OIMSITE SANITARY DISPOSAL SYSTEMS COST ANALYSIS APRIL 28, 1992 Prepared For: Environmental Protection Agency 401 M Street, SW Washington, D.C. 20460 Prepared by: WOODWARD-CLYDE FEDERAL SERVICES One Church Street, Suite 700 Rockville, MD 20850 (301) 309-0800 ------- ONSITE SANITARY DISPOSAL SYSTEMS COST ANALYSIS APRIL 28. 1992 Sfi Cass® ^ jgj Mlasta, Geovgra 3»»5 Prepared For: Environmental Protection Agency 401 M Street, SW Washington, D.C. 20460 Prepared by: WOODWARD-CLYDE FEDERAL SERVICES One Church Street, Suite 700 Rockvilie, MD 20850 (301) 309-0800 ------- ON SITE SANITARY DISPOSAL SYSTEMS COST ANALYSIS LO INTRODUCTION This report describes cost analyses of management practices that could be used to achieve the Onsite Sanitary Disposal Systems (OSDS) management measures for new and existing development presented in the "Management Measures for Sources of Nonpoint Pollution in Coastal Waters." The purpose of the cost analyses is to provide data to compare to current baseline OSDS costs for various locations throughout the coastal zone. These comparisons will serve as a basis for judging the economic achievability of the management measures. M TECHNICAL APPROACH Thirty-two hypothetical scenarios were developed for this analysis. Scenarios 1 through 16 are for new development and scenarios 17 through 32 are for retrofit of existing OSDS. To complete the analysis, general and specific assumptions have been made for the 32 design scenarios. Specific assumptions are included in the discussion for each scenario. The following is a list of the general assumptions for each of the 32 design scenarios: • One house occupied by four people equipped with two full baths, one kitchen sink, one utility sink, washing machine and dishwasher • Daily wastewater flow of 180 gallons/day (before installation of low flow plumbing fixtures • Drainfields were sized based on 180 gallons/day • Each house is equipped with low flow plumbing fixtures • Only low phosphate detergent is used • No house is equipped with a garbage disposal • The low flow plumbing cost for the new OSDS system is based on the difference between low flow plumbing and traditional plumbing fixtures. Designs were based on recommendations presented in EPA's "Design Manual - Onsite Wastewater Treatment and Disposal Systems" dated 1980 and TVA's design guidelines for constructed wetlands for OSDS. Specific new OSDS designs and costs were developed for the following scenarios: Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 1 April 28, 1992 ------- • Low, medium, and high percolation rates (120, 60, and 5 minutes/inch); • Conventional septic systems including a septic tank and a drainfield; • Recirculating sand filters including a septic tank, dosing tank, sand filter, pump, and a drainfield for nitrogen sensitive areas; • Vaults for areas with inadequate separation distance from the seasonally high water table; • Package treatment including a septic tank, package treatment, and drainfield for areas with inadequate separation distance from the seasonally high water table; • Constructed wetlands including a septic tank, dosing tank, pump, constructed wetland, and drainfield for areas with inadequate separation distance from the seasonally high water table or nitrogen sensitive areas; and • An evapotranspiration system for the Texas area. Retrofit designs were completed assuming that a conventional OSDS was already in place. Specific retrofit of existing OSDS designs and costs were developed for the following scenarios: • Low, medium, and high percolation rates (120, 60, and 5 minutes/inch); • An alternate trench system for OSDS where the drainfield has failed do to water overloads; • Recirculating sand filters for nitrogen sensitive areas; • Vaults for OSDS that have failed due to inadequate separation distance from the seasonally high water table; • Package treatment for OSDS that have failed due to inadequate separation distance from the seasonally high water table; • Constructed wetlands for OSDS that have failed due to inadequate separation distance from the seasonally high water table or for nitrogen sensitive areas; and • An evapotranspiration system for the Texas area. Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 2 April 28, 1992 ------- It should be noted that low flow plumbing fixtures were not included in the retrofit of existing OSDS for the recirculating sand filter, package treatment, and constructed wetlands system designs. Cost and effectiveness data were taken from Woodward-Clyde's "Urban BMPs Cost and Effectiveness Summary Data for 6217(g) Guidance - Onsite Sanitary Disposal Systems" dated 1992. Costs were based on 1988 dollars and the specific unit costs used in the analyses are as follows: ITEM • COST Septic Tank (1000 gallons) $1,750 Septic Tank (4000 gallons) $4,450 Pump out Septic Tank $120 Recirculating Sand Filter (including dosing tank and pump) $1,725 Drainfield $12/linear foot High Efficiency Dishwasher $480 High Efficiency Washing Machine $475 High Efficiency Kitchen and Laundry Faucets $57 High Efficiency Bathroom Faucet $47 High Efficiency Toilet $138 High Efficiency Shower Head $31 Pump and Dosing Tank for Constructed Wetland or Evapotranspiration System $1,050 Constructed Wetland $1.13/sq. ft. Evapotranspiration Evaporation Field $6.50/sq. ft. Package Treatment Unit $4,440 A summary of the various design costs are included in Table 1. The following is a list of specific assumptions used in each of the Scenarios. Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 3 April 28, 1992 ------- TABLE 1 - SUMMARY OF COSTS FOR OSDS BMP SCENARIOS NEW OSDS SCENARIO'S COSt ANALYSIS SCEN WATER PERC TYPE OF TANK DRAIN TANK DRAIN _OW FLOW TREAT. DESIGN CAPITAL O&M DESIGN NO. LOAD RATE SYSTEM SIZE FIELD COST FIELD pLutve. UNIT COST COST COST LIFE SIZE COST COST COST (GPD) (MIN/1N) (GAL) (SQ. FT.) (4) ($) ($) ($> ($) <*> ($)/YR (YRS) 1 5 ciow 1000 150 $1,750 $1,800 $100 $0 $355 $4,665 $40 36 2 180 5 RE.SAN.FIL 1000 150 $1,750 $1,800 $100 $1,725 $528 $5,903 $190 30 3 180 5 VAULTS . 4000 0 $4,450 $0 $100 $0 $445 $4,995 $2400 30 4 180 5 PACK TRT 1000 150 $1,750 $1,800 $100 $4,400 $795 $8,845 $800 30 5 180 5 CON.WET. 1000 150 $1,750 $1,800 $100 $1,500 $505 $5,655 $140 30 6 180 60 CONV 1000 400 $1,750 $3,340 $100 $0 $509 $5,699 $40 30 7 180 60 RE.SAN.FIL 1000 400 $1,750 $3,340 $100 $1,725 $682 $7,597 $190 30 8 180 60 VAULTS 4000 0 $4,450 $0 $100 $0 $445 $4,995 $2,400 30 9 180 60 3ACK TRT 1000 400 $1,750 $3,340 $100 $4,400 $949 $10,539 $800 30 10 180 60 CON.WET. 1000 400 $1,750 $3,340 $100 $1,500 $659 $7,349 $140 30 11 180 120 CONV 1000 900 $1,750 $7,515 $100 $0 $927 $10,292 $40 30 12 180 120 RE.SAN.FIL 1000 900 $1,750 $7,515 $100 $1,725 $1,099 $12,189 $190 30 13 180 120 VAULTS 4000 0 $4,450 $0 $100 $0 $445 $4,995 $2400 30 14 180 120 PACK TRT 1000 900 $1,750 $7,515 $100 $4,400 $1,367 $15,132 $800 30 15 180 120 CON. WET. 1000 900 $1,750 $7,515 $100 $1,500 $1,077 $11,942 $140 30 16 180 N/A EVAPOTRA 1000 2250 $1,750 $14,625 $100 $1,050 $1,743 $19,268 $120 30 > T3 N) 00 SO vO N) EXISTING OSDS BMP SCENARIO'S COST ANALYSIS SCEN WATER PERC TYPE OF TANK DRAJN TANK DRAN -OW FLOW TREAT. DESIGN CAPITAL O&M DESIGN NO. . LOAD RATE SYSTEM SIZE FIELD COST FIELD PLUMB. UNrr COST COST COST LIFE SIZE COST COST COST (GPD) (MIN/IN) (GAL) (SQ. FT.) ($) ($) (*> ($) ($) ($) ($)/YR (YRS) 17 180 5 ATL tRCH 1000 75 $0 $900 $1,500 56 18 180 5 RE.SAN.FIL 1000 150 $0 $0 $0 $1,725 $173 $1,898 $190 30 19 180 5 VAULTS 4000 150 $4,450 $0 $1,500 $0 $445 $6,395 $2,400 30 20 180 5 PACK TRT 1000 150 $0 $0 $0 $4,400 $440 $4,840 $800 30 21 180 5 CON. WET. 1000 150 $0 $0 $0 $1,500 $150 $1,650 $140 30 22 180 60 ATL TRCH 1000 200 $0 $1,670 $1,500 $0 $167 $3,337 $40 30 23 180 60 RE.SAN.FIL 1000 400 $0 $0 $0 $1,725 $173 $1,898 $190 30 24 180 60 VAULTS 4000 400 $4,450 $0 $1,500 $0 $445 $6,395 $2,400 30 25 180 60 PACK TRT 1000 400 $0 $0 $0 $4,400 $440 $4,840 $800 30 26 180 60 CON. WET. 1000 400 $0 $0 $0 $1,500 $150 $1,650 $140 30 27 180 120 ATL TRCH 1000 450 $0 $3,758 $1,500 $0 $376 $5,633 $40 30 28 180 120 RE.SAN.FIL 1000 900 $0 $0 $0 $1,725 $173 $1,898 $190 30 29 180 120 VAULTS 4000 900 $4,450 $0 $1,500 $0 $445 $6,395 $£400 30 30 180 120 PACK TRT 1000 