Technical Services to Develop the Partridge Lake Watershed Restoration Plan - Issued by the Town of Littleton, NH

1 REQUEST FOR QUALIFICATIONS FOR TECHNICAL SERVICES TO DEVELOP THE PARTRIDGE LAKE WATERSHED RESTORATION PLAN FOR THE TOWN OF LITTLETON AND THE PARTRIDGE LAKE PROPERTY OWNERS ASSOCIATION Contact: Mike Welch, NCIC Senior Project Manager for Littleton, New Hampshire Date of Issue: April 1, 2020 Submission Deadline: April 17, 2020, 4:00 PM I. INTRODUCTION Partridge Lake, located in Littleton, New Hampshire continues to experience an increasing number of cyanobacteria blooms coupled with decreased lake clarity, increased chlorophyll-a concentrations, anoxic conditions in the water column that fuels, excessive, internal nutrient loading from phosphorus. Because some forms of cyanobacteria are toxic to people as well as animals, the blooms have resulted in swimming advisories to protect the public and Partridge Lake is now on the New Hampshire Department of Environmental Services’ 303(d) list as impaired for Primary Contact Recreation (swimming) due to the cyanobacteria blooms. This project

will develop a revised watershed-based plan for Partridge Lake that meets the United States Environmental Protection Agency (USEPA) requirements for nine-element (a-i) watershed-based plans. The revised Partridge Lake Restoration Plan will build from and incorporate data, information, and recommendations from the Partridge Lake and Watershed Diagnostic Study (NHDES 2005) and the Partridge Lake Watershed Based Plan (Gomez and Sullivan 2008) with the goals of reversing the documented, decreasing lake quality trends, eliminate toxic algal blooms, and to seek a significant reduction or elimination of external and internal phosphorus loading to Partridge Lake. This project will be funded by a NHDES Clean Water State Revolving Fund Loan to be awarded to the Town of Littleton, NH. Photo courtesy of Google Earth 2020 2 II. PROJECT DESCRIPTION In 2008, the Partridge Lake Watershed Based Plan was completed to serve as a planning tool for the members of the Partridge Lake Watershed Partnership and municipal officials to identify watershed and in- lake pollutant load reduction and water quality goals, and to outline future planning, scheduling, and additional funding necessary to implement measures that will meet the water quality goals for Partridge Lake. The 2008 Watershed-based Plan (WBP) built upon the findings and recommendations presented in the Partridge Lake Littleton, New Hampshire Lake and Watershed Diagnostic Study (NHDES 2007) and set a goal of reducing external or watershed phosphorus loads by 25-30 percent. Achieving that goal would have resulted in an in-lake phosphorus concentration of approximately 11 µg/L (current surface layer phosphorus values range from 12 µg/L to 18 µg/L) based upon watershed management measures being implemented from the WBP suite of recommendations. However, those actions would not address the significant concentrations of phosphorus introduced to Partridge Lake each year from internal loading as evidenced by the summer, hypolimnetic mean phosphorus value of 293 µg/L. The internal loading of phosphorus in Partridge Lake exceeds all external sources of phosphorus combined by a factor of three. It is clearly evident that in order to achieve any in-lake water quality goals established for Partridge Lake, a combination of watershed-based and in-lake restoration measures will have to be proposed, evaluated, and incorporated into the Partridge Lake Watershed Restoration Plan for future implementation. This project leverages existing phosphorus source identification and loading analyses presented in both the Partridge Lake Littleton, New Hampshire Lake and Watershed Diagnostic Study and the Partridge Lake Watershed Based Plan (Appendices A and B) to develop the elements required for future implementation funding (USEPA Section 319 Clean Water Act) consideration of a USEPA watershed-based plan (https://www.des.nh.gov/organization/divisions/water/wmb/was/wbp_section319_guidance.htm) through NHDES Watershed Assistance Grants. Additionally, the project will “cross-walk” the previous study and plan, develop alternative analyses for individual subsurface disposal systems and municipal sewer relative to cost/benefit, study lake sediments and in-lake phosphorus concentrations at fully-mixed conditions to develop in-lake treatment recommendations/options, and calibrate lake response models respectively. The outcome of this project is the development of the Partridge Lake Watershed Restoration Plan that incorporates the nine, key elements (a-i) for watershed-based plans as required by the USEPA and NHDES. The completed plan will advise in-lake and watershed management and restoration actions for a minimum of ten years. It is expected that the plan will contain a broad range of feasible approaches, stakeholder commitments, and identified funding sources to implement watershed and in-lake phosphorus load reduction management and/or restoration measures. A summary of the USEPA mandatory, key elements (a-i) are presented below along with descriptors of how the proposed scope of work and professional services solicited with this RFQ will integrate with previous efforts in the Partridge Lake watershed. The Nine Elements for Watershed-based Planning required by the USEPA and NHDES a. An identification of the causes and sources or groups of similar sources that will need to be controlled to achieve the load reductions estimated in this watershed-based plan (and to achieve any other watershed goals identified in the watershed-based plan), as discussed in item (b) immediately below. Sources that need to be controlled should be identified at the significant subcategory level with estimates of the extent to which they are present in the watershed. – The Partridge Lake Littleton, New Hampshire Lake and Watershed Diagnostic Study and the Partridge Lake Watershed Based Plan provide two compendiums of information that will be reviewed and integrated into the development of the Partridge Lake Watershed 3 Restoration Plan. Internal phosphorus loading data acquisition and analyses will be a focus of the current scope of work associated with this key element. b. An estimate of the load reductions expected for the management measures described under paragraph (c) below (recognizing the natural variability and the difficulty in precisely predicting the performance of management measures over time). Estimates should be provided at the same level as in item (a) above (e.g., the total load reduction expected for stormwater BMPs, septic system upgrades, in-lake treatment). c. A description of the NPS management measures that will need to be implemented to achieve the load reductions estimated under paragraph (b) above (as well as to achieve other watershed goals identified in this watershed-based plan), and an identification (using a map or a description) of the critical areas in which those measures will be needed to implement this plan. – Identification of NPS management measure gaps in previous studies and plans will be carried out by the consultant. New BMP technologies will be recommended and in-lake treatments considered through cost/benefit analyses. d. An estimate of the amounts of technical and financial assistance needed, associated costs, and/or the sources and authorities that will be relied upon, to implement this plan. – The consultant will review past estimates for technical and financial assistance needed within the context of the Partridge Lake Littleton, New Hampshire Lake and Watershed Diagnostic Study and the Partridge Lake Watershed Based Plan. Current sources of financial assistance, permits and permission required, and up to date cost estimates will be generated for inclusion in the Partridge Lake Watershed Restoration Plan. e. An information/education component (ADA compliant where appropriate) that will be used to enhance public understanding of the project and encourage their early and continued participation in selecting, designing, and implementing the NPS management measures that will be implemented. – Consultant will work with the PLPOA, Town of Littleton, NHDES, etc. to build upon existing efforts and incorporate various forms of social media and other outreach platforms available to engage and maintain watershed- based awareness and commitments among stakeholders and the general public that interact with Partridge Lake. f. A schedule for implementing the NPS management measures identified in this plan that is reasonably expeditious. – The consultant will review previous studies and watershed plan documents to determine goals achieved to date and bring forward those goals in need of implementation and pair them with newly identified goals projected out ten years. g. A description of interim, measurable milestones for determining whether NPS management measures or other control actions are being implemented. – In the Partridge Lake Watershed, these will be a combination of BMPs in the ground, pollutant load estimates achieved, in-lake treatment, and water quality improvements measured through continued participation by the PLPOA with NHVLAP. h. A set of criteria that can be used to determine whether loading reductions are being achieved over time and substantial progress is being made towards attaining water quality standards and, if not, the criteria for determining whether this watershed-based plan needs to be revised. i. A monitoring component to evaluate the effectiveness of the implementation efforts over time, measured against the criteria established under item (h) immediately above. 4 III. BACKGROUND The project deliverable will be a USEPA “a –i” compliant watershed restoration plan for Partridge Lake in Littleton, New Hampshire. The restoration plan will also fulfill several recommendations in both the Partridge Lake Littleton, New Hampshire Lake and Watershed Diagnostic Study and the Partridge Lake Watershed Based Plan. Both watershed towns of Littleton and Lyman and the Partridge Lake Property Owners Association (PLPOA) would benefit from development of a watershed restoration plan for Partridge Lake to direct efforts toward the restoration of designated uses (swimming) and public health and safety relative to the elimination of toxic, algal blooms in Partridge Lake. The desired environmental outcome of restoration efforts is a reduction in the frequency and intensity of hepatotoxic cyanobacteria blooms, resulting in Partridge Lake’s removal from the 303(d) list of impaired waters for New Hampshire. Success will be measured through on-going water quality monitoring of Partridge Lake by the PLPOA and their continued participation with the New Hampshire Volunteer Lake Association (VLAP). Partridge Lake is a naturally occurring, mesotrophic lake located within the Town of Littleton, Grafton County, New Hampshire. The lake is impounded at the southwest end by a three-foot high concrete dam and has a surface area of 104 acres, a perimeter of 2.8 miles, a maximum depth of 50 feet, and a water volume totaling 85,955,900 cubic feet. The Partridge Lake watershed spans 896 acres and lies predominantly within Littleton with a small portion of watershed area situated in the Town of Lyman, New Hampshire. There are five, perennial streams and several seasonal tributaries that deliver surface water to Partridge Lake from the watershed. Approximately 75 percent of the land use within the watershed is characterized as mixed forest. Residential development accounts for 8 percent of the watershed. Recently, the PLPOA acquired significant acreage within the watershed to protect it from future development. The Partridge Lake Littleton, New Hampshire Lake and Watershed Diagnostic Study and the Partridge Lake Watershed Based Plan discuss and recommend the watershed-based phosphorus reductions needed in the watershed to achieve in-lake concentrations sufficient for eliminating cyanobacteria bloom occurrences. However, over a decade has passed since those recommendations were presented, and although small-scale, stormwater best management practices (BMPs) and land conservation initiatives have been achieved by the PLPOA, all watershed-based plans are to be re-evaluated every ten years to assess progress toward achievement of established goals and/or to revise and update those plans. This project will look back at previously collected data, published studies and plans, consider recent data acquisition, and facilitate the monitoring and data analyses required to generate a watershed restoration plan for Partridge Lake that not only builds upon the findings and recommendations established in earlier efforts but generates new in-lake water quality goal targets and in-lake and watershed restoration recommendations and implementation schedules that reflect available technologies and resources now available to the PLPOA and other project and watershed stakeholders. 