Memo for fiscal year 2022, updated 2021-02-23

[Archived] Question # 11:What are the alternative options to the Taylor Run Stream Restoration project in order to receive credits for our Chesapeake Bay mandate?


What are the alternative options to the Taylor Run Stream Restoration project in order to receive credits for our Chesapeake Bay mandate? Please include tree planting, bioretention filters, and any other options we have. (Vice-Mayor Bennett-Parker)


The Taylor Run Stream Restoration project is intended to restore the stream corridor, protect an exposed sanitary sewer pipe from damage, enhance local water quality and the stream’s riparian buffer, and help address state and federal Chesapeake Bay Total Maximum Daily Load (TMDL) cleanup mandates. City staff has performed extensive public engagement, incorporated feedback and revised the design where applicable, consistent with its commitment to collaborative planning.

This $4.5 million project – which is funded by a $2.25 million state water quality grant as well as $2.25 million in City funding – has been designed and Chesapeake Bay pollution reduction credits calculated in accordance with Virginia Department of Environmental Quality (VDEQ) and the U.S. Environmental Protection Agency (EPA) Chesapeake Bay Program.  These protocols are vetted and accepted best practices for use by numerous jurisdictions in the Bay area to perform stream restoration. The required regulatory steps and methodologies were followed in calculating pollution reduction credits of 295 lbs./yr. of total phosphorus to be achieved by the project. Three alternative scenarios suggested or recommended by some in the community were: (1) implementing green infrastructure and other best management practices (BMPs), (2) tree planting, and (3) purchase of credits. If any of these were to be successful they would need to generate an equivalent number of pollution credits.

Of note, the proposed Stormwater Utility 10-Year Plan CIP, in order to meet 100% of the state pollution reduction mandate by 2028, assumed the stream restoration projects (Taylor Run, Strawberry Run, and Lucky Run) were moving forward.  If an alternative is pursued, then the 10-Year Plan would need to be revised based on the funding impact of these alternatives, each of which come with very different levels of risk and costs.  Additionally, none of the alternatives would stabilize the sanitary sewer infrastructure which will need to be undertaken regardless. The fiscal impact of separating the sanitary sewer stabilization is discussed below.

Alternative Scenario 1: Implementing green infrastructure and other best management practices (BMPs)

Staff compared smaller scale BMPs that include green infrastructure (urban bioretention, bioswales, etc.) and underground BMPs (filtering devices) as alternatives as retrofits in the right-of-way and on public property.  Cost-benefit estimates for these alternatives range from $88,000 to $225,000 per pound of phosphorous reduced, respectively.  (Note these estimates do not include currently uncertain costs that may arise during the planning, scoping, design or implementation phases, or future maintenance and operation costs.) Using those per pound cost ranges, capital costs are estimated between $26 million and $66 million to implement between 300 and 400 new BMPs to achieve an equivalent amount of pollution credits. This would add (refer to footnote) between $41 and $89 to the annual stormwater fee for the majority of homeowners in the City. It is also important to note that due to the high cost per pound of phosphorous removal none of these BMPs would meet the eligibility requirements (of $50,000/lb. or less) to be considered for a VDEQ Stormwater Local Assistance Program grant. Therefore, the City would need to fully fund these smaller BMPs using local funds.

Alternative Scenario 2: Tree Planting

Staff compared tree planting per DEQ and EPA’s Recommendations of the Expert Panel to Define BMP Effectiveness for Urban Tree Canopy approach to generate pollution reduction credits. To achieve an equivalent pollution reduction, the City would need to plant between 421,000 and 686,000 trees at a low-end estimated cost of $84 million to $137 million and a high-end estimated capital cost of $126 million to $206 million. This would add (refer to footnote) between $113 and $287 per year to they stormwater utility fee for the majority of homeowners in the City. Like Alternative Scenario 1 these costs do not include currently uncertain costs that may arise during the planning, scoping, design or implementation phases, or future maintenance and operation costs. The issue of where to plant this volume of trees also would need to be addressed.

Alternative Scenario 3: Purchase of Credits

Virginia nutrient trading credits are market-based mechanisms that vary in cost and availability and are typically purchased in association with private development projects. These nutrient credits are generated by installing permanent practices in the Bay watershed, which includes stream restoration, converting agricultural lands to forests, and other types of BMPs approved by EPA and VDEQ. These are typically done in more rural areas to maximize the return on investment for the credit supplier, meaning a credit supplier would not seek to do this work in the City. Based on the current market rates for phosphorous (approximately $35,000 per pound), this alternative would cost approximately $10 million depending on demand and availability (295 pounds x $35,000 = $10.3 million).  This would add (refer to footnote) $14 per year to the stormwater utility fee for the majority of homeowners in the City. Finally, and of note, these practices would not protect or enhance local water quality. The cost also does not include the additional cost for the stabilization of the sanitary sewer at Taylor Run, which needs to occur in the short term.

