Wastewater Treatment Capacity Analysis of the Ballenger-McKinney Wastewater Service Area of Frederick County, Maryland Updated

Transcription

1 Wastewater Treatment Capacity Analysis of the Ballenger-McKinney Wastewater Service Area of Frederick County, Maryland Updated prepared by: Michael Siegel,, on behalf of: Friends of Frederick County July 19, 2012, updated, September 24, 2012

2 Wastewater Treatment Capacity Analysis of the Ballenger-McKinney Wastewater Service Area of Frederick County, Maryland prepared by: Michael Siegel July 16, 2012, updated, September 24, 2012 Foreword This Analysis estimates build-out wastewater flows in the Ballenger-McKinney service area associated with Frederick County s Comprehensive Plan and potential revisions thereto. It then relates the build-out flows to the capacity of the wastewater treatment plants (WWTP) in the service area. As demonstrated herein, build-out wastewater flows far exceed existing and anticipated WWTP capacity in the Ballenger-McKinney service area. The Frederick County Division of Utilities and Solid Waste Management (DUSWM) prepared a build-out analysis of the Ballenger-McKinney service area in late 2011 as part of the County s Water 1 and Sewer Plan. DUSWM determined build-out flows in the service area to be mgd which is virtually identical with this updated Analysis, and within about 9 percent as it initially estimated. DUSWM s build-out flows exceed current wastewater capacity in the service area by 27 percent as shown in Figure 1, below. This figure does not include flows from yet additional acreage under consideration by the County to be designated for intensive development. When these flows are included, build-out flows exceed capacity by between 31 to 52 percent. The County s November, 2011 Water and Sewerage Plan confirms that a build-out approach applied herein is the correct approach and that this Analysis applies reasonable methods. DUSWM s August 27, 2012 Memo to the Board of County Commissioners ( DUSWM s Memo, or the Memo ) omits mention of its earlier build-out analysis, likely because its earlier analysis is incompatible with the contents of the Memo. Instead, the Memo confusedly compares a linear extrapolation of demand for a specific point in time (2030) with a build-out analysis. But a linear extrapolation is not a build-out analysis and cannot substitute for such. In contrast to DUSWM s linear extrapolation, a build-out analysis is concerned with the quantity of flows attributable to a specific increment of development, irrespective of time. DUSWM s linear 1 Frederick County Water and Sewer Plan, November, 2011, Wastewater Treatment Demand by Regional Service Area, Chapter 4, Table 4.03, p Page -1-

3 extrapolation does not assess build-out wastewater flows associated with the County Comprehensive Plan and potential revisions thereto. Accordingly, DUSWM s linear extrapolation has little applicability to a build-out analysis. As to the Memo s objection to the wastewater flow rates applied in this Analysis, this update demonstrates that significantly lower flow rates do not affect the conclusion that build-out wastewater flows in the Ballenger-McKinney service area far exceed existing and anticipated WWTP capacity in the service area. DUSWM s Memo is mistaken in its claims with respect to the flow rates applied in this Analysis: lacking data for Frederick County this Analysis uses WSSC commercial and industrial acreage flow rates as a benchmark for Frederick County. DUSWM s Memo fails to notice that WSSC s AWF rates were factored downward to account for its objections (they are factored further downward in this update, see Appendix A), the Memo mistakenly claims WSSC s average wastewater flow (AWF) rates applied include design and/or safety factors in excess of actual flows. Design and safety factors are specifically excluded from WSSC s AWF rates as is evident from the source document. 2 AWF constitutes influent to a WWTP. It is the appropriate figure to use for a build-out analysis; and, with respect to residential flows, this Analysis applies an overall rate of about 230 gpd for new housing units which is close to that of a townhouse unit. Together with inflow and infiltration (I/I), the 230 gpd figure compares favorably to the average 70 gpd per capita of indoor water use documented by WSSC for its service area. Use of a lower figure as DUSWM s Memo suggests is inappropriate. This update reflects adjustments for conservation, and for per acre wastewater flows from new commercial and industrial acreage. To account for conservation, this update factors build-out wastewater flows downward by 5 percent. The update also reflects additional information pertaining to the status of the City/County wastewater flow agreement. Further investigation shows that service area build-out flows exceed WWTP capacity due, in part, to over-designation of new acreage for industrial use. Land use data for 2002 and 2010 from the Maryland Department of Planning (MDP) show that for each newly developed acre of commercial land in Frederick County, one acre of new industrial land was also developed. 3 2 WSSC s AWF rates include only base wastewater flows (BWF, which is indoor water use returned to the sewer system) and I/I, as per WSSC Design Guidelines, Appendix C-6. 3 Maryland Department of Planning, Frederick County Land Use Change, 2002 to Page -2-

