ASSESSMENTS OF AQUIFER SENSITIVITY ON NAVAJO NATION AND ADJACENT LANDS
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ASSESSMENTS OF AQUIFER SENSITIVITY ON NAVAJO NATION AND ADJACENT LANDS
AND GROUND-WATER VULNERABILITY TO PESTICIDE CONTAMINATION ON THE NAVAJO 
INDIAN IRRIGATION PROJECT, ARIZONA, NEW MEXICO, AND UTAH  
(pdf file 6.7 Mb)

By Paul J. Blanchard



ABSTRACT
 
The U.S. Environmental Protection Agency 
requested that the Navajo Nation conduct an 
assessment of aquifer sensitivity on Navajo Nation 
lands and an assessment of ground-water 
vulnerability to pesticide contamination on the 
Navajo Indian Irrigation Project. Navajo Nation 
lands include about 17,000 square miles in 
northeastern Arizona, northwestern New Mexico, 
and southeastern Utah. The Navajo Indian 
Irrigation Project in northwestern New Mexico is 
the largest area of agriculture on the Navajo 
Nation. The Navajo Indian Irrigation Project 
began operation in 1976; presently (2001) about 
62,000 acres are available for irrigated agriculture. 
Numerous pesticides have been used on the 
Navajo Indian Irrigation Project during its 
operation.

Aquifer sensitivity is defined by the U.S. 
Environmental Protection Agency as "The relative 
ease with which a contaminant [pesticide] applied 
on or near a land surface can migrate to the aquifer 
of interest. Aquifer sensitivity is a function of the 
intrinsic characteristics of the geologic material in 
question, any underlying saturated materials, and 
the overlying unsaturated zone. Sensitivity is not 
dependent on agronomic practices or pesticide 
characteristics." Ground-water vulnerability is 
defined by the U.S. Environmental Protection 
Agency as "The relative ease with which a 
contaminant [pesticide] applied on or near a land 
surface can migrate to the aquifer of interest under 
a given set of agronomic management practices, 
pesticide characteristics, and aquifer sensitivity 
conditions."

The results of the aquifer sensitivity 
assessment on Navajo Nation and adjacent lands 
indicated relative sensitivity within the boundaries 
of the study area. About 22 percent of the study 
area was not an area of recharge to bedrock 
aquifers or an area of unconsolidated deposits and 
was thus assessed to have an insignificant potential 
for contamination. About 72 percent of the Navajo 
Nation study area was assessed to be in the 
categories of most potential or intermediate 
potential for contamination. About 6 percent of the 
study area was assessed to have the least potential 
for contamination, mostly in areas where the slope 
of the land surface is more than 12 percent. Nearly 
all fields on the Navajo Indian Irrigation Project 
were assessed to have the most potential for 
contamination.

The assessment of ground-water 
vulnerability to pesticide contamination on the 
Navajo Indian Irrigation Project was based on 
pesticide application to various crops on part of the 
Navajo Indian Irrigation Project during 1997-99. 
The assessment indicated that ground water 
underlying fields of beans, wheat, barley, and 
alfalfa was most vulnerable to pesticide 
contamination; ground water underlying fields of 
corn and potatoes was intermediately vulnerable to 
pesticide contamination; and ground water 
underlying fields of hay was least vulnerable to 
pesticide contamination.



Abstract from Water-Resources Investigations Report 02-4051 



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