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� <br /> � <br /> h1r. Ken Pruett <br /> � Octobcr 27, 2004 <br /> • It is imperati�c that fill placed for pond grading ar�d northern berm construction bz statically compacted <br /> � with the drum roller (vibration tumed of�. This is because vibrations from a vibrarory drum roller could <br /> ' adversely itnpact the water main in Uie benn. Static rolline will require several more passes ���ith the ? <br /> rolledcompactor than usual for fill conswction in order to achiece the recommended soil compaction. <br /> j These issues shou;d be discussed with the eanlnvork conVacror during the proiecYs pre-construction <br /> mezting. <br /> � • The analysis incorporated a uniform construction traffic surcharge �•alue of 2�0 psf imposed at the top of <br /> { the benn. Ne recotnmend ti�at we reaiew planned equipment loads on die benn in order to assess <br /> " potential geotechnical impacts to the benn during constniction. <br /> � • \Vith the exception of die liner material, we recommend that fill used ro construc[ the noahern pond <br /> slopc, and to raise grades at thc base of the pond, consist of clean pit run (gravelly sand �vith less than <br /> three percent by weight of fines). This material �vill be more suitable to compact using static roller <br /> � equipment. <br /> a <br /> • The topographic site plan indicates portions of the south benn slope adjacent to the spilh�ay are inclined <br /> at L7:1, with the remaining soutli Uerm slopc areas inclined at 2:1 or flatter. In order to stabilize the <br /> ` south benn slope, �ve recommend tillin� the steep portions with 4- to 1?-inch rock to establish a 2:1 <br /> � slope. The analysis indicates that, for both tlie "pond emptd' and "pond full and lined" r+ses, flattening <br /> the south slope in d�is manner incrcases the safety factor under both static and seismic lo�ding conditions <br /> � to acceptablc levels. <br /> ' • Because the facility will be ueed for storm�vater containment �cith controlled release, it is not likcly that <br /> the maximum �vater level wuui•1 rem�in at the de;ign eleeation long enou�h to decelop a free water <br /> � (phrcatic) surface tliroush the emUankment. 1-Iowe�er, in accordance �vith DSO requirements, our <br /> stability analysis included such a case, and yielded an unaccentabh� lo�c satety factor for that condition. <br /> �Ye reconunend lining the pond, in order to mititate the possible adverse effects of the development of a <br /> phrcatic �urface dirou�_h the emUankment. The lincr ma�� consist of a soil liner, pro�'id�:d it is constnicted <br /> �cith a minimum thickne,s of 13 inches, and consists of inorganic soil that contains no less than 30 <br /> percent by weight of fines (sift and clay-size particles passing the No. ?00 sieve). \Ve recommend <br /> eoinpac[ing the soil liner to a minimum of 9� percent of[lie soil's maximum dry density as determined by <br /> \STn1 Test Desienaticm D-693 (Standard Proctor). You ma}� also consider use of a flexiUle memUrane <br /> liner (HDPE or PVC); ho�a�ever, adherence of a topsoil l,ryer on thc liner surface ���ill be difficult unless <br /> thc liner is texwred, ur geo-cells d�signed tu rctain thc topsoil are used in conjunction�vith the PD[L. <br /> • The stability analysis indicntes no reduction in safety factor for the southem slope for the post- <br /> construction pond-full condition, pro��ided tl�e liner is in place. <br /> • Soils used in the conswction of the north slope of the berm, as �cell as those expuscd by pond <br /> excavation, will Ue subjcct to erosion. To ;uard against deterioration of the side slupe, by erosion, the <br /> slope,hould be appropriat�ly ��e�_etated or covered ��ith other ph}sical protectire barriers. <br /> AllDITION:�L SGR�'ICGS <br /> �! 7'erra Associates, [nc. should revie��� the tinal desien and speciCic�tions in order to ��erift� that earth�+�urk <br /> recommendations have Ueen propedy interpreted and incorporated into project design. \Ve should also provide <br /> geotechnical services during construction in order to obsen e complianc� �aith thc design concepts, specifications, <br /> and recommendations. This ���ill also allow for design ch.m;es if subsurface conditions differ from those <br /> anticipatcd prior to the start of construction. <br /> Project No. T-»69 <br /> P1gC No. i , <br /> � ;.'L^ <br /> � � <br />