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79-04 - Fox Chase PUD pt 13POTENTIAL IMPACT ON LOTUS LAKE FROM PROPOSED FOX CHASE STORM WATER RETENTION SYSTEM Prepared by: INSTRUMENTAL RESEARCH, INC. 7813 Madison St. NE Minneapolis, MN 55432 ��I /I f J / Attest: jj iz �,.._ " ` Delman R. Hogen, President CITY OF CHANHASSEN RE--CE1f AI I(;1 91981 C,041 , UNITY DEVELDF MENT DEPT. Date: August 12, 1981 The existing situation in the area east of Pleasant View Road is such that it is now acting as a buffer between the watershed to the south, east, and to the north of the development frontage. The soils are heavy enough to hold their vegetation under heavy rain and runoff load without the production of washout areas. The grass which is presently on these slopes is slowing the nutrients which wash down from the watershed above and probably holding most of them before they impact the marsh, area. The opening of this area will remove this buffer zone and make the reed canary marsh the primary buffer for the watershed. The placement of the temporary holding pond in the marsh will subsequently move the primary impact zone down to the cattail marsh as the reed canary marsh will cease to exist as an ecological entity and will probably not return to its former 'functional capability after the development period as a considerable amount of silt will be deposited over the vegetation. The value of a marsh as a nutrient holding area is based on a number of ecological parameters. The first, is that of the vegetation utilizing the nutrients which come down with the water flow to maintain a standing crop -of biomass which ties up both the major nutrients - phosphorus, nitrogen, and carbonf but also the other chemicals which are required for plant growth. The second, is. the slow decay rate of the vegetation from prior years which allows the area to build up a reservoir of plant nutrients and hold them back from the lake. The third, is the slowing of the water flow, thus reducing the kinetic ene,rgy of the water and allowing the soil particles to settle out prior to reaching'the lake. The effect is like that of a snow fence. Of the major nutrients which are imported to a lake system, the most important are: carbon, nitrogen, and phosphorus. Carbon is freely available from the air as carbon dioxide and from the lake as bicarbonate, so it is of no real concern in a run- off condition. In a clean lake the input of nitrogen compounds as nitrate, nitrite, or ammonia is critical. The only known method of preventing these compounds from reaching a lake is to tie them up in the vegetation of the watershed. This includes the upland grasses as well - as the vegetation in the marshlands. In a lake like Lotus Lake, this condition is not as clear cut because the lake presently has a large population of bluegreen algae. Certain members of this population are capable of fixing their own nitrogen from the air, and so the input of nitrogen compounds, assuming that the lake is intended to remain. in its present state, is probably not critical. However, if there is to be a clean-up program for this lake in the future, the added input of the nitrogen compounds becomes an important parameter. The third major chemical nutrient is phosphorus. It is the only major nutrient over which we have some,control because it readily adsorbs, that is sticks, to soil particles, and couples up to compounds like calcium and iron which render it only slightly soluable in water. If the phosphorus compounds are to be managed, they must be prevented from reaching the lake. - 2 - once they are in the lake water, they are available to bacteria in the system which will free them to the system and make them available to the aquatic plants as a nutrient. The easiest and least expensive method of control of the phos- phorus compounds is to tie them up in the vegetation of the water- shed and prevent their movement. In a natural system, an equilib- rium is established and the movement of nutrients to a lake is a long slow process. In an urbanized area this movement is very rapid due to the street storm sewers, vegetation changes, and human activities. Urbanization generally doubles the nutrient loading rate to a lake. The top half of the watershed in the area flowing through the Fox Chase development is already urbanized and it is only the meadow and marsh which are protecting the lake at the present time. The development of the meadow will remove the first buffer and the entire load will run into the reed canary marsh with the remainder being taken up in the cattail marsh. These systems are capable of holding a finite amount of nutrients and an overload of the system will cause -the excess to flow into the lake. Future considerations will require that the marshlands be managed to allow them to function as nutrient holding systems. It is my personal belief that the design of a development should be such that a minimum of water will flow from the individual - 3 - homesites. This will significantly reduce the movement of nutrients to the bottom of the watershed, which is usually a lake. It will also reduce the size of the required stormwater system and the required number of holding ponds needed to effectively reduce the flow of nutrients to the lake. The information which was developed from the site is based on the phosphorus loading only. The samples were taken from the soils — in the watershed, the two types of marshland, and from the lake. The sample data only address the loading of the soil or detritus (Partially decayed vegetation from previous seasons) and do not account for the nutrients presently tied up in the vegetation. The samples were taken at the surface of the systems and so the loading of the cattail marsh appears to be lower than the reed canary marsh. Cattails are more efficient users of the available nutrients and so the soil load is less:in this type of vegetation. The