September 29, 2010

West Credit still healthy, despite contamination

As published in The Erin Advocate

If the Town of Erin opts for communal sewage treatment, it will not be primarily to save the West Credit River from the impact of private septic systems. The river is actually doing quite well, in spite of some septic contamination, according to a report by Credit Valley Conservation (CVC).

Surface water quality is good and Brook Trout are spawning, even in the urban areas. Buffer zones of vegetation that help protect the water from human activity cover 84 per cent of the stream banks. Deep groundwater that supplies municipal wells has no impact from septic systems, no organic contaminants and no trace of other chemicals such as pesticides.

CVC spent about $350,000 to test the West Credit and monitor the local ecosystem in 2007-2008, analyze the results and produce this Existing Condition Report. It is the environmental component of Erin's Servicing and Settlement Master Plan (SSMP). The cost has been shared by all Credit watershed municipalities, with most of the funds coming from the Region of Peel.

Pollution levels in surface water have increased slightly since the mid-1970s, but are below limits considered acceptable by the federal and provincial governments. Contaminants flow from several sources, so it is not possible to measure how much originates with septic systems.

"Localized impacts were found to be mostly related to surface/stormwater runoff and the cumulative impact of the on-line ponds," said Jennifer Dougherty, Water Quality Engineer for CVC, in a recent presentation to Erin councillors. There are nine dams on the West Credit, creating impassable barriers for fish. The ponds collect sediment, boost water temperatures and alter vegetation and wildlife in the area.

Residential waste water is partially purified by septic tanks and drainage beds, then filtered in the soil. If septic systems are well-maintained, there is very little contamination. But with aging systems, poor soil conditions in some areas and a high concentration of village homes, there is more septic effluent in the shallow groundwater.

"There is an almost complete reduction in fecal bacteria," said Ray Blackport, a hydrogeologist who works with CVC and the Town. These bacteria can come from septic systems, but also from wildlife, pets, livestock and manure spreading. Higher levels of various harmful bacteria make water unsafe for swimming.

He noted that other septic contaminants such as nitrogen (nitrates), phosphorus, toxic organics from cleaning agents, heavy trace metals and dissolved inorganics such as chloride and sodium are of concern, because there is considerable exchange between the shallow groundwater and the river water.

Many farmers have taken steps to reduce the flow of contaminants from their land, and some land has been taken out of production, so it is possible (but not proven) that aging septic systems are contributing a greater proportion of the contamination than in the past.

Nitrates come from farms, urban stormwater runoff and septic systems. The highest nitrate levels are upstream of Hillsburgh, but the volume of contaminants drops in the core area of the village because a large volume of river water goes underground.

Nitrates are higher for short distances downstream of Hillsburgh and Erin village. The river recovers from these increases because vegetation absorbs nitrates. Higher levels of nitrates make it more difficult for fish and frog populations to spawn and prosper. West Credit nitrates average 2 mg per litre, while the federal guideline for nitrates is 3 mg per litre.

"Fortunately the buffer riparian area surrounding the West Credit River has a very high nitrogen removal capability," said Dougherty. "However, it is not wise to rely on our natural wetland/woodlands to filter out our contamination."

Chlorides come from road salt, dust suppression and septic systems (including water softener discharge). Higher levels can cause a decline in fish and frog populations in the long term. West Credit chlorides average 45 mg per litre, well below the draft federal guideline for protection of aquatic life of 128 mg per litre. They are increasing slightly faster than nitrates, however, and unlike nitrates they dissolve and accumulate in the system instead of dissipating.

The river is also affected by phosphorus, which comes from farm runoff, fertilizer application, urban stormwater and septic systems. High levels can lead to excessive algal and aquatic weed growth, which can reduce wildlife habitat and diversity.

This draft report was expected last January, but because CVC staff were busy with various obligations, it wasn't delivered to the Town until May. Councillors got a copy last month. On Sept. 14, a few members of the public, including some election candidates, attended an afternoon council meeting for a CVC presentation. The final report will be attached to the SSMP Background Issues Report this fall, and be available through the Town website.