Ground water contamination from on-site domestic wastewater management systems in a coastal catchment

A catchment management and groundwater monitoring program has been undertaken in several small coastal communities approximately 35 km south east of Hobart, Tasmania, Australia. Domestic wastewater disposal is on-site with absorption systems in sandy soils, while the shallow groundwater is increasingly being used in the community for non-potable uses. Lot sizes are typically less than 800 m 2 . The coastal waters are commonly used for primary contact recreational activities such as swimming and surfing in the summer months and bathing water quality during this period is of some concern. This paper presents the results from part of the groundwater monitoring program. Low levels of bacterial indicators have been identified in groundwater samples from 50 mm domestic wells. Some high nitrate concentrations have been recorded, usually associated with clusters of houses and, from this, several high-risk areas have been identified. In particular some linkages between on-site systems and effluent contaminated seeps along the beachfront have been confirmed. Whilst it does appear as though the failure of on-site systems is affecting, to a limited degree, the quality of shallow groundwater in the area, a clearer picture is emerging of the capacity of this area to adequately treat the effluent load from the relatively high lot density. The results from this study will afford the local council and planning agencies some useful guidelines for the future planning of developments