Implementation of SW retrofit and restoration projects in DC –

lessons learned

Peter Hill

DC Dept. of Health,

Watershed Protection Division

Review of stream conditions

• MS4 (storm sewer area) has extremely “blown out” streams – high sediment contribution from failing banks, high channel instability

• SW infrastructure is failing (esp. headwalls)• Biological diversity is low due to urban runoff

and sewer leaks• This occurs even in stream with low percentage

of impervious areas

Sources of these problems

• SW quantity not mitigated in large areas of the city

• Large areas of city with no SW quality control

• Aging sewer lines

Fenwick Branch sw outfallFt. Davis sw outfall (30 ft deep canyon)

What we’re doing…. SW retrofit prioritizationAddress Type Area Treated (in sq.

ft.) A: <200, B: 200-500, C: >500

Feasibility Notes What is specifically required in terms of road alteration?

FT DUPONT WATERSHED Ridge Road (next to DCP&R Rec center

Bioretention cells C Med-high Some excavation necessary on N side, S side abuts NPS property - this stormwater is responsible for broken storm pipe emptying into stream, severe stream downcutting

Curb cuts, some excavataion to allow for proper drainage

Ridge & 44th South side of Ridge

Infiltration Trench /

B Med-high Open lot could treat Stormwater from street if biocell was installed

Curb cut

Burns Rd Btw. Alabama & Ridge

Infiltration trenches/ Tiered

C Med-High High slope, the trenches might need to be tiered to allow for infiltration / this stormwater resp. for high degree of stream entrenchment

Currently there is no curb, repair of road could be done to allow for finished edge and sheet flow off into NPS property

Alabama & Burns area

Infiltration - bioretention cell in grassy triangle at intersection

C Med Triangle would need flow diversion across Burns, infiltration along Alabama would be easy (plenty of room)

Flow diversion "asphalt ridges" to divert water into the "triange"

Alabama Ave - from Burns to Mass

Infiltration trenches/rain gardens

C High Plenty of room on roadsides (on west side)

Curb cuts, minor excavation

Mass Ave (from Ala. To Minn. Ave.)

Curb cuts, infiltration trenches

C High Plenty of room on both sides (storm drains available for overflow)

Curb cuts, minor excavation

Ridge Road (n. of Ft. Davis)

Infiltration trenches B Med Excavation necessary Curb cuts

John P. Sousa middle school

Potential green roof/ rainbarrels

? ? Outside of Ft. Dupont subwatershed but potentially a good partnership w/ school

No coordination with DDOT, coordination with DCPS system needed

Ft. Dupont ON NPS LAND Ft. Dupont Drive

Infiltration Ditches

C (entirety of Ft. Dupont Dr.)

Very High Concrete channel in roadside ditch could be replaced with grass

No alteration to road, roadside swale might need some exacavation

Ice Rink parking lot (Ely st)

Infiltration strips in parking lots

C (large parking lot) High Large lot, grading is not right to divert into parking medians (infil. Strips better)

Minor alteration of parking lot, some flow deflectors

Access road to Refueling station

Curb removal C High Easy to divert stormwater to grassy areas at side of road

Curb cuts, flow diversion into biocells

Parking lot outside of Refueling

Infiltration strips, or small biocell

C Med Curb cuts

• Identification and prioritization of SW retrofit sites (field determined)

• Identification of estimated reduction loads

• Identification of required agency buy-in

(Most difficult area)

LID Demonstration projects

• Over 8 implemented• Over 25 in design phase• Funded with 319 and Ches. Bay Program funds

1 – Bancroft ES LID

2 – Ross ES LID

3 – Human Rights Campaign Foundation green roof

4 – Casey Trees Foundation green roof

5 – Police substation rain garden

6 – Capitol Hill LID

7 – Peabody ES LID

8 – Benning Road bioretention cell

SW Retrofits – lessons learnedProgrammatic issues• More costly than expected (20-60K/biocell

(.3-.6 acres treated)• DDOT right of way issues unresolved• Maintenance issues unresolved • Several agencies involved in each small

project• Clear directive from agency directors has

not been issued• Streamlined agency coordination has not

thus been achieved

Benning Rd bioretention cell

SW retrofits – lessons learned

Logistical/design issues• Significant space required• “Hand holding” needed• Each project unique – contractors

frequently unable to modify/adapt to ensure a successful project

• Issues of overflow/underdrains• Untested solutions – unexpected

problems• When designed correctly – THEY

WORK!

Bancroft elementary SW retrofit

Policy issues

• Will this type of sw be cost-shared by the local jurisdiction?

• How could these be incentivized through the permit process?

Peabody Elementary

Pavers installed at school’s request

Teachers sued when they were unhappy with result

SW retrofits - unanswered questions• Can these be projects be streamlined?• Can the city procure these projects effectively?• Is this a cost effective alternative to treat urban runoff?

Feature Area m^2 Area acres

% of DC Land

DC 177,456,155 43,850.4 DC Water 18,768,414 4,637.8 DC Land 158,687,741 39,212.6 Paved surfaces: roads, lots, alleys 35,312,371 8,725.9 22.3 Building rooflines 23,799,594 5,881.0 15.0 Sidewalks 8,418,799 2,080.3 5.3 Hardened surface 67,530,764 16,687.2 42.6 Un-hardened surface 91,156,977 22,525.4 57.4

SW retrofits – predicting costs• Back of envelope calculation….assuming that it was technically possible

• 8,726 acres of paved roads, lots, alleys in DC: 22.3 % of DC land

• *.67 (area not in CSO) = 5,846 acres• If average LID/biocell treats 0.35 acres, we would need

16,702 LID projects• Low cost is currently 20K/cell• Total cost for retrofitting the MS4 area= $334,040,000• This does not account for roofs and sidewalks, only

high pollutant load areas

DC’s Wetland restoration projects

WPD has completed two large wetland restoration projects (35 & 18 acres) in the Anacostia River in partnership with the US Army Corps of Engineers. These have the promise of providing additional wildlife habitat as well as capturing nutrients and sediment. A new 7 acre project is currently under construction.

DC’s Wetland restoration projects- lessons learned

• Removal efficiencies for wetlands are typically determined by treatment wetlands (ie.. closed system). Efficiencies for tidal systems is not known and may be much lower.

• Invasive species can be a significant problem. Getting the elevation right can reduce invasive pressure by some species.

• Resident Canada goose herbivory is a major problem in urban and suburban areas and can dramatically affect a wetland restoration project. Without a hunting season, it is extremely difficult to do anything about this overpopulation of an introduced species. Fencing is the typical method used to address geese, but is not a suitable long term solution.

DC’s Wetland restoration projects- lessons learned

• USACE is experienced in wetland creation/restoration, but costs are extremely high in urban areas. $220,000-$175,000 per acre are the costs that include all ACE planning, coordination, and construction. Multi-year delays are common since funding is dependent upon congressional earmarks.

• Other avenues for contracting out this aspects of this work / partnering with non-profits might be more cost effective and would involve the public more