Wastes were emplaced in three 6m deep cells, finished to a flat profile, membrane covered, soiled and seeded. The start dates for the cells were 1993, 1997 and 1998. The cells are clay lined and have leachate collection systems. The base of the cells is below the local water table level and the operator suspects some ingress of groundwater. Dry weather flow data for the whole landfill suggest this could contribute as much as 50% of the overall flow (see Appendix 3). In capped cells, where rainfall ingress is restricted, it is possible that the contribution of groundwater becomes greater than 50%. Estimated L/S ratios from rainfall ingress are low, at ~0.1 to ~0.23 (see Appendix 3).
Data on filtered (0.45 µm) and unfiltered samples, provided by the operator, indicated that a significant proportion of Pb, and to a lesser extent Cd, may be associated with particulates, but that soluble concentrations were nevertheless high (Pb up to several hundred mg/l; Cd several tens of µg/l). The results contain no data for redox potential, organic indicators, nitrogen compounds or As.
Time series graphs of the data received are shown in Figures 2.7a and 2.7b (1993 cell), 2.8a and 2.8b (1997 cell) and 2.9a and 2.96b (1998 cell). The following interpretive comments are made.
• Concentrations of major components are very peaky in all three cells.
• TDS in the 1997 cell is anomalously low, at around one sixth of those in the other cells. This may reflect the effects of groundwater ingress or may indicate short-circuiting of surface water. The results from the 1997 cell are therefore regarded as being unrepresentative of this waste type.
• The leachate in the 1993 and 1998 cells contains high concentrations of inorganic salts, with TDS typically in the range 50 to 150,000 mg/l. The highest concentrations occur before capping. This would be consistent with post-capping flows being derived to a greater extent from groundwater ingress, that by-passes much of the waste mass.
• The relative abundance of major ions is:
Cl >> SO4 (no data for alkalinity or NOx)
K ≈ Na >> Ca (Na not measured; abundance estimated by difference, from TDS data);
• pH values are close to neutral, with very few spikes to higher pH values (max 9.5).
• Heavy metal concentrations are mostly low, except for Pb and Cd. Pb concentrations again span several orders of magnitude but are lower than in the leachate from dry scrub residues, while Cd concentrations are similar.
1 – 1000 mg/l Fe, (Pb)
100 – 1000 µg/l Pb, Zn, (Cd), Ni)
10 – 100 µg/l Cu, Cd, Ni, Cr, (Zn), (Pb) 1 – 10 µg/l (Cu), (Ni), (Hg)
<1 µg/l Hg
Conductivity
0 50000 100000 150000 200000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
conductivity in uS/cm
Total solids
0 50000 100000 150000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
pH values
6 7 8 9 10 11
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
pH value
Suspended solids
0 50 100 150
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Sulphate
0 500 1000 1500 2000 2500 3000 3500
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Chloride
0 20000 40000 60000 80000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Calcium
0 1000 2000 3000 4000 5000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Potassium
0 5000 10000 15000 20000 25000 30000 35000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Figure 2.7a Site E leachate quality data from fly ash and wet scrub APC residues, 1993 cell:
Zinc
0 0.5 1 1.5 2
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Copper
0 0.05 0.1 0.15
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Nickel
0 0.05 0.1 0.15 0.2
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Chromium
0 0.2 0.4 0.6 0.8 1
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Lead
0.01 0.1 1 10 100
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Cadmium
0 0.5 1 1.5 2 2.5
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Mercury
0 0.0005 0.001 0.0015 0.002 0.0025 0.003
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Iron
0 5 10 15 20
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Figure 2.7b Site E leachate quality data from fly ash and wet scrub APC residues, 1993 cell:
heavy metals
Conductivity
0 10000 20000 30000 40000 50000 60000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
conductivity in uS/cm
Total solids
0 10000 20000 30000 40000 50000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
pH values
6 7 8 9 10 11
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
pH value
Suspended solids
0 50 100 150
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
NO DATA
Sulphate
0 200 400 600 800
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Chloride
0 4000 8000 12000 16000 20000 24000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Calcium
0 200 400 600 800 1000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Potassium
0 2000 4000 6000 8000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Figure 2.8a Site E leachate quality data from fly ash and wet scrub APC
Zinc
0 0.1 0.2 0.3
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Copper
0 0.002 0.004 0.006 0.008 0.01
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Nickel
0 0.05 0.1 0.15 0.2
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Chromium
0 0.1 0.2 0.3 0.4 0.5
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Lead
