{"data":{"id":"us-va/12vac5-610-597","jurisdiction":"us-va","citation":"12VAC5-610-597","heading":"Fill systems","body":"A. Fill systems are systems where the infiltrative surface and some portion of the treatment medium is comprised of fill material and not a naturally occurring undisturbed soil. Fill systems may be located in-ground, shallow-placed, or above ground. Fill systems addressed in these regulations are the Wisconsin Mound system, the noncarbonaceous mountain colluvium system, and the sand-on-sand system.\n\nB. Elevated Sand Mounds. Septic tank effluent may be utilized with elevated sand mounds. Pretreatment shall be required when effluent strength exceeds residential strength wastewater and may be required where hydrologic conditions meet the minimum criteria contained in this chapter. For the purpose of siting an elevated sand mound, the criteria in Table 4.4 shall apply. For the purposes of establishing minimum setback distances between an elevated sand mound and various structures or topographic features, the mound shall be considered an absorption field and distances shown in Table 4.2 utilized.\n\nC. Sand-on-sand systems. Sand-on-sand is a process of modifying a soil absorption system site using fill material which is similar in texture to the original, naturally occurring material. Filling is accomplished in accordance with 12VAC5-610-965.\n\n1. Criteria for utilizing septic effluent. Septic tank effluent may be utilized with sand-on-sand systems. For the purpose of siting a sand-on-sand system, the criteria in Table 4.4 shall apply. Sand-on-sand systems may be utilized with septic tank effluent when the following criteria are met:\n\na. Soil texture. In order to assure effluent dispersal under adverse conditions, while maintaining adequate treatment capacity, shallow-placed systems are limited to Texture Group I and IIa soils. The use of Texture Group IIb, III and IV soils for sand-on-sand systems is prohibited.\n\nb. Soil structure. Sand-on-sand is restricted to soils classified as entisols (i.e., a young soil with no horizon development) and which have a texture of sand, loamy sand, coarse sandy loam, or sandy loam texture.\n\nc. Depth of soil. A minimum of 18 inches of naturally occurring undisturbed soil, measured from the ground surface, is required before encountering soils with bedrock, or a seasonal or permanent water table. Additionally, to assure adequate hydraulic dispersal capacity, no restrictive horizons may occur within 30 inches of the ground surface.\n\nd. Separation distances. Table 4.2 contains the minimum setback distances between an absorption field and various structures or topographic features.\n\ne. Estimated or measured infiltration rates. When siting a sand-on-sand system, the estimated or measured infiltration rate shall not exceed 30 minutes per inch within the sidewall area of the trench or within 18 inches of the infiltrative interface where effluent encounters undisturbed soil.\n\nf. Slope. Sand-on-sand is prohibited where the slope of the original site exceeds 5%.\n\n2. Criteria for utilizing secondary effluent.\n\na. Depth of soil. A minimum of 12 inches of soil, measured from the ground surface, is required before encountering bedrock, or a seasonal or permanent water table. Additionally, to assure adequate hydraulic dispersal capacity, no restrictive horizons may occur within 24 inches of the ground surface.\n\nb. Separation distances. Table 4.2 contains the minimum setback distances between an absorption field and various structures or topographic features.\n\nc. Estimated or measured infiltration rates. The estimated or measured infiltration rate shall not exceed 30 minutes per inch within the sidewall area of the trench, if any, or within 18 inches of the infiltrative interface where effluent encounters undisturbed soil.\n\nD. Fill systems in mountain colluvium. The criteria for conventional, in-ground trench systems contained in Table 4.3 shall be complied with to the greatest extent possible. However, fill material consisting of colluvial soil derived from sandstone (noncarbonaceous) in the mountainous area may be considered on a case-by-case basis for placement of subsurface soil absorption systems.\n\nTable 4.1.\n\nMinimum Separation Distances for Pretreatment Units, Conveyance Lines, and Header Lines.\n\nStructure or Topographic Features\n\nMinimum Horizontal Distance\n\nProperty Lines\n\n5\n\nBuilding Foundations\n\n10\n\nBasements\n\n20\n\nDrinking Water Wells (all classes)\n\n50\n\nCisterns Bottom Elevation Lower than Ground Surface in Area of Pretreatment Unit)\n\n100\n\nShellfish Waters\n\n70\n\nNatural Lakes \u0026 Impounded Waters and Streams\n\n50\n\nDeveloped Springs (when the spring is down slope)\n\n100\n\nDrainage Ditches:\n\nDitch Bottoms above Seasonal Water Table\n\n10\n\nDitch Bottom below Seasonal Water Table and Ditch Normally Contains Water\n\n50\n\nLateral Ground Water Movement Interceptor\n\n50\n\nLow Point of Sink Holes When Placed within the Bowl of the Sink Hole\n\n100\n\nUtility Lines\n\n10\n\nTable 4.2.