4 Within the Ballenger-McKinney service area, for each new acre of land designated for commercial development, three acres are designated for new industrial development (including the City of Frederick). Including the Eastalco site, this figure doubles such that nearly 6 acres is designated for new industrial use for each acre designated for new commercial uses. Background Frederick County, Maryland is located within the Washington/Baltimore region. Interstate-270 joins the County with and its suburban environs, and I-70 joins it with points north and with Baltimore and its environs to the east. Between 2000 and 2010, the County s population grew from 195,277 (see, to 233,285 (Census) for an average annual population growth rate of 1.95 percent. Despite the onset of a national recession and regional slow-down, and a decline in total jobs between 2005 and 2010, the rate of job growth in Frederick County has outpaced its rate of population growth over the 2000 to 2010 period. During the 2000 to 2010 period, the number of at-place jobs (full and part-time jobs located within the County) increased from 103,859 to 129,184 (US BEA) for an average annual increase of 2.44 percent. Accordingly, the ratio of at-place jobs to the County s resident population grew from.532 to.554 from 2000 to These data are reflective of the County s continuing and growing status as an employment center. Substantial additional growth is anticipated in the County over the next few decades. The County s 2010 Comprehensive Plan projects a 2030 population of 331,700 which represents an increase of 42.1 percent over the 2010 population of 233,385 (Census) for an average annual population growth rate of just over 2 percent. 4 The large majority of new housing and job growth in the County is planned to be concentrated in its southern tier. Growth in the southern tier will occur largely within the service areas of the City of Frederick s Gas House Pike wastewater treatment plant (WWTP) and the County s newly expanded and enhanced Ballenger-McKinney WWTP that is currently under construction. The current average capacity of these two WWTP s are 8.0 and 15.0 million gallons per day (mgd), respectively (NPDES, with the latter increasing to18 mgd with the planned Potomac River outfall). The City of Frederick currently has an allotted capacity in the Ballenger-McKinney WWTP of about mgd per its Flow Allocation Agreement with the County. Both the Gas House Pike and 4 The County forecasts employment to grow from 142,412 in 2010 to 167,257 in This figure appears to represent at-place employment. 5 Third Amendment to Flow Allocation Agreement, July 23, This agreement might be revised to allow for a greater capacity allocation to the City. Any such revision would not Page -3-

