Section 096-500-4 - Stormwater standardsThe stormwater standards described in this Section include basic, general, phosphorous, urban impaired stream, flooding and other standards.
A. Applicability.This section applies to: 1) A project that requires a Stormwater Management Law permit, other than a stormwater permit by rule (PBR)issued pursuant to Section 6 of this Chapter;2) A project that requires a Site Law permit; and3) Changes to a project licensed pursuant to the Stormwater Management Law or Site Law that requires a modification of a project's license, as described in Section 16 of this Chapter. For the purpose of determining the applicability of the general and phosphorous standards, when a project is located in separate watersheds, the area of the entire project is considered in determining whether a standard applies. For example, if a portion of a project drains to a lake, and another portion drains to a non-lake water body, the project needs to meet the applicable standards for each watershed.
B.Basic standards.The basic standards apply to all projects described above. The applicant must demonstrate that the erosion and sedimentation control, inspection and maintenance, and housekeeping standards specified in Appendices A, B, and C to this Chapter, respectively, are met, and that the grading or other construction activity will not impede or otherwise alter drainageways so as to have an unreasonable adverse impact on a wetland or waterbody, or an adjacent downslope parcel.C.General standards. The general standards apply as described below in addition to the basic standards described in Section 4(B). (1) When the general standards must be met. A project must meet the general standards if the project results in: (a) Direct watershed of an urban impaired stream. 20,000 square feet or more of impervious area, or 5 acres or more of developed area, in the direct watershed of an urban impaired stream; or(b) Any other non-lake watershed. One acre or more of impervious area, or 5 acres or more of developed area anywhere else for a project that is not in the direct watershed of a lake.(2) Treatment requirements. To meet the general standards, the applicant must demonstrate that a project's stormwater management system includes treatment measures that will provide pollutant removal or treatment, and mitigate for the increased frequency and duration of channel erosive flows due to runoff from smaller storms and potential temperature impacts, unless the Department determines that channel protection and/or temperature control are unnecessary due to the nature of the resource. This must be achieved by using one or more of the methods described in this Section as follows: (a)Treatment level.A project's stormwater management system must: (i) Provide treatment of no less than 95% of the impervious area and no less than 80% of the developed area;(ii) Where treatment of 95% of the impervious area is not practicable, the Department may allow treatment of as low as 90% of the impervious area if the applicant is able to demonstrate that treatment of a greater depth of runoff than specified in the standards will result in at least an equivalent amount of overall treatment of the impervious area. The treatment depth of runoff must be increased by 0.05 inch for each 1% that the treatment area is decreased. Treatment must still be provided for no less than 80% of the developed area; or(iii) Provide treatment in accordance with Table 1. Table 1
Stormwater Treatment Based on Percentage of Parcel Developed
Percentage of Developed Area to Land Available for Development* | Percentageof Total Impervious Area Requiring Treatment** | Percentage of Total Developed Area Requiring Treatment** |
>70 | 95 | 80 |
65 | 92.5 | 77.5 |
<60 | 90 | 75 |
* Including all contiguous land area owned by the applicant, but not including land with greater than 25% sustained slope or consisting of a protected natural resource.
