Site Assessment and Preparation

Chapter Introduction

Site assessment and preparation are the first critical step in any landscaping project. An accurate diagnosis of the terrain helps you avoid costly errors, structural damage, and plant failures. This chapter covers the essential skills required for the Red Seal exam: soil analysis, topographical surveys, drainage, underground utilities, and grading calculations. You must master these concepts both theoretically and practically, as they represent a significant portion of exam questions.

Soil Analysis

Soil Classification and Texture

Soil texture is determined by the relative proportions of sand, silt, and clay. The USDA soil texture triangle is the reference tool for classifying soils into 12 main categories. For the exam, you must know the distinctive properties of each class:

Soil Type	Particle Size	Drainage	Water Retention	Compaction	Suitability for Planting
Sand	0.05 – 2.0 mm	Excellent	Low	Low	Poor (rapid drought)
Silt	0.002 – 0.05 mm	Moderate	Moderate	Moderate	Good
Clay	< 0.002 mm	Poor	High	High	Poor (root asphyxiation)
Loam	Balanced mixture	Good	Good	Low	Excellent

Loam is the ideal soil for most plantings: it contains approximately 40% sand, 40% silt, and 20% clay. This composition provides a balance between drainage, aeration, and water retention.

Field Texture Test (Ribbon Method)

To quickly identify a soil on site, use the ribbon method:

12.Take a slightly moist soil sample (approximately 25 g).

13.Knead it between your thumb and index finger.

14.Form a ribbon by pressing the soil between your fingers.

If the ribbon measures less than 2.5 cm before breaking: sandy or silty soil.

If the ribbon measures 2.5 to 5 cm: silty clay soil.

If the ribbon measures more than 5 cm: clay soil.

Soil pH and Amendments

pH measures the acidity or alkalinity of soil on a scale of 0 to 14. Most ornamental plants prefer a pH between 6.0 and 7.0 (slightly acidic to neutral). Some plants require specific conditions:

Acid-loving plants (rhododendrons, azaleas, blueberries): pH 4.5 – 5.5

Lime-loving plants (lilacs, clematis): pH 7.0 – 8.0

To adjust pH:

Increase pH (soil too acidic): apply dolomitic lime (CaCO₃ + MgCO₃). The typical rate is 2 to 4 kg per 10 m² to raise the pH by one unit in loamy soil.

Decrease pH (soil too alkaline): apply elemental sulfur (S) at a rate of 0.5 to 1 kg per 10 m², or use sphagnum peat moss.

Calculating the amount of amendment:

Quantity (kg) = Area (m²) × Recommended rate (kg/m²)

Example: to treat 50 m² of lawn with lime at 0.3 kg/m²:

50 × 0.3 = 15 kg of lime

Compaction and Drainage Testing

The drainage test (simplified perc test) is performed as follows:

31.Dig a hole 30 cm in diameter and 30 cm deep.

32.Fill it with water and let it drain completely.

33.Fill it again and measure the drainage time.

Less than 15 minutes: excessive drainage (sandy soil) — plan for organic amendments.

15 to 60 minutes: adequate drainage.

More than 60 minutes: insufficient drainage — requires a French drain or a stone bed.

Compaction is measured with a penetrometer. A resistance greater than 300 psi (2,070 kPa) indicates severe compaction that prevents root penetration. The solution is subsoiling (decompaction) to a depth of 30 to 60 cm using a subsoiler or a decompaction fork.

Topographical Surveys and Grading

Measuring Instruments

The optical level (or automatic level) is the standard instrument for site surveys. It allows you to measure elevation differences with an accuracy of ± 1.5 mm per 30 m. The rotary laser level is preferred for large areas because it projects a horizontal plane over 360°.

The level rod (graduated staff) is used with the level. Readings are taken in meters with two decimal places (e.g., 1.245 m).

Differential Leveling Principle

The fundamental leveling formula is:

Elevation of sighted point = Elevation of known point + Backsight − Foresight

In notation:

ΔH = elevation difference

Elevation of point B = Elevation of point A + (backsight on A) − (foresight on B)

Practical example:

Point A: known elevation = 102.50 m

Backsight on A = 1.35 m

Foresight on B = 0.85 m

Elevation of B = 102.50 + 1.35 − 0.85 = 103.00 m

Slopes and Drainage Calculations

Slope is expressed as a percentage (%) or as a ratio (1:50, 1:100).

