N.H. Admin. Code § Env-Wq 704.11

Current through Register No. 50, December 12, 2024

Section Env-Wq 704.11 - Trench Construction

(a) Pipe trench bedding material for excavation below grade shall be screened gravel or crushed stone meeting the ASTM C33/C33M stone size No. 67 standard in effect when the stone is used, available as noted in Appendix D.

(b) Subject to (c), below, the pipe sand blanket material shall be graded sand free from organic materials, graded such that 100 percent passes a 1/2-inch sieve and a maximum of 15 percent passes a #200 sieve.

(c) In lieu of the sand blanket specified in (b), above, a stone envelope 6 inches thick completely around the pipe using 3/4-inch stone may be used.

(d) Pipe bedding material shall extend from a horizontal plane through the pipe axis to 6 inches below the bottom of the outside surface of the pipe.

(e) Pipe sand blanket material shall cover the pipe a minimum of 12 inches above the crown of the outside surface.

(f) Compaction shall be in 12-inch layers for bedding and blanket materials.

(g) Backfill material shall be compacted in no more than 3-foot thick layers to the ground surface except for road construction where the final 3 feet shall be compacted in no more than 12-inch thick layers to the road base surface.

(h) Trench backfill material in roadway locations shall be natural materials excavated from the trench during construction, excluding:

(1) Debris;

(2) Pieces of pavement;

(3) Organic matter;

(4) Top soil;

(5) Wet or soft muck;

(6) Peat or clay;

(7) Excavated ledge material;

(8) Rocks over 6 inches in the largest dimension; and

(9) Any material not approved by the engineer.

(i) Trench backfill at cross-country locations shall be as described in (h), above, except that top soil, loam, muck or peat may be used provided the completed construction will be stable, and provided that access to the sewer for maintenance and reconstruction is preserved.

(j) Backfill shall be mounded 6 inches above original ground at cross country locations.

(k) Base course for trench repair shall meet the requirements of Division 300 of the "Standard Specifications for Road and Bridge Construction" of the New Hampshire department of transportation as available at http://www.nh.gov/dot/org/projectdevelopment/highwaydesign/specifications/index.htm

(l) Where sheeting is placed alongside the pipe and extends below mid-diameter, the sheeting shall be cut off and left in place to an elevation not less than one foot above the top of the pipe and at least 3 feet below finished grade.

(m) Trenches for sewer pipes with slopes over 0.08 feet per foot, trenches for sewer pipes below seasonal high ground water level, and trenches for sewer pipes downstream of and within the hydraulic influence of waterways or wetlands shall have impervious trench dams constructed every 300 feet to prevent potential disturbance to pipe bedding and blanket materials.

(n) Precautions shall be taken to avoid groundwater pooling at the surface by providing drainage to a suitable outlet at catch basins or run-off swales.

(o) For trenches for sewer pipes in ledge, excavation shall extend to at least 12 inches below the bottom of the sewer pipe.

(p) All sewers shall be marked using metal-impregnated marking tape or tracer wire that can be located using metal detection equipment.

N.H. Admin. Code § Env-Wq 704.11

(See Revision Note at chapter heading for Env-Wq 700) #8590, eff 3-25-06

Amended byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.