Table : Reservoir Bottom 2016 TDS Results (mg/L) and Class A Exceedances, (>500 mg/L) Exceedances are bolded. HB @ SB @ FP @ Site Name HB @ DH SB @ DH FP @ DH FP @ Cove Intake Intake Intake Median 631 640 470 481 456 524 516 Mean 647 653 514 514 498 523 517 Min 612 616 420 413 438 432 435 Max 647 653 514 514 498 523 517 Number of 5 5 6 6 9 9 9 Samples (n) Number of 5 5 2 3 3 5 5 Exceedances % Exceedance 100% 100% 33% 50% 33% 56% 56% The CWD treatment cannot currently remove salts such as chloride or sodium from drinking water. Chloride concentrations in the Hobbs Brook reservoir increased dramatically compared to 2015, with 100 percent of HB @ DH surface samples and 92 percent of weekly intake samples exceeding the SMCL of 250 mg/L (Tables 22 and 23; Figure 9). By contrast, only 22 percent of weekly intake samples exceeded the SMCL in 2015 and no samples exceeded the SMCL in 2014 (Figure 9). The dramatic change in the chloride exceedances is likely due to severe drought conditions resulting from below normal rainfall in 2015 and 2016 (see section 10.2 Reservoir Retention Times, Table 48). The lack of rainfall minimized the dilution of salt-impacted base-flow. Sodium concentrations were also in excess of the 20 mg/L ORS Guideline (Tables 24 and 25). However, this guideline is regularly exceeded at all sampling locations throughout the Cambridge watershed (Figures 10, 12, and 14). Table : Reservoir Surface 2016 Cl Results and SMCL Exceedances (>250 mg/L) Exceedances are bolded. HB @ SB @ FP @ DH HB @ HB @ Site Name HB @ DH Intake SB @ DH Intake Upper Middle Weekly Weekly Median 319 337 285 279 209 188 206 Mean 322 343 284 279 218 210 215 Min 132 188 267 166 157 112 179 Max 552 522 306 329 299 312 259 Number of 6 6 5 51 6 51 7 Samples (n) Number of 4 5 5 47 2 15 2 Exceedances % Exceedance 67% 83% 100% 92% 33% 29% 29%
Table : Reservoir Bottom 2016 TDS Results (mg/L) and Class A Exceedances, (>500 mg/L) Exceedances are bolded. Site Name HB @ DH HB @ Intake SB @ DH SB @ Intake FP @ DH FP @ Cove FP @ Intake Median 631 640 470 481 456 524 516 Mean 647 653 514 514 498 523 517 Min 612 616 420 413 438 432 435 Max 647 653 514 514 498 523 517 Number of Samples (n) 5 5 6 6 9 9 9 Number of Exceedances 5 5 2 3 3 5 5 % Exceedance 100% 100% 33% 50% 33% 56% 56% The CWD treatment cannot currently remove salts such as chloride or sodium from drinking water. Chloride concentrations in the Hobbs Brook reservoir increased dramatically compared to 2015, with 100 percent of HB @ DH surface samples and 92 percent of weekly intake samples exceeding the SMCL of 250 mg/L (Tables 22 and 23; Figure 9). By contrast, only 22 percent of weekly intake samples exceeded the SMCL in 2015 and no samples exceeded the SMCL in 2014 (Figure 9). The dramatic change in the chloride exceedances is likely due to severe drought conditions resulting from below normal rainfall in 2015 and 2016 (see section 10.2 Reservoir Retention Times, Table 48). The lack of rainfall minimized the dilution of salt-impacted base-flow. Sodium concentrations were also in excess of the 20 mg/L ORS Guideline (Tables 24 and 25). However, this guideline is regularly exceeded at all sampling locations throughout the Cambridge watershed (Figures 10, 12, and 14). Table : Reservoir Surface 2016 Cl Results and SMCL Exceedances (>250 mg/L) Exceedances are bolded. Site Name HB @ Upper HB @ Middle HB @ DH HB @ Intake Weekly SB @ DH SB @ Intake Weekly FP @ DH Median 319 337 285 279 209 188 206 Mean 322 343 284 279 218 210 215 Min 132 188 267 166 157 112 179 Max 552 522 306 329 299 312 259 Number of Samples (n) 6 6 5 51 6 51 7 Number of Exceedances 4 5 5 47 2 15 2 % Exceedance 67% 83% 100% 92% 33% 29% 29%
2016_FINAL.docx