5 Figure 1. Partridge Lake Subwatersheds. Partridge Lake and Watershed Diagnostic Study, NHDES 2007 IV. SCOPE OF WORK The Town of Littleton and its project partners, New Hampshire Department of Environmental Services (NHDES) Nonpoint Source Management Program and the Partridge Lake Property Owners Association (PLPOA) seek an expert in watershed-based management and restoration plans, limnology, watershed, and in-lake treatment techniques and strategies to coordinate efforts associated with the development of the Partridge Lake Watershed Restoration Plan. The partnership formed to lead this project comprises a diverse group, with a wide range of relevant backgrounds and skills and who are committed to partnering with the individual, firm, or firms contracted to complete this scope of work. However, expertise relative to watershed modeling, in-lake response models, cost/benefit analyses, limnology, in-lake treatment technologies, and the development of in-lake water quality goals is sought along with the ability and commitment to draft and publish the final watershed restoration plan. The Town of Littleton, New Hampshire has applied for and received approval for a Clean Water State Revolving Loan for planning projects to hire an environmental consultant and or firm(s) to lead the watershed restoration plan development efforts for Partridge Lake. The consultant will work collaboratively with the Town of Littleton, the PLPOA and their partners to coordinate the development of the restoration plan and to complete the selected tasks in Table 1. 6 Table 1. Proposed Tasks and Anticipated Roles for Consultant and Project Partners Proposed Consultant Tasks Project Partner (Town of Littleton, PLPOA, and NHDES) Roles Objective 1: Site Specific Project Plan (SSPP) Deliverable 1: Completed SSPP to address NHVLAP sampling plan, assimilative capacity, watershed load, in-lake response modeling, and NPS load reduction management measures. Task 1: Prepare and submit draft SSPP for watershed- based plan development work for review and comment. Project partners review and comment. Send mark-up back to consultant. Task 2: Address draft SSPP comments and submit final SSPP to NHDES. Signatures on SSPP cover page Objective 2: Water quality data, Diagnostic Study, Partridge Lake Watershed Plan, and previous water quality target review, for assimilative capacity (phosphorus) development. Deliverable 2: Memo detailing the data and outcomes review of previous studies and the watershed- based plan for Partridge Lake, the calculation of the current assimilative capacity for phosphorus. Task 3: Gather all available water quality data and determine if acceptable for use in analysis of assimilative capacity. Work with consultant to identify historical water quality data and collect new data through NHVLAP Task 4: Determine the historical and current total phosphorus and chlorophyll-a levels for Partridge Lake. Provide historical water quality reports and studies to consultant Task 5: Determine the assimilative capacity of Partridge Lake for phosphorus and prepare summary of water quality criteria. Include examination of resulting chlorophyll-a and dissolved oxygen as it relates to existing impairments. Objective 3: Established water-quality goal for phosphorus in Partridge Lake. Deliverable 3: Documentation and technical guidance for the process required for formally arriving at the water-quality goal for phosphorus and setting the goal through cooperation with project partners. Task 6: Establish process for determining the water quality goal for phosphorus. Guide project partners to collect ice-out and sediment samples to inform this process and modeling efforts. Review previous WBP process to establish a goal, update, and present results to project partners. Establish Water Quality Goal Committee and work with consultant to develop current goal-setting process and final phosphorus goal. Collect in-lake and sediment samples. Task 7: Facilitate meeting among project partners to formally adopt the water quality goals for Partridge Lake Provide support for meeting planning, hosting, and facilitation. Objective 4: Confirmed historical pollution sources, identification of current and future sources, and incorporation of internal phosphorus loading as a quantified pollution source. Deliverable 4: Technical memo identifying historical, current (including in-lake internal loading) and future pollution source loads by land use type and source group by subwatershed for each parameter. Refined/revised pollution source loads for each subwatershed based upon site-specific knowledge using field, ground-truthing methods. 7 Task 8: Determine annual pollution source loads for the watershed using the ENSR-developed Lake Loading Response Model (LLRM) or other approved method as detailed in the SSPP. Use aerial photography and Landsat imagery to characterize the watershed (NOAA; C-CAP; NH GRANIT mapper, etc.). Submit summary memo of current annual pollution source load estimates. Task 9: Conduct watershed pollutant source, land use and updated septic survey to identify and document potential pollution sources and ground-truth the available imagery. Work with consultant to acquire historical data and resources. Task 10: Estimate in-lake phosphorus concentration and associated chlorophyll-a concentration, Secchi transparency and probability of algal blooms using in-lake response model(s) reference in the approved SSPP. Include determination of internal loading contribution. Task 11: Complete watershed build-out analysis. Town of Littleton and PLPOA assist with data acquisition. Task 12: Run modelling scenarios to predict future pollutant loading, including natural background, build-out under current zoning, near-term development, future development, and others to meet water quality goals under those scenarios. Objective 5: Estimated pollution reductions and actions needed to maintain the water quality goal and future watershed conditions of Partridge Lake in Littleton, NH. Deliverable 5: Technical memo describing and prioritizing the NPS management measures that will be used to achieve the load reduction estimated, as well as other watershed goals identified in the watershed-based plan, and identification of the critical areas where those measures will be needed to implement the plan. Task 13: Determine pollutant load reductions needed in order to achieve water quality goals. Task 14: Review and revise (as necessary) best management practice (BMP) recommendations from 2008 watershed-based plan. Identify new locations needing BMPs, and recommend new technologies to achieve pollutant load reductions sufficient to achieve goals. Work with consultant to review implementation actions achieved since 2008 in watershed, land-use and ownership changes, willing project partners for BMP installs etc. Task 15: Provide conceptual BMP designs and costs for each identified, watershed NPS pollutant reduction site. Provide information relative to property ownership and potential for letters of commitment to have BMPs installed on private properties. Task 16: Produce an alternatives analysis for in-lake treatment options relative to phosphorus inactivation/sequestration/filtration etc. that includes costs estimates needed to achieve water quality goal. NHDES representatives will work with consultant relative to in-lake treatment policies and procedures within the agency. Task 17: Estimate pollutant load reduction attributable to each site specific, watershed-based BMP and in-lake treatment method(s). Objective 6: A sustainable information/education strategy (ADA compliant) that will be used to enhance stakeholder understanding of and investment in the Partridge Lake Restoration Plan and encourage early and continued participation in selecting, designing, and implementing the NPS management measures that will be implemented. 8 Deliverable 6: An education/outreach and social media plan that runs concurrently with development of the Watershed Restoration Plan and throughout the ten-year implementation period. This will be a “living and dynamic” platform/document accessible in both digital and hard copy formats (ADA compliant). Task 18: Compile and evaluate work completed in previous watershed-based plan for Partridge Lake to form strategy for existing education and outreach plan. The PLPOA will assist consultant with information gathering and progress to date on previous objectives in the watershed-based plan from 2008. Task 19: Work with PLPOA, Town of Littleton, and NHDES Education/Outreach Coordinator to build education and outreach strategy for Partridge Lake Watershed Restoration Plan. Objective 7: Publish the Partridge Lake Watershed Restoration Plan - Littleton, NH Deliverable 7: An updated, revised, and fully, USEPA-compliant (a-i) watershed-based plan that incorporates watershed and in-lake nutrient sources and measures, costs, and resources to control them has been developed, submitted to, and subsequently approved by NHDES and the USEPA. Task 20: Compile work completed in above tasks into a draft Partridge Lake Watershed Restoration Plan and distribute to project partners for review and comment. Project partners perform a timely review and provide comments by requested deadlines. Task 21: Incorporate comments from project partners on DRAFT WRP, make revisions, and prepare for public meeting to present DRAFT Partridge Lake WRP. Task 22: Participate in public meeting to present DRAFT Partridge Lake Watershed Restoration Plan, incorporate public comments into DRAFT, and develop final WRP. Logistical management and co- facilitation of meeting by project partners. Task 23: Submit final Partridge Lake Watershed Restoration Plan to Town of Littleton and the PLPOA. 9 V. PROJECT SCHEDULE It is expected that the consultant’s work on this project will begin in early summer 2020 and continue until early 2022. It is understood that final scheduling will depend upon the agreed scope of services and timeline between the selected consultant and the Town of Littleton and the need to collect and analyze sufficient environmental data (ice-out, fully mixed lake condition phosphorus and sediment samples) required for model calibration and in-lake treatment dosing and cost estimates, etc. VI. REQUIRED QUALIFICATIONS SUBMISSIONS Qualification packages shall include the following components: 1. Name, address, brief history, and description of the firm, including qualifications. 2. Related projects, areas of expertise, and experience. a. Include a description of other watershed-based planning and/or implementation projects this firm has completed in the last ten years. b. Provide firm expertise in the realm of lake biology, limnology, and in-lake treatment recommendations for internal nutrient loading in the northeastern, United States. c. Provide a list of references including names, titles, and contact information for recent projects completed in New England. 3. Description of the firm’s approach to performing the tasks detailed in the Scope of Work, including a timeline, recommended adjustments, and discussion of the relative effort anticipated to be expended on each Objective and Task. 4. A list of any additional services not included in this RFQ that you recommend the Town of Littleton and the PLPOA consider in order to achieve the most effective Watershed Restoration Plan for Partridge Lake, Littleton, New Hampshire. Responses should demonstrate and document that the individual/firm has the professional experience to proceed with the work tasks as described in the Scope of Work in this RFQ. A complete and timely submittal as described in this RFQ is required in order to be considered. VII. SELECTION CRITERIA Selection will be based on the assessment of the qualifications package to meet the following criteria. 