An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »


Section 14: Surface Water Pathway - Environmental Threat

14.1 Distinctive Features of the Threat

  • The Maximum score for the environmental threat is 60 rather than 100.
  • Bioaccumulation comes into play for this threat as well as for the human food chain threat.
    • The Maximum value for waste characteristics is 1,000 rather than 100. This means that high threat scores can be obtained with relatively few target points.
    • Aqueous samples are required for Level 1 concentrations. Frequently, however, Level II can "max out" the threat score at 60.

  • A variety of sensitive environments plus wetlands are the targets. There is no assessment of "nearest environment" in this threat.

14.2 Selecting the Most Hazardous Substance for the Threat

  • Three factors are considered in selecting the most hazardous substance for the threat:
    • Ecotoxicity (fresh water or salt)
    • Persistence (river or lake)
    • Bioaccumulation Potential (fresh water or salt)
  • Because of parallelism between the threats, the issues in determining the most hazardous substance have already been discussed in Section 12 and Section 13 of this course. Here is an opportunity for a quick review:
    • How do I distinguish between fresh water, salt water, and brackish water?

      "Definitions" HRS Guidance Manual, Definitions, pages 229-230 for freshwater, brackish water, saltwater.

      "Procedure" HRS Guidance Manual, "Determining Salinity...", pages 239, 241
    • If I have targets in both fresh water and salt water, how do I chose the proper value for ecotoxicity and bioaccumulation potential?
      HRS Rule, page 51621, last 3 bullets and page 51622, last bullet

    • How do I select the proper value for persistence?
      Internet Training Section 12

  • The most hazardous substance for the environmental threat is the substance with the highest product of ecotoxicity, persistence, and bioaccumulation potential factor value (BPFV). Enter this product at line 15 of HRS Table 4-1, page 51608

14.3 Waste Characteristics

The algorithm for combining the values for the most hazardous substance with the value for hazardous waste quantity for the surface water pathway should already be familiar:

  • Ecotoxicity times persistence times quantity capped at 108. Then the BPFV is brought in and the product capped at 1012. The maximum score for waste characteristics from HRS Table 2-7 on page 51592 is now 1,000, not 100.

Waste Characteristics Factor Category(2)

  • When hazardous waste quanitity is at its maximum value of 1,000,000, be aware that two substances with the same most hazardous value of 5 x 106 may trigger different values for waste characteristics because of the impact of the 108 cap in the calculation. This point was discussed at the end of Section 13.2 of this course.

14.4 Targets: Sensitive Environments in HRS Table 4-23

  • Two types of sensitive environments are considered as targets:
    • Those listed in HRS Table 4-23 - Wetlands
  • These sensitive environments must lie on or contiguous to the in-water segment of the hazardous substance migration path to be included in the pathway assessment.
  • Turn to HRS Table 4-23, page 51624 and review it carefully, including the footnotes. To help focus your attention, search for those types of sensitive environments you are most apt to encounter in the parts of the nation where you work.
    HRS rule, Table 4-23, page 51624
    • Notice that some of the sensitive environments are established by statute and will, therefore, have regulatory definition, a promulgation or listing of specific areas, a regulatory agency responsible for the environment, and some reporting requirements. (Examples: National Park or Marine Sanctuary)
    • Others of the sensitive environments define a classification that will require the exercise of documented professional judgment. (Examples: Habitat known to be used by a Federal endagered species or a spawning area critical for the maintenance of a fish species within a river.)
    • You must be familiar with this list before beginning a Preliminary Assessment, a Site Inspection, or an HRS Documentation Record.
  • Appendix A of the HRS Guidance Manual is your life-saver for understanding and applying HRS Table 4-23.
    • Section A.2 has definitions. Turn to page A-9 for "Habitat known to be used by Federal designated or proposed endangered or threatened species." 
    • Section A.3 has notes on identifying and delineating sensitive environments. Turn to page A-27 for notes on "Habitat known to be used by Federal designated or proposed endangered or threatened species."
    • Section A.4 gives sources of information for identifying the sensitive environments. Turn to page A-38 for sources of information on "Habitat known to be used by Federal designated or proposed endangered or threatened species."
  • The value assigned to each sensitive environment is stated in HRS Table 4-23. That value is assigned to the highest-scoring segment of surface water.
    • If two or more sensitive environments are co-located, add the values.

14.5 Targets: Wetlands

  • Wetlands, as well as the sensitive environments listed in HRS Table 4-23, are targets for the environmental threat.
    • Wetlands must meet the criteria stated in 40 CFR Section 230.3. This definition emphasizes vegetation types "typically adapted for life in saturated soil types."
  • The EPA definition of wetlands is different from the definition used by the U.S. Fish and Wildlife Service and on the National Wetland Inventory (NWI) maps.
    • For a comparison of the two definitions and an understanding of which types of wetlands appearing on the NWI are most apt to meet the HRS criteria, turn to pages    A-20 through A-23 of the HRS Guidance Manual.
  • Wetlands that are important to the HRS score should be field-verified at the site inspection.
    • Some wetlands that appear on the USGS topographic maps no longer exist.
    • Other wetlands are found that do not appear on the maps.
    • Not all wetlands meet the criteria of 40 CFR 230.3.
  • Wetland values are assigned on the basis of frontage or perimeter.
    • Frontage on both sides of a stream or river is counted. This is illustrated in the HRS Guidance Manual by Highlights 8-61 through 8-64 beginning at page 333.
    • Perimeter is measured when the target is an isolated wetland or the probable point of entry (PPE) is within the wetland. This is illustrated in the HRS Guidance Manual by Highlight 8-65 on page 337. The segmentation of a wetland into zones of contamination is illustrated in Highlight 8-68 on page 342.
    • In HRS Table 4-24, page 51625, how many points are assigned for less than 0.1 miles of frontage or perimeter?

