Decrease in acid mine drainage release rate from mine pit walls in Brunner Coal Measures

Figures & data

Figure 1. Locations of wall wash sampling sites. BCM, Brunner Coal Measures; PCM, Paparoa Coal Measures.

Figure 2. Rainfall data in the Reefton and Buller areas around the time wall wash data was collected (Reefton data is from NIWA and Buller data is from Solid Energy NZ Ltd).

Figure 3. Photographs of sampling sites showing distribution of precipitates. A, Site A pit wall −3 days old. B, C, Site B pit wall. D, Site C road cut. E, Site D pit wall. F, Site E portal cutting.

Table 1. Sample descriptions, pH values and calculated acidity for wall wash samples.

Sample	Description	Age years	Date	pH	Acidity
Site A 1	Sandy mudstone, grey-muddy ppt	3 (d)	29/04/16	2.06	427
Site A 2	Sandy mudstone, grey-muddy ppt	3 (d)	29/04/16	3.09	40
Site A 3	Sandy mudstone, grey-muddy ppt	3 (d)	29/04/16	3.19	32
Site A 4	Mudstone, slaking, Fe–Ox	1	29/04/16	2.69	100
Site A 5	Mudstone, slaking, Fe–Ox	1	29/04/16	2.52	148
Site A 6	Silty sandstone, Fe–Ox	1	29/04/16	2.48	162
Site B 1	Medium–coarse sandstone, cross bedded, white ppt	4	22/04/16	3.39	20
Site B 2	Medium–coarse sandstone, Fe–Ox + white ppt	4	22/04/16	3.65	11
Site B 3	Mudstone, Fe–Ox + white ppt	4	22/04/16	4.13	4
Site B 4	Medium sandstone, Fe–Ox + white ppt	4	22/04/16	4.38	2
Site B 5	Medium sandstone, Fe–Ox + white ppt	4	22/04/16	3.96	5
Site B 6	Medium–coarse sandstone, Fe–Ox	4	22/04/16	3.53	14
Site B 7	Medium sandstone, white ppt	4	22/04/16	4.49	2
Site C 1	Medium sandstone, Fe–Ox + white ppt	10	29/04/16	5.24	0
Site C 2	Medium sandstone, Fe–Ox	10	29/04/16	3.55	14
Site C 3	Mudstone	10	29/04/16	3.03	46
Site C 4	Mudstone, slaking, Fe–Ox	10	29/04/16	3.53	14
Site D 1	Silty sandstone, Fe–Ox	18	22/04/16	3.2	31
Site D 2	Medium–coarse sandstone, Fe–Ox	18	22/04/16	3.86	7
Site D 3	Medium–coarse sandstone, Fe–Ox	18	22/04/16	4.44	2
Site D 4	Medium–coarse sandstone, Fe–Ox	18	22/04/16	3.92	6
Site E 1	Mudstone, Fe–Ox + white ppt	62	27/09/16	3.53	14
Site E 2	Medium–coarse sandstone, Fe–Ox, some lichen	62	27/09/16	6.76	0.01
Site E 3	Medium sandstone, Fe–Ox, some lichen	62	27/09/16	5.68	0.1
Site E 4	Coarse sandstone, Fe–Ox	62	27/09/16	6.3	0.02
Site E 5	Medium–coarse sandstone, Fe–Ox, some lichen	62	27/09/16	5.57	0.13
Site E 6	Medium–coarse sandstone, Fe–Ox	62	27/09/16	5.89	0.06
Site F 1	Coarse sandstone, abundant lichen	138	30/09/16	6.1	0
Site F 2	Medium–coarse sandstone, abundant lichen	138	30/09/16	6.58	0.01
Site F 3	Coarse sandstone, weak Fe–Ox, abundant lichen	138	30/09/16	5.88	0.06
Site F 4	Mudstone, weak Fe–Ox, abundant lichen	138	30/09/16	6.6	0.01
Site F 5	Sandstone, weak Fe–Ox	138	30/09/16	6.43	0.02

ppt, precipitate; (d), days, acidity units mg/l (H₂SO₄).

Table 2. Major cation and trace element concentrations in wall wash samples.

