Session 5c: Future Growth (FG) Representation

1. Session 5c:Future Growth (FG) Representation Virginia Tech Biological Systems Engineering Department DEQ TMDL Modeling Workshop; Richmond November 19-20, 2013

2. To describe several ways that Future Growth (FG) can be represented in TMDL modelling Objective

3. Future Growth Critical to reasonable assurance Pollutant-specific effects – intention is to take a conservative approach Incorporated into future conditions (TMDL) model Variety of available data sources

4. Future Growth (FG) Representation Adjustment of model land use distribution Adjustment of pollutant loading Consider net effects – typically conservative approach is taken

5. Partial Build-out, i.e. Opequon Creek Comprehensive Plan, i.e. Phelps Branch Population growth trends and zoning, i.e. Little Otter River Agricultural census trends Variations in FG Representation + Assumptions based on BPJ

6. Future urban development would occur within Frederick County’s “Urban Development Areas” and “Commercial Centers”. • Agricultural and forestry land uses within these areas would potentially decrease to 0% under full buildout. • Water, transitional, and urban greenspace areas would not change. • Commercial and residential land uses within these areas would increase in proportion to their existing ratios. • 25%, 50%, and 100% build-out scenarios were evaluated; 25% chosen for the TMDL in consultation with local TAC Opequon Creek Assumptions

7. Opequon Creek

8. Limit growth to the Upper Phelps Branch sub-watershed, which conforms to a primary growth area • Allow developed land use to increase by 15% (30 acres) in the watershed • Reduce other land use acreages to accommodate future growth: 2/3 from existing forest and 1/3 from existing agricultural land uses • Allocate construction permit acreage as 5% of developed acreage Phelps Branch Assumptions

9. Phelps Branch

10. All Ag Reductions based on % Ag zoned for Development. Little Otter River forest reductions all based on % Forest zoned for Development. Buffalo Creek forest reductions based on % Population change and Parcel data. Little Otter River Assumptions

11. Parcels as Indicators of Potential Growth

12. Current DEQ DRAFT guidance • All bacteria TMDLs should include WLAFG • If a watershed has no existing permitted dischargers, or the existing WLA in the watershed represents < 10% of the TMDL, the future growth WLA should be set at 2% the TMDL. • If the existing WLA in the watershed represents >10% of the TMDL, the future growth WLA should be set at 1% the TMDL. • Other growth factors may be appropriate and should be considered with best professional judgment. WLA Minimum Allowance for FG?

13. WLAFG simulated as a point source at the impaired segment’s outlet • % of TMDL load at timestep with flow derived assuming WQS WLA Minimum Allowance for FG?

14. Questions?