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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5102

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Summary

This report describes the environmental setting of the Granger Drain and DR2 basin watersheds in the context of how agricultural practices, which include agricultural chemical applications and irrigation practices, interface with natural settings and hydrologic processes. These watersheds are part of the National Water-Quality Assessment Program (NAWQA) Agricultural Chemicals: Source, Transport, and Fate Study designed to understand the human and natural factors that control water quality within agricultural settings nationwide. The Granger Drain and DR2 basins are located within the Yakima River basin in south central Washington, and are dominated by a mixture of irrigated agriculture, pasture, and animal feeding operations. Granger Drain basin covers approximately 62 square miles and the DR2 basin, nested within the Granger Drain basin, has a drainage area of 2.1 square miles. Temperatures range from an average monthly low of 23.9 in January to an average monthly high of 88.5 in August.

Based on field mapping conducted by USGS in 2003 and 2004, the major crops within the Granger Drain basin consist of alfalfa and other hays, asparagus, corn, hops, mint, pasture, juice grapes, wine grapes, and apple, pear, and cherry orchards. The DR2 basin contains a less diverse mixture of crops with most agricultural land dedicated to the production of corn, juice grapes, and pasture. Numerous dairies varying in size from a few hundred dairy cows to more than a thousand dairy cows operate in the Granger Drain and DR2 basins. The dairy industry substantially influences the crops grown in the basin as dairies require enormous amounts of corn and alfalfa for feed.

Estimates of agricultural chemical applications indicate, with varying degrees of confidence, that the most abundantly applied fungicides in the DR2 basin in 2004 were sulfur, fenarimol, triflumizole, and myclobutanil; the most abundantly applied herbicides were EPTC, glyphosate, acetochlor, and metolachlor (all of which are commonly used on corn); and the most abundantly applied insecticides were petroleum distillates, disulfoton, chlorpyrifos, and carbaryl.

Because the region lies in the rain shadow east of the Cascade Mountains, it receives about 7 inches of precipitation per year. Agriculture within these basins and surrounding areas relies on extensive irrigation provided by canals located within these basins. Two large canals cross the Granger Drain basin from west to east: the Roza Canal to the north and the Sunnyside Canal to the south. Water delivered to farms in the Granger Drain basin eventually drains to Granger Drain, which enters the Yakima River. For the period of record (2000–2003), total annual discharge from Granger Drain ranged from 9,310 to 14,700 cubic feet, with a mean of 12,300 cubic feet. Flow in Granger Drain is higher during the summer irrigation season and lower during the winter non-irrigation season. During the irrigation season, average monthly flows in the Granger Drain ranged between 34 and 52 cubic feet per second. Stream flows during the non‑irrigation season dropped to monthly averages between 18.2 and 20.7 cubic feet per second.

The ground-water system in the Granger Drain basin consists of a surficial unconfined to semi-confined aquifer composed of the unconsolidated surficial deposits. This aquifer is bounded on the bottom, north, and south by basalts of the Columbia River Basalt Group. Basalt aquifers underlying the surficial aquifer are believed to be isolated from the surficial aquifer and stream systems. Recharge to the surficial aquifer is largely the result of applied irrigation water, with a much smaller amount resulting from winter precipitation.

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