Section

Comment

2.303 (D)

This section should include meeting the channel and flood protection requirements of 9VAC25-870-66 or meeting the Safe Harbor provisions as options for compliance for sediment basin discharges in lieu of analysis of the downstream channel to the limit of analysis.  This is stated in Minimum Standard 19(n) (9VAC25-840-40).

3.302.3

The Guidance Document should clarify (as is done in Section 3.302.1(A)(1)) that the energy balance requirement applies only if a natural conveyance system is reached before the limits of analysis.  As an example, this is clearly explained in Section 11.5.2.1.7 of the VDOT Drainage Manual:

“The point where the limit of analysis occurs does not need to be included in the evaluation of adequacy, but the system from the outfall or point of discharge up to (but not including) the limits of analysis must be analyzed. If there is a natural channel anywhere in the system from the outfall up to the limit of analysis (but not including the point defining the limit of analysis), then the energy balance will apply.”

The suggested text keeps in line with the long-standing Virginia Statewide Stormwater Runoff Standard (Virginia Erosion and Sediment Control Handbook, Chapter 4) in which a receiving channel may be assumed adequate if the total drainage area to the point of analysis is 100 times greater than the contributing drainage area of the project site.  If the channel is adequate, there remains no reason or benefit to apply the energy balance reduction.  This section may also be improved by creating a list of specifically excluded water bodies, such as tidal waters, and rivers such as the James, the New, the Dan, the Roanoke, and the Rappahannock.  However, at some point, the exclusion must still come back to a limit based on a comparison of the site area to the watershed area (considering the headwaters of these rivers) – in lieu of regulatory changes, this must be 100 times the site area, unless a locality has adopted more stringent technical criteria.

3.302.3

“A manmade lake or reservoir not created for the purpose of managing post-development stormwater should be considered a natural stormwater conveyance system.”

It should be noted that this statement was not in the pre-publication copy sent via email by DEQ on July 8, 2022, despite both the pre-publication copy and the final copy available on the Virginia Regulatory Town Hall website being dated July 1, 2022. 

This modifies the definition of a natural conveyance system (as defined in 9VAC25-870-10) and adds an unnecessary and wasteful burden on development, particularly when the receiving waterbody has a watershed greater than 100 times the site area and is controlled by a release structure.  A suggested improvement would be to either clarify the applicability based on the 1% limits of analysis as described above in VDOT’s Drainage Manual and/or create a list of specifically excluded controlled water bodies such as Kerr Lake, Smith Mountain Lake, Lake Gaston, Lake Anna, Claytor Lake, etc.

3.302.3 (A)

3.304 (C) (3)

“RV_developed = the un-attenuated volume of runoff from the site in the developed condition”

This modifies the definition as written in the regulations.  “Un-attenuated” does not appear in 9VAC25-870-66(B)(3).

3.302.4

This section limits the definition of a natural conveyance system (as defined in 9VAC25-870-10) by saying flood-prone areas (included in the definition of a natural conveyance system and also specifically defined in 9VAC25-870-10) would only be evaluated for inclusion in a natural conveyance system on a case-by-case basis.  Instead of modifying the definition in the regulations to say all flood-prone areas will be evaluated on a case-by-case basis, the additional guidance document should describe certain situations (such as a steeply sloped riparian buffer) that warrant further evaluation.  The 1-year storm is not a channel forming or flooding event in natural channel design parameters.  A more appropriate flood event to analyze and determine the flood-prone area would be the 2- or 10-year storm event.

3.303

“The applicable flood protection criteria depends on whether or not pre-development localized flooding exists downstream from the site.”

If 10-10 detention is acceptable when there is existing flooding, common sense suggests that 10-10 detention should also be typically beneficial and acceptable when there is not existing flooding.  This guidance creates unnecessary burden in analysis on the development community and unnecessary burden in review on DEQ.  This is counterintuitive to DEQ’s stated goals of streamlining review/approval and eliminating redundancy.

There may be instances, such as development that is upstream of another SWM facility or a part of a connected storm drain system, in which unnecessary detention may align discharge peak times in a negative way.  These types of scenarios are uncommon and could be evaluated on a case-by-case basis, as to not discourage the reduction of peak flows through detention.

3.303.1(C)(3)

3.303.2(B)(3)

The limits of analysis is inconsistent with the regulations, 9VAC25-870-66(C)(3)(c).  This statement should read “The stormwater conveyance system enters a mapped floodplain or other flood-prone area, adopted by ordinance, of any locality” not just a “FEMA floodplain”.

3.305.1

3.305.2

All references in these sections to 10-yr 24-hour storm velocity are inconsistent with the regulations.  The VSMP Regulations and all other VA state standards evaluate erosive velocities based on the 2-yr 24-hour storm.

3.305.2

3.307 (D)

“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).”

“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.”

9VAC25-870-66(D) is written such that discharges of sheet flow from level spreaders are to be treated the same as those from pervious or disconnected impervious areas, however, they are subject to different technical criteria in this guidance.  By the regulations, requirements of section 3.305.2 (A through N) should only apply when there is an increase in runoff volume or velocity compared to the pre-developed condition.  Otherwise, discharges from level spreaders should only be subject to the requirements set forth in 3.305.1 (A).

3.305.2

“The length of sheet flow path to the down-gradient stormwater conveyance system should be less than or equal to the following…”

This requirement is not stated in the regulations and ignores the condition where the pre-development downstream flow path may be shallow concentrated flow.

