M. K. Shalati, Director Union County Public Works Department. F. Stephen Swartz, PE Swartz Engineering Consultants, Inc

Transcription

1 Water Reclamation: Not Yet Viable in Union County by M. K. Shalati, Director Union County Public Works Department F. Stephen Swartz, PE Swartz Engineering Consultants, Inc Introduction This study was undertaken to determine the feasibility of water reclamation and reuse in the the Twelve Mile Creek basin of Union County which lies in the west-central part of the County. Currently the basin is sparsely developed. It does include the Town of Waxhaw and portions of the Towns of Wedhngton, Indian Trail, and Stallings. It also contains a small portion of the City of Monroe, plus the unincorporated communities of Mineral Springs, Wesley Chapel and Houston. In addition, several residential subdivisions exist in the basin and more are being developed. The Charlotte outer belt highway, just north of the Union - Mecklenburg County line, is currently under construction. This transportation artery is expected to significantly influence continued development in the area. At the time of the study, Union County s Twelve Mile Creek Wastewater Treatment Plant ( WWTP ) was being upgraded from a spray irrigation facility to a tertiary treatment facility for discharge of treated effluent to the creek under an NPDES Permit. Figure 1 presents the liquid process schematic for the tertiary treatment facility. The discharge point is approximately 2.1 miles upstream of the North Carolina - South Carolina border. Effluent design limits for the upgraded Twelve Mile Creek WWTP were believed to be appropriate for water reclamation under the newly promulgated requirements for reclaimed water issued by the NC Department of Environment and Natural Resources, Division of Water Quality (DWQ). A comparison of the design limits and the DWQ reclaimed water quality limits is given Table

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3 Table 1: Effluent Criteria at the Twelve Mile Creek WWTP Criteria DWO Limit WWTP Design BOD5 (mga) 1 5 TSS (mg/l) 5 5 Fecal Coliform (#/looml) 14 <1 NH3 1 4 <OS Turbidity 1 <1 The Union County Public Works Department recognized that strategic advantages might be gained for both its wastewater and potable water utilities through a program of water reclamation. As a result, the Department decided to conduct an initial feasibility study on the concept of water reclamation at the Twelve Mile Creek WWTP, and distribution of reclaimed water for reuse within.the Twelve Mile Creek drainage basin. Study b ject ives The purpose of the initial study was to conceptually assess the probable feasibility of reclaiming water in the Twelve Mile Creek basin, and as a result, to determine if more detailed phases of a study should be undertaken. The probable feasibility of such an undertaking was to be determined through the answers to the following questions: A. Will the effluent quality at Twelve Mile Creek WWTP meet DWQ reclaimed water criteria? B. What is the probable customer demand for reclaimed water, and when during the year will it be made? C. What capital and operating costs will be involved in order to reclaim water for reuse at 12-Mile Creek WWTP and distribute it to interested customers in the basin? D. What are the operating requirements for a water reclamation program? E. What is the probable cost to the customer for reclaimed water? F. What advantages to Union County Utilities are offered by a water reclamation program? G. What financing options exist for such a project? Study Methods. Identification of hiph volume water customers: The County s record of annual billings to industrial, institutional and corporate water customers of Union County was examined to identify potential reclaimed water customers. This examination showed one industrial, twelve institutional, and -3 -

4 seventeen corporate customers that fit the profile of potential reclaimed water customer. Two of these were irrigation only customers, customers that only purchased water for irrigation and not for human consumption. Other potential reclaimed water users who were not current water customers were identified through a map search, interviews with members of the development community and the Centralina Council of Governments, and a visual inventory of the area via automobile. Additional potential reclaimed water customers identified by these efforts include: Stonebridge and Pebble Creek golf courses Western Union, Parkwood Middle & Parkwood High Schools Wesley Chapel Swim & Racquet Club Wesley Woods and Brandon Oaks residential subdivisions Hunters Oaks Planned Urban Development Car wash under construction on NC 16 north of Waxhaw Interview potential customers to determine interest in usina reclaimed water: htial screening of the list of potential customers revealed several with high potential. These high potential customers were interviewed to determine their interest in using reclaimed water and the types of uses anticipated. Table 2 below summarizes the results of these interviews. During the interviews, concerns were expressed about the mineral and bacterial content of the reclaimed water. Factual information about these concerns must be gathered and analyzed to address and allay these concerns. Bacterial content can be addressed with disinfection and residual disinfectant levels in the reclaimed water. Mineral content can only be determined after the Twelve Mile Creek Treatment Plant is operating. Table 2: Interest in Use of Reclaimed Water CUSTOMER INTEREST TYPE OF USE Parkdale Mills Yes Cooling water Stonebridge Residential No Landscape irrigation Stonebridge Golf Course Yes Irrig., slream augment. & vehicle wash Radiator Specialty Corp. Yes Process water Berry Triplas Yes Process water Developer Yes Landscape Irrigation -4-

