The concentrations of trace metals as presented in Table 1 conform to compliance values as
stipulated in the Environmental Permit (EP) issued by the Government of PNG. The metals
include; Mn, Zn, Ni, Co and Cu, all record monthly averages below their RPC values. The
monthly average concentration of Mn is <50mg/L in tailing pore water which is below the EP
limit of ≤500mg/L. similarly, concentrations of Co (<0.1mg/L), Ni (0.34mg/L), Cu
(0.05mg/L) and Zn (<0.31mg/L) are all falling way below their EPSC of ≤5.0mg/L,
≤8.0mg/L, ≤5.0mg/L and ≤50mg/L respectively. This implies that the metals named here are
present in the tailing water but are below the recommended permissible concentrations. They
do not pose any immediate threat that can possibly compromise the ecological quality of the
local benthic environment.
The analytes Cd, Pb, Se, As, Ag, Hg and Cr6+ are heavy metals with toxicity attributes at
lower concentrations with EPSC values below “�
” numerals and their quantities present in
the tailing water of Basamuk refinery are also shown in Figure 2. Laboratory results
representing their average monthly concentrations in the tailing effluent showed a value of
<0.01mg/L for all of the aforementioned metals, suggesting that all these metals are
ecologically safe to be disposed. It is therefore assumed that it will have negligible immediate
impact in the marine ecosystem. Average daily fluctuations in conce
displayed a near uniform concentr
routine checks done by the refinery
ore blend being processed were unif
3.2 Flow Discharge Velocity
Discharge velocity of the flow of ta
significance is attributable to densi
150m below sea0level. It requires a
plume shearing or dispersal of tailin
the whole DSTP system. At the co
current and get settled at the seafloo
The daily average flow discharge
graphically represented in Figure 3
within the permitted velocities. The
values are between 16770
2075 m
the results that the tailings have been
�������1� Average Daily Flow Disc
�'�= Daily Average, &��� � = Minimu
Permit Standard.
ons in concentrations of the metals were also obser
ved but a
rm concentration. This indicates that the environme
ntal c
the refinery maintain consistencies all day and th
e homogen
sed were uniform.
he flow of tailing presents a vital component of th
e DSTP s
able to density current scenario at the terminal of the tailin
It requires a consistent flow to maintain density
current and
rsal of tailing materials [10; 11]. In fact, it supports the adv
m. At the correct velocity the tailing materials can travel in
at the seafloor [6].
w discharge velocities of the tailing from the stud
y lo
in Figure 3 which indicates that the tailings have been d
locities. The recommended range is 800 – 2500m3
/h and in
2075 m
3
/h with a monthly average of 1270 m3
/h. It is obv
ngs have been discharged at compliance velocities.
ly Flow Discharge Velocity of Tailing Effluent Stream. The daily fluctuation values of the discharge velocities as highlighted in the red circles in
Figure 3 between the days 308 and 21027 show significant fluctuations. These fluctuating
were noted to be within the safety limits, however, this type of inconsistencies can, to some
extent, promote critical conditions at the discharge terminal and cause density current.
Studies have established that such slight changes in the discharge velocities can cause plume
shearing, where light tailing materials and some metals can be dispersed from the density
current and can be available in the water column above the seafloor [12]. The fate of such
dispersed materials can provoke discontentment in the community due to its implications on
the surrounding environment and marine biota [10]. Measures taken to stabilize the
fluctuations will definitely reduce that environmental risk.
3.3 Acidity (pH) of Tailing Effluent
The pH analysis decides the acidity or alkalinity of the tailing effluents prior to discharge.
This is important as the refinery uses high pressure acid leaching (HPAL) technology to
extract the targeted metals from the slurry. Counter0current decantation and addition of
limestone/lime to the leached slurry were strategies used for neutralization [5]. Therefore, the
need for continuous assessment of pH is necessary to prove that the tailing effluents are
within compliance values and to further maintain ecological quality of the natural systems of
the disposal site.
The daily average reading for the month of August, 2013 is graphed in Figure 4. The pH
values stated in the EP section WD0L3 (115) condition 46 recommended a minimum value of
6.5 and maximum of 9.0 units. The daily pH values of tailing water fluctuate between a
minimum value of 8.12 and maximum of 8.55 with an average of 8.12. From the graph, it is
quite obvious that varying pH values are within the recommended range conforming to the
ecological safety standards as contained in the EP. Thus, the tailing waste was adequately
neutralized [6] to alkalinity levels (pH above 7) as shown by the monthly average pH value of
8.12 units. Conversely, the pH values of the discharge are similar to that of seawater,
blending in well with the pH of the natural seawater, eradicating any immediate
environmental concerns that tailing pH might provoke.
Write the main points for the above information
1. Concentrations of trace metals in tailing water at Basamuk refinery in PNG are below compliance values stipulated in the Environmental Permit (EP) issued by the Government.
2. Metals including Mn, Zn, Ni, Co, and Cu are present in the tailing water but below recommended permissible concentrations, posing no immediate threat to the ecological quality of the benthic environment.
3. Heavy metals Cd, Pb, Se, As, Ag, Hg and Cr6+ have average monthly concentrations below recommended EPSC values, indicating they are ecologically safe for disposal.
4. Flow discharge velocity of the tailing effluent is within permitted velocities, ensuring proper dispersal and density current maintenance.
5. Fluctuations in discharge velocities within safe limits but can promote critical conditions at discharge terminal and cause density current.
6. pH values of tailing effluent within recommended range (6.5-9.0), conforming to ecological safety standards in EP and similar to natural seawater pH, eliminating immediate environmental concerns.