HomeMy WebLinkAbout1996-064
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RESOLUTION NO. 96-64
A RESOLUTION ADOPTING THE OFFICIAL CITY OF
STILLWATER STORM WATER UTILITY POLICY
WHEREAS, City Council has identified necessary improvements to the storm water system
and;
WHEREAS, City Council has identified the costs of these storm water improvements and;
WHEREAS, City Council has passed Ordinance No. 821 which authorized the creation of a
storm water utility;
NOW, THEREFORE, it is hereby resolved that the City of Stillwater City Council hereby
adopts the document known as the storm water drainage utility city policy as the official policy
for implementing storm water utility.
Adopted by Council this 19th day of March, 1996.
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Attest:
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Mo Ii Weldon, City Clerk
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STORM WATER DRAINAGE UTILITY
CITY POLICY
BACKGROUND
The City of Stillwater adopted an Ordinance which establishes a Storm Water Utility
throughout the entire City. The purpose of the utility is to fund the improvement, repair and
maintenance of the storm sewer system and fund the costs of meeting new State and Federal
regulations regarding environmental issues.
The Ordinance states that revenue for running the Storm Water Utility Program shall be
derived by the creation of a storm water utility fee. This fee shall be determined by the City
Council and shall be just and equitable, based on the impact a property has on the storm water
system.
OBJECTIVE
The purpose of this policy is to provide a specific program for setting the storm water
charges for all properties in the City. Also this policy will set forth a detailed methodology for
addressing credits and adjustments to the adopted program for special cases where a property
owner has taken actions that reduce the impact hislher property has on the storm water system.
The standard procedure for determining the storm water drainage fee for any given parcel
shall be based on a formula that calculates the anticipated impact that property has on the storm
water system. Since impact is generally a function of the quantity of storm water generated, the
factors which increase storm water quantity shall be used as a method of measure.
The Runoff Potential shall be the basis for setting storm water rates for various land use
types. Runoff Potential is a function of the amount of impervious surface and the rainfall
Intensity Index for a given rainfall event. Different land use types have different quantities of
impervious surface and different rainfall Intensity Indexes. In general, the Runoff Potential will
be high for multi-family and industrial/commercial development, and low for undeveloped land
or open space.
The formula for determining Runoff Potential is as follows:
RUNOFF POTENTIAL = 3.0*C*I
Where:
C = A runoff coefficient which quantifies the amount of impervious surface and
rate of infiltration.
I == Rainfall Intensity Index which quantifies the run off rate of a 2" rainfall event
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LAND USE C I Runoff Pot.
Single and Two Family .35 3 3
Multi Family .70 4 8
CommerciallIndustrial .80 5 12
Central Business District .90 6 16
Institutional .60 3.5 6
Active Open Space .15 2.5 1
Vacant Land 0
RATE STRUCTURE
Rates will be determined based on the Runoff Potential, the Area (in acres) of the given
property, and the Base Charge as determined by the council. This way each land use will have a
rate based on a multiple of the base charge.
QUARTERL Y RATE = Base Charge * Runoff Potential * Area
Base Charge = Rate charged per single family and duplex unit
Runoff Potential = The number from the table above, expressing amount of run off
Area = Acres of site or # dwellings/# units for single and multi-family
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U sing the above formulas the following table has been created:
LAND USE
RATE
Single/two family
Multi family
Active open space
Institutional
Commercial/Industrial
Central Business District
1 base charge per dwelling
1 base charge per unit
1 base charge per acre
6 base charges per acre
12 base charges per acre
16 base charges per acre
The single family category works out to 1 Base Charge because it is assumed that the
average single family lot is 1/3 acre in size and the Runoff Potential for each is 3 * 1/3= 1 Base
Charge. Similar logic holds true for multi-family residential, these land uses have higher Runoff
Potentials at higher densities, so the charge rate is tied to the number of units.
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. CREDITS
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In cases where a property is substantially different from the norm, and in cases where a
property has storm water facilities in place that act to diminish the impact of storm water, the
property may be eligible for a credit.
Three types of credits are possible. . Land use intensity credits apply to properties where
the actual Runoff Potential is much less than the theoretical Runoff Potential. Rate of discharge
credits are available for properties that operate a holding pond that reduces peak flows. Water
quality credits will be available for properties that operate a wet pond that meets National Urban
Runoff Program (NURP) standards.
A property owner who wishes to apply for an exemption or credit will need to provide a
written request, along with all the information stipulated in this policy, to the City Engineer.
The City Engineer will review the information and determine if a credit or exemption is
warranted within six (6) months of the request. The City Engineer will present the request and
findings to the City Council. The Council will make the final determination as to whether a
credit or exemption are warranted.
City staff will make the appropriate adjustments to the next utility bill after the Council's
decision. Under no circumstances will the credit or exemption be retroactive.
A. Land Use Intensity Credits
1. Criteria: When actual runoff generated by a parcel differs from the theoretical
amount by more than 25%, the parcel's drainage fee may be adjusted to reflect
actual runoff.
