No abstract

Soil gas surveying is a method gaining in popularity for groundwater chlorinated solvent pollution studies, particularly in the USA. Previously published methods have advocated on-site analysis; this study presents a simple method where samples are transported to a laboratory for analysis, hence minimizing the need for specialized field analytical equipment and trained field personnel. Tests show the method provides reliable results, comparable with those of established on-site analysis methods. The soil gas surveying method has been applied to a contaminated industrial site where it was successful in defining an area of significant chlorinated solvent pollution. Preliminary analyses from investigation boreholes indicate that this area has severe groundwater pollution.

A regional ground‐water quality survey from 28 wells in the Coventry area of the United Kingdom identified widespread ground‐water pollution. Chlorinated hydrocarbon solvents (CHSs) were detected at concentrations exceeding l microgram per liter (μg/I) in all industrial and public water supply wells within the urban area. Of the CHSs analyzed, trichloroethene was most ubiquitous and was also detected at the highest concentrations, reaching a maximum of 547 μg/I at the industrial “Site A” during this study. By comparison with CHS pollution, inorganic and trace element concentrations were elevated relative to assumed baseline levels only in some industrial wells. The limited extent of inorganic contamination may be due to (1) retention of pollutants within the unsaturated zone, (2) ground‐water mixing in wells, (3) ferric hydroxide precipitation resulting in heavy metal coprecipitation, and (4) sorption on sand grains coated with ferric hydroxide. For inorganic determinants, a pollution index was devised which ranked zinc and boron as primary indicators of inorganic contamination. Regionally, concentrations of CHS and inorganic determinants did not reveal any significant correlation with depth.

An important aspect of any detailed groundwater quality investigation is determining the vertical distribution of pollutants. This may best be achieved by using permanent sampling systems installed in dedicated boreholes. However, the availability of open boreholes in the UK, coupled with the relative expense of installing dedicated systems, has increased the value of methods for obtaining level-determined samples from such boreholes. This paper presents a qualitative appraisal of three such methods, based on the use of portable pumps and packers, frequently combined with flow logging. The methods were tested in four open boreholes penetrating a multi-layered aquifer. In the most successful applications, vertical profiles of chlorinated hydrocarbon solvent concentrations were defined which were thought to be representative of those in the aquifer.

This paper provides a method of identifying land contaminated with chlorinated hydrocarbon solvents by sampling and analysing soil gas. Relationships are presented which enable levels of soil gas contamination to be related to levels of soil and groundwater pollution. Two case studies are presented. Soil gas surveying of an industrial site with severe groundwater pollution demonstrated that standards for contaminated land are insufficient to protect groundwater. Solvent levels in groundwater were one to two orders of magnitude higher than UK permitted concentrations in drinking water, whereas soil contamination values did not reach polluted levels. Surveying of a site occupied by a disused fire station showed significant differences in patterns of soil gas and groundwater pollution. This is explained by direct pollution of groundwater though the well at the site and/or possible flow of polluted groundwater to the site from adjacent areas.