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155 Derby Street - drainage plansBobrek Engineering & Construction, LLC PO Box 2185, Danvers, MA 01923 978.406.9619 - www.gobobrek.com Wharfside Condominium Trust (21-010) Page 1 of 3 April 5, 2022 155 Derby Street – Drain Connection, REV2.doc April 5, 2022 Ms. Deborah Duhamel, P.E. Assistant City Engineer City of Salem 98 Washington Street, 2nd Floor Salem, MA 01970 RE: 155 Derby Street – Roof Drain Connection Request (Revision 2, April 5, 2022) Dear Deb, On behalf of the Wharfside Condominium Trust at 155 Derby Street in Salem, Bobrek Engineering & Construction, LLC (BEC) submits this revised letter of request to replace an existing 4” roof-drain service lateral into a sewer main with a 6” into the drainage system on Derby Street. This lateral replacement has been developed as a result of an investigation of a sinkhole formed from a roof leader outlet recently discovered in an alley between 155 and 149 Derby Street. This existing roof-drain pipe exits from the eastern side of the building in the direction of the abutting building of 149 Derby Street where it discharges into the alleyway between the buildings. The soil under this pipe has been washed out, creating a void between the two building foundations in the alleyway. BEC has been retained by 155 Derby Street to investigate the drain service existing condition and permit a replacement drainage service for the property to delete the existing alleyway roof drain pipe. Existing Conditions The building at 155 Derby Street is a two-tiered multi-unit, multi-use facility which contains a commercial usage on the first floor and residential on the floors above. Roof runoff from the entire building is split into two sub-catchments: The western catchment of the building (lower tiered section – 990 sf) discharges all runoff to an interior, 4” cast-iron pipe in this half of the buildings basement. BEC reviewed City records of service laterals and also completed a dye test to verify connection to either the drain or sewer main in Derby Street; and was verified to be connected to the 36” brick sewer. Therefore, this 4” roof drain cast iron pipe exits the building and discharges into the City of Salem’s sewer system on Derby Street. This western building half’s roof drain piping was verified by BEC to be directly connected to two (2) roof drains and a sump pump. The eastern catchment of the building (upper tiered section – 1,130 sf) discharges to an interior, 4” PVC pipe. This pipe discharges in the 18” wide alley between 155 and 149 Derby Street. According to the current condo owners, this pipe was originally connected to the sewer service, but was separated approximately 15 years ago during interior renovations. This pipe was installed with the outlet buried into the concrete surface between the two buildings in the alleyway. Over the years, the stormwater Bobrek Engineering & Construction, LLC PO Box 2185, Danvers, MA 01923 978.406.9619 - www.gobobrek.com Wharfside Condominium Trust (21-010) Page 2 of 3 April 5, 2022 155 Derby Street – Drain Connection, REV2.doc runoff washed out the soil below the surface to a depth of 5’ below the sill elevations of both 155 and 149 Derby Street. Ownership at 155 Derby Street has had a plumber verify all sanitary sewerage connections to be directly connected to the buildings sewer service, and all roof drains to be