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HomeMy WebLinkAboutCorrespondence - 80 FLAGSHIP DRIVE 9/12/1995 i JL� THOMAS s N-11LEVE ASSOCIATES, G September 12, 1995 John C. Chessia, P.E. Coler & Colantonio, Inc. 101 Accord Park Drive, Suite One Norwell,MA 02061-1685 Re: Central Metal Finishing 80 Flagship Drive North Andover, MA 01845 Dear Mr. Chessia: We are in receipt of your September 5, 1995, Engineering Review of Central Metal Finishing, 80 Flagship Drive. We offer these responses and additional information for your review and look forward to working with you in resolving any further issues or concerns you may have. The following responses coincide with your numbered comments: The woods and grass area included in Subcatchment 1 have been labeled on the hydrology plans. The woods and grass area shown in Subcatchment 1 was drafted incorrectly, the woods/grass limit represented on the post-developed hydrology plans was used for the analysis of pre and post conditions and has been revised on the pre-developed hydrology plans. With the woods/grass limit shown in this location, a flow length of 30' of light wooded area is used for analysis. The soil pile that exists on site has established vegetation growth, therefore has been included as open space (Soil D). The gravel parking area is located within the limits of Subcatchment 1 and is shown in the CN calculations for that subcatchment. In the Tc calculations for Subcatchment 3 (Pre-Developed), Path 3 contains flow down the soil pile. The flow path down this pile is 30' long at a slope of 26.7%. A spot grade has been added to the pre-developed hydrology plans to help clarify where the slope calculations came from. • ENGINEERS • • LAND SURVEYORS • • LAND USE PLANNERS • U.S. Route #1 Topsfield, MA 01983 447 Old Boston Road FAX (508) 887-3480 (508) 887-8586 Mr. John C. Chessia Page 2 September 12, 1995 5. The drainage divide between Subcatchments 2 and 3 has been moved to include the proposed grading. The limits of Subcatchments 2, 3 and 4 have been revised to conform to the new proposed detention pond. Please find attached revised calculations for Subcatchments 2, 3 and 4, Pond 1, Reaches 1 and 2 and Design Point #1. A Hydrologic Summary has been provided for your review. By reviewing the table, these changes have no adverse effects on the project, they actually produce less runoff than before. 6. The tree/grass area shown in the north easterly portion of the site is correct on the post- developed hydrology plans. All calculations regarding the woods/grass area, pre and post, was done with the delineation of this area as shown on the post-developed hydrology plans. The Pre-developed hydrology plans have been revised to reflect this change. (See response 2). 7. Street drainage in the Town of North Andover is designed on the 10 year storm event. By examining the pre-developed flow rate from our site to the catch basin located approximately 160' west of our site on Flagship Drive, where our pre-developed flow enters the existing drainage system, we have flow rates for the 10 and 100 year storm events of 5.4 and 8.6,CFS respectively. The post-developed flow rates into the existing drainage system on Flagship Drive, Design Point #1, are 5.2 and 7.9 CFS for the 10 and 100 year storm events respectively. We have decreased the flow into the system in both cases. Since street drainage is designed for a 10 year storm event, it is possible that higher storm events may produce a lag time in the system. Located west of our site on the abutters property, Tru Green-Chemlawn, there exists a catch basin, rim elevation of 239.94, that is tied into the existing drainage system on Flagship Drive. This drainage system enters the central detention pond for the North Andover Business Park, the 100 year flood plain elevation of this pond is 236.3'. The invert out on the catch basin located on the north west corner of the proposed parking lot on our site is 241.45, 1.5' higher than the rim of the catch basin on the abutters property. If the drainage system was surcharged down slope from the point at which our drainage system enters the existing system, water would discharge up and out of the existing catch basin rim on the abutters property at elevation 239.94. This area would have to flood up to elevation 241.45 before it would have any effect on the drainage system proposed. 8. The top of the pond has been increased to 6' wide with 2:1 slopes on either side. A detailed cross section of the pond and emergency spillway has been added to the plans. 9. A pipe inlet detail has been added to the plans. 