Water quality in the Chihuahua-Sacramento aquifer is reported to be generally good with acceptable values of total dissolved solids and related parameters of the NOM-127-SSA1-1994 (1994) for drinking water quality. In relation to the Tabalaopa-Aldama aquifer, the parameters are within the norm, with the exception of one well with high iron content and another well with nitrates in the upper limits which are due to local sources of contamination; pumping has ceased from these wells.
Regarding the water quality of the SWWTP, some of the parameters of the treated effluent monitored are: chemical oxygen demand (COD), biological oxygen demand (BOD5), total suspended solids (TSS), sediment solids (SED), fecal coliforms, helminth, grease and oils, methylene blue active substances (SAAM), Kjeldahl total nitrogen (NTK), total nitrogen (N–NH3, N–NO2, N–NO3), pH, temperature, chlorine (CL2), and phosphorus (P). Some of the concentrations recorded in December 2012 are shown in Table 2.
Further analyses are currently being performed to determine the relationship between source water quality and NOM-14 standards to determine if further treatment is needed before recharge. Such analyses will also allow comparisons with NOM-27 standards which need to be met at the point of abstraction from the aquifer if the native groundwater is used as a drinking water supply. It will also allow comparisons with native groundwater to ensure any existing non-potable uses of groundwater from production wells will not be adversely affected by the MAR operation.
In Table 2 there are too few samples analyzed to date (0–2) to determine the reliability of the analyses and the consistency of the quality of treated wastewater to be used for recharge, which are required to then evaluate whether there is a need for further treatment. Table 2, when updated after more monitoring with more samples and more analyses, is expected to show whether the treated wastewater meets the requirements indicated in NOM-014, regarding the permissible limits of contaminants not regulated by standard (BOD ≤ 30 mg/l) and TOC ≤ 16 mg/l, in surface recharge systems. It will also reveal which parameters need to be removed in the vadose zone, and by what proportion to meet groundwater requirements and NOM-127.
Based on the information from the studies and the secondary treatment level of the SWWTP, MAR by means of infiltration lagoons is proposed. The feasibility of this approach will be further evaluated through conducting a pilot project, hydrogeochemical analysis and the development of numerical models. During 6 months of operation of the pilot project, water quality parameters will be monitored, residence time will be evaluated and the amount of water recovered will be recorded, see Fig. 5 (NRMMC, EPHC and NHMRC 2009).