Carbonaro R.F.,Manhattan College |
Carbonaro R.F.,Johns Hopkins University |
Stone A.T.,Mutch Associates LLC.
Environmental Chemistry | Year: 2015
MnIII,IV (hydr)oxides are believed to be the principal oxidants of CrIII in the subsurface. In nearly all previous work on this subject, the CrIII reactant was prepared from inorganic salts (e.g. nitrate, chloride, sulfate). In our present work, CrIII complexes with the synthetic chelating agents iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) were reacted with hydrous manganese oxide (HMO) over a wide pH range to examine rates of reaction and product distribution. Capillary electrophoresis was used to quantify changes in reactant (CrIII-IDA and CrIII-NTA) and product (CrVI, free IDA and free NTA) concentrations as a function of time. In addition, a small number of experiments were performed using solutions prepared from CrIII alum (KCr(SO4)2·12H2O(s)) as the CrIII reactant. CrIII-IDA and CrIII-NTA were oxidised to CrVI, but rates were considerably lower than those obtained using inorganic CrIII. Within the timescales of our experiments, complete conversion of CrIII-NTA occurred at pH >7, but not under moderately acidic conditions, even when there was a large stoichiometric excess of HMO. MnCl2 addition experiments indicated that the observed reaction inhibition was attributable to MnII generation during the reaction. Our previous work has shown that citric acid, IDA, NTA and ethylenediaminetetraacetic acid solubilise CrIII from amorphous Cr(OH)3(s) at appreciable rates. The results of this study show that HMO is capable of oxidising the resulting soluble CrIII complexes, providing a viable mechanism for CrIII oxidation to CrVI over a wide pH range. © 2015 CSIRO.
Mutch R.D.,Mutch Associates LLC. |
Carbonaro R.F.,Mutch Associates LLC. |
Carbonaro R.F.,Manhattan College |
Changa-Moon D.C.,Mutch Associates LLC. |
And 5 more authors.
Journal of Hazardous, Toxic, and Radioactive Waste | Year: 2015
In situ sparging of gaseous CO2 was demonstrated through laboratory and pilot-scale testing to be an effective means to neutralize a caustic brine plume (CBP) and to reduce levels of mercury and other heavy metals in groundwater. The CBP exhibits high pH levels ranging from 10.5 to 12, densities as high as g/mL, high dissolved silica concentrations, and mercury ranging from 50 to μg/L. The CBP lies at the base of a moderately permeable aquifer at depths ranging from 30 to 50 ft below ground surface. The pilot test involved a single sparge well and 13 monitoring wells screened at varying depths and radial distances up to 100 ft. The pilot test demonstrated that pH within an aquifer volume of approximately 184 m3 (6, 500 ft3) could be reduced to near neutral pH. Sparging caused intermittent mounding of groundwater levels, particularly in the piezometric surface of the basal portion of the aquifer, where the sparge well was screened. The piezometric surface in the basal portion of the aquifer rose to several feet above the ground surface during active sparging and then rapidly declined upon cessation of sparging. However, the rise in the overlying groundwater table was considerably muted by the lower vertical hydraulic conductivity of the aquifer. At its peak during the sparging, the groundwater table rose to within approximately a foot of the surface. Pre- and post-sparging aquifer testing indicated that the transmissivity of the aquifer was reduced by approximately 75% and the storativity was substantially increased. These changes in aquifer properties are believed to be primarily associated with the residual saturation of CO2 gas from the sparging and exsolution of CO2 gas from the groundwater in areas immediately adjacent to CO2 channels where groundwater is expected to have near saturation levels of CO2. © 2014 American Society of Civil Engineers.
LaBarre W.J.,Towson University |
Ownby D.R.,Towson University |
Lev S.M.,Towson University |
Lev S.M.,U.S. Science and Technology Policy Institute |
And 2 more authors.
Water Research | Year: 2016
Concerns have been raised over diffuse and non-point sources of metals including releases from copper (Cu) roofs during storm events. A picnic shelter with a partitioned Cu roof was constructed with two types of stormwater control measures (SCMs), bioretention planter boxes and biofiltration swales, to evaluate the ability of the SCMs to attenuate Cu in stormwater runoff from the roof. Cu was measured as it entered the SCMs from the roof as influent as well as after it left the SCMs as effluent. Samples from twenty-six storms were collected with flow-weighted composite sampling. Samples from seven storms were collected with discrete sampling. Total Cu in composite samples of the influent waters ranged from 306 to 2863 μg L-1 and had a median concentration of 1087 μg L-1. Total Cu in the effluent from the planter boxes ranged from 28 to 141 μg L-1, with a median of 66 μg L-1. Total Cu in effluent from the swales ranged from 7 to 51 μg L-1 with a median of 28 μg L-1. Attenuation in the planter boxes ranged from 85 to 99% with a median of 94% by concentration and in the swales ranged from 93 to 99% with a median of 99%. As the roof aged, discrete storm events showed a pronounced first-flush effect of Cu in SCM influent but this was less pronounced in the planter outlets. Stormwater retention time in the media varied with antecedent conditions, stormwater intensity and volume with median values from 6.6 to 73.5 min. Based on local conditions, a previously-published Cu weathering model gave a predicted Cu runoff rate of 2.02 g m-2 yr-1. The measured rate based on stormwater sampling was 2.16 g m-2 yr-1. Overall, both SCMs were highly successful at retaining and preventing offsite transport of Cu from Cu roof runoff. © 2015 Elsevier Ltd.