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

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

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

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

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

Ratings of depth to water table

Net Recharge Net recharge or groundwater recharge is estimated using Williams and Kissel's equation: PI = (P - 10.28)2/(P + 15.43) for hydrologic soil group A PI = (P - 15.05)2/(P + 22.57) for hydrologic soil group B PI = (P - 19.53)2/(P + 29.29) for hydrologic soil group C PI = (P - 22.67)2/(P + 34.00) 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

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

Ratings of Net Recharge

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

Rating of Aquifer media

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

Rating of Soil Media

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

Rating of Topography

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

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

Rating for Impact of Vadose zone

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: 102 - 106

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

Ratings of Hydraulic Conductivity

DRASTIC Index

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

Distribution of Nitrate concentration across United States

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

Thank you!!!! Any Questions