** Percentage may be pro-rated for values between 60% and 70% in left-hand column.
(b)Upgradient runoff.The runoff from any upgradient area must be either directed away from the stormwater treatment measure or that measure, not including buffers, must be sized to address the runoff volume from the upgradient area at 50% of the sizing requirements for an area that is landscaped, unless the upgradient area is on soil with hydrologic condition A or B.(c)Mitigation.The Department may allow the portion of a project's impervious or developed acreage that must be treated to be reduced through mitigation by eliminating or reducing an untreated off-site or on-site impervious stormwater source within the same watershed (see 06-096 CMR 501) if a project is not in a direct watershed of an urban impaired stream. The Department may, on a case-by-case basis, also determine that mitigation may include providing stormwater treatment for existing developed areas that do not require treatment under this Chapter.(d)Redevelopment project. This subparagraph describes how much treatment is required for a redevelopment project. (i) The requirement for treatment is scaled based on the pollutant discharge that, if the stormwater was untreated, would result from the redevelopment project. The Department will assign a pollutant ranking based on Table 2, and may, on a case-by-case evaluation of individual projects, modify the ranking by up to 2 points in light of project-specific features. Table 2
Pollutant Impact Rankings of Various Redevelopment Land Uses
Land Use | Pollutant Ranking |
Roads where idling may occur periodically due to traffic volume and intersections; High use parking lots | 5 |
Other roads; Medium use parking lots | 4 |
Other parking lots and driveways; Flat asphalt rooftops; Roofs on an industrial facility | 3 |
Other rooftops; Bikeways; Grassed areas mowed more than twice per year; Walkways/foot traffic-only pavement | 2 |
Non-grass landscaped areas; Stormwater treatment/storage systems (except buffers) | 1 |
Forest; Meadow mowed no more than twice per year; | 0 |
The method for determining the treatment requirement for redevelopment projects includes:
a. For the existing condition, calculating a weighted average of impact by multiplying the land area (in acres) of each type of existing land use by its pollutant ranking. Add these values together to get an existing impact rating.b. For the proposed condition, calculating a weighted average of impact by multiplying the land area (in acres) of each type of proposed redevelopment land use by its pollutant ranking. Add these values together to get a proposed impact rating.c. Divide the existing impact rating by the number of total redevelopment acres.d. Divide the proposed impact rating by the number of total redevelopment acres.e. Subtract the value in Item c from the value in Item d. Note: this value can be a negative number. Use this value in the left column of Table 3 (below) to determine the applicable treatment level required for the redevelopment project. Table 3
Treatment Levels for Redevelopment Projects
Ranked Impact Change Due to Redevelopment | Percentage of Developed Area that Must be Treated |
0.0 or less | 0% (Stormwater projects) 50% (Site projects) |
>= 0.0 to <= 1.0 | 60% |
>1.0 to <=2.0 | 70% |
> 2.0 to<= 3.0 | 80% |
> 3.0 | Same treatment level as for new development |
(ii) Priority for treatment must be given to areas with the highest pollutant ranking to the maximum extent practicable.(iii) The developed area of the redevelopment project must be treated to the level required based on the pollutant impact ranking in accordance with Table 3. If the Department determines that it is not practicable to meet the general standards for redevelopment on site, the Department may allow equivalent treatment or mitigation on an off-site parcel within the same watershed as an alternative for stormwater treatment.(iv) If a redevelopment project is located in geographically separate watersheds, treatment requirements must be calculated for each separate watershed.(3)Types of treatment measures allowed(a)Wetpond.A stormwater management system using a wetpond must detain, above a wetpond's permanent pool, a runoff volume equal to 1.0 inch times the subcatchment's impervious area plus 0.4 inch times the subcatchment's landscaped area. If located within the direct watershed of a stream, the pond must be designed to release this stored volume over a period of 24 to 48 hours through an underdrained gravel outlet. A wetpond must have a storage volume below the permanent pool elevation at least equal to 2.0 inches times the subcatchment's impervious area plus 0.8 inch times the subcatchment's non-impervious developed area, plus any required treatment for upgradient runoff in accordance with Section 4(C)(2)(b)above, and must have a mean depth of at least three feet, and a length to width ratio of 3:1 or greater.If the permanent pool volume is relatively evenly distributed (within 25% of each other) between separate wetponds in series, the required permanent pool volume may be reduced by 20%; if the permanent pool volume is relatively evenly distributed (within 25% of each other) between three separate wetponds in series, the required permanent pool volume may be reduced by 40%.(b)Vegetated soil filter. A stormwater management system using a vegetated soil filter to control runoff must detain a runoff volume equal to 1.0 inch times the subcatchment's impervious area plus 0.4 inch times the subcatchment's other landscaped area plus any required treatment for upgradient runoff in accordance with Section 4(C)(2)(b), above. The system must be designed in accordance with Section 4(C) of Appendix E of this Chapter. Discharges to groundwater from vegetated soil filters as described in Appendix E, Section 4(B) of this Chapter are considered de minimis discharges for the purposes of the Waste Discharge Licensing Program, and do not require a waste discharge license.
