1996 report on West Falmouth, MA Wastewater Facility
[Note: This letter was part of a Buzzards Bay NEP effort in the mid to late 1990s to raise awareness of Town of Falmouth residents and municipal officials about the eutrophication of West Falmouth Harbor, and the role of the town’s sewage treatment facility and landfill as contributing nitrogen sources. Our efforts led to other studies by the Massachusetts DEP and the Cape Cod Commission resulting in new requirements for advanced nitrogen removal at the town’s wastewater facility. The town’s advanced nitrogen removing wastewater facility came on line in the fall of 2005. It will take 5 to 10 years for the benefits of this facility to be felt in the harbor, due to the transit time of groundwater. In 2006, Massachusetts DEP approved a nitrogen TMDL for the West Falmouth Harbor Watershed (available at the oceanscience.net website). Because the wastewater facility is already using best available technology to reduce nitrogen additional measures to meet the TMDL will eventually be needed including sewering additional homes in the watershed.]
[Note: Not all graphics are loaded onto this web page. A copy of the original report is available from the Buzzards Bay NEP office.]
west-falmouth-update-aug96.pdf pdf version of this page(not all graphics included)
Board of Selectmen August 23, 1996
59 Town Hall Square
Falmouth, MA 02540
Re: Update on Buzzards Bay NEP assistance on West Falmouth Harbor Nitrogen Management needs
Dear Honorable Selectmen,
As you may recall, last year the Buzzards Bay NEP(1) prepared for the town of Falmouth a progress report on work undertaken by the Buzzards Bay NEP, the town, the Cape Cod Commission and others to document sources and impacts of nitrogen inputs in the West Falmouth Harbor watershed. The Buzzards Bay NEP’s objective in this endeavor is to provide technical, and where feasible, financial assistance to help the Town of Falmouth to develop a nitrogen management strategy for West Falmouth Harbor. Such a nitrogen management plan is not only a requirement by DEP for the upgrade of the town’s wastewater plant, but is also essential for ensuring that the town protects the valuable coastal resources of West Falmouth Harbor.
Since preparing that report, the Buzzards Bay NEP has met with key department heads and staff to refine estimates of nitrogen loading to the Harbor and better define potential management options. The Town of Falmouth has also taken action to address some of the information gaps that relate to this problem. Enclosed is our second progress report that highlights revised estimates of nitrogen loading and better defines potential management options to further the Town’s goals of protecting and restoring West Falmouth Harbor.
If you have any questions, or would like me to meet with you, please do not hesitate to call me.
Joseph E. Costa
cc. Brian Currie, Falmouth Planning Department; Raymond Jack, Falmouth Utilities Manager; Bill Owen, Falmouth DPW; Bob White, Falmouth WWTP; Falmouth Board of Health; Ed Eichner, Cape Cod Commission; Ron Lyberger, DEP-BMF, John Higgins, DEP-DWPC, Pamela Truesdale, Buzzards Bay Coalition; John Ramsey, ACI; Brian Howes, WHOI wfalup2
Progress Report #2
Nitrogen management issues and options for West Falmouth Harbor
prepared for the Town of Falmouth
Buzzards Bay NEP National Estuary Program
August 23, 1996
In the Buzzards Bay Comprehensive Conservation and Management Plan(2), nitrogen inputs from development and agriculture were identified as potential threats to many portions of Buzzards Bay, particularly in shallow, poorly flushed embayments. In the Management Plan, West Falmouth Harbor was identified as a site of potential nitrogen management action.
Data collected through the joint Buzzards Bay NEP-Coalition Citizen’s Water Quality Monitoring Program, Falmouth Pond Watchers, and others suggest that West Falmouth Harbor now has good water quality, particularly in the outer half of the bay, but that the innermost portions of the embayment are more eutrophic, and already exceed the most stringent levels of total nitrogen allowed under Falmouth’s coastal protection bylaws. Moreover, nitrogen concentrations in the northeast portion of the Harbor appear to be quickly increasing suggesting entry of a groundwater plume from the town’s wastewater treatment plant.
