GEOTECHNICAL INVESTIGATION - London, Ontario · Geotechnical Investigation – Proposed Residential...

GEOTECHNICAL INVESTIGATION PROPOSED RESIDENTIAL DEVELOPMENT

126 OXFORD STREET WEST LONDON, ONTARIO

Submitted to:

STEVEN UNDERHILL

LDS PROJECT NO. GE-00201

DECEMBER 14, 2018

Distribution (via email):

Steven Underhill: [email protected]

Geotechnical Investigation – Proposed Residential Development 126 Oxford Street West London, Ontario

Decemeber 14, 2018 i

Table of Contents

1. INTRODUCTION ............................................................................................................. 1

2. INVESTIGATION PROGRAM ......................................................................................... 3

3. REVIEW OF BACKGROUND DOCUMENTATION ......................................................... 4

3.1 UTRCA Regulated Lands Mapping ............................................................................................... 4 3.2 Review of Geologic Mapping ........................................................................................................ 4 3.3 Well Record Review ...................................................................................................................... 5

4. SUMMARIZED CONDITIONS ......................................................................................... 6

4.1 Site Description ............................................................................................................................. 6 4.2 Test Pit Program ........................................................................................................................... 6 4.3 Shallow Groundwater Conditions .................................................................................................. 7

5. GEOTECHNICAL COMMENTS AND RECOMMENDATIONS ........................................ 8

5.1 Site Preparation and Site Grading ................................................................................................ 8 5.2 Excavations and Groundwater Control ......................................................................................... 9

5.2.1 Excavations ........................................................................................................................... 9 5.2.2 Excavation Support ............................................................................................................... 9 5.2.3 Groundwater Control ........................................................................................................... 10

5.3 Building Components .................................................................................................................. 10

5.3.1 Foundation Design .............................................................................................................. 10 5.3.2 Basement Construction ....................................................................................................... 11

5.4 Retaining Wall Considerations .................................................................................................... 12 5.5 Site Services ............................................................................................................................... 12

6. PRELIMINARY HYDROGEOLOGICAL COMMENTS ....................................................14

6.1 Source Water Protection Considerations .................................................................................... 14 6.2 LID Considerations ...................................................................................................................... 14 6.3 Potential Impacts to Existing Wells ............................................................................................. 15 6.4 Potential Impacts to Seepage Areas ........................................................................................... 16 6.5 Potential Impact from Uncontrolled Erosion and/or Sediment Discharge ................................... 16

7. CLOSING .......................................................................................................................17

Appendices

Appendix A – Drawings

Appendix B – Test pit Summary

Appendix C – MECP Well Record Summary


Decemeber 14, 2018 1

1. INTRODUCTION

LDS Consultants (LDS) has been retained by Steven Underhill to conduct a Geotechnical Investigation for

a proposed residential development at 126 Oxford Street West, in London. The site was formerly occupied

by a residence, which has since been demolished. The subject property is located at 126 Oxford Street

West, in London, Ontario. A key plan is provided below as Figure 1, for reference.

Figure 1: Key Plan

It is understood that current development plans include the construction of a multi-family residence with

basement.

LDS has reviewed the Record of Pre-Application Consultation provided by Zelinka Priamo. Within the

consultation notes, the City of London has identified that a Slope Stability Analysis and Geotechnical

Investigation is required to support the proposed development. The scope of work and budget for the

Geotechnical Investigation was outlined in an email to the client dated November 15, 2018.



The City has also identified that a Scoped Hydrogeological Report is required for the site. Although this

report does not include the full program typically associated with a Hydrogeological Report, preliminary

comments have been incorporated, as appropriate. A more comprehensive field program (including

installation of monitoring wells) would be required to prepare a Scoped Hydrogeological Report.

Authorization to carry out this work was received from the client. This document has been prepared for the

purpose of providing geotechnical comments and recommendations for the design and construction of a

proposed residential development, in London, Ontario.

This report provides a summary of the test pit findings (documenting soil and groundwater conditions at the

site). The report also includes geotechnical comments and recommendations for the proposed residential

development, including: site preparation (including structural fill and engineered fill requirements),

excavations and groundwater control, foundation design, basement construction, stormwater

considerations (including LID and stormwater infiltration opportunities), site servicing (including re-use of

excavated materials as trench backfill), pavement design, slope stability considerations, and preliminary

hydrogeological comments.

This report is provided on the basis of the terms noted above, and on the assumption that the design will

follow applicable codes and standards. The site investigation and recommendations provided in this report

follow generally accepted practice for geotechnical consultants in Ontario. The format and content of this

report has been guided to address specific client needs. Laboratory testing, where applicable, follows ASTM

or CSA Standards.



2. INVESTIGATION PROGRAM

LDS carried out a field program consisting of a pair of test pits. The test pits were advanced at the site by

a local excavation-contractor, using a backhoe. Two test pits were advanced at the site and were excavated

to a maximum depth of 3.6 m (12 feet) below existing grade.

