Testing

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Section 8.2 - 8.9 content text (only) Appendix C as A SCROLLING DOCUMENT!!!

Mention training courses

Soil Characterization Testing[edit]

The soil component of an LID BMP contributes substantially to its stormwater treatment performance and overall function. If the soil is overly compacted or very finely textured, it may drain too slowly. If the soil is highly organic or contains excessive amounts of chemical fertilizer it may contribute to nutrient loads to receiving waters rather than reduce them. If the soil is too shallow it may not provide adequate treatment of contaminated stormwater or may not support healthy vegetation. Whether it be the engineered filter media of bioretention cells, the growing media of green roofs or the topsoil of enhanced swales, vegetated filter strips and soil amendment areas, it is important that the soil provide a healthy growing environment for plantings while being within design specifications for key parameters specific to the type of BMP.

It is most important to sample and test soil characteristics as a part of Construction and Assumption inspections, to confirm the BMP has been constructed with materials that meet design specifications and that installation of the soil component is acceptable. Testing to confirm that the material meets quality specifications (i.e., particle-size distribution, organic matter, pH, cationic exchange capacity, nutrients and soluble salts) needs to be completed prior to it being delivered to the construction site. Testing to confirm that installation of the soil component is acceptable (i.e., depth and compaction) should be performed after the installed material has been allowed to settle for at least two (2) weeks, and prior to planting.

Sampling and testing is also recommended as a part of Verification inspections, to determine if the BMP is being adequately maintained and if soil characteristics are still within acceptable ranges. It may also be done as part of Forensic inspection and Testing (FIT) work to help diagnose the cause of poor vegetation cover, drainage or treatment performance and decide on corrective actions.

Maximum allowable bulk density values by soil texture class (Sustainable Sites Initiative, 2009). Click to enlarge.[1]
Critical soil characteristics, acceptance criteria and tests by LID BMP type

