Results of Radon Testing
(Memo to Mayor & Council)
September 27, 1999
Subject: Results of Radon Testing in Tucson Water System
(City-Wide and Outside the City)
Over 500 water samples from throughout the Tucson Water system were tested for radon levels during August and September 1999. If the expected USEPA standard of 300 pCi/L at the point of entry to the water distribution system is applied to the radon test results, 43% of Tucson's groundwater supply exceeds the proposed standard. Under the more restrictive requirements of the 1995 Water Consumer Protection Act, which apply to groundwater quality at the source (i.e., at the wellhead), 51% of Tucson's groundwater supply would exceed the proposed standard.
It is recommended that once the proposed USEPA radon regulation is published (it has been undergoing extended review by the Office of Management and Budget), staff from Tucson Water and the City Attorney's Office pursue options that the Mayor and Council wish considered further to comply with the proposed regulations and local ordinances.
Background
As directed by the Governing Body at the Special Study Session on August 18, 1999, the Tucson Water Department has completed new tests for radon throughout the water system. Previously, in the absence of a specific regulation, the Utility had not regularly tested for radon. The new series of tests evaluated radon levels in over 500 sample locations throughout the water delivery system. This testing process was carefully monitored to ensure that the laboratories employed for this effort followed proper sampling and analytical standards. Some sample points were retested to ensure the accuracy of the radon test results.
Test Locations
Three different types of locations within the water system were sampled for radon:
- Wellhead – all 189 operating wells throughout the central water system and isolated systems were sampled (with the exception that the radon level for the 9 TARP wells, whose operation is covered by the TARP Consent Decree, was as measured at the TARP treatment plant).
- Point of Entry (POE) – locations where water "enters" the distribution system downstream from pressure tanks or boosters. A POE typically represents the production of one well, but may represent a number of wells whose output is blended together. No customers receive water prior to a POE. A total 153 POEs are represented in the test results, the majority of which are equivalent to individual well test results.
- Distribution System and Reservoirs – Locations within the distribution system including 30 reservoirs and 257 "dedicated sample points", which are special spigots installed on customer service lines between the distribution main and the meter. These sample points are protected from contamination to ensure accurate water quality tests.
Test Results
Schedules of radon test results for each sample point are provided in the attachments:
- Attachment A – Schedule of 1999 Wellhead Radon Levels
- Attachment B – Schedule of 1999 Point of Entry Radon Levels
- Attachment C – Schedule of 1999 Distribution System and Reservoir Radon Levels
Accompanying each schedule is a large format map showing the location of each sample point on the schedule. The mapped sample points are also color-coded by level of radon found, in picocuries per liter (less than 200, 201-300, 301-600, 601-1200, and 1201 or more pCi/L).
The radon levels found in the Tucson Water system demonstrate, as expected, that radon levels are highest when measured at the wellhead, and then decline as the water enters the distribution system. The decline is due to a combination of the radon gas decaying over time and escaping the water as it is agitated. The test results are briefly described below:
- Wellhead – 189 active wells; median radon level 282 pCi/L; range 12 – 1,500 pCi/L; 48% of the wells exceed projected USEPA standard of 300 pCi/L (which is meant to apply to POEs only); these 48% of the wells produce 51% of Tucson's groundwater supply. (However, under the WCPA, the water quality standard must be met at the wellhead rather than the POE.)
- Point of Entry – 153 POEs; median radon level 250 pCi/L; range 12 – 1,430 pCi/L; 38% of the POEs exceed projected USEPA standard of 300 pCi/L (which applies to POEs only); these 38% of the POEs produce 43% of Tucson's groundwater supply.
- Distribution System – 287 locations including reservoirs and "dedicated sample points"; median radon level 221 pCi/L; range 13 – 1,260 pCi/L; 37% of the sample points exceed projected USEPA standard of 300 pCi/L (which is meant to apply to POEs only).
Status of USEPA Regulation
USEPA's proposed regulation regarding the level of radon in drinking water was to have been issued in August 1999. However, the proposed rule has not yet been published as it is still undergoing review by the federal Office of Management and Budget and the USEPA.
Discussion
The operational implications of this radon test data for the Tucson Water system may be more readily determined once the proposed radon regulation is published. Clearly, the impact appears significant for the Tucson Water system when considering the total volume of our groundwater supply (43%) that exceeds the projected standard – measured at the POEs – of 300 pCi/L. Staff will continue to analyze the test data in anticipation of the issuance of the rule, and will make a brief presentation today about the test results and associated issues.
Recommendations
- It is recommended that staff be directed to continue to prepare for the issuance of the USEPA radon regulation, and to analyze the rule once it is published. Of particular interest are any changes in the regulation that might have resulted from review by the Office of Management and Budget, such as a change to the proposed "alternate" MCL related to the Multimedia Mitigation program option, and any clarification as to how such programs are to function.
- After this analysis is completed, staff will return with a discussion of options and costs for complying with the regulation. Options that the Mayor and Council may wish staff to explore include the Multimedia Mitigation program option, expanded use of low-radon groundwater, and blending and treatment options.
- Staff suggests that any option or combination of approaches for dealing with radon in groundwater should (1) first and foremost, protect public health, (2) provide sufficient water supplies for the Tucson community, and (3) be affordable to water customers.
Respectfully submitted,
Luis G. Gutierrez
City Manager
