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Home My WebLink AboutStormwater Report - 50 BRIDLE PATH 5/16/2003 RESTORATION AND MITIGATION PLAN RECEIVED to accompany a Notice of Intent and Request for Waiver MAY 1 6 2003 50 Bridle Path, North Andover NORTH ANDOVER PLANNING DEPARTMENT Prepared for: Peter& Caroline O'Neill 50 Bridle Path North Andover,MA 01845 Prepared by: SEEKAMP ENVIRONMENTAL CONSULTING,INC. 29 South Main Street Newton,NH 03858 Laurianne Powers Project Scientist October 22,2002 INTRODUCTION: Seekamp Environmental Consulting, Inc., (SEC) has prepared the ensuing Restoration and Mitigation Plan on behalf of Peter and Caroline O'Neill, in support of a Notice of Intent and Request for Waiver from the Town of North Andover 50-foot No Build wetland setback. The proposed project involves reconstruction and conversion of an existing three-season porch to all-season living space. As stated in the Project Narrative submitted with the Notice of Intent, the existing development was constructed prior to the enactment of the North Andover Wetlands Protection Bylaw and associated Regulations; as such, the existing structures and clearing do not conform to the 50-foot No Build and 25-foot No Disturb Zones. The entire rear facade of the existing single family house, including the enclosed porch, are within the 50-foot No Build Zone; therefore, the proposed project cannot be designed to meet this setback. Our rationale for requesting the Waiver from the 50-foot No Build setback, as well as our assessment of the project's conformance to the"Conditions for Approval" outlined in Section HI (E)(2)(A) of the North Andover Bylaw, is further expounded in the aforementioned Project Narrative. REVISED PROJECT DESIGN: In response to input received from both the Conservation Commission and its Administrator, Ms. Julie Parrino, during the October 9, 2002 public hearing and the ensuing October 17th site walk, the applicant has agreed to revise the project design in order to meet the perceived intent of the North Andover Bylaw. The original design called for an expansion of the existing structure by four(4)feet towards the southern property boundary, and replacement of the existing support pilings with a concrete foundation. As compensation for anticipated impacts to groundwater infiltration, the applicant proposed to construct an infiltration pipe(consisting of perforated PVC pipe encased in filter fabric and surrounded by crushed stone), which would collect stormwater from both the foundation drain and the entire roof surface of the proposed addition, and would daylight approximately 72' downslope of the existing structure. The revised project design incorporates several of the comments and suggestions provided by the Commission, including the replacement of the existing footings with PVC pipe, rather than the concrete foundation proposed in the original design. The applicant has also reduced the size of the proposed addition from four (4)feet to 26.5 inches(approximately 2.2 feet) on the south side of the existing structure, which represents the additional width necessary to match the depth of the existing kitchen countertop. The existing support pilings will be replaced, as noted above, and will be relocated approximately 2 feet interior to their current location. This will, in effect, move the point of disturbance further from the wetland boundary. The proposed additional living space will be cantilevered using steel I-beams to eliminate the need for additional support pilings (and resultant disturbance to the substrate). 1 REVISED IMPACT ANALYSIS: The proposed project will permanently impact 165 s.f. of 50-foot No Build Zone, which represents 25 s.f, of additional impervious area created by the proposed expansion. This impact calculation represents a 15 s.f. reduction of impact from the original proposal, which would have created an additional 40 s.f of impervious area and impacted 180 s.f. of No Build Zone. Temporary impacts will increase slightly with this alternative, as additional surface area within both the 25-foot No Disturb Zone and 50-foot No Build Zone will be temporarily altered in order to accommodate the proposed mitigation measures. ENHANCED STORMWATER ATTENUATION: In addition to providing infiltration of roof runoff from the proposed addition via the installation of a perforated infiltration pipe (as proposed in the original design), the applicant proposes to further enhance the ability of the buffer zone to assimilate stormwater runoff by infiltrating roof drainage from