Instead of tying the issue of post-development stormwater discharges to NEH Part 60 Chapter 15 which speaks in terms of Time of Concentration, this section should focus on whether the discharge mimics the pre-development rate and volume in line with Va. Code § 62.1-44.15:28 A 10.  For example, the pre-development runoff may be shallow concentrated flow across a rolling farmland or karst swale; or, a sheet flow discharge to a wetland or RPA may be more beneficial (provide greater infiltration) when located more than 100 feet from the main channel.

3.307

All discharges that are made in accordance with the Virginia Stormwater Management Act and/or VSMP Regulations and do not require/propose construction, improvement, or modification of downstream flowpaths should not be subject to obtaining easements or agreements from downstream property owners.  This section should specifically exclude discharges to an existing stormwater conveyance system that is not being modified.

4.400 – 4.404

This section must be clarified to convey that this a suggested process and that demonstration of the inability to achieve compliance onsite is not a requirement for the use of offsite nutrient credits (4.404(A)).  See 9VAC25-870-69(B), which states the operators shall be allowed to utilize offsite options under certain criteria.

Chapter 5

This section of good engineering practices should be more specifically defined in section 5.100 as suggestions and not requirements.  Good engineering practices relies on the judgement of engineers through the design practice and do not always include the steps or processes described in this section.  This chapter should be emphasized as suggestions for the engineering community and not requirements for DEQ or local authorities to adhere to in their reviews

5.200 (A) and (B)

“Post-development drainage areas and drainage divides should replicate, as nearly as practicable, the pre-development drainage areas and drainage divides. See Va. Code § 62.1-44.15:28 A 10.”

This statement misrepresents Va. Code § 62.1-44.15:28 A 10.  It replaces the parameters of rate of flow, runoff characteristics, and site hydrology with “drainage areas and drainage divides” and ignores the provision that the law provides for improvement of existing erosion and flooding conditions.  It should be noted that the existing channel and flood protection requirements already address Va. Code § 62.1-44.15:28 A 10, including the change in runoff volume incurred by changes in drainage divides. 

“Post-development drainage areas should deviate from the pre-development condition by no more than plus or minus 10%.

Because after-development runoff can be exponentially changed whether drainage areas/divides are modified or exactly the same, a 10% change in area is substantively irrelevant to the intent of the Virginia Stormwater Management Act and VSMP Regulations or the effects of stormwater runoff on the Commonwealth.  Varying pre-development conditions including topography, site size, and geographic location, urban versus rural settings, and linear development projects make application of this new criteria highly impractical.

A better application of this concept would be to use a ±10%-20% change in area to trigger an evaluation of the impacts by way of the adopted technical criteria:

• Areas that increase must meet the criteria of channel and flood protection, Safe Harbor, or 9VAC25-870-66(D) for sheet flow.  Any requirements in addition to the adopted technical criteria are not warranted as there is otherwise no restriction on the allowable increase in runoff volume caused by development in Virginia (whether that increase be from change in land cover or change in watershed area is irrelevant)
• Areas that decrease must either demonstrate a runoff volume that is similar to the pre-development condition or describe how the reduction in runoff volume on the adjacent/downstream properties does not have a negative impact (for example, demonstration that there are no ponds or wetlands immediately downstream that rely on the runoff water from the site to fill/hydrate).

5.301(D) 5.302(D)

“The hydrologic soil group (HSG) used for post-development CN selection should be based on the ultimate development condition of the subject land-disturbing activity…For disturbed soils (e.g., pre-development soil profiles that will be mixed or removed or fill material from other areas will be introduced), the design professional should:

1. Adjust the pre-development HSG by at least one factor (i.e., HSG A to HSG B; HSG B to HSG C; HSG C to HSG D) when selecting the post-development CN. See Section 5.302 D herein; or …”

A requirement to adjust the post-developed CN for disturbed soils is not stated in the VSMP Regulations, current and previous Virginia Stormwater Handbooks, or previous Agency guidance (Virginia Runoff Reduction Method, GM 16-2001).  Universal application of an adjustment for any disturbed soil would translate to a substantial additional burden on land development, particularly in rural areas where pre-development lands are undisturbed.

Modification of the pre- to post- HSG is not possible with the Agency provided VRRM spreadsheets.  If you do not provide matching soil area totals, the VRRM worksheet returns an error and does not compute.

Full implementation of DEQ Spec. No. 4 (Soil Compost Amendment) per the specifications is not practical in western parts of the state due to the slope limitations in the specification.

A suggested modification to these sections would be to provide further clarification limiting the applicability of HSG adjustment.  For example, limiting pre- and post- development adjustment to situations where pre-construction infiltration testing was performed.

An alternate suggestion would be clarification that implementation of an adjustment is optional at the discretion of the design professional (as long as if the adjustment is applied it is applied based on consistent criteria from pre- to post- development).  Hydrologic soil grouping, like all stormwater computations, is based on a set of assumptions including but not limited to large scale soil mapping from USDA; there must be understanding regarding the level of accuracy relative to the engineering factor of safety present in stormwater design.

5.600

“The design professional should screen for the relative risk of encountering acid sulfate soils within the proposed limits of clearing and grading.”

The guidance and landrehab.org website are unclear whether brown category (sulfide occurrence documented) triggers the requirement for a site investigation.

In consideration of the number, availability, and capacity of “qualified professionals with experience in acid sulfate soil recognition and remediation” out there, it should be clarified that the determination of “relative risk” and the need for further testing (as described in 5.600(B through D) should be at the discretion of the design professional.

6.500

The certification statements should include language similar to the BMP as-builts and other required certifications such as “In my professional opinion…” or “To the best of my knowledge...”.