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HomeMy WebLinkAbout; Sewer Basins IJ & 2A; Sewer Basins IJ & 2A; 1988-08-01DRAFT Sewer Study Unsewered Portion of Sewer Basins IJ & 2A August, 1988 Wilson Engineering Consulting Engineers c List of Tables Table 1-1 Existing Parcels within Study Area 2-1 Unit Construction Costs 3-1 Projected Flow from Study Area 3-2 Cost Comparison Table of Contents List of Tables List of Figures Chapter 1 Chapter 2 Chapter 3 Chapter 4 Introduction and Study Area Study Area Design and Cost Criteria Flow Factors Average Daily Flows Peak Flows Design Criteria Gravity Sewers Unit Costs Gravity Sewers Alternative Analysis and Cost Estimates Projected Flows Existing Sewers Alternative Analysis Alternative 1 Alternative 2 Recommendation Alternative Cost Allocation Acreage Lots Projected Units Existing Sewered lot List of Figures Figure Title 1-1 Study Area 2-1 Peaking Factor Chart 3-1 Alternative 1 3-2 Alternative 2 CHAPTER 1 INTRODUCTION AND STUDY AREA The purpose of this report is to provide an analysis of the routing and cost to provide sewer service to the lots within the study area. The study area consists of an unsewered area within Growth Management Zones 1 and 2 along El Camino Real. There are fifteen existing houses within the study area, fourteen of which are served by septic systems. The septic systems have been in place for a number of years and the leach fields on a number of the houses are beginning to fail. This report is intended to provide recommendations and costs to sewer the existing houses and provide service for the empty parcels. STUDY AREA Figure 1-1 shows the study area. As shown in this figure the area is bounded generally on the east by El Camino Real, the north by Chestnut Ave., the west by Holly Brae Lane, and on the south by Palisades Drive. Figure 1-1 also shows the Assessor's parcel number of all lots within the study area and indicates the lots which have existing houses. Parcel number 207-180-04 is currently connected to the sewer on Palisades Drive and Parcel 207-180-06 is pumping to the sewer on Skyline Drive. All other houses within the study area are on septic systems. Although there are sewers which surround the study area, due to topography, all of the lots within the study are too low to be served by the closest sewers. Table 1-1 provides a tabulation of the lots included within the study area, the acreage of each lot, and the estimated possible number of units which could be built on each lot. The table also tabulates whether or not there is an existing house on each lot. The table includes three possible lot splits. As can be seen in the chart, there are approximately 24.02 acres within the study area. There is a possibility of 61 units to be built out and at the present time there are 15 houses. The possible unit count is based on the existing zoning. For the purpose of estimating units for these lots, we utilized the growth management control point density of 3.2 units/acre. n LEGEND 207-063-27 0 STUDY AREA LOTS WITHIN STUDY AREA WITH HOUSES ASSESSOR'S PARCEL NUMBER POSSIBLE LOTS SPLITS FIGURE l-l STUDY AREA Table 1-1. Existing Parcels within Study Area Lot 167-080-41 167-080-42 167-080-33 167-080-34 167-080-35 167-080-36 167-080-06 167-080-07 167-230-24 167-230-25 207-063-10 207-063-11 207-063-12 207-090-15 207-090-16 207-090-17 207-090-18 207-090-20 207-063-24 207-063-25 207-063-27 207-063-28 207-063-29 207-063-30 207-063-31 207-180-02 207-180-03 207-180-04 207-180-05 207-180-08 207-180-09 207-180-10 207-180-12 Acres 1 .30 .43 .44 .45 .50 .56 .54 .58 .91 .39 .50 .58 .51 .44 .51 .64 .69 .02 .19 .32 .36 .37 .46 .85 .70 .64 .53 .42 .71 .56 .68 .55 .69 24.02 acres Possible Units 4 1 1 1 1 1 1 1 2 4 1 1 1 1 1 2 2 6 7 4 1 1 1 2 2 2 1 1 2 1 1 1 2. 61 Existing House X X X X X X X X X X X X X X X units 15 houses 207-180-06'.43 Pumped lot not included in study area but could be connected to system. o CHAPTER 2 DESIGN AND COST CRITERIA The criteria presented in this chapter have been used to size and estimate costs for facilities evaluated in this report. FLOW FACTORS The wastewater collection system is sized based on peak flow. To determine peak flow one must estimate average flow and then convert it to peak flow based on an appropriate peaking factor. Average Daily Flows The average daily flow from the study area was projected using 220 gallons per day per equivalent dwelling unit. Peak Flows The ratio of the peak flow to the average flow varies with the number of equivalent dwelling units being projected. The larger the number of equivalent dwelling units, the smaller the peaking factor. Figure 2-1 was utilized to convert average flows to peak flows. DESIGN CRITERIA The design criteria for this report were based on the City