5 Ballenger-McKinney WWTP s currently discharge treated wastewater into the Monocacy River subject to the limits of their respective NPDES permits. The Ballenger-McKinney WWTP is anticipated to have a future capacity of 18.0 mgd upon securing of permits and completion of the Potomac River outfall that would allow for diversion of discharge above 15 mgd to the Potomac River. Long-term plans show that 100 percent of the discharge from the Ballenger-McKinney WWTP could be diverted to the Potomac outfall ( Build-out Wastewater Flows, Water and Sewerage Plan, Frederick County, MD, Approved Plan, November, 2011, p. 4-4) with anticipated average day build-out effluent of 24.1 mgd a potential discharge to the Potomac of 26.7 mgd (including flows from the City s WWTP and excluding any treated wastewater re-use potential at the Eastalco industrial site). 6 Summary Existing and planned development in the Gas House Pike and Ballenger-McKinney service area per the County s 2010 Comprehensive Plan and subsequent approved development requests greatly exceeds the current, and planned capacity and previously modeled build-out flows of these two WWTP s. As shown in Figure 1, existing and planned residential and commercial/industrial development in the Gas House Pike and Ballenger-McKinney WWTP service area exceeds existing and planned treatment capacity by between about 9 and 12 mgd (with conservation). These amounts include additional land in the service area being considered for intensive development beyond that included in the 2010 Comprehensive Plan. The lower figure reflects capacity of 18 mgd at Ballenger- McKinney WWTP. The higher figure reflects capacity of 15 mgd at the Ballenger-McKinney WWTP. Accordingly, build-out wastewater flows in the service area exceed existing and anticipated WWTP capacity by about 35 to 53 percent. affect total capacity within the service area. 6 Further examination of the County s 2011 Water and Sewerage Plan indicates its modeled flows of 26 mgd (see Figure 1, p. 4-4) likely assume closure of the City of Frederick s WWTP. The Plan states it includes flows that may be tributary to the B-McK WWTP. The City s WWTP has since been upgraded and is likely to continue operating at its currently permitted capacity for the foreseeable future. Page -4-

6 Figure 1. WWTP Capacity and Build-out Demand Analysis, Summary Table. 15 mgd 18 mgd DUSWM, 15 mgd WWTP Capacity Gas House Pike and Ballenger-McKinney Build-out Demand Existing Demand Comprehensive Plan, New Residential Commercial Industrial Subtotal, Existing plus 2010 Comp Plan Post-2010 Approved Development Requests, New Residential Commercial Industrial Infill and Public/Institutional Demand, before Conservation Demand, adjusted for Conservation ? Over/(Under) Existing Capacity Percent over/(under) capacity 52.7% 35.1% 26.7% Source: PEFA; Frederick County, November, Note: It is unknown if DUSWM s build-out demand includes conservation. Abbreviations: mgd = millions of gallons per day. B-McKinney = Ballenger-McKinney WWTP. Existing Demand Existing demand at the City s Gas House Pike and the County s Ballenger Mc-Kinney WWTP averages 6.47 and 5.82 mgd, respectively, for a total CY 2011 service area demand of 12.3 mgd. These figures reflect methods recommended in Guidance Document for Wastewater Capacity Management Plans (MDE, 2006). Consistent with this document, existing demand for the Gas House Pike WWTP represents the most recent 3-calender year average, and the most recent calender Page -5-

7 year for the Ballenger-McKinney WWTP. Both figures represent WWTP effluent as reported by their respective operators based on daily plant logs and monitoring reports current through mid As shown in Figure 2, flows from three other existing WWTP s are to be diverted to the expanded Ballenger-McKinney WWTP. These consist of the New Market and Monrovia WWTP s with average flows of.094 and.090 mgd, respectively, and leachate flows from the County landfill that average.144 mgd for a total of.33 mgd ( Operation of Wastewater Treatment Plans and Their Collection Systems, Frederick County, effluent, CY 2011). 7 As also shown in Figure 2, average existing wastewater demand in the Gas House Pike and Ballenger-McKinney WWTP service area amounts to mgd. Less current WWTP capacity, these WWTP s have sufficient available capacity to accommodate new wastewater flows of mgd, or mgd considering the 3.0 mgd capacity to be added at Ballenger-McKinney by construction of the planned Potomac outfall. Figure 2. Average Existing WWTP Capacity and Demand. Gas House Pike and Ballenger-McKinney Service Area Amount (mgd) Source Document Treatment Capacity Gas House Pike 8.00 NPDES Ballenger-McKinney NPDES Total, Existing Capacity Existing Demand (effluent) Gas House Pike WWTP 6.47 Operator, 3-yr avg. Ballenger-McKinney WWTP 5.82 Operator, CY 2011 New Market WWTP 0.09 Frederick County, 2011 Monrovia WWTP 0.09 Frederick County, 2011 County Landfill Leachate WWTP 0.14 Frederick County, 2011 Total, Existing Demand Net Capacity, 15 mgd Net Capacity, 18 mgd Source: PEFA. 7 See: 20Their%20Collection%20Syste_2.PDF Page -6-

