Stormwater quizzes

Infiltration quiz

Answers below

1. Using information from the Minnesota Stormwater Manual, which of these classification systems is not used for determining infiltration rates from boring logs
   1. Hydrologic soil group
   2. USGS published values for saturated hydraulic conductivity
   3. USDA soil classification
   4. Unified Soil Classification
2. True or False: A 3-foot separation distance is widely applied in determining the feasibility of infiltration at sites. This value is based on extensive research at sites employing stormwater best management practices.
3. True or False: If soil or ground water contamination is detected at a site, infiltration is prohibited
4. True or False: Values used in determining infiltration rates and thus feasibility of infiltration at a site are based on instantaneous measurement of water infiltration into a soil
5. Which of these is not recommended for measuring infiltration rates at a site?
   1. Modified Phillip-Dunn permeameter
   2. Double-ring infiltrometer
   3. Guelph permeameter
   4. Soil tensiometer
6. Which of these is typically not an important reason why we prefer to infiltrate stormwater runoff when it is feasible?
   1. It provides numerous co-benefits, such as habitat creation and carbon sequestration
   2. It helps alleviate flood potential for small- and medium-intensity storms
   3. It keeps rain water close to it's source, thus somewhat mimicking natural hydrology
   4. It effectively reduces the potential for many pollutants to reach receiving waters
7. True or false: Recent research (e.g. Villanova) indicates that properly designed, constructed, and maintained infiltration practices have, on average, been underdesigned (i.e. they infiltrate less water than expected or designed)
8. True or false: Infiltration rates increase with time in a vegetated infiltration practice due to water flow within macropores associated with root channels and invertebrates (e.g. earthworms)
9. In applying a field-measured infiltration rate at a site, it is recommended you reduce the measured rate by
   1. 0 percent
   2. 10 percent
   3. 50 percent
   4. 90 percent
10. True or False: If a Soil Survey indicates the soil at your 2 acre site is a sandy loam and you are planning an infiltration practice with a surface area of 7500 square feet, you should take one boring to verify this

Answers

1. b - USGS published values. While these values may have utility in some cases, they are not included as options in the Manual. See Design infiltration rates.
2. False: It is generally believed the 3-foot value is based on applications to septic system drainfield measurements, where the 3-foot separation is widely applied. There is no significant body of evidence supporting a specific value for separation for stormwater infiltration practices. Studies show significant pollutant attenuation in the upper 6 inches of soil containing high organic matter contents, while a 3-foot separation may be inadequate for coarse-textured soils containing low organic matter concentrations. This is an area needing more research.
3. False: The CSW permit specifies infiltration is prohibited when contaminants will be mobilized. If infiltration practices can be located on a site such that contaminants on the site will not be mobilized, infiltration is acceptable.
4. False: Steady-state infiltration rates are applied in determining soil infiltration rates and feasibility at sites. Infiltration into soil, particularly unsaturated soil, is complex. Put on your physics cap and read more here.
   1. d - soil tensiometer. Tensiometers are used to measure soil water (moisture) content. See Determining soil infiltration rates
   2. a - provides numerous co-benefits. Co-benefits can be incorporated into the design of infiltration systems, but they are not a fundamental characteristic of infiltration practices. See Green Infrastructure benefits of infiltration practices
5. (d) Soil tensiometer, which is used for determining soil water (moisture) content, not infiltration rate
6. (a) This answer is somewhat negotiable, but typically we utilize infiltration for water quality and/or water quantity benefits. Other benefits can be incorporated into a practice, but they rarely are the reason for selecting infiltration at a site.
7. False: Just the opposite. Traditional design has been based on assumed vertical infiltration into underlying soil. Infiltration is three-dimensional and thus also occurs through the sidewalls of a practice. Also, designs in Minnesota assume an infiltration practice instantaneous fills with water. However, infiltration occurs as a practice is filling. This was considered to be offset by water bypassing an infiltration practice during intense rains, but recent data suggests this bypass accounts for a relatively small percentage of annual runoff (perhaps 2% or less). This is another area needing more research. See [1], [2], [3].
8. We aren't sure. Studies in other situations, such as agricultural and native prairies and forested situations, suggest this is true, but we lack studies for stormwater practices.
   1. 50 percent. It is unclear where this value came from, though Wisconsin has applied reduction factors for many years
9. False. Field measurements are recommended. If soil borings are used instead, at least 3 borings are recommended for this project. See Recommended number of soil boring, pits, and permeameter tests for bioretention design.

