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Mr. Joe Lamanna <br /> November 11, 2016 <br /> Page 2 <br /> estimated 20 to 70 gallons per minute based on Darcy and Glover bank storage calculations. <br /> Dewatering rates may be higher at the time of construction and shortly after construction as <br /> material adjacent to the trench drains. <br /> Our understanding of ground water conditions and potential system discharge are based on visual <br /> observations, the provided survey efforts and water level data from nearby monitoring wells. <br /> Investigative excavations are recommended early in the construction process, as described below, <br /> to better understand potential underdrain system flow rates. <br /> Underdrain Design <br /> The underdrain is designed to drain the shallow ground water down gradient from the western <br /> boundary of the Spier Property. The underdrain will be constructed as a trench backfilled with <br /> highly permeable gravel and perforated pipe, which should enable the capture of ground water and <br /> transmission of ground water in a northern direction to the McCann Ditch. The underdrain system <br /> is intended to transmit water whenever the water level at the location of the collection trench rises <br /> to the elevation of the drain and is designed to control the elevation of ground water at that location. <br /> The effective depth of the drain and the achievable water level will be constrained by the elevation <br /> of the outlet point at the McCann Ditch. <br /> The location and extent of the underdrain system is presented generally in the attached Figure 2. <br /> The drain will include two main components: 1) a collector trench located as close as practical to <br /> the western Spier Property boundary and 2) a transmission trench that will facilitate the discharge <br /> of ground water to the McCann Ditch. The collector trench will extend the entire length of the <br /> western property boundary of the Spier Property. <br /> The trench in both portions of the underdrain system will be at least 24 inches wide and will be <br /> excavated to allow for the installation of perforated pipe at the identified elevations. In addition, <br /> the collector trench shall be excavated such that the trench intercepts native alluvial gravel material <br /> to provide for communication with the gravels of the in-situ alluvial material. Overburden in the <br /> areas of the collection trench may be as deep as seven feet. The transmission trench shall be <br /> excavated to a depth of no more than 6 inches below the proposed elevation of the perforated pipe <br /> to be installed in the trench. The elevations of the proposed pipe alignment are presented in the <br /> longitudinal cross section attached as Figure 3. <br /> As a first step of the construction process and prior to ordering and delivering materials, test <br /> excavations should be made to confirm the thickness of overburden material, depth of gravel <br /> material and depth to water. During this process, ground water flow and water level during and <br /> after excavation should be observed to confirm whether any potential confined pressure exists that <br /> may impact drain flows. <br /> The trench shall be backfilled with Boral #9 gravel material, which we understand is available on <br /> site. Gravel material shall be backfilled until the proposed pipe elevations are achieved, then the <br /> pipe shall be installed and additional gravel backfilled around and on top of the pipe to a depth of <br /> approximately 1 foot below the ground surface. We recommend 8-inch PVC perforated pipe with <br /> a slot size of 0.05 inches(50-slot)for installation, but high-density polyethylene pipe (HDPE) can <br /> also be considered. If HDPE is used, 8-inch pipe is also recommended. In the collector trench <br /> area, geofabric material shall be installed on top of the gravel to limit fine grained material from <br />