The URL can be used to link to this page

Home My WebLink AboutVHB Sewer Capacity Report Engineers Scientists Planners Designers 99 High Street, 13th Floor, Boston, Massachusetts 02110 P 617.728.7777 F 617.728.7782 www.vhb.com To: Barnstable DPW Date: June 10, 2025 R1: June 19, 2025 Project #: 84033.25 From: Jon Moser, PE Richard P. Mathews Jr., PE Rick Dupuis, P.E. Rea Malik, E.I.T. Re: Hanover Hyannis II – Sewer Capacity Analysis In connection with the application to the Zoning Board for a special permit to develop a multi-family residential development along Wilkens Lane (Hanover Hyannis II), the Barnstable Department of Public Works (DPW) requested that the applicant determine whether the wastewater flows from the Hanover Hyannis II development exceed the existing capacity of the Independence Drive and Bearses Way sewer sheds, including a cursory review of the Bearses Way Pump Station. To aid the analysis, the DPW provided a SewerGEMS model (model), shape files (SHP), and excel spreadsheets with existing/ proposed sewer generation flows, for parcels located within the Independence Drive and Bearses Way sewer sheds, and the 2017 Flow Metering Report. On behalf of the applicant, New England Development (NED), VHB updated the DPW’s model to reflect the latest sewer generation flow for each existing parcel within the sewer sheds and the proposed sewer generation for Hanover Hyannis II. Updating this information allowed us to determine, based on the DPW’s model, if the proposed sewer generation flow from Hanover Hyannis II would exceed the existing capacity of the Independence Drive and Bearses Way sewer sheds, which both flow to the Bearses Way Pump Station. The sewer analysis summarized above and attached hereto as Exhibit A indicates that the proposed Hanover Hyannis II development falls within the existing sewer infrastructure capacity. Specifically, DPW’s model, with updated information, indicates that the pipe full capacity (%) for the sewer mains within Perseverance Way is 22.1%, the pipe full capacity for the sewer mains within Independence Drive is 25.2%, the pipe full capacity for the sewer mains within Enterprise Road is 48.8%, and the pipe full capacity for the main leading to Bearses Way Pump Station is 41.7%. Since each sewer main is below 50% in the updated model, the SewerGEMS model confirms that the main sanitary sewer pipe receiving flow from the proposed Hanover Hyannis II development has sufficient capacity to handle the additional peak flow. The sewer analysis also evaluated whether the existing Bearses Way Pump Station could handle the new flow generated by Hanover Hyannis II. The total peak flow to Bearses Way pump station from the updated SewerGEMS model, including the Hanover Hyannis II project, is 2,464,580 GPD, which converts to a flowrate of 1,712 gpm. The existing Bearses Way Pump Station pump flow rates, as observed in the 2017 Flow Monitoring Report, provided to VHB by Barnstable DPW, provide greater than 2,070 gpm pumping capacity. Therefore, the existing Beareses Way Pump Station can handle the new sewer generated by Hanover Hyannis II. Barnstable DPW Ref: 84033.25 June 19, 2025 Page 2 Engineers Scientists Planners Designers 99 High Street, 13th Floor, Boston, Massachusetts 02110 P 617.728.7777 F 617.728.7782 www.vhb.com EXHIBIT A • Sewer Analysis • Pump Station Analysis Barnstable DPW Ref: 84033.25 June 19, 2025 Page 3 Engineers Scientists Planners Designers 99 High Street, 13th Floor, Boston, Massachusetts 02110 P 617.728.7777 F 617.728.7782 www.vhb.com Sewer Analysis Existing sewer flow data was obtained from DPW shape files and adjusted using peak factors to generate a conservative estimated peak flow for each parcel within the Independence Drive and Bearses Way sewer shed. The Cape Cod 5 pump station flow, which flow s to the Bearses Way Pump Station, was included in the SewerGEMS model. Additionally, 500 gallons per day/ inch diameter/ mile for all gravity sewer pipes was incorporated into the model to account for standard infiltration and inflow (I/I) contributions. Existing sewer flow data, for parcels with a proposed use change or revised sewer flow, was obtained from DPW excel spreadsheets, adjusted using the applicable peak factors, and then inputted into the model to ensure that the sewer flow projections were conservative and reflective of a worst-case scenario. Peak sewer flows for the proposed Hanover Hyannis II development was provided by NED, based on bedroom count and Title V flow rates, which were incorporated into the model. The data was analyzed to confirm that the proposed developments do not overload the