OAR 340-050-0070: Best Management Practices for Site Selection and the Use and Application of Bulk Biosolids and Domestic Septage: Criteria for Site Selection and Approval

(1) Normally, tillable agricultural land is suitable for the land application of biosolids and domestic septage. (2) To be considered for biosolids or domestic septage land application, sites should meet all the following conditions: (a) Sites should be on a stable geologic formation not subject to flooding or excessive runoff from adjacent land. If periodic flooding cannot be avoided, the period of application should be restricted and soil incorporation is recommended. (b) At the time when liquid biosolids or domestic septage are applied, the minimum depth to permanent groundwater should be four feet and the minimum depth to temporary groundwater should be one foot. Sites approved for year-round application should be evaluated carefully to ensure that groundwater separation distances conform with these requirements. (c) Topography of the site should be suitable to allow normal agricultural operations. Where needed, runoff and erosion control measures should be constructed. In general, liquid biosolids or domestic septage should not be surface applied on bare soils where the ground slope exceeds 12 percent. Well-vegetated sites with slopes up to 30 percent may be used for dewatered or dried biosolids, or for liquid biosolids or domestic septage application with appropriate management to prevent runoff. (d) Soil should have a minimum rooting depth of 24 inches. The underlying substratum to at least 24 inches should not be rapidly draining so that leachate will not be short-circuited to groundwater. (e) Sites with saline and/or sodic soils should be avoided. (3) Discretion should be used in approving application of biosolids or domestic septage on land that is in close proximity to residential areas. (a) A buffer strip large enough to prevent nuisance odors or wind drift is needed. Size of the buffer strip will be determined by the Department on a case-by-case basis and depend upon the method of application used, total solids content, and proximity to sensitive areas, for example: (A) Direct injection: no limit required; (B) Truck spreading (liquid): 0 to 200 feet; (C) Spray irrigation: 50 to 500 feet; (D) Cake or dried solids: 0 to 50 feet. (b) Buffer strips should be provided along well traveled highways. The size of the buffer strip will vary with local conditions and should be left to the discretion of the Department field representative. (c) No bulk Class B biosolids or domestic septage should be spread at the site closer than 50 feet to any ditch, channel, pond or waterway or within 200 feet of a domestic water source or well.