cross-contamination between aquifers. Waterstops are generally made of
high-quality ball clay, such as bentonite. The single aquiclude should be no less
than 5 m thick, with the filled ball clay 2–3 m vertically higher than the top plate of
aquiclude. Pressurized water monitoring wells shall be layered to stop water, and
phreatic water monitoring wells shall not penetrate the bottom plate of aquiclude
under the unconfined aquifer.
(c) Post-construction cleaning
Monitoring wells should be cleaned one week after constructed. The methods can
be determined according to wellbore structure, well pipe materials and aquifer
types, and it is advisable to apply a combination of methods to the same well. Well
cleaning should follow the Technical Specifications for Water Supply Pipelines and
Wells (GB50296–1999).
For areas with low background value of sand content, well cleaning can be
ended if groundwater effluent is visually clear. For areas with high background
value of sand content, well cleaning is deemed completed if the error is less than
10% for three consecutive measurement of water parameters, such as potential of
hydrogen (pH), temperature, dissolved oxygen, conductivity and turbidity.
(d) Information records
Detailed records specific to monitoring wells should be kept, including the location,
structure, orientation relationship with the site, and especially waterstops.
2.2.5 Sampling
(1) Frequency
Monitoring wells take groundwater samples once every quarter or four times a year;
Original landfill leachate is sampled once every quarter or four times a year, in
order to synchronize the monitoring of landfill leachate and groundwater.
(2) Quality control
(a) Preparation before sampling
The containers used for sampling should be carefully cleaned before use. For
specific requirements and methods, please refer to the Technical Guidelines for
Environmental Monitoring in Groundwater Investigation.
Generally, the water pumped for cleaning wells is no less than 3 to 5 times the
well volume or 30 min. The specific pumping volume or duration depends on the
actual circumstances, such as cleaning equipment, well specifications, test items
and samples. The well cleaning does not complete until water-related parameters
(pH, conductivity, water temperature, dissolved oxygen, oxidation reduction
potential (ORP), and etc.) are stabilized.
26
2 Environmental Background Investigation of Groundwater …
high-quality ball clay, such as bentonite. The single aquiclude should be no less
than 5 m thick, with the filled ball clay 2–3 m vertically higher than the top plate of
aquiclude. Pressurized water monitoring wells shall be layered to stop water, and
phreatic water monitoring wells shall not penetrate the bottom plate of aquiclude
under the unconfined aquifer.
(c) Post-construction cleaning
Monitoring wells should be cleaned one week after constructed. The methods can
be determined according to wellbore structure, well pipe materials and aquifer
types, and it is advisable to apply a combination of methods to the same well. Well
cleaning should follow the Technical Specifications for Water Supply Pipelines and
Wells (GB50296–1999).
For areas with low background value of sand content, well cleaning can be
ended if groundwater effluent is visually clear. For areas with high background
value of sand content, well cleaning is deemed completed if the error is less than
10% for three consecutive measurement of water parameters, such as potential of
hydrogen (pH), temperature, dissolved oxygen, conductivity and turbidity.
(d) Information records
Detailed records specific to monitoring wells should be kept, including the location,
structure, orientation relationship with the site, and especially waterstops.
2.2.5 Sampling
(1) Frequency
Monitoring wells take groundwater samples once every quarter or four times a year;
Original landfill leachate is sampled once every quarter or four times a year, in
order to synchronize the monitoring of landfill leachate and groundwater.
(2) Quality control
(a) Preparation before sampling
The containers used for sampling should be carefully cleaned before use. For
specific requirements and methods, please refer to the Technical Guidelines for
Environmental Monitoring in Groundwater Investigation.
Generally, the water pumped for cleaning wells is no less than 3 to 5 times the
well volume or 30 min. The specific pumping volume or duration depends on the
actual circumstances, such as cleaning equipment, well specifications, test items
and samples. The well cleaning does not complete until water-related parameters
(pH, conductivity, water temperature, dissolved oxygen, oxidation reduction
potential (ORP), and etc.) are stabilized.
26
2 Environmental Background Investigation of Groundwater …