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HomeMy WebLinkAbout1979-06-05; City Council; 5577-2; Revision of the EDU measureCITY OF CARLSBAD Initial: AGENDA BILL NO . ^T^97 - ^L^^>^e^e-Jt "**"<£Dept. Head DATE: June 5, 1979 ' ' . c> Atty ^ DEPARTMENT: Engineering • C. Mgr. —Y\ SUBJECT: REVISION OF THE MEASURE OF AN EQUIVALENT DWELLING UNIT STATEMENT OF THE MATTER Based on a memorandum from the Public Works Administrator, which was discussed at a Council workshop, the equivalent dwelling unit (EDU) meausre should be revised down- ward. Presently, the City utilizes a flow of 270 gallons per day per EDU. The Pub- lic Works Administrator's report recommends a change to 253 gallons per day per EDU. EXHIBITS 1. Memorandum from the Public Works Administrator dated October 12, 1978. " 2. Resolution No. ^jq/ Determining the Number of Gallons of Sewage Equal to One Equivalent Dwelling Unit and Adopting it as a Regulation Pursuant to Section 13.08.081(f) of the Carlsbad Municipal Code. RECOMMENDATION If Council concurs, adopt Resolution No. Council Action: 6-5-79 Council adopted Resolution No. 5791, redetermining the number of gallons of sewage equal to one EDU and adopting it as a regulation pursuant to Section 13.08.081 (f) of the Municipal Code, and rescinding Resolution No. 5478. '•*-.. C MEMORANDUM TO: City Manager FROM: Public Works Administrator .DATE: October 12, 1978 SUBJECT: CARLSBAD'S CAPACITY I t^£NC IN A/WATER POLLUTION CONTROL FACILITY SUPPLEMENTAL REPORT #5 Council requested staff to report, at a minimum of six-month intervals, on items relating to use of existing capacity, the possibility of leasing addi- tional capacity and policy recommendations regarding our capacity at the Encina Water Pollution Control Facility. While the last'labeled supple- mental report (number 4) was dated October, 1977, the last information up- date and policy recommendation was a June 23, 1978 memorandum wherein the City Council acted to establish the equivalent dwelling unit (EDU) flow rate at 270 gallons per day per unit until-such time as flow rate records showed they were otherwise. As Council will recall, the 270 figure was arrived at after consideration of flow rate per capita, household occu- pency, the figure of 280 used in planning projections, etc. During the four months since City Council acted on the June 23, 1978 policy memorandum, there has been considerable interest in actual, rather than es- timated, flow rates at the Encina facility. We now have 12 months of flow meter readings, from a meter which JAC operational personnel say is accurate, upon which to base conclusions. Since we first started using equivalent dwelling units as our control, we have continually reanalyzed our techniques to improve their accuracy and reliability. In addition, we now have the benefit of 12 months of usable flow meter readings. Using this expanded information base, staff will make recommendations to City Council. It should, however, be kept in mind that our figures should be continually reanalyzed against existing flow rates, and, as further corrections are deemed necessary, those corrections should be made. The following table contains information used in establishing our flow rates: Column I shows the flows attributable by the Encina meter to Carls- bad for the period from October, 1977 through and including September, 1978. Column 2 shows the running total of the number of permits issued; that is, at any one point in time these are the total number of outstanding permits Issued in the City's service area. Column 3 shows the gross EDU flow rate. In my opinion, the information used to obtain the gross EDU flow rate gives a result which is less than accurate. A major reason for the inaccuracy is because the running total of permits is based on the number issued, not the number connected or flowing; therefore, there may be some hookups that are not contributing flow to our sewer system at any one point in time. To ar- rive at the true value of flow rate per EDU, we must consider only those /•*»• -2- permits that are connected and flowing. There are always a number of issued permits for facilities that are under construction, unoccupied, awaiting sale or experiencing a seasonal fluctuation. Factors affecting the number of non-contributing facilities are weather, season, economics and the state of the construction market. Our review of these factors indicate that dur- ing the period of analyses the number of permitted units actually hooked up and flowing ranged from 84£ to 88.5$ of total permits issued. The actual percentage figure used is shown in Column 4. This percentage increased as the period progressed because, due'to the moratorium, fewer permits v/ere issued and the earlier issued permits v/ere constructed and on-line. Multi- ply! ng the percentage factor by the total number of permits issued results, in my opinion, in the best avai I able estimate of actual on-line and flowing EDUs (Column 5). When this number is divided into the recorded flow for the corresponding month, the result is the adjusted average flow per EDU for that month (Column 6). This adjusted figure gives us a better picture of how actual^ flows may vary during the year due to use patterns. It also eliminates variations caused by the administrative act of issuing a permit. COLUMN MO/YR OCT 77 . NOV 77 DEC 77 JAN 78 FEB 78 MAR 78 APR 78 MAY 78 JUN 78 JUL 78 . AUG 78 SEP 78 FLOW (MGD) 2.411 2.136 2.864 3.642* 3.497* 3.249 3.574* 2.659 2.707 2.282 2.590 2.880 CONNEC- TIONS 12,097 12,110 12,138 12,145 12,162 12, 188 12,195 12,21 1 12,429 12,521 12,551 12,724 ESTIM. GROSS EDU 199.3 176.4 236.0 299,9 287.5 266.6 293. 