County of Fairfax, Virginia - Wetland Studiesnewsletters.wetlandstudies.com/docUpload/2010-08... · 8/19/2010 · Fairfax County remains committed to addressing the benthic impairment

County of Fa i r fax , V i r g i n i a To protect and enrich the quality of life for the people, neighborhoods and diverse communities of Fairfax County

August 19, 2010

Gregory Voigt Office of Standards, Assessment and TMDLs (3WP30) U.S. EPA Region III 1650 Arch Street Philadelphia, PA 19103

Reference: Draft Benthic Total Maximum Daily Load (TMDL) Development for Accotink Creek, Virginia

Detailed Comments on June, 2010 Draft Report

Dear Mr. Voigt: The purpose of this letter is to provide detailed comments on the Draft Benthic TMDL Development for Accotink Creek, Virginia. The draft report was posted to the Virginia Department of Environmental Quality (VA DEQ) and U.S. Environmental Protection Agency (EPA) websites on July 5 and 6, 2010, respectively. On July 28, 2010, Ms. Sharon Bulova, Chairman of the Fairfax County Board of Supervisors (BOS), submitted general comments on the Board's behalf that expressed concerns regarding potential negative consequences of the draft TMDL as proposed. The Board also mentioned that County staff would be providing additional technical and detailed comments under separate cover. Fairfax County appreciates the opporturiity to provide additional, more detailed comments and recommendations to EPA. This letter provides the County's major comments on the draft TMDL, and a detailed comment matrix is enclosed.

Fairfax County remains committed to addressing the benthic impairment in Accotink Creek and fully supports innovative approaches to environmental management. The County has made significant investments to protect and begin restoration of the watershed and it is critical that the TMDL support these ongoing efforts. A TMDL that does not have a reasonable assurance for success will likely undermine our previous efforts and derail future efforts. For these reasons, we continue to have serious concerns about the change to a flow-based regulatory approach because it is still not clear how using "flow" as a "surrogate" for sediment will be more effective than addressing sediment directly. Further, considering the cost and limitations of current technology to reduce flow in already developed watersheds, there is a high probability that in addition to not being able to withstand legal challenge, the TMDL will undermine community support for other stormwater management efforts.

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Department of Public Works and Environmental Services Director's Office

12055 Government Center Parkway, Suite 659 Fairfax, VA 22035-5502

Phone: 703-324-5033, TTY: 1-800-828-1120, Fax: 703-324-1818 www.fairfaxcounty.gov/dpwes

Mr. Gregory Voigt Draft Benthic Total Maximum Daily Load (TMDL) Development for Accotink Creek, Virginia Detailed Comments on June, 2010 Draft Report Page 2 of7

As a result, we continue to recommend that the agency develop a sediment TMDL for Accotink Creek in a manner generally consistent with the approach used by VA DEQ and approved by EPA for Popes Head Creek, Bull Run and Difficult Run. This approach addresses the urban runoff and sedimentation issues while preserving the flexibility to select the most effective technologies to implement the TMDL. However, given the fact that we have made this comment repeatedly throughout the TMDL development process and EPA has instead persisted with the unique "flow" approach, we offer the following comments on the June, 2010 Draft Report. The County's major comments on the draft TMDL can be grouped into three broad categories: technical, implementation and legal issues, as follows.

Technical Issues The enclosed comment matrix identifies a number of technical issues with the draft TMDL, some of the most significant of which are listed below.

• Flow Rate vs. Flow Volume: The draft TMDL repeatedly confuses flow rate with flow volume. Throughout the document, "volume" should be replaced with "flow rate". Flow velocities that cause shear stress to exceed critical levels are the cause of channel erosion. Those velocities are related to flow rate not flow volume. See Comment 3-20 and several other editorial comments related to use of the word "volume". The intent of this TMDL could be met, for example, by detaining storm flows to avoid flow velocities being above the critical shear stress, while not necessarily retaining volume. Basing this TMDL on volume and not flow rate could lead to extraordinary, unnecessary implementation costs. While we oppose the flow-based TMDL approach, at a minimum, it is recommended that EPA correct language throughout the draft report to clarify that the TMDL is targeting flow rate and not flow volume.

• Soils: The EPA analysis based on STATSGO data vastly overestimates the extent of Hydrologic Soils Group B (moderate infiltration rates) in the watershed and vastly underestimates the extent of Hydrologic Soils Group D (very slow infiltration rates). See Comment 2-2. This analysis has significant implications for both the selection of appropriate attainment streams and the feasibility of attaining the TMDL. Fairfax County strongly recommends the use of the more detailed soils data that are readily available on the County's website.

• Attainment Streams: The criteria used to select the attainment streams do not demonstrate that the streams selected are appropriate. Critical evaluation criteria were inadequately reviewed by EPA: soil type, slope and watershed size and shape all have substantial impacts on hydrology and therefore should be carefully considered in the selection of attainment streams. The report provides a number of criteria used to identify the attainment streams, however, it does not discuss how the attainment watersheds are hydrologically similar to Accotink Creek. In essence it seems that the attainment streams were selected simply because they were the only attaining streams available. Based on our internal analyses of watershed size, land use, and soil type, we would expect flow rates in Accotink Creek to be higher than the attainment streams, even under a completely natural

Mr. Gregory Voigt Draft Benthic Total Maximum Daily Load (TMDL) Development for Accotink Creek, Virginia Detailed Comments on June, 2010 Draft Report Page 3 of 7

condition. See Comments 5-4 and 5-5. While we oppose the approach used to select the attainment streams used to develop the draft TMDL, at a minimum, it is recommended that EPA include language stating the TMDL can be modified in the future i f more appropriate attainment streams are identified.

• Estimation of the Flow Rate Reduction: In the draft TMDL, the discharge level for a 1-year 24-hour duration storm was determined using the annual maxima of daily discharges. This was then placed in a flow duration curve of all daily discharges to determine the target flow rate, which is shown to have an exceedance probability of approximately 2.2 percent (see Figure 5-5). If we assume that the point at which the Accotink Creek FDC crosses the attainment stream composite FDC represents the demarcation between storm flows and base flows (see Figure 5-4), this exceedance probability appears to be very low for a 1-year event. We would expect the 1-year event to have an exceedance probability that is closer to the point where the FDCs cross. This underscores the fact that values derived from an extreme value distribution (annual maxima) should not be placed on the parent distribution (daily average) and interpreted the same way. See Comment 5-9. While we oppose the flow-based TMDL approach, at a minimum, it is recommended that EPA include language stating that the TMDL can be modified in the future, by either VA DEQ or EPA, i f more robust analyses are used, including but not limited to comparing Accotink to these or other unimpaired streams, and the results demonstrate that an alternative TMDL and/or alternative WLAs/LAs are appropriate.

• Basis for TMDL Allocations: The draft TMDL describes the rational method and the method used to develop land-use specific runoff coefficients and relative flow contributions to the 1-year recurrence flow rate. However, the EPA description of the analysis is vague and does not convey the actual role of the rational method or the correct use of runoff coefficients. The text should detail the actual methods used to generate Table 6-1, including the percent imperviousness and runoff coefficients, and more accurately describe the role of the rational method in TMDL and WLA calculations. The County used more accurate percent impervious values within the (albeit, questionable) rational method of the TMDL (see Comment 6-2), and the land-use specific percent reduction decreased from 55.4 percent to 50.4 percent, a nearly 10 percent decrease. The "relative contribution" of transportation doubled, from 16 percent to 32 percent of the storm flow, while the relative contribution of medium density residential and low density residential decreased from EPA-reported values by 36 percent and 50 percent, respectively. Given the significant regulatory impact of TMDL implementation, this wide variability of impact on different existing land uses - and thus on different existing landowners affected directly or indirectly by the TMDL - is unacceptable. While we greatly question the use of the rational method for WLA development, EPA should at a minimum use the more accurate percent impervious values reported in the comment matrix.

Implementation Issues: Even i f all of the technical issues identified here and in the enclosed matrix were addressed, the County has significant concerns about the implementation issues raised by EPA's surrogate


approach, using flow rate in place of the identified stressor, sediment. The draft TMDL fails to adequately demonstrate that the proposed surrogate approach will more effectively address the benthic impairments in Accotink Creek when compared to a TMDL that directly targets sediment. The County believes that the flow-based approach will delay any improvement in the benthic community.