The ground surface elevations at the test pit locations were surveyed by LDS using a Trimble R10 GPS

rover. The locations of the test pits are summarized below, and illustrated on Drawing 3, in Appendix A.

ID Northing

(m N) Easting

(m E) Elevation

(m)

TP1 4759800.2 478069.1 236.8

TP2 4759893.4 478073.5 238.6

The depth to groundwater seepage and short-term water level observations were obtained prior to

backfilling the test pits.

The fieldwork was supervised by a member of LDS’ technical staff. All samples recovered from the site

were returned to LDS for detailed examination and selective testing. Laboratory testing for this investigation

included routine moisture content determinations which was carried out on select samples of the silty

subgrade soils collected from the site. Laboratory testing, where applicable, follows ASTM or CSA

Standards.

Collected samples will be disposed of, following the issuance of the Geotechnical Report, unless prior

arrangements have been made for longer term storage.

The information in this report in no way reflects on the environmental aspects of the soil.



3. REVIEW OF BACKGROUND DOCUMENTATION

3.1 UTRCA Regulated Lands Mapping

In May 2006, Ontario Regulation 157/06 came into effect in the UTRCA watershed, which locally

implements the Generic Regulation (Development, Interference with Wetlands and Alterations to Shoreline

and Watercourses). This regulation replaces the former Fill, Construction and Alteration to Waterways

regulations, and is intended to ensure public safety, prevent property damage and social disruption due to

natural hazards such as flooding and erosion. Ontario Regulation 157/06 is implemented by the local

Conservation Authority, by means of permit issuance for works in or near watercourses, valleys, and

wetlands.

A review of the UTRCA Regulation Limit confirms that the site is located within this limit. The regulatory

flood line is located outside of the property limits, to the east of the site. Property owners must obtain

permission from the UTRCA (obtaining a Section 28 Permit) before beginning any development, site

alteration, construction, or placement of fill within the regulated area.

3.2 Review of Geologic Mapping

Physiographic mapping for Southwestern Ontario (Chapman, L.J. and Putnam, D.F. 2007. Physiography

of Southern Ontario; Ontario Geological Survey, Miscellaneous Release-Data 228), identifies that the site

is located near the southern limit of the physiographic region known as the Stratford Till Plain, near the

boundary with the Caradoc Sand Plains and London Annex. An excerpt from the aforementioned mapping

(available from Google Earth) is provided on Drawing 2, in Appendix A.

Quaternary geology mapping for the area (Pleistocene Geology of St. Thomas Area (West Half), Ontario

Department of Mines, Preliminary Geological Map No. P238) indicates that the study area consists of

modern alluvium, comprised of gravel, sand and silt, with organic remains. The site is located along the

west side of the Thames River spillway. An excerpt from the aforementioned mapping is provided on

Drawing 2, in Appendix A.

Bedrock geology mapping for Southwestern Ontario (Ontario Geological Survey. 1:250 000 scale, Bedrock

Geology of Ontario. Ontario Geological Survey, Miscellaneous Release Data 126, Revised 2006) indicates

that bedrock in the general area consists of limestone, dolostone and shale from the Dundee formation,

from the Middle Devonian Period.

Geological publications describe the limestone as grey – brown medium to thickly bedded limestone and

dolostone, containing fossils, bituminous partings and microsatellites. Bedrock topography mapping and

well records in the area indicate that the bedrock surface is below 60+ metres of overburden soils in the

vicinity of the site.



Bedrock was not encountered during the fieldwork for this investigation, and is not documented within the

MECP well records within 500 m of the site.

3.3 Well Record Review

A review of Ministry of Environment, Conservation, and Parks (MECP) well records for this area was carried

out to review the water levels recorded in the nearby potable wells. Figure 2 (Appendix C) shows the

location of the wells (with Well Registration No.) which are in close proximity to the site. A summary of well

records is also provided in Appendix C, for reference.

Water supply records were not indicated within 500 m of the subject site. Nine observation wells were

located within this range, set within shallow to intermediate depth overburden aquifers (3.0 to 20.1 m below

ground surface). Static water levels in these observation wells are recorded at depths ranging between 1.5

to 5.3 m below ground surface.

The well record information generally reflects shallow groundwater conditions encountered in the test pits

for this investigation.



4. SUMMARIZED CONDITIONS

4.1 Site Description

The site is currently vacant, bounded by residences to the east and west, Oxford Road West to the north,

and backs onto Empress Avenue Park to the south. An excavation exists within the site in the location of

the previous building extending to an approximate depth of 1.5 to 2.0 meters below surrounding grades.

Site topography is gently sloping downward toward the south beyond excavation limits, a slope exists

between the subject site and the residence to the west.

During the site reconnaissance work at the site, a Slope Stability Rating Chart was prepared for the slope

along the west side of the site.

A mixture of young and mature trees are present at the site, particularly along the slope.

