Source Control Begins at Home

To determine whether further regulation of industrial wastewaters would be sufficient to permit sewage works to meet more stringent discharge standards, an exercise was mounted to quantify the contribution from domestic sources. A 4 week daily sampling programme was conducted by the Sacramento Regional County Sanitation District. As many of the substances were metals, further analyses were made of their concentrations in tap water, in the water leaving the treatment works, and in the raw waters used (ground and surface). All 10 metals monitored were found in the raw waters, and the only one significantly reduced by treatment was copper. Samples at the consumers' taps often showed increased concentrations with lead, mercury and zinc in older properties, copper and zinc in newer. Between the tap water and the wastewater, all metals except arsenic increased; copper by a factor of 12-15, cadmium by 4-5, lead by 2-4, mercury by 2-3, silver by 4-10, and zinc by 100-130. Similar increases had previously been found in 3 other Californian counties. Domestic percentage contributions to the total of each received at the Sacramento sewage works were: arsenic 86, zinc 59, mercury 50, copper 47, nickel 34, chromium 20, lead 14, cadmium 12 and silver 9. Better advice to householders as to the contents and disposal of domestic products, especially as to which products contained which contaminants, is accordingly recommended.