• Constraints on Implementation Including Stream Restoration: As written, the WLA section will greatly constrain the ability of the County to use a comprehensive, integrated approach to address the benthic impairments in this watershed. In particular, the WLA section for Municipal Separate Storm Sewer Systems (MS4s) should acknowledge other BMPs that can lead to improvement of the benthic community. At the public meeting on July 26, 2010, EPA staff stated that this TMDL will not prevent MS4s from continuing stream restoration activities in the watershed. However, there is a major difference between "will not prevent" and "will encourage". Should this section remain as written in the final TMDL, it will almost certainly require the County to re-direct resources entirely towards flow reduction (and consequently, will thereby prevent restoration activities). The County prefers an integrated approach, and stream restoration is a major component of our Watershed Management Plans, which are being developed with the cooperation of stakeholders and have a strong scientific foundation. Overall, the County opposes the flow-based TMDL approach, but at a minimum the WLA section should include language that allows sediment-related BMPs to be used to comply with this TMDL, as detailed in Comment 6-15. In addition, it is recommended that EPA include language stating that the TMDL can be modified in the future i f more appropriate stressors are identified (sediment, toxicity, etc.)

• New Development and Redevelopment: The draft TMDL implies that all new construction and redevelopment will incorporate stormwater management practices that result in zero net increase in runoff. However, this is not necessarily true and, more importantly, is an implementation policy decision that is beyond the scope of this TMDL. This TMDL requires a 48.4 percent reduction in the 1-year, 24-hour flow rate from the Fairfax County MS4. Within this constraint, new and redevelopment can be subject to a wide array of stormwater management practices including practices that result in increased runoff. If the County MS4 plans to achieve a 48.4 percent reduction across the entire MS4, then certain land areas and land uses within the MS4 area can achieve a smaller reduction as long as others achieve a higher reduction, as detailed in Comment 6-22. The same incorrect assumption is stated regarding nonpoint sources in the TMDL, and it is in error for the similar reasons. Similarly, the TMDL language inappropriately seems to suggest that the amount of construction in the watershed is being regulated. See Comment 6-6. Please revise the aforementioned language to reflect the technical approach to the TMDL, as opposed to making statements related to future growth policies or other specific implementation policies. These implementation policy issues would be more appropriately addressed during the future TMDL Implementation Plan development process, and are clearly beyond the scope of the TMDL.


• Implementation through Permit Requirements: As stated in Comments 6-4 and 6-14, the County believes that the assumption made in the TMDL that 90 percent of the watershed drains through regulated MS4 outfalls is not accurate. However, given that assumption, it is clear that EPA intends for the vast majority of TMDL implementation to take place through MS4 permit requirements. This makes the comment made by EPA staff at the July 26, 2010 public meeting that the TMDL need not consider economic impact or feasibility a cause for great concern. If TMDL implementation is to be driven for the most part by permit requirements, it is vital that feasible implementation measures be identified and their costs assessed prior to incorporating the TMDL into any permits. The County encourages to VA DEQ and VA DCR to facilitate an open post-TMDL stakeholder process to evaluate reasonable/feasible implementation actions and potential VPDES and VSMP permit provisions.

For clarity regarding the process for establishing implementation-related policies related to the foregoing three bulleted comments or implementation issues, we request that the TMDL include a new section dedicated to the implementation planning process. The text we propose for this section is included in the detailed comment matrix as Comment 6-23 and is based on similar text presented in another pending draft TMDL in this region (VA DEQ/ICPRB, Bacteria TMDLs for the Hunting Creek, Cameron Run, and Holmes Run Watersheds -DRAFT REPORT, July 19, 2010):

Legal Issues We have significant doubts about the lawfulness of the proposed TMDL, which seeks to regulate flow as a surrogate for sediment. We believe that the Clean Water Act (CWA or Act) does not provide EPA with the statutory authority or the regulatory discretion to create a TMDL that would impose upon the County MS4 or landowners restrictions on the flow of water within the impaired portion of Accotink Creek.

Regulatory actions must adhere to the clear intent of Congress. It is our understanding that the CWA sets forth distinct definitions for pollution and pollutant, and the use of those terms clearly constrains the scope of EPA's regulatory authority in this instance.1 CWA Sect. 303(d)(1)(C) authorizes EPA, in establishing TMDLs, to regulate pollutants and not pollution. Additionally, CWA Sect. 402(p)(3)(B)(iii) requires municipal separate stormwater sewer systems to obtain permits to reduce the discharge of pollutants.

The definition of pollutant is not ambiguous and cannot be construed to mean flow. In fact, EPA's own analysis concludes that flow is pollution and not a pollutant. It appears that the proposed TMDL may be circumventing the unambiguous statutory limitations of the CWA by regulating flow as a surrogate for sediment.

1 Under the CWA pollutant refers, generally, to material, chemicals, or wastes that are discharged into water. Pollution, however, is man-made or man-induced alteration of chemical, physical, biological, and radiological integrity of water.


We also have concerns with the legality of the proposed Accotink Creek TMDL because the report has failed to provide adequate evidentiary support to justify the regulation of flow. CWA Sect. 303(d)(1)(C) provides that any TMDL shall reduce the load of the relevant pollutant to "a level necessary to implement the applicable water quality standard". A TMDL, therefore, must have a demonstrable likelihood of meeting the applicable water quality standard.

As a preliminary matter, there are no existing water quality criteria for benthic organisms (or sediment or flow) in Virginia. Instead of adopting such criteria through the required public process (i.e., rulemaking), this TMDL is establishing de facto criteria for defining Virginia's General Standard (9VAC25-260-20) based on reference watershed conditions. These de facto criteria effectively amend Virginia's General Standard and, accordingly, constitute new or revised water quality standards. Failure to comply with standard rulemaking procedures in conducting its unilateral amendment of Virginia's water quality standards appears unlawful and could render the TMDL based on that action invalid as well.

Even i f the relevant water quality criteria had been lawfully promulgated by or for Virginia, the proposed TMDL (a reduction in flow in Accotink Creek) must therefore be shown to be a means by which EPA believes the benthic community will be restored and maintained at a non-impaired level. However, the TMDL proposes reductions in flow without sufficient evidentiary support that the elimination of the purported cause of the impairment (excessive stormwater runoff) will result in restoration of the benthic community to non-impaired levels. Further, the proposed Accotink Creek TMDL fails to demonstrate any correlation between the degree of reduction in flow and the attainment of the applicable water quality standard. In short, as drafted, this TMDL imposes drastic, costly, and unattainable regulations on the County without providing adequate data establishing that the proposed TMDL is likely to restore the benthic macroinvertebrate population.

The lack of evidence to support the regulation of flow as a TMDL is compounded by reliance on flawed and erroneous data. All action must be rationally based on the facts. Such facts obviously must be accurate, and all relevant evidence must be considered.

We believe there are numerous technical deficiencies in the TMDL as listed in the enclosed matrix. For example, the report overstates the relationship between flow and sediment loads. The data suggest that 25 percent of the variation in sediment loads is not attributable to flow, yet the proposed TMDL regulates only flow at the expense of other possible contributors. Further, the report grossly overestimates the contribution by permittees of stormwater to Accotink Creek, which effectively ignores other significant sources of stormwater runoff. Finally, the numerous dissimilarities between the Accotink Creek watershed and the attainment stream watersheds used to establish the TMDL endpoint undermine the reliability of data used to establish the proposed flow TMDL. These and other technical deficiencies could render the TMDL legally deficient.


Finally, the regulation of pollution as opposed to pollutants intrudes upon the traditional role of state and local governments' control over land use and development. The stated policy of the CWA and other provisions within the Act is to preserve the role of the States over the use of the land. However, the proposed Accotink Creek TMDL threatens to upset this important balance. For instance, the TMDL could be interpreted to inappropriately limit the percentage of land that can be under construction simultaneously in the Accotink Creek watershed, which would require Fairfax County (or VA DCR) to take the unprecedented action of denying construction permit applications that fully comply with all other state and local regulatory requirements. For all of the foregoing reasons, the County is concerned that the TMDL is not in conformance with the intent of the CWA.

In conclusion, we appreciate the opportunity to comment on the Draft Benthic Total Maximum Daily Load (TMDL) Development for Accotink Creek, and we expect to receive comments and responses to all issues prior to issuance of a final TMDL. It remains our opinion that this flow TMDL has not adequately been developed and will result in unintended consequences undermining our efforts to protect and restore the Accotink Creek watershed. We continue to believe that the best course of action for this highly urbanized watershed is to proceed with the sediment TMDL approach that was used in Bull Run, Difficult Run and Popes Head Creek. In any case, it is essential that the comments presented here and in the enclosed matrix be carefully considered and addressed. We request and would appreciate the opportunity to meet with EPA and/or the Louis Berger Group to discuss our comments in more detail as well as alternatives to addressing the impairment.

