SITE INFORMATION AND CORRESPONDENCE_2005-CURRENT

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REGIONAL BOARD RESPONIEP(SWRCB/OCC FILE A-1634) • -3- STATE BOARD DRAFT WATER QUALITY ORDER PETITION FOR REVIEW OF WASTE DISCHARGE REQUIREMENTS ORDER NOS. R5-2004-0028 AND R5-2004-0029 CITYOFMANTECA WASTEWATER QUALITY CONTROL FACILITY changing the restriction to limiting surface water discharge during periods when there is an adequate downstream river velocity, however Manteca has not provided adequate justification that a downstream river velocity of 0.5 fps is sufficient to mitigate environmental effects of the discharge, especially relating to thermal impacts. This velocity requirement is proposed in the Draft Order, based on a dilution model that the Regional Board found was not properly calibrated, or shown to be accurate for Manteca's discharge (see footnote 30 of Draft Order). Even though the Draft Order supports these findings, the Draft Order proposes using a stream velocity recommended by the Discharger's model. Furthermore, since adoption of Order No. R5-2004-0028, Manteca has begun efforts to install a flow monitoring station at the Manthey Road bridge, approximately 2500 feet downstream of the discharge. Applying the 0.5 fps requirement without taking into account that the measurement will now also include the flows from the wastewater plant and the Brown Sand and Gravel discharge, or that the cross sectional area of the river may be different at that location, potentially provides a more lenient discharge requirement than proposed by the uncalibrated or verified model, and may not protect water quality. It is uncertain how the river velocities vary between the proposed flow monitoring station and the point of discharge, or whether 0.5 fps velocity at the point of discharge provides adequate flows to comply with the Thermal Plan. Since Manteca has not provided adequate justification to allow discharges when downstream flow is at or above 0.5 fps, Items 4 and 5 of the Draft Order should be deleted. These changes could be made to Order No. R5-2004-0028 after Manteca has provided adequate justification. However, if the State Water Board decides to keep the flow revisions in the Order, then the Regional Board recommends some minor changes to provide clarification. Item 4 of the Draft Order, which modifies Effluent Limitations B.8 of Order No. R5-2004-0028, should be modified to read: "Effective I February 2009, and in compliance with provisions I and 4, the 30-day average dry weather discharge flow shall not exceed 9.87 million gallons per day less the amount of treated wastewater from the wastewater quali y control facility that is disposed of on land at agronomic rates. All discharges shall be during periods when there is a net downstream San Joaquin River flow veloci of 0.5 foot per second or more immediately upstream oftW the point of discharge." I interpret this Draft Order language to allow the Regional Board to require Manteca to evaluate whether the flow velocity, as measured at the proposed flow meter location, will need to be adjusted to comply with a limitation established immediately upstream of the point of discharge. Item 5 should also be modified to revise Provisions H.4.b. to read: "The discharger shall demonstrate the ability to store effluent and discharge to surface waters only during periods when there is a net downstream San Joaquin River flow velocity of 0.5 fps or more immediate.y upstream ofat the point of discharge."