[HISTORY: Adopted by the City Council of the City of Harrisburg 5-14-2013 by Ord. No.
6-2013.[1] Amendments noted where applicable.]
CROSS-REFERENCES
Stormwater Management Act: see 32 P.S. § 680.1 et
seq.
A.
For all regulated activities, unless specifically exempted in § 9-903.2:
(1)
Preparation and implementation of an approved SWM site plan
is required.
(2)
No regulated activities shall commence until the City of Harrisburg
issues written approval of a SWM site plan, which demonstrates compliance
with the requirements of this Part 9.
(4)
The SWM site plan approved by the City of Harrisburg shall be
on site throughout the duration of the regulated activities.
B.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this Part 9 and to meet all
requirements under Title 25 of the Pennsylvania Code (including but
not limited to Chapter 102, Erosion and Sediment Control) and the
Clean Streams Law. Various BMPs and their design standards are listed
in the Erosion and Sediment Pollution Control Program Manual (E&S
Manual), No. 363-2134-008 (April 15, 2000), as amended and updated.
C.
For all regulated activities, stormwater BMPs shall be designed,
installed, implemented, operated, and maintained to meet the purposes
and requirements of this Part 9 and to meet all requirements under
Title 25 of the Pennsylvania Code and the Clean Streams Law,[1] conform to the state water quality requirements, and meet
all requirements under the Stormwater Management Act and any more
stringent requirements as determined by the City of Harrisburg.
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
D.
The City of Harrisburg may, after consultation with PADEP and/or
DCCD, approve measures for meeting the State Water Quality Requirements
other than those in this Part 9, provided that they meet the minimum
requirements of, and do not conflict with, state law, including, but
not limited to, the Clean Streams Law.
E.
All regulated activities shall include, to the maximum extent practicable,
measures to:
(1)
Protect health, safety, and property.
(2)
Meet the water quality goals of this Part 9 by implementing
measures to:
(a)
Minimize disturbance to floodplains, wetlands, natural slopes,
existing native vegetation and woodlands.
(b)
Create, maintain, or extend riparian buffers and protect existing
forested buffers.
(c)
Provide trees and woodlands adjacent to impervious areas whenever
feasible.
(d)
Minimize the creation of impervious surfaces and the degradation
of waters of the commonwealth and promote groundwater recharge.
(e)
Protect natural systems and processes (drainageways, vegetation,
soils, and sensitive areas) and maintain, as much as possible, the
natural hydrologic regime.
(f)
Incorporate natural site elements (wetlands, stream corridors,
mature forests) as design elements.
(g)
Avoid erosive flow conditions in natural flow pathways.
(h)
Minimize soil disturbance and soil compaction.
(i)
Minimize thermal impacts to waters of the commonwealth.
(j)
Disconnect impervious surfaces by directing runoff to pervious
areas wherever possible, and decentralize and manage stormwater at
its source.
(3)
Applicants are encouraged to incorporate the techniques for
low-impact development practices described in the "Pennsylvania Stormwater
Best Management Practices Manual (BMP Manual)" to reduce the costs
of complying with the requirements of this Part 9 and the state water
quality requirements.
F.
Impervious areas.
(1)
The measurement of impervious areas shall include all of the
impervious areas in the total proposed development, even if development
is to take place in stages.
(2)
For development taking place in stages, the entire development
plan must be used in determining conformance with this Part 9.
(3)
For projects that add impervious area to a developed parcel,
the new impervious area is subject to the requirements of this Part
9; and any existing impervious area that is within the new proposed
limit of disturbance is also subject to the requirements of this Part
9.
(4)
Limits of existing impervious surfaces shall be determined based
upon the predominant land use of the subject tract(s) for the period
of time 10 years prior to the proposed development plan, using the
limits in place during the development of the Paxton Creek or Spring
Creek Act 167 Plans, as depicted on the 2003 photogrammetric mapping
(not the composite existing Land Use Maps), or the limits in place
based upon 2012 photogrammetric mapping prepared for The Harrisburg
Authority, whichever is greatest, but not greater than the maximum
impervious coverage prescribed by the current (2012) Zoning Ordinance.
G.
If diffused flow is proposed to be concentrated and discharged onto
adjacent property, the applicant must:
(1)
Document that adequate downstream conveyance facilities exist
to safely transport the concentrated discharge, or otherwise prove
that no erosion, sedimentation, flooding, or other harm will result
from the concentrated discharge.
(2)
Provide an executed easement for newly concentrated flow across
adjacent properties.
