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Attachment B 2 <br /> Comments on Tidal Dilution of the Stockton Regional Wastewater <br /> Control Facility Discharge Into the San Joaquin River <br /> April 2001 <br /> c. Using the higher lateral dispersion coefficient, the Report calculates the maximum <br /> exchange flow between east and west boxes as 0.33% of the tidal flow. The <br /> Report then uses 0.5% of the tidal flow for modeling purposes. <br /> d. The Report does not discuss changing channel topography. Bottom contours and <br /> channel depth influence mixing. <br /> 3. Field study and analysis used to substantiate the assumed lateral dispersion is flawed: <br /> a. To accurately estimate the lateral dispersion at critical flow, the analysis should <br /> be performed at flows approaching critical flow. The study was performed at an <br /> estimated flow rate of 1250 cubic feet per second (cfs), which could be as much <br /> or more than 10 times greater than the critical flow. <br /> b. The 17 January 2001 sampling began one hour after high tide instead of <br /> immediately afterward. This delay allowed the current to change directions. The <br /> samples did not accurately correlate with the distance upstream. Samples taken at <br /> the 500 foot transect could have been 1,500 feet upstream at high tide. The study <br /> tried to account for this by taking samples downstream. The data should have <br /> been discarded and samples taken another day. <br /> c. The colorimetric testing has considerable variation, as demonstrated by the <br /> replicate samples taken from the effluent boil (7.28 mg/L and 9.40 mg/L). <br /> Laboratory analysis would be much more accurate. <br /> d. The study only analyzed upstream samples just after high slack tide. The study <br /> would have been more representative if additional samples had been taken at <br /> similar transects downstream just after low tide. <br /> e. The influence Bums Cutoff has on mixing was not analyzed not considered. The <br /> Report assumes mixing will be the same upstream and downstream. This is <br /> uncertain due to the differing channel geometries. <br /> f. The Board was not notified prior to performing the study and did not have the <br /> opportunity to review the study plan nor oversee the taking of samples. <br /> g. The Report does not discuss whether a quality assurance plan was implemented <br /> while sampling. There is only the mention of laboratory QA/QC procedures. <br /> h. The Report does not discuss if field standard operating procedures were <br /> developed and implemented while performing water quality sampling. <br /> 4. The Report uses a minimum monthly average flow of 150 cfs. This flow was <br /> determined from the Flow Report (see Attachment A). The Board has found <br /> deficiencies in the Flow Report that make the findings questionable. Based on the <br /> Board's analysis of actual flows during above average wet years, the minimum 10- <br /> year monthly average flow could be much less at design conditions. <br />