soil loading data is presented from the top of the water shed to the lake and presently shows an increasing load per unit of dry weight soil. one sample was taken from a small sedimentation pocket at the intersection of Ridge Road and Pleasant View Road to show the loading of stormwater runoff. The information following is based on the analysis of the marsh- lands and the lake water. To address it to the whole lake system, some assumptions were made based on D.N.R. data concerning Lotus Lake in terms of area and volume. See the attached data sheets. After looking at the site, the planned controls for storm runoff, and some of the soil loading values, it is my opinion that the storm water controls should be placed back from the wetlands and that the design of the outflow make the best use of all the available wetland for nutrient control. The permanent facility should be upgraded from an orifice to a five-day settling pond for the ten year storm. There is sufficient data available to substantiate this retention period. The ten year storm is men- tioned as it is the present criteria for Chanhassen's designs. The overflow from the pond to exceed the ten year storm should be by perforated cap to the capacity of the pond and then spread. out over the marsh to make the best use of the available marshland. - 5 - I Soils Loading Data 1. Site: The top of Pleasant View Road on the south side of the watershed. The sample was taken from the east side of the road, 19 mg (P)A9 of dried soil 2. Site: Pleasant View Road midway down to the blacktop spill -over area. The sample was taken from the east side of the road. 32 mg (P)A9 of dried soil 3. Site: Bottom of the steep slope on the dirt road at the bottom of the meadow. 41 mg (P)Ag of dried soil 4. Site: Taken from the edge of the boring site near the edge of the meadow close to the marsh edge. 37 mg (P)A9 of dried soil 5. Site: Outer edge of the reed canary marsh. This material was taken from the wet detritus in the marsh. 151 mg (P)A9 of dried detritus 6. Site: Cattail marsh 55 mg (P)Ag of dried detritus n 7. Site: Lotus Lake, at the existing boat launch site. .0851 mg (P)/liter water Other Sites 1. Site: Corner of Ridge Road and Pleasant View Road. The sample was taken from sediment laid down from runoff water. 66 mg (P)Ag of dried soil 2. Site: Steep slope in the proposed development area. The angle of the slope is estimated at between 35 degrees and 45 degrees from the horizontal. 50 mg ( P) Ag of dried soil Lake area 241 acres Lake volume 5080 acre feet Lake volume 6.25 x 109 liters Average depth 20 feet Wetland area 13 acres Wetland depth 3 feet (assumed) Wetland volume 39 acre feet (assumed) Wetland volume 4.80 x 107 liters (assumed) Lake phosphorus load (assuming equal concentrations from the surface to the bottom) .0851 mg (P)/liter Chlorophyll a concentration in the surface waters 64 mg/cu meter Wet weight phosphorus loading in the cattail marsh 21.83 mg (P)Ag Present Total Phosphorus in the marshland 1048 kg (wet weight) Present Total Phosphorus in the lake 532 kg 1.5 acre of marsh = 11.5/ of available marshland = 121 kg of phosphorus = 22.7% of the total phosphorus in the lake = 7.7/ of the total phosphorus in wet basin, excluding the sediment loads presently tied up in the lake bottom. These numbers do not include the living biomass except for the algae in the lake sample. The method used- for the determination of phosphorus is the persulfate digestion and ascorbic acid detection of total phosphorus from Standard Methods for the Examination of Water and Wastewater', 14th edition. The samples were mixed completely and wet samples were analyzed. A sample was weighed at the same time, dried and weighed again to determine the water content. West Pleasant View Road Association August 18, 1981 Mr. Don Ashworth City Manager City of Chanhassen 690 Coulter Drive Chanhassen, MN 55317 Dear Don: Enclosed are the two reports by Mateffy Engineering and Instrumental Research, Inc. These were submitted to the Corps of Engineers at the public hearing. I know you receive lots of reports, but I would appreciate if you and your staff could read these over. I learned a tremendous amount on wetlands at the meeting. I am sending copies to key people on your staff that are listed below. Thanks a million. Sincetely, Frank Beddor, Jr. FB:mmb enclosures cL Bob Waibel BIT1 Monk Scott Martin Russ Larson Craig Mertz CITY CP CHANHASSEiN ; CEIVEF _A11rr 1 91981 F"C'M UNITY DEVELONVIENT DEPT. 117-rl Put �74 Cob Freshwater Society 2500 Shadywood Road, Box 90 Navarre, Minnesota 55392 (612) 471-8407 July 7, 1981 Georgette Sosin Lotus Lake Association 7400 Chanhassen Road Chanhassen, Minnesota 55317 Letter of Concern to the Chanhassen City Council: Thank you for the opportunity of addressing the water quality concerns of the Lotus Lake area. ave inc UILled a copy of our ore ine Fell being mailed next we .!Ie in e a e Minnetonka area. Thousands more will be distributed throughout the state by various Lake Associations. The theme of the Shoreline Brochure is that the last place to manage a lake is in the lake. Proper land management is crucial to maintaining and preserving water'quality. Biologist Del Hogen has stated to the Chanhassen City Council that their primary task is to preserve the wetlands in their area. These wetlands will be crucial for providing nutrient adsorption and control of non -point pollution from the developed areas already in existence. The use of wetlands for nutrient abatement near present deveropmentis one of the 'keys to maintaining the water quality of Lotus Lake. Future development must be,weighed against its impact on the surrounding watershed. After all, the value of lake property is directly tied to the quality of water in that lake. Any development which destroys wetland acreage lessens your line of defense against erosion and the runoff of phosphorus, nitrogen, and other various chemicals and metals which eminate from developed areas. Wetlands not only act as a filtering system for various pollutants but they help hold water periods of heavy rain thus minimizing the affects of storms and flooding. Water resources hold an inherent value for everyone. Some people value water for its fish and wildlife, some people value its irrigation potential, its r Membership Organization of the Freshwater Biological Research Foundation Membership contributions are tax-deductible. 