1. Specialized Experience of the Project Team (40%) a. Overall experience directly related to the successful completion of similar watershed-based planning projects that include incorporation of USEPA’s Nine Elements (a – i), data analysis, monitoring, outreach, and working with diverse stakeholders to achieve project goals b. Understanding of and demonstrated experience with limnology and technologies relative to addressing internal nutrient loading through a variety of treatment measures available in New England and/or the Northeastern U.S. c. Demonstrated ability to identify structural and non-structural BMPs and generate pollutant load analyses for BMPs, and conceptual implementation guidance (design, costs, etc.) for BMPs d. Demonstrated ability to complete work within similar schedules as the one presented in this RFQ 2. Project Personnel (30%) a. Principal team members’ roles and participation levels, availability, qualifications and experience, and supporting team members, including subcontractors 3. Project Approach (30%) a. Demonstrated strong understanding of the scope of work, project schedule, and expected deliverables outlined in the RFQ 10 Note: Do NOT provide a cost estimate, fee schedule, or any type of price proposal at this time After the qualifications-based ranking and selection process is complete, the Town of Littleton will request from the highest-ranked consultant a task-based cost proposal. The Town will proceed with contract negotiations with that consultant. If the parties cannot come to terms, The Town will request from the second-ranked consultant a task-based cost proposal and follow the same procedure, working with each of the next-ranked qualified candidate(s) in order of their scores, until a contract has been successfully negotiated. VIII. REQUEST FOR QUALIFICATIONS QUESTIONS Any questions about this RFQ raised by an individual/firm will be answered in a summary digest. The summary digest will be provided to those who contact The Town of Littleton and request to be put on an email list to receive the digest. The cut-off date for questions and requests to be put on the email list to receive the digest summary of questions and answers is April 9, 2020. Please email Mike Welch, NCIC Senior Project Manager for Town Littleton, New Hampshire, at mwelch@ncic.org to ask a question and/or to be put on the email list to receive responses. The summary digest will be provided via email on April 13, 2020 to all consultants on the response list. IX. TIMELINE April 1, 2020 Request for Qualifications release April 9, 2020 Deadline for submittal of questions on this RFQ (4:00 p.m.) April 13, 2020 Questions and answers digest distributed to consultants April 17, 2020 Deadline for receipt of qualification packages to this RFQ (4:00 p.m.) April 24, 2020 Anticipated final selection of contractor and notification to all firms. Due Date: Complete submittals should be sent by email in digital format (PDF) to Mike Welch, NCIC Senior Project Manager for Town Littleton, New Hampshire, at mwelch@ncic.org by 4:00 p.m. EST on April 17, 2020. Please enter Partridge Lake RFQ Submittal as the subject line. X. DISCLAIMER This RFQ does not commit the Town of Littleton to award a contract or pay any costs incurred during the preparation of any submittal. The Town of Littleton reserves the right to reject any or all of the submittals while adhering to applicable laws. To participate in the project and receive payment, the selected firm will be required to enter into a contract which stipulates that the contractor is eligible to receive Federal funding and certifies compliance with State and Federal rules related to grant-funded projects. 11 Appendix A Partridge Lake Littleton, New Hampshire Lake and Watershed Diagnostic Study (NHDES 2007) 12 Appendix B Partridge Lake Watershed Based Plan (Gomez and Sullivan 2008) Partridge Lake Watershed Based Plan Prepared for: Partridge Lake Property Owners Association Littleton, New Hampshire Prepared by: February 2008 This document was developed through collaboration with the New Hampshire Department of Environmental Services and Partridge Lake Property Owners Association to guide the nonpoint source pollution reduction efforts to improve the water quality of Partridge Lake by reducing phosphorus and eliminating cyanobacteria. This restoration plan follows EPA Section 319 watershed plan guidelines and addresses each of the nine required components. Partridge Lake Watershed Based Plan 2008 i TABLE OF CONTENTS List of Tables and Figures............................................................................................................................ iii Executive Summary ....................................................................................................................................... i 1 Introduction........................................................................................................................................1-1 1.1 Purpose .....................................................................................................................................1-1 1.2 Plan Scope ................................................................................................................................1-1 1.3 Water Quality Objectives .........................................................................................................1-2 1.4 Watershed Description .............................................................................................................1-3 1.5 Prior Work ................................................................................................................................1-5 1.5.1 Volunteer Lake Assessment Program ..................................................................................1-5 1.5.2 DES Diagnostic Study..........................................................................................................1-5 2 Causes and Sources of Nonpoint Source Pollution............................................................................2-1 2.1 Phosphorus in Groundwater .....................................................................................................2-1 2.2 Stormwater Runoff ...................................................................................................................2-2 2.3 Shoreline and Beach Erosion....................................................................................................2-3 2.4 Internal Phosphorous Loading..................................................................................................2-4 2.5 Agricultural Operations ............................................................................................................2-4 3 Nonpoint Source Management Measures ..........................................................................................3-1 3.1 Groundwater BMPs ..................................................................................................................3-1 3.1.1 Homeowner Education.........................................................................................................3-1 3.1.2 Group Maintenance ..............................................................................................................3-2 3.1.3 Upgrade Individual Systems/Retrofits .................................................................................3-2 3.1.4 Community or Cluster System .............................................................................................3-3 3.2 Stormwater BMPs ....................................................................................................................3-3 3.2.1 Tributary BMPs....................................................................................................................3-4 3.2.2 Selected Subwatersheds/Tributaries...................................................................................3-12 3.2.3 Road BMPs ........................................................................................................................3-19 3.2.4 Shoreline BMPs .................................................................................................................3-22 3.3 Land Use, Protection, and Conservation ................................................................................3-23 3.4 Agricultural Operations and Pasture Management.................................................................3-24 3.5 Residential Practices through Education ................................................................................3-27 3.6 Alum Treatments ....................................................................................................................3-27 3.7 Summary of Recommendations..............................................................................................3-28 4 Estimated Load Reduction from Planned Management Measures ....................................................4-1 4.1 Groundwater .............................................................................................................................4-1 4.2 Stormwater BMPs ....................................................................................................................4-3 4.2.1 Stormwater Retrofits ............................................................................................................4-3 4.2.2 Road Ditch improvements....................................................................................................4-4 4.2.3 Street Sweeping....................................................................................................................4-4 4.3 Land Use Changes ....................................................................................................................4-5 4.4 Internal Loading Treatment ......................................................................................................4-5 4.5 Shoreline and Beach Improvements .........................................................................................4-5 4.6 Homeowner Education .............................................................................................................4-6 5 Technical & Financial Assistance Needed.........................................................................................5-1 5.1 Financial Assistance .................................................................................................................5-1 5.2 Technical Assistance ................................................................................................................5-2 6 Education and Outreach .....................................................................................................................6-1 6.1 Partridge Lake Watershed Partnership .....................................................................................6-1 6.2 Lake Guide ...............................................................................................................................6-1 6.3 Septic Survey............................................................................................................................6-1 Partridge Lake Watershed Based Plan 2008 ii 7 Implementation Schedule And Milestones to Measure Progress.......................................................7-1 8 Criteria to Determine Progress in Attaining Water Quality Standards & Load Reductions..............8-1 9 Monitoring Component......................................................................................................................9-1 10 Bibliography ....................................................................................................................................10-1 Appendix 1: 2007 Partridge Lake Septic Survey and Results. Appendix 2: Additional Specifications for Proprietary Stormwater BMPs. Appendix 3: Time of Concentration and Curve Number Calculations. Partridge Lake Watershed Based Plan 2008 iii LIST OF TABLES AND FIGURES Table 1-1: Characteristics of Partridge Lake, NH.....................................................................................1-4 Table 1-2: Lake Phosphorus Concentration as an Indicator of Trophic Status.........................................1-6 Table 2-1: Septic System Setback Distances in the Partridge Lake Watershed........................................2-2 