[HISTORY: Adopted by the Earth Removal Stormwater Advisory Committee 4-14-2015.[1] Amendments noted where applicable.]
GENERAL REFERENCES
Earth removal — See Ch. 134.
Flood damage prevention — See Ch. 141.
Forest lands — See Ch. 145.
Stormwater management — See Ch. 198.
Wetlands — See Chs. 215 and 344, Art. III.
Zoning — See Ch. 218.
Road openings — See Ch. 248.
Subdivision rules and regulations — See Ch. 381, Part 1.
[1]
Editor's Note: This enactment also superseded former Ch. 352, Earth Removal Stormwater Advisory Committee, consisting of Art. I, Soil Erosion and Sediment Control, adopted as filed 12-7-2001, as amended, and Art. II, Stormwater Design Criteria, adopted 4-1-2008, as amended.
A. 
Stormwater management permits are separate from other development permits granted by other Town authorities. Projects that must obtain permits from the Planning Board, Conservation Commission, Zoning Board of Appeals, or other Town approving authority may also be required to obtain a stormwater management permit.
B. 
Full stormwater management permits. You must file an application for a full stormwater management permit for any of the following activities:
(1) 
Excavating, grading, or other land-disturbing activity of an area of more than 40,000 square feet or a volume of earth resulting in a total quantity of 1,000 cubic yards per lot or parcel as defined in Chapter 218, Zoning, § 218-4, Definitions; or
(2) 
Excavating, grading, or other land-disturbing activity resulting from construction as shown on a definitive subdivision plan. Permits are not required for definitive subdivisions approved prior to the effective date of this chapter unless an emergency situation exists as described in § 198-6.
C. 
Limited stormwater management permit. You must file an application for a limited stormwater management permit for any of the following activities:
(1) 
Excavating, grading, or other land-disturbing activity which disturbs an area greater than 20,000 square feet but less than 40,000 square feet or a volume of earth greater than 500 cubic yards but less than 1,000 cubic yards per lot or parcel as defined in Chapter 218, Zoning, § 218-4, Definitions.
(2) 
Excavating, grading, or other land-disturbing activity disturbing an area of land greater than 5,000 square feet if soil cut or filled exceeds four feet in vertical depth at its deepest point as measured from the natural ground level.
A. 
Two copies of a completed application form signed by the applicant and the landowner.
B. 
Filing fee as specified in § 352-3 below, check(s) payable to the Town of Groton.
C. 
Stormwater management plan pursuant to Chapter 198 and report with calculations demonstrating compliance with Chapter 356, Article II, Stormwater Design Criteria, and the Massachusetts Stormwater Standards.
D. 
Long-term operation and maintenance plan (operation and maintenance plan pursuant to § 198-8).
E. 
Operation and maintenance plan for temporary and permanent erosion control measures.
F. 
Full stormwater management permit application shall contain, at a minimum:
(1) 
Two copies of the site plan, prepared and stamped by a registered professional engineer. The site plan shall include the following information:
(a) 
A locus map, legend, and North arrow;
(b) 
A scale showing one inch equals 40 feet or less;
(c) 
Title blocks identified by project name or parcel;
(d) 
Delineation of the total land area to be disturbed;
(e) 
Boundary lines of lots and delineation of land area where activity is to be performed;
(f) 
Contours showing existing and proposed elevations and/or contours at one-foot intervals;
(g) 
Symbols for sediment and erosion control practices, including detail and elevation;
(h) 
Existing and proposed roadways;
(i) 
Delineation of wetland resources pursuant to the Code of Groton and the Wetlands Protection Act regulations;
(j) 
Delineation of the one-hundred-year floodplain, as shown on the Federal Emergency Flood Insurance Rate maps;
(k) 
Street profiles showing proposed and existing grades and elevations;
(l) 
Proposed stormwater management systems;
(m) 
All bodies of water, including streams, rivers, lakes and ponds, within 100 feet of the proposed activity;
(n) 
Location of all existing underground utilities [Reminder: The applicant must call Dig Safe at (888) 344-7233 prior to commencement of construction.];
(o) 
A description of construction activities, in sequence, which specifies the expected date of soil stabilization and completion;
(p) 
Temporary and permanent soil erosion and sediment control measures;
(q) 
Temporary and permanent seeding and other vegetative controls; and
(r) 
A survey of existing vegetation, including the following information:
[1] 
Major upland vegetation located on the site, including trees, shrub layer, ground cover and herbaceous vegetation;
[2] 
Location of all trees with a caliper 12 inches or larger, noting specimen trees and forest communities; and
[3] 
Line clearly showing the limit of vegetation clearing and specimen trees to be saved.
(2) 
If permanent or temporary structural soil erosion control, sediment control, or stormwater BMPs are required, the detailed engineering plans shall include information on these measures, including but not limited to:
(a) 
Detailed location in plan view;
(b) 
Spillway or outlet control designs showing calculated stage elevations;
(c) 
Emergency spillway designs showing a section with one-hundred-year storm stage elevation;
(d) 
Notes and construction specifications;
(e) 
Type and size of sediment basin or trap;
(f) 
Volume of storage required;
(g) 
Pipe lengths, materials, and sizes;
(h) 
Storage depth below outlet or cleanout elevation;
(i) 
Embankment height and elevation; and
(j) 
Location of any portable safety fences surrounding any basin or trap.
G. 
Limited stormwater management permit. Two copies of the plan showing the parcel or parcels on which the activity is to take place. The plan shall be drawn to scale and show, at a minimum, the following information:
(1) 
A survey of the parcel or parcels on which the activity is to take place. If a survey plan is not available, a copy of the Assessors Map or sewage disposal system plan may be used.
(2) 
Any proposed soil erosion and sediment control measures.
(3) 
Any existing or proposed roadways, driveways or parking areas.
(4) 
Any areas subject to protection under the Wetlands Protection Act, MGL C. 131, § 40, or Chapter 215, Wetlands, of the Code of the Town of Groton.
(5) 
Existing building or buildings to be constructed.
(6) 
Any proposed grading or changes in topography.
(7) 
Location of a stabilized construction entrance.
(8) 
Proposed limits of vegetation clearing.
(9) 
Location of all existing underground utilities. [Reminder: The applicant must call Dig Safe at (888) 344-7233 prior to commencement of construction.]
[Amended 3-21-2017]
A. 