Randolph Bartlett, PE Deputy Director

Enclosure: As stated

cc: Shawn Garvin, Regional Administrator, US EPA, Region III Jon Capacasa, Director, Water Protection Division, US EPA, Region III David Paylor, Director, VA DEQ Craig Lott, TMDL Modeling Coordinator, VA DEQ Bryant Thomas, Water Permits and Water Planning Manager, VA DEQ Northern Regional Office (NRO) Katie Conaway, Regional TMDL Coordinator, VA DEQ NRO David Johnson, Director, VA DCR J. Douglas Fritz, MS4 Program Manager, VA DCR James Patteson, Director, Fairfax County Department of Public Works and Environmental Services (DPWES) Howard J. Guba, Deputy Director, Fairfax County DPWES

Sincerely,

Draft Benthic Total Maximum Daily Load (TMDL) Development for Accotink Creek, Virginia Matrix of Detailed Comments on June, 2010 Draft Report

TMDL Section No. Comment 1.0 Introduction 1-1 Page 1-3: The statement that "EPA is therefore establishing this TMDL to meet all Consent Decree

commitments" is inaccurate and should be changed to read "EPA is therefore establishing this TMDL to meet this Consent Decree commitment." This TMDL only meets the commitment related to the benthic impairment in Accotink Creek. More than 600 other TMDLs have been or are being completed to meet the Consent Decree.

1.0 Introduction 1-2 Page 1-4: The text should include an explanation of the basis for the statement that "Implementation of these bacteria and PCB TMDLs will not eliminate the benthic impairments in the Accotink Creek Watershed."

2.0 Watershed Characterization

2-1 Page 2-2, Topography: The resolution of the DEM data from USGS needs to be included.


2-2 Pages 2-2 and 2-3, Soils: The County questions the use of STATSGO data - a nationwide, low resolution soils data layer - when more accurate and higher resolution soils data are readily available on the County's website for the entire Accotink Creek watershed including the City of Fairfax, Town of Vienna and Fort Belvoir (http://www.fairfaxcounty.gov/maps/metadata.htm.) An Analysis of the County soils data shows dramatically different conditions in the Accotink Creek watershed than are presented in the draft TMDL, as seen in the following table:

Hydrologic Acres Percentage of Acres (County Percentage of Soils Group (STATSGO) the Watershed Soils Data) the Watershed

(STATSGO) (County Soils Data)

B 26,347 86% 4,043 12% C 4,300 14% 3,549 11%

C/D 3 <l% n/a n/a D 3 <1% 23,308 71%

N/A n/a n/a 1,782 6% Total 30,652 100% 32,682 100%

The EPA analysis based on STATSGO data vastly overestimates the extent of Hydrologic Soils Group B (moderate infiltration rates) in the watershed and vastly underestimates the extent of Hydrologic Soils Group D (very slow infiltration rates). By characterizing soils at the level of soil association, the analysis misses the impact of urbanization on Accotink Creek. Compaction and grading have made a

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TMDL Section Comment significant portion of the watershed into D soils, unsuitable for infiltration.

In addition to Hydrologic Soils Group, the County soils data also include an "infiltration rating" which is a more direct measure of the suitability of any given soil for infiltration. This type of infiltration rating data is used in preliminary site design to determine the suitability of a given parcel for infiltration-based stormwater management practices and are summarized for the Accotink Creek watershed in the following table:

Infiltration Rating (Description) Acres Percentage of the Watershed

Good (No significant problems expected) 5,461 17% Fair (Minor potential problems affecting design or construction)

186 <\%

Marginal (Significant problems that must be considered in design or construction)

18,204 56%

Poor (Major problems that must be addressed during the design and construction to ensure satisfactory performance of structures)

8,274 25%

N/A 557 2% Total 32,682 100%

It is clear from these data that a majority of the soils in the Accotink Creek watershed are not suitable for infiltration-based stormwater management practices. Thus it is critical that any attempt to regulate stormwater flow in the Accotink Creek Watershed be based on flow rate and not volume and that an integrated approach be taken for implementation, allowing the use of a broad range of practices including stream restoration.


Page 2-5, Land Use: Table 2-4 should include a column showing how the County land use types were grouped into the "urban" and "other" categories described in the text. It is incorrect to include the gold courses and estate and low-density residential categories as "urban, yet this appears to be EPA's assumption.

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TMDL Section mam Comment 2.0 Watershed Characterization

2-4 Page 2-10, Permitted Discharge Facilities: It is not clear whether the permittees listed in Table 2-6 are for industrial wastewater discharges or for stormwater discharges associated with industrial activity. Please clarify. Also, the title of Table 2-6 needs clarification as Phase IMS4 permits are also individual permits but are not listed.


2-5 Page 2-11: The title of Table 2-7 should be changed to read "General Permits issued to Concrete Products Facilities and Discharges of Storm Water Associated With Industrial Activity in the Accotink Creek Watershed." These are only two kinds of general permit issued by the state. Construction stormwater and Phase II MS4 permits are also general permits.


2-6 Page 2-13, Construction Stormwater Permits: The time period for the construction stormwater permit acreages presented needs to be included in order to allow an assessment of whether the information presented is representative of typical conditions in the watershed. A table of the construction stormwater permits used to calculate the acreages presented also needs to be included. These permits are transient in nature, so a time series of recent permit activity would be more informative than an arbitrary snapshot. The VDOT construction area (79.7 acres) does not appear to include the ongoing High-Occupancy Toll (HOT) Lanes construction. The HOT lanes project involves construction of two new lanes in each direction from the Springfield Interchange to just north of the Dulles Toll Road (14 miles). A five mile section of this project, from Backlick Road to Gallows Road, is located within the Accotink Creek watershed.

3.0 Environmental Monitoring

3-1 Page 3-5, Taxonomic Richness: The range of Average Total Taxa described in the text for Figure 3-2 (from 5 to 20) does not match the range shown in the figure itself (from 7 to 11). This inconsistency between the figure and text needs to be corrected.


3-2 Page 3-6, Taxonomic Composition: It is worth noting that there was a substantial improvement (increase) in the Average Composition of Mayfly Nymphs at station 1AACO006.10 from 0.8 percent in 1994-1996 to 4.4 percent in 2006-2008. However, as above, the text and figure do not match, with the text indicating 4.4 percent and the figure showing only 3.9 percent. This inconsistency between the figure and text needs to be corrected.

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TMDL Section No. Comment 3.0 Environmental Monitoring

3-3 Page 3-9, Trophic Group: Once again, it is worth noting that there was a substantial improvement (in this case a decrease) in the Average Composition of Scrapers at station 1AACO006.10 from 6.2 percent in 1994-1996 to 3.8 percent in 2006-2008. Again, there is a discrepancy, as the text states that the composition of scrapers decreased from upstream to downstream, while Figure 3-7 shows the two most upstream stations (1 AACO014.57 and 1AACO009.14) as having the lowest Average Composition of Scrapers in the watershed. This inconsistency between the figure and text needs to be corrected.


3-4 Page 3-11, Figure 3-8: The text states that "at station 1AACO006.10, the VSCI scores decreased between the 2006 and 2008 sampling periods," but the data presented in Table 3-3 clearly show two substantial increases during this period, one from Spring 2006 (24.3) to Fall 2006 (41.9) and another from Spring 2008 (25.7) to Fall 2008 (35.9), with an overall increase from Spring 2006 to Fall 2008. This inconsistency between the figure and text needs to be corrected.


3-5 Page 3-14, Embededness: The text states that the average embedness score for the 2006-2008 sampling period was 11, while the average for the earlier sampling period (1994 to 1996) was higher at 17. Does this represent an improvement over time as rocks and snags are less covered in silt sand and mud in the more recent sampling period? The difference between the scores needs to be clarified in the text.


3-6 Page 3-16, Hill Memo 2007: This memo is cited on pages 3-16 and 3-17 but is not included as an Appendix to the document. Please provide a copy of this memo for stakeholder review.


3-7 Page 3-17, Table 3-6: LRBS sampling was only performed on the lower portion of the mainstem, below Lake Accotink. The results say the stream has less sediment than expected. How does this equate to heavy stream erosion? What is the effect of Lake Accotink? Is the reservoir effect occurring?


3-8 Page 3-20, Ambient Water Quality Monitoring: Please explain why "only data collected since 1996 was analyzed." This is not consistent with the benthic data presented in the draft TMDL, some of which were collected prior to 1996.


3-9 Page 3-22, Specific Conductance: Conductivity is high. In an analysis of over 1000 Maryland Biological Stream Survey (MBSS) sampling sites, the Maryland Department of the Environment (MDE) found 247 was the median for undisturbed streams and found high correlation with chlorides, which persist in groundwater long after winter spikes. Based on a similar Biological Stressor Identification study for Cabin John Creek, high conductivity from chlorides was implicated as the cause of poor biological quality. Was this examined in Accotink Creek?

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TMDL Section M i l t Comment 3.0 Environmental Monitoring

3-10 Page 3-24, Total Suspended Solids: The text states that "the majority of elevated TSS occurrences correspond with high flow conditions in the stream." Yet there are several instances shown in Figure 3-21 where high TSS values do not coincide with high flow (see Spring 1997, Summer and Winter 1998, Spring and Fall 2004.) Please explain what caused these high TSS observations in the text. These types of observations question the protectiveness of regulating flow as opposed to sediment to address the benthic impairment, as relatively large loads of sediment could be discharged during low flow conditions.