900 $0 $0 $0 $4,400 $440 $4,840 $800 30 31 180 120 CON. WET. 1000 900 $0 $0 $0 $1,500 $150 $1,650 $140 30 32 180 N/A EVAPOTRA 1000 2250 fco $14,625 $0 $1,050 $1,568 $17,243 $120 30 ------- NOTE: CONV. RE.SAN.FIL CON. WET. ALT.TRCH. PACK.TRT. EVAPOTRA Conventional Septic System Recirculation Sand Filter Constructed Wetland Alternate Trench Package Treatment Evapotranspiration System Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 5 April 28, 1992 ------- 2.1 New QSDS - Scenarios 1 through 16 Scenario #1: Conventional OSDS for High Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.) and a drainfield. • Drainfield size based on a loading rate of 1.2 gpd/sq. ft. • The septic tank is pumped out once every three years. Scenario #2: Recirculating Sand Filter for High Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), a recirculating sand filter, and a drainfield. • Drainfield size based on a loading rate of 1.2 gpd/sq. ft. • The septic tank is pumped out once every three years. Scenario #3: Vault for High Percolation Rate Soils • Treatment consists of a vault/holding tank (4000 gal.). • No drainfield is necessary when a holding tank is used. • The holding tank is pumped out twice a month. Scenario #4: Package Treatment for High Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), a package treatment unit, and a drainfield. • Drainfield size based on a loading rate of 1.2 gpd/sq. ft. • The septic tank is pumped out once every three years. Scenario #5: Constructed Wetland for High Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), constructed wetland, and a drainfield. Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 6 April 28, 1992 ------- • Drainfield size based on a loading rate of 1.2 gpd/sq. ft. • Septic tank is pumped out once every three years. Scenario #6: Conventional OSDS for Medium Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.) and a drainfield. • Drainfield size based on a loading rate of 0.45 gpd/sq. ft. • The septic tank is pumped out once every three years. Scenario #7: Recirculating Sand Filter for Medium Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), a recirculating sand filter, and a drainfield. • Drainfield size based on a loading rate of 0.45 gpd/sq. ft. • The septic tank is pumped out once every three years. Scenario #8: Vault • Treatment consists of a holding tank (4000 gal.). • No drainfield is necessary when a holding tank is used. • The holding tank is pumped out twice a month. Scenario #9: Package Treatment for Medium Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), a package treatment unit, and a drainfield. • Drainfield size based on a loading rate of 0.45 gpd/sq. ft. • The septic tank is pumped out once every three years. Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 7 April 28, 1992 ------- Scenario #10: Constructed Wetland for Medium Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), constructed wetland, and a drainfield. • Drainfield size based on a loading rate of 0.45 gpd/sq. ft. • Septic tank is pumped out once every three years. Scenario #11: Conventional OSDS for Low Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.) and a drainfield. • Drainfield size based on a loading rate of 0.2 gpd/sq. ft. • The septic tank is pumped out once every three years. Scenario #12: Recirculating Sand Filter for Low Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), a recirculating sand filter, and a drainfield. • Drainfield size based on a loading rate of 0.2 gpd/sq. ft. • The septic tank is pumped out once every three years. Scenario #13: Vault • Treatment consists of a holding tank (4000 gal.). • No drainfield is necessary when a holding tank is used. • The holding tank is pumped out twice a month. Scenario #14: Package Treatment for Low Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), a package treatment unit, and a drainfield. • Drainfield size based on a loading rate of 0.2 gpd/sq. ft. • The septic tank is pumped out once every three years. Woodward-Clyde Federal Services April 28, 1992 80040000h:\wp\cost ana\report.osd 8 ------- Scenario #15: Constructed Wetland for Low Percolation Rate Soils • Treatment consists of a septic tank (1000 gal.), constructed wetland, and a drainfield. • Drainfield size based on a loading rate of 0.2 gpd/sq. ft. • Septic tank is pumped out once every three years. Scenario #16: Evapotranspiration System • This site has a high water table and the soil is impermeable. • This site is assumed to be in Texas. • Treatment consists of a septic tank (1000 gal.)and an evapotranspiration drainfield. • Drainfield size is based on a loading rate of 0.08 gpd/sq. ft. • The septic tank is pumped out once every three years. 