Current through Register 1531, September 27, 2024
(1)
Objectives.
(a) To
replicate natural conditions of infiltration, evapotranspiration, and runoff.
In typical natural conditions, approximately 50% of stormwater infiltrates, 40%
leaves land through evapotranspiration, and 10% leaves the land as
runoff.
(b) To promote
decentralized stormwater management systems modeled after natural hydrologic
features and infiltration practices that facilitate local groundwater recharge
[Low-Impact Development (LID) techniques].
(c) To promote water conservation and
efficiency through stormwater capture, treatment and reuse.
(2)
General
Provisions.
(a) The stormwater
design standards and criteria shall apply to all projects under DEC
review.
(b) All Applications,
regardless of whether the project is subject to the Wetlands Protection Act or
not, shall design the stormwater management system in compliance with the
Massachusetts DEP Stormwater Management Standards, January,
2008, (SMS) and the
Massachusetts Stormwater Handbook,
February 2008, (Handbook). The Applicant shall submit a completed and endorsed
Stormwater Management Form that indicates compliance with the SMS, in addition
to any supporting calculations indicating compliance with the required
standards -
http://www.mass.gov/dep/water/laws/policies.htm#storm.
(c) Stormwater management systems shall
comply with the following:
1. The Handbook
which includes the SMS, Stormwater Best Management Practices, Documenting
Compliance, Stormwater Report Checklist and TSS Removal Calculation
Sheet.
2. Devens Stormwater
Pollution Prevention Plan (Stormwater Plan).
3. Devens Water Resources Protection
Report.
4. The Design Standards and
Criteria outlined in 974 CMR 4.08(3).
(d) Where there is a conflict between the
requirements set forth below and the Handbook and/or Plan, the Plan and the
requirements in 974 CMR 4.08(2)(c)1. through 4. shall govern.
1. There shall be no negative impact from
stormwater runoff on abutting properties and to any public or private water
supply or designated potential future supply.
2. Irrigation water shall be derived from
detained treated stormwater (stormwater harvesting), or roof drainage to the
maximum extent feasible. On-site cisterns may be installed to store water for
irrigation.
3. For all stormwater
improvements, drainage calculations shall be prepared by the Applicant's
Engineer in accordance with the SMS requirements and shall include design
criteria, pre- and post-development drainage areas, and other information to
verify the size and effectiveness of the proposed stormwater management
technique. "Predevelopment" drainage areas shall be considered to be "green
fields", regardless of any development or improvements on the site at the time
of application. Calculations shall be made separately for each drainage
facility, showing its location, the total upstream drainage area, the
underlying soil types and the flow paths for the times of concentration, the
design runoff, facility size, slope, and capacity and velocity of water through
all the site drainage system.
4.
Proposed activity that will temporarily or permanently disturb any land area at
or below the elevation of the 100-year floodplain shall be avoided to the
maximum extent feasible, unless there are exceptional circumstances where such
areas cannot be avoided. Under such circumstances, the Applicant shall
demonstrate, to the satisfaction of the DEC, that there shall be no temporary
or permanent loss of flood storage area. For any areas within the 100-year
floodplain where the DEC authorizes disturbance, temporary stabilization
measures shall be implemented at all times, until permanent stabilization is
achieved. No construction laydown areas or equipment shall be stored within the
100-year floodplain without emergency removal/relocation measures in place and
approved by the DEC.
5. Recharge
may not be required for land designated as an Area of Concern, if, according to
the Base Closure Team in accordance with Base Realignment and Closure Act
requirements, recharge will negatively impact ongoing environmental
remediation.
6. All projects,
including flood management and culvert replacement projects, shall incorporate
LID techniques for stormwater management to the maximum extent feasible. For
projects proposing traditional closed drainage systems, the Applicant shall
demonstrate to the satisfaction of the DEC why LID stormwater management design
methods are not feasible. For LID stormwater controls not referenced in 974 CMR
4.08 or the Handbook, or for which pollutant removal rates have not been
provided, the effectiveness and pollutant removal of the structural control
must be documented through prior studies, literature reviews, or other means
and a stormwater management system.
In addition to LID controls outlined in this section (974 CMR
4.08) or the Handbook, flood management and culvert replacement projects shall
assess, and to the maximum extent feasible implement, stream
daylighting1 and improved channel
connectivity2.
