FAQ:  Phosphorus Inactivation at Ashumet Pond
 

1. Why is the Air Force Center for Environmental Excellence (AFCEE) performing a phosphorus inactivation project this fall? Groundwater impacted by past operation of the MMR wastewater treatment plant plume is discharging phosphorus to Ashumet Pond. The ecology of the pond is generally considered to be stable and there are no indications of imminent decline. However, there are indications that the health of the pond could further decline if no action is taken. Consequently, the AFCEE has taken an active role in assessing the trophic health (measure of biological activity) of Ashumet Pond and determining the need for future action.

The current trophic status of the pond is generally considered as Meso-Eutrophic, meaning that it is not in poor health, but not perfect conditions for recreational fishing or swimming activities. Inactivating phosphorus within a 28-acre area in the deep portions of the pond should substantially remove this critical plant growth nutrient from the water of the hypoliminion (i.e. bottom waters), resulting in a reduced fall alga bloom when the pond turns over. This should also reduce phosphorus regeneration from bottom sediments in coming seasons. Reduced regeneration should lower overall algal production and result in improved trophic health.

2. Where in the pond will the treatment occur? The attached figure shows the location of the area to be treated. The injection of inactivant chemical (involving the combination of alum and sodium aluminate) will occur at depths of 35 feet within the area of the pond having water depths greater than 40 feet. This involves an area of approximately 28 acres. This approach is being used to ensure that the inactivation reaction occurs below the pond’s thermocline (vertical zone of greatest water temperature change) in cold waters that have low dissolved oxygen but maximum dissolved phosphorus concentrations in the late summer. In addition, these depths are devoid of fish due to the extremely low dissolved oxygen late in the summer.

3. How much phosphorus-inactivating compound will be added to which parts of Ashumet Pond? It is estimated that approximately 1375 gallons of aluminum sulfate and approximately 980 gallons of sodium aluminate (mixture is called Alum) will be added to a small portion (approximately 5 acres) of the proposed project area (approximately 28 acres) and monitored for a period of 24-48 hours. If no evidence of negative affects has been observed, then the remaining area would be treated. It is estimated that approximately 6073 gallons of aluminum sulfate and approximately 4508 gallons of sodium aluminate (Alum) would be used to complete the treatment. The estimated amount of Alum is calculated for an application based on current pond water chemistry. Monitoring pond water chemistry right before the actual application occurs provides the data needed to calculate an exact amount of alum to be used for the application.

4. When will the phosphorus inactivation project be completed? The actual application is expected to take between 3 to 4 days. Water bodies treated with inactivants have demonstrated many years of improved water quality including clarity, improved extent of oxygenated water (fish habitat) and reduced algae growth. However, these improvements are dependent upon stable or declining phosphorus loading from other watershed sources.

5. What types of monitoring will be performed to ensure successful application of phosphorus inactivating compound? Monitoring will be conducted before, during and after the application. Monitoring will be conducted by a Certified Lakes Manager (CLM) on-site during the entire application process as well as monitoring activities prior to the application. The proposed monitoring approach is summarized below.

Three Monitoring Stations: located at deep basin (45-foot depth contour of pond)

Sampling Frequency:

During:

6. What criteria or indicators will be used to determine success or failure of the phosphorus inactivation project? Criteria used for determining the need to inactivate the phosphorus are the same as those used for determining the success or failure of the treatment. Data have been collected and used to gauge the trophic status such as, the depth of water clarity, concentration of dissolved oxygen at different depths in the pond during summer months, and amount of plant life (chlorophyll a). This data will help to determine whether the expected successes of increased water clarity, decreased dissolved phosphorus, decreased amounts of plant life (chlorophyll a) and increased dissolved oxygen occur after the application. It is expected that the amount of dissolved phosphorus will be an immediate measure of success or failure. Another indicator of success or failure would be the presence or absence of dead fish after the application. Short term failures do not imply a long term failure of the project. The pond may need to be monitored over many years to ultimately gauge the success or failure of the project and its intended goal of providing improved trophic health over time.