separately connected to other piping. Ownership has provided a plumbing inspection report documenting this condition from Dash Drains, dated January 13, 2022 which is attached to this letter. Stormwater Analysis & Design The property at 155 Derby Street contains a total of approximately 2,650 square feet which is approximately 90% occupied by the building’s footprint, allowing no ability for on-site stormwater retention/infiltration on-site. Currently stormwater at the property either directly enters the City’s sewer utilities (western half) or passively runs-off the site and enters the catch basins directly in-front of the building on Derby Street (eastern half). To confirm the provided capacity of the existing roof drains and lateral connections is sufficient, BEC has completed a pipe sizing calculator utilizing the rational method. Each of the pipes were analyzed during the 25-year storm event, which in this case is 7.48” of rainfall. The Western and Eastern roof drains were analyzed individually which resulted in a peak discharge rate of 0.15 cubic feet per second (cfs) and 0.27 cfs, respectively. Using a 4” vertical pipe for our sizing calculations, the maximum capacity of each vertical roof drain is 1.9 cfs. This confirms the capacity of the vertical portion of the pipes is sufficient. The total flow of the proposed connection to the drainage main in the roadway, will be a summation of the two flows outlined above or 0.42 cfs. Performing the sizing analysis for a 4” PVC pipe (assumed 2% slope), resulted in a maximum flow capacity is 0.27 cfs which is insufficient. Analyzing a 6” PVC pipe, the resultant maximum flow capacity equates to 0.79 cfs. As a result of these calculations, BEC is proposing the property owner to replace the existing 4” PVC roof-drain discharging from the building with a 6” PVC drain service lateral pipe. Please see the attached “BEC Drainage Calculations Sheet” for reference to these computations. Therefore, the project proposes:  Delete existing roof drain piping outlet into the alley between the buildings  Re-pipe interior roof drain piping to discharge from the building at two separate locations, maintaining the highest elevation possible  Install roof drain discharge piping outside the building face with an air-gap into a sub-surface roof drain pipe to pass under the sidewalk, and connect to the nearest catch basin  Install pipe protection at discharge including heat-trace tape and small bollards to deter any pedestrian or snow removal damage  Cut and cap the existing drain connection on the sewer main on Derby Street in accordance with City Standards. Please refer to the attached ‘Proposed Drain Connection Plan, dated April 4, 2022’ developed by BEC for this project. Bobrek Engineering & Construction, LLC PO Box 2185, Danvers, MA 01923 978.406.9619 - www.gobobrek.com Wharfside Condominium Trust (21-010) Page 3 of 3 April 5, 2022 155 Derby Street – Drain Connection, REV2.doc Lastly, in the event of a City municipal drainage system surcharge, the system has been designed to provide an air-gap at the connection point of the underground piping to the buildings roof drain piping. Therefore, if the City’s the system is surcharged, the system will overflow to the exterior passively prior to causing any flooding in the building. The interior plumbing will be completed in accordance with Massachusetts Plumbing Codes by a