HomeMy WebLinkAbout12/19/2001 Env Bd PacketCity of Lino Lakes
Environmental Board Meeting
December 19, 2001
6:30 p.m.
AGENDA
1. CALL TO ORDER
2. APPROVAL OF MINUTES
3. APPROVAL OF AGENDA
4. OPEN MIKE
5. ACTION ITEMS
A. Pheasant Hills Preserve 12TH Addition
6. DISCUSSION ITEMS
A. NEMO /GTS /Mike Grochala
B. Peltier Island/Ordinance Update
C. WUI /Fire Risk Assessment/Milo Bennet
7. DEPARTMENT REPORTS
A. Forestry
B. Solid Waste Recycling
8. ADJOURN
AGENDA ITEM 5A
STAFF ORIGINATOR: Marty Asleson
DATE: December 19, 2001
TOPIC: Pheasant Hills Preserve 12th Addition, Preliminary Plat
BACKGROUND:
The Developer is asking for a PDO review and preliminary plat approval for a
development to be called Pheasant Hills Preserve 12th Addition. A site map is included
with this report. (Exhibit 2). The developer, Mr. Ed Vaughn, is proposing to build 7 Lots
on the site. Proposed access to Pheasant Hills Preserve 12 Addition is through the
construction of a bridge from the northern end of Rough Grouse Trail in the Quail Ridge
Development.
Pheasant Hills Preserve 12th Addition (The Wards Lake Island) was reviewed at the
September 25th Environmental Board Meeting. At that time, a proposed plat with
existing and proposed contour lines was reviewed by staff, and environmental issues in
relationship to this plat discussed in the report to the Environmental Board. The
Minnesota Department of Natural Resources also gave comment. Please refer to the
attached Environmental Board Greensheet from September. (Exhibit 1)
A short time after the Environmental Board Review, a different grading /preliminary plat
plan was received for consideration. The first plan should not have been reviewed.
A reduced new plan is included in the packet. The new plan shows the house sites
without fill except for the two Tots on the SE side.
The plan shows existing and proposed grading
The plan shows house pad elevations and locations
The plan shows two created ponds.
The plan shows an infiltration swale on the north edge.
The plan shows a wetland delineation line.
The plan shows a bridge access and road proposal with a retaining wall.
The plan shows a Tree Preservation Limit.
Other Information: DNR Protected Water Elevation = 883.7
100 Year Flood Elevation = 887.6
Lowest Basement Opening = 889.6
Lowest Basement = 888
Pond 2
NWL = 883.5
HWL = 887.6 100 YR. Flood
HWL = 883.87 1 Year Storm
Pond 1
NWL = 888.0
HWL = 888.6 100 Year Flood
HWL = 888.1 1 Year Storm
Emergency Overflow: 883.87 /Pond 2, 888.1 Pond 1
The plan does not show The DNR established OHW line.
The plan does not show future soil- disturbance issues within the "Tree Preservation
Limits ".
The site is in a High Ecological Value Zone and a Lake Protection Zone (Exhibit 8)
SITE ANALYSIS:
Ecological Zones:
According to the City of Lino Lakes Environmental Management Plan, Pheasant Hills
12th Addition is located in a Lake Protection Zone and a High Ecological Value Zone
(Exhibit 8). Lake Protection Zones indicate that no development should occur, or
extraordinary measures should be taken with resource management techniques in
planning projects in these areas. The High Ecological Value Zones are areas where
protection strategies such as buffer systems, surface water treatment, conservation
easements, land trust strategy should be used to protect surrounding resources.
Vegetation:
Within these Ecological Zones are Vegetation classifications that include Cattail Marsh
and Shrub Thicket surrounding the Island. The Island itself is classified as a recently
developed forest. This is true on the outside perimeter where there is a constant water
influence on the vegetation. The inside area of the island is however, very nice
woodland with some very large burr and white oak species. Please see (Exhibit 12).
Wetlands:
Pheasant Hills Preserve 12R1 Addition is surrounded by a PSS1 /EM Cd wetland. (Exhibit
13).
Surface Water:
Wards Lake is situated in a Natural Environment Basin. Wards Lake is Public Waters.
As presented in the Environmental report in September, keeping volume and discharge
rates to predevelopment numbers is important.
Water from Sherman, Centerville and CD 25 south of Birch flows into Wards Lake. In
effect, in has been pointed out that Wards Lake is now a "settling pond" for Reshaneau
Lake (Exhibit 7). Water from virtually all directions flow to the Reshanear Lake inlet.
This includes water from the South side of the island. Any contaminants leaving the
North end of the island will eventually reach Roundeau Lake and the very sensitive
ground water on the West end of the island.
The effects of increased water storage in this basin can be seen during spring melt and
storm events. Water seems to be backing up into the George Watch basin to the North.
A recent watershed calibration study has shown that the lower part of the watershed
district is now experiencing a basin storage shortage. High water levels for storm
events seem to be changing. All efforts should be made in development proposals to
consider this in structural planning and surface water volume management.
Buffers:
The September, 2001 Environmental Board report also states the need to maintain
vegetation buffering on the shore areas. Table 1, Buffer Strategy of the Applied
Ecological Services Technical Report, suggests a 200 foot buffer in high -risk ecological
resource areas (Exhibit 3). Pheasant Hills Preserve is located in a high -risk natural
resource area. The 200 buffer width is recommended in areas where there are lake
margin wetlands.
Surface Water Treatment:
Attenuation of hydraulic pulses is needed in a case like Wards Lake Island. Storm water
treatment train techniques can positively effect this pulse attenuation. The pulse occurs
because storm water is conveyed to holding ponds and released over 1 or 2 days,
flushing contaminants with in the process. Attached please find literature Open Space
Through Stormwater Management (Exhibit 9).
The developer obviously does not have the room for a 200 -foot buffer in this area.
Maintaining existing vegetation as much as possible, restoration with proper and
incorporating any of the best management practices as developed by Barr Engineering
(exhibit 4), could help to attenuate hydraulic pulsing, surface water volume evacuation,
and mitigate contamination of the Lake and ground water systems.
Ponds 1 & 2: Create a Hydraulic Spike. These are located in ineffective soils. These
ponds do not have enough elevation difference between the bottoms of the pond and
the water table.
Soils:
The Regional Hydrologic Assessment —Anoka County Sand Plane, Minnesota shows the
area to the West of the island, including the western most tip of land, as very sensitive
to ground water pollution. (Exhibit 5). Travel time for contaminants is from hours to
minutes to reach the first layer of the ground water system. An area that is extremely
low in sensitivity to ground water pollution surrounds most of the rest of the island. This
area is labeled as taking from years to a century for contaminants to reach the first level
of the groundwater. The Study sited above includes flow systems, aquifer capacity,
ground water chemistry, and near - surface deposits and bedrock considerations.
Barr Engineering (Exhibit 9) establishes the need for site - sensitivity analysis, to prevent
ground water contamination. Any kind of infiltration system must consider the above
study considerations the Barr report states. Furthermore, Barr states that the seasonal
high water table must be far enough below the bottom of the infiltration basin (at least 3
feet) to allow the structure to function hydraulically and to allow trapping and treatment
of pollutants by the soil (MPCA 2000).
Both proposed ponds on the island are typical storm water conveyance, non- attenuated
water holding devices. Both ponds are excavations into organic soils (Exhibit 6), below
the normal water levels of the lake. Again, the western pond is in an extremely
sensitive, ground -water area. Recommendations based on Barr Engineering BMPS
suggest neither pond should be built.
Swale:
The proposed infiltration swale on the North side of the island appears to be set in
organic soils. This swale design is also contradicted in the Barr BMP Manual.
Alternatives might include using the two proposed lot areas on the eastern side of the
island for an infiltration /stormwater management area. Lot reduction may be necessary
to accommodate some of the concerns of surface water runoff. The infiltration swale on
the north side would have little benefit in terms of infiltration, and would not meet criteria
for suggested BMS for such a swale. Existing vegetation would be lost as well in the
process. Another possible alternative might be to move the swale idea to the North side
of the proposed road and design a filter system that would move surface water to an
infiltration area on the East (where ground water pollution is less of a concern).
Removing two lots on the West Side of the island would allow for a suitable area that
could be used for infiltration and surface water treatment. The site would need to be
reestablished with native vegetation. In addition, the lots themselves should be
designed with on -lot infiltration as suggested in Metropolitan Council /Barr Engineering
Co BMP manual for Surface Water Management (Exhibit 10). One other alternative
would be to cluster houses in one area of the island and use the rest of the island for
surface water management.
Trees:
The Grading, Drainage, Erosion Control and Tree Preservation Plan shows a "Tree
Preservation Limit" line for Pheasant Hills Preserve 12th Addition. I have indicated to the
developer that we need an inventory of the trees on the island to develop such a plan.
Our Tree Ordinance makes the inventory mandatory in proposed soil disturbance areas.
The entire island is a proposed soil disturbance area. Only the proposed house pad
locations are shown on the maps. Missing are driveways, surface water treatment
areas, backfill issues on landscaping, etc. Lot 5 for example would have 5.7 feet of
basement excavation. Lot 5 would be the eastern most lot. Lot 1, would have 3.2 feet
of excavation. There is always more room needed around house construction projects
to build, and utilities can disturb the soil enough to warrant tree removal. There are
some very nice old growth oaks on the island and good planing may save some of them.
Restoration:
Trees lost on this site should be replaced with similar species as much as space is
available. There should be no tennis court types of backyard projects carved -out on
proposed lots.
Ground story vegetation reestablishment in all areas disturbed should be replanted with
a native vegetation seed mixture as designated by the City of Lino Lakes. A 5 -year
financed management plan needs to be submitted by the developer to ensure the
reestablishment and management of this vegetation. A natural- environment information
sheet specifically discussing environmental issues in these areas should be given to all
new residents. Covenants, as part of a homeowner association should prohibit the
removal of vegetation of any sort in shore -land management and restoration areas.
Construction:
All efforts can be lost with out proper sequencing on the Project. Protection of Trees,
existing vegetation, swale and infiltration areas, as well as solid precautions to prevent
erosion needs to be spelled out in a management plan. This plan should contain
sequence information as listed in the Barr Engineering BMP manual (Exhibit 11).
RECOMMENDATION:
1. Redesign Surface Water plan. Use Barr Engineering BMP Manual. Reduce
hydraulic spiking in ponding situations. Use infiltration /ponding design in areas
where they would be effective and non - polluting. Ponds 1 and two do not work.
2. Reduce Lots /or cluster Houses. Use rest of the island for Surface water treatment
including buffering.
3. Move swale idea to South side of island. Incorporate rainpond idea into treatment
train along proposed road to flow water to the infiltration area on East end of the
Island.
4. Produce tree inventory. Needed for planning.
5. Replace Trees lost in areas of disturbance.
6. Restore all areas disturbed for road /bridge and surface water treatment/infiltration
with native tree shrub and ground story vegetation. Materials replaced to be
determined by inventory, and species list specified by the City. Site should be
restored to pre - disturbance vegetation densities.
7. Incorporate on -lot infiltration practices as described in Barr Engineering BMP
manual.
8. Use BMP's for sequencing as described in the Barr Engineering BMP Manual.
Develop a management plan based on this manual. Plan should include protection
measures for trees, vegetation, swale and infiltration areas, and erosion control
measures.
9. Submit a 5 -year management plan that uses the services of a company experienced
in native plant re- establishment. Show financial commitment for this management.
10. Initiate covenants with homeowner association for the protection of vegetation, and
the prohibiting of vegetation removal.
11. Place areas of the island in land trust as an alternative to covenants.
12. Develop an education program for new residents moving on the island. Brochure
information at the least should be developed describing vegetation management.
ATTACHMENTS:
EXHIBIT 1: Staff Report from Sept. 26 Environmental Board Meeting
EXHIBIT 2: Pheasant Hills 12th - location map
EXHIBIT 3: Buffer Strategy
EXHIBIT 4: Infiltration Basins
EXHIBIT 5: Pheas. Hills 12th - Island/Groundwater /Sensitivity to Contaminants
EXHIBIT 6: Pheas. Hills 12th - Soils
EXHIBIT 7: Pheas. Hills 12th - Surface Water
EXHIBIT 8: Pheas. Hills 12th - Ecological Zones
EXHIBIT 9: Open Space through Stormwater Management
EXHIBIT 10: On -Lot Infiltration
EXHIBIT 11: Sequencing
EXHIBIT 12: Pheas. Hills 12th - MN Land Cover Classification System
EXHIBIT 13: Pheas. Hills 12th - National Wetland Inventory
nos
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L ALL FABRICATED METAL TO BE HOT
DIPPED GALVANIZED AFTER
FABRICATION AND PAINTED BLACK
2. CONCRETE STRUCTURE TO BE
REINFORCED AS RECOMMENDED BY
FABRICATOR.
POND OUTLET DETAIL
NOTE:
Rock size should be 1" to 2" in size
such as MnDOT CA -1 or CA -2 course aggregate.
A geotextile fabric may be used under the rock
to prevent migration of the underlying soil
into the stone.
883.42
DNR PROTECTED ELEV
100 YR ELEV =887.6
LOWET BASEMENT OPE
LOWEST BASEMENT=
8:..7
NG =889.6
ROCK EN RANCE TO CONS RUCTION SI
PLYCSITE
883.22
FILTRATION
OCATE TO
SEE DETAIL
WALE FIELD.
VOID TREES.
SECTION FOR S
TREE PRESER ATION LIMITS
RETAINING WALL
883.38
883.03
3.42
883.78
\883.71 •
884.76
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84.E
SILT
883.62
SILT FENCE
884.50
RETAINING WALL
884.2
884.52
884
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TREE PRESERVATION LIMITS
884.07
884.29
RETAINING WALL
884.30
884.