7. What is the industry experience with phosphorus inactivation and longevity of treatment?

Adding Alum to a lake or pond is a phosphorus management tool that has been used throughout the United States and internationally for approximately 30 years. Each lake or pond is unique in its response to this type of treatment, however for this reason extensive monitoring is planned for this project.

A similar treatment was applied in Barnstable at Hamblin Pond in 1995. There were negative impacts to fish in the pond as well as positive effects in water quality parameters of the pond. A large number of yellow perch died directly after the application. Monitoring data indicate that the recreational fishery has recovered from the negative impact from the Alum application approximately 5 years after the application. Water quality monitoring indicates a significant improvement in the overall trophic health of Hamblin Pond. The clarity of the lake has increased significantly, dissolved phosphorus has decreased and an increased amount of dissolved oxygen in the deeper portions of the pond has occurred over time. More information on other case studies presented at previous meetings is available from AFCEE.

8. Why have fish kills occurred in association with some phosphorus inactivation projects? Each situation and project is unique and very lake/pond specific. In general, poor project oversight and management appear to have been key issues. Some projects have been plagued by poorly directed contractors performing the application in the field. Some applications were not stopped when conditions suggested that a treatment should be postponed, while other projects did not monitor conditions closely enough to determine a problem during the application. Most other projects have applied the Alum to the surface of a lake/pond with application covering the majority of the pond surface.

The project at Ashumet Pond will be of limited extent (approximately 14% of the total pond surface area, and 10% of the total pond volume) and will be applied in the deepest portions of the pond. Contractors will perform the application only with oversight by a Certified Lakes Manager (CLM). This will allow the project to move forward in a manner that is responsive to weather, pond conditions, and fishery response. The CLM will stop the project at any time when field conditions indicate that work should be stopped.

9. There are three state-listed "Species of Special Concern" identified in the Ashumet Pond area. Where are they expected to live in relation to the proposed inactivation area? The three Species of Special Concern are two species of shoreline vascular plants and a species of freshwater mussel. The plant species are known to occupy the shallow water edges of the pond and will not be impacted by the Alum application. The freshwater mussel species is expected to reside in shallow waters containing enough dissolved oxygen for them to live. Freshwater mussels are not expected in the deep oxygen poor portions of the pond where the inactivation would occur. No mussels have been observed in bottom samples from the deep areas of the pond.

10. What potential affects could the Alum treatment have on fish and benthic fauna (animals living in the bottom of the pond)?

Short term: The application potentially could release free Aluminum ions that, under certain pH ranges, could negatively impact aquatic life and potentially lead to fish kills. The location, depth and size of the application and proper dosage are expected to minimize the risk of a fish kill and impacts to benthic organisms.

Long term: Habitat availability for fish and benthic organisms is expected to increase from increased oxygen at greater depths resulting from lowered biological productivity (plant growth).

11. If Ashumet Pond lies in both Towns of Mashpee and Falmouth, why was a Notice of Intent (NOI) only filed with Mashpee? The area of application lies solely within the Town of Mashpee. Information about the proposed project has been shared with and presented to the Town of Falmouth Conservation Commission and Falmouth citizens. Falmouth pond abutters have been provided the opportunity to participate and comment on AFCEE’s proposal and will be kept informed about any developments.

12. What is AFCEE’s plan for the future? AFCEE is continuing to monitor the pond and move forward with its two-part strategy of reducing phosphorus inputs to Ashumet Pond. This strategy includes the inactivation of phosphorus within the pond with the targeted inactivation described above and reducing the load of phosphorus from the watershed (groundwater plume) into shallow pond bottom areas. Reducing the watershed input of phosphorus with a geochemical barrier requires laboratory and field testing of different geochemical barrier methods in the footprint area (where the groundwater enters the bottom of the pond) of the phosphorus plume. This work is currently underway.

If you would like further information about this project, please contact Douglas E. Karson, Community Involvement Specialist at (508) 968-4678 X 2 or by e-mail at doug.karson @mmr.brooks.af.mil.