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Primary Practice Peak Elevation (ft) Storage Provided (cf) Exfiltration Rate Outflow (cfs) Pond 1P – Infil. Bed (Pea Gravel, 3.0') 646.82 340 0.30 in/hr 0.00 Pond 4P – Infil. Bed Sand/Fill (4.0') 648.14 293 0.40 in/hr 0.52* Pond 5P – Infil. Bed (Pea Gravel, 2.5') 648.51 100 0.30 in/hr 0.02 Pond 6P – Infil. Bed (Pea Gravel, 5.7') 645.64 2,521 0.30 in/hr 0.00 *Pond 4P's primary outflow is reported as 0.52 cfs at the pond-summary level but 0.31 cfs at the outlet-device level within the HydroCAD output; this discrepancy has not yet been reconciled (see Findings). Findings Based on the current HydroCAD models, the 25-year post-developed peak discharge does not exceed the 10-year pre- developed peak at either site discharge point: 2.12 cfs vs. 2.20 cfs at Seneca Street (AP1), and 0.52 cfs vs. 1.39 cfs at the Basin (AP2). Two items remain open and are noted for completeness: a 150 cf residual difference between pre- and post-developed volume at Seneca Street, and unresolved HydroCAD storage/routing warnings on Ponds 1P, 4P, and 5P. Recommendation It is recommended that the Planning Board accept this memorandum and the accompanying HydroCAD calculations as the current basis of stormwater design for this site plan application. Respectfully submitted, [ P.E. Seal / Stamp ] ____________________________ Jason Havens, P.E. Waves AE Page 50 of 84