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The history of Farm Pond in Massachusetts, its use as a potential source of public drinking water, and the management plan to maintain its water quality. Topics include water rights, seepage, bathymetry, eutrophication, and storm sewers.
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Table of Figures Figure 1. Farm Pond watershed map showing current land use ....................................... Figure 2. National Resources Conservation Survey soils of Farm Pond Watershed ......... 8 Figure 3. Farm Pond Bathymetric Map ......................................................................... 14 Figure 4. Farm Pond Field Activities Map .................................................................... 15 Figure 5. Farm Pond Temperature and DO Depth Profiles: Summer 2014. ................... 17 Figure 6. Farm Pond Watershed Limit. ......................................................................... 30 Table of Tables Table 1. Morphometric Characteristics of Farm Pond and its Watershed. ........................ Table 2. Farm Pond Secchi Disk Transparency: 1998-2008. ......................................... 18 Table 3. Farm Pond Water Quality Characteristics – May and August 2014.................. 19 Table 4. Farm Pond TSI Calculations: 2005 & 2014. .................................................... 24 Table 5. Farm Pond Groundwater Meter Seepage Rates. ............................................... 27 Table 6. Summary of LLRM Calculated Nutrient Loads to Farm Pond. ........................ 32 Table 7. Predicted In-Pond TP Concentrations. ............................................................. 33 Table 8. Predicted Chl-a and Secchi Disk Transparency Depths. ................................... 34 List of Appendices General Aquatic Glossary A. Historical Reports and Prior Information B. Town of Sherborn Information C. Hydrologic calculations D. Field Survey Notes E. Water Quality Data F. Aquatic Vegetation Survey G. Nutrient Loading Model H. Pond Management Options I. Watershed Management Options J. BMP Operation & Maintenance Plan K. Letter from Mass. Division of Fisheries and Wildlife
Overview of Report The Farm Pond Management Report ("Management Report") summarizes recent diagnostic field work, watershed evaluation and analysis, review of pond management options, and recommended actions for conserving and protecting the recreational, ecological, and aesthetic features of the Pond. The authors, Fay, Spofford, and Thorndike (FST) of Quincy, MA (formerly doing business as Norfolk Ram Group) assisted by Dr. David Mitchell, CLM, were selected by the Town of Sherborn (the "Town") and the Farm Pond Advisory Committee (FPAC) as the technical consultant for this project in February
B datasheet), and information researched by a local resident (FPAC 2011; Johnson 2015; MHC undated). Adoption of the name Farm Pond dates back to identification on the 1831 State Series map. During the 19th^ century, Farm Pond was used for tourism, fishing and other recreational purposes, as well as commercial ice harvesting (Johnson 2015). In addition, picnic areas were established at two private beaches. Water drawn from the Pond supplied a “modern” cranberry bog located to northeast between Farm Road and Farm Pond but long abandoned (Johnson 2015). The derelict outlet structure located along the northeastern shoreline and the earth-covered rock berm were also reported to be constructed as part of the cranberry cultivation operations.
Figure 1. Farm Pond watershed map showing current land use
After the Hospital shut down in 2003, the pipe was capped at the Medfield end. The Sherborn Fire Department subsequently established a dry hydrant on Forest Street to intercept the water drawn from the Pond. In 2010 an Act of the Legislature deeded Farm Pond to the Town of Sherborn. Farm Pond is shown on historical USGS maps, including the 1893 Franklin quadrangle map and the 1940 Medfield quadrangle map (USGS 1893; 1940). Both maps clearly show an outlet channel on the northeastern shoreline. The 1893 USGS map lacks the earth covered rock berm that isolates a small eastern embayment. However, in the 1940 version there is an outlet from the eastern embayment which eventually confluences with the original outlet channel (USGS 1940). These features are consistent with the description and chronology of the operation of the former cranberry bog. The most recent USGS map does not show a direct outlet from the Pond (USGS, 1987). 1.1.2 Current Land Use Current land use was determined through mapping with data layers taken from Massachusetts GIS data viewer (MA DEP 2014). Current land use and approximate acreage (rounded) in the Farm Pond watershed include: · Forest – 268.4 acres (approximately 66% of watershed); · Residential (both low and very low residential) – 54.1 acres (13%); · Wetland (includes both wooded and shrub wetlands) – 39.6 acres (10%); · Cropland – 35.9 acres (9%); · Pasture – 10 acres (2%); and · Recreational (primarily the Sherborn Town Beach) – 1.1 acres (<1%). The total impervious surface (road, parking lots, driveways, rooftops) found in the watershed was estimated at 25.03 acres or 1.2% of the watershed (MA DEP, 2014). This is significantly less than for the rest of Sherborn, where impervious cover was estimated at 5.15% (EPA, 2010). The Sherborn zoning map indicates that virtually all of Farm Pond’s watershed is zoned “RC” or residential with a 3 acre minimum lot size (Town of Sherborn 2002) (see Appendix B). Based on a watershed windshield survey, there are no apparent active sub- divisions within the watershed nor any signs of impending development. Information regarding the regulations for the public beach is also included in Appendix B. 1.2 Watershed Soils Soils in the Farm Pond watershed were identified from National Resource Conservation Service (NRCS) data layers available at the Massachusetts Geographic Information System (GIS) data viewer (MA DEP 2014). Watershed soils are depicted on Figure 2, with the legend for the individual soils provided on the following page.