Any minor surface flows which occur at the site under existing conditions, are generally expected to follow

the gentle topography of the site, with flows directed toward the south and west. During the site

reconnaissance work in November, evidence of groundwater seepage and surficial erosion was noted on

the slope along the west side of the site.

No surface water features are present at the site, or in the immediate vicinity of the property. The Thames

River is located approximately 670 m east of the site.

4.2 Test Pit Program

Two test pits were advanced at the site to examine the soil and shallow groundwater conditions. The

approximate locations of the test pits are shown on Drawing 3, appended.

It should be noted that topsoil quantities should not be established from the information provided at the test

pit locations only. General descriptions of the subsurface conditions are summarized in the following

sections. A detailed test pit summary is provided in Appendix B, for reference.

The soils observed in the test pits generally consisted of a layer of topsoil or fill overlying natural silt and

sand, as described below.

Granular Fill

Test Pit TP1, located within the excavation, was surfaced with a layer of granular fill. The fill was described

as brown, medium grained in texture, in a loose and moist to very moist state (based on visual and tactile

observations and observed excavator resistance).

Topsoil



Test Pit TP2 was surfaced with a layer of topsoil, described as brown sandy loam. The topsoil thickness

was approximately 0.30 m. It should be noted that topsoil quantities should not be established from the

information provided at the test pit locations only.

Silt

Underlying the topsoil and fill, a layer of native silt was encountered in both test pits, and extended to depths

ranging from between 1.8 to 2.8 m below ground surface (corresponding to elevations ranging from 235.6

to 236.4 m). The silt was described as brown in colour, and contains trace sand and fine gravel. The silt

was in a in a stiff to very stiff state, based on visual and tactile observations and observed excavator

resistance. Moisture content determinations conducted on recovered samples of the silt generally range

between 5.5 to 12.3 percent, generally indicative of moist soil conditions.

Silty Sand

Each test pit encountered and was terminated within a layer of silty sand. The silty sand was described as

brown, containing trace to some silt, trace gravel. The silty sand was in a compact state, based on visual

and tactile observations and observed excavator resistance.

Groundwater seepage within this layer was encountered at each test pit location. Moisture content

determinations conducted on recovered samples of the silt generally range between 15.3 to 21.2 percent,

generally indicative of very moist conditions.

4.3 Shallow Groundwater Conditions

Short term water level observations from the open test pits at the time of completion are recorded in the

test pit summary (Appendix B). Both test pits encountered groundwater seepage at depths ranging between

2.7 and 2.9 m below ground surface (corresponding to elevations ranging from 234.1 to 235.6 m).

ID Elevation

(m)

Measurements – November 22, 2018

Depth to Groundwater Seepage (m)

Groundwater Elevation (m)

TP1 236.86 2.74 234.12

TP2 238.55 2.90 235.65

Shallow groundwater will vary in response to climatic or seasonal conditions, and, as such, may differ at

the time of construction, with higher levels anticipated during seasonal (spring-high) conditions.



5. GEOTECHNICAL COMMENTS AND RECOMMENDATIONS

At the time of writing of this report, it is understood that development plans include the construction of a 2-

storey multi-family residence with a basement, and associated parking at the rear accessed directly from

Oxford Street West. The test pits generally revealed a layer of topsoil and fill underlain by natural silt and

silty sand.

The following sections of this report provide geotechnical comments and recommendations to assist with

the design and construction of the proposed residential development.

5.1 Site Preparation and Site Grading

It is anticipated that some site grading activities will be required, including the removal of existing fill and

topsoil from the area to be developed. The test pits encountered approximately 0.3 m of topsoil at existing

grade and approximately 0.45 m of fill within the existing excavation. It should be noted that areas of thicker

topsoil and or fill may be present.

Surficial topsoil may be stockpiled on site for possible re-use as landscaping fill. In the event that material

is disposed of offsite, testing of the material for transport should conform to MECP Guidelines and

requirements.

Where exposed subgrade soils are approved by the geotechnical consultant, and grades need to be raised

to reach design elevations, it is anticipated that grades will be restored using structural / engineered fill.

Following the removal of the topsoil / organics, and prior to fill placement, the exposed subgrade should be

inspected by a geotechnical engineer. Any loose or soft zones noted in the inspection should be over

excavated and replaced with approved fill.

Where exposed subgrade soils are approved by the geotechnical consultant, and if grades need to be

raised to reach design elevations, it is anticipated that grades will be restored using structural / engineered

fill. The engineered fill should consist of suitable, compactable, inorganic soils, which are free of topsoil,

organics and miscellaneous debris. For best compaction results, the fill material should have a moisture

content within about 3 percent of optimum, as determined by Standard Proctor testing.

The placement of the engineered fill should be monitored by the geotechnical consultant to verify that

suitable materials are used, and to confirm that suitable levels of compaction are achieved. Engineered fill

material should be placed in maximum 300 mm (12 inch) thick lifts and uniformly compacted to 100 percent

Standard Proctor Maximum Dry Density (SPMDD). Additional notes regarding the engineered fill placement

are provided in Appendix A.