8 Future WWTP Demand Upon decommissioning of the Monrovia, New Market, and County landfill WWTP s, no other public WWTP s are planned within these service areas. The County anticipates all new wastewater flows within the Ballenger-McKinney service area (excepting the Eastalco site) and some additional flows from the City of Frederick to be directed to the Ballenger-McKinney WWTP. Once the City s Gas House Pike WWTP reaches capacity, the City would direct excess flows to the Ballenger- McKinney WWTP up to its capacity allotment in the facility. New Wastewater Flows per the 2010 Comprehensive Plan The Ballenger-McKinney service area, as described in the Frederick County Comprehensive Plan of 2010, includes: 1) portions of the City of Frederick not served by the City s Gas House Pike WWTP, 2) designated growth areas contiguous with the City of Frederick, 3) unincorporated areas of Ballenger Creek 4) areas of the County SE of the City of Frederick 5) Spring Ridge/Bartonsville 6) Town of New Market and CGA 7) Lake Linganore 8) Town of Urbana and CGA 9) Libertytown 10) Walkersville The County s 2010 Water Resources Element (WRE, p. 35) provides an inventory of new residential units within the Ballenger-McKinney and Gas House Pike WWTP service areas. These units are distinguished between those with zoning (referred to as pipeline ) and areas with residential land use designation (referred to as undeveloped potential units ). The sum of the pipeline and undeveloped potential units are designated in the WRE as Total Potential Dwelling Units [new]. Together, total zoned and land use designated dwelling units in the Gas House Pike and Ballenger- McKinney service area per the 2010 Comprehensive Plan amount to 23,095 units. Of these, 9,405 are associated with the City of Frederick and 13,690 are elsewhere within the Ballenger-McKinney WWTP service area. For purposes of this analysis, dwelling units associated with the City of Frederick per the 2010 Comprehensive Plan are assigned an average flow of 225 gpd to account for likely higher densities attributable to multi-family (condo or apartment) units. Likewise, the County s 2010 Comprehensive Plan dwelling units are assigned an average flow of 225 gpd to also account for multi-family units. Post-2010 dwelling units per recent approved development requests are assigned an average flow of 250 gpd, consistent with the R-1 to R-5 residential densities assigned in the staff report and MDE guidance. Crum/Thatcher residential flows are estimated based on the proposed number of SFD, Page -7-