Table 3-1: Comparison of Stormwater BMPs Considered for Phosphorus Removal...............................3-9 Table 3-2: Peak Flow and Runoff Volumes for Selected Tributaries to Partridge Lake. .......................3-10 Table 3-3: Comparative Costs of Selected BMPs for Partridge Lake Subwatersheds............................3-11 Table 4-1: Phosphorus Load Reduction Estimates for Clustered Septic System Improvements..............4-3 Table 4-2: Phosphorus Load Reduction Estimates for Stormwater Treatment Devices. ..........................4-3 Table 4-3: Phosphorus Load Reduction Estimates for Smaller Subwatersheds. ......................................4-4 Table 5-1: Estimated Financial Assistance Required for Partridge Lake BMP Implementation..............5-1 Table 7-1: Partridge Lake Watershed Based Plan Task/Milestone Schedule. ..........................................7-2 Table 7-2: Partridge Lake Phosphorus Reduction Implementation Summary..........................................7-3 Table 8-1: Water Quality Indicators to Determine Progress in Removing Lake from 303(d) List ..........8-2 Figure 1-1: Partridge Lake Watershed. .....................................................................................................1-8 Figure 1-2: Partridge Lake Subwatersheds. ..............................................................................................1-9 Figure 1-3: Soil Types in the Partridge Lake Watershed. .......................................................................1-10 Figure 1-4: Partridge Lake Watershed Topography................................................................................1-11 Figure 2-1: Partridge Lake Annual TP Loading per Subwatershed (based on 2000-2001 data). .............2-5 Figure 2-2: Agricultural Areas in the Partridge Lake Watershed. ............................................................2-6 Figure 3-1: Schematic of a Stormwater Wetland......................................................................................3-5 Figure 3-2: Example StormTreat System Installation. ..............................................................................3-6 Figure 3-3: StormFilter Schematic............................................................................................................3-7 Figure 3-4: Aqua-Filter Schematic. ..........................................................................................................3-8 Figure 3-5: Subwatershed J.....................................................................................................................3-15 Figure 3-6: Subwatershed D. ..................................................................................................................3-16 Figure 3-7: Subwatershed G. ..................................................................................................................3-17 Figure 3-8: Subwatershed A. ..................................................................................................................3-18 Figure 3-9: Potential Ditch Improvement Areas Along Partridge Lake Road. .......................................3-21 Figure 3-10: Areal Coverage of 2007 Septic Survey. .............................................................................3-25 Figure 3-11: Cross Sectional View of a Perched Beach. ........................................................................3-26 Partridge Lake Watershed Based Plan 2008 iv Acronyms and Abbreviations CN curve number CWA Clean Water Act DES New Hampshire Department of Environmental Services EPA United States Environmental Protection Agency ft feet gpd gallons per day ha hectare, a unit of area equal to 10,000 square meters, equivalent to 2.471 acres kg kilograms lbs pounds m meters mg/L milligrams per liter mg/m3 milligrams per cubic meter NPS nonpoint source PLPOA Partridge Lake Property Owners Association ppb parts per billion (equivalent to µg/L) ppm parts per million (equivalent to mg/L) Tc time of concentration TMDL Total Maximum Daily Load TP total phosphorus TSS total suspended solids µg micrograms VLAP Volunteer Lake Assessment Program Partridge Lake Watershed Based Plan 2008 i EXECUTIVE SUMMARY Recent water quality data and observations at Partridge Lake in Littleton, NH have indicated algae (cyanobacteria) blooms, decreased water clarity, increased chlorophyll a concentrations, and hypolimnetic (bottom layer) oxygen deficits. The blooms of cyanobacteria (Anabaena) have prompted the New Hampshire Department of Environmental Services (DES) to list Partridge Lake on the 2008 Draft 303(d) list of impaired waterbodies. To reverse decreasing water quality trends and eliminate cyanobacteria blooms, watershed and internal phosphorus loading to Partridge Lake must be reduced. To initiate the course of action for water quality improvements within Partridge Lake, the Partridge Lake Property Owners Association (PLPOA) applied to the DES in February 2006 for an EPA Section 319 Watershed Assistance and Restoration Grant. The grant application identified performance targets, milestones, and tasks required to remediate phosphorus loading within the watershed. Specifically, the PLPOA outlined the strategy it would implement prior to December 31, 2008 to address problems associated with stormwater runoff, septic systems, land use/development, and beach erosion that were contributing to the phosphorous loading and water quality problems within Partridge Lake. This Watershed Based Plan will serve as a planning tool for the members of the Partridge Lake Watershed Partnership and municipal officials to identify watershed and in-lake pollutant reduction and water quality goals, and outline future planning, scheduling, and additional funding necessary to implement measures that will meet the water quality goals for Partridge Lake. To improve water quality conditions in Partridge Lake, a goal of reducing external or watershed phosphorus loads by 25-30 percent has been established. In terms of actual loading this would translate into approximately 10.0 kg TP reduction annually, based on annual loading of 39.8 kg from surface and groundwater inputs (minus precipitation). This would result in an in-lake phosphorus concentration of approximately 11 µg/L as a future water quality goal. The current mean epilimnetic phosphorus concentration of Partridge Lake is 12 µg/L. The middle and lower layers of Partridge Lake, however, exhibit elevated phosphorus concentrations. To achieve the phosphorus load reductions, several different phosphorus sources within the Partridge Lake watershed would need to be addressed. The specific watershed actions that would lead to a 25-30 percent phosphorus load reduction include: • Implementing tributary, road, and shoreline best management practices (BMPs) to reduce sediment/nutrient loads from stormwater runoff; • Replacing old and failing septic systems that may be directly discharging to Partridge Lake; • Upgrading individual septic systems, by increasing the set-back distance to surface waters and constructing replacement septic systems where adequate soils with sufficient depth to bedrock and groundwater exist, to maximize phosphorus uptake by soils; and • Educating watershed residents on practices that they can implement to reduce stormwater runoff and septic-based phosphorus contributions to Partridge Lake. Upon implementation of the management measures to control watershed phosphorus loads, in-lake restoration may need to be considered to achieve the in-lake water quality goal. In addition to current watershed and in-lake restoration actions, future watershed actions such as zoning overlay and land conservation practices may be necessary to prevent an increase in phosphorus loads associated with development or redevelopment. As part of the Watershed Based Plan, the Partridge Lake Watershed Partnership completed a septic survey for lakefront properties and will begin implementing selected BMPs outlined in the management plan. Septic survey results were used to target specific areas that may be contributing groundwater phosphorus loading to the lake. BMP design and construction will occur during the summer of 2008. Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-1 1 INTRODUCTION 1.1 Purpose The purpose of this Watershed Based Plan is to outline a general strategy for the implementation of nonpoint source (NPS) pollution control measures in the Partridge Lake watershed to help restore the water quality of Partridge Lake, an impaired waterbody. Under the Environmental Protection Agency (EPA) National NPS 319 Program Guidance, States need a watershed-based plan meeting EPA guidance in order to use “incremental 319 funds” to implement management measures to help restore an impaired waterbody. The Partridge Lake Property Owners Association (PLPOA) has been actively monitoring the water quality of Partridge Lake for more than 17 years through the Volunteer Lake Assessment Program (VLAP). Recently, the volunteer lake monitors and biologists from the New Hampshire Department of Environmental Services (DES) have noted algae (cyanobacteria) blooms, decreased water clarity, increased chlorophyll a concentrations, and hypolimnetic (bottom layer) oxygen deficits in Partridge Lake. The blooms of cyanobacteria (Anabaena) have prompted the DES to list Partridge Lake on the 2008 Draft 303(d) list of impaired waterbodies. Partridge Lake is currently listed (2006 303(d) list) for dissolved oxygen impairment. To reverse decreasing water quality trends and eliminate cyanobacteria blooms, watershed and internal phosphorus loading must be reduced. The logical sequence for restoring a waterbody is to first address watershed phosphorus loading prior to addressing the internal phosphorus loading. To initiate the course of action for water quality improvements within Partridge Lake, the PLPOA applied to the DES in February 2006 for a Watershed Assistance and Restoration Grant. The grant application identified performance targets, milestones and tasks required to remediate Areas of Concern within the watershed that were identified in the Partridge Lake and Watershed Diagnostic Study (DES, 2007). Specifically, the PLPOA outlined the strategy it would implement prior to December 31, 2008 to address problems associated with stormwater runoff, septic systems, land use/development, and beach erosion that were contributing to the phosphorous loading and water quality problems within Partridge Lake. 1.2 Plan Scope One of the performance targets identified in the grant application was to develop a Watershed Based Plan that outlined remediation measures for phosphorous reduction within the Partridge Lake watershed. The Watershed Based Plan, discussed herein, was developed in accordance with DES guidelines and is structured to address the required elements defined in the EPA guidance document entitled, “Handbook for Developing Watershed Plans to Restore and Protect Our Waters.” This plan supplements the Partridge Lake and Watershed Diagnostic Study (DES, 2007) by further examining the causes and sources of pollution within the watershed, and outlining remediation measures and monitoring efforts that will be implemented to ensure that improvements in the water quality of Partridge Lake are attained. A description of the Partridge Lake watershed is also included, largely reiterated from DES, 2007. The scope of this plan describes recommended actions that can reasonably be accomplished through an on-the-ground effort within a ten-year timeframe (2007 to 2016) in the Partridge Lake watershed. This plan integrates the analysis and recommendations presented in the Partridge Lake Diagnostic Study (DES, 2007), which outlines the need for a reduction in watershed based sources of phosphorus in order to Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-2 address actual in-lake total phosphorus (TP) concentration and the potential in-lake treatment (to reduce internal loading). In order to track the implementation of this plan and to help measure progress towards achieving its goals and objectives, the recommendations are presented in a temporally phased approach. Throughout this plan, actions and goals will be referred to in three phases: • Phase 1 refers to the immediate and short-term actions associated with this plan; Phase 1 tasks should be completed by the end of 2008. • Phase 