Formula: Slope (%) = (Vertical drop ÷ Horizontal distance) × 100

Example: a patio must have a 2% slope to drain water. If the length is 6 m:

Required drop = 6 m × 0.02 = 0.12 m (12 cm)

Recommended slope standards:

Surface	Minimum Slope	Maximum Slope
Lawn	1%	5%
Pedestrian walkway	1%	8%
Driveway	1%	12%
Paved patio	1.5%	2%
Grassed embankment	2%	33% (3:1)

Earthwork Volume Calculations

The volume of soil to be excavated or backfilled is calculated according to the site shape:

Volume of a rectangular prism: V = Length × Width × Depth

Volume of a triangular embankment: V = (Base × Height ÷ 2) × Length

Volume of a cone (soil pile): V = (π × r² × h) ÷ 3

Bulking factor: excavated soil increases in volume. Bulking is approximately 25% for loamy soil, 30% for clay, and 15% for sand. Conversely, compacted soil occupies less volume than undisturbed soil.

Practical calculation:

Volume to excavate = 10 m × 8 m × 0.5 m = 40 m³

Bulked volume (loam, 25%) = 40 × 1.25 = 50 m³ (volume to transport)

Underground Utilities and Safety

Locating Underground Infrastructure

Before any excavation work, you must locate underground utilities. In Canada, the Click Before You Dig service (or the equivalent provincial service) coordinates the location of gas, electrical, water, sewer, and telecommunications lines. Ground markings use a standardized color code:

Color	Infrastructure
Red	Electricity
Yellow	Gas, oil, steam
Blue	Potable water
Green	Sanitary and storm sewers
Orange	Telecommunications
Violet	Irrigation, fuel

Safety rules for excavation:

Maintain a minimum distance of 1 m from marked utility lines when using mechanical equipment.

Use hand tools (shovel, trowel) within the 1 m zone around utility lines.

Verify the actual depth of utility lines — markings indicate horizontal position, not depth.

Natural gas lines are often buried at 0.6 to 1.2 m depth.

Water lines are typically at 1.5 to 2.4 m (below the frost line).

Trench and Embankment Regulations

The Canada Labour Code and provincial standards require shoring measures for trenches deeper than 1.2 m. For trenches from 1.2 m to 3 m, the slope must have a maximum angle of 1:1 (45°) in stable soils. In loose or saturated soils, the slope must be reduced to 1.5:1 or less.

Drainage and Water Management

Drainage Systems

The French drain (agricultural drain) is the most common method for removing excess water:

87.Dig a trench 30 to 45 cm wide, at a depth of 60 to 90 cm.

88.Place geotextile fabric at the bottom and along the walls.

89.Install a perforated pipe (PVC or polyethylene) 10 to 15 cm in diameter, with a slope of 0.5 to 1%.

90.Fill with crushed stone (2.5 to 5 cm) up to 15 cm from ground level.

91.Fold the geotextile over the stone.

92.Backfill with the excavated soil.

Calculating the drain slope:

Slope (%) = (Vertical drop ÷ Length) × 100

For a 20 m drain with a 1% slope:

Drop = 20 × 0.01 = 0.20 m (20 cm)

Dry Well and Retention Basin

A dry well is an excavation filled with crushed stone that allows stormwater to infiltrate into the soil. Typical sizing: 1.5 m diameter × 2 m deep for a 50 m² roof area. The bottom must be at least 1 m above the water table (groundwater level).

The retention basin is sized according to the formula:

Retention volume (m³) = Impermeable surface area (m²) × Rainfall depth (m)

For 25 mm (0.025 m) of rain on a 100 m² driveway:

Volume = 100 × 0.025 = 2.5 m³

Soil Preparation for Planting

Organic and Mineral Amendments

Compost is the most commonly used organic amendment. It improves soil structure, increases water retention capacity, and promotes microbial activity. The recommended rate is 5 to 10 cm thickness incorporated to a depth of 20 to 30 cm.

Calculating compost volume:

Volume (m³) = Area (m²) × Thickness (m)

For a 25 m² garden bed with 8 cm of compost:

Volume = 25 × 0.08 = 2 m³

Sphagnum peat moss is used to acidify soil and improve water retention in sandy soils. Note: its extraction is environmentally controversial; leaf compost or composted bark are sustainable alternatives.

Base Fertilization

Base fertilizer (starter fertilizer) is incorporated into the soil before planting. Common NPK ratios are 10-20-10 or 12-24-12 (high in phosphorus for root development). The typical rate is 1 to 2 kg per 10 m².