50a industrial cooling potential, its aesthetic and recreational purposes and everyone needs .safe water to drink. Very often these uses come into play in the same resource and the challenge is balancing those uses so society is best served and the natural balance is preserved. The question is — "How do we learn to live in harmony with a resource we desperately need to use'. _`There are many interests in the. Lotus Lake area which need to be considered in deciding how'the lake should be used now and in the. future. It`s impossible to please everyone, but with sound management practices and the basic understanding of the.lake's ecology,' your chances of maintaining \ the water quality of Lotus Lake -are very good. And clean water is a benefit to us all. Sincerely, Christine Olsenius Coordinator CO/gm August 7, 1981 1352 Raymond Avenue St. Paul, Minnesota 55108 Col. William W. Badger c/o Corps of Engineers Commander and District Engineer St. Paul District 1135 U.S. Post Office and Custom House St. Paul, -Minnesota 55101 Attention: Reg. Functions Branch T. M. Fell Dear Sir: Attached is a copy of the statement for record regarding Notice of Public Hearing Proposed Sedimentation Basin - Lotus Lake, Carver County, Minnesota. This statement was made at the Public Hearing, August 5, 1981 at Chanhassen City Hall. The material is respectfully submitted for decision making on this matter. Assembled information is presented describing potential effects on the Type II wetl.a.nd and adjacent environs on the extreme northwestern bav of Lotus Lake. Sincerely, Grady E. Mann GEM: jn Attach STATEMENT FOR RECORD ON LOTUS LAKE, CARVER COUNTY PUBLIC HEARING AUGUST 5, 1981 As background, my name is GRADY E. MANN, 1352 Raymond Avenue, St. Paul, Minnesota 55108. Personal experience in the wet- lands field spans better than 25 years with the U.S. Fish and Wildlife Service. With that organization I worked on wetland inventory, research, preservation, management and administra- tion in many parts of the Upper Midwest. Most of my field work has.been in Minnesota, Wisconsin, Michigan, Iowa and the two Dakotas. Since 1972 I have served as a private wetland consultant for the Minnesota Department of Natural Resources on several projects, completing the last major statewide pro- ject for their Bureau of Planning and Research in 1978-79. In 1974, I completed a major seven -month project with the Province of Saskatchewan Department of Environment. This Saskatchewan wetland policy project covered some 120,000 square miles in the developed area of Saskatchewan where millions of small wet- lands are located. Up to the present, many other projects have been completed -- all in the field of wetland preservation and management. My full report on hydrological and land use aspects is now sub- mitted to Mr. Fell. There is no need to take up valuable time on that, except to say that this report ranged over several case examples on wetland economics, wetland nutrient entrapment, de- struction of wetland nutrient functions, and appeals for preserva- tion of wetlands,.plus many others. Many of the technical water chemistry and biological points were well documented and described by Mr. Del Hogan tonight. -1- Purposely, wildlife aspects were omitted from this previously. submitted twenty-three page report. Those aspects will be briefly covered here. This presentation boils down to the use of Type II wetlands by wildlife in this part of Minnesota. For factual material I will rely on a 1978-79 report titled: KNOWN USES OF 8 WETLAND TYPES BY VARIOUS WILDLIFE SPECIES IN MINNESOTA Specifically, this is REPORT 2 resulting from a 1978 MINNE80TA STATEWIDE WETLANDS - WILDLIFE FIELD STUDY, written by myself, and prepared for the Bureau of Planning and Research, Minnesota Department of Natural Resources, St. Paul, Minnesota.. Information for REPORT 2 resulted from statewide field inter- views with Minnesota Department of Natural Resource wildlife field managers, researchers, and administrators. Those inter- viewed, when we totalled it, had a background of better than 1,000 cumulative man-years of training and field experience in wetland preservation, management, research and wildlife adminis- tration. Those selected for interview were authorities on specific wildlife species. Many were recognized as international authorities. With this background, now to the Type II wetland on the north- western bay of Lotus Lake. Of all the wildlife species covered on the 1978-79 Minnesota DNR project, I'll include only three for this discussion tonight. Ranges of the pheasant, white-tailed deer, and some of the ducks overlapped onto this location in Carver County. FOR THE WHITE-TAILED DEER: In the statewide project, for deer, we separated discussion into two broad zones -- the FARMLAND GAME ZONE, and the woodland area of the north. For the discussion tonight, I'll rely on those uses by deer of Type II wetlands with- in the FARMLAND GAME ZONE. 50M I Known Uses of Type II wetlands by white-tailed deer: 1. Provide essential spring green -up areas for necessary nutrient requirements. 2. Later in the season, if dry, provide excellent fawning locations. 