Comparison results versions 1.3.2 and 1.2

WOt report 100 of Adriaanse & Beltman (2017) indicates that concentrations at the drinking water abstraction points may be up to a factor of 2 higher than those of DROPLET 1.2. This is due to increased mass fluxes by drainage calculated by FOCUS_MACRO 5.5.3 (and 5.5.4), compared to MACRO 4.4.2 (see section 3.7 of Report 100).  

WOt report 160 of De Jong, Poot & Adriaanse (2019) demonstrates that in regulatory practice of the Netherlands the introduction of DROPLET 1.3.2 is expected to have no impact for evaluation of the drinking water criterion.  

The differences are caused by:

  1. The application rates of 1 kg/ha for the hypothetical substances used in Adriaanse & Beltman (2017) are a factor 10 to 100 larger than the ones for real substances used in De Jong, Poot & Adriaanse (2019), thus leading to higher concentrations at the drinking water abstractions points
  2. Adriaanse & Beltman (2017) applied a spray drift deposition percentage of 1%, while De Jong, Poot & Adriaanse (2019) applied a percentage of 0.5%
  3. Some of the hypothetical substances used by Adriaanse & Beltman (2017) are prone to discharge via drainage because of their low sorption coefficient (Koc of 10 L/kg) and/or long half-life in soil (DT50,soil of 300 d)
  4. Adriaanse & Beltman (2017) used a worst case fcorrFOCUSscen (correction factor for the peak concentration correcting implicit choices concerning contributing areas made in the FOCUS D3 scenario) of 3 (peak mainly caused by drainage entries) instead of 1 (peak mainly caused by spray drift entries). They did so, even if the date of the peak coincides with the application date. Thus they assumed that the peak concentration at the application date was caused by spray drift deposition and drainage entries, occurring both at the day of application.