Full-time inspection and testing is recommended for engineered fill placement which will support new

buildings.

5.2 Excavations and Groundwater Control

5.2.1 Excavations

Once the site grading activities are complete, excavations for the proposed buildings and site services are

generally expected to extend through and terminate within natural subgrade soils or within engineered fill

material.

All work associated with design and construction relative to excavations must be carried out in accordance

with the Occupational Health and Safety Act (OHSA). Based on the results of the geotechnical investigation

and in accordance with Section 226 of Ontario Regulation 213/91, the silt deposits are classified as Type 2

soil and the silty sand deposits are classified as Type 3 soil.

For excavations, which extend through or terminate in Type 2 soil, temporary excavation side slopes can

be cut near vertical for the bottom 1.4 m and then must be cut back at a maximum inclination of 1H:1V from

that point. For excavations, which extend through or terminate in Type 3 soil, temporary excavation side

slopes can be cut back at a maximum inclination of 1H:1V from the base of the excavation.

In the event that construction occurs in seasonally wet conditions or when frozen soil conditions are present,

care will be required to maintain safe excavation side slopes, and suitable excavation bases. The contractor

should use a reasonable effort to direct surface run-off away from open excavations.

5.2.2 Excavation Support

In the event that excavation support systems are utilized for the site, the following table provides

recommended soil parameters for the natural subgrade soils contacted in the boreholes to assist in the

design of engineered shoring systems.

Soil

Soil Angle of Internal Friction

(o)

Unit Weight

(kN/m3)

Coefficient of Active Earth Pressure

Ka

Coefficient of Passive Earth Pressure

Kp

Silt 28 20 0.48 3.0

Silty Sand 24 19.5 0.32 3.0

The design and use of the support system should conform to the requirements set out in the most recent

version of the Occupational Health and Safety Act for Construction Projects and approved by the Ministry

of Labour. The shoring system should be designed in accordance with the guidelines provided in the

Canadian Foundation Engineering Manual (CFEM).



Where applicable, the lateral earth pressure acting on the excavation support system may be calculated

with the following equation:

P = K ( h+q)

where, P = lateral earth pressure in kPa acting at depth h;

= natural unit weight, a value of 19.5 kN/m3 may be assumed;

h = depth of point of interest in m;

q = equivalent value of any surcharge on the ground surface in kPa.

K = earth pressure coefficient, 0.45

The above expression assumes that no hydrostatic pressure will be applied against the shoring system. In

the event that shoring extends through wet soils, a suitable drainage barrier should be provided to provide

adequate porewater pressure relief.

5.2.3 Groundwater Control

It is anticipated that the groundwater table is located at an elevation of 234.5 m or lower. Shallow

groundwater will vary in response to climatic or seasonal conditions, and, as such, may differ at the time of

construction, with higher levels possible in wet seasons.

Conventional groundwater control methods are expected to be suitable for excavations at the site, to

address surface water infiltration and minor shallow groundwater seepage for excavations which do not

extend below the stabilized groundwater table. Groundwater control measures at the site should help to

maintain stable excavated slopes; reduce saturated soil conditions to allow for possible reuse of excavated

material; and provide a dry and stable base for excavations and construction operations. Care should be

taken to direct surface water away from open excavations.

5.3 Building Components

5.3.1 Foundation Design

All footings exposed to seasonal freezing conditions should be protected from frost action by at least 1.2 m

(4 ft.) of soil cover or equivalent insulation. Building foundations are not expected to encounter the shallow

groundwater. It is recommended that all strip and pad footings contain concrete reinforcing bars to aid in

supporting any loose or soft zones within the footprint of the previous building.

For design of footings on the natural subgrade soils below 1.2 m below existing grades (design frost depth),

an allowable bearing pressure (net stress increase) of 145 kPa (3000 psf) can be used for the design of

footings.



Site review to confirm the condition of the subgrade soils at the footing base level should be undertaken by

the geotechnical engineer at the time of excavation. In the event that unsuitable soils are removed and

grades are restored using engineered fill, a design bearing capacity on approved engineered fill of 145 kPa

is considered appropriate.

Footings at different elevations should be located such that the higher footings are set below a line drawn

up at 10 horizontal to 7 vertical from the closest edge of the lower footing. It is important to note that if

servicing easements are located between residential lots, the servicing excavations which encroach on the

building foundations are checked to ensure that they do not undermine the building foundations.

Provided that the stability of the soils exposed at the founding level is not compromised as a result of

construction activity, precipitation, cold weather conditions, etc., and the design bearing pressures are not

exceeded, the total and differential settlements of footings are expected to be less than 25 mm and 19 mm,

respectively.

It should be noted that the recommended bearing capacities have been calculated by based on the

observations of the soil and groundwater conditions within the test pit program at the site. Where variations

occur between the test pit locations, and during construction, site verification by the geotechnical consultant

is recommended to confirm soil conditions and verify soil bearing capacity.