(3)
Design Standards and
Criteria. All stormwater management systems shall meet the
following:
(a) Biofiltration basins shall be
the preferred method to reduce curbing, piping and structures and provide
additional overland treatment and recharge. They shall be designed in
accordance with the Handbook, in addition to the following:
1. Any low-flow outlets shall be designed to
prevent clogging.
1 "Stream daylighting" means the
practice of exposing some or all of a previously buried river, stream, and/or
stormwater drainage and restoring the watercourse to a more natural
condition.
2 "Channel connectivity" means the
degree to which hydrologic components of a river system or watershed are
joined, or connected, by various transport mechanisms including streams,
non-tidal wetlands, riparian buffers, or underground aquifers.
2. For bioretention cells,
abutting pavement, that are designed to capture sheet flow, the edge of
pavement shall be reinforced to ensure the integrity of pavement is maintained
(curb stops, stone, turf, landscape timbers, plantings or other acceptable
methods or combination thereof.)
(b) All projects shall manage all stormwater
on-site, unless granted an exemption by the DEC that this requirement is not
feasible.
1. If a project is granted an
exemption under 974 CMR 4.08(3)(b), all stormwater runoff from the site must
satisfy the requirements of
974 CMR 3.04(4)(b)
before being discharged to the Devens
Municipal Separate Storm Sewer System (MS4).
2. If a project is granted an exemption in
accordance with 974 CMR 4.08(3)(b)1., the developer of the project shall
propose a Mitigation Project to be implemented as a component of project
approval, and the DEC will publicize the project's annual Total Suspended
Solids (TSS) removal worksheets on the DEC's website. A "mitigation project"
shall mean an infrastructure project designed to mitigate adverse water quality
impacts from a previously completed project, or from an area which has no
stormwater treatment and management facilities, by improving the quality of
stormwater runoff onsite or at an off-site location.
(c) In addition to compliance with the SMS,
the postdevelopment peak rate of stormwater discharge off-site shall not be
greater than the predevelopment peak rate of stormwater discharge for the 2,
10, 25, 50 and 100-year storm events from any point of discharge on the site.
In accordance with 974 CMR 4.08(2)(d)3., predevelopment peak rate calculations
shall reflect the "green field" site condition, regardless of any existing
development or impervious coverage on the site at the time of
application.
(d) There shall be no
stormwater structures and/or point source discharges within 25 feet of the
boundaries of any Resource Area, unless the Applicant can demonstrate no
adverse impact to the Resource Area.
(e) Side slopes above the design water level
shall be 3:1 (horizontal to vertical) or flatter and conform to the slope of
the existing topography without abrupt or unnatural breaks in slope, unless
otherwise permitted under 974 CMR 4.08(4).
(f) Banks of wet ponds, swales not within
maintained landscaped areas (such as lawns or parking lots), and other channels
shall be vegetated with native woody plant material within ten feet of the high
water elevation and with herbaceous plant material at the edge of the pond at
the high water elevation. Trees shall not be planted on fill
embankments.
(g) Shelves below the
design water level (as described in the Stormwater Plan) shall be vegetated
with hydrophytic native plant species at a density needed to establish full
coverage by the next growing season. Plant plugs or pre-vegetated coir-mesh
blankets or carpets are recommended materials.
(h) Recommended post-construction erosion
control methods include geotextile and /or biodegradable erosion control
fabrics staked or anchored to the slope, with loose weave to allow vegetative
cover to be established. Vegetative cover shall consist of native woody plant
species installed as live brush or nursery stock, or native grasses.
(i) Stormwater management systems shall be
designed to meet an average annual pollutant removal equivalent to 90% of the
average annual load of Total Suspended Solids (TSS) related to the total
post-construction impervious area on the site AND 60% of the average annual
load of Total Phosphorus (TP) related to the total post-construction area on
the site3.
1.
Average annual pollutant removal requirements in 974 CMR 4.08(3)(h) are
achieved through one of the following methods:
a. Installing BMPs that meet the pollutant
removal percentages developed consistent with EPA Region 1's BMP Accounting and
Tracking Tool (2016) or other BMP performance evaluation tool provided by EPA
Region 1, where available. If EPA Region 1 tools do not address the planned or
installed BMP performance, then any federally or State-approved design guidance
or performance standards (e.g. the Handbook) may be used to
calculate BMP Performance;
b.
