IJERD – International Journal of Environmental and Rural Development (2023) 14-1

Research article
erd

Nitrogen Removal from Mining Dewatering and theResearch
Fate articleofWater Release to a River
BARRY NOLLER*
Sustainable Minerals Institute, University of Queensland, Australia
Email: b.noller@uq.edu.au
Received 30 January 2023

Accepted 15 May 2023(*Corresponding Author)

Abstract Seepage water in underground mining voids arises from interception with aquifers
that may become contaminated with nitrogen (N)-based explosive during undergroundblasting operations. The nitrogen-contaminated water may be pumped from undergroundmining voids and stored at the surface or discharged to a nearby river without treatment if
sufficient dilution is achieved to minimize effects on the aquatic environment and pastoral
activities. Maximum N concentration in dewatering water was observed to be 200 times thereceiving water of the nearby river when compared against ANZECC/ARMCANZ (2000)
water quality guidelines. This study sought to identify sources of N contamination ofunderground seepage water, pumped to the surface for discharge to the nearby river. The levelof protection (for an aquatic ecosystem) specified the water quality objectives to be achieved
following water release. The ANZECC/ARMCANZ (2000) has three levels of aquatic
ecosystem protection, and ‘Level 2 Aquatic Ecosystem’ was selected being described asapplying to slightly–moderately disturbed systems including rural streams receiving runoff
from land disturbed to varying degrees by grazing or pastoralism, nearby or adjacent to urban
areas. The study considered river flow data, underground dewatering production, discharge
rates, and river water quality for upstream and downstream of the discharge point, as well as
quantities of explosives used underground at specified % N in explosives estimated to remain
following blasting. The most important nitrogen form present in the mine discharge
wastewater was found to be oxidized-N (>93%). Only 0.54 % of end-of-pipe discharge wasmeasurable in the downstream river and indicated that rapid dilution and removal of oxidizedN (nitrate/nitrite) by biota could be achieved. The level of oxidized-N expressed as load
discharged to the river showed that the quantity of N discharged was similar in magnitude to
the spillage of 4% explosive.
Keywords nitrogen, explosive, mining, dewatering, discharge, cattle, aquatic species

INTRODUCTION
Seepage water in underground mining voids arises from interception with aquifers that may becomecontaminated with nitrogen-based explosives during underground blasting operations. Ammonium
nitrate used commonly as an explosive is the same as the common fertilizer. Nitrogen (N)contaminated water may be pumped from underground mining voids and stored at the surface fortreatment or discharged to a nearby river without treatment if sufficient dilution is achieved tominimize effects to the aquatic environment and pastoral activities and can be demonstrated andapproved by Government regulators. Existing nitrogen (N)-contaminated water added upstream
arises from local agricultural and urban activities and may affect the aquatic ecosystem. This study
sought to identify sources of nitrogen contamination of underground mining seepage water, pumped
to the surface for discharge to the nearby river and if additional nitrogen (N)-contaminated water
pumped to the river gives further effects on the aquatic ecosystem. The level of protection (for an
aquatic ecosystem) specified the water quality objectives to be achieved following water release
follows the ANZECC/ARMCANZ (2000) levels of aquatic ecosystem protection.