883.75
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883.42
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883.24
883.22
83.13
883.61
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FILTRATION
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82.80
TREE PRESER ATION LIMITS
SILT FENCE
882.93
883. .0
883.38
883.03
884.02
RETAINING WALL
883.78
SILT FENCE
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ROCK ENTRANCE
884.76
884.32
883.59
$84.26
SILT FENCE
883.62
884.1
884.6
883.8
SILT FENCE
884.50
RETAINING WALL
884.2
GRADING /EROSION CONTROL NOTES.
- -
BALE'ECK
•
84.52
1. WHERE SOIL CORRECTIONS AND /OR FILLING OCCUR WITHIN TIC STREET RIGHT -OF -WAY, THE
BACKFILL MATERIAL SHALL BE COMPACTED TO 955 OF THE STANDARD MOISTURE DENSITY
RELATIONSHIP 01 SOILS EASTM D- 698 -70) EXCEPT THE TOP THREE FEET (3) OF THE BACK -
FILL WHICH SHALL BE COMPACTED TO 1002 DENSITY. AN INDEPENDENT TESTING FIRM SHALL
TEST THE STREET SECTION IN FILL AREAS AND PROVIDE THE RESULTS OF THESE TESTS TO
THE CITY. ENGINEER AND THE CLIENT.
2. THE CONTRACTOR SHALL INSTALL SILT FENCE PRIOR TO COMMENCING GRADING ACTIVITIES
AND SHALL MAINTAIN SAID FENCE FOR THE DURATION OF CONSTRUCTION ACTIVITIES.
3. THE CONTRACTOR SHALL LIMIT HIS ACTIVITIES TO THE GRADING LIMITS SHOWN ON THE
GRADING PLAN. ALL CONSTRUCTION ACTIVITIES SHALL COMPLY WITH THE LOCAL ORDINANCE.
4. THE CONTRACTOR SHALL INSTALL SNOW FENCE. AS DIRECTED BY THE ENGINEER. TO PROTECT
TREE ROOTS.
5. THE CONTRACTOR SHALL SCHEDULE HIS OPERATIONS TO MINIMIZE THE DISTURBED AREA AT
ANY GIVEN TIME.
6. ALL DISTURBED NON- STREET AREAS SHALL BE RESTORED WITH A MINIMUM OF 4• TOP SOIL
AND SEED OR SOD AS DIRECTED BY THE ENGINEER, WITHIN 72 HOURS OF COMPLETION OF
THE GRADING ACTIVITY IN THAT PERTICULAR AREA.
A. ALL SEED, SOD. MULCH AND FERTILIZER SHALL CONFORM WITH THE FOLLOWING
MN /DOT SPECIFICATIONS, AS MO01115D BEL0V.
ITEM SPECIFICATION NUMBER
SOD
SEED
M1LCHtTYPE 1.0125 ANCHORED)
FERTILIZER
GENERAL PLACEMENT
3878
3876
3882
3881
2575
B. 50D SHALL BE PLACED BEHIND CURB IMIEADIATELY FOLLOWING 014E BACKFILLING
UNDER CITY STREET AND UTILITY PROJECT.
C. THE SEED MIXTURE SHALL CONSIST OF A MN /DOT TYPE 500 UNLESS NOTED ELSE-
WHERE ON THE PLAN.
7. FOLLOWING STREET CONSTRUCTION. T)E DEVELOPER SHALL CLEAN THE STREETS ON AN ON-
GOING BASIS AS REQUIRED BY THE CITY.
8. UNLESS OTHERWISE NOTED, THE SILTATION PONDS ARE TEMPORARY, AND SHALL BE REMOVED
AND RESTORED TO THE ORIGINAL CONTOUR BY THE DEVELOPER FOLLOWING THE PERMANENT
ESTABLISHMENT Or TURF ON 752 0< THE DRAINAGE AREA THE PONDS AND POND OUTLETS
SHALL BE CONSTRUCTED UNDER THE GRADING CONTRACT.
9. RIP -RAP SHALL BE PLACED AT ALL STORM SEWER OUTLETS UNDER THE UTILITY CONTRACT
AND SHALL CONFORM WITH APPLICABLE CITY AND WATERSHED DISTRICT STANDARDS AND
SPECIFICATIONS.
10 VERTICAL GRADING TOLERANCE SHALL BE WITHIN 02 FEET OF THE CITY APPROVED
GRADING PLAN
TYPICAL
SLOPE
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M I N N E S O T A
PHEASANT HILLS
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12TH ADDITION
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1402 Pheasant Hills Drive
Ling Lakes. MN 50038
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-- ------- _ -__ -- _ 509'42'27"W 422A
II T N
Line Of Outlet D, PHEASANT HELLS PRESERVE
S Las. 0! N. 1100 FL 0l Oullot D. PHEASANT HILLS PRESERVE -. `
389'42'271W 1303.55
- -- --- --- --- -'--- 97Y4.5t 132645 --- -- - ----
N. Line Of Outlot 0 PHEASANT !ILLS PRESERVE •-••". -
•
1
-S Line Of N 1100 F1. Of Outlot D. PHEASANT HILLS PRESERVE - -,`
N. Line Of S 400 Ft. 01 N. 1500 Ft. Of
001101 0, PHEASANT HILLS PRESERVE
60000
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PHEASANT HILLS PRESERVE
389.22'45"W 600.02
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Edge Of Wetland -''
61'
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Edge 0! Wetland ,/
NORTH
100 200
SCALE IN FEET
Has
CONTOUR
SPOT ELEV.
CURRENT ZONING: R -X (RURAL EXECUTIVE)
PROPOSED ZONING: RI -X (SINGLE FAMILY)
PROPOSED BUILDING SETBACKS:
FRONT = 30 FEET
SIDE - 10 FEET
REAR = 30 FEET
Description of PHEASANT HILLS PRESERVE 'Island Property'
April 6. 2001
Outlot D. PHEASANT HILLS PRESERVE. Anoka County. Minnesota.
EXCEPT that port of Outlot D. PHEASANT HILLS PRESERVE being In the
West one half of the Northwest one - quarter. Section 27, Township 31,
Range 22 Anoko County, Minnesota described os follows:
Commencing at the Southeast corner of the West one -half of said
Northwest one - quarter, Section 27; thence North 01 degrees 00
minutes 55 seconds West along the East line of said West one -
hall, Northwest one quarter. Section 27 a distance of 57.73 feat
to the Southeast corner of said Outlot 0 for o point of beginning
of the tract to be described; thence North 01 degrees 00 minutes
55 seconds West, along the East line of said Outlet 0 a distance
of 910.02 feet; thence South 89 degrees 22 minutes 49 seconds
West, o distance of 580.47 feet; thence South 01 degrees 00
minutes 55 seconds East, porallel with the East line of said
Outlot 0. a distance of 548.90 feet; thence North 89 degrees 22
minutes 49 seconds East, parallel with the South line of said
Northwest one quarter. Section 27. a distance of 416.00 feet;
thence South 01 degrees 00 minutes 55 seconds East, parallel with
the Eost Tine of said Outlot D a distance of 370.14 feet to the
Northerly right - of-way line of C.S.A.H. No. 10 (Anoka County.
Right -of -Way Plat No. 11); thence North 85 degrees 24 minutes 36
seconds Eaat along said right-of-way line o distance of 28.66
feet; thence continuing along said right - of-way line along a
curve concave to the North (which has a radius of 3879.72 feet. a
delta angle of 02 degrees 00 minutes 31 seconds, and on arc
length of 136.02 feet) a chord bearing and distance of North 86
degrees 24 minutes 53 seconds Eaat. 136.01 lest to the point of
beginning.
and EXCEPT the North 1100 feet of Outlet D. PHEASANT HILLS PRESERVE,
Anoka County. Minnesota.
And EXCEPT the South 400 feet of the North 1500 feet of the East 600
feet of Outlot D. PHEASANT HILLS PRESERVE. Anoka County, Minnesota.
/
N8912491' 309.80
Outlot B
•
SW
S89'22'49"W 580.47
N89•22'49•E 41609
Parsed With S Lk* Of NW l /4E
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.......... ......T`t' .. .. .. -..
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,r;:h Street .......... .
SEC., Of W l/2. NW I /4,
Sec 27, Fop JL Rn9 22 --'��
CITY OF
M I N N E S O T A litioZikEs
Proposed Plat OF
PHEASANT HILLS
PRESERVE
127H ADDITION
UNHOIM9nnpp
ED VAUGHAN
1432 Pheasant Hills Drive
Lino lakes. NN 66038
lorslee _ _ TI
rE..NE , NN -NW ,
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PRELIMINARY PLAT
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91 -1331
Sheet 1 of 1
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STAFF ORIGINATOR: Marty Asleson
DATE: September 19, 2001
TOPIC: Pheasant Hilis Preserve 12th Addition, Preliminary AGENDA
ITEM
Plat/PDO, Comp Plan Amendment - MUSA
BACKGROUND:
Pheasant Hilis Preserve 12th Addition is the area in the Wards Lake Subwatershed
district known as the "island ". Intentions of the developer are stated in the September
10 cover letter to Jeff Smyser from Loucks and Associates. This is a planned
development overlay proposal.
Seet 2 CI 206 1
Ovirbureortit 3004
The island is in Wards Lake. Wards Lake is public water. Access to the island is
proposed through the construction of a bridge. A DNR permit has been issued for this
bridge crossing and stormwater outfalls. Tom Hovey from the Minnesota Department of
Natural Resources points out that this permit should not be interpreted as support for
the proposed development.
The site is within the shoreland district and is subject to the City of Lino lakes shoreland
ordinance. Our shoreland ordinance lists this lake as a Natural environment basin.
Setback requirements are 150 feet from the ordinary high water for any building
structure. The shore impact Zone is 75 feet from the shore is an area defined as that
area where no vegetation removal is allowed, and house setbacks must be at least 50%
of the distance from the structure to the Lake. It is virtually impossible to meet the City
Shoreland Ordinance with this development proposal.
The grading plan shows literally every part of the island graded for eight single - family
dwelling lots. All vegetation would be removed.
According to the Anoka County Sand plain pollution sensitivity cover, the area to the
north and west, and heading to the south is very sensitive to potential for aquifer
contamination. This area has an estimated travel time for contaminants to reach the
uppermost aquifer in the "hours to minutes" range.
Mr. Hovey makes a recommendation consistent with previous Environmental Board
recommendations to reduce impervious surfaces and maintain runoff volume and rate
discharge rates to pre - development levels through appropriate landscaping, impervious
reduction, and ponding use.
Tom makes an additional point to say that in all likely hood homeowners will want to
excavate the wetland in the shoreland area to have open water close to their houses,
and avoid planting vegetation that would block their view of the lake. He recommends
covenants to be put in place that would further restrict landowner activity in the Shore
Impact Zone and Lake if development proceeds on the island.
Topography shows the island consisting of two hills. Elevations range from 895 to 885.
FEMA floodplain maps show the entire Wards Lake area as 100 -year floodplain.
Our Ecological Delineation describes the island as a 3c, "recently developed forest ".
Observations from the Quail Ridge Development or the Pheasant Hills Preserve
Development sides looking in to the island would lead one to label this as 3c. However,
upland portions of the island have many old growth trees.
Lino Lakes Management Handbook recommends as much buffering as possible around
the Wards Lake wet areas. The island is a unique element within the Wards Lake
watershed. The island should follow the same recommendations for the buffering as are
recommended for the wet areas around the edge of the island.
From an ecological standpoint, this site would be better suited to building one or two
house sites. The Conservation Development Modal starts with the land, and what the
land can support as a starting point for development. Usually, PDO's better enable this
modal. Perhaps the developer can re -look at his proposal and start with the sensitive
nature of the land in this area.
OPTIONS:
1. Approve as is.
2. Table with approval pending further administrative action
3. Recommend denial.
RECOMMENDATION:
3. Recommend denial as the plan stands right now.
Council Member introduced the following resolution and moved
its adoption:
CITY OF LINO LAKES
RESOLUTION NO. 98 -
RESOLUTION
WHEREAS, ,
AND WHEREAS,
NOW, THEREFORE, BE IT RESOLVED BY THE CITY COUNCIL OF THE CITY OF
LINO LAKES, MINNESOTA:
Adopted by the Lino Lakes City Council this xxth day of xxxxxxx, 1998.
Kimberly A. Sullivan, Mayor
Marilyn G. Anderson, Clerk- Treasurer
The motion for adoption of the foregoing resolution was duly seconded by Council
Member and upon vote being taken thereon, the following voted in
favor thereof:
The following voted against same:
Whereupon said resolution was duly passed and adopted.
CERTIFICATION
1 hereby certify that the above is a correct copy of a resolution duly passed,
adopted and approved by the City Council on date.
Marilyn G. Anderson, Clerk- Treasurer
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• Table 1.
BUFFER STRATEGY
Potential Placement and Allowed Uses
In Lino Lakes
Buffer
Width
Where
Why
Allowed Uses
200 Feet
High risk ecological resources
• Lake margin wetlands
•
99% Attenuation of
hydraulic pulses
•
•
•
Stormwater
management
Native
landscaping
Wetland biofilter
• High quality /health wetlands
•
99% attenuation of
sediments
• Areas with high restoration .
potential, key areas in
green ways
•
99% attenuation of
macronutrients
•
Reestablish
ecotones
•
Green way trail
•
Ecological
restoration
100 Feet
All large external wetlands
1
• High quality internal
wetlands
•
75% attenuation of
hydraulic pulses
•
•
Restored
landscapes
Greenway trail
• Streams, waterways
•
75 %attenuation of
sediments
• Seepage zones
•
75% attenuation of
macronutrients
•
Ecological
restoration
• Areas with moderate slope
•
Reestablish
ecotones
50 Feet
Savanna areas
• Dry Prairies
•
Protect/restore and
retain upland
•
•
•
Restored
landscapes
Greenway trail
Ecological
restoration
• Mesic prairie
• Internal low quality wetlands
0:98212 :122199 105 Lino Lakes Existing Conditions Report
0
CD
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Exhibit �{
Infiltration Basins
Description
An infiltration basin is stormwater runoff impoundment designed to
capture a stormwater runoff volume, hold this volume and infiltrate
it into the ground over a period of days. It does not retain a perma-
nent pool of water. Infiltration basins are typically off -line, end -of-
pipe BMPs. A flow splitter or weir is usually used to divert runoff
from a storm sewer system into the infiltration basin.