LID BMP Type

Soil Characteristic

Acceptance Criteriai

Test
Bioretention / Bioswales / Dry swale
Textureii Loamy Sand or Sandy Loam; 70 to 88% sand-sized particles; 12 to 30% silt- and clay-sized particles; <20% clay-sized particles. Particle-Size Distribution (PSD), or % Sand/Silt/Clay (i.e., Soil Texture) plus Sand Fraction
Organic Matter (OM) 3 to 10% by dry weightii Walkley-Black method when OM <7.5% or Loss On Ignition (LOI) method when OM ≥7.5%iii
Soil pH 6.0 to 7.8 pH of a Saturated Pasteiii
Cationic Exchange Capacity (CEC) >10 meq/100 g Cationic Exchange Capacity Test
Phosphorusiv 12 to 40 ppm Extractable Phosphorus
Soluble Saltsv ≤2.0 mS/cm (0.2 S/m) Electrical Conductivity of a Soil-Water Slurry (2:1 water to soil ratio by volume)iii
Depth +/- 10% of design specification Soil Cores, Test Pits or Cone Penetration Tests
Compactionvi Surface Resistance: ≤110 PSI; Sub-surface Resistance: ≤260 PSI Bulk Density: ≤1.60 g/cm3 Cone Penetration Tests or Bulk Density Tests
Permeability i ≥25 mm/h (KS ≥ 1 x 10-5 cm/s); and i ≤203 mm/h (KS ≤ 0.02 cm/s). Surface Infiltration Rate Tests
Enhanced swale (topsoil)
Texture Same soil texture classification as specified in the final design or recorded on the as-built drawing Particle-Size Distribution (PSD), or % Sand/Silt/Clay (i.e., Soil Texture) plus Sand Fraction
Organic Matter (OM)ii 5 to 10% by dry weight Walkley-Black method when OM <7.5% or Loss On Ignition (LOI) method when OM ≥7.5%iii
Soil pH 6.0 to 7.8 pH of a Saturated Pasteiii
Phosphorusiv 12 to 40 ppm Extractable Phosphorus
Soluble Saltsv ≤2.0 mS/cm (0.2 S/m) Electrical Conductivity of a Soil-Water Slurry (2:1 water to soil ratio by volume)iii
Depth +/- 10% of design specification Soil Cores, Test Pits
Compaction Surface Resistance: ≤110 PSI; Sub-surface Resistance: Use soil texture class and "Soil & Texture Class Table" (below) to determine maximum acceptable value; Bulk Density: Use PSD to interpolate maximum bulk density value from bulk density figure beside this table. Cone Penetration Tests or Bulk Density Tests
Permeability i ≥15 mm/h (KS ≥ 1 x 10-6 cm/s) Surface Infiltration Rate Tests
Vegetated filter strips and Soil Amendment Areas (topsoil)
Texture Same soil texture classification as specified in the final design or recorded on the as-built drawing Particle-Size Distribution (PSD), or % Sand/Silt/Clay (i.e., Soil Texture) plus Sand Fraction
Organic Matter (OM)ii 5 to 10% by dry weight Walkley-Black method when OM <7.5% or Loss On Ignition (LOI) method when OM ≥7.5%iii
Soil pH 6.0 to 7.8 pH of a Saturated Pasteiii
Phosphorusiv 12 to 40 ppm Extractable Phosphorus
Soluble Saltsv ≤2.0 mS/cm (0.2 S/m) Electrical Conductivity of a Soil-Water Slurry (2:1 water to soil ratio by volume)iii
Compaction Surface Resistance: ≤110 PSI; Sub-surface Resistance: Use soil texture class and "Soil & Texture Class Table" (below) to determine maximum acceptable value; Bulk Density: Use PSD to interpolate maximum bulk density value from bulk density figure beside this table. Cone Penetration Tests or Bulk Density Tests
Permeability i ≥15 mm/h (KS ≥ 1 x 10-6 cm/s) Surface Infiltration Rate Tests
Green roof (growing media)
Texture See product vendor or BMP designer for specifications Particle-Size Distribution (PSD), or % Sand/Silt/Clay (i.e., Soil Texture) plus Sand Fraction
Maximum Media Density See product vendor or BMP designer for specification Maximum Media Density Test (ASTM E2399/E2399M-15)
Water Storage Capacityvii Extensive: ≥35% by volume / Intensive: ≥45% by volume Both part of Maximum Media Density Test (ASTM E2399/E2399M-15)
Air-Filled Porosityvii ≥10% by volume Part of Maximum Media Density Test (ASTM E2399/E2399M-15)
Permeability, Saturated Media See product vendor or BMP designer for specification Part of Maximum Media Density Test (ASTM E2399/E2399M-15)
Organic Matter See product vendor or BMP designer for specification Walkley-Black method when OM <7.5% or Loss On Ignition (LOI) method when OM ≥7.5%iii
Soil pHviii 6.5 to 7.8 pH of a Saturated Paste
Soluble Saltsviii ≤0.85 mS/cm (0.085 S/m) Electrical Conductivity of a Saturated Media Extract (SME)solution
Phosphorusix 2.2 to 40 ppm Electrical Conductivity of a Saturated Media Extract (SME)solution
Notes
i Values represent acceptable ranges for established BMPs (i.e., in operation for 3 years or more). For Construction and Assumption inspections, final design and soil or media product specifications and permissible tolerance ranges should be used as the acceptance criteria, which may be smaller ranges than the values in this table.
ii Suggested range for diagnosing suspected problems with drainage function, vegetation cover or vegetation condition for established BMPs constructed with filter media that meets recommended guidelines (CVC & TRCA, 2010)[2]. For proprietary filter media products, different ranges may be acceptable. Product specifications should be provided by the media supplier. Test results should be compared to the media supplier’s specifications and permissible tolerance ranges
iii Based on Ontario Ministry of Food and Rural Affairs’ Soil Fertility Handbook guidance on soil fertility testing for crop production (OMAFRA, 2006)[3].
iv Based on Minnesota Pollution Control Agency (MPCA, 2015) for minimum to sustain plant growth and Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA, 2014) for a maximum to avoid unnecessary fertilization that would have low or no effect on plant health.
v Based on the threshold for non-saline soils (Whitney, 2012).
vi Interpolated value from bulk density figure beside this table. based on a sandy loam soil containing at least 70% sand-sized particles.
vii Based on German green roof standards (FLL 2008). Specifications will vary depending on the green roof growing media product. Product specifications should be provided by the media supplier. Test results should be compared to the media supplier’s specifications and permissible tolerance ranges.
viii Based on Penn State University Center for Green Roof Research (Berghage et al. 2008).
ix Based on Penn State University Center for Green Roof Research (Berghage et al. 2008) for the minimum to sustain plant growth and Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA, 2014) for the maximum to avoid unnecessary fertilization that would have low or no effect on plant health.


Acceptable Soil Cone Penetrometer Readings (Soil & Texture Class)

Surface Resistancei
'Sub-surface Resistancei
All Soil Textures Sandy (includes loamy sand, sandy loam, sandy clay loam and sandy clay) Silty (includes loam, silty loam, silty clay loam, and silty clay) Clayey (includes clay loam and clay)
≤ 110 PSIii ≤ 260 PSI ≤ 260 PSI ≤ 225 PSI
≤ 7.7 kg/cm2 ≤ 18.3 kg/cm2 iii ≤ 18.3 kg/cm2 ≤ 15.8 kg/cm2
≤ 758 kPaiv ≤ 1793 kPa ≤ 1793 kPa ≤ 1551 kPa
Notes
i Adapted from Gugino et al. (2009)[4]
ii PSI = pounds per square inch (lb/in2)
iii kg/cm2 = kilogram per square centimetre.
iv kPa = kilopascals

For further information regarding soil characteristics, acceptance criteria per LID BMP type and associated testing tools and protocols scroll down to the embedded 2016 guide below.