licensed plumber and BEC has not completed an interior Engineered Plumbing Design for this project. City’s Drainage Main Conditions The City of Salem has provided BEC with CCTV videos of the existing 24” drain on Derby Street, performed by BMC, Corporation of Billerica, MA. Attached is BMC’s pipe inspection report which documents several repair areas, some minor longitudinal cracking and minor amounts of sand/gravel. Based on the video, the pipe is in a satisfactory condition to accept the existing and proposed flows described in this letter. As noted above all stormwater runoff from the property at 155 Derby Street either directly or passively enters the City’s sewer & drainage systems. The proposed roof drain piping will be directly connected to the City’s catch basins abutting the building, and no work is proposed to take place at the City’s drain main. Conclusion This document has been developed to provide sufficient information to permit deleting an existing connection of an existing roof-drain lateral into the City’s sewer system at 155 Derby Street, with a new roof-drain service lateral connection into the City’s drainage system as directed by the City to the catch basins on Derby Street. This project not only will eliminate additional Inflow & Infiltration (I/I) into the City’s sewerage system but will provide a safe and effective way to remove a roof drain erosion issue between two buildings. This project is to be completed as quickly as possible to repair the existing structural safety hazard which currently exists between the buildings. Thank you for your time and consideration when reviewing this project. Please contact me should you have any questions or would like to discuss further at 978-406-9619 or john@gobobrek.com. Yours truly, Bobrek Engineering & Construction, LLC John Bobrek, P.E. President Enclosures:  BEC Closed Drainage System Calculations  BEC Proposed Drain Connection Plan  BMC, Corp Derby Street Drain Pipe Inspection Report  Dash Drains Plumbing Report, January 13, 2022 BOBREK ENGINEERING & CONSTRUCTION, LLC CLOSED DRAINAGE SYSTEM CALCULATIONS 25-YEAR FREQUENCY Project:155 DERBY ST, SALEM, MA Notes: n=0.013 for reinforced concrete pipe Proj. #:2021-XX n=0.010 for high density polyethylene pipe (smooth interior) Date:12/08/21 c=0.95 (impervious areas) By:BTP c=0.20 (for lawn/planting areas) Ckd by: Line Length Area Imp.Area Perv.CA SUM Time of Rainfall Req. Cap.Pipe Slope Flow Full Design Vel.Rim Inv. Elevations Pipe Cover Time in From To (ft)(acres)(acres)CA Concen.I (in./hr.)Qd (cfs)(in)(ft/ft)Qf (cfs)Vf (fps)Vd (fps)Comments Elev.(ft)Upper Lower Q/Qf Pipe Upper Roof Basement 25 0.04 0.00 0.04 0.04 6.00 7.48 0.27 4 1.000 1.90 21.72 12.9 PVC 0.14 -0.33 0.03 Lower Roof Basement 25 0.02 0.00 0.02 0.02 6.00 7.48 0.15 4 1.000 1.90 21.72 10.9 PVC 0.08 -0.33 0.04 Basement Main 25 0.00 0.06 6.00 7.48 0.42 6 0.020 0.79 4.03 3.5 PVC 0.53 -0.50 0.12 Page 1 CONCRETE SIDEWALKDWE24"DWHHTDTCBUPEEX. 