3. Provide summer and fall feeding locations. NOW, TO PHEASANTS. A close look at past and current ranges of this species proved an interesting study in itself. A 1978 map (Fig. 6 in Report 2) showed the heaviest pheasant density in Minnesota now to be in Carver, southwestern Hennepin, western Scott and LeSueur counties. This represents a complete shift in pheasant density from 1961, when traditional high density pheasant populations were known to be in southwestern and west -central Minnesota. This change, a shift to the east, was largely due to past de- struction of wetlands and major changes in land use both in southern and west -central Minnesota. Now to PHEASANT USE OF TYPE II WETLANDS. The report mentioned that pheasant use was applied to that type of wetland, usually soggy, which could have standing water for short periods after heavy runoff. Vegetative cover was more permanent than for Type I wetlands. Known uses by pheasants of Type II wetlands as listed were: 1. During dry years provide highly preferred nesting sites within and on edges. 2. Serve as winter cover in east -central region. Used for a longer period than same wetland type in south- western Minnesota because of reduced wind action and slower buildup of snow. Furnish winter cover for 600 of the time in east -central region. 3. Provide high quality escape cover during fall. -3- 4. Provide highly preferred nesting sites if dry and undisturbed. 5. Furnish feeding locations if wet or dry and un- disturbed. 6. Increase roosting site possibilities if dry and undisturbed. 7. Provide escape cover if dry and undisturbed. NOW TO WATERFOWL USES OF TYPE II WETLANDS. Wood ducks represent a primary species for this part of Carver County but others fre- quent the general locale. Report 2 had this special note on Type II wetlands for the waterfowl discussion -- "Provide essentially same uses as Type I wetlands but only after heavy snow melts and rains leave standing surface water above soggy meadow depressions". With that specific reference waterfowl uses listed were as follows: 1. Provide spring migration stopover points. 2. Provide spring migration feeding sites as these shallow areas warm early. 3. Distribute breeding pairs over the landscape in early spring or early summer. 4. Furnish seasonal feeding sites when reflooded in mid - season. 5. Provide nesting sites in the basin bottom when dry, undisturbed and not reflooded. 6. Enhance the overall wetland complex helping that complex attract migrating ducks to a given waterfowl zone. 7... Furnish part of the dynamic mosiac of wetlands essential to production of invertebrate foods for breeding pairs. NON -GAME SPECIES were touched on briefly in the 1978-79 report. But, perhaps, these represent one of the most important aspects for the Type II wetland on Lotus Lake. Non -game species depend heavily on wetlands as do many of the game species of Minnesota. As one ISOLATED example REPORT 2 listed known uses by colonial -4- nesting birds of eight wetland types. Information came from statewide investigations by Carroll Henderson, DNR non -game specialist. Type II wetlands provide important feeding grounds for the great blue heron, cattle egret, black -crowned night heron, and yellow - crowned night heron. These wildlife points on use of Type II wetlands are.respect- fully submitted. GEM: jn Grady E. Mann -5- Corps of Engineers Page Nine O, ...The important point is not the absolute value of a particular wetland for one or More .functional characteristics; but that all wetlands possess some value for one or more of a variety of important functional characteristics. Such value is irregardless of wetland type or size. Although a particular wetland alteration may constitute only a minor change, the cumulative effect of numerous such piecemeal changes often results in a major impairment of the wetland resource. And from the University of Minnesota, we heard concerns frorr Dr, 14ilton W. Weller., the Chairman of the Department of Entomology, Fisheries, and Wildlife: "Lotus Lake rests in a deep basin with steep sides with considerable potential for inputs of silt, fertilizer, and other pollutants. For such a deep lake, the water quality looks marginal now, and information on turbidity, causes of turbidity (such as silt, organic debris, algae, etc.), and Nitrogen and Phosphorous levels of the lake should be recorded. To enhance wildlife values of the area, everything poss' e should be done to preserve natural emergent vegetation a onQ the shoreline as well as in all shallow, marshy bays. These also help st s - ine erosion whi often it responsib e f muddy shallows an murky waters, ore importantly, such marsh edges help to strain out silt and organic debris washed in by heavy rains, and they take up and store excess nutrients common in fertilizers. Such nutrients in excess feed dense algal blooms." "...If major housing developments occur, ideally they should have man-made settling, basins in the uplans especially designed for silt catching as a first step in s eries of water -purification processes. The natural wetlands then will clean up the nutrient load. This system would be much more efficient, would not destroy the esthetic and hydrologic values of the natural wetlands, and could be used in a pleasant setting within a housing development.41 Corps of Engineers Page Ten And finally the Field Office supervi �g t .S.y, Fish and wildlife Service sent us an opinion. Richard F. Berry's report follows: ,J The U.S. Fish and Wildlife Service has been approached by the Lotus Lake Homeowner's Association and the West Pleasant View Road Association concerning proposed construction activities and their effects on wetlands associated with Lotus Lake and the lake's water quality. The two citizens' groups were particularly concerned with: 1 . Derrick Land Company'_s proposed_ housing,_developmen-t, and the associated placement of a sedimentation basin in wetlands, The effect -of these _projects, and others, on wetlands and Lotus Lake_'s water quality would be variable, and would depend on~the-extent of each project's-disruption of existing land features. The greater the disturbance to the existing natural areas,.thegreaterVthee_possibility of adverse environmental effects on Lotus Lake_and its associated wetlands. The wetlands of concern in the proposed project areas are dominated by sedges, rushes, cattail, reed canarygrass, willows and submergent or floating -leaved aquatic plants such as pondweed, duckweed, waterlilies, and the American lotus. These areas were formerly referred to as Type 2, 3, and 4 wetlands. 