Sediment Accumulation Testing[edit]

A primary function of LID BMPs is to capture and retain sediment, trash and debris that are suspended in stormwater runoff. Over time, sediment and natural debris accumulates in certain portions of a BMP, particularly in pretreatment devices (e.g., forebays, gravel diaphragms, hydrodynamic separators, vegetated filter strips, grass swales, catchbasin/manhole sumps) and at inlets, where inflowing runoff is slowed down and spread out, which promotes sedimentation of suspended materials by design.

Without adequate inspection and maintenance (at least annually), accumulated sediment and debris in pretreatment devices and inlets can inhibit the flow of stormwater into the BMP or be transported onto the filter bed . Extensive sediment accumulation on the surface of a filter bed will eventually lead to drainage problems due to clogging of the filter media with fine-textured sediment. When sediment accumulation on the surface of a filter strip or swales becomes excessive the BMPs begin to export sediment and associated pollutants into receiving waters rather than retain them.

Key Components, Test Methods and Equipment[edit]

Key components of LID BMPs that should be the subject of sediment accumulation testing (i.e., depth measurements) are described in the table below along with recommended test methods. Depth measurements should be recorded on inspection field data forms provided on each associated BMP's I&M page on the wiki, used to determine if sediment removal maintenance is needed.

Picture of a typical Secchi disk to help measure sediment depth in underground holding structures. (Photo Source: Wildco, 2018[5]
Key components and test methods for sediment accumulation testing by BMP type

LID BMP Type

Key Components

Recommended Test Method
Bioretention / Bioswales / Dry swale / Enhanced grass swales / Vegetated filter strips
Inlets; Pretreatment devices Use a tape measure or probe to measure the depth from the bottom elevation of the pretreatment device or surface of the filter bed (adjacent to the inlet structure), below any stone or mulch cover present, to the highest elevation of accumulated sediment present. For catchbasins, manholes and hydrodynamic separator pretreatment devices a sludge sampler (e.g., “sludge judge” sampler) should be used to sample the sediment and estimate depth accumulated in sumps. Record the measurement and remove the sediment if it exceeds trigger values for follow-up action.
Filter Bed Use a tape measure or probe to measure sediment depth from the surface of the filter bed, below any stone or mulch cover present, to the elevation of accumulated sediment present in at least five (5) locations evenly distributed over the filter bed surface area. Record the measurements, calculate the mean sediment depth and compare to trigger values to determine if follow-up/corrective actions are needed.
Underground infiltration systems (Soakaways, infiltration trenches, infiltration chambers and perforated pipe storm sewer systems
Inlets; Pretreatment devices Use tape measure or probe to measure the depth from the bottom elevation of the inlet pipe or pretreatment device, below any stone or mulch cover present, to the highest elevation of accumulated sediment present. For catchbasins, manholes and hydrodynamic separator pretreatment devices a sludge sampler (e.g., “sludge judge” sampler) should be

used to sample the sediment and estimate depth accumulated in sumps. A measuring tape or staff gauge installed in the structure and set to the bottom elevation can provide another means of tracking sediment accumulation. Record the measurement and remove the sediment if it exceeds trigger values.

Filter Bed (Applicable to vault-type infiltration chamber systems only) - Use a tape measure or probe to measure sediment depth from the surface of the gravel bed to the elevation of

accumulated sediment in at least five (5) locations evenly distributed over the bed surface area. Record the measurements, calculate the mean sediment depth and compare to trigger values to determine if follow-up/corrective actions are needed.

Cisterns (Rainwater Harvesting & Rain barrels)
Cistern From outside the cistern use a tape measure or probe to measure the depth from a fixed point (e.g., rim of the access hatch) to the bottom elevation of the cistern and to the highest elevation of accumulated sediment present. Subtract the two values to calculate the sediment depth. A sludge sampler (e.g., “sludge judge” sampler) may also be used to sample the sediment and estimate depth. A staff gauge installed on the cistern wall and set to the bottom elevation provides another means of measuring sediment depth that does not require entry into the confined space. Record the measurement and remove the sediment if it exceeds trigger values for follow-up action.
Measuring sediment depth in a catchbasin utilizing the "two prong method" (Photo Source: King County, 2010)[6]

Standard Equipment Used[edit]

Equipment needed for sediment accumulation testing can include the following:

  • Safety apparel (hard hat, steel toed boots, gloves and eye protection)
  • Safety cones or barriers (for restricting access around open hatches/grates/manhole covers)
  • Clipboard, inspection field data forms, pens
  • Pick shovel (for opening catchbasin grates or manhole covers)
  • Measuring tape
  • Probe (rigid)
  • Secchi disk
  • Sludge sampler
  • Rope
  • Flashlight or headlamp
  • Harness
  • Tripod (certified and tested)
  • Winch (certified and tested)
  • Multi-gas detector (recently calibrated and tested)

Sediment accumulation testing should be conducted frequently during construction (e.g., weekly and after any storm event of 15 mm depth or greater), as part of Assumption inspection work, once construction is fully completed and sediment accumulated on the CDA, in conveyances (e.g., gutters, catchbasins, storm sewers) and pretreatment devices has been removed, and as part of Routine Operation and Verification inspections.

For further information regarding soil characteristics, acceptance criteria per LID BMP type and associated testing tools and protocols scroll down to the embedded 2016 guide below.

Surface Infiltration Rate Testing[edit]

For LID BMPs like bioretention and bioswales, enhanced swales, vegetated filter strips and permeable pavements, the rate at which stormwater infiltrates through the BMP surface greatly affects its drainage performance. If the surface infiltration rate (i) is too low, inflowing stormwater will quickly begin to pond on the surface and, once the overflow outlet elevation is reached, will by-pass treatment by the BMP. In extreme cases the BMP may pond water on the surface for longer than 24 hours, creating nuisance conditions (e.g., poor vegetation cover, ice formation, ideal mosquito breeding ground habitat).

Causes of excessively low surface infiltration rates include use of soil during construction that does not meet design specifications, accumulation of fine sediment on the soil surface or in permeable pavement joints or pore spaces, and over-compaction of the soil, that can occur during construction or routine operation. Therefore it is important to test the surface infiltration rate of LID BMPs as part of Assumption and Verification inspections. As part of Assumption inspections it helps determine if the BMP is ready to be assumed by the property owner. As part of Verification inspections it provides an indication of whether or not the surface drainage performance of the BMP is still within an acceptable range, if it is being adequately maintained, and to diagnose the cause of any problems with drainage or vegetation detected through visual inspection or other types of testing. Tests may also be done as part of Forensic Inspection and Testing (FIT) work to diagnose the cause of problems with drainage or vegetation, with the number and locations of test determined by the nature of the problem being investigated.

Natural or Simulated Storm Event Testing[edit]

Continuous Monitoring[edit]

Green Roof Irrigation System Testing[edit]

Green Roof Leak Detection Testing[edit]

Cistern Pump Testing[edit]

Embedded Reference Guide[edit]

To gain further insight into various testing requirements/methods, acceptance requirements, associated tools, equipment and components from STEP on the inspection and maintenance of different BMP LID practices, please see our complete guide here or embedded below:

load PDF

References[edit]

  1. Sustainable Sites Initiative. 2009. The Sustainable Sites Initiative: Guidelines and Performance Benchmarks. American Society of Landscape Architects, Lady Bird Johnson Wildflower Center at The University of Texas at Austin, United States Botanic Garden and Sustainable Sites Initiative, Austin, TX. https://digital.library.unt.edu/ark:/67531/metadc31157/
  2. CVC and TRCA, 2010. Low Impact Development Stormwater Management Planning and Design Guide. Version 1.0. https://cvc.ca/wp-content/uploads/2014/04/LID-SWM-Guide-v1.0_2010_1_no-appendices.pdf
  3. OMAFRA. 2006. Soil Fertility Handbook Publication 611. Guelph, Ontario, Canada. http://www.omafra.gov.on.ca/english/crops/pub611/pub611.pdf.
  4. Gugino, B.K., Idowu, O.J., Schindelbeck, R.R., van Es, H.M., Wolfe, D.W., Moebius, B.N., Thies, J.E., and Abawi, G.S. 2009. Cornell Soil Health Assessment Training Manual, Edition 2.0, 2009, Cornell University, College of Agriculture and Life Sciences, New York State Agricultural Experiment Station(NYSAES), Geneva, New York. ISBN 0-9676507-4-7. https://www.canr.msu.edu/foodsystems/uploads/files/cornell_soilhealth.pdf
  5. Wildco. 2018. Secchi Disk Kit, Fieldmaster®. Accesses May 5 2022: https://shop.sciencefirst.com/wildco/student-water-samplers/5979-fieldmaster-student-secchi-disk-non-calibrated-line-for-student-use-only-200mm.html
  6. King County. 2010. Tips for Successful Drainage Facility Self-Inspection. Department of Natural Resources and Parks. File Name: 0906_DrainTIPS.indd lpre. Developed: June, 2010. https://www.seatacwa.gov/home/showpublisheddocument/31441/637662770980630000