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OBJECTIVE
The objective of this study is to identify sources of N contamination of underground seepage waterfrom a mining operation that is pumped to the surface for discharge to a nearby river and to identify
if the level of protection (for an aquatic ecosystem) of the specified water quality criteria can beachieved following water release.
METHODOLOGY
The study is based on a site in Queensland, Australia, and considered river flow data, undergrounddewatering production from mining, discharge rates, and river water quality upstream anddownstream of the discharge point (Noller, 2006).
The level of protection (for an aquatic ecosystem Environmental Value - EV) is the level ofaquatic ecosystem condition specified by water quality objectives (WQOs) to be achieved for theintended water. The Queensland Water Quality Guidelines (QWQG, 2006) were developed
concurrently with the EVs and water quality objectives (WQOs) and release process. These aretechnical guidelines for deriving WQOs for rivers in Queensland and include locally and regionally
relevant water quality data for fresh, estuarine, and marine waters.
The ANZECC/ARMCANZ (2000) established three levels of aquatic ecosystem protection thatare applied by QWQG (2006). The levels of aquatic ecosystem protection are: (i) Level 1: Highecological/conservation value ecosystems - effectively unmodified or other highly valued systems;(ii) Level 2: Slightly–moderately disturbed ecosystems - ecosystems in which aquatic biologicaldiversity may have been adversely affected to a relatively small but measurable degree by humanactivity; and (iii) Level 3: Highly disturbed ecosystems - measurably degraded ecosystems of lower
ecological value. The EVs and WQOs identified that the study river is: A level 2 Aquatic Ecosystem.
This is described by ANZECC/ARMCANZ (2000) as an ‘Ecosystem in which aquatic biologicaldiversity may have been adversely affected to a relatively small but measurable degree by humanactivity’. The biological communities remain in a healthy condition and ecosystem integrity is largely
retained. Typically, such systems have slightly to moderately cleared catchments and/or reasonably
intact riparian vegetation. Slightly–moderately disturbed systems could include rural streams
receiving runoff from land disturbed to varying degrees by grazing or pastoralism. This description
fits the surrounding area of the study mine and river.
Ammonium nitrate is the key explosive used in the underground workings at the study mine.
The quantities of ammonium nitrate explosives with specified % N used at the underground minegave an estimate of remaining explosives following blasting. As a general rule, 1 tonne of rock uses
1 kg of explosive. Some ammonium nitrate may be spilt during charging and was estimated to be 4%
based on collecting residues and weighing them (Noller, 2006).
Water quality was collected and analyzed for dewatering from an underground source, to thedischarge point, following discharge to a local river, upstream and downstream at the following sites:(i) Dewatering from underground; (ii) Dewatering storage tank at exit to discharge pipe before
discharge to the local river; (iii) Downstream local river beyond mixing zone; and (iv) Upstream ofthe local river, including an historical gauging site of 40 years operation. Water samples werecollected by mine staff and water quality data was measured by the mine laboratory for pH, total
dissolved solids (TDS), suspended solids (SS), N forms as total unfiltered nitrogen, total filtered N,
nitrite and nitrate (oxidized-filtered), particulate N (>0.45 µm), organic-N (total - oxidized-N) andammonium ion (filtered). Filtration for N was conducted on-site using 0.45 µm cartridge membranefilters with a plastic syringe.
The site water budget included water quality of water consumed on site, water discharged
quantities, and surface runoff from sub-catchments on site. The Queensland regulator has a large
number of monitoring sites and gauging stations on the study site river (N and M, 2006). An upstream
gauging station with 40 years of records was selected as having the most complete and relevant set
to the discharge of the study mine (Noller, 2006).

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RESULTS AND DISCUSSION
Table 1 gives the average monthly river flow (ML) for September to February at the main upstream
gauging station which corresponds to the release of water from the mine. January and February andthe annual summer rains (see Table 1 for rainfall during the study period). The data record formonthly flow at the upstream gauging station over 40 years had the corresponding average monthly
flow for the period ending 2,400 hrs. and was 68,970 ±178,630 ML. According to the Queensland
Environmental Authority water from the mine must not be discharged to the river when the flow rate
at the main upstream gauging station is less than 20 ML (Noller, 2006). For the period November–
December (Table 1) the total underground transfer from the discharge tank to the river was 11,222
kL/month, based on a rate of 362 kL/day. The accumulated groundwater from the mine that wasdischarged to the river contained a consistently high total N level that was primarily oxidized-N.
Table 1 Monthly River flow (ML) at the main upstream gauging station over
40-years period
Month
September
OctoberNovember
DecemberJanuary
February

MeanaStandard deviationa

14,575
17,384
31,67850,762
115,284
210,310Percent (%)

23,85027,49147,532
11,106
319,054379,291

Monthly rainfall (mm)at mineb

44.41
1.34
15.17
16.52
15.64
8.79

134
216
141
-

Source and explanation: a. NR&M (2006); b. Noller (2006)

Table 2 gives a summary of ammonium nitrate used by the mine during the period from
September to February. It is noted that all explosives were consumed in the explosion, apart fromspillage (Noller, 2006). Assuming that spillage was 4%, 2,009 kg ammonium nitrate was dissolvedin the underground water system from September to February. The established guide of 4,000
kg/month was equivalent to 1,400 kg-N/month and the loss of 160 kg is 56 kg-N. The calculated loadof N released from the rising water main, discharge tank, and via the pipe was compared with thetotal ammonium nitrate used and spillage at the mine (Table 2). Percent N in explosives gave a total
N budget, together with an estimate of how much remains following blasting.
Table 2 Total ammonium nitrate (as % of explosive use) consumption over a 6-month
periodExplosive Accounting
period (% Explosive
use)a
May
OctoberNovember
DecemberJanuary
February
Total

Total ammonium
nitrate (kg)a
7,467.4
11,778.9
4,099.1
6,435.7
10,714.8
11,784.2
52,280.0

Spillage ammonium
nitrate estimated at
4% (kg)a
299
471
164
257
426
471
2091

Total
ammonium
nitrate-N (kg)b
2,614
4,122
1,435
2,253
3,750
4,124
18,298Spillage-N
estimated at 4%
(kg)b
104.5
164.9
57.4
90.1
150.0
165.0
731.85

Source and explanation: a. Noller (2006); b. Factor for ammonium nitrate - N = Total x 0.35; molecular weight = 80