(c)Infiltration. A stormwater management system using infiltration to control runoff must retain a runoff volume equal to 1.0 inch times the subcatchment's impervious area plus 0.4 inch times the subcatchment's developed area that is landscaped, plus any required treatment for upgradient runoff in accordance with Section 4(C)(2)(b) above, and infiltrate this volume into the ground. The system must be designed in accordance with Appendix D of this Chapter. An infiltration system serving a development regulated under the Site Law may be required to meet additional standards in accordance with 06-096 CMR 375(7). Infiltration from a stormwater infiltration system is considered de minimis for purposes of the Waste Discharge Licensing Program and does not require an individual waste discharge license if the standards in Appendix D to this Chapter are met.
NOTE:Drywells and subsurface fluid distribution systems may need to be registered with and meet other requirements of the Department's Underground Injection Control Program.
(d)Buffers. A stormwater management system using buffers to control runoff must meet the design and sizing requirements described in Appendix F to this Chapter.(e)Innovative treatment measures.The Department may, on a case-by-case basis, approve alternative treatment measures to those described in Subsections 4(C)(3)(a) through 4(C)(3)(d)above. Innovative treatment measures may be either proprietary or non-proprietary, and must provide at least as much pollutant removal as the treatment measures listed above and as much channel protection and temperature control, unless the Department determines that channel protection and/or temperature control are unneeded due to the nature of the resource. Any person proposing the use of an innovative treatment measure may be required to provide reports or studies, subject to Department review and approval, demonstrating the control efficiency of the measure. The use of an innovative treatment measure does not preclude the need to meet other required Stormwater Management Law standards.(4)Low impact development credit.Low impact development strategies can reduce stormwater storage volume requirements through the use of non-structural stormwater management techniques that minimize impervious cover, thereby reducing both the size and cost of stormwater management structures. The use of low impact development strategies is optional and voluntary for all projects, but projects using this credit are eligible to reduce the portion of the project's impervious or developed acreage that must be treated. (a) Projects incorporating low impact development strategies under this Section must be reviewed and approved by the Department on a case-by-case basis, and must: (i) Protect as much undisturbed land as possible to maintain pre-development hydrology and allow rainfall infiltration;(ii) Protect natural drainage systems such as wetlands, watercourses, ponds and vernal pools to the maximum extent practicable;(iii) Minimize land disturbance including clearing and drainage to the extent practicable;(iv) Minimize the decrease in the time of concentration from pre-construction to post-construction to the extent practicable;(v) Minimize soil compaction to the extent practicable;(vi) Utilize low-maintenance landscaping that encourages the retention and planting of native vegetation, and minimizes the use of lawns, fertilizers and pesticides;(vii) Minimize impervious surfaces and break up or disconnect the flow of runoff over impervious surfaces to the extent practicable;(viii) Provide vegetated open-channel conveyance systems discharging into and through stable vegetated areas; and(ix) Provide other source controls to prevent or minimize the use or exposure of pollutants at the site in order to prevent or minimize the release of those pollutants into storm water runoff.(b) In order to qualify for low impact development credit, applicants must treat at least 50 percent of the runoff volume from developed areas with low impact development strategies. Low impact development credits, which reduce the amount of developed area that must be treated, will be awarded based on the percentage of developed area treated with low impact development strategies, and shall be pro-rated from between 10 percent and 20 percent, as follows: Percentage of Developed Area Treated With Low Impact Development Measures | Low Impact Development Credit |
50% | 10% |
75% | 15% |
100% | 20% |