In 1994 the Buzzards Bay NEP completed a subwatershed evaluation for Buzzards Bay embayments (Buzzards Bay NEP, 1994). In this report, West Falmouth Harbor ranked very high in its value of natural resources and high in the likely effectiveness of potential management action taken in its subwatershed, making West Falmouth Harbor the second highest ranked embayment in Buzzards Bay for priority of management action. In this report, and in another prepared for the town by Howes et al. (1992), the Falmouth Wastewater Treatment Facility was identified as the largest source of nitrogen to the watershed.
In 1995, Aubrey Consulting Inc. (ACI), partly with Buzzards Bay NEP funding, completed a flushing study to help the town define nitrogen management options. The Buzzards Bay NEP is using the estimates of hydraulic turnover time of the West Falmouth Harbor cited in this report to develop the specific nitrogen loading limits for this embayment.
1) The Buzzards Bay NEP will establish a workgroup composed of representatives of the town of Falmouth (Planning, Health, DPW, etc.), DEP-Southeast, DEP-Bureau of Municipal Facilities, CZM, the Cape Cod Commission, and the BBP to develop a multi-agency consensus on all the issues surrounding nitrogen management for the West Falmouth Harbor drainage basin.
Target Date: September 1996
What are the sources of nitrogen to West Falmouth Harbor?
In analyzing N sources in the West Falmouth Harbor subbasin, Howes et al. (1992), the Buzzards Bay Project (1994), and ACI (1995) concur that the largest existing source of nitrogen in the West Falmouth Harbor watershed is the Falmouth Sewage Treatment Facility. In our 1994 study, the Buzzards Bay NEP estimated that the facility accounted for about 65% of the watershed loading with residential property, at 23%, being the second largest source (principally from septic systems and to a lesser extent lawns).
The loading estimates for the Howes et al. and Project studies were based on a watershed subbasin delineated by the Buzzards Bay NEP in cooperation with USGS in 1991. This watershed was based on 10 ft groundwater contours. In this watershed delineation, Falmouth’s Solid Waste Disposal Facility (“landfill”) was just outside of the watershed boundaries, but because of uncertainties in the delineation, the landfill had been conservatively included in some loading estimates for the Harbor.
In early 1995, the Cape Cod Commission developed a new groundwater map for the Sagamore Groundwater Lens using new well data and 5 foot groundwater contours. The revised watershed for West Falmouth Harbor (Fig. 1) is considerably different, and most importantly now unquestionably includes the landfill. The landfill is important as a nitrogen source not only from the household and commercial debris buried at the site, but also because the towns septage lagoons were in use at the site between 1975 and 1987.
The plumes from these sources are still in transit to West Falmouth Harbor, and they must now be included as part of any nitrogen management strategy for the Harbor. The three studies described above included the landfill in the loadings to the embayment, but in each study it was only a minor source because the assumed loads were underestimated. As described below, new well monitoring conducted by the Town of Falmouth indicate that the landfill and abandoned septage lagoon site is a considerably larger source of nitrogen than previously recognized.
Loadings from abandoned septage lagoon site at town landfill site
Howes et al. (1992) and Buzzards Bay NEP (1994) assumed the landfill site, including the septage lagoons (see photograph also in Appendix A) contributed about 500 kg/y. ACI (1995a) assumed a lower estimated loading of 112 kg/y, based on an assumed 63 ppm recharge concentration under the lagoons reaching groundwater. ACI did not take into account the existing plume and discharge volumes in transit from the lagoons when they were in actual use. In light of the town’s recent groundwater monitoring data, none of these studies accurately estimated the load from the landfill and abandoned septage lagoons.
Shown in Fig 2. is the annual volume of septage accepted at the lagoons during the 1980’s as reported in Town of Falmouth Annual Reports. It is unknown what volumes were received prior to 1981 when a gate was installed at the lagoons and the town began keeping records. It is likely that the 1970’s volumes were at least as great as in later years because, even though Falmouth had a smaller population, the Town annual reports note a severe problem with after hour unreported dumping at the unsecured site (likely from septage haulers from outside Falmouth).