5 Determine location of potential customers aeoaravhicallv within the basin: Through interviews with utility department staff the locations of large water users was determined and marked on a digital map of the basin. Other potential reclaimed water customers were located through interviews with members of the development community and visual observation. Exhibit A is a map of the Twelve Mile Creek basin showing the location of existing and planned Union County wastewater facilities and the identified potential reclaimed water customers. Exhibit A shows that potential reclaimed water customers can be logically grouped into three geographic regions of the basin. One group is generally in the area of Mineral Springs; another in the area between Stallings and the Airport; and a third in the Weddington-Marvin area. The largest potential demand for reclaimed water exists in the Mineral Springs area. The geographic grouping demonstrates that most of the potential demand lies within the East Fork sub-basin of Twelve Mile Creek. This sub-basin contains numerous County-owned wastewater 'interceptors as shown on Exhibit A. The existing rights-of-way for these interceptor lines plus existing highway right-of way provide natural corridors for reclaimed water distribution lines. Examination of the location of potential customers and available rights-of-way corridors reveals a logical set of reclaimed water transmission line routes that would minimize acquisition of additional rights-of-way. Potential reclaimed water use in each of the three geographic areas of the basin taken fiom County records of large industrial, institutional and corporate water customers is summarized below: &a Potential Use East Fork: Mineral Springs MG per Month * East Fork: Stallings-Airport West Fork: Weddington-Marvin Total MG per Month.574 MG per Month MG per Month * Not counting speculative Golf Course Based on the totals of the chart above and the relative distance fiom the Twelve Mile Creek. Wastewater Treatment Plant as shown in Exhibit A, the West Fork grouping was judged to not warrant further analysis at this time. -5 -

6 I Interviews were conducted with several selected, larger potential users to determine significant demand quantities and timing of demand. Based on these interviews, preliminary user demand calculations were made to determine probable distribution system hydraulic demands. Existing potential demand in the Marvin-Weddington area is significantly less than the other two areas and is considerably remote from the source. Therefore, it was judged not to warrant hrther consideration in the study. Determine the preliminarv enaineerina desian of deliverv facilities and probable cost: This Phase I study indicated that the probable capital cost of the first phase of a reclaimed water utility in the Twelve Mile Creek basin is approximately $2,15,, itemized in Table 3. Table 3: Ouinion of Probable Construction Cost Estimated Cost Site work Pumps Electrical, VFD s Meters & controls Yard piping Valves & fittings Chlorination Facilities Piping Subtotal Contingency (15%) Legal, technical, admin. (15%) Total $ 2, 6, 2, 1, 3, 15, 75, $1,6 19, 243, 243, $2.15. Probable annual operating costs are estimated at approximately $79,, broken down as shown in Table

7 Table 4: Probable Annual ODerating Costs Function Estimated Annual Cost [$/vear) Power: 15 1/2 time operating Labor: 2 man-hours per day Disinfection: (est.) Total 49,3 15, 15, 79.3 Calculate the probable users costs of reclaimed water: Costs of service incurred in providing reclaimed water to the Mineral Springs/Waxhaw area of the Twelve Mile Creek drainage basin include annual operating costs plus annual debt service on any borrowed funds used to finance the construction of the system. These costs are estimated at: Operating Costs... $ 79,3 / year Debt Service*... 24,7 Total $ 284. /year *Assumes 2-year Revenue Bond at 7% interest and 12% coverage requirement The collateral economic value of a reclaimed water system in Union County was considered. Several categories of economic value accrue to the County s water and wastewater utilities from existence of reclaimed water service. Use of reclaimed water reduces the demand on the water treatment plant for the manufacture of drinking water. This reduced demand allows the County to postpone construction of additional treatment capacity into the future. Also, the costs to produce the amount of reclaimed water used are avoided. Mostly, these avoided costs are in reduced power and chemical utilization. A recent study in Piedmont North Carolina calculated the value of postponed water treatment capacity to be $.47 per 1 gallons. While this calculated value may not be totally appropriate for Union County, it indicates a value in the range of $.3 to.5 per 1 gallons to be reasonably appropriate. In another vein, future wastewater treatment construction costs can be expected to be less than they would otherwise be because of water reclamation. If DWQ issues mass discharge limits for facilities that also reclaim water as they have indicated, then removal capacity of future expansion can be less -7-