Retaining the volume of runoff equivalent to, or greater than, one inch
multiplied by the total post-construction impervious surface on the development
site;
3 Pollutant removal is calculated
based on average annual loading and not on the basis of any individual storm
event.
c. Meeting a
combination of retention and treatment that achieves the above standards;
or
d. Utilizing off-site mitigation
in accordance with 974 CMR 4.08(3)(b) that meets the above standards within the
same USGS HUC12 as the development site.
2. Maintenance and redevelopment activities
related to existing roads, including repaving, drainage infrastructure
improvements, adding shoulder, or correcting intersections shall be exempt from
other requirements in this part. Projects of this nature should consider
options to improve any existing conditions by incorporating LID techniques or
other stormwater best management practices and include in the construction
permit application process a narrative describing that investigation's
conclusions and chosen results when possible. Any road construction that
increases the impervious surface by more than a single lane width will not be
covered under this exemption and shall be subject to all requirements in 974
CMR 4.08.(3)(h).
(j) To
support compliance with the MS4 Permit, all BMPs must be optimized for the
removal of phosphorus. The justification and design of such BMPs must also
include a methodology for assessing BMP performance. Pollutant removal shall be
consistent with EPA Region 1's evaluation tool.
(4)
Design Standards and Criteria
for Detention/Retention/Recharge Basins. The design of stormwater
and infiltration basins and associated structures shall:
(a) Minimize basin size to 5,000 square feet
per basin or less (by using smaller catchment areas and/or alternative
stormwater management design methods) and minimize disturbance to natural or
reestablished vegetated areas to the maximum extent feasible. If a basin
exceeds 5,000 square feet, the Applicant shall demonstrate to the satisfaction
of the DEC why a smaller size is not feasible. If a basin is a constructed
stormwater wetland, it may exceed 5,000 square feet upon approval by the DEC.
Constructed stormwater wetlands shall be designed in compliance with the
SMS.
(b) Be located in naturally
occurring low spots. Layout of the basins shall complement the natural
topographic movement of the site [see
974 CMR
3.08(4): Figure
D] Rigid basin layout [see
974 CMR
3.08(5): Figure
E] shall be avoided in all instances, unless the basin's layout
complements the overall design concept of the Site Plan.
(c) Utilize banks steeper than 3:1
(horizontal to vertical) only to tie into headwall/outfall structures. Banks
steeper than 3:1 shall transition to slopes of less than 3:1 as quickly as
possible to minimize areas of potential erosion. Specific post-construction
erosion control methods shall be detailed to ensure temporary and permanent
stabilization of such areas will be achieved. Rip-rap/trap rock solutions shall
not be acceptable, except as water dissipaters below storm water outfalls or as
channel liners for steep swales.
(d) Have an emergency outlet to accommodate
storm flows in excess of the 100-year storm event. A minimum one foot freeboard
distance shall be established between the 100-year flood elevation and the top
of embankment.
(e) Design
basins/infiltration structures using the Natural Resource Conservation Service
TR-20 methodology in accordance with the SMS.
(f) Locate the floor of all
basins/infiltration structure/swales a minimum of four feet above the high
groundwater elevation. High groundwater testing shall be conducted before the
basin design at the proposed location of each basin in compliance with
310 CMR 15.103:
Soil Profile), or reliable data pursuant thereto shall be
provided.
(g) Conduct a falling
head soil permeability test in retention/infiltration basins before the basin
design in all basins and infiltration structures. Soil with a percolation rate
of two minutes per inch or faster can be used to confirm the first NRCS
Hydrologic Soil Group A with a Texture Class of Sand and an infiltration rate
of 8.27 inches per hour from the Rawls, et.al. table in the
SMS. To use infiltration rates faster than 8.27 inches per hour, use 50% of the
infiltration rate obtained from the falling head soil permeability
test.
(h) Conduct percolation tests
in detention basins before the basin design and shall be conducted in
compliance with
310 CMR
15.105.
(i) Include fencing and/or screening of
stormwater detention/retention basins if the DEC determines that safety or
appearance require such measures.
(5)
Design Standards and Criteria
for Certain Structural LID Techniques.
(a)
Vegetated Roofs
. Shall comply with the Handbook and the
DEC Policy for Construction of
Vegetated Roofs dated August 2011.