Table 3 gives the calculated and measured loads of N from underground dewatering anddischarged to the river, including a summary of the oxidized-N discharged from the mine to the river,showing that the quantity of N discharged was similar in magnitude to the spillage of 4% explosive.
Table 4 gives the predicted and measured oxidized–N concentration in the river based on end-ofⒸ ISERD73

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pipe discharge and river mean flow. The difference between measured and calculated concentrations
indicates lower recent flow in the river compared with the historical record. Some particulate formsof N arose from the mine dewatering, but most N present was filterable, as expected from explosive
residues. Some particulate N (100 µg/L) was also present in river water (Noller, 2006), but data was
not included in Tables 3-5.
Table 3 Calculated and measured loads of nitrogen from underground dewatering
Measured nitritenitrate-N end ofpipe (µg/L)a21,80019,80017,60018,900-End of pipe
discharge (kL)aMonth
OctoberNovember
DecemberJanuarySum

5,260
11,222
7,157
9,030
-

Nitrogendischarged end ofpipe (kg-N)a
114.7
222.2
126.0
170.7
633.6

Spillage of 4%
explosive
as -N (kg)a
269.4
297.5
(Nov-Jan)
165.0
731.85

Source and explanation: a. Noller (2006)

Table 4 Predicted and measured nitrate and nitrate – N concentration in riverMonthRiver mean
monthly
flow (ML)a

End of pipe
discharge(kL)b17,384
31,67850,762
115,284

5,260
11,222
7,157
9,030

OctoberNovember
DecemberJanuary
Range

MeasuredOxidized -N
end of pipe(µg/L)b
21,80019,80017,60018,900

Dilutionratiob
3,305
2,823
7,093
12,767Predicted
Oxidized -N
river (µg/L)b

MeasuredOxidized-N
river (µg/L)b

6.6
7.0
2.5
1.5
1.5-7.0

997
254
166
12
997-12

Source and explanation: a. NR&M (2006); b Noller (2006)

Table 5 Nitrogen in underground seepage water and following discharge to river

Rising water main (µg/L)

20,900Total N (filtered<0.45µm)a
19,200Discharge Tank (µg/L)

19,900End of pipe discharge (µg/L)
River upstream 10m (µg/L)
River downstream 10m(µg/L)
River main upstream
gauging station 40 years(µg/L)
Queensland water quality
guideline (µg/L)b,c

Site

Total Na

Oxidized-Na

Ammonia-Na

20,000270

20,50031,3000.10

20,20018,70018,700

130

500

400

50

60

1,100

0.50

0.17

70

750

-

0.29

21

<250

-

<10

<10

Source and explanation: a. Noller (2006); b. QWQG (2006) annual median; c. QWQG (2006) guideline for OrganicN <200µg/L =total-N – oxidized-N

Table 5 gives N in underground seepage water and following its discharge to the river. The mostimportant N form present in the mine discharge wastewater was found to be oxidized-N (>93%).
Only 0.54 % of end-of-pipe discharge was measurable in the downstream river and indicated that
rapid dilution and removal of oxidized-N by biota could be achieved. The level of oxidized-N
expressed as load discharged to the river showed that the quantity of N discharged was similar inⒸ ISERD

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magnitude to the spillage of 4% explosive. The accumulated groundwater from the mine that isdischarged to the river contains a consistently high total N level that is primarily oxidized-N.
The historical upstream gauging station data for the river (Table 5) shows that total N has been
consistently higher than the Queensland water quality guideline Level 2 water quality guideline,
including upstream of the mine, for a long period of time. The results in Tables 5 and 6 show that theriver has had a consistently high nitrogen load that exceeds the current guideline. An additional loadto the river was added by the mine discharge. Table 6 gives water quality in underground seepage
water and following discharge to the river for pH, total dissolved solids, and suspended solids. pH
was marginally lower than the mine dewatering which also contributed to salinity. Suspended solids
remained at or lower than the guideline.
Table 6 Water quality in underground seepage water and following discharge to the river
Site
Rising water main
Discharge Tank
End of pipe discharge
River upstream 10m
River downstream 10m
River main upstream
gauging station 40 years
Queensland water quality
guidelines

pHa

Total dissolved solids (mg/L)a

Suspended solids (mg/L)a

8.18
8.18
8.16
7.90
7.8

2,280
2,280
913
247
260

6
6
2
4
5

7.7

-

-

6.5-8.2-<6

Source and explanation: a. Noller (2006); b. QWQG (2006) annual median.

