ANSI/AWWA C105/A21.5 addresses polyethylene encasement for ductile-iron pipe systems.

Polyethylene encasement is used as a corrosion-control measure by separating the buried pipe from direct contact with potentially corrosive soil.

Appendix A provides guidance for evaluating soil and environmental conditions that may affect corrosion of ductile-iron pipe. Its purpose is to assist qualified personnel in determining whether polyethylene encasement should be used.

The Appendix emphasizes that soil-corrosion assessment cannot be based on a single analytical result. Factors such as moisture, temperature, soil depth, time between sampling and testing, groundwater conditions, stray current and previous local pipe performance may materially affect the evaluation.

Soil resistivity measures the resistance of the soil to the flow of electrical current.

Low-resistivity soil generally allows corrosion currents to flow more readily and may therefore represent a more aggressive environment for buried metallic infrastructure.

Appendix A identifies three possible resistivity approaches:

• Four-pin field measurement 
• Single-probe field measurement 
• Water-saturated soil-box laboratory measurement 

For laboratory evaluation, the soil is brought to a water-saturated condition and measured using a soil-resistance meter and soil box. The Appendix notes that saturated testing is useful because the soil may not be naturally wet when sampled, while the buried pipe may experience saturated conditions during part of its service life. 

Soil resistivity can change substantially with:

• Moisture content 
• Temperature 
• Dissolved salts 
• Soil texture 
• Compaction 
• Groundwater exposure 

Appendix A recommends interpreting resistivity using the lowest meaningful result, while considering the soil’s typical moisture condition and the method used to obtain the measurement. 

Soil pH provides information about acidity, alkalinity and chemical conditions that may influence corrosion.

Appendix A identifies several important pH ranges:

• pH 0–4: strongly acidic soil, often associated with elevated corrosion rates 
• pH 6.5–7.5: conditions may be favourable for sulfate-reducing activity 
• pH above 8.5: may indicate high dissolved-salt content and correspondingly low resistivity 

The Appendix describes direct pH measurement using a calibrated combination electrode inserted into the soil sample.

Oxidation-reduction potential, commonly called redox potential or ORP, helps determine whether the soil is predominantly aerated or anaerobic.

This is important because sulfate-reducing bacteria typically develop under oxygen-deficient conditions. These microorganisms may produce sulfides and contribute to a corrosive environment around buried iron pipe.

Appendix A interprets redox potential approximately as follows:

• Greater than +100 mV: sufficiently aerated conditions 
• 0 to +100 mV: possible transitional or anaerobic conditions 
• Negative potential: definite anaerobic conditions favourable to sulfate-reducing activity 

The standard describes measurement using a pH/mV meter and a combination ORP electrode inserted into the soil sample. It also warns that exposure to air may rapidly alter the redox potential of a freshly excavated soil. Redox testing should therefore be performed as soon as practicable after sampling.

A positive sulfide reaction may indicate a potential corrosion problem caused by sulfate-reducing bacteria.

Appendix A describes a qualitative sodium azide–iodine test. In this procedure, a reagent containing sodium azide and iodine is introduced to a soil sample.

Sulfides catalyze the reaction, producing nitrogen gas:

• Strong bubbling or foaming indicates a positive sulfide result 
• Slight bubbling indicates a trace result 
• No reaction indicates a negative result 

The test is qualitative rather than a quantitative determination of total sulfur or sulfate concentration.

These terms should not be confused.

Sulfide may be produced under anaerobic conditions by sulfate-reducing microorganisms. AWWA Appendix A uses a qualitative sulfide reaction as part of the soil-corrosivity evaluation.

Sulfate is an oxidized sulfur species commonly present in soil and groundwater. It may serve as a nutrient source for sulfate-reducing bacteria under favourable anaerobic conditions.

Appendix A.1 does not assign scoring points based directly on a quantitative sulfate concentration.

Therefore, quantitative sulfate analysis may be useful as a complementary investigation, but it should not be substituted for the Appendix A sulfide test without clearly identifying the deviation.

Moisture is one of the most important factors affecting buried-pipe corrosion.

Appendix A does not require a precise gravimetric moisture percentage for its scoring system. Instead, it uses a relative assessment based on the prevailing field condition.

Lab-Elite may also determine gravimetric moisture content as a complementary measurement.

However, the numerical moisture percentage should not automatically replace the AWWA field classification because:

• A submitted sample may dry during transport 
• One sample may not represent seasonal conditions 
• Drainage and groundwater prevalence are site characteristics 
• Appendix A scoring is based on the prevailing condition

Lab-Elite reviews:

• Pipe type 
• Planned burial depth 
• Sampling locations 
• Project specification 
• Requested tests 
• Need for field ORP or resistivity measurements 

Samples are logged with:

• Project identification 
• Sample number 
• Sampling depth 
• Location 
• Date and time 
• Reported moisture condition 
• Container condition 

Preparation is selected according to the parameter being measured.

Excessive drying, grinding or air exposure may alter:

• Moisture 
• Redox potential 
• Sulfides 
• Resistivity 

Therefore, a single generic preparation procedure should not automatically be applied to every test.

The selected package may include:

• Saturated soil-box resistivity 
• Direct soil pH 
• ORP 
• Qualitative sulfides 
• Gravimetric moisture content 
• Soil description 

Results are reviewed and the applicable AWWA Table A.1 points are assigned.

The report presents:

• Individual results 
• Measurement conditions 
• Assigned points 
• Total score 
• Method limitations 
• Deviations 
• Recommended complementary investigations

For a complete Lab-Elite Appendix A package, a practical recommended submission is:

Approximately 1.5–2.0 kg of representative soil per sampling location

This quantity permits:

• Soil-box resistivity 
• pH 
• ORP 
• Sulfide screening 
• Moisture determination 
• Soil description 
• Repeat preparation if necessary 

Additional material may be required for:

• Coarse or heterogeneous soil 
• Replicate testing 
• Particle-size analysis 
• Chlorides and sulfates 
• Organic content 
• Additional geotechnical characterization 

The exact quantity should be confirmed before sampling because the required mass depends on the soil-box volume and the number of requested determinations.

• New municipal water mains 
• Ductile-iron pipe replacement 
• Water-treatment plant piping 
• Pumping stations 
• Transmission mains 
• Industrial water systems 
• Mining-site water infrastructure 
• Rural and remote water networks 
• Corrosion investigations 
• Failure analysis 
• Infrastructure-rehabilitation projects 
• Evaluation of polyethylene encasement requirements

The Appendix explicitly states that it is for information only and is not part of the normative body of the standard. 

The Appendix states that the methods should be used by qualified personnel experienced in soil analysis and conditions potentially corrosive to ductile-iron pipe.

Soil properties may change over short distances and with depth.

Air exposure can alter anaerobic soil conditions.

The prevailing drainage condition cannot always be determined from a transported laboratory sample.

The total should be considered with:

• Project specification 
• Local pipe history 
• Groundwater 
• Stray current 
• Soil layering 
• Installation conditions 
• Corrosion-engineering advice

Lab-Elite can combine the core Appendix A laboratory parameters into one coordinated package.

We recognize that resistivity, ORP, sulfides and moisture cannot always be treated using the same sample-preparation approach.

Each assigned point is shown separately rather than reporting only a final conclusion.

Reports include the analytical results, scoring logic and key limitations needed by engineers and water utilities.

Additional soil, aggregate and water analyses can be incorporated when required by the project.

Samples can be accepted from municipalities, consultants and infrastructure projects throughout Quebec and Canada.