Effects of Rainfall on E. coli Concentrations at Door County, Wisconsin Beaches

Table 4

E. coli concentrations (^∗MPN/100 mL) from beach water collected at time intervals following the triggering of a rain event at Ellison Bay beach. Using Scheffe matrix analysis, E. coli concentrations measured in the first four hours after the rain event was triggered were significantly different from the seasonal mean E. coli concentration for this beach (𝑃<.001). Likewise, E. coli concentrations measured at 8 hours or 12 hours after the rain event was triggered were significantly different from the seasonal mean E. coli concentration for this beach (𝑃<.001 and 𝑃<.002, resp.). If rainfall was sufficient to trigger multiple rain event notifications on one day, then multiple events were sampled.

Date of Rain Event	Outfall Pipe 1–3 Hours	1–4 hours After	8 hours After	12 hours After	24 hours After
	After Rain Event	Rain Event	Rain Event	Rain Event	Rain Event
6/4/07	n/a	1348.9	>2419.6	488.4	613.1
6/4/07	n/a	1783.3	>2419.6	1732.9	461.1
6/4/07	n/a	2202.9	1413.6	1046.2	59.1
6/18/04	n/a	58.1	29.2	41.3	9.7
6/18/07	n/a	41.8	30.5	20.5	13.2
6/20/07	n/a	131.1	55.6	58.3	2.0
7/10/07	n/a	4.3	30.9	29.4	5.2
7/12/07	n/a	29.9	81.6	36.8	4.1
8/20/07	n/a	37.5	48.0	60.9	6.3
8/23/07	n/a	10.3	47.3	37.9	15.6
8/28/07	n/a	114.8	44.3	55.6	5.2

∗Most probable number.