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HomeMy WebLinkAbout2002-11-01 OPH Ltr to Owner & Contractor Re Erosion Control & Tree IssuesNovember 1,-2002 Mr- Ro centur 6920 Memorial Avenue IL. E C Oak park Hei 55082 Sti Const 1260 Hel-mo Avenue, Oakdale, MN 55128 P raters _ Des-i As,sociate-s', Inc.. 7300 Hudson Blvd., Suite 220 Oakdale, :MN 55128, Re: Erosion Control and Tree Issues at- Centur Power Buildin Expansion Erosion Control: Browns Creek Watershed District Board did not find the above. r to be in violation- of their board rules. The Cit of Oak Park H still- has concerns on the erosion control and',is awaitin documentation of the tree 41 inventor Field chan have been made to the tree preservation plan (drawin Cl and the. radin and-,erosion c ontrol C2 I-plan ( drag in }!without p r ior 9 knowled or consent of th Cit `I-hese' pla .►will need -to be -revised and resubmitted to the+ 'Cit and •to Browns Creek Watershed District f approval .r The revised plans n to specif both the te' mpo-rar erosion control measures that . at will be applied this fall to prevent a fbil-ure of -the,hillside next sp and permanent erosion control measures that will prevent future failures. The permanent controls must also include h the en plans to remove the sediment that has accumu'lated behind the series of silt fences and blend the g rades, into existin g rades. A cost estimate for the temporar and permanent controls should be included with the plan. Given the default in followin existin - plans the cit ma re the postin of securit to complete this project. Since winter is q uickl y approachin all reasonable efforts should be made to expedite the installation of the curb and g utter, establish the final rou g radin g and the installation of temporar erosion control. To this end the revised plans must be provided to the Cit as soon as- possible and no later than 12:00 P.M. (noon) on November 7, 2002. The revised plans -should provide for both temporar erosion controls that can be installed prior to si frost- - Tree Cit U.S.A. Century Power Erosion and Tree Protection November 1, 2002 penetration to minimize erosion due to spring runoff and rainfall. Also the plans must address permanent erosion controls that will be installed on these steep slopes that are contrary to approved plans. The permanent erosion control plan should include measures that will be equal to reducing the slopes back to a maximum of 3:1 and have vegetative cover that will grow on shady hillsides. The City will review the plans within two working days of their submittal. Temporary erosion control measures specified in these plans should be installed and inspected by the owner's engineer no later than November 15, 2002. The owner's engineer will then certify to the City that the temporary erosion controls meet or exceed Best Management Practices (BMPs) for erosion control recommended by the Minnesota pollution Control Agency in their manual "Protecting Water Quality to Urban Areas ". Unauthorized field changes have resulted in the slope being steeper than designed. With these slopes mechanical equipment cannot be used to remove the sediment from the fences. The steep slopes need to be stabilized prior to frost so we do not loose the hill into the woods with spring runoff. The erosion control plan that was approved as part of the building plans require the removal of sediment from the fence wherever the sediment reaches Y2 of the height of the fence. The Browns Creek permit requires removal at 1/3 of the fence height. Instead of sediment removal there have been additional fences installed in front or closely behind the fence that was failing. In one spot there now exists four fences a weak retaining wall. Two of the fences have been overtopped by sediment. If sediment is allowed to fill in more than 0 inches in the current fence, the additional weight of all this material on the lower fences may cause a failure of all four fences and release the stored sediment into the woods. The following erosion control measures are the minimum required for the temporary erosion control plan and are to be implemented immediately on the site. 1. sediment deposits on the new fences must be removed when they reach six inches deep. As an alternative, the conditions of the original erosion control plan could be complied with and the sediment removed from all of the fences followed by the repair and replacement all of the original sedimentation fences. If the sediment removal and repair option is chosen these repairs must be completed by November 7, 2002. 2. The erosion control fences installed partway up the hill must have the flap buried a minimum of six inches below the ground and the soil firmly packed around the flap by November 7, 2002. 3. Erosion control inspections shall be performed and documented with a written record at least weekly until frost is well established in the ground and after every rainstorm. In the spring an inspection shall be made and documented prior to the spring melt and no later than March 1 , 2003. Weekly inspection and inspections after each rainstorm will be made and documented after March 1, 2003 and until final slope stabilization has been completed with permanent vegetative cover. Century Power Erosion and Tree Protection November X, 2002 4. To prevent erosion during spring run oft, the slopes need to be stabilized prior to frost. At a minimum all slopes over 5:1 will be: a. Topped with black dirt as specified in the landscaping plan. If bulldozers or other equipment is used to spread the dirt, the final passes of the equipment should be such that the track or tire marks do not form channels that point down the hillside. With a tracked vehicle, the final pass should be up the hillside leaving a series of cleat marks perpendicular to the slope and will work as hundreds of small check dams rather than hundreds of small erosion channels. b. Seed the with a grass seed mixture for side slopes and woodland transitions that have limited sun. The seed mixture should be specified by a landscape architect that is practiced in erosion control and native plant restoration. The MNDOT 5A Modified or 5B is listed in the MNDOT spec book for woodland transition with up to 50% shade. c. Install and securely stake down erosion blanket material that will help minimize erosion in the spring. d. Areas with slopes less than 5.1 will be planted and stabilized in accordance with the approved landscape plan. Tree Preservation: The city Arborist has, on multiple occasions, requested additional information that was reported to have been mailed to the city earlier this week. As of October 31 2002 we have not received the revised tree inventory map (drawing C -1) showing the significant trees on site and the significant trees which were removed or damaged in the process of construction. A forester, land surveyor, or landscape architect must certify this revised drawing. If the revised tree inventory map is not received by 12:00 P.M. noon on Thursday November 7, 2002. The Tree Protection ordinance requires the plan to be reviewed and approved prior to the start of construction. The submitted plan, drawing C -1, was not approved when the city Arborist could not reconcile the trees that were found on the site with the trees shown on plans. several species of significant trees were found on the site but not shown on the plan. Also a tabulation of the significant trees removed and remaining was not provided. Based on the assurances from the owner's representatives that an amended plan would be forthcoming a building permit was issued and construction started. A listing of significant trees has recently been received but a map showing the locations of significant trees has not been received. The construction limits of the project were altered during construction and the tree protection fencing and erosion control fencing was not installed in accordance with the submitted plans. According to the contractor's site superintendent the changes were made to save trees. The city compared the Century Power Erosion and Tree Protection November 1, 2002 submitted plans with the trees found within the construction site and immediately adjacent to the erosion control fence. staff estimates that the changes made have resulted in the loss of 84 caliper inches of oak trees Trees that have silt fences dug through their roots system near their trunks and trees where dirt has been bulldozed against the trunks are considered construction damaged and counted the same as removed trees. The actions listed above with a November 7, 2002 deadline that are not addressed to the satisfaction of staff will be forwarded to the city council at their meeting on Tuesday November 12, 2002. Staff recommendation to the city Council will be that all work on the building project not related to erosion control and slope stabilization cease until these site issues as outlined in this letter are addressed to the satisfaction of staff. The city is prepared to issue stop work orders if these matters are not immediately addressed. I await your response. Sincerely, Jay E. Johnson, P.F. Public works Director CC: Mayor and city council Browns creek water shed District Administrator Kim Karnper, Acting city Administrator Judy Hoist, Finance Director Mark J. Verling, city Attorney Kris Danielson, community Development Director Kathy Widin, city Arborist Mitch Johnson, FOR, Engineer for BCwD