Three Valley schools where radon was found in March have been cleared of the naturally-occurring, radioactive gas, according to school district officials.
Tests performed in March by Colorado Vintage Companies found levels of radon exceeding the EPA's guideline of 4.0 picocuries per liter in one room at Gardnerville Elementary School, one room at Pau-Wa-Lu Middle School and in two rooms at Carson Valley Middle School.
Levels marginally exceeded the guideline, ranging from 4.1 picocuries per liter at Carson Valley Middle School to 5 picocuries per liter at Pau-Wa-Lu.
However, after adjusting heating and air systems in the rooms, new tests performed in April showed radon levels below 2.0 picocuries per liter.
In many cases, the rooms just needed more fresh outdoor air, which, according to Colorado Vintage Companies, reduces radon entry as well as improves indoor air quality.
Continuous radon monitors were used in the latter testing, which differentiated between day and nighttime levels.
"The second set of CRM test results show that there is no need for additional remediation," district Chief Financial Officer Holly Luna wrote in an update to school board members.
The same could not be said for Whittell High School at Lake Tahoe, where original tests showed seven rooms with elevated radon levels, ranging from 4.2 picocuries per liter to 13 picocuries per liter. The new tests showed levels ranging from .6 picocuries per liter to 9.6 picocuries per liter. Four of the original locations still yielded elevated levels.
"CVC did not make many adjustments to the existing HVAC system as this system is anticipated to be completely replaced over the summer break with bond funding," Luna said. "This changeover would negate any HVAC adjustments completed prior to the system replacement. CVC's recommendation was to install the new HVAC/boiler system and then re-test radon levels upon completion."
There is one area of Whittell, room 18 and its office, that's not part of the main building and will require separate mitigation.
"CVC recommends minor HVAC adjustments and active soil depressurization mitigation, similar to systems placed at Zephyr Cove Elementary School," Luna said. "DCSD maintenance staff will complete adjustments and active soil depressurization systems during the same time that the main building's system is being replaced so that the entire site may be re-tested at one time."
Radon has been a problem at Lake Tahoe. Produced by decaying uranium in granitic soils, the colorless, odorless gas usually dissipates into the air, but can enter buildings through crawl spaces. Once trapped, the gas' radioactive decay can pose serious health risks. According to the Nevada Radon Education Program, long-term exposure to the gas is the leading cause of lung cancer among nonsmokers.
Last year, elevated radon levels at Zephyr Cove Elementary School prompted the district, working with the Environmental Protection Agency, to install a ventilation system (active soil depressurization) that prevented the gas from entering the buildings. The mitigation worked, but school officials decided to create a district-wide radon policy that included testing all schools for the gas and following up with necessary mitigation.
Colorado Vintage Companies also recommended that the district train a maintenance employee to conduct radon measurements. They said it would cost about $5,000 in equipment but would allow the district to verify radon levels after any significant change to an HVAC system.
Luna said the district will continue to update the community.
"As before, a copy of the latest CVC report with recommendations will be available on the district Web site (dcsd.k12.nv.us)," she said.
