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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