Vegetation quiz

Answers below

1. True or false: All green stormwater infrastructure practices include vegetation
2. Trees intercept rainfall and to some extent snowfall. Roughly what percent of average annual precipitation does a deciduous tree intercept in Minnesota?
   1. 1
   2. 10
   3. 30
   4. 50
3. Which of the following statements is inaccurate?
   1. Plants for extensive green roofs are generally drought tolerant species
   2. Shrubs and some trees can be planted on intensive green roofs
   3. Only annuals can be planted on extensive green roofs
   4. The most common genus planted on green roofs in Minnesota is sedum
4. Which of the following is inaccurate
   1. Cover crops need to be reapplied every growing season
   2. The primary purpose of a cover crop is to capture sediment that has been detached
   3. Cover crops may need to be applied multiple times in phased projects
   4. Oats and winter wheat are common cover crops
5. True or false: When considering erosion prevention using mulches, do not use wood chips, as these are suspended and transported in stormwater
6. Which of these is not a benefit of native perennial vegetation?
   1. Habitat creation
   2. Improved long-term infiltration
   3. Increased biodiversity
   4. Requires no maintenance
7. True or false: Plant palettes for dry swales and bioretention practices are similar
8. True or false: It is not acceptable to have trees in bioretention practices
9. Which is least accurate?
   1. Nearly all phosphorus in tree leaves is released when exposed to leaching (e.g. rainfall)
   2. Phosphorus content of tree leaves changes with age and size within a species
   3. Phosphorus content of tree leaves by tree species can vary by as much as a factor of 5
   4. Leaves from a tree species contain more phosphorus than seeds for the same species

Answers

1. False. Permeable pavement and underground infiltration are examples of green infrastructure practices that may not be vegetated. They are considered GSI practices because they infiltrate water near the point of precipitation and therefore mimic natural systems.
2. 30. Coniferous trees can intercept nearly twice as much as deciduous trees on an annual basis. This of course varies with tree health, age, species, and location in Minnesota.
3. Only annuals can be planted on extensive green roofs
4. The primary purpose of a cover crop is to capture sediment that has been detached. Comment: The primary goal is to prevent sediment detachment.
5. True
6. Requires no maintenance. Comment: Native plantings require fairly intensive maintenance during the establishment period.
7. True. Both practices require plants that can tolerate temporary submergence in part of the practice and dry conditions in other parts of the practice. These correspond with Zones 4 (floodplain) and 5 (upland) in Plants for Stormwater Design (Shaw and Schmidt, 2003).
8. False. Trees are acceptable but there are certain design considerations, including tree placement and potential increased maintenance associated with leaf drop.
9. Nearly all phosphorus in tree leaves is released when exposed to leaching (e.g. rainfall). Comment: This is somewhat subjective, since about 60-90 percent of total phosphorus is released within 48 hours in laboratory studies.

