The following is a map unit description from the "Soil Survey of Norfolk and Suffolk Counties, Massachusetts (Peragallo, 1989)"
NpD-Newport silt loam, 15 to 25 percent slopes. This is a deep, moderately steep, well drained soil on side slopes of hills in the Boston Basin and along the Plymouth County line. Areas are long and narrow and range from 6 to 50 acres in size. Some of the areas are on eroded slopes that have been revegetated.
Typically, the surface layer is dark brown silt loam about 5 inches thick. The subsoil is light olive brown silt loam about 17 inches thick. The substratum is firm, light yellowish brown silt loam to a depth of 60 inches or more. In many areas the coarse fragments in the soil are 50 to 75 percent, by volume, flat, dark gray shale and slate and are 1 to 15 inches long.
Included with this soil in mapping are small areas of Paxton soils in positions on the landscape similar to those of the Newport soil. Also included are a few small areas of Urban land where the soil is covered with impervious surfaces, such as pavement or buildings. Included soils and areas of Urban land make up about 15 percent of this map unit.
Permeability: Moderate in the surface layer and the subsoil and slow in the substratum.
Available water capacity: Moderate.
Soil reaction: Very strongly acid to moderately acid throughout.
Depth to bedrock: More than 60 inches.
Depth to the seasonal high water table: 1.5 to 2.5 feet.
Hydrologic group: C.
Most areas of this soil are used as individual homesites. Other areas are used for parks and playgrounds.
This soil is poorly suited to cultivated crops, hay, or pasture because of slope and the erosion hazard. A permanent vegetative cover is needed to control erosion, especially on the Boston Harbor Islands, where the soil is exposed to wave action.
Potential productivity for northern red oak on this soil is moderately high. Management concerns are slope and the hazard of erosion. Plant competition is moderate if conifers are grown. Constructing access roads and trails with grades between 2 and 1 0 percent and installing water bars help to control erosion. Minimizing soil disturbance and retaining the spongelike mulch of leaves help to reduce runoff and to control erosion. Thinning crowded stands to accepted standard stocking levels allows more vigorous growth. In thinning operations it is important to remove diseased, poorly formed, and otherwise undesirable trees. Shelterwood cutting, seed-tree cutting, and clearcutting help to establish natural regeneration or to provide suitable planting sites. Removing or controlling competing vegetation allows best growth of newly established seedlings.
Tile drains around building foundations help to lower the seasonal high water table. In some areas extensive land shaping is needed because of slope. Landscaping designed to drain surface water away from buildings also prevents damage to the interior by the seasonal high water table. Slope, the seasonal high water table, and potential frost action are the main limitations for road construction. Constructing roads on the contour, if possible, and planting roadbanks to well adapted grasses help to control erosion. Constructing roads on well compacted, coarse textured base material and providing adequate side ditches and culverts help to prevent the damage to pavement by the seasonal high water table and potential frost action.
Slope and permeability are limitations to use of the soil as sites for septic tank absorption fields. Unless the absorption fields have expensive and elaborate design, the effluent will rise to the surface. Soils that are better suited to use as sites for septic tank absorption fields are generally nearby.
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