2 refers to mid-term actions and may require more detailed study or coordination. This phase generally refers to actions that should be performed from 2009 through 2011. • Phase 3 refers to longer term action and goals for which prerequisites are needed. For the purpose of this document, Phase 3 refers to activities in the watershed that may take place five to ten years from now. 1.3 Water Quality Objectives The primary goal of this plan is to remove Partridge Lake from the State’s 303(d) list of impaired waterbodies. To meet this goal, the initial objective of reducing external phosphorus loading to Partridge Lake has been established. This will in turn reduce or eliminate cyanobacteria blooms allowing the lake to meet New Hampshire’s Water Quality Standards. Through the initial phase of this project, the target for reduction of watershed inputs (from surface water and groundwater) of phosphorus is 25-30%. In terms of actual loading this would translate into approximately 10.0 kg TP reduction annually. This target was determined through discussions with DES personnel, and an evaluation of the modeling predictions (e.g., Vollenweider, Dillon-Rigler) presented in DES, 2007. The loading reductions would result in an in-lake phosphorus concentration of approximately 11 µg/L as a future water quality goal. The phosphorus load reduction and in-lake phosphorus water quality goal is based in part on an empirical method known as the Vollenweider Relationship, which predicts the lake’s trophic status (the degree of lake aging or nutrient status of a lake) as a function of the areal phosphorus loading. The model also predicts in-lake phosphorus concentrations. The relationship was developed by assessing a large number of lakes for which a linear relationship between the log of the phosphorus loading and the log of the ratio of the lake’s mean depth to hydraulic residence time was established. Using the characteristics of Partridge Lake, a phosphorus load reduction of 25-30% was proposed that will likely allow the lake to meet water quality goals by reducing in-lake phosphorus concentrations. The specific actions that will be investigated to achieve these water quality objectives include: • Implement Best Management Practices (BMPs) to reduce sediment/nutrient loads from stormwater runoff; • Replace old and failing septic systems and examine alternatives; • Educate watershed residents on practices that they can implement to reduce phosphorus contributions to Partridge Lake; and • Examine steps that can be taken to control the internal loading of phosphorus in Partridge Lake once the external sources of phosphorus are reasonably controlled. Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-3 1.4 Watershed Description Partridge Lake is a naturally occurring lake located within the town of Littleton, Grafton County, New Hampshire (Figure 1-1). The lake is impounded at the southwest end by a three foot high concrete dam and has a surface area of 104 acres (42.05 hectares), a perimeter of 2.8 miles (4,500 m), a maximum depth of 50 ft. (15.2 m), and a water volume totaling 85,955,900 cubic feet (2,434,000 m3). The lake characteristics are summarized in Table 1-1. For a comprehensive description of the watershed, refer to DES, 2007. The drainage area for Partridge Lake is approximately 1.33 square miles (344 hectares) and encompasses portions of the towns of Littleton and Lyman in northwestern New Hampshire. In addition to Partridge Lake, the watershed contains a few wetland areas, which comprise an area of approximately 22 acres. Precipitation, tributary flow, overland flow (not specific to any one tributary), and groundwater seepage constitute the hydrologic inputs to Partridge Lake. Tributaries include five year-round streams and several seasonal streams. The subwatersheds are presented in Figure 1-2. The outlet of Partridge Lake flows in a southwesterly direction from the lake and eventually enters Dodge Pond to the south. The climate of this region is characterized by moderately warm summers, cold, snowy winters, and ample rainfall, which is typically acidic. Generally, snow is present from mid-December to the end of March or early April. Ice-out for the lake usually occurs in mid-April. Partridge Lake is located in the EPA’s Nutrient Ecoregion 58 - Northeastern Highlands. The Northeastern Highlands comprise a relatively sparsely populated region characterized by nutrient poor soils blanketed by northern hardwood and spruce fir forests. Land-surface forms in the region consist of low mountains in the southwest and central portions to open high hills in the northeast. Many of the numerous glacial lakes in this region have been acidified by sulfur depositions originating in industrialized areas upwind from the ecoregion to the west. The range of reference conditions for total phosphorus in lakes in this ecoregion is 7-10 µg/L. For comparison purposes, the mean total phosphorus concentration in the metalimnion of Partridge Lake is 20 µg/L based on data collected since 1986. Partridge Lake is listed as a Warmwater Fishing body of water in the NH Atlas and Gazetteer and is listed by the NH Fish and Game Department as a suggested fishing location for chain pickerel, largemouth bass, northern pike, rock bass, and smallmouth bass in the Great North Woods Region of the State. The lake is predominately used by lake residents, transient boaters, and fishermen. There are three types of rock found in the Littleton area: granite, metamorphic rock (which often contain minerals such as feldspars, quartz, garnets, and graphite), and slate and sandstone. Soils within the watershed are comprised of a mix of Berkshire loams, Marlow and Peru fine sandy loams, and Tunbridge- Lyman rock outcrops (Figure 1-3). Loamy sand of the Colton, Adams, and Waumbek families, and Monadnock and Hermon soils are also found in the watershed. In general, soil permeability is rapid throughout the watershed. Depth to bedrock in most areas of the watershed is shallow, and ranges from 0.5 to 1.6 meters (1.6 to 5.2 feet). Depth to groundwater is 2 meters (6.6 feet) or greater in most areas of the watershed (DES, 2007). Approximately 75 % (711 acres) of the land use within the Partridge Lake watershed is characterized as mixed forest. Residential development comprises 71.8 acres (7.6 %) of the watershed area. Areas of low intensity residential development occur along most of the Partridge Lake shoreline. Development in the Partridge Lake watershed is generally characterized by seasonal cottages along the shoreline, with larger year round homes located farther back from the lake edge. Topography of the watershed is presented in Figure 1-4. Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-4 Table 1-1: Characteristics of Partridge Lake, NH. Parameter Lake Information / Morphometric Data Lake Name Partridge Lake Town Littleton County Grafton River Basin Connecticut Latitude 44o18’28”N Longitude 71o53’16”W Elevation (ft) 846 Shoreline Length (meters) 4,500 Watershed Area (ha) 344 (850 acres) Lake Area (ha) 42.05 (104 acres) Maximum Depth (m) 15.2 Mean Depth (m) 5.8 Volume (m3) 2,434,000 Areal Water Load (m/yr) 3.65 Flushing Rate (yr-1) 0.6 Phosphorus Retention Coefficient 0.71 Lake Type Natural with dam Source: DES, 2007 Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-5 1.5 Prior Work 1.5.1 Volunteer Lake Assessment Program New Hampshire’s Volunteer Lake Assessment Program (VLAP) is a cooperative program between the DES and lake residents and lake associations. The program was initiated in 1985 and serves a dual purpose by establishing a regular volunteer-driven lake sampling program to assist the DES in evaluating lake quality throughout the state, and by empowering volunteer monitors and lake residents with information about the health of their waterbody. This cooperative effort allows biologists and lake associations to make educated decisions regarding the future of New Hampshire’s lakes and ponds. Partridge Lake was added to VLAP in 1989 and the PLPOA has been actively monitoring water quality in the lake for over 17 years through this program. As part of this program, data is collected on parameters such as temperature, dissolved oxygen, chlorophyll a, E. coli bacteria, water transparency, turbidity, total phosphorous in the epilimnion (top layer), metalimnion (middle layer), and hypolimnion (bottom layer), species of phytoplankton, pH, acid neutralizing capacity, and conductivity. Data was collected from the lake and various tributaries by volunteer sampling three times in 2006 - once each in June, July, and August. An algal bloom was observed in November 2006; an additional water quality sample was collected from the lake deep spot at that time. Hypolimnetic TP ranged from 0.092 mg/L in June (under thermally stratified conditions) to 0.020 mg/L in November (under non-stratified conditions). Comparing the epilimnetic samples taken in August and November, TP increased from 0.007 mg/L to 0.026 mg/L. Chlorophyll a concentrations subsequently increased from 3.99 mg/m3 to 13.73 mg/m3. The data appear to confirm the theory that fall mixing is redistributing the phosphorus bound in sediments in the hypolimnion throughout the lake and likely triggering a surface algal bloom. According to VLAP monitors, late summer and early fall algal blooms have been observed over the past few years in the lake. These algal blooms, along with other observations of water quality such as decreases in Secchi depth readings, increases in chlorophyll a concentrations, and decreases in oxygen concentrations within the hypolimnion, led the DES to conduct a diagnostic study within the lake. 1.5.2 DES Diagnostic Study Due to declining water quality conditions observed through the VLAP, DES biologists conducted a 1-year diagnostic study of Partridge Lake from June 1, 2000 to May 31, 2001. The goals of this study were to gain more information about the lake and its watershed, to determine sources of phosphorous within the watershed, and to make recommendations for the overall enhancement and protection of Partridge Lake through watershed management and/or in-lake restoration. The study involved constructing a hydrologic and phosphorous budget, conducting an anonymous septic system survey, determining the lake’s trophic status, and evaluating a number of biological and physical parameters such as temperature and dissolved oxygen levels, pH and acid neutralizing capacity, conductivity, turbidity, phytoplankton communities, chlorophyll a, transparency, and the distribution of aquatic plants. The water budget quantified hydrologic inputs (e.g., precipitation, tributary, direct runoff and groundwater) and outputs (e.g., evaporation, outflow, and groundwater recharge) to determine the major hydrologic sources to Partridge Lake. Results of the analysis showed that inputs from overland runoff (including gauged and un-gauged tributaries) contributed the greatest quantity of water to Partridge Lake Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-6 (62 %), followed by groundwater inputs (24 %), and direct precipitation (14 %). Further analysis of the overland runoff revealed that sub-watersheds with year-round tributaries contribute the greatest source of overland flow to the lake (41 %), while those sub-watersheds with un-channelized inputs or seasonal inputs contributed a total of 21 % of the overland runoff. Of these tributaries, Tributary J was the largest contributor (34 %), followed by Tributary A (21 %), Tributary G (19 %), and Tributary H (15 %). Figure 1-2 shows a map of Partridge Lake Subwatersheds. The diagnostic study also quantified the phosphorous budget for Partridge Lake by multiplying measured total phosphorous (TP) concentrations by the respective hydrologic inputs and outputs. The analyses of external phosphorous inputs into Partridge Lake revealed that near-shore groundwater inputs represented the largest input of phosphorous (44% or 23.4 kg TP) during the study period followed by overland runoff (31% or 16.4 kg TP), and wetfall / dryfall precipitation (25% or 13.1 kg TP). The internal loading of phosphorous is also considered to be a significant bioavailable source during certain times of the year. DES noted that it is difficult to quantify the actual amount of phosphorus released into the water column from lake sediments; however, that does not underscore