The soils can be generally classified as predominantly Hinckley loamy sand, Merrimack fine sandy loam, and Canton fine sandy loam; All of which are well drained Soils with Hydrologic Soil Rating of “A”. Wetlands and low-lying areas are characterized by Swansea and Freetown muck which are poorly drained hydric soils.
422B Canton fine sandy loam, 3 to 8 percent slopes, extremely stony 253D Hinckley loamy sand, 15 to 25 percent slopes 1 Water 253D Hinckley loamy sand, 15 to 25 percent slopes 424C Canton fine sandy loam, 8 to 15 percent slopes, extremely bouldery 254A Merrimac fine sandy loam, 0 to 3 percent slopes 103C Charlton-Hollis-Rock outcrop complex, 3 to 15 percent slopes 253E Hinckley loamy sand, 25 to 35 percent slopes 104D Hollis-Rock outcrop-Charlton complex, 15 to 25 percent slopes 253D Hinckley loamy sand, 15 to 25 percent slopes 422C Canton fine sandy loam, 8 to 15 percent slopes, extremely stony 420C Canton fine sandy loam, 8 to 20 percent slopes 253D Hinckley loamy sand, 15 to 25 percent slopes 253C Hinckley loamy sand, 8 to 15 percent slopes 253E Hinckley loamy sand, 25 to 35 percent slopes 254B Merrimac fine sandy loam, 3 to 8 percent slopes 424C Canton fine sandy loam, 8 to 15 percent slopes, extremely bouldery 254B Merrimac fine sandy loam, 3 to 8 percent slopes 73B Whitman fine sandy loam, 0 to 5 percent slopes, extremely stony 103C Charlton-Hollis-Rock outcrop complex, 3 to 15 percent slopes 254B Merrimac fine sandy loam, 3 to 8 percent slopes 223A Scio silt loam, 0 to 3 percent slopes 420B Canton fine sandy loam, 3 to 8 percent slopes 256A Deerfield loamy fine sand, 0 to 5 percent slopes 253C Hinckley loamy sand, 8 to 15 percent slopes 51A Swansea muck, 0 to 1 percent slopes 253E Hinckley loamy sand, 25 to 35 percent slopes 253B Hinckley loamy sand, 3 to 8 percent slopes 1 Water 260B Sudbury fine sandy loam, 3 to 8 percent slopes 6A Scarboro mucky fine sandy loam, 0 to 1 percent slopes 253E Hinckley loamy sand, 25 to 35 percent slopes 103D Charlton-Hollis- Rock outcrop complex, 15 to 25 percent slopes 253C Hinckley loamy sand, 8 to 15 percent slopes 71B Ridgebury fine sandy loam, 3 to 8 percent slopes, extremely stony 424C Canton fine sandy loam, 8 to 15 percent slopes, extremely bouldery 256B Deerfield loamy sand, 0 to 5 percent slopes 255C Windsor loamy sand, 8 to 15 percent slopes 254A Merrimac fine sandy loam, 0 to 3 percent slopes 424C Canton fine sandy loam, 8 to 15 percent slopes, extremely bouldery 424D Canton fine sandy loam, 15 to 25 percent slopes, extremely bouldery 424C Canton fine sandy loam, 8 to 15 percent slopes, extremely bouldery 254C Merrimac sandy loam, 8 to 15 percent slopes 253D Hinckley loamy sand, 15 to 25 percent slopes 254B Merrimac fine sandy loam, 3 to 8 percent slopes 73B Whitman fine sandy loam, 0 to 5 percent slopes, extremely stony 52A Freetown muck, 0 to 1 percent slopes 52A Freetown muck, 0 to 1 percent slopes 310B Woodbridge fine sandy loam, 3 to 8 percent slopes 254B Merrimac fine sandy loam, 3 to 8 percent slopes 104D Hollis-Rock outcrop-Charlton complex, 15 to 25 percent slopes 103D Charlton-Hollis- Rock outcrop complex, 15 to 25 percent slopes 254B Merrimac fine sandy loam, 3 to 8 percent slopes 424C Canton fine sandy loam, 8 to 15 percent slopes, extremely bouldery 260B Sudbury fine sandy loam, 3 to 8 percent slopes 5 Saco silt loam, 0 to 3 percent slopes 251A Haven very fine sandy loam, 0 to 3 percent slopes