Limited stormwater management permit. The filing fee for administration (public hearing notice, mailings, etc.) of a limited stormwater permit is $100, check made payable to the Town of Groton. This fee is deposited into a revolving fund established for this purpose. There is no project review fee unless the Committee determines that technical expertise is required to review the application.
B. 
Full stormwater management permit. The filing fee for administration (public hearing notice, mailings, construction inspections, etc.) of a full stormwater management permit is $500, check made payable to the Town of Groton. This fee is deposited into a revolving fund established for this purpose.
C. 
Project review fee. The cost for the consultant to review the project shall be the amount deposited into the revolving fund; the applicant is responsible for the cost of the project review. The Committee shall utilize the following procedure:
(1) 
Request a written estimate from the consultant on the cost to review the project, including the cost to attend meetings with the design engineer and public hearing(s), if necessary;
(2) 
The Committee shall vote to accept the estimate with a provision that the cost to review the project shall not exceed the estimate without written approval from the Committee; and
(3) 
The Committee shall inform the applicant of the cost estimate for project review and of any additional costs that may be incurred.
(4) 
The applicant shall submit a check made payable to the Town of Groton for the project review fee prior to the commencement of the project review by the consultant.
A. 
A full or limited stormwater management permit shall be valid for two years from the date the permit is issued. If a project's construction is not completed within one year from the date the permit is issued, it is the responsibility of the applicant to request an extension. The Committee may grant extensions for additional time, provided that the applicant submits a written request for renewal no later than 30 days prior to expiration of the permit.
B. 
All projects that receive a permit must obtain a certificate of completion at the completion of construction and BMP installation; however, the permit will remain in effect for projects with long-term operation and maintenance conditions.
A. 
When the construction of a project is completed, the applicant shall request that the Committee conduct a final inspection. For full stormwater management permits, the applicant must submit a statement from a registered professional engineer certifying that the project was completed in accordance with the approved plans and construction conditions of the permit. The applicant shall also submit an on-the-ground surveyed as-built plan prepared by a professional land surveyor. The Committee shall determine whether the project complies with the approved plans, construction conditions of the permit, and Chapter 198, Stormwater Management. If completion is satisfactory, the Committee shall issue a certificate of completion.
B. 
Operation and maintenance of stormwater BMPs is critical to the intended post-construction performance of the stormwater management system and is therefore critical that the completion of a project include ongoing operation and maintenance. To ensure that the stormwater BMPs are operated and maintained according to the long-term operation and maintenance plan pursuant to Chapter 198, Stormwater Management, the permit conditions may include annual submission of inspection maintenance logs for all stormwater BMPs. The inspection maintenance logs shall be submitted to the Committee no later than June 1 annually.
A. 
It is critical to the performance and function of stormwater BMPs that they are maintained properly; therefore, long-term operation and maintenance permit conditions may be required to ensure the ongoing maintenance of the stormwater BMPs according to the long-term operation and maintenance plan.
B. 
All projects that receive a full stormwater permit will include long-term operation and maintenance conditions that are separate from construction conditions unless the project is:
(1) 
A single-family house.
(2) 
A housing development and redevelopment projects comprised of detached single-family dwellings on four or fewer lots, provided that there are no stormwater discharges to a critical area.
(3) 
A multifamily housing development and redevelopment projects with three or fewer units, including condominiums, cooperatives, apartment buildings and townhouses, provided that there are no stormwater discharges to a critical area.
C. 
Construction permit conditions and operation and maintenance conditions shall be separately listed on the permit document. The certificate of completion only applies to completion of construction and construction-related conditions. It does not apply to the long-term operation and maintenance conditions.
D. 
After a project is issued a certificate of completion, the responsible party or owner as listed in the long-term operation and maintenance plan shall submit annual BMP inspection and maintenance logs to the Committee and if applicable an updated long-term operation and maintenance plan on or before June 1.
E. 
Failure to submit BMP inspection and maintenance logs to the Committee by June 1 of each year may result in fines in accordance with Chapter 198, § 198-13D, Noncriminal disposition.
Massachusetts promulgated regulations that include Stormwater Management Standards (formerly the Massachusetts Stormwater Policy), through amendments to 310 CMR 10.00, Wetlands Protection Regulations, and 314 CMR 9.00, 401 Water Quality Certification for Discharge of Dredged or Fill Material, Dredging, and Dredged Material Disposal in Waters Within the Commonwealth. Recognizing that the Massachusetts Stormwater Management Standards shall be met for all projects within the jurisdiction of these regulations, and that the Massachusetts Stormwater Handbook, which includes additional guidance to these regulations, may change over time, all stormwater management designs must meet the design criteria or standards in the Massachusetts Wetland Protection Regulations and 401 Water Quality Certification Regulations or within this manual, whichever is more stringent in the protection of the Town's environmental and infrastructure resources and as authorized through any permitting agencies under whose purview the project falls.
These regulations apply to land-disturbing activities as outlined in Chapter 198, Stormwater Management — Low-Impact Development. The land-disturbance thresholds apply to development or redevelopment involving multiple separate activities in discontinuous locations or on different schedules that all together exceed the disturbance thresholds under § 198-4, Applicability.
A. 
Low-impact development (LID)/green infrastructure techniques must be incorporated into development and redevelopment projects in the Town unless it can be shown per § 352-9A(1) that the use of LID techniques is not feasible. Applicants must use decentralized systems that involve the placement of a number of small treatment and infiltration devices located close to the various impervious surfaces that generate stormwater runoff in place of a centralized system comprised of closed pipes that direct all drainage from the entire site into one large detention basin.
(1) 
The applicant must demonstrate to the Committee that the use of LID techniques is not feasible given existing site constraints. The Committee or its designated agent will determine if the documents submitted are adequate to demonstrate the use of LID techniques is not feasible.
B. 
The site planning process shall be documented and submitted to the Committee and shall include the following steps:
(1) 
Perform site analysis: identify and map important natural features such as streams and drainageways, floodplains, wetlands, recharge groundwater protection areas, high-permeability soils, steep slopes and erosion-prone soils, woodland conservation areas, farmland, and meadows.
(2) 
Layout preferred development scenario: prepare preferred site development layout that minimizes total impervious area, reflects the existing topography, and uses existing hydrologic features. Potential layout may consider cluster development, parking garages, taller buildings, reduced road widths, smaller parking areas, permeable paving, and green roofs. Roadway layouts shall minimize disturbance of natural drainage patterns by following existing grades.
