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Memo- Flooding/Sanitary Sewer ProblemsMemorandum To: Honorable Mayor and Members of the City Council From: Steven J. Stadler, Public Works Director Date: August 27, 1997 Subject: Flooding /Sanitary Sewer Problems Update Area 1 Shady Oak sump pond Public Works Department The purpose of this memo is to update City Council on current status of actions regarding flooding and sanitary sewer backup problem areas. At the August 5 City Council meeting, staff explained the nature of problems and corrective action taken or anticipated in each of seven (7) problem areas of the city. This list has since grown to eight (8) as we've added a local stormwater flooding area at the intersection of 2" Street NE and Monroe Avenue North. An update of actions taken or underway in each area follows. General A front -page article was written and published in the September /October Hopkins Highlights. The article pointed out the unusually heavy rainfall of July and the types of problems it caused, explains the problem of infiltration into the sanitary sewer system, mentions the city ordinance prohibiting sump or other clear water connections, provides guidance to residents if they have an improper connection, and asks for resident cooperation as the city attempts to identify improper connections. A newspaper column was written by the City Manager and published in the August 27 Hopkins SunSailor. The column explains the July '97 rainfall, the city's response to problems which surfaced following the July 1987 storms, and the city's intention to prudently act on the new series of problems associated with this years heavy rains. Shady Oak pond needs dredging and an outlet. Staff proposes to add dredging of this pond with a current CIP 1999 ,dredging project for the siltation pond east of the Nine Mile Cove development project. Dredging will increase storage capacity and reduce the likelihood of flooding onto private property, 2" Street North or Shady Oak Road. Flow from a pond outlet was considered in design of the Shady Oak Road storm drainage improvements south of Excelsior Boulevard. These improvements will be completed next year as a part of the Excelsior Boulevard reconstruction project. However, a pond outlet must be constructed as well as some work on the existing pond areas in the City of Minnetonka just west of Shady Oak Road. Staff plans to pursue these drainage modifications in conjunction with the year 2000/2001 Shady Oak Road reconstruction project. Area 2 Hilltop Park low area Staff has investigated this low ponding area including a survey of critical elevations. A lower drain inlet can be installed and connected to an existing storm inlet at the low point in 4 Street North. Staff intends to complete this work next year and has budgeted an estimated $15,000 in the 1998 Storm Sewer Utility budget. Area 3 - alley drainage Staff intends to increase inlet capacity and reduce the current blockage problem by installing an additional inlet in this alley or modifying the current inlet grate. Drainage will still be limited to the capacity of the existing 12" pipe under the alley and 1 Street North. This work will be done in 1998. Area 4 - lust north of Maetzold Field Stormwater: Staff will investigate options of improving drainage from the south end of the alley to the existing 36" pipe running from the inlets at the south end of 13t Avenue to Maetzold Field. Specifically, staff wants to provide an overland flow route from the alley to 13 Avenue. This should not be difficult or expensive but it may involve relocating an existing private chain link fence. Work should be done this fall or next year. Sanitary Sewer: Staff has discussed the specifics of our problem areas with three engineering consulting firms and requested proposals to study the impact of rainfall induced flow in this area of the sanitary sewage collection system. The proposals will include a cost for implementing a sump pump /foundation drain inspection program. Proposals are expected early next week. If consultant services are used, it would most likely occur late this fall and next winter. Staff will review the proposals and, of course, request City Council approval before entering into an engineering services agreement. In addition, we have begun taking action to determine what, if any, problems may exist in the pipes which could reduce pipe flow capacity. City utility crews have begun sodding and /or jetting the critical sewer pipes serving this area. They will document any pipe restrictions or other problems. The sewer pipes will then be inspected with a video camera for conditions including: pipe slope, pipe joint condition, roots or other potential blockage problems. Rodding/jetting should be completed next week with video inspection shortly thereafter. The last video inspection was done in 1988. Area 5 - alley drainage area Staff expects that the proposed 1998 6 Avenue North storm sewer project will improve drainage from this area. This is because stormwater from the 6 Avenue North/3` Street intersection must now combine with the water from this alley before it continues south from 2 Street to 1 Street North. The 6th Avenue project