Chloride quiz

Answers below

1. True or false: The drinking water standard for chloride is based on human toxicity
2. True or false: The aquatic life standard for chloride is based on toxicity
3. A stream in a highly developed urban area shows winter spikes in chloride concentration, but low concentrations during the remainder of the year. This stream is likely which of the following.
   1. Highly responsive to overland runoff from snow and ice melt events
   2. Is largely fed by groundwater baseflow
   3. Is in strong hydrologic connection with stormwater practices such as infiltration and wet ponds
4. True or false: A major concern with sodium chloride in road salt application is the effect chloride has on clay structure, particularly dispersive properties of soils.
5. True or false: Because chloride is an anion, it is always highly mobile in soil
6. Salt accumulation in lakes is a concern. Why? Select all answers that apply.
   1. It inhibits lake ice formation
   2. It can affect aquatic life
   3. It directly affects lake clarity
   4. It can interfere with lake mixing
7. From the study by Overbo et al. (2019), rank the following chloride sources in Minnesota, from largest to smallest.
   1. Wastewater (includes inputs from water softening)
   2. Industrial sources
   3. Road salt
   4. Fertilizers
   5. Livestock
8. Which statement is most accurate for chloride in stormwater runoff from urban areas receiving sodium chloride deicer application.
   1. Very high concentrations (>10,000mg/L) throughout winter, low concentrations (<50 mg/L) the remainder of the year
   2. High concentrations in winter, with occasional very high concentrations, with relatively low concentrations that gradually decrease through the remainder of the year
   3. High concentrations in winter and immediate low concentrations in spring and through the remainder of the year
   4. High concentrations throughout the year
9. A large stormwater infiltration system is constructed upstream of a baseflow fed stream in an ultra-urban area. The highest concentrations of chloride occur in October. Why?
   1. Local road authorities are testing salt application equipment in October
   2. Salt piles are created and contribute to runoff in October
   3. There is a delay in the time it takes infiltrated water to reach the stream
   4. No road salt is applied in winter and the chloride is coming from vegetation during leaf drop
10. What is the Smart Salting Assessment tool (SSAt)?
    1. A web-based tool to help permitted stormwater entities determine compliance with Total Maximum Daily Loads
    2. A web-based tool to assist public and private winter maintenance organizations in determining where opportunities exist to improve practices, make reductions in salt use, and track progress
    3. A tool to help entities identify alternatives to use of chloride-based deicers

Answers

1. False: The standard (Secondary Maximum Contaminant Level of 250 mg/L) is based on salty taste in drinking water.
2. True
3. Highly responsive to overland runoff from snow and ice melt events
4. False: Sodium causes clay dispersion
5. False: In acidic soils that have anion exchange capacity, such as some tropical soils, chloride can be adsorbed. Chloride may also be retained in other soils through chlorination reactions with organic matter. Also, chloride may become trapped in interpore spaces in soils, thus restricting mobility. However, in general, chloride in Minnesota soils is considered to be a highly mobile chemical and is thus often used as an environmental tracer.
6. Salt accumulation in lakes can affect aquatic life and interfere with mixing. Indirectly it may affect lake clarity if there are impacts to phosphorus cycling, which can lead to algae formation.
7. Road salt > fertilizer = wastewater > livestock > industrial sources
8. High concentrations in winter, with occasional very high concentrations, with relatively low concentrations that gradually decrease through the remainder of the year. There is residual chloride in soil and streets following snow melt, resulting in low but steadily declining concentrations from spring into fall.
9. There is a delay in the time it takes infiltrated water to reach the stream. Even if road salt were not applied to the area, which is unlikely, there is no established relationship between vegetation and chloride concentrations in receiving waters.
10. The Smart Salting Assessment tool (SSAt) is a web-based tool to assist public and private winter maintenance organizations in determining where opportunities exist to improve practices, make reductions in salt use, and track progress. It can be used to assess compliance with TMDLs.

Pretreatment quiz

Answers below

1. Pretreatment practices designed to remove solids typically remove particles larger than
   1. 5 microns
   2. 10 microns
   3. 100 microns
   4. 300 microns
2. While the particle size distribution in runoff varies widely depending on factors such as land use, a typical median particle size for urban runoff is
   1. 1 micron
   2. 10 microns
   3. 75 microns
   4. 200 microns
3. Based on the first two questions (above), is the following statement accurate? “I put in a pretreatment practice and it is removing 100 pounds of sediment annually. I can therefore claim a 100 pound credit toward my TSS Total Maximum Daily Load.”
4. True or false: Minnesota does not certify specific pretreatment practices, but strongly recommends pretreatment practices be approved through Washington State’s TAPE or New Jersey’s NJCAT programs, or has undergone modeling with SHSAM.
5. Vegetated filter strips are effective pretreatment practices but, like any practice, have limitations. Which of the following is not a limitation for filter strips.
   1. They tend to require more space than other pretreatment practices, which often limits retrofit suitability.
   2. They are not easily accessible which makes maintenance more difficult.
   3. They tend to require more space than other pretreatment practices, which often limits retrofit suitability.
   4. During winter months, they will become frozen and covered by ice and snow to some extent, which diminishes their effectiveness if flows become channelized.
6. In general, which type of device is most suitable for ultra-urban settings?
   1. Forebay
   2. Vegetated filter strip
   3. Underground settling device
   4. Above-ground screening devices
7. True or false: Screening devices are among the most effective water quality pretreatment practices
8. In order to achieve maximum sediment removal, forebays are typically designed to contain what percent of the water quality volume?
   1. 5
   2. 10
   3. 25
   4. 50

