HYDROGEOLOGICAL STUDY for CONSTRUCTION DEWATERING Proposed 12-Storey Apartment Building 115 & 117 Erb St. East, Waterloo, Ontario

Transcription

1 HYDROGEOLOGICAL STUDY for CONSTRUCTION DEWATERING Proposed 12-Storey Apartment Building 115 & 117 Erb St. East, Waterloo, Ontario SUBMITTED TO: Mr. Lee Kieswetter 3150 Boomer Line Heidleberg, ON N0B 1YO FILE NO / H17069 / August

2 August 29, 2017 FILE NO.: H17069 Mr. Lee Kieswetter 3150 Boomer Line Heidleberg, ON N0B 1YO Dear Mr. Kieswetter: RE: HYDROGEOLOGICAL STUDY for CONSTRUCTION DEWATERING Proposed 12-Storey Apartment Building 115 & 117 Erb St. East, Waterloo, Ontario This report is a scoped hydrogeological study specifically addressing the requirements of the Region of Waterloo in respect to construction dewatering for a proposed twelve-storey apartment building at 115 & 117 Erb St. East in Waterloo and in relation to the Region s nearby William Street Pumping Wells. If you have any questions or concerns regarding the report, please contact the undersigned at your convenience. Yours truly, CHUNG & VANDER DOELEN ENGINEERING LTD. William (Sandy) Anderson, M.Sc., P.Eng. Senior Hydrogeologist and Engineer

3 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page i TABLE OF CONTENTS 1.0 INTRODUCTION BACKGROUND INFORMATION SITE SETTING TOPOGRAPHY & DRAINAGE REGIONAL HYDROGEOLOGY & SOURCE WATER PROTECTION SITE HYDROGEOLOGIC SETTING Geology Hydrogeology CONSTRUCTION DEWATERING IMPACT EVALUATION OF PROPOSED DEWATERING REFERENCES... 7 LIST OF FIGURES Figure 1 Site & William Street Wellfield Locations App A Figure 2 Hydrogeologic Cross-Section A-A at William Street Wellfield App A APPENDICES Appendix A Appendix B Appendix C Figures Borehole Logs Dewatering Model Results

4 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page INTRODUCTION This report presents a scoped Hydrogeological Study for a proposed twelve-storey apartment building at a 0.29-hectare property at 115 & 117 Erb Street East in Waterloo (Figure 1). The Study specifically addresses the Region of Waterloo requirements in respect to construction dewatering, particularly in relation to the potential for impact to the Region s nearby William Street Pumping Wells. CVD discussed with Region of Waterloo Source Water Protection staff to confirm an appropriate scope of work for the Study. While the dewatering assessment provided in this report generally addresses the requirements of the Ministry of Environment and Climate Change (MOECC) for a Category 3 Permit To Take Water (PTTW), confirmatory hydraulic testing of the aquifer with monitoring wells is recommended prior to submission of a PTTW application. The proposed twelve-storey apartment will include two levels of underground parking and the structure is expected to be founded on some combination of spread footings (for a six-storey portion of the building) and a centralized raft slab foundation (for the higher twelve-storey portion). Much of the parking structure will be located below the water table and the owner plans to incorporate a water-tight design to eliminate the need for permanent dewatering. Nevertheless, construction will require that the water table beneath the Site be temporarily dewatered during an approximately six to eight-month period. 2.0 BACKGROUND INFORMATION Background information utilized in completing this Study are cited in Section 6.0 and include: published government geological maps. regional-scale hydrogeological studies commissioned by the Region of Waterloo. a 2006 hydrogeological study for construction dewatering of the nearby Bauer Lofts development property. A geotechnical investigation (CVD, 2010) and a Phase 1 Environmental Site Assessment (ESA) (CVD, 2012) have been completed to support the proposed development project. The subject property is currently the site of two residences and is surrounded by residential and/or institutional land uses. No actual or potential sources of contamination, either on or adjacent to the property, were identified by the 2012 Phase 1 ESA. The geotechnical investigation included the drilling of 5 boreholes on December 16 to 17, 2009, with boreholes depths ranging from 7.3 to 12.7 m. Borehole logs and a map showing the locations are provided in Appendix B. Geodetic elevations have been established for the boreholes using a geodetic benchmark and the ground and bottom elevations have been added to the logs in Appendix B.

