Lake tests seem to confirm sewage pond leaching
2 Oct 2008
Lake tests seem to confirm leaching from sewage ponds
Tests in Lake Horowhenua after the recent overflow of nearby sewage ponds appear to confirm the lake suffered from extra pollution because of the event, Greens Co-Leader Russel Norman says.
This week the Green Party obtained, under the Official Information Act, details of tests by Horizons Regional Council from various sites in Lake Horowhenua on September 4 in relation to what Horizons calls, "...an alleged incident involving the Levin STP [sewage treatment plant]".
The tests came after the sewage ponds overflowed on August 20.
A letter dated September 29 from Horizons says in its conclusion, "It is our assessment, based on the results displayed above, that there was a zone of nitrogen leaching apparent in lake waters in the vicinity of the Levin STP on the 4 September 2008 and that the concentrations of nitrogen (particularly soluble inorganic nitrogen) were elevated when compared to long term SOE [state of the environment] data."
According to Horizons, last minute earth banks built by Horowhenua District Council would have effectively reduced "the transport pathways" of many overflow contaminants headed for the lake, but "nitrogen compounds are highly soluble in water and leach easily through the soil profile and subsurface flow". The overflow is referred to as an "enrichment and leaching event" with the effect unknown, however "...any increase in nitrogen leaching into the lake waters has the potential to increase the risk, duration and frequency of toxic algal blooms and other eutrophication effects in Lake Horowhenua". (See attached letter).
Says Dr Norman, "This comes after reports in September that E. coli contamination was found between the plant and the lake after the overflow, but it seems the impact of this contaminant was lessened by panicked bunding and through dilution by groundwater.
"Horowhenua Mayor Brendan Duffy was wrong when he said on August 14, six days before the overflow, that my warnings the ponds could overflow were 'completely out of order and ill-informed'. His Chief Executive David Ward's quoted comments on August 14 that 'there is no threat of sewage discharge into Lake Horowhenua' was also misleading. There was a real threat, as events showed.
"Mr Duffy blaming grazing cows alone for the E.coli found in the area contaminated (Horowhenua Mail, September 4, 2008) when there were millions of litres of sewage overflowing defies belief.
"It's time for the district council to stop denying there is a problem and put sewage and other waste disposal at the top of its budget list."