Answers

1. 100 microns
2. 75 microns
3. Not accurate. Using data from a literature review and assuming pretreatment will remove particles down to 100 microns in diameter, a device removing 100 pounds of sediment would remove about 25% of the solids in runoff captured by the device.
4. True
5. (b) Vegetated filter strips are typically easy to access.
6. (c). Underground practices, in general, are more suitable for ultra-urban settings
7. False Screening devices are primarily designed to remove gross solids, including trash.
8. b

Green infrastructure O&M quiz (September 2021)

1. True or false: Snow storage is recommended in filtration and infiltration practices as a way of treating water and enhancing infiltration
2. Which of these is not a typical annual maintenance recommendation for bioretention practices?
   1. Regenerating the soil or media
   2. Removing and replacing dead plants
   3. Checking the BMP and associated piping/conveyances for clogging
   4. Assessing performance, such as observing drawdown times and observing evidence of flooding
3. What is the maximum recommended slope on a green roof (without reinforcement)?
   1. 1:2
   2. 2:10
   3. 2:12
   4. 2:20
4. True or false: Pretreatment practices should be installed prior to constructing the permanent BMP
5. True or false: The contributing drainage area to a BMP is the total impervious and pervious area contributing runoff to the BMP
6. True or false: A green infrastructure practice always includes vegetation
7. Why are design phase O&M considerations recommended?
8. What is the recommended frequency for vacuuming of permeable pavement?
   1. Biennially
   2. Annually
   3. Biannually
   4. Quarterly
9. Mulch is generally not recommended for an infiltration or filtration practice. Why?
   1. It introduces weeds to the practice
   2. It leaches phosphorus
   3. It introduces insect pests to the practice
   4. It can clog pipes, inlets, and outlets
10. Which of the following is not a recommended component of a site-specific O&M plan?
    1. The plan should contain a maintenance agreement
    2. The plan should provide any operating procedures related to the practices
    3. The plan should provide clear maintenance expectations, activities, and schedules
    4. The plan should identify who is responsible for the maintenance and the type of expertise that will be needed for distinct O&M activities
    5. The plan should include an anticipated budget for O&M activities
    6. The plan should include an example O&M inspection checklist and an example maintenance report

Answers

1. False. Snow storage is generally not recommended in filtration and infiltration practices. The stored snow can compact the soil or media and reduce hydrologic performance. There may also be water quality concerns, particularly with chloride from road salts.
2. Regenerating the soil or media should not be needed annually. Certain practices, such as compaction or accumulation of metals and salts, may require that soil or media be regenerated.
3. 2:12. For more information, link here.
4. True. Pretreatment practices can provide protection of the post-construction practice while it is being constructed. Pretreatment practices must be regularly maintained.
5. True, the contributing drainage area includes impervious and pervious areas draining to a practice. Link here.
6. False. Permeable pavement is the best example of a green infrastructure practice that does not include vegetation. Green infrastructure is designed to mimic nature and capture rainwater where it falls. Green infrastructure reduces and treats stormwater at its source while while also providing multiple community benefits such as improvements in water quality, reduced flooding, habitat, carbon capture, etc.
7. Considering operation and maintenance in the design phase can prevent or minimize O&M issues once the practice is constructed. Design phase considerations vary with the practice. Examples include ensuring the contributing area is not too large, the proper vegetation is selected, and the proper type and amount of pretreatment is identified.
8. Biannually, in spring and fall
9. (d) A bit of a trick question. Under certain conditions, any of these four can be problematic. However, the primary reason is that mulch clogs inlets, outlets, and pipes. Answer (d) is also the only statement that is not phrased as being always true.
10. (a) A maintenance agreement is a separate component and not part of the maintenance plan