T.F. Green Airport Improvement Program - FEIS Chapters - PVD

T.F. Green Airport Improvement ProgramEnvironmental Impact Statement and Final Section 4(f) Evaluation5.11.3.1 Direct Impacts MethodologyImpacts to water resources were determined based on proposed changes in grading, surface cover, and landuse. Direct impacts are effects caused by the action and occur at the same time and place and would potentiallyoccur in the local receiving waters (Buckeye Brook, Tuscatucket Brook, etc.). The analysis evaluates potentialdirect impacts to water resources in two categories: hydrologic effects and water quality impacts. Hydrologiceffects relate to the effect of grading and ground surface types on the flow of water overland and into a streamor lake. Water quality impacts are based on the types of contamination that may enter the receiving waters,which can range from pollutants on the ground such as oils, metals, and salts to changes in temperature due torunoff flowing across warm pavement. Water quality impacts were evaluated for each stormwater drainagearea affected, including Airport property, areas of proposed land acquisition, and the existing and proposedoff-Airport roadways. Impacts from pollutant loading were determined in the water quality analysis withineach drainage area using the Simple Method (Schueler, 1987) which is based on annual rainfall, site percentimpervious cover, land use type, and pollutant loading coefficients based on land use. The impact of deicingactivities was considered in the water quality analysis as an increase in the number of departing flights willincrease the amount of glycol used at the Airport.The amount of impervious surface within a given drainage area was used to estimate relative increases in runoffvolume and peak flow for each of the receiving waters. The impervious surfaces in the Study Area werecalculated using aerial photography, mapping, and GIS to calculate the area extent of roads, structures andother impervious surfaces. This analysis has been revised since the DEIS and now assumes that the existingroadways will not be removed within the acquisition areas with the exception of roadways that are to be relocated,such as Airport Road, or are physically impacted by the Airport Improvement Program.5.11.3.2 Indirect Impacts MethodologyIndirect impacts are effects that occur later in time or farther away geographically. Indirect impacts could occurin larger water bodies downstream (Mill Cove, Brush Neck Cove) where the flows from multiple tributaries mixtogether. Indirect impacts would encompass effects that occur later than the direct impacts. Indirect impacts onhydrology and water quality would be determined by the same methods described above for direct impacts.5.11.3.3 Construction Impacts MethodologyTemporary construction impacts were determined based on the type, extent, and location of disturbanceassociated with demolition, grading, construction, and utility work. The relative potential for encounteringcontaminated materials (such as near the former Truk-Away Landfill site off the Airport property nearRunway 34) during excavation would affect the overall risk of construction-related water quality effects.5.11.3.4 Cumulative Impacts MethodologyThe cumulative impact analysis considers the total effect on the downstream receiving waters (Brush Neck Coveand Mill Cove) on a watershed basis extending back to 1939 (the earliest date for which aerial photographs ofthe Airport were available) and forward to the anticipated operations in 2020 and 2025, after construction iscomplete. The cumulative impact analysis also considers the ongoing effects of Airport activities and thesurrounding land uses on water quality and peak flows to determine whether an incremental impact thatappears minor may have a significant effect on an impaired resource.Chapter 5 - Environmental Consequences 5-211 July 2011\\mawatr\ev\09228.00\reports\FEIS_Final_July_2011\PVD_CH05_Environmental_Cons_JUL_2011.doc