Copper Corrosion / Ammonia / Chloramination Case History
North Central Indiana Groundwater System
Have you ever heard anything good said about the lead/copper first draw sampling program? I doubt if you have. A North Central Indiana municipality doesn’t like having to ask our homeowners to take first-draw samples every six months, or even three years; any more than other municipalities across the United States. The last thing they would have thought was that when they failed copper back in 1992, it would save them nearly $30,000 per year? They actually have something very, very good to report about the lead and copper testing program.
This report will briefly discuss the following two aspects of their copper corrosion inhibitor program that Water Solutions Unlimited helped them administered for the past twelve years:
1. How the municipality successfully initiated a corrosion inhibitor program to get them back into compliance with the lead/copper regulation.
2. How the corrosion inhibitor reduced copper pinhole leaks in the distribution system and saved the utility thousands of dollars of repairs each year.
The municipality is located approximately twenty miles north of Indianapolis, IN. Their population is approximately 6,000 and they have 2,450 water services. The average water production is approximately one million gallons per day. The treatment process consists of aeration, detention, followed by sand pressure filters.
Corrosion Control Program Brings Us Back into Compliance
In 1992 they began testing for lead and copper by taking forty, first draw samples from homeowner taps. The utility passed lead, but failed copper miserably. Figure 1 summarizes their test results:
Figure1
Fall, 1992 Lead/Copper Results
Lead
Minimum Maximum 90th Percentile
<0.005mg/L 0.140mg/L 0.009mg/L
Copper
0.513mg/L 3.340mg/L 2.840mg/L
Obviously, they greatly exceeded the 1.3 mg/L action level. They decided not to delay initiating a corrosion control program. Water Solutions Unlimited, Inc. (WSU) of Franklin, IN was contacted and asked for their recommendations and assistance.
WSU developed the Desktop Study and Optimal Corrosion Control Program (OCCP). The OCCP and phosphate chemical feed permits were approved by the Indiana Department of Environmental Management (IDEM) in the spring of 1993.
Was the Water Corrosive?
The municipality’s water is not corrosive. The Langelier Saturation Index (LSI) is +0.53 and is actually scale producing. The Ryznar Index is 6.58. Failing copper or lead was the last thing that they thought would happen. Figure 2 shows the typical water quality parameters for their system.
Figure 2
Water Quality Parameters
pH 7.64
Temperature 13 C
Total Alkalinity
as CaCO3 339 mg/L
Calcium as Ca 79.8
Conductivity 570 umhos
Water Solutions Unlimited recommended using corrosion coupon tests along with first-draw sampling to monitor our progress. While they were waiting for the chemical feed permit to be approved by IDEM, they began using the corrosion coupons to develop a baseline of data on the corrosivity of the finished water before chemical treatment was started. After initiating the feed of the corrosion inhibitors they continued to monitor using the corrosion coupons and first-draw samples. Two or three different corrosion inhibitor blends were tried over an eighteen-month period. The coupon data helped “zero-in” on which inhibitor-blend to use and the optimum feed rate that should be fed. Figure 3 shows a sampling of the coupon results over the past twelve years. Corrosion rates have decreased from 8.37 mils per year in March of 1993, to 3.18 mils per year in April of 2004. Some results have been as low as 0.99 mils per year in the past year.
Figure 3
Copper Corrosion Coupon Results
March 25, 1993 – May 18, 1993 8.37 mils per year (No Treatment)
February 11, 2004 – April 13, 2004 3.18 mils per year (Phosphate)
June 9, 2003 – August 13, 2003 0.99 mils per year (Phosphate)
Tipton Municipal Utilities initially passed their first round of tests in June of 1996. The municipality has been on reduced monitoring for several years. The latest lead/copper test results are shown in Figure 4.
