Kodiak Drilling is often installing monitoring wells for environmental consultants who are evaluating sites for petroleum hydrocarbon contamination.  Maxxam Labs has recently published an article related to F3 and F4 PHCs in groundwater.  Maxxam recommends the use of low flow sampling in silty conditions to prevent soil particles from being included in the sample.  You can read the article by clicking  Solubility for F3 F4.