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HomeMy WebLinkAbout1978-07-04; City Council; 5434-2; Equivalent Dwelling UnitI h - CITY OF CARLSBAD AGENDA BILL NO. 4-4'3 .L/ * DATE : JULY 4, 1978 DEPARTMENT: Engi neeri ng Initial: Dept . Hd.zg C. Atty. VFh C. Mgr, Subject: EQUIVALENT DWELLING UNIT - QUANTITY DETERMINATION ~~ - -~ ~ ___ Statement of the Matter Pursuant to Cit Council's request on June 20, 1978, staff has prepared a draft resolut on setting the volume of sewage flow equal to one equivalent dwel ing unit at 270 gallons per day. Exhibits 1. Memorandum to City Manager dated June 23, '1978. 2. Resolution No. S47/p. ' Recommendations That the Council adopt Resolution No. \7+'7 f setting the volume of sewage flow equal to one equivalent dwelling unit at 270 gallons per day. Council action: 7-5-78 Resolution No. 5478 was adopted, determining the number of gallons of sewage equal to one equivalent dwelling unit and 'adopting it as a regulation pursuant to Section 13.08.180(f) of the Carlsbad Municipal Code. MEMORANDUM TO : City Manager FROM : Pub1 ic Works Administrator DATE : June 23, 1978 SUBJECT: EQUIVALENT DWELLING UNIT - QUANTITY DETERMINATION In Carlsbad the number of connections to our sewer system were, his- torical ly, never of concern. AI I connections to the system were averaged City-wide and were either a function of the number of living units (single and multiple-residential) or, in non-residential land uses, the number of toilets on the system. No consideration was given to industrial waste (non-sanitary flows). Planning projections were done on the basis of the rate of consumption of plant capacity and, based on the projections of these capacity needs, plant expansion programs were ptanned. The number of actual connections and, therefore, the number of gallons per connec- tion, were never of particular concern. When preparing the staff report of February 25, 1977, our concern was primarily focused on the slowness of the Phase Ill expansion project, plant metering inaccuracies and an accel- erated building rate. Our remaining capacity in Encina was described as being six to eight years' worth at the old building rate, but only two to three years if the new building rate continued. The actual growth rate showed even this was highly optimistic in that our remaining capacity was used in a matter of months. Because of delays in the Phase Ill project and the rapid growth rate being experienced, our concern focused on a way to anticipate the growth rate so as to know when to recommend corrective action allowing us to stay within our legal capacity. Several factors came into play in determining how much capacity we, in fact, had. Our legal capacity in the Encina Water Pol lution Control Faci I ity, upon completion of Phase I IA, was 3.43 MGD. While on other occasions we had exceeded our previous legal capaci- ties, that occurred only under circumstances where expansion projects were underway and almost completed. With the delays in the Phase Ill project and the uncertainties as to State and Federal approvals required for the project, it was necessary to develop a previously unnecessary set of controls. In my staff reports, I recommended our legal capacity should be 3.43 MGD minus the amount for which we were obligated by contract to the expansion of the Plaza Camino Real Shopping Center. This amount was estimated, in the EIR for the five-store complex, to be 0.112 MGD in ad- dition to existing flows. The balance of 3.318 MGD was available to ser- vice existing connections and any additional connections to the system. Because of the inaccuracy of the main plant meter, we never knew Carlsbad's actual flow rate. The system used at that time (and now) was to determine the average daily flow from the main plant meter and subtract from it the sum of flows from the other five JAC members' meters. Obvi- ously, any inaccuracies accrued to Carlsbad. Because of known inaccuracies City Manager -2- June 23, 1978 in the main plant meter, the plant's flow and, hence, Carlsbad's flow was "estimated" from Apri I , 1975 to December, 1976. Because of this history of inaccuracies, it was impossible to determine when Carlsbad was approach- ing its legal capacity limits. It was proposed to control our system on the basis of the number of connections (EDUS). We had to assign a value in GPD to the EDU so that when the total EDUs on line were multiplied by that value, the resultant would not exceed our legal available capacity. Several factors were considered when establishing an EDU value in- cluding the emperical ly determined standards that average daily flow per residential unit was 280 GPD; average sewage flow per capita was 100 GPD; and average occupancy per household in Carlsbad approximated 2.6 per dwell- ing unit. These are standards used in numerous engineering texts, regional planning documents or project reports. the average flow for the six months prior to the time of the report (Oc- tober, 1976 through March, 1977) was 270.8 GPD per connection. Also considered was the fact that By using 270 GPD per EDU we could, in my opinion, handle all permits presently in process (estimated to be 11,590 as of the first part of April, 1977); allow for a slow-down to the recommended cutoff point of 11,900 EDUs and stilt not exceed our legal limit of 3.318 MGD (3.43 MGD - 0.112 MGD). At the present time we have 12,195 connections on line. An important determination in my rationale was that if, after all con- nections permitted as a result of my recommended EDU rate were on I ine, we were not showing a history of exceeding our legal limit, the Council could allow more connections. On the other hand, if, because of estimating an EDU rate that was too low, we exceeded our legal limit, we could not recall ex- isting connections. It was necessary to use an EDU rate that was conserva- tive, supportable and close enough to be acceptable and yet one which would allow us to control the number of connections while - not exceeding our legal capacity in the treatment plant. My recommendation then and now is that we use an equivalency factor of 270 GPD per EDU and that this figure continue to be used until we show, by actual flow records, that it is less - and until we revise Chapter 13 of the Municipal Code incorporating a more real istic way of predicting and control- ling flow from all existing future connections. ToUQd.hXgR--- Ronald A. Beckman, P.E. Pub I i c Works Admi n i strator RAB: veb I. I 1 I I I 1: 2c 21 22 ' 23 24 25 26 27 28 RESOLUTION No. 5478 A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF CARLSBAD, CALIFORNIA, 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. WHEREAS, Section 13.08.081 of the Carlsbad Municial Code )rovides for the determination of the amount of sewage generated irom particular buildings or uses based on a unit of measure of me equivalent dwelling unit which is defined as equal to an ipproximation of the amount of sewage generated by an average ;ingle family residence; and WHEREAS, .Subsection 13.08.081(f) of said' section authorizes :he City Council to adopt regulations for applying it, including i determination of the number of gaIlons of sewage which shall !qual one equivalent dwelling unit; and WHEkEAS, the City Council desires to make that determination, [pori recommendation of the Public Works Administrator, in his iemorandum of June 23, 1978; NOW, THEREFORE, BE IT RESOLVED by the City Council of the lity of Carlsbad as follows: 1. That the above recitations are true and correct. 2. That the City Council determines that 270 gallons per day if sewage shall be equal to one equivalent dwelling unit, 3. That this determination is adopted as a regulation Nursuant to Subsection 13.08.081(f) of the Carlsbad Municipal Code, an adjourned PASSED, APPROVED AND ADOPTED at / regular meeting of the ity Council of the City of Carlsbad, California, held on the ,// .. 1 2 z 4 5 c1 c 7 € S 1c 11 19 .20 21 22 * 23 24 25 26 27 28 v I. I. - .. 5th day of July , 1978 by the following cote, to wit: AYES: ' Councilmen Packard, Skotnicki , Anear, Lewis and Counci 1 woman Cas1 er NOES : None ABSENT: None ATTEST : p&aL. CT) RONALD C. PACKARD, Mayor Margaret E. ..dams MARGARET E. ADAMS, City Clerk 2.