sent to the disposal center by the enterprise. The landfill site adopts the cement
solidification technology to transform toxic and harmful pollutants into substances with relatively stable physical and chemical properties with low solubility, low mobility and low toxicity, effectively preventing leaching of various
heavy metals (cadmium, chromium, copper, lead, nickel, zinc, etc.). The
security landfill site solidifies 7852.61 tons of wastes to be landfilled every
year.
(3) The typical site is located in the middle of Dashi River alluvial-proluvial fan
and on the terrace sandwiched by Dashi River and Ciwei River. The terrain is
basically flat, with single genetic type and simple morphotype of landform, and
the Quaternary is about 49 m thick. Three layers of groundwater are mainly
distributed within the Quaternary sediments with a buried depth of 49 m, with
the groundwater types of perched water, phreatic water–confined water and
confined water from top to bottom. The rigid landfill pit basically cuts through
the phreatic-confined aquifer, and this layer of groundwater shall be selected as
the target aquifer for monitoring and analysis. The target aquifer is widely
distributed within the site area and occurs in silty soil with a buried depth of
13–15 m. The aquifer roof elevation is about 26.27–27.33 m, the floor elevation is about 24.88–26.40 m, the thickness is about 0.4 m–1.5 m, the flow
direction is from west to east as a whole, and the hydraulic gradient is 1.25%.
The permeability coefficient of the target aquifer is 0.06 m/d calculated in the
water lifting test, the porosity of the aquifer is 0.45 calculated in the tracer test,
and the vertical dispersity and horizontal dispersity are 0.10 m and 0.035 m,
respectively.
(4) There are six groundwater monitoring wells in the typical site, including one
full-field background well, one full-field diffusion well, one landfill background
well, and three landfill pollution monitoring wells. The monitoring horizon is
phreatic-confined aquifer. Samples are taken once every quarter, including the
following 23 analysis and test items: volatile phenols, hexavalent chromium,
pH value, total hardness, chloride, total dissolved solids, total Escherichia coli,
cyanide, ammonia nitrogen, arsenic, cadmium, copper, mercury, nickel, lead,
zinc, iron, manganese, fluoride, nitrite, nitrate, sulfate and permanganate index.
According to the monitoring results from 2011 to 2014, except for the total
dissolved solids and total hardness, other indicators did not exceed the limits of
Grade 3 in the Quality Standard for Ground Water GB/T 14848-1993, mainly
due to regional groundwater quality problems. From 2012 to 2014, concentrations of total dissolved solids and total hardness in groundwater had seasonal
fluctuations and there was no further deterioration. Compared with the
requirements of the Draft Guide, the natural background ions (required) are not
monitored, not all of the regular indicators (required) are monitored, and the
characteristic indicators (optional) such as organophosphorus, total petroleum
hydrocarbons, halogenated hydrocarbons and monocyclic aromatic hydrocarbons are not monitored at the site.
5.5 North China
327
solidification technology to transform toxic and harmful pollutants into substances with relatively stable physical and chemical properties with low solubility, low mobility and low toxicity, effectively preventing leaching of various
heavy metals (cadmium, chromium, copper, lead, nickel, zinc, etc.). The
security landfill site solidifies 7852.61 tons of wastes to be landfilled every
year.
(3) The typical site is located in the middle of Dashi River alluvial-proluvial fan
and on the terrace sandwiched by Dashi River and Ciwei River. The terrain is
basically flat, with single genetic type and simple morphotype of landform, and
the Quaternary is about 49 m thick. Three layers of groundwater are mainly
distributed within the Quaternary sediments with a buried depth of 49 m, with
the groundwater types of perched water, phreatic water–confined water and
confined water from top to bottom. The rigid landfill pit basically cuts through
the phreatic-confined aquifer, and this layer of groundwater shall be selected as
the target aquifer for monitoring and analysis. The target aquifer is widely
distributed within the site area and occurs in silty soil with a buried depth of
13–15 m. The aquifer roof elevation is about 26.27–27.33 m, the floor elevation is about 24.88–26.40 m, the thickness is about 0.4 m–1.5 m, the flow
direction is from west to east as a whole, and the hydraulic gradient is 1.25%.
The permeability coefficient of the target aquifer is 0.06 m/d calculated in the
water lifting test, the porosity of the aquifer is 0.45 calculated in the tracer test,
and the vertical dispersity and horizontal dispersity are 0.10 m and 0.035 m,
respectively.
(4) There are six groundwater monitoring wells in the typical site, including one
full-field background well, one full-field diffusion well, one landfill background
well, and three landfill pollution monitoring wells. The monitoring horizon is
phreatic-confined aquifer. Samples are taken once every quarter, including the
following 23 analysis and test items: volatile phenols, hexavalent chromium,
pH value, total hardness, chloride, total dissolved solids, total Escherichia coli,
cyanide, ammonia nitrogen, arsenic, cadmium, copper, mercury, nickel, lead,
zinc, iron, manganese, fluoride, nitrite, nitrate, sulfate and permanganate index.
According to the monitoring results from 2011 to 2014, except for the total
dissolved solids and total hardness, other indicators did not exceed the limits of
Grade 3 in the Quality Standard for Ground Water GB/T 14848-1993, mainly
due to regional groundwater quality problems. From 2012 to 2014, concentrations of total dissolved solids and total hardness in groundwater had seasonal
fluctuations and there was no further deterioration. Compared with the
requirements of the Draft Guide, the natural background ions (required) are not
monitored, not all of the regular indicators (required) are monitored, and the
characteristic indicators (optional) such as organophosphorus, total petroleum
hydrocarbons, halogenated hydrocarbons and monocyclic aromatic hydrocarbons are not monitored at the site.
5.5 North China
327