(5)Exceptions from the general standards. This Section describes exceptions from the general standards. (a)Pretreatment measures. A project that includes measures to pretreat runoff to a filter or infiltration system in a Department-approved, flow-through sedimentation device may reduce the runoff volume to each treatment measure described in Section 4(B)(3)(b) and (c) by 25%.The pre-treatment credit does not apply to subsurface underdrained filter structures using chambers.(b)Discharge from a wetpond.A project using a wetpond for stormwater treatment that does not discharge to the direct watershed of a stream other than a major river segment is not required to incorporate channel protection storage above the wetpond's permanent pool or to install an underdrain. The underdrain may also be omitted from a wetpond when discharging to a wetland if the Department determines that filtering and temperature reduction, normally provided by an underdrain, are not necessary for maintaining the functions of the wetland.(c)Linear portion of a project. For a linear portion of a project, treatment may be reduced to no less than 75% of the linear portion's impervious area and no less than 50% of the linear portion's developed area. This exception does not apply to a linear portion of a project subject to the urban impaired stream standard.(d)A utility corridor or portion of a utility corridor. A utility corridor or portion of a utility corridor that meets the following criteria is not required to meet the general standards: (i) The project or portion of the project does not include impervious area;(ii) Disturbed areas are restored to pre-construction contours and revegetated within one month in the growing season following construction;(iii) Mowing of the revegetated right-of-way occurs no more than once during any twelve month period; and(iv) A vegetation management plan for the project has been reviewed and approved by the Department.(e)Wetland road crossing. That portion of a road crossing a wetland is not required to meet the general standards if the design provides for passage of flows through a culvert(s), bridge span, or use of a permeable base material that will allow flow under the road. (f)Roofs. Runoff from sloped, non-asphalt roofs of non-industrial facilities need to be treated for thermal impact and for channel protection only.(g)Treatment requirement for certain developed area approved or constructed prior to January 1, 2006 and not being redeveloped.A project requiring a Site Law permit is not required to meet the general standards for runoff from developed area constructed and operated in accordance with a Stormwater Management Law permit issued prior to January 1, 2006, provided the area is not being redeveloped. If a project requiring a Site Law permit includes a developed area constructed prior to that date that did not require a Stormwater Management Law permit, then the project must provide treatment of runoff in accordance with the general standards from at least 50% of that developed area. Priority for treatment must be given to areas with the highest pollutant ranking to the maximum extent practicable, using the ranking system in Table 2 of this Chapter. This Subsection does not apply to developed areas located within the direct watershed of an urban impaired stream or other waterbody that is impaired due to urban runoff or developed area proposed to be redeveloped.
D.Phosphorus standard. The phosphorus standard applies as described below in addition to the basic standards described in Section 4(B) of this Chapter. (1) When the phosphorus standard must be met .If a project is located in a lake watershed, the phosphorous standard must be met as follows: (a) When the project is located in the direct watershed of a lake most-at-risk. A development with 20,000 square feet or more of impervious area, or 5 acres or more of developed area in the direct watershed of a lake most-at risk must meet the phosphorous standard. The general standards may be used if the lake is not severely blooming and if the project results in less than 3 acres of impervious area and less than 5 acres of developed area. Severe blooming lakes are a subset of lakes most-at-risk as listed in 06-096 CMR 502; or(b) When the project is located in any other lake watershed. A development with one acre or more of impervious area or 5 acres or more of developed area in any other lake watershed may use the general standards if the project results in less than 3 acres of impervious area and less than 5 acres of developed area.(2) Description of phosphorus standard. An allowable per-acre phosphorus allocation for each lake will be determined by the Department. The Department's determination is based upon current water quality, potential for internal recycling of phosphorus, potential as a cold-water fishery, volume and flushing rate, and projected growth in the watershed. This allocation will be used to determine phosphorus allocations for a project unless the applicant proposes an alternative per-acre phosphorus allocation that is approved by the Department. If the project is a road in a subdivision, only 50% of the parcel's allocation may be applied to the road unless phosphorus export from both the road and the lots is subject to this Chapter, in which case the entire allocation for the parcel may be applied. If the allocation is exceeded by a proposed project, the applicant must demonstrate that the phosphorus export using the Department's methodology will be reduced to meet the phosphorus allocation. Compensation may also be allowed in accordance with 06-096 CMR 501. NOTE: Volume II of the Maine Stormwater Management BMP manual provides examples for calculating per-acre phosphorus allocations and determining if stormwater phosphorus export from a project meets or exceeds the parcel's allocation.