In the early 1990’s the septage lagoons settling basins were excavated. It was reported to the Project by DPW staff that solids in the lagoons were removed offsite, and subsoils beneath the lagoons were used to cap the adjoining landfill area. The Buzzards Bay NEP has not yet located a copy of a report documenting the areas excavated and to what depth. The site was fairly extensive and may have included both settling and infiltrating areas. Preliminary plans for the excavated areas now include possible use as an infiltration area for runoff from the landfill cap.
From a nitrogen management point of view, the plume for the septage lagoons must be considered a nitrogen source in two ways. First, the nitrogen concentrations in the front two thirds of the plume represent characteristics of the septage lagoons when they were in use from the 1970s to late 1980s. Septage is very high in nitrogen, typical averaging 588 ppm (US EPA, 1984). It is unclear how much of the septage nitrogen from the abandoned septage lagoons actually reached groundwater when the facility was in operation. In contrast, the back third of the plume represents characteristics of rainwater infiltration during the 1990s percolating through any residual materials left after excavation of the site around 1990. That residual materials remain is suggested by the fact that in March 1995, 7 years after the lagoons were abandoned, monitoring conducted by the Town of Falmouth in a well placed in a well near the center of the lagoon site showed ammonia concentrations of 60 ppm (well 5). Groundwater 300 yards downstream of the entire lagoon site showed a remarkable 124 ppm ammonia (well 558 and 6S, Fig. 3). This ammonia will eventually be converted to nitrate. Thus a plume exceeding 120 ppm nitrogen is still emanating from the abandoned and purportedly remediated site.
This finding has two important implications. First, despite the apparent remediation of the site, sufficient contamination of subsoils exist so that rainfall recharge at the site contributes sizable amounts of nitrogen to groundwater, Second, concentrations of nitrogen in the portion of the plume that correspond to when the lagoons were in use are likely far higher than the 120 ppm concentrations that are resulting from rainwater infiltration.
In the absence of any documentation of concentrations in the leading edge of the plume (from the period when the lagoons were in use), the Buzzards Bay NEP is assuming that 40% of the septage nitrogen reached groundwater, resulting in a potential theoretical groundwater concentration of 240 ppm. We believe this to be a worst case upper limit, but until new wells are sited in the down gradient plume, it will be used as a conservative management estimate.
In our earlier report we assumed that the septage lagoon site would be capped as part of the planned landfill capping, and was shown as “a given” under or future loading scenario for West Falmouth Harbor. This was an incorrect assumption. Not only will the landfill capping not include the abandoned septage lagoon site, but to do so would be an expensive undertaking given that the elevation of the excavated lagoon area is now well below the surrounding land elevation and considerable amounts of fill would be required for capping to be effective. This fact requires that all management options be considered carefully in dealing with the abandoned septage lagoon site. In particular, the high nitrogen levels apparently still emanating from the site suggest that there may remain contaminated soils that could be removed as an alternative to capping. Given the fact that the lagoons covered a very large geographic area, this possibility should be investigated. To this end, in July 1996, the Town of Falmouth excavated areas of the septage lagoons (using a Bobcat) to collect sediment samples for total nitrogen analysis.
2) The Town of Falmouth will provide the following information to the Buzzards Bay NEP for circulation and review by the nitrogen management workgroup:
a) any reports sent to DEP regarding the closing and remediation of the lagoons,
b) copies of any contracts or work orders of contractors hired to remediate the site, and
c) well soil logs for the landfill monitoring wells 5 and 6.
d) draft and final data reports on soil samples and locations sampled at the septage lagoons.
Target Date: September 12, 1996
3) After review of the above materials, the Buzzards Bay will arrange a meeting with the West Falmouth Harbor workgroup including the town’s contractor, DEP and the CCC to discuss management options for the site, including whether or not the site should be used for infiltrating runoff from the landfill cap and whether additional areas of the site need excavation.
Target Date: September 30, 1996
4) The town of Falmouth should install at least one well with multiple sampling depths or a well cluster along either Rt. 28 or 28A along the likely path of the abandoned septage lagoon plume in order to better document loadings in the plume from the period when the lagoons were in use. (This well should not to be confused with the 3 wells being installed along the path of the sewage treatment facility plume.) These should be installed after discussions with the CCC’s technical staff. If a well is not installed, worst case loading assumptions should be used for loading analyses and management actions.
