Effluent samples were typically collected weekly to biweekly and prior to increasing AMD flow rate. They were collected directly into method-specified sample bottles and chilled at 2-6oC until analysed by RJ Hill Laboratories Limited or at the University of Canterbury Environmental Engineering Laboratory. The AMD was also sampled from influent into the BGCRs. Samples for water quality parameters measured using portable instruments (temperature, pH, conductivity, ORP/Eh, DO and turbidity) were collected in HDPE sampling bottles. Water quality probes were then inserted into the sampling bottles, and data was recorded when readings stabilised. Water quality probes were inserted directly into the feed tank for measuring AMD. Most samples were collected head-space free in non- preserved HDPE sample bottles unless otherwise indicated below. All sampling was performed prior to increasing metal loading (and flow) rates.
Metal (Fe, Al, Cu, Ni, Zn, Mn, As, Cd, Pb and As), total sulphur, cations (Ca, Mg, K and Na), total nitrogen (TN), total kjeldahl nitrogen (TKN), total oxidised nitrogen (TON; includes summation of nitrate (NO3-) and nitrite (NO2-)), total phosphorous (TP), dissolved organic carbon (DOC), total organic carbon (TOC), faecal coliforms and five day biochemical oxygen demand (BOD) concentrations were analysed and measured by RJ Hill Laboratories Limited. Total suspended solids and acidity/alkalinity were analysed in the University of Canterbury Environmental Engineering
Laboratory. The only exceptions included acidity and alkalinity samples collected on 7 and 20 June 2007 (weeks 9.4 and 11.3, respectively), which were analysed by RJ Hill Laboratories Limited.
4.1.6.1 Metals
Metal samples were analysed using ICP-MS. Dissolved metals were analysed by APHA Method 3125B (APHA, 1998) for samples collected until week 9.5 and filtered as described in Section 2.2.3 in Chapter 2. The only exception was that most samples were filtered using disposable Waterra WAT45 groundwater filters containing 0.45 µm polyethersulphone filter media. Acid-soluble metals were analysed by APHA Method 3125B (APHA, 2005) with dilute nitric acid extraction for samples collected after week 9.5. Metal samples were preserved with 1:1 nitric-acid preserved to maintain pH<2.0.
For AMD samples, Fe2+ was measured at the time of sample collection following Hach Method 8146 (1,10 Phenanthroline Method) and analysed using a Hach Spectrophotometer at 510 nm (Hach Company, 2003) as previously described in Section 2.2.2. Ferric Fe was calculated as the difference between total Fe and Fe2+. From BGCR effluent samples, Fe3+ concentrations were assumed to be zero due to low DO (<1.0 mg/L) and Eh (0-80 mV).
4.1.6.2 Sulphur
Total sulphur concentrations were measured using ICP-OES as previously described in Section 2.2.3. Total sulphur concentrations were computed as mg/L of sulphate for comparative purposes (to determine sulphate removal). It was assumed that the majority of sulphur in the AMD samples was present as sulphate due to high DO (91.7-99.1% saturation) and Eh (709-803 mV) conditions; however, sulphur was likely prevalent in BGCR effluent in reduced states such as monosulphide, hydrogen sulphide, mobile metal sulphides, and potentially mercaptans or other sulphur and organic- sulphur complexes based on low and Eh readings and olfactory observations of a hydrogen sulphide odour.
4.1.6.3 Acidity and Alkalinity
Acidity (pH 3.7) and total acidity (pH 8.3) were analysed using a modified version of APHA Method 2310B (APHA, 2005), and alkalinity (pH 4.5) was analysed using a modified version of APHA Method 2320B (APHA, 2005) as previously discussed in Section 2.2.3. Calculated acidity was explained in Section 1.3.3 and computed using Equation 1.9 (modified from Watzlaf et al., 2004); however, acidity contribution from Mn was excluded for this study. Therefore, metal acidity contributions were only computed from Fe, Al, Cu, Ni and Zn. Other metals (e.g. Cd, As and Pb) contributed minimal acidity (<0.4%) so were not included in calculated acidity. Manganese contribution was excluded since its removal in BGCRs is not expected due to the high solubility of MnS (Watzlaf et al., 2004; Wildeman et al., 2006). It typically accounted for <1% of molar loading and <0.6% of acidity loading (median concentration was 1.65 mg/L (1.40-2.61 mg/L)).
4.1.6.4 Water Quality Parameters Measured with Portable Probes including pH, Conductivity, Dissolved Oxygen and Oxidation-Reduction Potential/Eh
Water quality parameters including pH, conductivity, DO and ORP/Eh were measured at the time of sampling using portable water quality instruments as previously described in Section 2.2.2. Instruments were calibrated just prior to sample collection using fresh standards and validated to ensure they maintained calibration following measurements.
4.1.6.5 Other Cations, Anions and Nutrients
The cations Ca, Mg, K and Na were filtered by RJ Hill Laboratories Limited using 0.45 µm filters prior to analysis via ICP-MS following APHA Method 3125B (APHA, 1998) as previously described in Section 2.2.3. Total kjeldahl nitrogen was analysed following modified versions of methods APHA 4500-Norg B and APHA-NH3 F (phenol/hypochlorite colorimetry) with sulphuric acid digestion with copper sulphate catalyst following a modified version of APHA 4500-Norg D (APHA, 1998). Samples were preserved with sulphuric acid to achieve pH<2. Total oxidised nitrogen was analysed by automated Cd reduction with a flow injection analyser following APHA 4500-NO3--I (Proposed in APHA, 1998). Total nitrogen was computed by summing concentrations of TKN and TON. Total P was analysed following method APHA 4500-P E (modified from manual analysis) using acid persulphate digestion, ascorbic acid colorimetry and a discrete analyser (APHA, 1998). Samples were preserved with sulphuric acid to achieve pH<2.
4.1.6.6 Organics and Biological Parameters
Dissolved organic carbon (DOC) samples were filtered using the same process as previously described for dissolved metal samples and analysed following method APHA 5310B, which included catalytic oxidation and infrared detection for determining total carbon (TC) and acidification followed by purging to measure total inorganic carbon (TIC) (APHA, 1998). Dissolved organic carbon represented the difference between TC and TIC, which both excluded filtered carbon fractions >0.45 µm in diameter. For samples collected after week 9.5, TOC was measured instead of DOC (e.g.. samples were not filtered after week 9.5). Faecal coliform was analysed following method APHA 9222B utilising membrane filtration count on mFC agar at 44.5oC for 24 hours (APHA, 1998). Samples were collected non-headspace free in sterile polycarobonate containers and submitted for analysis immediately upon collection. Biochemical oxygen demand was analysed following method APHA 5210B (APHA, 1998). No seeding was implemented as part of the BOD analysis.
4.1.6.7 Total Suspended Solids and Turbidity
Total suspended solids represent the fraction of solids obtained on a 1.2 um Whatman® GF/C glass- fibre filter and were measured following APHA Method 2540D (APHA, 1998) using vacuum filtration as previously described in Section 2.2.3. Turbidity measurements were performed using a Hach Model 2100P portable turbidimeter at the time of sample collection following the methodology previously described in Section 2.2.2.