Measurement of groundwater

When the well depth or diameter is unknown or a water-level measurement is not possible, purging should be carried out by pumping the well for a pre-determined period of time (e.g., at least 30min). Measurement of groundwater parameters should be monitored at intervals during the purging process and at the time of sample collection (Figure 3). 

The recommendations on water management (Section 3.9) contain some very valuable approaches. The site-specific management requirements of local climate and geography are clearly recognized, as well as the necessity to address salinity on a catchment and community scale. While the standards do not take up the requirement of a watershed-scale approach, they do mention that measures of groundwater recharge and discharge control must be implemented, if salinity is present. 

Figure 119.3 Geographical variations in urinary iodine excretion in Denmark before iodine fortification of salt. Median urinary iodine excretion among inhabitants of various Danish cities before iodine fortification of salt, and the estimated number of people living in areas with different levels of urinary iodine excretion. Values were compiled from different studies of urinary iodine excretion, or estimated from measurements of groundwater iodine content. Geographical variation in iodine intake in Denmark is mostly determined by differences in groundwater iodine content. Pedersen etal., (1999) Rasmussen etal., (2000).

Interim Groundwater Measures (See Groundwater Section of this table)... 

Considerable work has been done on the behavior of pollutant species at air-water and air-soil interfaces. For example, wet and diy deposition measurements of various gaseous and particulate species have been made over a wide range of atmospheric and land-cover conditions. Still, the problem is of such complexity that species-dependent and particle-size-dependent rates of transfer from the atmosphere to water and soil surfaces are not completely understood. There is much to be learned about pollutant transfer at water-soil interfaces. Concern about groundwater contamination by mineral... 

As discussed before, groundwater samples can be collected when a sufficient volume of water has been removed from the well (e.g., three to five well volumes) and groundwater parameters have stabilized. If parameters have not stabilized after five well volumes have been removed, then the well may be sampled (acceptance of sampling following the fifth purge volume is dependent on the study objectives). Table 1 summarizes the criteria used for establishing the stability of groundwater parameters. The time intervals between the parameter measurements depend on the well characteristics and the hydraulic properties of the aquifer and must be sufficiently spaced to provide results representative of aquifer properties. ... 

There are no measurements of the actual concentrations of diisopropyl methylphosphonate in groundwater at the RMA during the years of active production of the nerve gas Sarin (i.e., 1953-1957) (EPA 1989). The first actual measurements of the concentration of diisopropyl methylphosphonate in the groundwater on the arsenal and surrounding property to the north and west were made in 1974 (Robson 1981). The concentrations of diisopropyl methylphosphonate in the groundwater ranged from 0.5 g/L (analytical detection limit) to as much as 44,000 g/L near the abandoned waste disposal ponds. Diisopropyl methylphosphonate was discharged into a lined reservoir at the RMA in 1956 and was still present 20 years later in concentrations of about 400,000 g/L (Robson 1977). 

The development of mass spectrometric techniques for nuclide identification using a tandem Van de Graaff accelerator at the University of Rochester Nuclear Structure Laboratory by H. Gove, K. Purser, A. Litherland, and numerous associates has provided an excellent means for the precise measurement of 36C1 concentrations in natural water [43]. Thus far, about 40 groundwater related samples which have been collected and purified chemically by H. Bentley have been analyzed for 36C1 by D. Elmore, H. Bentley, and others using the University of Rochester machine. Some of these samples are listed in Table 2. 

Care should be taken in interpreting reported pH values, which may have been determined in the field or in the laboratory after the sample had been stored for an unknown period of time. Only the field measurement of pH is meaningful and, in the case of a groundwater, even the field measurement is reliable only if it is made immediately after sampling, before the water can exchange CO2 with the atmosphere. 

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. 

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