Dutch to English Bus/Financial Other

Van bodemverontreiniging is sprake indien zich op en/of in de bodem van de locatie hogere concentraties van schadelijke stoffen bevinden dan op grond van natuurlijk voorkomen is te verwachten gelet op de streefwaarden vastgelegd in de circulaire van 4 februari 2000 (kenmerk DBO/1999226863) behorende bij de Wet bodembescherming, de stand van de wetenschap, dan wel daarvoor in de plaats tredende of aanvullende algemeen gangbare kwaliteitseisen.

My problem is not what "de stand van de wetenschap" means (at least I think I know what it means here!), but rather how it fits in to the sentence. It seems to be hanging in mid-air in the sentence and I'm not sure what it refers back to.

Does it refer back to "behorende bij", in which case the meaning is that the circular forms part of the Wet bodembescherming and also forms part of scientific knowledge? Or, does it refer back to "gelet op..", in which case the meaning is: "in view of the target values set out in the circular of 4 February 2000 (reference DBO/1999226863), or in view of / based on scientific knowledge, or the general accepted quality standards...?

Thank you in advance to anyone who can help clarify this for me.