1 217.8 217.8 182.3 206.4 226.3 CONTRIB. CONNECT. ef1° 84.0 84.0 84.5 84.5 84.5 85.5 85.5 85.5 86.5 87.0 88.5 . 89.0 ADJUSTED CONNEC- TIONS 10,161 10,172 -10,257 '•10,263 10,277 10,421 10,427 10,440 ~, 10,751 10,893 11,108 1 1 , 324 ADJUSTED EDU FLOW RATE 237.3 . 210.0 279.2 354.9 .340.3 311.8 342.8 254.7 251.8 209.5 233.2 254.3 COMMENT DRY DRY WET WET WET WET WET DRY DRY DRY DRY DRY * EXCEEDED LEGAL PLANT CAPACITY -3- Since our capacity is based on average flows, we must consider the impact of the rainy seasons. If we use all of the information available, we get .an average EDU flow rate of 273.3 (versus our 270 as established by reso- lution). This figure includes the months of December, January, February, March and April when we had rains that exceeded two and one-half times .normal rainfall. This resulted in an abnormally high amount of inflow in- to our systems. It is my recommendation that we analyze only the dry months (October, November, May, •June, July, August and September) and add a wet weather factor to compensate for a more normal rainy season. My calcula- tions (see Appendix "A") indicate that 230,000 gallons per day, average daily flow, are attributable to infiltration and inflow. This amount should be subtracted from our legally available capacity before determin- ing our average dry weather flow rate for each EDU. AVAILABLE CAPACITY When City Council acted to lease capacity from the Encinitas Sanitary Dis- trict, one of their concerns was the ab-ility to return the capacity within five years. While no action was taken at that time, staff suggested, and Council considered, reserving the 75,000 gal Ion capacity. The Encinitas contract calls for return of the capacity on or before September 30, 1982. No provision is made for extension and the Encinitas Sanitary District wouldn't negotiate to provide for it. The Phase III project schedule in- dicates completion by mid-1982. This assumes no delays in project review by the Federal Government, no strikes, no delays'in equipment delivery, etc. We cannot add capacity to the project or, for that matter, even receive a grant fund offer to construct the project until the San Diego Region com- plies with certain "Clean Air Program" requirements. Other additional sources of capacity we considered were a rerating of existing treatment 'plant facilities or the completion of Burroughs' "zero-flow" project. The rerating is highly unlikely at this time especially since we are under a cease-and-desist order from the Regional Water Quality Control Board! The Burroughs project has slipped considerably and we have no confidence when or if it will occur. I believe that it would be prudent to keep the 75,000 gallons of capacity uncommitted at this time. I wiI I use only our own capacity (3.43 MGD) in all subsequent calculations. From our capacity of 3.43 MGD we must subtract the 0.23 MGD assigned to handle wet weather flows. The balance, 3,200,000 gallons, is available to handle the flow from all our connections. The existing connections (12,724) can be expected to flow at an average dry weather flow of 3,000,319 gallons per day. This must be subtracted from the 3.2 MGD. We also have a balance of 48,750± (dry weather) gallons per day additional capacity committed to the balance of the Plaza Camino Real Shopping Center expansion. This also must be subtracted from our balance. 3,200,000 - (3,000,319 + 48,750) = 150,930. Dividing 150,930 by 235.8 gives 640 EDUs of capacity available. To deter- mine total EDUs we must add existing permits (12,724) to those that may be made available (640) and add the shopping center's capacity estimated to be 207 (48,750 i- 235.8). This gives an EDU total of 13,751 (12,724 + 640 + 207) .4. EDU.VALUE DETERMINATION It must be kept in mind that the 230,000 gallons per day allotted for wet - weather flow must be shared by all connections in determining a usab'le EDU figure. If it is equally allotted to each of the 13,751 EDUs determined to be available it equals 16.7+ gallons per EDU (230,000 gallons * 13,751 EDUs). This figure must be added to the 235.8 dry weather flow figure to obtain the average daily flow per EDU. 235.8 + 16.7+ = 252.5+ gallons per'day per EDU (use 253) Acceptance by the City Council of the figures used in this report will ne- cessitate changes in two areas: (I) A new resolution would have to be adopted modifying the flow rate per EDU; and (2) the ordinances which es- tablish flow rates on a square footage basis, or otherwise, in our Municipal Code, would have to be modified. • RECOMMENDATION It is recommended that City Council direct staff to prepare a resolution establishing a new EDU