Hydrogeologic Factors

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. 

Groundwater Gradients Groundwater gradients should be consistent seasonally, with moderate steepness such that a steady flow of electron acceptors is supplied to the plume, without being too steep to cause migration of a plume beyond the ability of microbes to contain it. 

Permeability The rate of microbial ability to metabolize hydrocarbons is limited primarily by the availability of electron acceptors and nutrient supply. In 

Moisture Content/Field Capacity Within the vadose zone, moisture content is important since microbial growth is limited by excessively wet or dry soil. Moisture content, expressed as a percentage of the field (or holding) capacity, indicates the ratio of moisture to air in the soil. The recommended range for optimal growth is between 40 and 70%. 

Depth to Contamination In general, the shallower the release in the vadose zone, the more rapid the diffusion of soil gas, and the greater the indigenous microbial density. 

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Many of the factors that influence the c.xtcnt of contamination are site specific, cither climatic or hydrogeological. Other factors that influence the extent of contamintition relate to land surface features such as topography or dcNclopmcnt, which determine exposure routes. Additional important... 

The time frames associated with the later two phases are dependent on the volume of residual hydrocarbon that remains following initial recovery, hydrogeologic conditions, among other factors, and are further discussed in Chapters 9 and 10, respectively. Important factors such as the presence and extent of residual hydrocarbons, and conceptual understanding of relative permeability and transmissivity as they relate to NAPL recovery, are further discussed below. 

Selection of approach or combination of approaches to LNAPL recovery and ultimately aquifer rehabilitation and restoration is dependent on numerous factors as discussed in the previous chapters. The case histories presented below reflect different remediation approaches and strategies in response to varying geologic and hydrogeologic conditions, site-specific constraints, and regulatory environment. A variety of LNAPL recovery systems are first discussed, including ... 

The cost of this system is very site specific. It is dependent on many factors, including hydrogeology, geology, and water chemistry. There is currently only one example of the actual costs for the use of this technology. In the treatment performed at a former AT T plant, solvent was removed at a cost of 132/lb. The total cost of operations at the site was 3.44 million (D14286J, p. 7). 

Thomas, M.A. (2003) Arsenic in Midwestern Glacial Deposits-Occurrence and Relation to Selected Hydrogeologic and Geochemical Factors. U. S. Geological Survey Water-Resources Investigations Report 03-4228, Columbus, OH. 

Geologic and hydrogeologic conditions are perhaps the most important factors in establishing the environmental suitability of the area for a landfill site. Data on these factors are required to assess the pollution potential of the proposed site and to establish what must be done to the site to control the movement of leachate or gases from the landfill. 

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