4" C.I. PIPEINV OUT: 94.15159 DERBY STREETWETWWG24"DTCONCRETE SIDEWALKEWGSTACK(TYP.)155 DERBY STREETCBCBROOF LINE(APPROX.)5010SCALE = 1":10'20 FEET2.0" ASPHALT TOPCOURSECUT BACK 12" ON EACHSIDE OF TRENCH12" MINIMUMROADWAY OR SIDEWALK12" COMPACTEDGRAVELPAVEMENT SUB-BASECOURSETYPICAL UTILITY TRENCHNOT TO SCALEINSIDEDIAMETER34" CRUSHED STONE6"NOTES:1. PROVIDE EXPANSION JOINTS AT MIN. 30 FT. O.C. WITH PRE-MOLDED JOINT FILLER.8" GRAVEL SUB-BASE2. PROVIDE CONTROL JOINTS AT 6' O.C.3. PROVIDE BROOM FINISH IN DIRECTION PERPENDICULAR TOCURB.12"4. CEMENT CONCRETE SHALL BE 4000 PSI-TYPE II5. EXISTING GRAVEL SUB-BASE TO REMAIN IN AREAS WHERENO TRENCHING IS PROPOSED.6. SEE ROADWAY/SIDEWALK RECONSTRUCTION DETAIL FORGRAVEL APPLICATION IN AREAS OF PROPOSED TRENCHING.CONCRETE SIDEWALK1/2" PREFORMEDEXPANSION JOINTSECTIONCEMENT CONCRETE SIDEWALKRESTORATION DETAILNOT TO SCALEBLDG. FACE ORFIXED OBJECTEXPANSION JOINTSEALANT(WHEN REQ'D)12" COMPACTEDGRAVELSUBGRADETEMPORARY TRENCH PAVEMENTNOT TO SCALETRENCH WIDTH &PAYMENT LIMITMINIMUM OF 2'OVERLAP FILTER FABRICCOMMON FILL AND ON-SITE FILLMATERIAL GEOTECHNICALLYSUITABLE FOR REUSE ON-SITE ASBACKFILLSUBGRADEEXPANSION JOINT TOEXISTING CONCRETE ASAPPLICABLEWIDTH VARIESFINISHED GRADE(TREATMENT VARIES)MIN. 1.0% SLOPEMAX. 2.0% SLOPE4" BINDER4" THICK CONCRETESIDEWALKCURBPERMANENT TRENCH PAVEMENTNOT TO SCALEEX. 4" PVC PIPEINV: 100.82149 DERBY STREETCBSGTSSGTWWGWHH24"DTUPDWEX. DMHRIM: 100.00INV. 92.30DERBY STREETSGTVGC (TYP.)GGSGTWWSGTEX. DMHRIM: 101.50INV. 91.85S160 DERBY STREETEX. SMHRIM: 100.26INV. 89.01156 DERBY STREETDANIELS STREETDANIELS STREETWGKOSCIUSZKO STREETPALFREY COURT12"DEXTEND 4" PVC ROOF DRAINTO DAYLIGHT LOCATION (BY OTHERS)REMOVE EXISTING 4" PVC PIPEFILL IN VOID BETWEENBUILDINGS, PER STRUCTURALENGINEER.RE-PIPE ROOF DRAIN PIPINGTO EXTERIOR TO DAYLIGHTLOCATION (BY OTHERS)INSTALL 4" SDR 35 DRAIN PIPETO CATCH BASIN FROM DAYLIGHTLOCATIONMAINTAIN 36" MINIMUM ADASIDEWALK PATH (TYP)INSTALL 6" SDR 35 DRAIN PIPETO CATCH BASIN FROM DAYLIGHTLOCATIONPROVIDE CLEANOUTAT ANY BENDS (TYP)CUT AND CAP EXISTING ROOFDRAIN AT SEWER CONNECTIONROADWAYSIDEWALK, MAINTAIN MINIMUM 36" PEDESTRIAN CLEARANCEAIR GAP CONNECTIONSIZE UP DOWNSTREAM PIPEROOF DRAIN, MAINTAIN HIGHEST ELEVATION POSSIBLEBUILDING FACECATCH BASINHEAT TRACE TAPE & PROVIDE PIPE PROTECTIONFROM PEDESTRIAN/SNOW DAMAGECONNECT DRAINPIPE AT HIGHESTELEVATION POSSIBLETO CATCH BASINSAWCUT EXISTING ASPHALT AND PROVIDE PERMANENTTRENCH PAVEMENT AS SHOWN IN DETAILS (TYP IMPACTED AREAS)DR BY:CHK BY:PROJ NO:DATE:SCALE:SHT NO:SHEET NAME:STAMP:REVDESCRIPTIONDATEPROJECT INFOCLIENT INFONORTHDRAIN CONNECTION 155 DERBY ST. SALEM, MA 01970 PO BOX 2185DANVERS, MA 01923WWW.gobobrek.COMWHARFSIDECONDOMINIUMTRUST155 DERBY ST,SALEM, MA01970GENERAL NOTES1.BASE MAPPING OF THE PROJECT SITE IS BASED ON AN ON-THE-GROUND TAPE SURVEYPERFORMED BY BOBREK ENGINEERING & CONSTRUCTION IN NOVEMBER 2021.2.CONTRACTOR IS TO NOTIFY ENGINEER IMMEDIATELY OF ANY DISCREPANCIES PRIOR TOPROCEEDING WITH PROPOSED WORK.3.THIS PLAN DOES NOT NECESSARILY DEPICT THE EXACT LOCATION AND SIZE OF ALL UTILITIESWHICH MAY EXIST AT THIS TIME INSIDE OR OUTSIDE OF EXISTING OR PROPOSED BUILDINGS, ONTHE SUBJECT PROPERTY, WITHIN THE STREET RIGHT-OF-WAY, OR ON ABUTTING LOTS.4.THE ADJACENT ABUTTER(S) MUST BE NOTIFIED PRIOR TO THE START OF CONSTRUCTION.5.THE CONTRACTOR IS RESPONSIBLE FOR VERIFYING AND RECORDING THE EXACT LOCATION OFEACH PROPOSED UTILITY CONNECTION.6.CONTRACTOR SHALL VERIFY TYPE, SIZE AND MATERIAL OF ALL EXISTING UTILTIES PRIOR TO ANYINSTALLATION OF PROPOSED FIRE SERVICE.7.ALL WATER AND SEWER WORK MUCH COMPLY WITH CITY OF SALEM REQUIREMENTS. ALL PIPINGWITHIN 10' OF THE BUILDING FOUNDATION SHALL CONFORM TO MASSACHUSETTS BUILDING,PLUMBING, AND/OR ELECTRICAL CODES, AS DEEMED APPROPRIATE.8.CONTRACTOR SHALL BE RESPONSIBLE FOR REPAIRING ANY EXISTING UTILITIES AND/ORSTRUCTURES