flow rate at 253 gallons per day per EDU-and to pre- pare such other ordinance changes as may be required to administer available capacity. It Is further recommended that City Council accept that 640 EDUs (not to exceed 13,751 EDUs total issued) are available and that on the advice of Special Counsel, concurred in by the City Attorney, this capacity be re- tained by the City until the resolution of current litigation regarding claims on capacity. Upon resolution of the litigation, the City Council should consider an allocation system to handle equitable distribution of available capacity. Ronald A. Beckman, P.E. Public Works Administrator RAB:VEB Attachment: Appendix "A" APPENDIX "A" Brown & Caldwell, in their 1976 report on Carlsbad's sewer system, indi- cated that our flow from Infiltration was approximately 100 gallons per acre per day for the existing sewered area. Our sewered area is approxi- mately 5,000 acres. This equates to approximately 500,000 gallons per day for each of the four months of our normal wet weather season. This figure must be augmented by an undetermined amount to compensate for peak flow into the system caused by inflow. This is the situation when our streets are flooded by momentary peaks in wet weather causing water to infiltrate through manhole covers and the like into our sewer system. Another technical method of determining infiltration and inflow considers the length and size of underground pipe. This method uses a factor of 500 gallons per day per inch-mile of sewer (two miles of eight-inch diameter sewer equals 16 inch-miles; one mile of 16-inch diameter sewer equals 16 inch-miles). In addition, a factor should be added for each manhole. Normal manhole factors in textbooks use from 500 to 5,000 gallons per day per man- hole. This allows for deteriorated condition, the use of brick manholes and for a high groundwater table. Since our system is relatively new, uses pre- cast concrete to a large extent and, for the most part, is well above the groundwater table, I propose to use a factor of 100 gallons per day per man- hole.' Our sewer system has approximately 750 inch-miles of sewer line (70± miles of eight-inch through 39-inch line) and I700± manholes. (750 x 500) + (1700 x 100) = 375,000 -f 170,000 = 545,000"galions per day Since we must account for deterioration of the system, I propose to use a safety factor of 25%, 1.25 x 545,000 = 681,250 .This is the additional flow per day that can be expected during the rainy season and for a short period thereafter. To equate this additional wet weather flow, which lasts on the average of four months per year, to an average daily flow figure for the entire year, we take one-third (four months wet weather divided by 12 months per year); therefore, 681,250 - 3 = 227,083 (use 230,000) This amount of capacity is used for wet weather flow arid, therefore, must be subtracted from our total available capacity. 3.43 MGD - .23 MGD = 3.2 MGD available capacity CQ CO 1 2 3 4 5 6 7 8 9 10 11 12 13_: o: S* < °> o-"S| 14 °° i| §£>2 ift 5^5i 15 fefcgQ- 16S <m cc5 17 18 19 20 21 22 23 24 25 26 27 28 c o RESOLUTION NO. 5791 A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF CARLSBAD, CALIFORNIA REDETERMINING THE NUMBER OF GALLONS OF SEWAGE EQUAL TO ONE EQUIVALENT DWELLING UNIT AND ADOPTING IT AS A REGULATION PURSUANT TO SECTION 13.08.081(f) OF THE CARLSBAD MUNICIPAL CODE AND RESCINDING RESOLUTION NO. 5478. WHEREAS, Section 13.08.081 of the Carlsbad Municipal Code provides for the determination of the amount of sewage generated from particular buildings or uses based on a unit of measure of one equivalent dwelling unit which is defined as equal to an approximation of the amount of sewage generated by an average single family residence; and WHEREAS, Subsection 13.08.081(f) of said section authorizes the City Council to adopt regulations for applying it, including a determination of the number of gallons of sewage which shall equal one equivalent dwelling unit; and WHEREAS, the City Council by the adoption of Resolution No. 5478 made such determination and now/ upon recommendation of the Public Works Administrator, in his memorandum of October 12, 1978/finds it necessary to revise that determination; NOW, THEREFORE, BE IT RESOLVED by the City Council of the City of Carlsbad, California as follows: 1. That the above recitations are true and correct. 2. That the City Council determines that 253 gallons per day of sewage shall be equal to one equivalent dwelling unit. 3. That this determination is adopted as a regulation pursuant to Subsection 13.08.081(f) of the Carlsbad Municipal Code. mtn = < en 0^| SSSgz O tn o 1 2 3 4 5 6 7 8 9 10 11 12 13 a f- 5 E T Km D 13 £ £ 8 S 16 17 18 19 20 21 22 23 24 25 26 27 28 4. That Resolution No. 5478 is hereby rescinded. PASSED, APPROVED AND ADOPTED at a regular meeting of the City Council of the City of Carlsbad, California, held on the 5th day of June ,1979, by the following vote, to wit: AYES: Councilman Packard, Skotnicki, Anear, Lewis and Councilwoman Casler NOES: NONE ABSENT: NONE RONALD c. PACKARD, Mayor ATTEST: . S\. V\(LuJLjL ALETHA L. RAUTENKRANZ, City Cleijk (SEAL) ; 2.