Publication Summary

Studies over the last 10 years have documented extensive nitrate contamination of the Northcentral Sumas-Blaine Surficial Aquifer in Whatcom County largely from agricultural sources. The aquifer is a candidate for long-term monitoring. However, spatial and temporal variability of nitrate concentrations in shallow groundwater in an agricultural setting poses a challenge to identify long-term trends.

This study investigates two alternative methods, volunteer well owner sampling and commercial field test kits, that may help to reduce the cost of a large-scale monitoring program.

Studies over the last 10 years have documented extensive nitrate contamination of the Northcentral Sumas-Blaine Surficial Aquifer in Whatcom County largely from agricultural sources. The aquifer is a candidate for long-term monitoring. However, spatial and temporal variability of nitrate concentrations in shallow groundwater in an agricultural setting poses a challenge to identify long-term trends.

This study investigates two alternative methods, volunteer well owner sampling and commercial field test kits, that may help to reduce the cost of a large-scale monitoring program.

Fifty-three water-supply wells in the Northcentral Sumas-Blaine Surficial Aquifer were sampled and tested for nitrate+nitrite-N in June 1999. Volunteer well owners sampled 29 wells and mailed samples to Ecology for analysis at Manchester Environmental Laboratory. At the same time, an Ecology sampling team sampled 38 wells including 14 of the wells sampled by volunteer well owners. The 38 Ecology samples were tested for nitrate+nitrite-N at Manchester Environmental Laboratory and for nitrate-N by the sampling team using a commercial field test kit.

Results show that nitrate+nitrite-N concentrations remain elevated in large portions of the aquifer. Concentrations ranged from 0.012 to 22.1 mg/L with a mean of 9.95 mg/L and median of 10.3 mg/L. Over 50 percent of the wells sampled showed nitrate+nitrite-N concentrations in excess of 10 mg/L, the nitrate drinking water standard for public water-supply systems. Nitrate+nitrite-N concentrations from this study are similar to results from previous studies of the Northcentral Sumas-Blaine Surficial Aquifer in 1990, 1991, and 1997. Volunteer results compared favorably with Ecology co-samples showing a linear correlation coefficient of 0.9774.

To reduce monitoring costs, volunteer well owner results can be included in a monitoring program provided the samplers are adequately trained. Test kits may be useful for monitoring; they provide immediate results at a lower cost but they introduce additional variability.

Link to EIM data for User Study ID SUMAS