Laserfiche WebLink
STATE OF CALIFORNIA— EALTH AND HUMAN SERVICES AGE19-10 � <br /> GRAY DAMS Gwenwr — <br /> DEPARTMENT OF HEALTH SERVICES <br /> 7141744 P STREET <br /> P.O. BOX 942732 <br /> SACRAMENTO,CA 942347320 <br /> (916) 322-2308 <br /> November 23, 1999 <br /> Gary M. Carlton, Executive Officer o _. <br /> California Regional Water Quality Control Board ^r <br /> Central Valley Region n�' <br /> 3443 Routier Road, Suite A "– <br /> Sacramento, CA 95827-3003 — <br /> Dear Mr. Carlton: <br /> COMMENTS ON RISK ASSESSMENT FOR CITY OF STOCKTON WASTEWATER <br /> PERMIT <br /> Thank you for the opportunity to comment on the "Comprehensive Health Risk <br /> Assessment, Final Report, for the City of Stockton Wastewater NPDES Permit" by EOA, <br /> Inc., dated May 1996. The City of Stockton and its consultants have used a population- <br /> based risk assessment to support a contention that there is no additional public health <br /> benefit for the addition of year-round filtration for virus removal to the current plant <br /> operations. <br /> General Comments <br /> We find the approach used by the City was applicable, but did not provide adequate <br /> information on situations that might result in illness, the frequency with which these <br /> situations might occur, and what can be done to prevent them. Specifically, the <br /> following items require further examination: <br /> 1. How sensitive is the City's analysis to the assumed size of the initially susceptible <br /> population (ISP)? Does the assumption of a very large ISP diminish the difference <br /> between Scenario 1 (no recreation) and Scenario 2 (no discharge)? The "initial <br /> susceptible" population used in the study (2.8 million) is 4 orders of magnitude larger <br /> than the estimated exposed population (less than 300). This raises concerns <br /> whether potentially significant impacts on the exposed recreating public might be <br /> masked by inclusion in a large non-exposed public. <br /> 2. What is the actual range of virus reduction provided by the treatment plant? The <br /> study concluded virus reduction rates of less than 3 logs pose a significantly <br /> increased risk of infection among recreational users, but did not adequately assess <br /> how likely the treatment plant is to produce effluent with less than 3 logs virus <br /> reduction. The report states that sampling shows that removal rates range from 3.4 to <br /> 6.4 logs. Further reading, however, reveals that the sampling conducted was only <br /> sufficient to determine the two removal rates cited. Two data points do not <br />