Organic Micropollutants in Effluent Recharge to Groundwater

Abstract

Groundwater pollution by organic material derived from the recharge of raw, untreated sewage effluent has been studied at the sewage treatment works at Whitchurch in Hampshire. This organic investigation consisted of two parts; the validation of the sampling and analytical techniques and the field investigation. Sampling points for the survey included open boreholes lined with uPVC or mild steel as well as specially designed buried in-situ groundwater samplers of uPVC or stainless steel construction. Laboratory leaching tests show significant pollution of sampled water by nylon and uPVC components and indicate that all plastics must be avoided in sample point construction. The in-situ samplers with stainless steel bodies and PTFE sampling tubes proved satisfactory. The organic field survey showed that the organic pollution plume is coincident with the inorganic plume from the effluent recharge site. The total organic content of the effluent is reduced through infiltration; 85 per cent is removed in the unsaturated zone and a further 14 per cent during 300 m of lateral flow. The number of organic compounds at significant concentrations also is greatly reduced through infiltration. The most persistent micropollutant identified as coming solely from the sewage is dichlorobenzene which is present at about 9 µg/l below the recharge lagoons and 1 µg/l in the pollution plume 300 m from the site.