Stormwater reuse treatment requirements and screening-level risk assessment at two urban spatial scales

Abstract

Monitoring was conducted at two urban spatial scales (lot-scale road surface and residential subdivision) to assess treatment requirements for non-potable stormwater reuse by irrigation. A screening-level risk assessment was also made focusing on metals, nutrients, cations and pesticides. Composite stormwater samples were taken at two locations in Toowoomba, Australia. Road runoff had higher treatment requirements for suspended solids but less for disinfection. No organic load or salinity reduction is generally needed, and pH adjustment is an occasional requirement for road runoff only. For both stormwaters, hardness was rated at very soft, which may potentially increase corrosion of irrigation equipment. Sodium adsorption ratios were also low indicating a limited risk of soil degradation under irrigation. Nutrient and metal concentrations also pose a low risk. High turbidity and low alkalinity of road runoff makes it easier to treat with coagulants compared to the subdivision runoff. Pesticide analysis of 121 compounds found road runoff concentrations below levels of detection, except for Simazine and Hexazinone. Although detectable, these pesticide concentrations were within Australian drinking water guidelines.