The Carlisle Mosquito Online

Friday, March 26, 2010

ConsCom considers Benfield plan impacts on wetlands

At the March 18 public hearing, civil engineer Mark Beaudry presented the Conservation Commission (ConsCom) with a revised plan that preserves more of the upland forest adjacent to the proposed Benfield Farms affordable housing. The project, on town land off South Street, includes 26 residential units, associated driveways, parking, stormwater management, and an on-site septic system and public water supply. Beaudry, of Meridian Associates, represents the applicant, Neighborhood of Affordable Housing (NOAH).

Beaudry noted that one of the goals of low impact development is to minimize the amount of impervious surface created by a construction project. Reconfiguring the driveway and parking and showing a slightly smaller building footprint reduced the impervious surface area by 32%, allowing a decrease in the size of the stormwater control areas. These changes, along with moving the stormwater areas, mean that 27,000 fewer square feet of upland forest will be disturbed. The state Natural Heritage and Endangered Species Program has required less alteration in order to protect the overwintering habitat of the Blue-spotted Salamanders that breed in the vernal pool. The project is located in both Priority and Estimated Habitat for the salamanders.

Wetland boundaries

Beaudry said that the electronic drawing file that was recently purchased by the town from the original consultants, MetroWest, was used for the revised plan. This more accurately depicts the wetlands boundaries. The flags have now been fully replaced along the edges of the bordering vegetated wetlands. This clears the way for a determination of whether the boundaries have changed since the original delineation in 2003.

Beaudry reported that Mason Associates has tentatively marked the location of the 200-foot Riverfront Area (RA) of Spencer Brook, which flows along the Benfield Conservation Land at the rear of the parcel. They expect a definitive determination of the Riverfront Area by the end of March.

The existing grades will be maintained under the revised design for the sewage disposal area. An earlier plan had terracing around the proposed leaching field. This and the well are proposed to be located on the conservation parcel. Beaudry indicated that the locations of the buildings and infrastructure are also now flagged on the site.

“Intermittent” stream rationale

South Street resident Ray Kubacki asked whether the commission’s February 11 determination that the stream along the west side of the housing site is “intermittent” was based on information from abutter Jeffry Kiel. Commissioner Tricia Smith replied, “Only partially.”

Intermittent streams have no regulatable 200-foot Riverfront Area. Beaudry had submitted an affidavit from Kiel indicating that in 2005 and 2007 the stream dried up for a sufficient period to meet the criteria for “intermittent” in the Wetlands Protection Act Regulations. Kiel dated his documenting photos with the front pages of the Boston Globe.

Kubacki asked, “Is there other data that was the basis for the decision?” Responding in the affirmative, Smith and Conservation Administrator Sylvia Willard explained that the upgradient area contributing runoff to the stream and the flow rate of water are not large enough to define it as “perennial.”

The United States Geologic Survey has a hydrologic model called StreamStats that the ConsCom and others have run. According to Willard, this stream has a watershed of 0.34 square miles (sq. mi.) and a flow rate of 0.002 cubic feet per second (cfs). Willard said that the threshold in the Wetlands Regulations for a stream to be considered perennial is a contributing watershed of 0.5 sq. mi. and a flow rate of 0.01 cfs. “It’s the science,” she summarized.

The public hearing was continued to April 1 at 8: 30 pm. ∆


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