Target Date for well siting: September 30, 1996
Target Date for well installation (if opted for): October 15, 1996
Loadings from solid waste disposal area at town landfill site
The rest of the landfill is a less important nitrogen source to the Harbor, but groundwater concentrations at well 7S were 15.8 ppm, but still more than an order of magnitude higher that what ACI used (1.5 ppm) in their loading assessment. The landfill plume is also high in certain benzene compounds. These compounds are less of a marine pollution issue than a drinking water concern, and are not being addressed in this study, but should be reviewed by the Falmouth Board of Health.
What do the towns monitoring wells tell us about plume migration?
It has been noted in the press that most of the town’s groundwater monitoring wells in West Falmouth do not show appreciable groundwater contamination. As noted by the Buzzards Bay Project at a Board of Selectmen’s meeting last fall, this is true with respect to the town’s wastewater primarily because most of the down gradient monitoring wells are not sited along the principal path of the sewage treatment facility plume (Fig. 4). That is, the wells were primarily sited on either side of the so-called “Class III area” (principal path of the plume) in order to determine if groundwater outside of the Class III became contaminated. Except for the wells adjoining or under the spray irrigation area or infiltration ponds (2, 15, 16, 17), only wells 6 and 11 were placed down gradient in the plume. We believe however that well 11 was placed at too great a depth and that the sampling screens are in fact under the plume (see Fig. 5), and cannot be used to track the plumes progress or nitrogen concentrations.(3)
Under the spray irrigation areas, groundwater nitrate concentrations sometimes exceed 12 ppm(4). Until the last sampling date, well 6, probably near the periphery of the spray irrigation area plume (but not infiltration basins, has been consistently above 5 ppm since fall 1992. The drop at well 6 could be due to the reduction in the use of the spray area since 1994.
Based on groundwater flow rates and water quality data, particularly nitrogen levels in Snug Harbor, ACI, the BBP, and Brian Howes believe that the leading edge of the plume is just now reaching the harbor during the past few years. Without additional monitoring wells it will be difficult to develop a good estimate of how much nitrogen is now entering the Harbor from the plume at this time, and how much the loading rates will increase in the next few years.
Last September, the Town of Falmouth changed laboratories measuring nutrients in the groundwater. The Buzzards Bay NEP found good agreement between the new Town contractor (Envirotech Laboratories and the Buzzards Bay NEP’s contractor (Howes Laboratory, WHOI) on the September 1994 sampling (see Fig. 6).
Like the monitoring wells at the Sewage Treatment Facility, the monitoring wells around the landfill are ill suited to document the travel path or loadings to West Falmouth Harbor, and most are not along the path of the plume (Fig. 3). Only well 7 is useful for estimating loading from recharge from solid waste disposal area and wells 6 and 558 (not shown on map) are in the plume path of the septage disposal area. In Fig. 3, dissolved inorganic nitrogen concentrations (ammonia+nitrate) from a March 1995 sampling are shown in brackets(5). Generally, wells with DIN concentrations over 5 ppm usually had most of their DIN as ammonia. Where two wells are located together (two depths, D=deep, S=shallow), only the higher DIN value for the site is shown. Not shown on the map is a new well 558, which is several hundred feet down gradient along the plume path from wells 6S, 6D. Well 558d had a DIN concentration 113.9 ppm in the 3/95 sampling, consistent with the 124.2 ppm DIN in well 6S. Both wells 6s and 558d had DIN concentrations over 100 ppm in a 10/94 sampling as well. Other studies of sewage plumes show that nitrogen is often conserved in these kinds of plumes, with the ammonia in the groundwater converted to comparable concentration of nitrate down gradient of these sites. For comparison, in the 3/95 sampling, upgradient well 1D had a DIN concentration of less than 0.1 ppm (<0.1 ppm nitrate (the detection limit) plus 0.04 ppm ammonia). These values are probably near the background DIN concentrations of groundwater in West Falmouth before contamination from the landfill.