5 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page SITE SETTING 3.1 TOPOGRAPHY & DRAINAGE The property is relatively flat with a topographic fall of about m (+/-) from about masl near the residences off Erb Street to about masl in the southern half of the property. The northern half of the property is mostly impervious to low-permeability surfaces, including the houses, driveways and a packed-gravel parking area. The southern half of the property is grassed. Drainage at the property is expected to follow topography toward the lower southern area and then toward the surrounding storm sewer systems on the municipal roads and adjacent private parking lots. Ultimately, all drainage in the area is directed to the north-flowing Laurel Creek, located about 250 m (+/-) west of the property (Figure 1). 3.2 REGIONAL HYDROGEOLOGY & SOURCE WATER PROTECTION The property is located on the eastern flank of the Waterloo Moraine (P. F. Karrow, 1993), within an area underlain by a poorly to well sorted ice-contact sand deposit and commonly interlayered with clayey to sandy silt till deposits. The hydrogeology of the Moraine has been characterized in considerable detail through studies commissioned by the Region over the past 25 years. The Moraine and areas flanking it contain a multilayered aquifer-aquitard complex ranging in thickness up to 130 m. Three overburden aquifers, a bedrock aquifer and four overburden aquitards have been identified by various Region studies, although it is noted that one or more of these aquifers/aquitards may be absent at any given location. Figure 2 is a cross-section showing the hydrogeological setting at the nearby William Street Well Field, located about 550 m southwest of the subject property (Figure 1). Total overburden thickness in the area is on the order of m. The three overburden wells operated by the Region (W1B, W1C and W2) are within Regional Aquifer 2 (Figure 2). William Street Well W3 is located in Regional Aquifer 4, the bedrock aquifer. The unconfined Regional Aquifer 1 and the Regional Aquitards 2, 3 and 4 have also been identified at the William St. Well Field. Regional Aquifer 1 is the water table aquifer and is not used for water supply in the area. The Source Water Protection initiatives in the Region of Waterloo (GRCA, November 2015) have established four Well Head Protection Areas (A,B,C & D), WHPA-A for the immediate 100-m zone around each municipal well and WHPA-B to D based on groundwater times of travel to each well (or well field) of 2, 5 and 25-years, respectively. In addition, relative groundwater vulnerability to contamination scores (on an increasing scale from 1 to 10) have been established for all lands within the WHPAs around each well. The subject property is in the WHPA-D around the William Street Well Field and has been assigned a vulnerability score of 2. This means that groundwater beneath the property (at an unspecified depth) can be expected to travel to the Wells in just over years and there is a modest vulnerability of the groundwater in the area being contaminated based on hydrogeological considerations.

6 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page SITE HYDROGEOLOGIC SETTING Geology The Site borehole data indicate an interlayered sequence of geological deposits beneath the property; mostly find to medium sands deposits and typically capped by interlayers of silt and/or clayey silt till. The lateral continuity of the till interlayers is poor; not being encountered at all at BH2 and BH4, being about 3-m thick in the upper 5 to 6 m at BH1 and BH5 and then considerably thicker (8-m) at BH Hydrogeology Although monitoring wells were not installed in the site boreholes to confirm the water table depths/elevations, the soil-water content measurements and water level observations at the time of drilling (particularly in BH2, BH4 and BH5) indicate the water table is on the order of 1 to 2 meters below grade and found at elevations on the order of about 320 to 321 masl, depending on typical seasonal fluctuations. Based on the soil descriptions, the hydraulic conductivity of the upper saturated fine to medium sand deposit is expected to be on the order of 10-5 to 10-4 m/s (Based on Freeze and Cherry, 1979). Based on the elevation of the water table upper, it is expected that the upper interlayered sand aquifer encountered beneath the property correlates with Regional Aquifer 1 as shown near surface at the William Street Wellfield (Figure 2). The saturated thickness of Aquifer 1 in this area is estimated to be in the 10 to 15 m range based on the data presented in Figure CONSTRUCTION DEWATERING The design plan for the second-floor underground parking level (i.e. P3 ) would have elevations in the range of to masl (see Appendix A). This is approximately 3 to 4.5 m below the estimated high water table of 321 masl. The design will incorporate water-tight construction so that there will be no need for permanent dewatering. The geotechnical engineer for the project (CVD) has estimated that the maximum excavation elevation will be masl (+/-) for a proposed foundation (i.e. 1.5 m lower than lowest basement floor elevation). To construct the foundation, the water table will need to be lowered to approximately 0.5 m below the excavation (i.e., to masl), for a total water table lowering of 6.4 m in the deepest part of the foundation. To estimate the dewatering rate, the Large Diameter Well Approximation model developed by Powers (1992 and 2007) has been used to model the unconfined water source. For this model, the 2700 m 2 rectangular dewatering area has been represented by an equivalent circular area with a 29.3-m radius. The flow to this area is modeled as flow to a single large-diameter excavation using established analytical solutions for flow to a well. With this method, the radius of influence is first calculated using the following form of the Cooper-Jacob Equation (Powers, 2007) that utilizes an aquifer storage