'the wetlands assoc iate__cLwJJ;b.. the--northern--end, of Lotus Lake are the last of_.the_,wetlands_ad acent to the lake that i have not -been_ dra_ined,or,filled.• They provide for floodwater storage, i',filtration of nutrients and sediment from runoff and provide breeding,, feeding, and resting habitat for waterfowl, songbirds, and furbearers. 's They also provide spawning areas for fish species resident in Lotus 1 Lake. Lotus Lake itself contributes greatly to the biological produc- tivity, recreational and aesthetic quality and land values of the area. ' i In reference to the Chanhassen Comprehensive Plan study now underway, Mr. Berry made this comment. "We support the Commission's efforts and goals regarding conservation of natural features, and believe that such a plan should be a major part of every city's planning for projects similar to those at issue here." In conclusion, we simply want to express our concerns based on the limited education we've received from experts in the area of freshwater preservation. The quality of life that we all share as residents of ,j POTENTIAL IMPACT ON LOTUS LAKE FROM PROPOSED FOX CHASE STORM WATER RETENTION SYSTEM Prepared by: INSTRUMENTAL RESEARCH, INC. 7813 Madison St. NE Minneapolis, MN 55432 r' ,, Attest: ; f�T` -�- ,'l , / ' ti Delman R. Hogen, President Date: August 12, 1981 The existing situation in the area east of Pleasant View Road is such that it is now acting as a buffer between the watershed to the south, east, and to the north of the development frontage. The soils are heavy enough to hold their vegetation under heavy rain and runoff load without the production of washout areas. The grass which is presently on these slopes is slowing the nutrients which wash down from the watershed above and probably holding most of them before they impact the marsh area. The opening of this area will remove this buffer zone and make the reed canary marsh the primary buffer for the watershed. The placement of the temporary holding pond in the marsh will subsequently move the primary impact zone down to the cattail marsh as the reed canary marsh will cease to exist as an ecological entity and will probably not return to its former functional -capability after the development period as a considerable amount of silt will be deposited over the vegetation. The value of a marsh as a nutrient holding area is based on a number of ecological parameters. The first, is that of the vegetation utilizing the nutrients which come down with the water flow to maintain a standing crop of biomass which ties up both the major nutrients - phosphorus, nitrogen, and carbon; but also the other chemicals which are required for plant growth. The second, is. the slow decay rate of the vegetation from prior years which allows the area to build up a reservoir of plant nutrients and hold them back from the lake. The third, is the slowing of the water flow, thus reducing the kinetic energy of the water and allowing the soil particles to settle out prior to reaching the lake. The effect is like that of a snow fence. Of the major nutrients which are imported to a lake system, the most important are: carbon, nitrogen, and phosphorus. Carbon is freely available from the air as carbon dioxide and from the lake as bicarbonate, so it is of no real concern in a run- off condition. In a clean lake the input of nitrogen compounds as nitrate, nitrite, or ammonia is critical. The only known method of preventing these compounds from reaching a lake is to tie them up in the vegetation of the watershed. This includes the upland grasses as well - as the vegetation in the marshlands. In a lake like Lotus Lake, this condition is not as clear cut because the lake presently has a large population of bluegreen algae. Certain members. of this population are capable of fixing their own nitrogen from the air, and so the input of nitrogen compounds, assuming that the lake is intended to remain in its present state, is probably not critical. However, if there is to be a clean-up program for this lake in the future, the added input of the nitrogen compounds becomes an important parameter. The third major chemical nutrient is phosphorus. It is the only major nutrient over which we have some control because it readily adsorbs, that is sticks, to soil particles, and couples up to compounds like calcium and iron which render it only slightly soluable in water. If the phosphorus compounds are to be managed, they must be prevented from reaching the lake. - 2 - once they are in the lake water, they are `•available to bacteria in the system which will free them to the system and make them available to the aquatic plants as a nutrient. The easiest and least expensive method of control of the phos- phorus compounds is to tie them up in the vegetation of the water- shed and prevent their movement. In a natural system, an equilib- rium is established and the movement of nutrients to a lake is a long slow process. In an urbanized area this movement is very rapid due to the street storm sewers, vegetation changes, and human activities. Urbanization generally doubles the nutrient loading rate to a lake. , The top half of the watershed in the area flowing through the Fox Chase development is already urbanized and it is only the meadow and marsh which are protecting the lake at the present time. The development of the meadow will remove the first buffer and the entire load will run into the reed canary marsh with the remainder being taken up in the cattail