Infiltration basins in this BMP Section refer to end -of -pipe infiltra-
tion systems that treat stormwater runoff from a few lots or proper-
ties as opposed to rainwater gardens which are primarily used for a
single lot application (see the On -Lot Infiltration BMP Section for
information on this type of BMP).
A key feature of an infiltration basin is its vegetation. It is important
to vegetate the bottom of the basin with deep- rooted plants to
increase the infiltration capacity of the basin. Roots create small
conduits for water to infiltrate. The root penetration and thatch
formation of the vegetation maintains and may enhance the original
infiltration capacity. Dense vegetation will also impede soil erosion
and scouring of the basin floor.
Infiltration basins are not appropriate for areas that contribute high
concentrations of sediment, or suspended solids, without adequate
pretreatment. Excessive sediment can clog the basin and take up
storage volume.
Infiltration basins require pretreatment of stormwater in order to
remove as many of the suspended solids from the runoff as possible
before the water enters the basin. Pretreatment, such as grit cham-
bers, swales with check dams, filter strips, or a sedimentation basin
should be a fundamental component of any BMP system relying on
infiltration. Good housekeeping measures should also be investi-
gated (e.g., street sweeping, reduction of sanding or salting practices,
etc.). Public education with respect to street and driveway sediments
should be provided in areas where an infiltration basin is proposed.
Metropolitan Council / Barr Engineering Co.
Purpose
Flow attenuation
Water Quantity
u
Runoff volume reduction
Pollution prevention
Soil erosion
A
Sediment control
A
Nutrient loading
A
Water Quality
Pollutant removal
Total suspended sediment (TSS)
Total phosphorus (P)
Nitrogen (N)
Heavy metals
Floatables
Oil and grease
Other
Fecal coliform
Biochemical oxygen demand
N/
N/
N/
•
•
•
11
11
11
11
■giG14 design benefit
EiSecondary design benefit
Little or no design benefit
3-155
Infiltration Basins
The design storm for an infiltration basin is typically a frequent, small storm such as the 1-year event. This
provides treatment for the "first flush" of stormwater runoff. Infiltration basins provide total peak discharge,
runoff volume and water quality control for all storm events equal to or less than the design storm. This infiltra-
tion reduces the volume of' runoff, removes many pollutants and provides stream baseflow and groundwater recharge.
Infiltration basins have limited capabilities for controlling peak discharge for storms greater than the design
storm. Because infiltration basins will not significantly affect peak discharges of runoff, they are best used in
conjunction with other BMPs; downstream detention is often still needed to meet peak - runoff -rate requirements.
Dissolved pollutants are effectively controlled for storm events Tess than the design storm, but these substances
may not be removed from the runoff water as it infiltrates, and some of them could move to the groundwater. For
this reason, the impact of infiltrated runoff on the groundwater should be considered, although in most cases, the
magnitude of this impact is unknown. Chloride from road salt is an example of a soluble material that will not be
removed during the infiltration process. Currently, there is much disagreement as to whether chlorides do indeed
pose a significant threat to groundwater. A general guideline for groundwater protection is to design infiltration
basins with the bottom of the basin a minimum of 3 feet above the seasonally high groundwater table. This is
consistent with the MPCA's guidelines for septic systems (MPCA, 2000). If the water table is too close to the
ground surface, infiltration practices should not be used.
Figure 1 provides a schematic of a typical infiltration basin. Figure 2 shows an infiltration basin with pretreat-
ment in the form of a settling pond.
Advantages
• Reduces the volume of runoff from a drainage area
• Can be very effective for removing fine sediment, trace metals, nutrients, bacteria, and oxygen- demanding
substances (organics)
• Reduces downstream flooding and protects streambank integrity
• Reduces the size and cost of downstream stormwater control facilities and/or storm drain systems by infiltrat-
ing stormwater in upland areas
• Provides groundwater recharge and baseflow in nearby streams
• Reduces local flooding
• Appropriate for small sites (2 acres or Tess)
Limitations
• Potentially high failure rates due to improper siting, design and lack of maintenance, especially if pretreat-
ment is not incorporated into the design
• Depending on soil conditions and groundwater depth, a risk of groundwater contamination may exist
• Not appropriate for treating significant loads of sediment and other pollutants due to the potential for clogging
3-156 Minnesota Urban Small Sites BMP Manual
Infiltration Basins
Top View
ti
Duo
e
protection ti
Flat basin floor with
dense grass turf
ftiprap settling
basin anti
level spreader
Backup undardrain
Emergency spillway
Side mew
Iva
Exffatration storage
rM'
Pretreated
fhorrrtwater
Met r
Backup widerd in pope in _in of standing water p s
Figure 1: Typical Infiltration Basin
Source: Schueler, 1987
Iniiet for
pretreatar
:flora-water
• Not appropriate for industrial or commercial sites where the release of large amounts or high concentrations
of pollutants are possible
• Requires a flat, continuous area
• Requires frequent inspection and maintenance
Design }"
Infiltration basins are generally known to have high failure rates. Such failure rates can be avoided with proper
design, taking the following into consideration:
• Careful site selection (discussed later, in the Site Sensitivity Analysis section)
• Incorporation of pretreatment and a bypass for high -flow events
Metropolitan Council / Barr Engineering Co. 3 -157
nfiltration Basins
awses f3Jtii]
sae :.ei.ii3n .5.2. 1,1 \ ;
tor 1pe0111".alio \ ii lcm p e
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Fat [!elms
sae: (figure 5.3.1.8
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avertkra
structure
sse Fie
6.1.1 3
j 5' minimum'
A..! -1
PLAN VIEW
everrowismemetty averltuws
prweided liar Seclkin
SEGTIO A� 1 .
NOTE;
Detail is a whom& rapraaaranam only, Actual conagtinallon Will vary
depenting on ftpe a site carisitainla affil apFacsials design aliens.
Figure 2: Infiltration Basin with Settling Pond Pretreatment
Source: Schueler, 1987
3-158 Minnesota Urban Small Sites BMP Manual
Infiltration Basins
Design
• Treatment of a small drainage area (lower sediment loadings)
• Careful consideration of depth of ponding and inundation times that reflect plant tolerances
• Good construction techniques that prevent smearing, over - compaction, and operation of the basin during the
construction period
• Performance of regular maintenance
All of these topics are discussed in further detail below.
Site Sensitivity Analysis
Before an infiltration system can be designed, a site sensitivity analysis must be performed. This evaluation may
eliminate an infiltration practice from consideration because of soil characteristics or potential effects on ground-
water. Because of varying geologic settings, a site evaluation needs to be tailored to the specific site conditions. A
team approach to this evaluation is recommended where various disciplines such as engineering, hydrogeology
and soil science are represented.
The applicability of infiltration basins on a site depends on numerous site factors, including soils, slope, depth to
water table, depth to bedrock or impermeable layer, contributing watershed area, land use, proximity to wells,
surface waters, foundations, and others. Generally, infiltration basins are suitable to sites with gentle slopes,
permeable soils, relatively deep bedrock and groundwater levels, and a small contributing watershed area (less
than 2 acres, ideally).
When performing a site evaluation, the following items should be considered:
• Runoff water quality: If runoff water will contain a significant concentration of soluble pollutants that could
contaminate groundwater, an infiltration basin should not be used. Specifically, infiltration basins are not
recommended for industrial and commercial land uses since there is a high potential for groundwater con-
tamination from chemical spills and maintenance (salting and sanding) activities. In site - specific cases where
infiltration basins are deemed acceptable for these land uses, the design must be located off -line and incorpo-
rate some form of upstream treatment (e.g., an upstream oil -grit separator or sand filter).
• Degree of detail: The level of detail required for the study should be considered. For instance, a small struc-
ture receiving runoff from a rooftop will not require as much detail as a structure serving a larger area and
having a higher potential pollutant load.
• Geologic (groundwater) sensitivity: A site with a highly sensitive geology, such as one with a carbonate or
surficial sand aquifer, may eliminate this practice from consideration.
• Depth to water table and bedrock: The seasonally high water table must be far enough below the bottom of
the infiltration basin (at least 3 feet) to alloy the structure to function hydraulically and to allow trapping and
treatment of pollutants by the soil. Similarly, the bottom of the infiltration basin should be at least 3 feet from
bedrock, although in the case of fractured bedrock, separations up to 10 feet may be required. This minimum
separation distance is required to trap or treat pollutants before they reach the groundwater or bedrock and to
maintain vegetation in the basin (MPCA, 2000).
Metropolitan Council / Barr Engineering Co. 3 -159
Infiltration Basins
Design
..:....:. ........ .
• Proximity to drinking water wells and building foundations: Basins should be located at least 150 feet away
from drinking water wells to limit the possibility of groundwater contamination, and should be situated at
least 10 feet downgradient and 100 feet upgradient from building foundations to avoid potential seepage
problems.
• Soil infiltration rate: The infiltration rate of the soil must be great enough to drain the structure in a reason-
able amount of time, generally 72 hours or less. Sites with clayey soils are not appropriate for infiltration
basins. Infiltration rates are discussed in further detail below. If the infiltration rate of the site's soils are not
acceptable, the filtration family of BMP systems should be considered.
• Size of the tributary drainage area: Although infiltration basins were originally designed to accommodate
larger drainage areas, research which has been undertaken to date indicates that large -scale infiltration is not
feasible. One of the main problems with centralized infiltration basins is that water from a large area is
expected to infiltrate into a relatively small area. This does not reflect the natural hydrologic cycle and
generally leads to problems (groundwater mounding, clogging, compaction). For these reasons, the contribut-
ing drainage area to any individual infiltration basin should be restricted to 2 acres or less.
General Design Considerations
Design Volume
Infiltration basin systems infiltrate a portion of the runoff from a rain event (usually the first flush or up to the
first inch) while the remaining runoff bypasses the infiltration basin. The design infiltration volume can be
calculated in many ways. Ultimately, the magnitude of the design infiltration volume depends on local authori-
ties' practices and requirements.
Off -Line Placement
The purpose of the basin is to temporarily store surface runoff for a specific design frequency storm and allow it
to infiltrate through the bottom and sides of the basin. A flow splitter or weir is usually used to divert runoff into
an off -line infiltration basin. Infiltration basins provide total peak discharge, runoff volume and water quality
control for all storm events equal to or less than the design storm. Storm events greater than the design storm
simply continue down the larger conveyance system, bypassing the infiltration basin.
Pretreatment
Infiltration basins are susceptible to high failure rates due to clogging from sediments, and therefore require
pretreatment of stormwater in order to remove as much of the suspended solids from the runoff as possible before
it enters the basin. Pretreatment, such as grit chambers, swales with check dams, filter strips, or sediment fore -
bays/traps should be a fundamental component of any BMP system relying on infiltration. Even when infiltrating
rooftop runoff, it is a practical decision to implement some form of pretreatment to remove sediments, leaf litter,
and debris. This pretreatment will help to ensure the proper functioning of the infiltrating facility and allow for
longer periods between maintenance. When designed properly, pretreatment devices may remove some 25 -30%
of sediment loads. Figure 2 shows and infiltration basin with pretreatment in the form of a settling pond.
3 -160 Minnesota Urban Small Sites BMP Manual
Infiltration Basins
Infiltration Rate
The soils of a prospective site are an important consideration when determining the suitability for infiltration.
County soil surveys are useful for preliminary screening of a site for soil infiltration rate. The Natural Resource
Conservation Service (formerly the Soil Conservation Service) Soil Group is found in the National Engineering
Handbook. Conservative estimates of infiltration rates for a range of hydrologic soil groups (A through D) have
been developed for some Minnesota authorities and are shown below (Riley - Purgatory -Bluff Creek Watershed
District, 1999).
Soil Group Rate (in/hr)
A 0.38
B 0.23
C 0.1
D 0.03
Max. Water Depth (ft)
2
1.4
0.6
0.2
If these estimates are deemed too conservative for the site, a geologic investigation of the specific site should be
conducted to verify higher infiltration rates. Infiltration rates should be measured in situ according to the stan-
dards presented in:
• Annual Book of ASTM Standards, 1997, Section 4, Vol 4.08, Soil and Rock (I): Designation D 3385 -94,
Standard Test Method for Infiltration Rate of Soils in Field Using a Double -Ring Infiltrometer, pp 331 -337.
• Annual Book ofASTMStandards, 1998, Section 4, Vol 4.09, Soil and Rock (II): Designation D 5093 -90,
Standard Test Method for Field Measurement and Infiltration Rate Using a Double -Ring Infiltrometer with a
Sealed -Inner Ring, pp 87 -92.
• Johnson, A.I., 1963, "A field method for measurement of infiltration," United States Geological Survey,
Water- Supply Paper, W 1544 -F, p. F1 -F27.
The depth of water within the infiltro -ter should be maintained at the following depths:
Hydrologic Soil Type Water Depth (Inches)
A 18
B 9
C 4
D 1
Notes on alternative infiltration measurement methods:
• Alternative methods other than reference standards should use a double -ring apparatus and be acceptable
to local authorities.
Metropolitan Council / Barr Engineering Co. 3 -161
Infiltration Basins
Design
• Proposed alternative infiltration rates must be representative of vertical water infiltration through the soil
surface (values that include lateral flow are not acceptable).
• Values that should not be used as alternative infiltration rates include, but are not limited to, the following:
hydraulic conductivity, saturated hydraulic conductivity, transmissivity, permeability and percolation rate.
Designers should use their best judgement to determine if the slowest or average measured infiltration rate in the
proposed basin area should be used for the design of the basin.