(3) 
Create a decentralized stormwater system: manage runoff at the source to the extent practical through the use of small decentralized structures, such as swales, bioretention areas, infiltration structures, filter strips, rain barrels, cisterns, dry wells, and vegetated areas. Increase the time of concentration (average time for rainfall to reach a point) by using open, vegetated drainage systems and maximizing overland or sheet flow.
No stormwater runoff generated from land development and redevelopment shall be discharged directly to a wetland, local water body, municipal drainage system, or abutting property, without treatment in compliance with these criteria.
A. 
Impervious and disturbed surfaces from development alter the natural hydrologic cycle by discharging stormwater directly to streams, rather than allowing it to infiltrate through the soils and into groundwater as it did before development. This increases flooding and reduces the base flow to streams that is needed in the summer months when there is little precipitation. The increased runoff from impervious surfaces also increases stream temperatures, since pavement and other impervious surfaces absorb substantial amounts of heat in the summer due to their dark coloring and lack of shade, which is transferred to runoff passing over the surface. The result is runoff that is dramatically warmer than natural groundwater inflow would have been under a natural hydrologic cycle. The purpose of these criteria is to maintain existing recharge rates to preserve existing groundwater levels and stream base flows and temperatures.
B. 
The volume of water to be recharged shall be based on the site soils. The volume of water to be retained from the developed site shall be calculated using the following equation:
Rev = [(S)(TIA)]/12
Where:
Rev
=
Recharge volume (cubic feet).
TIA
=
Total impervious area (square feet).
S
=
Soil-specific recharge factor (inches).
Hydrologic Group
Soil-Specific Recharge Factor
A
0.60
B
0.35
C
0.25
D
0.10
C. 
The following criteria shall also apply:
(1) 
All recharge systems must receive pretreatment prior to recharge. All pretreatment devices must meet the criteria outlined under § 352-12.
(2) 
The applicant must submit all recharge calculations. The capture area adjustment calculations described in the Massachusetts Stormwater Management Standards must be applied if runoff from all impervious surfaces is not directed to the treatment BMPs. In no case shall runoff from less than 65% of the site's impervious cover be directed to the BMPs intended to infiltrate the required recharge volume.
(3) 
Compaction of soils in designated recharge areas must be minimized during and after construction.
(4) 
If more than one soil type is present at the site, a composite soil-specific recharge factor shall be computed based on the proportion of total site area within each soil type. The recharge volume provided at the site shall be directed to the most permeable soil available.
(5) 
To qualify as a treatment BMP, a recharge system must discharge to soils with infiltration rates less than or equal to 2.4 inches per hour when used as a treatment BMP.
(6) 
At least 44% of the TSS must be removed prior to discharge to an infiltration structure used for treatment if the discharge is:
(a) 
Within a Zone II or interim wellhead protection area;
(b) 
Near an outstanding resource water or special resource water;
(c) 
Near a shellfish growing area, cold-water fishery, or bathing beach; or
(d) 
From a land use with higher potential pollutant loads as defined in the Massachusetts Stormwater Handbook.
(7) 
At least 80% of the TSS must be removed prior to discharge to an infiltration structure used for recharge if the discharge is within an area with a rapid infiltration rate greater than 2.4 inches per hour.
(8) 
The Committee may alter or eliminate the recharge volume requirement if the site is situated on unsuitable soils (i.e., marine clays) or karst or in an urban redevelopment area. In this situation, nonstructural practices (filter strips that treat rooftop or parking lot runoff, sheet flow discharge to stream buffers, and grass channels that treat roadway runoff) should be implemented to the maximum extent practicable and the remaining or untreated volume included in the water quality volume.
(9) 
The system should be designed based on the infiltration rates in Table 1, using the soil evaluation process outlined in Volume 3 of the Massachusetts Stormwater Handbook:
Table 1. Hydrologic Soil Properties Classified by USDA Soil Texture
Texture Class
Hydrologic Soil Group
Design Infiltration Rate (f)
(inches per hour)
Remarks
Sand
A
8.27
Loamy sand
A
2.41
Sandy loam
B
1.02
Loam
B
0.52
Silt loam
C
0.27
Sandy clay loam
C
0.17
Clay loam
D
0.09
Use Group D soils when estimating pre- and post-development annual recharge. However, do not locate recharge BMPs within areas with Group D soils.
Silty clay loam
D
0.06
Sandy clay
D
0.05
Silty clay
D
0.04
Clay
D
0.02
Source: Rawls, Brakensiek and Saxton, 1982
(10) 
Underground recharge systems may only be used to recharge stormwater runoff directly from rooftops. They may not be used to recharge stormwater runoff from other surfaces due to sediments in the runoff that may cause clogging of the recharge system and difficulty to rehabilitate these systems once they have failed.
(11) 
All infiltration structures used for treatment must be designed using the "Static" Method, which requires the structure to hold the entire water quality or recharge volume (as applicable) and does not allow credit for exfiltration as the structure is filling.
(12) 
The "Dynamic" Method of sizing infiltration structures assumes stormwater exfiltrates into the groundwater as the structure is filling and may be used for roof runoff devices and recharge devices that follow full treatment to remove 80% TSS from the stormwater runoff.
(13) 
All units/devices shall be designed to drain within 72 hours from the end of the storm.
(14) 
A mounding analysis must be performed when the vertical separation from the bottom of an exfiltration system to seasonal high groundwater is less than four feet and the recharge system is proposed to attenuate peak discharge from a ten-year or higher twenty-four-hour storm. The mounding analysis must demonstrate that the recharge volume is fully dewatered within 72 hours and that the groundwater mound that forms under the recharge system will not break out above the land or water surface of a wetland. The Hantush or other equivalent method may be used to conduct the mounding analysis.
(15) 
Recharge shall not be concentrated to one area. It shall be distributed to multiple areas throughout the site.
A. 
Pretreatment basins must be designed and located to be easily inspected and accessible to facilitate maintenance. Pretreatment devices must also be sized to accommodate a minimum of one year's worth of sediment and debris per § 352-12B(6).
B. 