7 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page 4 coefficient that is reflective of unconfined conditions (i.e., specific yield for the upper fine sand/silt). Then, using the calculated radius, the pumping rate is calculated using a form of Thiem Equilibrium Equation (Powers, 2007) for an unconfined aquifer. R = r + Square Root (Tt / (CS) where R = radius of influence due to pumping [m] T = aquifer transmissivity [m 2 /s] S = aquifer specific yield [unitless] r = radius of well [m] t = time since pumping started [min] C = an empirical constant to reflect the parameter units = 135 (from Powers) Q = k (H 2 h 2 ) / ( ln (R/r)) UNCONFINED where Q = groundwater inflow rate to the well [L/min], k = aquifer hydraulic conductivity [L/s] T = aquifer transmissivity [m 2 /s] H = pre-dewatering aquifer thickness (or thickness beyond R) [m] h = stabilized aquifer thickness at the well [m] r = radius of the well [m] R = radius of influence [m] For the model calculations, an unconfined aquifer thickness of 10 to 15 m and a hydraulic conductivity of 1x10-5 to 5x10-4 m/s were used, per the hydrogeological interpretations in Section Specific yield for the unconfined sand aquifer was set at a maximum of 0.3, which is reasonable for complete pore water drainage over a lengthy dewatering period. Model scenarios were completed for a short 1-week start-up scenario and up to 8 months pumping duration. These time variations are a good way to evaluate the expected decline in pumping rates over the required dewatering period, with the 1-week pumping being a typical short period for requiring a relatively quick water table lowering to allow soil excavation to commence, while the 4-week to 8- month durations reflect the reduced rates that can be expected with time of pumping. The results of the modelled dewatering are provided in Appendix C. The worst-case calculated pumping rate (2493 L/min) is for a 1-week duration and with the higher estimates of hydraulic conductivity and aquifer thickness. As expected, the model predicts that the pumping rate will decline significantly with duration for the remainder of the dewatering (i.e., depending on the precise aquifer parameters that influence pumping). The worst-case radius of influence for the equilibrated (long term) pumping is calculated by the model to be about 400 m, as measured from the centre of the Site. This theoretical worst-case zone of influence is unlikely to result in any significant water table drawdown at the William Street Well Field, given the 550-m distance to the Wellfield and since recharge from precipitation over the course of the

8 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page 5 dewatering will undoubtedly truncate the zone of influence. It is important to recognize that the model results are approximations based on the best available data and the assumptions/limitations inherent in the theoretical model itself (flat water table, uniform and isotropic aquifer parameters, aquifer thickness, etc.). In addition, the model does not account for additional water from direct rainfall in the excavation, delayed aquifer yield from the dewatered zone, and recharge from rainfall infiltration or possible recharge boundaries. To account for uncertainty in the aquifer parameters / model as well as additional water not included in the model, a factor of safety of 1.5 to 2 on the calculated pumping rate would normally be warranted. A more precise estimate of the dewatering rate and safety factor can be refined at the time permit application with in-situ hydraulic testing of monitoring wells. 5.0 IMPACT EVALUATION OF PROPOSED DEWATERING Region guidelines in respect to both construction dewatering and re-development proposals require an evaluation of the potential for water quality and quantity impacts to both Source Water and nearby Well Fields. In addition, MOECC applications for Permit To Take Water (PTTW) also require that the potential risk to existing water users and the natural functions of the ecosystem be evaluated. The overall purpose of this hydrogeological study is to evaluate whether the development proposal and the proposed dewatering are likely to result in unacceptable impacts and the level of detail provided in this study is commensurate with the limited level of risk posed. This is detailed in the following paragraphs. Well Interference With the William Street Aquifer 2 wells being about 550 m away and the estimated worst case radius of influence of the short-term construction dewatering of Aquifer 1 being about 400 m, it is concluded that the short-term dewatering poses little risk for impact to the William Street wells or any reduction in water taking. Water table monitoring during the dewatering would be appropriate to confirm the lack of impact. Wetland and Stream Baseflow There are no sensitive wetlands near the Site and the closest urban water course is Laurel Creek, located about 250 m away. Given that most modeling scenarios indicate a radius of influence less than 250 m, there is little chance for any impact to Laurel Creek. Furthermore, the water collected from the dewatering will be discharged into the adjacent storm sewer and this sewer leads to Laurel Creek. Geotechnical Considerations There are no anticipated geotechnical concerns with undertaking the dewatering, as there are no known sensitive clay soils in the area that are subject to settlement concerns. Potential Groundwater Contamination & Discharge Plan The water pumped during the dewatering will be discharged to the storm sewer. Permission for discharge will be obtained from the City and Region for this discharge. The Phase I and II ESA indicate that there is no known potential for the water pumped during the dewatering to contain contaminants. Nevertheless, during detailed testing to support a PTTW application, it is recommended that

