A data-driven approach for simplifying the estimation of time for contaminant plumes to reach their maximum extent.

Globally there exist a very large number of contaminated or possibly contaminated sites where a basic preliminary assessment has not been completed. This is largely, among others, due to limited simple methods/models available for estimating key site quantities such as the maximum plume length, further denoted as Lmax and the corresponding time T=TLmax, at which the plume reaches its maximum extent L=Lmax. An approach to easily obtain an estimate of TLmax in particular is presented in this work. Limited availability of high-quality field data, particularly of TLmax, necessitates the use of synthetic data, which constrains the overall model development works. Taking BIOSCREEN-AT (transient 3D model) as a base model, this work proposes second-order polynomial models, with only two parameters, for estimating Lmax and TLmax. This reformulation of the well established solution significantly reduces data requirement and workload for initial site assessment purposes. A global sensitivity analysis (Morris, 1991), using a large number of random synthetic data, identifies the first-order decay rate constants in the plume λEFF and at the source γ as dominantly most influential for TLmax. For Lmax, the first-order decay rate constant λEFF and groundwater velocity v are the two important parameters. The sensitivity analysis also identifies that these parameters non-linearly impact TLmax or Lmax. With this information, the proposed polynomial models (each for Lmax and TLmax) were trained to obtain model coefficients, using a large amount of synthetic data. For verification, the developed models were tested using four datasets comprising over 100 sample sets against the results obtained from BIOSCREEN-AT and the developed BIOSCREEN-AT-based steady-state model. Additionally, the developed models were evaluated against two well documented field sites. The proposed models largely simplify estimation, particularly, of TLmax, for which only very limited field or literature information is available.

Manganese release linked to carbonate dissolution during the start-up phase of a subsurface iron removal well in Khabarovsk, Russia.

Subsurface iron removal (SIR) is a proven pre-treatment technology for removing dissolved iron and manganese from groundwater. The start-up phase of a SIR well and the proper development of the reaction zone around the well are crucial for its subsequent performance. This study evaluates the start-up phase of a SIR production well in Khabarovsk, Russia during the first 194 SIR cycles. A strong release of manganese was observed, which led to concentrations twice as high as the background value of the pristine groundwater. Regular monitoring of the production well and its three adjacent observation wells showed that iron removal began immediately after start-up and that the reaction zone was completely formed within 25 SIR cycles. Closed-bottle batch tests and a flow-through leaching test revealed that the grain size of the aquifer material and groundwater pH are the primary controls on manganese release. During infiltration phases the dissolution of manganese-bearing carbonate minerals was caused by direct oxidation by O2, whereas the low groundwater pH of 6 seemed to be responsible for the manganese release during extraction.

Impact of riverbank filtration on treatment of polluted river water.

The impact of riverbank filtration (RBF) on the treatment of water from the River Yamuna at Mathura, which has disagreeable visual properties, has been investigated. The dissolved organic carbon (DOC) and colour of the river water were 4.0-6.8mg/L and 40-65 colour units (CU), respectively. Pre-chlorination is in practice to improve raw water quality. Chlorine doses as high as 60mg/L ahead of the water treatment units reduced colour by about 78%. Removal of DOC and UV-absorbance was less than 18%. In comparison to direct pumping of the river water, collection of water through RBF resulted in the reduction of DOC, colour, UV-absorbance and fecal coliforms by around 50%. However, riverbank filtrate did not conform to the drinking water quality standards. Therefore, riverbank-filtered water along with the Yamuna water were ozonated for different durations. To reduce DOC to the desired level, the dose of ozone required for the riverbank filtrate was found to be considerably less than the ozone required for the river water. RBF as compared to direct pumping of Yamuna water appears to be effective in improving the quality of the raw water.

Simulation of biological degradation of aromatic amines in river bed sediments.

Testfilter experiments are reported for river Elbe water spiked with aromatic amines in order to determine biodegradation rates. For river Elbe water the mean degradation rate of DOC (C0 = 6.64 mg l-1) was 26.7 +/- 8.8% after 6.8 days. No significant effect on the DOC degradation rate was observed with the addition of aromatic amines. Large differences in the biodegradation behaviour of the aromatic amines were observed: aniline was eliminated within 3 h, whereas the degradation of 2-nitroaniline was only 40% after 14 h effective contact time. Degradation curves were mostly of a simple logarithmic type, demonstrating first-order kinetics. The degradation rate of 2,4,6-trichloraniline increased by a factor of 20 within 6 weeks due to the adaptation of the testfilter biofilm. A linear relationship between available pKa-values and the logarithm of the experimental degradation rates was found. Thus, the results of the testfilter experiments may be extended to the estimation of the biodegradability of non-tested aromatic amines.

Determination of aromatic amines in surface waters and comparison of their behavior in HPLC and on sediment columns.

An analytical method based on solid-phase extraction (SPE) with a polymeric material, HPLC separation on a modified C18 material, and diode-array detection is presented for the determination of aromatic amines in the ng L(-1)-concentration range. These potentially toxic compounds in polluted water samples can be sampled by using SPE with an amino phase to clean the eluate. Column experiments were performed to characterize the transport behavior of aromatic amines in an aquifer sediment. For nineteen aromatic amines, linear correlations were found between the adsorption coefficient, Kd, estimated from column experiments, and capacity factors, k', measured by isocratic reversed-phase HPLC (RPHPLC).