The following letter was submitted to the Owen Sound Sun Times, but was not published.
Before June 12, 2012, E. Coli. readings at Sauble were routinely well below the Provincial limit of 100 cfu/100 ml (colony forming units per 100 millilitres). On June 12 the readings jumped to over 1000. After June 12 they returned to well below the limit.
Medical Officer of Health Hazel Lynn apparently said (Denis Langlois article June 15 OSST) that “faulty septic tanks in the area could also be to blame [for the high June 12 reading]”.
Dr. Lynn is wrong.
The 2001 Sauble Sewers Environmental Study Report indicated that 90% of the loading to the lake at Sauble comes via the River, and only 10% from the beach drains. The data suggests that 5% is from the drains North of Main Street. Assuming these numbers were valid for June 12th, and even making an ultra-conservative assumption that all of the E. Coli. in the beach drains was from faulty septic systems, it would mean that 50 of the observed 1000 count was from faulty septic systems.
That’s hardly grounds for “faulty septic tanks could be to blame”.
The only way faulty septic systems could cause such a spike is if a bunch of septic systems spread out along the Beach all plugged at the same time and all started by-passing their systems and sending raw sewage directly into the beach drains, and then about twenty-four hours later those same systems suddenly got fixed and started working properly again, all without anyone knowing about the illegal by-pass. Not quite impossible, but certainly a highly improbable coincidence.
So it was wrong and irresponsible for Dr. Lynn to say that faulty septic systems could be to blame for the high E. Coli. readings.
In the same article Dr. Lynn apparently also said that “heavy rain and waves can lead to higher bacteria levels in the water.”
Here Dr. Lynn is on more solid ground.
We know that much of the E. Coli. in the lake is attached to sediment, which on calm days tends to sit on the bottom.
We also know that a very gentle swell can deposit E. Coli. from the near-shore lake into the near-shore sand, and that birds contribute to E. Coli. in the near-shore sand.
When winds whip up bigger waves and a strong undercurrent two things happen. First the waves lapping onto the shore wash E. Coli. from the near-shore sand back into the lake. And second the turbulence below the water surface dislodges E. Coli. from the sediment. The result is a fairly sudden spike in E. Coli. readings.
June 11 had south winds 20 kilometers per hour and steady. June 12 had winds tending westerly and building to 25 km/hr., with thunderstorms in the early morning. Good for waves. Ideal for an E. Coli. spike.
Dr. Lynn needs to apologize to all those Sauble people she implicitly accused of by-passing their septic systems and of dumping raw sewage directly into the beach drains on June 12th. Dr. Lynn needs to make clear that it is completely implausible that the high readings were from “faulty septic systems”.