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110 Second Avenue #D7,Pacheco,CA 94553
<br /> McCAWBELL ANALYTICAL INC. Telephone:510-798-1620 Fax:510-798-1622
<br /> htty://www.mccgmpbell.com E-mail:main@mccampbell.com
<br /> amount of time that the water stood unpreserved prior to filtering & preserving dramatically affected the recovered
<br /> "dissolved"metals content.
<br /> Major element Initial to Final values changed as follows. Ca from 91 to 35 ppm; Mg from 34 to 16 ppm;Na from 430
<br /> to 350 ppm; Al from 9600 to 850 ppb; Fe from 8800 to 900 ppb; Mn from 2500 to 390 ppb. Ca & Mg probably
<br /> decreased due to carbonate pptn, & Fe & Mn to oxide pptn. The Na& Al changes are harder to explain but may be
<br /> substitution/exchange reactions for divalent Fe&Mn that are displaced from silicate lattices during their oxidation.
<br /> The aquifer water already contained some anomalous trace amounts of heavy metals, including 39 ppb As, 1.3 ppb Be,
<br /> 9.7 ppb Cr,23 ppb Co, 1.7 ppb Cd, 100 ppb Cu, 1.2 ppb Mo,27 ppb Pb,36 ppb Ni, 1.9 ppb Se, 35 ppb V,69 ppb Zn, in
<br /> addition to 8800 ppb Fe&2500 ppb Mn. It is not apparent why this natural water contains such high concentrations of
<br /> heavy metals, although complexing with organic ligands may be important. The high concentrations of Fe & Mn are \ '
<br /> most likely the result of bacteria-mediated oxidation of hydrocarbons .By the end of the experiment almost all of these V
<br /> had diminished significantly, possibly by their sorption on Fe & Mn oxides, or as trace substitutions into silicates in
<br /> exchange for Fe&Mn or as substitutions into ppted carbonates. Two trace elements increased, Se from 1.9 to 15ppb,& ;
<br /> Mo from 1.2 to 48 ppb. Both could have been have been oxidized up from less soluble lower valence solids such as
<br /> Se°,s or M002,s, or alternatively may have been mobilized by the decrease in Ca& Mg, if their Ca or Mg salts were at
<br /> saturation.
<br /> In the Final water, TRM total chrome was less than hexachrome, 3.2 vs. 8.4 ppb, but the TTLC hexachrome value of
<br /> 9.2 was in much better agreement. The TTLC Final water metals values are also reported, &the common elements that
<br /> form oxide /hyroxide solids, Fe, Mn&Al are significantly higher than their TRM values. Trace element comparisons ! /
<br /> range from good to slightly higher to erratic (significantly higher or lower), indicating that sampling & sub-sampling
<br /> techniques are extremely important for metals.
<br /> Soil
<br /> The Initial & Final soil metals values were generally in good agreement after correction for water content. The only
<br /> trace metal disagreements are Cu initial value = 82 vs. final = 47 mg/kg, Zn initial = 78 vs. final = 67. For major
<br /> elements, Ca initial = 5600 vs. final = 6300, & Na initial = 980 vs. final = 1200, which is opposite & therefore in
<br /> agreement with their decrease in concentration in the aquifer water.
<br /> Hexachrome
<br /> Water soluble hexachrome was not significantly generated by ozonation of this natural soil, although our normal 0.2
<br /> ppb RL was obscured by hexachrome in the blank. The 10-15 ppb amounts found in the glassware blanks exceeded the
<br /> 8-10 ppb found in the reacted soil indicating that at least a small ppm, sorption or decomposition reaction occurred in
<br /> the presence of soil. This was a first time use for this glassware & the trace generation of hexachrome in glassware
<br /> blanks was observed in a previous ozonation experiment that used different glassware. We will continue to run /
<br /> glassware blanks with fresh solution until hexachrome is absent to ensure lower RLs for future experiments. Water
<br /> soluble hexachrome (DISTLC extraction) was not detected (<20 ppb) in the soil before or after ozonation nor was
<br /> TTLC hexachrome(<800 ppb),although both were obscured by high reporting limits.
<br /> K2Cr2O7, a water soluble form of hexachrome, was chosen for spiking&was spiked at a concentration of 71 mg C+6/
<br /> L,for the LCS,LCSD&MS.Recoveries were reasonable, 82-91%for the LCS-LCSD,but water phase recoveries were
<br /> only 21-30%for the MS,dropping from 29-30%on days 1 &2 to 21%on day 5. Only 6.5%of the spike was recovered
<br /> from the soil phase of the MS on day 5 using TTLC 3060 methodology. One interpretation of the MS QC data is that
<br /> 70%of the water soluble chromate is reduced to tri-valent Cr,roughly equivalent to the available VOCs,&that— 1/3 of
<br /> the remaining chromate is ppted from the water phase (iron chromate?) & is recoverable as TTLC hexachrome. This
<br /> implies that a much lower concentration of spike would not be recovered at all, & begs the question as to why trace
<br /> amounts(10 ppb)are still present in the sample.
<br /> An explanation is that the Nernst equation,as well as chemical equilibria, dictate that the reduction of chromate is both
<br /> reaction&concentration dependent,so that:
<br /> Cr04 2+reduced entity=reduced Cr solid+oxidized entity,
<br /> so that the final equilibrium chromate concentration is dependent upon the concentration of the reduced entity & its
<br /> reduction potential,as well as the ratio of the reduced : oxidized entity. In other words, even trace levels of hexachrome
<br /> �r should be able to be decomposed with a stronger reducing agent but that the reducing agent present here was not
<br /> sufficient to decompose it to<0.2 ppb.
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