Total N in river upstream water was 500 µg/L which exceeded the Queensland water quality
guideline (Table 5). The river 10m below discharge was 1,100 µg/L Total N which also exceeded theguideline (QWQG, 2006). Some particulate N (100 µg/L) arose from the mine dewatering but mostN present was filterable (Noller, 2006).
Ammonia in the river upstream (60 µg/L) and downstream river (70 µg/L) both exceeded theQueensland water quality guideline level of 10 µg/L (Table 5). The addition of ammonia from themine to the river was therefore 10 µg/L and the level at the river downstream exceeded the QWQG
(2006) guideline. The discharge of any ammonia from the mine dewatering was compromised by theexisting river load.
Oxidized-N in the river upstream was 50 µg/L which exceeded the guideline (<40 µg/L). The
river downstream level was 170 µg/L and indicated an addition of 120 µg/L oxidized-N to the riverfrom mine dewatering. However, comparison with the end of pipe discharge and river downstream
oxidized-N indicated efficient removal of oxidized-N. The oxidized-N discharged from the end of
the pipe was in the key form of oxidized-N i.e., 18,700/20,200 X 100 = 92.6 % of Total-N. However,the discharge of any oxidized-N like ammonia from mine dewatering was compromised by theexisting river load. Although the oxidized-N at the end of the pipe was 18,700 µg/L, the difference
between the river upstream and river downstream was only 120 µg/L.
Organic-N concentration, calculated as the difference between total and oxidized-N, was very
low. The upstream river level was <100 µg/L compared with the river downstream level of 330 µg/L,
the latter exceeding the QWQG (2006) guideline figure of 200 µg/L. This may be due to the presenceof urea or a similar soluble organic form of nitrogen from pastoral and crop activities.
The most important N form present in the mine discharge was therefore the oxidized-N (>93%)
and organic-N was less important. Some particulate-N was also present. The fact that only 0.54 % of
end-of-pipe discharge remained measurable in the river downstream indicated that rapid dilution andremoval of oxidized-N by biota was occurring. Maximum N concentration in dewatering water forthis study was observed to be 200 times the receiving water of the nearby river when comparedagainst ANZECC/ARMCANZ (2000) water quality guidelines and ‘Level 2 Aquatic Ecosystem’ thatwas selected for this river receiving runoff from land disturbed to varying degrees by grazing or
pastoralism, nearby or adjacent to urban areas.
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CONCLUSION
The study showed that accumulated underground groundwater from the mine dewatering being
discharged to the river had a consistently high total N level that was primarily oxidized-N (>93%)
and was derived from 4% ammonium nitrate spillage from blasting. Although only 0.54 % of endof-pipe mine discharge was measurable in the downstream river and indicated that rapid dilution andremoval of oxidized-N by biota could be achieved, the Total N in river upstream water was 500 µg/L
which exceeded the QWQG (2006) water quality guideline (Table 5). The river 10m below discharge
was 1,100 µg/L Total N which also exceeded the guideline (QWQG, 2006), but most N present was
filterable (Noller, 2006). Ammonia in river upstream (60 µg/L) and downstream river (70 µg/L) bothexceeded the QWQG (2006) water quality guideline level of 10 µg/L (Table 5).
The selected ‘Level 2 Aquatic Ecosystem’ Slightly–moderately disturbed ecosystemsecosystems in which aquatic biological diversity may have been adversely affected to a relatively
small but measurable degree by human activity for the receiving water of the nearby river whencompared against ANZECC/ARMCANZ (2000) water quality guidelines for this river receiving
runoff from land disturbed to varying degrees by grazing or pastoralism, nearby or adjacent to urban
areas. However, the presence of excess Total N in the river water from upstream agricultural andurban activities compromised the mine water discharge. The discharge of any ammonia from themine dewatering was also compromised by the existing river load.
Thus, treatment options for the mine-discharged water were required and focused on the removalof oxidized N. Ammonia was effectively removed by a shift in the equilibrium of its dissolved form
prior to its transfer to the surface, i.e., the ammonia was either removed as nitrogen gas or converted
to nitrate. The co-cations in the solution are alkaline and alkaline earth metals and not hydrogen ionsas the pH are relatively high.
ACKNOWLEDGEMENTS
I acknowledge the use of the University of Queensland and its facilities of the former National
Research Centre for Environmental Toxicology that were located at Queensland Health Forensic andScientific Services, Coopers Plains QLD 4108, Australia for providing facilities, funding, and accessto the laboratory.
REFERENCESANZECC/ARMCANZ. 2000. ANZECC & ARMCANZ (2000) water quality guidelines. Canberra, Australia,
Retrieved from URL https://www.waterquality.gov.au/anz-guidelines/resources/previous-guidelines/
anzecc-armcanz-2000
Noller, B.N. 2006. Unpublished report. The University of Queensland.
NR&M. 2006. Old natural resources & mines. NR&M Watershed, Brisbane, Australia, Retrieved from URL
http://www.nrm.qld.gov.au/watershed/precomp/138007/
QWQG. 2006. Queensland water quality guidelines. Brisbane, Australia, Retrieved from URL http://www.
epa.qld.gov.au/environmental_management/water/water_quality_guidelines/Ⓒ ISERD

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