4 Va. Admin. Code § 25-130-817.72

Current through Register Vol. 41, No. 6, November 4, 2024

Section 4VAC25-130-817.72 - Disposal of excess spoil; valley fills/head-of-hollow fills

Valley fills and head-of-hollow fills shall meet the requirements of 4VAC25-130-817.71 and the additional requirements of this section.

(a) Drainage control.

(1) The top surface of the completed fill shall be graded such that the final slope after settlement will be toward properly designed drainage channels. Uncontrolled surface drainage may not be directed over the outslope of the fill. The maximum slope of the top of the fill shall be 20h:1v (5.0%).

(2) Runoff from areas above the fill and runoff from the surface of the fill shall be diverted into stabilized diversion channels designed to meet the requirements of 4VAC25-130-817.43 and to safely pass the runoff from a 100-year, 6-hour precipitation event. The appropriate surface drainage system shall be installed prior to placement of excess spoil in the fill area. Temporary diversions may be approved by the division for use during fill construction provided that erosion is minimized and no threat to the public or the environment results.

(3)

(i) A subdrainage system, constructed in accordance with 4VAC25-130-817.71(f)(3), shall be installed along the natural drainage system, extending from the toe to the head of the fill. The division may approve a lesser distance provided the standards of 4VAC25-130-817.71(f)(3) are met. A system of lateral underdrains shall connect this core to each area of potential drainage or seepage in the disposal area.

(ii) A filter system to ensure the proper long-term functioning of the subdrainage system shall be designed and constructed using current, prudent engineering practices.

(iii) The minimum size of the main underdrain shall be:

	Total Amount of Fill Material		Predominant Type of Fill	Minimum Size of Drain, in Feet
	Width	Height
	Less than 1,000,000 Cubic Yards
		Do:	Sandstone	10	4
			Shale	16	8
	More than 1,000,000 Cubic Yards
		Do:	Sandstone	16	8
			Shale	16	16

(iv) No more than 10 percent of the rock used in the underdrains may be less than 12 inches in size and no single rock may be larger than 25 percent of the width of the drain.

(v) Alternatives to the minimum sizes may be approved by the division provided the alternative is shown to convey, using accepted engineering analyses, the maximum anticipated discharge, including an appropriate factor of safety.

(b) Rock-core chimney drains. A rock-core chimney drain may be used in a head-of-hollow fill, instead of the underdrain and surface diversion system normally required, as long as the fill is not located in an area containing intermittent or perennial streams. A rock-core chimney drain may be used in a valley fill if the fill does not exceed 250,000 cubic yards of material and upstream drainage is diverted around the fill. The alternative rock-core chimney drain system shall be incorporated into the design and construction of the fill as follows:

(1) The fill shall have, along the vertical projection of the main buried stream channel or rill, a vertical core of durable rock at least 16 feet thick which shall extend from the toe of the fill to the head of the fill, and from the base of the fill to the surface of the fill. A system of lateral rock underdrains shall connect this rock core to each area of potential drainage or seepage in the disposal area. The underdrain system and rock core shall be designed to carry the anticipated seepage of water due to rainfall away from the excess spoil fill and from seeps and springs in the foundation of the disposal area. Rocks used in the rock core and underdrains shall meet the requirements of 4VAC25-130-817.71(f).

(2) A filter system to ensure the proper long-term functioning of the rock core shall be designed and constructed using current, prudent engineering practices.

(3) Grading may drain surface water away from the outslope of the fill and toward the rock core. In no case, however, may intermittent or perennial streams be diverted into the rock core. The maximum slope of the top of the fill shall be 33h:1v (3.0%). A drainage pocket may be maintained at the head of the fill during and after construction, to intercept surface runoff and discharge the runoff through or over the rock drain, if stability of the fill is not impaired. In no case shall this pocket or sump have a potential capacity for impounding more than 10,000 cubic feet of water. Terraces on the fill shall be graded with a minimum 3.0% grade toward the fill and a minimum 1.0% slope toward the rock core.

4 Va. Admin. Code § 25-130-817.72

Derived from VR480-03-19 § 817.72, eff. December 15, 1981; amended, eff. June 28, 1982; October 28, 1982; December 14, 1982; October 11, 1983; December 27, 1983; May 8, 1984; June 22, 1984; August 2, 1984; October 16, 1985; January 7, 1987; July 22, 1987; November 25, 1987; October 12, 1988; December 26, 1990; July 1, 1991; July 17, 1991; November 20, 1991; July 7, 1992; May 5, 1993; October 19, 1994.

Statutory Authority

§§ 45.1-161.3 and 45.1-230 of the Code of Virginia.