Lake Pocotopaug Lake and Watershed Restoration Evaluation ...

Table 20. Relative Wet Weather Total Phosphorus LoadingENSRStationLocationTotalArea(ac)Fractionof TotalArea(ac)WaterVolume(m 3 )2001 MedianTP Conc(mg/L)RelativeLoad*(kg/yr)PercentTotalLP-5 Hales Brook, at Lake Drive-upstream of Hales Pond 889 0.37 1306804 0.084 109.8 33.2LP-7 Bay Road Brook, downstream of Bay Road 156 0.07 229315 0.300 68.8 20.8LP-10 O'Neils Brook, upstream of Old Marlboro Road 53 0.02 77908 0.706 55.0 16.6LP-3 Christopher Brook, upstream of Christopher Road 466 0.20 685006 0.069 47.3 14.3LP-13 Storm drainage swale, end of Park Street (next to 5 0.00 7350 1.567 11.5 3.5house #5 with ornamental pond)LP-11 Day's Brook, downstream of Old Marlboro Road 55 0.02 80848 0.140 11.3 3.4LP-6 Candlewood Brook, upstream of Lake Drive 41 0.02 60269 0.178 10.7 3.2LP-4 Storm drain at bottom of Clark Hill 18 0.01 26459 0.196 5.2 1.6LP-8 Hazen Brook, end of private drive 20 0.01 29399 0.169 5.0 1.5LP-9 Storm drains at lake edge, between cottages at end 5 0.00 7350 0.417 3.1 0.9of Hawthorne and Emerson RoadLP-12 Storm drain at bottom of MohicanWangonk Trail 12 0.01 17640 0.121 2.1 0.6(north side of beach)LP-14 Storm drain at S. Wangonk Trail beach 3 0.00 4410 0.159 0.7 0.2*Loads based on estimated stormwater flows * median first flush concentrationTotal 330 1008.5 Loading SummaryTaking all methods described above into consideration, the range of likely loads to LakePocotopaug is somewhere between 280 and 859 kg/yr, and will vary depending on weatherpatterns. The watershed is the primary source of phosphorus, providing between 50 and 73%of the total load. Ground water and precipitation provided 9 – 17% of the total phosphorus loadcollectively. Waterfowl provides approximately 6 –11% and internal loading provides 12 – 22%of the TP load. The internal loading estimate is less than the load previously report but thisreduction not 100% attributable to the alum treatment. Initial internal loading was approximatedat 373 kg/yr, slightly lower than the 499 kg/yr estimated by Fugro (1993).Loading by sampling station produced values comparable to loading calculations presented inSection 8.1. Relative TP load was estimated at 330 kg/yr, slightly above the high range of thewet weather calculations. Relative loads were calculated based on first flush samples and arelikely to be the worst case scenario. In addition, best estimates allowed for the settling ofparticulate matter. Overall, all calculations of the TP load to Lake Pocotopaug presented hereare reasonable. Although the major tributaries comprise the bulk of the stormwater TP load,excessive stormwater phosphorus concentrations are present throughout the watershed.Lake Pocotopaug Restoration Evaluation 87May 2002