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HomeMy WebLinkAbout1991-11-20 Cloverdale Citizen Group Mtg (As Received 08-19-99)MEMORANDUM 8 119 1 9 q i)uL Schn-; Jpan-b5 (JuY paital ~-k-Prizt File No. 55100 ember 20, 1991 eeting with citizen group who are land owners around Cloverdale and McDonald Lake. The following is a summary of concerns, studies to be considered and suggested investigations and actions which were mentioned by the land owners present: a. Study alternative ways to get water to Cloverdale. b. What is possibility and ramifications of directing the runoff into McDonald Lake.-- 4 -■ C . Resident on Cloverdale wants outlet to McDonald if Clover& e reaches a certain elevation. Study the need to have such an overflow. d. Concerned about erosion control during coristruFtion of the school as well as any storm sewer down ravine's. e. Mr. Bischoff wants easement located further east as it leaves the school property which appears feasible. Concern with water quality and wanted information available on the use and function of wet storage, skimmers and any other quality enhancement features. '_g. Want to have testing of the lake water quality so that quality an be monitored. Would like analysis of various south and overflow elevations as it relates to downstream pipe construction depths & lower rates of runoff. 1. Major concern with construction activity, disruption of area destruction of trees, etc. for construction in the ravine. This is the main concern associated with Itpms a, b, and h above. j. One homeowner wanted storm sewer route investigation which would utilize lower land feature to the west of the easement route. k. oncern that Cloverdale is maintained at a level so that trees are not flooded and damaged. Someone asked about impact on local wells in the area. To: FROM: a S UB J CT: DA'T'E: B ARR ENGINEERING COMPANY ¥EMQRANUM All Concerned Parties Karen Chandler New Stillwater High School Site - Oak Park Heights November 27, 1991 Concerns were raised by Blackwood residents at a meeting in the y ood resi Novem Oak Park �elglits City Hall. Se Separate g ber 20, 1991 held p ate concerns were sent to the Watershed District trzet engineer from Paul Bischoff; those concerns are also Included, The concerns and responses nd the Watershed District en � ponces are listed below: 1. Is the an alternate drainage g route to Cloverdale Lake? Residents woul to see the gully and its trees avoided possible. d like . Response: The are man alternate e routes to Cloverdale Lake. However, e ,the chosen route follows existing g easements. A good choice for an alternate route would be one which follows existing gavels a shorter drainage easements and/or orter distance. A route which does not fall re wire the � ow existing drainage would project. It is the City q purchase of drainage easements, In the cost of the proje increasing ty of oak Park to determine �—�-- _ Y ,_�e�Iats�esp.�,��s�t� 2. can water be routed to Cloverdale Lake without going through the (the pond shared by the school site and Blackwood )? g south pond Response: Yes, but the south and ' P provides water quality treatment i an location. It also provides additional stormwater important er storage to slow dow flows. If the south pond is not used n s eel for s tornnwater s taro ffe oriel ware quality treatment, additional ponding r P g w � ouzel. be required no of the school site. The Watershed district is responsible • P bze for reviewing storznwater storage and water quality treatment options. P The Managers felt that it would be best to use the south pond for water uali q ty purposes. 3 • Connect McDonald Lake to Cloverdale Lake to control flood Cloverdale Lake ?). eleva on Hof Response: Any lowering f the g Cloverdale Lake overflow elevation will result in more water reaching McDonald Lake. Since McDonald Lake have an outlet this would result ' does not in an increase in the flood elevation of McDonald Lake. Therefore, such . a connection is not likely to be all unless there is an outlet constructed from McDonald Lake. 1 4. Minimize destruction in ravine when installing outlet tlet pipe, Response: The design and construction of the outlet i e is City P s the ��ty of Oak Park Heights' responsibility. However, it will require a Watershed District � atershed Dzstnct p and will be reviewed. Sediment and erosion controls and their effect on Cloverdale Lake water levels. sponse: Response: Response: 8. Keep Response: Response: Currently, runoff from the school construction site is not ' to leave the site for enter the south pond) until the City of Oak Park Heights g is constructs the south pond outlet. The advantage of this is sediment -laden water cannot reach Cloverdale Lake. The disadvantage of this is Cloverdale Lake is receiving about 25% less water, which could result in a lower water level on the lake. The School District and the contractor are concerned that the stormwater runoff generated from the j jl e Burin cons tru. oaa_ . 1 -ex_c ed_...t�e—s_t.orage and seepage capacity of the northwest ond. Therefore, they ' `ro :sin e � � ey will be p p g motive xnterz dra.lnage plans which may involve e to Cloverdale Lake. drainage A.n - interim drainage g y ge plans will require Watershed District approval. The Watershed District feels it is more important to keep the sediment -laden runoff out of Cloverdale Lake. If dro levels become a 'roblem, this decisi■ can be reviewe at .__x . - . .:r route change north of 53rd Street See response to concerns #1 and #4. Blackwood residents informed. water quality than on the water levels of Cloverdale Lake. 2 When will the Wat ,strict's stud of the effect of the y - ��.� SCh�o1 deyelopment on water levels be compleed? The study has been completed; the results will be summarized . rnmari�ed In a separate memorandum which will also be distributed. 7. Propose a route heading northeast to school ra e ` P P � to miss Baker property - The Watershed District will assist the City of Oak Park Heights eights and the School District in keeping the Blackwood residents informed. However, the ultimate responsibility lies with the City and the School tY a District. 