2908 49TH ST SW 2016-01-01 MF Import

r ISeptember 7, 2010 Mr. John Mustach I LBcA Job No. 10-036 Page 3 gullying and may gradually loosen and siough to its angle of repose. The Esperance Sand deposits are of moderately high permeabiliry and would allc,,v stormwater to seep through easily. Soil Ct�ndition During construction for the development of the subject plat, we observed the soils encocntered by excavation of its stonnwater detention pond located at the northeast corner of the plat sitc below Lot 7. Soils exposed on the cut banks of the pond were composed of a layer os light- brown to light-gray, fine to coarsc sand with a trace of gravel, up to about 10 to 12 feet thick. Underfying this sand layer is a gray Transitional Beds deposit of hard, clayey silt. Groundwatcr Condition "I'he surficial Gsperance Sand dcposits underlying the lots are of moderately high to high permeability, while the underlying Transitional Bcds clayey silt deposits aze of exVemely low permeability. Groundwater seepage perching on ihe clayey silt deposits was encountered by excavation of the dctention pond. '1'he depth to and the amount of this near-surface, perched groundwater would 17uctuate seasonally, depending on vegetation cover, precipitation, site utilization, eta It may dry up completely in the dry summer and fall months, and accumulate and rise in thc wet winter months. Because the clayey silt is at the lower elevation of the plat site, it is our opinion that groundwatcr should have little impact on the construction of the proposed concrcte block w�ll. RECOMMENllA'TIONS Gencral 7'he proposed block wall is to be constructed with 2.5 foot x 2.5 foot x 5 foot precast concrete blocks. 7'he block wall should have geogrid m�sh rcinforcement embedded in its backfill, except where the wall is no more than 5 feet tall. A drain line should be provided along the base behind the wall. The wall should be founded on a minimum 4-inch layer, 7/8-inch crushed rock, leveling base, placed over firm, undisturbed, Esperance Sand soil. Loose and disturbed soils, if LiU & ASSOCIATES, INC.