Questions and answers, December 15, 2016 webinar
Below are questions submitted during the December 15, 2016 webinar on Infiltration. Answers include links and if appropriate, links to additional information.
- 1. Why do you need 3 feet of separation from groundwater for infiltration but in the same pond footprint you can do wet pond construction which is in direct contact with groundwater:
- The Manual states: In general, there is no minimum separation distance required with ponds. Intercepting the groundwater table can help sustain a permanent pool. However, some source water protection requirements may dictate a separation distance or an impervious liner if there is a sensitive underlying aquifer and the bottom material of the pond allows for infiltration.
- 2. How much avg square ft cost for install and maintenance of this example system?
- 3. What kind of vegetation can handle the 6.5' maximum bounce mentioned?
- 4. Is there an example scope of work that would describe what a boring consultant is to gather the required documentation necessary for design of SWPPP.
- 5. What is the general thought of infiltration in areas that are in active karst features (less than 50 feet of soil cover) but it is not located in the DWSMA or Wellhead protection area? I have heard the term higher engineering review to determine if infiltration can be done in Karst areas but what does the higher enginnering review actually consist of?
- 6. does the manual address infiltration in D soils - as required by several watershed districts?
- 7. How much avg square ft cost for install and maintenance of this example system?
- 8. Is there a minimum offset distance if there is contaminated soil?
- 9. any discussion during design for routing around facility during establishment period?
- 10. Are infiltration practices still recommended near areas of high salt loading?
- 11. What storm event needs to infiltrate within 48 hours when including the bounce in the drawdown depth?
- 12. was mentioned that mndot grade 2 compost was not recommended for filtration practices due to nutrient leaching. Are there alternative recommendations other than peat moss?
- 13. media passes all tests. How to correct if perc failures occur after placement
- 14. At some point will we start focusing on treating different runoff in different ways? Parking lot runoff differently than roof runoff, etc. since they have different treatment needs versus putting all of the runoff together? It seems like we are just creating more dilluted runoff at times. It would also be nice to see more info on routing (bypasses) and not sending more than 1" to the treatment feature by separating quality from rate control.
- 15. How long does grade 2 compost leach
- 16. Can you talk a little about the use of stormwater-specific geotechnical borings versus interpretation of structural-specific borings (e.g. those for footings and foundations nearby a proposed practice)
- 17. Does the MPCA have a recommendation for when infiltration should not be used due to high blow counts/dense soils? What would be considered a high blow count?
- 18. Do you recommend vegetating large infiltration basins?
- 19. can you talk more about sub grade infiltration practices?
- 20. Many sites we work in have saturated soils within 3' of the existing ground and require mound septic systems. However, the soil borings show a C soil. How are we suppose to provide filtration when this in the case?
- 21. can you point out and discuss the underground systems/
- 22. Can you compare annual maintenance costs of infiltration basins vs. subgrade infiltration?
- 23. Design: Please clarify the bottom of the infiltration practice. Is it the floor of the basin or the bottom of the planting medium, ripped area, and abutment to the in situ soil.
- 24. Are you posting this presentation on line for us to review?
- 25. we are in sandy soils with some basins infiltrating at 10+ inches/hr. Is there a reccomended maximum infiltration rate for pollutant removal?