(3)Exception to the Department's phosphorus export standard.If an applicant can demonstrate that the standard calculations for determining phosphorus export are not appropriate due to unusual circumstances, such as the location and/or nature of the development proposal, and the phosphorus export will meet the project site's allocation, then the Department may make a determination that the phosphorus standard has been met.E. Urban impaired stream standard. The urban impaired stream standard applies as described below. (1)When the urban impaired stream standard must be met. A project must meet the urban impaired stream standard if the project is located in the direct watershed of urban impaired stream and requires a Site Law permit or permit modification.(2)Description of the urban impaired stream standard. To meet the urban impaired stream standard, the applicant must eitherpay a compensation fee or mitigate project impacts by reducing or eliminating an off-site or on-site pre-development impervious stormwater source as described in 06-096 CMR 501.(3)Exception where impervious area is replaced. Any portion of a project in which impervious area that pre-dates the Stormwater Management Law is replaced is not required to meet the urban impaired stream standard for that area provided the Department determines that the new use of the untreated area is not likely to increase stormwater impacts in the proposed project's stormwater runoff beyond the levels already present in the runoff in accordance with Table 2 of this Chapter.(4) Where there is a Department-approved management and monitoring plan in place, and monitoring demonstrates that a stressor in the watershed, which may be either a pollutant or a failure to meet a water quality standard, is contributing to the impairment of the urban impaired stream, the Department may require the applicant to use alternative, or additional stormwater treatment measures to address the identified stressor.F. Flooding standard. The flooding standard applies as described below. (1) When the flooding standard must be met. A project must meet the flooding standard if the project: (a) Results in three acres or more of impervious area or 20 acres or more of developed area; or(b) Requires a Site Law permit or permit modification.(2)Description of the flooding standard. To meet the flooding standard, the applicant must demonstrate that a project's stormwater management systems will meet the following: (a) The system must detain, retain, or result in the infiltration of stormwater from 24-hour storms of the 2-year, 10-year, and 25-year frequencies such that the peak flows of stormwater from the project site do not exceed the peak flows of stormwater prior to undertaking the project;(b) The design of piped or open channel systems must be based on a 10-year, 24-hour storm without overloading or flooding beyond channel limits;(c) The areas expected to be flooded by runoff from a 10-year or 25-year, 24-hour storm must be designated in the application, and no buildings or other similar facilities may be planned within such areas. This does not preclude the use of parking areas, recreation areas, or similar areas from use for the detention of storms greater than the 10-year, 24-hour storm. The applicant shall secure drainage easements from any downstream property owners across whose property may be flooded by runoff pursuant to Section 4(G)(2)(a);(d) Runoff from the project may not flood the primary access road to the project and any public road bordering the project as a result of a 25-year, 24-hour storm; and(e) If a wetpond is utilized for stormwater quality treatment under Section 4(C)(3)(a) of this Chapter, detention to meet the flooding standard must be provided above the permanent pool. NOTE: Please see Appendix H for 24-Hour Duration Rainfalls for Various Return Periods in Maine.
