Treatment plant capacity, population served
We visited the Carrolton Water Works in Orleans Parish. This is the main drinking water treatment facility for the City of New Orleans. The plant treats 122 million gallons per day (mgd) and serves 440,000 people. The source water is the Mississippi River. On October 6, 2005, the boil water order was lifted for about 269,000 people. The boil water order for the remaining customers was lifted on October 7, 2005.
At the time of our visit, the facility was operating with a highly reduced staff.
The Water Purification Superintendent described the process required to restore water service to New Orleans:
After power was restored, water was produced quickly. Initially, raw water was coagulated but not disinfected. In general, chemical addition processes (coagulation and disinfection) were not affected significantly. However, filtration was impacted severely. The pipe galleries were flooded, rendering filter controllers and instrumentation inoperative. Filters were operated manually until controller operation was reestablished. The plant currently is maintaining about 1 mg/L free chlorine (no ammonia added).
The distribution system was valved off in a controlled fashion, with service reestablished slowly. Large pipe breaks were repaired quickly. Distribution system problems came from numerous small breaks (perhaps hundreds) at service points, e.g., hydrants sheared of by storm-propelled vehicles and broken plumbing from homes moved in the storm. The six pipe crossings over the industrial Canal were positively valved off to isolate the contiguous portions of the city.
Requirements for Reestablishing Water Service
The State of Louisiana set several requirements for reestablishing water service: (1) uninterrupted treatment capable of producing water meeting microbiological standards, (2) backup electrical service in place, (3) capacity to receive and store treatment chemicals, and (4) maintenance of adequate pressure in an uninterrupted fashion. The boil water order was in effect until all requirements could be met. Plant personnel collected 300-400 samples in exploratory sampling and three days of compliance sampling. Most samples were collected at hydrants. Only 11 samples tested positive for coliforms (only one fecal coliform-positive sample).
(1) Chlorine Stability
By not adding ammonia, the plant has switched from chloramination to chlorination. As a result, staff are concerned that chlorine residuals may dissipate more rapidly than in the past.
(2) Continuing Boil Water Orders
Orleans Parish East and the South Shore are still under boil water orders.
Submitted by James Jensen
and Pavani Ram
October 19, 2005