- Lake Forest Association (LFA) - Caretakers of Eastwood Lake in Chapel Hill, NC.
I collected our first regular season water samples beginning at 9:19 am on Thursday, May 24 2018. The following results indicate moderate levels of normal bacterial contamination.
#1 Dock 150 cfu
#2 Cedar Fork Creek 80 cfu
#3 Booker Creek 90 cfu
Caution level is individual reading above 400 cfu, or per-site average above 200 cfu. CFU = colony forming units per 100ml.
Lake water temperature was 81-82F/27.0-27.5C, with the lower temperature at the Dock near the swimming beach. The SECCI clarity reading was 24 inches, up from 23 inches on May 23. The increase in clarity indicates that runoff from rainwater may be passing through the lake and we are not accumulating silt or concentrating algae at this time.
We had a similar elevated reading one year ago at this time. There was significant rainfall in the week preceding this sampling, as was the case last year. There was only about 0.2 inches of rain in the 72 hours before the samples were taken, and that was better than last year; the test protocol recommends samples not be taken following a rainfall. The weather station at the park: KNCCHAPE91 reported a total rainfall of up to 6.8 inches for the preceding week, although the website that accumulates this information was not reporting either the total rainfall or the elevation of the site above sea level correctly. The lake dam is at 296 ft. above sea level, and the weather station is about 8 ft. above the water level (304 ft.). It is reporting its elevation at 500 ft. I had about 4.9 inches of rain in my yard for the same period, and my rain gauge is at 488 ft., and the location is near the North boundary of the watershed.
We sample three sites in the lake: near the docks, and close enough to the two tributary streams that we can determine if we are getting any significant differential from either source. The bacteria we monitor lives in the gut of warm blooded animals and is dispersing and dying in the water. So getting a higher reading downstream is a bit unusual, but it indicates that the event that caused that higher reading has passed. The bacteria came into the lake from both sources in enough water to move on through fairly quickly. It is likely that it has cleared our lake system completely by the time you read this report.
I am not planning on doing a retest at this time because we are well below the caution threshold and we have more rain forecast for the next several days. Coordinating getting the samples to the lab in Reidsville is very time sensitive, and often must be done on short notice. If the rest of June has normal or below normal rainfall, we may take our next regularly scheduled test (week before Independence Day) a few days early.