Laserfiche WebLink
STATE OF COLORADO <br />COLORADO GEOLOGICAL SURVEY— <br />serving the people of Colorado <br />Department of Natural Resources <br />1313 Sherman Street, Room 715 <br />Denver, CO 80203 <br />Phone: (303) 866-2611 <br />Fax: (303) 866-2461 <br />MEMORANDUM <br />To: South Platte River Basin Roundtable <br />From: Ralf Topper, CGS liaison <br />Date: May 7, 2007 <br />Subject: Consumptive/non-consumptive water use by residences using <br />individual sewage disposal systems. <br />In February 1974, then State Engineer Jeris Danielson asked staff to investigate the <br />consumptive use of water by homes using leach fields for sewage disposal. In preparing a <br />plan of augmentation, developers relying on leach fields for effluent disposal were <br />submitting the figure of 10% consumptive use within the system. The State Engineer had <br />accepted this value without knowing whether or not the figure is accurate. Staff spent <br />considerable time reviewing the published literature, but found no direct studies pertaining <br />to consumptive use of residential septic systems. Literature with ancillary information <br />useful to their investigation, however, was obtained. In addition, a number of persons and <br />agencies were contacted to solicit additional information and input. Based on their <br />findings, staff concluded that 80% of the water entering a house was used by toilets and in <br />bathing. Applying estimates for in-house consumption and evaporation they determined <br />that 8.4% of the water would be consumptively used before entering the septic tank. <br />Evaluating the results of a then new (1976/77) field investigation by Dr. Paul Trost in <br />conjunction with consumptive use determinations using the Blaney-Criddle or similar <br />methods, staff determined that during the growing season approximately 9.6% of the <br />water was consumed within the leach field. On an annual basis, this amounted to only <br />3.9%. Thus on an annual basis the total consumptive use (in-house + leach field) was <br />