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HomeMy WebLinkAboutRushy Marsh Farm Pond Dredge Memo October 21, 2025 Barnstable Conservation Commission 230 South Street Hyannis, MA, 02601 Re: Rushy Marsh Farm Pond Dredge 1541 Main Street, Cotuit, MA 02635 DEP File No. 003-6313 Dear Barnstable Conservation Commission, On behalf of the Applicant, New Rushy Marsh Realty LLC, Goddard Consulting LLC (Goddard) is pleased to submit this memorandum as a supplement to the Notice of Intent filed for 1541 Main Street in Cotuit to further document site conditions and ecological effects of the proposed pond dredging project. 1.0 Introduction and Background On November 11, 2024, Goddard performed a wetland delineation and assisted with conducting a pond bathymetry study at the locus site. Wetland resources delineated in the field consisted of the bank of an inland pond and a fringe Bordering Vegetated Wetland (BVW) at the margins of the pond. Vegetation downgradient of the BVW boundary is dominated by highbush blueberry, blue flag iris and pickerelweed. Vegetation upgradient of the BVW boundary is dominated by pitch pine, red oak and rhododendron. The areas surrounding the pond are meticulously maintained and heavily planted but are landscaped in a relatively natural condition with many native plant species. At the time of the delineation, Goddard also assisted the surveyor in conducting a pond bathymetry study. This portion of the field assessment utilized typical land surveying methodologies but employed a small johnboat with an extended survey rod to obtain elevations below the water surface. This bathymetry is shown on the site plans submitted by Tetra Tech with the Notice of Intent filing. Also at this time, Secchi readings were taken in the pond. This measurement is conducted by lowering a disk with alternating black and white quadrants into the water column until the depth where the disk is no longer visible. This depth is known as the Secchi depth. The Secchi depth is a proxy measurement of water clarity, which is affected by factors such as dissolved organic matter, suspended sediment, and algal density. Generally, a greater Secchi depth indicates a healthier water body. At the time of measurement, the average Secchi depth in the pond was 68 centimeters (26.8 inches), which is typically considered to be poor, and approaching a point which may cause detrimental effects to aquatic organisms. 2.0 Observed Site Conditions The pond regularly exhibits very high coverage by water lilies (Nymphaea spp.). Cover by water lilies regularly exceeds 50% and has reached as high as nearly 80%. This observation, combined with the recorded Secchi depths, indicates that the pond is likely experiencing eutrophic conditions (i.e. high nutrient concentrations). This is likely the result of the substantial biomass present in and around the pond. As vegetation dies off at the end of the growing season, trees drop leaves, etc., this material enters the pond, where it decays, releasing its bound nutrients and contributing to the formation of Rushy Marsh Farm Pond Dredge 1541 Main Street, Cotuit, MA 02635 DEP File No. 003-6313 Page | 2 muck on the pond bottom. This process is typically considered a positive feedback loop in which plants convert solar energy and nutrients in the soil and/or water to biomass via photosynthesis (i.e. primary productivity), plant matter dies and decays thereby contributing to increased nutrient levels, which promotes greater primary productivity, exacerbating this cycle. The water lilies are a primary contributor to this process. This feedback loop results in the degradation of the aquatic environment. Vegetative diversity will be limited due to competition by water lilies. Increasing inputs of organic matter (and latent organic matter present in decades or centuries of accumulated muck) contributes to proliferation of microorganisms which can result in depressed dissolved oxygen, which is critical for sustaining life. Eventually, the accumulation of organic matter will result in this pond filling in. 3.0 Recommendations After our site investigation, Goddard recommended that dredging the pond may be a viable option to improve pond conditions. Dredging will serve a few different purposes. First, dredging serves to deepen the pond. Deepening the pond will limit the ability of water lilies to grow and proliferate, reducing one principal contributor to the feedback loop of pond eutrophication. Water lilies will only grow in water up to approximately 3-6’ deep. The dredging project proposes deepening the pond to approximately 7’ in the center, effectively relegating water lily growth to the shallower margins of the pond, thereby limiting their ability to contribute to the feedback loop. Decay of the substantial biomass of the water lilies at the end of each growing season also can cause oxygen depletion. Dredging also serves to remove decades or centuries of accumulated muck from the pond bottom. This muck stores a tremendous amount of organic matter and contributes to nutrient loading in the form of nitrogen and phosphorus, which in turn contributes to the proliferation of vegetation in the pond. Again, this contributes to the feedback loop. By removing this muck, the amount of nitrogen and phosphorus available for plant growth will be greatly reduced, which will in turn reduce an input to the feedback loop. Extending the proposed dredging into native soils below the accumulated muck will serve to improve the effectiveness of the work. For the purposes of this project, removal of native subsoil (in addition to muck) is proposed primarily to extend the duration of the aquatic health improvement, increase