marsh. These systems are capable of holding a finite amount of nutrients and an overload of the system will cause the excess to flow into the lake. Future considerations will require that the marshlands be managed to allow them to function as nutrient holding systems. It is my personal belief that the design of a development should be such that a minimum of water will flow from the individual - 3 - homesites. This will significantly reduce the movement of nutrients to the bottom of the watershed, which is usually a lake. It will also reduce the size of the required stormwater system and the required number of holding ponds needed to effectively reduce the flow of nutrients to the lake. The information which was developed from the site is based on the phosphorus loading only. The samples were taken from the soils in the watershed, the two types of marshland, and from the lake. The sample data only address the loading of the soil or detritus (Partially decayed vegetation from previous seasons) and do not account for the nutrients presently tied up in the vegetation. The samples were taken at the surface of the systems and so the loading of the cattail marsh appears to be lower than the reed canary marsh. Cattails are more efficient users of the available nutrients and so the soil load is less:in this type of vegetation. The soil loading data is presented from the top of the water shed to the lake and presently shows an increasing load per unit of dry weight soil. one sample was taken from a small sedimentation pocket at the intersection of Ridge Road and Pleasant View Road to show the loading of stormwater runoff. The information following is based on the analysis of the marsh- lands and the lake water. To address it to the whole lake system, some assumptions were made based on D.N.R. data concerning Lotus Lake in terms of area and volume. See the attached data sheets. u After looking at the site, the planned controls for storm runoff, and some of the soil loading values, it is my opinion that the storm water controls should be placed back from the wetlands and that the design of the outflow make the best use of all the available wetland for nutrient control. The permanent facility should be upgraded from an orifice to a five-day settling pond for the ten year storm. There is sufficient data available to substantiate this retention period. The ten year storm is men- tioned as it is the present criteria for Chanhassen's designs. The overflow from the pond to exceed the ten year storm should be by perforated cap to the capacity of the pond and then spread out over the marsh to make the best use of the available marshland. - 5 - Soils foadinq Data 1. Site: The top of Pleasant View Road on the south side of the watershed. The sample was taken from the east side of the road. 19 mg (P)A9 of dried soil 2. Site: Pleasant View Road midway down to the blacktop spill -over area. The sample was taken from the east side of the road. 32 mg (P)A9 of dried soil 3. Site: Bottom of the steep slope on the dirt road at the bottom of the meadow. 41 mg (P)Ag of dried soil 4. Site: Taken from the edge of the boring site near the edge of the meadow close to the marsh edge. 37 mg (P)A9 of dried soil 5. Site: Outer edge of the reed canary marsh. This material was taken -from the wet detritus in the marsh. 151 mg (P)A9 of dried detritus 6. Site: Cattail marsh 55 mg (P)Ag of dried detritus a 7. Site: Lotus Lake, at the existing boat launch site. .0851 mg (P)/liter water Other Sites 1. Site: Corner of Ridge Road and Pleasant View Road. The sample was taken from sediment laid down from runoff water. 66 mg (P)/kg of dried soil 2. Site: Steep slope in the proposed development area. The angle of the slope is estimated at between 35 degrees and 45 degrees from the horizontal. 50 mg (P)/kg of dried soil Lake area 241 acres Lake volume 5080 acre feet Lake volume 6.25 x 109 liters Average depth 20 feet Wetland area 13 acres Wetland depth 3 feet (assumed) Wetland volume 39 acre feet (assumed) Wetland volume 4.80 x 107 liters (assumed) Lake phosphorus load (assuming equal concentrations from the surface to the bottom) .0851 mg (P)/liter Chlorophyll a concentration in the surface waters 64 mg/cu meter Wet weight phosphorus loading in the cattail marsh 21.83 mg (P)/kg . Present Total Phosphorus in the marshland 1048 kg (wet weight) Present Total Phosphorus in the lake 532 kg 1.5 acre of marsh = 11.5/ of available marshland 121 kg of phosphorus = 22.7/.of the total phosphorus in the lake = 7.7/ of the total phosphorus in wet basin, excluding the sediment loads presently tied up in the lake bottom. These numbers do not include the living biomass except for the algae in the lake sample. - The method used for the determination of phosphorus is the p ersulfate digestion and ascorbic acid detection of total phosphorus from Standard Methods for the Examination of Water an'd Wastewater• 14th edition. The samples were mixed completely and wet samples were analyzed. A sample was weighed at the same time, dried and weighed again to determine the water content. REPORT ON FAX CHASE DEVELOPMENT CHANHAS EN , INNESOTA AUGUST 3, 1981 PREPARED BY 119 mateffy engineering &A000ctateo, Inc. ARCHITECTS ENGINEERS PLANNERS 842 5TH AVE. N.W. NEW BRIGHTON, MINNESOTA REPORT ON FOX CHASE DEVELOPMENT LOCIATED IN CITY OF CHANHASSEN, MINNESOTA I here;--certj--L'--v that' this Report was prepared by me- or under my direct supervision and that I am a duly Registered Professional -Eng-iveer under the laws of the State of Minnesota. LESLIE H. MA-=FFY, P 'IF August 3, 1981 . 