CORRESPONDENCE_1971-1981 - Laserfiche WebLink

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- 77 Jr ruary 7,. 1 Project 2 Recommendations 1 Require the site. operator to construct the impervious soil liner up the sides of the trench to seal off the permeable sand Tens exposed near the north end of the trench and any similar sands exposed elsewhere in the sides of the trench. 2. Since the in6place materials permeability is significantly higher than the 10 cm/sec. level required for a' Class: il-J site, require either placement of the impervious soil liner or a gravel drain, against the remaining sides of the trer►ch. . Assumiril that, a second trench will be excavated west of and parallel to the first, require monitoring wells to be located (a) at the north end of the existing trench* (b) at the northwest corner of the future trench, and (c) the west side of the midpoint of the future trench. The wells: should be drilled to a depth .of 60 feet and be` Constructed to intercept percolation from the bottom of the hole up to".within 20 feet or the surface. Upon receipt of these recommendations, Beta Aisociates drilled3-test honings at the locations shown on the attached Plate 1 , Site Sketch. Each well boring was logged to its total depth and a grounwater sample was collected ,and submitted for baseline chemical analysis as required by :monitor.t-ng and reporting program No. 73-183, attached to the Discharge Requirements. Legs of the well boriiog-and results of baseline chemical analysis are attacher. in the appendices to this letter. Each boring was completed as a rnoniioring well .in accordance with the specifications shown on Plate 2, Monitoring, Well l: Deta if, Plate 3, Trench Detail, dhows the FMC disposal trench in both plan view and cross section. 'rhe upper 2--feet of .the trench floor has been co,cipacted toachieve permeabilities less than 10-b miser_. CYavei drains with a depth of 2-feet have been installed along each trench wal:1 terminating in the sump at the low end of the trench. Compacted.>soil• liners have been placed adjacent to granular lenses which crop out on-the. north side of each trench wall . These soil liners consist of silty clay and have been compacted to 85% of their relgtive maximum density. This results in permeabiiities in the range of 10� cm/sec. (see soil test data in Appendix B of thls letter) . PROPOSED DISPOSAL OPERATION Portions of the waste stream to be handled at the Forward Site Consists of dry, solid wastes which are currently stored at .grcund surface at the FMC Plant. The remainder are suspected of t+,v�, g a variablt. moist,:re content and are currently contained in pond enclosures on the plant property. GBetac_ lssociates `x