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HomeMy WebLinkAboutSP202100004 Correspondence 2021-08-16Inboden Environmental Services, Inc. IES 5790 Main Street Mt. Jackson, VA 22842 (540)477-3300 FAX: (540) 477-3360 WEB: www.4ies.com CLIFTON INN AND COLLINA FARM ONSITE WASTEWATER MANAGEMENT — EXPANSION FEASIBILITY EVALUATION JULY 30, 2021 BACKGROUND Clifton Inn and Collina Farm are located on adjoining properties with separate existing on -site sewage systems. Shimp Engineering, Inc. (Shimp) is evaluating potential expansions on both properties to support more guests and/or events. Inboden Environmental Services, Inc. (IES) has been retained to evaluate options for expansions and/or modifications of existing on -site wastewater systems to serve the potential expansions. This document is a summary of the evaluation by IES. Wastewater Expansion Scenarios IES evaluated the onsite wastewater systems and potential for expansion at both Clifton Inn and Collina Farm using existing design documents field, evaluations along with concept designs and calculations. Based on those findings, IES developed wastewater management scenarios to meet minimum desired expansion and maximum expansion proposed as outlined by Shimp. IES then developed cost opinions for these scenarios. Intermediate expansion scenarios between the minimum and full build -out could be designed and implemented for an intermediate cost. Because the occupancy (usage) of the facilities is highest on weekends and low during the week, IES recommends multi -day flow equalization to reduce the maximum flow and load to the treatment and disposal systems. Flow equalization tanks store septic tank effluent during high flows days and pumps out an equalized flow over the course of a week to the treatment system. This reduces the size and cost of the treatment and disposal systems or allows existing system to serve additional buildings. CLIFTON INN WASTEWATER SYSTEMS AND EXPANSION Overview The Clifton Inn site has multiple buildings that are served by several on -site wastewater systems The Inn building currently has seven guest rooms, laundry washing, and a restaurant which are served by an existing alternative on -site system (AOSS). The remainder of the buildings at the Clifton Inn Farm are served by separate Conventional Onsite Septic Systems (COSSs), consisting of a septic tank with a gravity dosed drainfield. These buildings are the guest rooms to the east of the Inn building and north of the parking circle. IES was unable to evaluate these systems and recommends that these systems be evaluated in detail as part of a separate scope. The Clifton Inn AOSS has multiple setting tanks, a sewage pump tank, a Biomicrobics FAST treatment unit and a pressure dosed disposal system comprised of four drip zones and four Inboden Environmental Services Inc. Tel. (540) 477-3300 1 of 6 Clifton Inn and Collin Farm Onsite Wastewater Management Preliminary Capacity Evaluation gravity -dosed drainfield areas. This AOSS was constructed based on the engineered construction drawings from McKee Carson in 2000. IES evaluated the system in June 2021 and is working with Clifton to establish scheduled operations. Based on limited analytical results and IES's assessment, the AOSS can be managed to provide design level of treatment for the existing sewage flows. System Redundancy and Alarms The current AOSS flows by gravity through the treatment system to the effluent storage tanks that can store nearly one day of flow. The disposal system has duplex effluent pumps allowing it to be fully functional with one pump out of service. Float switches in the effluent tanks send high level indicator to the control panel that has an audible and visual alarm system. At alarm high level, the effluent tanks have an additional four hours of storage providing time to respond and address the conditions. Future expansions will include redundant pumps for critical locations and high alarms for tanks with effluent filters and/or pumps. The control panels will likely be fitted with remote alarming capability so that operations staff can receive alarms via cellular phones. Intended Expansion Overview IES understands proposed expansions for the Clifton Inn site to be as follows: • Permitted restaurant capacity of 80 seats (current permitted capacity is 52 seats) • Convert existing event space to a permanent 75-person day event center. • Add additional guest rooms to bring total up to 50 including 15 existing rooms. Minimum Expansion— Improvements to Existing System and added Event Center The existing AOSS serving the Inn building could be improved and modified to handle more flow using the existing disposal system. IES believes a reasonable minimum expansion would be to upgrade this system to bring permitted restaurant capacity to 80 seats and handle sewage from the proposed 75 person event center. Treatment System Modifications The existing restaurant and inn are served by existing septic tanks under the porch that provide pretreatment. The septic tanks are not equipped with effluent filters. An additional septic tank with effluent filter will be added to reduce loading on the FAST system. A septic tank and pump tank will be added for a new, small, Event Center which is currently served by portable bathrooms. Septic tank effluent will be pumped to the to an upgraded FAST - treatment system. A flow equalization tank will be installed to reduce peak weekly flows. To improve nitrogen removal and treatment to meet effluent limits, a nitrification system needs to be added. IES recommends an OSI AdvanTex textile