Melanie D. Davenport
Sent via: Melanie.Davenport@DEQ.Virginia.gov
Re: Guidance Memo No 22-2012
Dear Ms. Davenport,
We have received the Guidance Memo referenced above and have taken the opportunity to review and provide comment. We appreciate DEQ’s efforts in creating a document that will help the development community better understand the intent behind Virginia’s Stormwater Management Regulations. We understand many other firms and organizations have taken the time to review as well; therefore, we expect DEQ will take comments from the design community into serious consideration as this community applies the regulations on a daily basis. It is the design community’s experiences that find unintended consequences and situations where a set rule will not be applicable in all situations.
We hope the comments DEQ receives will assist in a revision to the Guidance Memo such that another revision may be posted for public comment until there is a final version that addresses all comments or explanations have been publicized to understand why comments are not addressed.
In an effort to understand our firms’ experiences, we are a team of Professional Engineers, and Stormwater Reviewers who have worked in West Virginia, Tennessee, North Carolina, and South Carolina. We have practiced Stormwater Design prior to the inception of the VSMP regulations. We believe that of the five states we have worked, Virginia has the most complex set of Stormwater regulations. With this being said, a Guidance like this is helpful assuming it represents the VSMP regulation correctly.
Our firm offers the following comments:
Guidance Section 2.302 D. (Page 9) Runoff coefficients or curve numbers used in runoff computations should correspond to a bare earth condition. See Section 5.303 herein.
Guidance Section 2.303 F. (Page 11) Runoff coefficients or curve numbers used in runoff computations should correspond to a bare earth condition. See Minimum Standard #6, 9VAC25-840-40 6, and Section 5.303 herein.
Comment:
State Code 9VAC25-840-40 (6b) states, “Runoff coefficients used in runoff calculations shall correspond to a bare earth condition or those conditions expected to exist while the sediment basin is utilized.”
We believe the State Code is more applicable as there are situations where a drainage area to a sediment trap or basin may include offsite drainage areas that are not permitted to be disturbed and those areas shall not be required to use a runoff coefficient or curve number for bare earth conditions. Eliminating the “or those conditions expected to exist while the sediment basin is utilized” portion of the State Code in the Guidance creates a document conflicting with a State Code.
Guidance Section 3.30.1 (C) (3a) (Page 16) Permissible (non-erosive) velocities. Reinforced Concrete Pipe (RCP). Post-development stormwater velocities should be less than or equal to 10 feet per second (ft/sec).
Comment:
There are many types of pipes used for drainage, i.e. CMP, HDPE, RCP, etc. Each type of product has special manufactured processes that may affect the allowed velocity in the pipe. For example, this section only references Reinforced Concrete Pipe, and there are different types and classes of Reinforced Concrete Pipe that may have different maximum velocities recognized by the manufacturer. Additionally, the American Concrete Pipe Association states “At velocities up to 40 feet per second, the severity of velocity-abrasion effects depends upon the characteristics of the bed load.” With this being said, there are several factors that will affect maximum velocity and the designer shall have to prove the material and bed load supports that velocity. We suggest permissible velocities over 10fps shall be allowed provided the designer can provide documentation from an industry association or manufacturer supporting the proposed velocity. We suggest this should be the same for man made channel linings of which this Guidance does not address.
Guidance Section 3.302.3 Discharges to Natural Stormwater Conveyance Systems. (Page 18) A manmade lake or reservoir not created for the purpose of managing post-development stormwater should be considered a natural stormwater conveyance system.
Comment:
Our firm has provided DEQ several statements regarding this interpretation. We would ask you refer to letters we have written to Erin Belt over the last year. We feel strongly that a lake or reservoir created by a manmade dam is a stormwater conveyance system created by man, and managed by man; therefore, meets the definition of manmade stormwater conveyance system. The guidance in its current form conflicts with State Code 9VAC25-870-10 that states,
“Stormwater conveyance system" means a combination of drainage components that are used to convey stormwater discharge, either within or downstream of the land-disturbing activity. This includes:
1. "Manmade stormwater conveyance system" means a pipe, ditch, vegetated swale, or other stormwater conveyance system constructed by man except for restored stormwater conveyance systems;
2. "Natural stormwater conveyance system" means the main channel of a natural stream and the flood-prone area adjacent to the main channel; or
3. "Restored stormwater conveyance system" means a stormwater conveyance system that has been designed and constructed using natural channel design concepts. Restored stormwater conveyance systems include the main channel and the flood-prone area adjacent to the main channel.”
A manmade lake or reservoir that conveys stormwater meets the portion of manmade stormwater conveyance system definition in the State Code that states, “other stormwater conveyance system constructed by man.”
We have experience designing developments on Smith Mountain Lake and more recently Lake Anna. There are discharges that have been designed, permitted, and constructed that met manmade channel protection criteria or sheet flow criteria. We have monitored those situations and have experienced no degradation to those lakes at these points of discharge. Classifying these discharges to natural stormwater water conveyance channels will require best management practices to meet the energy balance method. This will create maintenance burdens that are not necessary as these best management practices will not provide any more protections to downstream properties. Considering these lakes outflows are managed by man, and the sizes of the watersheds to these lakes are so large, there is no benefit to classify these lakes as natural stormwater conveyance systems. We suggest eliminating this sentence from the definition as it does not match state code and conflicts with the definition of manmade stormwater conveyance system.
Guidance Section 3.302.5 (page 20) Channel Protection Analysis Point. Where applicable, the allowable peak flow rate should be based on the area of the site that drains to the point of discharge in the pre-developed condition.