9 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page 6 confirmatory groundwater testing for typical contaminants be completed. In addition, provision to remove any sediment in the discharge water should be undertaken. Respectfully submitted, CHUNG & VANDER DOELEN ENGINEERING LTD. William (Sandy) Anderson, M.Sc., P.Eng. Senior Hydrogeologist and Engineer

10 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page REFERENCES The following documents, maps, or other publications have been used in the preparation of this report. Quaternary Geology of the Stratford Area, Ontario Geological Survey, Map 2559, 1:50,000, Karrow, P. F. (1987). Hydrogeologic Study of the Waterloo Moraine, Terraqua Investigations Ltd. (October 1995). Region of Waterloo Tier 3 Assessment, Aqua Resource et al. (March 2009). Grand River Source Protection Plan, GRCA (November 2015). Grand River Source Protection Approved Assessment Report, GRCA (August 2012) Background Hydrogeological Assessment, William St. and Seagram Water Supply System, Terraqua Investigations Limited (1997). Hydrogeological Study for Construction Dewatering, Bauer Lofts Property, Waterloo, Ontario Anderson Geologic Limited (May 2006). Supplementary Phase Two Environmental Site Assessment, 181 King Street South, Waterloo, Ontario, CVD Engineering Ltd. (January 2015). Geotechnical Investigation, Proposed 12-Storey Apartment Building, 115 & 117 Erb St. East, Waterloo, Ontario, CVD Engineering Ltd. (January 2010). Phase 1 Environmental Site Assessment, 115 & 117 Erb St. East, Waterloo, Ontario, CVD Engineering Ltd. (November 2012).

11 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page A APPENDIX A Figures

12 Creek LEGEND ODC Property CVD Erb St Borehole m BH1 Erb St. CVD Monitoring Well (187 King) 22 m BH5 [321 +/-] Region Monitoring Well (William) m oo M Creek [320 +/-] CVD Monitoring Well (181 King) 23 m re Region William Street Supply Well e Av Laurel St.. ia m [323.0] Approximate Aquifer 1 Water Level W ill (316.98) Approximate Aquifer 2 Water Level Cross-Section A W1C OW5 [ /-] (314 +/-) W2/W3/W1B ( /-) William Street Wellfield OW10 (315 +/-) [323 +/-] BH22 [323.0] N BH501 [323.5] m A Scale 1:6,000 Map Source: Ontario Base Maps, 2002 (1982 air photography) Kin gs t. Figure 1 Site & William Street Wellfield Locations Hydrogeological Study 115 & 117 Erb St E Waterloo, Ontario 311 VICTORIA STREET NORTH KITCHENER / ONTARIO / N2H 2E1 / Drawn By: SA Date: Aug File No.: H17069