the effectiveness of future maintenance and to avoid alternative control methods that may be more impactful and less effective (such as herbicide application to open water). The soil map unit surrounding the pond is Carver coarse sand (252B), which has a typical profile of coarse sand to 67” below 3” of partially decomposed plant material. The surficial geology of the area is mapped as glacial stratified deposits, coarse. These two mapped features corroborate each other and are supported by Goddard’s field observations. The implication of this is that the locus pond exists simply because it intercepts groundwater. There is no data to suggest that this pond is perched on clay or any similar feature. Therefore, excavating into the underlying subsoil (which can be reasonably presumed to be simply coarse sand) is unlikely to have any adverse effects on the pond or its existing hydrology, including recharge to groundwater. Rushy Marsh Farm Pond Dredge 1541 Main Street, Cotuit, MA 02635 DEP File No. 003-6313 Page | 3 Additionally, the fact that the pond does not have a surface water outlet lends itself well to dredging. This significantly reduces concerns regarding sedimentation or turbid water migrating to other surface waters, which could have adverse downstream impacts. Deeper ponds are better able to support aquatic fauna and moderate temperature fluctuations. Deeper ponds also discourage the growth of rooted vegetation (such as water lilies) and can maintain a higher dissolved oxygen level. 4.0 Alternatives Analysis Goddard has also evaluated alternatives to the proposed dredging protocol to ensure that dredging is the preferred means of pond management here. The primary alternative evaluated was implementing an herbicide application regime. Herbicide application could serve to effectively reduce or eliminate water lilies from the pond and limit their impact on the feedback loop. However, herbicide applications will either eliminate water lilies from the pond entirely or require recurring applications ad infinitum to maintain a reduced level of water lily cover, neither of which is desirable. By implementing the proposed dredging protocol, we can structurally control water lily cover. Shallower areas around the perimeter will be conducive to their growth. Deeper areas in the center of the pond will preclude their growth. This will inherently limit the proliferation of water lilies without the need for recurring herbicide applications. Herbicide application also does not solve the problem of the latent nutrients present in the accumulated muck; in fact, it contributes to this problem by killing water lilies which will in turn contribute to muck accumulation. The Applicant has investigated the feasibility of using barley bales for pond management purposes. First, the mechanism by which barley bales function is not well understood. They do not kill algae but may help to inhibit new algae growth. Since water lilies are a primary target of this pond management proposal, barley bales will not help with addressing that problem. Further, they do nothing to remove accumulated sediment/muck and associated nutrient loads. Other alternatives were also evaluated, such as phosphorus inactivation, artificial circulation/aeration, drawdown, and mechanical harvesting/hydroraking. In general, these options are not preferred because they require ongoing or repeated work, which can negatively impact surrounding vegetation and is not a preferred option for the Applicant. Phosphorus inactivation with alum applications (or similar) may require repeat application, risks impact to pH and generally does not reduce abundance of macrophytes (e.g. water lilies) effectively. Mechanical harvesting/hydroraking similarly requires repeat implementation. While it does remove plant biomass from the pond, it is a purely reactive strategy, doing nothing to prevent plant overgrowth, instead only responding to it, and similarly not addressing latent nutrients in accumulated muck. Artificial circulation/aeration requires constant maintenance to ensure continued effectiveness and similarly is minimally effective in managing macrophytes. Drawdown is impractical in this pond due to its relatively small size and lack of any infrastructure with which to conduct a drawdown, which would likely require alteration of bank and/or BVW to install. Rushy Marsh Farm Pond Dredge 1541 Main Street, Cotuit, MA 02635 DEP File No. 003-6313 Page | 4 Photos of a comparable pond dredging project conducted at Memorial Pond in Walpole, MA, are provided below. This project was conducted on behalf of the Town of Walpole with the intent to “improve environmental conditions” of the pond, which otherwise suffered from excessive weed growth. According to field observations of scientists from Water & Wetlands in 2024, the initial dredging was a success, with documented improvements to surface dissolved oxygen and Secchi depth. Photos were obtained from Walpole Conservation Commission website. View of pond prior to dredging. View of pond during dredging activities. Rushy Marsh Farm Pond Dredge 1541 Main Street, Cotuit, MA 02635 DEP File No. 003-6313 Page | 5 View of pond after completion of dredging. 