It is unknown if the septage lagoon plume has yet reached West Falmouth Harbor. Considering that the abandoned lagoons are approximately 11,000 feet from the shore of the bay, and a 1.5 foot per day average groundwater travel time is typical for many parts of Cape Cod, 20 years may be a conceivable lag time between inputs at the landfill and inputs to the receiving waters. Actual transit time is most likely to be between 15 and 30 years. Thus, inputs from 1975 at the septage lagoons site could be now arriving or could soon arrive at the Harbor
What is the status of the buildout study and future loading analysis?
The Buzzards Bay NEP has developed a spreadsheet application for conducting buildout and loading assessments. The Falmouth Planning Department used this spreadsheet last spring and completed an evaluation of existing nitrogen loading and buildout for the watershed. The Planning Department provided the Buzzards Bay NEP with this data which are shown in Appendix B. These findings are also summarized in the Table 1. The buildout is still being reviewed by the Planning Department and actual property frontage on unsubdivided parcels is being added to refine the analysis. The buildout analysis shows that there remains considerable growth potential in this watershed.
Revised loading estimates for the West Falmouth Harbor watershed
In Table 2 are shown revised potential loadings from the various existing sources discussed above. One of the most significant findings in the current analysis is that plumes from the landfill, especially from the abandoned septage lagoons appear to be the second largest source of nitrogen in the watershed.
Why was the flushing study conducted?
The Town of Falmouth requested and received funding from the Buzzards Bay NEP to conduct a flushing study so that the town could apply the tiered nitrogen loading limit strategy identified in the Buzzards Bay Comprehensive Conservation and Management Plan. This mass-loading nitrogen management strategy was developed by the Buzzards Bay NEP and has been adopted by the Cape Cod Commission.
The Town of Falmouth hired ACI to conduct this study. ACI found that the estuary as a whole had a hydraulic residence time of 0.52 days, but that uppermost reaches of the estuary such as Snug Harbor, Harbor Head, and Oyster Pond have residence times of 4.5, 14.8, and 106.8 days respectively. Application of the Buzzards Bay NEP’s methodology requires an average flushing time for the upper 1/3 of the estuary which was not estimated by ACI, but an estimate of this calculation is shown in Table 3. If for example the upper 1/3 of the estuary has an average residence time of 2.4 days(6), then the nitrogen loading limit for this estuary if it had an ORW classification (most stringent level of protection) should be 17,300 kg/y. If the estuary were classified as SA (a mid or typical level of protection), the loading limit would be 34,600 kg/y.
When discussing possible nitrogen loading limits, and when considering well nitrogen monitoring data as described in the preceding section of this report, there is the tendency to focus on acceptable groundwater concentrations of nitrogen on Cape Cod. However, when it comes to protecting coastal embayments, it is the mass load of nitrogen (that is volume times concentration) that must be evaluated, and this loading rate will translate into an embayment-specific ground water concentration. For example, if the West Falmouth Harbor watershed were to have a nitrogen loading target of 34,600 kg/y, this would translate to an average watershed groundwater concentration target of 6.3 ppm. If the watershed had a 17,300 kg/y limit, then the groundwater target would be 3.2 ppm.
It is worth noting that the Town of Falmouth already has a nitrogen loading bylaw in place, and ACI made an attempt to evaluate West Falmouth Harbor conditions, now and in the future. The ACI report notes that water quality monitoring conducted by the Project-Coalition Citizens’ Water Quality Monitoring Program, and Falmouth’s Pond Watcher Program, show that total nitrogen concentrations in most of West Falmouth Harbor already exceed the town’s most stringent total nitrogen limit of 0.32 ppm, and many portions of the Harbor exceed the middle level of protection of 0.5 ppm (see Fig. 7). ACI attempted to predict how total nitrogen concentrations in the Harbor would be elevated both as the town’s sewage treatment facility plume reached the Harbor, and under buildout conditions. Because this report was prepared while other assessments were ongoing such as the new watershed delineation, ACI’s report did not include the septage plume in transit for the period of when the septage lagoons were in use, infiltration of rainwater recharge occurring through residual materials remaining at the lagoon site, and the revised watershed buildout potential. For these reasons, ACI’s conclusions need to be revisited.
