Status and Effect of Impervious Area Estimates in the TMDL

Presented to the Potomac Watershed Roundtableby Michael S. Rolband

P.E., P.W.S., P.W.D., LEED® AP

Wetland Studies and Solutions, Inc.5300 Wellington Branch Drive . Suite 100

Gainesville . Virginia 20155www.wetlandstudies.com

January 7, 2011

Current Surface Area Estimate:

Note 1. Surface area acreages were received in a 6/2/2010 e-mail from Peter Claggett (USGS) to Mike Rolband (WSSI).

EPA will formally update the surface areas for the creation of the Phase II WIPs. The data was expected to be available to a limited audience this week (per a phone discussion between Peter Claggett (USGS) and Bethany Bezak (WSSI) on 1/3/2011), but further information was not available to WSSI at the time this presentation was prepared.

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Model Version Analysis Year Impervious Surface (ac) Pervious Surface (ac)

Phase 5.3 2002 675,917 1,885,935Phase 5.3mod 1

(excluding suburb and rural wooded areas)2001 1,569,377 3,442,346

Percent Increase from Phase 5.3 -- 132% 83%

Impervious and Pervious Urban Areas

Wetland

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We expect that the:

•Impervious load will more than double because it is equal to the area times the loading rate(EPA has indicated that the loading rates will not change);

•Pervious load will stay the same (or close) because it is based on fertilizer sales; and

•Load reduction requirement will increase because the WIP requires the urban sector to reduce a percentage of the urban load.

(Note that the original WIP required the urban sector to retrofit a percentage of the impervious area; the final WIP requires a load reduction instead. This is an improvement!)

This will affect all sectors because the sum of pollutants in the Bay must remain constant.

Potential Effect:How Does This Update Affect the TMDL?

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Potential Effect:

2,238,449 additional Urban lb/yr1. What sector will this come from?Note:•Forest acreage must change 6 times faster2 than urban impervious areas for the TN loads to equate;•Air loads will not change;•WWTP loads are based on permits;•This leaves Ag and Septic.

The total TN load is from real-world data.

It can not change.

1. The additional urban load equates to the 2009Progress TN load from impervious urban surfaces (1,695,795 lb/ac/yr) times 132%. WSSI assumed no change in the TN load from pervious surfaces.2. Urban impervious TN loading rate = 11.8 lb/ac/yr Forested TN loading rate = 2.0 lb/ac/yr Ratio = 12:1

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Potential Effect:

636,097 additional Urban lb/yr1. What sector will this come from?Note:•Forest acreage must change 21 times faster than urban impervious areas for the TP loads to equate;•Air loads will not change;•WWTP loads are based on permits;•There is no TP load from Septic;•This leaves Agriculture.

The total TP load is from real-world data.

It can not change.

1. The additional urban load equates to the 2009Progress TP load from impervious urban surfaces (481,891 lb/ac/yr) times 132%. WSSI assumed no change in the TP load from pervious surfaces.2. Urban impervious TP loading rate = 2.1 lb/ac/yr Forested TN loading rate = 0.1 lb/ac/yr Ratio = 21:1

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Potential Effect:

137,680 additional Urban lb/yr1. What sector will this come from?Note:•Forest acreage must change 21 times faster than urban impervious areas for the sediment loads to equate;•WWTP loads are based on permits;•There is no sediment load from Septic or Air;•This leaves Agriculture.

The total sediment load is from real-world data.

It can not change.

1. The additional urban load equates to the 2009Progress sediment load from impervious urban surfaces (104,303 lb/ac/yr) times 132%. WSSI assumed no change in the sediment load from pervious surfaces.2. WSSI assumes sediment to be proportional to TP.

WIP Allowable Loads Are Not Equitable Among Watersheds, Even Considering AgWaste Loads (related to people) are un-equitably shared by basins in the WIP

Total Nitrogen (TN) Loads by Watershed

Watershed1 Population2

Septic+Urban+Wastewater3 Septic+Urban+Wastewater+Ag3

TN (total) TN (unit) TN (total) TN (unit)lb/yr lb/cap.-yr lb/yr lb/cap.-yr

Potomac 2,769,358 6,975,000 2.52 13,334,000 4.81Rappahannock 275,000 1,365,000 4.96 3,880,000 14.11York 423,550 2,133,000 5.04 3,537,000 8.35James 2,499,455 15,948,000 6.38 20,201,000 8.08Eastern Shore 51,594 213,000 4.13 1,103,000 21.38Total 6,018,957 26,634,000 4.43 42,055,000 6.991 Analysis represents only the portions of each watershed within Virginia. Portions of the watersheds that extend outside of Virginia are not included in this analysis.2 U.S. Census Bureau, Population Division, 2009 Population Estimate, obtained from http://www.census.gov/popest/files/CO-EST-2009-ALLDATA.csv on 8/30/2010.3 Allocations are based on the Virginia Chesapeake Bay TMDL Phase I Watershed Implementation Plan (Nov. 2010).

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WIP Allowable Loads Are Not Equitable Among Watersheds , Even Considering AgWaste Loads (related to people) are un-equitably shared by basins in the WIP

Total Phosphorus (TP) Loads by Watershed

Watershed1 Population2

Septic+Urban+Wastewater3 Septic+Urban+Wastewater+Ag3

TP (total) TP (unit) TP (total) TP (unit)lb/yr lb/cap.-yr lb/yr lb/cap.-yr

Potomac 2,769,358 551,000 0.20 1,225,000 0.44Rappahannock 275,000 173,000 0.63 706,000 2.57York 423,550 245,000 0.58 402,000 0.95James 2,499,455 1,504,000 0.60 2,126,000 0.85Eastern Shore 51,594 17,000 0.33 128,000 2.48Total 6,018,957 2,490,000 0.41 4,587,000 0.761 Analysis represents only the portions of each watershed within Virginia. Portions of the watersheds that extend outside of Virginia are not included in this analysis.2 U.S. Census Bureau, Population Division, 2009 Population Estimate, obtained from http://www.census.gov/popest/files/CO-EST-2009-ALLDATA.csv on 8/30/2010.3 Allocations are based on the Virginia Chesapeake Bay TMDL Phase I Watershed Implementation Plan (Nov. 2010).

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WIP Allowable Loads are not EquitableBecause of Loads From Significant Dischargers

Current Permitted Flow-Weighted Average Concentrations (mg/L) for Significant Dischargers by Watershed1

Basin Flow-weighted Average

Concentration (mg/l)TN TP

Shenandoah-Potomac 4.12 0.20Rappahannock 4.00 0.30York 3.08 0.42

James 6.02 0.42

Eastern Shore 4.93 0.30Potomac Embayment 3.0 0.181. Concentrations were calculated from design flows and waste loads provided by Russ Baxter (DEQ – Chesapeake

Bay Program) via e-mail on 9/21/2010, except as noted below.2. TP concentration in the York basin and TP and TN concentrations in the James basin are from Page 33 of the

Virginia Chesapeake Bay TMDL Phase I Watershed Implementation Plan (Nov. 2010).