5.0 Conclusion Dredging was proposed as the preferred alternative for multiple reasons. First, it is a one-time solution that does not require repeated follow-ups or ongoing maintenance. It is a proactive solution, limiting the proliferation of water lilies by a structural means (i.e. altering water depth). Further, it is the only option that truly removes latent nutrients stored in the pond by physically removing accumulated muck. We believe the proposed project complies with the performance standards for Land Under Water Bodies and Waterways as outlined below. Text from the Wetlands Protection Act is bolded. Where the presumption set forth in 310 CMR 10.56(3) is not overcome, any proposed work within Land under Water Bodies and Waterways shall not impair the following: The water carrying capacity within the defined channel, which is provided by said land in conjunction with the banks; The project will improve the carrying capacity of the pond by increasing its volume. Ground and surface water quality; The project is proposed specifically to improve ground and surface water quality by removing accumulated sediments that contribute to adverse effects caused by nitrogen and phosphorus loading. The capacity of said land to provide breeding habitat, escape cover and food for fisheries; and The project will prevent eutrophication as described above, thereby reducing the resulting loss of habitat and the potential for adverse impacts to wildlife. Leaving shallower depths intact Rushy Marsh Farm Pond Dredge 1541 Main Street, Cotuit, MA 02635 DEP File No. 003-6313 Page | 6 around the perimeter of the pond provides an area of refuge to protect existing habitat, and deepening the pond expands and diversifies available habitat. The capacity of said land to provide important wildlife habitat functions. A project or projects on a single lot, for which Notice(s) of intent is filed on or after November 1, 1987, that (cumulatively) alter(s) up to 10% or 5,000 square feet (whichever is less) of land in this resource area found to be significant to the protection of wildlife habitat, shall not be deemed to impair its capacity to provide important wildlife habitat functions. Additional alterations beyond the above threshold may be permitted if they will have no adverse effects on wildlife habitat, as determined by procedures established under 310 CMR 10.60. The work is expected to result in substantially improved habitat functionality, with no discernible negative impacts following two growing seasons, by reducing the overgrowth of water lilies with the goal of improving vegetative diversity, reducing nutrient loading, and limiting infilling of the water body with accumulating sediment. This will serve to ensure that overwintering areas for mammals, reptiles and amphibians are not lost, and that food, shelter and breeding areas for wildlife are maintained and improved. Work on a stream crossing shall be presumed to meet the performance standard […] The proposed work is not on a stream crossing. Notwithstanding the provisions of 310 CMR 10.56(4)(a), the issuing authority may issue an Order in accordance with M.G.L. c. 131, § 40 to maintain or improve boat channels […] The proposed work is not for maintaining or improving boat channels. Notwithstanding the provisions of 310 CMR 10.56(4)(a) or (b), no project may be permitted which will have any adverse effect on specified habitat sites of rare vertebrate or invertebrate species, as identified by procedures established under 310 CMR 10.59. The proposed work is not within any specified habitat sites of rare species. The proposed project meets the applicable performance standards for Land Under Water Bodies and Waterways. Dredging contributes to the protection of the interests identified in the Wetlands Protection Act by improving water quality, preventing pollution by nitrogen and phosphorus, and by improving habitat quality for both resident and transient wildlife. Please feel free to contact us at 508- 393-3784 if there are any questions regarding this submittal. Sincerely, Goddard Consulting, LLC Chris Frattaroli Scott Goddard, PWS, CWS Lead Wetland Scientist Principal Rushy Marsh Farm Pond Dredge 1541 Main Street, Cotuit, MA 02635 DEP File No. 003-6313 Page | 7 References: https://www.nalms.org/secchidipin/monitoring-methods/the-secchi-disk/what-is-a-secchi-disk/ https://www.nalms.org/secchidipin/monitoring-methods/the-secchi-disk/evaluating- eutrophication-by-secchi-depth/ https://www.iaenvironment.org/webres/File/Nutrient%20Science%20AdvisorsReport_2008.pdf https://extension.psu.edu/understanding-transparency-tube-measurements https://extension.psu.edu/barley-straw-for-algae-control https://conservect.org/southwest/wp-content/uploads/2018/01/Pond-Management.pdf https://www.mass.gov/doc/the-practical-guide-to-lake-management-in-massachusetts/download https://www.mass.gov/info-details/massgis-data-usgs-124000-surficial-geology https://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx https://pubs.usgs.gov/wri/wri994174/pdfs/wrir994174.pdf https://www.walpole-ma.gov/conservation-commission/slideshows/memorial-pond-dredge- project Qualifications: Scott Goddard holds a bachelor’s degree from Worcester Polytechnic Institute in Civil Engineering and a master’s degree from the Massachusetts Institute of Technology in Water Quality Engineering. Scott has over 30 years of experience in ecological consulting throughout New England consisting primarily of wetlands and wildlife permitting. He has successfully managed thousands of projects during his time at Carr Research Laboratory and as Principal at Goddard Consulting. Scott is a Professional Wetland Scientist, Certified Wetland Scientist and Licensed Soil Evaluator. Chris Frattaroli holds a bachelor's degree from the University of New Hampshire in Marine, Estuarine and Freshwater Biology. Chris has over 5 years of experience working in the jurisdiction of the MA Wetlands Protection Act, largely in southeast Massachusetts and Cape Cod. Chris has worked on hundreds of projects spanning both coastal and inland wetland resource areas, with a focus on ecological restoration and invasive species management.