1. Final Presentation of GIS in Water Resources
Determination of Aquifer Vulnerability using DRASTIC model across conterminous United States By
Karthik Kumarasamy
Final Presentation of GIS in Water Resources
Utah State University

2. Overview Concept of groundwater vulnerability DRASTIC Model
Data Sources and Preparation
Comparison with Nitrate concentration
Conclusion

3. Concept of groundwater vulnerability
Purpose: Management Tool to protect groundwater resources
Definition: Probability that a specific contaminant will be detected at or above a specified concentration in the subsurface at a specific location (EPA definition)
Some Vulnerability assessment models
DRASTIC
AVI
GOD
SEEPAGE
Ordinal Logistic Regression, etc

4. DRASTIC Model
DRASTIC
Empirical model developed by National Water Well Association and EPA
Parameters considered in DRASTIC
Depth to water table
Net Recharge
Aquifer media
Soil media
Topography (slope)
Impact of vadose zone media
(Aquifer hydraulic) Conductivity
Final DRASTIC Index = 5D + 4R + 3A + 2S + 1T + 5I + 3C
Study Area: Conterminous United States

5. Depth to water table Source: STATSGO Database Methodology:
Link the attribute table of Each State and component table to get the (Maximum value for the range in depth to seasonally high water table)
Append each state to get the final US map
(These steps are common for all maps using STATSGO data)
The field is known as wtdeph

6. Ratings of depth to water table

7. Net Recharge
Net recharge or groundwater recharge is estimated using Williams and Kissel's equation:
PI = (P )2/(P ) for hydrologic soil group A
PI = (P )2/(P ) for hydrologic soil group B
PI = (P )2/(P ) for hydrologic soil group C
PI = (P )2/(P ) for hydrologic soil group D
PI = average of A and D for Hydrologic soil group A/D
PI = average of B and D for Hydrologic soil group B/D
PI = average of C and D for Hydrologic soil group C/D
where,
PI = Percolation index
P = Annual average precipitation

8. Ratings of Net Recharge
DATA Source:
PRISM for precipitation data
STATSGO for soil hydrologic group

9. Ratings of Net Recharge

10. Ratings for Aquifer Media
Source: Shallow aquifers of conterminous United States (Groundwater atlas of US)
Other Rocks: 3
Carbonate-rock aquifers: 8
Igneous and metamorphic rock aquifers: 3
Sand stone and carbonate rock aquifers: 6
Sandstone aquifers: 6
Semiconsolidated sand aquifers: 4
Unconsolidated sand and gravel aquifers: 8

11. Rating of Aquifer media

12. Rating for Soil Media (Done based on the Soil Hydrologic group)
Source: STATSGO database
A: 8
B: 5
C: 4
D: 3
A/D: 6
B/D: 4
C/D: 4

13. Rating of Soil Media

14. Topography Topography (slope): Ratings STATSGO soil database
Methodology
(sloepl + slopeh) /2 * (comppct/100)

15. Rating of Topography

16. Impact of vadose zone
Data from Groundwater Atlas (shallowest principal aquifers of the conterminous United States) to determine the Vadose Zone ratings
Assuming that the same geology will be present above the water table as well

17. Rating for Impact of Vadose zone
Other Rocks: 1
Carbonate-rock aquifers: 6
Igneous and metamorphic rock aquifers: 4
Sand stone and carbonate rock aquifers: 6
Sandstone aquifers: 6
Semiconsolidated sand aquifers: 5
Unconsolidated sand and gravel aquifers: 8

18. Rating for Impact of Vadose zone

19. Ranges for Hydraulic Conductivity (GPD/ ft2) (Freeze and Cheery, 1979)
Other Rocks: little or no permeability
Carbonate-rock aquifers: 10-2 – 101
Igneous and metamorphic rock aquifers: 10-7 – 103
Sand stone and carbonate rock aquifers: 10-3 – 101
Sandstone aquifers: 10-3 – 101
Semiconsolidated sand aquifers: 1-103
Unconsolidated sand and gravel aquifers:

20. Ratings for Hydraulic Conductivity
Other Rocks:
Carbonate-rock aquifers: 1
Igneous and metamorphic rock aquifers: 1
Sand stone and carbonate rock aquifers: 1
Sandstone aquifers: 1
Semiconsolidated sand aquifers: 8
Unconsolidated sand and gravel aquifers: 10

21. Ratings of Hydraulic Conductivity

22. DRASTIC Index

23. Nitrate concentration Data
Source: usgs (NAWQA program)
Values are the median values of NO3 concentration

24. Distribution of Nitrate concentration across United States

25. Conclusion
Areas shown vulnerable by the DRASTIC model spatially coincide with nitrate concentration wells with high concentration of Nitrate
Even though there is subjectivity in the rating of parameters results match well

26. Thank you!!!! Any Questions