Section 15.228 - Placement and Accessibility of Septic Tank(1) Septic tanks shall be installed level and true to grade on a level stable base that has been mechanically compacted and on to which six inches of crushed stone has been placed to minimize uneven settling. If the septic tank is placed in fill, proper compaction is required to ensure stability and to prevent settling. Septic tanks shall have a minimum cover of nine inches. Systems buried greater than nine inches below grade must be equipped with risers on all tank top openings and the distribution box.(2) At least three manholes with readily removable impermeable covers of durable material shall be provided. The manholes over the inlet and outlet tees shall have a minimum opening of 20 inches and the center manhole shall have a minimum opening of eight inches. By July 1, 2007, manufacturers of fiberglass and polyethylene tanks shall comply with the center hole requirement. Access ports shall be placed at the center and over each inlet and outlet tee. For compartmental tanks, the center manhole shall be placed as access to the compartment connection. Inlet and outlet tees shall be made accessible for inspection and maintenance by providing precast concrete or equivalent watertight risers (with steps where appropriate) with covers over the access ports to within six inches of finish grade for system designs in excess of 1,000 gpd. For system designs of 1,000 gpd or less, at least one access port shall be accessible within six inches of final grade. Manholes brought to final grade shall be secured to prevent unauthorized access.(3) Septic tanks shall be accessible for inspection and maintenance. No structures shall be located directly upon or above the septic tank access locations which interfere with performance, access, inspection, pumping, or repair.(4) Septic tanks shall be inspected and maintained in accordance with 310 CMR 15.300 and applicable local requirements.