5 research outputs found
Environmental setting of the San Joaquin-Tulare basins, California /
Shipping list no.: 99-0138-P."National Water-Quality Assessment Program."Includes bibliographical references (p. 42-45).Mode of access: Internet
Modeling Nitrate at Domestic and Public-Supply Well Depths in the Central Valley, California
Aquifer
vulnerability models were developed to map groundwater
nitrate concentration at domestic and public-supply well depths in
the Central Valley, California. We compared three modeling methods
for ability to predict nitrate concentration >4 mg/L: logistic
regression
(LR), random forest classification (RFC), and random forest regression
(RFR). All three models indicated processes of nitrogen fertilizer
input at the land surface, transmission through coarse-textured, well-drained
soils, and transport in the aquifer to the well screen. The total
percent correct predictions were similar among the three models (69–82%),
but RFR had greater sensitivity (84% for shallow wells and 51% for
deep wells). The results suggest that RFR can better identify areas
with high nitrate concentration but that LR and RFC may better describe
bulk conditions in the aquifer. A unique aspect of the modeling approach
was inclusion of outputs from previous, physically based hydrologic
and textural models as predictor variables, which were important to
the models. Vertical water fluxes in the aquifer and percent coarse
material above the well screen were ranked moderately high-to-high
in the RFR models, and the average vertical water flux during the
irrigation season was highly significant (<i>p</i> <
0.0001) in logistic regression
Hydrogeologic framework of the Potomac-Raritan-Magothy aquifer system, northern Coastal Plain of New Jersey /
Includes bibliographical references (p. 18-21).Mode of access: Internet