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Assessment of on-site sewage disposal system impacts to ground and surface waters in an unconfined aquifer Goble, Heather Marie

Abstract

The objective of this project was to determine if on-site sewage disposal systems are contributing to degradation of water quality in the Brookswood aquifer, Anderson Creek and the Little Campbell River through the use of environmental monitoring and assessment methods that can be used as a template for similar investigations within other unconfined aquifers. This is a case study to provide an integrated mapping and monitoring protocol to assess nitrate contamination levels in unconfined aquifers and make recommendations for projected on-site sewage disposal system densities The Brookswood aquifer, located in South Langley, B.C., is largely unconfined and considered highly susceptible to contaminants due to its excellent storage capacity and high infiltration/percolation rates. The Little Campbell River and Anderson Creek are important spawning habitats for salmonids and thus sensitive to flow variations and nutrient loading. Groundwater (one hundred wells) and surface water quality (2 streams) were monitored in the aquifer area for nutrients (nitrate-nitrogen, phosphate), general water quality (chloride, conductivity, metals) and pathogen presence (fecal coliforms, bacterial source tracking) from July 2003 to April 2004. An analysis was also made of land use and septic system location and their relationship to the groundwater and surface water quality conditions. Six percent of wells had a maximum nitrate-nitrogen concentration of 10 mg/L or greater, the recommended guideline for Canadian drinking water quality. Groundwater nitrate concentrations were positively correlated with residential land use in unserviced areas and sewage disposal system densities. Management strategies for small septic systems to prevent unconfined aquifer deterioration are discussed. Further studies are recommended to determine if a link exists between greenhouse land use activities and surface or ground water quality. Little Campbell River nitrate concentrations were positively correlated to residential and greenhouse land use in the dry season. Anderson Creek nitrate concentrations were associated with crop land-use in the wet season. Surface waters exceeded recommended criteria for dissolved oxygen and temperature in both the Little Campbell River and Anderson Creek for the protection of aquatic life. Further studies were recommended to determine the cause of the low dissolved oxygen concentrations and potential remedial actions.

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