8/17/2010 SEWER COMMISSION Minutes

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Now York Mate Department of Environmental Conservation aQ Wolf Road, Albany, New York 12233 Robert F. Flacke Commissioner July 20, 1982 To: Professional Engineers Practicing in New York State Subject: Technical Information Pamphlet No> 24 (Revised) Gravity Sewers Conveying Raw and Partially Treated Wastewater one result of the emphasis of. the Construction Grants Program on nonconven® tional sewage conveyance systems is the need for clarification of the New York State Department of Environmental Conservation (NYSDEC) gravity sewer policy, particularly regarding minimum size and slope. This revised TIP addresses the NYSDEC standards and design criteria for minimum sizing of gravity sewers con— veying raw wastewater and partially treated wastewater respectively. A. Minimum Sizing for Sewers Conveying Raw Wastewater The policy of the NYSDEC in regard to minimum diameter of gravity sewers has been to comply with the guidelines prescribed by the Recommended Standards for Sewage Works — 1978 Edition, officially New York's standards for municipal sewage works. These "Ten State Standards" stipulate that 11no gravity sewer conveying raw sewage shall be less than eight (8) inches (20 am) in diameter.11 This eight (8) inch minimum has been challenged at times on the basis that six (6) inch diameter sewers are capable of effectively transporting raw sewage and may be installed at lower capital costs. Inquiries made to the public and private sector by this Department have reLiforced the premise that although six (6) inch gravity sewer systems have proven successful in limited raw sewage application' an eight (8) inch sewer is less susceptible to clogging and other associated problems and, therefore, is the appropriate choice in most cases. A survey has shown that although six (6) inch sewer pipe sections are slightly less expensive than equal lengths of eight (8) inch pipe' installation costs are similar, and in some cases, may be more expensive for six (6) inch sewers because of required minimum slope. It is, therefore, the policy of the NYSDEC that in applications involving the conveyance of raw sewage, all municipal gravity sewage collection systems (as defined by 40 CFR 35.2005(8)) shall have a minimum diameter of eight (8) inches in accordance with the Recommended Standards for Sewage Works — 1978 Edition, _ unless extraordinary circumstances warrant the consideration of six (6) inch diameter sewers. This policy determination is separate from andin no way amends the Standards for Waste Treatment Works — "Institutional and Commercial Sewage Facilities" published by NYSDEC. Those standards address other than municipal collection systems.