2.2 Retrofit Existing OSDS - Scenarios 17 through 32 Scenario #17: Alternate Trench for High Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • An alternate drainfield half the size of the existing drainfield is added to existing system. • Drainfield size based on a loading rate of 1.2 gpd/sq. ft. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are replaced with low flow plumbing fixtures. Scenario #18: Recirculating Sand Filter for High Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • A recirculating sand filter is added to existing system. Woodward-Clyde Federal Services April 28, 1992 80040000h:\wp\cost_ana\report.osd ------- • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Scenario #19: Vault • Existing treatment is replaced with a holding tank (4000 gal.). • No drainfield is necessary when a holding tank is used. • The holding tank is pumped out twice a month. • The existing plumbing fixtures are replaced with low flow plumbing fixtures. Scenario #20: Package Treatment for High Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • A package treatment unit is added to existing system. • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Scenario #21: Constructed Wetland for High Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • A constructed wetland is added to the existing system. • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Woodward-Clyde Federal Services 80040000h:Vwp\cost_ana\report.osd 10 April 28, 1992 ------- Scenario #22: Alternate Trench for Medium Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • An alternate drainfield half the size of the existing drainfield is added to existing system. • Drainfield size based on a loading rate of 0.45 gpd/sq. ft. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are replaced with low flow plumbing fixtures. Scenario #23: Recirculating Sand Filter for Medium Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • A recirculating sand filter is added to existing system. • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Scenario #24: Vault • Existing treatment is replaced with a holding tank (4000 gal.). • No drainfield is necessary when a holding tank is used. • The holding tank is pumped out twice a month. • The existing plumbing fixtures are replaced with low flow plumbing fixtures. Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 11 April 28, 1992 ------- Scenario #25: Package Treatment for Medium Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) a drainfield. • A package treatment unit is added to existing system. • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Scenario #26: Constructed Wetland for Medium Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • A constructed wetland is added to the existing system. • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Scenario #27: Alternate Trench for Low Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • An alternate drainfield half the size of the existing drainfield is added to existing system. • Drainfield size based on a loading rate of 0.2 gpd/sq. ft. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are replaced with low flow plumbing fixtures. Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 12 April 28, 1992 ------- Scenario #28: Recirculating Sand Filter for Low Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • A recirculating sand filter is added to existing system. • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Scenario #29: Vault • Existing treatment is replaced with a holding tank (4000 gal.). • No drainfield is necessary when a holding tank is used. • The holding tank is pumped out twice a month. • The existing plumbing fixtures are replaced with low flow plumbing fixtures. Scenario #30: Package Treatment for Low Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • A package treatment unit is added to existing system. • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Woodward-Clyde Federal Services 80040000h: Ywp\cost_ana\report. osd 13 April 28, 1992 ------- Scenario #31: Constructed Wetland for Low Percolation Rate Soils • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • A constructed wetland is added to the existing system. • A new drainfield is not required. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. Scenario #32: Evapotranspiration System • This site has a high water table and the soil is impermeable. • This site is assumed to be in Texas. • Existing treatment consists of a septic tank (1000 gal.) and a drainfield. • An evapotranspiration drainfield is installed in place of existing drainfield. • The septic tank is pumped out once every three years. • The existing plumbing fixtures are retained. 3^0 SUMMARY The costs for the various OSDS practices varied considerably. As could be expected, the percolation rate had a strong influence on the costs because of the impacts percolation rates have on drainfield sizes. 3J. New OSDS For the new OSDS, the conventional system is the most cost effective. However, a conventional system cannot be used in nitrogen sensitive areas and in areas with inadequate separation distance from the seasonally high water table. For nitrogen sensitive areas, recirculating sand filters and constructed wetlands could be used. Of these to systems, the constructed wetland is slightly less expensive (about $250). However, recirculating sand filters have been more widely Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 14 April 28, 1992 ------- applied. The TV A design procedure is relatively new and has only been widely applied to residences in Kentucky. In areas with inadequate separation distance, vaults, package treatment, and constructed wetlands were evaluated. The constructed wetlands are the most economical practice. Vaults have a very high maintenance cost and package treatment requires much more maintenance by the homeowner than constructed wetlands. The evapotranspiration system was evaluated because of the special characteristics of the Orange County, Texas area being evaluated for baseline cost. The system is very costly due to the size of the evaporation field required to handle the average daily loads. However, the cost of the system may be less than the cost of installing a centralized sewage treatment and collection system. 3.2 Retrofit of Existing OSDS For OSDS that have failing drainfields due to water,overloading, the alternate trench practice is an economical retrofit alternative. The alternate trench can be used initially to allow the exiting drainfield to revert to aerobic conditions. In most instances, flow can then be alternated between the new trench and the existing drainfield without causing the existing drainfield to again fail. In nitrogen sensitive areas, the recirculating sand filter and constructed wetlands practices can be implemented for under $2,000. Again the recirculating sand filter has been the more widely applied technology. In the event that the drainfield also needs to be replaced, the implementation of these practices should include low flow plumbing fixtures. The increased cost for this option would vary from $2,400 to $5,200 depending on the percolation rate of the soil. For retrofit due to inadequate separation distance, the constructed wetland is again the most economical alternative. For the special case of Orange County, Texas, the evapotranspiration system is still a costly practice (over $17,000 per household). However, this may still be more economical than installing a centralized sewage treatment and collection system. Woodward-Clyde Federal Services 80040000h:\wp\cost_ana\report.osd 15 April 28, 1992 ------- |