Page 249 - Hydrogeology Principles and Practice

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232 Chapter Six

Table 6.7 Composition of landfill leachate (after compilation of Christensen et al. 2001). Data for October 1985 and September 1986
describe the leachate composition pumped from containment cell 4 at Compton Bassett landfill site, west of England (after Robinson 1989).
−1
−1
All results in mg L , except pH and electrical conductivity (µScm ).
Parameter Range October 1985 September 1986
(acetogenic or acid phase) (methanogenic phase)
pH 4.5–9 6.5 7.4
Electrical conductivity 2500–35,000 15,000 10,400
Total solids 2000–60,000 550 230
Organic matter
Total organic carbon (TOC) 30–29,000
Biological oxygen demand (BOD) 20–57,000 15,750 580
Chemical oxygen demand (COD) 140–152,000 20,700 2000
BOD/COD ratio 0.02–0.80 0.76 0.29
Organic nitrogen 14–2500 – –
Inorganic macrocomponents
Total phosphorus 0.1–23 – –
Chloride 150–4500 1710 2020
Sulphate 8–7750 – –
Bicarbonate 610–7320 – –
Sodium 70–7700 – –
Potassium 50–3700 – –
Ammonium-N 50–2200 930 840
Calcium 10–7200 1410 143
Magnesium 30–15,000 – –
Iron 3–5500 787 24
Manganese 0.03–1400 – –
Silica 4–70 – –
Inorganic trace elements
Arsenic 0.01–1 – –
Cadmium 0.0001–0.4 – –
Chromium 0.02–1.5 – –
Cobolt 0.005–1.5 – –
Copper 0.005–10 – –
Lead 0.001–5 – –
Mercury 0.00005–0.16 – –
Nickel 0.015–13 – –
Zinc 0.03–1000 8.4 2.4

In the absence of engineered controls, the extent pollutants: dissolved organic matter; inorganic macro-
to which leachate from a landfill site contaminates components; heavy metals; and xenobiotic organic
groundwater is dependent on the hydraulic, geo- compounds (Christensen et al. 2001). Ranges of
chemical and microbiological properties of the values for the first three of these groups are given in
hydrogeological system (Nicholson et al. 1983). For Table 6.7. Xenobiotic organic compounds (aromatic
a comprehensive review of the biogeochemistry of hydrocarbons, halogenated hydrocarbons, phenols
landfill leachate plumes, the reader is referred to and pesticides) originating in household or industrial
Christensen et al. (2001). chemicals are usually present in relatively low con-
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Considering the example of a landfill receiving a centrations in the leachate (<1mgL for individual
mixture of municipal, commercial and mixed indus- compounds).
trial wastes, landfill leachate may be characterized Landfill leachate contamination of groundwater
as a water-based solution containing four groups of has a source in the internal, biogeochemical decom-