H.
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this Part 9.
I.
Where watercourses traverse a development site, drainage easements
(with a minimum width of 20 feet) shall be provided conforming to
the line of such watercourses. The terms of the easement shall prohibit
excavation, the placing of fill or structures, and any alterations
that may adversely affect the flow of stormwater within any portion
of the easement. Also, maintenance, including mowing of vegetation
within the easement, may be required, except as approved by the appropriate
governing authority.
J.
When it can be shown that, due to topographic conditions, natural
drainageways on the site cannot adequately provide for drainage, open
channels may be constructed conforming substantially to the line and
grade of such natural drainageways. Work within natural drainageways
shall be subject to approval by PADEP under regulations at 25 Pa.
Code Chapter 105 through the joint permit application process or,
where deemed appropriate by PADEP, through the general permit process.
K.
Any stormwater management facilities or any facilities that constitute
water obstructions (e.g., culverts, bridges, outfalls, or stream enclosures,
etc.) that are regulated by this Part 9, that will be located in or
adjacent to waters of the commonwealth (including wetlands), shall
be subject to approval by PADEP under regulations at 25 Pa. Code Chapter
105 through the joint permit application process or, where deemed
appropriate by PADEP, the general permit process. When there is a
question whether wetlands may be involved, it is the responsibility
of the applicant or his agent to show that the land in question cannot
be classified as wetlands; otherwise, approval to work in the area
must be obtained from PADEP.
L.
Should any stormwater management facility require a dam safety permit
under PADEP Chapter 105, the facility shall be designed in accordance
with Chapter 105 and meet the regulations of Chapter 105 concerning
dam safety which may be required to pass storms larger than a one-hundred-year
event.
M.
Any stormwater management facilities regulated by this Part 9 that
will be located on or discharged onto state highway rights-of-way
shall be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
N.
When stormwater management facilities are proposed within 1,000 feet
of a downstream municipality, the stormwater analysis shall be submitted
to the downstream municipality's engineer for review and comment.
O.
Minimization of impervious surfaces and infiltration of runoff through
seepage beds, infiltration trenches, etc., are encouraged, where soil
conditions and geology permit, to reduce the size or eliminate the
need for detention facilities.
P.
Infiltration BMPs should be dispersed throughout the site, made as
shallow as practicable, and located to maximize use of natural on-site
infiltration features while still meeting the other requirements of
this Part 9.
Q.
The design of facilities over karst shall include an evaluation and
implementation of measures to minimize adverse effects.
R.
Roof drains shall not be connected to streets, sanitary or storm
sewers, or roadside ditches in order to promote overland flow and
infiltration/percolation of stormwater where it is advantageous to
do so. When it is more advantageous to connect directly to streets
or storm sewers, then the City of Harrisburg shall permit it on a
case-by-case basis.
B.
The applicant must demonstrate that the following BMPs are being
utilized to the maximum extent practicable to receive consideration
for the exemptions:
(1)
Design around and limit disturbance of floodplains, wetlands,
natural slopes over 15%, existing native vegetation, and other sensitive
and special value features.
(2)
Maintain riparian and forested buffers.
(3)
Limit grading and maintain nonerosive flow conditions in natural
flow paths.
(4)
Maintain existing tree canopies near impervious areas.
(5)
Minimize soil disturbance and reclaim disturbed areas with topsoil
and vegetation.
(6)
Direct runoff to pervious areas.
C.
The applicant must demonstrate that the proposed development/additional
impervious area will not adversely impact the following:
D.
An applicant proposing regulated activities, after demonstrating compliance with § 9-903.2A, B and C, may be exempted from various requirements of this Part 9 according to the following table:
|
New Impervious Area Since Date of Adoption of this Part
9
(square feet)
|
Applicant Must Submit to City of Harrisburg
|
|---|---|
|
Combined sewer system: 0 to 250
MS4 system: 0 to 1,000
|
Exempt
Exempt
|
|
Combined sewer system: 250 to 5,000
MS4 system: 1,000 to 5,000
|
Volume controls and SWM site plan and report
Volume controls and SWM site plan and report
|
|
>5,000
|
Rate controls, volume controls, SWM site plan and report and
record drawings
|
|
NOTE: Gravel in the existing condition shall be considered pervious,
and proposed gravel shall be considered impervious.
|
E.