The following criteria shall be followed to ensure that the device will permit sufficient treatment of stormwater and allow for a reasonable required maintenance frequency for the stormwater treatment system (STS):
(1) 
Pretreatment devices shall be provided for each STS; and
(2) 
Pretreatment devices shall be designed to accommodate a minimum of one year's worth of sediment; and
(3) 
Pretreatment devices for bioretention areas should include a grass buffer or transition zone between pavement and bioretention (e.g., crushed stone entrance, cobbles) that allows sediment to drop out before entering the treatment device; and
(4) 
Pretreatment devices shall be designed to capture anticipated pollutants, such as oil and grease; and
(5) 
Pretreatment devices shall be designed and located to be easily accessible to facilitate inspection and maintenance; and
(6) 
Pretreatment structures shall be sized to hold an annual sediment loading. An annual sediment load shall be calculated using a sand application rate of 500 pounds/acre for sanding of roadways, parking areas and access drives within the subcatchment area, a sand density of 90 pounds per cubic foot and assuming a minimum frequency of 10 sandings per year. To obtain an annual sediment volume, perform the following calculation:
Area to be sanded (acres) x 500 pounds/Acre-Storm ÷ 90 pounds/ft3 x 10 storms/year = cubic feet of sediment/year
(7) 
The developer shall maintain any STSs used to trap sediment during construction to prevent sediment from leaving the site and shall remove all sediment from all STSs when construction is finished and the site is stabilized.
The following criteria shall be followed to control peak discharge rates and improve the overall effectiveness of the stormwater treatment systems. These are minimum design criteria.
A. 
At each analysis point, the post-development peak discharge rate shall be equal to or less than the pre-development peak discharge rate (based on a two-year, ten-year, twenty-five-year, twenty-four-hour storm); and
B. 
The one-hundred-year, twenty-four-hour storm event must be evaluated to demonstrate that there will not be increased flooding impacts off site. If this evaluation shows that increased off-site flooding will result from peak discharges from the one-hundred-year, twenty-four-hour storms, BMPs must also be provided to attenuate these discharges; and
C. 
The site shall be designed to ensure that all runoff from the site, up to the maximum design storm for the particular structure, will actually enter the control structure. For example, the control structure may be designed for the twenty-five-year storm, while the drainage system may only be sized to handle a ten-year storm, with larger storms flooding the distribution system and traveling overland. This overland flow, or overflow, must be directed into the peak control structure; and
D. 
For each design storm, the applicant shall account for all run-on and run-off (including off-site impacts) in both pre- and post-development conditions; and
E. 
Emergency spillways shall be designed for the full range of design storms assuming the primary outlet structure is not functioning; and
F. 
Use SCS methods (TR-20 or TR-55) to develop hydrographs and peak flow rates for the proposed development site. The hydrograph time interval (dT) in TR-20 should be no greater than 0.1 hour. All areas shall be accounted for in the pre-/post-runoff calculations. The total tributary area that contributes flow from the proposed site, including runoff entering the site through piped drainage or surface runoff from off-site sources, shall be included even if a portion does not contribute flow to the BMP. The objective is for the development's storm drain design to account for total runoff leaving the site; and
G. 
Use curve number (CN) values as provided in Table 2 to calculate stormwater runoff rates for pre-/post-construction ground surface conditions; and
H. 
Any site that was wooded within the last five years shall be considered undisturbed woods for all pre-construction runoff conditions, regardless of clearing or cutting activities that may have occurred on the site during that preapplication period; and
I. 
Off-site areas should be modeled as "present land use condition" in good hydrologic condition for the design storm events for both pre- and post-development calculations; and
J. 
The length of overland sheet flow used in time of concentration (tc) calculations shall be limited to no more than 50 feet for pre- and post-development conditions.
Table 2
Approved CN Values for the SCS Methods (TR-20, TR-55)
Hydrologic Soil Group
Pre-Construction Runoff Curve Number (CN Values)
A
B
C
D
Open space, such as lawns, parks, and cemeteries2
68
79
86
89
Woods and forest3
30
55
70
77
Impervious areas, such as paved parking lots, driveways and roofs
98
98
98
98
Gravel roads (processed, dense graded)
76
85
89
91
Dirt roads
72
82
87
89
Newly graded pervious areas (no vegetation)
77
86
91
94
Post-Construction Runoff-Curve Number (CN Value)
A
B
C
D
Open space, such as lawns, parks, and cemeteries2
68
79
86
89
Woods and forest that is selectively cleared3
43
65
76
82
Impervious areas, such as paved parking lots, driveways and roofs
98
98
98
98
Gravel roads (processed, dense graded)
76
85
89
91
Dirt roads
72
82
87
89
Newly graded pervious areas (no vegetation)
77
86
91
94
Source: TR-55, 1986
NOTES:
1.
The runoff curve numbers are for use in calculating runoff with TR-55 or other approved models.
2.
The open space CN values for lawns, parks, and cemeteries assumes a "poor" condition for grass cover since the post-construction amount of grass cover cannot be predicted or guaranteed.
3.
The pre-construction CN value for woods and forest is based on a "good" condition where the woods are undisturbed and brush adequately covers the soil. The post-construction CN value for woods and forest is based on a "fair" condition if any selective cutting is conducted since the soils typically become compacted due to the equipment used to remove the large white pines and there may be post-cutting wind damage to the remaining unsupported canopy. If the applicant can demonstrate that no disturbance will occur during construction, then the pre-construction CN value for woods may be used for the post-construction runoff calculations. A note should be placed on the plan indicating where selective cutting will occur.
A. 
Many stormwater management practices focus on controlling peak flow rates for larger storms, including the two-, ten- and one-hundred-year storms. This does not address the increased duration at which those high flows occur because of the increased volume of water from development compared to pre-development. For example, although the peak flows are kept the same, there is a much greater volume of water leaving the site under developed conditions and the streams have higher flows for longer durations than they did under predevelopment conditions. In addition, because the impervious development has limited recharge, base flow during non-storm event times is lower. The purpose of this criterion is to limit the total amount of time that a receiving stream exceeds an erosion-causing threshold based on pre-developed conditions. The following method shall be used: 24 hours extended detention of the post-development one-year, twenty-four-hour return frequency storm event pursuant to § 352-14A(1). This is not required for direct discharges to a lake or fourth-order stream. However, the recharge and water quality treatment requirements outlined above will still be required for these discharges.