13 NORTH William St. Well Field OW5-87 OW10-87 BH22 BH28 (offset) BH410 & BH501 SOUTH Elevation (masl) B si / cl f snd si snd snd / si si till C B cl f snd si si REGIONAL AQUITARD 2/3 REGIONAL AQUIFER 1 snd snd / gr cl-si till snd cl-si till snd cl-si till snd / gr cl-si till fill snd / gr snd / gr silt silt snd / gr si-snd silt REGIONAL AQUIFER 1 REGIONAL AQUITARD 2/3 fill si mc snd si snd / gr si / f snd si till fm snd 295 REGIONAL AQUIFER B 2 1C A gr/si cl till snd cl REGIONAL AQUITARD gr/snd snd / cl 285 W3 Bedrock Well ( masl) A gr LEGEND Water Level Elevation (black - May 2006, white - Nov 1987, blue - Jan 2016) Well Screen Soil Description cl - clay si - silt gr - gravel snd - sand f - fine m - medium c - coarse Note Borehole / Well Data and Aquifer Designations for William St. Well Field, OW5-87 and OW10-87 from Background Hydrogeological Assessment, William St. and Seagram Water Supply System (Figure 12), Terraqua Investigations Limited, m Horizontal Scale 1:1000 Vertical Scale 1:300 Vertical Exaggeration 3.3x 311 VICTORIA STREET NORTH KITCHENER / ONTARIO / N2H 2E1 / Figure 2 Hydrogeologic Cross-Section A-A At William Street Wellfield Hydrogeological Study 115 & 117 Erb St. E. Waterloo, Ontario Drawn By: SA Date: Aug File No.: H17069

14 PROPOSED APARTMENT BUILDING 115 & 117 ERB STREET EAST Waterloo, Ontario PRELIMINARY DOCUMENTS ERB STREET EAST R6000 R3000 PROPERTY LINE BEFORE ROAD WIDENING 4216 PROPERTY LINE AFTER ROAD WIDENING PRINCIPAL ENTRANCE 920 MAIL ROOM 10.0m MAX. FRONT YARD SETBACK (BY-LAW 1108) m MIN. FRONT YARD SETBACK (BY-LAW 1108 & ) ADJACENT PROPERTY CURRENTLY ZONED: GR-1 OFFICIAL PLAN DESIGNATION: MIXED-USE MEDIUM DENSITY RESIDENTIAL GRCA REGULATORY PROPERTY LINE FLOOD ELEVATION RFE: 322.9m EXTENT OF UNDERGROUND PARKING 6100 EXIT 20.0m SIDE YARD SETBACK (BY-LAW 1108) 12 STOREY PORTION EXTENT OF TOWER ABOVE EXTENT OF PROPOSED MR-12 OFFICIAL PLAN DESIGNATION: MIXED-USE MEDIUM HIGH DENSITY RESIDENTIAL ZONING/OP BOUNDARY GARBAGE/ ABOVE GRADE MOVE-IN PARKING ENTRANCE ADJACENT PROPERTY CURRENTLY ZONED: GR-1 OFFICIAL PLAN DESIGNATION: LOW DENSITY RESIDENTIAL PROPOSED RETAINING WALL STOREY PORTION 3.0m SIDE YARD SETBACK (BY-LAW 1108) EXTENT OF PROPOSED MR-6 OFFICIAL PLAN DESIGNATION: MIXED-USE MEDIUM DENSITY RESIDENTIAL 10.0m SIDE YARD SETBACK (BY-LAW 1108) PROPERTY LINE EXTENT OF BUILDING ABOVE PROPOSED 12 STOREY APARTMENT BUILDING GROUND FLOOR AREA:1,155.3 sq.m. (12,436.0 sq.ft.) BUILDING FLOOR AREA(INCLD'S UNDERGROUND PARKING): 13,540.1 sq.m. (145,749.2 sq.ft.) EXTENT OF BALCONY ABOVE (TYP.) LANDSCAPED AREA (5% SLOPE) RAMP DN. ADJACENT PROPERTY CURRENTLY ZONED: MR-25 OFFICIAL PLAN DESIGNATION: MIXED-USE HIGH DENSITY RESIDENTIAL EXIT PROPERTY LINE EXTENT OF UNDERGROUND PARKING LANDSCAPED AREA m SIDE YARD SETBACK (BY-LAW 1108) BELOW GRADE PARKING ENTRANCE EXTENT OF BUILDING ABOVE TRUCK TURNAROUND (BY-LAW 1108 & ) 7.5m MIN. REAR YARD SETBACK PROPOSED RETAINING WALL LANDSCAPED AREA GARAGE BELOW PROPERTY LINE ADJACENT PROPERTY CURRENTLY ZONED: MR-4 OFFICIAL PLAN DESIGNATION: MIXED-USE MEDIUM DENSITY RESIDENTIAL SITE PLAN TOTAL PARKING REQUIRED By-Law 1108:118 SPACES TOTAL PARKING REQUIRED BY-LAW : 114 SPACES TOTAL PARKING PROVIDED:112 SPACES 1st FLOOR = LOBBY & PARKING TYP. FLOOR (2-6) = 14 UNITS (70 UNITS) TYP. FLOOR (7-12) = 4 UNITS (24 UNITS) TOTAL UNITS = 94 (48 PARCEL 1, 46 PARCEL 2) PROJECT: DATE: SCALE: 1:250 REFERENCE: - SK 1.1

