A.
Projects must meet the standards of the Massachusetts Stormwater
Management Standards as promulgated by the Massachusetts DEP as well
as Section 2.3.6 of the Massachusetts MS4 permit. A copy of these
standards is maintained by the office of the Planning Board.
B.
When the proposed discharge may have an impact upon a sensitive receptor,
including streams, storm sewers, and/or combined sewers, the Planning
Board may require an increase in these minimum requirements, based
on existing stormwater system capacity and standards of other Town
boards, including, but not limited to, the Board of Health and the
Conservation Commission.
A.
Stormwater management measures shall be required to satisfy the minimum
control requirements and shall be implemented in the following order
of preference:
(1)
Infiltration, flow attenuation, and pollutant removal of runoff on-site
to existing areas with grass, trees, and similar vegetation and through
the use of open vegetated swales and natural depressions. Low impact
development strategies are preferred over conventional collect and
convey systems, including minimizing impervious surfaces, incorporating
stormwater management facilities into landscaping islands, bioretention
basins, pervious pavers, etc.;
(2)
Reuse of stormwater generated on site to replace water used in industrial
processes or for irrigation;
(3)
Stormwater detention structures for the temporary storage of runoff
which is designed so as not to create a permanent pool of water;
(4)
Stormwater retention structures for the permanent storage of runoff
by means of a permanent pool of water; and
(5)
Retention and evaporation of stormwater on rooftops or in parking
lots.
B.
Infiltration practices shall be utilized to retain the one-inch volume
of rainfall that falls on impervious surfaces on-site. A combination
of successive practices may be used to achieve the applicable minimum
control requirements. In the event that the one-inch volume of rainfall
cannot be retained on-site, a justification shall be provided by the
applicant based on site conditions.
C.
Best management practices shall be employed to minimize pollutants
in stormwater runoff prior to discharge into a separate storm drainage
system or water body, consistent with the requirements of the Stormwater
Design Manual as well as the Massachusetts MS4 permit.
D.
All stormwater management facilities shall be designed to provide
an emergency overflow system, and incorporate measures to provide
a nonerosive velocity of flow along its length and at any outfall.
E.
The designed release rate of any proposed stormwater structure shall
be designed to prevent any increase in flooding or stream channel
erosion would result at a downstream dam, highway, structure, or normal
point of restricted stream flow.
F.
A decentralized approach to stormwater management, including installing
different best management practices throughout the site, should be
included. Traditional collect and convey systems should be minimized.
Additional policy, criteria, and information, including specifications
and design standards, may be found in the Stormwater Design Manual
and the erosion and sediment control guidance documents and may also
be utilized.
A.
Infiltration systems.
(1)
Infiltration systems shall be equipped with washed stone and/or filter
fabric adjacent to the soil or other sediment removal mechanisms;
(2)
Infiltration systems greater than three feet deep shall be located
at least 10 feet from basement walls;
(3)
Due to the potential for groundwater contamination from dry wells,
they shall not be an acceptable method for management of runoff containing
pollutants, unless stormwater discharges to dry wells are pretreated
consistent with the Stormwater Design Manual or Massachusetts MS4
permit prior to discharge to each dry well;
(4)
Infiltration systems designed to handle runoff from commercial or
industrial impervious parking areas shall be a minimum of 100 feet
from any drinking water supply well;
(5)
Infiltration systems shall not be used as sediment control basins
during construction. The bottoms of all infiltration facilities shall
be protected from heavy equipment during construction;
(6)
Infiltration basins shall be constructed with a three-foot minimum
separation between the bottom of the structure and the seasonal high
groundwater elevation, as determined by a licensed soil evaluator;
and
(7)
Infiltration basins shall be designed with an overflow route from
the basin to the downstream design point in the event of a storm which
exceeds the capacity of an infiltration system.
B.
Retention and detention ponds shall be designed and constructed in
accordance with the criteria set forth in the Stormwater Design Manual.
C.
The applicant shall utilize natural topography and land cover such
as natural swales and depressions as they exist prior to development
to the degree that they can accommodate the additional flow of water.
D.
The Planning Board shall give preference to the use of swales in
place of the traditional use of curbs and gutters based on a case-by-case
review of stormwater management plans by the Director of Planning
and Conservation or their designee and Planning Board.
E.
The applicant shall consider public safety in the design of any stormwater
facilities. The banks of detention, retention, and infiltration basins
shall be sloped at a gentle grade into the water as a safeguard against
personal injury, to encourage the growth and stabilization of vegetation
and to allow the alternate flooding and exposure of areas along the
shore. Basins shall have a minimum 4:1 slope to a depth two feet below
the control elevation. Side slopes must be stabilized and planted
with vegetation to prevent erosion and provide pollutant removal.
F.
Where a stormwater management plan involves direction of some or
all runoff off of the site, it shall be the responsibility of the
applicant to obtain from adjacent property owners any easements or
other necessary property interests concerning the discharge of water
to adjacent properties. Approval of a stormwater management plan does
not create or affect any such rights.
G.
All applicants for projects which involve the storage or use of hazardous
or toxic chemicals, materials or waste shall incorporate handling
and storage best management practices that prevent such chemicals,
materials and waste from contaminating runoff discharged from a site
into infiltration systems, receiving water bodies or storm drains,
and shall include a list of such chemicals, materials and waste and
their amounts in the application. When appropriate, gate valves or
other structures shall be incorporated into the design in order to
stop the discharge of any hazardous or toxic materials from the property.
H.
Runoff from parking lots shall be treated by oil and water separators
or other controls to remove oil and sediment prior to discharge to
any stormwater best management practices consistent with the Stormwater
Design Manual and Section 2.3.6 of the Massachusetts MS4 permit.
I.
The basic design criteria methodologies, and construction specifications,
subject to the approval of the Planning Board and Director of Planning
and Conservation or their designee, shall be those generally found
in the most current edition of the stormwater design manual as well
as Section 2.3.6 the Massachusetts MS4 permit.
J.
Protection of the public water supply (including retention of the
recharge of the groundwater supply) is vital to the health and safety
of the Town. Accordingly, the stormwater management system and site
grading must be designed to maximize recharge of stormwater runoff
into the groundwater. No runoff originating within the DEP Zone II
or DEP Zone III of the Dry Brook Public Water Supply Well is to be
diverted out of said Zone II and Zone III, unless the Planning Board,
based on the recommendations of an independent peer review engineer,
determines that such 100% retention of runoff is not feasible due
to the unique characteristics of the project site, grants a waiver
to this requirement, and the applicant provides what the Planning
Board determines to be reasonable and appropriate mitigation.
K.
South Hadley contains water bodies that are classified as impaired
waters. The applicant should determine whether or not the proposed
project is located within a watershed that discharges to an impaired
water. In the event a project is located within a watershed that discharges
to an impaired water, the applicant shall determine the pollutant
causing the impairment and design the project's stormwater best
management practices to optimize removal for that pollutant. Projects
that are located in watersheds discharging to water bodies that are
impaired for phosphorus or nitrogen should include best management
practices that are optimized to reduce phosphorus or nitrogen consistent
with Appendixes F and H of the Massachusetts MS4 permit. The applicant
should consult the most recent "Integrated List of Waters" for Massachusetts
to determine the list of impaired waters for South Hadley.