(1) 
The one-year, twenty-four-hour return frequency storm event (one-year storm) shall be detained for an additional 24 hours longer than the predevelopment runoff discharge time.
A. 
Stormwater treatment devices shall be used to handle water quantity as well as treat water quality. The water quality volume shall be calculated as:
WQV = [(1 inch)*(TIA)]/12
Where:
WQV
=
Water quality volume (ft3).
TIA
=
Total impervious area (square feet).
12
=
Conversion factor (inches per foot).
B. 
If discharging to a cold-water fishery, the stormwater water quality volume must be treated through either infiltration, an underdrain discharge system, or gravel wetland that allows the water to cool before being discharged. An underdrain system works by forcing the stormwater through a soil filter located above a gravel-packed drain and allowing for slow release of the water. The cool soils and gravel help to cool the water before it is discharged.
A. 
Stormwater management systems shall be designed to remove 80% of the average annual post-construction load of total suspended solids (TSS).
B. 
If a stormwater discharge is located within the watershed of a water body with a total maximum daily load (TMDL), pollution prevention and structural BMPs that are consistent with the TMDL must be selected. The applicant shall submit a narrative describing how they will meet the requirements of the TMDL.
Stormwater discharges to critical areas, as defined in the Massachusetts Stormwater Handbook, shall use specific source control and pollution prevention measures and the specific structural stormwater best management practices outlined in the Massachusetts Stormwater Handbook.
Redevelopment projects must meet the same criteria as new development to the maximum extent practicable. At a minimum, existing stormwater conditions must be improved, including reduction of peak rates, reduction of discharge volume, increased recharge, and increased water quality treatment.
The following criteria shall be met for erosion control, prior to any land disturbance activities commencing on the site:
A. 
Development shall be oriented to the site so that the cutting and stripping of vegetation and grading are minimized.
B. 
Prior to any land disturbance activities commencing on the site, the developer shall physically mark limits of no land disturbance on the site with tape, signs, or orange construction fence, so that workers can see the areas to be protected. These areas must be inspected by a representative of the Committee before clearing commences.
C. 
Appropriate erosion and sediment control measures shall be installed prior to soil disturbance. Measures shall be taken to control erosion within the project area. Sediment in runoff water shall be trapped and retained within the project area. Wetland areas and surface waters shall be protected from sediment. Erosion controls must be inspected by a representative of the Committee before clearing commences.
D. 
Runoff shall be controlled and conveyed into storm drains and other outlets so it will not erode the land or cause off-site damage; sediment in runoff shall be trapped by using staked straw bales, silt fencing, or sedimentation traps, or other approved erosion control devices.
E. 
Sediment basins shall be constructed where necessary to detain runoff and to trap sediment during construction.
F. 
Sediment shall be removed once the volume reaches 1/4 the height of the silt fence or straw bale.
G. 
Off-site runoff shall be diverted from highly erodible soils and steep slopes to stable areas.
H. 
Erosion and sediment controls shall be coordinated with the sequence of grading, development and construction operations; control measures shall be in effect prior to commencement of each increment/phase of the process.
I. 
Land disturbance activities exceeding two acres in size shall not be disturbed without a sequencing plan that requires stormwater controls to be installed and the soil stabilized, as disturbance beyond the two acres continues. Mass clearings and grading of the entire site should be avoided. Prior to any construction on the site, the applicant shall submit a construction phasing plan to the Committee for review and approval. The plan shall show how construction will proceed with a minimum of disturbance at any one time and shall specify approximate dates for initial disturbance and final stabilization for each phase.
J. 
Soil and other materials shall not be stockpiled or redistributed, either temporarily or permanently, in locations or in such a manner as would cause suffocation of tree root systems.
K. 
Topsoil shall be stripped from disturbed areas, stockpiled in approved areas and stabilized with temporary vegetative cover if it is to be left for more than 30 calendar days; perimeter sediment controls shall be installed around each area of stockpiled topsoil.
L. 
Soil stockpiles shall be stabilized or covered at the end of each workday.
M. 
The area of disturbance shall be kept to a minimum. Disturbed areas remaining idle for more than 14 days shall be stabilized.
N. 
Grading shall be kept to a minimum; tree removal shall be minimized.
O. 
For active construction areas such as borrow or stockpile areas, roadway improvements and areas within 50 feet of a building under construction, a perimeter sediment control system shall be installed and maintained to contain soil.
P. 
A stabilized construction entrance shall be constructed at all entrance/exit points of the site to reduce the amount of soil carried onto roadways and off the site.
Q. 
Dust shall be controlled at the site.
R. 
On the cut side of roads, ditches shall be stabilized immediately with rock riprap or other nonerodible liners or, where appropriate, vegetative measures such as sod.
S. 
All graded areas beyond the street right-of-way shall be covered with four inches of topsoil and planted with a native species of vegetative cover, sufficient to prevent erosion.
T. 
Temporary seeding, mulching or other suitable stabilization methods shall be used to protect exposed soil areas during construction; as feasible, natural vegetation shall be retained and protected; during the months of October through March, when seeding may be impractical, an anchored mulch or sod shall be applied as approved by the Committee or by the Committee's designee; diversions and/or prepared outlets may be required in critical areas during construction.
U. 
Permanent seeding should be undertaken in the spring from March through May and in late summer and early fall from August to October 15. During the peak summer months and in the fall after October 15, when seeding is found to be impractical, an appropriate temporary mulch shall be applied. Permanent seeding may be undertaken during the summer if plans provide for adequate mulching and watering.
V. 
Permanent vegetation and erosion control structures, as necessary, shall be installed, preferably immediately after construction is completed but otherwise no later than the first full spring season immediately thereafter; they shall comply with the erosion and sedimentation vegetative practices recommended by the U.S. Soil Conservation Service.
W. 
Temporary ground cover or erosion/sedimentation controls shall be established on any unbuilt lots as required by the Committee.
X. 
Native species shall be used for revegetation.
Y. 
All slopes steeper than 3:1 (h:v, 33.3%), as well as perimeter dikes, sediment basins or traps, and embankments shall, upon completion, be immediately stabilized with sod, seed and anchored straw mulch, or other approved stabilization measures. Areas outside of the perimeter sediment control as shown on the Erosion and Control Plan shall not be disturbed.
Z. 
Monitoring and maintenance of erosion and sediment control measures throughout the course of construction shall be required. The applicant shall submit to the Stormwater Committee a complete operation and maintenance plan for temporary and permanent erosion control measures, as part of the application package.