Figure 4
August, 2002 Lead/Copper Results
Lead
Minimum Maximum 90th Percentile
<0.001mg/L 0.041mg/L 0.009mg/L
Copper
0.260mg/L 1.000mg/L 0.860mg/L
The 90th percentile test results have been reduced from 2.84 mg/L to 0.86 mg/L, a reduction of 70%. All results are less than the 1.3 mg/L action level and they can sleep comfortably the night before they test for lead and copper in the future.
But That’s Only Part of This Story!
Prior to testing for lead and copper in 1992, the utility experienced an average of 23 to 25 pinhole leak service work orders a year. Please see Figure 5. Typically, they would get calls from homeowners telling them that water was “bubbling-up” in a yard or street. Ninety percent of the time the leak occurred at the flare fitting where the copper pipe connects to the corporation-stop, where the service line is connected to the water main.
Figure 5
Yearly History of Pinhole Leak Repairs
Year Number of Repairs
1991 23
1992 25
1993 20
August 9, 1993 Started Corrosion Inhibitor
1994 14
1995 10
June, 1996 Passed Pb/Cu Testing, to be in Compliance
1996 10
1997 10
1998 10
1999 11
2000 10
Reduced Chlorine, went to Chloramination
2001 4
2002 5
2003 5
2004 4
The average cost to repair each leak was estimated to be $1,580. This included having three men for two full days of work; and parts, equipment and material to return the site to normal conditions. Since being on the corrosion control program, they have reduced the number of leaks to an average of five per year. The municipality still has over 900 flared corporation stops in their system. Figure 6 outlines the costs.
Figure 6
Cost Per Leak Calculation
3 men X 16 hours X $22.50 per hour = $1,080.00
Parts, equipment, and material 500.00
Average Total Cost $1,580.00
The cost of the corrosion inhibitor chemical is $6,000.00. If you add in yearly additional operational costs to feed the chemical of $800 and chemical feed equipment amortized over three years of $550, you come up with a total yearly cost of the corrosion control program of $7,350.00. Figure 7 shows those costs.
Figure 7
Yearly Corrosion Control Program Costs
Cost of chemical $6,000.00
Operational Costs 800.00
Equipment amortized over three years 550.00
Yearly Total Costs $7,350.00
Up until the end of the year 2000, the corrosion program reduced the average number of leaks by 15 per year. This equals a yearly savings of $23,700.00 per year. If you subtract the cost of the corrosion inhibitor program you get a yearly savings of $16,350.00.
Switch to Chloramination
During the year of 2001, Water Solutions Unlimited also recommended that w hey go to chloramination for their disinfection program, due to the 1.0 mg/L of ammonia as NH3-N in the water coming from the groundwater aquifer. In the past they were feeding 10-12 mg/L of chlorine in an attempt to carry a free chlorine residual in the distribution system. Going to chloramines cut their chlorine feed rate by 6 mg/L. They pay $0.30 per pound for gas chlorine. This reduced their chlorine costs by $5,479.00 per year. At the same time they also reduced the number of pinhole copper leaks from 10 per year to 5 per year. This saved an additional $7,900.00. Figure 8 shows the total, overall savings per year to be $29,729.00.
Figure 8
Final Yearly Savings
Yearly Savings as of 2000 $16,350.00
Chlorine Savings 5,479.00
Pinhole Leak Reduction savings (10 to 5) 7,900.00
Final Yearly Cost Savings $29,729.00
The MUNICIPALITY HAS SAVED OVER $200,000 SINCE 1994!
Conclusion
Don’t get them wrong. They don’t like intruding upon our homeowners to sample for lead and copper. But, it’s not very often that they are able to save their municipality this much money each year, and have valuable manpower available for other important projects. They probably would never have looked at using a chemical additive to solve their copper pinhole leak problem, if it hadn’t been for their failing lead and copper. Knowing what they know now, they would gladly recommend that utilities use corrosion inhibitors and corrosion coupon monitoring to solve copper corrosion problems. If natural ammonia exists in the aquifer, then use it and disinfect with chloramines.