2. Required information by applicant:
a) Complete site plan
b) Site area and percentage of "impervious" surface
3. Calculation Procedure:
a)
Calculate unit runoff by rational method, using actual percent impervious
surface, 2" rainfall, clay soils.
b)
Compare with "Standard" Runoff Potential (see Runoff Potential Table)
c)
If calculated unit runoff differs from standard by 25% or more, adjust
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Parcel's Runoff Potential value by ratio of actual unit runoff to standard
unit runoff.
4. Exceptions:
a) No adjustments to single family parcels will be granted, as their fees do
not depend on lot size or intensity.
b) For parcels with drainage easements, reduce parcel size to non-easement
area, then calculate unit runoff.
B. Rate of Discharge Credits
1. Criteria: When peak runoff from site is limited to pre-development levels by on-
site facilities owned and maintained by property owner, up to 25% reduction in
drainage fee can be granted.
2. Required information by applicant:
a) Complete site plan
b)
Area of site draining to each intake point
c)
% improved surface draining to each intake point
d) Specific details about intake
e) Calculation of peak outflow rate for 5-year and 100-year design rainfall,
using modified rational method with concentration time of 30 min. or
more.
3. Calculation Procedure
a) Divide site into areas which drain to each drainage intake.
b) Select design rainfall
c) Route rainfall through pond using modified rational method, choose time
of concentration at least 30 min., and use "C" value calculated from
composite of Land Uses. Determine peak outflow rate by summing all
area.
d)
Check other rainfall events to determine "worst" case
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e)
Calculate per-development rates for parcel using "C" = .20 and assuming
no on-site detention.
f)
If peak 5-year outflow is less than predevelopment -- 10% credit
If peak 1 DO-year outflow is less than predevelopment -- additional
15% credit
4. Exceptions. Special Cases
a) Off site water drains to intake -- owner has right to drain this water
through the site without detention. Grant credits if owner provides
sufficient control for owner's portion of the total flow. (This will require
applicant to provide information about watershed beyond parcel).
b) Intake facility owned by City or others (i.e. City has easement for pond) --
No Credits
c) Cost of pond construction funded by City - No Credits (i.e. Tax Increment
Financing Assistance)
d)
Shared Ponding Situation: All ponds have an outflow. If outflow on
another's land, no credits (as in B above), except if the pond is capable of
meeting size requirements for both properties and the properties in
question have an agreement to maintain and share the pond. The pond
must be located partially on both properties.
e) Pond is an official wetland or public water - No Credit.
C. Water Quality Credits
1. Criteria: When a parcel provides on-site treatment facilities which function to
improve the quality of runoff exiting the site, up to 50% of the drainage fee may
be credited depending on treatment effectiveness.
2. Required information by applicant:
a) Area of site draining to pond and percent impervious
b) Volume of pond below outflow elevation.
3. Calculation procedure for wet ponds:
a)
Wet ponds shall be built in accordance to NURP standards and be rated
according to the Walker Pondnet model.
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b)
Divide site into areas draining to each facility.
c) Determine the volume ofrun off from each area of the site for a 2.5" storm
event using rational method or approved SCS method.
d) Calculate or verify actual pond volume in acre feet below outlet elevation.
e) Calculate Pondnet effectiveness ratio.
PONDNET EFFECTIVENESS RATIO = Actual Pond Volume
Pondnet Required Volume
f) Determine credit from following chart:
PONDNET EFFECTIVENESS RATIO
% CREDIT
o - .39
.40 - .59
.60 - .79
.80 - .99
1.0 +
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10%
20%
35%
50%
4.
Exceptions and special cases
a) Off-site water drains to treatment area -- Ignore effects of off-site water in
calculating pond efficiency
b) Parcel shares pond facility -- If parcel has water normally ponded on site,
calculate volume of pond on that site below outfall. Then calculate credit
per normal procedure.
c) Cost of pond construction funded by City -- No credits (i.e. Tax Increment
Financing Assistance)
d) Pond is an official wetland or public water - No credit.
Refer to Stillwater Ordinance No.
Adopted by the Stillwater City Council this 2nd day of January, 1996.
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STORM WATER UTILITY ANNUAL COSTS
Catch Basin Cleaning
Additional Street Sweeping (for water quality)
Pond Dredging
Lily Lake Maintenance
Lake Testing/Monitoring
Storm Water Management Plan
Miscellaneous Repairs
Administration
Drainage Plan Review
$ 5,000
$ 5,000
$10,000
$ 5,000
$ 5,000
$10,000
$20,000
$ 5,000
$ 5.000
Total Annual Operating Expenditures
$70,000
5 YEAR IMPROVEMENT PROJECT
ESTIMATED COST
Brick Pond
Lily Lake Improvement Project
Hazel Ct. Wash Out
2nd & 4th St. Ravine Project
Reconstruction Projects
$ 55,000
$100,000
$200,000
$500,000
$200,000
LONG TERM IMPROVEMENT PROJECTS
Brown's Creek Diversion/Protection
Downtown DiversionIFlood Improvements
North Hill Storm Improvements
Ravine Erosion Control Projects
$1,000,000
$ 200,000
$ 300,000
$ 500,000