5.3.2 Basement Construction

It is anticipated that the basement floors can be constructed using cast slab-on-grade techniques. It is

recommended that a minimum 200 mm (8 inch) thick compacted layer of 19 mm (¾ inch) clear stone be

placed between the prepared subgrade and the floor slab to serve as a moisture barrier.

The portion of exterior basement walls below finished groundwater level should be damp-proofed and

designed to resist a horizontal earth pressure ‘P’ at any depth ‘h’ below the surface as given by the following

expression:

P = K ( h+q)

where, P = lateral earth pressure in kPa acting at depth h;

= natural unit weight, a value of 19.5 kN/m3 may be assumed;

h = depth of point of interest in m;

q = equivalent value of any surcharge on the ground surface in kPa.

K = earth pressure coefficient, assumed to be 0.4

The above expression assumes that the perimeter drainage system prevents the build-up of any hydrostatic

pressure behind the wall.



In general, the excavated soils from the building footprints, which are free of topsoil and organics are

generally expected to be suitable for re-use as foundation wall backfill. Some soil conditioning may be

required in wet or winter conditions.

5.4 Retaining Wall Considerations

During LDS site visit, it was noted that the condition of the existing retaining wall along the west edge of the

property has been subject to some lateral instability. The slope at this location has an overall height ranging

from 2.0 to 3.5 m in height, and an average inclination of 28° (1.9H:1.0V). It recommended that the retaining

wall be rehabilitated or replaced to mitigate potential slope instability and/or loss of ground for the adjacent

property.

The retaining wall design should account for any surcharge loading. It is noted that the building is expected

to have a basement level, and building foundations will be set near the same elevation at the base of the

wall. Adequate drainage should be incorporated into the retaining wall design such that hydrostatic pressure

does not accumulate behind the wall.

An allowable bearing pressure (net stress increase) of 145 kPa (3000 psf) can be used for the retaining

wall bases. Site review to verify the condition of the subgrade soils at the retaining wall base level should

be undertaken by the geotechnical engineer at the time of excavation.

Vegetation on the slope should be maintained where possible, and re-established within disturbed areas to

minimize surface erosion.

5.5 Site Services

The subgrade soils within site serving trenches (constructed at conventional depths) are generally expected

to comprise of natural subgrade soils. Although no bearing problems are anticipated for flexible or rigid

pipes founded on natural deposits or approved fill, localized base improvement along the trench bottom

may be required for excavations which terminate in wet subgrade soils. The extent of base improvement or

stabilization is best determined in the field during construction, with consultation from a geotechnical

engineer.

Pipe bedding material should be compacted to a minimum 95 percent SPMDD. Water and sewer lines

installed outside of heated areas should be provided with a minimum 1.2 m of soil cover for frost protection.

Backfill above the bedding aggregate can consist of the excavated (inorganic) soils, compacted in maximum

300 mm thick lifts to a minimum of 95 percent SPMDD. A program of in-situ density testing should be set

up to ensure that satisfactory levels of compaction are achieved.



The inorganic material excavated from the service trenches may be used for construction backfill provided

that reasonable care is exercised in handling the material. In this regard, the material should be within 3

percent of the optimum moisture as determined by the Standard Proctor density test. Stockpiling of material

for prolonged periods of time should be avoided. This is particularly important if construction is carried out

in wet, adverse weather.



6. PRELIMINARY HYDROGEOLOGICAL COMMENTS

6.1 Source Water Protection Considerations

Where proposed developments are being planned, it is important to determine the presence of Significant

Groundwater Recharge Areas and High Vulnerability Aquifers in the area. These areas are protected under

the Clean Water Act (2006).

In general, Significant Groundwater Recharge Areas are defined as areas where water seeps into an

aquifer from rain and melting snow, supplying water to the underlying aquifer. A highly vulnerable aquifer

occurs where the subsurface material offers limited protection from contamination resulting from surface

activities.

LDS accessed the Thames-Sydenham Source Protection Region interactive mapping website and the

MECP Source Water Protection Information Atlas website to determine whether the RSC Property is

located in any identified areas of environmental concern, as they relate to local groundwater quality. The

following observations were made by LDS upon review of the mapping:

• The RSC Property is located within the Upper Thames Source Protection Area.

• The RSC property is not located in any of the following designated areas listed in the Thames-

Sydenham and MECP Source Protection mapping:

o Wellhead Protection Area, Wellhead Protection Area E (GUDI), Wellhead Protection Area

Q1 or Wellhead Protection Area Q2;

o Intake Protection Zone or Intake Protection Zone Q;

o Issue Contributing Area;

o Significant Groundwater Recharge Area;

o Highly Vulnerable Aquifer; or,

o Event Based Area.

An excerpt from the mapping is provided on Drawing 5, appended.

6.2 LID Considerations

From a quantitative standpoint, incorporating effective Low Impact Development (LID) strategies which

promote at-source infiltration structures into the design of the residential development design as part of a

storm water management strategy is primarily dependent on (but not limited to), native soil infiltration rates

and depth to seasonal high groundwater table.