The purpose of this section is to ensure consistency of stormwater
management planning between local ordinances and NPDES permitting
(when required) and to ensure that the applicant has a single and
clear set of stormwater management standards to which the applicant
is subject. The City of Harrisburg may accept alternative stormwater
management controls, provided that:
(1)
The applicant, in consultation with the City of Harrisburg,
PADEP and/or DCCD, states that meeting the requirements of the volume
controls or rate controls of this Part 9 is not possible or creates
an undue hardship.
(2)
The alternative stormwater management controls, proposed by
the applicant, are documented to be acceptable to the City of Harrisburg,
PADEP and/or DCCD for NPDES requirements pertaining to post construction
stormwater management requirements.
F.
Forest management and timber operations are exempt from rate and
volume control requirements and SWM site plan preparation requirements
of this Part 9, provided the activities are performed according to
the requirements of 25 Pa. Code Chapter 102. It should be noted that
temporary roadways are not exempt.
G.
Agricultural activities are exempt from the requirements of this
Part 9, provided the activities are performed according to the requirements
of 25 Pa. Code Chapter 102.
H.
Linear roadway improvement projects that create additional impervious
area are not exempt from the requirements of this Part 9. However,
alternative stormwater management strategies may be applied at the
joint approval of the City of Harrisburg and the Dauphin County Conservation
District (if an NPDES permit is required) when site limitations (such
as limited right-of-way) and constraints (as shown and provided by
the applicant), preclude the ability of the applicant to meet the
enforcement of the stormwater management standards in this Part 9.
All strategies must be consistent with PADEP's regulations, including
NPDES requirements.
I.
The City of Harrisburg may, after an applicant has demonstrated compliance with § 9-903.2A, B and C, grant a modification of the requirements of one or more provisions of this Part 9 if:
(1)
The literal enforcement will exact undue hardship because of
peculiar conditions pertaining to the land in question, provided that
such modification will not be contrary to the public interest and
that the purpose and intent of this Part 9 is observed; and
(2)
The applicant submits a request for a modification, in writing,
stating in full the grounds and facts of unreasonableness or hardship
on which the request is based, the provision or provisions of this
Part 9 involved, and the minimum modification necessary.
B.
Stormwater runoff volume controls shall be implemented using the
Design Storm Method or the Simplified Method. For regulated activities
equal to or less than one acre, this Part 9 establishes no preference
for either method; therefore, the applicant may select either method
on the basis of economic considerations, the intrinsic limitations
on applicability of the analytical procedures associated with each
methodology, and other factors.
(1)
The Design Storm Method (CG-1 in the BMP Manual) is applicable
to any sized regulated activity. This method requires detailed modeling
based on site conditions.
(a)
Do not increase the post-development total runoff volume when
compared to the predevelopment total runoff volume for the two-year
twenty-four-hour storm event.
(b)
For hydrologic modeling purposes:
[1]
Existing nonforested pervious areas must be considered meadow
(good condition) for predevelopment hydrologic calculations.
[2]
Twenty percent of existing impervious area, when present on
the proposed project site and contained within the new proposed limit
of disturbance, shall be considered meadow (good condition) for predevelopment
hydrologic calculations for redevelopment.
(2)
The Simplified Method (CG-2 in the BMP Manual) is independent
of site conditions and should be used if the Design Storm Method is
not followed. This method is not applicable to regulated activities
greater than one acre. For new impervious surfaces:
(a)
Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(b)
At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow, i.e., it shall
not be released into surface waters of the commonwealth. Removal options
include reuse, evaporation, transpiration, and infiltration.
(c)
Wherever possible, infiltration facilities should be designed
to accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first 0.5 inch of the permanently
removed runoff should be infiltrated.
C.
All applicable worksheets from Chapter 8 of the BMP Manual must be
used when establishing volume controls.
D.
Actual field infiltration tests at the location of the proposed elevation
of the stormwater BMPs are required when 1,000 square feet or greater
of new impervious surface is added. Infiltration tests shall be conducted
in accordance with BMP Manual. The infiltration tests for new impervious
surfaces of 5,000 square feet or greater shall be certified by a registered
geologist or professional geotechnical engineer in the commonwealth,
certified soil scientist or geomorphologist. The City of Harrisburg
shall be notified 24 hours prior to infiltration tests being conducted
so as to provide an opportunity for the City to witness the tests.
Infiltration rates of all approved BMPs shall be field verified during
construction, immediately prior to installing of the device.
E.