AA. 
Temporary sediment trapping devices shall not be removed until permanent stabilization is established in all contributory drainage areas. Similarly, stabilization shall be established prior to converting sediment traps/basins into permanent (post-construction) stormwater management facilities. All facilities used as temporary measures shall be cleaned prior to being put into final operation.
BB. 
All temporary erosion and sediment control measures shall be removed after final site stabilization. Disturbed soil areas resulting from the removal of temporary measures shall be permanently stabilized within 30 days. The applicant's engineer shall submit written certification that this condition has been met.
Prior to the start of construction, the applicant must submit a narrative addressing pollution prevention measures to be taken at the site during the construction period. If the proponent is required to have a NPDES permit, a copy of the SWPPP can be filed in lieu of the narrative. The narrative must include emergency contact information during construction activities.
There shall be no illicit discharges from the site. The applicant shall submit an illicit discharge compliance statement verifying no illicit discharges exist on the site. For redevelopment projects, the applicant must provide a summary of the steps taken to verify no illicit discharges.
A. 
A long-term operation and maintenance plan (O&M plan) for the permanent stormwater management system is required at the time of application for all projects. The long-term O&M plan shall be prepared by a professional engineer and at a minimum identify:
(1) 
The names and addresses of the stormwater management system(s) owners;
(2) 
The names and addresses of party or parties responsible for operation and maintenance, including how future property owners will be notified of the presence of the stormwater management system and the requirement for proper operation and maintenance;
(3) 
Emergency contact information in the event a BMP is failing and creating a safety hazard;
(4) 
Provisions to notify the appropriate reviewing entity of a change in responsible party;
(5) 
The person(s) responsible for financing maintenance and emergency repairs, including contact information (address, phone number, e-mail address);
(6) 
The routine and nonroutine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks, including what actions trigger a maintenance task to be performed and the frequency with which the tasks will be performed;
(7) 
BMP-specific O&M activities for each component of the stormwater system;
(8) 
Recordkeeping consistent with DEP requirements, including log forms that will be submitted to the Committee as part of the long-term operation and maintenance permit conditions;
(9) 
A list of easements with the purpose and location of each;
(10) 
A plan that is drawn to scale and shows the location of all stormwater BMPs in each treatment train along with the discharge point;
(11) 
Include for informational purposes description and delineation of public safety features;
(12) 
Estimated operations and maintenance budget for the routine and nonroutine maintenance tasks outlined under Subsection A(6) above; and
(13) 
The signature(s) of the owner(s).
B. 
The Stormwater Committee shall make the final decision of what maintenance option is appropriate in a given situation. The Stormwater Committee will consider natural features, proximity of site to water bodies and wetlands, extent of impervious surfaces, size of the site, slopes, the types of stormwater management structures, and potential need for ongoing maintenance activities when making this decision. Once approved by the Stormwater Committee, the operation and maintenance plan shall be recorded at the South Middlesex Registry of Deeds by the applicant and shall remain on file with the Stormwater Committee and shall be an ongoing requirement as part of the stormwater management permit.
Driveways pursuant to Chapter 235 of the Code of the Town of Groton shall comply with the following:
A. 
The stormwater runoff from all impervious areas shall not discharge into the public right-of-way. The peak rate of runoff at the street shall not increase from the predeveloped rate during the two-, ten-, twenty-five- or one-hundred-year storm event, unless an increase is authorized by the Board of Selectmen or its designee. Stormwater runoff may discharge directly into rights-of-way of new subdivision roads if the overall stormwater management plan for the street is designed to accommodate the runoff and a catch basin is located within 10 feet of the downslope side of the driveway. The purpose is to prevent ice jams in the winter.
A. 
Proposed residential, commercial, or industrial subdivisions shall apply these stormwater management criteria to the land development as a whole. Individual lots in new subdivisions shall not be considered separate land development projects but rather the entire subdivision shall be considered a single land development project. Hydrologic parameters shall reflect the ultimate land development and shall be used in all engineering calculations.
B. 
General approach. Storm drains, culverts, swales, detention basins and related facilities shall be designed to permit the unimpeded flow of all natural watercourses, to ensure adequate drainage at all low points along streets, to control erosion and to intercept stormwater runoff along streets at intervals reasonably related to the extent and grade of the area being drained. The peak rate of runoff at the boundaries of the development shall not be increased from the predevelopment rate during the two-, ten-, twenty-five- or one-hundred-year storm event, unless an increase is authorized by the Committee, following consultation with the Conservation Commission and consideration of the ability of receiving wetlands or water bodies to absorb the increase and the consequences of providing detention capacity. The proposed lot grading shall be shown on the plans so that the proposed stormwater management system can be properly evaluated.
C. 
Design basis. Facility design shall accommodate the following:
(1) 
Closed drainage system (storm sewers) and swales: twenty-five-year Rational Formula storm.
(2) 
Detention basins: one-hundred-year TR-20 or TR-55 Type III twenty-four-hour storm event.
(3) 
Culverts, other stream crossings shall be designed in accordance with the Massachusetts Stream Crossings Handbook and Massachusetts River and Stream Crossing Standards.
(4) 
All tributary areas shall be assumed to be fully developed in accordance with Chapter 218, Zoning, unless publicly owned or deed restricted. Storm drainage systems shall be designed to handle all runoff water from the tributary watershed. The Rational Formula shall be used to determine pipe sizing for the piped drainage system. The United States Soil Conservation Service (USSCS) TR20 or TR55 methodology, where applicable, shall be used to determine no net increase in the off-site rate of runoff for detention and infiltration systems. Adequate physical access for maintenance purposes shall be provided to detention and infiltration facilities. Water velocities in pipes and paved gutters shall be between two feet and 10 feet per second and not more than five feet per second on unpaved surfaces.
D. 
Closed drainage system (storm sewers).
(1) 
All drain pipes shall be at least 12 inches inside diameter and made of reinforced concrete conforming to Massachusetts Department of Transportation specifications for Class III pipe or such higher class as may be required by the depth of cover, which shall be not less than 36 inches where the pipe is subject to vehicular loads. Manhole covers and grates shall be in conformance with Massachusetts Department of Transportation Specifications 201, designed and placed so as to cause no hazard to bicycles. No catch basins shall serve as manholes. Trash racks shall be installed at both ends of all culverts.