Where feasible, larger -scale infiltration measurements are encouraged. Procedures such as the Pilot Infiltration
Test are described in the State of Washington's Stormwater Management Manual (Washington State Department
of Ecology, 1999). This document is currently available on the internet at www.ecy.wa.gov. This type of proce-
dure can minimize some of the error associated with smaller -scale tests and provide an indication of a longer -term
infiltration rate that better represents the future conditions of the site.
Duration of Ponding:
The depth of the infiltration basin should be adjusted so that maximum drain time is 72 hours for the total runoff
volume. However, certain types of vegetation (turf, for example) will require a shorter ponding duration to
survive storm events. The design ponding duration should be determined by plant inundation tolerances.
Average Depth
After the infiltration rate of the soil has been determined, the maximum depth of the infiltration basin can be
calculated with the following equation:
d = (f) * (Tp)
Where: d = maximum design depth (inches),
f = soil infiltration rate (in/hr), and
T = design ponding time (hours).
The maximum depth and ponding time of the infiltration area should promote the survival of vegetation. The
maximum depth should be no greater than 2 feet; the ponding time no greater than 72 hours.
In recent monitoring studies (Galli, 1992) one of the causal factors of failure was noted to be the depth of water
retained in the basin. The weight of the water is thought to compact the basin, decreasing its infiltration potential.
The depth of storage should be limited to a maximum 2 feet in order to minimize the compaction of the basin.
Basin Slopes:
The bottom of the basin should be graded as flat as possible to provide uniform ponding and infiltration of the
runoff across the floor. The side slopes of the basin should be no steeper than 3H:1 V (flatter slopes are preferred)
to allow for proper vegetative stabilization, easier mowing, easier access, and better public safety. Designs for
infiltration basins should emphasize accessibility and ease of maintenance.
3 -162 Minnesota Urban Small Sites BMP Manual
Infiltration Basins
Basin Shape
The length and width of the basin will be determined by the characteristics of the site in question (topography,
size and shape). A desirable length -to -width ratio for an infiltration basin is 3:1 or greater.
Vegetation
A key feature of an infiltration basin is its vegetation. It is important to vegetate the bottom of the basin with
deep - rooted plants to increase the infiltration capacity of the basin. Roots create small conduits for water to
infiltrate. The root penetration and thatch formation of the vegetation maintains and may enhance the original
infiltration capacity. Soluble nutrients are taken up during plant growth, improving the pollutant - removal capac-
ity of the basin. Dense vegetation will also impede soil erosion and scouring of the basin floor.
Immediately following basin construction, the bottom and side slopes of the basin should be stabilized with a
dense stand of water - tolerant grass. Use of low- maintenance, rapidly germinating grasses, such as red top
(Agrostis alba) can be used. Likewise, vegetative buffers around the perimeter of the basin are recommended for
erosion control and additional sediment and nutrient removal. A diversity of plant species should be planted to
allow for best survivability. Plants that are tolerant of both wet weather and drought should be used. Plantings in
an infiltration basin should be able to withstand periods of ponding and maintain or enhance the pore space in the
underlying soils. A list on the last page of this BMP section provides some plant recommendations based on
different site conditions (Rozumalski, 2001).
Inflow /Bypass
If runoff is delivered by a storm drain pipe or along the main conveyance system, the infiltration practice must be
designed as an off-line practice.
To prevent incoming flow velocities from reaching erosive levels, which can scour the basin floor, inlet channels
to the basin should be stabilized. Riprap may be used for this purpose. The riprap should be designed to terminate
in a broad apron, which spreads the runoff more evenly over the basin surface to promote better infiltration.
A bypass system should be implemented for all infiltration basins. A bypass flow path or pipe should be incorpo-
rated in the design of an infiltration basin to convey high flows around the basin. This will necessitate the con-
struction of a flow splitter upstream of the basin. The bypass serves several functions. Specifically, the bypass
can be used as the normal outlet during 1) stabilization of the site (while the inlet to the basin is blocked off), 2)
basin maintenance and 3) winter conditions.
Overflow
All infiltration basins must have an emergency spillway capable of passing runoff from large storms without
damage to the impounding structure. The overland flow path of surface runoff exceeding the capacity of the
infiltration system should be evaluated to preclude erosive concentrated flow. If computed flow velocities do not
exceed the non - erosive threshold, overflow may be accommodated by natural topography.
Groundwater Mounding:
Calculations to determine groundwater mounding may be necessary in cases where slope stability is a concern
and/or a high water table is encountered. A hydrogeologist should be consulted about the potential for ground-
water mounding in these areas. The results from groundwater mounding calculations should be regarded as an
indication of the mounding potential rather than as an accurate representation of the actual mounding depth.
Metropolitan Council / Barr Engineering Co. 3-163
Infiltration Basins
Design
Cold Weather Considerations
Consideration should be given to the operation of infiltration basins during the winter period. Winter sanding of
roads can clog an infiltration basin without adequate pretreatment, and winter salting will increase the potential
for the chloride contamination of groundwater.
If infiltration practices are used as a stand - alone, all -season water quality treatment facility, then oversizing (to
account for reduced infiltration rates) and/or extended pretreatment should be considered. Doubling the storage
volume for surface infiltration devices is recommended. Redundant pretreatment (more than one pretreatment
device in series) is recommended for all infiltration facilities receiving runoff from roads.
Another option is the use of a seasonally operated facility (Oberts, 1994). A seasonally operated infiltration basin
combines several techniques to improve the performance of infiltration practices in cold climates. Two features —an
underdrain system and level control valves —are useful in cold climates. In the beginning of the winter season,
the level - control valve is opened and the soil is drained. As the snow begins to melt in the spring, the underdrain
and the level - control valves are closed. The snowmelt is infiltrated until the capacity of the soil is reached. Then
the facility acts as a detention facility, providing storage for particles to settle.
Infiltration Basins Plant List
Source: Fred Rozumalski
Mesic -Dry Soils (Sunny)
Native
Butterfly Flower
Purple Prairie Clover
Purple Coneflower
Bee balm
Little Bluestem
Spiderwort
Asclepias tuberosa
Dalea purpureum
Echinacea purpurea
Monarda fistulosa
Schizachyrium scoparium
Tradescantia bracteata
Mesic -Dry Soils (Shady)
Native
Wild Columbine
Wild Geranium
Obedient Plant
Jacob's Ladder
Solomon's Seal
Zig Zag Goldenrod
Canada Violet
Culver's Root
Aquilegia canadensis
Geranium maculatum
Physostegia virginiana
Polemonium reptans
Polygonatum b ?orum
Solidago flexicaulis
Viola canadensis
Veronicastrum virginium
Non - Native
Yarrow "Coronation Gold"
Feather Reed Grass "Karl Foerster"
Daylily
Blazingstar "Kobold"
Silverfeather Grass
Garden Phlox
Black -Eyed Susan "Goldsturm"
Non - Native
White Comfrey
Tufted Hair Grass
Bigroot Geranium
Daylily
Hosta "Royal Standard"
Tigerlily
Achillea "Coronation Gold"
Calamogrostis "Karl Foerster"
Hemerocallis spp.
Liatris "Kobold"
Miscanthus sinensis
Phlox paniculata
Rudbeckia fulgida " Goldsturm"
Symphytum grandiflorum
Deschamsia caespitosa
Geranium macrorrhizum
Hemerocallis spp.
Hosta "Royal Standard"
Lilium tigrinum
3-164 Minnesota Urban Small Sites BMP Manual
Infiltration Basins
Wet Soil (Sunny)
Native
Giant Hyssop
Canada Anemone
Marsh Milkweed
New England Aster
Turtlehead
Joe -Pye Weed
Obedient Plant
Boneset
Queen of the Prairie
Blueflag Iris
Great Blue Lobelia
Switchgrass
Mountain Mint
Tall Meadow Rue
Culvers Root
Golden Alexander
Wet Soils (Shady)
Native
Cardinal Flower
Ostrich Fern
Virginia Bluebells
Sensitive Fern
Shrubs (Sunny)
Black Chokeberry
Red -Osier Dogwood
Low Bush Honeysuckle
Annabelle Hydrangea
Pussy Willow
High Bush Cranberry
Shrubs (Shady)
Black Chokeberry
Red -Osier Dogwood
Low Bush Honeysuckle
Annabelle Hydrangea
Agastache foeniculum
Anemone canadensis
Asclepias incarnata
Aster novae - angliae
Chelone glabra
Eupatorium maculatum
Physostesia virginianum
Eupatorium perfoliatum
Filpendula rubra
Iris versicolor
Lobelia siphilitica
Panicum virgatum
Pycnanthemum virginianum
Thalictrum dasycarpum
Veronicastrum virginicum
Zizia aurea
Lobelia cardinalis
Matteuccia struthiopteris
Mertensia virginica
Onoclea s ens ibilis
Aronia melanocarpa
Cornus serecia
Diervilla lonicera
Hydrangea arborescens
"Annabelle"
Salix discolor
Viburnum trilobum
Aronia melanocarpa "alata"
Cornus serecia
Diervilla lonicera
Hydrangea arborescens
"Annabelle"
Metropolitan Council / Barr Engineering Co.
Non - Native
Joe -Pye "Gateway"
Daylily
Siberian Iris
Tigerlily
Switchgrass "Heavy Metal"
Non Native
Pink Turtlehead
Daylily
Obedient Plant
Eupatorium purpuescens
"Gateway"
Hemerocallis spp.
Iris sibirica
Lilium tigrinum
Panicum virgatum "Heavy Metal"
Chelone layonii
Hemerocallis spp.
Physostegia virginiana
3 -165
Infiltration Basins
Sequencing
Care should be taken during construction to minimize the risk of premature failure of the infiltration basin. This
failure is caused by the deposition of sediments from disturbed, unstabilized areas. This can be minimized or
avoided by proper sequencing.
• Ideally, construction of the infiltration basin should take place after the site has been stabilized.
• No runoff should enter the infiltration basin prior to completion of construction and the complete stabilization
of the tributary areas.
• Diversion berms or silt fence should be placed around the perimeter of the infiltration basin during all phases
of construction. Sediment and erosion controls should be used to keep runoff and sediment away from the
infiltration basin.
• Initial excavation of the basin should be carried out to within one foot of the final grade of the basin floor.
Final excavation of the basin floor should be delayed until all disturbed areas in the drainage area are stabi-
lized. All excavation should be performed by equipment with tracks exerting relatively light pressures. This
will prevent compacting of the basin floor, which would reduce the infiltration capacity.
• In order to avoid soil compaction, absolutely no equipment should be driven in the area of the basin before
and after its construction.
• After final grading, the basin floor should be tilled to a depth of at least 6 inches to provide a well - aerated,
porous surface texture. Six inches of compost should be tilled in at this time if soils are even the slightest bit
compacted. This will help to facilitate infiltration and root growth.
• During and after excavation, all excavated materials should be placed downstream, away from the infiltration
basin, to prevent redepositing during runoff events.
• Immediately following basin construction, the bottom and side slopes of the basin should be stabilized with a
dense stand of appropriate plants.
Construction
Experience has shown that the longevity of infiltration practices is strongly influenced by the care taken during
construction. The construction sequence and specifications for each infiltration practice must be precisely fol-
lowed.
• Infiltration basins should not be used as temporary sediment traps during construction.
• Infiltration basins will operate as designed only if they are constructed properly. There are three main rules
that must be followed during the construction of an infiltration basin:
— Basins should be constructed at the end of development construction
— Smearing of the soil at the interface with the basin floor must be avoided and/or corrected by raking or
rototilling
— Compaction of the basin during construction must be minimized
3-166 Minnesota Urban Small Sites BMP Manual
Infiltration Basins
• Before the development site is graded, the area of infiltration basin should be roped off to prevent heavy
equipment from compacting the underlying soils.
• Light earth- moving equipment should be used to excavate the infiltration basin. Use of heavy equipment
causes compaction of the soils beneath the basin floor and side slopes, resulting in reduced infiltration
capacity. Since some compaction of soils will occur during construction, the basin floor should be tilled with
a rotary tiller to restore infiltration rates after final grading.
Maintenance
Maintenance is required for the proper operation of infiltration basins, as it is with all BMPs. Plans for infiltra-
tion basins should identify owners, parties responsible for maintenance, and an inspection and maintenance
schedule. The use and regular maintenance of pretreatment BMPs will significantly minimize maintenance
requirements for the basin.
• Pretreatment devices associated with basins should be inspected and cleaned at least twice a year, and ideally
every other month.
• Once the basin has gone on -line, inspections should occur after every major storm for the first few months to
ensure proper stabilization and function. Attention should be paid to how long water remains standing in the
basin after a storm; standing water within the basin more than 72 hours after a storm indicates that the infiltra-
tion capacity may have been overestimated. Factors responsible for clogging (such as upland sediment ero-
sion and excessive compaction of soils) should be repaired immediately. Also, the newly established vegetation
should be inspected several times to determine if any remedial actions (reseeding, irrigation, etc.) are necessary.
• Thereafter, the infiltration basin should be inspected at least twice per year. Important items to check include:
differential accumulation of sediment, erosion of the basin floor, condition of riprap and the health of the
vegetation. Eroded or barren spots should be replanted immediately after inspection to prevent additional
erosion and accumulation of sediment.
• Sediment removal within the basin should be performed when the sediment is dry enough so that it is cracked
and readily separates from the basin floor. This also prevents smearing of the basin floor.
• Light equipment, which will not compact the underlying soil, should be used to remove the top layer of
sediment. The remaining soil should be tilled and revegetated as soon as possible.
• Vegetation should be maintained to control weed growth and maintain the health of the vegetation in the
basin. Weed once monthly during the first two growing seasons. After that, weeding two or three times per
growing season may suffice.
Metropolitan Council / Barr Engineering Co. 3-167
Infiltration Basins
Sources
1. Center for Watershed Protection. 2001. "Infiltration Basins" fact sheet in Stormwater Manager's Resource
Center. www.stormwatercenter.net. Ellicott City, MD.