1.3 Review of Historical Data and Reports Collection of water quality data and field observations are used to establish the current conditions of a waterbody. However, it is also important to detect long-term environmental trends, to determine if pond water quality is improving or deteriorating or if there has been a shift in trophic state (see Section 2.2). To conduct this comparison, it is necessary to identify reliable historical data. Historical water quality data and field observations on Farm Pond were available from three State surveys (MA DEQ 1974; 1983; MA DEP 2013). These survey results include water quality data, temperature and dissolved oxygen (DO) profiles, secchi disk transparency (SDT) depths, observations of phytoplankton and aquatic macrophytes, and shoreline features (see Appendix A). More recent data is available from the Farm Pond Advisory Committee (FPAC), drawn from that organization’s monitoring efforts conducted since the late 1990s (Trainor 2011; 2014). This data includes seasonal measurements of Secchi disk transparency (SDT), total phosphorus (TP), and pH, from 1998 to 2008; temperature and dissolved oxygen (DO) depth profiles from the thermally stratified periods in 2000 and 2001; and an aquatic vegetation map (Boyda 2005). Additional water quality data may be available from FPAC, but it is reportedly in the form of raw field data which have not been transcribed from field sampling forms (Trainor, pers. comm. 2014). FST did not include these data in this analysis. Additional qualitative information regarding Farm Pond water quality was obtained from Dr. Marianne Moore of Wellesley College (Moore, pers. comm. 2014; 2015). Dr. Moore has taken her college classes to the Pond on multiple occasions and she remarked on the excellent water clarity regularly observed over the years. She also postulated that phytoplankton growth in Farm Pond may be chemically limited by both nitrogen and phosphorus and biotically by grazing by zooplankton that undergo a diurnal migration to avoid fish predation (i.e., rise to feed at night and return to aphotic zone at day). 1.4 Preliminary Hydrologic Budget A preliminary hydrologic budget was constructed for Farm Pond. The hydrologic inputs (inflows) to Farm Pond are a combination of tributary flow, runoff from the watershed, direct precipitation onto the Pond and any contributions from groundwater seepage. Losses (outflows) from the Pond occur through outlet flow and evaporation. Historically, there were consumptive withdrawals piped to the Medfield State Hospital but this practice has been discontinued.
Several factors need to be taken into consideration when evaluating these estimates. Watersheds are characterized by a combination of steep and flat relief (topography), a variety of land uses and a mosaic of soils. The Farm Pond watershed is relatively steep on the western and northern shorelines but is largely forested in land use. Given the steep and close proximity to ledge (bedrock) in much of the western watershed, the higher value (1.34 cfs) is likely to be more representative. The hydraulic residence time (HRT) is calculated as the Pond’s volume divided by annual inflow. For Farm Pond, the HRT was estimated at 2.5 years and its inverse, the flushing rate, was calculated at 0.40 flushes per year. These values indicate that water movement in and out of Farm Pond is very slow and that any pollutant reaching the pond will not be easily flushed out.
