3000 ROCKEFELLER AVE PARKING GARAGE 2018-01-02 MF Import

� ' S:i/;\NOhI �1��iLSQf•�!. I1�C. and operated to dcwater lhe ad��ance outwash as the cxcavation depth approaches the primary water-bcaring zone and thc piczometric surface in thc advance outwash. We completed a de�vutcring analysis for thc project bascd on the soil and groundwater conditions dcscribed in Section 9.0 and aquifcr parameters estimated from lhe slug tcsting (Scction G.0 and rlppendix D). Our analysis indicates that a dcep dewatering system consisting of 12 perimcter wells will �c required for initial dcpress��rization of thc advance outwash aquifer. Eight wells shouid be instalicd on approximately 50-foot centers along the western-most excavation edge and along half of the northern excavation edgc (westem hal�; two wells should bc inst�lled along thc south cdgc about 1 ZS to l50 fcct apart; and two wclis should bc installcd along the cast excavation edgc ncar thc north corncr, about SO to100 fcet apart. The wcll diameter should be G to S inches and thc maximum well dcpth will probably not cxcecd 100 fect. Thc rotal discharge from thc 12-wcll systcm will likcly be from ]00 to 250 gallons per minutc. Pollowing the initial depressurization, a secoud dewatcring system consisting of a vacuum cxtraction/wcll point systcm, installcd ,u an anglc into thc soil, �+�ould providc construction dewatering of the primary water-bearing unit (ad��ance ouhvash) as the excavation approaches the piczometric surface and thc top of thc aquifcr. Thc u�cll points should be: 1) operated while continuing the usc of die decp dcwatciing wcll systcm; 2) installcd Gom within the ercavation and around thc entire perimeter of thc cxcavation; and, 3) installed on approxim�tely 6- to 9-foot ccntcrs, altcmating �vith soil nail locations. Thc ��•cIl points ��ould bc installcd through and bchind thc cxisting soil nail ��all cscavation f:ice and angled dowmvard into thc aquifcr. Installation of the well point system should begin approximatcly 15 fect above thc bottom of the aquifcr. '1'he total discharge from thc ��acuum estractionhvcll point system will likely bc from I50 l0 200 gallons per minute. Additional lifts ancUor ��ell points may bc rcquired if signi(icant �+�atcr-bcaring •r.ones arc cncountcrcd bclow thc primary �eatcr-bcaring zonc. 10.12 Yolentially Contaminaled Ground«�ater Collection, Trcatment, ancl Uisposal In addition to contaminated soil, contaminatcd groundwatcr is present on site and will require action during conslruction. B:�scd on thc analytical test results, somc of this groundwatcr may not be suitablc for discharging direcUy into the se��cr and would thcreforc rcquirc isolation for trcatment ancllor disposal. The constn�ction ground��ater from the soil nail drainagc matcrial, dewateiin�, ��ells, ��cll points, and any swnps that may be used, would need to Ue collected, an:�l}'��d (testcd). possihly Ue:ued, and then dispused. If an:il1'sis indicates that the eround��ater .i. i.n��i. u.�ris �:i ,,�,�i�a 3I - I-0964d-005 l9