Table 3 The relative weights and rates of DRASTIC parameters (Aller 1985) and (Secunda et al. 1998) for various hydro-geological settings
Rating | depth to the water table | Net recharge | Aquifer media | Soil media | Topography | Impact of vadose zone | Hydraulic conductivity |
|---|---|---|---|---|---|---|---|
Range (m) | Range (mm/yr) | Range | Range | Range (%) | RANGE | Range (m/day) | |
10 | 0–1.5 |  | Karst limestone | Thin or absent | 0–2 | Karst limestone |  > 80 |
9 | 1.5–4.5 |  > 250 | Basalt | Sandy | 2–6 | Basalt |  |
8 |  | 175–250 | Sand and gravel | Peat |  | Sand and Basalt | 40–80 |
7 | 4.5–9 |  |  | Shrinking |  | Metamorphic/Igneous |  |
6 |  | 100–175 | Bedden sand-ston, | Sandy loam |  | Limstone/sandstone | 30–40 |
5 | 9–15 |  | Glacia till | Loam | 6–12 |  |  |
4 |  |  | Weathered | Silt loam |  |  | 12–30 |
3 | 15–22 | 50–100 | Metamorphic/igneous | Clay loam | 12–18 | Sily/clay/shale |  |
2 | 22–30 |  | Massive shale | Muck |  |  | 4–12 |
1 |  > 30 |  < 50 |  | Non-shrinking |  > 18 | Confining layer |  < 4 |