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Also stated that it only takes 7 to 8 feet of sandy soil to filter out any contaminates.
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Not true for any of the metals including lead. Not true for almost any contaminates (some hydrocarbons can be filtered with absorbent sand.) Sand and other soils can hold or sequester lead, but only until more lead trickles down from above or until the sequestered lead is dissolved in solution. As soon as rain below a pH of 7 hits lead (the norm around here), it begins to dissolve and travel. It will continue to travel until in accumulates (usually in an aquifer), concentrates and precipitates out as salts.
To prevent the leaching of lead, soils must be sieved (like scooping turds out of kitty litter
) or heavily titrated with lime and other pH raising chemicals to ensure the lead cant dissolve and leach.
BTW Clay type soils can hold or sequester concentrations of lead and other contaminates 1000 times greater than sands due to the tremendous surface area and cohesion effect of clay particles.