Analyses for a suite of pesticides, including atrazine and simazine, are available for the Blue Lake quarterly since 1997 (n=53). In all cases the concentration are reported at or below the analytical detection limit, predominantly 0.5μg/L. The current ADWG for atrazine is 0.1μg/L, which suggests a more sensitive detection should be sought.
Of 140 pesticide samples collected from the unconfined aquifer there were five instances where atrazine exceeds 0.5μg/L (Unit nos. 7022-0252 GAM21 and 7022-1538 GAM23 only), while simazine is consistently at or below 0.5μg/L. Atrazine and simazine are mostly below 0.5μg/L in Mount Gambier’s stormwater (65 of 75 samples), but peak concentrations of 12 and 5μg/L respectively have been measured. Analysis of degradation by-products would prove useful in understanding the rate of attenuation within the aquifer.
An atrazine concentration of 7 ng/L was detected in Blue Lake (measured in samples collected in May 2005 and October 2006). This lies within the range of concentrations found in two groundwater samples (0.33 and 26 ng/L) and Mount Gambier’s wastewater (38 ng/L) in October 2006 but is far below the detection limit of 500 ng/L commonly reported for atrazine inenvironmental samples and also below the Australian drinking water quality guideline value of 100 ng/L (NHMRC-NRMMC, 2004)