8 than currently permitted. This is due to the avoidance of discharging those regulated constituents in the effluent stream through reclamation and reuse. A precise value of this cost avoidance cannot be calculated at this time, but certain other operating costs could be used as proxies for th~s value. For example, labor costs of operating the water reclamation facilities could be absorbed by the wastewater treatment utility as a proxy for the value of lowered future construction costs. These costs are in the range of $.1 to.15 per 1 gallons. Another consideration is the fact that the useful economic life of the transmission and distribution piping system is approximately 4-5 years. This is far longer than the typical term of a revenue or general obligation bond. If the cost of pipe depreciation is considered as the annual economic cost of the piping system instead of the principal payment on the debt, the cost of service is also lowered. In Union County s case, this could reduce the unit cost of service by approximately $ per 1 gallons. However, this amount of cash would have to be provided from some other source in order for the County to meet its debt service obligations. Potential reclaimed water rates in the Twelve Mile Creek Basin - Mineral Springs / Waxhaw area could range from full cost of service at the highest to fully credited for economic value at the lowest. Potential reclaimed water rates - Mineral Springs / Waxhaw Area Full cost of service.....$2.2 to 2.5 per 1 gallons Potential Credits: Postponed water construction......$.3 per 1 gallons Lowered future WWTP costs (proxy)... $.1 per 1 gallons Economic life of pipes......$.25 per 1 gallons Fully credited economic value service......$ 1.55 to 1.85 per 1 gallons -8-

9 Study Results The findings of the conceptual feasibility study are: 1. A source of reclaimable water will exist upon the commencement of operations of the Twelve Mile Creek WWTP (probably in Fall 1997). 2. Another source of reclaimable water exists at the Crooked Creek WWTP. 3. Customer interest in reclaimed water ekists in the Twelve Mile Creek basin, but more specific data about the water is needed to confirm this expressed interest. 4. Potential demand for reclaimed water is spread widely across the basin, requiring long distribution pipelines. 5. Customer interest in reclaimed water for residential and homeowner association landscape irrigation is present in the basin. However, it can not be located nor quantified in this study due to the reactive nature of development to utility availability. Several golf course / housing developments are currently under construction and are excellent candidates for reclaimed water customers. For example, the Emerald Lake Golf Course / Alexis Point development near the US 74 - Stouts Road intersection. 6. The development community needs to know of reclaimed water availability (or probable availability) during its planning stages for its interest to be manifested. 7. Preliminary indications of probable demand and location tend to indicate that reclaimed water can be relatively efficiently supplied to potential customers. However, the largest portion of the capital costs to implement a reclaimed water system is in the piping costs. Therefore, smaller systems or staged implementation would be required to keep the user costs reasonable. 8. An unused elevated water tank at Parkdale Mills could possibly be integrated into the distribution system for peak demand attenuation.. 9. Loss of revenue to the potable water utility will initially be realized. 1. Several important strategic and planning advantages accrue to Union County utilities through implementation of a reclaimed water program. 11. Additional financing options can possibly be realized for a reclaimed water program. 12. The probable cost of reclaimed water to the customer is comparable to potable water, and if economic values are recognized, can be lower.!3. The user costs are not sufficiently different from potable water rates to warrant further study. -9-

10 --- TWELVE MILE CREEK BASIN LIMITS I I SCALE 1" = 2 MILES CREEK - EXISTING SEWER LINES PROPOSED SEWER LINES POTENTIAL CUSTOMERS RECLAIMED WATER FACILITY UNION COUNTY RECLAIMER WATER EXHIBIT A FEASIBILIT" SUUDY TWELVE MILE CREEK BASIN DATE