9 SFA and MF units at 250, 225, and 175 gpd, respectively. Accordingly, the average flows associated with new dwelling units in the Gas House Pike and Ballenger-McKinney WWTP service areas per the 2010 Comprehensive Plan amount to 5.20 mgd. Wastewater flows from new commercial and industrial (C/I) acreage per the 2010 Comprehensive Plan are estimated based upon C/I acreage identified in the County s 2010 Comprehensive Plan as undeveloped. A total of 755 acres (2010 Comprehensive Plan, pp to ) are designated as commercial or mixed use. Included in the 755 acres are 547 acres designated in previous County plans as industrial/employment that were annexed into the City in the two years preceding adoption of the 2010 Comprehensive Plan (2010 Comprehensive Plan, p ). The annexed acreage is assigned to the commercial category for purposes of this analysis as its zoning is unknown at this time. However, were the annexed acreage to have retained industrial zoning, associated wastewater flows would be substantially greater. The total 755 commercial acres are assigned a developed average wastewater flow of 2,850 gpd per acre, inclusive of base flows and I/I (inflow and infiltration). Industrial acreage associated with the 2010 Comprehensive Plan is estimated based on a developed average flow of 4,350 gpd per acre, inclusive of base flows and I/I. The foregoing acreage flow rates are conservatively based upon those of commercial and industrial acreage documented by the Washington Suburban Sanitary Commission (WSSC) for Montgomery and Prince George s counties, and are adjusted downward for Frederick County (see Appendix A). 8 Based on the foregoing, average wastewater flows in the Ballenger-McKinney and Gas House Pike wastewater service areas associated with undeveloped commercial acreage per the 2010 Comprehensive Plan amount to 2.18 mgd, and industrial flows amount to 9.80 mgd for a combined C/I flow of mgd. Combining new residential, commercial, and industrial (C/I) average wastewater flows associated with the 2010 Comprehensive Plan yields planned average flows of mgd shown in Figure 3. 8 Note, WSSC flow rates are factored down for applicability to Frederick County. Per WSSC s design manual, its average wastewater flows (AWF) used as a benchmark for this Analysis include only base wastewater flows plus inflow and infiltration. AWF does not include other flows attributable to pipeline or pump design or safety factors. See: Page -8-

10 Figure 3. Planned WWTP Build-out Flows per the 2010 Comprehensive Plan. Units/Acres Amount (mgd) Source Document Residential (units) County 13, WRE, 2010, p. 35. City 9, WRE, 2010, p. 35. Sub-total, Residential 5.20 Commercial/Industrial (acres) Commercial (City and County) Comp Plan, pp to Industrial (County) 2, Comp Plan, pp to Sub-total, C/I Public/Institutional, Infill 0.13 Total, Residential and C/I Source: PEFA. Post-2010 Approved Development Requests WWTP Flows Subsequent to adoption of the 2010 Comprehensive Plan, the County has approved development requests that would increase the number of potential new dwelling units and C/I acreage. Increases associated with these approved development requests are accounted for in a County Development Division staff report, 2011 Comprehensive Plan and Zoning Review, Approved Requests Analysis (May 12, 2012, revised July 3, 2012). 9 The staff report applies somewhat more consolidated regions/subareas than the 2010 Comprehensive Plan. Those areas in the staff report listed below are essentially consistent with those in the 2010 Comprehensive Plan that lie within the Gas House Pike and the Ballenger-McKinney wastewater service areas. 1) Frederick 2) New Market 3) Urbana 4) Walkersville 5) Adamstown 9 See: _ pdf Page -9-

11 With respect to Adamstown, future industrial uses and wastewater flows associated with redevelopment and re-use of the Eastalco site are assumed to be treated on-site and to not generate additional flows to the Ballenger-McKinney WWTP. Otherwise, only 10 acres of land designated for commercial use in the Adamstown area is included in this analysis. The staff report identifies a total of 12,416 new planned dwelling units over and above those included in the 2010 Comprehensive Plan in the Ballenger-McKinney service area. Wastewater flows associated with these units amount to an average of 3.10 mgd at 250 gpd per unit. The staff report identifies a total of 318 acres planned for commercial development above that included in the 2010 Comprehensive Plan in the Ballenger-McKinney service area. The associated average wastewater flow upon development of this acreage amounts to 0.91 mgd. The staff report identifies a total of 494 acres for industrial development above that included in the 2010 Comprehensive Plan in the Ballenger-McKinney service area, and exclusive of 2,048 acres at the Eastalco site. Flows from the Eastalco site are assumed to be treated on-site. With zero Eastalco flows to the Ballenger-McKinney WWTP there would be additional average industrial flows of 2.15 mgd above that included in the 2010 Comprehensive Plan from within the WWTP s service area. A recent proposed annexation by the City of Frederick of the proposed Crum/Thatcher developments could generate average additional residential flows of.28 mgd and commercial flows of.32 mgd. 10 A change in the restriction of Lansdale residential units to non-age restricted increases its average flows by about.08 mgd. Post-2010 flows from approved development requests and other minor sources amount to an average of 7.05 mgd as shown in Figure and 0.8 million square feet office (msf) from Thatcher and Crum, respectively, 0.31 msf of retail from Crum, per their annexation files.. Page -10-