the entire rear facade of the single family house. Existing drain pipes on the northern and southern house corners will be tied to infiltration units, as depicted on the revised plan. Runoff from the northern-most drain will connect to the infiltration pipe originally designed to infiltrate runoff from the roof of the proposed addition. Runoff from the southern corner of the house will be directed into a separate infiltration pipe, which will outlet upslope of wetland flags A4- A5. The site currently does not provide groundwater recharge; the proposed measures, collectively, will therefore substantially improve the ability of the area to infiltrate stormwater runoff. PROPOSED BUFFER ZONE ENHANCEMENT/RESTORATION: As an additional measure, the applicant proposes to restore a portion of the 25-foot No Disturbance Zone, including an approximately 10-foot wide strip that parallels the eastern property boundary and is currently maintained as a landscape feature, with several ornamental shrubs(rhododendrons) and bark mulch. The applicant proposes to enhance this area by removing the bark mulch and planting native shrubs, which will provide enhanced wildlife habitat value, and will create a vegetative barrier that will restrict future activities within this area. The applicant has agreed to cease mowing the restoration area, which will ultimately revert to a natural understory(herbaceous layer). A second area will be provided in the vicinity of the existing crushed stone patio, located upslope of wetland flags A4-A5. This area currently provides little or no wildlife habitat value, and limited protection to the adjacent resource area. The area will be abandoned, planted with supplementary shrubs, and allowed to revert to a natural state. Restoration of the areas defined above will provide approximately 800 s.f. of buffer zone enhancement and will provide an essential physical barrier to encroachment where there 2 once was none. The shrubs that will be planted within the restoration areas include the following: Proposed Restoration Planting: Common name Scientific Name Size Number Hghbush blueberry Vaccinium corymbosum 24' 5 lEghbush cranberry Viburnum trilobum 24' 5 Chokeberry Aronia arbutifolia 24' 5 The above-referenced shrubs will be planted in clusters of 2 or 3, in order to provide a more natural effect. The species selected for inclusion in the enhancement plantings produce fruit and seeds that provide an excellent food source for a number of song and game birds and small mammals. (See below) Highbush blueberry (Vaccinium cotymbosum): Physical Characteristics/Growth Form: -Broad-leaved, deciduous shrub - 6-12 ft. height - 6-12 ft. aerial spread -Produces white or pinkish bell flowers (mid-May through early June) -Produces bluish/black fruit (early July through late August) Wildlife Benefits: IFEghbush blueberry provides fruit, cover and nesting for several birds, including mourning dove, eastern kingbird, American robin, gray catbird, and rufous-sided towhee. In addition, blue jays, black-capped chickadees, eastern bluebird, brown thrashers, skunk, chipmunk and mice utilize the fruit and plant parts of this shrub. 3 Highbush cranberry (Viburnum trilobum): Physical Characteristics/Growth Form: -Broad-leaved, deciduous shrub - 6-16 ft. height - 6-12 ft. aerial spread,/�� -Produces white, flat-topped clusters of flowers (late May—early June) -Produces red to orange berries (early September; persist through late February) Wildlife Benefits: Highbush cranberry provides food for eastern bluebirds, cedar waxwings, cardinals, and small mammals. The plant provides emergency food for several species during winter. Red chokeberry (Aronia arbutifolia): Physical Characteristics/Growth Form: -Broad-leaved, deciduous shrub - 6-12 ft. height - 3-6 ft. aerial spread -Produces white flowers (early through mid-May) -Produces black fruit (early September through mid-December) Wildlife Benefits: Red chokeberry provides food for bobwhites, brown thrashers, cedar waxwings, eastern meadowlark, as well as several small and hooved mammals. The fruit serves as emergency food in winter to a number of species. 4 SUMMARY: The existing conditions of the site are such that the activities proposed within the buffer zone will not detrimentally affect the adjacent wetland resource. In fact, the restoration and enhancement measures proposed above will result in a net improvement in the ability of the buffer zone to protect the adjacent resource area. 5 m l� vli n yn� ��Qlu G, I w It �� AWO iNO �rn ros IN ;Jill WIN v, .