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Selected Pesticides in Groundwater from the Pearl Harbor Aquifer, Oahu, Hawaii

Project Chief: Charles D. Hunt, Jr.
Project Period: August 2008 through December 2008
Cooperator: Hawaii Department of Agriculture Pesticides Branch
Location: Island of Oahu

Problem

The State of Hawaii Department of Agriculture (DOA), Pesticides Branch regulates the distribution and use of pesticides and is concerned about the potential for pesticides to leach and be detected in drinking water sources. The U.S. Geological Survey (USGS) report entitled "Ground-Water Quality and its Relation to Land Use on Oahu, Hawaii, 2000-01" showed single detections of "recent-use" pesticides bentazon, imazaquin, and metsulfuron methyl in groundwater from the Pearl Harbor Aquifer, as well as numerous detections of longer-used pesticides atrazine, bromacil, diuron and hexazinone. The DOA is interested in a second round of sampling for these and other pesticides so that regulatory options can be developed using current data. Imazaquin, metsulfuron methyl, and imidacloprid (used as a termiticide) are the compounds of most interest to DOA in this round of sampling.

Objectives

The objective of this study was to determine concentrations of selected pesticides in groundwater from the Pearl Harbor Aquifer, Oahu.

Approach

Water samples were collected from 10 groundwater sites around the perimeter of Pearl Harbor. The samples were collected according to procedures described in the USGS National Field Manual for the Collection of Water Quality Data. Samples were analyzed for selected pesticides at the USGS National Water Quality Laboratory in Arvada, Colorado using high performance liquid chromatography/mass spectrometry (Furlong and others, 2001). Blank and replicate samples were collected for quality assurance purposes. In addition, replicate samples were collected for analysis by other laboratories.

Findings

Water samples were collected from nine wells and one spring between October 27 and November 5, 2008 and shipped to the laboratory under chain-of-custody protocols.

No pesticides were detected in the spring. Imazaquin was detected in samples from 3 of the 10 groundwater sites sampled. Metulfuron methyl, imidacloprid, and bentazon were not detected. Other pesticides detected include atrazine (and a degradate), bromacil, and diuron (and a degradate). No compounds were detected in a field blank of organic-free water poured at the site and mimicking the sampling, shipping, and laboratory stages of the sampling chain. A field replicate at one site detected all 6 pesticides detected in the primary sample at that site, and at closely comparable concentrations. No compounds were detected in set blanks prepared and analyzed at the laboratory for internal quality assurance.

PDF file Site location map 1.3 Mb PDF
PDF file Well construction diagram 14 Kb PDF
Excel file Analytical results 45 Kb Excel

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Page Last Modified: Tuesday, 15-Jan-2013 19:09:37 EST