Stormwater Pollution Prevention Plan - Phoenix Sky Harbor ...

Non-Mining MSGP 2010 General Permit
Appendix D. Calculating Hardness in Surface Waters Receiving Stormwater Discharges for
Hardness Dependent Metals
Overview
Benchmarks have been adjusted for six hardness-dependent metals (i.e., cadmium, copper, lead, nickel,
silver, and zinc) to further ensure compliance with water quality standards and provide additional
protection for endangered species and their critical habitat. For any sectors required to conduct
benchmark samples for a hardness-dependent metal, ‘hardness ranges’ are included from which
benchmark values are determined. To determine which hardness range to use, the permittee must collect
data on the hardness of the facility’s surface water(s) that receive discharges or the hardness of the
discharge itself based on the type of the receiving water body. Once the site-specific hardness data have
been collected, the corresponding benchmark value for each metal is determined by comparing where the
hardness data fall within 25 mg/L ranges, as shown in Table 1.
Table 1. Hardness Ranges to Be Used to Determine Benchmark Values for Discharges to
Perennial or Intermittent Waterbodies.
All Units
Benchmark Values (mg/L, total)
mg/L Cadmium Copper Lead Nickel Silver Zinc
0-25 0.0020 0.0036 0.014 0.15 0.0007 0.0362
25-50 0.0040 0.0070 0.030 0.260 0.0007 0.0651
50-75 0.0060 0.0102 0.047 0.367 0.0017 0.0918
75-100 0.0079 0.0134 0.065 0.468 0.0030 0.1170
100-125 0.0096 0.0170 0.082 0.566 0.0046 0.1417
125-150 0.0117 0.0197 0.100 0.660 0.0065 0.1652
150-175 0.0136 0.0221 0.118 0.752 0.0087 0.1883
175-200 0.0154 0.0228 0.136 0.842 0.0112 0.2108
200-225 0.0173 0.0289 0.154 0.930 0.0138 0.2329
225-250 0.0192 0.0316 0.172 1.017 0.0168 0.2547
250-275 0.0173 0.0349 0.190 1.102 0.0183 0.2761
275-300 0.0210 0.0378 0.209 1.186 0.0213 0.2972
300-325 0.0246 0.0408 0.227 1.269 0.0244 0.3181
325-350 0.0266 0.0438 0.245 1.351 0.0278 0.3387
350-375 0.0284 0.0467 0.263 1.433 0.0312 0.3591
375-400 0.0302 0.0496 0.281 1.513 0.0349 0.3793
Table 2. Hardness Ranges to Be Used to Determine Benchmark Values for Discharges to
Ephemeral Waterbodies.
All Units
Benchmark Values (mg/L, total)
mg/L Cadmium Copper Lead Nickel Silver Zinc
0-25 0.0059 0.0063 0.0293 1.287 0.0003 0.344
25-50 0.0116 0.0121 0.0636 2.313 0.0010 0.618
50-75 0.0172 0.0177 0.0995 3.260 0.0020 0.871
75-100 0.0228 0.0233 0.1363 4.158 0.0032 1.112
100-125 0.0286 0.0283 0.1736 5.022 0.0047 1.343
125-150 0.0338 0.0341 0.2113 5.860 0.0065 1.568
150-175 0.0393 0.0394 0.2492 6.676 0.0084 1.787
Stormwater Discharges Associated With Industrial Activity – Appendix D D-2