0.001 0.01 0.1 1 10 100
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Cadmium
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
0.75
Mercury
0 0.0001 0.0002 0.0003 0.0004 0.0005
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Iron
0 2 4 6 8
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Figure 2.8b Site E leachate quality data from fly ash and wet scrub APC residues, 1997 cell:
heavy metals
Conductivity
0 20000 40000 60000 80000 100000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
conductivity in uS/cm
Total solids
0 20000 40000 60000 80000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
pH values
6 7 8 9 10 11
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
pH value
Suspended solids
0 50 100 150
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
NO DATA
Sulphate
0 200 400 600 800 1000 1200
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Chloride
0 10000 20000 30000 40000 50000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Calcium
0 1000 2000 3000 4000 5000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Potassium
0 3000 6000 9000 12000 15000
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Figure 2.9a Site E leachate quality data from fly ash and wet scrub APC residues, 1998 cell:
Zinc
0 0.02 0.04 0.06 0.08 0.1 0.12
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Copper
0 0.004 0.008 0.012 0.016
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Nickel
0 0.005 0.01 0.015 0.02
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
0.27
Chromium
0 0.02 0.04 0.06 0.08 0.1
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
0.41
Lead
0.001 0.01 0.1 1 10
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Cadmium
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
0.21 0.27
Mercury
0 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Iron
0 2 4 6 8 10
Jan-93 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 date
concentration in mg/l
Figure 2.9b Site E leachate quality data from fly ash and wet scrub APC residues, 1998 cell:
heavy metals
Site C - fly ash in "big bags"
Site C is an engineered containment site, located above the water table. Big bags containing fly ash are mono-filled and the spaces between them filled with clean sand to assist physical stability of the mass.
It is not known whether the fly ash also contains other APC residues. When final levels are reached, the cells are capped with a geomembrane and bentonite and seeded with grass. The cell for which data have been obtained is thought to be partly up to level, and hence partly restored. The L/S ratio for the cell is not known but is expected to be low, given its young age and the partial capping. The relevance of L/S ratio is minor, for wastes emplaced in big bags, because most infiltration will by-pass the bags, passing preferentially through sand-filled spaces.
Analytical data for a restricted number of parameters have been obtained for a cell begun in 1993. The data received are annual averages of quarterly samples. The data for most parameters are shown as time series graphs in Figure 2.10. In addition, analysis for minor organics showed: PAH <1 µg/l, oil ≤1 mg/l and EOX ~5 mg/l
The following interpretive comments may be made.
• Despite the use of big bags, significant concentrations of contaminants occur in the leachate.
• As expected, with annual averages, the data do not exhibit the peakiness that was observed in individual measurements at Site E. Daily leachate flows may exhibit greater variation of quality than the data in Figure 2.10.
• The concentration of chloride, at 1,000 to 5,000 mg/l, is one to two orders of magnitude lower than at Site E. This is not unexpected, given the use of big bags. However, sulphate concentrations (1000 to 2000 mg/l) are comparable with those from bulk deposits at Site E. Other major ions were not analysed.
• Despite its apparently dilute nature, the leachate contains significant concentrations of organic matter and nitrogen: COD concentrations are in the region of 50 to 300 mg/l and TKN typically 5 to 25 mg/l. Given the dilute nature of the chloride concentrations, the COD levels are consistent with TOC concentrations in the range 100 to 1000 mg/l quoted by Hjelmar (1996) for initial leachates from bulk deposits.
• pH values are consistently near neutral.
• Concentrations of heavy metals are low:
100 – 1000 µg/l Zn, (Pb) 10 – 100 µg/l Pb, Ni, Cr, Cu
• No results were received for redox potential, major cations, alkalinity, NOx, As, Cd, Hg, Mo.
COD
0 100 200 300 400
1992 1994 1996 1998 2000 2002
concentration in mg/l
Chloride
0 1000 2000 3000 4000 5000 6000
1992 1994 1996 1998 2000 2002
concentration in mg/l
TKN
0 10 20 30 40
1992 1994 1996 1998 2000 2002
concentration in mg/l
Sulphate as SO4
0 500 1000 1500 2000 2500
1992 1994 1996 1998 2000 2002
concentration in mg/l
pH value
6 7 8 9
1992 1994 1996 1998 2000
pH value
Zinc
0 1000 2000 3000 4000
1992 1994 1996 1998 2000
concentration in ug/l
Nickel
0 20 40 60 80 100
1992 1994 1996 1998 2000
concentration in ug/l
Copper
0 20 40 60 80
1992 1994 1996 1998 2000
concentration in ug/l
Chromium
0 20 40 60 80 100
1992 1994 1996 1998 2000
concentration in ug/l
Lead
0 25 50 75 100 125
1992 1994 1996 1998 2000
concentration in ug/l
Figure 2.10 Site C leachate quality data from cell containing MSW incinerator fly ash in big bags