2. Galli, J. 1992. Analysis of Urban BMP Performance and Longevity in Prince George's County, Maryland.
Metropolitan Washington Council of Governments. Washington, DC.
3. King County Department of Natural Resources. 1998. King County, Washington Surface Water Design
Manual. King County, Washington.
4. Maryland Department of the Environment. 1998. Maryland Stormwater Design Manual, Volumes One and
Two. Baltimore. -
5. Massachusetts Dept. of Environmental Protection. 1997. Stormwater Management. Volume Two: Stormwater
Technical Handbook. Boston.
6. Minnesota Pollution Control Agency. 2000. Protecting Water Quality in Urban Areas: Best Management
Practices for Dealing with Storm Water Runoff from Urban, Suburban and Developing Areas of Minnesota.
St. Paul.
7. Oberts, G 1994. "Performance of Stormwater Ponds and Wetlands in Winter." Article 71 in The Practice of
Watershed Protection. Center for Watershed Protection. Ellicott, City, MD.
8. Ontario Ministry of the Environment. 1999. Stormwater Management Planning and Design Manual. Draft
Final Report. Toronto.
9. Riley Purgatory Bluff Creek Watershed District. 1999. Proposed Rules and Statement of Need and Reason-
ableness for the Riley Purgatory Bluff Creek Watershed District—Review Draft. Prepared by Barr Engineer-
ing Company. Minneapolis.
10. Rozumalski, Fred. 2001. Plant List. Barr Engineering Company, Minneapolis.
11. Schueler, Tom. 1987. Controlling Urban Runoff. A Practical Manual for Planning and Designing Urban
BMPs. Metropolitan Washington Council of Governments, Washington D.C.
12. US Environmental Protection Agency. PA Preliminary Data Summary of Urban Storm Water Best Manage-
ment Practices. Report EPA - 821 -R -99 -012. August, 1999.
13. Washington State Department of Ecology, Water Quality Program. 1999. Stormwater Management in Wash-
ington State. Volume V Runoff Treatment BMPs. Olympia.
3 -168 Minnesota Urban Small Sites BMP Manual
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Legend
Htuh Eeoingtcal Vale Zone
Protected lone
Ecological Enhancement (all areas
outside other two zones)
j (Q Lakes
This zone consists of largely upland
areas considered under various natural
vegetative cover types, such as oak
savannas, mesic forests, and prairie
remnants.
This zone refers to areas of the city that
fall outside the other two zones.
Developing an Ecologically -Based Greenway System
Greenway Zones and Their Interrelationship with
Community Development
As the above map illustrates, three zones are identified within the greenway
system. The following considers each of these.
Protected Zone: This zone largely consists of water bodies, wetlands and
parks that are protected from development under current regulatory controls.
Under protected status, no development will occur.
High Ecological Value / Greenway Trail Corridor Zone: This zone consists of
largely upland areas as defined under various natural vegetative cover types,
such as oak savannas, mesic forests, and prairie remnants. The zone should be
viewed as an area where ecological protection opportunities are very high and
that protection of these values should be a foremost consideration in the
development process. It is within this zone that protection strategies such as
buffer systems, conservation easements, and trusts, and so forth can be used
to protect higher value natural resources. Also included in this zone are lineal
corridors that Zink the higher quality natural areas together and provide space
for the proposed city-wide greenway trail corridor.
Currently, development in the high ecological value zone is allowed in
accordance with development requirements as stipulated by city codes and
ordinances. Beyond these regulatory requirements, the ecological values of
these lands are not substantively protected. In addition, land ownership rights
and economic development pressures preclude the possibility of arbitrarily
limiting development in this zone. Given this, fostering a conservation
approach to development is the most advantageous way of preserving the key
ecological values in this zone while at the same time allowing development to
proceed in an economically viable fashion.
Ecolog ical Enhancement Zone: This zone refers to areas of the city that fall
outside the other two zones. Typically, this includes lands that are defined
under agriculture designation and thus do not currently exhibit high ecological
value, but offer opportunities for significant ecological enhancements as part
of future land use decisions. An example of this is transitioning some
agriculture fields into prairie communities as part of a conservation
development. Also included under this zone are areas already developed,
such as a residential subdivision, where ecological enhancements are still
possible, albeit perhaps on a more limited basis.
The main objective of this zone is to articulate that the opportunities to
expand the footprint of high quality natural areas, and thus the greenway
system, within the city are very extensive and that sound ecological protection
strategies should not be limited only to areas that currently exhibit higher
ecological qualities. Quite to the contrary, under the mantra of a conservation
development approach to planning, protecting and enhancing the ecological
values of all lands should be considered whenever development occurs in the
community. Further, every attempt should be made to link these newly
created natural areas to the larger greenway system as depicted on the map
wherever opportunity to do so exists. This linkage should be both in the form
of a natural landscape features as well as linear trail corridors that allow for
human access and appreciation of these natural amenities.
Handbook for Environmental Planning and Conservation Development
City of Lino Lakes
4.3
• Echlb'd- Open s ace through stor
p
managazuenticT
Helping to structure growth on the urban fringe
Many current events described in
the media point to the continua- .
tion of a past trend: like it or not,
most future growth will continue to occur
in the suburbs. At subdivision and land
development review meetings, one of the
most frequently discussed topics is
stormwater management. Unimaginative
engineering approaches to stormwater
management, though, often leave subdivi-
sions pockmarked with city depressions in
remote corners collecting debris, while re-
maining "on standby" to control runoff
from rare storm events. The costs are
borne by future home buyers, but the ob-
jectives of protecting water resources and
reducing flooding downstream are not
fully realized.
This article advocates a holistic approach
that views stormwater as a vital part of the
hydrologic cycle involving management
practices to insure infiltration, control runoff
pollution, reduce thermal impacts and con-
trol peak flows. Management practices for
this kind of control put the landscape to
work by utilizing processes of nature such
as vegetative filtering during conveyance,
cooling through shade trees, detention
through depression storage, and infiltration.
When implemented in settings that prior to
the introduction of impervious surfaces did
not experience much runoff, such manage-
ment practices can be designed to form sys-
tems that function as an extension of the ex-
isting riparian landscape. The public is
beginning to accept that bodies of water,
wetlands, and floodplains are best used as
permanent open space, protected through
land use controls. These open spaces follow
stream valleys and can be expanded and en-
hanced through stormwater management
practices on adjacent development sites (Fig-
ure 1).
Such management practices are also open
space features and are designed in accor-
dance with performance standards.
Stormwater management measures and ri-
parian lands can be integrated to form a
14 JOURNAL OF SOIL AND WATER CONSERVATION
J. Toby Tourbier
functional riparian "greenway" or open
space system. When viewed comprehensive-
ly, stormwater management offers an oppor-
tunity to structure the present pattern of en-
vironmentally destructive sprawling
subdivisions known as -the suburban
model," and provides as a bonus the protec-
tion of vegetation and wildlife.
The responsibility for accommodating
land use and related stormwater manage-
ment measures lies with municipalities who
execute a review and approval process that
is guided by subdivision and land develop-
ment ordinances. Housing is expected to be
the rust component of the economy to re-
spond to the long awaited upturn from the
current recession. Municipalities now have
an opportunity to formulate an approach en-
abling stormwater management to function
as a tool to help structure growth that is cer-
tain to occur.
The stormwater concern
Stormwater management had its origin.in
what was known in legal language as the
"common enemy rule ": draining runoff away
from houses and backyards as fast as possi-
ble. As populations grew, this practice
proved to be detrimental because one per-
son's backyard drained into someone else's
front yard. The runoff then accumulated, re-
sulting in flood damage downstream. For
many years the federal government was
heavily involved in flood control, only to
discover an ever - increasing spiral of expen-
ditures, but still mounting flood losses.
Today, the pollution associated with runoff
is an additional concern. The first flush of
urban runoff from cities such as Washington,
D.C., was found to be as polluted as raw
sewage, due to paved surfaces collecting
phosphorous -rich dust, nitrogen from acid
rain, and automobile related trace metals.
Urban and suburban runoff today is the sin-
gle biggest source of water pollution, limit-
ing the full use of one third of the nation's
waters (6). In October 1992 the U.S. Envi-
r(1 fl own taI Protection Age I t gan requir-
jtlg 1hai all construction sites of live ages or
more apply for a National Pollutant Dis-
charge Elimination System permit (14). In
implementing these guidelines. many states.
<uch as Pennsylvania. will place special em-
phasis on watersheds of high quality or ex-
ceptional value. Responsibility for imple-
mentation, however. lies at the municipal
level. offering an opportunity to formulate
an approach involving environmental
groups, municipal decision makers. develop-
ers. and their consultants, who through a
joint effort can turn a liability into an open
space asset. This can be implemented
through a comprehensive stormwater man-
agement plan and ordinance.
Comprehensive stormwater man-
agement
Sustainable development, the theme of
the 1992 Earth Summit in Rio de Janeiro, im
plies that we maintain natural systems with-
out impairing their capability for self renew-
al. Stormwater is an essential component of
the water cycle, and management practices
should ensure that natural processes, such
as natural purification of runoff and ground -
water recharge to sustain base flow of
streams. are bring maintained. A compre-
hensive approach views stormwater as a re-
source and sees the land as a treatment
medium.
When we examine the interdependence
of stormwater issues, we see the opportuni-
ties and shortcomings of current practices.
Many practices are ironic. We apply nitrogen
and phosphorus fertilizers and install sprin-
kler systems to irrigate lawns and landscape
features in subdivisions, yet nutrient rich
stormwater is intentionally being prevented
from reaching those plants by curbs, gutter
inlets, and storm drains.
Runoff from paved surfaces is so rich in
nitrogen and phosphorus that NPDES per -
mits (14) are now required for its discharge.
Stormwater can be directed to irrigate land-
scape features (rather than using drinking
water for irrigation), and the nitrogen and
phosphorus it contains can enhance the
growth of vegetation in the landscape.
Rather than flushing stormwater down the
stream we can filter it through the upper soil
horizons to resupply groundwater, thus
maintaining dry weather flow of urban streams
and sustaining their aquatic community.
Figure 1. Streams, floodplains, and wetlands Corm linear riparian open spaces. Land areas used for
stormwater management practices in adjacent subdivisions should be arranged to act as a riparian
extension to jointly form greenways.
JANUARY- FEBRUARY 1994 15
Increase
In Area of
I.ecrrleus
Bartsees
Re
Infiltration
l
Reduatlen
of Dry
Weather
Strewn Plow
t7'
Reduction
of Ground
Water
1 d
Runoff
Mere
Frequent Oeor-
bank
Flew el Dtreanis
Flood
Damage
L..■■••■
Strome Bask
Ereulsa
Runoff
Pollution
Eroelee led
Ingresses
U S ded
Sellds
Increased
Leads of N.
P. Pb. Cu.
Za and SOD
Siltation
of Streams
end
Reservoirs
Deterioration
of
Stream Health
Figure 2. Interaction of stormwater problems.
•
A comprehensive strategy for stornwater man-
agement implies (a)
1) A joint approach for the following tasks
controlling increases in runoff peaks, (b) prevent-
ing losses in infiltration (c) controlling runoff pol-
lution, and (d) reducing thermal pollution;
2) linking together a "treatment trait" of mea-
sures with functions that complement each other
to implement tasks shown above, and
3) a clustering and combination of
stormwater measures to form a vegetated ri-
parian greenway that, together with flood -
plains and wetlands, form a stream valley
Figure 3. Typical changes in runoff flows from paved surfaces affecting
the water budget.
etas
EMS
TEAlP ATIOE
NATURAL
GROOM
COVED
SNAGGY 1E►
■1[T1ATan
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2OS
n
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471
PAVED
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WSW
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PAVED
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Sees J.T. T..Wr sad R Vhge.wa. Warr Rsrear hatroefra Tarak F A Mmsd at d Mmans r hater Ilbafr
Rsneaw At Las/ anakM.vot p. 3.
16 JOURNAL OF SOIL AND WATER CONSERVATION
and open space system that structures ex-
pansion on the urban fringe and offers sec-
ondary benefits by (a) providing a scenic
setting for adjacent uses, (b) forming corri-
dors of natural areas for wildlife protection
and passive recreation, and (c) by separating
and screening incompatible uses.
Interactions of stormwater problems
Stormwater problems all relate to increas-
es in impervious surfaces and tend to inter-
act-Tr tgtrre 2 ' ustrates. a effect is the
conversion of "natural" streams into "urban"
streams. Higher and more extended flooding
leads to streambank erosion and to the
"slumping" of streambanks. This in turn
causes the toppling of riparian vegetation,
loss of shade, stream warming, and reduced
oxygen—carrying capacity. Sediments caused
by erosion from streambanks and from con-
struction sites combine with runoff pollu-
tants from paved surfaces: nitrogen, phos-
phorus, lead, zinc, copper, and oxygen
consuming wastes. Through siltation,
streams and reservoirs become shallow and
more responsive to warming. These phe-
nomena coincide with reduction of base
flow, particularly in headwater streams,
caused by the sealing of the ground with
impervious surfaces and the reduced infiltra-
tion of precipitation. All of these conditions
lead to a deterioration of stream health.
Storm sewers' effect on water quality is
shown by differences in streambeds at their
point of discharge, expressed in benthic
algal growth (caused by nutrients), organic
slime on rock (caused by carbon), discol-
ored or black stones upon turning (caused
hw 1jrc'carbons). and silt plumes t•edimen-
tation ).` all of which affect the entire food
chain and the species abundance and diver-
.it }' of aquatic life. including fish (8 . The in-
teraction of these problems distinguish
urban stream., (3).
For stormwater management to compre-
hensively protect the quality of streams. it
needs to address the multiplicity of prob-
lems. rather than solely controlling peak
flows. The interaction of problems offers an
opportunity to solve a range of problems si-
multaneously, as the following descriptions
illustrate.
Controlling increases in runoff peaks.
Many municipalities have passed ordinances
requiring that post - development runoff
peaks not exceed pre - development peaks.
