Virginia Regulatory Town Hall View Comments

Department of Conservation and Recreation

Virginia Soil and Water Conservation Board

Stormwater Management Regulations AS 9 VAC 25-870 [4 VAC 50 ‑ 60]

Action	Amend Parts I, II, and III of the Virginia Stormwater Management Program Permit Regulations to address water quality and quantity and local stormwater management program criteria.
Stage	NOIRA
Comment Period	Ended on 4/16/2008

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4/16/08 10:55 am

Commenter: Maita Pang, Imbrium Systems

Comments to the VSMP Regulations (I, II and III)

4VAC50-60-160. D3. "Comprehensive hydrologic and hydraulic computations of the pre-development and post-development runoff conditions for the required design storms, considered individually."

Water Quality should ideally not be computed based on a outdated peak flow rate methodologies (Rational Method, TR-20 or TR-55) when more advanced hydrology calculation methods (SWMM) are available and can be employed to analyze actual long-term, historical rainfall data and resulting runoff and pollutant loadings. Use of peak flow rates are commonly used for water conveyance design and came about as a result of flood protection, not water quality. The peak flow methods are easy to use, however they make too many assumptions based on static parameters and not dynamic parameters. They do not account for known variances in environmental conditions (hydrology, pollutant loads and antecedent conditions) and should not be used for water quality. This interpretation of a simplified hydrology for the area does not allow for accurate assessment of annual pollutant removal performance. The preferred hydrology and sizing methods would be to base WQ_f and WQ_v (targeting the WQ_v 80^th to 90^th % - supported by EPA, WEF and ASCE) from advanced hydrology continuous simulation methodologies that utilize long-term historical rainfall data (> 25 years). This can account for antecedent conditions and variable pollutant loadings.

Also, as our climate changes, use of up to date (recent) rainfall records for all hydrology calculation methodologies is important to account for the changes being experienced, as opposed to out-dated rainfall records (greater than 5 years old) which is very common.

Sand Filters listed in Table 1, are credited with 65% Phosphorous removal. This is exceptionally high when considering pollutant removal efficiencies based on field testing and credits given to Sand Filters from other state jurisdictions and additionally the pollutant removal unit process limitations. Performance data from the International Stormwater Database and many other sources indicate much lower performance capability of sand filters. The International Stormwater Database an average of 47% Total Phosphorous (TP) removal, with a standard deviation of 16%.

Most other state jurisdictions have given sand filters credit of only 40 to 50% TP removal, to name a few jurisdictions; MDE, NYS DEC, NJ DEP, DC DOE, and NC DWQ. Most of the corresponding state stormwater manuals were sponsored or written by the Center for Watershed Protection. The EPA fact sheet only provides 33% credit for Total Phosphorous Removal of Sand Filters (Table 2.0 Typical Pollutant Removal Efficiency) http://www.p2pays.org/ref/41/40466.pdf

From a pollutant removal unit process stand point, the physio-chemistry should be analyzed to determine what make most sense. TP is comprised of two phases; particulate-bound Phosphorous and dissolved Phosphorous. The phase that rapidly plagues our water quality, promotes algae blooms resulting low dissolved oxygen levels is the biologically active portion (dissolved phase). Sand and even soil matrixes have virtually no ability to capture the dissolved phase of phosphorous, as this material migrates with the flow of water, unless absorbed. The two mechanisms that can capture the dissolved phase are biological uptake and absorption. Sand Filters have neither capability as they function to only physically filter particulate-bound pollutants, so these practices only have the ability to capture only the particulate-bound phosphorous portion of the total phosphorous, hence why they are generally limited to the 40 to 50% TP capture rate.

It is suggested that the State of Virginia should review and reduce the Phosphorous removal credit of Sand Filters to better reflect true capability and more recent sound field test data.

4VAC50-60-60C

CommentID: 1397