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QUALITY ASSURANCE AND QUALITY CONTROL

By Norma Fisher,2014-05-19 11:52
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QUALITY ASSURANCE AND QUALITY CONTROL

Supplemental Text for manuscript to be submitted to Geochemical Transactions

    Church, C.D., et al., “Microbial sulfate reduction and metal attenuation in pH 4 acid

    mine water

QUALITY ASSURANCE AND QUALITY CONTROL FOR WATER ANALYSES

    Several techniques were used to assure the quality of the analytical data for water

    samples. These techniques included calculation of speciated charge imbalance, analysis

    of a field blank, replicate analyses of environmental samples, and analysis of standard

    reference water samples (SRWS) prepared by the U.S. Geological Survey (USGS).

    The speciated charge imbalance (C.I.) was calculated using the geochemical code

    WATEQ4F [1]. The C.I. was calculated as follows: (sum cations?sum anions)C.I.(percent)??100 (1) (sum cations?sum anions)/2

    where “sum cations” and “sum anions” are in units of milliequivalents per liter. The

    charge imbalance calculated by WATEQ4F is twice the value that is typically reported

    for cation-anion balance because the term in the denominator is the average

    milliequivalents, rather than the sum of the milliequivalents. The C.I. is calculated on the

    speciated results rather than the raw analytical data because C.I. is dependent on

    speciation, especially for acidic solutions. The C.I. for the eight Penn Mine samples

    ranged from -12% to 11%, and the mean C.I. was -3%. The charge imbalance is primarily

    affected by the major ion chemistry and the errors are likely the result of analytics or

    unanalyzed constituents. Nordstrom et al. [2] considered samples analyses with charge

    imbalance of ?11 to be of sufficiently high quality for speciation calculations.

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    A field blank collected in Nov. 2001 was analyzed with the environmental

    samples to detect potential field or laboratory contamination. The field blank data are , all constituents in the field 4

    reported in table S1. With the exception of Fe, Cl, and SOblank were below their method detection limits (table S1). Concentrations of Fe and SO 4

    were less than 0.5% of the lowest measured sample concentration, therefore

    contamination of these constituents is considered. The concentration of 1.0 mg/L of Cl in

    the field blank was only about twice the detection limit; however it is possible that

    concentrations of Cl in the environmental samples have a slight positive bias.

     For each of the four environmental water samples collected during 2002, a

    replicate sample was collected for analysis of major cations and trace metals. Results of

    the replicate analyses are given in Table S2. Values of relative percent difference for

    environmental samples (RPD

    ) were computed using equation 2, where R1 and R2 E

    represent the concentrations in the two replicate analyses.

    (R1?R2)RPD??100 (2) E(R1?R2)

    2For analytes below the method detection limits, RPD were not calculated. E

    RPD values (Table S2) were less than 15 % for all constituents in all four replicate E

    samples. The mean of the absolute RPD values for each constituent was less than 10% Efor all constituents except Cr (11%). For stable isotopes, replicate results (Table S1) were

    interpreted in terms of absolute difference (AD, Table S2). Values of AD among

    replicates were within 0.1 per mill for all O and S isotope measurements and within 1 per

    mill for H isotopes (Table S2).

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    Several SRWS prepared by the USGS Water Resources Discipline Branch of

    Quality Services were analyzed as “unknowns” along with the environmental samples to

    check for accuracy. Standard reference water samples M6, AMW4, T159, and T163 were

    used to check the analytical methods for major cations and trace metals [3,4]. The

    compiled results for the SRWS include the number of analyses (n), concentrations,

    standard deviation or range of analyses, reported most probable value (MPV), F-

    pseudosigma (deviation), and the relative percent difference (Table S3). The relative ) S

    percent difference between mean measured concentration and MPV for the SRWS (RPDwas calculated using equation 3:

    (measured mean concentration?MPV) RPD ??100 (3) SMPVAnalytical accuracy improves with increasing concentration; reduced accuracy near the

    method detection limit is the result of decreasing signal to noise ratio. Manganese (Mn)

    and boron (B) had high RPD for one or more SRWS. However, the environmental S

    samples for this study had Mn concentrations ranging from 2.4 to 8.2 mg/L, more than

    100 times higher than either SRWS. Therefore, the relatively high RPD for Mn on one S

    SRWS is not a large concern in terms of study results. With regard to B, the RPD ranged S

    from -12.9 to -34.4 for three SRWSs with MPVs from 0.011 to 0.032 mg/L.

    Concentrations of B in environmental samples from Penn Mine ranged from 0.11 to 2.8

    mg/L, approximately 10 to 100 times greater than the range of B in the SRWSs. As with

    Mn, the results for B from the SRWSs are not a large concern with regard to the

    conclusions of this study. Additional information about the USGS SRWS program can be

    obtained at URL http://bqs.usgs.gov/srs.

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References Cited

    1. Ball, JW, Nordstrom, DK: User's manual for WATEQ4F, with revised

    thermodynamic data base and test cases for calculating speciation of major,

    trace, and redox elements in natural waters. U.S. Geological Survey Open-File

    Report 91-183, 1991, 189 p. http://pubs.er.usgs.gov/usgspubs/ofr/ofr91183.

    2. Nordstrom, DK, McCleskey, RB, Hunt, AG, Naus, CA: Questa baseline and

    pre-mining ground-water quality investigation. 14. Interpretation of ground-

    water geochemistry in catchments other than the Straight Creek Catchment,

    Red River Valley, Taos County, New Mexico, 2002-2003. U.S. Geological

    Survey Scientific Investigations Report 2005-5050, 2005, 84 p.

    3. Farrar, JW: Results of the U.S. Geological Survey’s analytical evaluation

    program for standard reference samples distributed in October 1999. U.S.

    Geological Survey Open-File Report 00-227, 2000, 143 p.

    http://bqs.usgs.gov/srs/Report_Fall99.pdf.

    4. Connor, BF, Currier, JP, Woodworth, MT: Results of the U.S. Geological

    Survey’s analytical evaluation program for standard reference samples

    distributed in October 2000. U.S. Geological Survey Open-File Report 01-137,

    2001, 116 p. http://bqs.usgs.gov/srs/Report_Fall00.pdf.

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    Supplemental Figure

     Figure S1. Image collected using a down-hole camera during the sampling of sediments from the Penn Mine workings

    Sediments were recovered from flooded mine workings of the Penn Mine, a Cu-Zn

    mine abandoned since the early 1960s. Water chemistry, solid-phase characterization, and

    microbial characterization results all indicate conditions that support anaerobic processes

    such as sulfate reduction in the deep mine workings. At this site, sulfate-reducing bacteria

    play a role in attenuating metals at moderately low pH.

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