Variations in concentrations of trichloroethylene and related compounds in ground water obtained from seven ground water samplers were used to compare the performance of three submersible pumps, a centrifugal pump, two peristaltic pumps, and a bailer. Two‐ and 4‐inch diameter submersible pumps and a centrifugal pump produced samples whose trichloroethylene concentrations, on the average, did not differ significantly from each other. Ground water samples collected by using a peristaltic pump and silicone tubing had significantly lower trichloroethylene concentrations than samples from the submersible pumps. Concentrations of 1,2‐dichloroethylene and trichloroethylene in ground water samples collected by using a bailer were indistinguishable from those in samples taken by a submersible pump when the concentrations were as much as 96 and 76 micrograms per liter, respectively, but were 15 and 12 percent lower when concentrations were as low as 29 and 23 micrograms per liter, respectively. Tests of different configurations of sampler placement in observation wells indicate that pump placement, rate of pumping, duration of pumping, and the uniformity of the vertical and lateral distribution of trichloroethylene in ground water near the well screen have a potentially significant influence on trichloroethylene concentrations in ground water samples and that these factors can have a greater effect than the type of sampler used.
right for production of the two species in eq 1 1 at equal probability, i.e., from a symmetric intermediate or transition state. The fact that mass 48 product is more prominent when initial Fe(1I):NO is 1:2 rather than 1:l reflects the expected greater rate of H15N180 production. The shifting proportions of the three kinds with time is caused by changing relative production rates of the two kinds of HNO. If the intermediate produced by Fe(I1) reduction of NO is identical with the species produced in pulse radiolysis, as we believe to be the case for the product of HN20f decomposition, it would occur predominantly as NO-under the conditions of these experiments, since its pK, is reported to be 4.7.35The formation constant for Fe(N0)2+ is independent of pH in aqueous sulfate (pH 0.5-3.3) and has the value of 0.634 f 0.023 atm-I at 25.0 OC ( I = 2.20 M). At pH 4.6 in the presence of 2.0 M acetate, the constant is 29.0 * 1.5 atm-l and increases to 70 atm-' at [OAc-] = 3 M. Acetate ligation is involved in this enhancement, probably one ion per Fe(I1) center. With decreasing Fe(II)/NO ratio and above pH 4 the presence of dinitrosyl complex is detected stoichiometrically, with a constant of formation (from Fe(N0)2+ + NO) of 0.98 f 0.15 atm-' (pH 4.6, [OAc-] = 2.0 M, I = 2.20 M). From
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