04/26/2000 Env Bd Packet - Laserfiche WebLink

Home Search

Technical Note 108 Can Urban Soil Compaction Be Reversed? Soil compaction appears to be an inevitable result of current construction practices (see Technical Note 107). The key question is whether it is possible to reverse soil compaction. Numerous soil scientists have evaluated practices that can avoid compaction during construction or reverse it after it occurs (Table 108.1). These practices include selective grading, special construction equip- ment, reforestation, mechanical loos- ening, and the use of soil amend- ments. This note reviews what is cur- rently known about how well these practices work and evaluates their potential as a stormwater management strategy in urban watersheds. The consensus among soil scientists is that alleviating urban soil compaction is a very hard job. Indeed, Randrup (1998) notes that once a soil is compacted, it is extremely difficult to restore its origi- nal structure, particularly if the compaction extends several feet below the surface. The only truly effective tech- nique for avoiding compaction is prevention. gatw..11,21 :ag. W3' '.i.7liAlr: :i ILVi'I.i^ Z11^- ' Techniques to Avoid Compaction During Construc- tion The traditional remedy for soil compaction has been to require contractors to loosen soil by tillage, ripping or other techniques before lawns are estab- lished (much as a farmer plows a field). However, Randrup (1998) could find no significant difference in soil bulk density between Danish construction sites that had been loosened and those that had not. Similarly, Paterson and Bates (1994) found that tilling resulted in only a minor improvement in compaction in urban soils in Washington, D.C. (See Table 108.1). Another common technique for avoiding soil compaction is the practice of selective grading, where only the most critical portions of the site are mass graded, and the remainder of the site is cleared but not graded. Again, neither Randrup (1998) nor Lichter and Lindsay (1994) were able to detect any improve- ment in soil bulk density in the selectively graded construction sites. These soils still experienced ex- tensive compaction by construction equipment, stockpiling and vehicle traffic. The only soils where compaction was prevented were areas that were fenced to exclude all construction activity. In the past several decades, specialized equip- ment has been developed to minimize compaction (e.g., terralifts, and subsoil excavators). Rolf (1994) detected a modest improvement in bulk density Table 108.1: Reported Activities That Restore or Decrease Soil Bulk Density iecrease`in Bulk Densi' (gms /cc) Tilling of Soil Specialized Soil "Looseninc .05to0.15 Soil Amendmen Compost Amendment Randrup, 1998 and Lichter and Lindsey, 1994 Patterson and Bates19 Kolsti et al., 1995 Reforestation 0.25 to 0.35 See Technical Note 107 666 Watershed, Protection ..Techniques'. Vol. 3;, No. 2 • January. 2000