Comment:
In the cases as described herein on lakes, the predeveloped condition at the point of discharge is most often sheet flow for a small drainage area. Any development creates concentrated runoff and can only be discharged to the lake. Meeting the allowable peak flow rate is typically impracticable as the energy balance method will define an allowable peak flow rate of zero. Consideration shall be given to situations where this is not feasible.
Guidance Section 3.305 Sheet Flow (Page 24)
A. Piped or channelized stormwater runoff converted to sheet flow prior to discharge should
comply with 9VAC25-870-66 B (see Section 3.302 herein) and 9VAC25-870-66 C (see
Section 3.303 herein) or “Safe Harbor” (see Section 3.304 herein).
Comment:
VA State Code 9VAC25-870-66 D states,
“Increased volumes of sheet flow that will cause or contribute to erosion, sedimentation, or flooding of down gradient properties or resources shall be diverted to a stormwater management facility or a stormwater conveyance system that conveys the runoff without causing down-gradient erosion, sedimentation, or flooding.”
In cases where stormwater management can create a sheet flow condition from a piped or channelized flow that does not cause down gradient erosion, sedimentation, or flooding, we believe the State Code allows a solution that doesn’t require meeting 9VAC25-870-66B or 9VAC25-870-66C. A specific example would be discharging to a lake that has a watershed so large the quantity of runoff will not impact the downstream properties. Installing a level spreading device that will create a sheet flow condition that does not erode the shorelines, nor carries sedimentation to the lake, nor increases the lakes flood levels meets the State Code. We suggest providing language that addresses these situations, or simply reference Sate Code rather than put more restrictive requirements to what the State Code allows.
Guidance Section 3.305.2 Discharges of sheet flow from level spreaders.
Page 27 – B. Virginia Erosion and Sediment Control Handbook Table 5-14
Comment:
The table in this section does not match VESCH Table 5-14, Velocities have been reduced. The same table is referenced in Section 3.305.1 (B) with the correct values from VAESCH Table 5-14. It is recommended to revise the table.
Page 29 - G. The area of sheet flow should be located outside the limits of clearing and grading and be protected by erosion and sediment controls, or the area should undergo soil restoration via full implementation of DEQ Stormwater Design Specification No. 4 (Soil Compost Amendment) immediately prior to establishing permanent stabilization.
Comment:
In general, we believe this is good practice; however, in a situation where sheet flow has been created to discharge to a lake regulated by the Federal Energy Regulatory Commission which enforces shoreline management regulations that require shoreline stabilization, this could not be met. The limits of disturbance would be required to include the shoreline stabilization measures. We suggest language to allow this situation to occur.
Guidance Section 3.307 Drainage Easements (Page 33) D. Offsite discharges of sheet flow from a level spreader, with the exception of those discharges meeting the requirements of Safe Harbor (Section 3.304) herein, should be encompassed with a drainage easement. The minimum width of the easement should be the length of the level spreader plus 5 feet on each side. The minimum length of the easement should be the distance of the sheet flow path to the down-gradient stormwater conveyance system.
Comment:
In general, we believe this is good practice; however, in a situation where sheet flow has been created to discharge to a lake regulated by the Federal Energy Regulatory Commission which enforces shoreline management regulations that require shoreline stabilization, this could not be met. The owner of the lake will not give easements as their permitting process to install shoreline stabilization covers the necessary requirements an easement would grant. We suggest language that will allow permits in these situations to substitute as easements.
Guidance Section 4.404 STEP 4: Offsite compliance options. (Page 39)
A. Design professionals should investigate the use of offsite compliance options if the
required total phosphorus load cannot be achieved onsite through the implementation of
ESD, RR, and PR practices
Comment:
Guidance Section 5.200 Pre- vs Post- Development Drainage Areas/Divides
B. Post-development drainage areas should deviate from the pre-development condition by
no more than plus or minus 10%.
Comment:
We recently worked on a project where the natural low discharged to a location that was problematic. The only solution was designing a best management practice to meet Safe Harbor rules with a level spreader to create the sheet flow condition that represented the pre-developed condition. The locality did not want this to occur due to problems downstream and requested re-directing runoff to a manmade channel piped offsite to a location that avoided the natural downstream issue. Best Management Practices were designed to re-direct the post developed runoff to another location meeting VSMP regulations creating a better situation for the downstream property and resolving the issue. This section of the guidance will not allow this solution.
Additionally, it can be very difficult to match pre-development drainage divides. The VSMP regulations require pre-developed conditions to be analyzed to define allowable conditions for the post developed condition; therefore, if drainage divides must change the pre-developed condition analysis will require additional best management practices due to the increase in post developed drainage area. We believe defining a limit on drainage area deviation will create hardships that may not be overcome in any type of design.
We recommend eliminating this Section of the Guidance.
Furthermore, we believe DEQ shall give more time for public review as we received two different copies of the Guidance Memo. One copy was received two different ways from the Virginia Tech BMP Clearinghouse and from DEQ on behalf of the Director, Mike Rolband, both by email. These copies were stamped DRAFT. It was not until August 18th that we recognized what was posted on Town Hall website for public comment was different than what we received in emails from DEQ and Virginia Tech. We have also noted that the public has commented on the DRAFT copy. We can only assume they are unaware of the difference. It shall also be noted both the DRAFT copy and the copy on Town Hall website are dated July 1st, 2022. Unfortunately, we believe the publication of the document has been misleading and DEQ shall ensure everyone knows the difference between the two copies.
We appreciate the opportunity to provide comment and trust DEQ will take all comments under consideration when determining how to finalize the guidance.
Respectfully,
Sheldon R. Bower, PE
Parker Design Group, Inc