.CCOM AECOM 300-300 Town Centre Boulevard 905 477 8400 tel Markham, ON, Canada L3R 5Z6 905 477 1456 fax www.aecom.com February 7, 2013 Ms. lsa James Planner Town of W hitchurch-stouffville 111 Sandiford Drive Stouffville, ON L4A OZ8 Dear Ms. James: Project No: 60272713 Regarding: Peer Review Preliminary Hydrogeological Investigation, Regulatory Requests, Site Plan Approval Comment Responses, and Response to Preliminary Geotechnical Investigation, 6233, 6441 & 6245 Main Street, Stouffville, Ontario, SPA 12.004 We are pleased to provide our peer review of the following reports: Technical Memorandum Preliminary Hydrogeological Investigation, Proposed Pace Redevelopment- Lloyd Street and Main Street, Stouffville, Ontario, prepared by Golder Associates Ltd., January 17, 2013; Response to comments on Lloyd Street- Pace Savings and Credit Union Limited, Site Plan Approval- 2nd Submission, 181 Project No. W06028.01 00 F2182, prepared by SCS Consulting Group Ltd., January 17, 2013; Response to Peer Review Comments of Preliminary Geotechnical Investigation Site Plan Application Pace Redevelopment, Stouffville, Ontario, prepared by Golder Associates Ltd., August 24, 2012; and Regulatory Requests for 6233, 6441 & 6245 Main Street, Stouffville, Ontario, prepared by Golder Associates Ltd., January 18, 2013. The means and methods of the site investigation and the corresponding data reduction were not reviewed. AECOM did not perform independent site investigations or testing. Preliminary Hydrogeological Investigation AECOM provides the following peer review of the Golder Associates Ltd. (Golder) Preliminary Hydrogeological Investigation Proposed Pace Redevelopment- Lloyd Street and Main Street, Stouffville, Ontario, prepared for Geranium Corporation, dated January 17, 2013. L_2013-02-07_Peer Review_60272713_T3. 0oc
Page 2 A.:COM February 7, 2013 It is understood that the proposed development will consist of a six storey building with two levels of underground parking for mixed commercial/residential use. The site is located at the southeast corner of Main Street and Lloyd Street in the Town of Stouffville. The objective of this exercise is to review the hydrogeological investigation prepared by Golder to verify the methods/calculations/recommendations adopted are in conformance with generally accepted hydrogeological standards and practice. It is our overall assessment that the report has adopted hydrogeological methodologies and approaches that follow the principles of generally accepted practice. Notwithstanding this, we have a few comments for your consideration as outlined below: 1. The number of groundwater monitoring wells (6), standpipe piezometers (2), and monitoring well nest (1 shallow well and 1 deep well) are considered to be sufficient to provide reasonable characterization of the hydrogeological conditions at the site. 2. The type of hydraulic testing conducted (i.e., single well response tests and a short term pumping test), as well as the duration of these tests (i.e., 4-hour pumping test) are considered to be sufficient to provide reasonable estimates of the hydraulic properties of the soils for the purposes of providing preliminary dewatering rate estimates. 3. The report would greatly benefit from the addition of a hydrostratigraphic crosssection, as well, but to a lesser extent, a potentiometric surface map showing groundwater flow direction and a figure showing the radius of water level drawdown related to the pumping test. 4. Inconsistencies in rounding or not rounding of calculated results were identified throughout the memorandum, but they do not affect the overall interpretation, results or conclusions presented. 5. Section 1.2 - Scope of Work a) We support the installation of three additional groundwater monitoring wells outside of the initial geotechnical drilling program for the specific purpose of hydraulic testing. 6. Section 2.1 - Estimates of Hydraulic Conductivity b) Measured and calculated hydraulic conductivity values seem reasonable for the soils present at the site. c) In our opinion, the Aquifer Anisotropy Ratio (Kz/Kr) used for single well response test analysis (Attachment B) should be 0.5 or less for the glacially deposited (glaciofluvial and/ or glaciolacustrine) fine and coarse-grained soils. However, this difference does not affect the overall interpretation, results or conclusions presented. 7. Section 2.2- Estimate of Transmissivity d) The transmissivity and corresponding hydraulic conductivity value presented for the coarse-grained soils seem reasonable for soils present at the site. The approach to calculate these values is consistent with standard hydrogeological practices. L_20 13 02~ 07_Peer Revlew_60272713_ T3.Coc
