Lsas

01. Site Investigation. A site investigation conducted by a soil scientist or hydrogeologist determining whether the LSAS effluent will adversely impact the waters must be submitted to the Director for review and approval. (7-1-25) 02. Installation Permit Plans. Installation permit application plans for an LSAS submitted for approval must include provisions for inspection by the design engineer, designee, or Director of the work during construction. (7-1-25) 03. Module Size. The maximum size of any subsurface sewage disposal module must be ten thousand (10,000) gallons per day. Developments with greater than ten thousand (10,000) gallons per day flow must divide the system into absorption modules designed for ten thousand (10,000) gallons per day or less. (7-1-25) IDAHO ADMINISTRATIVE CODE IDAPA 58.01.03 – Individual/Subsurface Sewage Department of Environmental Quality Disposal & Cleaning of Septic Tanks Rules Section 013 Page 24 04. Standard LSAS Design Specifications. (7-1-25) a. All design elements and application rates must be developed using sound engineering practice and provided by a professional engineer licensed by the state of Idaho. (7-1-25) b. All design and installation requirements for standard systems apply to LSASs unless otherwise specified in this section. (7-1-25) c. Within thirty (30) days of completing system installation, the design engineer must provide either as-built plans or a certificate that the system was installed in substantial compliance with the installation permit application plans. (7-1-25) d. Effective soil depths, in feet, below the bottom of the absorption module to the site conditions must be equal to or greater than the following table: (7-1-25) e. The disposal area absorption module must be located so the separation distances provided in the following table, in feet, are maintained or exceeded: EFFECTIVE SOIL DEPTHS Limiting Layer Design Soil Group A B C Impermeable Layer 8 8 8 Fractured Bedrock or Extremely Permeable Material 12 8 6 Normal High Groundwater Level 12 8 6 Seasonal High Groundwater Level 2 2 2 TABLE -- SEPARATION DISTANCES Feature of Interest Design Soil Group A B C All Domestic Water Supplies Sewage Volume - 2,500-5,000 GPD 250 200 150 Sewage Volume - 5,000-10,000 GPD 300 250 200 Property Lines Sewage Volume - 2,500-5,000 GPD 50 50 50 Sewage Volume - 5,000-10,000 GPD 75 75 75 Building Foundations - Basements Sewage Volume - 2,500-5,000 GPD 50 50 50 Sewage Volume - 5,000-10,000 GPD 75 75 75 Downslope Cut or Scarp Impermeable Layer - Below Base 100 50 50 IDAHO ADMINISTRATIVE CODE IDAPA 58.01.03 – Individual/Subsurface Sewage Department of Environmental Quality Disposal & Cleaning of Septic Tanks Rules Section 013 Page 25 (7-1-25) f. No LSAS may be installed above a downslope scarp or cut unless approved by the Director. (7-1-25) g. A minimum of two (2) disposal systems must be installed, each sized to accept the daily design flow, and a replacement area equal to the size of one (1) disposal system must be reserved. (7-1-25) h. The vertical and horizontal hydraulic limits of the receiving soils must be established and flows must not exceed such limits to avoid hydraulically overloading any absorption module and replacement area. (7-1-25) i. The distribution system must be pressurized with a duplex dosing system. (3-31-22) j. An effluent filter between an extended treatment system or lagoon system and the large soil absorption area must be installed. (7-1-25) k. Observation pipes must be installed to the bottom of the aggregate throughout the drainfield. (7-1-25) l. The drainfield disposal area must be constructed to allow for surface drainage and to prevent erosion. (7-1-25) 05. Monitoring and Reporting. Before an installation permit is issued, the Director will approve a monitoring and reporting plan that contains the following minimum criteria. (7-1-25) a. Monthly recording and inspection for ponding in all observation pipes. (3-31-22) b. Monthly recording of influent flows based on lapse time meter or event meter of the dosing system. (7-1-25) c. Monthly recording of groundwater elevation measurements at all monitoring wells if high seasonal groundwater is within fifteen (15) feet of the ground surface. (3-31-22) d. Semi-annual groundwater monitoring at all monitoring wells. (3-31-22) e. An annual “LSAS” report including operation, maintenance, and monthly and annual monitoring data, must be filed with the Director no later than January 31 of each year for the last twelve (12) month period. (7-1-25) 06. Operation and Maintenance. Before an installation permit is issued, an operation and maintenance plan must be approved by the Director and contain the following minimum criteria: (7-1-25) a. Annual or more frequent rotation of the disposal systems, and whenever ponding is noted. (3-31-22) b. A detailed operation and maintenance manual, fully describing and locating all elements of the system and outlining maintenance procedures needed for operation of the system and who is responsible for system maintenance, must be submitted to the Director before system use. (7-1-25) Separation Distance - Between Modules 12 12 12 TABLE -- SEPARATION DISTANCES Feature of Interest Design Soil Group A B C IDAHO ADMINISTRATIVE CODE IDAPA 58.01.03 – Individual/Subsurface Sewage Department of Environmental Quality Disposal & Cleaning of Septic Tanks Rules Section 050 Page 26 c. A maintenance entity must be specified to provide continued operation and maintenance according to the operator requirements in IDAPA 58.01.16, Wastewater Rules, and approved by the Director before issuance of an installation permit. The entity may assume the responsibilities of a service provider if a service provider is required. (7-1-25) 014. -- 049. (RESERVED)