DAMAGED DURING CONSTRUCTION.9.CONTRACTOR SHALL PROTECT ADJACENT PROPERTIES DURING CONSTRUCTION AND RESTORETHEM TO THEIR ORIGINAL CONDITION (IF DISTURBED).10.A UTILITY AS-BUILT SHALL BE PERFORMED BY THE ENGINEER OF RECORD.11.IN LOCATIONS WHERE A 10' HORIZONTAL SEPARATION AND/OR 18" VERTICAL SEPARATIONBETWEEN WATER AND SEWER SERVICES CAN NOT BE ACHIEVED, THE SEWER SERVICE SHALL BEENCASED IN CONCRETE.12.CONTACT THE TOWN OF SALEM FOR THE MARKING OF SALEM MUNICIPAL UTILITIES, CONTACTDIG-SAFE AT 1-888-344-7233 OR 1-800-322-4844 AT LEAST 72 HOURS PRIOR TO EXCAVATION.13.DURING EXCAVATION AND CONSTRUCTION OF PIPES AND STRUCTURES, TRENCHES MUST BEADEQUATELY BRACED AND PROTECTED AGAINST CAVE-IN.14.ALL TRENCHES IN THE PUBLIC RIGHT OF WAY MUST BE PAVED AT THE END OF EACH WORKINGDAY. NO UN-PAVED TRENCHES SHALL BE LEFT OVERNIGHT.15.CONTRACTOR TO RESTORE ALL DISTURBED LANDSCAPE AREAS TO PRE-CONSTRUCTIONCONDITION UPON COMPLETION OF THE PROJECT.16.CONTRACTOR TO VERIFY INVERTS PRIOR TO INSTALLATION, AND SHALL NOTIFY ENGINEER OFANY DISCREPANCIES.17.INTERIOR PLUMBING SHALL BE COMPLETED IN ACCORDANCE WITH PLUMBING CODES,INCLUDING PRESSURE TESTING INTERIOR PIPING TO ENSURE WATERTIGHT CONDITIONS IN THEEVENT OF A SYSTEM SURCHARGE.18.BOBREK ENGINEERING & CONSTRUCTION HAS NOT PROVIDED AN INTERIOR PLUMBINGENGINEERING DESIGN AS PART OF THIS PROJECT.19.CONTRACTOR TO INSTALL RIGID INSULATION FOR ANY PIPING WITH LESS THAN 4' OF COVER20.CONTRACTOR TO INSTALL PIPE WITH MINIMUM PITCH ALLOWED, AND FIELD VERIFY ALLELEVATIONS. CONTACT ENGINEER IF ANY DISCREPANCIES ARE FOUND. DESIGN ISPERFORMANCE BASED, THEREFORE NO ELEVATIONS HAVE BEEN DESCRIBED.21.SURFACE MATERIALS TO BE REPLACED IN-KIND.DRAIN DAYLIGHT CONNECTION AT SIDEWALKEXAMPLE PHOTO FOR REFRENCE NOT TO SCALEPLANCONNECTIONDRAINAGEC-1001"=10'JANUARY 202220-010BTPEJR11/19/22CITYCOMMENTS2CITY4/4/22COMMENTS VideoCount CD Code Fr To RemarksImRefIn1%JntIn20.0 ST Start of Survey0.0 AMH Manhole DMH 1440.0 MWL Water Level 1021.3 CL Crack Longitudinal 1229.5 RPP Repair Patch 12 unknown substance34.6 RPP Repair Patch 11 brick and rock37.5 TB Tap Break-in 6.000 1039.5 CL Crack Longitudinal 1241.0 TB Tap Break-in 6.000 0242.6 CL Crack Longitudinal 1251.7 TB Tap Break-in 6.000 0152.8 S01 CL Crack Longitudinal 1272.6 F01 CL Crack Longitudinal 1274.6 TB Tap Break-in 6.000 1185.6 S02 CL Crack Longitudinal 12108.5 F02 CL Crack Longitudinal 12108.5 AMH Manhole DMH 167108.5 FH End of SurveyTotal Length Surveyed108.5 Ft Scores Pipe Ratings IndexPipe Ratings Index 1.70 PeakPeak 20 Mean PipeMean Pipe 0.20Pipe RatingPipe Rating 240Structural:O&M: 108.5 Date Cleaned P/O # Media No Date 2016/10/11 Setup 65 Surveyor ZC Drainage Street Derby St. Weather City Salem Flow control Location CatPurpose Use StormwaterShapeEgg ShapedMaterialConcrete Pipe (non-reinforced)Lining Total lengthHeight18Width12insJoint length Up DMH 144 Rim to invert FtDownDMH 167 Rim to invert FtDirectionDownPrecleanN Year rehabilitated Additional info Further location details StructuralMiscellaneous O & MHydraulic Constructional System Owner Year laid Tabular Report of PSR DMH 144 A NECEforCertificate #U-614-06021733 Time 10:06Survey Customer NECE Grade to invert Rim to gradeGrade to invert Rim to grade Length Surveyed 108.5 Pressure Northing Easting ElevationCoordinate System GPS Accuracy Project Pre Paving Project Work Order Ft Ft Ft PipeLogix Inc.Phone:866-299-3150Fax:760-406-6023