A waiver from the infiltration requirement, regardless of the area
of new impervious surface, must be requested, in writing, and include
a report prepared and sealed by a registered geologist or professional
geotechnical engineer in the commonwealth, or by a soil scientist
or geomorphologist sealed by a registered professional. The report
should include an analysis of field work performed on site supporting
the location of testing, basis for establishing the limiting zone,
and soils analyses with infiltration rates of likely locations of
prospective BMPs. All other provisions of the approving agency shall
be satisfied prior to issuance of a waiver.
F.
If it is determined by the approving agency that infiltration of
all or part of the increased runoff volume is not feasible, the increased
volume shall be routed through a BMP that is deemed acceptable by
the approving agency to provide volume reduction, flow attenuation,
and water quality enhancement, which include underdrained filters,
underdrained bioretention, swales with check dams, ponds/wet basins,
and constructed wetlands. (See Table E-1, Appendix E, for a complete
list.) Underdrained systems shall retain the increased volume for
not less than 24 nor more than 72 hours.
A.
For lands contained within the City of Harrisburg that have not had
release rates established under an approved Act 167 stormwater management
plan, post-development discharge rates shall not exceed the predevelopment
discharge rates for the one-year, two-year, ten-year, twenty-five-fifty-year
and one-hundred-year storms.
B.
For lands contained within the City of Harrisburg that have had release
rates established under an approved Act 167 stormwater management
plan [Paxton Creek and Spring Creek (West)]:
(1)
Post-development discharge rates shall not exceed the predevelopment
discharge rates for the one-year, fifty-year, and one-hundred-year
storms.
(2)
For the two-, ten-, and twenty-five-year storms, the post-development
peak discharge rates shall be in accordance with the approved Act
167 plan release rate map, or, for areas situated outside the limits
of the Paxton Creek or Spring Creek watersheds, the post-development
discharge rates shall not exceed the predevelopment discharge rates.
C.
For lands contained within a Paxton Creek Watershed Provisional No-Detention
District:
(1)
These watershed areas may discharge post-development peak runoff without detention facilities. However, the applicant must prove that the local runoff conveyance facility which transports runoff from the site to the Main Channel has adequate capacity to safely transport unattenuated increased peak flows for a twenty-five-year storm in accordance with § 9-903.5. Also, in the case of the site draining to a combined sewer, peak sewage flows shall be included in the hydraulic analysis. If there is inadequate capacity, the applicant shall either use 100% release rate control or provide increased capacity of downstream drainage facilities to convey increase peak flows consistent with § 9-903.5. When determining if adequate capacity exists in the local watershed drainage network, the applicant must assume that the entire local watershed is developed per current zoning and that all new development will use the least restrictive runoff controls specified by this Part 9.
(2)
Increases in peak flow to a combined sewer shall be considered
in evaluating the site's Act 537 sewage facility planning.
D.
Off-site areas that drain through a proposed development site are
not subject to release rate criteria when determining allowable peak
runoff rate; however, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site.
E.
For a proposed development site which is located within two or more
release rate districts, the maximum runoff discharged at any point
shall be equal to the release rate for the district in which the discharge
point is located. In the event that a portion of the site is located
in a provisional no-detention area, no runoff from portions of the
site located in areas subject to release rate controls may be drained
to or through the provisional no-detention area.
Any downstream capacity hydraulic analysis conducted in accordance
with this Part 9 shall use the following criteria for determining
adequacy for accepting increased peak flow rates:
A.
Natural or man-made channels or swales must be able to convey the
increased runoff associated with a twenty-five-year return period
event within their banks at velocities consistent with protection
of the channels from erosion. Acceptable velocities shall be based
upon criteria included in the PADEP Erosion and Sediment Pollution
Control Program Manual.
B.
Natural or man-made channels or swales must be able to convey the
increased twenty-five-year return period runoff without creating any
hazard to persons or property.
C.
Culverts, bridges, storm sewers, or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with PADEP, Chapter 105 regulations (if applicable), and, at a minimum,
pass the increased twenty-five-year return period runoff, except for
facilities located within a designated floodplain which must, at a
minimum, conform to FEMA and local floodplain ordinance requirements.
D.
Combined sewer systems must pass or convey flows from the tributary
area for a twenty-five-year return period plus the peak sewage flows
from the tributary service area, (4.0 x average daily flow). The resulting
energy grade line (EGL) in the main shall remain one foot below the
basement floor elevations of properties serviced by the sewer, and
the EGL shall not exceed the elevation of the CSO structure overflow
weirs or otherwise cause sewage to enter the waters of the commonwealth.
Increases in peak flow from a proposed development shall be considered
as part of the proposed development's Act 537 sewage facility
planning.
