Opinion by
Mathies Coal Company appeals an Environmental Hearing Board (EHB) order upholding limitations by the Department of Environmental Resources (DER) on the amount of iron, manganese and aluminum in the discharge from Mathies’ treatment plant. These limitations were imposed in an amended National Pollutant Discharge Elimination System (NPDES) permit which allowed an increased discharge from the plant. We affirm in part, reverse in part and remand.
Our scope of review of an EHB decision is limited to a determination of whether an error of law has been committed, constitutional rights have been violated or any findings of fact are unsupported by substantial evidence. Einsig v. Pennsylvania Mines Corp., 69 Pa. Commonwealth Ct. 351, 452 A.2d 558 (1982).
*313Mathies contends that EHB incorrectly ruled that DER had no duty or discretion to consider evidence of economic or aquatic impacts when issuing the NPDES permit. We agree.
In support of its ruling, EHB stated that (1) DER was required to apply the specific water quality standards in 25 Pa. Code §93.7, (2) DER calculated the effluent limitations from a formula (mass balance equation)1 considering these standards as well as the actual or estimated lowest seven-consecutive-day average receiving stream flow occurring once in ten years (Q7-10)2 and (3) the issue of the Q7-10 value was removed from contention by a stipulation of the parties.
*314However, DERs regulations provide that the water quality standards for a receiving stream are only “one of the major factors” in developing discharge limits. 25 Pa. Code §93.5(a).3 Therefore, DER generally has discretion to consider other factors when enforcing these standards by limiting discharge from a particular source. See Lucas v. Department of Environmental Resources, 53 Pa. Commonwealth Ct. 598, 420 A.2d 1 (1980) (25 Pa. Code §93.5(a) allows discharge limitations to be established on an individual case-by-case basis).
Moreover, because such discretion exists, DER must consider, where applicable, the economic and aquatic impacts of its actions pursuant to Section 5(a) of The Clean Streams Law.4 This Court has so interpreted *315Section 5(a). See Department of Environmental Resources v. Borough of Carlisle, 16 Pa. Commonwealth Ct. 341, 330 A.2d 293 (1974).5
DER contends that Mathies has waived its right to challenge the use of the mass balance equation to calculate the effluent limitations because it did not specifically do so below. However, by contesting DERs failure to consider the economic and aquatic effects of limiting the discharge, Mathies certainly contested DERs use of the formula to effect the limitations.
The weight to be given each factor considered when issuing a permit must be determined by DER based on the circumstances.6 However, DER may not use the mass balance equation to avoid affording the required individualized consideration to permit applicants. Therefore, we affirm the EHB order in part,7 but reverse the order insofar as it determines that DER was not required to consider evidence of economic and aquatic impacts when issuing the NPDES permit and remand this case for such consideration.
*316Order
The Environmental Hearing Board order, No. 82-212-G dated June 10, 1985, is affirmed in part, reversed in part and this case is remanded for proceedings consistent with the foregoing opinion.
Jurisdiction relinquished.