API PUBL 4722-2002 pdf download.Groundwater Sensitivity T O O L K I T.
In addition, the software asks the user if a regional contaminant (such as nitrate) is above the MCL ( either s ec ondar y or pr im ar y) . If it is , then the Res our c e Value is def ined as being LOW. Examples of regional contaminants include nitrate, radium, coliform, and some wide-scale man- made contaminants (wide-scale means not from a particular site of interest). In many cases, the regional contaminant will come from diffuse non-point sources rather than from a particular site. The Resource Value addresses the potential of usage for that aquifer, and considerations regarding the aquifer proximity to surface water bodies or other discharge points to another unit are addressed in other sections of the toolkit. The final Resource Value is the lower of the two usability criteria unless the answer to question 4 is “yes,” in wh i c h case the sof tware autom atic ally upgr ades the r es our c e value to at leas t a MEDIUM.
The Receptor Vulnerability section addresses the impact of a release to groundwater to existing (not potential) receptors that are using groundwater from any hydrogeological unit. An aquifer may be affected by horizontal migration of a contaminant to the extraction point, or by vertical migration from a shallower unit. Two key points are: 1. Analysis of vertical vulnerability will not be needed for the shallowest water-bearing unit, as there is no water-bearing unit above it. 2. The main receptor vulnerability screen allows the user to start with either vertical or horizontal vulnerability, but it is recommended that the user begin by addressing vertical vulnerability first, if there is an upper water-bearing unit above the water-bearing unit of interest. Note that this has been designed by the software development committee to be a conservative analysis and will tend to over predict the risk to existing receptors from an actual or potential release from the site of interest.
VERTICAL VULNERABILITY The Vertical Vulnerability section addresses the potential for the vertical migration of contaminants from a shallower water-bearing unit to the unit of interest. The toolkit addresses the case in which groundwater from an upper aquifer can seep through an aquitard (confining layer) or an artificial penetration to affect the water-bearing unit of interest. Factors that are related to how easily contaminants can travel through the vadose (unsaturated) zone are handled in the Natural Sensitivity section of the software. The vertical transport section examines transport occurring in the following scenario: The unit of interest may receive contaminated groundwater from an upper water-bearing unit by either: 1) groundwater flow through an aquitard or through an artificial penetration (such as an inadequately sealed well or a well that has been screened across multiple units).
The first question is designed to rule out potential transport through aquitards if there is strong hydrogeologic/stratigraphic information that the aquitard is likely to prevent vertical transport to this water-bearing unit. The second question provides a quantitative tool to estimate the resulting concentration in this water-bearing unit after groundwater migrating from the upper water-bearing unit through the aquitard mixes with groundwater in this water-bearing unit. This calculation is based on potentiometric level, aquifer thickness, concentration in the contaminated unit, mixing layer thickness, and ultimate length of plume in the upper unit. The equations used in this calculation may be viewed by clicking the “See graphic of flow-through aquitard” button. Once the concentration has been calculated, the user may compare the lower unit concentration to the MCL or other relevant regulatory standard to answer Question 2. Mass flux information associated with transport through the aquitard is also provided.