its importance. The total phosphorus range for the summer epilimnetic values for New Hampshire lakes ranges between 1 and 121 µg/L, with a median value of 12 µg/L. The total phosphorus concentration in the metalimnion (thermocline) layer also falls within the mean range, with a mean concentration of 20 µg/L, however this concentration is more conducive to fostering chlorophyll a production and algal blooms. In the bottom layer of the lake, or hypolimnion, the total phosphorus concentration is considered excessive, with a mean summer concentration of 293 µg/L (a concentration greater than 40 µg/L is classified as excessive by the DES). Generally, the in-lake total phosphorus concentration can be an indicator of its trophic status, as shown in Table 1-2. Trophic states of ponds can range within and between three basic categories: oligotrophic, mesotrophic, and eutrophic. In 2001, Partridge Lake received 11 trophic points and was classified as mesotrophic. The Dillon/Rigler Model classifies a lake as oligotrophic, mesotrophic or eutrophic by comparing calculated annual loadings with permissible annual loadings. These calculations were performed to determine Dillon/Rigler Trophic Status for Partridge Lake with and without internal loading. The solution of the Dillon/Rigler equation for Partridge Lake data shows the existing trophic status of the lake as oligotrophic if internal loading is not entered into the equation. A more realistic look at Partridge Lake, however, must take into account this internal source of phosphorus, and thus, based on this, the lake would then be classified as mesotrophic (DES, 2007). Table 1-2: Lake Phosphorus Concentration as an Indicator of Trophic Status. Phosphorus Concentration (µg/L) Trophic Category 10 Oligotrophic 10 - 20 Mesotrophic > 20 Eutrophic Analysis of the total phosphorous concentration data shows that as the summer progresses, internal phosphorus loading from the bottom sediments is a major contributor to the lake’s nutrient budget. During the summer, internal loading occurs when the hypolimnion loses oxygen. This lack of oxygen causes a chemical reaction in the sediments that ultimately results in the release of phosphorus into the water column (known as internal loading). For example, total phosphorous concentrations were greater than 200 µg/L during most of the summer sampling events in 2000. Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-7 Analysis of total phosphorous concentration within Partridge Lake since it was added to VLAP in 1989 demonstrates that concentrations within the hypolimnion are excessively high and have been consistently higher than those in the epilimnion. Moreover, these concentrations have been particularly elevated during the past 10 years and the internal loading phenomena described earlier is suspected to be the cause of the cyanobacteria blooms that have been observed in recent summers. Through review of the data collected during the diagnostic study, the DES determined that certain activities that were occurring within the watershed may be contributing to a decrease in water quality. The lake was classified as borderline between advanced mesotrophic and early eutrophic conditions, which indicates that the lake is showing signs of impact, and that the aging of the lake may be accelerated because of those impacts. DES documented certain activities around the watershed that may be contributing to decreases in water quality over time, and formulated a number of recommendations to help maintain the lake’s current trophic status and potentially increase the water quality through conscientious and proactive watershed management. These areas of concern are discussed in more detail throughout this plan. Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-8 Figure 1-1: Partridge Lake Watershed. Attached as .pdf Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-9 Figure 1-2: Partridge Lake Subwatersheds. Attached as .pdf Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-10 Figure 1-3: Soil Types in the Partridge Lake Watershed. Attached as .pdf Section 1 - Introduction Partridge Lake Watershed Based Plan 2008 1-11 Figure 1-4: Partridge Lake Watershed Topography. Attached as .pdf Section 2 - Causes and Sources of Nonpoint Source Pollution Partridge Lake Watershed Based Plan 2008 2-1 2 CAUSES AND SOURCES OF NONPOINT SOURCE POLLUTION Partridge Lake has been listed on the 2006 Draft 303(d) List as impaired due to dissolved oxygen conditions that lead to blooms of cyanobacteria. The suspected cause of these blooms is due to the internal nutrient loading of phosphorous during hypolimnetic anoxic events that occur within the lake. Partridge Lake is influenced by two distinct types of phosphorus loading that occur during certain times of the year: internal loading and external loading. Phosphorus is a key nutrient influencing plant growth in lakes. Soluble reactive phosphorus is the amount of phosphorus in solution that is available to plants. Total phosphorus includes the amount of phosphorus in solution (reactive) and in particulate form. Under certain conditions particulate phosphorus can be converted to soluble reactive phosphorus. Internal loading occurs when phosphorus builds up in lake sediments and is released into the deepest parts of the water column. When sufficient water circulation or “turnover” of the lake occurs, the elevated phosphorus levels are circulated throughout the water column which can lead to algal blooms in areas with sufficient light penetration. This phenomenon is particularly common in the late summer and fall months. External loading is the introduction of total phosphorus from all other sources within the watershed. The phosphorus from external sources mixes with lake waters and, if in dissolved form, is immediately available to support algae growth. The remainder of the particulate phosphorus settles to the bottom of Partridge Lake. Some of it settles quickly in its particulate form while a portion may be converted to dissolved phosphorus, used by plants and other organisms. As these plants and organisms die, organic and condensed phosphorus settles to the lake bottom. When this settling action happens, external loading can contribute to internal loading as more phosphorus is added to the lake sediments, and under the right conditions can be released as dissolved phosphorus. External loading must be controlled to prevent internal loading from increasing. The DES Diagnostic Study quantified three primary external pathways for total phosphorus to enter Partridge Lake: groundwater (44%), surface run-off (31%), and precipitation (25%). Once the targeted watershed sources of phosphorus are addressed (25-30% reduction), attention can be focused on in-lake remediation. The major sources of phosphorus pollution sources to Partridge Lake are discussed below. The following sub-sections are a summary of our analysis building upon the recommendations in the DES Diagnostic Study. Note that the recommended management measures to address these sources are presented in Section 3, and the load reduction estimates are provided in Section 4 of this Plan. 2.1 Phosphorus in Groundwater Groundwater is the largest external phosphorus source to Partridge Lake. Suspected causes of phosphorus inputs to groundwater are likely due to the presence of septic systems in close proximity to the lake, in conjunction with the soil, bedrock and water table characteristics around Partridge Lake. All of the homes around Partridge Lake are on subsurface systems or holding tanks. Phosphorus loading problems are common in areas with older systems, highly permeable soils (e.g., sands), mineral-poor soils, nearby surface waters, and high system densities. A number of factors can influence the shape and movement of contaminant plumes from septic systems. Climate, soils, slopes, landscape position, geology, regional hydrology, and hydraulic load determine Section 2 - Causes and Sources of Nonpoint Source Pollution Partridge Lake Watershed Based Plan 2008 2-2 whether the plume will disperse broadly and deeply or, more commonly, migrate in a long and relatively narrow plume along the upper surface of a confining layer or on the surface of the groundwater (EPA, 2002a). The soil survey indicates that there are limitations for septic system use based on shallow depth to bedrock in many areas of the watershed, and also due to highly permeable sandy soils throughout the area. The soil types and depth to bedrock (e.g., 0.5 to 1.6 m) around most of the watershed is allowing water that infiltrates into the soil to travel rapidly down gradient toward the lake. The age of septic systems compounded with the soil characteristics likely lead to ineffective treatment of septic nutrients before the septic leachate enters into the groundwater. DES noted that this leachate, coupled with phosphorus release from decaying organic matter, are rapidly picked up in shallow groundwater moving towards the lake, and are deposited near-shore in groundwater seepage to the lake. The PLPOA has estimated that there are approximately 68 dwellings in the immediate vicinity of the lake’s edge (i.e., within 300 feet); 19 of these properties are considered to be year-round dwellings, whereas the remaining 49 are seasonal. Analysis of data from the DES diagnostic study revealed that the largest source of phosphorus to Partridge Lake resulted from near-shore groundwater seepage inputs (e.g., 44% or 23.4 kg TP) and that septic systems likely have the largest influence on the amount of total phosphorus entering the lake. All of the properties around the lake are on subsurface systems as there is currently no centralized sewer system in place to service this area. Analysis of results from the septic system survey conducted around Partridge Lake in 2001 show that 36% of the septic systems were more than 20 years old and have reached or exceeded their designed life span. The septic survey conducted in 2007 revealed that 42% of septic systems are currently more than 20 years old. The 2007 septic survey results are presented in detail in Appendix 1. The results provide a clearer picture of the septic system conditions and distribution of lake residents. Table 2-1 shows the distribution of the septic system setback distances of the respondents to the 2007 survey. Table 2-1: Septic System Setback Distances in the Partridge Lake Watershed. Setback Distance (feet) Number Percentage of Total 0-50 4 10% 51-100 16 41% 101-150 14 36% 151-200 3 8% 201-250 1 3% 250+ 1 3% Total 39 100% Management measures to address groundwater loading are presented in Section 3 and the associated load reductions are presented in Section 4. 