Waters Protection Ordinance
(WPO)

¹ The au­thor­it­ies shall as­sess wheth­er waste wa­ter en­ter­ing a body of wa­ter by way of dis­charge or in­filt­ra­tion is con­sidered to be pol­luted or non-pol­luted, tak­ing ac­count of:

a.

the type, the amount, the char­ac­ter­ist­ics and the tem­por­al oc­cur­rence of po­ten­tial wa­ter pol­lut­ants sub­stances in the waste wa­ter;

b.

the con­di­tion of the re­ceiv­ing wa­ters.

² Dur­ing in­filt­ra­tion of waste wa­ter, they shall also take ac­count of wheth­er:

a.

waste wa­ter can be pol­luted be­cause of ex­ist­ing soil pol­lu­tion or the un­sat­ur­ated sub­soil;

b.⁴

waste wa­ter is suf­fi­ciently pur­i­fied in the soil or in the un­sat­ur­ated sub­soil;

c.

guide val­ues un­der the Or­din­ance of 1 Ju­ly 1998⁵ on the Pol­lu­tion of Soil (SoilPO) can be main­tained in the long term, ex­cept­ing in­filt­ra­tion in­to a plant in­ten­ded for this pur­pose, or onto roads next to em­bank­ments or grass verges.

³ Pre­cip­it­a­tion wa­ter run­ning off built-up or sealed sur­faces is as a rule con­sidered to be non-pol­luted waste wa­ter if it:

a.

ori­gin­ates from roof sur­faces;

b.⁶

ori­gin­ates from roads, paths and areas on which no sub­stan­tial amounts of po­ten­tial wa­ter pol­lut­ants are un­loaded, pro­cessed and stored and if they are suf­fi­ciently pur­i­fied by in­filt­ra­tion in­to the ground. In as­sess­ing wheth­er amounts of sub­stances are sub­stan­tial, the risk of ac­ci­dents must be taken in­to con­sid­er­a­tion;

c.⁷

ori­gin­ates from track in­stall­a­tions where there is a long-term guar­an­tee that pesti­cides will not be used or if pesti­cides have been suf­fi­ciently re­tained and de­graded by a bio­lo­gic­ally act­ive lay­er of soil.