SWASH is an acronym for Surface WAter Scenarios Help and is an overall user-friendly shell, managing the communication and data transfer between three models involved in Step 3 calculations for the FOCUS Surface Water Scenarios. These scenarios have been developed as part of the EU evaluation process under 91/414/EEC (See FOCUS Website).  Spray drift, drainage and run-off are the routes of pesticide entry into surface waters. Using spray-drift deposition tables and the MACRO, PRZM and TOXSWA models the exposure concentrations in surface waters can be assessed. To carry out the FOCUS Surface Water Scenarios, a drift assessment tool and two pesticide fate models have to be run in the correct sequence see figure below.  

Sequence of tools and models used to calculate pesticide
exposure in the proposed Step 3 EU FOCUS Surface Water Scenarios.