3-11 Page 3-26, Total Nitrogen: The text states that "Screening values vary from 0.62 to 2.23 mg/L." Why do screening values vary? Because of this variation, it is not possible to tell which observations in Figure 3-24 exceed the screening values. Please highlight the exceedances in the figure so that they can be identified spatially and temporally.


3-12 Page 3-27, Ortho-Phosphorus: The text states that "ortho-phosphorus concentrations ranged between 0.002 and 0.1 mg/L with a total average of 0.03 mg/L" but does not indicate whether this is high or low relative to concentrations that would affect benthic health. What is the point of evaluating a potential stressor i f its concentrations are not compared to environmentally-relevant levels? Please clarify the text to indicate the meaning of these results.


3-13 Page 3-27, Total Phosphorus: The text states that "Screening values vary from 0.03 to 0.4 mg/L." Why do screening values vary? Because of this variation, it is not possible to tell which observations in Figure 3-26 exceed the screening values. Please highlight the exceedances in the figure so that they can be identified spatially and temporally.


3-14 Page 3-28, Phytplankton Chlorophyll a: The text states that "Chlorophyll a values ranged from 0.5 to 21.2 |J.g/L with an average of 4.7 u-g/L" but does not indicate whether this is high or low relative to concentrations that would affect benthic health. What is the point of evaluating a potential stressor if its concentrations are not compared to environmentally-relevant levels? Please clarify the text to indicate the meaning of these results.


3-15 Page 3-32, Fish Tissue and Sediment Contamination Monitoring Program: The first sentence of the last paragraph on page 3-32 repeats the beginning of the previous sentence almost verbatim and should be deleted.


3-16 Page 3-34, Second to last bullet: this bullet refers to sampling conducted at 1 AACO012.58. Should this be 1AACO012.78?

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TMDL Section ^ o i l l l Comment 3.0 Environmental Monitoring

3-17 Page 3-34: Fish tissue sampling highlighted organic pollutants, mercury, and arsenic in concentrations above screening values, and water toxicity testing highlighted potentially toxic effects on fathead minnows. Thus toxicity is a possible stressor in the watershed, and reduction of flow may not sufficiently improve benthic health. It is critical for the post-TMDL VPDES permitting process to be flexible and iterative based on evaluations of whether the identified stressor - in this case sediment with stormwater being used as a surrogate - is indeed causing the benthic impairment.


3-18 Page 3-35, Discharge Monitoring Reports: The text simply states that DMRs indicated that all VPDES permitted facilities are discharging in compliance with their permits, without stating what constituents the facilities are permitted to discharge. Please provide a summary of the DMR data by facility and parameter monitored to substantiate the statement that all VPDES-permitted facilities are in compliance with their permits.


3-19 Page 3-40: The last sentence of the first paragraph on this page, which states that the stream restoration project was not able to allow for biological community improvement, contradicts the first sentence of the same paragraph, which states that a statistically significant improvement in the VSCI, HBI and EPT taxa scores was seen just two years after the restoration was complete. EPA appears to be ignoring findings from their own study which demonstrate the value of stream restoration in improving the benthic community. The fact that post-restoration scores were not above the level of impairment does not rule out restoration as an important component of a comprehensive implementation plan to de-list the impaired segments. The tone of Section 3.3.2 and 3.3.3 is unnecessarily negative in order to support EPA's determination of stormwater as a surrogate for the primary stressor. This negative tone is disappointing, as EPA should be embracing and commending efforts by stakeholders to restore and improve water quality. Restoration should be encouraged as a mechanism of MS4 compliance with this TMDL. Control of stormwater alone will likely not result in de-listing of these impaired segments.

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TMDL Section Mdllll Comment 3.0 Environmental Monitoring

3-20 Page 3-40, Recommendations - EPA and USGS Study: The text states that the "reduction of stormwater runoff volumes [...] should be addressed." This statement is inaccurate and should be changed to "stormwater runoff flow rates." Stormwater volume is not the stressor being discussed; instead it is stormwater flow rate, or more precisely, the flow velocities. Throughout the document, "volume" should be replaced with "flow rate." Channel erosion is caused by flow velocities that lead to shear stress being above a critical level. Those velocities are related to flow rate not flow volume. As long as water velocities are below the critical shear value, the channel will not be degraded. In other words, the benthic impairment can be addressed by delaying peak storm flows (as stated in the last sentence on Page 3-40), which is equivalent to reducing the shear stress on the stream channel. The distinction between stormwater volume and flow rate is critical to this TMDL. This is a critical comment based on the soil type analyses presented in Comment 2-2, as a majority of the soils in the Accotink Creek Watershed may be unsuitable for infiltration (volume control). Volume control may require much larger BMPs and thus much higher implementation costs than necessary to meet the intent of this TMDL.

4.0 Stressor Identification Analysis

4-1 Page 4-5, Stormwater Runoff and Sedimentation: Given the amount of evidence presented to support the identification of sediment as the most probable stressor of the benthic community in Accotink Creek, wouldn't the most appropriate and effective approach be to develop a sediment TMDL? At a minimum, the Wasteload Allocations section should include language that allows for sediment-controlling BMPs to be used by MS4s to comply with this TMDL, as described in Comment 6-15.

4.0 Stressor Identification Analysis

4-2 Page 4-6: The third sentence in the second paragraph describes a flow-frequency analysis that was done for the City of Fairfax, which is a small, relatively highly urbanized portion of the watershed. The following sentence draws conclusions regarding the hydrology of the entire watershed based on this smaller study. This is an inappropriate extrapolation, and the text needs to be revised to qualify the applicability of the conclusions drawn.

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TMDL Section -No.,::! Comment 4.0 Stressor Identification Analysis

4-3 Page 4-7: The text states that Figure 4-1 "demonstrates that there is a very strong relationship between stream flow and sediment loads." While there is clearly a relationship between streamflow and sediment loads, it is not a direct relationship. The R2 value of 0.7557 means that almost 25 percent of the variation in sediment loads is not explained by flow. As such, a substantial portion of the sediment loading will not be controlled by a reduction in flow rates. A sediment TMDL would allow for more comprehensive, and perhaps more scientifically-valid, approaches to restore the impaired segments. At a minimum, the Wasteload Allocations section should include language that allows for sediment-controlling BMPs to be used by MS4s to comply with this TMDL, as described in Comment 6-15.

The text also states that the sediment rating curve was developed using data collected from 1993 to 2007. This is not consistent with the benthic data window (1994 to 2008) or the water quality data window (1996 to 2008). How does the flow-TSS relationship change i f the data window mirrors that of the benthic and water quality data? A single data window should be selected and applied consistently across all data sets.

5.0 TMDLEndpoint Identification

5-1 Page 5-1, Second paragraph: The text states that the TMDL for Accotink Creek uses "a 'surrogate' approach in place of the traditional 'pollutant of concern' approach" and that this "is appropriate because the pollutant (i.e. sediment) load in Accotink Creek is a function of the amount of stormwater runoff generated from the Accotink Creek watershed." This argument is true of any non-point source pollutant load because rainfall events wash the pollutant off the land surface and into the receiving water. Will flow TMDLs now be established for all impairments caused by non-point sources?

As noted in an earlier comment, while the relationship between sediment and flow is strong, it is not a direct relationship. Substituting flow for sediment, the actual pollutant of concern, therefore fails to account for almost 25 percent of the variability in sediment loads. The TMDL fails to demonstrate how using a less accurate surrogate (flow) is more effective than targeting the pollutant of concern identified as the primary stressor impacting the benthic community (sediment).

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TMDL Section No. Comment 5.0 TMDL Endpoint Identification

5-2 Page 5-1, Third paragraph: The text states that "recommendations from EPA's Study [...] emphasize that reduction of stormwater runoff volumes and associated pollutants of concern is needed to improve water quality in the watershed." This statement ignores the fact that the ultimate goal of the TMDL is to restore the benthic community, not simply to improve water quality. In order to achieve this goal, the tools available for implementation must include stream restoration which can be used to stop erosion of streambanks, reconnect streams to their floodplains and improve instream habitat. The most effective way to do this is to establish a TMDL for sediment directly rather than using the surrogate approach. At a minimum, the Wasteload Allocations section should include language that allows for sediment-controlling BMPs to be used by MS4s to comply with this TMDL, as described in Comment 6-15.

5.0 TMDL Endpoint Identification

5-3 Page 5-2, Last paragraph: The text reads "FDCs | \ . . ] respond to changes in a watershed's hydrologic characteristics" but a more appropriate verb would be "reflect" as the FDCs simplv portrav graphically whatever data are selected.


