Sustainable Agriculture Literature Review - Boulder County

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Summary
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4. Water Pollution
Agriculture in the U.S. is the largest contributor to non-point source water pollution
according to the Environmental Protection Agency (EPA). Agriculture often contributes
to surface and groundwater pollution by increasing the discharge of chemicals and
sediment, waterlogging irrigated land, and causing salinization. While agriculture
contributes significantly to water pollution it is also heavily impacted itself by polluted
water, as poorly treated wastewater can contaminate crops and transmit diseases
throughout the food chain.
The most significant agriculturally derived water contaminant in the U.S. is nitrate.
Nitrate pollution from agricultural operations comes from nitrogen runoff primarily from
animal manures, synthetic and organic fertilizers, and atmospheric deposition. In the
Front Range urban corridor, the Colorado Department of Agriculture tested over 40
groundwater sources for nitrate leaching from the surrounding agricultural land and
industry. Roughly twelve percent of the wells were found with nitrate levels exceeding
the allowable EPA maximum concentration level.
Apart from nitrate, pesticides represent the most significant water pollution and health
concern for agriculture. In the South Platte River Basin, pesticides have been detected
in over 90 percent of the wells sampled in both urban and agricultural areas. The high
level of detection places the basin in the highest 25 percent of all water basins tested
nationally. The most commonly detected pesticide was atrazine, which was found in
roughly 61 percent of the wells sampled. Alachlor, metolachlor, and simazine were also
detected.
The storage and competing uses of water along the Front Range place additional
concerns on pollution from agriculture. According to the Colorado Water Resources
Research Institute, most of the reservoirs along the Colorado Front Range have rates of
eutrophication that are a cause for concern. High rates of eutrophication typically
occur when runoff from over or recently fertilized and manured agricultural lands deliver
large amounts of nitrogen and phosphorus to water bodies that are nutrient limited.
While increased levels of nutrients in irrigation water may be advantageous for farmers
since they help reduce the need for fertilizers, they also present a multitude of problems
for managers of municipal drinking water.
Management emphasis has now shifted from irrigation to drinking water for many Front
Range Reservoirs. This creates problems as reservoirs used for irrigation water have
different management priorities than drinking water reservoirs. Drinking water needs to
be more pure and has tighter standards, such as maximum contaminant levels for
nitrates (NO3), manganese (Mn), and iron (Fe).
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