(2) 
Interceptor drains. Interceptor drains shall be designed and constructed and incorporated into the drainage system where warranted by groundwater elevations.
E. 
(Reserved)
F. 
Structures. Catch basins will be required at all low points and on both sides of the roadway on continuous grade at intervals of not more than 300 feet. Drainage patterns at intersections shall be evaluated and catch basins designed and constructed so as to prevent any flooding at the intersection. Any catch basins used shall be at least six feet deep and four feet in diameter (inside measurements), with a forty-eight-inch or greater sump below pipe invert, and shall be constructed of precast concrete units. Manholes used shall be at least four feet in diameter (inside measurements) and shall be constructed of precast concrete units, with formed inverts (unless waived by the Board to allow the use of concrete blocks). Oil and grease traps shall be installed on all structures that discharge to a resource area as defined by 310 CMR, the Wetlands Protection Act, and where required by the Board. Manhole covers and catch basin grates shall be in conformance with Massachusetts Department of Transportation Standard Specifications for Highways and Bridges Section 201, with catch basin grates designed and placed so as to cause no hazard to bicycles. Standard catch basin frames and grates and manhole rims and covers are specified in Chapter 381, Part 2, of the Subdivision Rules and Regulations,[1] Construction Appendix. Granite curb inlets shall be provided at all catch basins located within the roadway.
[1]
Editor's Note: For the Subdivision Rules and Regulations, see Part 1 of Ch. 381.
G. 
Swales. Drainage swales shall have cross-sectional areas adequate to carry a ten-year storm and be treated as follows:
Slopes
(percent)
Treatment
0.75 to 4
6 inches of loam seeded
4 to 10
6 inches of minimum dimension angular stones for a water depth of 1 foot, with a 12-inch gravel subbase (SSH&B M 1.03.0 type A)
H. 
Waterways. Open brooks or tributary ditches which are to be altered shall be shaped to a cross section and gradient and provided with stream bottom hardening, all acceptable to the Planning Board. Safety fencing may be required where important because of slope, bank instability, stream depth or flow rate or other reasons. Proposed finished grade for detention basins shall not be more than seven feet above or below existing grade unless specifically authorized by the Board in unusual topographic circumstances.
I. 
Connections. Proper connections shall be made with any existing drains in adjacent streets or easements which prove adequate to accommodate the drainage flow from the subdivision. In the absence of such facilities or the inadequacy of the same, it shall be the responsibility of the developer to extend drains from the subdivision as required to properly dispose of all drainage from said subdivision in a manner determined to be proper by the Board and to secure for the Town any necessary drainage rights.
J. 
Floodplains.
(1) 
District. All subdivision proposals and other proposed new development shall be reviewed to determine whether such proposals will be reasonably safe from flooding. If any part of a subdivision proposal or other new development is located within the Floodplain District established under Chapter 218, Zoning, it shall be reviewed to assure that:
(a) 
The proposal is in compliance with § 218-29B(2) of Chapter 218, Zoning.
(b) 
The proposal is designed consistent with the need to minimize flood damage.
(c) 
All public utilities and facilities, such as gas, electrical and water systems, shall be located and constructed to minimize or eliminate flood damage.
(d) 
Adequate drainage systems shall be provided to reduce exposure to flood hazards.
(e) 
Base flood elevation (the level of the one-hundred-year flood) data shall be provided for that portion within the Floodplain District.
(2) 
Identification. All one-hundred-year floodplains will be calculated and identified on the definitive subdivision where not identified on the Federal Emergency Management Agency (FEMA) maps.
The Conservation Commission shall enforce the following general performance standards:
A. 
Minimize pre-project to post-project changes in site hydrology.
B. 
Pre-project and post-project hydrology should remain fundamentally the same as it pertains to protecting wetlands functions and values. Of course, some minor degree of change in hydrology is inevitable in any engineering/construction project, and within reasonable limits, the Commission shall permit such variation when, in its judgment, such changes will not produce a significant impact on wetlands functions and values. The use of aboveground vegetated swales, infiltration methods, and other low-impact drainage designs will be given preference over subsurface drainage structures.
C. 
Erosion control may require limiting stormwater discharge volumes and velocities. Therefore, the Commission may require the construction of such stormwater control structures, and specify particular engineering and design details, as it deems necessary to protect wetland resources, values, and functions.
D. 
Minimize change in runoff water quality. The Commission shall impose conditions that, in its judgment, reduce undesirable water quality changes to levels that will not harm wetland functions or values, immediately or cumulatively. The Commission may require the construction of specific structures to improve stormwater runoff quality, such as wet detention basins for pollutant removal and broad riprap swales for aeration.
E. 
Requirements for hydraulic calculations. In accordance with the above, the Conservation Commission shall require, as part of the application for permit, complete hydrological calculations for the one-, two-, five-, ten-, twenty-five-, and one-hundred-year storm events. Such calculations shall include:
(1) 
Runoff from all impervious surfaces associated with the project, including individual lot construction; and
(2) 
Both pre- and post-project calculations for discharge volumes, concentration times, discharge velocities, and other quantities that the Commission may require for complete information.
F. 
Requirements for turtle and amphibian migration shall include:
(1) 
Curbing incline no greater than 45° from the horizontal (with the exception of "roundings" and catch basins).
(2) 
Hay bales are to be arranged in a staggered formation where appropriate. This is to allow migration paths for amphibians.
A. 
Bioretention design guidelines. Bioretention systems offer excellent pollutant removal, while providing some retention of stormwater runoff. Bioretention systems rely on the soil and planting media to remove pollutants and provide absorption of stormwater runoff. The following design standards should be followed to achieve the maximum benefit:
(1) 
Construction components. Bioretention systems are constructed in an excavated hole and consist of, from bottom up:
(a) 
Optional stone reservoir to provide additional holding capacity.
(b) 
A minimum three-inch-thick transition layer of 3/8-inch pea gravel.
(c) 
A layer of lightly compacted soil media at least 18 inches thick.
(d) 
Vegetation consisting of dense plantings of woody shrubs, herbaceous perennials and, if the soil media is deep enough for the roots, small trees. The plants should be native if possible and must be both drought and flood tolerant.
(e) 
A cover of three inches of aged, fibrous bark mulch.
(f) 
A maximum six-inch depression for surface stormwater storage.
