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From page 109... ... Appendix D Potential Impacts of Highway Stormwater Infiltration on Water Balance and Groundwater Quality in Roadway Environments (White Paper #2) 1 Introduction .................................................................................................................................... Read the entire page →
From page 110... ... NCHRP Project 25-41 1 Introduction Infiltration of stormwater from urban highways has many potential benefits, but also has the potential to result in environmental and infrastructure impacts associated with the volume of water infiltrated (i.e., water balance impacts) and the introduction and/or mobilization of pollutants into groundwater (i.e., groundwater quality impacts) Read the entire page →
From page 111... ... NCHRP Project 25-41 of criteria for evaluating infiltration feasibility that are applicable in all cases. Project planning and design professionals should exercise appropriate judgment in considering potential water balance and groundwater quality impacts associated with infiltration of stormwater from highways. Read the entire page →
From page 112... ... NCHRP Project 25-41 Source: Location: Annual Fluxes (as percent of precipitation) : is either pasture or wooded pasture. Read the entire page →
From page 113... ... NCHRP Project 25-41 2.1 Potential Changes in the Water Balance Project activities have the potential to alter the water balance of a site (and smaller watersheds) as a result of changes in land cover (i.e., addition of impervious surface, compaction of pervious areas) Read the entire page →
From page 114... ... NCHRP Project 25-41 Southern California chaparral, ET made up 83 to 97 percent of the water balance, and deeper infiltration was less than 10 percent. This is consistent with the estimates made by Sanford and Selnick (2013) Read the entire page →
From page 115... ... NCHRP Project 25-41 Potential benefits. In regions where aquifers are actively managed for water supply, an increase in infiltration may be desirable and even encouraged. Read the entire page →
From page 116... ... NCHRP Project 25-41 therein. As a specific example, environmental clearance documents for the Rancho Mission Viejo planned community in Orange County, California (California FEIR No 589) Read the entire page →
From page 117... ... NCHRP Project 25-41 • Pollutant mobility – pollutants that are more mobile in the vadose zone (the unsaturated zone between the groundwater table and the ground surface) have a higher potential to contaminate groundwater than those which do not move through the vadose zone as readily. Read the entire page →
From page 118... ... NCHRP Project 25-41 conditions are conducive. Compost amendments in shoulder treatments and/or stormwater controls can also be sources of nutrients at levels of concern if not appropriately specified and sourced. Read the entire page →
From page 119... ... NCHRP Project 25-41 Decomposition is possible in both soil media and water, but the time frame can range between days and years depending on the conditions and the specific compounds (Pitt et al. Read the entire page →
From page 120... ... NCHRP Project 25-41 3.1.4 Pathogenic Microorganisms Pathogens, including bacteria and viruses, are ubiquitous in urban stormwater runoff. They originate from anthropogenic sources, such as human waste, dog waste, and failing septic systems, as well as natural sources, such as bird and animal droppings. Read the entire page →
From page 121... ... NCHRP Project 25-41 likelihood of groundwater contamination. However, metals are of increased concern when infiltration facilities are located in rapidly-infiltrating inert materials, such as sand or gravels, or when infiltration occurs in close proximity to sites with elevated stormwater concentrations, such as industrial sites and maintenance yards. Read the entire page →
From page 122... ... NCHRP Project 25-41 Table 2. Summary of Potential Stormwater Contaminants of Concern for Groundwater Quality Constituent Roadway-related Sources Relative Abundance in Roadway Stormwater Runoff in Soluble Phase Mobility through Vadose Zone Relative Stormwater-Related Contamination Risk Potential for Remaining Risk after Mitigation Measures (See Section 4.4) Read the entire page →
From page 123... ... NCHRP Project 25-41 3.2 Potential for Groundwater Impacts Associated with Existing Soil and Groundwater Contamination Legacy contamination of soil and groundwater is common in areas that have previously been used for urban development or agricultural uses. The most common constituents of concern are volatile organic compounds; especially chloroform, solvents like PCE and TCE, and the gasoline oxygenate MBTE. Read the entire page →
From page 124... ... NCHRP Project 25-41 3.3 Potential Risks to Groundwater Quality from Roadway Contaminant Spills The U.S.DOT estimates that 7 percent of all trucks travelling the nation's roadways are carrying hazardous material (Federal Highway Administration 2009) Read the entire page →
