Assessment of groundwater nitrate pollution potential in Central Valley aquifer using DRASTIC and Geodetector-based Frequency Ratio method.

Authors: Anil Shrestha*,
Topics: Water Resources and Hydrology
Keywords: Geodetector, DRASTIC, nitrate, groundwater, Central Valley
Session Type: Paper
Day: 4/14/2018
Start / End Time: 2:00 PM / 3:40 PM
Room: Galvez, , Marriott, 5th Floor
Presentation File: No File Uploaded

Groundwater nitrate contamination in Central Valley (CV) aquifer is widespread throughout the valley because of excess nitrogen fertilizer leaching down into the aquifer. The percolation of nitrate depends on several hydrogeological conditions of the valley. Groundwater contamination vulnerability mapping uses hydrogeologic conditions to predict vulnerable areas. This paper presents a new Geodetector-based frequency ratio method (GFR) method for mapping contamination vulnerability and compared results with that from standard DRASTIC method. The DRASTIC method combines the individual weights and rating value for Depth to water, Recharge rate, Aquifer media, Soil Media, Topography, Impact of vadose zone, and Hydraulic Conductivity. The GFR method incorporates frequency ratio method (often used in landslide susceptibility mapping) and weights of factors objectively determined by Geodetector to generate nitrate susceptibility map of CV. Both methods revealed San Joaquin and Tulare basin as vulnerable region with higher index values. Higher number of watersheds above mean susceptibility index and higher number of watershed in the higher interval range using natural break classification were found in the GFR model. The model assessment results showed higher coefficient value and higher PD values were between PWN>5 and GFR index than DRASTIC index suggesting GFR is a better and more objective method for groundwater contamination vulnerability mapping in CV aquifer.

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