      The assignment of a value of 0 for less than 0.1 mile of frontage or perimeter is important when planning sample locations. Wrong location, no points.
      HRS Table 4-24, page 51625

  • Total wetland frontage within the Target Distance Limit (TDL) is divided up into the frontage within Level I, Level II, and within each of the dilution ranges for potential.
    • This is the key difference between the listed sensititve environments in HRS Table 4-24 and wetlands. Wetland frontage is assigned to individual surface water segments. The listed environments have their value assigned as a block to the highest-valued segment they lie within, in whole or in part.

14.6 Benchmarks and Levels of Contamination

  • Environmental benchmarks (freshwater and saltwater) are found in SCDM.
    • For each sampling point that meets observed release criteria, determine whether it is Level I or Level II by comparing the concentration of those substances that meet the observed release criteria against the appropriate benchmark for the sampling point.
  • Look at the formula at the top of the middle column of HRS page 51625 or press here:

    HRS rule, page 51625

  • Sum all the wetland frontage within the zone of Level I concentrations and assign that frontage a value from HRS Table 4-24, page 51625.
  • Sum the values for all the listed sensitive environments on HRS Table 4-23 that lie within the zone of Level I concentrations.
  • Sum the values for wetlands and listed sensitive environments. This sum is multiplied by 10 for Level I concentrations. Enter the product in HRS Table 4-1, page 51608.
  • The zone of Level II concentrations, if any, extends downstream (or beyond) to the farthest sampling point that documents an observed release but has no substances in the release that meet or exceed an environmental benchmark.
    • The formula and the procedure for assigning a value are the same as for Level I except the multiplier for Level II is 1 rather than 10.
  • The zone of potential contamination, if any, extends from the most downstream (or farthest) sampling point which documents actual contamination to the TDL and no farther.

    Listed Sensitive Environments and Wetlands
    • Within this zone of potential contamination, analyze separately for each dilution range. Within each dilution range, add the value assigned to wetland frontage in that range to the sum of the values of sensitive environments within that range. Multiply the resulting sum by the appropriate dilution weight from HRS Table 4-13, page 51613.
    • Sum the dilution-weighted values for environmental targets (wetlands plus sensitive environments) and multiply the sum by 1/10 for potential. Enter this value for potential contamination in HRS Table 4-1, page 51608.

14.7 Levels of Contamination by Threat

  • Sampling points within the in-water segment that meet observed release criteria are likely to give different levels of contamination for three threats. This is for two reasons.
    • An observed release sediment or aqueous sample for the human food chain can document actual contamination only if it contains a substance with a BPFC of 500 or greater.
    • The aqueous benchmarks for the drinking water and the environment threats a different and the food chain threat requires tissue samples for Level I.

  • An aqueous sample with TCE at 100 ug/l gives different results for each threat.
  Aqueous Sample
Drinking Water Level I against a benchmark of 5 ug/l
Human Food Chain Potential because BPFV is only 50
  • For the surface water pathway, it may be worthwhile to make a base map that shows the surface water bodies and the sampling points and then to make a map for each threat that shows the interpretation of the sampling points (Level I, Level II, Potential) and the targets associated with the threat.
  • The score for the surface water pathway is the sume of the three threats, capped at 100.

14.8 Questions and Answers

What is the difference in HRS target value between a Level I sample that picks up a bit more than 0.1 mile of wetland frontage versus a Level I sample that picks up a bit less than 0.1 mile?

The wetland values for the frontage is either 25 or 0. Since the multiplier for Level I targets is 10, the difference in target values is the difference between 250 and 0.

If the average tidal cycle chloride content at a sampling point is 1,500 mg/l, should you use the freshwater or the saltwater benchmark?

Use the lower of the two benchmarks.

  • If the sensitive environment being evaluated is in fresh water, use fresh water value, except: if no fresh water value is available, use marine value if available.
  • If the sensitive environment being evaluated is in salt water, use marine value, except: if no marine value is available, use fresh water value if available.
  • If the sensitive environment being evaluated is in both fresh water and salt water, or is in brackish water, use lower of fresh water or marine values.

The PPE from the site is on a small stream with a streamflow of 25 cfs. The stream discharges into a large stream within about a mile from the site. The large stream has a streamflow of 250 cfs.

Three samples document observed releases to the small stream. The nearest sample is Level I and the next two are Level II.

There is wetland frontage along both the small and the large stream and habitats known to be used by two Federal designated endangered species are collocated with the wetlands.

The wetland frontage by zone of contamination is approximately:

Wetland Frontage by Zone of Contamintaion  
Level I 100 feet
Level II 1400 feet
Potential (25 cfs) 3000 feet
Potential (250 cfs) 800 feet

What is the score for environmental targets?

  Score for Environmental Targets  
Level I 10 for Level I x (o=(75+75)) 1500
Level II 1 for Level II x (25+(0)) 25
Potential 25 x 0.1 (dilution)
25 x 0.01 (dilution)
sum = 2.75 x 1/10 for potential
Targets   800 feet

The sensitive environments are assigned to Level I and are not counted in any of the other segments. A wetland value of 0 is assigned for the Level I frontage. All the other segments pick up a wetland value of 25. The value for potential is not rounded because it is less than 1. The HRS also instructs that the targets score not be rounded.

Navigate to another section of the course:

        Table of Contents      
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20