Longevity of the effectiveness of interim soil lead hazard control measures and influencing factors

A 7-year follow-up was conducted to determine factors associated with the longevity of interim soil lead hazard control measures that had been applied to housing in the Cleveland OH area. The approach involved (1) visual determination of the treatment integrity, (2) collection of information regarding 14 factors that may contribute to longevity of treatment integrity and (3) collection of one composite soil sample from treated areas with visual failure at each house and another composite sample from areas without visual failure. For the 200 houses studied, an average of 4 different soil areas were treated. For 96% of these areas, the treatments used were: (1) re-seeding, (2) mulch/wood chips and (3) gravel. Of a total of 191,034 ft(2) of treated soil areas observed, less than one-third, i.e. 59,900 ft(2) (31.3%) exhibited visual failure at the time of follow-up. Hazard control method and the presence/absence of shade were the only factors found to significantly affect visual failure rates. Of the three most commonly used control measures, the lowest visual failure rate was for re-seeding, 29.1% after a mean of 7.3 years; for non-shaded areas, which had been re-seeded, the failure rate was 22.2% compared to 35.7% for shaded areas. At 116 of the 193 houses (60%) that had both visually failed and visually non-failed treated soil areas, the geometric mean soil lead concentration was higher in the failed areas (p=0.003). The actual difference was only 13% with most levels equal to or exceeding 400 ppm. However, when compared to the US EPA limit for bare soil in other residential areas (1200 ppm) the percent equal to or exceeding the limit was much higher in the visually failed areas, 33.1%, than in areas where such failure was not observed, 22.0%.