trickling filter by Orenco Systems Inc. (OSI). We calculate that one OSI AdvanTex AX100 pod would need to be installed. The existing FAST tank could be repurposed as a recirculation tank. Inboden Environmental Services Inc. (540) 477-3300 2 of 6 Clifton Inn and Collin Farm Onsite Wastewater Management Preliminary Capacity Evaluation Inboden Environmental Services, Inc. (IES) estimated influent flow, concentrations, and loading at average and peak occupancies. The population and flow rate assumptions and computed flows were compared with water usage data to verify appropriateness of our assumptions. Therefore, peak daily flow is: 2,220 gpd. With the addition of 7-day flow equalization, the weekly average flow is 1,350 gpd. A minimum 5,300-gallon working volume is required. IES has examined the Equalization volume for a second scenario based on full build -out of additional guest rooms and event space. The equalization tank can be sized for full build -out to avoid the need to add further separate tankage later. Minimum Scenario - Dispersal System Design Effluent could be managed using the existing disposal system consisting of drip dispersal and gravity drainfields. Based on TL-2 effluent and an application rate of 0.167 gal/day per square foot, the minimum required active adsorption area is 12,000 W. Based on record documents provided to IES, approximately 20,000 square feet of drip dispersal area and 11,300 square feet of gravity dispersal area are currently installed on site. It is not clear to IES whether there are any existing reserve drainfield areas. If additional area is required, IES has preliminarily identified at least 36,000 square feet of additional suitable soil area. This area would have to be confirmed with additional soil evaluations. A Nitrogen Dilution Management Area (NDMA) is the area surrounding and including the disposal area where rain fall will infiltrate the soil and dilute nitrogen entering the groundwater from the disposal system. The predicted effluent and dilution water should have less than 5 mg/L total nitrogen (TN) at the down -gradient limit of the project boundary. With an effluent of 20 mg/L, an area of 3.42 acres is required. IES identified sufficient area up -slope and down -slope of the drip dispersal area to meet this requirement. Up to 4.02 acres are available. Build -out Expansion — Minimum Scenario plus New Lodging and Event Center In this scenario the existing AOSS would be expanded and upgraded to accommodate the 75- person Event Center, the 80-seat restaurant and 35 additional guest rooms. IES estimated influent flow, concentrations, and loading at average and peak occupancies. Expansion Overview An equalization tank would be installed to balance out weekend flows with lower weekday flows. The calculated equalization volume required for 7-day flow equalization of all flow on the site is 9,500 gallons. Equalized flow to the treatment and disposal system is 4,000 gpd. With improved effluent quality, the existing drainfield will likely have capacity for the full flow with minimal improvements and modifications. The upgraded and expanded AOSS would consist of the following components: 1. Septic tank(s) with effluent filters for all new wastewater flows. 2. A new septic tank with effluent filter for the existing wastewater flows (same as in the minimum scenario) 3. An equalization tank sized for both the new and existing wastewater flows per above. 4. A mixed Pre -Anoxic tank. 5. An aerobic Membrane Bioreactor Inboden Environmental Services Inc. (540) 477-3300 3 of 6 Clifton Inn and Collin Farm Onsite Wastewater Management Preliminary Capacity Evaluation 6. A polishing denitrification stage 7. A new control panel. 8. The existing effluent pump tank and pumps would be utilized. 9. A small equipment building with controls, storage, chemical feed, aeration blowers, flow meters, and effluent filter system sized for full build -out. 10. The existing drip dispersal system with minimal modifications and repairs (see below). Build -out Expansion - Dispersal System Design Effluent could still be managed using the existing subsurface drip dispersal System. But a reserve area would need to be established and permitted. Based on high quality (TL-3) effluent and an application rate of 0.167 gal/day per square foot, the required active drip disposal area is 20,000 112. Based on an application rate of 0.17 gal/day per square foot, the required active gravity disposal area is 11,000 W. Based on record documents provided to IES, approximately 20,000 square feet of drip dispersal area and 11,300 square feet of gravity dispersal area are currently installed on site. It is not clear to IES whether there are any existing reserve drainfield areas. If additional area is required, IES has preliminarily identified at least 36,000 square feet of additional suitable soil area. This area would have to be confirmed with additional soil evaluations. With 4.02 acres available to serve as the Nitrogen Dilution Management Area (NDMA), system effluent TN must be less than 16 mg/L to meet 5 mg/L total nitrogen (TN) at the project boundary. IES identified sufficient area up -slope and down -slope of the drip dispersal area to meet this requirement. Appendix A includes a concept drawing of the disposal area and NDMA. COLLINA FARM EXPANSION SCENARIOS The Collina Farm property currently has only the existing Collina Farm guest house served by an OSI AdvanTex system with drip disposal. IES believes that the AOSS is effective and may have some additional capacity. If additional wastewater generating activities