5-4 Page 5-4: The criteria used to select the attainment streams do not demonstrate that the streams selected are appropriate. The first two criteria simply reflect where DEQ monitoring and USGS stream gage data are available and say nothing about the comparability of the watersheds. The next three criteria, ecoregion, drainage area and land use, were largely ignored in selecting the attainment streams. Catoctin Creek is in the Northern Piedmont and Buffalo Creek is in the Piedmont, while the lower impaired section of Accotink Creek is in the Southeastern Plains Ecoregion (see Figure 5-1). In terms of drainage area, the three streams are not comparable as the attainment streams are several times larger in size (see Table 5-1). Also, it is clear from Table 5-2 that land use in the three watersheds is vastly different: the Accotink Creek watershed is primarily urban, while Buffalo is forested and Catoctin is agricultural.

In addition, critical evaluation criteria were not adequately reviewed by EPA: soils, slope and watershed shape all have substantial impacts on hydrology and therefore should be carefully considered in the selection of attainment streams. The draft TMDL does not present any comparison of slope or watershed shape, and an analysis of slope and shape in the three watersheds needs to be performed and included in the text. The information presented in Table 5-3 demonstrates that soil types in the three watersheds are not comparable. Two watersheds, even i f they are completely undeveloped and unimpaired, would be expected to exhibit different hydrology i f their soil types are substantially different. In Comment 2-2, we demonstrated that the STATSGO data used to estimate the soil

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TMDL Section Comment hydrologic groups in the Accotink Creek watershed vastly overestimate the category B soils while underestimating category D. The Buffalo and Catoctin Creek watersheds are both dominated by category B soils, meaning that they have dramatically different hydrologic properties than the Accotink Creek watershed.

While the report provides a number of criteria used to identify the attainment streams, there is no discussion of how a determination was made that the attainment watersheds were hydrologically similar to Accotink Creek, hi fact, much of the information presented in Section 5.2 suggests that the attainment watersheds selected are unlikely to have similar hydrologic responses to the Accotink Creek watershed. The assumption that using unit-area flows is a valid means of comparing flows from different watersheds is in our view, unjustified and fundamentally incorrect.

There are a number of more defensible approaches that could be used to establish an attainment condition. One such approach would be to use data from a large number of watersheds where the stream attainment condition was being met and develop regression equations that related flow to key watershed characteristics that drive hydrologic response (e.g drainage area, soils, slopes, watershed shape, etc.) The regression equations could then be used to generate a flow duration curve for Accotink Creek that represented an attainment condition. While it is understood that limited data may make it difficult to implement such an approach, at a very minimum a modeling analysis should be completed to demonstrate that the hydrologic response from the attainment watersheds and Accotink Creek (in the undeveloped state) are similar. Without such information, it is practically impossible to determine whether the attainment streams and watersheds represent an appropriate endpoint or target.

At a minimum, it is recommended that EPA include language stating the TMDL can be modified in the future i f more appropriate attainment streams are identified.

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TMDL Section mmm Comment 5.0 TMDL Endpoint Identification

5-5 Page 5-4: Having selected the attainment streams based solely on data availability, the statement is then made that "it was deemed more appropriate to use a composite FDC that combines the flow distribution values for Catoctin Creek and Buffalo Creek." The TMDL fails to explain how a composite of two inappropriate attainment streams can result in a more accurate representation of attainment stream conditions. Incorporating more streams does not necessarily make the comparison more representative. Compositing the FDCs for these two creeks may introduce more uncertainty. At a minimum, EPA should present the individual FDCs for Catoctin Creek and Buffalo Creek, in order to provide a transparent data analysis, and allow stakeholders to see the differences between these two streams. Our internal data analyses show an approximately 20 percent difference in the high flow rates for the two FDCs. EPA should disclose such a substantial difference, which could significantly affect the wasteload allocations developed for this TMDL.


5-6 Page 5-9, Table 5-4: Biomonitoring results at station 1ALOE001.99 are included in Table 5-4 but not mentioned in the text. Suggest deleting from table as it is already crowded. VSCI scores in both attainment streams are generally well above the impairment cutoff value of 60. Is this being considered as part of the margin of safety for the TMDL? We are concerned that selecting attainment streams that are well above the attainment threshold essentially establishes requirements above what is required under the federal Clean Water Act.


5-7 Page 5-11, Step 2 of Accotink Creek FDC development: the text reads "Convert the USGS data from flow rate (ft 3) to ..." but should read "(ftVday)" - ft 3 alone is a volume, not a rate. There seems to be substantial confusion on this point throughout the TMDL, which needs clarification because it has huge implications on the analyses for this TMDL and potential implementation requirements. Most notably, as described in Comment 3-20, the identified stressor is stormwater flow rate not stormwater volume. One approach to addressing the benthic impairment could be to delay peak storm flows (as stated in the last sentence on Page 3-40), which is equivalent to reducing the shear stress on the stream channel. It is not necessary to eliminate volume to protect the beneficial use. As long as water velocities are below the corresponding critical shear value, the channel will not be degraded. As such, this TMDL should clarify that the WLAs are expressed in terms of reductions in storm flow rate, not storm volume.

Also, EPA should note that the TMDL units must be in "per day" to comply with the Anacostia River decision by the District of Columbia Circuit and the subsequent EPA guidance related to TMDL development.

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TMDL Section INdlll Comment 5.0 TMDL Endpoint Identification

5-8 Page 5-11, Last paragraph: The text states that "The resulting FDCs, shown in Figure 5-4, indicate that the non-impaired composite FDC provides an expected hydrologic response when compared to the impaired Accotink Creek FDC." There is no reason to expect that the Accotink Creek FDC would be identical to the composite FDC, given the significant differences in soils, land use, ecoregion and watershed size. Figure 5-4 simply shows that the composite FDC and the Accotink Creek FDC are different, as expected.


5-9 Page 5-12, Estimation of the Flow Volume Reduction: Here again, there seems to be confusion regarding the difference between flow rate and volume. The FDCs plot cubic feet per acre per day vs. percent exceedance, so the calculated reduction is a reduction in flow rate, not volume. The 1-year, 24-hour storm event in Fairfax County corresponds to 2.7 inches of rainfall. However, as described in Comment 6-1, rainfall intensity is never actually considered during TMDL calculations.

In the draft TMDL, the discharge level for a 1-year 24-hour duration storm was determined using the annual maxima of daily discharges. This was then placed in a flow duration curve of all daily discharges to determine the target flow rate, which is shown to have an exceedance probability of approximately 2.2 percent (see Figure 5-5). If we assume that the point at which the Accotink Creek FDC crosses the attainment stream composite FDC represents the demarcation between storm flows and base flows (see Figure 5-4), this exceedance probability appears to be very low for a 1-year event. We would expect the 1-year event to have an exceedance probability that is closer to the point where the FDCs cross. This underscores the fact that values derived from an extreme value distribution (annual maxima) should not be placed on the parent distribution (daily average) and interpreted the same way.

At a minimum, it is recommended that EPA include language stating the TMDL can be modified in the future i f more robust analyses are used to compare Accotink to the impaired streams, and the results demonstrate that the established WLAs are inappropriate.


5-10 Page 5-12: It should be noted that flow gage location can affect the results of the TMDL analyses. The WLA (percent reduction in flow) is applied to the entire watershed. However, a majority of the open space appears to be located at the bottom of the watershed (Figure 2-2). If the gage were at the mouth of the watershed, due to a higher proportion of open space, the FDC (normalized by drainage area), and thus the wasteload allocations (WLAs), would likely be slightly lower.

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TMDL Section 5.0 TMDL Endpoint Identification

No. 5-11

<:#6_nMeflt:::5:!:M • Page 5-13, Figure 5-4: The X-axis is incorrectly labeled as "Precent [sic] of Time the Daily Flow Volume is Equaled or Exceeded" when it should be "Percent of Time the Daily Average Flow Rate is Equaled or Exceeded." The Y-axis is incorrectly labeled as "cubic feet/acre" when it should be "cubic feet/acre day."


5-12 Page 5-14, First paragraph: the method presented for determining the 1-year, 24-hour flow is actually the recurrence interval for the maximum daily average flow rate measured at the USGS gage. The term "24-hour flow" is misleading because it seems to relate to a rainfall record, in which 24 hours would be the duration of the rainfall event.


5-13 Page 5-14, Second paragraph: The text states that "EPA regulations require that TMDL allocations be expressed as daily loads." Thus is it clear that this TMDL must express the TMDL and WLAs as flow rate (ft3/acre/day) as opposed to volume (ft3/acre). That being said, is it appropriate to consider a flow rate as a daily load based on the aforementioned EPA regulations? Flow rate can never be expressed as a daily load since it does not include a corresponding pollutant concentration.


5-14 Page 5-15, Figures 5-5 and 5-6: The X-axes of both figures are incorrectly labeled as "Percent of Time the Daily Flow Volume is Equaled or Exceeded" when they should be "Percent of Time the Daily Average Flow Rate is Equaled or Exceeded."