9. Some residents are more concerned about the effect of the development on the The Watershed District is also concerned about water uali the Managers • q ty, which is why agers are requiring the application of Best Management quality to reduce the water i g q ty mpacts. For this project and future 10. Can discharge from south and be Tess than 10 cfs? fs? Response: As the outflow from the south and is reduced, used, the flood level of the south increases. ncreases. The 100 -year flood elevation for the south pond was set at Elevation 920.0 when the Blackwood 2nd and 3rd Additions received a Watershed District permit. One of the ermit conditions required P tons requxz~ed that the area sa ounding the pond be preserved in a drainage easement the minimum building elevation, g up to evation, which was set at 921.0. However, it appears that the 3rd Addition, which contains the south and has snot been platted. If this is true, the flood elevation for the south pond and, hence, the drainage easement, could be increased, causing g a reduction in the outflow rate from the south pond. An important point is that flows in the draina ewav will li g � to Cloverdale Lake be higher than the outflow rate from the south . Pond. This � s because the s tormwater runoff from the lake's direct tributary area will not flow through the south pond prior to discharge to the e lake° It is the �i 's res onsi�il�t.�� de�� _ e outlet° the -- - watershed District will review the design. �.�..�....�� -- (ii. / Can flav� °s? development to the north, Best Management Practices include � ude temporary and permanent erosion and sediment controls and the use of wet ' deten to the Metropolitan ton basins. According tropolitan Council, some water quality degradation may be unavoidable as a result of urbanization. Watershed management techniques (such as ponds and erosion controls) can artial1 offset only P y et these effects. n discharge levels be established: one for high flows and g d One for low Response: Yes but since the south and outflows are ��- pond already low, there may be no � advamag c ans t uctua s uc an sue ._ _.u� : 12, Will this project affect domestic wells? Response: Studies conducted as art of the EPA's Nationwide P a�onw�.de Urban Runoff Program concluded that there was no significant impact to infiltration P groundwater from basins (such as the south pond). The EPA's . cnteria for infiltration basins specifies that a minimum distance of two to four feet separate the bottom of the basin from the water table. Therefore, Oak Park efare, the City ark Heights should determine the - to the depth- water prior to construction of the outlet pip P er table pe 3 13. The Blackwood residents want long-term water quality monitoring, q arty rnon�torzng, Response: The Watershed District has a water quality . q y nnonztorzng plan in place. Cloverdale Lake (and possibly McDonald Lake) could be incorporated plan. The lake(s) � ed into the p (s) would be monitored every three or five Y ears. 14. Can the outlet pipe from the south and be placed further west? p p urther west . Response: See response to concerns #1 and #4. 15. Nitrogen and phosphorus levels are a concern of the Blackwood residents. Response: In terms of lake water quality, hos horus levels Y p p eIs are of more concern than nitrogen levels. If nitrogen levels in Cloverdale Lake increase, an increase in algae growth is not likely. However, if phosphorus levels P evels increase, an i increase in algae growth is likely. Also see response t p to concern #9. 16. The Blackwood residents are concerned about setting lake levels so high that mature trees are destroyed. Response: The flood levels of Cloverdale and McDon ►� aid Lakes were set based on ultimate development of the watershed. Ultimate development was determined based on available land use lans. The development site consistent oprx�ent of the school s to is consistent with those land use plans. Thereforr rn nt will not result in flood levels higher than those cop ut d. g ose previously The flood levels of Cloverdale and/or McDonald Lakes c an not be lowered unless there . .is.._an Qut�et cstrv.cted foze .�..� ..w.....w ...�.._. r__... .. _. _. ... M..._..___.. N on ..�.. ..,.__.. _.,r . , McDonald Lake. An important note is that the 908 flood elevation set for • Cloverd�,le Lake is an estate of the overflow elevation. To determa.ine the exact overflow . ow elevation, it will have to be surveyed. This could be done at the time of construction. 17. Has an Environmental Assessment Worksheet been • prepared for the project? Response: According to the information provided on the . P Watershed District's permit application form, an environmental assessment an (either E.A.W. or an E.I.S,) was prepared in May of this ear. The Watershed District ed D�stnct has not received a copy of the document, so it has not been reviewed. ed. Either the School District or the City should provide the Watershed District with a -� copy of the document. 18. How much water will be reaching Cloverdale g Lake as a result of development? Re •onse: The Watershed District's study of the effect ffect of development on water levels a.nswers the_ .quest .on regarding olume of water. er. eptio 0 4 ;A. tie 6* "' 4J 19. What can Cloverdale Lake and the adjoining marsh handle? Response: In terms of runoff volume, there is a certain amount of storage capacity g P ty available in the combined lake and marsh before it overflows into McDonald Lake. Again, this is addressed in the Watershed District's study. 20. Could the outlet from the south pond be raised ten feet to avoid destroying the gully? � g Response: If the outlet from the south pond was raised ten feet, there would be very little storage available for the reduction of the pond outflow rates, assuming the same flood elevation of 920 is to be maintained. If the same size outlet was installed as is currently planned but ten feet higher, the g q flood elevation would increase between five and ten feet. See also the responses to concerns #1, #4, and #10. 21. Will the on -site ponding provide storage or will flows just be passed through? / P g Response: The o ■ ' • • I ite and a� ro . to_...the. north (1 be ,,�,,,e,,.:,; roves .'.eszYx�e �arav '•rekary:.. Fc.aeFri = M constructed at the time of devl iu rovide r st r , ■ a the rat e of � n — �� enou � - . a _ .�.e �th at runoff from e s •�, existin ,-� ... .... ..�...�. y..;..v > �c�. �,. ..^ =�� �1 �� w SA.1�ae�an ...��ay : "!.?s rate of runoff. ._._. �...�� ��: 22. Of what use are skimmers? Response: Skimmers trap floatable materials (oil, grease, styrofoam, etc.) to prevent . them from being transported downstream. Sump manholes P rov sedimentation and act as skimmers.