Sample	Na	Mg	K	Ca	Al	Fe	Zn	Ni	Mn	As	Cu	Cd	Co	Sb
Site A 1	6.6	79	19.9	250	96	1890	16.7	3.8	11.4	3.3	0.053	0.01	1.9	–
Site A 2	4.7	19.2	17.4	45	5.4	19.1	0.62	0.22	2.2	0.0028	0.0011	0.00091	0.088	–
Site A 3	4.4	9.1	9.2	70	2.3	9.1	0.36	0.21	0.7	0.0054	0.0018	0.00061	0.069	–
Site A 4	0.83	3	1.46	1.38	22	42	0.43	0.09	0.44	0.0012	0.077	0.00046	0.028	–
Site A 5	<	90	<	21	220	3500	14.1	3.4	10	0.27	0.84	0.013	1.33	<
Site A 6	1	28	0.6	10.2	46	490	3.9	0.62	1.8	0.092	0.164	0.0026	0.22	–
Site B 1	5.4	330	3.8	19.8	128	3.7	25	2.2	45	0.003	1.04	0.021	1.2	<
Site B 2	12.1	5700	6.2	420	15.2	3.9	28	8.5	27	<	0.113	0.0061	5.2	<
Site B 3	0.64	46	0.93	16.7	2.3	2.5	0.87	0.196	1.18	0.0015	0.027	0.0006	0.095	<
Site B 4	9.2	4800	5.7	172	11.1	4	14.9	43	70	<	0.096	0.0045	31	<
Site B 5	4	3700	1.2	69	10.9	0.3	31	4.9	92	<	0.23	0.006	8.5	<
Site B 6	0.42	83	1.25	5.6	7.7	0.54	2.3	0.45	3.2	<	0.023	0.00054	0.23	<
Site B 7	3.1	2500	5.7	127	3.9	14.8	22	12.9	89	<	0.056	0.0056	5.1	<
Site C 1	1.4	1.26	1.99	2.9	0.074	0.09	0.026	0.0043	0.068	<	0.0022	<	0.001	<
Site C 2	1.51	7.7	0.92	11.3	11.5	0.31	0.27	0.057	0.56	<	0.0121	0.00035	0.0198	<
Site C 3	0.64	12.7	0.23	13.2	26	4.4	0.48	0.123	0.92	<	0.037	0.00079	0.038	<
Site C 4	0.97	1.53	0.55	4.7	2.3	0.55	0.066	0.0133	0.099	<	0.0075	0.00008	0.0036	<
Site D 1	1.06	13.3	1.58	27	3.2	0.77	0.38	0.067	0.41	<	0.032	0.00038	0.027	<
Site D 2	1.52	34	1.36	26	10.8	0.29	1.06	0.25	1.66	<	0.039	0.00119	0.12	<
Site D 3	1.32	8.6	2.1	3.9	4	0.14	0.29	0.067	0.34	<	0.021	0.00033	0.036	<
Site D 4	7.6	3600	4.7	250	17.1	0	21	5.4	27	<	0.2	0.0069	3.6	<
Site E 1	2	0.26	3.7	0.68	2.1	0.36	0.31	0.04	0.08	<	0.034	0.00038	0.0168	<
Site E 2	1.49	0.06	1.65	0.13	0.01	<	0.031	0.0008	0.0009	<	0.0026	<	<	<
Site E 3	0.63	0.05	0.98	0.07	0.024	0.1	0.009	<	0.0007	0.001	<	<	<	0.0004
Site E 4	3.2	0.15	4	0.38	0.004	<	0.027	0.0013	0.0015	<	0.0043	<	<	<
Site E 5	1.38	0.07	0.9	0.1	0.003	<	0.012	0.0006	0.0017	<	0.0007	<	<	<
Site E 6	1.79	0.12	1.06	0.25	0.005	<	0.0156	0.0016	0.0034	<	0.0008	<	0.0005	<
Site F 1	1.97	0.03	1.94	0.14	<	<	0.0128	<	0.0008	<	0.0015	<	<	<
Site F 2	6.5	0.11	4.8	0.61	0.011	<	0.05	0.002	0.0027	<	0.0065	0.00007	<	0.0007
Site F 3	3.7	0.29	2.2	1.25	0.012	<	0.039	0.0008	0.0021	<	0.0015	0.00008	<	0.0004
Site F 4	13.7	0.6	10.1	2.5	0.026	<	0.049	0.0027	0.005	<	0.0076	0.00007	<	0.001
Site F 5	3.3	0.14	2.2	0.34	0.005	<	0.077	0.0012	0.0015	<	0.0034	0.0002	<	0.0002

All units mg/l. <, below detection.

Figure 4. Average acidity data with power function fit to data from 1 to 62-year-old pit walls. (♦) 3 day data, not included in the fit.

Figure 5. Average composition of acidity released by pit walls of different ages.

Figure 6. Relationships between Zn and selected trace element concentrations in all wall wash samples: A, Ni; B, Co; C, Mn; and D, Cd.

Figure 7. Relationship between Zn concentration in wall wash and acidity release.

Figure 8. Raw data and averaged acidity data from wall wash samples with values for acidity in un-impacted streams from Brunner Coal Measures. Stream chemistry values are during low flow.

Table 3. Compilation of chemical data for un-impacted streams draining only Brunner Coal Measures under low flow conditions.

Area	Site	pH	Fe	Al	Acidity	Reference
Buller Coalfield	MT6	3.9	0.13	0.173	7.5	Davies (2009)
Buller Coalfield	MT6	4.5	0.12	0.175	2.8	Davies (2009)
Buller Coalfield	MT6	4.05	0.2	0.18	5.9	SENZ data
Buller Coalfield	MT6	4.08	<	0.16	4.9	SENZ data
Buller Coalfield	MT6	4.5	0.1	0.08	2.2	SENZ data
Buller Coalfield	MT6	4.56	<	0.1	1.9	SENZ data
Buller Coalfield	MT6	4.66	<	0.12	1.7	SENZ data
Reefton Coalfield	Un-named	4.13	0.39	0.563	7.7	Pope et al. (2010a)
Te Kuha Coalfield	TKS3	4.1	0.24	0.38	6.5	SML data
Te Kuha Coalfield	TKS3	4.5	0.15	0.22	3.1	SML data

Fe and Al concentrations in mg/l, acidity units mg/l (H₂SO₄). SENZ, Solid Energy New Zealand; SML, Stevenson Mining Ltd.

Davies H. 2009. Geochemical change following pH remediation in Mangatini Stream, Stockton Coal Mine, New Zealand [MSc]. University of Otago; p. 181.

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Pope J, Newman N, Craw D, Trumm D, Rait R. 2010a. Factors that influence coal mine drainage chemistry, West Coast, South Island, New Zealand. New Zealand Journal of Geology and Geophysics. 53(Special Edition - Mine Drainages):115–128. doi: 10.1080/00288306.2010.498405

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