11/20/2025 CONSERVATION COMMISSION Minutes

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Town of Mashpee Conservation Commission 16 Great Neck Road North Mashpee, MA 02649 "best available nitrogen-reducing technology" list to set local performance standardsFalmouth, for example, uses a 12 mg/L limit, which effectively excludes older, weaker performers while allowing the newer high- performing technologies. In response to questions,he emphasized that some widely used products, such as the "Sledgehammer" system, do not appear on MassDEP's best available nitrogen-reducing technology list and based on their design, are unlikely to achieve nitrogen reductions comparable to Nitrex or Nitro. The key technical difference is the provision of an external carbon source. Older aerated systems rely solely on the organic carbon present in incoming wastewater to fuel denitrification, which appears to limit their performance to around 17 mg/L of nitrogen in practice. By contrast, wood-chip systems supply abundant carbon in an anoxic zone, allowing denitrifying bacteria to convert nitrate to harmless nitrogen gas much more completely. Mr. Baumgaertel discussed the longevity of the wood-chip media. Under anoxic conditions, wood decomposes very slowly. Stoichiometric calculations suggest up to a century's worth of available carbon, though a conservative practical estimate might be on the order of 20 years. If performance declines, the wood- chip media can be vacuumed out of the tank and replaced, making long-term maintenance manageable. Because advanced treatment reduces nitrogen loading to the leach field, homeowners may also see longer leach field lifespans compared to standard systems, offsetting some of the cost of advanced treatment. On phosphorus, he noted that technology development has lagged because there are few regulatory requirements for phosphorus removal in on-site systems. Several approaches exist. One is to keep effluent near the soil surface where finer particles (silts, clays, and organic matter)provide better phosphorus binding and where plant roots can take up nutrients. Shallow dispersal systems, such as drip dispersal or products like GeoMat, keep effluent within roughly a foot of the surface and can be trenched in with minimal soil disturbance. Another approach uses electrochemical plates made of iron or aluminum to release ions that bind with phosphorus and form solid minerals. Some technologies incorporate these plates in tanks or leach fields (he mentioned Fuji Clean and Waterloo ECP as examples), with the bound phosphorus precipitating either onto filters or in the soil absorption area. A third method involves dosing septic tanks with alum, which effectively binds phosphorus but introduces aluminum, a regulated compound, creating a new compliance challenge. Because phosphorus removal is rarely required, companies have invested less in bringing such technologies through Massachusetts' approval process. When asked which systems are currently the best options, Mr. Baumgaertel replied that Nitrex and NitROE are the most promising high-performing nitrogen-removal technologies available today, with NitROE substantially further along in the Massachusetts approval pipeline. He added that he is aware of other manufacturers working to adapt their long-established products to achieve lower nitrogen effluent levels, and he hopes more "best available" options will emerge,particularly from larger companies with existing manufacturing capacity. He explained that Massachusetts is a difficult regulatory environment, and some vendors have focused on other regions with simpler approval pathways, which has slowed adoption in the Commonwealth. Mr. Baumgaertel also addressed questions about MassDEP's testing requirements and data transparency. He noted that the 50-system field installations for provisional approval typically cover a range of site conditions and that gathering enough installations is itself a challenge because homeowners are wary of adopting provisional technologies that may not receive final approval. He encouraged commissioners and residents to explore performance data directly through the MassTC website's data viewer, where users can filter by technology, use type, and performance metrics. He also referenced an EPA-sponsored study at Schubel Pond in Barnstable, where 13 advanced nitrogen-removal systems have been monitored monthly for several years, demonstrating strong real-world performance. 4