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WASTEWATER FLOW DETERMINATION METHODS AVERAGE DAILY FLOW VOLUMES EHD SEWAGE STANDARDS DATA (gallons per day) 30 gals/Office Employee x Unknown No. of Employees and Customers 3,720 gpd Assume 1 Employee and Customer per 400 sq. ft: 49,500 sq.It x 1 person/400 sq. ft = 124 Employees/Customers Toilet Fixture Counts for a Store=25 toilets x 150 gals/fixture 3,750 gpd Total Parking Stalls Provided : 120 Stalls x 15 gals/Stall for 1,800 gpd Industrial Buildings. Accounts for Employees and Customers Comparable Data from Carmelo's Industrial Park Facility-Tracy,CA —1,000 gpd Average of Wastewater Flow Determination Methods, 3,090 gpd Excluding Comparable Data from Carmelo's Industrial Park Facility Data from EHD staff for the Carmelo Park Facility, which is on a flowmeter, reveals the average daily flow volume fluctuates around 600 gpd, with peak flows of approximately 800 gpd. The wastewater flow determination methods presented above suggest an extremely high average daily flow. Therefore, a figure of 1,000 gpd will be used for: 1.) Mounding Analysis as presented in Section III C., 2.)Nitrate Loading Calculations as presented in Section IV B., 3.) Filter bed sizing as presented in Section IV C., and 4.) Septic Tank Hydraulic Retention Time, also presented in Section IV C. This flow volume of 1,000 gpd incorporates a 20%to 40% safety factor over the average daily flow volumes from Carmelo's Industrial Park. Daily wastewater flows for the Madruga Business Park Facility will be quantified by a flowmeter to be installed on the effluent discharge pipe to the disposal field. It will be the determination of EHD on how effluent volume through the meter is to be quantified. This may be by taking a meter reading on a daily basis, or over a specified period of time and dividing by the number of days between readings to arrive at an average gpd. Therefore,the flowmeter must be readily accessible for easy reading. B. Nitrate Loading Mass Balance Since there will be only toilets and sinks at the Madruga Road Business Park, wastewater characteristics emanating from the facility are anticipated to be dissimilar to typical household domestic wastewater. The nitrogen in the wastewater may be at a higher concentration than what would normally be found in a typical domestic or household system. This can be attributed to the lack of a dilution effect that graywater would provide, such as showers, laundry, and dishwashing. The scientific literature cites nitrogen concentrations in residential septic effluent typically ranging from 17 mg N/L for basins, sinks, etc. to 140 mg N/L for toilet wastes. Therefore, considering a 70/30 percent usage for toilet water volume and sink water volume, respectively, a value of 103 mg N/L in the septic effluent will be used to calculate nitrate-nitrogen loading for this project. For comparison purposes, data from Wastewater Engineering, 3'Ed. would classify 103 mg N/L as an extremely high strength wastewater. A value of 62 mg N/L is typically used for residential calculations. Page -7- Ckesney Consulting