Additional questions have been raised about the potential for credits as part of the RiverRenew clean waterways initiative to remediate the City’s combined sewer outfalls (CSO). The Virginia water quality trading program does not include trading with point source discharges like wastewater treatment plants.  Trading credits with Alexandria Renew following completion of the CSO remediation project may be an option, if allowed by VDEQ. Credits from the CSO mitigation project would be calculated annually based on the CSO volumes being captured and stored, and then sent to Alex Renew for treatment to wastewater standards before discharge.  Credits would be calculated by taking the difference between the existing annual CSO wasteload allocation in the Bay TMDL and the CSO flow that is treated and discharged by the plant.  There is considerable schedule risk in meeting the state 100% pollution reduction mandate associated with this approach, which includes the RiverRenew construction schedule, the performance of the plant, increased rainfall due to climate change (potentially triggering more CSO events) with additional risk from potential changes in regulations that may affect allocations, changes to permit limits, modeling changes, and a reliance on these credits by the state to account for underperformance in other sectors.  More importantly, the nature of wastewater is such that the capture and treatment of the CSO flows does not generate many total suspended solids (TSS) or sediment credits, leaving the City well below its mandated reduction.  Therefore, implementing this alternative would require the City pursue other alternatives to generate sediment credits.  At the current market rate pricing, it would cost around $10 million to purchase sediment credits depending on demand and availability.

Additional Fiscal Impact if no stream restorations are undertaken:

If the City chooses to defer or cancel the Taylor Run Stream Restoration project, it brings into question the use of stream restorations as a key strategy in the City’s toolkit to meet its Bay mandates. The City’s three, currently approved stream restoration projects will cost the City approximately $3.7 million, with another $3.7 million coming in VDEQ grants.  In contrast, the total cost of a “BMPs alone” strategy to reduce an equivalent amount of phosphorous for the City would be between $79 million and $201 million, which is currently not programmed in the Ten-Year Stormwater Capital Plan. This would add (refer to footnote)between $106 and $274 per year to the stormwater utility fee for a majority of homeowners. It would require the installation of over 900 total green infrastructure and underground BMPs in rights-of-way and on public property. If Council chooses one of the above scenarios for Taylor Run, or removes stream restoration from the City’s toolkit, staff would need to provide additional refined projections on the fiscal impacts and risk, and revise the City’s Stormwater Utility 10-Year Plan.

Although the City is currently ahead of schedule in meeting Bay mandates, a change in strategies at this time, in staff’s professional opinion, would significantly increase the risk of the City staying in regulatory compliance with its MS4 permit.  If non-compliant, the City could potentially be subject to fines and/or consent orders and other punitive measures. These would likely include prescriptive actions and schedules of interim milestones to demonstrate positive trajectory to meet the requirements, including the identification of adequate funding and scheduling to implement alternative BMPs to achieve milestones. These punitive measures would likely be administered through aggressive oversight by VDEQ.

Finally, if the sanitary sewer stabilization were done separately, it will still require impact to Taylor Run and the park. The sanitary sewer runs parallel to the trail and within the southern stream bank for most of the way until it crosses to the northern side of the stream near the acidic seepage wetland, where the sheet pile for the manhole is located.  Separately stabilizing the sanitary infrastructure in lieu of incorporating this work into a more holistic stream restoration would require tree removal for access – presumably the pedestrian trail as well as down to the stream to access the sanitary sewer crossings exposed in the stream bed – to allow heavy equipment access to stabilize the sanitary crossings by encasing the pipe in concrete.  

Since larger trees within the sanitary easement pose a serious risk to the sanitary infrastructure, removal of those larger trees may be required.  (Tree roots can grow around the pipe, and if they fall due to ongoing erosion, can cause a break and release raw sewage into the stream and disrupt service for nearby residents.)  In order to minimize disturbance and grading, the sheet pile in place for the downstream manhole would remain.  Early cost estimates of separately performing stabilization of the sanitary sewer crossings through encasement in concrete would be roughly $400,000 to $600,000 and is not included in the alternative scenarios.


[i] Impact on the stormwater utility fee depicts the financing of costs over a 20-year period with the fee impact measured midway for illustrative purposes at the 10-year period. Actual fee impact would be greater in earlier years and less in later years.

[ii] Calculations reflect annual impact on most single family detached homes, with large homes paying more and townhouses less. Commercial properties would pay more based on their level of impervious surface. 

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