Page 3 A:'COM February 7, 2013 8. Section 3.0- Summary of Hydrogeological Conditions e) It is agreed that the interpreted vertical hydraulic gradient at the site is downwards, however it is important to note that a small upwards hydraulic gradient was observed between the shallow and deep wells at BH12-2 during the September 12, 2012 monitoring event. 9. Section 4.1 -Assumed Construction Dewatering Program f) The assumptions made regarding the potential method, depth and extent of dewatering are reasonable given the anticipated groundwater conditions and construction design. g) Based on the table in Section 4.1 it is unclear how the till soils above the silty sand to sand unit will be dewatered or if Golder simply considers the contribution from these soils to be negligible to the overall dewatering rate estimate due to their low hydraulic conductivity. 10. Section 4.2- Dewatering Zone of Influence h) The dewatering zone of influence presented for the silty sand to sand unit and the shallow zone, mainly fine-grained soils seem reasonable for type of soils present at the site. The approaches to calculate these values are consistent with standard hydrogeological practices and approximately match the pumping test results. 11. Section 4.3- Dewatering Rate Estimates i) The steady state groundwater flow rate estimates presented for depressurization of the confined silty sand to sand aquifer unit and the shallow fine grained soils seem reasonable given the hydrogeological conditions and proposed construction at the site. The approach to calculate these values is consistent with standard hydrogeological practices. j) The volume of overburden storage seems underestimated; particularly if the volume of water stored in the dewatering zone of influence is also taken into account (this condition seems likely given the assumption of non-watertight vertical soil support for the excavation -Section 4.1 ). k) We assume the total requested construction dewatering rate of 200m 3 /day is based on experience given the estimated rates for steady-stage flow, direct rainfall inputs and removal of overburden storage. I) It is agreed that a Category 3 PTTW submission is appropriate given the expected rate and duration of construction dewatering. A factor of safety or contingency dewatering rate higher than that predicted may be useful during formal PTTW submission to provide flexibility during construction. m) In our experience, the MOE generally does not issue PTTWs for passive water takings such as a sub-slab drainage system. However, this is considered on a case-by-case basis and should form part of the consultation with the MOE prior to PTTW submittal. 12. No guidance related to groundwater monitoring, mitigation, dewatering discharge, or contingency actions were provided in the Report. L_2013 02-07 _Peer Review_60272713_T3.0oc
Page 4.CCOM February 7, 2013 Response to Comments on Site Plan Approval AECOM has reviewed comment/response number P1.16 of the Response to comments on Lloyd Street- Pace Savings and Credit Union Limited, Site Plan Approval- 2"d Submission, 181 Project No. W06028.0100 F2182, prepared by SCS Consulting Group Ltd. (SCS), January 17,2013, and have the following comments: Construction dewatering will require a Category 3 PTTW, not a Category 1 PTTW as indicated in the response by SCS; The recommended construction dewatering flow rate was estimated by Golder to be 2.3 Lis or 200m 3 /day. The 1.7 Lis or about 150 m 3 /day, as indicated by SCS, refers to the volume of dewatering required to remove water from overburden storage; and The long term dewatering flow rate of 0.7 5 Lis or 65m 3 /day, is consistent with the steady-state dewatering flow rate estimated by Golder. No other comment/responses in the letter provided by SCS were reviewed by AECOM. Golder Peer Review Responses AECOM previously provided peer review comments on the Phase I Environmental Site Assessment 1 (AECOM letter dated July 16, 2012) and the Preliminary Geotechnicallnvestigation 2 (AECOM letter dated July 26, 2012). We reviewed our July 2012 comments with respect to the responses provided by Golders and have presented our responses below. Regulatory Requests -Phase I ESA Our July 2012 peer review of the Phase I ESA presented the following: Golders concluded that no issues of environmental concern were identified in association with the site. AECOM generally agrees though we recommend the following: follow-up should be conducted with the MOE, the Region and the Town to ensure that no potential environmental concerns were identified; and Any deleterious debris found on the site during demolition must be removed and disposed of properly. The January 18, 2013 Regulatory Request letter states that as of January 18, 2013, no response has been received from the MOE, the Town or the Region. When a response is received, Golder will forward them to the proponent with comments if the results alter the findings of the June 2012 Phase I ESA. AECOM is satisfied with this response. 1. Phase I Environmental Site Assessment, 6233, 6237, 6241 and 6245 Main Street, Stouffville, Ontario, dated June 2012 2. Preliminary Geotechnical Investigation, Site Plan Application Redevelopment Stouffville, Ontario, dated June 7, 2012 1.._2013 02-07 _Peer Revlew_60272713_T3.Doc
Page 5 A:'COM February 7, 2013 Preliminary Geotechnical Investigation Our July 2012 peer review of the Preliminary Geotechnical Investigation presented several items for clarification/additional comment. The responses provided by Golder in their August 24, 2012 letter have addressed these items to AECOM's satisfaction. Should you have any questions, please do not hesitate to contact the undersigned. Sincerely, AECOM Canada Ltd. Jason Cole, M.Sc., P.Geo. Hydrogeologist Jason. Cole@aecom. com Rob Frizzell, M.Sc., P.Geo. Senior Hydrogeologist Rob.Frizze/l@aecom. com Patty Wong, B.Sc., P.Geo Senior Geologist Patty. Wong@aecom.com L_2013 02 07_Peer Review_6027271 3_TJ_Ooc