Laserfiche WebLink
- -�� �••�.�. L� �laririea. =combs uses the Walker method for determining <br /> 4111 • watershed phosphorus removal for the wetland. The underlying assumption in <br /> the Walker method is that phosphorus removal occurs in the permanent pool <br /> below a ponds' normal elevation. It is not clearly stated in the permit <br /> application whether the 54 ac-in pond and pool volume includes or excludes <br /> the available flood storage. If the flood storage is included, then using <br /> the 54 ac-in is not a valid volume for determining the phosphorus removal <br /> potential of the wetland. I am also concerned about including wet detention <br /> areas that can be easily short circuited by storm water flows. Especially <br /> Pond 2 on the grading and erosion control plan. This pond would provide <br /> little in the way of water quality improvement for the 150 ac watershed <br /> tributary to this wetland. It is my opinion that pond 2 should not be <br /> included in the water quality computations for this wetland alteration. <br /> Also, if the outlet elevation is to remain at 896.33, then only the wet <br /> detention below this elevation should be used to estimate water quality <br /> enhancement potential of the wetland. <br /> . 3) Soil Erosion <br /> The city's ordinance requires that soil loss from the construction area <br /> must be less than 5 tons per acre during the construction period. McCombs <br /> has compute a soil loss of 7. 6 tons per acre. This means that the sediment <br /> and erosion control plan for this project is not in compliance with city <br /> requirements. An assumption was made that during construction the entire <br /> constr - <br /> _ • =even o .oing <br /> construction in phases and leaving some areas in turf this avoids soil <br /> disturbance. Another option is to provide mulch or erosion matting to <br /> prevent exposure of bare soil. This should be done in addition to the silt <br /> fencing already indicated on the erosion control plan. Once an area is open <br /> for construction, all land area not needed for construction purposes should <br /> be mulch or covered. These practices may improve erosion controls and limit - <br /> the predicted erosion to less than 5 tons per acre. <br /> • <br />