This page provides a summary of significant recent changes to this website and to anticipated changes in the near future. We anticipate this page will be updated infrequently (i.e. every one or two months).
- Table with design infiltration rates
- The table now contains one value for B soils (0.3 inches/hour). The previous version of the manual included rates of 0.3 and 0.6 inches/hour based on texture. The value of 0.6 was not supported by literature and a technical group determined there should be one value for B soils.
- The design rate for D soils is 0.06 inches/hour. This replaces the previous value of <0.2 inches/hour and is in line with the Minimal Impact Design Standards calculator.
- A/D, B/D, and C/D soils are assigned infiltration rates of 0.06 inches/hour, corresponding with a D soil. These soils are subject to seasonal high water tables, at which time they behave like a D soil.
- Safety factors - safety factors, previously called correction factors, are applied to field measured infiltration rates. They are intended to account for natural variability in infiltration rates of soils and in decreased infiltration performance of a BMP over time. A safety factor of 2 shall be applied to infiltration BMPs other than permeable pavement. A safety factor of 2.5 shall be applied to permeable pavement. For example, a measured infiltration rate for a bioretention system of 1.0 inches per hour shall be divided by the safety factor of 2, resulting in an infiltration rate of 0.5 inches per hour. In Version 2.X of the Manual, safety factors were calcualted using information in a table.
We completed migration of content from the 2008 Manual to this website during the last week of March. We do not anticipate further significant changes in Manual content during the wiki website rollout in April. Following that, we hope to incorporate the following changes into the Manual:
- new information on green roofs in May and June;
- updates to the bioretention section in early to mid summer
- incorporation of information on trees in late summer and early fall;
- new sections on stormwater Minimal Impact Design Standards; and
- new information on iron-enhanced filters this summer.
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