As previously noted in our September posts, PA DEP has convened a BMP Manual Revision Committee. In their notification to attendees, they noted that

Much has been learned since the release of the manual and it is a goal to capture as many stormwater situations as possible. However, it is also understood that it is not practical to capture all situations…

… recommended updates may include edits to existing portions, complete omissions, or additions of new material.  All changes much be justified through acceptable principles of engineering or science.  If unable, to do so, subgroups may bring new ideas before the bigger committee for consideration and feedback.

Following, and in a series of consecutive posts, we will outline the focus of each Sub-Group as presented at the first Commitee Meeting

A. Subgroup Topic:  Alternate Control  Guidelines

CG-1 will likely remain, as currently established, for projects located within Special Protection Watersheds.  Recommendations for change, however, will still be considered.

The key is to find whether there are other acceptable guidelines that are protective to receiving streams and that can stand the test of scrutiny.

Ideas thrown out so far:

1. 1-year, 24-hour storm for non-Special Protection &  non-SW impaired streams
2. Revisit CG-2 for projects greater than 1 acre. (with added detail analysis/routing for peak control)
3. Matrix or Tiered Approach based on Watershed Characteristics:
   1. Stream Order
   2. Special Protection
   3. Stream Impairments
   4. Public Drinking Water Supply
4. PWD Model
   1. Water Quality -which includes GW Recharge  (1 inch from DCIA)
   2. Channel Protection (ED of 1-yr 24 hour for DCIA, Q<0.24cfs/ac; 24 to 72 hrs)
   3. Flood Control  (Act 167 or default Rate Control for 1 through 100 year storms)
5. A hybrid of those listed.

Questions:

Do we need to come up with a separate CG for streams impaired by stormwater?  (i.e. TMDL compliance)

It has been argued that CG-1 is overly conservative, particularly when a meadow assumption is used for existing conditions.  Does the subgroup agree/disagree?   What changes would the group recommend?

Does the group believe that a tiered or regionalized approach is necessary due to the diversity of Pennsylvania regions and watersheds?  Does the group believe it is feasible?

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