Abstract-Interrelationships between surface water and groundwater dynamics of ␣-and ␥-hexachlorocyclohexane (HCH) were investigated by determining their detection frequency and concentrations in surface water that originated primarily from surface runoff of snow and rain and in surface water that originated from ground water. In the prairie ecozone in Saskatchewan, where lindane (␥-HCH) is currently used, lindane and ␣-HCH were detected in about 50% of water samples taken from lakes and ponds that are recharged primarily by surface runoff (N ϭ 43 sites). Maximum concentrations for lindane and ␣-HCH were 0.011 and 0.004 g/L, respectively. Isomers of HCH were not detected in any of the eight prairie springs that were examined (N ϭ 10 samples). These springs originate from ground water located beneath agricultural lands. In the montane ecozone of Alberta where lindane is not used for agricultural purposes, only ␣-HCH was detected frequently in the Waterton and Athabasca rivers. From 1976 to 1992, ␣-HCH was detected in 81% of water samples from the Waterton River with no significant difference in detection frequency through the year ( 2 for 12 months ϭ 14.6, d.f. ϭ 11, p ϭ 0.20, N ϭ 163 samples). The site on the Waterton River is located downstream from a series of large lakes with multiyear storage of surface water. In contrast, discharge for the Athabasca River originates primarily from surface water during summer and ground water during winter. Detection frequency for ␣-HCH during these seasons was 53% and 2%, respectively, with the annual pattern a normal distribution. These results indicate that HCH isomers were not detected frequently in surface waters that originate from ground water.
Natural springs provide an opportunistic subject for assessing aquifer contamination. To determine the frequency and level of aquifer contamination by herbicides in the Canadian prairie, a study of natural springs draining small surficial aquifers a few hectares in area was carried out in southern Saskatchewan. All but one of the aquifers investigated received herbicide applications either for agricultural purposes or brush control. Elevated tritium isotope activities (10–60 TU) confirmed recent recharge of these aquifers. No wells were present on these aquifers. Therefore, the possibility of contamination by direct entry down wells was eliminated from the study. Large volume extraction technology permitted detections of herbicides at ng L−1 levels. This is the first study of herbicides in natural springs in Canada. Herbicides were detected in 23% of samples collected. The most frequently detected analytes being atrazine (6‐chloro‐N2‐ethyl‐N4‐(isopropyl)‐1,3,5‐triazine‐2,4‐diamine), picloram (4‐amino‐3,5,6‐trichloropicolinic acid) and 2,4‐D ((2,4‐dichlorophenoxy)acetic acid), with detections in 12, 7, and 7% of samples collected, respectively. The results show that shallow aquifer contamination occurs in the absence of wells. However, the levels detected were in the ng L−1 (ppt) range, which is much less than levels commonly reported in most well surveys. None of the herbicide concentrations exceeded any guidelines for drinking water, livestock, irrigation, and aquatic life including Canadian, Provincial, World Health Organization, and USEPA guidelines.
Treatment of urban stormwater by clarification, with flocculant addition, was studied in Toronto, Canada using a pilot-scale clarifier with removable lamellar plates. Almost 90 stormwater runoff events were characterised at the study site and found fairly polluted. The previous research phase indicated good treatability of this stormwater by lamellar clarification with flocculant addition (total suspended solids, TSS, removal of 84%, at a surface load of 15 m/h), but there were concerns about cleaning plates after storm events. With the aid of numerical modelling, hydraulic improvements to the clarifier inlet zone were retrofitted in 2004 and permitted the removal of the lamellar pack without a loss in treatment efficiency. In the modified clarifier, a cationic polymeric flocculant dosage of 4 mg/L with conventional clarification provided a TSS removal of 77%, at surface loads up to 43 m/h. The use of the polymer did not increase the acute toxicity of the treated effluent. The clarifier sludge was severely polluted by several heavy metals and would require special disposal. The treatment process tested could be well applied in projects requiring intensive stormwater treatment at compact sites.
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