What does 'en route' mean for MARPOL Annex V?

I have received the following msg from a ship:

Good afternoon, the ship drifting in the South China Sea, the crew is divided opinion about food waste dumping overboard. We need your expert opinion, as there are differences in the interpretation of the words "enroute" "underway" in MARPOL.
Thank you in advance.

This made me look through certain sources and the answer is as such:

Good day!

Thank you for the question. The answer is multi-step:

1) First of all 'en route' in MARPOL has nothing to do with 'underway' or 'making way through water' in COLREG.

2) By IMO Resolution MEPC 55/23 ANNEX 18 UNIFIED INTERPRETATION TO REGULATION 15.2.1 OF THE REVISED MARPOL ANNEX I for Annex I “en route” was defined as “the ship is underway at sea on a course or courses, including deviation from the shortest direct route, which as far as practicable for navigational purposes, will cause any discharge to be spread over as great an area of the sea as is reasonable and practicable.”

3) Law company Black Rome LLP indicate that Annex I meaning is applied to Annex V as well (http://www.lexology.com/library/detail.aspx?g=5bf88ba3-a196-4164-b58f-28017073c603). Same approach can be seen in the the Dutch Supreme court decision of 2014 for Annex II (http://www.mainportlawyers.com/content/dutch-supreme-court-hands-down-judgment-interpretation-%E2%80%98en-route%E2%80%99-context-marpol-convention).

4) However by the Dutch Supreme court decision of 2014 for Annex II, basis Article 31 of the Vienna Convention,  'en route' should mean not only the above but also that a vessel is at a course at a certain speed causing the discharge to be spread over as great an area of the sea as is practicable.

5) SUMMARY:
For Annexes I, II, and V “en route”  = the ship is underway at sea making a certain speed on a course or courses, including deviation from the shortest direct route, which as far as practicable for navigational purposes, will cause any discharge to be spread over as great an area of the sea as is reasonable and practicable.

+

It is very important to mind the below quoted postulates of IMO Resolution MEPC.219 (63) 2012 GUIDELINES FOR THE IMPLEMENTATION OF MARPOL ANNEX V, 2.7.1 :

• Although discharge into the sea of limited types of garbage is permitted under Annex V, discharge of garbage to port reception facilities should be given primary consideration.
• In general the discharge shall take place when the ship is en route and as far as practicable from the nearest land. Attempts should be made to spread the discharge over as wide an area as possible and in deep water (50 metres or more).
• Prevailing currents and tidal movements should be taken into consideration when discharging into the sea is permitted.

Hope now you have the best answer.

Thank you and best regards,
Alexey O. Chepok