are proposed, IES recommends the current flows and loading to the system be evaluated. Therefore, the existing AOSS at Collina Farm was not considered in this evaluation. IES examined two scenarios for the development of the Collina Farm property. The minimum development scenario would involve installing only enough treatment and disposal infrastructure for the Event Center at maximum guest count of 285. If desired, certain tanks and elements could be sized to also accommodate future expansion. The full build -out Scenario is defined as 15 additional guest rooms and a 300 guest event capacity with 15 staff. The owner may elect to immediately install the full build -out and realize some savings by avoiding costs of a contractor remobilizing and re -excavating some piping to add components. Minimum Scenario — Events Center Only Design Summary The minimum scenario would be able to serve an Event Center for 285 guests and 15 staff. Equalized flow to the treatment and disposal system is 1,350 gpd. The new AOSS would consist of the following: 1. Septic tank(s) with effluent filter for the Event Center only. 2. A flow equalization tank. Inboden Environmental Services Inc. (540) 477-3300 4 of 6 Clifton Inn and Collin Farm Onsite Wastewater Management Preliminary Capacity Evaluation 3. A Recirculation tank with a nitrate recycle pump 4. A single OSI AdvanTex AX100 unit 5. Effluent pump tank with pumps 6. A control panel 7. A small structure with control system, flow meters, and effluent filter system. 8. Drip dispersal system (see below). Minimum Scenario - Dispersal System Design Effluent will be disposed in a new subsurface drip dispersal system. IES has preliminarily identified up to 30,000 W of total suitable area for a Drip Dispersal system area and reserve area (See drawings of approximate areas on imagery in Appendix A.) Further soil evaluations with Soil Profile Descriptions (SPDs) will need to be performed by a qualified professional to confirm the type and extent of the suitable soils. Based on an application rate of 0.25 gal/day per square foot, the minimum required active adsorption area is 5,400 fl2. A replacement area at least equal to this area must also be reserved. IES. Note that the proposed disposal area application rate will have to verified with further evaluation during the design and permitting process. The Nitrogen Dilution Management Area (NDMA) required to meet 5 mg/L total nitrogen (TN) at the project boundary with an effluent of 20 mg/L is 2.3 acres. IES identified sufficient area up - slope and down -slope of the drip dispersal area to meet this requirement. Up to 3.56 acres are available. Build -out Scenario - New Events Center and Cabins/Lodging Design Summary This scenario would accommodate wastewater flow from the Event Center with 300 guests and 15 staff and 15 two -person bedrooms in cabins/glamping facilities. Equalized flow to the treatment and disposal system is 2,350 gpd. The new AOSS would consist of the following: 1. Septic tank(s) with effluent filter for the Event Center and cabins/glamping units. 2. An equalization tank. Since the AOSS will require total nitrogen reduction, an additional 1,000-gallon anoxic resident volume for denitrification will be included (the pump submergence volume is included in this value). Therefore, the total equalization tank size would be 6,500-gallons. 3. A Recirculation tank with a nitrate recycle pump 4. Two OSI AdvanTex AX 100 unit (connections can be provided for a second unit to be added later) 5. Effluent pump tank with pumps 6. A control panel. 7. A small equipment building with controls, storage, chemical feed, a ventilation and odor control system, flow meters, and effluent filter system. 8. Drip dispersal system (see below). Build -out Scenario - Dispersal System Design Effluent will be managed with a subsurface drip dispersal system. IES has preliminarily identified up to 30,000 square feet of total suitable area for a Drip Dispersal system area and reserve area (See drawings of approximate areas on imagery in Appendix A). Further soil Inboden Environmental Services Inc. (540) 477-3300 5 of 6 Clifton Inn and Collin Farm Onsite Wastewater Management Preliminary Capacity Evaluation evaluations with Soil Profile Descriptions (SPDs) will need to be performed by registered professional to confirm the quality and extent of the suitable soils. Based on an application rate of 0.25 gal/day per square foot, the minimum required active adsorption area required is 9,400 W. A replacement area at least equal to this area must also be reserved. Again, the proposed disposal area application rate will have to verified with further evaluation during the design and permitting process. With 3.67 acres available to serve as the Nitrogen Dilution Management Area (NDMA), effluent TN must be less than 18 mg/L to meet 5 mg/L total nitrogen (TN) at the project boundary. IES identified sufficient area up -slope and down -slope of the drip dispersal area to meet this requirement. LIST OF [APPENDICES Appendix A: Conceptual Drainfield Areas and Nitrogen Dilution Management Areas for Clifton Inn and Collina Farm Inboden Environmental Services Inc. (540) 477-3300 6 of 6 COLLINA FARM BUILDING NITROGEN DILUTON MANAMENT AREA (NDMA) - 160,000 SOFT PRELIMINARYILY IDENTIFIED SUITABLE DRIP DISPOSAL AREA - 28,000 SQFT Ste. N � -,� t APPENDIX A - COLLINA FARM POTENTIAL DRAINFIELD AREAS NOTE THAT FULL SOIL EVALUATIONS BY A REGISTERED PROFESSIONAL WILL NEED TO BE PERFORMED TO CONFIRM THE EXTENT AND QUALITY OF THE SOILS. INBODEN ENVIRONMENTAL SERVICES July 12, 2021 Y11 0, 0