The Town of Reading utilizes nine groundwater wells in the Ipswich River Basin for itsmunicipal water supply. The source water is difficult to treat, the major challenge beingthe level of disinfection byproducts. Historical running annual average totaltrihalomethane (TTHM) levels ranged from 60 to 90 micrograms per liter (ug/L) in thedistribution system. In March 2004, the secondary disinfectant was changed from freechlorine to monochloramine, with resulting TTHM levels of 25 to 40 ug/L. Haloaceticacid (HAA5) levels were approximately the same prior to and after the conversion tochloramines, with running annual average (RAA) values in the range of 25 - 35 ug/L.The Town began proactively monitoring for N-Nitrosodimethylamine (NDMA) sincethe conversion to chloramine. Typical levels were less than 10 nanograms per liter(ng/L). In late February 2005, an increase in NDMA levels was observed. Follow-upsampling confirmed levels ranging from 11 to 39 ng/L. Based on this, the Townvoluntarily discontinued the addition of ammonia for the formation of monochloramineon March 31, 2005 and returned to free chlorine for secondary disinfection until thesource of NDMA formation could be understood.This paper describes the results of detailed investigations of key characteristics of thenatural organic matter (NOM) in the raw and treated water. Lab work includedseparation and isolation of NOM fractions based on size (ultrafiltration) andhydrophobicity (resin adsorption) resulting in three isolates from each water sample: ahigh molecular weight (HMW) fraction, a hydrophobic (HPO) fraction, and ahydrophilic (HPI) fraction. Each was tested in the laboratory and characterized as tocertain key properties, specifically, ultraviolet (UV) absorbance, chlorine demand, and a broad arrayof disinfection byproduct (DBP) formation assessments under both free chlorine andchloramine conditions. Both regulated (THMs and HAAs) and unregulated DBPcompounds (the remaining four bromo-chloro HAAs, two cyanogen halides and theeight nitrosamines) were examined. Includes table, figure.