Based on the soil conditions encountered at the borehole locations, the majority of the subgrade soils are

sand and sandy silt soils, which may be considered suitable for enhanced infiltration measures to be utilized

at the site.

As part of final land development design efforts, further onsite review will be required to confirm if fill

materials used during site grading support the proposed infiltration methods, and to more accurately predict

the performance of the proposed infiltration structures.

For general guidance, the following table outlines some constraints to be considered when designing LID

measures for the site.

SWMP

Physical Constraints for SWMP Types

Topography Soils – Minimum Infiltration Rate

Groundwater Area

Infiltration Trench None 15 mm/hr > 1 m below bottom < 2 ha

Reduced Lot Grading < 5% 15 mm/hr None None

Soak-away Pit None 15 mm/hr > 1 m below bottom < 0.5 ha

Rear Yard Ponding < 2% 15 mm/hr > 1 m below bottom < 0.5 ha

Grassed Swales < 5% None None < 2 ha

Pervious Pipes None 15 mm/hr > 1 m below bottom None

Vegetated Filter Strips < 10% None > 0.5 m below bottom < 2 ha

Sand Filters None None > 0.5 m below bottom < 5 ha

In general, from a quantitative stand point incorporating effective at-source infiltration structures into final

land development design as part of a storm water management strategy is primarily dependent on (but not

limited to), native soil infiltration rates and depth to seasonal high groundwater table. The shallow

groundwater is more than 5 m below the ground surface, and the estimated infiltration rates of the natural

sandy soils encountered at the borehole locations are above 15 mm/hr, making the site well suited to the

use of various at-source infiltration measures.

Further analyses can be undertaken at detailed design stage to further assess and refine post-development

water balance contributions to the site.

6.3 Potential Impacts to Existing Wells

Well records for the area do not indicate the presence of shallow water supply wells in the area. However,

a well survey to verify these findings has not been conducted, and may be considered as part of the scope

of work for a more detailed Hydrogeological Assessment for the site. In the event that shallow wells are

identified in the area, contingency measures for potential impacts to the shallow water supply should be

considered.



6.4 Potential Impacts to Seepage Areas

Seepage areas were noted in the slope during the site reconnaissance work by LDS. A review of the

seepage areas should be carried out by an ecologist to identify their significance, and to determine if base

flows to the seeps need to be maintained. Once the significance of the seeps are identified, mitigation

measures can be established to minimize negative impacts to the seeps and the contributing base flows,

as appropriate.

6.5 Potential Impact from Uncontrolled Erosion and/or Sediment Discharge

The use of suitable sediment and erosion control measures are recommended during construction. In

addition to implementing sediment and erosion controls during construction, regular inspection and

maintenance will also be necessary to ensure that adjacent properties and site drainage are not negatively

impacted during construction. The following general mitigation measures are suggested as best

management practices:

Construction BMPs During Site

Grading and Construction

Following Construction

Delineate work areas to limit construction activities ✓

Prevent wind-blown dust. ✓

Reuse of excavated natural soils as service trench backfill, where suitable soil conditions are encountered. The use of native backfill can help to minimize the change in hydraulic conductivity within the service trenches.

✓

Re-establishing vegetative cover in disturbed areas following the completion of the construction work. In areas which are susceptible to erosion, additional measures may include the use of sod or other materials to protect the exposed subgrade soils.

✓

Inspection of sediment and erosion control measures at the site should be planned during construction.

The frequency of inspections will depend on weather conditions (such as periods with rainfall or snowmelt).

At a minimum, inspections are expected to include checks on siltation barrier installations to confirm that it

is properly installed and secured, including inspection for evidence of damage or tears, and overtopping or

undermining by surface stormwater flows; checking condition of storm drain inlets, and documenting areas

where seeding / sodding / mulching is implemented to re-establish vegetative cover.



7. CLOSING

The geotechnical recommendations provided in this report are applicable to the project described in the

text. LDS would be pleased to provide a review of design drawings and specifications to ensure that the

geotechnical comments and recommendations provided in this report have been accurately and

appropriately interpreted.

It is important to note that the geotechnical investigation involves a limited sampling of the subsurface

conditions at specific test pit locations. The conclusions and recommendations presented in this report

reflect site conditions existing at the time of the investigation and a review of available information which

has been presented in the report. Should subsurface conditions be encountered which vary materially from

those observed in the test pits, we recommend that LDS be consulted to review the additional information

and verify if there are any changes to the geotechnical recommendations.

The comments given in this report are intended to provide guidance for design engineers. Contractors

making use of this report are responsible for their construction methods and practices, and should seek

confirmation or additional information if required, to ensure that they understand how subsurface soil and

groundwater conditions may affect their work.

No portion of this report may be used as a separate entity. It is intended to be read in its entirety.

We trust this satisfies your present requirements. If you have any questions or require anything further,

please feel free to contact our office.