of Carlsbad standards and standards of the industry. Gravity Sewers All gravity sewers have been designed to convey peak wet weather flow. For pipes with a diameter of 10 inches and smaller, the sewers have been designed to convey this flow when flowing one-half full. For pipes with a diameter of 12 inches and larger, the sewers have been designed to convey peak wet weather flows when flowing three-fourths full by depth. Manning's equation with n = 0.013 was used to size all gravity sewers. All new sewers were designed to maintain a minimum velocity of 2 feet per second to prevent the deposition of solids. o ll. LJ O cc UJ O LJ CL < o 0.01 0.02 OR LESS 0.05 O.I 0.2 0.5 2.0 5.0 AVERAGE FLOW (MILLION GALLONS PER DAY) 10.0 O FIGURE 2-1 PEAKING FACTOR CHART UNIT COSTS The unit costs used to estimate costs in this report were based on recent construction bid prices. The costs in this report are based on an Engineering News Record Los Angeles Construction Cost Index of 5,500. Gravity Sewers Table 2-1 presents the unit costs used to develop costs for gravity sewers. These costs include a 35 percent allowance for construction contingencies, legal, engineering and administrative costs. The costs per foot include manholes. c Table 2-1. Unit Construction Costs Pipe Type/Size-Inches Cost Per Foot, dollars Gravity Sewers 6" 55 8" 65 C CHAPTER 3 ALTERNATIVE ANALYSIS AND COST ESTIMATES The study area can be divided into two distinct sewering areas. The first area contains those lots which must be sewered along El Camino Real due to their topography. The second area consists of the houses along Holly Brae Lane which are up on the side of the valley and can sewer to existing lines in Palisades Drive. PROJECTED FLOWS Table 3-1 provides an estimate of the projected flows from the study area. Those units which flow toward El Camino Real are tabulated separately from those which are along Holly Brae Lane. The total peak flow generated by the study is 33,500 gallons per day. EXISTING SEWERS There are two existing sewer lines which could be utilized to serve all or a portion of the study area. Eventually all the sewage from the study area will reach the corner of El Camino Real and Tamarack Avenue. At that point there is an interceptor system connecting with the North Agua Hedionda system to convey the sewage to Encina for treatment. Thus all flow collected in El Camino Real must be conveyed to Tamarack at El Camino Real before it can be connected to an existing sewer. , The houses along Holly Brae Lane have sufficient elevation so that they could flow into the existing sewer on Palisades Drive. This sewer flows down Palisades Drive and eventually connects with the manhole at the corner at Tamarack and El Camino Real. For the purposes of this study we have utilized these two point of connections to develop the various alternatives. ALTERNATIVE ANALYSIS We have developed two alternatives to sewer the study area. The first alternative ulitizes one line tied into Palisades Drive to serve the houses along Holly Brae Lane and the second line in El Camino Real is to serve the lines which flow toward El Camino Real. The second alternative ties the houses along Holly Brae Lane into the line on El Camino Real. Table 3-1. Projected Flow From Study Area Area Units Average, Peak, ragd mgd El Camino Real 34 units .012 .030 Holly Brae 27 units .002 .005 Total 61 units .014 .035 Alternative 1 Figure 3-1 shows Alternative 1. As shown in this alternative, the houses along Holly Brae Lane are connected into the existing sewer on Palisades Drive. The houses which sewer toward El Caraino Real are served by a line which flows down El Camino Real to Tamarack. For the purposes of this alternative, the existing 6-inch line which currently serves Parcel 207-181-04 has been utilized to connect the houses along Holly Brae to Palisades Drive. This line has been extended into Holly Brae and along Holly Brae to the end of the Alder Avenue cul-de-sac. This line serves 11 existing homes and 3 possible future homes along Holly Brae Lane while the line in El Camino Real serves the remainder of the study area. The pumped house on Holly Brae Lane could also be connected to this line. Alternative 2 Figure 3-2 shows Alternative 2. Under Alternative 2, the houses along Holly Brae Lane are connected directly to the line at El Camino Real and are not connected to the line on Palisades Drive. This alternative has all 8-inch piping. Recommended Alternative Table 3-2 provides a cost comparison between the two alternatives. The cost for Alternative 1 is $346,000 and the cost for Alternative 2 is $338,000. Due to the complexity of estimating costs and the uncertainties which may arise during design and construction, the cost differential shown between