Laserfiche WebLink
Blaney-Criddle Model explanation and use <br />July 28, 1998 <br />Page 6 <br />ESTIMATION OF FACILITY STORAGE REQUIREMENT: <br />A. FIVE DAY EFFLUENT STORAGE: <br />The Arizona State reuse regulations (A.A.C. R18-9-702.F) require the <br />faciliry to have a minimum of five days starage to prevent the discharge of <br />effluent under certain conditions, (such as where the ground is already wet <br />from rain or when the effluent quality will not meet permit requirements), <br />unless other means of disposal are available. <br />If the facility is located in an area where the ground freezes, effluent <br />irrigation is not allowed (during these periods) and the effluent must be <br />stored or discharged under an NPDES permit. <br />If the facility has an NPDES permit to discharge the water, the reuse <br />program does not mandate a five day storage requirement. However, if the <br />facility discharges under an NPDES permit, the facility still has to meet <br />those permit discharge limits and requirements. It is suggested that all <br />facilities review and address their needs for effluent starage. <br />B. STORAGE FOR PRECIPITATION: <br />Normal precipitation is accounted for in the basic water balance <br />calculation. However, to accommodate a precipitation event which would <br />necessitate a full 5 days of storage, five days of rain is added to the storage <br />requirement as a safety factor. This calculation is done by taking the <br />maximum precipitation month (the wettest month) multiplying it by 5/30 <br />and converting this to gallons per acre. Then the quantity of precipitation <br />in gallons over the area (acreage) of the ponds is estimated. An alternate <br />mare conservative precipitation calculation (not contained in this model) <br />would be to estimate the quantity of water from a 10 year 24 hour rain <br />event over the pond areas. Additional consideration (not in this model) <br />needs to be taken for surface runoff that may enter the effluent storage <br />system. The Blaney-Criddle model presented here assumes that the <br />impoundments are protected from this additional water source. <br />C. STORAGE OF UNUSED EFFLUENT (long term water balance) <br />The model presented here estimates a cumulative water balance over a five <br />year period. It estimates the maximum unused monthly quantity of <br />effluent.