1.
For the purposes of stormwater management system design, the area of roof
covered by vegetation may be considered pervious and subtracted from the total
proposed impervious area.
2.
Vegetated Roofs within the Viewshed Overlay district shall comply with
974 CMR
3.04(8)(i)5. and
6.
3. Landscaping plans for
projects incorporating vegetated roofs and/or walls shall show the design and
location of vegetated roofs and walls.
(b)
Permeable Paving (Porous
Asphalt, Paving Stones and Pervious Concrete). May be used where
the underlying soils have a permeability of at least 0.3" per hour, but shall
not be used on high-traffic/high speed areas or on stormwater "hotspots" with
high pollutant loads. Permeable paving shall meet the SMS specifications (or
alternatives approved by the DEC), in addition to the following:
1. Lined on the sides with a nonwoven
geotextile fabric to prevent influx of fines (no liner on bottom).
2. A gravel trench surrounding the edge of
the pavement connecting to the stone reservoir below the surface of the
pavement may be required as a backup in the event of surface clogs.
3. Installed by a qualified contractor with
experience in permeable paving installation.
4. Specification layer depths required by the
SMS may be increased based on volume storage requirements
(c)
Additional Requirements for
Pervious Concrete.
1.
Top Layer: six inches of pervious concrete placed in
two three-inch courses.
2.
Second Layer: four-inch course consisting of 1*1/3 "
crushed stone (structural support).
3.
Third Layer: 14
inches of open graded "bank run gravel" (Reservoir base).
4.
Fourth Layer: six
inches of 3/8 " crushed gravel (Capillary barrier).
(d)
Reinforced Turf
Parking/Emergency Access. May be constructed where the underlying
soils have a permeability of at least 0.3" per hour, but shall not be used on
high-traffic/high-speed area or on stormwater "hotspots" with high pollutant
loads. Turf parking shall be designed to meet the SMS and the following
specifications:
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image
* Alternative comparable
reinforcement methods will be considered by the DEC on a case-by-case
basis.
(6)
Closed Drainage Systems.
(a) LID swale systems shall be utilized in
parking lots not subject to truck traffic, truck and container storage, and
other railroad related vehicles/equipment, to the maximum extent
feasible.
(b) Closed Drainage
Systems (CDS) and swales shall be designed to accommodate the 25-year storm
event based on the Rational Method without surcharging. The CDS shall be
designed in accordance with the SMS. Intensity/duration/frequency curves for
the Worcester area, as presented in
Technical Paper 40 of the National
Weather Service, and the
Massachusetts Hydrology Handbook for
Conservation Commissioners, March 2002, shall be used in the drainage
design calculations. The minimum time of concentration shall be five minutes.
Click to
view image
(c)
All drainage structures shall be constructed of precast concrete.
(d) Catch basins shall have oil traps and
provide a four-foot sump.
(e)
Details for all drainage structures shall be provided.
(f) Flow capacities shall be calculated,
using two feet per second (fps) minimum velocity and ten fps maximum velocity
under a two-to-25-year design storm event. The designer shall account for
partial pipe flow capacities, if applicable to the design.
(g) Catch basin to catch basin connections
are prohibited in paved areas.
(h)
Subsurface infiltration systems are considered closed drainage systems and
shall at a minimum meet an 80% TSS removal rate prior to infiltration to reduce
maintenance and potential for system failure and replacement.
(7)
Monitoring and
Maintenance of Stormwater Facilities. An Operation and Maintenance
Plan (O&M Plan) for stormwater management systems is required at the time
of application for all projects. The O&M Plan shall be designed to ensure
compliance with
314 CMR 4.00:
Massachusetts Surface Water Quality Standards, the Stormwater
Plan and the DEC annual stormwater reporting form requirements. The O&M
Plan shall be shown on the site plan(s) and shall include at a minimum the
following:
(a) The name(s) of the owner(s) for
all components of the system.
(b) A
statement that the Applicant is responsible for the operation and maintenance
of the entire on-site system, including emergency repairs.
(c) If applicable, a statement providing
stormwater management easements to the DEC as necessary for access for facility
inspections and maintenance, and preservation of stormwater runoff conveyance,
infiltration, and detention areas and facilities, including flood routes for
the 100-year storm event. The purpose of each easement shall be specified in
the maintenance agreement signed by the property owner.