5-15 Page 5-16, Table 5-6: The table presents flow rates, not volumes, so the word "Volume" should be replaced with "Rate" in all instances. The units of the first column (ft 3) are incorrect and should be ft3/day.


5-16 Page 5-16: It should be noted that evaluation of the effectiveness of this TMDL's WLAs (i.e., whether the 2.2 percent exceedance storm event has decreased) will require a long-term record of post-TMDL flow measurements. The "shifting" of a FDC cannot be measured with only a few years of data.

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TMDL Section No. Comment 6.0 TMDL Allocation

6-1 Page 6-2, Basis for TMDL Allocations: The text describes the rational method and the method used to develop land-use specific runoff coefficients and relative flow contributions to the 1-year recurrence flow rate. However, the EPA description of the analysis is vague and does not convey the actual role of the rational method and there appears to be some confusion over what a runoff coefficient is and how to use it. The rational method is based on rainfall intensity in inches/hour. However the rainfall intensity, /, is never used for the analysis (e.g., the 1-year, 24-hour rainfall intensity of 2.7 inches is never used) and thus the rational method simply calculates a potential "relative contribution," it does not actually calculate "existing conditions." This whole method of allocating flow (ft3/acre day) among land uses is in error. No runoff coefficents are applicable because what is being done in Table 6-1 has nothing to do with rainfall-runoff relationships.

Scheuler's Simple Method is based on rainfall in inches, but the runoff coefficient used from the simple method has nothing to do with the rational method. The simple method uses it with annual rainfall to generate annual runoff. Further, the equation given for Rc is incorrect: it should be Rv = 0.05+0.9 I . Use of 0.91 also implies the analysis has incorporated the conversion factor of 0.9 for the percentage of annual rainfall events with no runoff, again, not appropriate for the rational method.

The text needs to detail the actual methods used to generate Table 6-1 and more accurately describe the role of the rational method in TMDL and WLA calculations. In essence, is the purpose of using the rational method simply to allow for comparison of open space to non-open space runoff? Would other spreadsheet methods, such as the SCS method, be more appropriate for this watershed? In particular, the drainage areas are likely far above the threshold of accuracy for the rational method (a rule of thumb is 40 acres maximum drainage area for the rational method). A more appropriate method should be used to evaluate relative runoff from the open versus non-open space.

At a minimum, it is recommended that EPA include language stating the TMDL can be modified in the future i f more robust analyses are used to compare Accotink to the impaired streams, and the results demonstrate that the established WLAs are inappropriate.

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6-2 Page 6-3, Table 6-1: How was the percent imperviousness calculated for each land use type? The following table compares the percent imperviousness from the draft TMDL and from the County planimetric data used to develop the Accotink Creek WMP.

Fairfax County Land Use Type TMDL Percent Planimetric Percent Imperviousness Imperviousness

Open Space 15 1 Golf Course 9 1 Estate Residential 21 5 Low Density Residential 22 8 Medium Density Residential 25 14 High Density Residential 31 32 Institutional 24 26 Low Intensity Commercial 42 58 High Intensity Commercial 52 76 Industrial 38 50 Transportation 27 59

It is surprising, for instance, that in the draft TMDL transportation has an imperviousness of only 27 percent, and that open space is as high as 15 percent. What are these numbers based on? The text needs to describe the methodology, as these calculations significantly affect the WLA calculations.

The County used these more accurate percent impervious values within the (albeit, questionable) rational method of the TMDL, and the land-use specific percent reduction decreased from 55.4 percent to 50.4 percent, nearly a 10 percent decrease. The "relative contribution" of transportation increased by nearly 100 percent, from 16 percent to 32 percent of the storm flow, while the relative contribution of medium density residential and low density residential decreased from EPA-reported by 36 percent and 50 percent, respectively. EPA should use the more accurate percent impervious values reported above.

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TMDL Section mmm Comment 6.0 TMDL Allocation

6-3 Page 6-3, TMDL Allocations: The text states that equal reductions were applied to all land use categories except for open space. The text needs to clarify why flows are broken our by land use when the same percent reduction is applied virtually across the board. Again, does this imply that the role of the rational method is simply to allow for comparison of open space to non-open space runoff, in order to calculate percent reductions for WLA development (i.e., the non-open space land uses must reduce flow beyond 48.4 percent in order to "make up" for the open space, for which reductions are not required)?

6.0 TMDL Allocation

6-4 Page 6-4: The text states that "EPA conservatively estimates that 10 percent of the existing stormwater flow in the Accotink Creek watershed does not drain to a permitted storm sewer system." This seems like an arbitrary estimate, particularly since it is applied to all land use types, regardless of the likelihood that they do or do not drain to an MS4 (estate residential, golf courses and open space are all unlikely to discharge runoff through an MS4.) The text needs to describe the effect of this assumption on the subsequent WLA calculations. What i f the non-MS4 area was much higher or lower? How would the resulting WLAs be affected?

The assumption that 90 percent of the stormwater flow in the watershed drains through a permitted system means that the vast majority of TMDL implementation will be through permit requirements. This makes the comment made by EPA at the July 26, 2010 public meeting that the TMDL need not consider economic impact or feasibility even more disturbing. If compliance with the TMDL will be required of permittees in the watershed, isn't it vital to identify feasible implementation measures and assess costs prior to establishing the TMDL?

6.0 TMDL Allocation

6-5 Page 6-5, WLA Development: The text reads ".. .individual and industrial stormwater permits..." It should read ".. .general and individual industrial stormwater permits..."

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TMDL Section Comment 6.0 TMDL Allocation

6-6 Page 6-5, WLAs for Construction Stormwater Permits: There are several instances of language in the TMDL that is disconcerting from an MS4/construction permitting perspective. The language should be edited to reflect the technical approach to the TMDL, as opposed to making statements related to future growth policies. This TMDL does not regulate or mandate land use decisions (e.g., the level of construction activity) in the watershed. Instead it establishes an allowable loading for the pollutant of concern (or its surrogate). For instance the text on page 6-6 reads:

"EPA believes that this 5% WLA of the total TMDL is a reasonable estimate of the temporary increase in stormwater flows from future construction activities within the Accotink Creek watershed. While there may at time be a greater construction demand, construction activities are temporary. As current construction is completed, new construction can be started as long as the amount of acreage under construction remains within 5% of the total acreage. "

The last sentence is inappropriate. It seems to suggest that this TMDL can limit the acreage under construction. Instead, the WLA sets a numeric goal for runoff from construction sites, and construction within the watershed can represent ANY acreage (whether 5 percent or 90 percent) within the watershed as long as the WLA is achieved. It would be EPA's responsibility to re-open and adjust the TMDL assumptions i f they were found to be invalid (as opposed to suggesting that the assumptions lead to consequential regulatory requirements).

As such, as an example of the edits needed in the TMDL, the last sentence should be deleted and replaced with the following: "Based on the approach to this TMDL, the WLA for construction stormwater permits in Table 6-4 will apply whether the percentage of total acreage under the construction is higher or lower than 5 percent".

It should also be noted that construction stormwater permits are currently issued by DCR, but under Virginia's proposed stormwater regulations, which are set to go into effect no later than December 11, 2011, that permitting authority will be delegated to localities.

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TMDL Section mmm Comment 6.0 TMDL Allocation

6-7 Page 6-6, Table 6-4: Was the WLA for construction stormwater permits determined based on acres (5 percent of the watershed area or 1,515.4 acres) or flow rate (5 percent of the WLA or 34.1 ft3/acre day)? The inclusion of acres in the WLA table seems to suggest that this TMDL can limit the acreage under construction, which is incorrect.

The WLA for construction stormwater permits is described as a "set aside," but Table 6-4 indicates that a 55.5 percent reduction in flow rate will be required from construction. It is not clear how such a reduction can be achieved during construction. Construction sites generally have few opportunities to detain or retain stormwater. More importantly, the impact of construction activities on the benthic impairment is not due to elevated stormwater flow rates; instead the impacts are due to sediment loading. The WLA section should include language that allows sediment-related BMPs to be used to comply with this TMDL.

6.0 TMDL Allocation

6-8 Page 6-6, Second paragraph: The text states that the reductions called for by the TMDL "can be accomplished by using Low Impact Development (LID) techniques, but this is not true. LID techniques generally bypass any stormwater beyond one half inch of rainfall. They will have no effect on the flow reductions needed for this TMDL. The text also states that "Redevelopment activities, in general, will have the greatest opportunity for load reductions..." but this should be "flow rate reductions."

6.0 TMDL Allocation

6-9 Page 6-6, Third paragraph: This paragraph highlights the challenge of assigning a WLA to non-point source such as stormwater. Please describe the potential effect of this "transfer" of land/regulation from Load Allocation to Wasteload Allocation. Is this a relevant issue to the implementation of this TMDL? Or simply a footnote?