12 Figure 4. Post-2010 Planned WWTP Flows. Residential (units) Units/Acres Amount (mgd) Source Document City, Crum/Thatcher 1, Annexation materials. County, approved development requests 12, County staff report, Approved Requests Analysis, 7/3/12. County, Lansdale age- to non agerestricted 1, Developer submission. Commercial/Industrial (acres) Residential, Sub-total 14, Commercial County staff report. Industrial County staff report. Crum/Thatcher, Office not avail Annexation materials, WSSC. Crum/Thatcher, Retail not avail Annexation materials, WSSC. C/I Subtotal (ex. Eastalco) Public/Institutional, Infill 0.21 Consultant estimate. Total (ex. Eastalco) 7.05 Source: PEFA. Notes: 1) Crum/Thatcher office flows estimated on 1.8 msf developed space at.133 average gpd per WSSC office, non-cbd/transit usage. 2) Crum/Thatcher retail flows estimated on 0.31 msf developed space at.247 average gpd per WSSC shopping centers usage. 3) Source documents are unclear if Crum/Thatcher units/acreage is included in 2010 Comprehensive Plan. They are assumed to not be for purposes of this analysis. Were they to be included in the 2010 Comprehensive Plan, wastewater flows would be modestly less than shown. 4) Estimated future flows do not include flows from un-used multi-year tap allocation agreements, emergency or public health requirements, or additional septage. A few other comparatively minor sources of wastewater flows to the Gas House or Ballenger- McKinney WWTP s exist. Residential and commercial infill could add another.11 mgd or so of wastewater flows. A modest rate of conversion of primarily residential and some C/I properties served by on-site septic systems could add another.11 or so mgd. Additional public/institutional flows (schools, hospitals, public buildings, parks and recreation, and colleges/universities) associated with the 2010 Comprehensive Plan and subsequent approved development requests would add another.21 mgd. Page -11-

13 Conclusion Build-out wastewater flows associated with existing and planned development in the Ballenger- McKinney and Gas House Pike wastewater service areas as per the 2010 Comprehensive Plan and subsequent approved development requests far exceed the current and planned capacity of these two facilities. Excepting the potential for on-site treatment of Eastalco flows (which are not included in the foregoing) no other facilities are planned to provide wastewater treatment in this area. As demonstrated herein, wastewater flows from existing development, the 2010 Comprehensive Plan, and approved development requests subsequent thereto, would generate an average of mgd to the Ballenger-McKinney WWTP (35.13 mgd total flow with conservation per Figure 1, less 8.0 mgd Gas House Pike WWTP capacity per Figure 2 = mgd). Accordingly, existing and planned build-out flows to the Ballenger-McKinney WWTP far exceed its anticipated expansion to 18 mgd. Page -12-

14 Publications and Documents 1. Guidance Document, Wastewater Capacity Management Plans, 2006, Maryland Department of the Environment. 2. Sewer Design Guidelines, Appendix C, WSSC Design Criteria for Sewer Systems, Frederick County, Water and Sewerage Plan, Chapter 4, November, Frederick County s Future, Many Places - One Community, A Comprehensive Plan for Frederick County Maryland, April, Water Resources Element, Frederick County, Maryland; A Functional Element of the 2010 County Comprehensive Plan, Adopted September 23, Operation of Wastewater Treatment Plants and their Collection Systems, Frederick County, Comprehensive Plan and Zoning Review Approved Requests Analysis, Frederick County Community Development Division, May 16, 2012, revised July 3, NPDES for City of Frederick Gas House Pike WWTP 9. NPDES for Frederick County Ballenger-McKinney WWTP. Page -13-