(d) An O&M Inspection and Maintenance
Schedule which shall include:
1.
Parking Lot Sweeping: with mechanized cleaning
equipment on an annual basis.
2.
Catch Basin Cleaning: Catch Basins and Infiltration
Chambers shall be inspected on a bi-annual basis. Any sediment accumulations in
excess of half of the unit's sump depth shall be removed. Material shall be
removed by a licensed contractor, who shall be responsible for disposing of the
material off-site in a manner consistent with all local, state and federal
regulations.
3.
Infiltration Swales: Ensure proper establishment of
full vegetative cover. Swale embankments and side slopes must be properly
maintained to ensure long-term stability. Annual and seasonal inspections are
required to ensure a healthy groundcover is maintained to avoid erosion and
promote infiltration. Bare spots shall be repaired and planted with native
ground cover material. Saplings and large shrubs shall be removed to maintain
integrity of the swale. Level spreader shall be inspected seasonally to remove
any buildup of sediment and ensure proper drainage flows.
4.
Detention/Retention Basin
Inspection and Maintenance: Wet and dry basins shall be inspected
annually to ensure inlets and outlets remain unobstructed. Inlets and outlets
and forebays shall also be inspected for potential sediment, erosion, cracking,
tree growth, damage to the emergency spillway and erosion within the basin and
on within the banks. Upper side slopes, embankment and emergency spillway shall
be mowed annually. Any tree saplings shall be removed. Accumulated sediment
shall be removed as necessary and at least once every ten years. Bare spots
shall be repaired and planted with native ground cover material.
5.
Biofiltration
Systems: Quarterly inspections for accumulated sediment shall be
performed. Debris, sediment accumulation, erosion shall be removed/repaired at
least twice a year. Any dead or damaged plantings shall be replaced. All
invasive species shall be removed on an annual basis. Re-mulch any void areas
by hand. Native grasses and plants shall be maintained by hand without the use
of fertilizers and limited use of organic herbicides. Trimming of surrounding
grasses shall be restricted to a minimum of five inches. When cation exchange
capacity of soil media decreases, the soil media shall be replaced to prevent
contaminants from reaching the groundwater.
6.
Sediment Trap/Oil-water Separator:
Shall be inspected annually for sediment and debris accumulation. Any sediment
accumulations in excess of half of the unit's sump depth shall be removed.
Material shall be removed by a licensed contractor, who shall be responsible
for disposing of the material off-site in a manner consistent with all
regulations.
7.
Sub-surface Infiltration Systems: Shall be inspected
annually for proper function and sediment accumulation. Accumulations of
sediment and/or materials that negatively impact the infiltration capacity of
the system shall be removed.
8.
Constructed Stormwater Wetlands: In the first three
years after construction, Applicants shall inspect the constructed stormwater
wetlands twice a year during both the growing and non-growing seasons. After
three years such inspections shall occur on a periodic basis. During these
inspections, the following information shall be recorded:
a. The types and distribution of the dominant wetland plants in
the marsh;
b. The presence and
distribution of planted wetland species;
c. The presence and distribution of invasive
wetland species (invasives shall be removed);
d. Indications that other species are
replacing the planted wetland species;
e. Percentage of standing water that is
unvegetated (excluding the deep water cells which are not suitable for emergent
plant growth);
f. The maximum
elevation and the vegetative condition in this zone, if the design elevation of
the normal pool is being maintained for wetlands with extended zones;
g. Stability of the original depth zones and
the micro-topographic features; and
h. Accumulation of sediment in the forebay and micropool; and
survival rate of plants (cells with dead plants must be replanted). Sediment
forebays must be cleaned annually.
(e) Applicants shall submit annual stormwater
monitoring and maintenance reports to the DEC addressing inspection and
maintenance of the BMPs. The reports shall include:
1. Descriptions of the condition of the BMPs;
2. Descriptions of maintenance performed; and
3. Receipts for maintenance performed. For ease of reporting, the DEC and
MassDevelopment have created standard annual reporting templates for use by all
Applicants. Failure to submit the required annual report is a violation of the
Unified Permit.
(f) The
O&M Plan must be signed by the owner and must include a provision that the
transfer of responsibilities is understood by future
owners.