MILL POND RESTORATION PROJECT Phase II 2002-2004 Prepared by the NASHUA REGIONAL PLANNING COMMISSION This project was funded in part by a New Hampshire Department of Environmental Services Nonpoint Source Program Local Initiative Grant with in-kind services provided by the City of Nashua, the Mine Falls Park Advisory Committee, and the NH DES Watershed Bureau . Nashua Regional Planning Commission Mill Pond Restoration Project 2002-2004 TABLE OF CONTENTS I. INTRODUCTION.........................................................................................................................................1 II. PROJECT SUMMARY AND GOALS ........................................................................................................1 III. PROJECT TASKS..........................................................................................................................................1 A. Task One - Quality Assurance Protection Plan...................................................................................2 B. Task Two - Monitor flows from the Gatehouse into Mill Pond ......................................................2 C. Task Three - Establish volunteer water quality monitoring program.............................................4 D. Task Four - Calculate drainage area and catch basin information...................................................5 1. Drainage to Outfalls 1-4 ....................................................................................................................5 2. Runoff Calculation.............................................................................................................................5 3. Construction of the Conway Ice Arena-Outfall 1 ..........................................................................7 4. Renovation of Nashua High School-South.....................................................................................7 5. Drainage to Outfall 5 .........................................................................................................................8 6. Drainage to Outfall 6 .........................................................................................................................8 7. Drainage to Outfall 7 and 8...............................................................................................................9 E. Task Five - Develop GIS database and map for Task 4 ...................................................................11 F. Task Six - Assess stormwater management measures.....................................................................12 G. Task Seven - Research treatment systems that could be used ........................................................16 1. Effectiveness of Swirl Separators in Stormwater Treatment......................................................16 H. Task Eight - Water quality sampling..................................................................................................17 1. In-Pond Sampling ............................................................................................................................18 a Transparency ................................................................................................................................19 b. Chorophyll-a.................................................................................................................................19 c. Total Phosphorous .......................................................................................................................20 d. pH ..................................................................................................................................................20 e. Acid Neutralizing Capacity (ANC) ...........................................................................................21 f. Conductivity.................................................................................................................................21 g. Gate House Sample on the Nashua River - August 16 ...........................................................21 2. Stormwater Outfall Sampling.........................................................................................................21 I. Task 9 - Mine Falls Park Master Plan Committee.............................................................................22 IV. CONCLUSION............................................................................................................................................24 V. GENERAL RECOMMENDATIONS ........................................................................................................24 = Page i. Nashua Regional Planning Commission Mill Pond Restoration Project 2002-2004 LIST OF TABLES Table III-1: Grass Treatment Swale......................................................................................................................8 Table III-2: Detention Pond Infiltration Volume..............................................................................................10 Table III-3: Summary of Drainage Calculations...............................................................................................11 Table III-4: Stormwater Catch Basin (CB) Assessment – July 17, 2003 .........................................................13 Table III-5: Stormwater Catch Basin Assessment – July 25, 2003 ..................................................................14 Table III-6: Dissolved Oxygen/Temperature Profile ......................................................................................18 Table III-7: Mill Pond Epilimnion Layer – 2 Meters.......................................................................................18 Table III-8: Hypolimnion Layer – 4 Meters .....................................................................................................19 LIST OF MAPS Map III-1: Outfall Watershed Drainage Areas................................................................................................11 Map III-2: Catch Basin Locations ......................................................................................................................15 Map III-3: Water Quality Sampling ..................................................................................................................17 Map III-4: Mine Falls Park .................................................................................................................................23 LIST OF APPENDICES: Appendix A Task Two – Gatehouse Flows Appendix B Task Four - Drainage Calculations for Outfalls 1-4 Prepared by the City of Nashua Engineering Department Appendix C Task Four - Drainage Calculations for Outfalls 1 For the Conway Ice Arena Prepared by Hayner/Swanson, Inc Appendix D Task Four - Drainage Calculations for Outfalls 5-8 For Nashua High School - South Prepared by Hayner/Swanson, Inc. Appendix E Task Seven - Vortechs Stormwater Treatment System NH Design and Operation Specifications Appendix F Task Eight – Laboratory ResultsAnd Field Observations for In-Pond Sampling Appendix G Task Eight – Laboratory Results for Outfall Stormwater Sampling Appendix H Task 9 – Public Outreach = Page ii. Nashua Regional Planning Commission Mill Pond Restoration Project 2002-2004 I. INTRODUCTION The Mill Pond Restoration Project Phase I in 200I assessed the water quality of the 20 acre Mill Pond as well as nonpoint sources of pollution (NPS) impacting the water quality of the pond, and the Nashua River Canal (Canal). Both Mill Pond and the Canal have seen increased growth of aquatic vegetation in the past few years. In 1998, the New Hampshire Department of Environmental Services (NH DES) surveyed Mill Pond as part of the Lake Monitoring for Trophic Classification Program. The survey, conducted on July 21, 1998, documented extremely dense growths of Coontail (Ceratphyllum demersum) and Milfoil (Myriophyllum heterophyllum), and indicated that algal mats covered 40% of the pond. Water quality analysis indicated total phosphorous levels of .046 and .098 milligrams per liter (mg/L), at 2.5 and 4 meters respectively, substantially above the recommended level of concern of 0.05 mg/L. The NH DES survey also noted that Mill Pond receives massive urban runoff from parking lots and other impervious areas in the watershed. Milfoil Coontail The drainage area of Mill Pond and the Canal was determined to be approximately 515 acres, with an estimated impervious surface coverage of 41% using Nashua Regional Planning Commission (NRPC) Geographic Information System (GIS) data. Eight outfalls drain directly into Mill Pond from the Nashua High School parking lots and athletic fields, Riverside Drive and approximately 20 businesses between Riverside Drive and West Hollis Street (Route 111). II. PROJECT SUMMARY AND GOALS The goal of the Mill Pond Restoration Project Phase II was to continue to assess drainage in the watershed and establish baseline water quality data in Mill Pond and the Canal. Water quality analysis indicates that conditions have not improved between 1999 and 2002. Untreated stormwater remained a problem during the study period. NRPC worked with many departments in the City of Nashua to ensure that five of the outfalls were rerouted to secondary stormwater treatment devices during construction at Nashua High School – South, and the new Conway Ice Arena. The remaining three outfalls are slated to be treated as part of the Army Corps of Engineers, Section 206, Aquatic Ecosystem Restoration Project. III. PROJECT