2.2 Stormwater Runoff The second largest contributor of phosphorous to Partridge Lake is from surface runoff or stormwater runoff within the watershed. These inputs accounted for 31 % (16.4 kg TP) of the total phosphorus load to Partridge Lake. In general, the residential development around lakes and ponds can lead to increases in the volume and rate of stormwater runoff as development occurs in a watershed. This, in turn, can lead to Section 2 - Causes and Sources of Nonpoint Source Pollution Partridge Lake Watershed Based Plan 2008 2-3 significant increases in phosphorus loading which can result in degradation of the surrounding surface waters. Based upon the results and observations made during the DES Diagnostic Study, and subsequent site investigations, specific problem areas of concern with regard to stormwater management within the Partridge Lake watershed were identified. Phosphorus load sources from stormwater include increased runoff in the subwatersheds and tributaries, and road runoff. Subwatershed and Tributaries 1. The DES report quantified the stormwater input of phosphorous from gauged and ungauged tributaries during their diagnostic study. The gauged tributaries accounted for 21 % (10.9 kg TP) of the total phosphorous load, whereas the ungauged tributaries accounted for 10 % (5.5 kg TP) of the total input. Of the gauged tributaries, Tributary J was the highest contributor of phosphorous (3.9 kg TP, 24 % of gauged tributary contribution), followed by Tributary G (2.9 kg TP, 18 %), and Tributary A (2.6 kg, 16 %) respectively. Figure 2-1 shows the relative percent phosphorus contributions from each subwatershed based upon the data collected in 2000-2001. Roads 1. Runoff from Old Partridge Lake Road. This is a steeply sloping hill with a paved road, within the drainage area of Tributary A, that meets Partridge Lake Road at the shoreline of the lake. Snowmelt and runoff travel down this hill carrying sediment, cross Partridge Lake Road, and erode sandy shoreline sediments adjacent to the lake and Tributary A. 2. Drainage ditches along Partridge Lake Road. Dirt drainage ditches exist along most of the shoreline roads. Some of these have culvert connections to the lake, sending turbid water into the shallows of the lake. Some ditches, however, are filled with sediment and road sand. 3. Winter Sand. To further exacerbate the runoff problem, sediment left on the road after winter maintenance activities is likely getting washed into the lake. Field observations verify that the main roads along the lake contain sand deposits along the edges. Stormwater runoff can also pick up phosphorus bound to sediment and other materials such as road sand and carry this material into the lake. 2.3 Shoreline and Beach Erosion The shoreline of Partridge Lake contains a few beaches that are occasionally replenished with fresh sand. During the DES diagnostic study, observable problems were noted with many of these beaches. Particularly, sand beaches are potentially damaging to the lake due to the filling in of shoreline habitat and the introduction of nutrients into the lake (phosphorus binds to sediment particles). Shallow areas newly created by beach erosion allow for greater areas of sunlight penetration, and may also encourage even more abundant plant establishment along the shoreline areas of the lake. Areas of the lakebed near eroding beaches often show signs of sedimentation. As new layers of sand cover shoreline habitat, the macroinvertebrate communities, fish spawning areas, and amphibian habitat may be smothered or destroyed. In addition to beach erosion, there are areas of the Partridge Lake shoreline that are steeply sloped and are either actively eroding or susceptible to erosion, largely due to overland runoff. The presence of roads with steep shoulders adjacent to the lakeshore can exacerbate the erosion areas. Erosion of the lake shoreline can lead to similar problems as described above, which can be intensified during storm events. Section 2 - Causes and Sources of Nonpoint Source Pollution Partridge Lake Watershed Based Plan 2008 2-4 2.4 Internal Phosphorous Loading Internal loading occurs when the bottom of the lake loses oxygen, causing a chemical reaction in the sediments that ultimately results in the release of phosphorus to the water column. As the bottom waters lose oxygen during the summer months internal loading occurs. This process adds to the overall phosphorus available for algae growth in the lake, and is likely the cause of the occasional algae bloom that Partridge Lake has experienced in recent summers. Internal loading of phosphorous within Partridge Lake is considered to be significant during certain times of the year. During the Diagnostic Study period lake stratification developed over the course of the summer. This stratification resulted in depleted oxygen concentrations within the hypolimnion (bottom layer), which in turn resulted in increased concentrations of total phosphorus in the hypolimnion. DES noted that it is difficult to estimate the actual amount of phosphorus released into the water column from lake sediments. The actual amount of phosphorus released into the water column of the lake from the sediments through internal loading is a significant phosphorus contributor to Partridge Lake. Through analysis of hypolimnetic phosphorus concentrations, the average annual internal phosphorus load in Partridge Lake was estimated as 70 kg/year (A. Chapman, DES, pers. comm.). This is more than all the external phosphorus sources to the lake combined (52.8 kg). 2.5 Agricultural Operations Although there is a small percentage of agriculture land within the Partridge Lake watershed, the types of operations (horse and cow pastures) have the potential to affect water quality if not carefully managed. There is one active horse pasture within the Partridge Lake watershed (Figure 2-2). The total area equals approximately 20 acres. The average horse generates 50 pounds of manure per day (Lawrence, et al., 2003). Many of the nutrients ingested by pasturing animals return to the environment in feces and urine. If the waste is allowed to enter streams and lakes through runoff, excessive amounts of these same nutrients can stimulate unwanted algae blooms and degrade water quality. There is also an old diary farm in the watershed which currently only pastures 10-12 young cows in the summer. This area in the past was a fully operational dairy farm, which at one time had approximately 80 cows. The area of the farmland is approximately 53 acres. This represents only a small percent of the total watershed area; however, these areas could have a historical impact on phosphorus loading into the lake. An average dairy cow generates 65 pounds of manure per day. Using general approximations of nutrient content in dairy cow manure, 80 cows can generate over 900 kg of phosphorus per year. The manure was probably spread onto the fields as fertilizer. The conversion of this farm into pasture land only may reduce the amount of phosphorus into this subwatershed. To verify this, the tributaries associated with the subwatersheds that contain this former dairy operation (Tributary G, in particular) should be re-sampled for phosphorus concentrations and compared to the data collected in 2000-2001 by DES. Section 2 - Causes and Sources of Nonpoint Source Pollution Partridge Lake Watershed Based Plan 2008 2-5 Figure 2-1: Partridge Lake Annual TP Loading per Subwatershed (based on 2000-2001 data). Attached as .pdf Section 2 - Causes and Sources of Nonpoint Source Pollution Partridge Lake Watershed Based Plan 2008 2-6 Figure 2-2: Agricultural Areas in the Partridge Lake Watershed. Attached as .pdf Section 3 – Nonpoint Source Management Measures Partridge Lake Watershed Based Plan 2008 3-1 3 NONPOINT SOURCE MANAGEMENT MEASURES This section contains recommendations for implementing management measures to control nonpoint source pollution in Partridge Lake watershed. The DES Diagnostic Study provided several recommended NPS management measures to address the water quality problems of Partridge Lake. These recommendations are examined further and discussed in more detail here. The potential BMPs will be evaluated taking into account the goals of the plan, capital costs, operation and maintenance costs, benefits and other factors including property ownership. 3.1 Groundwater BMPs Recommendation: Pursue improvements to individual septic systems and consider alternatives such as a community system. The soil survey for the area around Partridge Lake indicates that there are limitations for septic system use based on shallow depth to bedrock in many areas of the watershed, and also due to highly permeable sandy soils throughout the watershed (DES, 2007). DES reported an annual groundwater loading of 24.3 kg/year to Partridge Lake, which represents 44% of the total external inputs of phosphorus to the lake. The objective of reducing nutrients from septic systems throughout the watershed, particularly those closest to the lake shoreline or its tributaries within the 250 feet of the lake, will facilitate meeting the overall phosphorus load reduction target. The options for addressing the phosphorus loading to groundwater include: 1) Homeowner education and initiative, 2) Implementation of a group maintenance schedule, 3) Individual retrofits such as high-iron sand filters, or 4) Community or cluster system. 3.1.1 Homeowner Education As part of the DES Diagnostic study, an anonymous septic system survey was conducted within the watershed during the summer of 2001. Another septic survey of Partridge Lake watershed residents was conducted in July 2007 in which 75 paper surveys were sent out. Of those, 49 completed surveys were received for a 65% return rate (Figure 3-10 shows the location of those who completed the surveys). The results of the septic system survey reported that the approximate age of septic systems around the lake ranged from less than 5 years old to greater than 25 years old. The estimated life span of a state approved septic system in New Hampshire is between 15 and 20 years, providing that the system is used within the design specifications. Analysis of these results showed that approximately 90 % of the responders indicated that their septic systems were either new, operating well, or adequate; however 42% of respondents indicated their system was more than 20 years old. The complete results of the 2007 septic survey are contained in Appendix 1. The results of the recent septic survey support the idea that phosphorus in groundwater is the primary problem affecting external loading to Partridge Lake. The septic/groundwater phosphorus loading interaction at Partridge Lake is primarily a result of septic system position in relation to Partridge Lake, shallow groundwater table, and limiting soils as opposed to neglect of system maintenance or low pumping frequency. Section 3 – Nonpoint Source Management Measures Partridge Lake Watershed Based Plan 2008 3-2 The data obtained relative to system usage and loading can be used to estimate load reduction estimates (as described further in Section 4) and target management measures. In addition, the Lake Guide disseminated in the summer of 2007 highlighted the benefits of a healthy septic system. Educational activities directed at increasing general awareness and knowledge of onsite management efforts can improve the probability that simple, routine operation and maintenance tasks (e.g., inspecting for pooled effluent, pumping the tank) are carried out by system owners (EPA, 2002a). 3.1.2 Group Maintenance The recent septic survey indicated that 58% of respondents pump their septic tanks every two years on average, and 100% pump at least every 5 years. According to DES, accumulated sludge should be pumped out every one to three years for shorefront residents, and every 3-5 years for other dwellings farther back in the watershed. Even though septic pumping frequency at Partridge Lake is within DES recommendations, more frequent pumping may be beneficial in certain areas around the lake. An option to address this would be to requests bids from septic tank pumping contractors to perform the inspection and pump out certain tanks at a set rate and interval. This can be done by PLPOA as a follow-up to the septic survey. 3.1.3 Upgrade Individual Systems/Retrofits The upgrading of old or failing septic systems could occur through four channels: • Voluntary replacement; • Proven failure and subsequent order to replace the system from the health officer or DES; • Conversion from seasonal to year-round use or addition of bedrooms; or • Engineering study required by New Hampshire state law conducted prior to the house sale showing evidence that the septic system was in need of repairs or replacement. New Hampshire Revised Statutes Annotated 485-A:2 defines failure as “the condition produced when a subsurface sewage or waste disposal system does not properly contain or treat sewage or causes or threatens to cause the discharge of sewage on the ground surface or into adjacent surface or groundwater.” To ensure prompt and effective replacement of a failed subsurface system, the local official responsible for health code enforcement must prepare a written statement verifying that the existing system is in failure. This statement must be submitted to DES with the application to replace the existing system. Other options include providing low-interest loans to homeowners to pay for repairs and replacement systems or developing ordinances to mandate improvements when a septic system is failing. This would require additional manpower resources for diagnosing the problem, and prescribing corrective actions. It has been reported that if phosphorus from septic tanks causes groundwater contamination, it is possible to reduce the phosphorus concentration in system effluents through chemical additions such as aluminum phosphate, lime or ferric chloride to septic tanks (Canter and Knox, 1985). However, few phosphorus removal processes are well developed for onsite wastewater systems application. Those that have been successfully applied generally fall into the categories of chemical, physical, and biological systems. The high maintenance of the phosphorus attenuation applications has limited their effectiveness and use. Section 3 – Nonpoint Source Management Measures Partridge Lake Watershed Based Plan 2008 3-3 Phosphorus is rarely designed to be removed in onsite pretreatment because most soils have the innate ability to adsorb the nutrient for many years before it begins to migrate to nearby ground or surface waters. However, as onsite system sites age, there is the potential for serious environmental degradation, as witnessed by the thousands of inland lakes where older onsite development is increasingly being cited as the primary reason for lake eutrophication (EPA, 2002a). In these cases effluent filters on the outlets of septic tanks may help to control phosphorus in effluent. Individual systems will have to be evaluated on a case-by-case basis to determine appropriateness of the potential retrofit. Additional recommendations for wastewater treatment alternatives are presented in DES, 2007. 