9726 DATE REG. NO. August 3, 1981 14501 STEVEN W. THATCHER, P.E. DATE -REG. NO. August 3, 1981 PAUL D. -,KROEH:%-'-PRT DATE el� August 3, 1981 ULDIS V. ERDMANIS DATE MATEFFY ENGINEERING & ASSOCIATES, INC. 842 Fifth Avenue Northwest New Brighton, Minnesota 55112 TABLE OF CONTENTS INTRODUCTION PROPOSED DEVELOPMENT TOTAL DRAINAGE AREA LOCATION OF NORMAL HIGH WATER LEVEL WATER RUNOFF WETLANDS SEDIMENTATION AND NUTRIENT CONTROL CONCLUSIONS PAGE 1 PAGE 1 PAGES 1 - 3 PAGE 3 PAGES 3 - 4 PAGE 4 PAGES 4 - 5 PAGE 5 INTRODUCTION On July 25, 1981 Mateffy Engineering & Associates, Inc. was employed by the West Pleasant View Road Association to review and provide comments on the information submitted by the Derrick Land Company on the proposed Fox Chase Development, located in Chanhassen, Minnesota. Our fin- dings are enclosed in the body of this report. PROPOSED DEVELOPMENT The Derrick Land Company, 1770 Shelard Tower, Minneapolis, Minnesota 55426 has proposed Fox Chase Development on the shores of Lotus Lake on all parts of Government Lots 5 and 6 in Section 1, Township 116 North, Range 23 West, Carver County, Minnesota, including Lots 1 and 11 "Vineland". The proposed Fox Chase Development, herein called the Development, consists of a 52 unit residential subdivision to be built in an area of hilly wooded terrain, gently slopping meadow, leading to wetlands and the northwest shores of Lotus Lake. Soils in the area range from sandy clay to silty clay with the lower elevations being covered with decomposed peat and other organic matter. TOTAL DRAINAGE AREA We reviewed the drainage plans as provided by Westwood Planning and Engineering Company, herein referred to as the 1 Developer's Engineer, an employee of the Derrick Land Company, herein referred to as the Developer and data sub- mitted in a July 9, 1981 letter to Mr. William Monk, P.E., Engineer for the City of Chanhassen, herein referred to as the City Engineer. Please see Appendix #1. The Developer's Engineer presented the following information under site data. Drainage Area On Site Graded/No Cover Meadow or Wooded Off Site Meadow or Wooded TOTAL 15.02 Acres 14.50 Acres 29.52 Acres 11.80 Acres 41.32 Acres Mateffy Engineering & Associates, Inc. (MEA) reviewed the topography as supplied by the Developer's Engineer and the existing U.S. Geological Survey (USGS) maps of the area and conducted a check on the topographic information with survey crews and on August 1st, 1981 conducted an on site verifi- cation of the limits of the drainage area during a rain storm. Our analysis showed that the on site drainage area is 27.6 acres and the off site drainage area is 32.90 acres, 6 giving a total drainage area for this basin of 60.5 acres. This figure is 46.4 percent in excess of that shown by the Developer's Engineer. See Drawing 1 of 1. LOCATION OF NORMAL HIGH WATER LEVEL The normal high water level has been determined by the Minnesota Department of Natural Resources (DNR) to be eleva- tion 896.3. The location of this elevation was verified in the field by our field engineers and is shown on Drawing 1 of 1. We noted that this elevation was staked by other per- sons unknown to us. The drawings submitted by the Developer show this 896.3 elevation to be in several locations, one being back from the lake and one being closer to the lake. The drawing showing the dike for the sedimentation basin has it located below the 896.3 elevation and provides further confusion. WATER RUNOFF We estimate that the runoff in a 100 year storm of 24 hour duration will be approximately 15.1 acre-feet, which greatly exceeds that shown by the Developer's Engineer. Please see Appendix #2. Upon construction completion the temporary holding ponds would be removed and the design criteria of a 10 year frequency storm adopted by the City of Chanhassen will yield 3.5 acre-feet. Please see Appendix #2. The 3 final design as submitted by the Developer's Engineer will provide for less than 1.8 acre-feet of storage. The reason that we cannot give an exact figure for the storage capacity of the design is the fact that the area of the detention pond is unclear and the exact and final elevation and loca- tion of the dike is totally unclear as stated above in our discussion of the normal high water level. WETLANDS Presently the existing development drains into 5.5 acres of wetlands. It is the intention of the Developer to eliminate 3.5 acres of wetlands by constructing a bermed sedimentation basin across the wetlands. This will cause the area upstream from the berm to be silted in and the area downstream from the berm will have a very limited effect on the quality of the water because of the channel flow that will exist. Ponding of rain water in the wetlands will release the stored nutrients into the water and transfer them to Lotus Lake via the channel flow method. We feel that the removal of 3.5 acres of wetlands, protecting Lotus Lake is definitely detrimental to the environment. SEDIMENTATION AND NUTRIENT CONTROL Considering the flow detention times that would be available in the proposed sedimentation basin most of the fine El nutrient laden sediments will not be collected in the basin, but will continue out into the lake. For adequate sediment and nutrient retention a detention time of 1 to 5 days is required depending upon the proposed mode of operation to remove the sediments. CONCLUSIONS A. The quantity and quality of runoff should be more accurately stated. We do not feel that this has been adequately done and as a result the hydraulic capacities of the proposed structures will not be adequate to pro- tect the lake. B. The wetlands in the present state are now protecting the lake. We feel that all of the wetlands should remain in service and to the extent possible the sediment free runoff should be evenly spread over the entire wetlands. C. The design should include more substantial sediment and nutrient removal before allowing the water to drain to the wetlands area. 5 A `eh'ESTWOOD PLANNING & EN GHNEERiNG CO.r.lPANY APPENDIX #1 July 9, 1981 Mr. William Nonk, P.E. City of Chanhassen 690 Caulto Drive Chanhassen, NN 55317 RE: Fox Chase Dear Mr. Monk: We are herein submitting the final details and design cumouta- tions for the sedimentation erosion control on the above p.