Laserfiche WebLink
Mr. Bruce A. McNabb <br /> March 23 , 1994 <br /> Page 2 <br /> sketches would require the City to purchase an additional 75 tons <br /> of bentonite at a cost of $16,260. 00. This additional purchase <br /> increases the project cost by $14,896.60 (difference between the <br /> two bidders) . <br /> The intent of the plans and specifications for the seepage <br /> cutoff trench as designed is to install/construct the thin extruded <br /> plastic membrane sheeting flush with the vertical land-side wall of <br /> a narrow (6-in. max) , 5-ft deep trench, and backfill the trench on <br /> the water-side of the sheeting with an impervious (dry) mixture of <br /> bentonite and sand densified in place by vibration. Soil borings <br /> made along the alignment showed firm to stiff homogeneous clayey <br /> silts and silty clays which could be excavated with relatively <br /> smooth side walls by a conventional trenching machine; little or no <br /> sloughing of sidewalls is expected because of the firm to stiff <br /> soil consistency and low water table within the earth embankment. <br /> The alternate detail for the seepage cutoff trench as present- <br /> ed by Mid-States General & Mechanical Contracting Corp. is unac- <br /> ceptable primarily because it does not provide for firm backing/ <br /> support of the plastic membrane on the land-side face of the trench <br /> excavation during its installation, and the possibility that voids <br /> could be formed and/or incorporated behind the landside face of the <br /> membrane because of uneven sidewall excavation and/or poor back- <br /> filling techniques. <br /> Other objections to the detail are that the membrane does not <br /> extend to the full 5-ft depth, the soil cover to be placed over the <br /> sand-bentonite backfill increases from 1 cu.ft. to 4 cu. ft. on both <br /> sides of the bulkhead because of the wider excavation at the top of <br /> the trench, as well as the large increase in excavation and back- <br /> fill quantities. <br /> In view of these circumstances and the necessity of expediting <br /> this project, we recommend that a contract be awarded to Fisher- <br /> Stoune, Inc. in the amount of $126,773.50. <br /> Very truly yours, <br /> Bainbridge, Gee, Milanski & Assoc. , Inc. <br /> By: �lJ�JZ,.,. ,V .�'✓�t�Q.Gi�,.�.a._.� <br /> Edwin V. Milanski <br /> EVM/ts <br /> cc: Michael E. Kazunas <br /> Jim Mayhugh <br /> Van Silver <br />