Comparables:
Sitios Superfund

SUMMARY

This is a July 2000 U.S. Army Corps of Engineers (Philadelphia District) informational report for Philadelphia’s congressional delegation. It looks at why homes are sinking in Feltonville, the neighborhood across Roosevelt Boulevard from the Logan “sinking homes” area. It was a preliminary study funded with $150,000 under Section 566 of the Water Resources Development Act of 1996.

 

BACKGROUND

In the early 1900s the Wingohocking Creek was rerouted into brick sewers, and its valley was filled with loose, uncompacted coal ash, cinders, construction debris and soil. Rowhouses were built on top. In Logan, a 1986 gas explosion drew attention to the problem. A city report then found 957 homes affected, and more than 900 were eventually demolished. Feltonville residents later reported similar foundation settlement, which led to this study.

 

WHAT THE CORPS DID

• Built a topographic change map by comparing early-1900s five-foot contour maps with current two-foot contours to estimate fill depth.

• Drilled 13 test borings in June 2000.

• Did a walking visual assessment of building exteriors, plus a few interior looks.

• Video-inspected sewer laterals (the privately owned pipes running from each house to the city sewer) at 10 homes.

• Gathered city maps of water, gas and sewer lines into GIS.

 

KEY FINDINGS

• Fill depth: Parts of Feltonville sit on ash and cinder fill up to about 41 feet deep by boring, and 40–48 feet by mapping. Unfilled areas rest on decomposed schist or bedrock and aren’t settling significantly.

• Main cause: The loose, low-strength fill compresses under load. Water makes it much worse: it densifies the ash, weakens it, washes fine particles away (“piping”), and can even dissolve ash in acidic wastewater.

• Broken pipes speed up the damage. On the 4500 block of North Reese Street, the city’s 20-inch sewer main was broken at Wingohocking Street, with a matching dip in the street. One lateral (4510 Reese) had a fully broken bottom with water pouring into a void, and several others were cracked or distorted.

• Where the damage is: Building distress generally tracks the old creek path and the deepest fill. End-of-row units fare worst because they brace the rest of the row. When abandoned houses are demolished, neighbors become new end units, which can set off a domino effect along a block.

• Worst blocks: Luray (6th–7th), Courtland (6th–8th), Reese (Wingohocking–Annsbury), Raymond (3rd–5th) and Annsbury (4th–5th).

• Other contributors: Large London plane trees clog gutters and downspouts, so rainwater soaks in near foundations, and their roots get into laterals. Fire hydrants left open have flooded basements on Reese Street.

• Gaps in the method: Some distressed houses along 5th Street sit on fill that predates the old contour maps, so the map shows little or no fill there.

 

RECOMMENDATIONS

• Inspections: Do detailed structural inspections on the blocks listed above. Keep a GIS inventory of distressed buildings, update it with annual or semi-annual re-inspections, and set survey benchmarks on end units.

• Water and sewer: The Philadelphia Water Department should inspect sewer and water lines in fill areas, estimated at about $150,000. Homeowners’ laterals should be checked with video and dye tests and replaced with PVC or flexible-joint ductile iron where needed.

• Building and construction rules: Have an engineer design structural support wherever demolition leaves a gap or a new end unit. Require PE-certified foundations for any new construction on fill, such as piles to bedrock, grouting or vibrocompaction. Backfill utility repairs with compacted structural fill.

• Resident services: Set up a resident hotline for reporting changes and for getting open hydrants shut off.

• Trees and drainage: Fix downspouts, add gutter guards, and consider replacing the problem trees.

• Further mapping and testing: Extend fill-depth mapping downstream, for about $30,000. Test soil for lead, arsenic and mercury before any construction, since Logan’s ash contained elevated levels.

 

FUNDING AND LIMITS

Any further federal work would need a non-federal sponsor such as the City to cover 25% of costs. It would be limited to publicly owned, water-related facilities, and the report calls it a low budget priority. The report also notes that most homeowners’ insurance doesn’t cover subsidence. The Corps disclaims any warranty on property conditions, and the report is meant only for general informational use beyond its client.

• Rebuilding the house utility lines and the city sewers

• Adding street drain inlets to reduce flooding and water seeping into the ground

• Underpinning any rehabilitated house with pin piles down to bedrock

They noted that the houses could be stabilized but never made level again.