Graphical Approach for Determining Site - Specific Dilution - Attenuation Factors (DAFs): Technical Background Document and User’s Guide The DAF plays a key role in assessing potential impact from the soil - to - groundwater pathway at sites where groundwater quality is, or may be, affected by a leak, spill, or other accidental release of hydrocarbons or other chemicals of concern. A simplisti c, graphically - based approach for determining generic and site - specific DAFs was developed, allowing for varying levels of site specificity. Currently, to develop a DAF, one must make complicated calculations by hand or use computer - based modeling software. This publication consists of two documents. The first document describes the technical basis for the gr aphical approach for determining site - specific dilution attenuat ion factors. The second document, the user’s guide, provides a concise set of instructions for use of the graphical approach