3)Waiver of the flooding standard. A project is eligible for a waiver from the flooding standard as follows.(a) Discharge to a coastal wetland,a great pond, or a major river segment. A waiver is available for a project in the watershed of a coastal wetland, a great pond, or a major river segment provided the applicant demonstrates that the project conveys stormwater exclusively in sheet flow, in a manmade open channel, or in a piped system directly into one of these resources. In addition, the Department may allow a waiver for a project discharging directly into a river that is not a major river segment if the Department determines that the increase in peak flow from the site will not significantly affect the peak flow of the river or result in unreasonable adverse impact on any wetlands.
Prior to requesting a waiver as part of an application, the applicant shall secure drainage easements from any downstream property owners across whose property the runoff must flow to reach the ocean, great pond, or river. The applicant shall also demonstrate that any piped or open-channel system in which the runoff will flow has adequate capacity and stability to receive the project's runoff plus any off-site runoff also passing through the system.
(b) Insignificant increases in peak flow rates from a project site. Awaiver is available for a project resulting in only an insignificant increase in peak flow rates from a project site. The applicant shall demonstrate that the proposed increases in peak flow rates cannot be avoided by reasonable changes in project layout, density, and stormwater management design. The applicant shall also demonstrate that the proposed increases are insignificant because they will not unreasonably increase the extent, frequency, or duration of flooding at downstream flow controls and conveyance structures or have an unreasonable adverse effect on protected natural resources. In making its determination to allow a waiver from the flooding standard due to insignificant increases in peak flow rates, the Department shall consider cumulative impacts. If additional information is required to make a determination concerning increased flow, the Department may only consider a waiver after the applicant agrees, pursuant to 38 M.R.S. §344-B(3)(B), that the review period may be extended as necessary by the Department.(4)Additional design standards.The municipality, the Maine Department of Transportation, or the Maine Turnpike Authority may require a project to meet additional design standards.The applicant shall contact the appropriate entity when proposing a project that may cause flooding of a primary access road or public road and receive all necessary approvals prior to beginning construction.G.Easements and deed restrictions standard.The easements and deed restrictions standard applies as described below. (1)When the easements and deed restrictions standard must be met. A project must meet the easements and deed restrictions standard if the project requires specific off-site areas for the control, disposal, or treatment of stormwater runoff.(2)Description of the easements and deed restrictions standard(a)When an easement is required. The applicant must secure easements from affected property owners when the project results in any of the following on off-site property not owned by the applicant: (i) The flow type changes (for example, converting from sheet flow to channelized flow); (ii) The flow channel changes; or (iii) The flow causes or increases flooding. The Department may determine that the expected change in flow, channel or impact is so insignificant as to not require an easement under this Chapter. The Department may require the applicant to provide evidence that such impacts will not occur or, if they will occur, provide evidence of the extent of the impact and evidence that suitable easements have been obtained.
NOTE: The Department's decision to issue a stormwater permit, to require or not require an easement, or to specify the location or width of an easement is not intended to affect other federal, state or local requirements for easements or the availability of legal or equitable remedies for impacts due to stormwater runoff.
(b)Easement specifications and restrictions. The following specifications and restrictions apply to all easements established under this standard. (i)Land use restrictions. Suitable landuse restrictions must be included in the easements to prevent any activity that might affect drainage to, across, or from the area affected by the easement.(ii)Drainage easements. Drainage easements must include all off-site channels constructed to receive flows from the project and any off-site channels receiving increased peak flow rates from the project. Drainage easements must extend up to, but not include, the channel of any stream accepting flow from the project. Drainage easements must conform with the center line of the drainageway or pipe and must have a minimum width of 30 feet, or 10 feet on each side of the channel or pipe required to accommodate the flow from a 25-year, 24-hour storm, whichever is greater. A reduction in the minimum width may be approved by the Department if the full width is not available because of unavoidable physical limitations of the site. However, the minimum width allowed must still be sufficient to avoid an adverse impact on existing uses and to allow access for maintenance and repair.(iii)Flooding easements. Flooding easements must include all off-site areas flooded due to the project. These areas include, but are not limited to, those flooded due to the project overloading storm sewers, culverts, stormwater basins, and equivalent utilities with increased runoff; filling existing areas of runoff storage; diverting flows onto off-site properties; and impeding runoff from the project parcel or off-site areas. Flooding easements must conform to the greatest extent of inundation due to the increased runoff from a 25-year, 24-hour storm.(iv)Erosive flows. The flow through the easement or flooding within the easement may not cause erosion of soil or sedimentation.(c)Buffers. Buffers used for stormwater control must be protected from alteration through deed restrictions. NOTE: The Department has prepared suggested templates for deed restrictions that can be found in Appendix G of this Chapter.