Considering the fact that this watershed has two major point sources of pollution, the Falmouth wastewater treatment plant and the Falmouth landfill, and that water column total nitrogen concentrations already exceed the most stringent limits in Falmouth’s nitrogen loading bylaw, it may be unrealistic to pursue a ORW designation for West Falmouth Harbor. Rather, a SA limit is far more achievable. However it is likely that adoption of the SA limit will not adequately protect the most poorly flushed areas like Oyster Pond and Snug Harbor. Alternatively, the Town of Falmouth could pursue some lower level of acceptable loading for this estuary.
How will the upgrades to the Falmouth Sewage Treatment facility affect nitrogen loading to West Falmouth Harbor?
The installation of an aerator, and other improvements could partly decrease nitrogen loading to the facility through increased denitrification in the surface impoundments. (The surface aerated impoundments are high in particulate carbon, presumably not enough carbon is available for appreciable denitrification in groundwater plumes high in ammonia.) Because these improvements were not really intended to reduce nitrogen from the plant, the degree of nitrogen removal will need to be documented in wells immediately down gradient of the infiltration ponds. We expect that even with these potential nitrogen loading reductions, the sewage treatment facility would remain the largest source of nitrogen in the watershed.
What are the next steps?
It appears that our revised estimates of existing nitrogen loading to West Falmouth Harbor will exceed the most stringent water quality standards under Falmouth’s Nutrient Bylaw as well as the Buzzards Bay NEP’s tiered loading strategy. Nitrogen loading will also approach or exceed the mid-level limit for nitrogen loadings under both management strategies under buildout conditions. In the future, plume entry into the harbor, increased development, or increased discharge from the treatment plant could cause degradation of the waters and living resources in West Falmouth Harbor. If a nitrogen management strategy is adopted for the harbor, such a strategy could include a range of options such as improving nitrogen removal at the sewage treatment facility, fast tracking the capping of the town landfill, managing the plume of the abandoned septage lagoon site, limiting buildout in the watershed through zoning changes or procurement of open space, or upgrading failed septic systems with nitrogen removing alternative septic systems.
What might such a management strategy look like? Suppose the Town of Falmouth adopts a nitrogen loading limit of 17,300 kilograms of nitrogen per year for the watershed. Is such a target achievable? An example of how this target could be reached is as follows:
1) Discharge concentrations of the wastewater treatment plant reaching groundwater from the spray irrigation area and infiltration areas be halved to 6 and 10 ppm respectively,
2) new homes be required to have septic systems with enhanced nitrogen removal,
3) existing homes that require septic system replacement at time of property transfer under the new Title 5 regulations be upgraded to septic system with enhanced nitrogen removal, and
4) the former septage lagoon site be further remediated to ensure less than 1000 lb/year from this site.
Whether this is the best strategy for protecting and restoring West Falmouth Harbor needs to be discussed, but it is apparent from this example that the town’s goals for water quality protection can be achieved.
It is worth noting that a pump and treat approach for either the waste water treatment plant or landfill plumes is likely not a viable option because it is difficult and expensive to remove 10-20 ppm nitrogen concentrations with existing technology especially because of the volume of water that would need to be pumped. Rather, it will prove more cost effective in the long run to manage new inputs to groundwater. This issue is being addressed already at the landfill by capping and other limited public funds should be directed toward improving the operation of the treatment plant. In contrast to the landfill and treatment plant, concentrations in the existing plume are high enough to consider at least the economics of pump and treat technologies, but in this case, the first order of business is to identify the cause of continued high inputs of nitrogen at the site and to prevent an future contamination of groundwater from rainwater recharge.
Clearly many assumptions were made in developing the loading rates and limits included in this report, and some of these will need to be revised. It will be particularly important to estimate the amount of nitrogen in the septage lagoon plume now migrating to the harbor. The Buzzards Bay Project hopes to meet shortly with the proposed nitrogen management workgroup for West Falmouth Harbor to discuss the available information, identify information gaps, and explore what steps required to define an appropriate nitrogen management strategy for West Falmouth Harbor.
Overall, West Falmouth Harbor now has fair to good water quality and ranks intermediate among embayments monitored in Buzzards Bay. However, the upper-most regions of the estuary however have elevated nitrogen concentrations and the embayment will likely be sensitive to additional inputs.