This is accomplished by detaining and then
releasing accumulated runoff through a
basin outlet device sized to pass flows at
pre - development rates. In an attempt to
-play it safe," municipalities often set as a
design standard the control of the 10 to 100
year frequency storms with outlet devices so
big that they pass, unchecked, smaller
storms of two- to five -year frequency, which
are the cause of much of the flood damages
experienced today.
Even when designed to also control small-
er storms, detention basins do not reduce
the volume of -runoff, and only control peak
`aces & flow. Most of the thousan .sd; of de-
tenti o basins found in the areas surround-
ing our cities are constructed as so- called
-dry basins" that do not improve the quality
of urban runoff. Often unsightly, such basins
are usually found in far comers, using left
over spaces of subdivisions. Alternatives to
standard dry basins are "extended detention
basins" and -wet basins" with a permanent
pools that offer water quality improvement.
Such urban ponds are an aesthetic enhance-
ment and have been found to more than
double adjacent property values (11). They
are a delight for urban residents and provide
habitat for water related wildlife. A survey in
Columbia, Maryland, found that 75 percent
of homeowners preferred "wet ponds" for
stormwater management while only 17 per-
cent liked dry detention basins. Residents
overwhelmingly (94 percent) felt that it is
desirable to manage future stormwater
basins for fish and wildlife as well as for
flood and sediment control (1).
Preventing losses in infiltration. To
control the increased volume of runoff leav-
ing a site, and not lust the higher peak
flt,ws, ste s can be taken to maintain infiltra-
tion'. ure 3 presents a Nvater budget that
sFiows how groundwater recharge is re-
duced by impervious surfaces, while runoff
volumes rise. Annual precipitation in many
sections of Maryland, for example, is 112 cm
Riparian Forest Buffer
Figure 4. A "wooded wetland with infiltration trenches" as a functional
landscape enhancement.
(44 in). After infiltration, 30 cm/yr (12 in/yr)
of this total reemerges to support the base
flow of streams. Low density single family
residential development with an irnpervious-
ness of 20 percent has been shown to re-
duce this base flow by 12 percent to 27
cm/yr (10.6 in/yr) while commercial devel-
opment with an imperviousness of 90 per-
cent would reduce it by 90 percent to 3
cm/yr (1.2 in/yr) (5).
The use of stormwater infiltration devices
that infiltrate the first 1.25 cm (.5 in) of
runoff would maintain 29 cm/yr (11.6 in/yr)
of post development base flow (96 percent)
for single family residential uses and 22
cm/yr (8.7 in/yr) (72 percent) of the base
flow on commercial sites (5). As indicated
earlier, maintaining such base flow is partic-
ularly important for headwater streams.
Problems with standing water such as expe-
rienced in Maryland can be designed out
(2).
Infiltration rovides the added benefit of
water qu iry enhancement as impurities in
the "firsh" of runoff are filtered. Infiltra-
tion can be accomplished through measures
that enhance the landscape, such as the
woody wetland with infiltration trenches
shown in Figure 4.
Controlling runoff pollution. The Clean
Water Act has set goals to make the Nation's
waters fishable and swimmable. The Nation-
wide Urban Runoff Program (13) has docu-
mented the severity of the problem, and
models have been developed based on its
findings. This includes a highly practical
"Simple Formula" set forth by the Metropoli-
tan Washington Council of Governments (7)
that permits the quantification of runoff pol-
lution loading for development sites.
The major sources of runoff pollution
from urban areas are impervious surfaces
that collect nitrogen deposited through acid
JANUARY- FEBRUARY 1994 17
Figure 5. A "planted wooded vegetative filter strip" by Pohiig Builders,
Inc., Malvem, Pennsylvania. The gravel filled trench in the foreground
acts as a level spreader.
rain and phosphorus contained in dust, both
accumulating through "atmospheric deposi-
tion." Furthermore, there are automobile re-
lated deposits: copper from brake linings,
zinc from tire wear, lead, and other pollu-
tants that, upon decomposition, consume
oxygen. Runoff pollution has been found to
be largely unaffected by frequent street
cleaning activities and occurs in both down-
town areas and in suburban settings (13).
Runoff pollutants are most effectively con-
trolled through the use of vegetation that
can be planted to act as filter strips to slow
down flows, induce sedimentation, convert
nitrogen and phosphorus into plant tissue,
and encourage infiltration and the related
cleansing actions. Figur 5 shows a planted
vegetative filter strip with woody vegetation,
as advocated by the U.S. Department of
Agriculture. Its root zone acts as a filtering
device for below -ground lateral flows of nu-
trient enriched groundwater (12). Much re-
search on vegetative filters in the past has
concentrated on grassy filter strips, but exist-
ing woodlands are also reported to have a
high trap efficiency for surface filtration
(15). In residential areas filter strips can be
seeded with a grass and wildflower mix to
become an attractive wildflower meadow.
Cori 11111fTherrnal pollution. Directly
related to water quality is stream warming
through urban runoff and the resulting re-
duction of the water's oxygen-carrying ca-
pacity. Drainage improvements often lead to
the removal of riparian vegetation and result
in a loss of shade. A study by the Metropoli-
tan Washington Council of Governments
18 JOURNAL OF SOIL AND WATER CONSERVATION
concludes that there is an average tempera-
ture increase of 1.5 °F in headwater streams
for every 30 m (100 ft) of flow through
poorly shaded or open reaches of a stream
(4). A 23 m (75 ft) buffer of vegetation on
both sides of the stream can offset this prob-
lem and offer the additional benefit of
stormwater runoff filtration when used in
conjunction with level spreading devices
(Figure 6). Many management devices, such
as impoundments that cause stream warm-
ing, need to be shaded through planting.
Stormwater management planning
Proximity to open space, woodlands,
fields, clean streams, and scenic views are
among the reasons people give for moving
to the suburbs. In a tragic way, urbanization
tends to destroy many of these characteris-
tics. As an example, the 2.6 million new resi-
dents in the Chesapeake Bay Basin by the
year 2020 are projected to be living mostly
in low - density, large -lot developments with
inefficient infrastructure and extensive im-
permeable surfaces, all leading to an aggra-
vation of current runoff problems (16).
Stormwater management planning at the
urban fringe, the area where most land use
decisions are being made today, offers an
opportunity to influence the pattern of new
development in the suburbs by stitching to-
gether linear open space systems that follow
stream valleys to protect natural processes.
This can be accomplished most productively
on the municipal level through the formula-
tion of a stormwater management plan re-
flecting a three step process that starts with
(1) an analysis of issues, (2) leading to the
setting of standards, and (3) the passage of
an ordinance containing a procedure to
apply standards to development sites.
Following the above steps, a stormwater
management plan is currently being pre-
pared for London Grove Township, Pennsyl-
vania (10).
Realization and analysis of issues
On the local level, land use decisions are
being made by elected officials. These are
often laymen representing their constituen-
cy, relying on the advice of the municipal
engineer, the solicitor, and those serving on
the planning commission. Stewardship for
comprehensive water resource management
is only possible when there are knowledge-
able community leaders and an informed
constituency. This can be accomplished
through the preparation of a stormwater
management plan, containing a survey of
existing conditions and an analysis of prob-
lems and opportunities, presented in a docu-
ment that people can read to obtain back-
Ind infarmation.
In London Grove Township. Pennsylvania.
for example. the stormwater plan contains
an analysis of stormwater flow. thermal im-
pacts, runoff quality, erosion and sedimenta-
tion, and groundwater recharge. It further
contains a delineation of the outcrop area of
Cockeysville Marble, a high yielding aquifer
that is vulnerable to groundwater contami-
nation. The selection of management prac-
tices considers the origins of stormwater (di-
vided into three harmfulness classes) and
the classifications of streams in the township
as cold water fishery streams, some with
'exceptional value," and others as trout
stocking streams.
Setting standards
Municipalities have the legal authority to
set standards that relate to public health,
safety, and environmental quality. Standards
are numerical thresholds that separate ac-
ceptable and unacdeptable impacts. A stan-
dard that most municipalities have in their
books is that pre - development runoff peak
flows not exceed post - developme ...peak
flows. In order to rotect str „a,� a re-
source, sere n-
dar or the concerns described above.
A stormwater management ordinance
Stormwater management requirements are
often part of the subdivision regulations of a
municipality where, together with erosion
and sediment control, they take up but a
few pages. In order to achieve clean stream
goals, stormwater management should be
addressed through a separate ordinance that
iparian Forest Buffer
Riparian Forest Bider
Figure 6. The "wooded riparian forest buffer" shades the headwater
stream and keeps it cool. Concentrated storm flows are reconverted to
sheet flow through a level spreader and infiltrated in part before they
reach the stream.
relates to, and implements, the stormwater
plan. It should contain a statement of find-
ings, explain its legal base, and set forth de-
sign standards and criteria. The ordinance
should come into play whenever a change
in land use is being sought, giving the de-
veloper a comprehensive set of stormwater
management requirements, management
measures, and design standards and criteria.
Before development can commence, the de-
veloper should be required to make a plan
submission that follows a defined format
and is subject to a review and approval
process. Such a process should permit inter-
action between parties, and, if necessary, for
modifications to be made to the plan. There
should be defined permit requirements and
procedures including guidelines for fees, a
Attenuation at
Seduce Prior to
Colneatratlen
Coneeyaane
Pre - Treatment
b
Contention
for Peak
Central
V
Extended Detention/
Dententlee ter
Quality Centred
Infiltration
ter Northam'
ry lemaet
Mitigation le...
Temp raiIre Cantrell
Maintenance
Figure 7. Components of a stormwater management system.
JANUARY — FEBRUARY 1994 19
Eslulas Riparian
Forest
Ytennlat Stream
100 Year Floodplala
�Committed
Stawwara Meadow
forlgfuteadoa
Stormwater Measures to Form Greenways
leaky for Sediment Caaol
Gel Spreader for DI:tha wt
dgrnfo• ea
Riparian Form Beer
Dodo Sure Detention Bala
Strop Soli
Cenmweud Woody Milani
rah 1*fl t mdoa Derek's
We Estonded
Dote Basta
•
i 1 1
a:
1
3
3
rN
&mkt for
Whom Carrot
stop Mope Ater
- Cressy Swale
Chockdasss
Figure 8. The linkage of stormwater management measures forms greenways in the landscape. A
perennial stream and flooded wetland are surrounded with a forest buffer. Stormwater conveyed
through a grassy swale flows through a forebay and an extended detention basin before infiltrating
through a constructed woody wetland with infiltration trenches. In the system above, all small flows are
Infiltrated while larger flows are detained and slowly released.
schedule of inspections, requirements for a
performance bond, penalties for non com-
pliance, and an appeal process.
There are many benefits to such an ordi-
nance. For the developer, it sets a rationale
that will apply equally to every applicant.
For residents of the municipality it is the ve-
hicle through which water resources are
being protected. Steps that are lacking in
most current ordinances are a pre- and
post- development assessment of streams that
receive stormwater discharges, a review of
safety and aesthetic considerations of the de-
sign, a requirement for rigorous inspection
during construction, an "as built" documen-
tation of "hard" elements, annual inspec-
tions, and the testing of measures (BMPs) in
comparison with pre - development condi-
tions. What is lacking most of all is a holis-
tic approac that goes beyond peak flow
control. '
SL ?water management and nonpoint
pollution control have long been a concern
of the states and of the federal government.
Examples are the new NPDES permit regula-
20 JOURNAL OF SOIL AND WATER CONSERVATION
tions (Section 319 of the Clean Water Act),
and runoff control under the Coastal Zone
Act Reauthorization Amendments of 1990.
Success of any of these programs depends
on municipal decision makers and their per-
ception of the advantages of combining
management measures into open space sys-
tems as well as the public benefits of clean
water.
Open space greenways through
stormwater management
Stormwater management measures pre-
sented here can be linked to form functional
landscape elements on development sites
and combined to form continuous stream
valley systems or greenways. This opportu-
nity was realized in London Grove Town-
ship, Pennsylvania, (10) and Loudoun Coun-
ty, Virginia, (9) where the author worked as
a consultant, gaining the experience on
which this article is based.
A plan and ordinance ensures that
• ..ionfyrater management is vie ved compre-
hen ` i`'el`•, that a rational procedure is being
used for the selection of measures. and that
measures add up to form landscape ele-
ments that are an enhancement for the com-
munity.
The flow diagram in Figure 7 shows the
components of a stormwater management
system that can be linked to form a 'treat-
ment train,' starting with attenuation (vol-
ume reduction) at source prior to concentra-
tion, conveyance, and pre - treatment. This
1ea& To- °opitons such as runoff detention
(holding back and slowly releasing) or re-
tention (holding back total flow) for infiltra-
don. Finally there are considerations for sec-
ondary impact mitigation (e.g. temperature
control) and maintenance.
Figure 8 shows integration of these fea-
tures into the landscape. In the example
shown, a perennial stream and permanently
flooded wetland is surrounded with a 23 m
(75 ft) riparian forest buffer. A riparian area,
once barien of trees, has been reforested.
Stormwater conveyed through grassy swales
with check darns is pre- treated in a forebay,
permitting course sediment control. It is then
passed into a wet extended detention basin
that settles out fine suspended solids prior to
release into a constructed woody wetland
with infiltration trenches. Another system
shown conveys piped stormwater into a
forebay, permitting the separation of small
storms to be infiltrated in a blossoming
stormwater meadow, while bigger storms
are detained and slowly released by level
spreaders for discharge dispersion in the ri-
parian forest buffer.
All these elements combine to create a
scenic setting for people, wildlife, plant
communities. and water resources. This is an
example of how sustainable development
can achieve open space through stormwater
management, while structuring growth, and
. creating a function for designated open
space.
Conclusion
Municipalities should prepare stormwater
management plans and ordinances that treat
stormwater as a resource. This helps to meet
state and federal guidelines, protects public
health and safety, and can achieve open
space greenways. Stormwater management
should replenish groundwater supplies,
maintain the dry weather flow of urban
streams through infiltration and delayed dis-
charge. reduce stream warming, use vegeta-
tion to utilize water pollutants as fertilizer,
and reduce flooding. Management practices
can be designed to be tools for conviviality,
permitting cohabitation of people, plants,
and wildlife. adding to the quality of life.