3.1.4 Community or Cluster System Recommendation: Reserve/acquire land areas for potential cluster septic systems for future analysis. The Littleton Wastewater Treatment Plant is located on Meadow Street in Littleton, approximately 5 miles away from Partridge Lake. The nearest sewer connection to the lake is in the area of the Littleton Hospital, approximately 2.5 miles away. Connecting Partridge Lake residents to the town sewer is most likely cost prohibitive. Cluster systems are innovative systems that collect and treat sewage for many homes or groups of homes around a lake. First tier development around Partridge Lake could elect the alternative of a subsurface treatment system with conventional collection from clusters or groups of individual homes. These cluster systems are usually simple and cost effective alternatives for the secondary treatment of small flows. Installations are suitable for discharge volumes of 500 gpd to 300,000 gpd. Small areas of land (perhaps shared lots or open lots) are necessary for the installation of such systems; therefore the availability of land for this application may be a limiting factor. A centralized sewage treatment system may be feasible for Partridge Lake. These systems must be designed carefully given the concentrated amount of sewage material, as leachate from cluster systems may still pose threats to groundwater. There is limited land in the immediate vicinity of Partridge Lake available for a potential cluster sewage system due to existing development and site topography. There is vacant land away from the lake which may serve to accommodate a cluster system. Two options for clusters systems are presented in Section 4. Further study would be required to determine the feasibility of each cluster system option. 3.2 Stormwater BMPs A site visit was conducted in November, 2006 to investigate and verify problems areas in the watershed and to refine specific BMP recommendations. The site visit accomplished the following: • Map and prioritize locations of erosion problems along Partridge Lake Road; • Map and prioritize severity of drainage ditches along Partridge Lake Road; • Map and prioritize severity of shoreline bank erosion sites along South Shore Road; and • Shoreline survey to examine areas of beach erosion along Partridge Lake shoreline. To control stormwater and prevent it from further affecting Partridge Lake, several Best Management Practices (BMPs) were evaluated and considered. BMPs are policies, practices, procedures, or structures that help to prevent environmental damage and are developed specifically to address a particular source of pollution. Both structural BMPs and non-structural BMPs may be utilized to achieve reduction in phosphorus loadings to Partridge Lake. Examples of structural BMPs include detention ponds, stormwater wetlands, infiltration trenches, filtering systems, and conversion of individual septic systems Section 3 – Nonpoint Source Management Measures Partridge Lake Watershed Based Plan 2008 3-4 to a community or regional wastewater treatment system. Non-structural BMPs include street cleaning, land use regulations, zoning, and future development restrictions. Recommendation: Select appropriate and feasible BMPs for implementation around the lake that will decrease stormwater volume and sediment load. Specific recommendations for BMPs to address stormwater runoff in the Partridge Lake watershed are presented below. The Partridge Lake Watershed Partnership will be responsible for further evaluation and selection of the most feasible BMPs to implement. The evaluation of stormwater BMPs was focused on those structural measures that remove phosphorus as an excess of this pollutant is the primary cause of eutrophication of Partridge Lake. Stormwater BMPs that have been proven effective in removing phosphorus (at least 40% removal rate) are generally biologically oriented such as detention pond and wetland systems which allow for settling of solids and biological uptake of pollutants or infiltration and filtering systems that filter the pollutant out of the stormwater. Challenges to the effective treatment of phosphorus in stormwater at Partridge Lake include the lack of undeveloped public land, unclear road right-of-way and easement boundaries, steep topography adjacent to Partridge Lake, highly permeable soils, and the cold climate. In order to consider a BMP for implementation, its effectiveness for removing phosphorus had to be documented in the literature and not be based solely on manufacturer reported information. Stream turbidity values, measured in 2000-2001 from tributaries to Partridge Lake, suggest that the estimated TP loading through surface water may primarily be in dissolved form. (See Section 4.2.3 in DES, 2007.) This is important to consider when selecting an appropriate stormwater BMP. 3.2.1 Tributary BMPs The stormwater BMP concepts considered for implementation for Tributaries A, D, G, and J (detailed below) are a stormwater wetland and several innovative proprietary stormwater systems such as StormTreat, StormFilter, and Aqua-Filter. A description of these concepts follows. The specific location of any potential BMP associated with these tributaries must be permitted by the NH DES Wetlands Bureau. 3.2.1.1 Stormwater Wetland Stormwater wetlands (a.k.a. constructed wetlands) are engineered systems designed to simulate the water quality improvement functions of natural wetlands to treat and contain surface water runoff pollutants and decrease loadings to surface waters. As stormwater runoff flows through the wetland, pollutant removal is achieved by settling and biological uptake. Wetlands are among the most effective stormwater practices in terms of pollutant removal, and also offer aesthetic value. While natural wetlands can sometimes be used to treat stormwater runoff that has been properly pretreated, stormwater wetlands are fundamentally different from natural wetland systems. Stormwater wetlands are designed specifically for the purpose of treating stormwater runoff, and typically have less biodiversity than natural wetlands both in terms of plant and animal life. There are several design variations of the stormwater wetland, each design differing in the relative amounts of shallow and deep water, and dry storage above the wetland. A schematic of an example stormwater wetland is show below. Section 3 – Nonpoint Source Management Measures Partridge Lake Watershed Based Plan 2008 3-5 Figure 3-1: Schematic of a Stormwater Wetland. Source: Center for Watershed Protection. Section 3 – Nonpoint Source Management Measures Partridge Lake Watershed Based Plan 2008 3-6 3.2.1.2 StormTreat™ The system consists of a series of six sedimentation chambers and a constructed wetland which are contained within a modular 9.5-foot diameter tank. It is constructed of recycled polyethylene that connects directly to existing drainage structures. Influent is piped into the sedimentation chambers where larger-diameter solids are removed. The internal sedimentation chambers contain a series of skimmers that selectively decant the upper portions of the storm water in the sedimentation basins, leaving behind the more turbid lower waters. The skimmers significantly increase the separation of solids compared with conventional settling/detention basins. An inverted elbow trap serves to collect floatable materials such as oils within the inner tank. After moving through the internal chambers, the partially treated storm water passes into the surrounding constructed wetland through a series of slotted PVC pipes. The wetland is comprised of a gravel substrate planted with bulrushes and other wetland plants. Unlike most wetlands constructed for stormwater treatment; StormTreat conveys stormwater into the subsurface of the wetland and through the root zone, where greater pollutant attenuation occurs through such processes as filtration, adsorption, and biochemical reactions. The operation and maintenance of the StormTreat System is limited to annual inspections and solids removal on an as-needed basis. Figure 3-2: Example StormTreat System Installation. Source: http://www.stormtreat.com Section 3 – Nonpoint Source Management Measures Partridge Lake Watershed Based Plan 2008 3-7 3.2.1.3 StormFilter The StormFilter is a passive, flow-through, storm water filtration system that uses rechargeable, media- filled filter cartridges housed in underground concrete vaults. The siphon-actuated cartridges, which draw stormwater through the filter media, are installed in precast or cast-in-place concrete vaults with pipe underdrains cast into the concrete floor. Through mechanical filtration, ion exchange, and adsorption, the filter media removes total suspended solids (TSS), soluble metals, soluble phosphorus, nitrates, and oil and grease from storm water. Filter media for the cartridges are selected based on the pollutants expected at the site. The StormFilter has the flexibility to be fine-tuned with different media if actual pollutant loadings/concentrations at a site differ from expectations, vary with a change in land use, or change due to regulations. Based on the reported conditions for the Partridge Lake sub-watersheds, the manufacturer’s initial recommendation is to specify ZPG (zeolite, perlite, and granular activated carbon) for the filter media to remove phosphorus. Inspection/minor maintenance activities are combined since minor maintenance does not require special equipment and typically little or no materials are in need of disposal. Inspection/minor maintenance typically involves inspection of the vault itself and removal of vegetation, trash, and debris. Major maintenance typically includes cartridge replacement and sediment removal. Inspections and maintenance should be performed annually and after major storms. Figure 3-3: StormFilter Schematic. Source: http://www.contech-cpi.com Section 3 – Nonpoint Source Management Measures Partridge Lake Watershed Based Plan 2008 3-8 3.2.1.4 Aqua-Filter Stormwater Filtration System Aqua-Filter is a two stage treatment system that involves the removal of gross pollutants by the Swirl Concentrator, followed by the removal of fine sediments and water-borne pollutants by the Filtration Chamber. Stormwater enters the Swirl Concentrator by means of a tangential inlet pipe that induces a circular flow pattern. The swirling action encourages solids to drop out of the flow and move to the center of the chamber, thereby preventing re-suspension (even under high flow conditions). A baffle plate located in front of the outlet to the Swirl Concentrator traps free-floating oil and debris. The pre-treated "first flush" then enters into the filtration chamber where it is evenly distributed across the filter media bed and allowed to permeate through the filter media. The natural filter media, used for the filtration, are capable of removing the remaining water-borne pollutants such as dissolved oils, fine silts and clays, nutrients (phosphates), and heavy metals. The most commonly used media is medium grain perlite. Other filter media, such as zeolite, granulated activated carbon and synthetic textiles are available. Figure 3-4: Aqua-Filter Schematic. Source: http://www.aquashie