In earlier nitrogen loading evaluations, the town’s sewage treatment facility was the principal source of nitrogen in the watershed. A new delineation prepared by the Cape Cod Commission now means that the Falmouth Solid Waste Disposal Facility site is also within the harbor’s watershed. The plume from the landfill is a modest nitrogen source, but the plume from the now abandoned Falmouth septage lagoons, are a very significant source of nitrogen to the bay. The plume from the abandoned lagoons, which were in use from 1975 to 1987, is now in transit to West Falmouth Harbor, but it is not known if it has yet reached the estuary. In spring 1995, wells monitored by the Town near the landfill showed ammonia concentrations in excess of 120 ppm still leaching from these buried abandoned lagoons. It is likely that some of this ammonia will be converted to high nitrate concentrations downstream in the plume, well above the 10 ppm state and 5 ppm County drinking water standards. It is also likely that inorganic nitrogen concentrations in the parts of the plume that coincide with the period of operation of the septage lagoons are far higher than this residual 120 ppm.
Because the former septage lagoon site appears to remain a large source of nitrogen via rainfall recharge, potential use of the site as an infiltration site for the landfill cap runoff should be reconsidered.
Existing monitoring well locations downstream of the Town’s sewage treatment facility and the former septage lagoons are inadequate to document the movement and nitrogen loadings associated with these plumes through the watershed. Three new wells are planned for the wastewater treatment plant plume. Monitoring wells should also be considered for the septage lagoons plume along Rt 28 and possibly Rt 28A.
It appears that the leading edge of the sewage treatment facility plume is now reaching West Falmouth Harbor. We expect that water quality will continue to decline in West Falmouth Harbor as the full extent of the plumes from the landfill and treatment facility reach the harbor.
The restoration and protection of West Falmouth Harbor from nitrogen loading is achievable. The capping of the landfill will help reduce future loadings to West Falmouth Harbor. Other nitrogen management options that should be included in a management strategy for the Harbor include further enhancing the nitrogen removal capabilities of Falmouth’s sewage treatment facility, limiting inputs from new development (e.g. changing minimum lot size on unsubdivided land), extending sewering into areas of West Falmouth (viable with increased nitrogen removal efficiency by the wastewater facility is improved), requiring the use of alternative nitrogen removal septic systems on new and existing substandard systems, and minimizing future inputs from the abandoned septage lagoons.
Aubrey Consulting Inc. (ACI) 1995a. Hydrodynamic and water quality study of West Falmouth Harbor, MA. March 1995, 81 pp.
Aubrey Consulting Inc. (ACI) 1995b. Estimation of flushing rates in selected Buzzards Bay embayments. January 1995, 46 pp.
Buzzards Bay NEP. 1994. A Buzzards Bay embayment subwatershed evaluation: establishing priorities for nitrogen management action. Draft Final, May 3, 1994, 108 pp.
Howes, B.L., D.W. Bourne, and N.P. Milham. 1992. An assessment of nitrogen loading to West Falmouth Harbor from the Falmouth Technology Park and other sources. Prepared for the Falmouth Economic Development and Industrial Corporation, July 1, 1992. 14 pp.
US EPA. 1984. Septage treatment and disposal handbook. EPA-625/6-84-009. 300 pp.
1. The Buzzards Bay National Estuary Program is a planning and technical assistance unit of Massachusetts Coastal Zone Management, and is jointly funded by the Commonwealth and the US EPA. The Project is sometimes confused with two non-profit organizations. One of these is the Buzzards Bay Coalition, a not-for-profit education group, and the other is the Buzzards Bay Action Committee, a not-for-profit lobbying group composed of municipal officials.
3. 3 In Figure 5, the likely vertical migration range for deep migration was based on a slower horizontal groundwater movement (1 ft/day) and high recharge (16-18″ yr), and for shallow migration was based on fast horizontal groundwater movement (3 ft/day) and little recharge (9-10″/y).
4. 4 Well monitoring data discussed in this report from DeFeo, Wait and Pare, Inc. 1994. Report on groundwater monitoring for Falmouth Wastewater Treatment Plant, Sampling Program Sample Series #17, March 1994, and town of Falmouth DPW report to DEP dated December 1, 1994.