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conjunction with plans for structural practices (e.g., subsurface drain line or lawn/ground cover to help maintain the restored subsoil structure. Infiltration after construction- infiltration basin) serving the same or contiguous areas induced mixing and compression of such subsoil material can be notably rehabilitated with the Deep Ripping and Decompaction practice, which prepares the site for the appropriate long-term x Promotes successful long-term revegetation by restoring soil permeability, drainage and lawn/ground cover mix including deep taproot plants such as clover, fescue or trefoil, etc. needed water holding capacity for healthy (rather than restricted) root-system development of for all rehabilitated soils. trees, shrubs and deep rooted ground cover, minimizing plant drowning during wet periods and burnout during dry periods. Generally, soils in Hydrologic Soil Groups A and B, which respectively may include deep, well- drained, sandy-gravelly materials or deep, moderately well-drained basal till materials, are among Feasibility/Limitations the easier ones to restore permeability and infiltration, by deep ripping and decompaction. Among the many different soils in Hydrologic Soil Group C are those unique glacial tills having a natural The effectiveness of Deep Ripping and Decompaction is governed mostly by site factors such as: fragipan zone, beginning about 12 to 18 inches (30 – 45cm), below surface. Although soils in the original (undisturbed) soil’s hydrologic characteristics; the general slope; local weather/timing Hydrologic Soil Group C do require a somewhat more carefully applied level of the Deep Ripping (soil moisture) for implementation; the space-related freedom of equipment/implement and Decompaction practice, it can greatly benefit such affected areas by reducing the runoff and maneuverability (noted above in Recommended Application of Practice), and by the proper fostering infiltration to a level equal to that of pre-disturbance. selection and operation of tractor and implements (explained below in Design Guidance). The more notable site-related factors include: Soils in Hydrologic Soil Group D typically have a permanent high water table close to the surface, influenced by a clay or other highly impervious layer of material. In many locations with clay Soil subsoil material, the bulk density is so naturally high that heavy trafficking has little or no added In the undisturbed condition, each identified soil type comprising a site is grouped into one of impact on infiltration; and structural runoff control practices rather than Deep Ripping and four categories of soil hydrology, Hydrologic Soil Group A, B, C or D, determined primarily by a Decompaction should be considered. range of characteristics including soil texture, drainage capability when thoroughly wet, and depth to water table. The natural rates of infiltration and transmission of soil-water through the The information about Hydrologic Soil Groups is merely a general guideline. Site-specific data undisturbed soil layers for Group A is “high” with a low runoff potential while soils in Group B such as limited depths of cut-and-fill grading with minimal removal or translocation of the inherent are moderate in infiltration and the transmission of soil-water with a moderate runoff potential, subsoil materials (as analyzed in the county soil survey) or, conversely, the excavation and depending somewhat on slope. Soils in Group C have slow rates of infiltration and transmission translocation of deeper, unconsolidated substratum or consolidated bedrock materials (unlike the of soil-water and a moderately high runoff potential influenced by soil texture and slope; while analyzed subsoil horizons’ materials referred to in the county soil survey) should always be taken soils in Group D have exceptionally slow into account. rates of infiltration and transmission of soil- water, and high runoff potential. Sites made up with significant quantities of large rocks, or having a very shallow depth to bedrock, are not conducive to deep ripping and decompation (subsoiling); and other measures may be more In Figure 4, the profile displays the practical. undisturbed horizons of a soil in Hydrologic Soil Group C and the naturally slow rate of Slope infiltration through the subsoil. The slow rate The two-phase application of 1) deep ripping and 2) decompaction (deep subsoiling), is most of infiltration begins immediately below the practical on flat, gentle and moderate slopes. In some situations, such as but not limited to topsoil horizon (30 cm), due to the limited temporary construction access corridors, inclusion areas that are moderately steep along a project’s amount of macro pores, e.g.: natural subsoil otherwise gentle or moderate slope may also be deep ripped and decompacted. For limited fractures, worm holes and root channels. instances of moderate steepness on other projects, however, the post-construction land use and the Infiltration after the construction-induced relative alignment of the potential ripping and decompaction work in relation to the lay of the mixing and compression of such subsoil slope should be reviewed for safety and practicality. In broad construction areas predominated by material is virtually absent; but can be moderately steep or steep slopes, the practice is generally not used. restored back to this natural level with the Fig. 4. Profile (in centimeters) displaying the Local Weather/Timing/Soil Moisture two-phase practice of deep ripping and infiltration test result of the natural undisturbed Effective fracturing of compressed subsoil material from the exposed work surface, laterally and decompaction, followed by the permanent horizons of a soil in Hydrologic Soil Group C. vertically down through the affected zone is achieved only when the soil material is moderately establishment of an appropriate, deep taproot dry to moderately moist. Neither one of the two-phases, deep ripping nor decompaction (deep 3 4 Page 305 of 1493