\n\nMinimum Separation Distances.\n\nStructure or Topographic Features\n\nSoil Texture Group\n\nMinimum Distance (Ft) from Bottom or Sidewall of Subsurface Soil Absorption System Trench\n\nVertical\n\nHorizontal\n\nProperty Lines\n\nI, II, III, IV\n\n--\n\n5\n\nBuilding Foundations\n\nI, II, III, IV\n\n--\n\n10\n\nBasements\n\nI, II, III, IV\n\n--\n\n20\n\nDrinking Water Wells\n\nClass IIIA or IIIB\n\nI, II, III, IV\n\n--\n\n50\n\nClass IIIC or IV\n\nI, II, III, IV\n\n--\n\n100\n\nCisterns (Bottom Elevation Lower than Ground Surface in Area of Subsurface Soil Absorption System)\n\nI, II, III, IV\n\n--\n\n100\n\nShellfish Waters\n\nI, II, III, IV\n\n--\n\n70\n\nNatural Lakes \u0026 Impounded Waters\n\nI, II, III, IV\n\n--\n\n50\n\nStreams\n\nI, II, III, IV\n\n--\n\n50a\n\nDeveloped Springs (when the spring is down slope)\n\nI, II, III, IV\n\n--\n\n200e\n\nRock and Rock Outcropping\n\nI\n\n2\n\n2\n\nRock and Rock Outcropping\n\nII, III, IV\n\n1.5\n\n1.5\n\nPans and Impervious Strata\n\nI, II, III, IV\n\n1.5\n\n1.5\n\nDrainage Ditches:\n\nDitch Bottoms above Seasonal Water Table\n\nI, II, III, IV\n\n--\n\n10\n\nDitch Bottom below Seasonal Water Table and Ditch Normally Contains Water\n\nI\n\n--\n\n70a\n\nII\n\n--\n\n70a\n\nIII\n\n--\n\n50a\n\nIV\n\n--\n\n50a\n\nWater Table Depressor System\n\nI\n\n6b\n\n70\n\nII\n\n3b\n\n70\n\nIII\n\n2b\n\n50\n\nIV\n\n2\n\n50\n\nLateral Ground Water\n\nI\n\n--\n\n70c 10d\n\nMovement Interceptor\n\nII\n\n--\n\n70c 10d\n\nIII\n\n--\n\n50c 10d\n\nIV\n\n--\n\n50c 10d\n\nLow Point of Sink Holes When Placed within the Bowl of the Sink Hole\n\nI, II, III, IV\n\n--\n\n100\n\nUtility Lines\n\nI, II, III, IV\n\n--\n\n10\n\naThe set back distance may be reduced to 10 feet in Group III and IV soils and 20 feet in Group I and II soils if the subsurface soil absorption system is designed to produce unsaturated flow condition in the soil.\n\nbVertical Distance to the invert of the drain tile in the water table depressor system.\n\ncAbsorption trench up slope from interceptor.\n\ndAbsorption trench down slope from interceptor.\n\neArc of 180 degree up slope of spring and 100 ft. down slope.\n\nTable 4.3.\n\nSummary of Separation Distances between Systems Using Naturally Occurring Undisturbed Soils and Limiting Site Factors.\n\nSite Factor\n\nIn-Ground System1\n\nShallow-Placed System1\n\nSeptic Tank Effluent\n\nSecondary Effluent\n\nSeptic Tank Effluent\n\nSecondary Effluent\n\nBed Rock\n\n18\"\n\n12\"\n\nn/a\n\n18\"\n\nRestriction\n\n18\"\n\n12\"\n\nn/a\n\n18\"\n\nShrink-Swell Soil\n\n18\"\n\n12\"\n\nn/a\n\n18\"\n\nSlope\n\n50%\n\n50%\n\nn/a\n\n50%\n\nPerc Rate\n\n5-120 mpi\n\n5-120 mpi\n\nn/a\n\n5-45 mpi\n\nWater Table\n\n18\"\n\n12\"\n\nn/a\n\n12\"\n\n1The separation distances for in-ground and shallow-placed systems are measured from the trench bottom or other infiltrative interface vertically down to listed site factor.\n\nTable 4.4.\n\nSummary of Separation Distances between Fill Systems and Limiting Site Factors.\n\nElevated Sand Mound\n\nSand-on-Sand System2\n\nNoncarbonaceous Mountain Colluvium\n\nSite Factor\n\nSeptic Tank Effluent\n\nSecondary Effluent\n\nSeptic Tank Effluent\n\nSecondary Effluent\n\nSeptic Tank Effluent\n\nSecondary Effluent\n\nBed Rock\n\n24\"1\n\n24\"1\n\n60\"\n\n60\"\n\n18\"\n\n12\"\n\nRestriction\n\n24\"\n\n12\"\n\n30\"\n\n24\"\n\n18\"\n\n12\"\n\nShrink-Swell Soil\n\n24\"\n\n12\"\n\n40\"\n\n30\"\n\n18\"\n\n12\"\n\nSlope 25%\n\n25%\n\n25%\n\n5%\n\n5%\n\n50%\n\n50%\n\nPerc Rate\n\n5-120 mpi\n\n5-120 mpi\n\n5-30 mpi\n\n5-30 mpi\n\n5-120 mpi\n\n5-120 mpi\n\nWater Table\n\n24\"\n\n10\"\n\n18\"\n\n12\"\n\n18\"\n\n12\"\n\n124 inches refers to creviced bedrock. This distance may be reduced to 12 inches when noncreviced bedrock is encountered. See the Wisconsin Mound Soil Absorption System Siting, Design, and Construction Manual, January 1990.\n\n2The separation distance for sand-on-sand systems is measured from the ground surface vertically down to the listed site factor.","path":["Title 12. Health","Agency 5. Department of Health","Chapter 610. Sewage Handling and Disposal Regulations","Part IV. Site Limitations","Article 3. Systems Using Fill Material"],"source_url":"https://law.lis.virginia.gov/admincode/title12/agency5/chapter610/section597/","current_through":"2026 Regular Session (effective July 1, 2026)","vintage":"","retrieved_at":"2026-09-14T04:50:44Z","sha256":"e5e7f80dcfcbe3e64bc1b091515e903f972d6118f10a9573753cfd8358868471","source_id":"us-va-vac","stale":false,"prev":"us-va/12vac5-610-596","next":"us-va/12vac5-610-598"},"notice":"GroundRules: Original legal text. Not legal advice."}