Respectfully Submitted,

LDS CONSULTANTS INC.

Prepared By:

Nick M. Houlton, EIT. Geotechnical Services Office: 226-289-2952 Cell: 519-636-7519 [email protected]

Reviewed By:

Rebecca A. Walker, P. Eng., QPESA Principal, Geotechnical Services Office: 226-289-2952 Cell: 519-200-3742 [email protected]

mailto:[email protected]



APPENDIX A

DRAWINGS and NOTES

Drawing 1: UTRCA Regulated Lands

Legend

UTRCA Regulated

Lands

Regulatory Floodline

Source

City of London Digital

Mapping,

www.maps.london.ca

Site

126 Oxford Street West, London Ontario

Project

Proposed Residential Development

GE-00201

Scale

NTS

Drawing 2: Pleistocene Geology

Source

Ontario Department of Mines

Preliminary Geological Map

No. 238, Pleistocene Geology

of the St. Thomas Area (West

Half), Scale 1:50,000

Site


Project


GE-00201

Scale

NTS

Drawing 3 – Test Pit Location Plan

Source

City of London Digital Mapping

2015. LDS Survey

Site


Project


GE-00201

Scale

NTS

Drawing 4 – Slope Profile

Source

City of London Digital Mapping

2015. LDS Survey.

Site

126 Oxford Street,

London Ontario

Project


GE-00201

Scale

As shown

Drawing 5 – Source Protection Mapping

Source

Source Protection Information Atlas, Ministry of Environment, Conservation and Parks

Site

126 Oxford Street,

London Ontario

Project

Proposed Residential Development GE-00201

Scale

As shown

Notes for Engineered Fill Placement

1. The building footprint must be stripped of all topsoil contaminated fill material, and other unsuitable soils, and proof rolled. The exposed subgrade must be reviewed and approved by the geotechnical consultant prior to engineered fill being placed.

2. All excavations must be carried out in accordance with the Occupational Health and Safety Regulation of Ontario (Construction Projects - O.Reg. 213.91). The accompanying report identifies the soil type classification for the purposes of identifying appropriate excavation side slopes.

3. Minimum geometric requirements for engineered fill:

• Fill should extend outward (laterally) at least 0.5 m from the edge of the footing. From that point, the fill should extend downward at an inclination of 1 horizontal to 1 vertical to provide adequate support within the zone of influence below the footing.

• Top of the engineered fill mat should be provided with 1.2 m of soil cover or otherwise suitable frost protection to minimize frost effects on the surface of the engineered fill mat. Where adequate frost protection is not provided, additional review of the engineered fill mat is recommended at time of construction to identify any disturbed areas.

4. In areas where engineered fill is placed on a slope, the fill should be benched into the approved subgrade soils.

5. Material used for engineered fill must be free of topsoil, organics, and otherwise unsuitable or compressible soils. Any material proposed for use as engineered fill should be examined and approved by the geotechnical consultant prior to use onsite. Analytical testing may be required to confirm that imported fill material is suitable for use from an environmental standpoint.

6. Approved engineered fill should be placed in maximum 300 mm thick lifts, and uniformly compacted to 100% Standard Proctor dry density. For best compaction results, engineered fill should be within 3 percent of its optimum moisture content, as determined by the Standard Proctor density test.

7. Full time geotechnical monitoring, inspection and in-situ density (compaction) testing is required to review the materials being used and to verify the overall level of compaction achieved during fill placement.

8. Proper environmental protection will be required. In this regard, the following considerations are provided for reference

• Site grades should be maintained to promote drainage of surface water. Where possible, ponding of surface water on the engineered fill mat should be avoided.

• Protection against frost penetration will be required for exposed (approved) subgrade soils during cold-weather construction. Frost-laden and frozen material must not be utilized within the engineered fill lot.

• During summer construction, soil conditioning (such as addition of water) may be required to ensure that soil moisture content is suitable to achieve optimal compaction results.

9. The allowable bearing pressure specified in the accompanying report may be used provided that all conditions outlined above, and in the Geotechnical Report are adhered to.

APPENDIX B

TEST PIT SUMMARY

Test Pit Summary – 126 Oxford Street West, London

November 22, 2018

TP1 – Elevation: 236.86 m 0.00 – 0.45 m Granular Fill – brown, medium grained, loose, very moist. 0.45 – 1.83 m Silt – brown, trace gravel, trace sand, stiff to very stiff, moist 1.83 – 3.35 m Silty Sand – brown, trace gravel, compact, very moist 2.74 m - becoming saturated below 2.7 m depth 3.35 m Test Pit Terminated TP Terminated – Open to 2.7 m, with water measured at 2.7 m upon completion. TP2 – Elevation: 238.55 m 0.00 – 0.30 m Topsoil – brown, silty loam 0.30 – 0.90 m Granular Fill – brown, medium grained, trace building debris/garbage, loose, moist 0.90 – 2.90 m Silt – brown, trace to some sand, trace fine gravel, stiff, moist 2.90 m Test Pit Terminated TP Terminated – Open to 2.9 m, with minor seepage measured at base upon completion.

