Sampling groundwater

Analysis of groundwater samples from observation wells, geophysics... 

At the Taylor Road landfill (originally intended for the disposal of municipal refuse only), unknown quantities of hazardous wastes from industrial and residential sources were deposited. During the period when the landfill was active, soil and groundwater samples collected at the site were found to contain concentrations of volatile organic compounds and metals above acceptable safe drinking water standards. Analysis of samples collected from private drinking water wells indicated that contamination... 

Endosulfan (one or both of its isomers) has been identified in 24 surface water and 103 groundwater samples collected from 164 NPL hazardous waste sites where it was detected in some environmental media (HazDat 2000). 

Three out of nine groundwater samples extracted from Dobrich in northeastern Bulgaria contained endosulfan (isomers not specified) ranging from 0.020 to 0.025 pg/L in March 1996 (Pulido-Bosch et al. 1999). The suspected source of this pollution was from agricultural practices in the region. 

The problem gives the required equilibrium concentrations, since it is stated that the groundwater sample is saturated (that is, at equilibrium) with respect to these ions. 

A summary of U.S. groundwater analyses from both federal and state studies reported that trichloroethylene was the most frequently detected organic solvent and the one present in the highest concentration (Dyksen and Hess 1982). Trichloroethylene was detected in 388 of 669 groundwater samples collected in New Jersey from 1977 to 1979, with a maximum concentration of 635 ppb (Page 1981). Maximum concentrations ranging from 900 to 27,300 ppb trichloroethylene were found in contaminated wells from four states (Pennsylvania, New York, Massachusetts, and New Jersey) (Burmaster 1982). 

Two multi-residue methods are described. These methods have been used to determine concentrations of either parent herbicides or their metabolites in thousands of surface water and groundwater samples collected over the years 1995-2001 in corn-growing areas of the United States. " ... 

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

The goal of groundwater sampling is to obtain samples that are representative of the aquifer being investigated and to minimize the bias introduced by the methods employed to collect those samples. The purpose of the collection of representative samples is to investigate whether pesticide products in groundwater are present and, if present, at what concentration. 

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. ... 

Unless laboratory studies on material compatibility establish otherwise, it is recommended that equipment used to collect groundwater samples for pesticide analysis be constructed of metal, fluorocarbon polymer, or glass.However, for a water-supply well, inert well, pump, and plumbing materials are not likely to have been installed for all components. In this case, in-place well, pump type, and plumbing materials should be documented. 

The quantity of QC samples to be collected is dependent on the study design, but Aeld blanks and held replicates should represent approximately 5-10% of the groundwater samples collected for the study. QC samples should be collected on the same day, using the same supplies and equipment, and be stored and shipped under the same conditions as the groundwater samples collected for pesticide analysis. Document all procedures, equipment, and reference chemicals used to generate the QC samples. 

Place 400 mL of groundwater sample in a 1-L separatory funnel, and extract the aqueous phase twice with 200 mL of dichloromethane. 

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