Groundwater dissolved oxygen

As an example of modeling a fluid in redox disequilibrium, we use an analysis, slightly simplified from Nordstrom et al. (1992), of a groundwater sampled near the Morro do Ferro ore district in Brazil (Table 7.2). There are three measures of oxidation state in the analysis the Eh value determined by platinum electrode, the dissolved oxygen content, and the distribution of iron between ferrous and ferric species. 

We can compare the Eh measured for the Morro do Ferro groundwater (Table 7.2) with the Nernst Eh values (Eqn. 7.1) given by the reactions for dissolved oxygen and iron oxidation, as reported in the program output ... 

Vacuum/pressure vs. distance VOC concentrations in soil and groundwater under static and dynamic conditions C02 and 02 in soil vapor Increase in dissolved oxygen (DO) levels... 

Moisture content/field capacity Depth to impacted (contaminated) area Groundwater depth Dissolved oxygen Soil gas... 

Hydrogeologic factors for consideration include aquifer type, hydrogeologic gradient, permeability, recharge capability, depth to groundwater, moisture content/field capacity, dissolved oxygen (DO), depth to contamination, extent of contamination, and plume stability. 

The Redox Potential. The groundwaters at great depths in igneous rocks are essentially free from dissolved oxygen ( ). The redox potential is determined and buffered by the presence of redox couples, mainly Fe(111)/Fe(11). For the reaction... 

The formulation of the synthetic Grande Ronde groundwater used as starting solution in the dissolved oxygen experiments is given in Jones (9). Table I provides an analysis of the starting solution. 

Table IV. Dissolved Oxygen Data from 150°C Basalt + Synthetic Grande Ronde Groundwater Experiment (Run D2-16)...

Figure 1. Dissolved oxygen vs time data. The experiments were basalt + synthetic Grande Ronde groundwater (B+SW) and synthetic Grande Ronde groundwater (SW) at 300 bars. Determination of uncertainties for B+SW data points is discussed in Table IV. Uncertainties for SW data were derived from replicable tests.

The simulated groundwater used in these experiments was prepared to represent the compositon of groundwater from Well DC-6, Grande Ronde Formation, which samples water primarily from 200 m below the Umtanum unit on the U S DOE Hanford site near Richland, WA (1) Its composition is shown in Table II The groundwater used in these experiments was continually sparged with N2 gas before it entered the apparatus to reduce the dissolved oxygen level and to limit CO2 pickup ... 

We use water quality indicators, such as pH, temperature, conductivity (specific conductance), dissolved oxygen, oxidation-reduction potential (ORP), and turbidity, as groundwater well stabilization parameters. Stable values of three consecutive measurements of these parameters are considered an indication of a stabilized well. 

Table 3.4 lists the parameters in the order by which they would usually stabilize. Temperature and pH are usually the first ones to stabilize because they are not very sensitive to the influx of fresh water. That is why they are not as good stabilization indicators as the other parameters. Their measurements, however, are important for data interpretation and should always be made during groundwater sampling. Dissolved oxygen content and turbidity, which is the measure of the particulate matter content in water, are typically the last ones to stabilize. 

Monitor indicator parameters (pH, temperature, conductivity, ORP) in a flowthrough cell every 1-2 minute (min) during purging. At the same frequency, monitor dissolved oxygen and turbidity. Record all measurements in the Groundwater Sampling Form. 

---