Item 8 - Action MWMC SDC - Laserfiche WebLink

Home Browse Search

JUNE 10, 2004 E-MAIL, ESSENTIAL ELEMENTS OF THE METHODOLOGY This 175 value can be found in the SFD/Duplex row (8th row) in Appendix D - User Capacity Requirements of the SDC Methodology..." We need to revise this particular response because some of the information is inaccurate. In an effort to provide Mr. Jewett with information on June 9, 2004, to enable him to finalize his response, CH2M HILL inadvertently provided some incorrect information. The above calculation converting population to single family dwelling units is not the basis for determining the single family base flow impact and ultimately the single family SDC rate. In fact, the values that determine the amount of capacity that is being used by user type ("Base Flow Impact" colunm of Appendix D of the SDC Methodology) were taken from MWMC's existing SDC Methodology and updated to reflect dry season maximum month and peak flow impacts. The 175 gallons per day of base flow impact reflects historical sewer billing records. Specifically, the historical average billed volume (based on winter average water use) per single family residential account is approximately 175 gallons per day. This number is converted to dry season average flow impact by comparing total billed volumes to treatment plant dry season average flows (a factor of 1.37). Finally, dry season average flow impact is converted to dry season maximum month impact based on the system design peaking factor of 1.5. The calculation converting from flow per population to an estimated flow per single family dwelling unit as presented in the June 10, 2004, e-mall was performed by the consultants, completely independent of the SDC model as an initial check for the selected values listed in Appendix D of the MWMC SDC Methodology. This particular check calculation is difficult to derive accurately because of the difficulty in determining the average number of persons per household for the MWMC service area, as well as adjusting for industrial flows. The consultants performed several checks to ensure that the selected values in Appendix D were a reasonable basis for $DC assessment. For example, a dry season maximum month impact per equivalent dwelling unit (EDU) was estimated by dividing the existing dry season capacity requirements (43.8 mgd) by the estimated number of EDUs (approximately 125,000 -- calculated by dividing the total billed sewer volumes by the average volume per single-family residential account). This calculation yields a dry season maximum month impact of 350 gallons per day (gpd), compared to the 359 gpd used in the MWMC SDC Methodology. Furthermore, all of the values used to estimate the capacity requirements of a single-family dwelling unit compare favorably to other communities. The City of Albany, for example (whose methodology was submitted in the record by the Home Builders of Lane County) use an average flow requirement of 420 gpd. The biochemical oxygen demand (BOD) and total suspended solids (TSS) capacity measures used by MWMC are significantly more conservative or lower than those used in the Albany Methodology. In closing, we regret that this incorrect information was inadvertently put forward, and we hope that the above explanation will help clarify the basis for these particular assumptions in the MWMC SDC Methodology. As stated at the beginning of this memorandum, there is no change to the MWMC SDC Methodology or to the resulting SDC rates. However, we feel that it is important to issue this memorandum to avoid the potential for any future confusion and/or misinterpretation. S0406288-ATTD.DOC 2