2.0 Field Activities The following field activities were conducted by FST as part of the evaluation of Farm Pond: bathymetric map confirmation, water quality monitoring, aquatic vegetation survey, and groundwater in-seepage measurements. Field notes for the May and August work are provided in Appendix D. 2.1 Bathymetric Map Confirmation A bathymetric map provides the outline and details of the bottom depth contours of a pond. A detailed bathymetric map of Farm Pond was constructed in 2003 (Seering, A. 2003) following a detailed set of soundings. FST was provided with the GPS database that was the basis for the bathymetric map. Unfortunately, age of the database and lack of supporting software made this information electronically non-accessible so that generation of a new map was not possible. For our assessment, we manually superimposed the existing bathymetric contours on the Pond outline, as practicable (Figure 3) FST conducted a qualitative confirmation of depth measurements, by comparing points from the field book with the approximated existing contours. Based on this comparison, it was determined that no significant changes to the bathymetric map were required. 2.2 Water Quality Monitoring - 2014 Water quality monitoring of Farm Pond was conducted on May 29 and August 12, 2014 (see Figure 4). The May sampling represents a late spring period when water column nutrient levels are likely to be near their seasonal maximum due to spring runoff from the watershed and potential in-seepage from a high groundwater table. The August sample represents a mid-summer period when the Pond typically experiences high levels of biological activity. The August sample is highly important for diagnostic purposes since it provides evidence of the maximum expression of nutrient-based growth and often represents the most stressful conditions for aquatic life. During late summer, pond surface water temperatures are high, clarity is often at seasonal lows, nuisance algal blooms may occur, and dissolved oxygen may be absent in most deeper zones of the Pond. Measurements of temperature, dissolved oxygen (DO) pH, and specific conductivity and were taken at pre-selected depth intervals at the deep basin in Farm Pond (FP-1; Figure 3). Measurements were collected using a Yellow Springs Instruments (YSI) 600 XL multi- parametric probe. Total water depth at FP-1 was measured by a hand-held depth meter and location determined by a global positioning system (GPS) unit. Secchi disk transparency (SDT) depth (an estimate of water clarity) was measured.
Figure 4. Farm Pond Field Activities Map
The following sections provide an overview of the water chemistry; including that for physiochemical characteristics: temperature, dissolved oxygen and secchi disk transparency (Section 2.2.1); general water chemistry: pH, specific conductivity, alkalinity, hardness and chloride (Section 2.2.2); nutrients (Section 2.2.3); and biological parameters (Section 2.2.4). Laboratory reports of the water quality data for the two samples are provided in Appendix E. 2.2.1 Water Column Physiochemical Characteristics The temperature and dissolved oxygen depth profiles of Farm Pond during the two survey dates are shown in Figure 5. The profile in late May indicated rapid water temperature change within depths from 15 ft. to 30 ft. The thermocline (defined as the depth of greatest temperature change per unit depth interval) was located at approximately 17.5 ft. This seasonal thermal layering or stratification separates the Pond into three distinct layers: the warm, upper layer (termed the “epilimnion”); the zone of temperature change (“metalimnion”); and the cold, bottom waters (“hypolimnion”). Figure 5a indicates the Pond was thermally stratified during May and that DO concentrations are fairly constant to the bottom. There is a slight oxygen maxima seen within the metalimnion, presumably due to the colder temperature found there, since the amount of DO that can be dissolved in water increases with decreasing temperature. The abundance of DO at the bottom indicates the Pond is at an early stratification stage, not too long after vernal (spring) turnover. The temperature profile of Farm Pond in mid-August (Figure 5b) exhibits approximately the same thermocline depth as in May but, as expected, there is a greater water temperature difference between the epilimnion and hypolimnion. This is caused by the summer heating of the upper waters while the isolated bottom water temperature is largely unchanged. The major significant difference between the two profiles is the significantly lower bottom DO concentrations observed in August with DO measurements less than 4.0 mg/L below 25 ft. Comparison of 2014 data with historical State data shows similar patterns of temperature and DO seen in 1974; 1983 and 2005 (Appendix A). The State sampling surveys generally took place later in the summer season and typically demonstrate further depletion of hypolimnetic DO. The FPAC temperature profiles of 2000 and 2001 exhibit the seasonal progression of thermal stratification in the Pond. The profiles show surface water temperature increasing from spring to a seasonal maximum in late August and then decreasing as the Pond undergoes cooling during the fall. When the pond temperature is uniform throughout the Pond (i.e., isothermal), it undergoes complete mixing throughout the water column (i.e., fall turnover).
