August 31, 2022

Ms. Melanie Davenport

Commonwealth of Virginia

Department of Environmental Quality

Director - Division of Water Permitting

1111 East Main Street

Richmond, VA 23219

Re:      Guidance Memo No. 22-2012 Public Comment

Stormwater Management and Erosion and Sediment Control Design Guide

Dear Ms. Davenport:

Hewitt Solutions is an active and experienced design and consulting firm in the solar land development space that has worked very closely with DEQ for several years. We appreciate the opportunity to review the aforementioned guidance memo and offer the following comments: 

Section 2.302.C (Page 9)

• Clarify the requirements for instances where a Sediment Trap will be converted to a permanent SWM facility. What would be the standards for this type of design?

Section 2.303.D (Page 9)

• The VESCH says outfalls should be to an “adequate channel;” however, SWM regulations say concentrated outfalls should be to a “stormwater conveyance system.”  Both adequate channel and stormwater conveyance system have different definitions in their respective regulations. Clarify whether ESC outfalls are intended to be to a stormwater conveyance system or an adequate channel.

Section 2.303.D.1.d (Page 10)

• Sediment basin stipulation for an “adequate outfall” analysis requires 2-yr capacity and velocity checks to verify channel adequacy. Clarify that this is required of one cross-section at the basin discharge without further downstream analysis.

Section 2.303.E (Page 11)

• Clarify and define “structural integrity” required for sediment basins in the 25-yr storm. 
• VESCH Specification 3.14 states 25-yr storm but does not imply 24-hr storm. Clarify if Rational Method is not permitted in sediment basin design. 

Section 3.302.1.A.1 (Page 15)

• The last paragraph states “If a natural stormwater conveyance system is encountered before the limits of analysis is reached, the stormwater peak discharge should satisfy the requirements for discharges to natural stormwater conveyance systems.” Clarify that if the limit of analysis and a natural channel are reached simultaneously – for example, at a piped outfall confluence to a major waterway – that this does not require reverting to natural channel (energy balance) requirements.

Section 3.302.1.C.2.a (Page 16)

• For both subsections a and b, clarify the need for field-surveyed channel cross-sections. Public LiDAR is a better match for the general nature of limits of analysis calculations than field-surveyed cross-sections. In addition, field survey for additional downstream cross-sections is frequently unobtainable due to restrictions of private property access.

Section 3.302.1.C.3.a (Page 16)

• Clarify or reference source for 10 fps velocity limit in RCP; suggest a higher recommended maximum.

Section 3.302.3 (Page 18)

• In the past, existing natural swales that were not jurisdictional were not considered part of a stormwater conveyance system, though “…unimproved ephemeral channels, wetlands, or swales” are listed as part of the flood-prone area in this section. We support the inclusion of these features; clarify Section 3.302.4 to include them as well (see comment below.)

Section 3.302.3.A (Page 19)

• Variations in how the improvement factor should be applied has been experienced in the past given the description of “total land disturbance.” Suggest further clarifying the terms “site” and if improvement factor area designation of 1 acre applies to disturbed area within the given drainage area or, in fact, refers to total disturbed area for the project.

Section 3.302.4.B (Page 20)

• Clarify what information is required when submitting flood-prone area documentation and in which scenarios the documentation is acceptable. Approving certain buffers and areas on a “case-by-case basis” gives no further direction than exists today as to what is permissible. 

Section 3.303.1. (Page 20)

• Suggest providing additional guidance on definition of Point of Discharge and where it makes the most sense to select the analysis point. The existing receiving channel is often the logical choice for the point of analysis, but typically DEQ requires the analysis point to be at the LOD which is not quite in the stream bottom. 

Section 3.303.1A (Page 20)

• Suggest providing additional reasoning why reducing post development flows to equal to or less than pre-development conditions is not acceptable in areas where localized flooding is not experienced.

Section 3.305.1.B.1 (Page 25)

• Clarify requirement of 10-year velocity calculation for sheet flow in both the pervious/unconnected impervious and level spreader cases. A 2-year velocity calculation is standard practice to check for erosive velocities.

Section 3.305.2.A (Page 27)

• Suggest clarifying and updating this section: is the intent to specify that energy balance and channel protection must be met prior to concentrated flow being discharged through a level spreader that conforms to sheet flow requirements? This is not a requirement of 9VAC25-870-66.D.

Section 3.305.2.B (Page 27)

• Clarify why this allowable velocity table is different from the previous versions of this table pasted in this document. This version doesn’t match VESCH Table 5.14.

Section 3.307.D (Page 33)

• This section appears to dictate that an off-site drainage easement is required for “…any proposed off-site sheet flow paths…” but only includes a section on sheet flow from level spreaders. Clarify with specific carve-outs in this section confirming that no easements are required for pervious/unconnected impervious sheet flow. If engineering calculations as required in Section 3.305.1.A are provided showing that sheet flow volume and velocity are decreased/improved from existing condition, no easement should be required.
• This section states that level spreaders are subject to off-site sheet flow easements except in the Safe Harbor case. Clarify the exceptions to include scenarios in which the volume of sheet flow has decreased. If engineering calculations as required in Section 3.305.1.A are provided showing that sheet flow volume and velocity are decreased/improved from existing condition, no easement should be required.

Section 4.400 (Page 38)

• Consider modifying the VRRM to consider the positive impact of transitioning higher nutrient load land cover conditions to lower nutrient load land cover conditions, similar to how water quantity is analyzed in comparing pre and post conditions. This practice should be considered a pollutant removal practice and added to Section 4.403.B.

Section 5.200 B (Page 40)

• Suggest removing the “good engineering practice” of keeping post-dev drainage areas to within 10% of the pre-dev areas. This is not a stipulation of the stormwater code and is usually only done to comply with DEQ’s own requirement to route concentrated stormwater runoff to an approved stormwater conveyance system. Channel protection, flood protection, and sheet flow calculations and requirements as outlined elsewhere in the guidance memo more than protect downstream waterways in the case where pre- and post-DAs are greater than 10% different.

Section 5.301.D (Page 40)

• Suggest more clarity on pre-development analysis adjustments, as these are not typical. For example, are cultivated agricultural fields considered “previously disturbed”?

Section 5.500 (Page 44)

• Clarify the process for the “fast-tracked (expedited)” review that solar projects with an approved DEQ plan but not a prior approved interconnection date.
• Clarify the definition of solar panels that are “directly connected to the stormwater conveyance system” throughout this section.  

Section 5.500.D (Page 46)

• To our knowledge, the rain sensor guidance is not practicable: solar panels cannot physically rotate to 90-degrees (i.e. perpendicular to the ground) so that the horizontal impervious area is zero. Neither is it a fair assumption to require the minimum angle (parallel to the ground) for all calculations. Suggest refinement of this section.

6.500 Plan Submission Checklist (Page 50)

• If DEQ is not the VESCP authority, clarify if the ESC portion of the checklist need to be filled out, and if the checklist will be deemed incomplete if not.

• Clarify where to provide the latitude & longitude of SWM facilities: middle of facility, center of spillway, etc.

We appreciate your time and consideration of the comments within.

Respectfully,

The Hewitt Solutions Team