Water samples were collected using field-parameter stabilization and volumetric purge criteria to ensure samples were representative of the aquifer water quality. Samples for analysis of inorganic constituents were filtered through a 0.45 micron acetate filter. Samples collected for analysis of herbicides and their transformation products were filtered through a 0.7 micron backed glass-fiber filter. All samples were chilled immediately to 4 degrees Centigrade for handling and shipment. Laboratories received the samples within 1-4 days of sample collection. Inorganic samples were analyzed by the USGS National Water-Quality Laboratory in Lakewood, Col. using automated colorimetric procedures described by Fishman and Friedman (1989). Analyses for herbicides and their transformation products were made at the USGS Organic Geochemistry Research Laboratory in Lawrence, Kans. Using solid-phase extraction techniques, parent herbicides, the atrazine products deethylatrazine and deisopropylatrazine, and the cyanazine product cyanazine-amide were analyzed by gas chromatography/mass spectrometry (GC/MS)(Zimmerman and Thurman, 1999; Kish and others, 2000). Chloroacetanilide herbicide products (ethanesulfonic (ESA) and oxanilic acid (OXA) compounds) were analyzed by liquid chromatography/mass spectrometry (LC/MS) (Zimmerman and others, 2000; Lee and others, 2001). Glyphosate was analyzed by immunoassay using a proprietary method (Elizabeth Scribner, U.S. Geological Survey, oral communications, 2001).