AbstractA vegetable- and meat-canning facility located in the karst of southeastern Minnesota disposes 2.85105 m3 yr1 of wastewater by spray irrigation of an 83.7-ha field located atop the local groundwater divide. Cannery effluent contains high levels of chloride and nitrogen (organic and ammonia), in excess of 7000 mg/l and 400 mg/l, respectively. Nitrate-nitrogen concentrations are generally 5 mg/l. Agricultural, domestic, and municipal sources of chloride and nitrate are common in the region, and water supplies frequently exceed the drinking-water limit for nitrate-nitrogen of 10 mg/l. Fifty-two area wells and thirteen surface-water locations were sampled and analyzed for five ionic species, including: chloride (Cl), nitrate-nitrogen (NO3-N), sulfate (SO4), nitrite-nitrogen (NO2-N), and phosphate (PO4). Two distinct chloride plumes flowing outward from the groundwater divide were identified, and 65% of the wells sampled had nitrate-nitrogen concentrations in excess of 10 mg/l. The data were divided into two groups: one group of samples from wells located near the canning facility and another group from outside that area. A correlation coefficient of R2= 0.004 for Cl vs. NO3-N in the vicinity of the irrigation fields indicates essentially no relationship between the source of Cl and NO3. In areas of agricultural and domestic activities located away from the cannery, an R2 of 0.54 suggests that Cl and NO3 have common sources in these areas.
Rsum. Une conserverie de lgumes et de viande, situe sur le karst du sud-est du Minnesota, produit annuellement 2.85 105m3 deaux uses utilises pour larrosage de 84 ha situs sur un dme local des eaux souterraines. Les effluents de la conserverie prsentent des teneurs leves en chlorures et en azote total, respectivement 7000 mg/l et 400 mg/l. Les concentrations en N des nitrates sont en gnral infrieures 5 ppm. Les sources de chlorures et de nitrates des rejets domestiques, collectifs et de lagriculture sont frquents dans la rgion; aussi les eaux de consommation dpassent frquemment la limite de 10 ppm de N des nitrates fixe pour leau potable. Une mthode a t mise au point pour estimer la contribution des eaux uses de la conserverie la pollution locale par les nitrates. 52 puits et 13 sites deau de surface ont tchantillonns et analyss pour 5 ions: C1, NO3-N, SO4, NO2-N et PO4. Deux panaches distincts de chlorures partant du dme ont t identifis; 65% des puits prsentent des teneurs en N de nitrates suprieures 10 ppm. Les donnes ont t spares en deux groupes: les chantillons des puits proches de la zone irrigue par la conserverie et ceux extrieurs cette zone. Le coefficient de corrlation (R2= 0.004) entre les teneurs en chlorures et celles en nitrates, proximit des champs irrigus, montre labsence de relation entre les origines de ces deux ions. Loin de la conserverie, dans les zones dactivits agricoles et domestiques, la coefficient de corrlation (R2= 0.6) indique que chlorures et nitrates possdent dans ces zones une origine commune.