•�ject. I have met several times with Mr. Justin Jeffery, Area Engineer, Soil Conservation Service; and believe that it has been aoreed that the final design meets or exceeds the S.C.S. standards for erosion/sedimentation control.. The following is a follow-up to Mr. Jeffery's memo of 2 July 1981, a copy of which is attached. Item I - We reconfirm that all runoff from a 24 hour, 100 year event can be stored on -site vith no disci:,arne (8.13 ac/ft runoff v.s. 12.4 ac/ft storacej, ;;t a meeting on 6 July 1981 v'ith I-Ir. Jeffery, we revie,jed the sedimentation outlet desion. The desitin was based uoo,t the S.C.S. recommended 5 day dr?wdouin. The final details and calculations for the cutlets are attacned. Item II The Developer concurs that sedimentation basic; 1 will be constructed prior to the site grading operation, and basins 2 and 3 will follow as gr-- ding progresses to such a stage that they can bo constructed. Item III - The lou area at location 4 is not included in storage calculations, but is available to reduce peal: di.schsrges during and subsequent to the site grading. Item IV - The diversion is intended to reduce the amount of runoff from offsite draining through the graded areas of the site. APPENDIX #1 -1- '415 WAYZATA 6OULEVAFD, M NNEAFOLIS. MINNESOTA 5542b (5t21 546CISS Mr. William Monl;, F.E. July 9, 1981 Page 2 Item U - The Owner is pursuing the recommendation that the Cunningham Pond be lowered. to allow for tem- porary storage of runoff from that area. Item UI - The design was based upon the sedimentation gen- eration for the highest 30 day period based upon S.C.S. data. If it appears that sedimentation accumulation is exceeding the design, the ponds will be cleaned out periodically to accommodate the design storm (24 hour - 1DO_year). item VII - It is proposed to stop the site grading a minimum of 100 feet from the property to minimize the probability of that occuring; and, as noted in the m mo, storm sewer will be extended to this area as soon as practical. ' Item VIII- The Developer concurs. Item IX - The Developer concurs. Item X - This was discussed at the.6 July 1981 meeting with Mr. ?effery and it is agreed that any ease- ment/perm;,itsretc. necessary would be acquired prior to using this area as a pondir;g area. this pond is not needed for the overall erosion control system. I trust that with the information transmitted that the City Council requireiment of S.C.S. review and approval will have been accomplished. If you have any further -questions, comments, or recommendations, please do not hesitate to call. Sincerely, 14E 0DP LA`: fJING e- >y i N E E R i N G COMPANY Deb s llarhUla,tP.E. DM:dg cc: Don Hera, S.C.S. Justin Jeffery, S.C.S. Tim Fell, Corps of Engineers J. Davidson, D.N.R. K. Laughinghouse APPENDIX #1 -2- ' VIE STF','pOJ PLANNIt:; s �a FNGlNFFfzf'4G COG'PANY 1[IS WAr.'I.IA UUUL C VA 1111. VINN f .kpj, rr'N 55�jp (P I;) 5al. .50� -mor e5�lg 0 0 0 C111-CKE n Hy I IA ff- SF 5l1T NC) e -, � �_,, :�z .Fa .4 r i APPENDIX #1 —3— i� QI COMPANY �N h��RINQ .iAA5WktVAk%4,UINN€ (llkMN.WAWbhla015b MADE BY.. ,- z.__ .-,..---DATE (', tIV KED BY . _... - _-- DATE CALCULATIONS FOR-- 5 jarci3/"' 04:� y lam' k) JOB NO. __ SEC SHT. NO ,gg 144- oie U-1 le r d� r APPENDIX #1 -4- t F t� 6 vo I ��tS 49s MADE A N N I N Cl b kNWNWIINU COMFANY CHECKED DY_ CALCULATIONS FOR AV a-4- n -DATE JOB NO - DA rE SEC ".HT NO ?- Alr 9 .Vl a *. 44;& 44-3, APPENDIX #1 —5— l l c;IJJiJ. f�1+-k•I�ii-'; t U. t ovA►rA'wr or AL[YU1'U11! s �+ SU+ LCs+itwwtkM itmvKA FL 1 e COL10 UNG- 1 _ LANZ, I .IE }\_,h III+{ AN AkKA.i Present or Future Haternhed S)te 5`i. � r��� I).A, f,<•rt•ti g�. �'( r" Computed by ��+�t�— Date'heQked ly Dhte +'u[•ve qumla:rs Acres Moisture Condit.on 11 A R C 1" 1XID USE UF;CRIl'T:v'. Fer !'ra^tice il:+ „)I la :U119 nnil:) Pro.1+;r•t --r 15•t'L- 1+ •' f#1 1 Cultivated Lund: w[th"ut cunaer•vntr�):: Lretreatmenttera with conservation treetir:ent ,' V: 71 .18 _7III Pasture .)r range land: p.»r condition t,ft .04 86 good eondition I y1 61 '74 bu i Meadow: good condition 2lo V 78 71 7H Hood or Fore:it land: thin stand, poor cover, n„ mulch 41) ir`. 17 KS Open Spaces, lawns, parks, golf courses, ceme- teries, etc. good condition: grass cover on ;5 or r.+ore of the area 'q 61 74 80 fair condition: grass cover on to 7i 59 of the area 4;1 60 '19 84 Conr)e:c.el and business areas (F5% -.mpervious) 89 192 94 95 lndustrral distripts (;2% impervious) fS1 88 91 yj I - �yy Reaider,tial: Aver•ege lot size Averse T imervious I I8 acre or leas E5 77 85 90 r32 114 acrq 38 83 8 i 15 acre iJ "..i 77 81 H6 i`2 acre 25 SJI -0 80 H5 1 acre 20 4 51 b8 79 84 Paved parking lots, roof's, driveways, etc. W3 t38 r48 48 Struots and r„adu: 1'nvcnl wl tlr urL:r nn+t :)r.,rtu nawr.['u ,I/ rtS 'rH "p, }rnve1 .0 81) Ho) ++1 dirt 71 82 f5't 81, Other 7 ? _711 Total Aorea � 3� Product ?'ctal w / w','trj.t+,d II+u�.:i 1:urve lit. �`�: - LO�?•..� _i�JL �ry�r . ,tai � r— a,tr: U I 1,� 1 k,q (I r -' .ZI ._t- r1 APPENDIX #1 —6— FIGURE 42 SOIL LOSS AND SEDIIti;ENT SOURCE EVALUATION Location ��_r�,n �Y Compiled by Downstream Condition J?� r�i,*.<, A4gK AREA : } S. oZ Ac.R f-; KR AND LS S. Area No. Wt'd K L R (Ft.) S i Expected Surface Conditions: Time of Exposure: H,) ; #4 a d 4 0 rT�c Area sketch not to scale 1 2 3 Sub- Condition or Area Treatment KR 4 LS 5 C 6 7 - 8 A' P R1 Tons/ac. 9 10 11 12 Area A, Delivery Vol. (Acs.) x- ,(tors)i Rate_ I(Ac-fil, ►NO C Er I �'�� I � d� _ ! �•2{a I iS.t�� � j'y Q C:' j�v,. i i I �— I I ( 1 l � I I I I I 1 l I i 77-1 I Total *A = KR (LS) C P f = Average soil loss for construction time M in tonslac. from Table 35 For Remarks see reverse side. APPENDIX #1 —7- 223 9c7 LFot.i- FLf 9)1 f t, Ll 2.5 C-11 7717W i S, L C) Ilb Ic 87 17' -21 7. Y 17 yr, 11 APPENDIX #1 —8— Ji C OT v T &T F LZ)ATE C)Z^ /0 JCZ) 6-7 Z cc,, , -+ f Eli 4L Z5, 10 0 APPENDIX #1 -9- vas, --- 47;et� -7L APPENDIX #2 )XI-5 , = APPENDIX #2 -1--