Guemes Island Environmental Trust:

Water Quality Update

Sixteen years have passed since the United States Geological Survey (USGS) conducted its baseline study of the groundwater of Guemes Island. What has happened during all those years? Members of the Waterworks group decided to find out. In the Fall of 1991, USGS had collected water samples from 86 wells; in 2007 we were able to sample 54 of the same wells, and we hope to sample another eight or nine wells this Spring.

We measured the chloride concentrations (salt) and the electrical conductivity of the well water and compared our findings with the values determined by USGS in 1991. The good news is that overall we did see few changes in chloride concentrations. Especially in the interior of the island the chloride concentrations remained low, generally at 20 milligram per liter (mg/l) or below.

North Beach continues to be the area of concern, with several wells above the maximum acceptable chloride concentration of 250 mg/l. The values ranged from 14 – 350 mg/l, from very low to quite high. But even on North Beach, we saw in a few cases a decline in chlorides, most likely the result of lower water usage.

The best news is that wells that have been abandoned in the past, because of high chlorides, may actually recover. One of the two wells that used to provide water for the Potlatch Beach Water Association is now owned by the PUD. It is a back-up system in case something happens to the Reverse Osmosis System and in practice has not been used for many years. Chloride concentration went down from 300 to 30 mg/l. The Alverson Tract Property Owners’ old well, that served its community on North Beach for many years, was closed down in April, 2007. We determined a chloride concentration of 22 mg/l, a reduction from the 60-65mg/l about half a year earlier. On the other hand, a few abandoned wells north of Guemes Island Road along the waterside on North Beach still had chloride concentrations in the range of 140 –175 mg/l.

In both years the chloride concentrations were determined using the same field test-kit methods. Keep in mind that these kits have a limited accuracy, particularly at higher concentrations. The Maximum Contamination Level (MCL) of chlorides in drinking water, established by the Environmental Protection Agency, is 250 mg/l.

Electrical conductivity is an indication of the total ion concentration in the water, but it does not distinguish between particular ions, such as iron, magnesium, or sodium. It is measured with a conductivity meter. The temperature is recorded as well because conductivity increases with an increase in temperature. For various reasons, the conductivity data are harder to interpret than the chloride concentrations.

Chloride concentration and electrical conductivity and water temperature data will be posted on We are following the well-numbering system as used by the USGS and the identity of private well-owners remains confidential.

--Marianne Kooiman for GIET-Waterworks

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