DRASTIC Aquifer Vulnerability Index

Participant name

Date

Two candidate locations are being compared for a facility that will store and handle hazardous chemicals. Beyond ordinary site-suitability screening, the client wants an independent check on how vulnerable the groundwater itself is to contamination at each location. Your task: compute the DRASTIC Index for both sites, classify their vulnerability, and recommend the safer location — purely from a groundwater-pollution-risk perspective.

📘 DRASTIC Method & Rating Tables (click to expand / collapse)

DRASTIC Index = Σ (Rating × Weight) for D, R, A, S, T, I, C

Seven hydrogeological parameters, each rated 1–10 (higher = more vulnerable to contamination), multiplied by a fixed weight reflecting its relative importance, then summed. Weights never change between sites — only the rating does, based on that site's actual conditions.

Letter	Parameter	Fixed Weight
D	Depth to Water Table	5
R	Net Recharge	4
A	Aquifer Media	3
S	Soil Media	2
T	Topography (% slope)	1
I	Impact of Vadose Zone Media	5
C	Hydraulic Conductivity of the Aquifer	3

Rating Tables (abbreviated — classes needed for this exercise)

D — Depth to Water (m)	Rating
0 – 1.5	10
1.5 – 4.6	9
4.6 – 9.1	7
9.1 – 15.2	5
15.2 – 22.9	3
22.9 – 30.5	2
> 30.5	1

R — Net Recharge (mm/yr)	Rating
0 – 51	1
51 – 102	3
102 – 178	6
178 – 254	8
> 254	9

A — Aquifer Media	Rating
Weathered metamorphic / igneous	4
Sand and gravel	8

S — Soil Media	Rating
Clay loam	3
Sandy loam	6

T — Topography (% slope)	Rating
0 – 2%	10
2 – 6%	9
6 – 12%	5
12 – 18%	3
> 18%	1

I — Vadose Zone Media	Rating
Metamorphic / igneous	4
Sand and gravel with silt and clay	6

C — Hydraulic Conductivity (m/day)	Rating
0.04 – 4.1	1
4.1 – 12.2	2
12.2 – 28.5	4
28.5 – 40.7	6
40.7 – 81.5	8
> 81.5	10

Vulnerability Classification

DRASTIC Index	Vulnerability Class
< 100	Low
100 – 140	Moderate
140 – 180	High
> 180	Very High

Theoretical range: 23 (all ratings = 1) to 230 (all ratings = 10). Method: Aller et al. (1987), USEPA. All site data in this exercise are synthetic, for training purposes only.

📋 Given Site Data (click to expand / collapse)

DRASTIC assumes a contaminant is applied at the ground surface and moves vertically with infiltrating water — it does not model horizontal transport, contaminant-specific chemistry, or an existing contamination source. It answers "how vulnerable is this location in general", not "what happens to this specific chemical if spilled here." Rating tables reproduced here are abbreviated to the classes needed for this exercise; consult the full USEPA reference for complete rating tables across all parameter classes.