Comparables:
Sitios Superfund

SUMMARY

A geotechnical study by Lippincott Engineering Associates (Delanco, NJ) for the City of Philadelphia’s Department of Licenses & Inspections, dated August 25, 1986. The City hired the firm in April 1986 to find out why homes and streets in Logan were sinking and to recommend fixes. Moustafa Gouda, P.E., was the lead engineer. The report itself is about 45 pages, with the additional pages appendices. This report did not focus on environmental issues. 

 

STUDY AREA

17 blocks and 957 properties, bounded by Loudon St (north), Marshall St (east), Wingohocking St and Roosevelt Blvd (south), and 11th St (west). By the City’s count and Lippincott’s own survey:

• 13 houses were “imminently dangerous”

• 63 were “structurally dangerous”

• 65 were vacant

Conditions were visibly getting worse during the study.

 

ROOT CAUSES

• The neighborhood sits on a filled-in creek valley. Wingohocking Creek once ran through a valley about 40 feet deep. Around 1899–1900 it was enclosed in a large brick sewer under Courtland St. The valley was then filled with loose, uncompacted ash and cinder, up to 40 ft deep near the 900 block of Roosevelt Blvd and close to zero near Loudon and 11th. Filling was finished by 1913, and the rowhouses were built by about 1920 on shallow footings sitting in that fill.

• Ash and cinder are a poor base for buildings.

  • The fill is very loose, near its minimum density, and can compact by about 25–30% in volume.

  • It weakens sharply when soaked. In a field load test, flooding caused excessive settlement.

  • About 10% of it dissolves in water at pH 4, which matched local acid rain.

  • It is highly prone to “piping,” meaning flowing water carries the particles away.

• Leaking sewer pipes were the main driver. Normal settlement from the weight of the houses should have totaled about 6–12 inches and ended within 1–2 years of construction. The study found up to 2 ft of total settlement, 12–16 inches of differential settlement within a single house, and streets 24–30 inches lower than originally built. The explanation was broken pipes:

  • Downspouts drain into each house’s own sewer line (the lateral), which the owner is responsible for.

  • When those clay and cast-iron pipes cracked, water washed fill into the pipes and on into the City sewers. The lost fill caused more settling, which broke more pipe, so the problem fed itself.

  • Cleaning the shallow 20-inch Franklin St sewer removed more than 22 cubic yards of ash. It was nearly half full.

  • Camera inspections of the Franklin St and Hutchinson St lines found open joints, cracks and a partial collapse.

  • The worst damage was clustered along shallow sewer lines laid in the fill.

• Contributing factors:

  • Unusually wet years (1978, 1979 and 1983) lined up with residents’ reports of faster sinking.

  • Small earthquakes in 1980 and 1982 were judged a real risk because loose ash compacts under shaking.

  • Groundwater has probably risen 5–7 ft since the filling. The report found no sign the creek is still flowing underground.

 

CONCLUSION

If nothing was done, the report judged that “catastrophic failure of numerous dwellings is highly probable.” Likely triggers were heavy flooding, a moderate earthquake, undetected leaks or a sewer collapse.

 

RECOMMENDATIONS

• Houses

  • Demolish the imminently dangerous houses.

  • Have a structural engineer inspect the dangerous ones and demolish any that are unsafe.

  • Underpin the dangerous and distressed houses with small steel piles drilled from the basement down to firm decomposed rock. Do whole blocks at a time, not single houses. The estimate was about $20,000 per house.

  • Replace every house sewer line where there is more than 5 ft of fill, using ductile iron or PVC.

  • Fix gutters and downspouts ($3,000–5,000 per house), and check water and gas lines.

  • Monitor the houses that were unaffected.

• City infrastructure

  • Clean and inspect all area sewers and storm inlets, and line, repair or replace them as needed.

  • Expand drainage capacity.

  • Regrade streets and alleys so water doesn’t pond.

• New construction: Use deep foundations only, such as auger-cast piles down to natural soil, never shallow footings on the fill.

• Grouting the fill was rejected: it would cost at least twice as much as underpinning and would be a “passive” fix.

• Contractor estimates (Appendix P):

  • GKN Hayward Baker: about $15–20K per house for compaction grouting, over $20K for piles, and about $50K for chemical grouting.

  • Nicholson Construction: about $8M to put pin piles under 500 homes, or $9–28M for grouting.

 

ENVIRONMENTAL NOTES

The chemistry testing was done to explain the engineering behavior, not to screen for contamination. It covered only a few ash samples and gave rough ranges. In those samples, arsenic, cadmium, chromium and mercury were not detected, and lead, nickel and copper appeared only in trace amounts. This is not a substitute for a modern environmental site assessment, which is presumably why DEP’s 2020 investigation workplan cites it only as background.

 

CAVEATS

The building ratings are based on exterior inspection only.