7. At least 3 times a year, in the spring, summer and fall, the groundwater must be sampled at each sampling point of the monitoring wells established for the purposes of section 6 in order to perform the verification referred to in paragraph 3 of section 5.
During sampling, the piezometric level of groundwater must also be measured.
After a monitoring period of at least 5 years, if the analysis of the groundwater samples collected during that period has not revealed the presence of any substance referred to in paragraph 2 of section 5, the sampling frequency may be reduced to 1 sampling per year. The reduction in the sampling frequency applies as long as the analysis of groundwater samples shows that the conditions for the reduction are satisfied.