6.0 TMDL Allocation

6-10 Page 6-7, WLAs for Industrial Stormwater Permits: The first sentence should read "... facilities with individual or general industrial stormwater permits..."

6.0 TMDL Allocation

6-11 Page 6-7, Table 6-5: The heading for the individual permits should read: "Industrial Stormwater Individual Permits."

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6-12 Page 6-8, Table 6-6: The table heading should read: "WLAs for the Industrial Stormwater Permits" for consistency with Table 6-5. Also, the first category of permits in this table should be "IP Industrial." How were the Existing Conditions and Allocation flow rates determined? Is the allocation for industrial stormwater permits 15.44 ft /acre/day or is it a 55.4 percent reduction? If the former, will future permits need to "divvy up" the 15.44 ft3/acre/day among all industrial stormwater permittees? A percent reduction WLA is more appropriate for stormwater permittees, particularly given the uncertainties in land area under the various jurisdictions.

6.0 TMDL Allocation

6-13 Page 6-9, WLAs for MS4 Permits: It appears that the VDOT MS4 coverage area in the Fairfax County portion of Accotink Creek was determined based solely on the following major roads: 1-66, US-50, US-29,1-495 and 1-95. However, VDOT maintains virtually all of the roads in Fairfax County, not just the major roads, so this approach vastly underestimates the VDOT MS4 coverage area. This situation is unique to the state of Virginia and EPA must recognize this issue, as it will have significant implications on the implementation of this TMDL. The text refers to a VDOT communication to DCR dated March 2, 2010 but is not included as an Appendix to the document. Please provide a copy of this memo for stakeholder review. Why was the transportation land use category, which was readily available and presented in Tables 2-4 and 6-1, not used to determine the VDOT MS4 coverage area? This represents more than an order of magnitude difference (432.8 acres in Table 6-8 vs. 4,566 acres in Tables 2-4 and 6-1) and calls into question the credibility of the WLAs developed for this TMDL. The WLA calculations need to be corrected using the transportation land use category. Is the WLA for VDOT equal to 8.9 ft3/acre/day or is the WLA a 55.4 percent reduction? If the former, then the acreage under VDOT jurisdiction has a huge effect on the VDOT WLA. This confusion could have significant implications for the implementation of this TMDL. A percent reduction WLA is more appropriate for stormwater permittees, particularly given the uncertainties in land area under the various jurisdictions.

6.0 TMDL Allocation

6-14 Page 6-10, Table 6-9: How were the acreages presented in this table derived? Fairfax County has recently completed delineation of the areas draining to outfalls owned and operated by the County, and therefore regulated under the County's MS4 permit, in the Accotink Creek watershed. Based on those delineations, approximately 35 percent of the watershed drains through the County's MS4. This corresponds to roughly 10,600 acres, or about half of the acres presented in Table 6-9.

6.0 TMDL Allocation

6-15 Page 6-10, Section 6.3.3: This is a critical comment, please consider it carefully. As written, this WLA section will greatly constrain the ability of the County to use a comprehensive, integrated approach to address the benthic impairments in this watershed. In particular, the WLA section for MS4s should acknowledge other BMPs that can lead to improvement of the benthic community. At the

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TMDL Section Comment public meeting on July 26, 2010 EPA staff stated that this TMDL will not prevent MS4s from continuing stream restoration activities in the watershed. However, there is a major difference between "will not prevent" and "will encourage." Should this section remain as written in the final TMDL, it will almost certainly require the County to re-direct resources entirely to flow reduction (and consequently, will thereby prevent restoration activities). The County prefers an integrated approach, and stream restoration is a major component of our Watershed Management Plans, which we have spent years of effort and millions of dollars developing. These plans are scientifically-based and have been supported by local stakeholders, DEQ, DCR, and EPA. Addressing benthic impairments cannot rely on a "one size fits all" approach, and thus EPA should include language that allows non-flow-based BMPs to be used as a component of the MS4 compliance. Without this language, the County is concerned that the MS4 permit will necessarily require a TMDL Action Plan that solely focuses on flow reduction, as opposed to allowing a comprehensive approach that includes control of sediment and restoration of instream habitat. We recommend insertion of the following language immediately after Table 6-9:

"The MS4 WLAs are expressed in terms of flow rate and flow rate reduction, with the ultimate goal of reducing the impacts of sediment transport on benthic impairments. However, the MS4 permitting authority may allow for non-flow BMPs/actions to be used for implementation of these WLAs by MS4s, in order to encourage a comprehensive approach to addressing the benthic impairments. In this case, the non-flow BMPs/actions should be accompanied by a quantitative analysis of their effect on sediment transport and relate that effect to a corresponding flow reduction."

This language, which could be regarded as "flow reduction credits," will ensure that all implementation options remain available to MS4 permittees for compliance with the WLAs. For example, the decrease in stream channel shear stress associated with a given flow reduction could be equated to a corresponding sediment load/scour reduction. Thus, the reverse calculation could equate a given sediment loading/scour reduction to a corresponding flow rate reduction. Within this framework, sediment loading/scour BMPs (such as stream restoration) could be used within a comprehensive, integrated approach to comply with flow rate reduction requirements.

6.0 TMDL Allocation

6-16 Page 6-11, Tables 6-11 and 6-12: How can a margin of safety be both implicit and explicit? Sufficient conservative assumptions have been made throughout the TMDL development process to more than adequately constitute an implicit margin of safety. "Explicit" should be stricken from both tables.

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TMDL Section Mmm Comment 6.0 TMDL Allocation

6-17 Page 6-11, Last paragraph: The text reads "The Accotink Creek Benthic TMDL implicitlv expresses the allocations in dailv terms." Actually, the allocations are explicitly expressed in daily terms since the units are ft3/acre day. . Please replace "flow volume" with "flow rate."

6.0 TMDL Allocation

6-18 Page 6-12, Second paragraph: Why is an explicit margin of safety being added when the TMDL has already documented sufficient conservative assumptions to more than adequately constitute an implicit margin of safety? This is also not consistent with page E-6 which states that the margin of safety is implicit, or with the remainder of this section which goes on to recount all of the conservative assumptions made in developing the TMDL.

6.0 TMDL Allocation

6-19 Page 6-12, Third paragraph: Please explain how assigning 5 percent of the WLA to construction stormwater permits, which must then also reduce flow by 55.4 percent, causes the allocations for other sources to be further reduced?

6.0 TMDL Allocation

6-20 Page 6-12, Fourth paragraph: The text needs to clarify how a composite of two attainment streams constitutes a conservative approach when neither attainment stream was appropriate to begin with.

6.0 TMDL Allocation

6-21 Page 6-12, Fifth paragraph: As reflected in earlier comments, the data do not indicate that the attainment streams selected for TMDL development are in any way similar to Accotink Creek. The only similarity is that all three streams have DEQ biological monitoring and USGS flow gaging stations. The text states that the attainment streams were identified through "standard statistical approaches." Please describe these statistical approaches.

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TMDL Section l i t ! ! ! Comment 6.0 TMDL Allocation

6-22 Page 6-13, Future Growth: The text states that "In the Accotink Creek watershed, a future growth allocation is intrinsic to the TMDL" and "all new development and redevelopment will achieve no net increase in flow (as compared to pre-development conditions)." This language can be misleading and is disconcerting from an MS4 permitting perspective. It seems to imply that this TMDL can require that all new and redevelopment will incorporate stormwater management practices that result in zero net increase in runoff. However, this is not necessarily true and beyond the scope of this TMDL. This TMDL requires a 48.4 percent reduction in the 1-year, 24-hour flow rate from the Fairfax County MS4. Within this constraint, new and redevelopment can be subject to a wide array of stormwater management practices including practices that result in increased runoff. If the County can achieve a 48.4 percent reduction across the entire MS4, then certain areas can achieve a smaller reduction as long as others achieve a higher reduction. There is no reason to discuss "pre-development" and this term is confusing because it seems to imply a condition that represents a completely natural watershed. Please replace the third sentence of the future growth section with the following:

"This TMDL requires a 49.7 percent reduction in the 1-year, 24-hour flow rate across the Watershed. While new development and re-development could result in increased flow rates in localized areas, the net reduction across the entire watershed must be maintained."

