     

       CODE ENHANCEMENTS TO ISC3 FOR PSD CREDIT MODELING
       
SUBROUTINE CALC Enhancements by RTP Environmental Associates.

The following code is used for simple, intermediate, and complex
terrain processing, and RTP enhancements are described.

C                 Apply Intermediate Terrain Logic
C
                  IF (SIMPLE) THEN
C
C                    Simple Terrain Model Only
C
                     CALL PSIMPL
                  ELSE IF (COMPLX) THEN
C
C                    Complex Terrain Model Cnly
C
                     CALL PCOMPL
C
C**************************** RTP MODS ****************************
C
cc    Check for negative concentration values.  If so, do not allow
cc    PSD concentration credit for COMPLEX I, as it is        
cc    a screening model.
C
                  IF(HRVAL(1).LT.0)THEN
                  DO ITYP =1,NUMTYP
                     HRVAL(ITYP)=0.0
                  ENDDO 
                  ENDIF
C
C****************************************************************
C
                  ELSE IF (INTERM) THEN
C
C      Initialize simple and complex terrain holding variables
C
                     SIMCON = 0.0
                     COMCON = 0.0
                     DO ITYP = 1, NUMTYP
                        SIMPL(ITYP) = 0.
                        COMPL(ITYP) = 0.
                     END DO
C
C      Determine Which Model Predicts the Larger Conc.         
C      Save Simple Terrain Conc.
C
                     CALL PSIMPL
                     DO ITYP = 1, NUMTYP
                        SIMPL(ITYP) = HRVAL(ITYP)
                     END DO
C
C      Save Complex Terrain Conc.
C
                     CALL PCOMPL
                     DO ITYP = 1, NUMTYP
                        COMPL(ITYP) = HRVAL(ITYP)
                     END DO
C
C      Report Result for Model that Produces the Larger 
C      Concentration
C
C******************** RTP MODIFICATIONS ******************
C      IF CONC IS NEGATIVE, THEN THE PSD "CREDIT" IS VALID
C      ONLY FROM ISCST, AND NOT COMPLEX I, AS IT IS A
C      SCREENING MODEL.. THEREFORE, IF CONC FROM ISC (SIMCON) IS < 0 
C      USE IT IN INTERMEDIATE TERRAIN 
C      THE FOLLOWING OLD CODE IS COMMENTED OUT 
C                     IF (SIMCON .GE. COMCON) THEN
C************** AND IT BECOMES *******************
C
                     IF ((SIMCON .GE. COMCON).OR.(SIMCON .LT. 0.0)) THEN
                           DO ITYP = 1, NUMTYP
                              HRVAL(ITYP) = SIMPL(ITYP)
                           END DO
                        ELSE
                           DO ITYP = 1, NUMTYP
                              HRVAL(ITYP) = COMPL(ITYP)
                           END DO
                        END IF
                     END IF