REFERENCES CITED
I. Adams. W.A.. Dove. I..F... and Leedv. L.L. 19H..
Public Attitudes Toward Urban Wetlands fin-
Stormwater. Control and Wildlife Enhancement.
Wildlife Soc. bull. 12:299-503.
2. Ferguson. B.E. 1990. Urban Stormwater I jiItm-
tion, Purposes. Implementation. Results. J. Soil
and Water Cons. 45(61:601 -609.
3. Ferguson. B.E. 1991. Urban Stream Reclamation.
J. Soil and Water Cons. 46(5).
4. Galli, J. 1990. Thermal Impacts Associated with
Urbanization and Stormwater Management Best
Management Practices. Metropolitan Washing-
ton Council of Governments, Washington, D.C.
5. Maryland Department of Natural Resources.
1986. Minimum Water Quality Objectives and
Planning Guidelines for Infiltration Practices.
Sediment and Stormwater Division, Maryland
DNR. Annapolis.
6. National Water Quality Inventory. 1988. 1988
Report to Congress. U.S Government Printing Of-
fice. Washington. D.C.
7. Schueler. T. 1987. Controlling Urban Runoff.
Metropolitan Washington Council Governments.
Washington. D.C.
8. Schueler, T.. J. Galli, L. Herson, P. Kumble and
D. Shepp. 1991. Developing Effective BMP Sys-
tems for Urban Watersbeds. Metropolitan Wash-
ington Council of Governments, Washington,
D.C.
9. Tourbier, J.T.. and A. Walmsley. 1990. Mitiga-
tion Measures for Adverse Environmental Im-
pacts- General Plan 1990 -2010. Loudoun Coun-
ty, Virginia. Draft with Lane Kendig, Inc..
Philadelphia, P.S.
10. Tourbier, J.T., and A. Walmsley. (In press).
Stormwater Management Plan and Stormwater
Ordinance for London Grove Townsbip, Pennsyl-
vania. PA. Tourbier & Walmsley, Inc.
11. Tourbier, J.T., and R. Westmacott. 1992 Second
Edition. Urban Lakes and Ponds. The Urban
Land Institute. Washington, D.C.
12. U.S. Department of Agriculture. 1991. Rtpar an
Forest Buffers- Function and Design for Protec-
tion and Enbancement of Water Resources.
USDA Forest Service. Northeastern area, Radnor,
PA.
13. US. Environmental Protection Agency. 1982. Re-
sults of the Nationwide Urban Runoff Program.
U.S. EPA. Government Printing Office, Washing-
ton. D.C.
14. U.S. Environmental Protection Agency. 1990.
National Pollutant Discharge Elimination System
Permit Application Regulations for Storm Water
Discharger Final Rule. U.S. EP k, Washington.
D.C.
15. Wong, L.S., and R. McCuen. 1982. The design of
vegetative buffer strips for runoff and sediment
control. In Stormwater Management in Coastal
Areas. Tidewater Administration. Maryland De-
partment of Natural Resources. Annapolis.
16. Year 2020 Panel of the Chesapeake Bay Execu-
tive Council. 1988. Population Growth and De-
velopment in the Chesapeake Bay Watershed to
the Year 2020. Referred to in Conflicts of Urban
Sprawl Impact Water Quality in Cbesapeake
Bay - Effects of Population Growth and Develop-
ment on Water Quality. US. Water News. Octo-
ber. 1990. p. 7.
J. Toby Tourbier of Tourbier
& Walmsley, Inc.,
Pbiladelpbia, Pennsylvania,
19107 -2405, is a planning
consultant, autbor, and co-
author of a range of
stormwater related
documents. He is affiliated
with the Department of
Landscape Architecture and
Regional Planning at the
University of Pennsylvania,
and bas been an expert
witness and consultant to
units of government and to
developers.
JANUARY - FEBRUARY 1994 21
b& 10
On -Lot Infiltration
General Description
On -lot infiltration systems promote infiltration at the individual lot
level, controlling runoff at its source. These systems are off -line and
generally receive sheet flow runoff. The main feature that distin-
guishes these systems from other infiltration systems (such as
infiltration basins and trenches) is scale. These small systems accept
runoff from a single residential lot. Although infiltration basins and
trenches have many design features in common with on -lot infiltra-
tion systems, the Infiltration Basins and Infiltration Trenches BMP
Sections refer to larger lot, end -of -pipe facilities.
On -lot infiltration systems' primary function is to mitigate the
normal impacts of urbanization on the natural water balance. This is
done by turning water that would normally become surface runoff (a
waste product) into a resource that waters trees, recharges groundwa-
ter and provides stream baseflows. On -lot infiltration systems also
function to improve water quality by removing some pollutants from
the runoff as it infiltrates. Also, because these systems serve to
reduce the volume of runoff, they contribute to both erosion protec-
tion and flood control. Lastly, the use of these systems reduces the
size and cost of downstream water control facilities.
On -lot infiltration systems include:
• Reduced lot grading (Figure 1)
• Directing roof leaders to soakaway pits (Figures 2 through 4)
• Directing roof leaders to rain barrels (Figure 6)
• Directing roof leaders or other surface runoff to other vegetated
areas, such as rainwater gardens (Figures 7 through 10)
These source controls address measures that can be applied by the
developer or the homeowner. Public education programs within
municipalities can help to educate citizens on the role they can play
in the application of these systems.
On -lot infiltration systems are not to be used for infiltrating any
Metropolitan Council / Barr Engineering Co.
Purpose
Flow attenuation
Water Quantity
11
Runoff volume reduction
Pollution Prevention
Soil erosion
Sediment control
Nutrient loading
Water Quality
N/A
N/A
N/A
Pollutant Removal (Soakaway Pits
and Rainwater Gardens)
Total suspended sediment (TSS)
Total phosphorus (P)
Nitrogen (N)
Heavy metals
Floatables
Oil and grease
Other
Fecal coliform
Biochemical oxygen demand
(BOD)
•
•
•
•
11
•
11
11
•
11
Primary design benefit
Secondary design benefit
Little or no design benefit
3 -141
n-Lot Infiltration
runoff that could be significantly contaminated with sediment and other pollutants, such as runoff from high -
potential pollutant loading areas like garages and gas stations.
In general, on -lot infiltration systems can be implemented for soil types of loam and coarser. Some authorities
discourage infiltration systems at sites where soils have 30 percent or greater clay content, or 40 percent or
greater silt content. A soils analysis is helpful in assessing the viability of infiltration systems. More detailed
information on procedures for testing infiltration rates can be found in the Infiltration Basins and Infiltration
Trenches BMP Sections. If native soils are considered to have a low infiltration capacity, filtration systems should
be considered as an alternative to infiltration (see the Filtration Systems BMP Sections).
Advantages
• Can reduce the volume of runoff from a site, thereby reducing the size and cost of downstream stormwater
control facilities.
• Can be utilized in retrofit areas where space is limited and where additional runoff control is necessary.
• Rainwater gardens can provide an aesthetically pleasing amenity when designed to support perennial flowers
in the summer and display vividly colored or patterned shrubs in the winter.
• The potential for clogging of rainwater gardens is reduced compared to end -of -pipe infiltration techniques
(infiltration basins and trenches) because these systems generally accept runoff only from roofs (roof drain-
age contains fewer suspended solids than road runoff) or driveways, lawns and sidewalks.
• Can be used at sites where storm sewers are not available.
• Can provide groundwater recharge.
• Flowering plants and ornamental grasses incorporated into the design of rainwater gardens are attractive to
birds and butterflies.
Limitations
• Only applicable in small drainage areas of a half -acre or less.
• Water ponded on lots may take 24 to 48 hours to drain, which may restrict some of the use of the land.
• Some maintenance (unclogging soakaway pits, periodically removing sediment from rain barrels and rainwa-
ter gardens) is required to ensure the proper functioning of these systems. However, sediment accumulation
is an indication that the infiltration techniques are working. This sediment would otherwise have washed
downstream to a larger water body.
• Not recommended for lots with high sediment loadings or contaminated runoff.
• If the infiltration rate of the native soils is low, these systems may not function as desired.
• The bottom of these structures (with the exception of rain barrels) should be a minimum of 3 feet above the
seasonally high groundwater table to prevent the possibility of groundwater contamination.
3-142 Minnesota Urban Small Sites BMP Manual
On -Lot Infiltration
Reduced Lot Grading
Description
Development standards often require minimum lot grades of 2 percent for adequate drainage of stormwater away
from a building. Some authorities, however, have proposed reducing minimum lot grades from 2 to 0.5 percent to
promote infiltration. This option is mainly intended to promote infiltration by slowing stormwater runoff from the
roofs and yards and allowing it to soak into the lawn.
A reduction in the lot grading is generally a viable option if the land is naturally flat. In hilly areas, alterations to the
natural topography should be minimized. Developers and homeowners should check the acceptability of this
practice with the local municipality, because some municipalities may not permit its use.
Similarly, shallow depressions can be graded into lawns. Depressions need not be very deep to make a significant
contribution to overall surface storage capacity and stormwater quality. For example, a square lawn area 50 feet
on a side, sloping 2 percent toward the center, will create a low point 6 inches below the outside rim. This 6 -inch
slope over 25 feet of distance is barely noticeable, and is similar to standard grading practice for lawn areas. This
50 -foot by 50 -foot by 6 -inch -deep lawn area creates a storage capacity of 413 cubic feet. If adjacent impervious
surfaces, such as sidewalks, rooftops, and roads are designed to sheet flow into this concave lawn, their runoff can
gradually infiltrate into the soil as well. Catch basins located at the upper edge of the concave vegetated surfaces
can collect runoff from larger storms.
Figure 1 illustrates these lot grading changes on a residential lot.
Design Guidelines
• In order to ensure that foundation drainage problems do not occur, the grading within 6 to 12 feet of a build-
ing should be maintained at 2 percent or higher (local municipal standards should be reviewed to ensure that
the grading around a building is in compliance). Areas outside of this boundary may be graded at less than 2
percent to create greater depression storage and promote natural infiltration.
Figure 1: Examples of Lot Grading Changes
Source: Ontario Ministry of the Environment, 1999
Metropolitan Council / Barr Engineering Co.
3 -143
On -Lot Infiltration
Reduced Lot Grading
• Infiltration can be improved by tilling (scarification) of the lots with flatter grading to a depth of approximately
12 to 24 inches before sod is laid. This would also be of general benefit in all residential areas to address the
problems associated with soil compaction (loss of recharge potential) which occurs during construction. The
incorporation of compost or manure into the soil also increases infiltration. It should be noted that tilling this
deep may require special equipment.
• In areas where flatter lot grading is implemented, roof leaders that discharge to the surface should extend 6
feet away from the building.
Construction
• Soil compaction must be avoided wherever possible. For example, vehicles should never be parked on the
future lawn during construction.
• Mass grading should be avoided to keep native soil profiles intact and to minimize the area of soil compac-
tion.
• If soils become compacted through construction activities, the soil should be tilled to 18 inches and 6 to 12
inches of organic compost should be incorporated into the soil.
Soakaway Pits
Description
Soakaway pits, also known as downspout infiltration systems, roof leader infiltration systems and dry wells, can
be distinguished from infiltration trenches in terms of scale and sophistication of design. Soakaway pits are
designed to receive runoff from individual roof leaders, whereas infiltration trenches are used for large -lot appli-
cations (see the Infiltration Trenches BMP section for more detail).
Soakaway pits are small, excavated pits, backfilled with aggregate, used to infiltrate "good quality" stormwater
runoff, such as uncontaminated roof runoff. Rooftop runoff is discharged to the soakaway pit through the roof
leader, which extends directly into a stone -filled reservoir. Figures 2 through 4 show examples of soakaway pit
designs.
The use of soakaway pits is limited by a number of site constraints, including soil type, contributing drainage
area, depth to bedrock, and depth to groundwater. Rooftop gutter screens are needed to trap particles, leaves and
other debris, and must be cleaned regularly.
Soakaway pits for roof leader drainage have been implemented in Toronto, Maryland and Europe. A monitoring
study indicated that 60 percent of 25 soakaway pits studied were operating as designed (Lindsey et al., 1992).
Design Guidelines
If a formal, detailed design is required by local permitting authorities, the design requirements presented in the
Infiltration Trench BMP section can be followed for the design of soakaway pits (although no pretreatment other
than gutter screens is required of a soakaway pit that receives only roof runoff). Other design considerations
include:
3 -144 Minnesota Urban Small Sites BMP Manual
On -Lot Infiltration
Roof
Leader
Removable
Section
Filter
Screen
Figure 2: Roof Leader Discharge to Soakaway Pit
Source: Ontario Ministry of the Environment, 1999
75 - 150 mm
Soil Cover Dependent on Pit Depth
and Native Soil Characteristics
a,c
41!T;1,14,
.'fie -7k "9F "3^,n..�- -m,-
'Depth of pit dependent on soil characteristics
100 mm perforated pipe
Non -woven Filter cloth
Figure 3: Soakaway Pit Details
Source: Ontario Ministry of the Environment, 1999
Metropolitan Council / Barr Engineering Co. 3 -145
alloLt II
Sequencing
Description
A work schedule that coordinates the sequence of land - disturbing
activities with the installation of erosion and sedimentation control
practices.
A construction sequence schedule is a specified work schedule that
coordinates the timing of land- disturbing activities and the installation
of erosion - protection and sedimentation - control measures.
Purpose
To reduce on -site erosion and off -site sedimentation from land -
disturbing activities by installing erosion and sedimentation control
practices in accordance with a planned schedule.
Reduce on -site erosion and of site sedimentation by performing land -
disturbing activities and installing erosion - protection and sedimentation -
control practices in accordance with a planned schedule.
