2.0 Service Area Definition and Loading Calculations
Figure 1 below denotes the contributing service area for the proposed River Bend Creek Lift Station, which consists of new residential development. Neighboring land uses are also depicted. The entire service area is located within unincorporated El Paso County (PUD zoning) and within the service area of Security Sanitation District.
A map is provided in Appendix B which denotes the land uses and zoning of all land within a 1-mile radius of the lift station site. The proposed lift station will be located within the 0.2% Annual Chance Flood Hazard Boundary. Site Grading and Lift Station infrastructure is being designed no less than three (3) feet above the 100-yr, 1% Annual Chance Flood Hazard Area water surface elevation. A copy of the current Flood Insurance Rate Map (FIRM) is attached in Appendix B.
The Office of the State Engineer, State Board of Examiners of Water Well Construction and Pump Installation Contractors, Rules and Regulations for Water Well Construction, Pump Installation, Cistern Installation, and Monitoring & Observation Hole/Well Construction – 2 CCR 402-2, Effective Date January 1, 2005, Section 12.2.2 states: 12.2.2 Wells shall not be located closer than one hundred (100) feet horizontally to the nearest existing source of contaminants or fifty (50) feet from a septic tank, sewer line or other vessel containing contaminants. A request for variance must be submitted and written approval from the Board must be obtained prior to the construction of a well that cannot meet this spacing requirement.
There are no wells within the distances specified above for this location. Maps showing existing wells, topography, and wetlands in the vicinity of the lift station site are provided in Appendix B.
A photo of the posted sign for the new lift station is included in Appendix C. The sign was posted at the site on August 9, 2018 and is oriented such that it is clearly visible from the road nearest to the site.
The new residential development is planned to include 225 single family units (SFU’s) at full buildout. Of these 225 SFU, only 213 SFU will be serviced by the proposed lift station. Site topography will allow the remaining twelve (12) SFU to discharge by gravity into the existing sanitary sewer main in Southmoor Drive. No wastewater will be generated in the non-contributing area depicted in Figure 1. The following assumptions were made in calculating the hydraulic and organic loading from the new development:
- Per SFU Average Daily Flow (ADF) = 198 gpd/SFU (Historical ADF/SFE)
(Single Family Equivalent, SFE, equal to Single Family Unit, SFU) - Peaking Factor (Peak Hourly Flow / Average Daily Flow) = 2.7 (SSD Standard)
- SFE Average Occupancy = 2.6 persons (US Census Data, El Paso County Design Standard)
- Per Capita BOD5 Loading = 0.2 lb/person (CDPHE Reg 43 Design Standard, Tchobanoglous et al.)
These assumed values are consistent with those of similar developments in adjacent districts. The SFE unit wastewater volume contribution of 198 gal/SFE is based on a study conducted by GMS consulting Engineering (Appendix G). Based on these assumptions the projected wastewater flows are as follows:
| Category | Formula | Result |
|---|---|---|
| Service Area Population | = 213*2.6 | = 554 persons |
| Max. Month Average Daily Flow (ADF) | = 213*198 | = 42,174 gpd (29 gpm) |
| Peak Hourly Flow (PHF) | = 42,174 *2.7 | = 113,870 gpd (79 gpm) |
| Max. Month Average Daily Loading (ADL) | = 554*0.2 | = 111 lb BOD5/day |
These projected flows and loadings represent the proposed capacity of the River Bend Creek Lift Station as described in this Site Location Application.