15 About the Author Mr. Michael Siegel has thirty-five years of experience in the areas of community development, public, and environmental finance and public utilities, economic, and fiscal impact analysis. He is the founder of (PEFA). His areas of expertise include utility tariffs, demand forecasting, economic and fiscal impact analysis, and project feasibility. Clients include state and local governments, federal agencies, utilities, economic development authorities, NGO s, and land-owners. He has prepared several economic and fiscal impact studies, including the first econometric-based local fiscal impact model in the U.S. He prepared an analysis of reversion of the City of Bedford to a Town on the Town and Bedford County. More recently, he prepared a fiscal analysis of the proposed annexation of areas of Washington County, Virginia by the City of Abingdon. Other projects include the feasibility and fiscal impact of re-use of the former NSA Vint Hills station in Fauquier County, and the re-use potential of the former RACER/GM plant in Spotsylvania County. Mr. Siegel s utility regulation experience includes development of rate-setting software and training regimens for the U.S. EPA. More recently, he prepared the rate case for the Dhaka Electric Supply Corporation (DESCO) on behalf of the Bangladesh Energy Regulatory Commission. He has also analyzed the economic and fiscal impact of wind-power facilities in Virginia s Highland County. For the District of Columbia, he prepared an analysis of non-public special education residential providers for the District s State Education Office (now OSSE); provided expert testimony to Council on the revenue package for the District s $2.0 billion schools modernization legislation; and, served as an appointed Commissioner to the District s Public Education Finance Reform Commission. In the 1980's, Mr. Siegel prepared the economic and fiscal impact analyses of the U.S. Air Force s Peacekeeper Missile in Wyoming and Nebraska. Subsequently, he assisted with economic and fiscal impact analysis of the U.S. Navy s CVBG Homeport Everett in Washington State. While heading the Maryland Office of Commercial Revitalization and Maryland Main Street program, he developed and implemented the State s targeted revitalization loan program. Thereafter, he joined the Government Finance Officer s Association (GFOA) Research Center as Assistant Director where he headed the organization s environmental and fiscal planning group. Other projects include economic and fiscal analysis and development of econometric and allocation-based models for the U.S. Virgin Islands, Shelby County Tennessee, the Minnesota Department of Agriculture, Lancaster/Lincoln, NE; and, the impact of casinos in Vicksburg, MS and proposed casinos in Gettysburg, PA. Page -14-

16 Appendix A. Montgomery and Prince George s Average Wastewater Flow Rates (AWF). Average Wastewater Flows GPD per Acre, WSSC Montgomery Prince George s Original Analysis Updated Analysis Commercial 3,500 2,850 Office, high density 10,800 10,800 Office, moderate density 2,880 - Local, existing - 2,880 Convenience 2,880 - General 9,216 9,216 Ancillary* - 2,080 Community - 2,880 Highway 10,080 - Highway, existing - 2,880 Office Park 2,880 - Transition 2,880 - Miscellaneous* - 4,200 Shopping Center - 6,048 Industrial 5,300 4,350 Light 2,880 11,520 Heavy 5,760 5,760 Industrial Park 5,760 5,760 Low - 5,760 Source: PEFA, Washington Suburban Sanitary Commission (WSSC), Sewer Design Guidelines, Appendix C, Notes: 1) a) Base Sanitary Flow (BSF). Flow that is expected to be returned by the customer to the wastewater collection system. b) Average Wastewater Flow (AWF). Base sanitary flow plus an allowance for infiltration and inflow, WSSC Design Critera for Sewer Systems, Tables 19d and 19e (bold added). 2) * Ancillary amount reported by WSSC likely represents a typo in the source document and should be 2,880. Reported amount is shown. Miscellaneous amount is the correct amount for AWF which was reversed with BWF in the source document (by definition, AWF is greater than BWF). Page -15-