these alternatives may not reflect actual cost. Since this difference is so small as compared to the magnitude of the numbers, we feel that Alternative 1 should be the recommended alternative since it provides a flexibility to serve 11 of the existing 15 houses without the need to construct major facilities in El Camino Real. Since the purpose of this study is to provide an outlet for the existing homes, we feel Alternative 1 provides the City with the flexibility to put in a system to provide service to existing homes while allowing them to put in a financing program to fund the ultimate improvements needed for the study area. c o Table 3-2. Cost Comparison Alternative 1 Line A A,000' of 8" @ $65 per foot 260,000 Line B Existing 500' of 6" @ $55 per foot 27,500 900' of 8" @ $65 per foot 58,500 Subtotal 86,000 Total $346,000 Alternative 2 Line A 4,000' of 8" @ $65 per foot 260,000 Line B 1,200' of 8" @ $65 per foot 78.000 Total $338,000 FIGURE 3-1 ALTERNATIVE r n FIGURE 3-2 ALTERNATIVE 2 c CHAPTER 4 COST ALLOCATION Three methods of allocating costs will be presented in this chapter. The recommended alternative, Alternative 1 will cost approximately $346,000 to implement. We have developed three methods to spread these costs over the study area. The first is an acreage based method, the second is based on existing lots, and the third is based on projected units. Since one of the lots within the study area is currently served we feel that it is also important to discuss the allocation in cost to that lot in this chapter. COST ALLOCATION BASED ON ACREAGE There are 22.43 net acres within the study area. Since the total cost of improvement is estimated at $346,000 this would work out to $15,426 per net acre. The advantages of a cost split based on acreage is that the cost split could be worked out with no uncertainty and each existing lot if split would have a mechanism available to split the cost for the new parcels. This acreage cost split could be used for either a reimbursement agreement or an assessment district to fund the facilities needed to serve the study area. The disadvantage of an acreage based figure is that lots with a single home which vary in size would get varying assessment based on the total size of the lot. Thus those with larger lots would pay larger assessment though their use of the sewer may be identical to an adjacent lot with a lower assessment. If the lots between Skyline and Holly Brae are subdivided they could be added to the assessment area. COST ALLOCATION BASED ON LOTS Since there are 30 lots currently within the study area, allocation of cost based solely on lots would assess $11,530 per existing lots. The advantage of this type of assessment would be that cost allocation could be clearly defined based on the existing 30 lots. The disadvantage of this system is that there is no increased assessment for larger lots or for multiple lots which may develop from the existing parcels. If the lots between Skyline and Holly Brae are subdivided they could be added to the assessment area. COST ALLOCATION BASED ON PROJECTED UNITS From the existing zoning and general plan maps, we estimate that approximately 61 units could be developed within the study area. This number is probably on the high side and the ultimate build out of the study area could be much lower. Based on 61 units, the assessment per unit would be $5,672. The advantage of this system of allocation is that it is based on the use of the sewers. Each house would have roughly the same flow being contributed to the sewer so each house would be paying in proportion to its use of the system. The disadvantage of this system is that there is no way to accurately project at this time the total number of units which may ultimately be approved for the study area. This system could not be used for an assessment district spread. If a reimbursement agreement could be put together, there would be a risk that a greater or smaller number of lots than were actually being projected would ultimately be built. This would lead to either a greater or lesser amount being collected then what was actually spent on the improvements. EXISTING SEWERED LOTS Parcel number 207-180-04 is currently sewered. The sewer system serving this lot would be used for the recommended alternative. Since this property owner fronted costs for this section of the line, this lot should be fully reimbursed for all expenses incurred to date for sections of line utilized under the recommended alternative. However, this property owner should pay his share of the cost. Parcel number 207-180-06 is currently pumped. This parcel could also be sewered by gravity using the proposed system. If this parcel connects to the system he should also pay his share of the cost.