§ 73.52. Standard trenches.
(a) Design. The maximum slope of the undisturbed soil of a proposed absorption area where a trench system may be permitted is 25%. For slopes between 15% and 25%, detailed design in relationship to elevation shall be provided. The designer shall inspect the installation and verify that, to the best of his knowledge and belief, the system was installed in accordance with the plans and specifications. Copies of the plans and specifications and the designer’s report are to be attached to the applicant’s copy, sewage enforcement officer’s copy and the Department’s copy of the application for sewage permit.
(b) Construction. Trenches in an absorption area shall be constructed in accordance with the following:
(1) There shall be a minimum of two trenches per field.
(2) Trenches shall follow approximately the ground surface contours so that variations in trench depth shall be minimized.
(3) There shall be at least 6 feet of soil between the treatment tank or dosing tank and the nearest trench.
(4) The width of the bottom of the individual trench shall be 12 to 72 inches.
(5) The depth to the bottom of the absorption area shall be 12 to 36 inches.
(6) The bottom of the absorption area shall be level to a tolerance of 2 inches per 100 feet.
(7) The minimum width of undisturbed earth between trenches shall be 5 feet. When elevated sand mound trenches are used, the distance between trenches shall be measured from the toe of the sand of each trench.
(8) The minimum depth of aggregate material under laterals shall be 6 inches.
(9) Laterals shall be placed in the center of the trench. The first or last discharge hole of a lateral may be no more than 5 feet nor less than 2 feet from the ends of the trench.
(10) Laterals shall be level to a maximum tolerance of 4 inches of fall per 100 feet toward the terminal end of the lateral.
(11) The minimum depth of aggregate material over the laterals shall be 2 inches.
(12) The depth of aggregate shall be uniform throughout the absorption area.
(13) The top of the aggregate material shall be covered with geotextile fabric, untreated building paper or a 2-inch layer of hay, straw or similar material to prevent backfill material from settling into the aggregate.
(14) The minimum depth of earth cover over the aggregate in all installations shall be 12 inches. Where the top of the aggregate is less than 12 inches from the undisturbed soil surface, the soil cover shall extend beyond the absorption area by at least 3 feet on all sides.
(15) The backfill material shall consist of soil suitable for the growth of vegetation, and be seeded to control erosion.
(16) Trench laterals shall be fitted with end caps.
Authority The provisions of this § 73.52 amended under section 9 of the Pennsylvania Sewage Facilities Act (35 P. S. § 750.9); The Clean Streams Law (35 P. S. § § 691.1—691.1001); and section 1920-A of The Administrative Code of 1929 (71 P. S. § 510-20).
Source The provisions of this § 73.52 adopted August 2, 1971, effective August 14, 1971, 1 Pa.B. 1649; amended April 26, 1974, effective May 13, 1974, 4 Pa.B. 817; amended August 30, 1974, effective September 16, 1974, 4 Pa.B. 1805; amended January 21, 1983, effective January 22, 1983, 13 Pa.B. 508; amended November 7, 1997, effective November 8, 1997, 27 Pa.B. 5877. Immediately preceding text appears at serial pages (217332) to (217334).
Cross References This section cited in 25 Pa. Code § 71.63 (relating to retaining tanks); 25 Pa. Code § 73.44 (relating to pressurized distribution design); 25 Pa. Code § 73.53 (relating to seepage beds); 25 Pa. Code § 73.54 (relating to subsurface sand filter beds and trenches); and 25 Pa. Code § 73.55 (relating to elevated sand mounds).
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