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SC-CFBISD Riverchase-CS000324 MEMORANDUM FROM THE DEPARTMENT OF ENGINEERING COPY To: Jim Witt, City Manager From: Kent Collinn, P.E., Civil Engineer Date: March 24, 2000 Riverchase Elementary School / MacArthur Park Sidewalk Crossing In the days since our last meeting with thc CFBISD and TXU Electric personnel, I have had the opportunity to study the proposed crossing. Specifically, I have examined the potential locations in the field and in terms of topographic information. If the crossing is pursued in the future, the best location would likely be the cul-de-sac at the end of Bradford Drive. Although this is not the most direct route across to Starleaf, it would provide the shortest nm across private property and have thc shortest drop from the street to the elevation of the TXU property. That said, there are several problems with construction of the sidewalk regardless of the location. The first obstacle is the drop from the street. Any sidewalk intended for public use will have to meet ADA requirements. Therefore, one option to deal with this drop would be to run a ramp to the south or north along the property linc and then turn to the west when the ramp is at-grade with the TXU property. The problem with this option is that the City has very little or no right- of-way in which to locate the ramp. This option would require the purchase of an easement or right-of-way. The other option to deal with the elevation difference is to simply run a ramp from the cul-de-sac directly west into the TXU property. Again, this ramp would have to meet ADA requirements. However, construction of any structure in the floodplain will necessitate a flood study. Another concern is the condition of the soil along the proposed path. Based on observations, this soil is wet for much of the time. This could create a problem from a use standpoint. Water on or running across the sidewalk would be not only a nuisance but a safety hazard. Elevating the sidewalk may keep it dry, but it would dam water adjacent to it. This would eventually compromise the integrity of the sidewalk. The dammed up water could also become a health issue. Although the School District has agreed to accept these conditions and maintain the sidewalk, this may not be as simple as sweeping or washing the sidewalk. A more serious issue with the soil conditions is the ability to actually construct the sidewalk. It is doubtful that the soil is stable enough to support the sidewalk or the machinery necessary to excavate the soil and pour the sidewalk. There are no inexpensive methods for remedying this problem. It may be overcome by excavating deep enough to reach stable soils, but that depth is unknown at this point. Another option might be lime stabilization or other soil modification processes, but again the soil must be stable enough to support the necessary machinery. An investigation by a Geotechnical consultallt would be advisable prior to pursuing construction of "CITY OF COPPELL ENGINEERING - EXCELLENCE BY DESIGN'* the sidewalk. Also, keep in mind that any variance granted to the Hoodplain Management Ordinance would necessitate a balance between soil removed and soil/concrete added. In other words, no material could be placed within the floodplain without the removal of a like amount of material. Another potential problem with constructing a crossing at this time is the potential for existing wetlands along the proposed route. A requirement of the City's Floodplain Management Ordinance is that all applicable Federal or State regulatory permits must be completed prior to issuance of a floodplain development permit. The City or CFBISD would need to contract with an environmental consultant to perform a wetlands determination on the land prior to construction. If it was determined that wetlands existed where the crossing was proposed, then a wetlands mitigation plan would have to be developed and submitted for approval by the U.S. Corps of Engineers. Any wetland mitigation would increase the cost of the construction. These issues are problematic. The problems can be dealt with but would likely entail si~cynificant additional cost and/or delay. One alternate design that could overcome most of the construction and use problems would be a "boardwalk~ option as illustrated in the attached exhibit. The design would be a wooden plank walkway on piles such as is commonly used on beaches. This option would still require a soil/foundation analysis to determine the depth and number of piles. Routine maintenance would also be necessary. Obviously, this option would be very costly if this is to be a temporary walk, but it would solve most of the problems associated with a concrete sidewalk. Again, all options will have problems from a use, construction, maintenance, or cost stand ~oint. I would welcome the opportunity to discuss this with you further at your convenience. "CITY O!~ COPPELL ENGINEERING - EXCELLENCE BY DF, SIGN"