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Why was Gene Coulon Beach Closed?
King County Department of Natural Resources and Parks samples this beach weekly beginning in mid-May through mid-September. The data for this beach is shown in the table. The routine samples are collected in the middle of the swimming area. Bacteria counts from the sample collected on July 12 was 1300 colony forming units/100 ml of water sample (cfu/100ml). Any routine sample >1000 cfu/100ml is re-sampled to verify the count. The samples collected on July 14 were 240 cfu/100ml (west side of beach), 930 cfu/100ml (middle), and 1700 cfu/100ml (east side of beach). These samples resulted in closing the beach. A curious pattern in the bacteria counts for this beach is how there are ‘episodic’ high counts followed by low counts, and most of the high counts are on the east side of the swimming area.
What is the source of the bacteria that closed the beach?
We don’t know, but we do have some ideas of what might be some of the likely sources:
swimmers -but then the samples would tend to be similar across the swimming area and we saw low counts at the west end, medium counts in the middle, and high counts on the east end
waterfowl- again, if it were waterfowl the bacteria counts would tend to be uniform across the swimming area, or large persistent congregations of waterfowl would be observed in the eastern section of the swimming area. We don’t really see this, and there is excellent maintenance of the parks grounds with no obvious accumulations of bird droppings.
broken sewer pipe lines –if there were a broken sewer pipeline we would see much higher bacteria counts (10,000 to millions) and the counts would be high consistently, but we’ve observed high counts followed by low counts, followed again by high counts. A broken sewer line is unlikely here.
urban run-off from John’s Creek -we sampled the creek from the mouth to where it goes into pipes on the east side of Lake Washington Boulevard. The bacteria counts in John’s Creek are not low, but they are not high for an urban stream such as John’s Creek. None of the samples we collected were high enough to account for the high values in the swimming area. Alternatively, if there is an episodic source upstream, we may have missed it in our sampling (although there probably would have been higher residual bacteria in the stream if this were the case, and if it occurred as frequently as the data seems to indicate)
discharge of bilge water from boats – We have only one sample from the boat launch, and it was very low (14 cfu/100ml). But based on the episodic patterns of the data and proximity of the boat launch to the swimming beach, this remains a possibility. Most boaters are conscientious and dispose of their wastes in an appropriate manner, but one or two boat dumping wastes in this area could result in the recent closures of the beach.
What is the basis for reopening Gene Coulon Beach?
The samples collected on July 18, 19, 20, and 21 all met the criteria for opening the swimming beach. The routine sample collected on July 26 was 2500 cfu/100ml, which triggers an automatic re-sampling of the beach. The re-sampling conducted on July 28 met the criteria for opening the swimming beach. Based on the pattern of bacteria, where the east end of the beach tends to have the highest counts, Renton Parks, Public Health Seattle& King County and King County Department of Natural Resources decided that the beach could remain open, but swimming would remained closed in the eastern third of the swimming area to potentially reduce the risk of exposure during periods when we do not have bacteria data collections.
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