existing sewer infrastructure. Assumptions The following assumptions were made during the preliminary capacity analysis : › VHB created two scenarios “Existing System – PS to Outfall” and “Future System – PS to Outfall – Hanover Hyannis II” › Existing sewer generation flow data for each parcel within the sewer sheds was replaced with the latest sewer generation flow data provided by DPW. › As noted in the GHD SewerCAD Technical Memorandum, dated April 6, 2016, an infiltration and inflow (I/I) of 500 gallons per day/ inch diameter/ mile used for all gravity sewer pipe lengths was retained in the SewerGEMS model. › Title V sewer generation flows were multiplied by a peaking factor of 2.5. Title V sewer generation flows are designed for double average daily generation flows, so the 2.5 factor provides a 5 .0 peak factor. › Water usage flows were multiplied by a peaking factor of 4.5. Assuming 90 percent (0.9) of water usage becomes wastewater, multiplied with a peaking factor of 5.0, provides the 4.5 peak factor. › Sewer/ wastewater flows were multiplied by a peaking factor of 5.0. Sewer Flow Data Existing Sewer Flow from Water Usage Data › SHP files were provided by DPW containing water usage data in gallons per day (GPD) for parcels within the two sewer sheds. Using that data (noted as “WATER_USAGE_GPD_AMANDA” in the SHP file), the sewer flow inputted in the model was calculated as follows: • Parcels with water usage data available: water usage flow multiplied by a factor of 4.5 (0.9 x 5.0). • Parcels with no available data: assigned a sewer flow of 0. Barnstable DPW Ref: 84033.25 June 19, 2025 Page 4 Engineers Scientists Planners Designers 99 High Street, 13th Floor, Boston, Massachusetts 02110 P 617.728.7777 F 617.728.7782 www.vhb.com › DPW provided a steady state flow rate of 239,040 GPD for the Cape Cod 5 pump station which was inputted into the model manually. Existing Sewer Flow from Changes Data › Some parcels within the sewer sheds have experienced a change in sewer flow or have proposed sewer flow changes. Such parcels have been highlighted in the ‘SewerGEM figure – Sewer sheds, Sewer Flow Change’ PDF and associated updated flow data has been provided in the ‘Sewer Flow Changes 2019 to Present - 6-6-2025 to Client’ excel file, both provided by DPW. Depending on the type of flow data provided for each parcel, the sewer flow for such parcels were calculated as follows: • Parcels with water usage data: Water usage flow x 0.9 (90%) x 5.0 peaking factor. • Parcels with wastewater usage data: Sewer usage flow x 5.0 peaking factor. • Parcels with Title V sewer generation data: Title V sewer flow x 2.5 peaking factor. • Parcels with no available data: assigned a sewer flow of 0. • Parcels with data from both water usage and sewer flow changes used the more conservative flow. Proposed Data Calculation › NED provided a sewer peak flow of 127,875 GPD for the proposed Hanover Hyannis II project parcel which was inputted into the model manually. Flow to Pump Station Independence Drive › Flow into the pump station (PS) in the “Future System – Pump Loads” scenario: • Existing Sewer Flow from Water Usage Data = 128,936 GPD • Existing Sewer Flow with Sewer Changes = 332,636 GPD • Difference = 203,700 GPD increase Bearses Way › Flow into the pump station (PS) in the “Future System – Pump Loads” scenario: • Existing Sewer Flow from Water Usage Data = 2,113,480 GPD • Existing Sewer Flow with Sewer Changes = 2,336,705 GPD • Difference = 223,225 GPD increase Proposed Flow from Hanover Hyannis II development › Hanover Hyannis II • Title V flow = 51,150 GPD • Average daily flow = 25,575 GPD Barnstable DPW Ref: 84033.25 June 19, 2025 Page 5 Engineers Scientists Planners Designers 99 High Street, 13th Floor, Boston, Massachusetts 02110 P 617.728.7777 F 617.728.7782 www.vhb.com • Peak flow = 127,875 GPD › Total flow into the Bearses Way pump station (PS) in the “Future System – Pump Loads” scenario after the Hanover Hyannis II development = 2,464,580 GPD (increase of 127,875 GPD) Pump Station Analysis The total peak flow to Bearses Way Pump Station from the updated SewerGEMS model, including the Hanover Hyannis II project, is 2,464,580 GPD, which converts to a flowrate of 1,712 gpm. The existing Bearses Way Pump Station pump flow rates for the two pumps tested was greater than 690 gpm on the mag meter readings, as observed in The 2017 Flow Monitoring Report (Appendix C), provided to VHB by Barnstable DPW . Therefore, the three pumps at the Bearses Way Pumping Station should provide greater than 2,070 gmp pumping capacity, and can handle the new sewer generated by Hanover Hyannis II.