Calculating actual nitrogen content:

Nitrogen quantity (kg) = Fertilizer weight (kg) × (% nitrogen ÷ 100)

For 5 kg of 10-20-10 fertilizer:

Nitrogen = 5 × 0.10 = 0.5 kg N

Applicable Standards and Codes

Canadian Electrical Code, Part I

The Canadian Electrical Code, Part I (CSA C22.1 standard) governs the installation of outdoor electrical systems, including landscape lighting and electric irrigation systems. Key points:

Rule 8-200: outdoor lighting circuits must be protected by a ground fault circuit interrupter (GFCI) rated at 5 mA.

Buried cables must be installed at a minimum depth of 60 cm (armoured cable) or 45 cm (cable in conduit).

Low-voltage transformers (12 V) must be CSA-certified and installed at least 30 cm above ground level.

CSA B149.1 — Natural Gas and Propane Code

CSA B149.1 applies to natural gas and propane installations. For the landscaper:

Buried gas lines must be at a minimum depth of 45 cm (propane) or 60 cm (natural gas).

Lines must be polyethylene (PE) for buried installations, with a locating wire.

The minimum distance between a gas line and an electrical cable is 30 cm.

Outdoor gas appliances (fire pits, barbecues) must be installed at least 1 m from any building opening.

CSA Standards for Landscape Materials

CSA A23.1: concrete — specifications for slabs and foundations.

CSA A82: bricks and masonry blocks.

ASTM C936: concrete pavers (American standard often cited as a complement).

Common Pitfalls to Avoid

137.Confusing bulking and settlement: bulking increases volume (excavated soil), settlement decreases it (compacted soil). Never add them together.

138.Forgetting the minimum 1% slope for paved surfaces: a perfectly flat surface accumulates water and freezes in winter.

139.Neglecting the drainage test before planting: poorly drained clay soil causes root asphyxiation and plant death.

140.Using the wrong marking color: red = electricity, yellow = gas. A mistake can cause a serious accident.

141.Calculating pH without considering soil type: the rate of lime or sulfur varies by texture (clay soils require more amendment than sandy soils).

142.Confusing percentage slope and degree slope: a 100% slope = 45°. The conversion is not linear.

143.Forgetting the 10% safety factor in soil volume calculations: always order 10% extra to compensate for losses and irregularities.

144.Installing a French drain without geotextile: the geotextile prevents clogging by fine soil particles.

145.Digging near a marked utility line without manual verification: markings can be offset by a few centimeters.

146.Applying herbicide or amendment without knowing the soil pH: some products are ineffective or toxic at extreme pH levels.

Summary

Soil texture (sand, silt, clay) determines drainage, water retention, and compaction. Loam is the ideal soil.

The optimal pH for most plants is 6.0 to 7.0. Use lime to increase it, sulfur to decrease it.

Differential leveling is based on the formula: Point elevation = Known elevation + backsight − foresight.

Slopes are calculated as a percentage: Slope (%) = (Drop ÷ Distance) × 100. Paved surfaces require a minimum of 1 to 1.5%.

Bulking of excavated soil is 15 to 30% depending on soil type. Always plan for a 10% surplus in your orders.

Locate utilities before any excavation. Respect the 1 m distance for mechanical equipment.

The Canadian Electrical Code, Part I requires 5 mA GFCIs for outdoor circuits and minimum burial depths of 45 to 60 cm.

CSA B149.1 governs gas lines: minimum depth of 45 to 60 cm, 30 cm distance from electrical cables.

French drains require a slope of 0.5 to 1% and geotextile to prevent clogging.

Organic amendments (compost) are applied at 5 to 10 cm thickness, incorporated to a depth of 20 to 30 cm.

Self-Assessment Questions

161.A soil contains 50% sand, 30% silt, and 20% clay. What is its classification?

Answer: Loam.

163.Calculate the slope of a walkway that drops 15 cm over a length of 6 m.

Answer: (0.15 ÷ 6) × 100 = 2.5%.

165.You need to excavate 30 m³ of clay soil (30% bulking). What volume of soil will you need to transport?

Answer: 30 × 1.30 = 39 m³.

167.What is the minimum burial depth for an armoured electrical cable according to the Canadian Electrical Code, Part I?

Answer: 60 cm.

169.A French drain 25 m long must have a 1% slope. What is the total drop required?

Answer: 25 × 0.01 = 0.25 m (25 cm).

This chapter prepares you for exam questions on site assessment and preparation. Master the formulas, standards, and procedures described above. In the next chapter, we will cover the installation of irrigation systems and water management.

Site Assessment and Preparation