Then yard remediation may be a short-sighted remedy.  If contamination derives from historic sources, then yard remediation may literally unearth more contaminant.  Approach  Determine the lead minerals present in yards and the size of the particles.  Evaluate all potential sources.  Project #7, Sampling Statistics for Residential Yards  What are the basics statistics for lead in residential yards?  What is the confidence level of the number of samples taken as it relates to the area represented?  Why is a #80 mesh screen used to concentrate lead minerals?  What percent of a typical yard sample passes though an 80 mesh screen?  Significance  The accuracy of sampling fundamentally affects the assessment of risk in residential yards.