NOTES ON SAMPLE DESCRIPTIONS

1. All descriptions included in this report follow the Canadian Foundation Engineering Manual (CFEM) soil classification system, based

on visual and tactile examination which are consistent with the field identification procedures. Soil descriptions and classifications

are based on the Unified Soil Classification System (USCS), based on visual and tactile observations. Where grain size analyses

have been specified, mechanical grain size distribution has been used to confirm the soil classification.

Soil Classification

(based on particle diameter) Terminology & Proportion

Clay: < 0.002 mm Trace: < 10%

Silt: 0.002 – 0.075 mm Some: 10-20%

Sand: 0.075 – 4.75 mm Adjective, sandy, gravelly, etc.: 20-35%

Gravel: 4.75 mm – 75 mm And, and gravel, and silt, etc.: > 35%

Cobbles: 75 – 200 mm Noun, Sand, Gravel, Silt, etc.: > 35% and main fraction

Boulders: > 200 mm

2. The compactness condition of cohesionless soils is based on excavator / drilling resistance, and Standard Penetration Test (SPT)

N-values where available. The CFEM provides the following summary for reference.

Compactness of Cohesionless Soils SPT N-Value

(# blows per 0.3 m penetration of split-spoon sampler)

Very Loose 0 – 4

Loose 4 – 10

Compact 10 – 30

Dense 30 – 50

Very Dense 50+

3. Topsoil Thickness - It should be noted that topsoil quantities should not be established from information provided at the test hole

locations only. If required, a more detailed analysis with additional test holes may be recommended to accurately quantify the

amount of topsoil to be removed for construction purposes.

4. Fill material is heterogeneous in nature, and may vary significantly in composition, density and overall condition. Where uncontrolled

fill is contacted, it is possible that large obstructions or pockets of otherwise unsuitable or unstable soils may be present beyond the

test hole locations.

5. Where glacial till is referenced, this is indicative of material which originates from a geological process associated with glaciation.

Because of this geological process, till must be considered heterogeneous in composition and as such, may contain pockets and /

or seams of material such as sand, gravel, silt or clay. Till often contains cobbles or boulders and therefore, contractors may

encounter them during excavation, even if they are not indicated on the test hole summary. Where soil samples have been collected

using test pit sampling equipment, it should be understood that normal sampling equipment can not differentiate the size or type of

obstruction. Because of horizontal and vertical variability of till, the sample description may be applicable to a very l imited area;

therefore, caution is essential when dealing with excavations in till material.

6. Consistency of cohesive soils is based on tactile examination and undrained shear strength where available. The CFEM provides

the following summary for field identification methods and classification by corresponding undrained shear strength.

Consistency of

Cohesive Soils Field Identification

Undrained Shear

Strength (kPa)

Very Soft Easily penetrated several cm by the fist 0 – 12

Soft Easily penetrated several cm by the thumb 12 – 25

Firm Can be penetrated several cm by the thumb with moderate effort 25 – 50

Stiff Readily indented by the thumb, but penetrated only with great effort 50 – 100

Very Stiff Readily indented by the thumb nail 100 – 200

Hard Indented with difficulty by the thumbnail 200+

APPENDIX D

MECP WELL RECORD SUMMARY

Drawing 3 – MECP Well Locations

Source

Base drawing from Ministry of Environment, Conservation, and Parks www.ontario.ca/environment-and-energy/map-well-records, updated March 20, 2017.

Site

126 Oxford Street,

London Ontario

Project

GE-00201

Scale

As Shown

http://www.ontario.ca/environment-and-energy/map-well-records

http://www.ontario.ca/environment-and-energy/map-well-records

MECP Observation Wells

MECP Well ID

Registration Year

Well Type Depth of Well (m)

Depth Water Found (m)

Static Water Level (m)

Pump Rate (L/min)

4116213 7/25/2005 Observation Wells 5.3 NR NR NR

7112044 9/19/2008 Observation Wells 7.1 5.3 NR NR








MECP Test Hole Records

MECP Well ID

Registration Year

Well Type Depth of Well (m)

Depth Water Found (m)

Static Water Level (m)

Pump Rate (L/min)

4101249 12/14/1944 Test Hole 25.9 NR NR NR

4101258 12/15/1936 Test Hole 21.3 NR NR NR

7196089 12/20/2012 Test Hole 3.2 NR NR NR

7226931 7/4/2014 Test Hole 4.5 NR NR NR

4101250 1/11/1945 Test Hole 30.2 NR NR NR

7197735 2/7/2013 Test Hole 5.1 1.8 NR NR

7212717 10/30/2013 Test Hole 4.6 NR NR NR

7212718 10/30/2013 Test Hole 4.6 NR NR NR

7212719 10/30/2013 Test Hole 4.6 NR NR NR

NR: Not Recorded.

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