(2) 
Soil media. The soil media shall have a maximum fines content of 5% and shall consist of:
(a) 
Topsoil: 20% to 30%.
(b) 
Organic materials (combination of woodchips/mulch and compost): 20% to 30%.
(c) 
Sand: 50% to 55%.
(3) 
Filter fabric. Filter fabric should not be used between the soil media and native soils or soil media and transition stone/stone reservoir. The use of fabric between these layers will cause system failure due to clogging from fines located within the soil media. If an underdrain is to be used to drain the bioretention area, then filter fabric can be used between the underdrain bedding and the native soils to prevent the migration of native soils into the underdrain bedding.
B. 
Naturalized basin design guidelines.
(1) 
Naturalized basins have several advantages over traditional basins, including:
(a) 
The deeper root systems of the native plant materials encourage infiltration, recharging groundwater tables and increasing base flows.
(b) 
The plants trap pollutants, increasing the water quality of the discharge.
(c) 
The vegetation serves to cool water temperatures and slow stormwater velocities.
(d) 
They are visually more attractive and can help beautify a neighborhood, increasing property values.
(e) 
They require less maintenance. Generally, annual mowing and periodic trimming of trees and plants is sufficient.
(2) 
The following design standards shall be followed:
(a) 
The basin shall be easily accessible for maintenance.
(b) 
Construct the basin with a sediment forebay at the inlet, sized to hold a minimum of one year's worth of sediment accumulation if no other pretreatment is proposed.
(c) 
Construct the basin to have a natural low-flow channel with turf reinforcement material to remove pollutants and prevent erosion.
(d) 
Incorporate a naturally landscaped area at the ground surface. The ground surface around the basin shall be large enough to be in scale with the overall landscaped area. The purpose is to filter and soften views from residential areas.
(e) 
Plant all areas of the naturalized basin, including basin floors, side slopes, berms, impoundment structures, or other earth structures, with suitable native vegetation such as naturalized meadow plantings or lawn grass specifically suited for stormwater basins. Suggested plants include:
[1] 
Grasses: big bluestem, switchgrass and wildflower mixes. In wet areas, plant sweetflag and soft rush for color and texture.
[2] 
Shrubs: red chokeberry (Aronia arbutifolia); silky dogwood (Cornus ammomum); arrowwood (Viburnum dentatum); cranberrybush (Viburnum trilobum); service berry/shadbush (Amelanchier cavadensis or laevis); and elderberry (sambucus).
[3] 
Trees: red maple (Acer rubrum); river birch (Betula nigra); various willows.
(f) 
Trees may not be planted below the pool area of the basin. If shrubs are used, they must be adapted to wet or moist soil conditions.
(g) 
Mulch may be used in shrub beds located within the pool area with a non-floating-type mulch.
(h) 
Group trees or shrubs to avoid a spotty effect.
(i) 
Provide access to the basin for maintenance. Blend access area in with the surrounding landscape to the extent feasible.
(j) 
The forebay/sediment trap shall be at least 10 feet long and sized to hold at least the annual sediment loading and must meet the sizing requirements of the DEP Stormwater Standards.
(k) 
Maintenance access shall be planted with grass and at least 10 feet wide with a maximum slope of 15% and a maximum cross slope of 3%.
(l) 
Provide a means to prevent soil compaction on the floor of the basin during construction.
(m) 
Size treatment storage area to hold the water quality volume.
(n) 
The perimeter of all basins shall be curvilinear so that from most edges of the basin, the whole basin will not be in view. A more traditionally shaped (oval or rectangular) basin may be permitted when conditions such as topography, parcel size, or other site conditions warrant. Basins shall follow natural landforms to the greatest extent possible or be shaped to mimic a naturally formed depression.
(o) 
Place inlets and outlets to maximize the flow path through the facility. At a minimum, the flow path shall be twice as long as wide. Baffles, pond shaping or islands can be added within the permanent pool to increase the flow path. If there are multiple inlets, the length-to-width ratio shall be based on the average flow path length for all inlets.
(p) 
Minimum one foot of freeboard above the twenty-five-year storm elevation.
(q) 
The interior slopes of the basin within the pool area shall not exceed a slope of four horizontal to one vertical.
(r) 
A minimum of six inches of topsoil with at least six-percent organic content shall be provided for all planting ground cover beds or lawn areas.
(s) 
Low-flow outlets shall be designed to prevent clogging.
(t) 
For basins that cannot infiltrate the water quality volume, use a soil filter conforming to the following:
[1] 
Impoundment depth: Peak storage depth within the filter area for water quality volume may not exceed 18 inches.
[2] 
Pipe layout and spacing: Layout of the pipe underdrain system must be sufficient to effectively drain the entire filter area. There must be at least one line of underdrain pipe for every eight feet of the filter area's width. The slope of the pipe must be 1% or greater.
[3] 
Pipe bedding: Minimum 12 inches over top of drainage pipe, six inches thick at sides, and six inches below drainage pipe of clean, well-graded gravel.
[4] 
Filter bed: The soil must consist of loamy, coarse sand. The soil filter must extend across the bottom of the entire filter area. The soil must be at least 18 inches deep and underlain by a gravel bedding.
[5] 
Surface cover: The top of the underdrain system must be covered with a four-inch layer of sandy loam and then covered with plantings consisting of species tolerant of frequent inundation.
[6] 
Underdrain outlet: Each system must discharge to an area capable of withstanding concentrated flows and saturated conditions without eroding.
[Added 3-21-2017]
A. 
The Committee may waive strict compliance with any requirement of this chapter where such action:
(1) 
Is allowed by federal, state and local statutes and/or regulations;
(2) 
Is in the public interest; and
(3) 
Is not inconsistent with the purpose and intent of this chapter.
B. 
Any applicant must submit a written request to be granted such a waiver. Such a waiver request shall be accompanied by an explanation or documentation supporting the waiver request and demonstrating that strict application of this chapter does not further the purposes or objectives of this chapter.
C. 
All waiver requests shall be discussed by the Committee and a decision shall be made by the Committee within 30 days of receiving the waiver request.
D. 
If, in the Committee's opinion, additional time or information is required for review of a waiver request, the Committee may continue consideration of the waiver request to a date certain announced at the meeting. In the event the applicant objects to a continuance, or fails to provide the requested information, the waiver request shall be denied.