From page 125... ... NCHRP Project 25-41 4 Assessing and Mitigating Potential Stormwater Infiltration Impacts on Water Balance and Groundwater Quality This section is intended to provide guidance for assessing the potential for impacts of stormwater infiltration related to water balance and groundwater quality. This section also provides recommendations for mitigating these potential impacts to potentially improve the level of infiltration that can safely be achieved in the highway environment. Read the entire page →
From page 126... ... NCHRP Project 25-41 • Infrastructure damage, • Geotechnical hazards, • Inflow and infiltration into the sanitary sewer, • Conveyance of water in utility trenches, • Mobilization of groundwater contaminants, • Reduced separation to groundwater, resulting in greater risk of contamination (See Section 4.3) , and • Undesirable surface ponding. Read the entire page →
From page 127... ... NCHRP Project 25-41 way. These BMPs include bioretention areas (a smaller footprint area) Read the entire page →
From page 128... ... NCHRP Project 25-41 concern, other studies prepared by local jurisdictions may be informative to understand the feasibility and desirability of infiltrating highway runoff. Table 4. Read the entire page →
From page 129... ... NCHRP Project 25-41 potential conditions that may be encountered with a range of associated risks and a site-specific assessment is recommended. To assist in project planning, Table 5 provides risk indicators to help evaluate the potential for impacts and identify pollutants that may warrant greater analysis. Read the entire page →
From page 130... ... NCHRP Project 25-41 The following list includes indicators of elevated sources that may be applicable in the urban highway environment (SARWQCB 2009; WADOE 2012; U.S. Read the entire page →
From page 131... ... NCHRP Project 25-41 • Mapping of contaminated groundwater plumes and soils, which may be available from local groundwater management agencies or state environmental quality agencies. For example, spatial databases and layers containing contaminated sites were identified in California, New Jersey, Connecticut, and Alaska (see References) Read the entire page →
From page 132... ... NCHRP Project 25-41 4.5 Wellhead and Spring Protection Wellheads and springs, natural and man-made, are water resources that may potentially be adversely impacted by stormwater infiltration through the introduction of contaminants or alteration in water supply and levels. It is recommended that the locations of wells and springs be identified early in the design process and site design be developed to avoid infiltration in the vicinity of these resources. Read the entire page →
From page 133... ... NCHRP Project 25-41 4.6 Contaminant Spills As discussed in in Section 3.3, contaminant spills are a constant risk on roadways, with the potential to deposit high concentrations and volumes of pollutants before responders can control the source of the spill. However, the most common spills are petroleum hydrocarbons, and the risk of these spills contaminating groundwater can generally be mitigated with appropriate measures. Read the entire page →
From page 134... ... NCHRP Project 25-41 4.7 Special Considerations for Karst Topography Karst topography refers to a specific geologic formation that has been shaped by the dissolution of soluble bedrock elements. Karst topography is most frequently associated with limestone or dolomite rock, but may be present in other types of rock as well. Read the entire page →
From page 135... ... NCHRP Project 25-41 basin that underlies the Santa Ana River in northern Orange County. OCWD was actively involved in the development of the Technical Guidance Document, as they have an interest in enhancing groundwater supplied through infiltration and have significant concerns about the potential for groundwater contamination due to stormwater infiltration. Read the entire page →
From page 136... ... NCHRP Project 25-41 applicable criteria, maps, or other resources that have already been developed to assist in identifying areas where increased stormwater infiltration may be undesirable. Similarly, agencies or companies that operate other underground utilities may have specific concerns regarding infiltration of stormwater and/or resources to assist in evaluating feasibility and desirability. Read the entire page →
From page 137... ... NCHRP Project 25-41 Donaldson, B.M. Read the entire page →
From page 138... ... NCHRP Project 25-41 Pitt, R., S Clark, and K Read the entire page →

From page 109...

... Appendix D Potential Impacts of Highway Stormwater Infiltration on Water Balance and Groundwater Quality in Roadway Environments (White Paper #2) 1 Introduction ....................................................................................................................................