15 PROPOSED APARTMENT BUILDING 115 & 117 ERB STREET EAST Waterloo, Ontario PRELIMINARY DOCUMENTS RAMP UP P3 PARKING PLAN P3 PARKING PROVIDED: 54 SPACES PROJECT: DATE: SCALE: 1:250 REFERENCE: - SK 1.2

16 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page B APPENDIX B Borehole Logs

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23 Hydrogeological Study for August 29, 2017 Construction Dewatering FILE NO.: H & 117 Erb St. East, Waterloo Page C APPENDIX C Dewatering Model Results

24 Water Table Dewatering Model August CVD Project: H17069 Model Assumptions: Unconfined Aquifer, Isotropic, Flat Water Table Model Parameters: Pre-Dewatering Elevation 321 m Datum Estimated Seasonal High Required De-Watering Elevation m Datum 0.5 m below Deepest Excavation Drawdown Required 6.4 m Average Total Dewatering Area 2700 m 2 K (Hydraulic Conductivity) 1.0E-05 m/s 1.0E-04 m/s S (Specific Yield) 0.3 Assumes No Water Retention H (Total Aquifer Head) 10 m Total Aquifer Thickness R (Radius of Influence) Calculated from Jacob Eqn Applied to Circular Excavation r k T S t R Radius Equivalent Hydraulic "Dewatered" Specific Time of Area Radius Conductivity Transmissivity Yield Pumped Influence (m 2 ) (m) (m/s) (m 2 /s) (-) (min) (m) 1 week (7 days) E E weeks (28 days) E E month (90 days) E E month (240 days) E E week (7 days) E E weeks (28 days) E E month (90 days) E E month (240 days) E E Q (Groundwater Inflow) Calculated from Thiem Eqn (Un-Confined Aquifer) Applied to Circular Excavation r R H h k Q Q Radius Total Aquifer Equivalent of Aquifer Head at Hydraulic Inflow Inflow Area Radius Influence Head Excavation Conductivity Rate Rate (m 2 ) (m) (m) (m) (m) (m/s) (m 3 /day) (L/min) 1 week (7 days) E weeks (28 days) E month (90 days) E month (240 days) E week (7 days) E weeks (28 days) E month (90 days) E month (240 days) E

25 Water Table Dewatering Model August CVD Project: H17069 Model Assumptions: Unconfined Aquifer, Isotropic, Flat Water Table Model Parameters: Pre-Dewatering Elevation 321 m Datum Estimated Seasonal High Required De-Watering Elevation m Datum 0.5 m below Deepest Excavation Drawdown Required 6.4 m Average Total Dewatering Area 2700 m 2 K (Hydraulic Conductivity) 1.0E-05 m/s 1.0E-04 m/s S (Specific Yield) 0.3 Assumes No Water Retention H (Total Aquifer Head) 15 m Total Aquifer Thickness R (Radius of Influence) Calculated from Jacob Eqn Applied to Circular Excavation r k T S t R Radius Equivalent Hydraulic "Dewatered" Specific Time of Area Radius Conductivity Transmissivity Yield Pumped Influence (m 2 ) (m) (m/s) (m 2 /s) (-) (min) (m) 1 week (7 days) E E weeks (28 days) E E month (90 days) E E month (240 days) E E week (7 days) E E weeks (28 days) E E month (90 days) E E month (240 days) E E Q (Groundwater Inflow) Calculated from Thiem Eqn (Un-Confined Aquifer) Applied to Circular Excavation r R H h k Q Q Radius Total Aquifer Equivalent of Aquifer Head at Hydraulic Inflow Inflow Area Radius Influence Head Excavation Conductivity Rate Rate (m 2 ) (m) (m) (m) (m) (m/s) (m 3 /day) (L/min) 1 week (7 days) E weeks (28 days) E month (90 days) E month (240 days) E week (7 days) E weeks (28 days) E month (90 days) E month (240 days) E