity, k , m/day)

A
(0.01 ≤ k < 0.1),

B
(0.001 ≤ k < 0.01),

C
( k < 0.001),

Thickness of
Low-Permeable
Deposits, m 0 , m

Loamy Sands,
Light Sandy Loams

Heavy Sandy Loams,
Clays

Mixed A and C

m 0 ≤ 2 1 1 2

2 < m 0 ≤ 4 2 3 4

4 < m 0 ≤ 6 3 4 6

6 < m 0 ≤ 8 4 6 8

8 < m 0 ≤ 10 5 7 10

10 < m 0 ≤ 12 6 9 12

12 < m 0 ≤ 14 7 10 14

14 < m 0 ≤ 16 8 12 16

16 < m 0 ≤ 18 9 13 18

18 < m 0 ≤ 20 10 15 20

m 0 > 20 12 18 25

Less favorable groundwater protectability conditions correspond to category I,
and most favorable ones correspond to category VI. Suppose, for example, that the
groundwater table is at depth 7 m from the land surface (score 1 according to Table 1)
and there is a 3 m thick layer of loamy sand and light sandy loam in the unsaturated
zone (score 2 by lithology group A, Table 1.2). Then, by the sum of the scores ε = 3,
the groundwater protectability category is I . If the groundwater table is at depth
14 m (score 2, Table 1.1) and there is a 5 m thick layer of clays (score 6 by group
C, Table 1.2), then ε = 8, which corresponds to the groundwater protectability cate-
gory II.
Confined groundwater protectability can be assessed using Goldberg's qualitative
groundwater protectability assessment by the thickness of the overlying (low-perme-
able) confining bed, m 0 , also taking into account the data on the ratio of groundwater
hydraulic head in the confined and upper unconfined aquifers. If the hydraulic
conductivity k 0 of the confining bed is known, then a more refined groundwater
protectability assessment can be performed using the parameter α = m 0 / k 0 , physically
determining the water percolation time through the confining bed at a unit ground-
water hydraulic head gradient (flow directed downward). Taking k 0 as ranging from