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Population
- If you cannot remember how many points are assigned to each person at Level I, Level II, and potential, press this button. HRS Guidance Manual, Highlight 8-32, page 263.
- The principles of including residents, workers, and students and of assessing blended supply systems and standby intakes are the same as they were for the ground water pathway. To review those sections, press here. CLICK HERE for GW sections
- Examine the following HRS formula for the potential contamination factor value carefully:
Insert here the formula PC =, along with Wi = and i = from HRS page 51617
- If there are two or more intakes within the same type of surface water body (e.g., average annual flow of greater than 1,000 to 10,000 cfs), sum the population served by these intakes before entering HRS Table 4-14.
HRS rule, Table 4-14, pages 51615 - 51616 - When you exit HRS Table 4-14 with the dilution weighted values for population for the different dilution categories, no not forget to multiply the sum by 1/10 for potential. The tables in the PA Guidance Manual do this for you. You're expected to remember these things when you graduate to the HRS itself.
- Finally, the text on HRS page 51617 that follows the formula states a quirky rounding rule that applies to potential targets throughout the HRS: "If PC is less than 1, do not round it to the nearest integer; if PC is 1 or more, round to the nearest integer. Enter this value for potential contamination in Table 4-1." This rule prevents small target values from disappearing through rounding.
- This section illustrates a basic HRS principle: Read the small print or it will trip you up every time.
- If there are two or more intakes within the same type of surface water body (e.g., average annual flow of greater than 1,000 to 10,000 cfs), sum the population served by these intakes before entering HRS Table 4-14.
- Because intakes are frequently on rivers or lakes with large average annual stream flow, the HRS values for potential contamination may be very low uless the criterion of "quiet flowing river" applies. Be on the lookout also for situations where there are intakes supported by relatively small stream flow. For instance, a small reservoir with total inflows of less than 100 cfs can support populations of 10,001 to 30,000 people.
QUESTION: What HRS target value would such an intake receive?
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