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i Er i tr,Mr1 ?-D <br />obr ua y? 18, 2011 7 D <br />Page, l <br />CIVIL RES10URCES,LLC <br />a. It appears the applicant is relying on a ditch south of Cell A and west of the southern portion <br />of the Western Mutual Ditch to alleviate groundwater mounding at the southern end of the site. <br />Please indicate if the ditch is lined, or if it is permeable to accommodate groundwater <br />interception. During the pre-operation inspection, it appeared the ditch was lined with <br />concrete. If the ditch is lined, and/or it needs to be improved to function as a groundwater <br />drain, please provide plans and specifications of these improvements. The applicant must <br />demonstrate those improvements will allow the ditch to alleviate groundwater mounding. Or, <br />they must demonstrate the ditch currently has the capacity and design to alleviate <br />groundwater mounding. <br />The ditch located south of Cell A is an existing un-lined ditch that was excavated down into the <br />natural alluvium as shown on the following photograph: <br />If mounding occurs in this area this ditch will intercept and limit groundwater elevation to within <br />one to two feet above the ditch invert. The capacity of the ditch to convey flow at one foot of <br />depth is approximately 8 cfs which is over 1,000 times as much capacity as the aquifer flow <br />capacity based Darcy's law (K=3.3x10-5 ft/s; A=1 500'x30'=45,000 sf; dh/d1=.005 ft/ft). <br />Therefore, this ditch will effectively act as a constant head node/drain. <br />b. If the southern ditch is unlined, it may be prone to erosion if the flow rates exceed the carrying <br />capacity of the ditch. The applicant should submit documentation to the Division for review as <br />to the proposed maximum flow rate of the ditch and specifications as to how much water the <br />ditch can carry without experiencing erosion. Or portray and describe how the ditch will be <br />protected from erosion and still remain permeable for groundwater interception. <br />As documented in a. (above), the required flow rate to carry all of the aquifer flow to the river is <br />less than one cfs and therefore no significant erosion would be expected.