TMDL Implementation

6-23 For clarity regarding the process for establishing implementation-related policies related to the foregoing three bulleted comments or implementation issues, we request that the TMDL include a new section dedicated to of the implementation planning process. The following summary is based on text presented in another pending draft TMDL in this region (VA DEQ/ICPRB, Bacteria TMDLs for the Hunting Creek, Cameron Run, and Holmes Run Watersheds - DRAFT REPORT, July 19, 2010):

VA DEQ intends to develop a TMDL implementation plan that addresses, at a minimum, the requirements specified in the Code of Virginia, Section 62.1-44.19.7. State law directs the State Water Control Board to "develop and implement a plan to achieve fully supporting status for impaired waters. " The implementation plan "shall include the date of expected achievement of water quality objectives, measurable goals, corrective actions necessary and the associated costs, benefits and environmental impacts of addressing the impairments. " In addition, EPA outlines the minimum elements of an approvable implementation plan in its 1999 "Guidance for Water Quality-Based Decisions: The TMDL Process. " The listed elements include implementation actions/management measures, timelines, legal or regulatory controls, time required to attain

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TMDL Section Comment water quality standards, monitoring plans, and milestones for attaining water quality standards.

Watershed stakeholders will have opportunities to provide input and to participate in the development of the TMDL implementation plan. Regional and local offices of VA DEQ, Virginia Department of Conservation and Recreation (VA DCR), and other cooperating agencies are technical resources that can assist in this endeavor.

With successful completion of implementation plans, local stakeholders will have a blueprint to restore impaired waters and enhance the value of their land and water resources. Additionally, development of an approved implementation plan may enhance opportunities for obtaining financial and technical assistance during implementation.

It is expected that implementation of the TMDL will occur in stages, and that full implementation of the TMDL is a long-term goal. Actions identified during TMDL implementation plan development that go beyond what can be considered cost-effective and reasonable will only be included as implementation actions if there are reasonable grounds for assuming that these actions will in fact be implemented. If water quality standards are not met upon implementation of all cost-effective and reasonable BMPs, a Use Attainability Analysis (UAA) may need to be initiated since Virginia's water quality standards allow for changes to use designations if existing water quality standards cannot be attained.

In some streams for which TMDLs have been developed, factors may prevent the stream from attaining its designated use. In order for a stream to be assigned a new designated use, or a subcategory of a use, the current designated use must be removed. To remove a designated use, the state must demonstrate that the use is not an existing use, and that downstream uses are protected. Such uses will be attained by implementing effluent limits required under §301b and §306 of Clean Water Act and by implementing cost-effective and reasonable best management practices for nonpoint source control (9 VAC 25-260-10paragraph I). The state must also demonstrate that attaining the designated use is not feasible because of one or more of the following reasons:

1. Naturally occurring pollutant concentration prevents the attainment of the use.

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TMDL Section Comment 2. Natural, ephemeral, intermittent, or low flow conditions prevent the attainment of the use unless these conditions may be compensated for by the discharge of sufficient volume of effluent discharges without violating state water conservation.

3. Human-caused conditions or sources ofpollution prevent the attainment of the use and cannot be remedied or would cause more environmental damage to correct than to leave in place.

4. Dams, diversions, or other types of hydrologic modifications preclude the attainment of the use, and it is not feasible to restore the waterbody to its original condition or to operate the modification in such a way that would result in the attainment of the use.

5. Physical conditions related to natural features of the waterbody, such as the lack ofproper substrate, cover, flow, depth, pools, riffles, and the like, unrelated to water quality, preclude attainment of aquatic life use protection.

6. Controls more stringent than those required by §301b and §306 of the Clean Water Act would result in substantial and widespread economic and social impact.

This and other information is collected through a special study called a Use Attainability Analysis (UAA). All site-specific criteria or designated use changes must be adopted by the SWCB as amendments to the water quality standards regulations. During the regulatory process, watershed stakeholders and other interested citizens are able to provide comment.

7.0 Public Participation

7-1 Page 7-1, Preliminary TAC Meetings: The April 2008 meeting was held at NVRC's offices, not at the Fairfax County Government Center. The purpose of these meetings was to explore the potential for developing a non-traditional TMDL using either flow or impervious cover as the pollutant of concern. Fairfax County submitted a comment letter to DEQ on August 8, 2008 detailing concerns about applying either alternative in the Accotink Creek watershed and recommending that DEQ proceed with a traditional sediment TMDL. No response was ever received.

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TMDL Section iituii Comment 7.0 Public Participation

7-2 Page 7-1, TAC Meeting No. 1: In addition to the stressor analysis, which identified urban runoff and instream erosion (sediment deposition) as the primary stressor impacting the benthic community in Accotink Creek, the first TAC meeting was also used to present two alternative approaches to TMDL development: a sediment load duration curve approach linked to flow and an impervious cover model linked to sediment erosion models and to flow. NVRC submitted joint comments to DEQ on January 27, 2009 on behalf of the Fairfax County and the City of Fairfax reiterating concerns about the applicability of the proposed alternative approaches in the Accotink Creek watershed. A response was received on July 21, 2009 stating that EPA would be taking over development of the TMDL while DEQ took steps to clarify the State Water Control Board's authority to address flow related impairments. Assurances were made that the TMDL would not recommend cost prohibitive retrofits and that implementation would take place over multiple permit cycles. Finally, the letter stated that EPA had secured funding to develop an implementation plan for Accotink Creek. While it was helpful to get clarification of what would be expected from MS4 permit holders in terms of implementation, the letter did nothing to address the fundamental concerns raised regarding the applicability of both the sediment load duration curve and impervious cover approaches.


7-3 Page 7-1, TAC Meeting No. 2: While both technical approaches that had been presented at the First TAC were presented in more detail at the Second TAC, it was clear from the meeting that the impervious cover approach was heavily favored by EPA. An update was provided on the legal issues surrounding a flow TMDL, including the need for the state to proceed with a Notice of Intended Regulatory Action (NOIRA). Fairfax County, the City of Fairfax and NVRC submitted a joint comment letter to DEQ on September 18, 2009 reiterating concerns about the proposed approaches. A response was received from EPA on December 14, 2009 stating that a new approach had been selected that would be entirely based on flow duration curves. The letter stated that this new approach was selected because it would "direct the implementation efforts on the control policies, programs and measures which will best mitigate the effects of volume and velocity associated with storm water flows, thereby reducing the pollutant, sediment."

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TMDL Section Comment 7.0 Public Participation

7-4 Page 7-2, TAC Meeting No. 3: At the third TAC meeting, details on the new approach using flow as a surrogate for sediment were presented, including draft allocations calling for a 50 percent reduction in flow water shed-wide. The draft TMDL was not provided to the TAC at this time. Fairfax County, the City of Fairfax and NVRC submitted a joint comment letter to EPA on February 26, 2010, again reiterating the concern that a flow TMDL would limit the implementation options available to localities and could have significant unintended consequences. The letter also raised a number of specific technical issues with the TMDL presentation. No response was ever received. When Fairfax County inquired as to when a response might be forthcoming, EPA said that they would "provide a response to all comments received when the TMDL is established [which] will be sometime in August."


7-5 Page 7-2, Final Public Meeting: The draft TMDL was first made available to TAC members and the public on July 5, 2010. The final public meeting was held on July 26, 2010 at the Fairfax County Government Center. A number of valid questions were raised at the meeting but were dismissed by EPA staff as being related to implementation, with the statement being made that TMDLs are not required to consider feasibility or economic impact.

8.0 Reasonable Assurance

8-1 Page 8-1, Load Allocation: The reasonable assurance language for the LA overstates significantly the amount of funding available from the Commonwealth for these types of projects. The Virginia Revolving Loan program was only just recently made available for stormwater quality. Further, the amount of funding in the Virginia Water Quality Improvement Fund dedicated to urban stormwater is just a fraction of the overall amount allocated.

8.0 Reasonable Assurance

8-2 Page 8-2, Wasteload Allocations: Simply writing TMDL requirements into an MS4 permit does not constitute reasonable assurance that the requirements can be met. There is an argument from an enforcement standpoint that the wasteload requirements can be implemented through incorporating the specifics into permit conditions, but there is neither discussion relating to the assurance that the water quality objectives will be met nor discussion of the potential cost to achieve the TMDL requirements. How will this TMDL evaluate the effect of implementation on the benthic impairments?

Please acknowledge that the TMDL can be revised and updated i f sufficient evidence is provided suggesting that stormwater flow rate is not the appropriate stressor. EPA acknowledged that toxicity is a potential stressor, and we question whether flow reductions will result in the de-listing of the impaired streams.

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TMDL Section Comment 8.0 Reasonable Assurance

8-3 Page 8-3, Wasteload Allocations: As described in Comment 6-15, addressing benthic impairments cannot rely on a "one size fits all" approach, and thus the TMDL should include language that allows non-flow based BMPs to be used as a component of the MS4 compliance. Without this language, the County is concerned that the MS4 Permit will require a TMDL Action Plan that solely focuses on flow reduction, as opposed to allowing a comprehensive approach that includes control of sediment.

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Documents

County of Fairfax, Virginia - Wetland Studiesnewsletters.wetlandstudies.com/docUpload/2010-08... · 8/19/2010 · Fairfax County remains committed to addressing the benthic impairment