H.Redistribution of stormwater discharges standard. The redistribution of stormwater discharges standard applies as described below. (1)When the redistribution of stormwater discharges standard must be met.A project must meet the redistribution of stormwater discharges standard if the project discharges concentrated stormwater runoff through an open-channel or pipe to any point that is not an open channel, an inlet to a storm drain system, or a natural or man-made impoundment.(2)Description of redistribution of stormwater discharges standard. To meet the redistribution of stormwater discharges standard, the applicant must demonstrate that the project's concentrated flow will be converted to sheet flow to prevent erosion of the downstream receiving area. The conversion of concentrated flow to sheet flow must be done using properly designed level spreaders meeting the criteria below.(a)Discharge to a level spreader. The peak stormwater flow rate to a level spreader due to runoff from a 10-year, 24-hour storm must be less than 0.25 cubic feet per second (0.25 cfs) per foot length of level spreader lip.(b)Siting of level spreader. The level spreader must be sited so that flow from the level spreader will remain in sheet flow until entering a natural or man-made receiving channel.(3) This standard is not applicable for level spreaders discharging runoff to vegetated buffers used to meet the general standards. Requirements for these level spreaders can be found in Appendix F of this Chapter.I.Discharge to wetlands standard. The discharge to wetlands standard applies as described below. (1)When the discharge to wetlands standard must be met.A project must meet the discharge to wetlands standard if the project discharges stormwater a wetland, unless the affected area of wetland qualifies for an exemption pursuant to the Natural Resources Protection Act, 38 M.R.S. §480-Q(17), or unless the Department determines that the change in stormwater flow will not cause a loss of wetland functions and values.(2)Description of discharge to wetlands standard. To meet the discharge to wetlands standard, the applicant must demonstrate that the project's discharges into wetlands will not significantly alter the flow of stormwater to the wetland from that which occurred. In general, new or increased stormwater discharges into wetlands must be put into sheet flow using level spreaders designed to meet the requirements in Section 4(H), above. The Department may allow alternate stormwater treatment measures if those measures will not unreasonably adversely affect the wetland. The discharge of runoff to a wetland due to a 2-year storm may not increase the mean storage depth within a wetland more than two inches above pre-development levels for more than 24 hours from the end of the storm event, unless otherwise approved by the Department. The Department may consider cumulative impacts due to runoff from other projects when applying this standard to any wetland.
J.Discharges to public storm sewer systems standard. The discharges to public storm sewer systems standardapplies as described below. (1)When the discharges to public storm sewer systems standard must be met. A project must meet the discharges to public storm sewer systems standard if runoff from the project site will flow to a publicly-owned storm sewer system.(2)Description of discharges to public storm sewer systems standard. The applicant must obtain authorization from the system's owner to discharge into the system. At its discretion, the Department may require the applicant to demonstrate that the system has adequate capacity for any increases in peak flow rates and volumes to the system and to provide photo documentation that the outfall of the public storm sewer system is being properly maintained.06- 096 C.M.R. ch. 500, § 4
Title 12 M.R.S.A. §7755-A , which prohibits state agencies from issuing a permit that will significantly alter the habitat of any species designated as threatened or endangered species or violate protection guidelines may also apply.