Site F
7.1 Mixed wastes
Few data were collected on mixed non-hazardous, low organic waste landfills, and there are insufficient data to provide a meaningful overview of leachate quality or to propose source term data. This chapter discusses leachate quality at one mixed waste landfill and another that accepted vehicle fragmentiser wastes.
At Site D (see Appendix 3) mixed non-hazardous, low organic wastes have been deposited in a series of containment cells since 1985. The site is still operational. Cells that have reached final levels are capped with restoration soils. The waste inputs since operations began are shown in Figure 7.1. The
‘miscellaneous inorganic sludges’ comprises more than half the inputs and include small quantities (<5%) of some wastes that the site operator regards as borderline hazardous/non-hazardous, e.g.
sludges from industrial production processes, residues from soil decontamination and dewatered dredging sludges. Local regulations at Site D require that all contaminated soils are cleaned before landfilling. Figure 7.1 shows that ~30% of the inputs have a significant organic content, despite the exclusion of household wastes. The average organic content of the waste mix is ~10%. Leachate from all of these cells is combined and treated on site before discharge. Results for a restricted range of parameters have been obtained for monthly analyses of the influent to the plant, from 1986 to 2000 and are shown in Figure 7.2 and 7.3 as time-series graphs. General conclusions are summarised below.
• The leachate has developed as a typical dilute/medium strength methanogenic leachate, with chloride, TKN, COD and BOD concentrations similar to those found at many UK landfills.
• Landfill gas is collected and used for combined heat and power generation, confirming that there is a significant rate of anaerobic biological activity within the site.
• The leachate exhibits marked seasonal fluctuations in strength, similar to many UK landfills, with the lowest concentrations occurring during winter.
• There has been a long-term increase in TKN. This may indicate that an increasing proportion of the organic components are degrading at increasing rates. This is similar to the gradual increase that occurs at many UK landfills as the moisture content of the wastes increases towards the optimum for degradation.
• Short-lived extreme values in concentrations of heavy metals occurred at a time in the mid 1990s when COD and BOD were also erratic. This may have been associated with acetogenic conditions at the start of operations in new cells. Apart from arsenic (1,700 µg/l) and cadmium (64 µg/l) these peak metal values were not unusually high compared with those in acetogenic leachates at UK landfills.
• At most other times, levels of most metals are very low. However, arsenic is present consistently in the range 50-100 µg/l: this is higher than would be expected at a typical UK non-hazardous waste site, or co-disposal landfill.
• PAHs are present, typically at few tens of µg/l. Most of the PAHs consist of naphthalene, acenaphthalene and fluorene.
• Extractable organohalogens (EOX) levels, at ~10-50 µg/l, are lower than typically found in MSW leachates.
• Mineral oil is present only at sub-mg/l levels, which is lower than commonly found in existing UK leachates.
• Phenols have been detected only at sub-mg/l levels only, which is no higher than commonly found in existing UK leachates.
57%
6%
13%
4%
3%
1%
9%
7%
miscellaneous inorganic wastes, 4% organic construction &demolition, 4.5% organic commercial waste, 25% organic vehicle shredder waste, 6.5% organic public cleansing waste, 9.5% organic
non-recyclable coarse household waste, 25% organic thermally dried sewage sludge and compost, 15.5% organic miscellaneous wastes, 31% organic
Figure 7.1 Waste inputs at Site D, 1985-2000
COD
0 1000 2000 3000 4000
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in mg/l
BOD
0 100 200 300 400 500
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in mg/l
Chloride
0 400 800 1200 1600 2000 2400
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in mg/l
TKN
0 100 200 300 400
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in mg/l
EOX
0 20 40 60 80 100
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
PAH - EPA16
0 20 40 60 80 100
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
1200 Mineral oil
0 200 400 600 800
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
Phenols
0 200 400 600 800
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
Figure 7.2 Leachate quality data for low hazard, low organic wastes, Site D (major parameters and organics)
Zinc
0 100 200 300 400
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
1700
Arsenic
0 100 200 300 400
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
1700
Copper
0 20 40 60 80 100
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
Nickel
0 20 40 60 80 100
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
Chromium
0 50 100 150 200 250
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
Lead
0 50 100 150 200
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
Cadmium
0 20 40 60 80 100
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l most results
less than 1 ug/l
Mercury
0 0.5 1 1.5 2 2.5
Jan- 86
Jan- 88
Jan- 90
Jan- 92
Jan- 94
Jan- 96
Jan- 98
Jan- 00
concentration in ug/l
Figure 7.3 Leachate quality data for low hazard, low organic wastes, Site D (heavy metals)
7.1.1 Vehicle fragmentiser wastes
At Site E (see Appendix 3), vehicle fragentiser waste has been deposited in a 6 m deep cell since 1994.
The cell remains operational and uncovered. The base of the cell is below the level of the local water table and the operator suspects some ingress of groundwater. Dry weather flow data for the whole landfill suggest this could be as much as 50% of the overall flow (see Appendix 3). The estimated cumulative L/S ratio for the cell receiving fragmentiser waste is ~0.15.
Although the cell has received predominantly fragmentiser waste, it has ~1 m of bottom ash from sewage sludge incineration in the base. This was placed with the objectives of protecting the leachate collection system and attenuating any metals that might leach from the fragmentiser waste.
Leachate quality data from 2-monthly sampling have been received for a limited range of parameters.
Most are shown as time series graphs from 1994 to 1999 in Figure 7.4. General conclusions include:
• the pH value is near neutral;
• metals concentrations are very low;
• mercury (not graphed) was consistently below the detection limit of 0.05 µg/l;
• oil was consistently below the detection limit of 3 mg/l; and
• no other conventional analyses or trace organic analyses were undertaken.
These results, while of interest, do not include enough parameters to provide a clear impression of leachate quality from vehicle fragmentiser waste. Also, it is possible that the basal layer of ash may have affected the collected leachate quality. In view of concerns over the presence of PCBs and other contaminants in leachates from fragmentiser wastes additional data should be sought.
pH value
6.4 6.8 7.2 7.6 8.0 8.4
Jun-94 Oct-95 Mar-97 Jul-98 Dec-99
date
pH value
Lead
0 0.04 0.08 0.12 0.16
Jun-94 Oct-95 Mar-97 Jul-98 Dec-99
date
concentration in mg/l
Nickel
0 0.04 0.08 0.12
Jun-94 Oct-95 Mar-97 Jul-98 Dec-99
date
concentration in mg/l
Copper
0 0.01 0.02 0.03 0.04 0.05 0.06
Jun-94 Oct-95 Mar-97 Jul-98 Dec-99
date
concentration in mg/l
Chromium
0 0.005 0.01 0.015 0.02 0.025
Jun-94 Oct-95 Mar-97 Jul-98 Dec-99
date
concentration in mg/l
Cadmium
0 0.01 0.02 0.03 0.04
Jun-94 Oct-95 Mar-97 Jul-98 Dec-99
date
concentration in mg/l
Figure 7.4 Leachate quality from cell receiving vehicle fragmentiser waste (Site E)