The Prefect, after verification by the Director General of the Regional Health Agency that the decision will not have consequences contrary to the health of persons, may derogate from the quality limits set by the order mentioned in the first paragraph ofarticle R. 1321-38:
1° In the event of floods or natural disasters ;
2° Due to exceptional meteorological or geographical circumstances;
3° When surface water undergoes natural enrichment in certain substances likely to cause the values set by the decree mentioned in the first paragraph of article R. 1321-38 to be exceeded; natural enrichment is understood to mean the process by which a given body of water receives substances contained in the soil without human intervention;
4° In the case of surface waters of lakes no more than twenty metres deep, which take more than one year to replenish and which do not receive waste water.