Preserving the natural vegetation on -site to the maximum extent
practicable will minimize the impacts of development on stormwater
runoff. Preferably 65 percent or more of the development site should
be protected for the purposes of retaining or enhancing existing forest
cover and preserving wetlands and stream corridors.
Effectiveness
All land development that clears, grades or fills a significant land area.
The removal of existing surface ground cover leaves a site vulnerable
to accelerated erosion.
Good planningwill:
• Reduce land clearing
• Provide necessary controls
• Restore protective cover.
New development often takes place on tracts of forested land. In fact,
building sites are often selected because of the presence of mature
trees. However, unless sufficient care is taken and planning done, in
Metropolitan Council/Barr Engineering Co.
Purpose
Flow attenuation
Water Quantity
El
Runoff volume reduction
Water Quality
Pollution prevention
Soil erosion
Sediment control
Nutrient loading
Pollutant removal
Total suspended sediment (TSS)
Total phosphorus (P)
Nitrogen (N)
Heavy metals
Floatables
Oil and grease
Other
Fecal coliform
Biochemical oxygen demand
(BOD)
■ Primary design benefit
Secondary design benefit
❑ Little or no design benefit
3-63
c
"7 -�''
i
PHASE I
PHASE II r / k
, PHASE III f)
Description
A work schedule that coordinates the sequence of land - disturbing
activities with the installation of erosion and sedimentation control
practices.
A construction sequence schedule is a specified work schedule that
coordinates the timing of land- disturbing activities and the installation
of erosion - protection and sedimentation - control measures.
Purpose
To reduce on -site erosion and off -site sedimentation from land -
disturbing activities by installing erosion and sedimentation control
practices in accordance with a planned schedule.
Reduce on -site erosion and of site sedimentation by performing land -
disturbing activities and installing erosion - protection and sedimentation -
control practices in accordance with a planned schedule.
Preserving the natural vegetation on -site to the maximum extent
practicable will minimize the impacts of development on stormwater
runoff. Preferably 65 percent or more of the development site should
be protected for the purposes of retaining or enhancing existing forest
cover and preserving wetlands and stream corridors.
Effectiveness
All land development that clears, grades or fills a significant land area.
The removal of existing surface ground cover leaves a site vulnerable
to accelerated erosion.
Good planningwill:
• Reduce land clearing
• Provide necessary controls
• Restore protective cover.
New development often takes place on tracts of forested land. In fact,
building sites are often selected because of the presence of mature
trees. However, unless sufficient care is taken and planning done, in
Metropolitan Council/Barr Engineering Co.
Purpose
Flow attenuation
Water Quantity
El
Runoff volume reduction
Water Quality
Pollution prevention
Soil erosion
Sediment control
Nutrient loading
Pollutant removal
Total suspended sediment (TSS)
Total phosphorus (P)
Nitrogen (N)
Heavy metals
Floatables
Oil and grease
Other
Fecal coliform
Biochemical oxygen demand
(BOD)
■ Primary design benefit
Secondary design benefit
❑ Little or no design benefit
3-63
Sequencing
the interval between buying the property and completing construction much of this resource is likely to be de-
stroyed.
The property owner is ultimately responsible for protecting as many trees as possible, with their understudy and
groundcover. This responsibility is usually exercised by agents -the planners, designers and contractors. It takes 20
to 30 years for newly planted trees to provide the benefits for which we value trees so highly.
Forest and native growth areas allow rainwater to naturally percolate into the soil, recharging ground water for
summer stream flows and reducing surface water runoff that creates erosion and flooding. Conifers can hold up to
about 50 percent of all rain that falls during a storm. Twenty to 30 percent of this rain may never reach the ground
but is taken up by the tree or evaporates. Forested and native growth areas also may be effective as stormwater
buffers around smaller developments.
Planning
Purpose of the construction sequence schedule is to address erosion prevention and sediment control in an efficient
and effective manner. Appropriate sequencing of construction activities can be a cost - effective way to help
accomplish this goal. The plan can be open to changes that should be discussed at the erosion control project
meetings.
The generalized construction activities shown in the following table do not usually occur in a specified linear
sequence, and schedules will vary due to weather and other unpredictable factors. However, the proposed con-
struction sequence should be indicated clearly in the erosion - and - sedimentation- control plan.
• Construction access is normally the first land - disturbing activity. Exercise care not to damage valuable trees or
disturb designated buffer zones as well as establish initial areas on site for preservation.
• Trees should be protected around the drip line of the branches. Avoid activities that will compact the root zone.
• The preserved area should be situated to minimize the clearing of existing forest cover, to maximize the
preservation of wetlands, and to buffer stream corridors.
• The preserved area should be placed in a separate tract or protected through recorded easements for indi-
vidual lots.
• If feasible, the preserved area should be located downslope from the building sites, since flow control and
water quality are enhanced by flow dispersion through duff, undisturbed soils, and native vegetation.
• The preserved area should be shown on all property maps and should be clearly marked during clearing and
construction on the site.
• Principal sediment basins and traps should be installed before any major site - grading takes place. Erect
additional sediment traps and silt fences as grading takes place to keep sediment contained on site at appropri-
ate locations.
• Key runoff - control measures should be located in conjunction with sediment traps to divert water from planned
undisturbed areas out of the traps and sediment -laden water into the traps.
• Install diversions above areas to be disturbed prior to grading. Place necessary perimeter dikes with stable
3.64 Minnesota Urban Small Sites BMP Manual
Sequencing
outlets before opening major areas for development. Install additional needed runoff - control measures as
grading takes place.
The main runoff - conveyance system with inlet and outlet protection devices should be installed early, and used to
convey stormwater runoff through the development site without creating gullies and washes.
• Begin grubbing and grading as soon as key erosion- and sediment - control measures are in place. Once a
scheduled development area is cleared, grading should follow immediately so that protective ground cover can
be reestablished quickly.
• Install inlet protection for storm drains as soon as the drain is functional to trap sediment on site in shallow
pools and to allow flood flows to safely enter the storm - drainage system.
• Install outlet protection at the same time as the conveyance system to prevent damage to the receiving stream.
• Site clearing and project construction increases storm runoff, often making stream- bank - stabilization work
more difficult and costly.
• Do not leave any area bare and exposed for extended periods (see NPDES permit requirements). Leave
adjoining areas planned for development or ones that are to be used for borrow and disposal undisturbed as
long as possible to serve as natural buffer zones.
• Runoff control is essential during the grading operation. Temporary diversions, slope drains, and inlet and outlet
protection installed in a timely manner can be very effective in controlling erosion during this critical period of
development.
• After the land is cleared and graded, apply surface stabilization on graded areas, channels, dikes and other
disturbed areas. Stabilize any disturbed area where active construction will not take place for 21 working days
(see NPDES permit requirements) by temporary seeding and/or mulching or by other suitable means.
• Install permanent stabilization measures after final grading, in accordance with the vegetative plan. Temporary
seeding and/or mulching may be necessary during extreme weather conditions with permanent vegetation
measures delayed until a more suitable installation time.
• Coordinate building construction with other development activities so that all work can take place in an orderly
manner and on schedule. Experience shows that careful project scheduling improves efficiency, reduces cost
and lowers the potential for erosion and sedimentation problems.
• Landscaping and final stabilization is the last major construction phase, but the topsoil stockpiling, tree preser-
vation, undisturbed buffer area, and well - planned road locations established earlier in the project may deter-
mine the ease or difficulty of this activity.
All disturbed areas should have permanent stabilization practices applied. Unstable sediment should be removed
from sediment basins and traps and incorporated into the topsoil, not just spread on the surface.
• All temporary structures should be removed after the area above has been properly stabilized. Borrow and
disposal areas should be permanently vegetated or otherwise stabilized. In planning construction work, it may
be helpful to outline all land - disturbing activities necessary to complete the proposed project.
• Develop a list of all practices needed to control erosion and sedimentation on the site. These two lists can then
be combined in logical order to provide a practical and effective construction - sequence schedule.
Metropolitan Council/Barr Engineering Co. 3-65
Sequencing
Construction
Many timely construction techniques, such as shaping earthen fills daily to prevent overflows and constructing
temporary diversions ahead of anticipated storms, can reduce the erosion potential of a site. These type of activi-
ties cannot be put on the construction sequence but should be used whenever possible.
Following a planned construction- sequence schedule to control erosion should help keep field personnel aware of
the possibilities of erosion prevention through construction management.
Maintenance
Follow the construction sequence throughout project development. When changes in construction activities are
needed, amend the sequence schedule in advance to maintain management control. Orderly modification assures
coordination of construction and erosion - control practices to minimize erosion and sedimentation problems. When
major changes are necessary, you may want to send a copy of the modified schedule to the local permitting
authority.
Vegetation and trees should not be removed from the natural growth retention area, except for approved timber
harvest activities and the removal of dangerous and diseased trees.
3-66 Minnesota Urban Small Sites BMP Manual
Sequencing
1
Sequent ng Table
1
2
3
4
5
Construction Activity
Schedule Consideration
Identify and label protection areas (e.g..
buffer zones, filter strips, trees).
Site delineation should be completed before
construction begins.
Construction access. Construction entrance,
construction routes, equipment parking areas
and cutting of vegetation (necessary
perimeter controls).
First land- disturbing activity — Establish protected
areas and designated resources for protection.
Stabilize bare areas immediately with gravel and
temporary vegetation as construction takes place.
Sediment traps and barriers. Basin traps,
sediment fences, and outlet protection
(necessary perimeter controls).
Install principal basins after construction site is
accessed Install additional traps and barriers as
needed during grading.
Runoff control. Diversions, silt fence,
perimeter dikes, water bars, and outlet
protection.
Install key practices after principal sediment traps
and before land grading. Install additional runoff
control measures during grading.
Runoff conveyance system. Stabilize stream
banks, storm drains, channels, inlet and
outlet protection, and slope drains.
Where necessary, stabilize stream banks as early as
possible. Install principal runoff conveyance
system with runoff-control measures. Install
remainder of system after grading.
Grubbing and grading. Site preparation:
cutting, filling and grading, sediment traps,
barriers, diversions, drains, surface
roughening.
Begin major grubbing and grading after principal
sediment and key runoff control measures are
installed. Clear borrow and disposal areas only as
needed. Install additional control measures as
grading progresses.
Surface stabilization: temporary and
permanent seeding, mulching, sodding and
installing riprap.
Apply temporary or permanent stabilization
measures immediately at all disturbed areas where
work is delayed or complete.
Building construction: buildings, utilities,
paving.
Install necessary erosion and sedimentation control
practices as work takes place.
Landscaping and final stabilization:
topsoiling, planting trees and shrubs,
permanent seeding, mulching, sodding,
installing riprap.
Last construction phase - Stabilize all open areas,
including borrow and spoil areas. Remove and
stabilize all temporary control measures.
1 Maintenance
Maintenance inspections should be performed
weekly, and maintenance repairs should be made
immediately after periods of rainfall.
7
9
Source: MPCA , 2000
Metropolitan Council /Barr Engineering Co. 3-67
Sequencing
Sources
1. Mecklenburg, D. 1996. Rainwater and Land Development. Division of Soil and Water Conservation, Ohio
Department of Natural Resources. Columbus
2. Minnesota Department of Transporation. 2000. Standard Specifications for Construction. St. Paul.
3. Minnesota Pollution Control Agency. 2000. Protecting Water Quality in Urban Areas: Best Management
Practices for Dealing with Storm Water Runoff from Urban, Suburban and Developing Areas of Minne-
sota. St. Paul.
4. Ramsey Soil and Water Conservation District. 1989. Ramsey County Erosion and Sediment Control
Handbook. St. Paul.
3-68 Minnesota Urban Small Sites BMP Manual
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Agenda Item 6A
Environmental Board Meeting Date: December 19, 2001
Topic:
Summary:
Interim Ordinance Prohibiting Residential Development
Zoning /Subdivision Ordinance Update Process
The City is in the process of considering adoption of an Interim Ordinance
prohibiting new residential preliminary plats, residential rezoning, and allocating
MSUA reserve for new residential development. The purpose of the Interim
Ordinance, often called a "Moratorium" is to provide the city with an opportunity
to update its zoning and subdivision ordinances to implement the goals and
policies of the Comprehensive Plan.
The Interim Ordinance does not apply to the following:
1. Final Platting of approved preliminary plats
2. Development within the "Village" area
3. Minor subdivisions or plats resulting in the creation of four or fewer Tots,
provided that said subdivisions are within the existing MUSA
4. Commercial and Industrial development
5. Building Permits and Site Plan Reviews
The Planning and Zoning Board reviewed the proposed Interim Ordinance and
held a public hearing on December 12, 2001 and recommended approval of the
ordinance. The City Council will be considering approval of the First Reading of
the ordinance at the December 17, 2001 council meeting. Consideration of the
Second Reading is scheduled for January 14, 2002. If approved, the ordinance
will be published and go into effect on February 21, 2002 for a period of one
year.
Both the City Council and the Planning and Zoning Board emphasized the need
to complete the necessary ordinance revisions within the one year timeline. It is
important to note that the update of the ordinances will be based on the policies
setforth in the Comprehensive Plan. The process will not involve revisiting
issues within the plan itself. The process will involve examining the policies
setforth in the plan and developing a means to carry them out. This must be
understood clearly from the start to insure completion of the updates in a timely
manner.
To facilitate this process the council will establish a task force comprised of two
members each from the Environmental Board, Planning & Zoning Board, and
Economic Development Advisory Committee. The Task Force will be chaired by
council member Jeff O'Donnell. City staff and Alan Brixius of NAC will lead the
task force's discussion during the process. Staff will be asking the boards to
select their two representatives at the January meetings.
Staff is also in the process of setting up a Government Training Services
Workshop (GTS) as a kick -off to the project. The workshop will be held on
Saturday, January 26, 2002. The council is strongly encouraging all board
members to attend the workshop. It is extremely important that those board
members selected as task force representatives attend the workshop.