10. The rim of the Emergency Spillway structure has been lowered to elevation of 251.3, 0.1' higher then the 100 year flood plain elevation of 251.2. A beehive grate has been added to the outlet of the pond to protect the orifice from being plugged. Any storm greater than the 100 year event will exit the pond through the catch basin rim. We would not Mr. John C. Chessia Page 3 September 12, 1995 want to build a spillway that would direct emergency discharge directly onto the abutters property in a concentrated area. We feel that the emergency catch basin rim can handle emergency discharge. Any additional flow should be allowed to top the south and west sides of the pond and flow down the grass areas into the wetlands. 11. Soil test pits will be conducted on the site and in the location of the detention pond to determine soil classification and maximum seasonal groundwater elevations. 12. Roof drainage will be collected by roof drains per plan and discharged into the detention � v pond via a 10" pipe, outlet invert elevation = 249.0'. Overflow scuppers will be located ,�-- 1 on the south side of the building directing overflow into the pond as well. 13. The emergency spillway will use a standard catch basin grate, 24 openings, each opening approximately 2. 1/8" x 3 3/4". Please find attached equations used by Hydro Cad to calculate rectangular grates and revised calculations for Pond 1 showing the discharge of this grate. The original grate was entered.incorrectly and has been revised to reflect the conditions above. 14. The 100 year flood elevation for this development as represented on the Asbuilt/Permitted plans submitted for your reference was calculated by Neve Associates in 1989 to be elevation 236.3'. This calculation confirmed previous calculations of H.W. Moore Inc. and was accepted by the Planning Board and Conservation Commission DEP File#242-484. n 15. The precast concrete chemical storage units will now be located inside the building with ` appropriate provisions for spill containments and ventilation. 16. Spot grades have been provided which clarify that all storm water will drain away from the building and towards the detention pond along the curb at the south edge of the paved area. The slope along this curb has been increased to 0.6%. be 17. Spot elevations have been provided. 18. The revised grades will not require any wetland alteration. 19. The referenced railroad ties and parking spaces are to be deleted. Notation has been added to clarify this. with the Planning Board on Tuesday, September 19 1995 tourther discussY� We plan on meeting g y, p , and close this hearing. I hope this information provides you with sufficient data to complete your review and issue your approval of the project. Mr. John C. Chessia Page 4 September 12, 1995 If you should have any further questions please do not hesitate to contact me. Very truly yours, THOMAS E. NEVE ASSOCIATES, INC. John Morin, E.I.tT.,. Civil Engineering Consultant JM/km Attachments cc; North Andover Planning Board North Andover Conservation Commission 4 1429 JON.W PS Ho S EK.INCO a R November 17, 1995 Jahn C. Chessia,P.E. Coler& Colantonio,111c. 101 Accord Park Drive, Suite One Norwell,MA 02061-1685 Re: Central Metal Finishing 80 Flagship Drive North Andover,MA 01845 Dear Mr.Chessia: We are in receipt of your September 27, 1995, Supplemental Fngineering Review of Central Metal Finishing, 80 Flagship Drive, We offer these responses and additional irfori-,Yation for your review and use feel that with this additional infonnation all your questions and conccrus have been answered. The fc)llowing responses coincide with your numbered continents: 7. Find attached calculations and worksheets which shoe that andex full flow conditions freeboard (0.6 feet) still results in the proposed detention pond. Also, please note that the 100 year storm event produces volumes Which do not create full-flow conditions, therefore,this space is available if backflow over than what is expected is produced from the Flagship Drive drainage system. 8. Filter fabric has been provided under the rip rap slopes. 9. A detail of the Neenah Foundry beehive grate, Model No. R-4340-11, is attached and the model number has been added to the plan. one can see from the detail that the grate would not be more of a restriction than the orifice. 10. A V-Notch weir spillway has been added to the southern side of the detention basin. This spillway is designed to pass a 100 year storm with the outlet plugged (see calculations attached). if yo1j should have any t7 ier questions please do not hesitate to contact n1e, Very truly yours, THOM.A.S E.NEVE ASSOCIATES, TNC. John Morin. E.I.T. Civil Engineering Consultant Jt,4/krn AttacImients cc: North Andover. 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