will take the water from the 6t Ave /3` St intersection and run it directly into the 54" sewer pipe at 6 Ave/1 st St North intersection. Area 6 - 6 Ave North /3 Street North area Staff expects design/construction engineering services proposal by Sept 2" The scope of the services will include analyzing alternative designs and benefits/costs. City Council is scheduled to consider approval of engineering services agreement on Sept 16 Staff anticipates design completion this fall with construction start next spring. Area 7 Hobby Acres sanitary sewer backup area **same as Area 4 (sanitary sewer) above** Staff has discussed the specifics of our problem areas with three engineering consulting firms and requested proposals to study the impact of rainfall induced flow in this area of the sanitary sewage collection system. The proposals will include a cost for implementing a sump pump /foundation drain inspection program. Proposals are expected early next week. If consultant services are used, it would most likely occur late this fall and next winter. Staff will review the proposals and, of course, request City Council approval before entering into an engineering services agreement. In addition, we have begun taking action to determine what, if any, problems may exist in the pipes which could reduce pipe flow capacity. City utility crews have begun rodding and/or jetting the critical sewer pipes serving this area They will document any pipe restrictions or other problems. The sewer pipes will then be inspected with a video camera for conditions including: pipe slope, pipe joint condition, roots or other potential blockage problems. Rodding/jetting should be completed next week with video inspection shortly thereafter. The last video inspection was done in 1988. Area 8 - 2 " Street NE /Monroe Ave North This is a storm drainage flooding area. During the heavy rains of July the intersection area flooded as did Alliant -Tech parking lot. The water also backed up onto the property at 217 Monroe Avenue North. Staff has added this area as needing drainage improvements from major storms. Investigation will include the drainage ditch running west and north of this area, including existing culvert pipes, and the parking lot inlets /piping. MINNETONK 8 N R. , • • / I •IT • asfts 31 ?T L/L:1- 97 7 cz. 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THE CITY OF HOPKINS , MINNES01 HENNEPIN COUNTY SCALE 800' 0 BOO BM 1 la • • 7i • M Toorrr IL/ c40.0. ST. 1600' 9--Aviset hopkrns hihIi9 Heavy rcth'Ls cause iirokLevvis This July's heavy and frequent rain- falls overwhelmed the city's sanitary and storm sewer systems. The rainfall amounts from the July 1 storm have been experienced only three other times this century. After the July 1 storm, the heavy rainfalls continued on already saturated soils, causing severe runoff and basement infiltration prob- lems for many residents. Several low areas in the city collected excessive rainwater, causing road clo- sures and flooding in yards, garages and basements. Residents in some areas of the city also experienced sanitary sewer backups. At a recent City Council meeting, the city's Public Works Department person- nel and the city's storm drainage con- sulting engineer defined problem areas and explained actions that are underway to minimize future problems. Possible problem One suspected problem is excessive groundwater infiltration into the sanitary sewer system. Groundwater enters the sanitary sewer system through leaking manholes and pipe joints and from improper pipe connections, including those on foundation drain systems, roof drains or sump pump discharges. The city checks for leaking manholes and pipes with . simple visual inspections and the video taping of the inside of sanitary sewer pipes. Manholes and pipes then are typically repaired or replaced separately or during street improvement projects. Improper pipe connections can be very difficult to locate. During periods of saturated soil and high groundwater levels, water flowing from an improper connection can overload a typical 8 inch sanitary sewer pipe. An overloaded sys- tem results in basement sewer backups in some areas of the city. City ordinances City ordinances prohibit anyone from discharging storm water, groundwater, roof runoff, yard drainage, or any water other than sanitary sewage into the sani- tary sewer collection system. Help and cooperation needed If you have an improper pipe connec- tion to the city's sanitary sewer system from such things as a foundation or roof drain or sump pump, please disconnect it immediately. A competent plumbing contractor can help you correct this situ- ation. By doing this, you help improve the reliability of the city's sanitary sewer service for all residents. Elimination of a single improper connection could have a tremendous positive impact on areas of the city susceptible to sanitary sewer backups. If you know of or suspect an improper connection, please report it to Hopkins Public Works, 939 -1382. The city soon will be taking steps to identify possible improper connections. If contacted by Public Works, please cooperate fully. Our only goal is to improve service to all Hopkins residents and businesses.